Distinct dynamics and intrinsic properties in ventral tegmental area populations mediate reward association and motivation

Elum JE, Szelenyi ER, Juarez B, Murry AD, Loginov G, Zamorano CA, Gao P, Wu G, Ng-Evans S, Yee JX, Xu X, Golden SA, Zweifel LS

Cell Rep. 2024 Aug 27;43(9):114668. doi: 10.1016/j.celrep.2024.114668. PMID: 39207900.

Ventral tegmental area (VTA) dopamine neurons regulate reward-related associative learning and reward-driven motivated behaviors, but how these processes are coordinated by distinct VTA neuronal subpopulations remains unresolved. Here, we compare the contribution of two primarily dopaminergic and largely non-overlapping VTA subpopulations, all VTA dopamine neurons and VTA GABAergic neurons of the mouse midbrain, to these processes. We find that the dopamine subpopulation that projects to the nucleus accumbens (NAc) core preferentially encodes reward-predictive cues and prediction errors. In contrast, the subpopulation that projects to the NAc shell preferentially encodes goal-directed actions and relative reward anticipation. VTA GABA neuron activity strongly contrasts VTA dopamine population activity and preferentially encodes reward outcome and retrieval. Electrophysiology, targeted optogenetics, and whole-brain input mapping reveal multiple convergent sources that contribute to the heterogeneity among VTA dopamine subpopulations that likely underlies their distinct encoding of reward-related associations and motivation that defines their functions in these contexts.

Keeping it simple – a Simple Behavioral Analysis (SimBA) primer

NPP—Digital Psychiatry and Neuroscience 2, 13 (2024). doi: 10.1038/s44277-024-00014-9. PMID: 39099890.

Goodwin NL, Golden SA.

Neuroscience is approaching a critical juncture, transitioning from subjective behavioral observation to objective behavioral definition. This is now possible due to analytical tools using machine-guided solutions for animal markerless key-point pose tracking (see Table 1 for specialized terminology definitions) and behavioral detection. However, it is often challenging for behaviorists to adopt these approaches due to a lack of specialized computational knowledge. We and others have spent significant effort to solve this problem by democratizing access to these approaches, making them accessible to non-specialists. However, as these tools increase access to machine learning approaches, an emerging problem is ensuring that the predictions algorithms are making and the biology that they are defining are explainable and understandable. To address these challenges, we have introduced Simple Behavioral Analysis (SimBA) as an open-source, supervised machine learning based platform for the automated detection of behavior, with a focus on understanding how the underlying machine learning algorithms make their decisions.

An arginine-rich nuclear localization signal (ArgiNLS) strategy for streamlined image segmentation of single cells

Proc Natl Acad Sci U S A. 2024 Aug 6;121(32):e2320250121. doi: 10.1073/pnas.2320250121. PMID: 39074275.

Szelenyi ER, Navarrete JS, Murry AD, Zhang Y, Girven KS, Kuo L, Cline MM, Bernstein MX, Burdyniuk M, Bowler B, Goodwin NL, Juarez B, Zweifel LS, Golden SA.

High-throughput volumetric fluorescent microscopy pipelines can spatially integrate whole-brain structure and function at the foundational level of single cells. However, conventional fluorescent protein (FP) modifications used to discriminate single cells possess limited efficacy or are detrimental to cellular health. Here, we introduce a synthetic and nondeleterious nuclear localization signal (NLS) tag strategy, called “Arginine-rich NLS” (ArgiNLS), that optimizes genetic labeling and downstream image segmentation of single cells by restricting FP localization near-exclusively in the nucleus through a poly-arginine mechanism. A single N-terminal ArgiNLS tag provides modular nuclear restriction consistently across spectrally separate FP variants. ArgiNLS performance in vivo displays functional conservation across major cortical cell classes and in response to both local and systemic brain-wide AAV administration. Crucially, the high signal-to-noise ratio afforded by ArgiNLS enhances machine learning-automated segmentation of single cells due to rapid classifier training and enrichment of labeled cell detection within 2D brain sections or 3D volumetric whole-brain image datasets, derived from both staining-amplified and native signal. This genetic strategy provides a simple and flexible basis for precise image segmentation of genetically labeled single cells at scale and paired with behavioral procedures.

Simple Behavioral Analysis (SimBA) as a platform for explainable machine learning in behavioral neuroscience

Nature Neuroscience. 2024 May 22. doi: 10.1038/s41593-024-01649-9. PMID: 38778146.

Goodwin NL, Choong JJ, Hwang S, Pitts K, Bloom L, Islam A, Zhang YY, Szelenyi ER, Tong X, Newman EL, Miczek K, Wright HR, McLaughlin RJ, Norville ZC, Eshel N, Heshmati M, Nilsson SRO*, Golden SA*.

The study of complex behaviors is often challenging when using manual annotation due to the absence of quantifiable behavioral definitions and the subjective nature of behavioral annotation. Integration of supervised machine learning approaches mitigates some of these issues through the inclusion of accessible and explainable model interpretation. To decrease barriers to access, and with an emphasis on accessible model explainability, we developed the open-source Simple Behavioral Analysis (SimBA) platform for behavioral neuroscientists. SimBA introduces several machine learning interpretability tools, including SHapley Additive exPlanation (SHAP) scores, that aid in creating explainable and transparent behavioral classifiers. Here we show how the addition of explainability metrics allows for quantifiable comparisons of aggressive social behavior across research groups and species, reconceptualizing behavior as a sharable reagent and providing an open-source framework. We provide an open-source, graphical user interface (GUI)-driven, well-documented package to facilitate the movement toward improved automation and sharing of behavioral classification tools across laboratories.

An implantable device for wireless monitoring of diverse physio-behavioral characteristics in freely behaving small animals and interacting groups.

Neuron. 2024 Jun 5;112(11):1764-1777.e5. doi: 10.1016/j.neuron.2024.02.020. PMID: 38537641.

Ouyang W, Kilner KJ, Xavier RMP, Liu Y, Lu Y, Feller SM, Pitts KM, Wu M, Ausra J, Jones I, Wu Y, Luan H, Trueb J, Higbee-Dempsey EM, Stepien I, Ghoreishi-Haack N, Haney CR, Li H, Kozorovitskiy Y, Heshmati M, Banks AR, Golden SA*, Good CH*, Rogers JA*.

Comprehensive, continuous quantitative monitoring of intricately orchestrated physiological processes and behavioral states in living organisms can yield essential data for elucidating the function of neural circuits under healthy and diseased conditions, for defining the effects of potential drugs and treatments, and for tracking disease progression and recovery. Here, we report a wireless, battery-free implantable device and a set of associated algorithms that enable continuous, multiparametric physio-behavioral monitoring in freely behaving small animals and interacting groups. Through advanced analytics approaches applied to mechano-acoustic signals of diverse body processes, the device yields heart rate, respiratory rate, physical activity, temperature, and behavioral states. Demonstrations in pharmacological, locomotor, and acute and social stress tests and in optogenetic studies offer unique insights into the coordination of physio-behavioral characteristics associated with healthy and perturbed states. This technology has broad utility in neuroscience, physiology, behavior, and other areas that rely on studies of freely moving, small animal models.

Individual Differences in Volitional Social Self-Administration and Motivation in Male and Female Mice Following Social Stress.

Biol Psychiatry. 2024 Jan 18:S0006-3223(24)00033-7. doi: 10.1016/j.biopsych.2024.01.007. PMID: 38244753.

Navarrete J, Schneider KN, Smith BM, Goodwin NL, Zhang YY, Salazar AS, Gonzalez YE, Anumolu P, Gross E, Tsai VS, Heshmati M, Golden SA.

Background: A key challenge in developing treatments for neuropsychiatric illness is the disconnect between preclinical models and the complexity of human social behavior. We integrate voluntary social self-administration into a rodent model of social stress as a platform for the identification of fundamental brain and behavior mechanisms underlying stress-induced individual differences in social motivation.

Methods: Here, we introduced an operant social stress procedure in male and female mice composed of 3 phases: 1) social self-administration training, 2) social stress exposure concurrent with reinforced self-administration testing, and 3) poststress operant testing under nonreinforced and reinforced conditions. We used social-defeat and witness-defeat stress in male and female mice.

Results: Social defeat attenuated social reward seeking in males but not females, whereas witness defeat had no effect in males but promoted seeking behavior in females. We resolved social stress-induced changes to social motivation by aggregating z-scored operant metrics into a cumulative social index score to describe the spectrum of individual differences exhibited during operant social stress. Clustering does not adequately describe the relative distributions of social motivation following stress and is better described as a nonbinary behavioral distribution defined by the social index score, capturing a dynamic range of stress-related alterations in social motivation inclusive of sex as a biological variable.

Conclusions: We demonstrated that operant social stress can detect stable individual differences in stress-induced changes to social motivation. The inclusion of volitional behavior in social procedures may enhance the understanding of behavioral adaptations that promote stress resiliency and their mechanisms under more naturalistic conditions.

ASCL1 induces neurogenesis in human Müller glia.

Stem Cell Reports. 2023 Dec 12;18(12):2400-2417. doi: 10.1016/j.stemcr.2023.10.021. PMID: 38039971.

Wohlschlegel J, Finkbeiner C, Hoffer D, Kierney F, Prieve A, Murry AD, Haugan AK, Ortuño-Lizarán I, Rieke F, Golden SA, Reh TA.

In mammals, loss of retinal cells due to disease or trauma is an irreversible process that can lead to blindness. Interestingly, regeneration of retinal neurons is a well established process in some non-mammalian vertebrates and is driven by the Müller glia (MG), which are able to re-enter the cell cycle and reprogram into neurogenic progenitors upon retinal injury or disease. Progress has been made to restore this mechanism in mammals to promote retinal regeneration: MG can be stimulated to generate new neurons in vivo in the adult mouse retina after the over-expression of the pro-neural transcription factor Ascl1. In this study, we applied the same strategy to reprogram human MG derived from fetal retina and retinal organoids into neurons. Combining single cell RNA sequencing, single cell ATAC sequencing, immunofluorescence, and electrophysiology we demonstrate that human MG can be reprogrammed into neurogenic cells in vitro.

Post-Mating Inhibition of Female Sexual Drive via Heterogeneous Neuronal Ensembles in the Medial Preoptic Area

eLife. 2023 Nov 14; eLife12:RP91765.

Ishii KK, Hashikawa K, Chea J, Yin S, Fox RE, Kan S, Zhou C, Navarrete J, Murry AD, Szelenyi ER, Golden SA, Stuber GD.

The completion of mating acutely suppresses sexual motivatNovion in male mice. In contrast, relatively little is known about how the completion of mating affects sexual motivation and sexual behavior in female mice. How the brain responds to completion of mating is also unclear. Here, by using self-paced mating assay, we first demonstrate that female mice show decreased sexual motivation after the completion of mating. By using brain-wide analysis of activity-dependent labeling, we next pin-pointed the medial preoptic area as a brain region strongly responding to mating completion. Furthermore, using freely moving in vivo calcium imaging to compare neural activity of inhibitory and excitatory neurons in the medial preoptic area, we revealed that a subset of neurons responds significantly and specifically to mating completion but not to appetitive or consummatory behaviors. While there were excitatory and inhibitory neurons that showed positive response to the completion of mating, the response magnitude as well as the proportion of neurons responding to the event was significantly larger in the inhibitory neuron population. Next, by unbiased classification of their responses, we also found a subpopulation of neurons that increase their activity late after the onset of the completion of mating. These neurons were all inhibitory indicating that the completion of mating induces a prolonged inhibitory activity in the medial preoptic area. Lastly, we found that chemogenetic activation of medial preoptic area neurons that respond to mating completion, but not to appetitive behaviors, was sufficient to suppress female sexual motivation. Together, our data illuminate the importance of medial preoptic area as a brain node which encodes a negative signal that sustains low sexual motivation state after the completion of mating in female mice.

Lateral line ablation by ototoxic compounds results in distinct rheotaxis profiles in larval zebrafish.

Commun Biol. 2023 Jan 21;6(1):84. doi: 10.1038/s42003-023-04449-2. PMID: 36681757.

Newton KC, Kacev D, Nilsson SRO, Saettele AL, Golden SA, Sheets L.

The zebrafish lateral line is an established model for hair cell organ damage, yet few studies link mechanistic disruptions to changes in biologically relevant behavior. We used larval zebrafish to determine how damage via ototoxic compounds impact rheotaxis. Larvae were treated with CuSO4 or neomycin to disrupt lateral line function then exposed to water flow stimuli. Their swimming behavior was recorded on video then DeepLabCut and SimBA software were used to track movements and classify rheotaxis behavior, respectively. Lateral line-disrupted fish performed rheotaxis, but they swam greater distances, for shorter durations, and with greater angular variance than controls. Furthermore, spectral decomposition analyses confirmed that lesioned fish exhibited ototoxic compound-specific behavioral profiles with distinct changes in the magnitude, frequency, and cross-correlation between fluctuations in linear and angular movements. Our observations demonstrate that lateral line input is needed for fish to hold their station in flow efficiently and reveals that commonly used lesion methods have unique effects on rheotaxis behavior.

Incubation of palatable food craving is associated with brain-wide neuronal activation in mice.

Proc Natl Acad Sci U S A. 2022 Nov 8;119(45):e2209382119. doi: 10.1073/pnas.2209382119. PMID: 36603188

Madangopal R, Szelenyi ER, Nguyen J, Brenner MB, Drake OR, Pham DQ, Shekara A, Jin M, Choong JJ, Heins C, Komer LE, Weber SJ, Hope BT, Shaham Y, Golden SA.

Studies using rodent models have shown that relapse to drug or food seeking increases progressively during abstinence, a behavioral phenomenon termed "incubation of craving." Mechanistic studies of incubation of craving have focused on specific neurobiological targets within preselected brain areas. Recent methodological advances in whole-brain immunohistochemistry, clearing, and imaging now allow unbiased brain-wide cellular resolution mapping of regions and circuits engaged during learned behaviors. However, these whole-brain imaging approaches were developed for mouse brains, while incubation of drug craving has primarily been studied in rats, and incubation of food craving has not been demonstrated in mice. Here, we established a mouse model of incubation of palatable food craving and examined food reward seeking after 1, 15, and 60 abstinence days. We then used the neuronal activity marker Fos with intact-brain mapping procedures to identify corresponding patterns of brain-wide activation. Relapse to food seeking was significantly higher after 60 abstinence days than after 1 or 15 days. Using unbiased ClearMap analysis, we identified increased activation of multiple brain regions, particularly corticostriatal structures, following 60 but not 1 or 15 abstinence days. We used orthogonal SMART2 analysis to confirm these findings within corticostriatal and thalamocortical subvolumes and applied expert-guided registration to investigate subdivision and layer-specific activation patterns. Overall, we 1) identified brain-wide activity patterns during incubation of food seeking using complementary analytical approaches and 2) provide a single-cell resolution whole-brain atlas that can be used to identify functional networks and global architecture underlying the incubation of food craving.

Sex differences in appetitive and reactive aggression.

Neuropsychopharmacology. 2022 Sep;47(10):1746-1754. doi: 10.1038/s41386-022-01375-5. PMID: 35810200.

Aubry AV, Joseph Burnett C, Goodwin NL, Li L, Navarrete J, Zhang Y, Tsai V, Durand-de Cuttoli R, Golden SA*, Russo SJ

Aggression is an evolutionarily conserved, adaptive component of social behavior. Studies in male mice illustrate that aggression is influenced by numerous factors including the degree to which an individual finds aggression rewarding and will work for access to attack and subordinate mice. While such studies have expanded our understanding of the molecular and circuit mechanisms of male aggression very little is known about female aggression, within these established contexts. Here we use an ethologically relevant model of male vs. female aggression by pair housing adult male and female outbred CFW mice with opposite sex cage mates. We assess reactive (defensive) aggression in the resident intruder (RI) test and appetitive (rewarding) aggression in the aggression conditioned place preference (CPP) and operant self-administration (SA) tests. Our results show dramatic sex differences in both qualitative and quantitative aspects of reactive vs. appetitive aggression. Males exhibit more wrestling and less investigative behavior during RI, find aggression rewarding, and will work for access to a subordinate to attack. Females exhibit more bites, alternate between aggressive behaviors and investigative behaviors more readily during RI, however, they do not find aggression to be rewarding or reinforcing. These results establish sex differences in aggression in mice, providing an important resource for the field to better understand the circuit and molecular mechanisms of aggression in both sexes.

Toward the explainability, transparency, and universality of machine learning for behavioral classification in neuroscience.

Curr Opin Neurobiol. 2022 Apr;73:102544. doi: 10.1016/j.conb.2022.102544. PMID: 35487088.

Goodwin NL, Nilsson SRO, Choong JJ, Golden SA.

The use of rigorous ethological observation via machine learning techniques to understand brain function (computational neuroethology) is a rapidly growing approach that is poised to significantly change how behavioral neuroscience is commonly performed. With the development of open-source platforms for automated tracking and behavioral recognition, these approaches are now accessible to a wide array of neuroscientists despite variations in budget and computational experience. Importantly, this adoption has moved the field toward a common understanding of behavior and brain function through the removal of manual bias and the identification of previously unknown behavioral repertoires. Although less apparent, another consequence of this movement is the introduction of analytical tools that increase the explainabilty, transparency, and universality of the machine-based behavioral classifications both within and between research groups. Here, we focus on three main applications of such machine model explainabilty tools and metrics in the drive toward behavioral (i) standardization, (ii) specialization, and (iii) explainability. We provide a perspective on the use of explainability tools in computational neuroethology, and detail why this is a necessary next step in the expansion of the field. Specifically, as a possible solution in behavioral neuroscience, we propose the use of Shapley values via Shapley Additive Explanations (SHAP) as a diagnostic resource toward explainability of human annotation, as well as supervised and unsupervised behavioral machine learning analysis.

SMART: An Open-Source Extension of WholeBrain for Intact Mouse Brain Registration and Segmentation.

eNeuro. 2022 May 3;9(3):ENEURO.0482-21.2022. doi: 10.1523/ENEURO.0482-21.2022. PMID: 35396258.

Jin M, Nguyen JD, Weber SJ, Mejias-Aponte CA, Madangopal R, Golden SA.

Mapping immediate early gene (IEG) expression across intact mouse brains allows for unbiased identification of brain-wide activity patterns underlying complex behaviors. Accurate registration of sample brains to a common anatomic reference is critical for precise assignment of IEG-positive ("active") neurons to known brain regions of interest (ROIs). While existing automated voxel-based registration methods provide a high-throughput solution, they require substantial computing power, can be difficult to implement and fail when brains are damaged or only partially imaged. Additionally, it is challenging to cross-validate these approaches or compare them to any preexisting literature based on serial coronal sectioning. Here, we present the open-source R package SMART (Semi-Manual Alignment to Reference Templates) that extends the WholeBrain R package framework to automated segmentation and semi-automated registration of intact mouse brain light-sheet fluorescence microscopy (LSFM) datasets. The SMART package was created for novice programmers and introduces a streamlined pipeline for aligning, registering, and segmenting LSFM volumetric datasets across the anterior-posterior (AP) axis, using a simple "choice game" and interactive menus. SMART provides the flexibility to register whole brains, partial brains or discrete user-chosen images, and is fully compatible with traditional sectioned coronal slice-based analyses. We demonstrate SMART's core functions using example datasets and provide step-by-step video tutorials for installation and implementation of the package. We also present a modified iDISCO+ tissue clearing procedure for uniform immunohistochemical labeling of the activity marker Fos across intact mouse brains. The SMART pipeline, in conjunction with the modified iDISCO+ Fos procedure, is ideally suited for examination and orthogonal cross-validation of brain-wide neuronal activation datasets.

The Role of the Lateral Habenula in Suicide: A Call for Further Exploration.

Front Behav Neurosci. 2022 Mar 14;16:812952. doi: 10.3389/fnbeh.2022.812952. PMID: 35359586.

Marks RB, Wee JY, Jacobson SV, Hashimoto K, O'Connell KL, Golden SA, Baker PM, Law KC

Despite decades of significant effort in research, policy, and prevention, suicide rates have continued to rise to the current peak of 14.6 per 100,000 deaths. This has resulted in a concerted effort to identify biomarkers associated with suicidal behavior in the brain, to provide predictions that are better than the chance of discerning who will die by suicide. We propose that the lateral habenula (LHb), and its dysfunction during a suicidal crisis, is a critical component of the transition from suicidal ideations to self-harm. Moreover, the LHb-a key functional node in brain reward circuitry-has not been ascribed a contributory role in suicidal behavior. We argue that the LHb anchors a "suicide circuit" and call for suicide researchers to directly examine the role of the LHb, and its long-term modulation, in response to the negative affect in suicidal behavior. Discerning the neural mechanisms of this contribution will require the collaboration of neuroscientists and psychologists. Consequently, we highlight and discuss research on LHb as it relates to suicidal ideation, suicidal behavior, or death by suicide. In so doing we hope to address the bench-to-bedside translational issues currently involved in suicide research and suggest a developmental framework that focuses on specific structures motivated by theoretical anchors as a way to incorporate neurobiological findings within the context of clinical theory.

Automated procedure to assess pup retrieval in laboratory mice.

Sci Rep. 2022 Jan 31;12(1):1663. doi: 10.1038/s41598-022-05641-w. doi: 10.1038/s41598-022-06987-x. PMID: 35102217.

Winters C, Gorssen W, Ossorio-Salazar VA, Nilsson S, Golden S, D'Hooge R.

Despite decades of significant effort in research, policy, and prevention, suicide rates have continued to rise to the current peak of 14.6 per 100,000 deaths. This has resulted in a concerted effort to identify biomarkers associated with suicidal behavior in the brain, to provide predictions that are better than the chance of discerning who will die by suicide. We propose that the lateral habenula (LHb), and its dysfunction during a suicidal crisis, is a critical component of the transition from suicidal ideations to self-harm. Moreover, the LHb-a key functional node in brain reward circuitry-has not been ascribed a contributory role in suicidal behavior. We argue that the LHb anchors a "suicide circuit" and call for suicide researchers to directly examine the role of the LHb, and its long-term modulation, in response to the negative affect in suicidal behavior. Discerning the neural mechanisms of this contribution will require the collaboration of neuroscientists and psychologists. Consequently, we highlight and discuss research on LHb as it relates to suicidal ideation, suicidal behavior, or death by suicide. In so doing we hope to address the bench-to-bedside translational issues currently involved in suicide research and suggest a developmental framework that focuses on specific structures motivated by theoretical anchors as a way to incorporate neurobiological findings within the context of clinical theory.

Social mice seeking circuits.

Nature Neuroscience. 2021 Jun;24(6):761-762. doi: 10.1038/s41593-021-00861-1. PMID: 33963361.

Szelenyi ER, Goodwin NL, Golden SA.

Hu et al. show that the posterodorsal medial amygdala selectively controls social-reward seeking through its intersection with canonical dopaminergic reward circuits. To identify this circuitry, the authors developed an elegant new affiliative social operant procedure that separates social interaction from social-reward seeking.

Quantitative standardization of resident mouse behavior for studies of aggression and social defeat.

Neuropsychopharmacology. 2021 Aug;46(9):1584-1593. doi: 10.1038/s41386-021-01018-1. PMID: 33941861.

Kwiatkowski CC, Akaeze H, Ndlebe I, Goodwin N, Eagle AL, Moon K, Bender AR, Golden SA, Robison AJ.

Territorial reactive aggression in mice is used to study the biology of aggression-related behavior and is also a critical component of procedures used to study mood disorders, such as chronic social defeat stress. However, quantifying mouse aggression in a systematic, representative, and easily adoptable way that allows direct comparison between cohorts within or between studies remains a challenge. Here, we propose a structural equation modeling approach to quantify aggression observed during the resident-intruder procedure. Using data for 658 sexually experienced CD-1 male mice generated by three research groups across three institutions over a 10-year period, we developed a higher-order confirmatory factor model wherein the combined contributions of latency to the first attack, number of attack bouts, and average attack duration on each trial day (easily observable metrics that require no specialized equipment) are used to quantify individual differences in aggression. We call our final model the Mouse Aggression Detector (MAD) model. Correlation analyses between MAD model factors estimated from multiple large datasets demonstrate generalizability of this measurement approach, and we further establish the stability of aggression scores across time within cohorts and demonstrate the utility of MAD for selecting aggressors which will generate a susceptible phenotype in social defeat experiments. Thus, this novel aggression scoring technique offers a systematic, high-throughput approach for aggressor selection in chronic social defeat stress studies and a more consistent and accurate study of mouse aggression itself.

Rage Against the Machine: Advancing the study of aggression ethology via machine learning.

Psychopharmacology (Berl). 2020 Sep;237(9):2569-2588. doi: 10.1007/s00213-020-05577-x. PMID: 32647898.

Goodwin NL, Nilsson SRO, Golden SA.

Rationale: Aggression, comorbid with neuropsychiatric disorders, exhibits with diverse clinical presentations and places a significant burden on patients, caregivers, and society. This diversity is observed because aggression is a complex behavior that can be ethologically demarcated as either appetitive (rewarding) or reactive (defensive), each with its own behavioral characteristics, functionality, and neural basis that may transition from adaptive to maladaptive depending on genetic and environmental factors. There has been a recent surge in the development of preclinical animal models for studying appetitive aggression-related behaviors and identifying the neural mechanisms guiding their progression and expression. However, adoption of these procedures is often impeded by the arduous task of manually scoring complex social interactions. Manual observations are generally susceptible to observer drift, long analysis times, and poor inter-rater reliability, and are further incompatible with the sampling frequencies required of modern neuroscience methods.

Objectives: In this review, we discuss recent advances in the preclinical study of appetitive aggression in mice, paired with our perspective on the potential for machine learning techniques in producing automated, robust scoring of aggressive social behavior. We discuss critical considerations for implementing valid computer classifications within behavioral pharmacological studies.

Key results: Open-source automated classification platforms can match or exceed the performance of human observers while removing the confounds of observer drift, bias, and inter-rater reliability. Furthermore, unsupervised approaches can identify previously uncharacterized aggression-related behavioral repertoires in model species.

Discussion and conclusions: Advances in open-source computational approaches hold promise for overcoming current manual annotation caveats while also introducing and generalizing computational neuroethology to the greater behavioral neuroscience community. We propose that currently available open-source approaches are sufficient for overcoming the main limitations preventing wide adoption of machine learning within the context of preclinical aggression behavioral research.

Depression and Social Defeat Stress Are Associated with Inhibitory Synaptic Changes in the Nucleus Accumbens.

J Neurosci. 2020 Aug 5;40(32):6228-6233. doi: 10.1523/JNEUROSCI.2568-19.2020. PMID: 32561672.

Heshmati M, Christoffel DJ, LeClair K, Cathomas F, Golden SA, Aleyasin H, Turecki G, Friedman AK, Han MH, Menard C, Russo SJ.

Chronic stress in both humans and rodents induces a robust downregulation of neuroligin-2, a key component of the inhibitory synapse, in the NAc that modifies behavioral coping mechanisms and stress resiliency in mice. Here we extend this observation by examining the role of two other inhibitory synapse constituents, vesicular GABA transporter (vGAT) and gephyrin, in the NAc of male mice that underwent chronic social defeat stress (CSDS) and in patients with major depressive disorder (MDD). We first performed transcriptional profiling of vGAT and gephyrin in postmortem NAc samples from a cohort of healthy controls, medicated, and nonmedicated MDD patients. In parallel, we conducted whole-cell electrophysiology recordings in the NAc of stress-susceptible and stress-resilient male mice following 10 d of CSDS. Finally, we used immunohistochemistry to analyze protein levels of vGAT and gephyrin in the NAc of mice after CSDS. We found that decreased vGAT and gephyrin mRNA in the NAc of nonmedicated MDD patients is paralleled by decreased inhibitory synapse markers and decreased frequency of mini inhibitory postsynaptic currents (mIPSC) in the NAc of susceptible mice, indicating a reduction in the number of NAc inhibitory synapses that is correlated with depression-like behavior. Overall, these findings suggest a common state of reduced inhibitory tone in the NAc in depression and stress susceptibility.

Orexin signaling in GABAergic lateral habenula neurons modulates aggressive behavior in male mice.

Nat Neurosci. 2020 May;23(5):638-650. doi: 10.1038/s41593-020-0617-7. PMID: 32284606.

Flanigan ME, Aleyasin H, Li L, Burnett CJ, Chan KL, LeClair KB, Lucas EK, Matikainen-Ankney B, Durand-de Cuttoli R, Takahashi A, Menard C, Pfau ML, Golden SA, Bouchard S, Calipari ES, Nestler EJ, DiLeone RJ, Yamanaka A, Huntley GW, Clem RL, Russo SJ.

Heightened aggression is characteristic of multiple neuropsychiatric disorders and can have various negative effects on patients, their families and the public. Recent studies in humans and animals have implicated brain reward circuits in aggression and suggest that, in subsets of aggressive individuals, domination of subordinate social targets is reinforcing. In this study, we showed that, in male mice, orexin neurons in the lateral hypothalamus activated a small population of glutamic acid decarboxylase 2 (GAD2)-expressing neurons in the lateral habenula (LHb) via orexin receptor 2 (OxR2) and that activation of these GAD2 neurons promoted male-male aggression and conditioned place preference for aggression-paired contexts. Moreover, LHb GAD2 neurons were inhibitory within the LHb and dampened the activity of the LHb as a whole. These results suggest that the orexin system is important for the regulation of inter-male aggressive behavior and provide the first functional evidence of a local inhibitory circuit within the LHb.

Molecular adaptations of the blood-brain barrier promote stress resilience vs. depression.

Proc Natl Acad Sci U S A. 2020 Feb 11;117(6):3326-3336. doi: 10.1073/pnas.1914655117. PMID: 31974313.

Dudek KA, Dion-Albert L, Lebel M, LeClair K, Labrecque S, Tuck E, Ferrer Perez C, Golden SA, Tamminga C, Turecki G, Mechawar N, Russo SJ, Menard C.

Preclinical and clinical studies suggest that inflammation and vascular dysfunction contribute to the pathogenesis of major depressive disorder (MDD). Chronic social stress alters blood-brain barrier (BBB) integrity through loss of tight junction protein claudin-5 (cldn5) in male mice, promoting passage of circulating proinflammatory cytokines and depression-like behaviors. This effect is prominent within the nucleus accumbens, a brain region associated with mood regulation; however, the mechanisms involved are unclear. Moreover, compensatory responses leading to proper behavioral strategies and active resilience are unknown. Here we identify active molecular changes within the BBB associated with stress resilience that might serve a protective role for the neurovasculature. We also confirm the relevance of such changes to human depression and antidepressant treatment. We show that permissive epigenetic regulation of cldn5 expression and low endothelium expression of repressive cldn5-related transcription factor foxo1 are associated with stress resilience. Region- and endothelial cell-specific whole transcriptomic analyses revealed molecular signatures associated with stress vulnerability vs. resilience. We identified proinflammatory TNFα/NFκB signaling and hdac1 as mediators of stress susceptibility. Pharmacological inhibition of stress-induced increase in hdac1 activity rescued cldn5 expression in the NAc and promoted resilience. Importantly, we confirmed changes in HDAC1 expression in the NAc of depressed patients without antidepressant treatment in line with CLDN5 loss. Conversely, many of these deleterious CLDN5-related molecular changes were reduced in postmortem NAc from antidepressant-treated subjects. These findings reinforce the importance of considering stress-induced neurovascular pathology in depression and provide therapeutic targets to treat this mood disorder and promote resilience.

Regulation of impulsive and aggressive behaviours by a novel lncRNA.

Mol Psychiatry. 2021 Aug;26(8):3751-3764. doi: 10.1038/s41380-019-0637-4. Epub 2020 Jan 6. PMID: 31907380.

Labonté B, Abdallah K, Maussion G, Yerko V, Yang J, Bittar T, Quessy F, Golden SA, Navarro L, Checknita D, Gigek C, Lopez JP, Neve RL, Russo SJ, Tremblay RE, Côté G, Meaney MJ, Mechawar N, Nestler EJ, Turecki G.

High impulsive and aggressive traits associate with poor behavioural self-control. Despite their importance in predicting behavioural negative outcomes including suicide, the molecular mechanisms underlying the expression of impulsive and aggressive traits remain poorly understood. Here, we identified and characterized a novel long noncoding RNA (lncRNA), acting as a regulator of the monoamine oxidase A (MAOA) gene in the brain, and named it MAOA-associated lncRNA (MAALIN). Our results show that in the brain of suicide completers, MAALIN is regulated by a combination of epigenetic mechanisms including DNA methylation and chromatin modifications. Elevated MAALIN in the dentate gyrus of impulsive-aggressive suicides was associated with lower MAOA expression. Viral overexpression of MAALIN in neuroprogenitor cells decreased MAOA expression while CRISPR-mediated knock out resulted in elevated MAOA expression. Using viral-mediated gene transfer, we confirmed that MAALIN in the hippocampus significantly decreases MAOA expression and exacerbates the expression of impulsive-aggressive behavioural traits in CD1 aggressive mice. Overall, our findings suggest that variations in DNA methylation mediate the differential expression of a novel lncRNA that acts on MAOA expression to regulate impulsive-aggressive behaviours.

Taking action: empathy and social interaction in rats.

Neuropsychopharmacology. 2020 Jun;45(7):1081-1082. doi: 10.1038/s41386-019-0596-0. PMID: 31896768.

Venniro M, Golden SA.

Imagine you are walking and notice a person crying on the sidewalk visibly in distress. This individual is not familiar to you and has not requested any assistance, so you understandably hesitate to approach. A likely question you may ask yourself in that moment of indecision is whether you would like a stranger to offer support if you found yourself in a similar situation. Do you ultimately stop to offer emotional support? The ability to understand the circumstances of someone other than yourself is defined as empathy. Empathy is a complex behavior that facilitates the formation of social connections through interpersonal socialization and aid. A lack of empathy can contribute to the psychopathology of several neuropsychiatric diseases, including autism spectrum disorder and substance use disorder. Therefore, it is crucial to understand the psychological processes and neurobiological substrates of empathic behavior.

ANIMAL MODELS OF (OR FOR) AGGRESSION REWARD, ADDICTION, AND RELAPSE: BEHAVIOR AND CIRCUITS

The Journal of Neuroscience. 2019 May 22;39(21):3996-4008. doi: 10.1523/JNEUROSCI.0151-19.2019. PMID: 30833504

Golden SA, Jin M, Shaham Y.

Inappropriate and pathological aggression plays a leading role in the suffering and death of millions of people, and further places an untenable strain on the caregivers and families of those afflicted. In some cases, such as addictive drugs, aggression can be highly rewarding (appetitive) and continually pursued despite short- and long-term negative consequences. Similarly, recidivism (relapse) rates for repeat violent offenders are as high as relapse rates for drug addicts. Appetitive aggression and relapse to aggression seeking can be modeled in mice studies using conditioned place preference and self-administration procedures followed by a period of abstinence and subsequent tests for relapse to aggression preference and aggression seeking. These procedures allow for the study of the mechanisms that control the appetitive versus the consummatory (attack) phases of aggressive behavior. In this review, we first discuss the behavioral procedures developed to probe appetitive aggression in mouse models, spanning from Pavlovian to operant tasks, and we also describe the recently proposed phenomenon of “aggression addiction.” Next, we discuss the pharmacological and circuit mechanisms of aggression conditioned place preference and aggression self-administration, seeking, and relapse, highlighting mechanistic congruence and divergence between appetitive and consummatory phases of aggression. We conclude by discussing clinical implications of the studies reviewed.

NUCLEUS ACCUMBENS DRD1-EXPRESSING NEURONS CONTROL AGGRESSION SELF-ADMINISTRATION AND AGGRESSION SEEKING IN MICE.

The Journal of Neuroscience.  2019 Mar 27;39(13):2482-2496. doi: 10.1523/JNEUROSCI.2409-18.2019. PMID: 30655356.

Golden SA, Jin M, Heins C, Venniro M, Shaham Y.

We recently developed a mouse model of appetitive operant aggression and reported that adult male outbred CD-1 mice lever-press for the opportunity to attack subordinate male mice and relapse to aggression seeking during abstinence. Here we studied the role of nucleus accumbens (NAc) dopamine receptor (Drd)1- and Drd2-expressing neurons in aggression self-administration and aggression seeking. We trained CD-1 mice to self-administer intruders (9 d, 12 trials/d) and tested them for aggression self-administration and aggression seeking on abstinence Day 1. We used immunohistochemistry and in situ hybridization to measure the neuronal activity marker Fos in the NAc, and cell-type-specific colocalization of Fos with Drd1- and Drd2-expressing neurons. To test the causal role of Drd1- and Drd2-expressing neurons, we validated a transgenic hybrid breeding strategy crossing inbred Drd1-Cre and Drd2-Cre transgenic mice with outbred CD-1 mice and used cell-type-specific Cre-DREADD (hM4Di) to inhibit NAc Drd1- and Drd2-expressing neuron activity. We found that aggression self-administration and aggression seeking induced higher Fos expression in NAc shell than in core, that Fos colocalized with Drd1 and Drd2 in both subregions, and that chemogenetic inhibition of Drd1-, but not Drd2-, expressing neurons decreased aggression self-administration and aggression seeking. Results indicate a cell-type-specific role of Drd1-expressing neurons that is critical for both aggression self-administration and aggression seeking. Our study also validates a simple breeding strategy between outbred CD-1 mice and inbred C57-based Cre lines that can be used to study cell-type and circuit mechanisms of aggression reward and relapse.

Volitional social interaction prevents drug addiction in rat models

Nature Neuroscience. 2018 Oct 15. doi: 10.1038/s41593-018-0246-6

Venniro M, Zhang M, Caprioli D, Hoots J,  Golden SA, Heins C, Morales M, Epstein DH, Shaham Y.

Addiction treatment has not been appreciably improved by neuroscientific research. One problem is that mechanistic studies using rodent models do not incorporate volitional social factors, which play a critical role in human addiction. Here, using rats, we introduce an operant model of choice between drugs and social interaction. Independent of sex, drug class, drug dose, training conditions, abstinence duration, social housing, or addiction score in Diagnostic & Statistical Manual IV-based and intermittent access models, operant social reward prevented drug self-administration. This protection was lessened by delay or punishment of the social reward but neither measure was correlated with the addiction score. Social-choice-induced abstinence also prevented incubation of methamphetamine craving. This protective effect was associated with activation of central amygdala PKCδ-expressing inhibitory neurons and inhibition of anterior insular cortex activity. These findings highlight the need for incorporating social factors into neuroscience-based addiction research and support the wider implantation of socially based addiction treatments.

AGGRESSION ADDICTION AND RELAPSE: A NEW FRONTIER IN PSYCHIATRY.

Neuropsychopharmacology. 2018 Jan;43(1):224-225. doi: 10.1038/npp.2017.173. PMID: 29192664.

Golden SA, Shaham Y.

There is an increased risk for abnormal or pathological aggression in individuals suffering from psychiatric disorders. Aggression is commonly ethologically demarcated as either appetitive or reactive, each with its own behavioral characteristics, functionality, and neural basis that may transition from adaptive to maladaptive depending on genetic and environmental factors. One type, pathological appetitive aggression, is hypothesized to result from excessive activation of evolutionary conserved reward circuits, which also mediate the rewarding effects of addictive drugs. Indeed, inappropriate appetitive aggression shows core features of addiction: aggression is often sought despite immediate or long-term adverse consequences, and relapse (recidivism) rates among violent offenders are as high as relapse rates in drug addiction. Despite these similarities, pathological aggression seeking has not been commonly incorporated into the conceptual framework of addiction and psychiatric disorders. Such a reconceptualization may positively impact therapeutic strategies to prevent pathological aggression and decrease recidivism (relapse) rates after incarceration or inpatient treatment.

COMBINATORIAL PSYCHO-PHARMACOLOGICAL APPROACHES FOR THE TREATMENT OF ABNORMAL AGGRESSION.

Neuropsychopharmacology. 2018 Jan;43(2):233-234. doi: 10.1038/npp.2017.174. PMID: 28816241.

Golden SA, Takahashi A.

Aggression is a highly evolutionarily adaptive behavior that is critical for survival and reproduction, and therefore, strongly ethologically conserved across species. However, due to environmental or biological processes, aggressive behavior can transition from adaptive to maladaptive. This transition is associated with detrimental outcomes for both the individual exhibiting the behavior and their victims. Within the United States, an estimated 2.7 million individuals over the age of 12 report experiencing one or more violent victimizations annually (Truman and Morgan, 2016), and ~70% of victims of serious violence experience ongoing socio-emotional problems as a direct result (Langton and Truman, 2014). Due to the marked impact violence has on societal health and well-being, there have been efforts to identify the underlying risk factors associated with the development of abnormal aggression. Longitudinal prospective population-based studies have consistently associated future violence and crime with early-life adversities such as abuse or neglect. Strikingly, early-life neglect is one of the most damaging predisposing factors, even more so than inter-personal violence and physical or sexual abuse (Gilbert et al., 2009).  

Social stress induces neurovascular pathology promoting depression.

Nat Neurosci. 2017 Dec;20(12):1752-1760. doi: 10.1038/s41593-017-0010-3.

Menard C, Pfau ML, Hodes GE, Kana V, Wang VX, Bouchard S, Takahashi A, Flanigan ME, Aleyasin H, LeClair KB, Janssen WG, Labonté B, Parise EM, Lorsch ZS, Golden SA, Heshmati M, Tamminga C, Turecki G, Campbell M, Fayad ZA, Tang CY, Merad M, Russo SJ.

Studies suggest that heightened peripheral inflammation contributes to the pathogenesis of major depressive disorder. We investigated the effect of chronic social defeat stress, a mouse model of depression, on blood-brain barrier (BBB) permeability and infiltration of peripheral immune signals. We found reduced expression of the endothelial cell tight junction protein claudin-5 (Cldn5) and abnormal blood vessel morphology in nucleus accumbens (NAc) of stress-susceptible but not resilient mice. CLDN5 expression was also decreased in NAc of depressed patients. Cldn5 downregulation was sufficient to induce depression-like behaviors following subthreshold social stress whereas chronic antidepressant treatment rescued Cldn5 loss and promoted resilience. Reduced BBB integrity in NAc of stress-susceptible or mice injected with adeno-associated virus expressing shRNA against Cldn5 caused infiltration of the peripheral cytokine interleukin-6 (IL-6) into brain parenchyma and subsequent expression of depression-like behaviors. These findings suggest that chronic social stress alters BBB integrity through loss of tight junction protein Cldn5, promoting peripheral IL-6 passage across the BBB and depression.

An emerging role for the lateral habenula in aggressive behavior.

Pharmacol Biochem Behav. 2017 Nov;162:79-86. doi: 10.1016/j.pbb.2017.05.003.

Flanigan M, Aleyasin H, Takahashi A, Golden SA, Russo SJ.

Inter-male aggression is an essential component of social behavior in organisms from insects to humans. However, when expressed inappropriately, aggression poses significant threats to the mental and physical health of both the aggressor and the target. Inappropriate aggression is a common feature of numerous neuropsychiatric disorders in humans and has been hypothesized to result from the atypical activation of reward circuitry in response to social targets. The lateral habenula (LHb) has recently been identified as a major node of the classical reward circuitry and inhibits the release of dopamine from the midbrain to signal negative valence. Here, we discuss the evidence linking LHb function to aggression and its valence, arguing that strong LHb outputs to the ventral tegmental area (VTA) and the dorsal raphe nucleus (DRN) are likely to play roles in aggression and its rewarding components. Future studies should aim to elucidate how various inputs and outputs of the LHb shape motivation and reward in the context of aggression.

COMPULSIVE ADDICTION-LIKE AGGRESSIVE BEHAVIOR IN MICE.

Biol Psychiatry. 2017 Aug 15;82(4):239-248. doi: 10.1016/j.biopsych.2017.03.004. PMID: 28434654.

Golden SA, Heins C, Venniro M, Caprioli D, Zhang M, Epstein DH, Shaham Y.

BACKGROUND: Some people are highly motivated to seek aggressive encounters, and among those who have been incarcerated for such behavior, recidivism rates are high. These observations echo two core features of drug addiction: high motivation to seek addictive substances, despite adverse consequences, and high relapse rates. Here we used established rodent models of drug addiction to determine whether they would be sensitive to "addiction-like" features of aggression in CD-1 mice.

METHODS: In experiments 1 and 2, we trained older CD-1 mice to lever press for opportunities to attack younger C57BL6/J mice. We then tested them for relapse to aggression seeking after forced abstinence or punishment-induced suppression of aggression self-administration. In experiment 3, we trained a large cohort of CD-1 mice and tested them for choice-based voluntary suppression of aggression seeking, relapse to aggression seeking, progressive ratio responding, and punishment-induced suppression of aggression self-administration. We then used cluster analysis to identify patterns of individual differences in compulsive "addiction-like" aggressive behavior.

RESULTS: In experiments 1 and 2, we observed strong motivation to acquire operant self-administration of opportunities to aggress and relapse vulnerability during abstinence. In experiment 3, cluster analysis of the aggression-related measures identified a subset of "addicted" mice (∼19%) that exhibited intense operant-reinforced attack behavior, decreased likelihood to select an alternative reinforcer over aggression, heightened relapse vulnerability and progressive ratio responding, and resilience to punishment-induced suppression of aggressive behavior.

CONCLUSIONS: Using procedures established to model drug addiction, we showed that a subpopulation of CD-1 mice demonstrate "addiction-like" aggressive behavior, suggesting an evolutionary origin for compulsive aggression.

PERSISTENT CONDITIONED PLACE PREFERENCE TO AGGRESSION EXPERIENCE IN ADULT MALE SEXUALLY-EXPERIENCED CD-1 MICE.

Genes Brain Behav. 2017 Jan;16(1):44-55. doi: 10.1111/gbb.12310. PMID: 27457669.

Golden SA*, Aleyasin H*, Heins R, Flanigan M, Heshmati M, Takahashi A, Russo SJ, Shaham Y.

We recently developed a conditioned place preference (CPP) procedure, commonly used to study rewarding drug effects, to demonstrate that dominant sexually-experienced CD-1 male mice form CPP to contexts previously associated with defeating subordinate male C57BL/6J mice. Here we further characterized conditioned and unconditioned aggression behavior in CD-1 mice. In Exp. 1 we used CD-1 mice that displayed a variable spectrum of unconditioned aggressive behavior toward younger subordinate C57BL/6J intruder mice. We then trained the CD-1 mice in the CPP procedure where one context was intruder-paired, while a different context was not. We then tested for aggression CPP 1 day after training. In Exp. 2, we tested CD-1 mice for aggression CPP 1 day and 18 days after training. In Exp. 3-4, we trained the CD-1 mice to lever-press for palatable food and tested them for footshock punishment-induced suppression of food-reinforced responding. In Exp. 5, we characterized unconditioned aggression in hybrid CD-1 × C57BL/6J D1-Cre or D2-Cre F1 generation crosses. Persistent aggression CPP was observed in CD-1 mice that either immediately attacked C57BL/6J mice during all screening sessions or mice that gradually developed aggressive behavior during the screening phase. In contrast, CD-1 mice that did not attack the C57BL/6J mice during screening did not develop CPP to contexts previously paired with C57BL/6J mice. The aggressive phenotype did not predict resistance to punishment-induced suppression of food-reinforced responding. CD-1 × D1-Cre or D2-Cre F1 transgenic mice showed strong unconditioned aggression. Our study demonstrates that aggression experience causes persistent CPP and introduces transgenic mice for circuit studies of aggression.

Integrative Analysis of Sex-Specific microRNA Networks Following Stress in Mouse Nucleus Accumbens.

Front Mol Neurosci. 2016 Dec 23;9:144. doi: 10.3389/fnmol.2016.00144. 

Pfau ML, Purushothaman I, Feng J, Golden SA, Aleyasin H, Lorsch ZS, Cates HM, Flanigan ME, Menard C, Heshmati M, Wang Z, Ma'ayan A, Shen L, Hodes GE, Russo SJ.

Adult women are twice as likely as men to suffer from affective and anxiety disorders, although the mechanisms underlying heightened female stress susceptibility are incompletely understood. Recent findings in mouse Nucleus Accumbens (NAc) suggest a role for DNA methylation-driven sex differences in genome-wide transcriptional profiles. However, the role of another epigenetic process-microRNA (miR) regulation-has yet to be explored. We exposed male and female mice to Subchronic Variable Stress (SCVS), a stress paradigm that produces depression-like behavior in female, but not male, mice, and performed next generation mRNA and miR sequencing on NAc tissue. We applied a combination of differential expression, miR-mRNA network and functional enrichment analyses to characterize the transcriptional and post-transcriptional landscape of sex differences in NAc stress response. We find that male and female mice exhibit largely non-overlapping miR and mRNA profiles following SCVS. The two sexes also show enrichment of different molecular pathways and functions. Collectively, our results suggest that males and females mount fundamentally different transcriptional and post-transcriptional responses to SCVS and engage sex-specific molecular processes following stress. These findings have implications for the pathophysiology and treatment of stress-related disorders in women.

BASAL FOREBRAIN PROJECTIONS TO THE LATERAL HABENULA MODULATE AGGRESSION REWARD.

Nature. 2016 Jun 30;534(7609):688-92. doi: 10.1038/nature18601. PMID: 27357796.

Golden SA, Heshmati M, Flanigan M, Christoffel DJ, Guise K, Pfau ML, Aleyasin H, Menard C, Zhang H, Hodes GE, Bregman D, Khibnik L, Tai J, Rebusi N, Krawitz B, Chaudhury D, Walsh JJ, Han MH, Shapiro ML, Russo SJ.

Maladaptive aggressive behaviour is associated with a number of neuropsychiatric disorders and is thought to result partly from the inappropriate activation of brain reward systems in response to aggressive or violent social stimuli. Nuclei within the ventromedial hypothalamus, extended amygdala and limbic circuits are known to encode initiation of aggression; however, little is known about the neural mechanisms that directly modulate the motivational component of aggressive behaviour. Here we established a mouse model to measure the valence of aggressive inter-male social interaction with a smaller subordinate intruder as reinforcement for the development of conditioned place preference (CPP). Aggressors develop a CPP, whereas non-aggressors develop a conditioned place aversion to the intruder-paired context. Furthermore, we identify a functional GABAergic projection from the basal forebrain (BF) to the lateral habenula (lHb) that bi-directionally controls the valence of aggressive interactions. Circuit-specific silencing of GABAergic BF-lHb terminals of aggressors with halorhodopsin (NpHR3.0) increases lHb neuronal firing and abolishes CPP to the intruder-paired context. Activation of GABAergic BF-lHb terminals of non-aggressors with channelrhodopsin (ChR2) decreases lHb neuronal firing and promotes CPP to the intruder-paired context. Finally, we show that altering inhibitory transmission at BF-lHb terminals does not control the initiation of aggressive behaviour. These results demonstrate that the BF-lHb circuit has a critical role in regulating the valence of inter-male aggressive behaviour and provide novel mechanistic insight into the neural circuits modulating aggression reward processing.

Mefloquine in the nucleus accumbens promotes social avoidance and anxiety-like behavior in mice.

Neuropharmacology. 2016 Feb;101:351-7. doi: 10.1016/j.neuropharm.2015.10.013.

Heshmati M, Golden SA, Pfau ML, Christoffel DJ, Seeley EL, Cahill ME, Khibnik LA, Russo SJ.

Mefloquine continues to be a key drug used for malaria chemoprophylaxis and treatment, despite reports of adverse events like depression and anxiety. It is unknown how mefloquine acts within the central nervous system to cause depression and anxiety or why some individuals are more vulnerable. We show that intraperitoneal injection of mefloquine in mice, when coupled to subthreshold social defeat stress, is sufficient to produce depression-like social avoidance behavior. Direct infusion of mefloquine into the nucleus accumbens (NAc), a key brain reward region, increased stress-induced social avoidance and anxiety behavior. In contrast, infusion into the ventral hippocampus had no effect. Whole cell recordings from NAc medium spiny neurons indicated that mefloquine application increases the frequency of spontaneous excitatory postsynaptic currents, a synaptic adaptation that we have previously shown to be associated with increased susceptibility to social defeat stress. Together, these data demonstrate a role for the NAc in mefloquine-induced depression and anxiety-like behaviors.

Sex Differences in Nucleus Accumbens Transcriptome Profiles Associated with Susceptibility versus Resilience to Subchronic Variable Stress.

J Neurosci. 2015 Dec 16;35(50):16362-76. doi: 10.1523/JNEUROSCI.1392-15.2015.

Pfau ML, Purushothaman I, Feng J, Golden SA, Aleyasin H, Lorsch ZS, Cates HM, Flanigan ME, Menard C, Heshmati M, Wang Z, Ma'ayan A, Shen L, Hodes GE, Russo SJ.

Depression and anxiety disorders are more prevalent in females, but the majority of research in animal models, the first step in finding new treatments, has focused predominantly on males. Here we report that exposure to subchronic variable stress (SCVS) induces depression-associated behaviors in female mice, whereas males are resilient as they do not develop these behavioral abnormalities. In concert with these different behavioral responses, transcriptional analysis of nucleus accumbens (NAc), a major brain reward region, by use of RNA sequencing (RNA-seq) revealed markedly different patterns of stress regulation of gene expression between the sexes. Among the genes displaying sex differences was DNA methyltransferase 3a (Dnmt3a), which shows a greater induction in females after SCVS. Interestingly, Dnmt3a expression levels were increased in the NAc of depressed humans, an effect seen in both males and females. Local overexpression of Dnmt3a in NAc rendered male mice more susceptible to SCVS, whereas Dnmt3a knock-out in this region rendered females more resilient, directly implicating this gene in stress responses. Associated with this enhanced resilience of female mice upon NAc knock-out of Dnmt3a was a partial shift of the NAc female transcriptome toward the male pattern after SCVS. These data indicate that males and females undergo different patterns of transcriptional regulation in response to stress and that a DNA methyltransferase in NAc contributes to sex differences in stress vulnerability.

ACF chromatin-remodeling complex mediates stress-induced depressive-like behavior.

Nat Med. 2015 Oct;21(10):1146-53. doi: 10.1038/nm.3939. 

Sun H, Damez-Werno DM, Scobie KN, Shao NY, Dias C, Rabkin J, Koo JW, Korb E, Bagot RC, Ahn FH, Cahill ME, Labonté B, Mouzon E, Heller EA, Cates H, Golden SA, Gleason K, Russo SJ, Andrews S, Neve R, Kennedy PJ, Maze I, Dietz DM, Allis CD, Turecki G, Varga-Weisz P, Tamminga C, Shen L, Nestler EJ.

Improved treatment for major depressive disorder (MDD) remains elusive because of the limited understanding of its underlying biological mechanisms. It is likely that stress-induced maladaptive transcriptional regulation in limbic neural circuits contributes to the development of MDD, possibly through epigenetic factors that regulate chromatin structure. We establish that persistent upregulation of the ACF (ATP-utilizing chromatin assembly and remodeling factor) ATP-dependent chromatin-remodeling complex, occurring in the nucleus accumbens of stress-susceptible mice and depressed humans, is necessary for stress-induced depressive-like behaviors. We found that altered ACF binding after chronic stress was correlated with altered nucleosome positioning, particularly around the transcription start sites of affected genes. These alterations in ACF binding and nucleosome positioning were associated with repressed expression of genes implicated in susceptibility to stress. Together, our findings identify the ACF chromatin-remodeling complex as a critical component in the development of susceptibility to depression and in regulating stress-related behaviors.

Effects of acute and chronic social defeat stress are differentially mediated by the dynorphin/kappa-opioid receptor system.

Behav Pharmacol. 2015 Oct;26(7 Spec No):654-63. doi: 10.1097/FBP.0000000000000155.

Donahue RJ, Landino SM, Golden SA, Carroll FI, Russo SJ, Carlezon WA Jr.

Improved treatment for major depressive disorder (MDD) remains elusive because of the limited understanding of its underlying biological mechanisms. It is likely that stress-induced maladaptive transcriptional regulation in limbic neural circuits contributes to the development of MDD, possibly through epigenetic factors that regulate chromatin structure. We establish that persistent upregulation of the ACF (ATP-utilizing chromatin assembly and remodeling factor) ATP-dependent chromatin-remodeling complex, occurring in the nucleus accumbens of stress-susceptible mice and depressed humans, is necessary for stress-induced depressive-like behaviors. We found that altered ACF binding after chronic stress was correlated with altered nucleosome positioning, particularly around the transcription start sites of affected genes. These alterations in ACF binding and nucleosome positioning were associated with repressed expression of genes implicated in susceptibility to stress. Together, our findings identify the ACF chromatin-remodeling complex as a critical component in the development of susceptibility to depression and in regulating stress-related behaviors.

EXCITATORY TRANSMISSION AT THALAMO-STRIATAL SYNAPSES MEDIATES SUSCEPTIBILITY TO SOCIAL STRESS.

Nat Neurosci. 2015 Jul;18(7):962-4. doi: 10.1038/nn.4034.

Christoffel DJ*, Golden SA*, Walsh JJ, Guise KG, Heshmati M, Friedman AK, Dey A, Smith M, Rebusi N, Pfau M, Ables JL, Aleyasin H, Khibnik LA, Hodes GE, Ben-Dor GA, Deisseroth K, Shapiro ML, Malenka RC, Ibanez-Tallon I, Han MH, Russo SJ.

Postsynaptic remodeling of glutamatergic synapses on ventral striatum (vSTR) medium spiny neurons (MSNs) is critical for shaping stress responses. However, it is unclear which presynaptic inputs are involved. Susceptible mice exhibited increased synaptic strength at intralaminar thalamus (ILT), but not prefrontal cortex (PFC), inputs to vSTR MSNs following chronic social stress. Modulation of ILT-vSTR versus PFC-vSTR neuronal activity differentially regulated dendritic spine plasticity and social avoidance.

Locus-specific epigenetic remodeling controls addiction- and depression-related behaviors.

Nat Neurosci. 2014 Dec;17(12):1720-7. doi: 10.1038/nn.3871. Epub 2014 Oct 27.

Heller EA, Cates HM, Peña CJ, Sun H, Shao N, Feng J, Golden SA, Herman JP, Walsh JJ, Mazei-Robison M, Ferguson D, Knight S, Gerber MA, Nievera C, Han MH, Russo SJ, Tamminga CS, Neve RL, Shen L, Zhang HS, Zhang F, Nestler EJ.

Chronic exposure to drugs of abuse or stress regulates transcription factors, chromatin-modifying enzymes and histone post-translational modifications in discrete brain regions. Given the promiscuity of the enzymes involved, it has not yet been possible to obtain direct causal evidence to implicate the regulation of transcription and consequent behavioral plasticity by chromatin remodeling that occurs at a single gene. We investigated the mechanism linking chromatin dynamics to neurobiological phenomena by applying engineered transcription factors to selectively modify chromatin at a specific mouse gene in vivo. We found that histone methylation or acetylation at the Fosb locus in nucleus accumbens, a brain reward region, was sufficient to control drug- and stress-evoked transcriptional and behavioral responses via interactions with the endogenous transcriptional machinery. This approach allowed us to relate the epigenetic landscape at a given gene directly to regulation of its expression and to its subsequent effects on reward behavior.

Individual differences in the peripheral immune system promote resilience versus susceptibility to social stress.

Proc Natl Acad Sci U S A. 2014 Nov 11;111(45):16136-41. doi: 10.1073/pnas.1415191111.

Hodes GE, Pfau ML, Leboeuf M, Golden SA, Christoffel DJ, Bregman D, Rebusi N, Heshmati M, Aleyasin H, Warren BL, Lebonté B, Horn S, Lapidus KA, Stelzhammer V, Wong EH, Bahn S, Krishnan V, Bolaños-Guzman CA, Murrough JW, Merad M, Russo SJ.

Depression and anxiety disorders are associated with increased release of peripheral cytokines; however, their functional relevance remains unknown. Using a social stress model in mice, we find preexisting individual differences in the sensitivity of the peripheral immune system that predict and promote vulnerability to social stress. Cytokine profiles were obtained 20 min after the first social stress exposure. Of the cytokines regulated by stress, IL-6 was most highly up-regulated only in mice that ultimately developed a susceptible behavioral phenotype following a subsequent chronic stress, and levels remained elevated for at least 1 mo. We confirmed a similar elevation of serum IL-6 in two separate cohorts of patients with treatment-resistant major depressive disorder. Before any physical contact in mice, we observed individual differences in IL-6 levels from ex vivo stimulated leukocytes that predict susceptibility versus resilience to a subsequent stressor. To shift the sensitivity of the peripheral immune system to a pro- or antidepressant state, bone marrow (BM) chimeras were generated by transplanting hematopoietic progenitor cells from stress-susceptible mice releasing high IL-6 or from IL-6 knockout (IL-6(-/-)) mice. Stress-susceptible BM chimeras exhibited increased social avoidance behavior after exposure to either subthreshold repeated social defeat stress (RSDS) or a purely emotional stressor termed witness defeat. IL-6(-/-) BM chimeric and IL-6(-/-) mice, as well as those treated with a systemic IL-6 monoclonal antibody, were resilient to social stress. These data establish that preexisting differences in stress-responsive IL-6 release from BM-derived leukocytes functionally contribute to social stress-induced behavioral abnormalities.

Stress and CRF gate neural activation of BDNF in the mesolimbic reward pathway.

Nat Neurosci. 2014 Jan;17(1):27-9. doi: 10.1038/nn.3591.

Walsh JJ, Friedman AK, Sun H, Heller EA, Ku SM, Juarez B, Burnham VL, Mazei-Robison MS, Ferguson D, Golden SA, Koo JW, Chaudhury D, Christoffel DJ, Pomeranz L, Friedman JM, Russo SJ, Nestler EJ, Han MH.

Mechanisms controlling release of brain-derived neurotrophic factor (BDNF) in the mesolimbic dopamine reward pathway remain unknown. We report that phasic optogenetic activation of this pathway increases BDNF amounts in the nucleus accumbens (NAc) of socially stressed mice but not of stress-naive mice. This stress gating of BDNF signaling is mediated by corticotrophin-releasing factor (CRF) acting in the NAc. These results unravel a stress context-detecting function of the brain's mesolimbic circuit.

Fluoxetine epigenetically alters the CaMKIIα promoter in nucleus accumbens to regulate ΔFosB binding and antidepressant effects.

Neuropsychopharmacology. 2014 Apr;39(5):1178-86. doi: 10.1038/npp.2013.319.

Robison AJ, Vialou V, Sun HS, Labonte B, Golden SA, Dias C, Turecki G, Tamminga C, Russo S, Mazei-Robison M, Nestler EJ.

Chronic social defeat stress in mice produces a susceptible phenotype characterized by several behavioral abnormalities consistent with human depression that are reversed by chronic but not acute exposure to antidepressant medications. Recent work in addiction models demonstrates that the transcription factor ΔFosB and protein kinase calmodulin-dependent protein kinase II (CaMKII) are co-regulated in nucleus accumbens (NAc), a brain reward region implicated in both addiction and depression models including social defeat. Previous work has also demonstrated that ΔFosB is induced in NAc after chronic social defeat stress or after chronic antidepressant treatment, wherein it mediates a pro-resilience or antidepressant-like phenotype. Here, using chromatin immunoprecipitation assays, we found that ΔFosB binds the CaMKIIα gene promoter in NAc and that this binding increases after mice are exposed to chronic social defeat stress. Paradoxically, chronic exposure to the antidepressant fluoxetine reduces binding of ΔFosB to the CaMKIIα promoter and reduces CaMKII expression in NAc, despite the fact that ΔFosB is induced under these conditions. These data suggest a novel epigenetic mechanism of antidepressant action, whereby fluoxetine induces some chromatin change at the CaMKIIα promoter, which blocks the ΔFosB binding. Indeed, chronic fluoxetine reduces acetylation and increases lysine-9 dimethylation of histone H3 at the CaMKIIα promoter in NAc, effects also seen in depressed humans exposed to antidepressants. Overexpression of CaMKII in NAc blocks fluoxetine's antidepressant effects in the chronic social defeat paradigm, whereas inhibition of CaMKII activity in NAc mimics fluoxetine exposure. These findings suggest that epigenetic suppression of CaMKIIα expression in NAc is behaviorally relevant and offer a novel pathway for possible therapeutic intervention in depression and related syndromes.

Incubation of fear.

Curr Protoc Neurosci. 2013 Jul;Chapter 6:Unit 6.27. doi: 10.1002/0471142301.ns0627s64.

Pickens CL, Golden SA, Nair SG.

While fear and anxiety can grow over time in anxiety disorders, most efforts to model this phenomenon with fear conditioning in rodents cause fear that remains stable or decreases across weeks or months. Here, we describe several methods to induce conditioned fear that grows over the course of 1 month and is sustained for at least 2 months using an extended fear conditioning approach. These methods include a very reliable standard method that causes multiple fear measures to increase over months, as well as alternative methods.

Kalirin-7 mediates cocaine-induced AMPA receptor and spine plasticity, enabling incentive sensitization.

J Neurosci. 2013 Jul 3;33(27):11012-22. doi: 10.1523/JNEUROSCI.1097-13.2013.

Wang X, Cahill ME, Werner CT, Christoffel DJ, Golden SA, Xie Z, Loweth JA, Marinelli M, Russo SJ, Penzes P, Wolf ME.

It is well established that behavioral sensitization to cocaine is accompanied by increased spine density and AMPA receptor (AMPAR) transmission in the nucleus accumbens (NAc), but two major questions remain unanswered. Are these adaptations mechanistically coupled? And, given that they can be dissociated from locomotor sensitization, what is their functional significance? We tested the hypothesis that the guanine-nucleotide exchange factor Kalirin-7 (Kal-7) couples cocaine-induced AMPAR and spine upregulation and that these adaptations underlie sensitization of cocaine's incentive-motivational properties-the properties that make it "wanted." Rats received eight daily injections of saline or cocaine. On withdrawal day 14, we found that Kal-7 levels and activation of its downstream effectors Rac-1 and PAK were increased in the NAc of cocaine-sensitized rats. Furthermore, AMPAR surface expression and spine density were increased, as expected. To determine whether these changes require Kal-7, a lentiviral vector expressing Kal-7 shRNA was injected into the NAc core before cocaine exposure. Knocking down Kal-7 abolished the AMPAR and spine upregulation normally seen during cocaine withdrawal. Despite the absence of these adaptations, rats with reduced Kal-7 levels developed locomotor sensitization. However, incentive sensitization, which was assessed by how rapidly rats learned to self-administer a threshold dose of cocaine, was severely impaired. These results identify a signaling pathway coordinating AMPAR and spine upregulation during cocaine withdrawal, demonstrate that locomotor and incentive sensitization involve divergent mechanisms, and link enhanced excitatory transmission in the NAc to incentive sensitization.

EPIGENETIC REGULATION OF RAC1 INDUCES SYNAPTIC REMODELING IN STRESS DISORDERS AND DEPRESSION.

Nat Med. 2013 Mar;19(3):337-44. doi: 10.1038/nm.3090. 

Golden SA, Christoffel DJ, Heshmati M, Hodes GE, Magida J, Davis K, Cahill ME, Dias C, Ribeiro E, Ables JL, Kennedy PJ, Robison AJ, Gonzalez-Maeso J, Neve RL, Turecki G, Ghose S, Tamminga CA, Russo SJ.

Depression induces structural and functional synaptic plasticity in brain reward circuits, although the mechanisms promoting these changes and their relevance to behavioral outcomes are unknown. Transcriptional profiling of the nucleus accumbens (NAc) for Rho GTPase-related genes, which are known regulators of synaptic structure, revealed a sustained reduction in RAS-related C3 botulinum toxin substrate 1 (Rac1) expression after chronic social defeat stress. This was associated with a repressive chromatin state surrounding the proximal promoter of Rac1. Inhibition of class 1 histone deacetylases (HDACs) with MS-275 rescued both the decrease in Rac1 transcription after social defeat stress and depression-related behavior, such as social avoidance. We found a similar repressive chromatin state surrounding the RAC1 promoter in the NAc of subjects with depression, which corresponded with reduced RAC1 transcription. Viral-mediated reduction of Rac1 expression or inhibition of Rac1 activity in the NAc increases social defeat-induced social avoidance and anhedonia in mice. Chronic social defeat stress induces the formation of stubby excitatory spines through a Rac1-dependent mechanism involving the redistribution of synaptic cofilin, an actin-severing protein downstream of Rac1. Overexpression of constitutively active Rac1 in the NAc of mice after chronic social defeat stress reverses depression-related behaviors and prunes stubby spines. Taken together, our data identify epigenetic regulation of RAC1 in the NAc as a disease mechanism in depression and reveal a functional role for Rac1 in rodents in regulating stress-related behaviors.

Silent synapses in selectively activated nucleus accumbens neurons following cocaine sensitization.

Nat Neurosci. 2012 Nov;15(11):1556-62. doi: 10.1038/nn.3232.

Koya E, Cruz FC, Ator R, Golden SA, Hoffman AF, Lupica CR, Hope BT.

Cocaine-induced alterations in synaptic glutamate function in nucleus accumbens are thought to mediate drug-related behaviors such as psychomotor sensitization. However, previous studies have examined global alterations in randomly selected accumbens neurons regardless of their activation state during cocaine-induced behavior. We recently found that a minority of strongly activated Fos-expressing accumbens neurons are necessary for cocaine-induced psychomotor sensitization, whereas the majority of accumbens neurons are less directly involved. We assessed synaptic alterations in these strongly activated accumbens neurons in Fos-GFP mice, which express a fusion protein of Fos and GFP in strongly activated neurons, and compared these alterations with those in surrounding non-activated neurons. Cocaine sensitization produced higher levels of 'silent synapses', which contained functional NMDA receptors and nonfunctional AMPA receptors only in GFP-positive neurons, 6-11 d after sensitization. Thus, distinct synaptic alterations are induced in the most strongly activated accumbens neurons that mediate psychomotor sensitization.

MECHANISMS OF PSYCHOSTIMULANT-INDUCED STRUCTURAL PLASTICITY.

Cold Spring Harb Perspect Med. 2012 Oct 1;2(10). pii: a011957. doi: 10.1101/cshperspect.a011957.

Golden SA, Russo SJ.

Psychostimulants robustly induce alterations in neuronal structural plasticity throughout brain reward circuits. However, despite our extensive understanding of how these circuits modulate motivated behavior, it is still unclear whether structural plasticity within these regions drives pathological behavioral responses in addiction. Although these structural changes have been subjected to an exhaustive phenomenological characterization, we still have a limited understanding of the molecular mechanisms regulating their induction and the functional relevance of such changes in mediating addiction-like behavior. Here we have highlighted the known molecular pathways and intracellular signaling cascades that regulate psychostimulant-induced changes in neuronal morphology and synaptic restructuring, and we discuss them in the larger context of addiction behavior.

HDAC2 regulates atypical antipsychotic responses through the modulation of mGlu2 promoter activity.

Nat Neurosci. 2012 Sep;15(9):1245-54. doi: 10.1038/nn.3181. 

Kurita M, Holloway T, García-Bea A, Kozlenkov A, Friedman AK, Moreno JL, Heshmati M, Golden SA, Kennedy PJ, Takahashi N, Dietz DM, Mocci G, Gabilondo AM, Hanks J, Umali A, Callado LF, Gallitano AL, Neve RL, Shen L, Buxbaum JD, Han MH, Nestler EJ, Meana JJ, Russo SJ, González-Maeso J.

Histone deacetylases (HDACs) compact chromatin structure and repress gene transcription. In schizophrenia, clinical studies demonstrate that HDAC inhibitors are efficacious when given in combination with atypical antipsychotics. However, the molecular mechanism that integrates a better response to antipsychotics with changes in chromatin structure remains unknown. Here we found that chronic atypical antipsychotics downregulated the transcription of metabotropic glutamate 2 receptor (mGlu2, also known as Grm2), an effect that was associated with decreased histone acetylation at its promoter in mouse and human frontal cortex. This epigenetic change occurred in concert with a serotonin 5-HT(2A) receptor-dependent upregulation and increased binding of HDAC2 to the mGlu2 promoter. Virally mediated overexpression of HDAC2 in frontal cortex decreased mGlu2 transcription and its electrophysiological properties, thereby increasing psychosis-like behavior. Conversely, HDAC inhibitors prevented the repressive histone modifications induced at the mGlu2 promoter by atypical antipsychotics, and augmented their therapeutic-like effects. These observations support the view of HDAC2 as a promising new target for schizophrenia treatment.

Effects of inhibitor of κB kinase activity in the nucleus accumbens on emotional behavior.

Neuropsychopharmacology. 2012 Nov;37(12):2615-23. doi: 10.1038/npp.2012.121.

Christoffel DJ, Golden SA, Heshmati M, Graham A, Birnbaum S, Neve RL, Hodes GE, Russo SJ.

Inhibitor of κB kinase (IκK) has historically been studied in the context of immune response and inflammation, but recent evidence demonstrates that IκK activity is necessary and sufficient for regulation of neuronal function. Chronic social defeat stress of mice increases IκK activity in the nucleus accumbens (NAc) and this increase is strongly correlated to depression-like behaviors. Inhibition of IκK signaling results in a reversal of chronic social defeat stress-induced social avoidance behavior. Here, we more completely define the role of IκK in anxiety and depressive-like behaviors. Mice underwent stereotaxic microinjection of a herpes simplex virus expressing either green fluorescent protein, a constitutively active form of IκK (IκKca), or a dominant negative form of IκK into the NAc. Of all three experimental groups, only mice expressing IκKca show a behavioral phenotype. Expression of IκKca results in a decrease in the time spent in the non-periphery zones of an open field arena and increased time spent immobile during a forced swim test. No baseline differences in sucrose preference were observed, but following the acute swim stress we noted a marked reduction in sucrose preference. To determine whether IκK activity alters responses to other acute stressors, we examined behavior and spine morphology in mice undergoing an acute social defeat stress. We found that IκKca enhanced social avoidance behavior and promoted thin spine formation. These data show that IκK in NAc is a critical regulator of both depressive- and anxiety-like states and may do so by promoting the formation of immature excitatory synapses.

Structural and synaptic plasticity in stress-related disorders.

Rev Neurosci. 2011;22(5):535-49. doi: 10.1515/RNS.2011.044.

Christoffel DJ, Golden SA, Russo SJ.

Stress can have a lasting impact on the structure and function of brain circuitry that results in long-lasting changes in the behavior of an organism. Synaptic plasticity is the mechanism by which information is stored and maintained within individual synapses, neurons, and neuronal circuits to guide the behavior of an organism. Although these mechanisms allow the organism to adapt to its constantly evolving environment, not all of these adaptations are beneficial. Under prolonged bouts of physical or psychological stress, these mechanisms become dysregulated, and the connectivity between brain regions becomes unbalanced, resulting in pathological behaviors. In this review, we highlight the effects of stress on the structure and function of neurons within the mesocorticolimbic brain systems known to regulate mood and motivation. We then discuss the implications of these spine adaptations on neuronal activity and pathological behaviors implicated in mood disorders. Finally, we end by discussing recent brain imaging studies in human depression within the context of these basic findings to provide insight into the underlying mechanisms leading to neural dysfunction in depression.

A STANDARDIZED PROTOCOL FOR REPEATED SOCIAL DEFEAT STRESS IN MICE.

Nat Protoc. 2011 Jul 21;6(8):1183-91. doi: 10.1038/nprot.2011.361

Golden SA, Covington HE 3rd, Berton O, Russo SJ.

A major impediment to novel drug development has been the paucity of animal models that accurately reflect symptoms of affective disorders. In animal models, prolonged social stress has proven to be useful in understanding the molecular mechanisms underlying affective-like disorders. When considering experimental approaches for studying depression, social defeat stress, in particular, has been shown to have excellent etiological, predictive, discriminative and face validity. Described here is a protocol whereby C57BL/6J mice that are repeatedly subjected to bouts of social defeat by a larger and aggressive CD-1 mouse results in the development of a clear depressive-like syndrome, characterized by enduring deficits in social interactions. Specifically, the protocol consists of three important stages, beginning with the selection of aggressive CD-1 mice, followed by agonistic social confrontations between the CD-1 and C57BL/6J mice, and concluding with the confirmation of social avoidance in subordinate C57BL/6J mice. The automated detection of social avoidance allows a marked increase in throughput, reproducibility and quantitative analysis. This protocol is highly adaptable, but in its most common form it requires 3-4 weeks for completion.

FACS identifies unique cocaine-induced gene regulation in selectively activated adult striatal neurons.

J Neurosci. 2011 Mar 16;31(11):4251-9. doi: 10.1523/JNEUROSCI.6195-10.2011.

Guez-Barber D, Fanous S, Golden SA, Schrama R, Koya E, Stern AL, Bossert JM, Harvey BK, Picciotto MR, Hope BT.

Numerous studies with the neural activity marker Fos indicate that cocaine activates only a small proportion of sparsely distributed striatal neurons. Until now, efficient methods were not available to assess neuroadaptations induced specifically within these activated neurons. We used fluorescence-activated cell sorting (FACS) to purify striatal neurons activated during cocaine-induced locomotion in naive and cocaine-sensitized cfos-lacZ transgenic rats. Activated neurons were labeled with an antibody against β-galactosidase, the protein product of the lacZ gene. Cocaine induced a unique gene expression profile selectively in the small proportion of activated neurons that was not observed in the nonactivated majority of neurons. These genes included altered levels of the immediate early genes arc, fosB, and nr4a3, as well as genes involved in p38 MAPK signaling and cell-type specificity. We propose that this FACS method can be used to study molecular neuroadaptations in specific neurons encoding the behavioral effects of abused drugs and other learned behaviors.

IκB kinase regulates social defeat stress-induced synaptic and behavioral plasticity.

J Neurosci. 2011 Jan 5;31(1):314-21. doi: 10.1523/JNEUROSCI.4763-10.2011.

Christoffel DJ, Golden SA, Dumitriu D, Robison AJ, Janssen WG, Ahn HF, Krishnan V, Reyes CM, Han MH, Ables JL, Eisch AJ, Dietz DM, Ferguson D, Neve RL, Greengard P, Kim Y, Morrison JH, Russo SJ.

The neurobiological underpinnings of mood and anxiety disorders have been linked to the nucleus accumbens (NAc), a region important in processing the rewarding and emotional salience of stimuli. Using chronic social defeat stress, an animal model of mood and anxiety disorders, we investigated whether alterations in synaptic plasticity are responsible for the long-lasting behavioral symptoms induced by this form of stress. We hypothesized that chronic social defeat stress alters synaptic strength or connectivity of medium spiny neurons (MSNs) in the NAc to induce social avoidance. To test this, we analyzed the synaptic profile of MSNs via confocal imaging of Lucifer-yellow-filled cells, ultrastructural analysis of the postsynaptic density, and electrophysiological recordings of miniature EPSCs (mEPSCs) in mice after social defeat. We found that NAc MSNs have more stubby spine structures with smaller postsynaptic densities and an increase in the frequency of mEPSCs after social defeat. In parallel to these structural changes, we observed significant increases in IκB kinase (IKK) in the NAc after social defeat, a molecular pathway that has been shown to regulate neuronal morphology. Indeed, we find using viral-mediated gene transfer of dominant-negative and constitutively active IKK mutants that activation of IKK signaling pathways during social defeat is both necessary and sufficient to induce synaptic alterations and behavioral effects of the stress. These studies establish a causal role for IKK in regulating stress-induced adaptive plasticity and may present a novel target for drug development in the treatment of mood and anxiety disorders in humans.

Context-specific modulation of cocaine-induced locomotor sensitization and ERK and CREB phosphorylation in the rat nucleus accumbens.

Eur J Neurosci. 2009 Nov;30(10):1931-40. doi: 10.1111/j.1460-9568.2009.06982.x.

Marin MT, Berkow A, Golden SA, Koya E, Planeta CS, Hope BT.

Learned associations are hypothesized to develop between drug effects and contextual stimuli during repeated drug administration to produce context-specific sensitization that is expressed only in the drug-associated environment and not in a non-drug-paired environment. The neuroadaptations that mediate such context-specific behavior are largely unknown. We investigated context-specific modulation of cAMP-response element-binding protein (CREB) phosphorylation and that of four upstream kinases in the nucleus accumbens that phosphorylate CREB, including extracellular signal-regulated kinase (ERK), cAMP-dependent protein kinase, calcium/calmodulin-dependent kinase (CaMK) II and CaMKIV. Rats received seven once-daily injections of cocaine or saline in one of two distinct environments outside their home cages. Seven days later, test injections of cocaine or saline were administered in either the paired or the non-paired environment. CREB and ERK phosphorylation were assessed with immunohistochemistry, and phosphorylation of the remaining kinases, as well as of CREB and ERK, was assessed by western blotting. Repeated cocaine administration produced context-specific sensitized locomotor responses accompanied by context-specific enhancement of the number of cocaine-induced phosphoCREB-immunoreactive and phosphoERK-immunoreactive nuclei in a minority of neurons. In contrast, CREB and CaMKIV phosphorylation in nucleus accumbens homogenates were decreased by cocaine test injections. We have recently shown that a small number of cocaine-activated accumbens neurons mediate the learned association between cocaine effects and the drug administration environment to produce context-specific sensitization. Context-specific phosphorylation of ERK and CREB in the present study suggests that this signal transduction pathway is selectively activated in the same set of cocaine-activated accumbens neurons that mediate this learned association.

Targeted disruption of cocaine-activated nucleus accumbens neurons prevents context-specific sensitization.

Nat Neurosci. 2009 Aug;12(8):1069-73. doi: 10.1038/nn.2364. Epub 2009 Jul 20.

Koya E, Golden SA, Harvey BK, Guez-Barber DH, Berkow A, Simmons DE, Bossert JM, Nair SG, Uejima JL, Marin MT, Mitchell TB, Farquhar D, Ghosh SC, Mattson BJ, Hope BT.

Learned associations between effects of abused drugs and the drug administration environment are important in drug addiction. Histochemical and electrophysiological studies suggest that these associations are encoded in sparsely distributed nucleus accumbens neurons that are selectively activated by drugs and drug-associated cues. Although correlations have been observed between nucleus accumbens neuronal activity and responsivity to drugs and drug cues, no technique exists for selectively manipulating these activated neurons and establishing their causal role in behavioral effects of drugs and drug cues. Here we describe a new approach, which we term the 'Daun02 inactivation method', that selectively inactivates a minority of neurons previously activated by cocaine in an environment repeatedly paired with cocaine to demonstrate a causal role for these activated neurons in context-specific cocaine-induced psychomotor sensitization in rats. This method provides a new tool for studying the causal roles of selectively activated neurons in behavioral effects of drugs and drug cues and in other learned behaviors.

Long-lasting incubation of conditioned fear in rats.

Biol Psychiatry. 2009 May 15;65(10):881-6. doi: 10.1016/j.biopsych.2008.12.010.

Pickens CL, Golden SA, Adams-Deutsch T, Nair SG, Shaham Y.

Learned associations between effects of abused drugs and the drug administration environment are important in drug addiction. Histochemical and electrophysiological studies suggest that these associations are encoded in sparsely distributed nucleus accumbens neurons that are selectively activated by drugs and drug-associated cues. Although correlations have been observed between nucleus accumbens neuronal activity and responsivity to drugs and drug cues, no technique exists for selectively manipulating these activated neurons and establishing their causal role in behavioral effects of drugs and drug cues. Here we describe a new approach, which we term the 'Daun02 inactivation method', that selectively inactivates a minority of neurons previously activated by cocaine in an environment repeatedly paired with cocaine to demonstrate a causal role for these activated neurons in context-specific cocaine-induced psychomotor sensitization in rats. This method provides a new tool for studying the causal roles of selectively activated neurons in behavioral effects of drugs and drug cues and in other learned behaviors.

Differential effects of the hypocretin 1 receptor antagonist SB 334867 on high-fat food self-administration and reinstatement of food seeking in rats.

Br J Pharmacol. 2008 May;154(2):406-16. doi: 10.1038/bjp.2008.3. 

Nair SG, Golden SA, Shaham Y.

BACKGROUND AND PURPOSE:  Many studies have demonstrated a role of hypocretin 1 (orexin 1) receptors in home-cage food consumption in rodents. However, the role of these receptors in operant food self-administration or relapse to food seeking in animal models is unknown. EXPERIMENTAL APPROACH:  In Experiment 1, we trained food-restricted rats (16-20 g per day) to lever press for high-fat (35%) pellets (3-6 h per day, every other day). We then tested the effect of the hypocretin 1 receptor antagonist SB 334867 (10, 20 mg kg(-1), i.p) on pellet self-administration. In Experiment 2, we trained rats to self-administer the food pellets, and following extinction of the food-reinforced responding, we tested the effect of hypocretin 1 (3 and 6 mug, i.c.v) on reinstatement of food-seeking and the effect of SB 334867 on this reinstatement. In Experiment 3, we tested the effect of SB 334867 on reinstatement induced by non-contingent pellet exposure (pellet-priming) or the pharmacological stressor yohimbine (2 mg kg(-1), i.p). KEY RESULTS: SB 334867 attenuated high-fat pellet self-administration. In contrast, SB 334867 had no effect on reinstatement of lever presses induced by hypocretin 1, pellet-priming or yohimbine. CONCLUSIONS AND IMPLICATIONS: These data indicate that during dieting, hypocretin 1 receptors contribute to operant high-fat pellet self-administration, but not to relapse to food seeking induced by acute re-exposure to the food itself or by the induction of a stress-like state.

Peptide YY3-36 decreases reinstatement of high-fat food seeking during dieting in a rat relapse model.

J Neurosci. 2007 Oct 24;27(43):11522-32.

Ghitza UE, Nair SG, Golden SA, Gray SM, Uejima JL, Bossert JM, Shaham Y.

A major problem in treating obesity is high rates of relapse to maladaptive food-taking habits during dieting. This relapse is often provoked by acute re-exposure to palatable food, food-associated cues, or stress. We used a reinstatement model, commonly used to study relapse to abused drugs, to explore the effect of peptide YY3-36 (PYY3-36) on reinstatement of high-fat (35%, 45 mg pellets) food seeking induced by acute exposure to the pellets (pellet priming), a cue previously associated with pellet delivery (pellet cue), or yohimbine (2 mg/kg, a pharmacological stressor). Rats were placed on a restricted diet (16 g of chow per day) and lever-pressed for the pellets for 9-12 sessions (6 h/d, every 48 h); pellet delivery was paired with a tone-light cue. They were then given 10-20 extinction sessions wherein lever presses were not reinforced with the pellets and subsequently tested for reinstatement of food seeking. Systemic PYY3-36 injections (100-200 microg/kg) decreased pellet priming- and pellet cue-induced reinstatement of food seeking but not yohimbine-induced reinstatement. Arcuate nucleus (Arc) injections of PYY3-36 (0.4 microg per side) decreased pellet priming-induced reinstatement. The attenuation of pellet priming-induced reinstatement by systemic PYY3-36 was reversed by systemic (2 mg/kg) but not Arc (0.5 microg per side) injections of the Y2 receptor antagonist BIIE0246. Arc PYY3-36 injections did not decrease pellet cue-induced reinstatement. Finally, systemic PYY3-36 injections had minimal effects on ongoing food self-administration or heroin priming- or heroin cue-induced reinstatement of heroin seeking. These data identify an effect of systemic PYY3-36 on relapse to food seeking that is independent of Y2 receptor activation in Arc and suggest that PYY3-36 should be considered for the treatment of relapse to maladaptive food-taking habits during dieting.