Biological Psychiatry

The current state of mental health treatment for individuals diagnosed with major depressive disorder leaves billions of individuals with first-line therapies that are ineffective or burdened with undesirable side effects. One major obstacle is that distinct pathologies may currently be diagnosed as the same disease and prescribed the same treatments. The key to developing antidepressants with ubiquitous efficacy is to first identify a strategy to differentiate between heterogeneous conditions. Major depression is characterized by hallmark features such as anhedonia and a loss of motivation (1, 2), and it has been recognized that even among inbred mice raised under identical housing conditions, we observe heterogeneity in their susceptibility and resilience to stress (3). Anhedonia, a condition identified in multiple neuropsychiatric disorders, is described as the inability to experience pleasure and is linked to anomalous medial prefrontal cortex (mPFC) activity (4). The mPFC is responsible for higher order functions (5-8), such as valence encoding; however, it remains unknown how mPFC valence-specific neuronal population activity is affected during anhedonic conditions. To test this, we implemented the unpredictable chronic mild stress (CMS) protocol (9-11) in mice and examined hedonic behaviors following stress and ketamine treatment. We used unsupervised clustering to delineate individual variability in hedonic behavior in response to stress. We then performed in vivo 2-photon calcium imaging to longitudinally track mPFC valence-specific neuronal population dynamics during a Pavlovian discrimination task. Chronic mild stress mice exhibited a blunted effect in the ratio of mPFC neural population responses to rewards relative to punishments after stress that rebounds following ketamine treatment. Also, a linear classifier revealed that we can decode susceptibility to chronic mild stress based on mPFC valence-encoding properties prior to stress-exposure and behavioral expression of susceptibility. Lastly, we used a markerless pose tracking computer vision tool, SLEAP (31), to predict whether a mouse would become resilient or susceptible based on facial expressions during a Pavlovian discrimination task. These results indicate that mPFC valence encoding properties and behavior are predictive of anhedonic states. Altogether, these experiments point to the need for increased granularity in the measurement of both behavior and neural activity, as these factors can predict the predisposition to stress-induced anhedonia.

Anhedonia, inability to experience pleasure from rewarding or enjoyable activities, is the prominent symptom of depression that involves dysfunction of the reward processing system. Both genetic predisposition and life events are thought to increase the risk for depression, in particular life stress. The cellular mechanism underlying stress modulating the reward processing neural circuits and subsequently disrupting reward-related behaviors remains elusive. We identify the VTA-BLA-NAc pathway as being activated by sex reward. Blockade of this circuit induces depressive-like behaviors, while reactivation of VTA neurons associated with sexual rewarding experience acutely ameliorates the impairment of reward-seeking behaviors induced by chronic restraint stress. Our histological and electrophysiological results show that the VTA neuron subpopulation responding to restraint stress inhibits the responsiveness of the VTA dopaminergic neurons to sexual reward. Together, these results reveal the cellular mechanism by which stress influences the brain reward processing system and provide a potential target for depression treatment.

Psychiatric disorders, including eating disorders (EDs), are characterized by heterogeneity that limits diagnostic accuracy and treatment personalization. Precision psychiatry calls for tools to identify data-driven phenotypes beyond traditional categories. In a large cohort (N=809), we applied an unsupervised clustering pipeline to self-report and clinical variables to uncover ED subgroups. Repeated Spectral Clustering revealed four phenotypes: two aligned with DSM-5 diagnoses (anorexia nervosa restricting-type; bulimia nervosa), and two diagnostically mixed clusters, one characterized by higher psychopathology and trauma exposure, the other by prolonged illness duration. These clusters showed distinct profiles and outcomes. The higher predictability of data-driven clusters compared to DSM-5 categories suggests that unsupervised stratification may offer a complementary perspective on relevant heterogeneity. Our findings highlight how computational phenotyping can advance precision psychiatry by revealing meaningful patterns, informing prognosis, and guiding personalized interventions. This approach may help bridge the gap between clinical presentations and the need for stratified, patient-centered care.

Anorexia nervosa (AN) is a mental and behavioral health condition characterized by an intense fear of body weight or fat gain, restriction of food intake resulting in low body weight, and distorted body image. Substantial research has focused on general anxiety in AN, but less is known about eating-related anxiety and its underlying neurobiological mechanisms. We sought to characterize anxiety-to-eat in AN and to examine neurometabolite levels in the dorsal anterior cingulate cortex (dACC), a brain region putatively involved in modulating anxiety-related responses, using edited magnetic resonance spectroscopy. Sixteen women hospitalized with AN and 16 women of healthy weight without a lifetime history of an eating disorder (healthy controls; HC) completed a computer-based behavioral task assessing anxiety-to-eat in response to images of higher (HED) and lower energy density (LED) foods. The AN group reported greater anxiety to eat HED and LED foods relative to the HC group. Both groups reported greater anxiety to eat HED foods relative to LED foods. The neurometabolite myo-inositol (myo-I) was lower in the dACC in AN relative to HC. In the AN group only, myo-I levels negatively predicted anxiety to eat HED but not LED foods and was independent of body mass index, duration of illness, and general anxiety. These findings provide new insight into the clinically challenging feature of eating-related anxiety in AN, and indicate potential for myo-I levels in the dACC to serve as a novel biomarker of illness severity or therapeutic target in individuals vulnerable to AN.

BACKGROUNDMany neuropsychiatric disorders involve dysregulation of the dopaminergic (DA) input to the forebrain. Of particular relevance are DA projections stemming from the midbrain ventral tegmental area (VTA). A key neuromodulatory influence onto DAVTA neurons arises from lateral hypothalamic area hypocretin/orexin (OX) neurons. Despite being a major input, the differential action of orexin peptides A and B (OXA and OXB) on orexin receptors 1 and 2 in DA cells is poorly understood. We recently identified profoundly divergent functions of OX1R vs OX2R in DA cells in regulating sleep/wake architecture, brain oscillations and cognitive behaviors. OX2R, but not OX1R, loss dramatically increased time in EEG theta-rich (alert) wakefulness, reward-driven learning and attentional skills, but impaired inhibitory control. METHODSUsing genetically engineered mice whose DA cells selectively lack OX input via Hcrtr1 (DAOx1R-KO) or Hcrtr2 (DAOx2R-KO), we assessed intrinsic excitability and electrophysiological responses of DAVTA neurons and evaluated behavioral phenotypes across multiple domains. RESULTSWe uncover previously unrecognized effects of OX peptides on DAVTA cell response. In WT and control mice, we show that while OXA enhances, OXB diminishes DAVTA neuronal excitability. OX1R-deficient DA cells lose OXA responding and OX2R-deficient DA cells lose OXB responding. DA Ox1R loss generates anxiety-like behavior and context-dependent hyperactivity. In contrast, OX2R loss decreases sociability and, despite exhibiting enhanced reward-driven learning, mice show highly compromised aversion-driven learning. CONCLUSIONSWe evidence strikingly distinct functions of OX1R vs OX2R signaling in modulating the intrinsic excitability of DAVTA neurons and influencing DA-related behaviors. These data implicate OX[->]DA signaling pathways in neuropsychiatric endophenotypes relevant to obsessive-compulsive, attention-deficit/hyperactivity, and autism spectrum disorders, and raise important considerations for the development of OXR-targeted therapeutics.

Treatment-resistant depression (TRD), defined by unsuccessful response to multiple antidepressants, affects approximately one-third of individuals with major depressive disorder, yet its underlying molecular mechanisms remain poorly understood. Here, we developed a preclinical model of TRD in which mice exposed to chronic social defeat stress were sequentially treated with fluoxetine (FLX) and ketamine (KET), allowing behavioral stratification into antidepressant responsive and non-responsive mice. RNA sequencing of the nucleus accumbens (NAc) and prefrontal cortex (PFC) revealed transcriptional signatures associated with treatment outcomes. Prior exposure to FLX exerted a priming effect that facilitated molecular and behavioral responsiveness to KET in a subset of animals in both the NAc and PFC. However, this priming effect was absent in non-responders, despite identical treatment regimes, suggesting a transcriptional divergence underlying differential outcomes. Gene co-expression network analysis identified modules enriched for differentially expressed genes unique to stress-susceptible and FLX-KET nonresponsive mice, as well as modules overlapping with both stress susceptibility and antidepressant resistance. These findings suggest that failed antidepressant treatment can shape the brains molecular landscape in a way that influences subsequent treatment outcomes, and that resistance arises not simply from treatment failure but from an absence of adaptive molecular priming. This work provides insight into the gene networks contributing to antidepressant non-response and highlights a mechanistic framework for modeling TRD in preclinical systems. By identifying molecular correlates of sequential pharmacological resistance, our findings may inform the development of novel therapeutic strategies for individuals with TRD.

Individuals with depression exhibit intensified and generalized negative memories. However, how prior memories actually influence onset and/or progression of depression, particularly whether the strengthening or the generalization of prior memories play a key role, is poorly understood. Here, we introduced behavioral paradigms to differentiate between memory strengthening and generalization, and found that negative experiences that produced memory overgeneralization, but not strengthening, induced depression-like behaviors. Furthermore, we identified that the medial prefrontal cortex (mPFC) to the bed nucleus of the stria terminals (BNST) projection functionally linked memory generalization to depression, together with single-cell calcium imaging which revealed a significant overlap in the mPFCBNST neuronal ensemble encoding depression-like behaviors with that encoding generalized memory, but not memory strength. Circuit-based transcriptomic analysis and chromophore-assisted light inactivation demonstrated that triggering actin remodeling in the mPFCBNST neurons, a memory consolidation mechanism enhanced generalization while reducing memory strength, also induced depression-like behaviors. Collectively, these findings suggest generalization of negative memories as a primary factor that drives depression-like behaviors, highlighting the importance of early identification of individuals at risk for depression who exhibit overgeneralized negative memories, and targeting overgeneralized negative memories in the treatment of depression.

BackgroundMotivated behaviors are executed by refined brain circuits. Early-life adversity (ELA) is a risk for human affective disorders involving dysregulated reward behaviors. In mice, ELA causes anhedonia-like behaviors in males and augmented reward motivation in females, indicating sex-dependent disruption of reward circuit operations. We recently identified a corticotropin-releasing hormone (CRH) expressing GABAergic projection from basolateral amygdala (BLA) to nucleus accumbens (NAc) that governs reward-seeking deficits in adult ELA males--but not females. MethodsTo probe the sex-specific role of this projection in reward behaviors, adult male and female CRH-Cre mice raised in control or ELA conditions received excitatory or inhibitory Cre-dependent DREADDs in BLA, and then clozapine N-oxide or vehicle to NAc medial shell during reward behaviors. We determined the cell identity of the projection using immunostaining and electrophysiology. Using tissue clearing, light sheet fluorescence microscopy and deep learning pipelines, we mapped brain-wide BLA CRH+ axonal projections to uncover sex differences in innervation. ResultsChemogenetic manipulations in male mice demonstrated inhibitory effects of the CRH+ BLA-NAc projection on reward behaviors, whereas neither excitation nor inhibition influenced female behaviors. Molecular and electrophysiological cell-identities of the projection did not vary by sex. By contrast, comprehensive whole-brain mapping uncovered significant differences in NAc innervation patterns that were both sex and ELA-dependent, as well as selective changes of innervation of other brain regions. ConclusionsThe CRH/GABA BLA-NAc projection that influences reward behaviors in males differs structurally and functionally in females, uncovering potential mechanisms for the profound sex-specific impacts of ELA on reward behaviors.

Social dysfunction is common in depression and varies with stress exposure and genetic risk. The current study identifies a cell-type specific role for Fkbp5, a glucocorticoid receptor co-chaperone, in noradrenergic neurons engaged during social stress. Acute social stress upregulated Fkbp5 in the locus coeruleus (LC), whereas repeated exposure attenuated this effect. Noradrenergic Fkbp5 deletion (Fkbp5Nat) increased pro-social behavior exclusively in male mice. In the basolateral amygdala (BLA), social interaction reduced norepinephrine (NE) turnover in wild-type but not Fkbp5Nat mice. Consistently, proteomics revealed mitochondrial/energy and synapse-related remodeling in BLA neurons. Miniscope imaging showed that behavior-locked NE transients in BLA were selectively blunted in Fkbp5Nat mice during interaction with outbred CD1 conspecifics, while same-strain C57BL/6N encounters preserved NE dynamics. Together, this study indicates that Fkbp5 tunes LC-BLA output to social salience in a sex- and context-dependent manner, suggesting a circuit-specific route to normalize social salience without broadly suppressing noradrenergic function.

Understanding the alterations in brain function across different episodes of bipolar disorder (BD), including manic (BipM), depressive (BipD), and remission states (rBD), poses a significant challenge. In our cross-sectional study, we collected resting-state functional magnetic resonance imaging data from 117 BD patients (BipM: 38, BipD: 42, rBD: 37) and 35 healthy controls. Our aim was to delineate functional connections associated with episode dynamics, delineate common and specific patterns, validate them as biomarkers, and elucidate their biological underpinnings. Initially, we identified a common altered pattern within the subregions of the ventral-attention network, alongside specific patterns observed in the default mode network for BipM, the prefrontal network for BipD, and the limbic network for rBD. Using large-sample data from the Human Connectome Project, we further identified that these connectivity patterns exhibit relatively high reliability and heritability. Also, these distinct patterns accurately characterized the diverse episodes of BD and effectively predicted the corresponding clinical symptoms linked with each episode type. Importantly, using out of sample data to decode possible neurobiological mechanisms underlying these patterns, we found that regions of particular interest were enriched in multiple receptors, including MOR, NMDA, and H3 for specific alterations, and A4B2, 5HTT, and 5HT1a for common alterations. Moreover, both episode-specific and common patterns demonstrated a high enrichment for cell types such as L5ET, Micro/PVM,oligodendrites and Chandelier. Our study offers novel insights concerning episode dynamics in BD, paving the way for personalized medicine approaches tailored to address the various episodes.

Major depressive disorder (MDD) disproportionately affects women, yet the molecular mechanisms underlying female vulnerability remain poorly understood. The nucleus accumbens (NAc), a reward circuitry hub, is central to stress- and depression-related pathology. While NAc medium spiny neuron (MSN) transcriptional adaptations have been characterized in stressed male rodents, much less is known about female adaptations. To address this, we exposed female D1-Cre-RiboTag and A2A-Cre-RiboTag mice to chronic witness defeat stress (CWDS) and classified them as high- or low-social interactors. Ribosome-associated mRNA was isolated from MSN subtypes and analyzed by RNA sequencing, differential gene expression analysis (DEG), and weighted gene co-expression network analysis (WGCNA). Cross-species consensus WGCNA with male mouse and human transcriptomic datasets was performed to identify conserved, sex-specific signatures. We detected 9 differentially expressed genes (DEGs) in D1-MSNs and 630 in A2A-MSNs (FDR < 0.05). In D1-MSNs, DEGs were primarily upregulated in low interactors and enriched for energy homeostasis and cell adhesion. A2A-MSN DEGs included upregulated structural genes and downregulated neurotransmission-related genes. WGCNA identified 9 significant D1- and 5 significant A2A-MSN modules, with the most impacted enriched for PI3K-Akt-mTOR signaling and regulated by Nf1. Consensus analysis revealed a stress-associated, sex- and subtype-specific module enriched for PI3K-Akt-mTOR signaling conserved across mice and humans. These findings reveal female-specific MSN transcriptional adaptations to chronic social stress and implicate PI3K-Akt-mTOR signaling as a convergent molecular pathway. By highlighting MSN subtype-specific vulnerabilities, this work suggests potential therapeutic targets for alleviating stress-induced pathology in women with MDD.

Schizophrenia is associated with reduced activation ( hypofrontality) and neural disinhibition (reduced GABAergic inhibition) in the dorsolateral prefrontal cortex (dlPFC), as well as reversal learning deficits. Whilst reversal learning has been strongly linked to the orbitofrontal cortex, its dependence on the primate dlPFC - and its rodent analogue, the medial PFC (mPFC) - is less clear. Nevertheless, we hypothesized that the mPFC may be required for reversal learning if the reversal is demanding. Furthermore, even if the mPFC is not required, mPFC disinhibition may impair reversals, because it may disrupt processing in mPFC projection sites. To test these hypotheses, we combined bi-directional manipulations of mPFC GABAergic inhibition, using intracerebral drug microinfusion and chemogenetic/DREADD methods, with reversal testing on a food-reinforced two-lever discrimination task in rats. First, we induced mPFC functional inhibition and disinhibition, by microinfusion of the GABA-A receptor agonist muscimol or antagonist picrotoxin, respectively, and examined the impact on early reversals (reversals 1-3) and well-established serial reversals (reversal 5 onwards). Using classical performance measures and Bayesian trial-by-trial strategy analysis, we found that mPFC muscimol impaired early, but not serial, reversals, increasing perseveration and impairing exploratory (lose-shift) behavior at reversal 2. In contrast, mPFC picrotoxin impaired serial reversals, reducing exploratory (lose-shift) and exploitative (win-stay) behavior. Second, to inhibit mPFC GABAergic neurons, we expressed the inhibitory DREADD hM4Di in these neurons; chemogenetic mPFC disinhibition by activation of hM4Di also impaired serial reversal learning, primarily disrupting exploitation. Our findings suggest that mPFC hypoactivation and disinhibition disrupt distinct aspects of reversal learning by different mechanisms. Significance statementSchizophrenia is associated with reduced activation ("hypofrontality") and neural disinhibition (reduced GABAergic inhibition) within the prefrontal cortex (PFC). Yet, it is not clear if and how these distinct aspects of prefrontal dysfunction contribute to impaired reversal learning, a key feature of the cognitive inflexibility characterizing schizophrenia. Here, we combined bi-directional manipulations of prefrontal GABAergic inhibition with testing of reversal learning in rats. Increasing prefrontal functional inhibition (i.e., reducing prefrontal activation) selectively impaired early reversals, enhancing perseveration and reducing exploratory (lose-shift) behavior, whereas prefrontal disinhibition disrupted serial reversals, impairing both exploration and exploitation. Our findings suggest that reduced activation and disinhibition of PFC disrupt distinct aspects of reversal learning, by distinct mechanisms.

Adolescent inhibition of thalamo-cortical projections from postnatal day P20-50 leads to long lasting deficits in prefrontal cortex function and cognition in the adult mouse. While this suggests a role of thalamic activity in prefrontal cortex maturation, it is unclear how inhibition of these projections affects prefrontal circuit connectivity during adolescence. Here, we used chemogenetic tools to inhibit thalamo-prefrontal projections in the mouse from P20-35 and measured synaptic inputs to prefrontal pyramidal neurons by layer (either II/III or V/VI) and projection target twenty-four hours later using slice physiology. We found a decrease in the frequency of excitatory and inhibitory currents in layer II/III nucleus accumbens (NAc) and layer V/VI medio-dorsal thalamus projecting neurons while layer V/VI NAc-projecting neurons showed an increase in the amplitude of excitatory and inhibitory currents. Regarding cortical projections, the frequency of inhibitory but not excitatory currents was enhanced in contralateral mPFC-projecting neurons. Notably, despite these complex changes in individual levels of excitation and inhibition, the overall balance between excitation and inhibition in each cell was only changed in the contralateral mPFC projections. This finding suggests homeostatic regulation occurs within subcortically but not intracortical callosally-projecting neurons. Increased inhibition of intra-prefrontal connectivity may therefore be particularly important for prefrontal cortex circuit maturation. Finally, we observed cognitive deficits in the adult mouse using this narrowed window of thalamocortical inhibition (P20-P35). Significance StatementConnectivity between two brain regions, the thalamus and the prefrontal cortex, has been found to be reduced in patients with schizophrenia. Neuronal activity in thalamo-cortical projections is important for the proper development of sensory cortices. How thalamo-cortical activity regulates prefrontal cortex development is less well understood. Here, we show that decreasing activity in thalamo-prefrontal projections in mice during early adolescence alters synaptic connectivity to distinct neuronal projections within the prefrontal cortex that are already evident in adolescence. While some of these changes can be explained by reduced thalamo-cortical projections, other adaptations are intrinsic to the prefrontal cortex. These findings implicate adolescence as a critical period of cortical development and demonstrate this period as a potential target for therapeutic intervention.

Relapse vulnerability in substance use disorder (SUD) is primarily driven by cue-induced activation of neurons within the nucleus accumbens core (NAcore), among other contributing factors. Neuronal ensembles within the NAcore, defined here as selectively co-activated neurons during specific behavioral experiences, are essential during cocaine sensitization and recall. While transient synaptic plasticity (t-SP) has been widely observed in general neuronal populations within the NAcore during reinstatement, its ensemble-specific dynamics remain unclear. Here, we used c-Fos-TRAP2-based tagging to identify cocaine-seeking ensembles in mice following cocaine intravenous self-administration, extinction, and cue-induced reinstatement. Structural spine plasticity was assessed via confocal microscopy, and functional changes were measured using whole-cell electrophysiology across multiple reinstatement time points. Ensemble neurons exhibited enhanced dendritic spine head diameter (dh) and AMPA/NMDA (A/N) ratios following cue exposure, consistent with t-SP. Notably, spine classification revealed a reduction in mature spines during reinstatement, suggesting morphological remodeling rather than new spine formation in both ensemble and non-ensemble cells. Non-ensemble neurons exhibited classical functional transient synaptic plasticity, characterized by increased A/N ratios but no significant changes in dh. To begin assessing if presynaptic vesicle release impacts t-SP, paired-pulse ratio analysis indicated no differences in population or time point. Importantly, ensemble neurons displayed elevated A/N ratio following cocaine exposure, suggesting prior silent synapse maturation. These findings demonstrate that t-SP is not uniformly distributed across NAcore neurons but differs significantly between ensemble and non-ensemble neurons. By linking ensemble identity to both structural and functional plasticity, this study refines our understanding of cue-induced relapse mechanisms. Significance StatementRelapse in substance use disorder is strongly driven by cue-induced reactivation of neuronal ensembles in the nucleus accumbens core. While transient synaptic potentiation has been widely described in bulk neuronal populations within the nucleus accumbens core, its ensemble-specific expression has remained unclear. Here, we combined c-Fos-TRAP2 tagging, confocal imaging, and slice electrophysiology to show that transient synaptic potentiation is selectively expressed in behaviorally relevant ensembles. By linking ensemble identity with structural and functional plasticity during cue-induced cocaine seeking, these findings refine current models of relapse and identify ensemble-specific plasticity as a potential target for therapeutic intervention.

Deficits in motivation and pleasure are common across many psychiatric disorders, and manifest as symptoms of amotivation and anhedonia, which are prominent features of both mood and psychotic disorders. Here we provide evidence for a shared transdiagnostic mechanism underlying impairments in motivation and pleasure across major depression, bipolar disorder, and schizophrenia. We found that value signals in the ventromedial prefrontal cortex (vmPFC) during decision-making were dampened in individuals with greater motivational and hedonic deficits, regardless of the primary diagnosis. This relationship remained significant while controlling for diagnosis-specific symptoms of mood and psychosis, such as depression as well as positive and negative symptoms. Our results demonstrate that dysfunction in the vmPFC during value-based decision-making is specifically linked to motivational and hedonic impairments across various psychiatric conditions. These findings provide a quantitative neural target for the potential development of novel treatments for amotivation and anhedonia.

Major depressive disorder (MDD) and post-traumatic stress disorder (PTSD) are two of the most prevalent and disabling psychiatric conditions, both closely tied to stress exposure. While they have distinct diagnostic criteria, MDD and PTSD share considerable comorbidity, overlapping behavioral symptoms, and common neurobiological pathways. However, not all individuals exposed to chronic or traumatic stress develop these disorders, highlighting the importance of resilience, the capacity to maintain psychological and physiological stability under stress. An emerging yet understudied concept is cross-resilience: the idea that resilience to one form of stress may confer protection against another. While animal models have effectively captured individual differences in stress responses, few have explored whether resilience generalizes across distinct stress modalities or differs by sex. We examined cross-resilience using two validated rodent models: chronic social defeat stress (CSDS) and learned helplessness (LH). These paradigms model complementary aspects of stress vulnerability. We assessed how prior CSDS experience influenced subsequent responses to LH. We also evaluated the role of the noradrenergic system using wild-type and norepinephrine (NE)-deficient (VMAT2loxDBHcre KO) mice. Behavioral phenotyping was combined with molecular analyses in key brain regions involved in emotion, motivation, and fear processing: the ventral tegmental area (VTA), nucleus accumbens (NAc), and amygdala (AMY). We focused on BDNF and ERK/MAPK signaling pathways, known to mediate neuroplasticity and stress resilience. Our findings reveal sex-specific patterns of cross-resilience, with prior CSDS resilience predicting LH resilience in males but not females. Molecular results indicate distinct adaptations across brain regions and sexes, underscoring the biological complexity of resilience. These insights may inform personalized strategies for preventing and treating stress-related disorders.

Anorexia nervosa is a severe psychiatric disorder characterized by persistent food restriction and often excessive physical activity, implicating dysfunction in neural circuits governing motivation, reward, and behavioral persistence. The nucleus accumbens (NAc) is a central component of these circuits, yet synaptic and cellular adaptations within this region during anorexia-like states remain poorly defined. Using the activity-based anorexia (ABA) paradigm in adult female mice, we examined glutamatergic signaling and intrinsic neuronal properties in the NAc shell. ABA exposure produced rapid weight loss, reduced food intake, and progressively increased running-wheel activity. Biochemical analyses of NAc shell tissue revealed elevated membrane-associated GluA2 AMPA receptor protein. Consistent with this finding, whole-cell patch-clamp recordings from medium spiny neurons showed increased amplitude of spontaneous excitatory postsynaptic currents. ABA also enhanced intrinsic neuronal excitability, reflected by greater firing in response to depolarizing current injections. Together, these convergent biochemical and electrophysiological results demonstrate that ABA induces coordinated postsynaptic strengthening and increased intrinsic excitability in NAc shell medium spiny neurons. These adaptations suggest a sustained increase in accumbal output that may bias motivational circuit function and contribute to excessive activity and suppressed feeding during anorexia-like conditions, paralleling glutamatergic plasticity observed in other compulsive disorders, including substance use disorder.

Neuropsychiatric disorders, including depression and suicide, are becoming an increasing public health concern. Rising rates of both depression and suicide, exacerbated by the current COVID19 pandemic, have only hastened our need for objective and reliable diagnostic biomarkers. These can aide clinicians treating depressive disorders in both diagnosing and developing treatment plans. While differential gene expression analysis has highlighted the serotonin signaling cascade among other critical neurotransmitter pathways to underly the pathology of depression and suicide, the biological mechanisms remain elusive. Here we propose a novel approach to better understand molecular underpinnings of neuropsychiatric disorders by examining patterns of differential RNA editing by adenosine deaminases acting on RNA (ADARs). We take advantage of publicly available RNA-seq datasets to map ADAR editing landscapes in a global gene-centric view. We use a unique combination of Guttman scaling and random forest classification modeling to create, describe and compare ADAR editing profiles focusing on both spatial and biological sex differences. We use a subset of experimentally confirmed ADAR editing sites located in known protein coding regions, the excitome, to map ADAR editing profiles in Major Depressive Disorder (MDD) and suicide. Using Guttman scaling, we were able to describe significant changes in editing profiles across brain regions in males and females with respect to cause of death (COD) and MDD diagnosis. The spatial distribution of editing sites may provide insight into biological mechanisms under-pinning clinical symptoms associated with MDD and suicidal behavior. Additionally, we use random forest modeling including these differential profiles among other markers of global editing patterns in order to highlight potential biomarkers that offer insights into molecular changes underlying synaptic plasticity. Together, these models identify potential prognostic, diagnostic and therapeutic biomarkers for MDD diagnosis and/or suicide.

Relapse triggered by drug-associated cues or stress remains a major challenge in treating substance use disorders (SUDs), as re-exposure reliably provokes craving and reinstatement of drug seeking. Extinction-based interventions can reduce cue reactivity, yet extinction learning is often weak or context-dependent, limiting its clinical impact. Vagus nerve stimulation (VNS) enhances learning-related plasticity via widespread engagement of neuromodulatory systems and cortical circuits. Recent preclinical work shows that pairing extinction with VNS facilitates extinction learning and reduces cue-induced reinstatement of cocaine seeking, suggesting translational potential as an adjunct to exposure-based therapies. However, the circuit-level mechanisms underlying these effects remain unclear. To address this gap, we examined how VNS paired with extinction alters activity in medial prefrontal cortex (mPFC) networks that regulate drug seeking, focusing specifically on afferent projections from the basolateral amygdala (BLA) and ventral hippocampus (vHPC). Male rats received retrograde AAV-eGFP infusions into either the prelimbic (PL) or infralimbic (IL) cortex to label upstream projections, followed by cocaine self-administration, extinction training with VNS or sham stimulation, and cue-induced reinstatement. cFos immunolabeling in the BLA and vHPC revealed pathwayspecific modulation: VNS decreased overall BLA activity and reduced activation of BLA to IL projections, but increased activation of BLA to PL projections. In the vHPC, VNS selectively decreased activation of vHPC to IL projections without affecting PL-projecting neurons. Because these pathways synapse onto parvalbumin interneurons (PVIs) in the mPFC, we quantified PVI activation and found that VNS decreased overall prefrontal cFos expression, but increased PVI activity in the PL, and decreased PVI activity in the IL. Together, these results demonstrate that VNS paired with extinction reshapes prefrontal-amygdala-hippocampal circuits in a pathway-specific manner, potentially modulating feed-forward inhibition to reduce relapse-like behavior. These findings support VNS as a promising strategy to strengthen extinction learning and improve treatment outcomes in SUD.

BackgroundSynaptic function is increasingly recognized as a core property of genes implicated in psychiatric disorders. Defining the specific synaptic molecular systems underlying genetic risk is critical step toward therapeutic advances. Synaptic processes rely on rapid protein production driven by local translation of mRNA in context-specific synapses. Synaptic mRNA metabolism, transport and local translation is regulated by RNA-binding proteins (RBPs). Here, we hypothesized that genetic risk converges on localised transcripts with synaptic function and aimed to identify RBP regulatory systems that capture this shared schizophrenia genetic risk. MethodsWe use recent human and mouse bulk and single-synapse transcriptomic and proteomic datasets to test for enrichment of schizophrenia genetic risk among mRNAs stratified by localization and synaptic function employing gene set association (MAGMA) and heritability enrichment (S-LDSC) analyses. Prioritized transcripts were further analyzed for RBP control through motif enrichment analysis (Transite) of the 3UTRs of these transcripts. Candidate RBPs were then evaluated based on the strength of genetic association among their predicted binding targets. ResultsWe demonstrate that genes encoding localised mRNAs with synaptic function show significantly greater genetic association than other synaptic genes. We identified a subset of RBPs, RBFOX1/2/3, CELF4, HNRNPR, and nELAVL, whose motifs are enriched in localised synaptic mRNAs and whose targets are enriched for schizophrenia risk variants. These RBPs are prioritized as candidate regulatory systems through which genetic risk may converge on the transport, splicing and translation of localised transcripts with synaptic function. ConclusionsOur results highlight potential regulatory systems through which genetic variation influences synaptic mechanisms and provide a scalable framework for refining the link between genetic association and post-transcriptional regulation in neuropsychiatric disorders.