Psychedelics and Other Psychoplastogens for Treating Mental Illness

Novel psychoplastogen DM506 reduces cue-induced heroin-seeking and inhibits tonic GABA currents in the Prelimbic Cortex

Opioid use disorder is a major public health crisis that is manifested by persistent drug-seeking behavior and high relapse frequency. Most of the available treatments rely on targeting opioid receptors using small molecules that do not provide sustained symptom alleviation. Psychoplastogens are a novel class of non-opioid drugs that produce rapid and sustained effects on neuronal plasticity, intended to produce therapeutic benefits. Ibogalogs are synthetic derivatives of iboga alkaloids that lack hallucinogenic or adverse side effects. In the current study, we examine the therapeutic potential of DM506, a novel ibogalog lacking any cardiotoxic or hallucinogenic effects, in cue-induced seeking behavior following heroin self-administration. At a single systemic dose of 40 mg/kg, DM506 significantly decreased cue-induced seeking in both male and female rats at abstinence day 1 (AD1) following heroin self-administration. Upon re-testing for cue-induced seeking at AD14, we found that males receiving DM506 continued to show decreased cue-induced seeking, an effect not observed in females. Since there is evidence of psychedelics influencing tonic GABA currents, and opioid and psychoplastogen-mediated neuroadaptations in the medial prefrontal cortex (PrL) underlying its functional effects, we performed patch-clamp recordings on PrL slices of drug-naïve rats with an acute application or chronic incubation with DM506. Tonic GABA current was decreased in slices incubated with DM506 for 2 h. qPCR analysis did not reveal any differences in the mRNA levels of GABAA receptor α and δ subunits at AD14 in heroin and saline self-administered animals that received vehicle or DM506 at AD1. Overall, our data indicate that DM506 attenuates cue-induced heroin seeking and inhibits tonic GABA current in the prelimbic cortex.

Psilocybin Facilitates Fear Extinction: Importance of Dose, Context, and Serotonin Receptors

A variety of classic psychedelics and MDMA have been shown to enhance fear extinction in rodent models. This has translational significance because a standard treatment for post-traumatic stress disorder (PTSD) is prolonged exposure therapy. However, few studies have investigated psilocybin's potential effect on fear learning paradigms. More specifically, the extents to which dose, timing of administration, and serotonin receptors may influence psilocybin's effect on fear extinction are not understood. In this study, we used a delay fear conditioning paradigm to determine the effects of psilocybin on fear extinction, extinction retention, and fear renewal in male and female mice. Psilocybin robustly enhances fear extinction when given acutely prior to testing for all doses tested. Psilocybin also exerts long-term effects to elevate extinction retention and suppress fear renewal in a novel context, although these changes were sensitive to dose. Analysis of sex differences showed that females may respond to a narrower range of doses than males. Administration of psilocybin prior to fear learning or immediately after extinction yielded no change in behavior, indicating that concurrent extinction experience is necessary for the drug's effects. Cotreatment with a 5-HT2A receptor antagonist blocked psilocybin's effects for extinction, extinction retention, and fear renewal, whereas 5-HT1A receptor antagonism attenuated only the effect on fear renewal. Collectively, these results highlight dose, context, and serotonin receptors as crucial factors in psilocybin's ability to facilitate fear extinction. The study provides preclinical evidence to support investigating psilocybin as a pharmacological adjunct for extinction-based therapy for PTSD.

Identification of Psychoplastogenic Tropanes Lacking Muscarinic Activity

Tropane-containing small molecules like scopolamine are a promising class of psychoplastogens. However, their potent antagonism of all muscarinic receptor subtypes presents the potential for undesirable anticholinergic side effects. In an effort to decouple their neuroplasticity-promoting effects from their muscarinic activity, we performed phenotypic structure-activity relationship studies across a variety of structurally distinct subclasses of tropanes. We discovered several novel tropanes capable of significantly increasing cortical neuronal growth while exhibiting drastically reduced activity at all muscarinic receptor subtypes compared to scopolamine.

Psychedelic public health: State of the field and implications for equity

BACKGROUND

Psychedelic Public Health is an emerging discipline uniting the practices of public health with the potential benefits of psychedelics to reduce harm and promote health, wellness, and equity at community and population levels. Little is known regarding the current state of psychedelic public health despite rising psychedelic usage, evidence of its health efficacy, opening policy environments, and concerns regarding equity and potential harms.

METHODS

To characterize the current state of psychedelic public health, this survey reviewed relevant webpages from 228 universities housing accredited Schools and Programs in Public Health (SPPHs) and 59 Psychedelic Research Centers (PRCs) in the US and globally. The scan corresponded to the Prisma 2020 checklist, identifying URLs through keyword searches by Beautiful Soup python package and Google search engine web application. Measures were coded through webpage text analysis.

FINDINGS

Fewer than 10% (9.6%) of SPPHs engaged with psychedelics (2.6% substantially), while half (52.6%) of universities engaged (28.1% substantially). Among PRCs, only 10% indicated a collaboration with SPPHs, and fewer than 3% of PRC personnel held public health degrees. PRCs were preponderantly affiliated with medical schools. Although Indigeneity significantly contributes to Western therapeutic psychedelic protocols, only approximately one-quarter of active universities, SPPHs, or PRCs visibly addressed Indigeneity and only one PRC included Indigenous leadership. 92% of PRCs were led or co-led by people characterized as White-European and 88% by men. Only 20-43% of SPPHs, universities, and PRCs visibly addressed social determinants of health.

CONCLUSIONS

Public health schools, which train, study, and advise the future of public health, showed limited involvement in the growing psychedelic field, signifying a gap in psychedelic science and practice. The absence of public health's population-level approaches signifies a missed opportunity to maximize benefits and protect against potential harms of psychedelics at community and population levels.

Controlled ultrasonic interventions through the human skull

Transcranial focused ultrasound enables precise and non-invasive manipulations of deep brain circuits in humans, promising to provide safe and effective treatments of various neurological and mental health conditions. Ultrasound focused to deep brain targets can be used to modulate neural activity directly or localize the release of psychoactive drugs. However, these applications have been impeded by a key barrier-the human skull, which attenuates ultrasound strongly and unpredictably. To address this issue, we have developed an ultrasound-based approach that directly measures and compensates for the ultrasound attenuation by the skull. No additional skull imaging, simulations, assumptions, or free parameters are necessary; the method measures the attenuation directly by emitting a pulse of ultrasound from an array on one side of the head and measuring with an array on the opposite side. Here, we apply this emerging method to two primary future uses-neuromodulation and local drug release. Specifically, we show that the correction enables effective stimulation of peripheral nerves and effective release of propofol from nanoparticle carriers through an ex vivo human skull. Neither application was effective without the correction. Moreover, the effects show the expected dose-response relationship and targeting specificity. This article highlights the need for precise control of ultrasound intensity within the skull and provides a direct and practical approach for addressing this lingering barrier.

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.

Psilocybin reduces heroin seeking behavior and modulates inflammatory gene expression in the nucleus accumbens and prefrontal cortex of male rats

Preclinical and human studies indicate psilocybin may reduce perseverant maladaptive behaviors, including nicotine and alcohol seeking. Such studies in the opioid field are lacking, though opioids are involved in more >50% of overdose deaths. Psilocybin is an agonist at the serotonin 2A receptor (5-HT2AR), a well-documented target for modulation of drug seeking, and evidence suggests 5-HT2AR agonists may dampen motivation for opioids. We sought to investigate the therapeutic efficacy of psilocybin in mediating cessation of opioid use and maintenance of long-lasting abstinence from opioid seeking behavior in a rat model of heroin self-administration (SA). Psilocybin or 5-HT2AR antagonists ketanserin and volinanserin were administered systemically to rats prior to SA of 0.075 mg/kg/infusion of heroin, or relapse following forced abstinence. Psilocybin did not alter heroin taking, but a single exposure to 3.0 mg/kg psilocybin 4-24 hours prior to a relapse test blunted cue-induced heroin seeking. Conversely, 5-HT2AR antagonists exacerbated heroin relapse. To begin to elucidate mechanisms of psilocybin, drug-naïve rats received psilocybin and/or ketanserin, and tissue was collected from the prefrontal cortex (PFC), a region critical for drug seeking and responsive to psilocybin, 24 hours later for RNA-sequencing. 3.0 mg/kg psilocybin regulated ~2-fold more genes in the PFC than 1.0 mg/kg, including genes involved in the cytoskeleton and cytokine signaling. Ketanserin blocked >90% of psilocybin-regulated genes, including the IL-17a cytokine receptor, Il17ra. Psychedelic compounds have reported anti-inflammatory properties, and therefore we performed a gene expression array to measure chemokine/cytokine molecules in the PFC of animals that displayed psilocybin-mediated inhibition of heroin seeking. Psilocybin regulated 4 genes, including Il17a, and a subset of genes correlated with relapse behavior. Selective inhibition of PFC IL-17a was sufficient to reduce heroin relapse. We conclude that psilocybin reduces heroin relapse and highlight IL-17a signaling as a potential downstream pathway of psilocybin that also reduces heroin seeking.

Current Understanding on Psilocybin for Major Depressive Disorder: A Review Focusing on Clinical Trials

Previous studies suggested effectiveness of psilocybin in the field of mental health. FDA designated psilocybin as a "breakthrough therapy" for the treatment of treatment-resistant depression (TRD) in 2018. This paper provided a review of psilocybin's potential role in treatment of depression by focusing on published clinical trials. Studies showed that psilocybin, an agonist on 5-HT2A receptors, manifests antidepressant and anxiolytic effects by increasing glutamate transmission, reducing brain inflammation, decreasing default mode network activity. In terms of clinical trials, eleven studies (six open-label and five double blinded randomized clinical trials [DB-RCTs]) trials exploring psilocybin's impact on depression were found. Among open-label studies, a pilot study on TRD patients demonstrated significant reductions in depressive symptoms after two psilocybin sessions. Psilocybin also improved cognitive bias associated with depression. Extension studies confirmed sustained improvements and high remission rates. Among five DB-RCTs, two showed that psilocybin led to significant reductions in anxiety and depression in cancer patients, and the improvements sustained for over six months. In MDD, psilocybin showed rapid reductions in depression, with higher remission rates compared to escitalopram in a DB-RCT. Another DB-RCT showed that psilocybin induced higher decrease in depression around 6 hours after their administrations than placebo. The last DB-RCT showed that in patients with TRD, a single dose of psilocybin 25 mg, but not psilocybin 10 mg, resulted in superior antidepressant effect than psilocybin 1 mg. Overall, psilocybin showed promise in treating depression and anxiety, with notable safety profiles. Further research should explore optimal dosages and long-term effects.

Viscous dynamics associated with hypoexcitation and structural disintegration in neurodegeneration via generative whole-brain modeling

INTRODUCTION

Alzheimer's disease (AD) and behavioral variant frontotemporal dementia (bvFTD) lack mechanistic biophysical modeling in diverse, underrepresented populations. Electroencephalography (EEG) is a high temporal resolution, cost-effective technique for studying dementia globally, but lacks mechanistic models and produces non-replicable results.

METHODS

We developed a generative whole-brain model that combines EEG source-level metaconnectivity, anatomical priors, and a perturbational approach. This model was applied to Global South participants (AD, bvFTD, and healthy controls).

RESULTS

Metaconnectivity outperformed pairwise connectivity and revealed more viscous dynamics in patients, with altered metaconnectivity patterns associated with multimodal disease presentation. The biophysical model showed that connectome disintegration and hypoexcitability triggered altered metaconnectivity dynamics and identified critical regions for brain stimulation. We replicated the main results in a second subset of participants for validation with unharmonized, heterogeneous recording settings.

DISCUSSION

The results provide a novel agenda for developing mechanistic model-inspired characterization and therapies in clinical, translational, and computational neuroscience settings.

Chronic pain as an emergent property of a complex system and the potential roles of psychedelic therapies

Despite research advances and urgent calls by national and global health organizations, clinical outcomes for millions of people suffering with chronic pain remain poor. We suggest bringing the lens of complexity science to this problem, conceptualizing chronic pain as an emergent property of a complex biopsychosocial system. We frame pain-related physiology, neuroscience, developmental psychology, learning, and epigenetics as components and mini-systems that interact together and with changing socioenvironmental conditions, as an overarching complex system that gives rise to the emergent phenomenon of chronic pain. We postulate that the behavior of complex systems may help to explain persistence of chronic pain despite current treatments. From this perspective, chronic pain may benefit from therapies that can be both disruptive and adaptive at higher orders within the complex system. We explore psychedelic-assisted therapies and how these may overlap with and complement mindfulness-based approaches to this end. Both mindfulness and psychedelic therapies have been shown to have transdiagnostic value, due in part to disruptive effects on rigid cognitive, emotional, and behavioral patterns as well their ability to promote neuroplasticity. Psychedelic therapies may hold unique promise for the management of chronic pain.

Psilocybin analog 4-OH-DiPT enhances fear extinction and GABAergic inhibition of principal neurons in the basolateral amygdala

Psychedelics such as psilocybin show great promise for the treatment of depression and PTSD, but their long duration of action poses practical limitations for patient access. 4-OH-DiPT is a fast-acting and shorter-lasting derivative of psilocybin. Here we characterized the pharmacological profile of 4-OH-DiPT and examined its impact on fear extinction learning as well as a potential mechanism of action. First, we profiled 4-OH-DiPT at all 12 human 5-HT GPCRs. 4-OH-DiPT showed strongest agonist activity at all three 5-HT2A/2B/2C receptors with near full agonist activity at 5-HT2A. Notably, 4-OH-DiPT had comparable activity at mouse and human 5-HT2A/2B/2C receptors. In a fear extinction paradigm, 4-OH-DiPT significantly reduced freezing responses to conditioned cues in a dose-dependent manner with a greater potency in female mice than male mice. Female mice that received 4-OH-DiPT before extinction training had reduced avoidance behaviors several days later in the light dark box, elevated plus maze and novelty-suppressed feeding test compared to controls, while male mice did not show significant differences. 4-OH-DiPT produced robust increases in spontaneous inhibitory postsynaptic currents (sIPSCs) in basolateral amygdala (BLA) principal neurons and action potential firing in BLA interneurons in a 5-HT2A-dependent manner. RNAscope demonstrates that Htr2a mRNA is expressed predominantly in BLA GABA interneurons, Htr2c mRNA is expressed in both GABA interneurons and principal neurons, while Htr2b mRNA is absent in the BLA. Our findings suggest that 4-OH-DiPT activates BLA interneurons via the 5-HT2A receptor to enhance GABAergic inhibition of BLA principal neurons, which provides a potential mechanism for suppressing learned fear.

The Effects of Psychedelics on Neuronal Physiology

Psychedelics are quite unique among drugs that impact the central nervous system, as a single administration of a psychedelic can both rapidly alter subjective experience in profound ways and produce sustained effects on circuits relevant to mood, fear, reward, and cognitive flexibility. These remarkable properties are a direct result of psychedelics interacting with several key neuroreceptors distributed across the brain. Stimulation of these receptors activates a variety of signaling cascades that ultimately culminate in changes in neuronal structure and function. Here, we describe the effects of psychedelics on neuronal physiology, highlighting their acute effects on serotonergic and glutamatergic neurotransmission as well as their long-lasting effects on structural and functional neuroplasticity in the cortex. We propose that the neurobiological changes leading to the acute and sustained effects of psychedelics might be distinct, which could provide opportunities for engineering compounds with optimized safety and efficacy profiles.

Neuropharmacological Advances: Harnessing 5-HT2A Receptor Modulators and Psychoplastogens

This Patent Highlight explores the emerging role of 5-HT2A receptor modulators and psychoplastogens in neuropsychiatric treatment. It delves into these novel compounds' molecular mechanisms, therapeutic potential, and challenges, highlighting their therapeutic potential in mental health care.

Structural and biochemical alterations in dendritic spines as key mechanisms for severe mental illnesses

Severe mental illnesses (SMI) collectively affect approximately 20% of the global population, as estimated by the World Health Organization (WHO). Despite having diverse etiologies, clinical symptoms, and pharmacotherapies, these diseases share a common pathophysiological characteristic: the misconnection of brain areas involved in reality perception, executive control, and cognition, including the corticolimbic system. Dendritic spines play a crucial role in excitatory neurotransmission within the central nervous system. These small structures exhibit remarkable plasticity, regulated by factors such as neurotransmitter tone, neurotrophic factors, and innate immunity-related molecules, and other mechanisms - all of which are associated with the pathophysiology of SMI. However, studying dendritic spine mechanisms in both healthy and pathological conditions in patients is fraught with technical limitations. This is where animal models related to these diseases become indispensable. They have played a pivotal role in elucidating the significance of dendritic spines in SMI. In this review, the information regarding the potential role of dendritic spines in SMI was summarized, drawing from clinical and animal model reports. Also, the implications of targeting dendritic spine-related molecules for SMI treatment were explored. Specifically, our focus is on major depressive disorder and the neurodevelopmental disorders schizophrenia and autism spectrum disorder. Abundant clinical and basic research has studied the functional and structural plasticity of dendritic spines in these diseases, along with potential pharmacological targets that modulate the dynamics of these structures. These targets may be associated with the clinical efficacy of the pharmacotherapy.

Membrane Permeation of Psychedelic Tryptamines by Dynamic Simulations

Renewed scientific interest in psychedelic compounds represents one of the most promising avenues for addressing the current burden of mental health disorders. Classic psychedelics are a group of compounds that exhibit structural similarities to the naturally occurring neurotransmitter serotonin (5-HT). Acting on the 5-HT type 2A receptors (HT2ARs), psychedelics induce enduring neurophysiological changes that parallel their therapeutic psychological and behavioral effects. Recent preclinical evidence suggests that the ability of psychedelics to exert their action is determined by their ability to permeate the neuronal membrane to target a pool of intracellular 5-HT2ARs. In this computational study, we employ classical molecular dynamics simulations and umbrella sampling techniques to investigate the permeation behavior of 12 selected tryptamines and to characterize the interactions that drive the process. We aim at elucidating the impact of N-alkylation, indole ring substitution and positional modifications, and protonation on their membrane permeability. Dimethylation of the primary amine group and the introduction of a methoxy group at position 5 exhibited an increase in permeability. Moreover, there is a significant influence of positional substitutions on the indole groups, and the protonation of the molecules substantially increases the energy barrier at the center of the bilayer, making the compounds highly impermeable. All the information extracted from the trends predicted by the simulations can be applied in future drug design projects to develop psychedelics with enhanced activity.

Methylone is a rapid-acting neuroplastogen with less off-target activity than MDMA

Background

Post-traumatic stress disorder (PTSD) is a highly prevalent psychiatric disorder that can become chronic and debilitating when left untreated. Available pharmacotherapies are limited, take weeks to show modest benefit and remain ineffective for up to 40% of patients. Methylone is currently in clinical development for the treatment of PTSD. Preclinical studies show rapid, robust and long-lasting antidepressant-like and anxiolytic effects. The mechanism of action underlying these effects is not yet fully understood. This study investigated the downstream gene expression changes and signaling pathways affected by methylone in key brain areas linked to PTSD and MDD. It also sought to determine whether neuroplasticity-related genes were involved. We compared effects of methylone with MDMA to explore similarities and differences in their brain effects because MDMA-assisted psychotherapy has recently shown benefit in clinical trials for PTSD and methylone is a structural analog of MDMA.

Methods

Monoamine binding, uptake and release studies were performed and a high-throughput-screen evaluated agonist/antagonist activities at 168 GPCRs in vitro. We used RNA sequencing (RNA-seq) to probe drug-induced gene expression changes in the amygdala and frontal cortex, two brain areas responsible for emotional learning that are affected by PTSD and MDD. Rats were treated with methylone or MDMA (both 10 mg/kg, IP), and their responses were compared with controls. We performed functional enrichment analysis to identify which pathways were regulated by methylone and/or MDMA. We confirmed changes in gene expression using immunohistochemistry.

Results

Methylone, a monoamine uptake inhibitor and releaser, demonstrated no off-target effects at 168 GPCRs, unlike MDMA, which showed activity at 5HT2A and 5HT2C receptors. RNA-seq results revealed significant regulation of myelin-related genes in the amygdala, confirmed by immunohistochemistry. In the frontal cortex, methylone significantly upregulated genes implicated in neuroplasticity.

Conclusion

Results suggest that (1) methylone is a rapid-acting neuroplastogen that affects key brain substrates for PTSD and MDD and that (2) methylone appears to exhibit higher specificity and fewer off-target effects than MDMA. Together, these results are consistent with the reported clinical experiences of methylone and MDMA and bolster the potential use of methylone in the treatment of PTSD and, potentially, other neuropsychiatric disorders.

Modulation of long-term potentiation following microdoses of LSD captured by thalamo-cortical modelling in a randomised, controlled trial

BACKGROUND

Microdosing psychedelics is a phenomenon with claimed cognitive benefits that are relatively untested clinically. Pre-clinically, psychedelics have demonstrated enhancing effects on neuroplasticity, which cannot be measured directly in humans, but may be indexed by non-invasive electroencephalography (EEG) paradigms. This study used a visual long-term potentiation (LTP) EEG paradigm to test the effects of microdosed lysergic acid diethylamide (LSD) on neural plasticity, both acutely while on the drug and cumulatively after microdosing every third day for six weeks. Healthy adult males (n = 80) completed the visual LTP paradigm at baseline, 2.5 h following a dose of 10 µg of LSD or inactive placebo, and 6 weeks later after taking 14 repeated microdoses. Visually induced LTP was used as indirect index of neural plasticity. Surface level event-related potential (ERPs) based analyses are presented alongside dynamic causal modelling of the source localised data using a generative thalamocortical model (TCM) of visual cortex to elucidate underlying synaptic circuitry.

RESULTS

Event-related potential (ERP) analyses of N1b and P2 components did not show evidence of changes in visually induced LTP by LSD either acutely or after 6 weeks of regular dosing. However modelling the complete timecourse of the ERP with the TCM demonstrated changes in laminar connectivity in primary visual cortex. This primarily included changes to self-gain and inhibitory input parameters acutely. Layer 2/3 to layer 5 excitatory connectivity was also different between LSD and placebo groups. After regular dosing only excitatory input from layer 2/3 into layer 5 and inhibitory input into layer 4 were different between groups.

CONCLUSIONS

Without modulation of the ERPs it is difficult to relate the findings to other studies visually inducing LTP. It also indicates the classic peak analysis may not be sensitive enough to demonstrate evidence for changes in LTP plasticity in humans at such low doses. The TCM provides a more sensitive approach to assessing changes to plasticity as differences in plasticity mediated laminar connectivity were found between the LSD and placebo groups.

TRIAL REGISTRATION

 ANZCTR registration number ACTRN12621000436875; Registered 16/04/2021 https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=381476 .

Serotonin 2A Receptor (5-HT2AR) Agonists: Psychedelics and Non-Hallucinogenic Analogues as Emerging Antidepressants

Psychedelics make up a group of psychoactive compounds that induce hallucinogenic effects by activating the serotonin 2A receptor (5-HT2AR). Clinical trials have demonstrated the traditional psychedelic substances like psilocybin as a class of rapid-acting and long-lasting antidepressants. However, there is a pressing need for rationally designed 5-HT2AR agonists that possess optimal pharmacological profiles in order to fully reveal the therapeutic potential of these agonists and identify safer drug candidates devoid of hallucinogenic effects. This Perspective provides an overview of the structure-activity relationships of existing 5-HT2AR agonists based on their chemical classifications and discusses recent advancements in understanding their molecular pharmacology at a structural level. The encouraging clinical outcomes of psychedelics in depression treatment have sparked drug discovery endeavors aimed at developing novel 5-HT2AR agonists with improved subtype selectivity and signaling bias properties, which could serve as safer and potentially nonhallucinogenic antidepressants. These efforts can be significantly expedited through the utilization of structure-based methods and functional selectivity-directed screening.

A role for the serotonin 2A receptor in the expansion and functioning of human transmodal cortex

Integrating independent but converging lines of research on brain function and neurodevelopment across scales, this article proposes that serotonin 2A receptor (5-HT2AR) signalling is an evolutionary and developmental driver and potent modulator of the macroscale functional organization of the human cerebral cortex. A wealth of evidence indicates that the anatomical and functional organization of the cortex follows a unimodal-to-transmodal gradient. Situated at the apex of this processing hierarchy-where it plays a central role in the integrative processes underpinning complex, human-defining cognition-the transmodal cortex has disproportionately expanded across human development and evolution. Notably, the adult human transmodal cortex is especially rich in 5-HT2AR expression and recent evidence suggests that, during early brain development, 5-HT2AR signalling on neural progenitor cells stimulates their proliferation-a critical process for evolutionarily-relevant cortical expansion. Drawing on multimodal neuroimaging and cross-species investigations, we argue that, by contributing to the expansion of the human cortex and being prevalent at the apex of its hierarchy in the adult brain, 5-HT2AR signalling plays a major role in both human cortical expansion and functioning. Owing to its unique excitatory and downstream cellular effects, neuronal 5-HT2AR agonism promotes neuroplasticity, learning and cognitive and psychological flexibility in a context-(hyper)sensitive manner with therapeutic potential. Overall, we delineate a dual role of 5-HT2ARs in enabling both the expansion and modulation of the human transmodal cortex.

Therapeutic mechanisms of psychedelics and entactogens

Recent clinical and preclinical evidence suggests that psychedelics and entactogens may produce both rapid and sustained therapeutic effects across several indications. Currently, there is a disconnect between how these compounds are used in the clinic and how they are studied in preclinical species, which has led to a gap in our mechanistic understanding of how these compounds might positively impact mental health. Human studies have emphasized extra-pharmacological factors that could modulate psychedelic-induced therapeutic responses including set, setting, and integration-factors that are poorly modelled in current animal experiments. In contrast, animal studies have focused on changes in neuronal activation and structural plasticity-outcomes that are challenging to measure in humans. Here, we describe several hypotheses that might explain how psychedelics rescue neuropsychiatric disease symptoms, and we propose ways to bridge the gap between human and rodent studies. Given the diverse pharmacological profiles of psychedelics and entactogens, we suggest that their rapid and sustained therapeutic mechanisms of action might best be described by the collection of circuits that they modulate rather than their actions at any single molecular target. Thus, approaches focusing on selective circuit modulation of behavioral phenotypes might prove more fruitful than target-based methods for identifying novel compounds with rapid and sustained therapeutic effects similar to psychedelics and entactogens.

The Psychedelic Future of Post-Traumatic Stress Disorder Treatment

Post-traumatic stress disorder (PTSD) is a mental health condition that can occur following exposure to a traumatic experience. An estimated 12 million U.S. adults are presently affected by this disorder. Current treatments include psychological therapies (e.g., exposure-based interventions) and pharmacological treatments (e.g., selective serotonin reuptake inhibitors (SSRIs)). However, a significant proportion of patients receiving standard-of-care therapies for PTSD remain symptomatic, and new approaches for this and other trauma-related mental health conditions are greatly needed. Psychedelic compounds that alter cognition, perception, and mood are currently being examined for their efficacy in treating PTSD despite their current status as Drug Enforcement Administration (DEA)- scheduled substances. Initial clinical trials have demonstrated the potential value of psychedelicassisted therapy to treat PTSD and other psychiatric disorders. In this comprehensive review, we summarize the state of the science of PTSD clinical care, including current treatments and their shortcomings. We review clinical studies of psychedelic interventions to treat PTSD, trauma-related disorders, and common comorbidities. The classic psychedelics psilocybin, lysergic acid diethylamide (LSD), and N,N-dimethyltryptamine (DMT) and DMT-containing ayahuasca, as well as the entactogen 3,4-methylenedioxymethamphetamine (MDMA) and the dissociative anesthetic ketamine, are reviewed. For each drug, we present the history of use, psychological and somatic effects, pharmacology, and safety profile. The rationale and proposed mechanisms for use in treating PTSD and traumarelated disorders are discussed. This review concludes with an in-depth consideration of future directions for the psychiatric applications of psychedelics to maximize therapeutic benefit and minimize risk in individuals and communities impacted by trauma-related conditions.

The possible place for psychedelics in pharmacotherapy of mental disorders

Since its emergence in the 1960s, the serotonergic theory of depression bore fruit in the discovery of a plethora of antidepressant drugs affecting the lives of millions of patients. While crucial in the history of drug development, recent studies undermine the effectiveness of currently used antidepressant drugs in comparison to placebo, emphasizing the long time it takes to initiate the therapeutic response and numerous adverse effects. Thus, the scope of contemporary pharmacological research shifts from drugs affecting the serotonin system to rapid-acting antidepressant drugs. The prototypical representative of the aforementioned class is ketamine, an NMDA receptor antagonist capable of alleviating the symptoms of depression shortly after the drug administration. This discovery led to a paradigm shift, focusing on amino-acidic neurotransmitters and growth factors. Alas, the drug is not perfect, as its therapeutic effect diminishes circa 2 weeks after administration. Furthermore, it is not devoid of some severe side effects. However, there seems to be another, more efficient, and safer way to target the glutamatergic system. Hallucinogenic agonists of the 5-HT2A receptor, commonly known as psychedelics, are nowadays being reconsidered in clinical practice, shedding their infamous 1970s stigma. More and more clinical studies prove their clinical efficacy and rapid onset after a single administration while bearing fewer side effects. This review focuses on the current state-of-the-art literature and most recent clinical studies concerning the use of psychedelic drugs in the treatment of mental disorders. Specifically, the antidepressant potential of LSD, psilocybin, DMT, and 5-MeO-DMT will be discussed, together with a brief summary of other possible applications.

Preclinical models of treatment-resistant depression: challenges and perspectives

Treatment-resistant depression (TRD) is a subgroup of major depressive disorder in which the use of classical antidepressant treatments fails to achieve satisfactory treatment results. Although there are various definitions and grading models for TRD, common criteria for assessing TRD have still not been established. However, a common feature of any TRD model is the lack of response to at least two attempts at antidepressant pharmacotherapy. The causes of TRD are not known; nevertheless, it is estimated that even 60% of TRD patients are so-called pseudo-TRD patients, in which multiple biological factors, e.g., gender, age, and hormonal disturbances are concomitant with depression and involved in antidepressant drug resistance. Whereas the phenomenon of TRD is a complex disorder difficult to diagnose and successfully treat, the search for new treatment strategies is a significant challenge of modern pharmacology. It seems that despite the complexity of the TRD phenomenon, some useful animal models of TRD meet the construct, the face, and the predictive validity criteria. Based on the literature and our own experiences, we will discuss the utility of animals exposed to the stress paradigm (chronic mild stress, CMS), and the Wistar Kyoto rat strain representing an endogenous model of TRD. In this review, we will focus on reviewing research on existing and novel therapies for TRD, including ketamine, deep brain stimulation (DBS), and psychedelic drugs in the context of preclinical studies in representative animal models of TRD.

Cost-effectiveness of psilocybin-assisted therapy for severe depression: exploratory findings from a decision analytic model

BACKGROUND

There is growing evidence to support the use of the psychedelic drug psilocybin for difficult-to-treat depression. This paper compares the cost-effectiveness of psilocybin-assisted psychotherapy (PAP) with conventional medication, cognitive behavioural therapy (CBT), and the combination of conventional medication and CBT.

METHODS

A decision model simulated patient events (response, remission, and relapse) following treatment. Data on probabilities, costs and quality-adjusted life years (QALYs) were derived from previous studies or from best estimates. Expected healthcare and societal costs and QALYs over a 6-month time period were calculated. Sensitivity analyses were used to address uncertainty in parameter estimates.

RESULTS

The expected healthcare cost of PAP varied from £6132 to £7652 depending on the price of psilocybin. This compares to £3528 for conventional medication alone, £4250 for CBT alone, and £4197 for their combination. QALYs were highest for psilocybin (0.310), followed by CBT alone (0.283), conventional medication alone (0.278), and their combination (0.287). Psilocybin was shown to be cost-effective compared to the other therapies when the cost of therapist support was reduced by 50% and the psilocybin price was reduced from its initial value to £400 to £800 per person. From a societal perspective, psilocybin had improved cost-effectiveness compared to a healthcare perspective.

CONCLUSIONS

Psilocybin has the potential to be a cost-effective therapy for severe depression. This depends on the level of psychological support that is given to patients receiving psilocybin and the price of the drug itself. Further data on long-term outcomes are required to improve the evidence base.

Efficacy and Safety of Four Psychedelic-Assisted Therapies for Adults with Symptoms of Depression, Anxiety, and Posttraumatic Stress Disorder: A Systematic Review and Meta-Analysis

There has been a resurgence in psychedelic research for managing psychiatric conditions in recent years. This study aimed to present a comprehensive review of the current state of the field by applying a systematic search strategy for articles on the effectiveness and tolerability of four psychedelic-assisted therapies (psilocybin, lysergic acid diethylamide [LSD], 3,4-Methylenedioxymethamphetamine [MDMA], and ayahuasca) for adults with symptoms of depression, anxiety, and posttraumatic stress disorder (PTSD). Psychometric scores and adverse events were pooled using random-effects meta-analysis models with Hedges' g bias-corrected standardized mean differences (g) and rate ratios (RR) with 95% confidence intervals (CI). Bias evaluation followed PRISMA and Cochrane guidelines. Eighteen studies were identified, which suggested that psychedelic therapies were well tolerated and presented a large effect size for the management of depression symptoms in a transdiagnostic population with psilocybin (g = -1.92, 95% CI, -2.73 to -1.11) and MDMA (g = -0.71; 95% CI, -1.39 to -0.03). These are promising results that complement the current literature. However, evidence certainty was low to very low due to methodological limitations, small sample size, blinding, study heterogeneity, and publication bias. These results also highlight the need for more adequately powered studies exploring these novel therapies.

Beyond the 5-HT2A Receptor: Classic and Nonclassic Targets in Psychedelic Drug Action

Serotonergic psychedelics, such as psilocybin and LSD, have garnered significant attention in recent years for their potential therapeutic effects and unique mechanisms of action. These compounds exert their primary effects through activating serotonin 5-HT2A receptors, found predominantly in cortical regions. By interacting with these receptors, serotonergic psychedelics induce alterations in perception, cognition, and emotions, leading to the characteristic psychedelic experience. One of the most crucial aspects of serotonergic psychedelics is their ability to promote neuroplasticity, the formation of new neural connections, and rewire neuronal networks. This neuroplasticity is believed to underlie their therapeutic potential for various mental health conditions, including depression, anxiety, and substance use disorders. In this mini-review, we will discuss how the 5-HT2A receptor activation is just one facet of the complex mechanisms of action of serotonergic psychedelics. They also interact with other serotonin receptor subtypes, such as 5-HT1A and 5-HT2C receptors, and with neurotrophin receptors (e.g., tropomyosin receptor kinase B). These interactions contribute to the complexity of their effects on perception, mood, and cognition. Moreover, as psychedelic research advances, there is an increasing interest in developing nonhallucinogenic derivatives of these drugs to create safer and more targeted medications for psychiatric disorders by removing the hallucinogenic properties while retaining the potential therapeutic benefits. These nonhallucinogenic derivatives would offer patients therapeutic advantages without the intense psychedelic experience, potentially reducing the risks of adverse reactions. Finally, we discuss the potential of psychedelics as substrates for post-translational modification of proteins as part of their mechanism of action.

The potential of psychedelics for the treatment of Alzheimer's disease and related dementias

Alzheimer's Disease (AD) is a currently incurable but increasingly prevalent fatal and progressive neurodegenerative disease, demanding consideration of therapeutically relevant natural products and their synthetic analogues. This paper reviews evidence for effectiveness of natural and synthetic psychedelics in the treatment of AD causes and symptoms. The plastogenic effects of serotonergic psychedelics illustrate that they have efficacy for addressing multiple facets of AD pathology. We review findings illustrating neuroplasticity mechanisms of classic (serotonergic) and non-classic psychedelics that indicate their potential as treatments for AD and related dementias. Classic psychedelics modulate glutamatergic neurotransmission and stimulate synaptic and network remodeling that facilitates synaptic, structural and behavioral plasticity. Up-regulation of neurotrophic factors enable psychedelics to promote neuronal survival and glutamate-driven neuroplasticity. Muscimol modulation of GABAAR reduces Aβ-induced neurotoxicity and psychedelic Sig-1R agonists provide protective roles in Aβ toxicity. Classic psychedelics also activate mTOR intracellular effector pathways in brain regions that show atrophy in AD. The potential of psychedelics to treat AD involves their ability to induce structural and functional neural plasticity in brain circuits and slow or reverse brain atrophy. Psychedelics stimulate neurotrophic pathways, increase neurogenesis and produce long-lasting neural changes through rewiring pathological neurocircuitry. Psychedelic effects on 5-HT receptor target genes and induction of synaptic, structural, and functional changes in neurons and networks enable them to promote and enhance brain functional connectivity and address diverse mechanisms underlying degenerative neurological disorders. These findings provide a rationale for immediate investigation of psychedelics as treatments for AD patients.

Psilocybin-assisted therapy for depression: A systematic review and meta-analysis

The aim of this review was to determine the effect of psilocybin on depressive symptoms in patients diagnosed with life-threatening illnesses or major depressive disorder. Systematic searches were conducted to search for randomized clinical trials and open-label trials that evaluated depression symptoms after psilocybin therapy. Data was pooled using a random-effects model. The primary outcome was the standardized mean difference (SMD) in depression severity, determined by calculating the change in depression ratings from baseline to the primary endpoint in the psilocybin arm versus the control arm. The literature search yielded 1734 studies, and 13 studies (n = 686) were included in either qualitative and/or quantitative analyses. The meta-analysis included 9 studies (pooled n = 596) and yielded a large effect size in favour of psilocybin (SMD = -0.78; p<0.001). Risk ratios for response and remission were large and significant in favour of psilocybin. A review of open-label trials showed robust decreases in depressive symptoms following psilocybin administration. These findings provide preliminary evidence for antidepressant efficacy with psilocybin-assisted psychotherapy, however, further studies are needed to evaluate safety and efficacy and to optimize treatment protocols.

A Comprehensive Review of the Current Status of the Cellular Neurobiology of Psychedelics

Psychedelic substances have gained significant attention in recent years for their potential therapeutic effects on various psychiatric disorders. This review delves into the intricate cellular neurobiology of psychedelics, emphasizing their potential therapeutic applications in addressing the global burden of mental illness. It focuses on contemporary research into the pharmacological and molecular mechanisms underlying these substances, particularly the role of 5-HT2A receptor signaling and the promotion of plasticity through the TrkB-BDNF pathway. The review also discusses how psychedelics affect various receptors and pathways and explores their potential as anti-inflammatory agents. Overall, this research represents a significant development in biomedical sciences with the potential to transform mental health treatments.

Synthetic Strategies toward Lysergic Acid Diethylamide: Ergoline Synthesis via α-Arylation, Borrowing Hydrogen Alkylation, and C-H Insertion

Lysergic acid diethylamide (LSD), a semisynthetic ergoline alkaloid analogue and hallucinogen, is a potent psychoplastogen with promising therapeutic potential. While a variety of synthetic strategies for accessing ergoline alkaloids have emerged, the complexity of the tetracyclic ring system results in distinct challenges in preparing analogues with novel substitution patterns. Methods of modulating the hallucinogenic activity of LSD by functionalization at previously inaccessible positions are of continued interest, and efficient syntheses of the ergoline scaffold are integral toward this purpose. Here, we report novel C-C bond forming strategies for preparing the ergoline tetracyclic core, focusing on the relatively unexplored strategy of bridging the B- and D-ring systems last. Following cross-coupling to first join the A- and D-rings, we explored a variety of methods for establishing the C-ring, including intramolecular α-arylation, borrowing hydrogen alkylation, and rhodium-catalyzed C-H insertion. Our results led to a seven-step formal synthesis of LSD and the first methods for readily introducing substitution on the C-ring. These strategies are efficient for forming ergoline-like tetracyclic compounds and analogues, though they each face unique challenges associated with elaboration to ergoline natural products. Taken together, these studies provide important insights that will guide future synthetic strategies toward ergolines.

Bedside to bench: the outlook for psychedelic research

There has recently been a resurgence of interest in psychedelic compounds based on studies demonstrating their potential therapeutic applications in treating post-traumatic stress disorder, substance abuse disorders, and treatment-resistant depression. Despite promising efficacy observed in some clinical trials, the full range of biological effects and mechanism(s) of action of these compounds have yet to be fully established. Indeed, most studies to date have focused on assessing the psychological mechanisms of psychedelics, often neglecting the non-psychological modes of action. However, it is important to understand that psychedelics may mediate their therapeutic effects through multi-faceted mechanisms, such as the modulation of brain network activity, neuronal plasticity, neuroendocrine function, glial cell regulation, epigenetic processes, and the gut-brain axis. This review provides a framework supporting the implementation of a multi-faceted approach, incorporating in silico, in vitro and in vivo modeling, to aid in the comprehensive understanding of the physiological effects of psychedelics and their potential for clinical application beyond the treatment of psychiatric disorders. We also provide an overview of the literature supporting the potential utility of psychedelics for the treatment of brain injury (e.g., stroke and traumatic brain injury), neurodegenerative diseases (e.g., Parkinson's and Alzheimer's diseases), and gut-brain axis dysfunction associated with psychiatric disorders (e.g., generalized anxiety disorder and major depressive disorder). To move the field forward, we outline advantageous experimental frameworks to explore these and other novel applications for psychedelics.

Neuroplasticity: The Continuum of Change

Neuroplasticity is a term that is increasingly permeating mainstream discourse and being used by the popular press to simplify descriptions of how the brain changes in response to stimuli such as exercise, sleep, food, drugs of abuse, and medicines, among others. However, it is a complex, multifaceted concept representing a continuum connecting molecular, cellular, and circuit-level changes and their effects on human behavior. In this Viewpoint, we examine neuroplasticity from several perspectives to construct a holistic view of this ambiguous term. By engaging experts across various scientific disciplines, we attempt to provide an easy entry point to the concept of neuroplasticity for readers of ACS Chemical Neuroscience. By highlighting how neuroplasticity changes in both health and disease, we demonstrate that the concept is applicable to both adaptive and maladaptive responses to stimuli, underscoring its significance in chemical neuroscience.

Dendritogenic Potential of the Ethanol Extract from Lippia alba Leaves in Rat Cortical Neurons

A reduced dendritic complexity, especially in regions such as the hippocampus and the prefrontal cortex, has been linked to the pathophysiology of some neuropsychiatric disorders, in which synaptic plasticity and functions such as emotional and cognitive processing are compromised. For this reason, the identification of new therapeutic strategies would be enriched by the search for metabolites that promote structural plasticity. The present study evaluated the dendritogenic potential of the ethanol extract of Lippia alba, an aromatic plant rich in flavonoids and terpenes, which has been widely used in traditional medicine for its presumed analgesic, anxiolytic, and antidepressant potential. An in vitro model of rat cortical neurons was used to determine the kinetics of the plant's effect at different time intervals. Changes in morphological parameters of the neurons were determined, as well as the dendritic complexity, by Sholl analysis. The extract promotes the outgrowth of dendritic branching in a rapid and sustained fashion, without being cytotoxic to the cells. We found that this effect could be mediated by the phosphatidylinositol 3-kinase pathway, which is involved in mechanisms of neuronal plasticity, differentiation, and survival. The evidence presented in this study provides a basis for further research that, through in vivo models, can delve into the plant's therapeutic potential.

Psychoplastogens: A Novel Therapeutic Approach for Neurological Diseases and Disorders

Neurological diseases often involve changes in synaptic connectivity and plasticity. Psychoplastogens, substances that stimulate neuronal growth and enhance neural structures, show promise in mitigating these changes. They activate key biological targets, including AMPA receptors, TrkB, and mTOR. Substances like ketamine, scopolamine, N,N-dimethyltryptamine, and rapastinel have psychoplastogenic properties. In clinical trials, psychedelic psychoplastogens have demonstrated antidepressant, anxiolytic, and anti-addictive effects. The research described in this Patent Highlight suggests the potential for novel therapies in neurological disorders that leverage psychoplastogens, which modulate synaptic connections and plasticity.

Molecular and structural insights into the 5-HT2C receptor as a therapeutic target for substance use disorders

Substance use disorder (SUD) is a chronic condition, with maintained abuse of a substance leading to physiological and psychological alterations and often changes in cognitive and social behaviours. Current therapies include psychotherapy coupled with medication; however, high relapse rates reveal the shortcomings of these therapies. The signalling, expression profile, and neurological function of the serotonin 2C receptor (5-HT2C receptor) make it a candidate of interest for the treatment of SUD. Recently, psychedelics, which broadly act at 5-HT2 receptors, have indicated potential for the treatment of SUD, implicating the 5-HT2C receptor. The modern psychedelic movement has rekindled interest in the 5-HT2C receptor, resulting in many new studies, especially structural analyses. This review explores the structural, molecular and cellular mechanisms governing 5-HT2C receptor function in the context of SUD. This provides the basis of the preclinical and clinical evidence for their role in SUD and highlights the potential for future exploration.

Open-label study of consecutive ibogaine and 5-MeO-DMT assisted-therapy for trauma-exposed male Special Operations Forces Veterans: prospective data from a clinical program in Mexico

Background: Research in psychedelic medicine has focused primarily on civilian populations. Further study is needed to understand whether these treatments are effective for Veteran populations.Objectives: Here, we examine the effectiveness of psychedelic-assisted therapy among trauma-exposed Special Operations Forces Veterans (SOFV) seeking treatment for cognitive and mental health problems in Mexico.Methods: Data were collected from an ibogaine and 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT) clinical treatment program for SOFV with a history of trauma exposure. This clinical program collects prospective clinical program evaluation data, such as background characteristics, symptom severity, functioning (e.g., satisfaction with life, posttraumatic stress disorder symptoms, depression symptoms, anxiety symptoms, sleep disturbance, psychological flexibility, disability in functioning, cognitive functioning, neurobehavioral symptoms, anger, suicidal ideation), and substance persisting/enduring effects through online surveys at four timepoints (baseline/pre-treatment, one-, three-, and six-months after treatment).Results: The majority of the sample (n = 86; Mean Age = 42.88, SD = 7.88) were Caucasian (87.2%), non-Hispanic (89.5%), and males (100%). There were significant and large improvements in self-reported PTSD symptoms (p < .001, d = .414), depression (p < .001, d = .275), anxiety (p < .001, d = .276), insomnia severity (p < .001, d = .351), and post-concussive symptoms (p < .001, d = .389) as well as self-reported satisfaction with life (p < .001, d = .371), psychological flexibility (p < .001, d = .313) and cognitive functioning (p < .001, d = .265) from baseline to one-month follow-up.Conclusions: Data suggest combined ibogaine and 5-MeO-DMT assisted therapy has potential to provide rapid and robust changes in mental health functioning with a signal of durable therapeutic effects up to 6-months. Future research in controlled settings is warranted.

Psychedelics, With a Focus on Psilocybin: Issues for the Clinician

There has been a burgeoning interest in psychedelics among the public, state legislatures, psychiatrists and other clinical providers, and within the research community. Increasing numbers of studies evaluating psychedelics for depression, anxiety, posttraumatic stress disorder, and substance use disorders have been conducted or are underway. While discussing psychedelics in general, the focus of this paper is on psilocybin and its mechanism, how it exerts a psychedelic effect, dosing, and a review of the treatment studies of psilocybin, which were primarily for treatment-resistant depression and cancer-related anxiety. Future directions and potential limitations of studying and regulating psilocybin and other psychedelics are also discussed.

Discovery of Novel Oleamide Analogues as Brain-Penetrant Positive Allosteric Serotonin 5-HT2C Receptor and Dual 5-HT2C/5-HT2A Receptor Modulators

The serotonin 5-HT2A receptor (5-HT2AR) and 5-HT2CR localize to the brain and share overlapping signal transduction facets that contribute to their roles in cognition, mood, learning, and memory. Achieving selective targeting of these receptors is challenged by the similarity in their 5-HT orthosteric binding pockets. A fragment-based discovery approach was employed to design and synthesize novel oleamide analogues as selective 5-HT2CR or dual 5-HT2CR/5-HT2AR positive allosteric modulators (PAMs). Compound 13 (JPC0323) exhibited on-target properties, acceptable plasma exposure and brain penetration, as well as negligible displacement to orthosteric sites of ∼50 GPCRs and transporters. Furthermore, compound 13 suppressed novelty-induced locomotor activity in a 5-HT2CR-dependent manner, suggesting 5-HT2CR PAM, but not 5-HT2AR, activity at the level of the whole organism at the employed doses of 13. We discovered new selective 5-HT2CR PAMs and first-in-class 5-HT2CR/5-HT2AR dual PAMs that broaden the pharmacological toolbox to explore the biology of these vital receptors.

5-HT2AR and NMDAR psychedelics induce similar hyper-synchronous states in the rat cognitive-limbic cortex-basal ganglia system

The profound changes in perception and cognition induced by psychedelic drugs are thought to act on several levels, including increased glutamatergic activity, altered functional connectivity and an aberrant increase in high-frequency oscillations. To bridge these different levels of observation, we have here performed large-scale multi-structure recordings in freely behaving rats treated with 5-HT2AR psychedelics (LSD, DOI) and NMDAR psychedelics (ketamine, PCP). While interneurons and principal cells showed disparate firing rate modulations for the two classes of psychedelics, the local field potentials revealed a shared pattern of synchronized high-frequency oscillations in the ventral striatum and several cortical areas. Remarkably, the phase differences between structures were close to zero, corresponding to <1 ms delays. Likely, this hypersynchrony has major effects on the integration of information across neuronal systems and we propose that it is a key contributor to changes in perception and cognition during psychedelic drug use. Potentially, similar mechanisms could induce hallucinations and delusions in psychotic disorders and would constitute promising targets for new antipsychotic treatments.

In vivo mapping of pharmacologically induced functional reorganization onto the human brain's neurotransmitter landscape

To understand how pharmacological interventions can exert their powerful effects on brain function, we need to understand how they engage the brain's rich neurotransmitter landscape. Here, we bridge microscale molecular chemoarchitecture and pharmacologically induced macroscale functional reorganization, by relating the regional distribution of 19 neurotransmitter receptors and transporters obtained from positron emission tomography, and the regional changes in functional magnetic resonance imaging connectivity induced by 10 different mind-altering drugs: propofol, sevoflurane, ketamine, lysergic acid diethylamide (LSD), psilocybin, N,N-Dimethyltryptamine (DMT), ayahuasca, 3,4-methylenedioxymethamphetamine (MDMA), modafinil, and methylphenidate. Our results reveal a many-to-many mapping between psychoactive drugs' effects on brain function and multiple neurotransmitter systems. The effects of both anesthetics and psychedelics on brain function are organized along hierarchical gradients of brain structure and function. Last, we show that regional co-susceptibility to pharmacological interventions recapitulates co-susceptibility to disorder-induced structural alterations. Collectively, these results highlight rich statistical patterns relating molecular chemoarchitecture and drug-induced reorganization of the brain's functional architecture.

Psychedelics promote plasticity by directly binding to BDNF receptor TrkB

Psychedelics produce fast and persistent antidepressant effects and induce neuroplasticity resembling the effects of clinically approved antidepressants. We recently reported that pharmacologically diverse antidepressants, including fluoxetine and ketamine, act by binding to TrkB, the receptor for BDNF. Here we show that lysergic acid diethylamide (LSD) and psilocin directly bind to TrkB with affinities 1,000-fold higher than those for other antidepressants, and that psychedelics and antidepressants bind to distinct but partially overlapping sites within the transmembrane domain of TrkB dimers. The effects of psychedelics on neurotrophic signaling, plasticity and antidepressant-like behavior in mice depend on TrkB binding and promotion of endogenous BDNF signaling but are independent of serotonin 2A receptor (5-HT2A) activation, whereas LSD-induced head twitching is dependent on 5-HT2A and independent of TrkB binding. Our data confirm TrkB as a common primary target for antidepressants and suggest that high-affinity TrkB positive allosteric modulators lacking 5-HT2A activity may retain the antidepressant potential of psychedelics without hallucinogenic effects.

Tabernanthalog Reduces Motivation for Heroin and Alcohol in a Polydrug Use Model

Background

The potential use of psychedelic drugs as therapeutics for neuropsychiatric disorders has been limited by their hallucinogenic properties. To overcome this limitation, we developed and characterized tabernanthalog (TBG), a novel analogue of the indole alkaloids ibogaine and 5-methoxy-N,N-dimethyltryptamine with reduced cardiac arrhythmogenic risk and a lack of classical psychedelic drugs-induced sensory alterations. We previously demonstrated that TBG has therapeutic efficacy in a preclinical model of opioid use disorder (OUD) in rats and in a binge model of alcohol drinking in mice. Alcohol is commonly co-used in ∼35-50% of individuals with OUD, and yet, preclinical models that recapitulate this comorbidity are lacking.

Methodology

Here we employed a polydrug model of heroin and alcohol couse to screen the therapeutic efficacy of TBG on metrics of both opioid and alcohol seeking. We first exposed rats to alcohol (or control sucrose-fade solution) in the home-cage (HC), using a two-bottle binge protocol, over a period of 1 month. Rats were then split into two groups that underwent self-administration training for either intravenous heroin or oral alcohol, so that we could assess the impact of HC alcohol exposure on the self-administration of each substance separately. Thereafter, rats began self-administering both heroin and alcohol in the same sessions. Finally, we tested the effects of TBG on break points for heroin and alcohol in a progressive ratio test, where the number of lever presses required to obtain a single reward increased exponentially.

Results and Conclusion

TBG effectively reduced motivation for heroin and alcohol in this test, indicating its efficacy is preserved in animals with a history of heroin and alcohol polydrug use.

Alleviating anxiety and taming trauma: Novel pharmacotherapeutics for anxiety disorders and posttraumatic stress disorder

Psychiatric disorders associated with psychological trauma, stress and anxiety are a highly prevalent and increasing cause of morbidity worldwide. Current therapeutic approaches, including medication, are effective in alleviating symptoms of anxiety disorders and posttraumatic stress disorder (PTSD), at least in some individuals, but have unwanted side-effects and do not resolve underlying pathophysiology. After a period of stagnation, there is renewed enthusiasm from public, academic and commercial parties in designing and developing drug treatments for these disorders. Here, we aim to provide a snapshot of the current state of this field that is written for neuropharmacologists, but also practicing clinicians and the interested lay-reader. After introducing currently available drug treatments, we summarize recent/ongoing clinical assessment of novel medicines for anxiety and PTSD, grouped according to primary neurochemical targets and their potential to produce acute and/or enduring therapeutic effects. The evaluation of putative treatments targeting monoamine (including psychedelics), GABA, glutamate, cannabinoid, cholinergic and neuropeptide systems, amongst others, are discussed. We emphasize the importance of designing and clinically assessing new medications based on a firm understanding of the underlying neurobiology stemming from the rapid advances being made in neuroscience. This includes harnessing neuroplasticity to bring about lasting beneficial changes in the brain rather than - as many current medications do - produce a transient attenuation of symptoms, as exemplified by combining psychotropic/cognitive enhancing drugs with psychotherapeutic approaches. We conclude by noting some of the other emerging trends in this promising new phase of drug development.

Canalization and plasticity in psychopathology

This theoretical article revives a classical bridging construct, canalization, to describe a new model of a general factor of psychopathology. To achieve this, we have distinguished between two types of plasticity, an early one that we call 'TEMP' for 'Temperature or Entropy Mediated Plasticity', and another, we call 'canalization', which is close to Hebbian plasticity. These two forms of plasticity can be most easily distinguished by their relationship to 'precision' or inverse variance; TEMP relates to increased model variance or decreased precision, whereas the opposite is true for canalization. TEMP also subsumes increased learning rate, (Ising) temperature and entropy. Dictionary definitions of 'plasticity' describe it as the property of being easily shaped or molded; TEMP is the better match for this. Importantly, we propose that 'pathological' phenotypes develop via mechanisms of canalization or increased model precision, as a defensive response to adversity and associated distress or dysphoria. Our model states that canalization entrenches in psychopathology, narrowing the phenotypic state-space as the agent develops expertise in their pathology. We suggest that TEMP - combined with gently guiding psychological support - can counter canalization. We address questions of whether and when canalization is adaptive versus maladaptive, furnish our model with references to basic and human neuroscience, and offer concrete experiments and measures to test its main hypotheses and implications. This article is part of the Special Issue on "National Institutes of Health Psilocybin Research Speaker Series".

The Potential of Flavonoids and Flavonoid Metabolites in the Treatment of Neurodegenerative Pathology in Disorders of Cognitive Decline

Flavonoids are a biodiverse family of dietary compounds that have antioxidant, anti-inflammatory, antiviral, and antibacterial cell protective profiles. They have received considerable attention as potential therapeutic agents in biomedicine and have been widely used in traditional complimentary medicine for generations. Such complimentary medical herbal formulations are extremely complex mixtures of many pharmacologically active compounds that provide a therapeutic outcome through a network pharmacological effects of considerable complexity. Methods are emerging to determine the active components used in complimentary medicine and their therapeutic targets and to decipher the complexities of how network pharmacology provides such therapeutic effects. The gut microbiome has important roles to play in the generation of bioactive flavonoid metabolites retaining or exceeding the antioxidative and anti-inflammatory properties of the intact flavonoid and, in some cases, new antitumor and antineurodegenerative bioactivities. Certain food items have been identified with high prebiotic profiles suggesting that neutraceutical supplementation may be beneficially employed to preserve a healthy population of bacterial symbiont species and minimize the establishment of harmful pathogenic organisms. Gut health is an important consideration effecting the overall health and wellbeing of linked organ systems. Bioconversion of dietary flavonoid components in the gut generates therapeutic metabolites that can also be transported by the vagus nerve and systemic circulation to brain cell populations to exert a beneficial effect. This is particularly important in a number of neurological disorders (autism, bipolar disorder, AD, PD) characterized by effects on moods, resulting in depression and anxiety, impaired motor function, and long-term cognitive decline. Native flavonoids have many beneficial properties in the alleviation of inflammation in tissues, however, concerns have been raised that therapeutic levels of flavonoids may not be achieved, thus allowing them to display optimal therapeutic effects. Dietary manipulation and vagal stimulation have both yielded beneficial responses in the treatment of autism spectrum disorders, depression, and anxiety, establishing the vagal nerve as a route of communication in the gut-brain axis with established roles in disease intervention. While a number of native flavonoids are beneficial in the treatment of neurological disorders and are known to penetrate the blood–brain barrier, microbiome-generated flavonoid metabolites (e.g., protocatechuic acid, urolithins, γ-valerolactones), which retain the antioxidant and anti-inflammatory potency of the native flavonoid in addition to bioactive properties that promote mitochondrial health and cerebrovascular microcapillary function, should also be considered as potential biotherapeutic agents. Studies are warranted to experimentally examine the efficacy of flavonoid metabolites directly, as they emerge as novel therapeutic options.

Developmental Neurotoxicity Screen of Psychedelics and Other Drugs of Abuse in Larval Zebrafish (Danio rerio)

In recent years, psychedelics have garnered significant interest as therapeutic agents for treating diverse neuropsychiatric disorders. However, the potential for these compounds to produce developmental neurotoxicity has not been rigorously assessed, and much of the available safety data is based on epidemiological studies with limited experimental testing in laboratory animal models. Moreover, the experimental safety data available thus far have focused on adult organisms, and the few studies conducted using developing organisms have tested a limited number of compounds, precluding direct comparisons between various chemical scaffolds. In the present study, 13 psychoactive compounds of different chemical or pharmacological classes were screened in a larval zebrafish model for teratological and behavioral abnormalities following acute and chronic developmental exposures. We found that the psychedelic tryptamines and ketamine were less neurotoxic to larval zebrafish than LSD and psychostimulants. Our work, which leverages the advantage of using zebrafish for higher throughput toxicity screening, provides a robust reference database for comparing the neurotoxicity profiles of novel psychedelics currently under development for therapeutic applications.

Can psychedelics enhance group psychotherapy? A discussion on the therapeutic factors

BACKGROUND

Despite the growth of psychedelic research, psychedelic-assisted group psychotherapy (PAGP) has received little attention in comparison to individual psychedelic-assisted psychotherapy models.

METHODS

In this article, we aim to discuss the therapeutic potential of PAGP, as well as outline existing models and the challenges of this approach. Using Irvin Yalom's 11 therapeutic factors of group therapy as a basic framework, we analyse current literature from clinical studies and neurobiological research relative to the topic of PAGP.

RESULTS

We argue that combining psychedelic substances and group psychotherapy may prove beneficial for increasing group connectedness and interpersonal learning, potentially enhancing prosocial behaviour with direct opportunities to practice newly acquired knowledge about previously maladaptive behavioural patterns. Challenges regarding this approach include a more rigid therapy structure and potential loss of openness from patients, which may be ameliorated by adequate therapeutic training.

CONCLUSION

We hope for this article to support clinical research on PAGP by presenting a therapeutic framework and outlining its mechanisms and challenges.

Psychedelics promote neuroplasticity through the activation of intracellular 5-HT2A receptors

Decreased dendritic spine density in the cortex is a hallmark of several neuropsychiatric diseases, and the ability to promote cortical neuron growth has been hypothesized to underlie the rapid and sustained therapeutic effects of psychedelics. Activation of 5-hydroxytryptamine (serotonin) 2A receptors (5-HT2ARs) is essential for psychedelic-induced cortical plasticity, but it is currently unclear why some 5-HT2AR agonists promote neuroplasticity, whereas others do not. We used molecular and genetic tools to demonstrate that intracellular 5-HT2ARs mediate the plasticity-promoting properties of psychedelics; these results explain why serotonin does not engage similar plasticity mechanisms. This work emphasizes the role of location bias in 5-HT2AR signaling, identifies intracellular 5-HT2ARs as a therapeutic target, and raises the intriguing possibility that serotonin might not be the endogenous ligand for intracellular 5-HT2ARs in the cortex.

New and emerging approaches to treat psychiatric disorders

Psychiatric disorders are highly prevalent, often devastating diseases that negatively impact the lives of millions of people worldwide. Although their etiological and diagnostic heterogeneity has long challenged drug discovery, an emerging circuit-based understanding of psychiatric illness is offering an important alternative to the current reliance on trial and error, both in the development and in the clinical application of treatments. Here we review new and emerging treatment approaches, with a particular emphasis on the revolutionary potential of brain-circuit-based interventions for precision psychiatry. Limitations of circuit models, challenges of bringing precision therapeutics to market and the crucial advances needed to overcome these obstacles are presented.