Psychopharmacology

Tobacco use disorder is a chronic condition characterized by compulsive nicotine use, withdrawal, and relapse following abstinence. Impulsivity contributes to persistent nicotine use and poor cessation outcomes. This study examined whether nicotinic acetylcholine receptor (nAChR) modulators alter impulsive action in a nicotine self-administration Go/No-Go task in male and female rats. Rats acquired intravenous nicotine self-administration and were then trained in a Go/No-Go procedure in which active lever presses were reinforced during Go periods but not during No-Go periods. We then assessed the effects of varenicline (0.1-3 mg/kg), nicotine (0.1-0.6 mg/kg), and the nAChR antagonist mecamylamine (0.5-2 mg/kg) in the Go/No-Go procedure. Varenicline and nicotine pretreatment reduced active responding during both Go and No-Go periods, whereas mecamylamine selectively reduced responding during No-Go periods. Mecamylamine decreased the percentage of active responses during No-Go trials, indicating reduced bias toward the nicotine-associated lever. In contrast, nicotine and varenicline did not alter response allocation, suggesting that their effects reflected nonspecific reductions in responding rather than changes in impulsive action. No sex differences were observed. Substituting saline for nicotine during self-administration did not alter active responding during Go periods, but rats in the saline group had fewer active responses during No-Go periods than rats in the nicotine group. These results show that chronic nicotine self-administration increases impulsive action and that nAChR antagonism, but not agonism or partial agonism, reduces nicotine-related impulsive action. This work supports the utility of the Go/No-Go self-administration task for investigating nAChR-dependent mechanisms underlying nicotine-induced impulsivity.

In rats, cue-induced opioid craving intensifies (incubates) during abstinence from opioid self-administration and then remains high for a prolonged period. The prolonged plateau models persistent vulnerability to cue-induced craving and relapse in humans recovering from opioid use disorder. However, a very significant contributor to relapse vulnerability in these individuals is the presence of negative affective states that can persist for months to years, far beyond physical dependence. The goal of this study was to determine if the incubation of craving model recapitulates this aspect of relapse vulnerability. We began by comparing rats trained to self-administer oxycodone using a regimen leading to persistent elevation of cue-induced craving (6 h/d x 10 d) and rats trained to self-administer saline. We assessed somatic withdrawal signs in early abstinence and conducted behavioral tests modeling negative affect (open field, social preference, sucrose preference, and elevated plus maze) in late abstinence. Some somatic withdrawal signs were greater in oxycodone rats on abstinence day (AD)1, but cumulative scores did not differ between groups on AD1-3. On AD41-46, no group differences were found in behavioral tests modeling negative affect. To compare early and late abstinenceperiods, a second cohort of rats self-administered saline and oxycodoneand then received two cue-induced seeking tests (AD1 and AD40; oxycodone rats exhibited incubation of craving) and two series of negative affect tests (AD2-7 and AD41-48). While some time-dependent changes in affect were observed within each group, they were suggestive of reduced anxiety-like behavior in oxycodone rats. Finally, because rats are single-housed during our incubation studies, we compared drug-naive rats after 8-9 weeks of single vs pair housing and found no difference in behavioral tests modeling negative affect. We conclude that the persistence of elevated cue-induced craving observed after a standard opioid incubation regimen is not accompanied by negative affective states, probably due to lower drug intake during the intravenous regimen compared to non-contingent escalating dose regimens typically used to study withdrawal signs. This does not negate the utility of the incubation model for studying cue-induced opioid craving and its neurobiological basis.

Cannabis contains many bioactive compounds, including {Delta}9-Tetrahydrocannabinol (THC) and cannabidiol (CBD), which influence behavior through complex pharmacological interactions with endogenous targets. This study examines whether CBD influences THC-induced changes in motor activity, hypothermia, and antinociception traits across different THC:CBD ratios, sexes, and genetic backgrounds. Traits were measured in C57BL/6J (B6) and DBA/2J (D2) mice of both sexes following baseline intraperitoneal (i.p.) injection of vehicle (VEH) and two consecutive daily doses of VEH or THC (10 mg/kg) alone or in combination with 0.56, 5, or 10 mg/kg CBD (THC:0.56CBD, THC:5CBD, or THC:10CBD, respectively). Motor activity and hypothermia were quantified daily from 0 to 120 min following injection and antinociception was measured daily at 60 min. We found that CBD alters THC-induced changes in motor activity and hypothermia as a function of day, dose, time, sex, and strain. In D2 females, CBD dose-dependently attenuated the hypolocomotor effects of THC immediately following acute injection and enhanced these effects later at 75 min. Following repeated exposure, CBD dose-dependently enhanced THC-induced hypolocomotion in B6 females at 75 min and in D2 males at 30 min while attenuating THC-induced hypolocomotion in D2 females immediately following injection. In D2 females, CBD dose-dependently attenuated THC-induced hypothermia at 15 min and enhanced hypothermia relative to THC at 30 min in D2 males following acute injection. After repeated exposure, CBD dose-dependently enhanced THC-induced hypothermia in B6 females at 15 min and in D2 males from 30 to 120 mins, while attenuating hypothermia in D2 females at 30 min. No significant effects of CBD on antinociception were observed. Our results indicate that CBD can modulate some THC-induced traits acutely and after repeated exposure. Regulation of THC-induced behavioral responses is dependent on CBD dose, genetic background, and sex. A candidate gene search using brain gene expression in recombinant inbred mice revealed greater genetic variation in ion channel genes relative to key metabolic genes, suggesting an underlying pharmacodynamic mechanism. Future research and validation of molecular mechanisms underlying these differences is expected to enhance our understanding of potential health risks and clinical relevance of cannabis and cannabinoid compounds containing THC and CBD.

Opioid addiction and misuse are a serious national crisis that affects public health, as well as social and economic welfare. Mortality due to opioid misuse is further exasperated by the combination of opioids with non-opioid respiratory depressants such as xylazine that are resistant to mu opioid receptor antagonists such as naloxone. This study tested the hypothesis that oxytocin can mitigate the severe opioid induced respiratory depression (OIRD) and mortality induced by high doses of fentanyl or the combination of fentanyl with xylazine. Our results show OXT can improve survival and respiratory function in both male and female rats with opioid induced respiratory depression caused by fentanyl, as well as a combination of fentanyl and xylazine. The improvement in respiratory function by OXT post fentanyl-xylazine was significantly greater than the recovery using only naloxone. Chemogenetic activation of OXT receptor positive neurons in the ventral respiratory group (VRG) provided similar benefits to that of OXT administration in reversing OIRD. These results indicate OXT is a promising therapeutic target for reversing OIRD and the respiratory depression that occurs with the combination of opioids and xylazine, a situation where naloxone is only partially effective. Additional translational benefits of OXT include it can be repurposed as it is already a FDA approved drug for other uses, has a high safety profile, and is unlikely to induce the withdrawal or reversal of analgesia that occurs with naloxone. Key PointsO_LIOxytocin (OXT) improves survival and respiratory function in both male and female rats with opioid induced respiratory depression (OIRD) caused by fentanyl C_LIO_LIOXT also reverses OIRD induced by the combination of fentanyl and xylazine C_LIO_LIThe improvement in respiratory function by OXT post fentanyl-xylazine was significantly greater than the recovery using only naloxone C_LIO_LIChemogenetic activation of OXT receptor positive neurons in the ventral respiratory group (VRG) provided similar benefits to that of OXT administration in reversing OIRD C_LIO_LIThese results indicate OXT is a promising therapeutic target for reversing OIRD and the respiratory depression that occurs with the combination of opioids and xylazine C_LI

Sex differences in responses to chronic stress are implicated in the higher prevalence of major depression and PTSD in females. Evidence of sex differences in endocannabinoid (eCB) physiology suggests that eCB signaling contributes to sexual disparities in fear conditioning and extinction. In adolescent male Sprague-Dawley rats, exposure to chronic-mild-unpredictable stress (CMS) resulted in enhanced trace-fear conditioning that was reversed by CB1 activation (Reich et al, 2013). In the present study, we assessed the effects of CMS and CB1 activation on hippocampal-dependent trace and contextual fear conditioning in adolescent female Sprague-Dawley rats. CMS exposure enhanced trace freezing behavior during memory recall compared to non-stress controls. This effect was not observed in contextually conditioned females. The CB1 receptor agonist, ACEA (0.1 mg/kg), administered prior to trace memory recall, but not prior to acquisition, significantly decreased freezing in both stress and non-stress females. ACEA significantly reduced baseline freezing behavior during trace memory recall in both stress and non-stress rats, however ACEA either 1) did not affect or 2) impaired short and long-term extinction in stress and non-stress females. In contextually conditioned females, ACEA decreased freezing during memory recall, although the effect was more robust in stress rats. ACEA impaired long-term contextual extinction in stress females while facilitating this in non-stress controls. However, ACEA had no effect or impaired short-term contextual extinction in both stress and non-stress groups. The results demonstrate that CMS enhances hippocampal-dependent episodic fear memories but has limited effects on contextual fear conditioning in female rats. These findings have implications in the use of medical cannabinoid treatment of disorders such as PTSD, as well as recreational cannabis use in adolescent/young adult females.

BackgroundLoss of control over drinking is a hallmark feature of alcohol use disorder (AUD) that is modeled preclinically through escalation of ethanol consumption and aversion-resistant drinking. Prior work with other reinforcers suggests that within-session unpredictable, intermittent access (uIntA) promotes loss of control over intake. However, the effect of uIntA on voluntary ethanol consumption is unknown. MethodsMale and female Long-Evans rats (n=9-10/group) underwent seven weeks of daily voluntary ethanol (20% v/v) drinking sessions under either a continuous access (ContA) or uIntA schedule. Following four weeks of baseline, rats were rendered dependent using a two-week chronic intermittent ethanol vapor exposure procedure. Daily testing was maintained through one week into withdrawal from vapor exposure. On the final day of testing, ethanol was adulterated with quinine (30 mg/L) to assess aversion-resistant drinking. ResultsRats drinking under ContA and uIntA exhibited similar levels of average daily ethanol consumption at baseline. However, uIntA elicited a more robust dependence-induced escalation of ethanol consumption compared to ContA, with uIntA sustaining escalation through early protracted withdrawal. Additionally, while rats with ContA to ethanol remained sensitive to quinine even after chronic ethanol vapor exposure, uIntA promoted aversion-resistant drinking in ethanol dependent rats. ConclusionsThese results demonstrate that, compared to ContA, uIntA maintains ethanol drinking and exacerbates AUD-related symptomatology while also providing researchers with the ability to capture additional measures of motivation and drinking patterns without increasing experimental burden. This work positions uIntA as a powerful tool to assess psychological and neurobiological factors underlying loss of control over drinking.

Background and aimsPerseverative behaviours are commonly assessed using operant paradigms in which rodents work for drugs or food under physiological deprivation, limiting translational relevance to some behavioural addictions. Here we validated an operant paradigm in which the acquired behaviour is driven neither by physiological needs nor hedonic responses. MethodsMice were trained to lever-press for green light. Exp.1 used a within-subjects design to examine lever discrimination and whether responding could be "satiated" by light preexposure. Exp.2 examined instrumental contingency using a between-subjects design, with light delivery equated between contingent and non-contingent groups. Exp.3 replaced green light with dim red light producing less retinal photoreceptor excitation but comparable heat to assess non-photic cues. Exp.4 examined whether green light could affect food seeking different motivational states. ResultsIn Exp.1, green light supported lever discrimination. Among high responders, the satiation effect was modest (<15% reduction) and did not deter lever pressing. In Exp.2, instrumental contingency promoted response acquisition whereas random light delivery did not. In Exp.3, dim red light failed to sustain behaviour, producing [~]50% response decrement. In Exp.4, light potentiated food seeking under ad libitum feeding. Discussion and conclusionsResponse-contingent light serves as a reward to establish operant responding, which cannot be explained by alerting effects or thermal cues. Our study bridges the gap between animal models and findings from humans that coloured light may exacerbate smartphone use and that light therapy may reshape reward circuits in individuals with Internet gaming disorder symptoms [Li et al. (2026) Advanced Science 13:e14044].

Dopamine (DA) has been implicated in exploration-exploitation behaviour, i.e., exploring novel, potentially better options vs. exploiting known, previously rewarding options. Impairments in this trade-off occur in psychiatric disorders involving DAergic dysfunction, including addiction and schizophrenia. Pharmacological studies revealed a contribution of DA to exploration, but inconsistent findings suggest that interindividual variability in baseline DA may modulate effects. To address this, we investigated the effects of the DA precursor L-DOPA on exploration-exploitation during reinforcement learning in a sample of N = 75 healthy participants (n = 32 women), following a randomised, double-blind, placebo-controlled, pre-registered design (https://osf.io/p2r7u). We assessed whether putative baseline DA markers, including spontaneous eye blink rate, working memory (WM) capacity, and impulsivity, modulated drug effects and probed visual fixation patterns and pupil dilation as markers of exploration. L-DOPA had no overall effect on computational model parameters of random exploration, directed exploration or choice perseveration. WM capacity moderated drug effects on random exploration, with stronger effects at higher WM capacity. Remaining DA proxies showed no credible effects. Pooling the data from male participants with that from an earlier male-only study (Chakroun et al., 2020; total N = 74), L-DOPA increased uncertainty-dependent value weighting and perseveration strength, while decreasing habit updating, indicating a stronger tendency to repeat previous choices and slower decay of their influence over time. No credible drug effects were observed in female participants. Pupil dilation was tonically increased under L-DOPA and scaled with exploration behaviour and prediction error, confirming that pupillometry can index exploration-exploitation dynamics. Visual exploration patterns reflected uncertainty-driven sampling, but were unaffected by L-DOPA. Taken together, results suggest that DAergic modulation of exploration and perseveration behaviour may be contingent on cognitive capacity and sex, rather than exerting uniform effects across individuals.

Early life adverse (ELA) experiences such as child maltreatment (MALT) are associated with physical and mental illness, including substance use disorders (SUDs), but underlying neurobiological mechanisms remain unclear. This study examined long-term effects of infant MALT on adult brain serotonin (5HT) and dopamine (DA) receptors in corticolimbic regions involved in reward and emotional control, using positron emission tomography (PET) imaging, a translational infant MALT macaque model of cocaine use disorder (CUD) risk and a COC self-administration (SA) paradigm. The study focused on regional serotonin 5HT1A, 5HT2A, and dopamine D2/D3 receptor availability (BP) differences between MALT and Control animals using PET, both at baseline (pre-COC SA) and following chronic COC SA (once they reached a total of 100 mg/kg intake). We also examined whether levels of these neurochemical receptors predicted COC SA measures, including reinforcing effects and potency using fixed-ratio (FR) peak response rates and progressive-ratio (PR) peak breakpoint. Our findings showed long-term effects of infant MALT on 5HT, but not DA, receptors in corticolimbic circuits. Specifically, MALT animals showed lower 5HT1A BP in the anterior cingulate cortex (ACC), medial prefrontal cortex (mPFC), and hippocampus compared to Controls. A MALT by Sex interaction effect was detected in 5HT2A BP in the OFC, with lower levels in MALT than Control males, but not in females. In addition, upregulation of 5HT1A and 5HT2A receptors was detected following chronic COC SA in most PFC subregions, hippocampus, and NAcc, particularly in the Control group. These findings suggest long-term effects of ELA on adult 5HT, but not DA, receptors in corticolimbic regions involved in emotional and reward processes. We also found associations between PET baseline (pre-COC SA) receptor BP data and COC SA measures. In particular, a positive correlation between 5HT1A receptor BP in caudate and peak FR Response Rates, whereas amygdala 5HT1A receptor levels were positively correlated with peak PR breakpoint and negatively correlated with peak FR Response Rates. Overall, these findings suggest an important role of 5HT1A and 5HT2A PFC receptors in early COC-related changes in reward circuitry and of amygdala 5HT receptors on cocaine-maintained behaviors. The dynamic change of these 5HT1A and 5HT2A receptors following chronic COC exposure was blunted in animals with ELA. It would be important to understand the biological consequences of these dynamic changes in 5HT receptors and whether they are associated with other stages of the addiction cycle, for example COC relapse, which could inform future pharmacological interventions that target 5HT receptors for treatment of CUD. Simple SummaryWe studied the long-term effects of early life adversity (ELA) on adult brain dopamine (DA) and serotonin (5HT) signaling in corticolimbic regions involved in emotional and reward regulation. We used specific PET radioligands that bind to the DA D2/D3, 5HT1A and 5HT2A receptors, finding lower levels of 5HT, but not DA, receptors binding potential (BP) in animals that experienced ELA. We also found associations between PET receptor BP measures and reinforcing effects of cocaine in i.v. self-administration paradigms using fixed- and progressive-ratio reinforcement schedules. In addition, a strong upregulation of 5HT, but not DA, receptors was identified following chronic cocaine exposure in prefrontal cortex (PFC). Our findings suggest long-term effects of ELA on adult PFC 5HT1A and 5HT2A receptors. The findings also suggest an important role of 5HT1A and 5HT2A, more so than D2/D3, receptors in early cocaine-related changes in reward circuitry. The early dynamic changes of these 5HT receptors could serve as biomarkers for cocaine use disorder (CUD) and inform future pharmacological interventions.

RationaleAttention-deficit/hyperactivity disorder (ADHD) is associated with executive dysfunction involving inattention and impulsivity, with evidence of disrupted functional expression of the dopamine and noradrenaline transporters. ObjectiveWe investigated the dose-dependent modulation of anti-ADHD drugs on selective and sustained visual attention in low-, mid-and high-attention phenotypes. Two mathematical approaches, signal detection theory and theory of visual attention were applied to further characterise the effects and mechanisms. MethodsRats were trained to detect and respond to the presence or absence of a visual target to obtain food reward on a signal detection task. After attentional performance stabilised, the indirect catecholamine agonist, d-amphetamine (0.1; 0.2; 0.4 mg/kg), the dopamine (DA) and noradrenaline (NA) reuptake inhibitor methylphenidate (0.3; 1; 3 mg/kg), and the NA reuptake inhibitor atomoxetine (0.1; 0.3; 1 mg/kg), were administered systemically. ResultsLow-dose d-amphetamine produced baseline-dependent effects on attention, improving target discrimination only in rats with lower attentive performance, whereas methylphenidate did not significantly improve attention but increased guessing. In contrast, low-dose atomoxetine selectively impaired attention in low-attentive subjects, whereas high-dose atomoxetine generally impaired discrimination performance. All three drugs had expected effects on motor response output. ConclusionsAs well as demonstrating baseline-dependent effects of amphetamine on visual attention, the findings for methylphenidate and atomoxetine suggest important, apparently opposing effects on visual signal detection performance produced via blockade of the DA and NA transporters. The deleterious effects of atomoxetine on performance were especially noteworthy in view of its use as a treatment in ADHD.

The Reln gene encodes the extracellular glycoprotein Reelin that regulates synaptic plasticity and activity-dependent gene expression with implications in several neuropsychiatric disorders, including substance use disorder. While reduced Reln expression alters responses to psychostimulants and cannabinoid, its role in opioid-related behaviors remains unknown. Here, we examined whether Reln haploinsufficiency modifies behavioral and molecular responses to the synthetic opioid fentanyl. Heterozygous Reeler (Reln+/-) mice and wild-type littermates were assessed using using complementary contingent and non-contingent models of fentanyl exposure, including multi-phase fentanyl intravenous self-administration paradigm, conditioned place preference paradigm, locomotor assay, and dorsal striatal immediate early gene expression. Reln haploinsufficiency did not alter acquisition, extinction, or cue-induced reinstatement during self-administration, indicating stable opioid reinforcement and relapse-like behavior. Progressive ratio testing revealed a sex-dependent effect in which male Reln+/- mice showed reduced motivation for fentanyl compared to male wild-type mice. In contrast, following passive fentanyl exposure, Reln+/- mice exhibited enhanced fentanyl-induced locomotion and increased Fos immunoreactivity in the dorsal striatum, while CPP remained unchanged. Together, these findings demonstrate that Reln haploinsufficiency does not substantially modify opioid reinforcement or cue-driven drug seeking but enhances acute pharmacological sensitivity to fentanyl. These results identify Reln as a modulatory factor in opioid-responsive neural circuits that preferentially influences acute drug-evoked neuronal activation rather than the associative learning processes underlying opioid reinforcement.

The misuse of opioid medications is a significant health issue in the United States. Very few studies have investigated the effect of opioids on perineuronal nets (PNNs), scaffold-like structures that surround neurons and are involved in the regulation of plasticity-dependent mechanisms such as development, learning and memory, and acquisition of addiction-like phenotypes. Regulation of PNNs in the orbitofrontal cortex (OFC) during periods of drug intoxication or withdrawal is widely unknown. In this study, male Wistar rats were injected with fentanyl (0.125 mg/kg, s.c.) or 0.9% saline twice daily for 7 days and once on day 8 (7continuous days following by 3 days of abstinence) or twice daily for 15 days (5 continuous days followed by 2 days of abstinence for more than 3 weeks) and twice on day 16. Antinociception was evaluated using the tail immersion test immediately before and 30 minutes after injections. Whole-brain coronal slices were collected, and immunohistochemistry was used to identify Wisteria Floribunda Agglutinin (WFA)-positive PNNs and parvalbumin (PV)-expressing cells. Results confirmed that repeated fentanyl injections induced tolerance to the antinociceptive effects, which normalized following acute abstinence periods. WFA intensity decreased following 8 days of injections. Analyses confirmed significant correlations between PV+ density and tail withdrawal latency following 8 days of fentanyl injections. These data confirm that repeated fentanyl injections modulate both WFA+ and PV+ expression in the rodent brain and antinociceptive tolerance in a duration-dependent manner. Overall, these data suggest that perineuronal nets may mediate opioid-induced behavioral effects, such as antinociceptive tolerance, following repeated administration and abstinence in rats.

BackgroundContemporary research indicates that psychedelics induce notable neurophysiological changes, some lasting weeks to months after a single dose. However, most evidence derives from acute administration studies and limited post-acute follow-ups. Long-term naturalistic psychedelic users remain critically underexamined, yet may exhibit distinct neurobiological profiles informing our understanding of persistent alterations following repeated exposure. MethodsWe recorded resting-state EEG in 57 long-term psychedelic users (abstinent [&ge;]30 days) and 49 matched non-users across two independent sites under eyes-open and eyes-closed conditions. We analyzed oscillatory power, signal complexity, and source-localized effective connectivity, focusing on five canonical frequency bands and regions of the Default Mode, Salience, and Central Executive Networks. Analyses included linear mixed-effects modeling for power spectra and complexity results and a rank-based approach combining ordinary least squares regression with randomization inference for effective connectivity. ResultsWe observed predominantly null findings. No significant between-group differences emerged for oscillatory power. Complexity comparison yielded results contrary to our hypothesis: psychedelic users exhibited lower complexity values in the eyes-open condition. Effective connectivity revealed no within- or between-network differences that would survive statistical corrections. Additionally, we report a few small-magnitude effects uncovered by exploratory analyses. Conclusions Long-term naturalistic psychedelic users showed largely non-significant differences in oscillatory power, complexity, and network connectivity compared to non-users -- across several measures commonly reported as altered in acute administration studies. These findings raise the question of whether psychedelics neurophysiological signatures persist during abstinence despite repeated prior use, or whether they reflect homeostatic receptor adaptation, individual variability, or contextual factors. Null, incongruous, or subtle effects contribute to the existing evidence base, yet underscore the need for replication in larger, more ecologically valid populations to advance the emerging field of psychedelic neuroscience.

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.

Endocannabinoid (eCB) signaling is a key regulator of reward-related dopaminergic signaling, particularly in response to drugs of abuse, such as cocaine. To date, our understanding of this mechanism has primarily been limited to male subjects. Prior work establishes that female cocaine users have more adverse outcomes, and female rats show greater sensitivity to cannabinoid type 1 receptor (CB1R) regulation of cocaine self-administration. Therefore, we hypothesize that female rats exhibit enhanced eCB regulation of cocaine-evoked dopamine (DA). We used in vivo fiber photometry recording of the dopamine biosensor, dLight 1.3b, in the nucleus accumbens medial shell (NAcms) in response to cocaine in male and female rats. Rats were pretreated with cannabinoid-targeting drugs to investigate the effects of CB1R inactivation or augmentation of the eCB 2-AG on cocaine-evoked DA. Our results revealed that CB1R inactivation attenuates cocaine-evoked DA in male and female rats, but females showed enhanced sensitivity for CB1R regulation of cocaine-evoked DA. Cocaine-evoked DA was enhanced by augmenting 2-AG levels, and females again showed increased sensitivity to this manipulation. Finally, females show greater cocaine-evoked DA when in a non-estrous cycle compared to estrous, reinforcing that estrous cycle is a determinant of cocaine-evoked DA. These data indicate that females show enhanced eCB regulation of cocaine-evoked DA signaling, underscoring the importance of sex as a biological variable in our understanding of endocannabinoid regulation of drug reward. HighlightsO_LICB1R inactivation attenuates cocaine-evoked DA in NAcms, preferentially in females C_LIO_LI2-AG augmentation via MAGL inhibition enhances cocaine-evoked DA, with female bias C_LIO_LIEstrous phase modulates the dopamine response to a high dose of cocaine in females C_LIO_LIMale and female rats show similar baseline DA and locomotor responses to cocaine C_LI

Xylazine is a 2-adrenergic agonist typically used in as a sedative and analgesic in veterinary medicine. For some years, xylazine has been reported as an additive to fentanyl on the illicit drug market and has been associated with severe side-effects including severe ulcerations and potential amputations at the sites of injection along with an increased risk of respiratory depression and death. We recently reported that xylazine has modest {kappa} opioid agonist activity in vitro and in vivo and asked if other 2-adrenergic agonists had similar off-target activities. To test this hypothesis, we profiled US FDA-approved 2-adrenergic agonists at 320 G protein coupled receptors (GPCRs) to identify potentially deleterious and/or beneficial off-targets. Although all other tested 2-adrenergic agonists were devoid of {kappa} opioid agonist activity, each had a distinct pattern of activity at various GPCRs and differential patterns of signaling bias at 2-receptor subtypes. These findings suggest potential molecular targets for both side-effects and therapeutic activities among known 2-adrenergic agonists.

Opioid use disorder (OUD) is a chronic, relapsing disease driven by the reinforcing properties of opioids and perpetuated by avoidance of the negative affective states associated with the absence of the drug. Most available OUD treatments directly engage the {micro}-opioid receptor and may induce side effects that can compromise their therapeutic efficacy, thus underscoring the need for novel therapeutic alternatives. Calcitonin gene-related peptide (CGRP) is produced by a small population of neurons in the parabrachial nucleus (PBN) that has been shown to modulate itch, pain, as well as appetitive behaviors. Using a cell-specific nuclear labeling approach coupled with RNA-sequencing, we generated a baseline transcriptome of CGRPPBN neurons and confirmed expression of multiple genes associated with behavioral responses to appetitive stimuli, as well as enrichment of the {micro}-opioid receptor, suggesting that CGRPPBN neuron function may be sensitive to the presence of opioids. Indeed, cFos immunostaining showed that CGRPPBN neuron activity increases during early morphine abstinence and reduces gradually over 48 hours. Given the inhibitory effects of opioids on CGRPPBN neuron activity, we next tested whether these neurons could regulate opioid reinforcement. Using a mouse model of morphine intravenous self-administration, we found that chemogenetic inhibition of CGRPPBN neurons significantly reduced the number of morphine rewards earned in both single-dose and dose-response tests but did not affect context-induced morphine seeking after 21 days of abstinence. These results suggest that CGRPPBN neurons are sensitive to opioid administration and can regulate appetitive behaviors such as morphine-taking. Considering that CGRP signaling is regulated by opioid administration, molecular targets that regulate CGRP neurotransmission without direct -opioid receptor engagement may therefore serve as novel therapeutic avenues for the treatment of OUD. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=195 SRC="FIGDIR/small/712659v1_ufig1.gif" ALT="Figure 1"> View larger version (56K): org.highwire.dtl.DTLVardef@1fb9c9borg.highwire.dtl.DTLVardef@1e6ba79org.highwire.dtl.DTLVardef@dc60f5org.highwire.dtl.DTLVardef@61adaf_HPS_FORMAT_FIGEXP M_FIG C_FIG

BackgroundPavlovian responding is a core component of behavior and can be measured via Pavlovian-instrumental transfer (PIT), where Pavlovian responses bias instrumental actions. Standard single-lever PIT paradigms, which assess responses using a single-choice option, cannot dissociate the contribution of model-free versus model-based reinforcement learning. While indirect evidence suggests a role for model-free responding in single-lever PIT, the contribution of model-based strategies is unclear. It also remains unknown whether internal cognitive states, such as mind wandering, impair specifically model-based but not model-free PIT, as is theoretically expected. MethodsWe developed a novel, trial-by-trial two-stage PIT paradigm designed to computationally dissociate model-free and model-based Pavlovian responding by leveraging probabilistic state transitions and trial-wise outcome predictions. After each two-stage Pavlovian learning trial, participants performed a single-lever PIT trial as well as a query trial of explicit value judgment. Detailed task instructions were provided to support potential model-based strategies. Computational modeling was used to quantify individual learning strategies. We assessed mind-wandering questionnaires and thought probes. ResultsAnalysis of query and PIT trials revealed trial-by-trial updating of outcome expectations based on probabilistic task structure, consistent with model-based Pavlovian responding. Behavioral responses during PIT were best explained by a computational model-based reinforcement learning model. In contrast, we found little evidence for model-free Pavlovian responding. Higher levels of mind wandering were associated with reduced model-based control but did not impact model-free indices. ConclusionWe introduce a novel single-lever PIT paradigm that enables fine-grained dissociation of model-free versus model-based Pavlovian response systems. Our findings provide evidence that single-lever PIT can operate through model-based mechanisms, challenging the assumption that single-lever PIT is predominantly model-free. Our findings also indicate that internal attentional states selectively modulate model-based PIT. Given the involvement of Pavlovian responding in numerous psychiatric conditions, our paradigm offers new avenues for understanding maladaptive behavior. Author SummaryOur daily actions are often influenced by cues like the smell of food or the sound of phone notifications that signal potential rewards or losses. These Pavlovian cues can shape our instrumental behavior even though their outcomes do not depend on what we do - a process known as Pavlovian-instrumental transfer (PIT). Here we study the computational learning mechanisms that underlie such PIT effects. While it is often assumed that Pavlovian responding follows simple, automatic rules without a cognitive model of cue consequences (i.e., model-free), evidence also shows a role for cognitive anticipations in Pavlovian responding (i.e., model-based). In this study, we extend this evidence by showing that PIT responding can be driven by flexible model-based learning. We designed a task to test whether participants use model-free versus model-based strategies to guide PIT, providing detailed task instructions. Using reinforcement learning models, we found that most participants used model-based learning when forming cue-outcome associations. Importantly, peoples attention mattered: when they were more distracted and doing mind wandering, they relied less on model-based strategies. Our findings suggest that Pavlovian learning is complex, flexible, and influenced by internal mental states, opening new windows to understand decision-making problems in mental health conditions like addiction.

Esketamine is a fast-acting antidepressant drug which induces acute psychoactive effects. The most frequent is a dissociative state which seems unrelated to therapeutic efficacy. Other esketamine-induced effects, including psychedelic-like mystical experiences, have been poorly studied in terms of phenomenology and frequency, and may carry specific therapeutic relevance. In this study, we characterised esketamine-induced mystical experiences in relation with clinical outcomes. We conducted a longitudinal observational study and systematically measured acute subjective effects in patients receiving esketamine for treatment-resistant depression after each administration across the induction phase. A total of 45 patients were included, from two independent centres, totalling 352 esketamine administrations. Principal Component Analysis (PCA) supported the validity of the Mystical Experience Questionnaire (MEQ-30) for assessing esketamine-induced subjective effects, with components recovering dimensions previously validated with classic psychedelics. Mystical experiences (MEQ-30 score above 60) occurred in 58% of patients, with high inter- and intra-individual variability in frequency, intensity, and phenomenology across sessions. Higher mean and peak MEQ scores were associated with greater improvement in Montgomery-Asberg Depression Rating Scale scores from pre- to post-treatment, whereas the intensity of dissociative or other non-mystical effects was not. Positive mood and mystical MEQ dimensions in particular predicted therapeutic outcomes. Baseline spirituality also significantly predicted treatment outcomes and peak MEQ scores in the first week of treatment. These findings add to the growing body of evidence suggesting that psychedelic-like mystical experiences may be associated to therapeutic efficacy, not only in classic psychedelic-assisted therapy, but also in esketamine treatment.

Nicotine use disorder shows heterogeneity in treatment response, potentially reflecting differences in underlying neural circuitry, particularly in the presence of depression. We examined real-time neural dynamics during nicotine inhalation in two chronic users - one with depression and one without - using simultaneous hippocampal recordings from responsive neurostimulation (RNS) electrodes and scalp EEG. Oscillatory activity and hippocampal-cortical connectivity were analyzed in relation to mood and craving. Oscillatory activity tracked mood in the non-depressed individual but was attenuated or reversed in the depressed individual, suggesting reduced reward-related neural responsiveness. In contrast, both participants showed reduced alpha hippocampal-cortical connectivity following nicotine use, suggesting a shift from reward-seeking to reward and relief processing. These findings support a network-based framework of nicotine-driven neural dynamics and provide preliminary evidence that depressive status may modulate these processes. Although limited to two cases, this work highlights the potential for identifying neurophysiological subtypes of nicotine users and informs future efforts toward personalized treatment approaches.