Neuropsychopharmacology

Psychedelic drugs are emerging as potentially efficacious tools for treating psychiatric conditions and probing the neural basis of consciousness. Although drug administration context is widely believed to shape psychedelic effects, it remains unclear whether it can independently generate placebo and nocebo effects resembling psychedelic experiences and side effects. In a pre-registered experiment, 78 non-clinical participants inhaled inert medical air under placebo and control conditions while completing a time perception task and a resting-state period. In the placebo condition, the gas was presented as nitrous oxide, whereas in the control, it was correctly identified. Placebo administration increased altered states of consciousness, ego dissolution, dissociation, and side effects, but did not significantly impact time perception. Predictive modelling indicated that placebo-induced psychedelic effects were predicted by trait responsiveness to verbal suggestion and absorption. These findings demonstrate that context alone can induce psychedelic effects, with implications for its causal role in psychedelic action.

Delirium is an acute, fluctuating brain dysfunction that commonly follows surgery and systemic inflammation, disproportionately affects older adults, and remains difficult to quantify continuously over time and treat pharmacologically. Here, we tested whether the neuroactive steroid zuranolone, a positive allosteric modulator of synaptic and extrasynaptic GABA_A receptors, mitigates delirium-like abnormalities across two complementary murine delirium models, a lipopolysaccharide-induced systemic inflammation (LPS) model and a postoperative delirium (POD) model, primarily in young and aged mice, with selected analyses in super-aged mice. Using continuous EEG with a validated bispectral EEG (BSEEG) metric, we found that zuranolone attenuated delirium-like EEG slowing in the LPS model in young mice in a dose-dependent manner and retained efficacy in aged mice. In the POD model, prophylactic dosing provided limited benefit in young mice, whereas post-surgery treatment reduced postoperative BSEEG elevations. In aged mice, prophylactic dosing suppressed POD-associated BSEEG abnormalities, and in super-aged mice, prophylactic zuranolone improved survival after POD induction. In parallel, zuranolone reduced microglial density and activation markers (IBA1 and CD68 immunoreactivity) at 24 h after POD surgery and after LPS challenge, with effects that were particularly evident in peri-screw site tissue in young POD mice and more broadly distributed across regions in aged mice. Finally, in young mice, zuranolone improved a composite behavioral severity score in the LPS model, whereas behavioral effects in the POD model were modest and domain-specific. Together, these findings support zuranolone as a candidate strategy to reduce delirium-like electrophysiological and neuroimmune abnormalities, with the strongest effects in inflammation-driven and age-vulnerable contexts.

Special Operations Forces (SOF) sustain repeated low-level blast (LLB) exposures; while most remain resilient, a subset develop depression, sleep disruption and reduced wellbeing that threaten readiness. We asked whether sub-concussive LLB chronically injures an insula-centered cortico-striato-thalamic network and whether network architecture explains divergent outcomes. In a mouse model parameterized to SOF blast exposure monitoring data, ninety 3-psi blasts over three weeks produced persistent diffusion and connectivity deficits across insular, striatal, pallidal and thalamic nodes, accompanied by tauopathy, neuroinflammation, vascular amyloid, and durable sleep and metabolic abnormalities. In SOF Soldiers, measures of cumulative LLB exposure predicted right insula-striatal diffusion/neurite disruption and increased depression risk. Interventional multi-mediator modeling showed that right insula-striatal microstructural injury mediated the effect of LLB to increase depression risk, while moderator screening identified features that amplify or buffer this mediation, defining risk and resilience zones. These findings enable precision blast-medicine integrating exposure dose, circuit biomarkers and moderator profiles.

D1-type receptor (D1R)-mediated dopaminergic signaling within the nucleus accumbens shell (NAcSh) is essential for forming adaptive circuit changes that embed persistent memories associated with drug seeking and craving. While D1R is expressed in both NAcSh neurons and astrocytes, the specific contribution of astrocytic D1R to drug-related circuit plasticity remains poorly understood. Here, we demonstrate in mouse NAcSh slices that D1R agonists increase astrocytic Ca2+ activity, an effect that is attenuated by astrocyte-specific D1R knockdown. Furthermore, selective knockdown of astrocytic D1R in the NAcSh prior to cocaine self-administration inhibits cocaine-induced generation of silent synapses, therefore hampering the associated remodeling of NAcSh circuits. Behaviorally, knockdown of NAcSh astrocytic D1R expedites the extinction of cocaine seeking and reduces cue-induced reinstatement. These results identify astrocytic D1R as a fundamental component of NAcSh dopamine signaling during cocaine experience that remodels synaptic connections and neural networks underlying drug seeking and relapse.

Antidepressant efficacy varies widely, yet the circuit-level mechanisms that distinguish treatment responders from non-responders remain poorly understood in humans. Here, we used high-resolution neuroimaging of hippocampal-amygdala networks during an emotional mnemonic discrimination task that taxes hippocampal pattern separation to examine how antidepressant mechanism of action and perceived treatment response shape emotional memory circuitry (N = 117). Participants included individuals taking single-action antidepressants (selective serotonin reuptake inhibitors), multi-action antidepressants (serotonin-norepinephrine reuptake inhibitors, norepinephrine-dopamine reuptake inhibitors, or polypharmacy), and unmedicated controls matched on current depression severity. Antidepressant mechanism and treatment response were associated with distinct patterns of activity in hippocampal subfields (dentate gyrus (DG)/CA3 and CA1) and amygdala subnuclei, including the basolateral amygdala (BLA) and central amygdala (CEA), during emotional mnemonic discrimination. Among non-responders, the relative balance of hippocampal activity differed by antidepressant mechanism: those taking single-action antidepressants showed greater DG/CA3 than CA1 activity, whereas those taking multi-action antidepressants showed the opposite pattern. This suggests mechanistically specific differences in hippocampal computations associated with ineffective treatment. These effects were localized to the anterior hippocampus, with no significant effects observed in posterior regions. In contrast, responders exhibited stronger DG/CA3-BLA coactivation during negative mnemonic discrimination, a pattern absent in non-responders and unmedicated controls. Antidepressant-associated differences in amygdala subnuclei activity persisted beyond current symptom severity, suggesting medication-related modulation of emotional memory circuits rather than effects driven solely by depression severity. These findings provide evidence in humans that antidepressant use is associated with altered hippocampal-amygdala circuitry in a manner that depends on both pharmacological mechanism and treatment efficacy. Identifying circuit-level signatures of treatment response may inform mechanistically guided approaches to antidepressant selection and monitoring.

RationaleCholinergic signalling is critical for attentional control and signal detection, yet the contribution of specific acetylcholine receptor (AChR) subtypes remains poorly understood. Although the 7 nicotinic AChR (nAChR) holds promise as a target for cognition-enhancing therapy, clinical findings to date have been inconsistent. ObjectiveTo investigate the effects of putative cognitive enhancing drugs, including those targeting cholinergic transmission and 7 nAChRs on a visual signal detection task (SDT). MethodsMale and female Sprague Dawley rats were trained on an SDT. Cholinergic transmission was probed systemically with nicotinic and muscarinic receptor antagonists (mecamylamine and scopolamine), a cholinesterase inhibitor (galantamine), an M4-AChR positive allosteric modulator (PAM; VU0467154), an 7 nAChR antagonist (MLA), an 7 nAChR PAM (CCMI), and an 7 nAChR partial agonist (SSR-180,711). Dopaminergic transmission was probed using the catechol-O-methyltransferase (COMT) inhibitor, tolcapone. A novel, trial-level signal detection theory-based generalised linear mixed-effects model (SDT-GLMM) was used to index response bias and perceptual sensitivity (d'), the latter reflecting subjects ability to discriminate signal from noise. ResultsMecamylamine profoundly impaired SDT performance across all measures. Galantamine significantly improved d' at moderate doses but not when a distractor was present. MLA uniquely produced dose-dependent improvements in d' that were preserved under distraction. In contrast, positive allosteric modulation and agonism of 7 nAChRs impaired task performance. Scopolamine, VU0467154, and tolcapone had no consistent or interpretable effects on signal detection. ConclusionsThis work demonstrates that 7 nAChR modulation bidirectionally and dose-dependently regulates perceptual sensitivity, irrespective of attentional distraction. These findings have implications for targeted cognitive enhancement in disorders of attention.

Weak inhibition of mitochondrial complex I (mtCI) has been shown to have neuroprotective effects in cellular and animal models of Alzheimers and Huntingtons diseases, at least in part by enhancing mitochondrial biogenesis and function. Mitochondrial dysfunction has also been demonstrated in schizophrenia patients and mouse models of schizophrenia. We tested whether weak inhibition of mtCI would ameliorate mitochondrial and behavioral phenotypes in a mouse model of schizophrenia. In mice with four copies of the Gldc gene, 8 weeks of treatment with the weak mtCI inhibitor, the small-molecule tricyclic pyrone compound CP2, reversed spontaneous alternation deficits in the Y maze, startle habituation deficits, and social novelty deficits in the three-chamber social interaction test. Consistent with the mechanism of action, Western blots revealed that CP2 reverses the reduced expression of PGC-1, a master regulator of mitochondrial biogenesis, and of the VDAC1, a primary gatekeeper for the exchange of metabolites, ions, and ATP between mitochondria and the cytosol. These findings suggest that the improvement of mitochondrial function may represent a novel strategy to reverse pathophysiological and behavioral deficits in schizophrenia.

Schizophrenia is a severe psychiatric disorder associated with altered dopaminergic signaling and hippocampal circuit dysfunction. Although antipsychotic medications remain the standard treatment, many are limited by incomplete efficacy and adverse effects. Cariprazine, a dopamine D2/D3 receptor partial agonist, has a favorable clinical profile, but its effects on neuronal excitability and network activity remain incompletely understood. Here, we integrated nationwide real-world clinical data with in vitro electrophysiology, computational modeling, and molecular analyses to define the neuronal actions of cariprazine. Among Hungarian patients diagnosed with schizophrenia and receiving index-drug monotherapy with one of the three prespecified D2/D3 targeting antipsychotics, haloperidol was associated with worse survival and a higher cumulative incidence of first registered suicide attempt than cariprazine or aripiprazole in matched observational cohorts. In primary mouse hippocampal cultures, multielectrode array recordings showed that acute cariprazine treatment moderately reduced spontaneous firing in a dose-dependent manner and prolonged burst intervals while largely preserving network synchronization. These effects were milder than those of haloperidol and aripiprazole. Whole-cell patch-clamp recordings revealed cell-type-dependent effects, with reduced intrinsic excitability and increased firing irregularity mainly in regular- and stuttering-type neurons. Conductance-based modeling identified enhanced Kv1-mediated D-type potassium currents as sufficient to reproduce these effects. Consistent with this mechanism, chronic cariprazine treatment altered Kv1.2 protein distribution without changing Kcna2/Kcna3 or Drd1/Drd2/Drd3 transcript expression. These findings identify modulation of intrinsic excitability via Kv1/D-type potassium currents as a candidate cellular mechanism of cariprazine and provide a translational link between real-world evidence and circuit-level drug effects.

Antidepressants are widely prescribed for major depressive disorder, yet only one-third of patients achieve remission after initial treatment. Previous genome-wide association studies (GWAS) of clinically assessed antidepressant response combined multiple antidepressant classes, potentially obscuring class-specific effects. This study focused on selective serotonin reuptake inhibitors (SSRIs), often first-line due to better tolerability. Data from 15 cohorts across four ancestries were integrated: European (N = 3887; 11 studies), East Asian (N = 1068; 4), African (N = 277; 1), and Admixed American (N = 250; 1). GWAS of non-remission and percentage improvement were conducted within cohorts, followed by ancestry-specific meta-analyses and trans-ancestry meta-regression. Single nucleotide polymorphism (SNP)-based heritability was estimated in European samples. Polygenic scores were used for leave-one-out prediction and to assess shared genetic architecture with psychiatric traits. Gene-level and gene-set enrichment analyses were also performed. No genome-wide significant variants were identified for either outcome in any ancestry-specific or trans-ancestry analyses. However, trans-ancestry meta-regression yielded eight independent loci with suggestive associations (p < 1 x 10-5) for non-remission and 17 for percentage improvement. Gene-set analyses revealed nominal enrichment of the serotonergic synapse pathway for non-remission. SNP-based heritability estimates were not significantly different from zero for either outcome. Better SSRI response was nominally associated with lower genetic predisposition to major depressive disorder, post-traumatic stress disorder, and schizophrenia. This study represents the largest trans-ancestry GWAS of SSRI response, highlighting emerging biological signals. Limited power emphasises the need for larger and ancestrally diverse cohorts to better characterise the genetic architecture of antidepressant response.

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.

In treatment-resistant schizophrenia, clozapine treatment has been associated with longitudinal reductions in subcortical volumes, ventricular enlargement, and widespread cortical thinning. However, it is unknown how these structural changes relate to clozapines pharmacological profile and clinical efficacy. We combined five longitudinal datasets with MRI acquired before and on average 5 months after clozapine initiation in 143 individuals to quantify brain structural changes and their association with normative maps relating to neuroreceptor architecture and physiological systems, and improvement in symptom severity. Clozapine treatment was associated with grey matter volume reductions across multiple subcortical regions (including the amygdala, hippocampus, thalamus, caudate, putamen and nucleus accumbens), increases in pallidal volume, ventricular enlargement, and widespread cortical thinning. Cortical regions showing the greatest magnitude of thinning corresponded to areas with higher normative densities of serotonergic 5-HT1A, 5-HT2A and 5-HT4 receptors. Changes in subcortical volume or cortical thickness during clozapine treatment were not associated with changes in total or positive symptom severity. In addition, baseline subcortical volume, cortical thickness, or gyrification prior to starting clozapine did not predict subsequent symptom improvement. Cortical thinning may partly reflect clozapines activity at serotonergic receptors, which have been implicated in cortical network stabilisation and neuroplasticity, however structural remodelling during clozapine treatment may reflect a process independent from its clinical efficacy in improving core symptoms of psychosis.

The motivation to pursue drugs is a fundamental element of substance use. Different tasks assess motivation in the face of effort, punishment, or the absence of the drug, and recent studies have suggested that a shared latent variable may drive behavior across these tasks. The prelimbic cortex (PL) is implicated in these behaviors, but it is unknown if its role is driven by shared or distinct neural ensembles. We recorded PL activity using in vivo endoscopic calcium imaging in 32 male and female Sprague-Dawley rats as they completed cocaine or water self-administration, extinction, progressive ratio, and punished self-administration. We found that behavior across tasks was driven by a single latent variable in water, but not cocaine rats. We also found distinct neural populations that tracked reward pursuit. We found that one population of cost-sensitive neurons had significantly fewer neurons present during the progressive ratio task. A second population of reward-sensitive neurons had significantly fewer neurons present during the extinction task. Individual rats with more of these neurons present during the task had significantly higher levels of reward pursuit in the progressive ratio and extinction tasks, respectively. Furthermore, this relationship was true across cocaine and water rats, suggesting a general role in motivation independent of reward type. When we examined whether shared patterns of neural activity predicted shared patterns of behavior across the tasks, we found no relationships. Thus, our findings suggest that distinct facets of reward motivation are tracked by distinct ensembles in the PL, rather than a shared ensemble.

Relapse-prevention strategies aimed at reducing relapse following abstinence, primarily focus on reducing cravings that lead to drug-seeking triggered by stress, drug-related cues, or re-exposure to the drug. Because addictive drugs form persistent associative contextual memories, we investigated how reactivation of cocaine-related hippocampal memories influences subsequent drug-seeking. Here, we tagged dorsal dentate gyrus (dDG) memory ensembles involved in encoding either a first or fourth cocaine exposure (15mg/kg, i.p) in male and female c57BL/6 mice using a TetTag approach. Mice underwent cocaine conditioned place preference (CPP), extinction, and reinstatement. We assessed whether optical reactivation of tagged cocaine-related ensembles could substitute for a cocaine priming injection to reinstate CPP, whether reactivation altered cocaine-induced reinstatement, and if these effects differed depending on stage of drug exposure. We also compared these effects to reactivation of saline-associated ensembles. Cocaine produced robust locomotor activation during conditioning, and sensitization developed across repeated drug exposures. Reactivation of a cocaine-related engram alone did not reinstate CPP. However, reactivation of the first cocaine exposure engram attenuated cocaine-induced reinstatement. In contrast, reactivation of the fourth exposure engram did not confer this protective effect. Interestingly, reactivation of saline-associated ensembles also reduced cocaine-induced reinstatement specifically in females, suggesting dDG ensemble reactivation may modulate relapse-related behavior through interference or neuromodulatory disruption of cocaine-associated representations, consistent with our prior work. These findings raise the possibility that early contextual experiences form competing or destabilizing representations that interfere with later cocaine-seeking when reactivated. Females also displayed greater sensitivity to locomotor-inducing effects of cocaine memory reactivation, although this was dissociated from CPP. Together, these findings show that cocaine memories are distinct across drug experience and selective reactivation of dDG engrams can differentially influence drug-seeking.

Background. Psychotic-like experiences (PLEs) index early risk for psychotic disorders and are consistently associated with childhood trauma, yet underlying biological mechanisms remain poorly understood. DNA methylation (DNAm) may capture the biological embedding of early adversity, while adolescent exposures such as cannabis use may modify these processes. We examined epigenome-wide associations of childhood trauma and PLEs, tested the moderating role of early cannabis use, and evaluated DNAm as a potential mediator. Methods. We analysed data from the Avon Longitudinal Study of Parents and Children (ALSPAC), a UK population-based birth cohort. Childhood trauma was assessed prospectively and retrospectively. Epigenome-wide DNAm was measured in peripheral blood at ~17 years using the Illumina 450K array, and PLEs were assessed at 18 using a structured interview. Epigenome-wide association studies were conducted for trauma-DNAm and DNAm-PLEs associations in the final sample (n = 1,457), adjusting for demographic, biological, and technical covariates. Differentially methylated regions (DMRs) were identified using DMRff, followed by functional enrichment analyses. Cannabis use at 15.5 was modelled as a moderator with multiple imputation for missing data. Mediation was tested using the Divide-Aggregate Composite-null Test (DACT). Results. Childhood trauma was associated with widespread DNAm differences, primarily at the regional level, with enrichment in pathways related to cellular stress responses. In contrast, DNAm associated with PLEs was more limited and implicated loci involved in epigenetic regulatory processes. These signatures were largely distinct, and there was no evidence supporting mediation after multiple testing correction. Incorporating cannabis use altered the pattern and extent of DNAm associations, with stronger and more significant signals observed at both CpG and regional levels, although these did not translate into evidence of mediation. Conclusion. Childhood trauma and PLEs show distinct DNAm signatures in adolescence, with trauma-related DNAm reflecting broad stress-related processes and PLE-associated DNAm implicating regulatory mechanisms. We found little evidence that DNAm mediates the trauma-PLE association. Instead, adolescent exposures, particularly cannabis use, may distinctly influence trauma-related epigenetic variation with limited detectable downstream effects on PLEs. These findings support a context-dependent model of epigenetic risk and highlight the need for larger longitudinal studies to clarify causal pathways linking early adversity to psychosis.

Background: Tobacco use is prevalent in clinical high risk for psychosis (CHR-P) population and has widespread negative health consequences, but understanding of its neural substrates is limited. Abnormal default mode network (DMN) may underlie tobacco dependence in CHR-P. We investigated how tobacco use relates to DMN connectivity and how CHR-P status impacts this relationship. Methods: We used baseline substance use and resting-state functional magnetic resonance imaging data from the North American Prodrome Longitudinal Study (NAPLS2; CHR-P: n=211, mean age 19.2, 37.9% female; healthy control: n=132, mean age 19.9, 47.7% female). Voxel-wise connectivity was calculated from the left lateral parietal (LLP) node of the DMN to the rest of the brain. We regressed LLP-brainwide connectivity against tobacco use frequency in the past month to generate a spatial map of how connectivity relates to current tobacco use. Results: Brainwide connectivity analysis identified two clusters in R hippocampus (peak voxel at MNI [+30,-12,-27]) and in L parahippocampus (peak voxel at MNI [-27,-27,-27]), where higher LLP-cluster connectivity was associated with more frequent tobacco use. LLP - R hippocampus connectivity was higher in current tobacco users compared to non-tobacco users (t=-3.5466, df=101.88, p=0.0006), and higher in CHR-P than controls (t=-2.8651, df=279.47, p=0.0049). Among current tobacco users, there was a significant tobacco-by-diagnosis interaction on LLP - R hippocampus connectivity (estimate=0.306, SE=0.149, t=2.051, p=0.045) such that heavier tobacco use predicted hyperconnectivity only in CHR. Conclusions: More frequent tobacco use was associated with higher DMN-hippocampal connectivity in both CHR-P and controls. CHR-P diagnosis enhanced this relationship.

BackgroundResponding appropriately to threats is critical for survival. Dysregulated defensive responses are core features of psychiatric illnesses including panic disorder and post-traumatic stress disorder. Carbon dioxide (CO2) inhalation evokes defensive behaviors in both humans and mice. Here we investigated the role of acid-sensing ion channels (ASICs) in CO2-evoked jumping in mice. MethodsDefensive behaviors (jumping and freezing) were assessed in response to CO2 inhalation and basolateral amygdala (BLA) acidification. We tested the role of ASICs using global knockout mice and Asic1aloxP/loxP mice transduced with AAV-CMV-Cre or AAV-CaMKII-Cre in the BLA. Effects of CO2 on single neuron firing and local field potentials were studied via BLA microwire arrays. ResultsASIC1A disruption increased CO2-evoked jumping while reducing freezing, paralleled by increased BLA c-Fos induction. Acidification of the BLA recapitulated these effects. Virus-mediated ASIC1A disruption in BLA did not resolve the locus of ASIC1A action in jumping. CO2 inhalation suppressed firing in most BLA neurons, though a small number increased firing. ASIC1A disruption enhanced CO2-induced suppression of narrow waveform neurons (putative interneurons), and facilitated excitation of wide waveform neurons (putative principal neurons). Additionally, CO2 produced concentration-dependent broadband power suppression with selective theta enhancement, effects that were augmented by ASIC1A disruption. ConclusionsTogether, these findings suggest that ASIC1A promotes interneuron activity during acidosis and that its loss may reduce inhibition of principal neuron output, shifting defensive responses from freezing toward jumping. These results advance our understanding of how brain pH and ASICs regulate defensive behavior, with potential implications for understanding dysregulated defensive responses.

Across species, adolescence is a time of heightened reward sensitivity and enhanced impulsivity and risk-taking. In adults, these behavioral features are linked with a tendency to approach and interact with reward-associated cues - a behavior known as sign tracking - which is thought to reflect the transfer of incentive salience from reward to cue. Counterintuitively, adolescents are less likely to exhibit sign tracking, compared with adults, and more likely to exhibit goal tracking, or approach to the site of reward. To investigate a possible neural basis for this age difference, we recorded the activity of individual neurons in the nucleus accumbens (NAc) of male and female rats during Pavlovian conditioning in adolescence and adulthood. In a separate group, we used a fluorescent indicator (GRABDA) to measure dopamine release at the same ages. We found that cue-evoked NAc activity increased over the course of training in adolescents and then further in adulthood. The majority of adolescents were goal trackers or intermediates, for whom reward-evoked activity peaked during adolescence and declines in adulthood, correlating with increased prevalence and intensity of sign tracking. Meanwhile, cue-evoked dopamine release was markedly higher in sign trackers than in goal trackers at all time points. These results suggest that the progression from adolescence to adulthood may be accompanied by changes in the engagement of the mesolimbic dopamine system and/or the responsivity of NAc neural signaling to dopamine, contributing to limited sensitivity to reward cues, coupled with heightened sensitivity to primary rewards, in adolescent animals. Significance StatementAdolescence is a time of enhanced reward sensitivity, impulsivity, and risk-taking, making adolescents vulnerable to drug use and other risky behaviors. In adults, attraction to reward-associated cues - which can be modeled in animals using a behavior called sign tracking - plays an important role in risky behaviors. Surprisingly, we find that adolescents exhibit less sign tracking compared with adults. Here, we investigate the neural circuits underlying this age difference by monitoring neural activity and dopamine release in the nucleus accumbens (NAc), a key brain area for reward-seeking behavior, in the same animals as adolescents and as adults. We find that the majority of adolescents show a reduced neural sensitivity to reward cues, but a heightened neural response to the reward itself.

BACKGROUNDThe proliferation of the potent synthetic opioid fentanyl has exacerbated the ongoing crisis of substance use disorder and associated overdose deaths, yet the neurobiological mechanisms that underlie individual vulnerability to addiction and relapse remain poorly understood, particularly in the context of fentanyl use. The prefrontal cortex (PFC) has been identified as a key brain structure important for cognitive functions impacted in addiction, including inhibitory control of behavior and association of drug experience with specific cues, contexts, or actions. Although the heterogenous neuronal composition of the PFC complicates attribution of addiction-related behavioral regulation to specific cortical cell types and circuits, application of cell-type-specific methods in translationally relevant rodent models have begun to elucidate the key neural substrates of opioid addiction. METHODSWe used an intermittent access fentanyl self-administration (IntA SA) model to characterize individual variation and sex differences in addiction vulnerability in male and female rats. Longitudinal wireless fiber photometry recording was used to track calcium activity patterns in intratelencephalic (IT) neurons of the prelimbic cortex across acquisition of self-administration, escalation of fentanyl intake, extinction training, and cue-induced reinstatement of fentanyl seeking. RESULTSWe found that our fentanyl IntA SA paradigm produces distinct low- and high-risk addiction severity phenotypes and that female rats exhibited a greater propensity for high-risk classification, which was characterized by abundant and consistent fentanyl intake, robust responsiveness to conditioned and discriminative fentanyl-associated cues, and high levels of fentanyl-seeking during periods of drug unavailability, extinction training, and a cue-induced reinstatement test. Fiber photometry recordings revealed dynamic encoding of fentanyl-associated stimuli by prelimbic IT neurons across the IntA SA paradigm with event-related calcium transients observed in association with lever presses, fentanyl infusions, and presentation of conditioned and discriminative cues. CONCLUSIONSOur data indicate that fentanyl IntA SA is a translationally relevant paradigm that enables investigation of phenotypic diversity and the role of sex in fentanyl addiction. Longitudinal cell-type-selective calcium recordings revealed dynamic representation of fentanyl-associated stimuli by IT neurons of the prelimbic cortex consistent with a role for this cortical subpopulation in addiction-related behaviors.

Cannabis is one of the most widely used psychoactive substances worldwide, and cannabis use disorder (CUD) is increasingly recognized as a major public health concern. Clinical evidence indicates that women may be particularly vulnerable to developing addiction, exhibiting a faster transition from initial drug use to loss of control and increased relapse vulnerability. However, females remain underrepresented in both preclinical and clinical research, limiting our understanding of the neurobiological mechanisms underlying this susceptibility. Here, we investigated sex differences in behavioral and epigenetic susceptibility to cannabinoid addiction using a mouse operant self-administration model with the synthetic cannabinoid agonist WIN 55,212-2. Female mice displayed increased addiction-like behavior, characterized by greater persistence of responding during drug-free periods and enhanced compulsive-like drug seeking compared to males. miRNA profiling in the medial prefrontal cortex (mPFC) identified a female-specific epigenetic signature associated with the addiction-like phenotype, including downregulation of mmu-miR-669j, mmu-miR-7036b-5p, mmu-miR-878-3p, and mmu-miR-7017-3p, together with upregulation of mmu-miR-3092-5p in addicted females. Functional enrichment analyses of predicted target genes revealed pathways related to synaptic organization, axon guidance, neurotransmission, and structural plasticity. Together, these findings demonstrate sex-dependent differences in vulnerability to cannabinoid addiction-like behavior and identify a specific miRNA signature in the mPFC associated with this phenotype, highlighting potential targets for the development of sex-specific therapeutic strategies.

Mental illness poses a substantial global burden, yet existing psychotherapies and psychopharmacologies often produce limited outcomes. Psychedelic assisted therapies have emerged as potential transdiagnostic interventions. In particular, 3,4 methylenedioxymethamphetamine assisted therapy (MDMA AT) has generated interest for its rapid psychological effects and potential to enhance psychotherapy outcomes. However, the incremental efficacy of MDMA AT relative to control interventions across transdiagnostic outcomes remains unclear. Further, there have been emerging concerns regarding harm reporting quality in MDMA AT clinical trials. We conducted a systematic review and meta analysis of MDMA AT randomized controlled trials. Eleven publications representing eight controlled trials with 10 analyzed subgroups (n = 295 participants) were included in meta-analyses. Two additional secondary publications were included for harm reporting syntheses (k = 13 total). Across 114 extracted effect sizes, MDMA AT demonstrated a significant moderate-to-large incremental reduction in psychopathology relative to controls (g = 1.03, 95% CI [0.46, 1.60]), though heterogeneity was high (I squared = 76%). Incremental effects were larger versus inert placebos (g = 1.27) than active controls (g = 0.75). Symptom specific analyses indicated strong incremental effects for trauma reduction (g=1.46 [95% CI: 0.67, 2.25]) and smaller non-significant effects for depression (g=0.51 [95% CI: -0.06, 1.08]). Harm reporting quality synthesis showed only 23% of publications met high-quality reporting standards. Overall, MDMA AT demonstrates potential transdiagnostic efficacy, but small samples, confounding factors, and mediocre harm reporting highlight the need for larger more transparent clinical trials.