International Journal of Neuropsychopharmacology

RationalePsychedelic compounds such as psilocybin have attracted growing interest for their potential therapeutic effects in psychiatric disorders, with improvements in cognitive flexibility proposed as a possible mechanism of action. However, the effects of psychedelics on cognitive flexibility remain poorly understood. ObjectiveThis study aimed to examine the acute and post-acute effects of psilocybin (0.1, 0.3, 1 mg/kg) and lysergic acid diethylamide (LSD, (0.02, 0.04, 0.08 mg/kg) on cognitive flexibility in male rats. MethodsThis was tested using two variants of the probabilistic reversal learning task (PRLT): a touchscreen-based operant task and a more ethological foraging-based task. ResultsIn the touchscreen PRLT, acute psilocybin disrupted task engagement, with animals completing fewer trials and showing increased trial initiation latency, although psilocybin also showed a trend toward faster initial rule acquisition. However, psilocybin did not significantly alter the number of rule changes achieved, a canonical measure of cognitive flexibility, or feedback sensitivity. LSD similarly produced limited acute effects, although the highest dose reduced lose-shift probability, suggesting decreased sensitivity to negative feedback under some conditions. Post-acute effects of psilocybin were minimal in both PRLT variants and, where LSD effects were observed these occurred across different doses and timepoints without a consistent pattern. ConclusionsOverall, these findings suggest that serotonergic psychedelics do not robustly enhance reversal learning in these paradigms and that apparent learning effects may reflect transient disruptions in task engagement rather than improvements in cognitive flexibility. These results also highlight potential limitations of these PRLT paradigms for detecting psychedelic-induced changes in cognitive flexibility in rodents.

Major depressive disorder (MDD) and post-traumatic stress disorder (PTSD) are prevalent, chronic, and disabling mental health conditions which are difficult to treat. Ketamine has demonstrated effect for improving depression and PTSD symptoms independently but reports often overlook focused comorbid improvement of these symptoms within individuals. To address this, we assessed blood-based biomarker and psychological changes following low-dose oral ketamine treatment for adults with MDD alone (n=14) and comorbid MDD+PTSD (n=21). Before treatment, the MDD clinical group presented with more severe depression, lower serotonin levels and higher kynurenine levels than the MDD+PTSD group. Post-treatment there were no detectable differences in the biological response between clinical groups, with combined analysis revealing common decreases in circulating brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF-A). Additionally, post-treatment, both clinical groups showed improvements in anxiety, stress, social functioning, suicidal ideation, and general well-being measures, as well as individual improvements in depression scores and PTSD symptoms in the MDD- and PTSD-containing groups, respectively. Collectively, this study presents additional evidence that low-dose oral ketamine treatment can be effective for MDD and MDD+PTSD, individually and comorbidly, and that both MDD and PTSD clinical groups responded in the same biological manner.

Post-traumatic stress disorder (PTSD) is a highly prevalent, debilitating psychiatric condition. Existing treatments are ineffective for many patients. 3,4- methylenedioxymethamphetamine (MDMA)-assisted psychotherapy has demonstrated substantial clinical efficacy but relies on prolonged, resource-intensive therapeutic protocols that limit scalability and accessibility. Here, we investigated whether combining MDMA with exposure-based intervention could enhance therapeutic efficiency in a preclinical model of PTSD-like behavior. Using a learned helplessness paradigm in mice, we identified trauma-susceptible individuals based on persistent escape failures following inescapable stress. Traumatised mice subsequently received brief treatment regimens consisting of MDMA or saline vehicle administered with or without exposure to the traumatic cue. Behavioral outcomes were tracked longitudinally using active avoidance performance as the primary endpoint, complemented by assays of anxiety- like, depressive-like, cognitive, and social behaviors. MDMA treatment markedly reduced trauma-associated behavioral deficits. MDMA combined with exposure produced rapid and sustained recovery compared to control conditions. Statistical analyses revealed significant treatment- and time-dependent effects on avoidance behavior, indicating accelerated resilience acquisition in MDMA-treated groups. Additional behavioral assays demonstrated dose-dependent effects of MDMA on anxiety- and depression-related measures. Together, these findings provide proof-of-principle that pharmacological modulation with MDMA can enhance exposure-driven behavioral recovery, supporting a strategy to integrate MDMA into more efficient and accessible PTSD treatment frameworks. This work establishes a preclinical foundation for clinical studies aimed at optimizing MDMA-assisted interventions to improve scalability and patient access.

Accelerated 5x5 repetitive Transcranial Magnetic Stimulation (rTMS; five stimulation sessions per day for five days) is an effective treatment for Major Depressive Disorder (MDD), and has efficacy comparable to conventional once-daily rTMS. Considering the heterogeneity of symptoms in patients with MDD, it is critical to determine how accelerated 5x5 and conventional rTMS affect depression symptom domains. We compared symptom change over time in patients treated with either accelerated 5x5 rTMS (25 total sessions, n = 40) or conventional once-daily rTMS administered over six weeks (30 total sessions, n = 135). Accelerated 5x5 patients received either prolonged intermittent theta burst stimulation (piTBS) or personalized "resonant frequency" (RF) stimulation. Mixed-effects linear models were built to compare the two protocols, with the primary outcome variables being the Inventory of Depression Symptomology Self-Report (IDS), the Ruminative Response Scale (RRS), and the Profile of Mood States - Brief (POMS), yielding measures of 14 unique depression symptom domains. Both protocols led to similar improvements in all 14 depression symptom domains (all interaction term p-values > .05). Subsequent exploratory analyses demonstrated that accelerated 5x5 and conventional rTMS may differ in the time courses of their effects on anxiety, rumination, mood, depression, and vigor (p-values < .05, uncorrected). These results suggested that accelerated 5x5 rTMS has a similar efficacy in alleviating 14 depression symptom domains compared to conventional once-daily rTMS, and that either protocol may be appropriate for MDD patients with a variety of symptom profiles.

Background: Management of markedly treatment-resistant depression is characterized by low initial benefit and poor durability. Treatments with sustained benefits are needed. This report summarizes clinical outcomes and durability of both the active treatment arm (Early-Active) and the initially sham treatment arm (Delayed-Active) over the second and third years of the multicenter, prospective, implanted vagus nerve stimulation (VNS) RECOVER trial. Methods: A total of 436 participants (N=221 Early-Active and N=215 Delayed-Active, 65.8% females) were studied. Within each group, analyses of change in benefit (depressive symptoms, clinical impression, quality of life [QoL], daily function, and a composite measure) occurred with assessments at 12, 18, 24, 30, and 36 months. Two within-group methods of benefit appraisal over time were conducted: 1) a comparison of the degree of benefit change, and 2) a comparison of proportions of participants achieving benefit categories. Additionally, the degree of durability of benefit was assessed, comparing 12-24 months, 24-36 months, and 12-36 months. Results: For the Early-Active group: The 12-24-month and 12-36-month periods, but not the 24-36-month period, demonstrated significant improvement in benefit categories for depressive symptoms and clinical impression measures. Similarly, statistically significant increases in the proportions of participants achieving benefit during Year 2 for depressive and clinical impression measures occurred. For the Delayed-Active group: The 12-24-month (first exposure of this group to active VNS) and 12-36-month periods, but not the 24-36-month period, demonstrated statistically significant improvements in benefit categories for depressive symptoms and clinical impression measures. Additionally, statistically significant increases in the proportions of participants achieving benefit during Year 2 for depressive symptoms, clinical impression, QoL, daily function, and the composite measure were observed. Averaged across the depressive symptom and clinical impression measures, the Early-Active group demonstrated continued progression to higher benefit categories during Years 2 and 3, whereas the Delayed-Active group was characterized by the emergence of new benefit during Year 2 followed by further progression to higher benefit categories during Year 3. Durability: Robust durability of response was observed for both groups across all time intervals, with a median of 71.1% and 69.0% maintaining or improving benefit from 12 to 36 months for Early-Active and Delayed-Active, respectively. Conclusions: In a highly chronic and markedly resistant depressed sample, active VNS produced benefits that often emerged gradually, sometimes beyond one year after initiation, continued to improve in degree of benefit over time, and were highly durable. The time-associated benefit patterns observed in the sham group (Delayed-Active) closely resembled those of the initially active group (Early-Active) but were delayed by approximately one year, consistent with the delay in therapy activation.

Tobacco use is the leading preventable cause of death worldwide. Anxiety increases the risk for smoking, and smoking in turn increases the risk for anxiety disorders. There is therefore a need to identify interventions that reduce anxiety, in general and in the context of smoking, without producing sedation. Kava (Piper methysticum), a natural product with a long history of indigenous use, has been shown to have anxiolytic and calming effects and reduce nicotine withdrawal. The current study examined whether kava without the hepatotoxic flavokavains A and B (AB-free) could reduce anxiety-like behavior in mice repeatedly treated with nicotine. Male and female C57BL/6NCrl mice received either a control diet or an AB-free kava-supplemented diet and underwent two blocks of nicotine treatments. Mice underwent a first block of five every-other-day injections of nicotine (0.5 mg/kg) or saline, with open field testing after each injection, followed one week later by a nicotine challenge. A second block of injections was given using the same injection schedule, followed by a second challenge one week later, and two weeks afterward mice received a final challenge in a novel open field. During the first treatment block, AB-free kava significantly increased center time overall, an effect most pronounced in saline-treated animals, and increased locomotor activity, while nicotine decreased both measures. During the second challenge, nicotine reduced center time but not locomotor activity, and AB-free kava increased center time in saline-treated animals only. During the final challenge, nicotine reduced both measures, whereas AB-free kava increased center time regardless of nicotine treatment, and kava-treated animals also showed a near-significant increase in center entries. These results suggest that AB-free kava reduces anxiety-like behavior without inducing sedation but does not prevent nicotine-induced suppression of exploratory behavior.

Background: Emotion dysregulation is a core feature of bipolar disorder (BD), yet its behavioral expression during depressive episodes, and potential differences between its types, BD-I and BD-II, remain unclear. This study used automated facial-expression analysis during naturalistic affective film viewing to examine subtype-specific and context-dependent emotional responding in bipolar depression. Methods: The sample included 135 participants: 69 healthy controls and 66 patients with BD (BD-I, 23; BD-II, 43). Participants viewed nine emotionally evocative film clips spanning negative, positive, neutral, and socially threatening contexts, while their facial expressions were continuously recorded and quantified using computer vision-based facial-expression analysis. Results: Patients with BD-I showed a distinct, context-dependent facial-expression profile, characterized by greater negative responses across multiple contexts than other groups. Specifically, they showed increased sadness during sad, reward, and amusing clips, and elevated anger during sad and neutral clips. In socially threatening contexts, BD-I participants showed a multivalent pattern of elevated anger, fear, and joy, suggesting poorly coordinated or context-incongruent affective expression. In contrast, BD-II participants did not differ significantly from healthy controls on any emotion, despite depressive symptom severity comparable to BD-I participants. Conclusions: These findings suggest that facial-expression patterns in bipolar depression differ across subtypes. BD-I may be characterized by heightened negative reactivity and altered context-appropriate modulation of emotional expression, whereas BD-II may not show comparable alterations in overt facial output. Automated facial-expression analysis during naturalistic stimulation may provide a useful behavioral marker for characterizing subtype-specific affective disturbance in bipolar depression and related psychopathology.

BackgroundPsilocybin, a classic psychedelic, produces acute alterations in brain function, and has shown sustained therapeutic effects in psychiatric disorders. However, most studies focus on acute brain imaging readouts (e.g., fMRI) and rarely assess longer-term molecular changes. MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression, are enriched in the brain, and can be released into blood, potentially indexing brain-relevant molecular processes. We hypothesised that a single psilocybin dose would show acute changes in miRNAs with predicted relevance to neuroplasticity related signalling and immune/inflammatory regulation in healthy adults. MethodsIn a randomised, double-blind, placebo-controlled study (N=62; 31 psilocybin, 31 placebo), volunteers received psilocybin (0.17 mg/kg) or placebo. Blood was collected at baseline, 360 minutes, and 7 days after dosing. Plasma miRNAs were quantified by small RNA sequencing. Elastic net regression was used for feature selection, followed by differential expression analysis and validation with linear mixed models. Pathway enrichment used Reactome and Gene Ontology. ResultsTwo circulating miRNAs (let-7g-5p and miR-150-5p) met criteria for differentially expressed at 360 minutes following psilocybin administration, with no significant differences detected at 7 days or in the placebo condition under the statistical thresholds used. Over representation analysis suggested enrichment of molecular processes involved in neuroplasticity (e.g., TrkA, MAPK), inflammation (e.g., IL-6, TGF-{beta}), and transcriptional regulation (e.g., RNA polymerase II, SMAD2/3/4). ConclusionsA single oral dose of psilocybin was associated with transient alterations in circulating miRNA expression, consistent with an acute shift in circulating gene-regulatory miRNA signals, without sustained miRNA changes at 7 days. These findings provide initial evidence that circulating miRNA changes after psilocybin may reflect acute molecular process responses and support further investigation of circulating miRNAs as potential biomarkers of psychedelic-induced molecular responses.

Treatment-resistant depression and anxiety remain major challenges in psychiatry, particularly in female patients, who are disproportionately affected yet remain underrepresented in preclinical ketamine research. The present study investigated short- and long-term anxiolytic effects of acute subanesthetic ketamine administration in female Wistar-Kyoto (WKY) rats, a validated genetic model of treatment-resistant affective dysfunction. Subjects received a single intraperitoneal injection of saline vehicle or racemic ketamine (5, 10, or 15 mg/kg), followed by acoustic startle response (ASR) testing 24 hours and 7 days later. Oxidative stress was assessed using 8-oxo-2'-deoxyguanosine (8-oxo-dG) immunofluorescence in the basolateral amygdala (BLA), prefrontal cortex (PFC), and hippocampus, alongside analysis of parvalbumin-positive (PV+) interneurons. Ketamine treatment produced dose- and time-dependent behavioral effects with 10 mg/kg eliciting the strongest delayed anxiolytic-like response at 7 days, while 15 mg/kg showed more immediate behavioral effects at 24 hours. While ketamine did not alter PV+ cell count, it significantly increased oxidative stress markers globally in the BLA and prelimbic region of the PFC and specifically in the PV+ interneurons in the BLA. The findings suggest that ketamine's therapeutic effects in female WKY rats may involve region-specific modulation of stress circuitry and oxidative signaling rather than gross interneuron loss. Overall, the study provides evidence for sex-dependent and temporally dynamic effects of ketamine in a translational model of treatment-resistant anxiety and depression.

Background: Major depressive disorder (MDD) is a severe mental illness associated with severe clinical consequences and substantial societal burden. It's characterized by immune-inflammatory dysregulation and immune sensitization. Objective: To determine whether in vitro ketamine attenuates phytohemagglutinin (PHA)/lipopolysaccharide (LPS)-induced immune sensitization in patients with MDD and healthy controls (HCs). Methods: Whole blood from 18 patients with MDD and 18 HCs was stimulated with PHA/LPS and exposed to ketamine (0.3 M, 0.6 M, and 6 M) for 72 hours. Cytokines, chemokines, growth factors, and composite immune profiles, including M1/M2 macrophages, T helper (Th)1/2/17, the immune-inflammatory response system (IRS), and compensatory immunoregulatory system (CIRS), were synthesized and determined. Results: Under PHA and LPS stimulation in vitro, the MDD group exhibited markedly elevated immune profiles, including M1, M2, Th1, Th2, Th17, IRS, CIRS, chemokines, and growth factors, consistent with immune sensitization. Significant group-by-treatment interactions were observed for Th1-Th2, M2, growth factors, IL-12(p70), M1, and chemokines. Ketamine produced minimal changes in HCs but broader suppression in MDD, particularly at the highest concentration, without normalizing the sensitized immune phenotype. Among the immune markers with no notable group-by-treatment interactions, ketamine exerted diagnosis-independent effects, decreasing MIP-1{beta}, IL-1&{beta}, Th1, TNF-{beta} IRS, IFN-{gamma}, and IL-2 compared to the control condition. Conclusions: Ketamine exhibited two distinct immunoregulatory patterns: selective, disease-dependent attenuation of sensitized immune pathways and broader, diagnosis-independent suppression of the stimulated immune response, predominantly at higher concentrations. However, these effects were insufficient to normalize the immune-sensitized phenotype of MDD.

Anhedonia and motivational impairment are central features of major depressive disorder, yet the neural processes linking reward information to sustained goal-directed behaviour remain insufficiently understood. Using functional magnetic resonance imaging, we examined representations of reward levels during sustained effort expenditure (a construct in the RDoc framework) as a distinct component of reward processing in depressive patients under escitalopram treatment. Twenty-eight unmedicated patients with a current depressive episode and forty-three healthy control participants underwent fMRI scanning at two time points three weeks apart; patients started escitalopram immediately after the first measurement. Across participants, sustained effort expenditure engaged midbrain reward circuitry (ventral tegmental area, VTA), even in the absence of immediate reinforcement. A targeted analysis also revealed changes in activity of the dorsal raphe nucleus (DRN) in patients. Increases in VTA activity were associated with improvements in clinician-rated depressive symptoms, whereas self-reported anhedonia remained unchanged. By isolating neural mechanisms supporting sustained goal-directed behaviour, the study identifies novel and clinically relevant imaging phenotypes of reward processing and a potential pathway of escitalopram treatment in depression.

Background: Serotonin has been implicated in cognitive flexibility and pathological perseverative thinking (PT), including rumination, worry, and obsessions. However, evidence remains fragmented across pharmacological manipulations, clinical populations, and outcome measures. This multilevel meta-analysis examined whether serotonergic interventions influence PT and cognitive flexibility. Methods: Preregistered and following PRISMA guidelines, we synthesized studies investigating three classes of serotonergic manipulations: acute tryptophan depletion (ATD), serotonin elevation via selective serotonin reuptake inhibitors (SSRIs), and classic serotonergic psychedelics. Three multilevel random-effects meta-analyses with cluster-robust variance estimation were conducted: (A) effects of ATD on cognitive flexibility (N = 266; 10 effect sizes), (B) effects of serotonin elevation on cognitive flexibility (N = 654; 15 effect sizes), and (C) effects of serotonin elevation on pathological perseverative thinking (N = 1,100; 20 effect sizes). Across analyses, the total sample comprised 2,030 participants and 45 effect sizes. Results: ATD did not significantly impair cognitive flexibility (g = 0.15, 95% CI [-0.07, 0.38], p = .23), and no moderation by task type, sex, or age was observed. Serotonin elevation similarly did not improve cognitive flexibility (g = -0.07, 95% CI [-0.36, 0.22], p = .63), with no significant performance differences emerging between SSRIs, classical psychedelics, or tryptophan enrichment. In contrast, serotonin elevation was associated with a significant medium-to-large reduction in perseverative thinking (g = -0.58, 95% CI [-0.76, -0.41], p < .001). Notably, while both pharmacological classes effectively reduced cognitive rigidity, SSRIs demonstrated a marginally smaller magnitude of symptom reduction compared to acute psilocybin interventions (p = .081). Furthermore, samples with a higher proportion of female participants showed larger reductions in perseverative thinking ({beta} = -1.86, p = .014), while worries exhibited marginally smaller reductions relative to obsessions ({beta} = 0.42, p = .055). Publication bias tests were non-significant across analyses. Conclusions: Serotonergic interventions robustly reduce perseverative thinking but do not consistently alter performance on laboratory measures of cognitive flexibility. These findings suggest that serotonin may influence cognitive-emotional rigidity and the subjective experience of repetitive thought more strongly than objective executive task performance. The dissociation between task-based and phenomenological outcomes aligns with contemporary models of serotonergic plasticity and highlights perseverative thinking as a potentially transdiagnostic therapeutic target of serotonergic interventions.

Background and PurposeSerotonergic psychedelics affect behavior and physiology, but the relationships among these effects remain poorly understood. In rodents, the head-twitch response is used as a measure of psychedelic-like activity, yet it does not capture changes in physiological state or the performance of learned behaviors. Here, we investigated the acute effects of the 5-HT2A receptor agonist TCB-2 across several behavioral and physiological measures and examined how these effects were modified by pretreatment with the 5-HT2A receptor antagonist volinanserin. Experimental ApproachMice were tested in head-fixed and freely moving conditions. During a learned auditory trace-conditioning task, we measured licking, pupil area, eye position, and blinking. We measured locomotor activity in an open field and quantified head-twitch responses using a DeepLabCut-based method. To examine the contribution of 5-HT2A receptors, mice were pretreated with the 5-HT2A receptor antagonist volinanserin. Key ResultsTCB-2 caused pupil constriction without detectable changes in eye position or blinking when administered alone. TCB-2 also reduced licking at the highest dose, but the cue-locked temporal pattern of licking remained evident. In freely moving mice, TCB-2 reduced locomotor activity and produced a dose-dependent increase in head-twitch responses. Volinanserin partially attenuated TCB-2-induced pupil constriction and reduced head-twitch responses under some conditions, but it did not consistently prevent the other effects of TCB-2. Conclusions and ImplicationsTCB-2 produced distinct effects across physiological and behavioral measures rather than a uniform disruption of behavioral function. Pronounced pupil constriction and head-twitch responses occurred without detectable changes in eye position or blinking, while the temporal organization of conditioned licking was retained despite a reduction in its magnitude. The incomplete and variable effects of volinanserin preclude definitive conclusions about the receptor mechanisms underlying each response. Combining automated head-twitch detection with physiological and task-related measurements provides a broader framework for comparing the pharmacological profiles of serotonergic compounds. What is already knownO_LIClassical psychedelics produce characteristic effects primarily through serotonin 5-HT2A receptor activation. C_LIO_LIHead-twitch responses capture only one dimension of psychedelic-like drug action. C_LI What this study addsO_LITCB-2 reduced locomotion and licking while preserving the cue-locked pattern of conditioned licking. C_LIO_LIPupil constriction occurred without detectable changes in eye position or blinking. C_LI Clinical significanceO_LIMultidimensional phenotyping can distinguish the physiological and behavioral profiles of serotonergic compounds. C_LIO_LIComplementary measures may improve preclinical evaluation of emerging serotonergic therapeutics. C_LI

Post-traumatic stress disorder (PTSD) is associated with high rates of comorbid personality disorders, which may contribute to PTSD severity. Among veterans with PTSD, obsessive compulsive personality disorder (OCPD) is common, with reported prevalence estimates ranging from 7-44%. Despite this, the relationship between OCPD traits and PTSD severity remains poorly understood. This retrospective, cross-sectional study examined associations between PTSD severity and OCPD traits in a naturalistic sample of 99 Veterans evaluated by a single clinician in a PTSD/Trauma Recovery Services clinic. PTSD symptoms were measured with the PTSD Checklist for DSM-V (PCL-5), and OCPD traits were measured with the Pathological Obsessive-Compulsive Personality Scale (POPS). Relationships between these two constructs were examined using Pearson correlations. Overall PTSD severity was significantly and positively correlated with total OCPD traits (r = 0.46, p < 0.001). Among OCPD domains, maladaptive perfectionism showed the strongest association with PTSD severity (r = 0.44, p <.001), followed by emotional overcontrol and reluctance to delegate (both r = .38, p < .01), rigidity (r = .35, p < .01), and difficulty with change (r = .28, p < .05). These findings suggest OCPD traits impact PTSD symptom burden in veterans, warranting further research and clinical attention.

Serotonin (5-HT) 2A receptors (5-HT2AR) modulate corticolimbic circuits regulating fear extinction. Although activation of these receptors has been shown to facilitate fear extinction, the behavioral consequences of 5-HT2AR antagonism during extinction is not well defined. Here, we examined the systemic effects of two 5-HT2A receptor antagonists, the mixed 5-HT2A/2C antagonist MDL 11,939 (Glemanserin) and the selective 5-HT2A antagonist MDL 100,907 (Volinanserin) on fear extinction in adult C57BL/6J mice. Prior to drug administration, mice assigned to future treatment groups acquired comparable conditioned freezing responses during delay fear conditioning. Twenty-four hours later, acute administration of MDL 11,939 (1.0 mg/kg) or MDL 100,907 (0.01 mg/kg) increased freezing to the first conditioned stimulus (CS) presentation on Extinction Day 1, indicating enhanced expression of conditioned fear. However, acquisition of fear extinction differed between the respective cohorts of mice treated with the two 5-HT2AR antagonists. Repeated administration of MDL 11,939 significantly impaired extinction, as evidenced by increased freezing across extinction trials and an increased number of trials required to reach extinction criterion. In contrast, MDL 100,907 has reported affinity for did not significantly alter extinction under either acute or repeated dosing conditions. Because MDL 11,939 has reported affinity for 5-HT2C receptors, we tested potential contributions of 5-HT2C receptor antagonism in a separate cohort of mice using two doses of the selective 5-HT2C antagonist, SB 242084. Neither dose affected conditioned fear expression, extinction learning, or trials required to reach extinction criterion. Together, these findings demonstrate ligand-specific and dose-dependent effects of 5-HT2AR antagonism on fear extinction and suggest that distinct intracellular receptor signaling pathways may differentially regulate extinction-related behavior.

Emotion regulation is critical for adaptive functioning and mental health. Functional neuroimaging studies have identified distributed frontal, parietal, and limbic networks involved in emotion regulation, particularly during cognitive reappraisal. However, the neurochemical mechanisms underlying individual differences in emotion regulation remain poorly understood. The endogenous opioid system is a promising candidate because -opioid receptor systems acts as a stress buffer and modulates emotional responses to both rewarding and aversive stimuli We used positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) to examine whether baseline -opioid receptor (MOR) availability is associated with haemodynamic responses during emotion regulation through reappraisal. Participants underwent [11C]carfentanil PET imaging to quantify MOR availability and subsequently completed an fMRI task involving passive viewing of emotional images and cognitive reappraisal of their emotions during image viewing As expected, fMRI revealed engagement of the dorsolateral prefrontal cortex and inferior parietal lobule during cognitive reappraisal. Baseline MOR availability predicted blood oxygenation level-dependent (BOLD) responses in frontal, temporal, and parietal regions: individuals with higher MOR availability showed a larger difference between regulation and viewing trials in the temporal pole, angular gyrus, anterior insula, thalamus, and inferior frontal gyrus. These associations were driven primarily by stronger responses during passive viewing, although some regions also showed evidence of reduced responses during active reappraisal. These findings suggest that higher endogenous opioid tone is associated with stronger recruitment of distributed frontal, temporal, and parietal networks during emotional stimulus processing as well as attenuation of activity in some of these regions during cognitive reappraisal. Thus, while higher MOR availability is associated with enhanced neural responsiveness to emotional stimuli, these responses can nevertheless be effectively modulated through deliberate emotion regulation.

Background: The nicotine analog 6-methyl nicotine (6-MN) has appeared in commercial e-cigarette liquids, and other products, spurring interest in determining the extent to which it conveys similar effects to those of nicotine. Objective: To determine if 6-MN acts like nicotine to decrease body temperature, decrease nociception, suppress wheel activity and reinforce operant behavior when delivered by vapor inhalation using an Electronic Nicotine Delivery System (ENDS; "e-cigarette") approach in a rat model. Methods: Male and female (N=8 per sex) young adult Sprague-Dawley rats were evaluated for rectal temperature and nociceptive responses (warm water tail-withdrawal) to the inhalation of vapor from (-)-6-MN or (-)-nicotine in concentrations ranging from 5-30 mg/mL in the propylene glycol vehicle. Rats were then assessed for the reinforcing effects of nicotine and 6-MN using a vapor self-administration procedure and the rate suppressing effects of nicotine and 6-MN on wheel activity following injection. Results: Inhalation of nicotine or 6-MN for 30 minutes decreased the rectal temperature and increased tail-withdrawal latency of female and male rats in a concentration-dependent manner. The magnitude of the effects of 6-MN and nicotine were similar at similar vapor concentrations. Operant responding for 6-MN vapor was increased by pre-treatment with the antagonist mecamylamine. 6-MN was more potent than nicotine at suppressing wheel activity after injection. Conclusions: 6-MN induces effects very similar to those of nicotine, at a similar potency when inhaled and at a slightly increased potency when injected.

Psychedelic drugs offer a potentially promising avenue for novel therapeutics for the treatment of psychiatric conditions, including for mood and anxiety disorders. Emerging clinical studies have prompted increased preclinical research into mechanisms of action. However, post-acute behavioral outcomes in rodents remain inconsistent and difficult to reproduce across laboratories. To address this, we collected a large dataset of behavioral responses to psilocybin in mice (N=693) and used data-driven analyses to identify biological and experimental factors that modulated behavioral readouts. We examined the effects of sex, age, strain, stress protocol, and 5-HT1B signaling on the response to a single high dose of psilocybin measured in acute (head twitch responding and locomotion) or post-acute (sucrose preference, elevated plus maze, novelty-suppressed feeding) behavioral outcomes. We found that psilocybin displays a robust acute behavioral response and a more variable post-acute behavioral profile with a most robust response in sucrose preference. Sex, stress model, and 5-HT1BR activation emerged as key modulators of post-acute antidepressant-like and anxiolytic effects. Random forest classification was narrowly able to predict drug treatment based on post-acute behavioral outcomes and biological and experimental factors. These findings suggest that the heterogeneity seen in the response to psilocybin in mice reflects meaningful biological and experimental variables. Accounting for these factors may enhance translational relevance by identifying the conditions under which therapeutic-like effects are most robust and can support more reproducible models for understanding the neural mechanisms underlying the persisting behavioral effects of psilocybin.

Emerging evidence suggests that adults with a history of early life adversity (ELA), while more susceptible to psychopathology, may also be particularly sensitive to the benefits of contemplative practices. In the present study, we examined whether ELA was associated with greater mental health benefits following a contemplative-based social resilience training program, administered as a university elective course across all ten campuses of the University of California (n = 321; median age = 21 years; 74% female). While significant improvements in mental health were observed for all participants, those with higher ELA exhibited greater reductions in mental distress (3.5-fold larger, p = .007) and greater increases in well-being (2.5-fold larger, p = .010) relative to those with lower ELA. Replication in future studies and further research on the mechanisms underlying this enhanced benefit may improve our understanding of how adults with a history of ELA recover and may ultimately thrive.

The medial Prefrontal Cortex (mPFC) participates in emotional regulation, decision-making and behavioural flexibility. Cannabinoid receptor 1 (CB1) is widely expressed in the mPFC, particularly in GABAergic neurons, where it modulates synaptic transmission, contributing to the mPFC excitation-inhibition balance. Alteration of GABAergic activity and CB1 levels is indeed part of the pathophysiology of many psychiatric disorders, including depression, anxiety, and schizophrenia. Interestingly, both CB1 and mood disorders display important sex differences. In this work, we study the role of CB1 receptors in prefrontal GABAergic interneurons in emotional and cognitive processes in a sex-dependent manner. To achieve this objective, we deleted CB1 from all mPFC neurons and the GABAergic population in adult CB1-flox male and female mice, and GABAergic neuronal activity was assessed via calcium imaging with fiber photometry. Global CB1 deletion in mPFC neurons, specifically in GABAergic cells, altered emotional but not cognitive processes, with opposite patterns. This impairment was sex- and task-dependent. While pan-neuronal CB1 deletion had an anxiolytic effect on females, GABAergic CB1 deletion had the same effect on male mice, linked to increased GABAergic neuronal activity. By contrast, fear conditioning was primarily affected in males with neuronal CB1 depletion and in females with receptor deletion in inhibitory neurons. GABAergic CB1 deletion potentiates females freezing response during acquisition and recall 24 hours later, and is associated with decreased inhibitory neuronal activity during the tone-shock association. In conclusion, mPFC GABAergic CB1 deletion is associated with an anxiolytic phenotype but also heightened responses to conditioned cues in a sex-dependent manner.