Neuropsychopharmacology

Antipsychotic dosing regimens, commonly daily or via slow-release compounds, are designed to maintain steady-state plasma concentrations. They are guided by their plasma half-life that is typically in the range of several hours. This schedule contrasts with the slow time course of therapeutic efficacy, which often takes weeks to develop fully. This discrepancy led us to hypothesize that the effects of a single dose of an antipsychotic drug might be detectable well beyond the time window predicted by receptor occupancy. To test this, we administered a single dose of the antipsychotic drug clozapine to mice. We observed long-term behavioral effects and changes to cortical activity patterns up to several days after administration. Specifically, clozapine induced a decorrelation of activity in the dorsal cortex observable up to 9 days post administration. This effect was driven by a genetically and functionally distinct subset of layer 5 intratelencephalic neurons, possibly through a clozapine induced increase in the reliability of long-range inhibitory functional influence that exhibited a similar long-term change. Thus, our findings suggest that longer dosing intervals for antipsychotic drugs warrant clinical exploration.

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.

Despite decades of clinical implementation of medications for opioid use disorder (OUD), overdose mortality rates remain high, underscoring a critical gap in treatments that target brain mechanisms driving addiction. Mindfulness-Oriented Recovery Enhancement (MORE) has demonstrated efficacy in reducing opioid use and craving, hypothetically by restructuring the salience of drug and natural rewards. Yet, to date, MOREs neurobiological mechanisms remain unclear. In this first functional magnetic resonance imaging (fMRI) randomized controlled trial (RCT) of MORE for OUD (NCT04112186), we tested whether compared with an active psychoeducational supportive therapy (PST) control group, MORE rebalanced neural responses to drug and natural reward cues in inpatients with OUD receiving standard of care including medications. Compared with PST, eight weeks of MORE significantly reduced drug-biased activity in the dorsolateral prefrontal cortex (dlPFC) and posterior regions of the default mode network including the precuneus during downregulation of responses to drug cues relative to upregulation of responses to natural reward cues (even when controlling for passive cue viewing). The shift from drug to natural reward responses in the lateral and ventromedial PFC was associated with lower cue-induced craving exclusively in the MORE group. MORE also reduced medial PFC synchronization to naturalistic drug-related movie scenes and significantly extended abstinence duration at follow-up ([~]4 months post-treatment) relative to PST. Together, this neuroimaging RCT demonstrates that MORE normalizes function in PFC nodes of the reward, salience, and control systems, positioning MORE as a biologically-grounded adjunct to pharmacotherapy for OUD.

The growing perception of cannabinoids as benign has increased perinatal exposure to both {Delta}9-tetrahydrocannabinol (THC) and cannabidiol (CBD), yet their long-term effects on prefrontal circuitry remain incompletely defined. Here we used whole-cell and field electrophysiology in adult mice (P100-140) of both sexes to compare how in utero exposure to THC or CBD (GD5-18) remodels layer-5 pyramidal neurons in the medial prefrontal cortex (mPFC). We quantified intrinsic excitability, excitatory and inhibitory synaptic transmission, the net E/I ratio, spontaneous excitatory and inhibitory currents kinetics, and canonical forms of synaptic plasticity (endocannabinoid-mediated LTD and NMDA-dependent LTP). Both cannabinoids shifted the adult mPFC toward a more pro-excitatory state: the E/I ratio was altered in a compound- and sex-dependent manner, and endocannabinoid-mediated LTD was abolished across groups. THC recapitulated previously reported deficits, producing male-specific increases in intrinsic excitability and accelerating excitatory current kinetics in females, demonstrating a conserved cross-species vulnerability of prefrontal circuits to gestational THC. CBD produced distinct signatures: female offspring showed marked increases in spontaneous excitatory event frequency and amplitude, indicating large-scale reorganization of excitatory and inhibitory inputs, while male offspring exhibited a selective and profound impairment of LTP. The combination of universal eLTD loss and CBD-specific LTP impairment in males yields a bidirectional loss of plasticity: an emergent synaptic rigidity in which circuits are unable to potentiate or depress effectively. Together, these convergent and divergent effects establish that prenatal exposure to THC and CBD produces lasting, sex-dependent rewiring of mPFC circuitry. Our results caution that the non-intoxicating profile of CBD does not preclude durable developmental impact and underscore the importance of considering both compound identity and sex when assessing the neurodevelopmental risks of perinatal cannabinoid exposure.

Nearly one third of women of reproductive age in the United States are prescribed opioids annually; 14% of women fill an opioid prescription during pregnancy, and one in five report misuse. Opioid use during pregnancy has given rise to an increasing population of infants born with gestational opioid exposure. Although substantial clinical work has focused on treating these infants as they experience opioid withdrawal symptoms at the time of birth, notably few studies have examined the effects of gestational opioid exposure on brain development and long-term cognitive function. During typical brain development, endogenous opioids and their receptors are highly expressed by neural progenitor cells, neurons, and glia where they modulate cell proliferation, differentiation, and maturation. Thus, any disruption to the endogenous opioid system during the critical period of brain development may have lasting consequences on brain cell populations and the behaviors they influence. Indeed, opioid-exposed infants have smaller brains than age-matched peers and show significant neurodevelopmental impairment; they also have higher rates of learning disability at school age. To investigate how exposure to exogenous opioids during brain development affects neural maturation in the hippocampus, a brain region critical for learning and memory, our lab has developed a clinically relevant perigestational morphine exposure rat model. The current study reports that perigestational exposure to morphine delays postnatal hippocampal neuronal maturation, alters astrocyte and oligodendrocyte proliferation, and alters expression of brain-derived neurotrophic factor (BDNF), a protein crucial for healthy brain growth. Furthermore, we show that environmental enrichment rescues BDNF deficits, offering evidence for the effectiveness of non-invasive, non-pharmacological intervention for developmental consequences of perigestational opioid exposure.

Cannabis use is an increasingly common therapeutic for a variety of chronic diseases. In addition, people with sleep problems may self-medicate using cannabis products. However, genetic architecture of cannabis use and its shared genetic predispositions with sleep traits has not been systematically examined. We performed a meta-analysis of cannabis use within the All of Us and UK Biobank cohorts, consisting of 152,807 cases and 220,272 controls. Our meta-analysis identified 39 independent loci, including the previously reported CADM2 locus associated with cannabis use and replicating previous work. Additionally our associations include neuronal and sleep-regulating genes such as HTR1A, RAI1, SLC39A8, and NCAM1. Moreover, tissue-specific analyses revealed that the genetic architecture of cannabis use is heavily enriched within the central nervous system and specific brain cell types. In addition, we observed significant positive genetic correlations with clinical insomnia, insomnia-related medication usage, and objectively measured nighttime physical activity, alongside negative correlations with morningness chronotype and daytime activity. Fine-mapping and colocalization analyses identified shared genetic signals between cannabis use and clinical insomnia including a near-perfect colocalization at SLC39A8 and CADM2. Together, these results highlight the shared genetic risk between cannabis use and sleep disorders. Additionally, our findings indicate the importance of investigating the genetic effects of cannabis use as its use becomes more widespread, both recreationally and medicinally.

Ketamine is an NMDA receptor antagonist with rapid-antidepressant properties when administered at a sub-anesthetic dose. Preclinical models indicate that a direct injection of ketamine into lateral habenula (Hb), a small midbrain structure with an evolutionarily preserved role in aversive learning across mammals, can rapidly relieve depression-like behavior. However, there is limited evidence to explain how ketamine acts on the function of the human habenula. In a translational computational neuroscience study, 70 healthy adult volunteers were randomised in a 1:1 ratio to receive ketamine or placebo (NaCl 0.9%). We used an aversive Pavlovian conditioning paradigm combined with 7-Tesla functional neuroimaging to show that ketamine attenuates habenula response during aversive stimuli expectations and outcomes 24 hours post-infusion. We further present preliminary evidence suggesting that when aversive learning occurs after ketamine infusion, reduced habenula activity during the learning process may lead to downstream effects that diminish the aversive impact of negative affective memories. These findings provide translational support for preclinical models of ketamines mechanisms in humans.

Neuroimmune interactions have emerged as critical modulators of substance use disorders and may represent promising translational therapeutic targets. In prior work, we demonstrated that the cytokine granulocyte colony stimulating factor (G-CSF) is elevated in mice following cocaine exposure, with circulating levels correlating with cocaine intake and locomotor sensitization. Additionally, exogenous G-CSF enhances cocaine reward and increases low-dose cocaine self-administration. We have further shown that repeated G-CSF administration alters expression of glutamatergic synapse-associated proteins following cocaine-seeking behavior. Building on these findings, the present studies examined the molecular consequences of repeated administration of G-CSF, cocaine, or their combination, with a focus on glutamatergic signaling pathways. We also tested whether altered glutamate receptor expression contributes to G-CSF-mediated enhancement of cocaine reward. Repeated combined administration of G-CSF and cocaine produced robust changes in glutamate-associated and synapse-related protein expression within the nucleus accumbens and medial prefrontal cortex. These molecular adaptations were accompanied by increased synaptic density in the nucleus accumbens. Finally, pharmacological inhibition of calcium-permeable AMPA receptors within the nucleus accumbens reversed the G-CSF-induced enhancement of cocaine conditioned place preference. Together, these findings indicate that G-CSF enhances cocaine reward at least in part by promoting glutamatergic synaptic remodeling in the nucleus accumbens, identifying a neuroimmune-glutamate mechanism that may be leveraged for therapeutic intervention.

The nucleus accumbens (NAc) and its excitatory input from the medial prefrontal cortex (mPFC) form a critical circuit underlying drug-induced plasticity associated with addiction-related behaviors. However, baseline differences in excitatory signaling across NAc subcircuits and sex-specific neuroadaptations following opioid self-administration remain poorly understood. Here, we examined synaptic signaling in mPFC-NAc pathways in drug-naive mice and after abstinence from remifentanil self-administration. Under drug-naive conditions, AMPA receptor- mediated glutamatergic signaling was generally elevated in D2 medium spiny neurons (MSNs) of both the NAc core and shell across sexes, while females exhibited greater excitatory signaling in D1 MSNs of the NAc core compared with males. Pathway-specific analyses revealed that prelimbic cortex (PL) inputs to NAc core D2 MSNs displayed enhanced calcium-permeable AMPA receptor (CP-AMPAR) signaling and increased presynaptic release relative to D1 MSNs. Following abstinence from remifentanil self-administration, miniature excitatory postsynaptic current analyses showed increased excitatory drive at D1 MSNs and decreased drive at D2 MSNs, largely restricted to the NAc core. At PL-Core D1 MSN synapses, remifentanil reduced AMPA/NMDA ratios, consistent with increased CP-AMPAR incorporation in males and females, while increasing presynaptic signaling exclusively in males. In contrast, PL-Core D2 MSN synapses showed a reduction in presynaptic signaling across sex, while ostensibly weakening postsynaptic signaling selectively in males through reductions in CP-AMPAR signaling. At infralimbic cortex (IL)-shell inputs, a reduction in AMPAR rectification indices at D1 MSN synapses was produced by remifentanil, while release probability was decreased at D2 MSN synapses in males only. Together, these findings reveal sex- and pathway-specific synaptic adaptations within mPFC-NAc circuits that may be obscured by global measures of excitatory transmission and identify baseline circuit differences that may shape opioid-induced plasticity.

Fear extinction requires dynamic updating of cortical representations, yet the neural mechanisms underlying successful extinction remain poorly understood. Some psychoactive substances induce structural plasticity in medial prefrontal cortex (mPFC), possibly underlying their therapeutic potential. Here we investigated whether MDMA, which enhances fear extinction, induces prefrontal structural and functional plasticity, and measured its effects on ensemble representations during extinction. Longitudinal two-photon microscopy revealed that MDMA increased spine density and spinogenesis across prefrontal subregions. Miniscope Ca{superscript 2} imaging in infralimbic cortex (IL) during fear extinction revealed that IL became more correlated with the suppression of freezing behavior, consistent with a strengthening of its role in extinction. Longitudinal cell registration demonstrated accelerated representational drift across days in MDMA-treated mice; this effect was strongest in a functionally defined subpopulation of neurons that showed suppression of activity to conditioned cues. These findings demonstrate that MDMA facilitates structural and functional neuroplasticity, potentially underlying its enhancement of extinction learning.

Relapse to opioid use during abstinence is often triggered by drug-associated cues but the persistence of this effect across the lifespan is unknown. Using a rat model, we found that relapse provoked by heroin-predictive discriminative stimuli persisted for over one year of abstinence, suggesting enduring, potentially lifelong opioid relapse vulnerability.

Relapse remains a major challenge in opioid addiction treatment, underscoring the need for innovative therapies. Progress in neuromodulation therapies has been limited by insufficient mechanistic understanding of stimulation engagement and disease-related changes in the brain. We used a novel, focal transcranial magnetic stimulation (TMS) system to deliver high-density theta burst stimulation (hdTBS) combined with resting-state fMRI to test whether anterior cingulate cortex (ACC) stimulation reduces relapse-like behavior and alters functional circuitry in a rodent model of opiate dependence. The coil focality and stimulation parameters approximate human TMS protocols, and the targeted region represents a functional homolog of the human ACC. We trained rats to self-administer oxycodone intravenously for 14 days. We then introduced an electric barrier for 13 days, which caused cessation of drug self-administration. We assessed relapse to oxycodone seeking immediately after training (early abstinence) and after electric-barrier exposure (late abstinence). We administered daily hdTBS or sham stimulation for 7 days before the late-abstinence test. Sham-treated rats showed a time-dependent increase in oxycodone seeking during abstinence (incubation of oxycodone craving) and reduced ACC functional connectivity. In contrast, hdTBS prevented the incubation of oxycodone craving and restored ACC connectivity with the dorsal and ventral striatum. Tracer-based axonal-projection data further showed that stimulation-induced effects aligned with regions receiving dense projections from the stimulation site, suggesting that the projection architecture is critical to the propagation of focal stimulation across distributed networks. These findings identify ACC-centered circuits as mechanistically informed targets for TMS-based interventions that aim to reduce opioid relapse during abstinence. One sentence SummaryPrefrontal TMS stimulation reduced relapse-like behavior and restored corticostriatal circuits, highlighting translational targets for addiction treatment.

Opioid use disorder (OUD) is characterized by compulsive drug seeking and impaired executive control arising from maladaptive plasticity within cortico-striatal circuits. While transcriptomic studies have identified coding gene alterations in the nucleus accumbens (NAc) and dorsolateral prefrontal cortex (DLPFC), the contribution of the noncoding genome remains poorly defined. Here, we performed integrative transcriptomic analysis of postmortem human NAc and DLPFC to systematically identify and characterize long noncoding RNAs (lncRNAs) in OUD. We identified 36,225 lncRNA loci expressed across reward and executive regions, approximately half of which were previously unannotated. OUD was associated with widespread lncRNA dysregulation in NAc and DLPFC, with lncRNA-centered co-expression modules enriched for neuroimmune signaling, phosphorylation-dependent synaptic pathways, and intracellular receptor cascades. Notably, OUD disrupted circadian rhythmicity of lncRNAs to a degree comparable to or exceeding mRNAs, implicating temporal reorganization of noncoding networks in addiction pathology. Integration with single-nucleus transcriptomic data revealed pronounced neuronal and glial cell type specificity among OUD-associated lncRNAs. Together, these findings demonstrate that lncRNAs represent a critical regulatory layer in reward and executive circuits and suggest that spatial, temporal, and cellular remodeling of the noncoding transcriptome contributes to circuit dysfunction in OUD.

The 7-nicotinic acetylcholine receptor (7nAChR) has driven extensive research over the past three decades for its pro-cognitive potential. It is the leading druggable target for the cognitive deficits associated with schizophrenia and has motivated major pharmaceutical and clinical efforts to ameliorate similar impairments in other neurological disorders, such as Alzheimers disease (AD). Yet, a systematic evaluation of the role played by 7nAChR in cognition, and its mechanistic underpinnings, is still lacking. Here we report that 7nAChRs on principal and inhibitory forebrain neurons are largely inconsequential to mouse behavior, including in domains that are most sensitive to schizophrenia-related cognitive impairments. By contrast, loss of 7nAChR from astrocytes produces profound behavioral alterations that are cognitive domain-specific, are time-of-day dependent, coincide with reduced levels of the N-methyl D-aspartate receptor (NMDAR) co-agonist D-serine, and are fully restored by D-serine supplementation. Further, an 7nAChR partial agonist previously evaluated in Phase III trials for cognitive enhancement in schizophrenia and AD fails to augment behavior in mice lacking astrocytic 7nAChRs. Together, these findings identify astrocytes and D-serine/NMDAR signaling as a central mechanism through which 7nAChR, a major drug target, promotes cognitive behavior.

Only a subset of heroin users develop addiction, characterized by binge-like heroin use and preference for heroin over other rewards, including social rewards. We recently established a rat model of these features. We trained rats to lever-press for social interaction and heroin (or saline, control) infusions and then tested heroin- and social-seeking and heroin-vs.-social choice. During 3-5 abstinence weeks, we used 2-deoxy-2-[{superscript 1}F]fluoro-D-glucose (FDG) PET imaging to assess regional brain metabolic activity at rest (homecage) and during heroin and social seeking. We assessed regional differences in FDG uptake using unbiased voxel-wise analysis and statistical parametric mapping, and correlated FDG uptake with principle-component-analysis-derived addiction severity score incorporating heroin intake, binge-like episodes, and heroin preference. Compared with saline-trained rats, heroin-trained rats showed overall higher FDG uptake across multiple brain regions at rest and during both reward-seeking tests. Comparison of heroin-vs.-social-seeking in heroin-trained rats showed higher uptake in claustrum/lateral striatum and auditory cortex during social seeking. Analysis of individual differences showed that addiction severity was primarily associated with metabolic alterations under resting conditions rather than during heroin- or social-seeking. At rest, higher addiction severity was associated with lower uptake in piriform cortex and higher uptake in ventral hippocampus, whereas during heroin-seeking, addiction severity was associated with lower uptake in post-subiculum and cerebellum. Addiction severity was not associated with differences in social seeking or FDG uptake during social seeking. These findings identify neurometabolic features of social and heroin seeking and heroin addiction vulnerability that can potentially serve as brain biomarkers and targets for neuromodulation. Significance StatementHeroin addiction develops in only a subset of users, yet the determinants of vulnerability versus resilience to addiction remain largely unknown. We combined a rat model capturing key features of heroin addiction, including binge-like heroin intake and preference for heroin over social interaction, with behavioral heroin- and social-seeking assays and longitudinal whole-brain metabolic imaging using FDG-PET. We identified distinct patterns of neurometabolic alterations associated with heroin self-administration and addiction severity at rest and in the context of heroin seeking. In contrast, heroin self-administration and addiction severity were not significantly associated with neurometabolic alterations during social seeking. These findings highlight brain-wide neurometabolic features of vulnerability to heroin addiction that can serve as brain biomarkers and targets for neuromodulation.

Psychedelics show therapeutic potential for treating psychiatric disorders. While studies have emphasized the roles of cortical pyramidal cells, GABAergic neurons also express serotonin receptors and are therefore likely targets of psychedelics. In this study, we determine the effect of psilocybin on the activity dynamics of major GABAergic cell types in the mouse medial frontal cortex. Psilocybin reduces the firing of somatostatin-expressing interneurons, but increases the activity of parvalbumin-expressing interneurons. This cell type-specific response is unlikely to involve vasoactive intestinal peptide-expressing interneurons. Instead, pharmacological blockade and conditional knockout experiments demonstrate that psilocybin acts on the 5-HT1A receptor at SST interneurons, which contributes to the drugs long-term behavioral effects. Collectively, the results reveal that the classic psychedelic psilocybin alters cortical inhibition in a cell type-specific manner.

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.

Metabotropic glutamate 2/3 receptors (mGluR2/3) have been implicated in depression, anxiety, learning, and memory. However, their causal role in reward-related behaviors remains unclear. Here, we examined the effects of intraperitoneal administration of LY341495, a selective mGluR2/3 antagonist, on reward-related behaviors in mice. In a head-fixed temporal conditioning task, mice received a 10% sucrose solution every 10 seconds. After training, mice exhibited anticipatory licking and pupil dilation aligned with expected reward delivery, indicating successful reward prediction. LY341495 dose-dependently reduced licking behavior without disrupting temporal prediction, as normalization analyses revealed reduced gain but preserved timing. LY341495 also induced overall pupil dilation and attenuated reward-proximity pupillary responses. To determine whether reduced licking reflected general motor impairment, we assessed spontaneous locomotion in a freely moving open-field task. LY341495 did not affect locomotor activity or excretion, suggesting intact general motor and autonomic function. To further evaluate orofacial motor function, we measured ultrasonic vocalizations (USVs) during a social interaction task. LY341495 did not significantly alter USVs, indicating preserved mouth-related motor function independent of licking. In contrast, LY341495 dose-dependently reduced food intake in a freely moving feeding task. Moreover, social preference testing revealed that LY341495 reduced social interaction, suggesting impaired processing of non-food rewards. Together, these findings demonstrate that mGluR2/3 signaling regulates reward-seeking behaviors independently of general locomotor or orofacial motor function. These results provide new insights into glutamatergic mechanisms underlying reward processing and may have clinical implications for obesity, eating disorders, and psychiatric conditions involving motivational dysfunction.

Adolescents experience extensive neurocognitive development, with cannabis use potentially impacting developmental trajectories. Here, we comprehensively assess the influence of adolescent cannabis use onset on neurocognitive trajectories and consider how recent delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) may influence neurocognition. We use the large, diverse longitudinal Adolescent Brain Cognitive Development (ABCD) Study dataset, combining self-reported substance use with objective toxicological tests (hair, urine, breath, oral fluid). Longitudinal mixed methods of the full cohort (n=11,036, ages 9-17; 47% Female/53% Male) investigate time-varying cannabis onset on neurocognitive performance. Primary model covariates include sociodemographics, family history of substance use disorder, prenatal substance exposure, early psychopathology, other substance use, and nesting for participant ID, study site, and family ID. Secondarily, in participants with repeat toxicological hair testing (n=645; 38% Female/62% Male) at ages 12-16, we consider the influence of THC v. CBD v. Controls. Primary models included false discovery rate corrections (FDR-p<.05) while secondary models were interpreted at p<.01. Cannabis group interacted with age to show altered neurocognitive trajectories across domains (immediate recall and delayed memory, processing speed, inhibitory control, visuospatial processing, language, and working memory; {beta}s=-0.11- - 0.52). Secondary models indicated hair-identified THC exposure*age predicted worse episodic memory than in Controls ({beta}=-0.60, p=.007), with no difference between CBD exposed and Controls. Data suggest those who use cannabis show likely pre-existing better cognitive performance during late childhood, with reduced improvement or flattened trajectories over time. These neurocognitive trajectories in youth (ages 9-17) who initiate cannabis use were demonstrated after accounting for within-person change and numerous known confounds and improving accuracy in identifying cannabis use through incorporating toxicological measures. Continued monitoring of this cohort will clarify cannabinoid-cognition relationships into young adulthood, including the impact of timing of cannabis use initiation.

Abstinence from repeated cocaine exposure is associated with reduced GABA release from striatal medium spiny neurons that express D2 dopamine receptors (D2-MSN) and project to the ventral pallidum (VP). As a consequence, VP principle neuronal activity is increased and drives cocaine seeking. Abstinence from cocaine is also associated with increased expression of enkephalin in D2-MSNs. This study tested the hypothesis that release of enkephalin from D2-MSNs during cocaine abstinence inhibits GABA release from these same neurons and thereby drives VP excitation. To test this hypothesis, we used mice with conditional knockout of Penk, which encodes enkephalin, in D2-MSNs (D2-PenkKO mice). Cocaine abstinence was associated with reduced GABA release from D2-MSNs to the VP in ex vivo striatal slices from control mice, but not from D2-PenkKO mice. Application of exogenous met-enkephalin inhibited GABA release in D2-PenkKO slices but not in cocaine-abstinent controls, because GABA release was already suppressed in control mice. Optogenetically-evoked GABA release from D2-MSNs inhibited VP excitability in saline-abstinent controls and D2-PenkKOs but not in cocaine-abstinent controls. Additionally, cocaine abstinence suppressed spontaneous firing in control VP neurons, potentially due to adaptive depolarization of their action potential threshold. Our data strongly implicate cocaine-induced autocrine release of enkephalin from D2-MSNs as a key mechanism for GABA plasticity that drives increased VP neuron excitability during cocaine abstinence. Significance StatementGABA release from striatal D2 receptor-expressing medium spiny neurons (d2-MSNs) to the ventral pallidum restrains reward seeking. Following abstinence from long-term cocaine intake, however, GABA release becomes suppressed by an opioidergic mechanism, a form of synaptic plasticity implicated in increased cocaine seeking. The identity and source of the opioid peptide mediating this inhibition have remained unclear. Here, we show that enkephalin produced by D2-MSNs acts in an autocrine manner to reduce GABA release from these neurons, thereby disinhibiting downstream ventral pallidum neurons. Our findings identify D2-MSNs as the source and enkephalin as the opioid responsible for this striatal circuit plasticity. More broadly, this suggests a synaptic mechanism by which synthetic opioids may potentiate cocaine seeking and promote opioid-cocaine polysubstance use.