Toward a typology of hallucinogen users in the United States

BACKGROUND

Roughly one in ten American adults have used hallucinogens, and emerging evidence suggests that the prevalence of use is increasing. However, our understanding of the degree to which individuals "specialize" in the use of a particular hallucinogen or are poly-hallucinogen users remains incomplete.

METHODS

This study examined data from 6381 individuals reporting past-year hallucinogen use in the 2016-2018 National Survey on Drug Use and Health. Logistic regression examined the association between the number of distinct hallucinogens used and psychosocial/behavioral risks, and latent class analysis (LCA) characterized subgroups of hallucinogen users.

RESULTS

The vast majority of hallucinogen users, roughly 70%, are not "specialists" who use only one hallucinogen type; rather, lifetime poly-hallucinogen use is the norm. Critically, however, we also see that important differences exist within the population of hallucinogen users-half (51%) could be classified as LSD-Mushroom-Ecstasy users only (this group was disproportionally comprised of youth), nearly one third (30%) were Poly-Hallucinogen users (this group was disproportionately male and non-Hispanic White), and smaller proportions were limited primarily to use of LSD-Mushrooms (6%; these individuals were almost exclusively ages 35 and older) or Ecstasy Only (12%; these individuals were mostly younger adults ages 18-34).

CONCLUSIONS

Findings provide a fresh contribution to our understanding of poly-hallucinogen use in a time in which local and state governmental leaders, and people across the country, weigh the benefits and drawbacks of legalizing specific hallucinogenic drugs.

A systems omics-based approach to decode substance use disorders and neuroadaptations

Substance use disorders (SUDs) are a group of neuropsychiatric conditions manifesting due to excessive dependence on potential drugs of abuse such as psychostimulants, opioids including prescription opioids, alcohol, inhalants, etc. Experimental studies have generated enormous data in the area of SUDs, but outcomes from such data have remained largely fragmented. In this review, we attempt to coalesce these data points providing an important first step towards our understanding of the etiology of SUDs. We propose and describe a 'core addictome' pathway that behaves central to all SUDs. Besides, we also have made some notable observations paving way for several hypotheses; MECP2 behaves as a master switch during substance use; five distinct gene clusters were identified based on respective substance addiction; a central cluster of genes serves as a hub of the addiction pathway connecting all other substance addiction clusters. In addition to describing these findings, we have emphasized the importance of some candidate genes that are of substantial interest for further investigation and serve as high-value targets for translational efforts.

Driving while under the influence of hallucinogens: Prevalence, correlates, and risk profiles

BACKGROUND

Hallucinogen use is rising in the US, yet little is known regarding the prevalence and psychosocial/behavioral correlates of driving under the influence of these drugs.

METHODS

This study examined data from 4447 individuals ages 16-64 who reported past-year hallucinogen use in the 2016-2018 National Survey on Drug Use and Health. Prevalence estimates (with 95% confidence intervals [CIs]) were calculated for driving under the influence of hallucinogens (DUIH). Logistic regression examined psychosocial/behavioral correlates of DUIH, and latent class analysis (LCA) characterized subgroups of individuals reporting DUIH.

RESULTS

The prevalence of past-year hallucinogen use was 2.42% (CI = 2.30-2.54) and, in the general population, the prevalence of DUIH was 0.21%. Among past-year hallucinogen users, 8.94% (CI = 7.74-10.31) reported DUIH on at least one occasion over the previous 12 months. The probability of DUIH increased significantly with more frequent use. Compared to individuals who used hallucinogens and did not report DUIH, individuals reporting DUIH were significantly more likely to report mental health problems; use of other illicit drugs; selling drugs; a past-year arrest; or driving under the influence of alcohol, cannabis, or other illicit drugs. LCA identified three classes of individuals reporting DUIH, characterized by: use of and driving under the influence of cannabis; use of and driving under the influence of cannabis and other illicit drugs; and mental health concerns.

CONCLUSIONS

Nearly one in ten individuals who report using hallucinogens also report driving under the influence of hallucinogens-drugs that affect perception and risk-taking, with alarming implications for driving safety.

United States National Institutes of Health grant funding for psychedelic-assisted therapy clinical trials from 2006-2020

BACKGROUND

Medicine is currently experiencing a "psychedelic renaissance", said by many to have commenced in 2006. Since then, clinical trials have consistently demonstrated promising findings for psychedelic-assisted therapies in the treatment of various mental health conditions and addictions. While most of this work has been privately funded, governmental biomedical research funding bodies in countries such as Australia, Canada, Israel, New Zealand, and the United Kingdom have begun supporting it. Given that the United States National Institutes of Health (NIH) is the largest public funder of biomedical research in the world, it is important to understand the degree to which the organization is supporting clinical trials of psychedelic-assisted therapies. We are unaware of existing literature quantifying direct NIH grant support for psychedelic-assisted therapy clinical trials, so we sought to answer this important question by searching all NIH grants awarded since the beginning of the psychedelic renaissance.

METHODS

We queried NIH RePORTER, NIH's grant database, for grants awarded from 2006-2020 mentioning the psychedelics 3,4-Methylenedioxymethamphetamine (MDMA), 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT), ayahuasca, dimethyltryptamine (DMT), ibogaine, lysergic acid (LSD), mescaline, peyote, and psilocybin. We manually reviewed resulting grants to determine whether they directly funded psychedelic-assisted therapy clinical trials.

RESULTS

We identified zero NIH grants directly funding psychedelic-assisted therapy clinical trials during the study period.

CONCLUSION

While governmental biomedical research funding bodies in other countries have begun funding clinical trials of psychedelic-assisted therapies during the psychedelic renaissance, NIH has yet to directly fund a single psychedelic-assisted therapy clinical trial. Concerns about risks related to psychedelics, a federal law preventing promotion of legalization of Schedule 1 drugs, and prioritization of grants for other types of studies on psychedelics may explain the dearth of NIH funding for psychedelic-assisted therapy clinical trials.

Psychedelic Knowledge and Opinions in Psychiatrists at Two Professional Conferences: An Exploratory Survey

Despite resurgent interest in psychedelic-assisted therapy, our insights into psychiatrists' knowledge and opinions about medicinal psychedelic applications are surprisingly narrow. Therefore, we anonymously surveyed psychiatrists attending psychedelic didactic presentations at two national meetings about these issues using a 26-item questionnaire. Response rate was 40.20% (106/264). Respondents were 41.73 ± 13.31 years old (range: 24-80) and 64.42% were male. They largely believed psychedelics show treatment promise and strongly supported federal funding for medicinal psychedelic research. The most common concerns were the lack of trained psychedelic-assisted therapy providers, the logistics of psychedelic-assisted therapy delivery, the administration of psychedelics for patients with contraindications, and diversion. The most desired psychedelic-related educational topics were potential benefits of psychedelic-assisted therapy, how to conduct psychedelic-assisted therapy, psychedelic pharmacology, and psychedelic side effects. Factors associated with increased belief in psychedelics' treatment potential included working primarily in research, scoring higher on a psychedelic knowledge test, and reporting less concern about psychedelics' addictive potential. Working primarily in research and consult-liaison psychiatry fellowship training were positively associated with support for medicinal psychedelic legalization, while increased concerns about addictive potential and attending psychiatrist status were negatively associated. Support for legalization of non-medicinal psychedelic use was negatively associated with age and positively associated with support for legalization of medicinal psychedelic use.

Use of hallucinogens in Slovakia: Does it differ from global trends?

BACKGROUND

People have been using hallucinogens for thousands of years and interest in these substances has grown in recent years. The aim of this study was to determine the basic socio-demographic data, preferences, experiences, and attitudes associated with hallucinogen use in Slovakia.

METHODS

A cross-sectional research design was used whereby an online survey included participants who had had at least one experience with hallucinogens (N = 422, age M = 27.78; SD = 7.84; SE = 0.38; 35.1% females). Due to the illegal, intimate, and minority nature of the phenomena studied, data was collected using the snowball sampling method via an online social network in groups that declared a drug focus.

RESULTS

Users of hallucinogens were mostly employed (61,8%) and in some form of partnership (57,6%); they usually have a high school diploma (46,68%) or a university degree (45,41%). They most often use psilocybin mushrooms, while the age of initial use (M = 19,61; SD = 5,39) as well as lifetime frequency use (M = 18,26; SD =  24,21; Median =  10) are similar to global trends. Free use without rituals was preferred to ceremonial use. In general, our sample of hallucinogen users considered the integration of psychedelic experiences to be simple rather than challenging. Concurrently, they tended to see hallucinogens as useful to humans, but realised that they are not without risk and can be somewhat dangerous. Males used hallucinogens for the first time at a younger age (p < .05, r = -.12), used more hallucinogens during their lifetime (p <.001, r = -.23), and demanded decriminalisation and legalisation more (p <.01, r = -.13) than females.

CONCLUSION

Slovak users of hallucinogens in our sample showed similar usage trends as users abroad. Even though both males and females perceive and evaluate hallucinogens very similarly, females are significantly more careful in using these substances.

Ayahuasca, an ancient substance with traditional and contemporary use in neuropsychiatry and neuroscience

Ayahuasca is a botanical hallucinogenic preparation traditionally used for ritual and therapeutic purposes by native populations of the Northwestern Amazon. In the last decades, ayahuasca use has spread to Europe, the United States, Asia, and Africa, and interest in the possible therapeutic uses of ayahuasca for treating anxiety and mood disorder and substance-use disorders has increased both among the general public and the scientific community. Indeed, preclinical, observational, and preliminary clinical studies have corroborated some of these findings. In the present article, we present an overview of these studies and highlight the current uses of ayahuasca in neuroscience, such as a tool in the investigation of the neural basis of introspection and other complex cognitive processes.

Toxicology of Psychoactive Substances

A trend in the increasing use of prescription psychoactive drugs (PADs), including antidepressants, antipsychotics, and mood stabilizers, has been reported in the United States and globally. In addition, there has been an increase in the production and usage of illicit PADs and emergence of new psychoactive substances (NPSs) all over the world. PADs pose unique challenges for critical care providers who may encounter toxicology issues due to drug interactions, side effects, or drug overdoses. This article provides a summary of the toxicologic features of commonly used and abused PADs: antidepressants, antipsychotics, mood stabilizers, hallucinogens, NPSs, caffeine, nicotine, and cannabis.

How do serotonergic psychedelics treat depression: The potential role of neuroplasticity

Depression is a common mental disorder and one of the leading causes of disability around the world. Monoaminergic antidepressants often take weeks to months to work and are not effective for all patients. This has led to a search for a better understanding of the pathogenesis of depression as well as to the development of novel antidepressants. One such novel antidepressant is ketamine, which has demonstrated both clinically promising results and contributed to new explanatory models of depression, including the potential role of neuroplasticity in depression. Early clinical trials are now showing promising results of serotonergic psychedelics for depression; however, their mechanism of action remains poorly understood. This paper seeks to review the effect of depression, classic antidepressants, ketamine, and serotonergic psychedelics on markers of neuroplasticity at a cellular, molecular, electrophysiological, functional, structural, and psychological level to explore the potential role that neuroplasticity plays in the treatment response of serotonergic psychedelics.

Psychedelic perceptions: mental health service user attitudes to psilocybin therapy

Introduction

Despite the rapid advance of psychedelic science and possible translation of psychedelic therapy into the psychiatric clinic, very little is known about mental health service user attitudes.

Objectives

To explore mental health service user attitudes to psychedelics and psilocybin therapy.

Methods

A questionnaire capturing demographics, diagnoses, previous psychedelic and other drug use, and attitudes to psychedelics and psilocybin therapy was distributed to mental health service users.

Results

Ninety-nine participants completed the survey (52% female, mean age 42 years). The majority (72%) supported further research, with 59% supporting psilocybin as a medical treatment. A total of 27% previously used recreational psilocybin, with a male preponderance (p = 0.01). Younger age groups, those with previous psychedelic experience, and those with non-religious beliefs were more likely to have favourable attitudes towards psilocybin. A total of 55% of the total sample would accept as a treatment if doctor recommended, whereas 20% would not. Fewer people with depression/anxiety had used recreational psychedelics (p = 0.03) but were more likely to support government funded studies (p = 0.02). A minority (5%) of people with conditions (psychosis and bipolar disorder) that could be exacerbated by psilocybin thought it would be useful for them. One fifth of the total sample viewed psychedelics as addictive and unsafe even under medical supervision. Concerns included fear of adverse effects, lack of knowledge, insufficient research, illegality, and relapse if medications were discontinued.

Conclusions

The majority supported further research into psilocybin therapy. Younger people, those with previous recreational psychedelic experience, and those with non-religious beliefs were more likely to have favourable attitudes towards psilocybin therapy.

Supplementary information

The online version contains supplementary material available at 10.1007/s11845-021-02668-2.

Psychedelic Medicines in Major Depression: Progress and Future Challenges

The volume of research on the therapeutic use of psychedelic drugs has been increasing during the last decades. Partly because of the need of innovative treatments in psychiatry, several studies have assessed the safety and efficacy of drugs like psilocybin or ayahuasca for a wide range of mental disorders, including major depression. The first section of this chapter will offer an introduction to psychedelic research, including a brief historical overview and discussions about appropriate terminology. In the second section, the recently published clinical trials in which psychedelic drugs were administered to patients will be analysed in detail. Then, in the third section, the main neurobiological mechanisms of these drugs will be described, noting that while some of these mechanisms could be potentially associated with their therapeutic properties, they are commonly used as adjuvants in psychotherapeutic processes. The last section suggests future challenges for this groundbreaking field of research and therapy.

Hallucinogenic/psychedelic 5HT2A receptor agonists as rapid antidepressant therapeutics: Evidence and mechanisms of action

Major depressive disorder (MDD) is among the most prevalent mental health disorders worldwide, and it is associated with a reduced quality of life and enormous costs to health care systems. Available drug treatments show low-to-moderate response in most patients, with almost a third of patients being non-responders (treatment-resistant). Furthermore, most currently available medications need several weeks to achieve therapeutic effects, and the long-term use of these drugs is often associated with significant unwanted side effects and resultant reductions in treatment compliance. Therefore, more effective, safer, and faster-acting antidepressants with enduring effects are needed. Together with ketamine, psychedelics (or classic or serotoninergic hallucinogens) such as lysergic acid diethylamide (LSD), psilocybin, and ayahuasca are among the few compounds with recent human evidence of fast-acting antidepressant effects. Several studies in the 1950s to 1970s reported antidepressive and anxiolytic effects of these drugs, which are being confirmed by modern trials (LSD, one trial; psilocybin, five trials; ayahuasca, two trials). The effects of these drugs appear to be produced primarily by their agonism at serotonin (5-hydroxytryptamine, 5-HT) receptors, especially the 5-HT_2A receptor. Considering the overall burden of MDD and the necessity of new therapeutic options, the promising (but currently limited) evidence of safety and efficacy of psychedelics has encouraged the scientific community to explore more fully their beneficial effects in MDD.

Neurotoxicology Syndromes Associated with Drugs of Abuse

Substance use disorders-and their associated neurologic complications-are frequently encountered by neurologists as well as emergency room physicians, internists, psychiatrists, and medical intensivists. Prominent neurologic sequelae of drug abuse, such as seizure and stroke, are common and often result in patients receiving medical attention. However, less overt neurologic manifestations, such as dysautonomia and perceptual disturbances, may be initially misattributed to primary medical or psychiatric illness, respectively. This article focuses on the epidemiology, pharmacology, and complications associated with commonly used recreational drugs, including opioids, alcohol, marijuana, cocaine, and hallucinogens.

Who takes the trip? Personality and hallucinogen use among college students and adolescents

Research examining hallucinogen use has identified potential benefits, as well as potential harms, associated with use. The acute effects of hallucinogen use can be intense, disorienting, cognitively impairing, and may result in perceptual changes mimicking aspects of temporary psychosis. Hallucinogen use may also lead to the onset of more chronic issues, such as Hallucinogen Persisting Perception Disorder, which impairs daily functioning even when sober. However, research on factors that predict who will misuse hallucinogens is an understudied area. In particular, while sensation seeking, impulsivity, and emotion dysregulation have all been shown to be predictive of problematic substance misuse, there is almost no research on how these personality variables predict hallucinogen use. The present study assessed how these personality traits predicted hallucinogen use in a sample of college undergraduates (N = 10,251) and a sample of adolescents in an inpatient residential psychiatric hospital (N = 200). Results indicated that facets of sensation seeking, impulsivity, and emotion dysregulation positively predicted ever having used hallucinogens, earlier initiation of use, and lifetime use among college students. Findings also indicated that facets of sensation seeking, impulsivity, and emotion dysregulation positively predicted having ever used hallucinogens in the adolescent inpatient sample. Results highlight the need for more research on who is likely to misuse hallucinogens. If confirmed in future research, the findings presented herein indicate viable personality variables as predictors. This is especially important as there has been a recent explosion of research on the positive benefits of therapeutic hallucinogen use.

Potential safety, benefits, and influence of the placebo effect in microdosing psychedelic drugs: A systematic review

Microdosing psychedelic drugs-that is, taking sub-behavioral doses of lysergic acid diethylamide (LSD) or psilocybin-is a growing practice in Western societies. Taken mainly for creative or mood-enhancing purposes, thousands of users are increasingly being exposed to (micro)doses of psychedelic drugs. In this systematic review, we searched the available evidence from human studies, focusing our results in terms of three main axes: efficacy, safety, and the influence of the placebo effect in microdosing practices. While the available evidence has some strengths (e.g. large sample sizes, robust methodologies) there are also remarkable limitations (e.g. gender bias, heterogeneity of dosing schedules and drugs used). Highly contradictory results have been found, showing both the benefits and detriments of microdosing in terms of mood, creative processes, and energy, among other regards. This review provides a general overview of the methods and approaches used, which could be useful for improving future studies.

[Visual snow in hallucinogen-persisting perception disorder]

This article presents the case of a 24-year-old female patient who was referred to this department due to permanent flickering in front of both eyes. This flickering, described as being like visual snow in television, had started 1.5 years ago and was perceived to be very disturbing. Visual acuity, visual field and morphology of the anterior and posterior segment were bilaterally inconspicuous. A neurological examination including a magnetic resonance imaging of the cranium (cMRI) and visual evoked potentials (pattern-VEP) also showed no abnormalities. Furthermore, the patient suffered from schizophrenia. This also first occurred 1.5 years ago directly after consumption of a "narcotic cocktail" consisting of amphetamines, hallucinogens and alcohol. In a synopsis of the findings the patient was diagnosed with type II hallucinogen-persisting perception disorder. Treatment options for this disease are limited and the symptoms often remain permanently.

Automated quantification of head-twitch response in mice via ear tag reporter coupled with biphasic detection

BACKGROUND

Head-twitch response (HTR) is a manifestation of the serotonergic system behavioral pharmacology commonly used as a proxy of psychedelic drug action in rodents.

NEW METHOD

We developed a minimally invasive magnetic ear tag reporter and designed a detection system that performs a comprehensive characterization of each potential HTR event on an electromagnetic readout.

RESULTS

Magnetic ear tags were easy to install and generally well tolerated by the animals. On the low-threshold first phase of detection, the tags' signal recorded in a magnetometer was filtered and screened for potential HTR events. On the second phase, the detector performed a comprehensive spectral analysis evaluation of each event and identified the HTR characteristic distribution of power density. Our system delivered satisfactory performance in the identification of pharmacologically-induced HTR and discrimination power against common non-HTR behaviors.

COMPARISON WITH EXISTING METHODS

Our system offers a high-throughput solution for studying HTR in mice employing minimally invasive procedures and superior standalone discriminative power compared to our previously reported fully-automated approach.

CONCLUSIONS

High-throughput identification of HTR utilizing magnetic ear-tagging and biphasic detection delivers satisfactory detection and discrimination power employing less invasive procedures.

Focus on Adolescent Use of Club Drugs and "Other" Substances

Club drugs and "other" abusable substances are briefly overviewed as a reminder about the wide variety of known and unknown substances used by adolescents, the high potential for direct and interactive substance use effects to manifest acutely and chronically, and the vigilance needed to anticipate and recognize the new effects and drug-drug interactions arising as novel substances continue to be custom "designed," manufactured, and marketed to meet substance use trends. This article discusses dextromethorphan, flunitrazepam (Rohypnol), gamma-hydroxybutyrate, inhalants, ketamine, lysergic acid diethylamide, methylenedioxymethamphetamine, phencyclidine, Salvia divinorum (salvia), synthetic cannabinoids, and synthetic cathinones (bath salts).

Serotonergic hallucinogens/psychedelics could be promising treatments for depressive and anxiety disorders in end-stage cancer

In a recent issue of the BMC Psychiatry, the evidence of effectiveness of treatments for psychiatric conditions in end-stage cancer patients was reviewed (Johnson, 2018). The review was comprehensive, and included traditional and non-traditional/alternative treatments, including herbal medicines and spirituality. However, evidence showing that classic or serotonergic hallucinogens/psychedelics such as psilocybin and lysergic acid diethylamide (LSD) could be effective treatments for depressive and anxiety disorders in end-stage cancer was not included. In this commentary, we expand the information available on the original article by briefly reviewing data from recent placebo-controlled, double-blind, cross-over clinical trials showing evidence that administration of single (or few) doses of LSD and psilocybin was associated with rapid and sustained reductions in depressive and anxiety symptoms in patients with end-stage cancer and other life-threatening diseases (e.g., Bechterew's disease, Parkinson's disease, Celiac disease). Since these substances seem to produce rapid and sustained therapeutic effects with single (or few) doses and well tolerated, large-scale, prospective, multi-site studies of end-stage cancer and classical/serotonergic hallucinogens/psychedelics should be performed to improve our understanding of the therapeutic potentials of these drugs and their use on clinical practice.

Changes in neuronal activity in rat primary cortical cultures induced by illicit drugs and new psychoactive substances (NPS) following prolonged exposure and washout to mimic human exposure scenarios

The use of new psychoactive substances (NPS) is increasing despite associated health risks and limited pharmacological and toxicological knowledge. Information is available mainly for acute effects on specific targets like monoamine transporters and receptors. Recently, we have shown the ability of several NPS and illicit drugs to modulate neuronal activity during acute exposure. While these acute measurements provide valuable information regarding the potency and possible structure-activity relationships, an exposure scenario more representative of human exposure would increase insight and aid translation to the human situation. Therefore, we investigated the effects on neuronal activity after acute (30 min) and prolonged (5 h) exposure to amphetamine-type stimulants, cathinones, hallucinogens, piperazines and cocaine using rat primary cortical cultures grown on multi-well microelectrode arrays. To investigate the reversibility of effects, activity was also measured after a washout period of 19 h. During acute exposure, all compounds concentration-dependently decreased neuronal activity. Compared to acute exposure, prolonged exposure did not further decrease neuronal activity. Following washout, effects of 3 out of 11 drugs (methamphetamine, cocaine, and benzylpiperazine) were fully reversible, whereas effects induced by MDMA, PMMA and α-PVP were partially reversible. Neuronal activity did not recover after 19 h washout following exposure to the highest concentration of MDPV, 2C-B, 25B-NBOMe, and TFMPP. On the contrary, exposure to low concentrations of methylone, and to some extent of 2C-B, increased neuronal activity after the washout period. Hazard characterization of emerging NPS should include at least an acute exposure to determine a potency rank order. Supplementing the (acute and prolonged) exposure scenario with a washout period allows investigation of the reversibility of effects. The possibility of a neuronal network to regain activity after drug exposure appears independent of drug class or IC₅₀ values for acute and prolonged exposure. Even though neuronal activity (partly) recovers after washout following exposure to most drugs, it is perturbing that complete recovery of neuronal activity is observed only for a minority of the tested drugs.

Understanding Central Nervous System Effects of Deliriant Hallucinogenic Drugs through Experimental Animal Models

Hallucinogenic drugs potently alter human behavior and have a millennia-long history of use for medicinal and religious purposes. Interest is rapidly growing in their potential as CNS modulators and therapeutic agents for brain conditions. Antimuscarinic cholinergic drugs, such as atropine and scopolamine, induce characteristic hyperactivity and dream-like hallucinations and form a separate group of hallucinogens known as "deliriants". Although atropine and scopolamine are relatively well-studied drugs in cholinergic physiology, deliriants represent the least-studied class of hallucinogens in terms of their behavioral and neurological phenotypes. As such, novel approaches and new model organisms are needed to investigate the CNS effects of these compounds. Here, we comprehensively evaluate the preclinical effects of deliriant hallucinogens in various animal models, their mechanisms of action, and potential interplay with other signaling pathways. We also parallel experimental and clinical findings on deliriant agents and outline future directions of translational research in this field.

Role of mGlu2 in the 5-HT2A receptor-dependent antipsychotic activity of clozapine in mice

BACKGROUND

Serotonin 5-HT_2A and metabotropic glutamate 2 (mGlu2) are neurotransmitter G protein-coupled receptors (GPCRs) involved in the signaling mechanisms underlying psychosis and schizophrenia treatment. Previous findings in mGlu2 knockout (KO) mice suggested that mGlu2 is necessary for head-twitch behavior, a rodent phenotype characteristic of hallucinogenic 5-HT_2A receptor agonists. However, the role of mGlu2 in the behavioral effects induced by antipsychotic drugs remains poorly understood. Here, we tested antipsychotic-like behavioral phenotypes induced by the atypical antipsychotic clozapine in mGlu2-KO mice and wild-type control littermates.

METHODS

Locomotor activity was tested in mGlu2-KO mice and control littermates injected (i.p.) with clozapine (1.5 mg/kg) or vehicle followed by MK801 (0.5 mg/kg), PCP (7.5 mg/kg), amphetamine (6 mg/kg), scopolamine (2 mg/kg), or vehicle. Using a virally (HSV) mediated transgene expression approach, the role of frontal cortex mGlu2 in the modulation of MK801-induced locomotor activity by clozapine treatment was also evaluated.

RESULTS

The effect of clozapine on hyperlocomotor activity induced by the dissociative drugs MK801 and phencyclidine (PCP) was decreased in mGlu2-KO mice as compared to controls. Clozapine treatment, however, reduced hyperlocomotor activity induced by the stimulant drug amphetamine and the deliriant drug scopolamine in both wild-type and mGlu2-KO mice. Virally mediated over-expression of mGlu2 in the frontal cortex of mGlu2-KO mice rescued the ability of clozapine to reduce MK801-induced hyperlocomotion.

CONCLUSION

These findings further support the existence of a functionally relevant crosstalk between 5-HT_2A and mGlu2 receptors in different preclinical models of antipsychotic activity.

Advances and challenges in neuroimaging studies on the effects of serotonergic hallucinogens: Contributions of the resting brain

The effects of hallucinogenic drugs on the human brain have been studied since the earliest days of neuroimaging in the 1990s. However, approaches are often hard to compare and results are heterogeneous. In this chapter, we summarize studies investigating the effects of hallucinogens on the resting brain, with a special emphasis on replicability and limitations. In previous studies, similarities were observed between psilocybin, LSD, and ayahuasca, with respect to decreases in cerebral blood flow and increases in global functional connectivity in the precuneus and thalamus. Additionally, LSD consistently decreased functional connectivity within distinct resting state networks. Little convergence was observed for connectivity between networks and for blood flow in other brain regions. Although these studies are limited by small sample sizes and might be biased by unspecific drug effects on physiological parameters and the vascular system, current results indicate that neuroimaging could be a useful tool to elucidate the neuronal correlates of hallucinogenic effects.

Classic Hallucinogens and Mystical Experiences: Phenomenology and Neural Correlates

This chapter begins with a brief review of descriptions and definitions of mystical-type experiences and the historical connection between classic hallucinogens and mystical experiences. The chapter then explores the empirical literature on experiences with classic hallucinogens in which claims about mystical or religious experiences have been made. A psychometrically validated questionnaire is described for the reliable measurement of mystical-type experiences occasioned by classic hallucinogens. Controlled laboratory studies show that under double-blind conditions that provide significant controls for expectancy bias, psilocybin can occasion complete mystical experiences in the majority of people studied. These effects are dose-dependent, specific to psilocybin compared to placebo or a psychoactive control substance, and have enduring impact on the moods, attitudes, and behaviors of participants as assessed by self-report of participants and ratings by community observers. Other studies suggest that enduring personal meaning in healthy volunteers and therapeutic outcomes in patients, including reduction and cessation of substance abuse behaviors and reduction of anxiety and depression in patients with a life-threatening cancer diagnosis, are related to the occurrence of mystical experiences during drug sessions. The final sections of the chapter draw parallels in human neuroscience research between the neural bases of experiences with classic hallucinogens and the neural bases of meditative practices for which claims of mystical-type experience are sometimes made. From these parallels, a functional neural model of mystical experience is proposed, based on changes in the default mode network of the brain that have been observed after the administration of classic hallucinogens and during meditation practices for which mystical-type claims have been made.

A Review of Hallucinogen Persisting Perception Disorder (HPPD) and an Exploratory Study of Subjects Claiming Symptoms of HPPD

Hallucinogen persisting perception disorder (HPPD) is rarely encountered in clinical settings. It is described as a re-experiencing of some perceptual distortions induced while intoxicated and suggested to subsequently cause functional impairment or anxiety. Two forms exist: Type 1, which are brief "flashbacks," and Type 2 claimed to be chronic, waxing, and waning over months to years. A review of HPPD is presented. In addition, data from a comprehensive survey of 20 subjects reporting Type-2 HPPD-like symptoms are presented and evaluated. Dissociative Symptoms are consistently associated with HPPD. Results of the survey suggest that HPPD is in most cases due to a subtle over-activation of predominantly neural visual pathways that worsens anxiety after ingestion of arousal-altering drugs, including non-hallucinogenic substances. Individual or family histories of anxiety and pre-drug use complaints of tinnitus, eye floaters, and concentration problems may predict vulnerability for HPPD. Future research should take a broader outlook as many perceptual symptoms reported were not first experienced while intoxicated and are partially associated with pre-existing psychiatric comorbidity.