Psilocybin induces acute and persisting alterations in immune status in healthy volunteers: An experimental, placebo-controlled study

Exploring novel therapeutic strategies: Could psychedelic perspectives offer promising solutions for Alzheimer's disease comorbidities?

The increasing prevalence of dementia within an ageing global population, combined with prolonged life expectancy, accentuates Alzheimer's disease (AD) as a multifaceted healthcare challenge. This challenge is further compounded by the limited therapeutic options currently available. Addressing the intricacies of AD management, the mitigation of comorbidities has emerged as a pivotal facet of treatment. Comorbid conditions, such as neurobehavioral symptoms, play a role in shaping the clinical course, management, and outcomes of this pathology; highlighting the importance of comprehensive care approaches for affected individuals. Exploration of psychedelic compounds in psychiatric and palliative care settings has recently uncovered promising therapeutic potential, enhancing neuroplasticity, emotional processing and connection. These effects are particularly relevant in the context of AD, where psychedelic therapy offers hope not only for mitigating core symptoms but also for addressing the array of comorbidities associated with this condition. The integration of this comprehensive method offers a chance to significantly enhance the care provided to those navigating the intricate landscape of AD. Therefore, the current paper reviews the intricate link between more frequent additional health conditions that may coexist with dementia, particularly in the context of AD, and explores the therapeutic potential of psychedelic compounds in addressing these concurrent conditions.

Non-hallucinogenic psychedelics for mood and anxiety disorders: A systematic review

Psychedelics have re-emerged as promising treatments for mood disorders. The current model provides a moderate-to-high dose of a psychedelic agent (e.g., psilocybin) to reliably induce an altered state of consciousness. Unfortunately, the hallucinatory effects limit the treatment's potential scalability given patients' vulnerability and extensive monitoring costs, leading to growing interest in non-hallucinatory psychedelics (NHPs). This review's objective was to identify, summarize and synthesize all published pre-clinical and clinical studies evaluating NHPs for mood and anxiety disorders. We included five animal studies demonstrating antidepressant-like effects through assessments like forced swim test (FST) and open field test (OFT) without observing head-twitch response (HTR), and one case report that identified a patient who inadvertently combined trazodone and psilocybin and experienced potent antidepressant effects without psychedelic effects. These preliminary findings provide a strong impetus for further investigation in human samples with rigorously designed clinical trials that may delineate the potential antidepressant effects of psychedelics without hallucinatory effects.

Psilocybin and psilocin regulate microglial immunomodulation and support neuroplasticity via serotonergic and AhR signaling

BACKGROUND

Psilocybin, a serotonergic psychedelic, has demonstrated therapeutic potential in neuropsychiatric disorders. While its neuroplastic and immunomodulatory effects are recognized, the underlying mechanisms remain unclear. This study investigates how psilocybin and its active metabolite, psilocin, influence microglial inflammatory responses and neurotrophic factor expression through serotonergic and AhR signaling.

METHODS

Using in vitro models of resting and LPS-activated microglia, we evaluated the effects of psilocybin and psilocin on the expression of pro-inflammatory cytokines (TNF-α), anti-inflammatory cytokines (IL-10), and neuroplasticity-related markers (BDNF). Receptor-specific contributions were assessed using selective antagonists for 5-HT2A, 5-HT2B, 5-HT7, TrkB, and AhR.

RESULTS

Psilocybin and psilocin significantly suppressed TNF-α expression and increased BDNF levels in LPS-activated microglia. These effects were mediated by 5-HT2A, 5-HT2B, 5-HT7, and TrkB signaling, while AhR activation was required for psilocin-induced BDNF upregulation but not TNF-α suppression. IL-10 levels remained unchanged under normal conditions but increased significantly when serotonergic, TrkB, or AhR signaling was blocked, suggesting a compensatory shift in anti-inflammatory pathways.

CONCLUSION

Psilocybin and psilocin promote a microglial phenotype that reduces inflammation and supports neuroplasticity via receptor-specific mechanisms. Their effects on TNF-α and BDNF depend on distinct serotonergic and neurotrophic pathways, with AhR playing a selective role in psilocin's action. These findings clarify the receptor-mediated dynamics of psilocybin's therapeutic effects and highlight alternative anti-inflammatory pathways that may be relevant for clinical applications.

ALSUntangled #77: Psilocybin

ALSUntangled reviews alternate and off-label treatments prompted by patient interest. Here, we review psilocybin, a chemical derived from mushrooms and belonging in the category of drugs known as psychedelics. Psilocybin has plausible mechanisms for slowing ALS progression because of its ability to cross the blood brain barrier and effect neurogenesis and inflammation. Currently, there are no pre-clinical ALS models, case reports, or trials for psilocybin and ALS in the context of disease modifying therapy. Depending on dosing, there can be a high risk of psychological side effects including hallucinations and physical harm. Based on the above information, we do not currently support the use of psilocybin as a means to slow ALS progression.

Exploring Factors Affecting Psychological Flexibility After Psychedelic Experiences

Neurobiological effects and psychological models propose that psychedelics may promote psychological flexibility, suggesting a transdiagnostic effect by disrupting maladaptive patterns. The objective of this study was therefore to investigate the determinants of psychological flexibility change following a psychedelic use. This retrospective online survey included French individuals who had undergone a significant psychedelic experience. Participants were assessed for mystical experience intensity with the MEQ-30, and psychological flexibility via the AAQ-II, at three retrospective time points. Data analysis comprised descriptive statistics, correlation analysis, ANCOVA to evaluate the impact of psychedelic use variables on psychological flexibility, and linear regression to identify predictors of psychological flexibility changes. Data showed a positive correlation between mystical experience intensity and improvements in psychological flexibility, especially 1-month post-experience (p < .01), and during the 6 months before the survey (p < .01). Key predictors of changes in psychological flexibility included baseline AAQ-II scores, MEQ total scores and frequent psychedelic use, underlining the interaction between personal and experiential factors in determining therapeutic outcomes. In conclusion, this study highlights how the intensity of mystical experience and baseline psychological flexibility may be the key factors influencing changes in psychological flexibility post-psychedelic use, suggesting a potential therapeutic value.

Psilocin alleviates acute itch in mice: possible involvement of 5-HT2A receptors and kynurenine pathway

We aimed to investigate whether psilocin, the bioactive metabolite of the well-known psychedelic, psilocybin, may have antipruritic effects in mice by interfering with the kynurenine pathway and interacting with 5-HT2A receptors. Eight mice were randomly assigned to each of the study groups receiving either normal saline, compound 48/80, psilocin (0.3, 1, and 3 mg/kg), or psilocin (1 mg/kg) + 1-MT (0.3 mg/kg). The scratching bouts were documented in each group. The hallucinogenic properties of psilocin were documented using the head-twitch response (HTR) test. To confirm their involvement, we also quantified the expression levels of TNF-α, TLR-4, indoleamine-2,3-dioxygenase (IDO), and 5-HT2A receptors across various study groups. We found that psilocin (1 mg/kg) exerted the most significant antipruritic and hallucinogenic effects (P < 0.0001). The activity of 5-HT2A receptors in the skin tissue of mice was confirmed by western blot. When psilocin (1 mg/kg) was given together with 1-MT (0.3 mg/kg), the antipruritic effects became more pronounced as compared to when psilocin was given alone (P < 0.05). TLR-4 and TNF-α expression levels considerably reduced after psilocin was applied, both alone and together with 1-MT (P < 0.05, P < 0.01, respectively). We also observed significantly decreased activity of IDO in the treatment groups (P < 0.05, P < 0.01 after giving psilocin alone, and together with 1-MT, respectively). To our knowledge, this is the first study to confirm the effectiveness of psychedelics in battling pruritus. Our findings offer a novel repositioning for psilocin. This may be particularly beneficial for psychological conditions accompanied by pruritus.

Psilocybin therapy for mood dysfunction in Parkinson's disease: an open-label pilot trial

Mood dysfunction is highly prevalent in Parkinson's disease (PD), a main predictor of functional decline, and difficult to treat-novel interventions are critically needed. Psilocybin shows early promise for treating depression and anxiety, but its potential in PD is unknown, as safety concerns have excluded people with neurodegenerative disease from previous trials. In this open-label pilot (NCT04932434), we examined the feasibility of psilocybin therapy among people with mild to moderate stage PD plus depression and/or anxiety. 12 participants (mean age 63.2 ± 8.2 years, 5 women) received psilocybin (one 10 mg followed by one 25 mg dose) with psychotherapy. There were no serious adverse events, no medical interventions required to manage effects of psilocybin, and no exacerbation of psychosis. Ten participants experienced treatment-emergent adverse events; the most frequent were anxiety, nausea, and increased blood pressure. We observed no worsening of PD symptomology measured by the Movement Disorder Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS). On the contrary, non-motor (MDS-UPDRS Part I: -13.8 ± 1.3, p < 0.001, Hedges' g = 3.0) and motor symptoms (Part II: -7.5 ± 0.9, p < 0.001, g = 1.2; Part III: -4.6 ± 1.3, p = 0.001; g = 0.3) as well as performance in select cognitive domains (Paired Associates Learning [-0.44 ± 0.14, p = .003, g = 0.4], Spatial Working Memory [-0.52 ± 0.17, p = 0.003, g = 0.7], and Probabilistic Reversal Learning [2.9 ± 0.9, p = 0.003, g = 1.3]) improved post-treatment, and improvements were sustained until the final safety assessment one month following drug exposure. Baseline Montgomery-Asberg Depression Rating Scale (MADRS) and Hamilton Anxiety Rating Scale (HAM-A) scores were 21.0 ± 8.7 and 17.0 ± 3.7, respectively. Both improved to a clinically meaningful degree post-treatment; these improvements persisted to the final assessment three months following drug exposure (MADRS: -9.3 ± 2.7, p = .001, g = 1.0; HAM-A: -3.8 ± 1.7; p = 0.031, g = 0.7). This study provides the first data on psilocybin's effects in any neurodegenerative disease. Results suggest that psilocybin therapy in PD warrants further investigation.

The effect of low-dose psilocybin on brain neurotransmission and rat behavior

Psilocybin has various therapeutic effects in mental and psychological disorders, including depression and mood disorders, obsessive-compulsive disorders, substance addiction and anxiety. Pharmacodynamic properties of psilocybin depend on doses used and time after administration. The psilocybin dose range varies depending on whether it is used therapeutically or for recreational purposes in humans, but most animal studies require larger doses to induce an effect on brain neurotransmission and animal behavior. The aim of this study was to investigate the effect of psilocybin on the release of cortical neurotransmitters and rat behavior when it was administered subcutaneously at doses of 0.1, 0.3 and 0.6 mg/kg. Psilocybin affected the release of dopamine, noradrenaline, serotonin and acetylcholine in the frontal cortex as measured by microdialysis in freely moving rats. Psilocybin increased the release of aminergic transmitters in a non-linear manner with the dose of 0.3 mg/kg being the weakest. Psilocybin also increased the release of γ-aminobutyric acid, but glutamate release was enhanced only for the first 2 h after drug injection and was followed by a decrease for the rest of the experimental period. In contrast to 25I-NBOMe, an agonist of 5-HT2A receptors, psilocybin did not produce hallucinogenic activity expressed as wet dog shakes and did not disrupt sensorimotor gating in the acoustic startle response test. Furthermore, psilocybin showed anxiolytic effect in the light dark box test 1 h after administration. It also modulated the hypothalamic-pituitary-adrenal axis activity as it transiently increased serum corticosterone level, decreased serotonin, but increased dopamine turnover rates in the hypothalamus and inhibited the content of noradrenaline and adrenaline in the adrenal glands. The changes in the neurotransmitter release seem to play a role in psilocybin behavioral effects. The lack of hallucinogenic activity and disruptive effect on sensorimotor gating by psilocybin lower doses indicates that psychotomimetic effects did not occur. Psilocybin in contrast to 25I-NBOMe, ketamine and MDMA did not produce oxidative damage of DNA in the frontal cortex and hippocampus. Thus, the single low doses of psilocybin may have some beneficial properties and fewer harmful effects.

Psychedelics in neuroinflammation: Mechanisms and therapeutic potential

Neuroinflammation is a critical factor in the pathogenesis of various neurodegenerative and psychiatric disorders, including Alzheimer's disease, Parkinson's disease, and major depressive disorder. Psychedelics, such as psilocybin, lysergic acid diethylamide (LSD), and dimethyltryptamine (DMT), have demonstrated promising therapeutic effects on neuroinflammation, primarily through interactions with serotonin (5-HT) receptors, particularly the 5-HT2A receptor. Activation of these receptors by psychedelics modulates the production of pro-inflammatory cytokines, regulates microglial activity, and shifts the balance between neurotoxic and neuroprotective metabolites. Additionally, psychedelics affect critical signaling pathways, including the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), phosphatidylinositol-3-kinase/protein kinase B (PI3K/Akt), and mechanistic target of rapamycin (mTOR) pathways, promoting neuroplasticity and exerting anti-inflammatory effects. Beyond the serotonergic system, other neurotransmitter systems-including the glutamatergic, dopaminergic, noradrenergic, gamma-aminobutyric acid (GABAergic), and cholinergic systems-also play significant roles in mediating the effects of psychedelics. This review examines the intricate mechanisms by which psychedelics modulate neuroinflammation and underscores their potential as innovative therapeutic agents for treating neuroinflammatory and neuropsychiatric disorders.

Serotonergic psychedelics as potential therapeutics for post-COVID-19 syndrome (or Long COVID): A comprehensive review

RATIONALE

In our ongoing battle against the coronavirus 2019 (COVID-19) pandemic, a major challenge is the enduring symptoms that continue after acute infection. Also known as Long COVID, post-COVID-19 syndrome (PCS) often comes with debilitating symptoms like fatigue, disordered sleep, olfactory dysfunction, and cognitive issues ("brain fog"). Currently, there are no approved treatments for PCS. Recent research has uncovered that the severity of PCS is inversely linked to circulating serotonin levels, highlighting the potential of serotonin-modulating therapeutics for PCS. Therefore, we propose that serotonergic psychedelics, acting mainly via the 5-HT2A serotonin receptor, hold promise for treating PCS.

OBJECTIVES

Our review aims to elucidate potential mechanisms by which serotonergic psychedelics may alleviate the symptoms of PCS.

RESULTS

Potential mechanisms through which serotonergic psychedelics may alleviate PCS symptoms are discussed, with emphasis on their effects on inflammation, neuroplasticity, and gastrointestinal function. Additionally, this review explores the potential of serotonergic psychedelics in mitigating endothelial dysfunction, a pivotal aspect of PCS pathophysiology implicated in organ dysfunction. This review also examines the potential role of serotonergic psychedelics in alleviating specific PCS symptoms, which include olfactory dysfunction, cognitive impairment, sleep disturbances, and mental health challenges.

CONCLUSIONS

Emerging evidence suggests that serotonergic psychedelics may alleviate PCS symptoms. However, further high-quality research is needed to thoroughly assess their safety and efficacy in treating patients with PCS.

Concurrent stress modulates the acute and post-acute effects of psilocybin in a sex-dependent manner

There is renewed interest in psychedelics, such as psilocybin, as therapies for multiple difficult-to-treat psychiatric disorders. Even though psychedelics can induce highly pleasant or aversive experiences, depending on multiple personal and environmental factors, there is little research into how such experiences impact post-acute mood-altering actions. Here we aimed at offsetting this gap. First, we tested whether acute psilocybin effects differed between sexes. Adult male and female C57BL/6J mice received saline or psilocybin (5 mg/kg; i.p.), and head-twitch response (HTR) frequency was quantified. Notably, while psilocybin increased HTR frequency in both sexes, the effect was greater in females. We then tested if stress exposure during acute drug effects impacted post-acute psilocybin actions. Following drug treatment, mice were returned to their homecage or restrained for 1 h. Anxiety- and depression-like behaviors were assessed starting 24 h following drug administration, using the marble burying, novelty-suppressed feeding, and splash tests. Psilocybin induced anxiolytic-, but not antidepressant-like, which were fully blocked by stress in males, but only partially so in females. Lastly, we assessed the acute stress-psilocybin interaction on plasma corticosterone levels in a separate cohort of mice, treated as above. Both stress and psilocybin independently increased corticosterone levels, without additive or interactive effects being observed for either sex. Our data reveals the role of sex and peri-acute negative experiences in the acute and post-acute actions of psilocybin. These findings underline the importance of non-pharmacological factors, such as the quality of the psychedelic experience, in the mood-altering effects of psychedelics, holding significant for both their therapeutic and recreational use.

Consistent evidence that brain serotonin 2A receptor binding is positively associated with personality-based risk markers of depression

BACKGROUND

Using [18F]altanserin, a serotonin 2A receptor (5-HT2AR) antagonist Positron Emission Tomography (PET) tracer, a positive association between cortical 5-HT2AR binding and the inward-directed facets of neuroticism has been demonstrated in healthy individuals. Psilocybin, a 5-HT2AR agonist, shows promise for the treatment of depression, reducing neuroticism and mood symptoms potentially via hypothalamic-pituitary-adrenal (HPA) modulation. 5-HT2AR and neuroticism are both modulated by HPA axis function.

AIMS

In this study, we examined whether the association between 5-HT2AR binding and the inward facets of neuroticism can be replicated in an independent healthy cohort using the new 5-HT2AR agonist tracer [11C]Cimbi-36, and if their association is moderated by cortisol awakening response (CAR), an index of HPA axis function. If so, this could advance mechanistic insights into interventions that target the 5-HT2AR and reduce neuroticism.

METHOD

Eighty healthy volunteers underwent [11C]Cimbi-36 PET scans and completed the NEO personality inventory (NEO-PI-R) for the assessment of neuroticism. Salivary samples were available for determination of CAR in 70 of the participants. Using linear latent variable models, we evaluated the association between 5-HT2AR binding and inward facets of neuroticism, namely depression, anxiety, self-consciousness and vulnerability to stress, and whether CAR moderated this association.

RESULTS

The study confirms the positive association between 5-HT2AR binding and the inward facets of neuroticism (β = 0.01, 95% CI = [0.0005: 0.02], P = 0.04), and this association is independent of CAR (P = 0.33).

CONCLUSIONS

The findings prompt consideration of whether novel interventions such as psilocybin that actively targets 5-HT2AR and causes changes in personality could be particularly beneficial if implemented as a targeted approach based on neuroticism profiles.

Mushrooms, Microdosing, and Mental Illness: The Effect of Psilocybin on Neurotransmitters, Neuroinflammation, and Neuroplasticity

The incidence of mental health disorders is increasing worldwide. While there are multiple factors contributing to this problem, neuroinflammation underlies a significant subset of psychiatric conditions, particularly major depressive and anxiety disorders. Anti-inflammatory interventions have demonstrated benefit in these conditions. Psilocin, the active ingredient of mushrooms in the Psilocybe genus, is both a potent serotonin agonist and anti-inflammatory agent, increases neuroplasticity, and decreases overactivity in the default mode network. Studies using hallucinogenic doses of psilocin under the supervision of a therapist/guide have consistently demonstrated benefits to individuals with depression and end-of-life anxiety. Microdosing psilocybin in sub-hallucinogenic doses has also demonstrated benefit in mood disorders, and may offer a safe, less expensive, and more available alternative to full doses of psilocybin for mood disorders, as well as for other medical conditions in which inflammation is the principal pathophysiology.

Exploring the Potential of Psychedelics in the Treatment of Headache Disorders: Clinical Considerations and Exploratory Insights

PURPOSE OF REVIEW

Exploration of the potential of serotonergic psychedelic drugs, such as psilocybin and LSD, as potential treatments for headache disorders. This review addresses the need for well-informed physician guidelines and discusses mechanisms, safety, and efficacy of these treatments. Further research, including the consideration of combination with psychotherapy, is needed.

RECENT FINDINGS

Psychedelics demonstrate promising outcomes as treatments for headache disorders. Recent findings indicated that some patients who underwent brief periods of treatment with psychedelics experienced a reduction in headache attack frequency, severity, or duration. When prescription medications are ineffective at treating headache disorders, or are habit-forming, patients often turn to alternative options. There is anecdotal evidence that psychedelic drugs like LSD and psilocybin can effectively treat and prevent pain in patients with headache disorders, such as migraine or cluster headache. It is vital that physicians treating patients who self-treat with psychedelics be well-informed about the mechanisms and their effects to best advise their patients and coordinate their care well. This is a review assessing the literature on the mechanisms, safety, and efficacy of psychedelic drugs as a headache management intervention. We believe there is evidence that may support further investigation into the clinical use of psychedelic medications to treat cluster headache and migraine, including the consideration of use in conjunction with other interventions like cognitive behavioral therapy or acceptance and commitment training.

Early psilocybin intervention alleviates behavioral despair and cognitive impairment in stressed Wistar rats

Chronic stress exerts profound effects on mental health, contributing to disorders such as depression, anxiety, and cognitive impairment. This study examines the potential of psilocybin to alleviate behavioral despair and cognitive deficits in a rodent model of chronic stress, focusing on the interplay between the Hypothalamic-Pituitary-Adrenal (HPA) axis and the Endocannabinoid System (ECS). Twenty-two male Wistar rats were divided into control and stress groups. Animals within the stress group were exposed to predator odor and chronic social instability to induce chronic stress, and were either sham treated, or given psilocybin. Behavioral assessments were conducted using the Open Field Test, Sucrose Preference Test, Novel Object Recognition, Elevated Plus Maze, and Forced Swimming Test to evaluate locomotion, anhedonia, memory, anxiety, and behavioral despair, respectively. Blood and brain samples were analyzed for biochemical markers. Results indicated that psilocybin significantly reduced stress-induced behavioral despair and cognitive impairments, likely through ECS-mediated downregulation of the HPA axis. These findings suggest that early intervention with psilocybin has sustained beneficial effects on stress-related behavioral and cognitive disturbances, underscoring its potential as a novel therapeutic approach for stress-related mental health disorders.

The immunomodulatory effects of classical psychedelics: A systematic review of preclinical studies

Emerging evidence suggests that classical psychedelics possess immunomodulatory and anti-inflammatory properties; however, these effects are yet to be well-established. This systematic review aims to provide a timely and comprehensive overview of the immunomodulatory effects of classical psychedelics in preclinical studies. A systematic search was conducted on six databases, including CINAHL, EMBASE, MEDLINE, PsychINFO, Scopus, and Web of Science. Eligible studies targeting classical psychedelics for evaluation of their effects on inflammatory markers and immunomodulation have been included for analysis. Data was extracted from 40 out of 2822 eligible articles, and their risk of bias was assessed using the Systematic Review Center for Laboratory Animal Experimentation (SYRCLE) tool and Quality Assessment Tool for In Vitro Studies (QUIN). Studies examined 2,5-dimethoxy-4-iodoamphetamine (DOI; n = 18); psilocybin (4-PO-DMT; n = 9); N,N-dimethyltryptamine (DMT; n = 8); lysergic acid diethylamide (LSD; n = 6); 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT; n = 3); psilocin (4-HO-DMT; n = 3); and mescaline (n = 2). In 36 studies where inflammatory cytokine levels were measured following psychedelic administration, a decrease in at least one inflammatory cytokine was observed in 29 studies. Immune cell activity was assessed in 10 studies and findings were mixed, with an equal number of studies (n = 5 out of 10) reporting either an increase or decrease in immune cell activity. Classical psychedelics were found to alleviate pre-existing inflammation but promote inflammation when administered under normal physiological conditions. This information is anticipated to inform future clinical trials, exploring classical psychedelics' potential to alleviate inflammation in various pathologies.

Neurobiological mechanisms of antidepressant properties of psilocybin: A systematic review of blood biomarkers

Psilocybin represents a novel therapeutic approach for individuals with major depressive disorder (MDD) who do not respond to conventional antidepressant treatment. Investigating the influence of psilocybin on the pathophysiological processes involved in MDD could enhance our neurobiological understanding of the presumed antidepressant action mechanism. This systematic review aims to summarize the results of human studies investigating changes in blood-based biomarkers of MDD to guide future research on potentially relevant analytes that could be monitored in clinical trials. A systematic search was performed in MEDLINE, Embase, and Web of Science to retrieve studies investigating changes in serum and plasma levels of neurotrophic, immunologic, neuroendocrine, and metabolic markers. Nine studies were included, describing findings on 15 biomarkers, exclusively in healthy participants. Studies consistently reported a decrease in interleukin-6, C-reactive protein, and eosinophils, and an increase in cortisol, prolactin, oxytocin, thyroid-stimulating hormone, adrenocorticotropic hormone, brain-derived neurotrophic factor, and free fatty acids following psilocybin administration. Less consistent effects were observed on interleukin-1β, interleukin-8, tumour necrosis factor-alpha, soluble urokinase plasminogen activator receptor, and growth hormone. The results are in line with preclinical studies and provide initial support from human studies that psilocybin potentially leads to beneficial effects on biomarkers of MDD. However, given the limited number of studies, findings should be approached with caution prior to replication. Further research should include larger samples, clinical populations, longer-term assessment, rigorous experimental designs, and account for the potential confounding of psychological stress related to the psychedelic experience.

Psilocybin reduces grooming in the SAPAP3 knockout mouse model of compulsive behaviour

Psilocybin is a serotonergic psychedelic compound which shows promise for treating compulsive behaviours. This is particularly pertinent as compulsive disorders require research into new pharmacological treatment options as the current frontline treatments such as selective serotonin reuptake inhibitors, require chronic administration, have significant side effects, and leave almost half of the clinical population refractory to treatment. In this study, we investigated psilocybin administration in male and female SAPAP3 knockout (KO) mice, a well-validated mouse model of obsessive compulsive and related disorders. We assessed the effects of acute psilocybin (1 mg/kg, intraperitoneal) administration on head twitch and locomotor behaviour as well as anxiety- and compulsive-like behaviours at multiple time-points (1, 3 and 8 days post-injection). While psilocybin did not have any effect on anxiety-like behaviours, we revealed that acute psilocybin administration led to enduring reductions in compulsive behaviour in male SAPAP3 KO mice and reduced grooming behaviour in female wild-type (WT) and SAPAP3 KO mice. We also found that psilocybin increased locomotion in WT littermates but not in SAPAP3 KO mice, suggesting in vivo serotonergic dysfunctions in KO animals. On the other hand, the typical head-twitch response following acute psilocybin (confirming its hallucinogenic-like effect at this dose) was observed in both genotypes. Our novel findings suggest that acute psilocybin may have potential to reduce compulsive-like behaviours (up to 1 week after a single injection). Our study can inform future research directions as well as supporting the utility of psilocybin as a novel treatment option for compulsive disorders.

Psilocin, the Psychoactive Metabolite of Psilocybin, Modulates Select Neuroimmune Functions of Microglial Cells in a 5-HT2 Receptor-Dependent Manner

Neuroinflammation that is caused by microglia, the main immune cells of the brain, contributes to neurodegenerative diseases. Psychedelics, including psilocybin and lysergic acid diethylamide (LSD), possess certain anti-inflammatory properties and, therefore, should be considered as drug candidates for treating neuroinflammatory pathologies. When ingested, psilocybin is rapidly dephosphorylated to yield psilocin, which crosses the blood-brain barrier and exerts psychotropic activity by interacting with the 5-hydroxytryptamine 2A receptors (5-HT2ARs) on neurons. Since microglia express all three 5-HT2R isoforms, we hypothesized that, by interacting with these receptors, psilocin beneficially modulates select neuroimmune functions of microglia. We used microglia-like cell lines to demonstrate that psilocin, at non-toxic concentrations, did not affect the secretion of tumor necrosis factor (TNF) by immune-stimulated microglial cells, but significantly inhibited their phagocytic activity, the release of reactive oxygen species (ROS), and nitric oxide (NO) production. The inhibitory activity of psilocin on the latter two functions was similar to that of two selective 5-HT2R agonists, namely, 25I-NBOH and Ro60-0175. The role of this subfamily of receptors was further demonstrated by the application of 5-HT2R antagonists cyproheptadine and risperidone. Psilocin should be considered a novel drug candidate that might be effective in treating neuroimmune disorders, such as neurodegenerative diseases, where reactive microglia are significant contributors.

Less is more? A review of psilocybin microdosing

BACKGROUND

The applications of psilocybin, derived from 'magic mushrooms,' are vast, including a burgeoning practice known as microdosing, which refers to the administration of sub-hallucinogenic doses of psychedelic substances to obtain benefits without experiencing significant cognitive and perceptual distortion. However, current research is fairly new with several limitations and gaps that hinder adequate conclusions on its efficacy.

AIMS

This semi-structured review aimed to identify and highlight research gaps in the field of psilocybin microdosing for future research.

METHODS

A Preferred Reporting Items for Systematic Reviews and Meta-Analyses based strategy was employed, utilizing a chain of keywords and key phrases across multiple databases, augmented by a cross-sectional Google search for relevant grey literature in the form of the top 10 search results. A total of 40 studies and 8 unique websites were identified, summarized and tabulated into four distinct categories, namely non-clinical, clinical, observational and anecdotal evidence.

RESULTS

The majority of available evidence originates from observational studies, while non-clinical and clinical study findings remain comparatively sparse and inconsistent. Web-based findings were consistent with current research findings. Key research gaps were highlighted: the imperative for more randomized placebo-controlled trials, exploration of dose-response ranges, psychological and personality testing of participants, utilization of active placebos, greater diversity in study populations, an increase in psilocybin-exclusive microdosing studies and the refinement of animal models.

CONCLUSION

Definitive conclusions regarding the efficacy of psilocybin microdosing remain elusive, emphasizing the need for further study. Numerous research gaps necessitate consideration for future investigations.

Therapeutic modulation of the kynurenine pathway in severe mental illness and comorbidities: A potential role for serotonergic psychedelics

Mounting evidence points towards a crucial role of the kynurenine pathway (KP) in the altered gut-brain axis (GBA) balance in severe mental illness (SMI, namely depression, bipolar disorder, and schizophrenia) and cardiometabolic comorbidities. Preliminary evidence shows that serotonergic psychedelics and their analogues may hold therapeutic potential in addressing the altered KP in the dysregulated GBA in SMI and comorbidities. In fact, aside from their effects on mood, psychedelics elicit therapeutic improvement in preclinical models of obesity, metabolic syndrome, and vascular inflammation, which are highly comorbid with SMI. Here, we review the literature on the therapeutic modulation of the KP in the dysregulated GBA in SMI and comorbidities, and the potential application of psychedelics to address the altered KP in the brain and systemic dysfunction underlying SMI and comorbidities. Psychedelics might therapeutically modulate the KP in the altered GBA in SMI and comorbidities either directly, via altering the metabolic pathway by influencing the rate-limiting enzymes of the KP and affecting the levels of available tryptophan, or indirectly, by affecting the gut microbiome, gut metabolome, metabolism, and the immune system. Despite promising preliminary evidence, the mechanisms and outcomes of the KP modulation with psychedelics in SMI and systemic comorbidities remain largely unknown and require further investigation. Several concerns are discussed surrounding the potential side effects of this approach in specific cohorts of individuals with SMI and systemic comorbidities.

Inter-individual variability in neural response to low doses of LSD

The repeated use of small doses of psychedelics (also referred to as "microdosing") to facilitate benefits in mental health, cognition, and mood is a trending practice. Placebo-controlled studies however have largely failed to demonstrate strong benefits, possibly because of large inter-individual response variability. The current study tested the hypothesis that effects of low doses of LSD on arousal, attention and memory depend on an individual's cognitive state at baseline. Healthy participants (N = 53) were randomly assigned to receive repeated doses of LSD (15 mcg) or placebo on 4 occasions divided over 2 weeks. Each treatment condition also consisted of a baseline and a 1-week follow-up visit. Neurophysiological measures of arousal (resting state EEG), pre-attentive processing (auditory oddball task), and perceptual learning and memory (visual long-term potentiation (LTP) paradigm) were assessed at baseline, dosing session 1 and 4, and follow-up. LSD produced stimulatory effects as reflected by a reduction in resting state EEG delta, theta, and alpha power, and enhanced pre-attentive processing during the acute dosing sessions. LSD also blunted the induction of LTP on dosing session 4. Stimulatory effects of LSD were strongest in individuals with low arousal and attention at baseline, while inhibitory effects were strongest in high memory performers at baseline. Decrements in delta EEG power and enhanced pre-attentive processing in the LSD treatment condition were still present during the 1-week follow-up. The current study demonstrates across three cognitive domains, that acute responses to low doses of LSD depend on the baseline state and provides some support for LSD induced neuroadaptations that sustain beyond treatment.

Psilocybin for the treatment of Alzheimer's disease

Alzheimer's disease (AD) stands as a formidable neurodegenerative ailment and a prominent contributor to dementia. The scarcity of available therapies for AD accentuates the exigency for innovative treatment modalities. Psilocybin, a psychoactive alkaloid intrinsic to hallucinogenic mushrooms, has garnered attention within the neuropsychiatric realm due to its established safety and efficacy in treating depression. Nonetheless, its potential as a therapeutic avenue for AD remains largely uncharted. This comprehensive review endeavors to encapsulate the pharmacological effects of psilocybin while elucidating the existing evidence concerning its potential mechanisms contributing to a positive impact on AD. Specifically, the active metabolite of psilocybin, psilocin, elicits its effects through the modulation of the 5-hydroxytryptamine 2A receptor (5-HT2A receptor). This modulation causes heightened neural plasticity, diminished inflammation, and improvements in cognitive functions such as creativity, cognitive flexibility, and emotional facial recognition. Noteworthy is psilocybin's promising role in mitigating anxiety and depression symptoms in AD patients. Acknowledging the attendant adverse reactions, we proffer strategies aimed at tempering or mitigating its hallucinogenic effects. Moreover, we broach the ethical and legal dimensions inherent in psilocybin's exploration for AD treatment. By traversing these avenues, We propose therapeutic potential of psilocybin in the nuanced management of Alzheimer's disease.

Psilocybin for dementia prevention? The potential role of psilocybin to alter mechanisms associated with major depression and neurodegenerative diseases

Major depression is an established risk factor for subsequent dementia, and depression in late life may also represent a prodromal state of dementia. Considering current challenges in the clinical development of disease modifying therapies for dementia, the focus of research is shifting towards prevention and modification of risk factors to alter the neurodegenerative disease trajectory. Understanding mechanistic commonalities underlying affective symptoms and cognitive decline may reveal biomarkers to aid early identification of those at risk of progressing to dementia during the preclinical phase of disease, thus allowing for timely intervention. Adult hippocampal neurogenesis (AHN) is a phenomenon that describes the birth of new neurons in the dentate gyrus throughout life and it is associated with spatial learning, memory and mood regulation. Microglia are innate immune system macrophages in the central nervous system that carefully regulate AHN via multiple mechanisms. Disruption in AHN is associated with both dementia and major depression and microgliosis is a hallmark of several neurodegenerative diseases. Emerging evidence suggests that psychedelics promote neuroplasticity, including neurogenesis, and may also be immunomodulatory. In this context, psilocybin, a serotonergic agonist with rapid-acting antidepressant properties has the potential to ameliorate intersecting pathophysiological processes relevant for both major depression and neurodegenerative diseases. In this narrative review, we focus on the evidence base for the effects of psilocybin on adult hippocampal neurogenesis and microglial form and function; which may suggest that psilocybin has the potential to modulate multiple mechanisms of action, and may have implications in altering the progression from major depression to dementia in those at risk.

Human pluripotent stem cells as a translational toolkit in psychedelic research in vitro

Psychedelics, recognized for their impact on perception, are resurging as promising treatments with rapid onset for mood and substance use disorders. Despite increasing evidence from clinical trials, questions persist about the cellular and molecular mechanisms and their precise correlation with treatment outcomes. Murine neurons and immortalized non-neural cell lines harboring overexpressed constructs have shed light on neuroplastic changes mediated by the serotonin 2A receptor (5-HT2AR) as the primary mechanism. However, limitations exist in capturing human- and disease-specific traits. Here, we discuss current accomplishments and prospects for incorporating human pluripotent stem cells (PSCs) to complement these models. PSCs can differentiate into various brain cell types, mirroring endogenous expression patterns and cell identities to recreate disease phenotypes. Brain organoids derived from PSCs resemble cell diversity and patterning, while region-specific organoids simulate circuit-level phenotypes. PSC-based models hold significant promise to illuminate the cellular and molecular substrates of psychedelic-induced phenotypic recovery in neuropsychiatric disorders.

Roflumilast: Modulating neuroinflammation and improving motor function and depressive symptoms in multiple sclerosis

BACKGROUND

Multiple sclerosis (MS) is an autoimmune disease causing central nervous system demyelination, often associated with depression. Current treatments for MS do not effectively address both physical disability and depression. Roflumilast, a phosphodiesterase-4 inhibitor with anti-inflammatory properties, has shown promise for autoimmune diseases.

METHODS

We used an experimental autoimmune encephalomyelitis (EAE) rat model to study roflumilast's effects. Motor dysfunction and depression symptoms were assessed, and histopathological analysis evaluated its anti-inflammatory properties. Flow cytometry examined the drug's impact on brain microglia. TNF-α, IL-1β, and IL-6 levels in hippocampal tissue were assessed using ELISA kits.

RESULTS

Roflumilast improved motor dysfunction and depression symptoms in EAE rats. Histopathological analysis revealed reduced inflammation, demyelination, and axonal loss in the spinal cord. Roflumilast suppressed microglial cell activation and conversion to pro-inflammatory M1-type cells. Flow cytometry showed roflumilast inhibited inflammatory marker expression in microglia and their activation in the hippocampus. IL-6 was identified as a roflumilast target for suppressing hippocampal inflammation.

LIMITATIONS

This study used an animal model and did not assess long-term or potential side effects of roflumilast treatment.

CONCLUSIONS

Roflumilast holds promise as a treatment for depression and motor impairment in MS. Its anti-inflammatory properties, reducing inflammation and inhibiting microglial activation, suggest its potential for MS therapy. However, further research is needed to evaluate long-term effects and safety in MS patients.

High-resolution tracking of unconfined zebrafish behavior reveals stimulatory and anxiolytic effects of psilocybin

Serotonergic psychedelics are emerging therapeutics for psychiatric disorders, yet their underlying mechanisms of action in the brain remain largely elusive. Here, we developed a wide-field behavioral tracking system for larval zebrafish and investigated the effects of psilocybin, a psychedelic serotonin receptor agonist. Machine learning analyses of precise body kinematics identified latent behavioral states reflecting spontaneous exploration, visually-driven rapid swimming, and irregular swim patterns following stress exposure. Using this method, we found that acute psilocybin treatment has two behavioral effects: [i] facilitation of spontaneous exploration ("stimulatory") and [ii] prevention of irregular swim patterns following stress exposure ("anxiolytic"). These effects differed from the effect of acute SSRI treatment and were rather similar to the effect of ketamine treatment. Neural activity imaging in the dorsal raphe nucleus suggested that psilocybin inhibits serotonergic neurons by activating local GABAergic neurons, consistent with psychedelic-induced suppression of serotonergic neurons in mammals. These findings pave the way for using larval zebrafish to elucidate neural mechanisms underlying the behavioral effects of serotonergic psychedelics.

Deciphering psilocybin: Cytotoxicity, anti-inflammatory effects, and mechanistic insights

A decade of clinical research has indicated psilocybin's effectiveness in treating various neuropsychiatric disorders, such as depression and substance abuse. The correlation between increased pro-inflammatory cytokines and the severity of neuropsychiatric symptoms, along with the known anti-inflammatory potential of some psychedelics, suggests an immunomodulatory role for psilocybin. This study aims to understand the mechanism of action of psilocybin by investigating the cytotoxic and immunomodulatory effects of psilocybin and psilocin on both resting and LPS-activated RAW 264.7 murine macrophages. The study evaluated the cytotoxicity of psilocybin and psilocin using an LDH assay across various doses and assessed their impact on cytokine production in RAW 264.7 cells, measuring cytokine expression via ELISA. Different doses, including those above and below the LC50, were used in both pre-treatment and post-treatment approaches. The LDH assay revealed that psilocybin is almost twice as cytotoxic as psilocin, with an LC50 of 12 ng/ml and 28 ng/ml, respectively. In resting macrophages, both psilocybin and psilocin triggered significant release of TNF- α after 4 h, with the lowest doses inducing higher levels of the cytokine than the highest doses. IL-10 expression in resting cells was only triggered by the highest dose of psilocin in the 4-hour incubation group. In LPS-stimulated cells, psilocin reduced TNF- α levels more than psilocybin in pre-treatment and post-treatment, with no significant effects on IL-10 in pre-treatment. Psilocin, but not psilocybin, induced a significant increase of IL-10 in post-treatment, leading to the conclusion that psilocin, but not psilocybin, exerts anti-inflammatory effects on classically activated macrophages.

Psychedelic Therapy: A Primer for Primary Care Clinicians-Psilocybin

BACKGROUND

The primary psychoactive drug in magic mushrooms, psilocybin, induces profound alterations in consciousness through the 5-HT2A receptor. This review consolidates current research findings to elucidate the pharmacology, safety profile, and clinical applications of psilocybin.

AREAS OF UNCERTAINTY

Despite initial concerns that psilocybin could cause psychosis, contemporary research has demonstrated that psilocybin is generally safe. The most common adverse effects are nausea and headache, yet both tend to be transient. Serious adverse events can generally be avoided in controlled settings such as clinical trials. However, in the largest clinical trial to date, there were a total of 7 reported cases of suicidal ideation, up to 12 weeks after receiving a single 25 mg dose of psilocybin. That being said, all 7 cases did not respond to the treatment. Although selective serotonin reuptake inhibitors may blunt the hallucinogenic qualities of psilocybin, preliminary research suggests that they may enhance its antidepressant effects.

THERAPEUTIC ADVANCES

In clinical trials, psilocybin has shown promise for treating major depressive disorder and treatment-resistant depression. Initial studies indicated that 42%-57% of patients underwent remission after psilocybin-assisted therapy, which suggests that psilocybin is more effective than existing antidepressant medications. Clinical data have also demonstrated that psilocybin can manage substance use disorders and end-of-life anxiety with clinical outcomes that are sustained for months and sometimes years after 1 or 2 doses.

LIMITATIONS

However, larger Phase II trials with more than 100 depressed participants have shown a much smaller remission rate of 25%-29%, though these studies still observed that psilocybin causes a significant reduction in depressive symptoms.

CONCLUSIONS

Aside from ketamine, psilocybin is the most clinically well-researched psychedelic drug, with trials that have enrolled hundreds of participants and multiple therapeutic applications. Phase III trials will determine whether psilocybin lives up to the promise that it showed in previous clinical trials.

Psychosocial moderators of polygenic risk scores of inflammatory biomarkers in relation to GrimAge

GrimAge acceleration has previously predicted age-related morbidities and mortality. In the current study, we sought to examine how GrimAge is associated with genetic predisposition for systemic inflammation and whether psychosocial factors moderate this association. Military veterans from the National Health and Resilience in Veterans study, which surveyed a nationally representative sample of European American male veterans, provided saliva samples for genotyping (N = 1135). We derived polygenic risk scores (PRS) from the UK Biobank as markers of genetic predisposition to inflammation. Results revealed that PRS for three inflammatory PRS markers-HDL (lower), apolipoprotein B (lower), and gamma-glutamyl transferase (higher)-were associated with accelerated GrimAge. Additionally, these PRS interacted with a range of potentially modifiable psychosocial variables, such as exercise and gratitude, previously identified as associated with accelerated GrimAge. Using gene enrichment, we identified anti-inflammatory and antihistamine drugs that perturbate pathways of genes highly represented in the inflammatory PRS, laying the groundwork for future work to evaluate the potential of these drugs in mitigating epigenetic aging.

Making Sense of Psychedelics in the CNS

For centuries, ancient lineages have consumed psychedelic compounds from natural sources. In the modern era, scientists have since harnessed the power of computational tools, cellular assays, and behavioral metrics to study how these compounds instigate changes on molecular, cellular, circuit-wide, and system levels. Here, we provide a brief history of psychedelics and their use in science, medicine, and culture. We then outline current techniques for studying psychedelics from a pharmacological perspective. Finally, we address known gaps in the field and potential avenues of further research to broaden our collective understanding of physiological changes induced by psychedelics, the limits of their therapeutic capabilities, and how researchers can improve and inform treatments that are rapidly becoming accessible worldwide.