Psilocybin restrains activity-based anorexia in female rats by enhancing cognitive flexibility: contributions from 5-HT1A and 5-HT2A receptor mechanisms

Psilocybin-enhanced fear extinction linked to bidirectional modulation of cortical ensembles

The psychedelic drug psilocybin demonstrates rapid and long-lasting efficacy across neuropsychiatric disorders that are characterized by behavioral inflexibility. However, its impact on the neural activity underlying sustained changes in behavioral flexibility has not been characterized. To test whether psilocybin enhances behavioral flexibility by altering activity in cortical neural ensembles, we performed longitudinal single-cell calcium imaging in the mouse retrosplenial cortex across a 5-day trace fear learning and extinction assay. We found that a single dose of psilocybin altered cortical ensemble turnover and oppositely modulated fear- and extinction-active neurons. Suppression of fear-active neurons and recruitment of extinction-active neurons predicted psilocybin-enhanced fear extinction. In a computational model of this microcircuit, inhibition of simulated fear-active units modulated recruitment of extinction-active units and behavioral variability in freezing, aligning with experimental results. These results suggest that psilocybin enhances behavioral flexibility by recruiting new neuronal populations and suppressing fear-active populations in the retrosplenial cortex.

Separate or inseparable? Serotonin and dopamine system interactions may underlie the therapeutic potential of psilocybin for anorexia nervosa

Psilocybin, a serotonergic psychedelic, has emerged as a promising treatment for a range of mental health conditions, including anorexia nervosa. Recent insights from animal models and human imaging studies suggest psilocybin enhances cognitive flexibility and modifies reward processing - two core processes disrupted in anorexia nervosa. Both cognitive flexibility and reward processing are highly dependent on interactions between serotonin (5-HT) and dopamine (DA) systems in key brain regions such as the prefrontal cortex and nucleus accumbens. Psilocybin's influence on neuroplasticity, particularly in promoting structural and functional changes in neural circuits, underpins its therapeutic potential. While its effects are predominantly attributed to activity of the 5-HT2A receptor subtype, recent evidence suggests a broader network of brain receptor interactions, particularly those with dopaminergic pathways, plays a crucial role. Investigations using rodent models reveal that psilocybin induces both rapid and enduring neuroplastic changes, improving cognitive flexibility through these complex neurochemical mechanisms. Advances in real-time in vivo neurochemical recording now allow simultaneous monitoring of 5-HT and DA signalling, which will provide essential insights into their distinct and coordinated actions during cognitive performance. This integrative framework highlights the need for further research into psilocybin's dual modulation of 5-HT and DA systems to optimize its therapeutic applications for anorexia nervosa, a life-threatening condition that is characterized by impairments in cognitive flexibility and reward processing.

The Emergence of Psilocybin in Psychiatry and Neuroscience

Psilocybin, a naturally occurring psychedelic compound, has garnered renewed scientific interest for its potential in treating psychiatric and neurological disorders. This review systematically examines the latest research on psilocybin's pharmacokinetics, pharmacodynamics, clinical efficacy, and safety profile. Emerging evidence supports its efficacy in conditions such as major depressive disorder (MDD), treatment-resistant depression (TRD), anxiety, alcohol use disorders (AUD), and cancer-related distress. Despite promising outcomes, significant barriers remain, including methodological constraints, regulatory hurdles, and limited population diversity in clinical trials. Advances in biosynthetic production and optimized psychotherapeutic integration are necessary to ensure scalability and accessibility. Future research should focus on long-term safety, dosing precision, and neurobiological mechanisms to refine its therapeutic applications. This review provides a critical foundation for advancing evidence-based clinical integration of psilocybin.

Endogenous opioid receptors and the feast or famine of maladaptive feeding

Maladaptive feeding comprises unhealthy eating patterns that jeopardize survival, including over- and underconsumption. These behaviors are often coordinated by endogenous opioid receptors (EORs). Here, we explore the involvement of EORs in obesity and anorexia nervosa (AN), two disorders associated with dysregulated feeding behavior and relevant animal models. While seemingly opposing metabo-psychiatric states, our goal is to highlight common circuit and synaptic mechanisms underlying obesity and AN with a focus on EOR functionality. We examine the neural substrates underlying maladaptive feeding and comorbid conditions including pain, suggesting a role for EOR-driven plasticity in the pathogenesis of both obesity and AN.

Exploring Psilocybe cubensis Strains: Cultivation Techniques, Psychoactive Compounds, Genetics and Research Gaps

Psilocybe cubensis, a widely recognized psychoactive mushroom species, has played a significant role in both historical and modern therapeutic practices. This review explores the complex interplay between genetic diversity, strain variability and environmental factors that shape the biosynthesis of key psychoactive compounds, including psilocybin and psilocin. With many strains exhibiting substantial variability in their phenotypic characteristics and biochemical content, understanding and documenting this diversity is crucial for optimizing therapeutic applications. The review also highlights advances in cultivation techniques, such as submerged fermentation of the mycelium, and innovative analytical methodologies that have improved the precision of compound quantification and extraction. Although there is limited scientific information on P. cubensis due to nearly four decades of regulatory restrictions on psychedelic research, recent developments in genetic and biochemical studies are beginning to provide valuable insights into its therapeutic potential. Furthermore, this review emphasizes key knowledge gaps and offers insights into future research directions to advance the cultivation, scientific documentation of strain diversity, regulatory considerations and therapeutic use of P. cubensis.

Psychedelic enhancement of flexible learning weeks after a single dose

Psychedelic drugs have shown therapeutic potential for the treatment of multiple neuropsychiatric disorders chiefly by promoting long-lasting plasticity in the prefrontal cortex (PFC). A critical function of the PFC is the ability to apply previously learned rules to novel scenarios, a skill known as cognitive flexibility. Here, we show that a single dose of 25CN-NBOH - a serotonin 2A receptor-preferring psychedelic - improves performance on a relatively complex flexible reversal learning task in mice, measured 2-3 weeks after the dose. This effect was seen in both male and female mice. This behavioral finding complements previous cellular results showing that a single psychedelic dose induces long-term structural changes in the PFC and uniquely demonstrates sustained improvements in cognitive flexibility in a novel behavioral paradigm weeks after the initial psychedelic dose in mice. This high throughput task also provides a rapid, automated way to assess other candidate psychedelics for their impact on cognitive flexibility in mice.

Pharmacotherapeutic strategies for the treatment of anorexia nervosa - novel targets to break a vicious cycle

INTRODUCTION

Anorexia nervosa (AN) has one of the highest mortality rates of all mental illnesses. No approved pharmacological treatments exist for AN, but novel neurobiological targets show promise.

AREAS COVERED

Studies show that in individuals with AN, there are alterations in brain neurotransmitter signaling, alongside associated mental rigidity and comorbid anxiety and depression. Available and new therapies could be used to improve alterations in neurobiology and behavior. This narrative review serves as a review of previously published literature assessing the efficacy of traditional pharmacotherapy in treating AN while also exploring novel treatments, including dissociative anesthetics, psychedelics, cannabinoids, hormones, neurosteroids, and ketogenic nutrition.

EXPERT OPINION

If best practice psychotherapeutic interventions have failed, we recommend a neuroscience and brain research-based medication approach that targets dopamine neurotransmitter receptors to enhance cognitive flexibility and illness insight while reducing dread and avoidance toward food. It is furthermore essential to recognize and treat comorbid conditions such as anxiety, depression, or obsessive-compulsive disorder as they interfere with recovery, and typically do not resolve even with successful AN treatment. Novel strategies have the promise to show efficacy in improving mood and reducing specific AN psychopathology with hopes to be used in clinical practice soon.

Psilocybin increases optimistic engagement over time: computational modelling of behaviour in rats

Psilocybin has shown promise as a novel pharmacological intervention for treatment of depression, where post-acute effects of psilocybin treatment have been associated with increased positive mood and decreased pessimism. Although psilocybin is proving to be effective in clinical trials for treatment of psychiatric disorders, the information processing mechanisms affected by psilocybin are not well understood. Here, we fit active inference and reinforcement learning computational models to a novel two-armed bandit reversal learning task capable of capturing engagement behaviour in rats. The model revealed that after receiving psilocybin, rats achieve more rewards through increased task engagement, mediated by modification of forgetting rates and reduced loss aversion. These findings suggest that psilocybin may afford an optimism bias that arises through altered belief updating, with translational potential for clinical populations characterised by lack of optimism.

Unraveling psilocybin's therapeutic potential: behavioral and neuroplasticity insights in Wistar-Kyoto and Wistar male rat models of treatment-resistant depression

RATIONALE

Our study aimed to unravel the unknown mechanisms behind the exceptional efficacy of Psilocybin (PSI) in treating treatment-resistant depression (TRD). Focusing on Wistar-Kyoto (WKY) rats with a TRD phenotype and Wistar (WIS) rats as a normative comparison, we investigated behavioral and neuroplasticity-related responses to PSI, striving to shed light on the distinctive features of its antidepressant effects.

OBJECTIVES

We set out to assess the behavioral impact of acute and prolonged PSI administration on WKY and WIS rats, employing Novel Object Recognition (NORT), Social Interaction (SI), and Forced Swimming Test (FST). Our secondary objectives involved exploring strain-specific alterations in neuroplasticity-related parameters, including brain-derived neurotrophic factor (BDNF) and activity-regulated cytoskeleton-associated protein (Arc).

METHODS

Conducting post-acute and extended assessments after a single PSI administration, we applied behavioral tests and biochemical analyses to measure serum BDNF levels and neuroplasticity-related parameters in the prefrontal cortex. Statistical analyses were deployed to discern significant differences between the rat strains and assess the impact of PSI on behavioral and biochemical outcomes.

RESULTS

Our findings uncovered significant behavioral disparities between WKY and WIS rats, indicating passive behavior and social withdrawal in the former. PSI demonstrated pronounced pro-social and antidepressant effects in both strains, each with its distinctive temporal trajectory. Notably, we identified strain-specific variations in BDNF-related signaling and observed the modulation of Arc expression in WKY rats.

CONCLUSIONS

Our study delineated mood-related behavioral nuances between WKY and WIS rat strains, underscoring the antidepressant and pro-social properties of PSI in both groups. The distinct temporal patterns of observed changes and the identified strain-specific neuroplasticity alterations provide valuable insights into the TRD phenotype and the mechanisms underpinning the efficacy of PSI.

Potential Differences in Psychedelic Actions Based on Biological Sex

The resurgence of interest in psychedelics as treatments for psychiatric disorders necessitates a better understanding of potential sex differences in response to these substances. Sex as a biological variable (SABV) has been historically neglected in medical research, posing limits to our understanding of treatment efficacy. Human studies have provided insights into the efficacy of psychedelics across various diagnoses and aspects of cognition, yet sex-specific effects remain unclear, making it difficult to draw strong conclusions about sex-dependent differences in response to psychedelic treatments. Compounding this further, animal studies used to understand biological mechanisms of psychedelics predominantly use one sex and present mixed neurobiological and behavioral outcomes. Studies that do include both sexes often do not investigate sex differences further, which may hinder the translation of findings to the clinic. In reviewing sex differences in responses to psychedelics, we will highlight the direct interaction between estrogen (the most extensively studied steroid hormone) and the serotonin system (central to the mechanism of action of psychedelics), and the potential that estrogen-serotonin interactions may influence the efficacy of psychedelics in female participants. Estrogen influences serotonin neurotransmission by affecting its synthesis and release, as well as modulating the sensitivity and responsiveness of serotonin receptor subtypes in the brain. This could potentially influence the efficacy of psychedelics in females by modifying their therapeutic efficacy across menstrual cycles and developmental stages. Investigating this interaction in the context of psychedelic research could aid in the advancement of therapeutic outcomes, especially for conditions with sex-specific prevalence.