Neuropsychopharmacology

Addictive drugs hijack the neuronal mechanisms of learning and memory in motivation and emotion processing circuits to reinforce their own use. Regulator of G-protein Signaling 14 (RGS14) is a natural suppressor of post-synaptic plasticity underlying learning and memory in the hippocampus. The present study used immunofluorescence and RGS14 knockout mice to assess the role of RGS14 in behavioral plasticity and reward learning induced by chronic cocaine in emotional-motivational circuits. We report that RGS14 is strongly expressed in discrete regions of the ventral striatum and extended amygdala in wild-type mice, and is co-expressed with D1 and D2 dopamine receptors in neurons of the nucleus accumbens (NAc). Of note, we found that RGS14 is upregulated in the NAc in mice with chronic cocaine history following acute cocaine treatment. We found significantly increased cocaine-induced locomotor sensitization, as well as enhanced conditioned place preference and conditioned locomotor activity in RGS14-deficient mice compared to wild-type littermates. Together, these findings suggest that endogenous RGS14 suppresses cocaine-induced plasticity in emotional-motivational circuits, implicating RGS14 as a protective agent against the maladaptive neuroplastic changes that occur during addiction.

Prenatal environmental insults increase the risk of neurodevelopmental psychiatric conditions in the offspring. Structural modifications of dendritic spines are central to brain development and plasticity. Using maternal immune activation (MIA) as a rodent model of prenatal environmental insult, previous results have reported dendritic structural deficits in the frontal cortex. However, very little is known about the molecular mechanism underlying MIA-induced synaptic structural alterations in the offspring. Using prenatal (E12.5) injection with poly-(I:C) as a mouse MIA model, we show that upregulation of the serotonin 5-HT2A receptor (5-HT2AR) is at least in part responsible for some of the effects of prenatal insults on frontal cortex dendritic spine structure and sensorimotor gating processes. Mechanistically, we report that this upregulation of frontal cortex 5-HT2AR expression is associated with MIA-induced reduction of nuclear translocation of the glucocorticoid receptor (GR) and, consequently, a decrease in the enrichment of GR at the 5-HT2AR promoter. The translational significance of these preclinical findings is supported by data in postmortem human brain samples suggesting dysregulated nuclear GR translocation in frontal cortex of schizophrenia subjects. Repeated (twice a day for 4 days) corticosterone administration augmented frontal cortex 5-HT2AR expression and reduced GR binding to the 5-HT2AR promoter. However, virally (AAV)-mediated augmentation of GR function reduced frontal cortex 5-HT2AR expression and improved sensorimotor gating processes via 5-HT2AR. Together, these data support a negative regulatory relationship between GR signaling and 5-HT2AR expression in mouse frontal cortex that may carry implications for the pathophysiology underlying 5-HT2AR dysregulation in neurodevelopmental psychiatric disorders.

Inhibiting the actin motor ATPase nonmuscle myosin II (NMII) with blebbistatin (Blebb) in the basolateral amgydala (BLA) depolymerizes actin, resulting in an immediate, retrieval-independent disruption of methamphetamine (METH)-associated memory. The effect is highly selective, as NMII inhibition has no effect in other relevant brain regions (e.g. dorsal hippocampus [dPHC], nucleus accumbens [NAc]), nor does it interfere with associations for other aversive or appetitive stimuli, including cocaine (COC). To investigate a potential source of this specificity, pharmacokinetic differences in METH and COC brain exposure were examined. Replicating METHs longer half-life with COC did not render the COC association susceptible to disruption by NMII inhibition. Therefore, transcriptional differences were next assessed. Comparative RNA-seq profiling in the BLA, dHPC and NAc following METH or COC conditioning identified crhr2, which encodes the corticotrophin releasing factor receptor 2 (CRF2), as uniquely upregulated by METH in the BLA. CRF2 antagonism with Astressin-2B (AS2B) had no effect on METH-associated memory after consolidation, allowing for determination of CRF2 influences on NMII-based susceptibility after METH conditioning. Pretreatment with AS2B occluded the ability of Blebb to disrupt an established METH-associated memory. Alternatively, the Blebb-induced, retrieval-independent memory disruption seen with METH was mimicked for COC when combined with CRF2 overexpression in the BLA and its ligand, UCN3 during conditioning. These results indicate that BLA CRF2 receptor activation during learning can prevent stabilization of the actin-myosin cytoskeleton supporting the memory, rendering it vulnerable to disruption via NMII inhibition. CRF2 represents an interesting target for BLA-dependent memory destabilization via downstream effects on NMII.

Psilocybin, a serotonergic psychedelic, can produce rapid and enduring antidepressant effects in patients with major depressive disorder (MDD)[1, 2], yet the neural mechanisms underlying these effects remain unclear. Negative affective biases are an important neuropsychological mechanism central to the development and perpetuation of MDD[3]. Using a translational rodent model, we previously demonstrated that psilocybin modulates negative affective biases which, we hypothesize, contribute to its antidepressant effects[4]. Here, we identify the prelimbic subregion (PrL) of the rat medial prefrontal cortex (mPFC) as a key locus for the modulation of affective biases by psilocin, the active metabolite of psilocybin, and reveal a cell-type-specific bidirectional regulation of synaptic transmission. Psilocin selectively suppressed excitatory synaptic input to cortico-amygdala (CA) projection neurons, but enhanced excitatory transmission to other, putatively cortico-cortical, targets. Interestingly, suppression of the excitatory input to CA cells by psilocin, and modulation of affective biases by psilocybin, were both dependent on 5HT1A and 5HT2A receptor signaling. Consistent with the long-term therapeutic effects of rapidly acting antidepressants[1, 2, 4, 5], psilocin produced sustained changes to affective biases evident 24 hours after PrL infusion. In parallel, the suppressed excitatory transmission shifted to enhanced inhibitory synaptic input selectively in CA cells. Finally, chemogenetic inhibition of CA neurons in PrL recapitulated both the acute and sustained modulation of negative affective biases by psilocybin, as well as positively biasing new reward memories. Together, these findings identify modulation of the PrL cortico-amygdala circuit as a key substrate for affective bias modification by psilocybin, an effect which could explain its rapid and sustained antidepressant actions.

MDMA is a promising adjunct to psychotherapy and has well-known abuse liability, although less than other amphetamine analogs. While the reinforcing dopamine (DA)-releasing properties of MDMA are on par with methamphetamine (METH), MDMA is a far more potent serotonin (5-HT) releaser, via the 5-HT transporter (SERT). MDMA-mediated 5-HT release in a major reward center, the nucleus accumbens (NAc), drives prosocial behaviors via 5-HT1BR activation. We hypothesized that this prosocial mechanism contributes to the reduced reinforcing properties of MDMA compared to METH and used a platform of assays to predict the balance of prosocial and abuse-linked effects of (R)-MDMA, a novel entactogen in clinical development. NAc DA release, measured by GRAB-DA photometry in vivo, increased in proportion to MDMA (7.5 and 15 mg/kg, i.p.) and METH (2 mg/kg i.p.)-conditioned place preference (CPP). Using conditional knockouts (cKOs) for DAT and SERT, microdialysis, and photometry, we found that MDMA-released 5-HT limited MDMA-released DA through actions in the NAc, rather than at ventral tegmental area DAergic cell bodies. SERT cKO reduced the MDMA dose required for CPP three-fold. This enhanced MDMA-CPP and increased DA release were replicated by intra-NAc infusion of either a 5-HT reuptake inhibitor (escitalopram) to prevent MDMA interaction with SERT, or a 5-HT2CR antagonist (SB242084), but not by the 5-HT1BR antagonist NAS-181. These data support separate mechanisms for the low abuse potential versus prosocial effect of MDMA. Using this platform of assays, (R)-MDMA is predicted to have prosocial effects and low abuse potential.

The medial prefrontal cortex (mPFC) plays a pivotal role in attention by exerting top-down control to allocate cognitive resources toward behaviorally relevant stimuli based on learned context and expectations. mPFC neurons project to multiple cortical and subcortical regions, including the locus coeruleus (LC)--the brains primary source of norepinephrine (NE). The mPFC also receives inputs from the LC, which release NE to modulate mPFC neuronal activity and downstream cellular signaling. While enhanced functional connectivity between the mPFC and LC in mice during sustained attention tasks suggest an important role for the mPFC-LC circuit, functional evidence directly implicating this circuit in attention is lacking. Here, we investigated the role of the mPFC-LC circuit in attention by comparing selective chemogenetic manipulation of mPFC neurons that project to the LC (mPFC-LC projectors) to non-specific chemogenetic manipulation of mPFC neurons. Selective activation of mPFC-LC projectors in mice performing the rodent continuous performance test (rCPT), a translational sustained attention task, robustly improves attentional performance by enhancing discrimination while non-selective activation of mPFC neurons increases attentional performance by increasing responsiveness. Behavioral effects of mPFC-LC projector activation were mediated by recruitment of a microcircuit involving LC-NE neurons and glutamate and GABA peri-LC neurons while effects of non-selective activation of mPFC neurons were mediated by engaging downstream targets such as the nucleus accumbens (NAc) as well as the LC/peri-LC region.

Psilocybin has been shown to improve symptoms of depression and anxiety when combined with psychotherapy or other clinician-guided interventions. To understand the neural basis for this pattern of clinical efficacy, experimental and conceptual approaches that are different than traditional laboratory models of anxiety and depression are needed. A potential novel mechanism is that acute psilocybin improves cognitive flexibility, which then enhances the impact of clinician-assisted interventions. Consistent with this idea, we find that acute psilocybin robustly improves cognitive flexibility in male and female rats using a task where animals switched between previously learned strategies in response to uncued changes in the environment. Psilocybin did not influence Pavlovian reversal learning, suggesting that its cognitive effects are selective to enhanced switching between previously learned behavioral strategies. The serotonin (5HT) 2A receptor antagonist ketanserin blocked psilocybins effect on set-shifting, while a 5HT2C-selective antagonist did not. Ketanserin alone also improved set-shifting performance, suggesting a complex relationship between psilocybins pharmacology and its impact on flexibility. Further, the psychedelic drug 2,5-Dimethoxy-4-iodoamphetamine (DOI) impaired cognitive flexibility in the same task, suggesting that this effect of psilocybin does not generalize to all other serotonergic psychedelics. We conclude that the acute impact of psilocybin on cognitive flexibility provides a useful behavioral model to investigate its neuronal effects relevant to its positive clinical outcome.

Cocaine use disorder remains a critical public health concern with limited treatment options. Astrocytes are increasingly recognized as active regulators of neurotransmission and are emerging as important contributors to addiction neurobiology. Here, we examined how chemogenetic activation of astrocytic Gq signaling within the ventral tegmental area (VTA) influences cocaine-associated behaviors in drug-naive and cocaine-experienced rats. Using a subthreshold dose of cocaine in a conditioned place preference (CPP) paradigm, we found that VTA astrocyte Gq activation facilitated the acquisition of cocaine CPP in drug-naive rats but suppressed the development of cocaine CPP in cocaine-experienced rats. Additionally, chemogenetic activation of VTA astrocyte Gq signaling suppressed voluntary cocaine intake in a self-administration paradigm. Together, these findings demonstrate that VTA astrocyte Gq signaling shapes cocaine-associated behaviors in a drug history-dependent manner, highlighting VTA astrocytes as a potential therapeutic target in cocaine use disorder.

Addiction is marked by aberrant decision-making and an inability to suppress inappropriate and often dangerous behaviors. We previously demonstrated that inactivation of the rostromedial tegmental nucleus (RMTg) in rats causes persistent food seeking despite impending aversive footshock, an effect strikingly similar to the punishment resistance observed in people with a history of protracted drug use [1]. Here, we extend these studies to demonstrate chemogenetic silencing of RMTg axonal projections to the ventral tegmental area (VTA) (RMTg{lozenge}VTA pathway) causes rats to endure significantly more footshock to receive cocaine infusions. To further test whether activation of this circuit is sufficient to suppress reward seeking in the absence of an overtly aversive stimulus, we used temporally specific optogenetic stimulation of the RMTg{lozenge}VTA pathway as a "punisher" in place of footshock following lever pressing for either food or cocaine reward. While optical stimulation of the RMTg{lozenge}VTA pathway robustly suppressed lever pressing for food, we found that stimulation of this circuit had only modest effects on suppressing responding for cocaine infusions. Even though optical RMTg{lozenge}VTA stimulation was not particularly effective at reducing ongoing cocaine use, this experience nevertheless had long-lasting consequences, as reinstatement of drug seeking in response to cocaine-associated cues was profoundly suppressed when tested nearly two weeks later. These results suggest the RMTg may serve as a useful target for producing enduring reductions in drug craving, particularly during periods of abstinence from drug use.

Dopamine regulates the frequency of motor actions, but it is unclear whether it similarly regulates the duration of discrete behaviors. Here, we show that dopamine signaling within the medial accumbens shell reinforces actions while simultaneously constraining their duration. When mice hold down a lever to continuously self-stimulate dopamine axons in the medial accumbens shell, hold-downs are rarely longer than 5 seconds, and higher stimulation frequencies elicit shorter, but more numerous, lever hold-downs. This disengaging property of medial accumbens shell dopamine also applies to consummatory behavior, as mice are quicker to both terminate and reinitiate bouts of licking paired with high frequency dopamine axon stimulation. Dopamine D1 receptors underpin this disengaging property of dopamine signaling, as we demonstrate a D1 agonist shortens both self-stimulation hold-downs and bouts of consummatory behavior. Altogether, we uncover an anatomically defined role of dopamine, which is to disengage its own reinforcing properties through D1 receptor signaling.

Dopamine (DA) signaling plays an essential role in reward valence attribution and in encoding the reinforcing properties of natural and artificial rewards. The adaptive responses from midbrain dopamine neurons to artificial rewards such as drugs of abuse are therefore important for understanding the development of substance use disorders. Drug-induced changes in gene expression are one such adaptation that can determine the activity of dopamine signaling in projection regions of the brain reward system. One of the major challenges to obtaining this understanding involves the complex cellular makeup of the brain, where each neuron population can be defined by a distinct transcriptional profile. To bridge this gap, we have adapted a virus-based method for labeling and capture of dopamine nuclei, coupled with nuclear RNA-sequencing, to study the transcriptional adaptations, specifically, of dopamine neurons in the ventral tegmental area (VTA) during cocaine taking and cocaine craving, using a mouse model of cocaine intravenous self-administration (IVSA). Our results show significant changes in gene expression across non-drug operant training, cocaine taking, and cocaine craving, highlighted by an enrichment of repressive epigenetic modifying enzyme gene expression during cocaine craving. Immunohistochemical validation further revealed an increase of H3K9me3 deposition in DA neurons during cocaine craving. These results demonstrate that cocaine-induced transcriptional adaptations in dopamine neurons vary by phase of self-administration and underscore the utility of this approach for identifying relevant phase-specific molecular targets to study the behavioral course of substance use disorders.

The cognitive enhancing effects of methylphenidate are well established, but the mechanisms remain unclear. We recently demonstrated that methylphenidate boosts cognitive motivation by enhancing the weight on the benefits of a cognitive task in a manner that depended on striatal dopamine. Here we considered the complementary hypothesis that methylphenidate might also act by changing the weight on the opportunity cost of a cognitive task. To this end, fifty healthy participants (25 women) completed a novel cognitive effort discounting task that was sensitive to opportunity cost, and required choices between task and leisure. They were tested on methylphenidate, sulpiride or placebo and also underwent an [18F]DOPA PET scan to quantify baseline dopamine synthesis capacity. Methylphenidate boosted choices of cognitive effort over leisure across the group, and this effect was greatest in participants with more striatal dopamine at baseline. The effects of sulpiride did not reach significance. This study strengthens the motivational account of methylphenidates effects on cognition and suggests that methylphenidate reduces the cost of mental labor by increasing striatal dopamine.

BackgroundThe link between cannabis use and schizophrenia is well-established in epidemiological studies, especially among adolescents with early-onset use. However, this association in rodent models is less clear. This meta-analysis examined the effects of adolescent cannabinoid exposure on distinct schizophrenia-like behaviours in rodents and how experimental variations influence outcomes. MethodsFollowing a pre-registered protocol (CRD42022338761), we searched PubMed, Ovid Medline, Embse and APA PsychInfo for English-language original studies until 2022. We synthesised data from experiments on schizophrenia-like behaviour in rats and mice after repeated peri-pubertal (onset between P23-P45) cannabinoid exposure. Risk of bias was assessed using the SYRCLEs tool. ResultsWe included 291 experiments from 91 articles across 9 behavioural tests. We found meta-analytic evidence supporting that CB1R agonists, both natural and synthetic, elicited broad schizophrenia-like behavioural alterations, including impaired working memory (g =-0.58 [CI: -1.00,-0.16]), novel object recognition (g=-0.63 [CI: -0.97,-0.30]), novel object location recognition (g=-0.70 [CI: -1.22,-0.28]), social motivation (g=-0.40 [CI: -0.63, -0.16]), pre-pulse inhibition (g=-0.48 [CI: -0.89, -0.08]), and sucrose preference (g=-0.92 [CI: -1.87,0.04]). By contrast, effects on novelty-induced locomotion were negligible. Subgroup analyses revealed similar effects across sexes and species. Substantial variance in the protocols and moderate-to-high heterogeneity in behavioural outcomes were observed. We found CBD may attenuate novelty-induced locomotion in an open field and enhance fear memory recall, but data was limited. DiscussionThis is the first meta-analysis to comprehensively assess the link between cannabinoids and schizophrenia-like behaviours in rodents. Our results support epidemiological links between early cannabis use and schizophrenia-like phenotypes, confirming the utility of animal models. Standardising protocols will optimise models to strengthen reproducibility and comparisons, our work provides a framework for refining rodent models to elucidate biological pathways linking cannabis and schizophrenia.

mGluR2 receptors are widely expressed in limbic brain regions associated with memory, including the hippocampal formation, retrosplenial and frontal cortices, as well as subcortical regions including the mammillary bodies. mGluR2/3 agonists have been proposed as potential therapeutics for neurological and psychiatric disorders, however, there is still little known about the role of these receptors in cognitive processes, including memory consolidation. To address this, we assessed the effect of the mGluR2/3 agonist, eglumetad, on spatial memory consolidation in both mice and rats. Using the novel place preference paradigm, we found that post-sample injections of eglumetad impaired subsequent spatial discrimination when tested 6 hours later. Using the immediate early gene c-fos as a marker of neural activity, we showed that eglumetad injections reduced activity in a network of limbic brain regions including the hippocampus and mammillary bodies. To determine whether the systemic effects could be replicated with more targeted manipulations, we performed post-sample infusions of the mGluR2/3 agonist 2R,4R-APDC into the mammillary bodies. This impaired novelty discrimination on a place preference task and an object-in-place task, again highlighting the role of mGluR2/3 transmission in memory consolidation and demonstrating the crucial involvement of the mammillary bodies in post-encoding processing of spatial information.

Background/ObjectivesPersistent cognitive impairments are prevalent in methamphetamine (meth) use disorder and contribute to maladaptive decision-making and increased relapse vulnerability. There are currently no effective treatments for meth-associative cognitive deficits, and their neurobiological underpinnings remain incompletely understood. This study investigated the effects of chronic meth self-administration on episodic-like recognition memory and evaluated whether pharmacological potentiation of metabotropic glutamate receptor subtype 2 (mGlu2) could rescue these deficits. MethodsAdult male Sprague-Dawley rats underwent 7 days of limited- (1h/day) followed by 14 days of extended-access (6h/day) meth self-administration, followed by 30 days of abstinence. Recognition memory was assessed using the object-in-place (OIP) task. A positive allosteric modulator of mGlu2 receptors, LY-487379 (25 mg/kg, s.c.), was administered prior to the memory test. In parallel, changes in total and surface mGlu2/3 protein levels in the prelimbic and perirhinal cortices were evaluated. ResultsRats with extended access to meth self-administration exhibited escalated drug intake and persistent deficits in OIP memory. Administration of LY-487379 reversed this deficit. Total mGlu2/3 protein levels were unaltered; however, meth exposure was associated with a significant increase in surface mGlu2/3 receptor expression in both cortical regions examined. ConclusionsThese results demonstrate that chronic meth produces persistent cognitive dysfunction that can be rescued by mGlu2 receptor potentiation. The observed increase in surface mGlu2/3 expression may represent a compensatory response to chronic glutamatergic dysregulation, but it appears to be insufficient to restore cognitive function alone, without pharmacological enhancement. The current data encourage further exploration of mGlu2 role in stimulant-associated cognitive dysfunction. HighlightsChronic methamphetamine self-administration produced persistent deficits in episodic-like recognition memory in male rats and dysregulation of mGlu2/3 receptors in the prelimbic and perirhinal cortices. Systemic pharmacological potentiation of mGlu2 receptors rescued meth-associated memory deficits. mGlu2 receptor potentiation may represent a promising therapeutic strategy for treating stimulant-associated cognitive dysfunction. Increased surface mGlu2/3 expression may represent a compensatory adaptation to post-methamphetamine glutamatergic dysfunction, but it is not sufficient to restore cognition alone, without pharmacological enhancement.

Schizophrenia is marked by poor social functioning that can have a severe impact on quality of life and independence, but the underlying neural circuity is not well understood. Here we used a translational model of subanesthetic ketamine in mice to delineate neural pathways in the brain linked to social deficits in schizophrenia. Mice treated with chronic ketamine (30 mg/kg/day for 10 days) exhibit profound social and sensorimotor deficits as previously reported. Using three- dimensional c-Fos immunolabeling and volume imaging (iDISCO), we show that ketamine treatment resulted in hypoactivation of the lateral septum (LS) in response to social stimuli. Chemogenetic activation of the LS rescued social deficits after ketamine treatment, while chemogenetic inhibition of previously active populations in the LS (i.e. social engram neurons) recapitulated social deficits in ketamine-naive mice. We then examined the translatome of LS social engram neurons and found that ketamine treatment dysregulated genes implicated in neuronal excitability and apoptosis, which may contribute to LS hypoactivation. We also identified 38 differentially expressed genes (DEGs) in common with human schizophrenia, including those involved in mitochondrial function, apoptosis, and neuroinflammatory pathways. Chemogenetic activation of LS social engram neurons induced downstream activity in the ventral part of the basolateral amygdala, subparafascicular nucleus of the thalamus, intercalated amygdalar nucleus, olfactory areas, and dentate gyrus, and it also reduces connectivity of the LS with the piriform cortex and caudate-putamen. In sum, schizophrenia-like social deficits may emerge via changes in the intrinsic excitability of a discrete subpopulation of LS neurons that serve as a central hub to coordinate social behavior via downstream projections to reward, fear extinction, motor and sensory processing regions of the brain.

BackgroundThe dorsolateral striatum (DLS) is a key site for coordinating the alcohol-induced stimulant response, a behavioral marker predictive of future alcohol use disorder. Although ethanol (EtOH) affects all brain cells, little is known about the contribution of non-neuronal DLS cell types to EtOH-induced stimulation. MethodsWe used ex vivo two photon calcium imaging, in vivo fiber photometry of astrocyte and neuronal GCaMP, and astrocyte-specific manipulations in mice to determine DLS astrocyte contributions to EtOH-induced stimulation and voluntary EtOH drinking behavior. Using fiber photometry of GRAB-ACh sensors and cell-type specific chemogenetics, we also assessed the role of cholinergic signaling in observed astrocyte EtOH effects. ResultsAs expected, intraperitoneal EtOH injections (0.5-2g/kg) evoked a stimulant response, evidenced by increased locomotion compared to saline. In parallel, EtOH dose-dependently decreased astrocyte calcium activity but had minimal effects on direct and indirect pathway neuronal activity. Mimicking this reduction with astrocyte-specific expression of CalEX, a calcium extruding pump, facilitated EtOH stimulation compared to mice expressing a control fluorophore. Hence, EtOH-induced suppression of DLS astrocyte activity contributes to stimulation. Astrocyte calcium signaling is a well-known target of neuromodulation. Fiber photometry recordings of extracellular acetylcholine (ACh) levels via GRAB-ACh imaging showed inhibition of ACh release by acute EtOH. We virally expressed the excitatory chemogenetic actuator hM3Dq in striatal cholinergic interneurons to assess whether artificially increasing ACh release blocks EtOH-induced inhibition of astrocytic calcium activity. Despite facilitating ACh release, this manipulation did not impact astrocyte calcium activity under control (saline) or EtOH conditions. Together, this work identifies DLS astrocytes as key contributors to EtOH-induced stimulation and highlights the importance of considering astrocyte-neuron interactions in evaluating alcohol effects.

Cocaine use disorder (CUD) remains a major public health concern with no FDA-approved pharmacotherapy, underscoring the need to define the cellular and molecular adaptations produced by voluntary cocaine taking. The nucleus accumbens (NAc) is a key substrate for cocaine reinforcement and drug-seeking behavior, but interpretation of the functional role of its cellular heterogeneity in these behaviors is limited by past bulk transcriptomic studies. Here, we used single-nucleus RNA sequencing to profile the NAc of male and female rats that self-administered intravenous cocaine for 10 consecutive days versus yoked saline controls. After quality control, we analyzed 36,766 nuclei spanning major neuronal, glial, and vascular cell populations. Pseudobulk differential-expression analyses identified 478 cocaine-associated cell type-specific transcriptional changes that were concentrated in discrete medium spiny neuron (MSN) subclasses and astrocytes. D1 Ebf1+ MSNs showed the largest transcriptomic response, accounting for [~]40% of all differential-expression events, followed by D2 Stk32a+ MSNs, astrocytes, and D1 Ppm1e+ MSNs. These responses were largely cell type-specific, indicating that cocaine self-administration engages multiple molecular programs rather than a uniform accumbens-wide transcriptional signature. Immediate-early gene module-score analyses further revealed cocaine-associated activation states in select neuronal and non-neuronal cell populations, including D1 Ebf1+ MSNs, Drd3+ neurons, Sst+ interneurons, astrocytes, and oligodendrocytes. Gene-set, pathway, and upstream-regulator analyses nominated synaptic organization, axon guidance, RAS/MAPK signaling, NMDA receptor-associated signaling, and CREB-related transcriptional regulation as candidate mechanisms of cocaine-evoked plasticity. Together, these data provide a cell type-resolved resource for understanding how voluntary cocaine taking alters the rat NAc transcriptome and identifies discrete neuronal and glial cell populations for future mechanistic studies using preclinical CUD models.

Fentanyl is a potent synthetic opioid associated with overdose. However, little is known about fentanyl-induced molecular adaptations in the habenula and amygdala, two brain regions implicated in opioid use and withdrawal. We performed bulk RNA-sequencing in the rat habenula and amygdala to identify transcriptomic changes associated with fentanyl intake. Rats self-administered intravenous saline or fentanyl over 22-24 days. Ninety minutes following the final session, brains were collected for transcriptomic profiling. In Hb, we identified 453 differentially expressed genes (DEGs) between saline and fentanyl rats, with upregulated genes associated with synaptic transmission and ionic conductance. In amygdala, we identified 3,041 fentanyl-associated DEGs with upregulated genes implicated in metabolic and vesicular functions. Downregulated genes in both regions were enriched for extracellular matrix functions. Integration of DEGs with single-cell RNA-sequencing data from rodents and humans revealed that fentanyl DEGs were enriched in specific habenula and amygdala cell type markers. Furthermore, fentanyl downregulated DEGs in amygdala were enriched in genes associated with risk for substance use disorders. Together, we define how fentanyl intake alters transcriptional programs in the rat habenula and amygdala, and we link these changes to specific human cell types and risk genes for neuropsychiatric disorders and addiction.

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.