Pharmacological fingerprint of antipsychotic drugs at the serotonin 5-HT2A receptor.

The intricate involvement of the serotonin 5-HT2A receptor (5-HT2AR) both in schizophrenia and in the activity of antipsychotic drugs is widely acknowledged. The currently marketed antipsychotic drugs, although effective in managing the symptoms of schizophrenia to a certain extent, are not without their repertoire of serious side effects. There is a need for better therapeutics to treat schizophrenia for which understanding the mechanism of action of the current antipsychotic drugs is imperative. With bioluminescence resonance energy transfer (BRET) assays, we trace the signaling signature of six antipsychotic drugs belonging to three generations at the 5-HT2AR for the entire spectrum of signaling pathways activated by serotonin (5-HT). The antipsychotic drugs display previously unidentified pathway preference at the level of the individual Gα subunits and ß-arrestins. In particular, risperidone, clozapine, olanzapine and haloperidol showed G protein-selective inverse agonist activity. In addition, G protein-selective partial agonism was found for aripiprazole and cariprazine. Pathway-specific apparent dissociation constants determined from functional analyses revealed distinct coupling-modulating capacities of the tested antipsychotics at the different 5-HT-activated pathways. Computational analyses of the pharmacological and structural fingerprints support a mechanistically based clustering that recapitulate the clinical classification (typical/first generation, atypical/second generation, third generation) of the antipsychotic drugs. The study provides a new framework to functionally classify antipsychotics that should represent a useful tool for the identification of better and safer neuropsychiatric drugs and allows formulating hypotheses on the links between specific signaling cascades and in the clinical outcomes of the existing drugs.

Antipsychotic-induced epigenomic reorganization in frontal cortex of individuals with schizophrenia.

Genome-wide association studies have revealed >270 loci associated with schizophrenia risk, yet these genetic factors do not seem to be sufficient to fully explain the molecular determinants behind this psychiatric condition. Epigenetic marks such as post-translational histone modifications remain largely plastic during development and adulthood, allowing a dynamic impact of environmental factors, including antipsychotic medications, on access to genes and regulatory elements. However, few studies so far have profiled cell-specific genome-wide histone modifications in postmortem brain samples from schizophrenia subjects, or the effect of antipsychotic treatment on such epigenetic marks. Here, we conducted ChIP-seq analyses focusing on histone marks indicative of active enhancers (H3K27ac) and active promoters (H3K4me3), alongside RNA-seq, using frontal cortex samples from antipsychotic-free (AF) and antipsychotic-treated (AT) individuals with schizophrenia, as well as individually matched controls (n=58). Schizophrenia subjects exhibited thousands of neuronal and non-neuronal epigenetic differences at regions that included several susceptibility genetic loci, such as NRG1, DISC1, and DRD3. By analyzing the AF and AT cohorts separately, we identified schizophrenia-associated alterations in specific transcription factors, their regulatees, and epigenomic and transcriptomic features that were reversed by antipsychotic treatment; as well as those that represented a consequence of antipsychotic medication rather than a hallmark of schizophrenia in postmortem human brain samples. Notably, we also found that the effect of age on epigenomic landscapes was more pronounced in frontal cortex of AT-schizophrenics, as compared to AF-schizophrenics and controls. Together, these data provide important evidence of epigenetic alterations in the frontal cortex of individuals with schizophrenia, and remark for the first time on the impact of age and antipsychotic treatment on chromatin organization.

Ethopharmacological evaluation of antidepressant-like effect of serotonergic psychedelics in C57BL/6J male mice.

Serotonergic psychedelics such as psilocybin, lysergic acid diethylamide, and DOI exert a hallucinatory effect through serotonin 5-HT2A receptor (5-HT2A) activation. Recent studies have revealed that serotonergic psychedelics have therapeutic potential for neuropsychiatric disorders, including major depressive and anxiety-related disorders. However, the involvement of 5-HT2A in mediating the therapeutic effects of these drugs remains unclear. In this study, we ethopharmacologically analyzed the role of 5-HT2A in the occurrence of anxiolytic- and antidepressant-like effects of serotonergic psychedelics such as psilocin, an active metabolite of psilocybin, DOI, and TCB-2 in mice 24 h post-treatment. Mice with acute intraperitoneal psychedelic treatment exhibited significantly shorter immobility times in the forced swimming test (FST) and tail-suspension test (TST) than vehicle-treated control mice. These effects were eliminated by pretreatment with volinanserin, a 5-HT2A antagonist. Surprisingly, the decreasing immobility time in the FST in response to acute psilocin treatment was sustained for at least three weeks. In the novelty-suppressed feeding test (NSFT), the latency to feed, an indicator of anxiety-like behavior, was decreased by acute administration of psilocin; however, pretreatment with volinanserin did not diminish this effect. In contrast, DOI and TCB-2 did not affect the NSFT performance in mice. Furthermore, psilocin, DOI, and TCB-2 treatment did not affect the spontaneous locomotor activity or head-twitch response, a hallucination-like behavior in rodents. These results suggest that 5-HT2A contributes to the antidepressant effects of serotonergic psychedelics rather than anxiolytic effects.

Mechanisms and molecular targets surrounding the potential therapeutic effects of psychedelics.

Psychedelics, also known as classical hallucinogens, have been investigated for decades due to their potential therapeutic effects in the treatment of neuropsychiatric and substance use disorders. The results from clinical trials have shown promise for the use of psychedelics to alleviate symptoms of depression and anxiety, as well as to promote substantial decreases in the use of nicotine and alcohol. While these studies provide compelling evidence for the powerful subjective experience and prolonged therapeutic adaptations, the underlying molecular reasons for these robust and clinically meaningful improvements are still poorly understood. Preclinical studies assessing the targets and circuitry of the post-acute effects of classical psychedelics are ongoing. Current literature is split between a serotonin 5-HT2A receptor (5-HT2AR)-dependent or -independent signaling pathway, as researchers are attempting to harness the mechanisms behind the sustained post-acute therapeutically relevant effects. A combination of molecular, behavioral, and genetic techniques in neuropharmacology has begun to show promise for elucidating these mechanisms. As the field progresses, increasing evidence points towards the importance of the subjective experience induced by psychedelic-assisted therapy, but without further cross validation between clinical and preclinical research, the why behind the experience and its translational validity may be lost.

Droplet-based bisulfite sequencing for high-throughput profiling of single-cell DNA methylomes.

The genome-wide DNA methylation profile, or DNA methylome, is a critical component of the overall epigenomic landscape that modulates gene activities and cell fate. Single-cell DNA methylomic studies offer unprecedented resolution for detecting and profiling cell subsets based on methylomic features. However, existing single-cell methylomic technologies are based on use of tubes or well plates and these platforms are not easily scalable for handling a large number of single cells. Here we demonstrate a droplet-based microfluidic technology, Drop-BS, to construct single-cell bisulfite sequencing libraries for DNA methylome profiling. Drop-BS takes advantage of the ultrahigh throughput offered by droplet microfluidics to prepare bisulfite sequencing libraries of up to 10,000 single cells within 2 days. We apply the technology to profile mixed cell lines, mouse and human brain tissues to reveal cell type heterogeneity. Drop-BS offers a promising solution for single-cell methylomic studies requiring examination of a large cell population.

Ethopharmacological evaluation of antidepressant-like effect of serotonergic psychedelics in C57BL/6J male mice.

Serotonergic psychedelics such as psilocybin, lysergic acid diethylamide, and DOI exert a hallucinatory effect through serotonin 5-HT 2A receptor (5-HT2A) activation. Recent studies have revealed that serotonergic psychedelics have therapeutic potential for neuropsychiatric disorders, including major depressive and anxiety-related disorders. However, the involvement of 5-HT2A in mediating the therapeutic effects of these drugs remains unclear. In this study, we ethopharmacologically analyzed the role of 5-HT2A in the occurrence of anxiolytic-and antidepressant-like effects of serotonergic psychedelics such as psilocin, an active metabolite of psilocybin, DOI, and TCB-2 in mice. Mice with acute intraperitoneal psychedelic treatment exhibited significantly shorter immobility times in the forced swimming test (FST) and tail-suspension test (TST) than vehicle-treated control mice 24 h post-treatment. These effects were eliminated by pretreatment with volinanserin, a 5-HT2A antagonist. Surprisingly, the decreasing immobility time in the FST in response to acute psilocin treatment was sustained for at least three weeks. In the novelty-suppressed feeding test (NSFT), the latency to feed, an indicator of anxiety-like behavior, was decreased by acute administration of psilocin; however, pretreatment with volinanserin did not diminish this effect. In contrast, DOI and TCB-2 did not affect the NSFT performance in mice. Furthermore, psilocin, DOI, and TCB-2 treatment did not affect the spontaneous locomotor activity or head-twitch response, a hallucination-like behavior in rodents. These results suggest that 5-HT2A contributes to the antidepressant effects of serotonergic psychedelics rather than an anxiolytic effects.

Automated Detection of Psychedelic-Induced Head-Twitch Response in Mice.

Head-twitch response (HTR) allows for the detection and classification of behavior associated with serotonin 2A receptor (5-HT2AR) activation upon psychedelic administration in rodent models. This activation and functional output can be utilized to provide insights into molecular mechanisms associated with psychosis and to identify signaling processes related to existing and novel antipsychotic and psychedelic compounds. Here we describe the use of a magnetic ear tag reporter coupled with automated quantification and biphasic detection to identify HTR in mice treated with the classical psychedelic 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI).

Droplet-based bisulfite sequencing for high-throughput profiling of single-cell DNA methylomes.

Genome-wide DNA methylation profile, or DNA methylome, is a critical component of the overall epigenomic landscape that modulates gene activities and cell fate. Single-cell DNA methylomic studies offer unprecedented resolution for detecting and profiling cell subsets based on methylomic features. However, existing single-cell methylomic technologies are all based on use of tubes or well plates and these platforms are not easily scalable for handling a large number of single cells. Here we demonstrate a droplet-based microfluidic technology, Drop-BS, to construct single-cell bisulfite sequencing libraries for DNA methylome profiling. Drop-BS takes advantage of the ultrahigh throughput offered by droplet microfluidics to prepare bisulfite sequencing libraries of up to 10,000 single cells within 2 d. We applied the technology to profile mixed cell lines, mouse and human brain tissues to reveal cell type heterogeneity. Drop-BS will pave the way for single-cell methylomic studies requiring examination of a large cell population.

The crosstalk between 5-HT2AR and mGluR2 in schizophrenia.

Schizophrenia is a severe brain disorder that usually produces a lifetime of disability. First generation or typical antipsychotics such as haloperidol and second generation or atypical antipsychotics such as clozapine and risperidone remain the current standard for schizophrenia treatment. In some patients with schizophrenia, antipsychotics produce complete remission of positive symptoms, such as hallucinations and delusions. However, antipsychotic drugs are ineffective against cognitive deficits and indeed treated schizophrenia patients have small improvements or even deterioration in several cognitive domains. This underlines the need for novel and more efficient therapeutic targets for schizophrenia treatment. Serotonin and glutamate have been identified as key parts of two neurotransmitter systems involved in fundamental brain processes. Serotonin (or 5-hydroxytryptamine) 5-HT2A receptor (5-HT2AR) and metabotropic glutamate 2 receptor (mGluR2) are G protein-coupled receptors (GPCRs) that interact at epigenetic and functional levels. These two receptors can form GPCR heteromeric complexes through which their pharmacology, function and trafficking becomes affected. Here we review past and current research on the 5-HT2AR-mGluR2 heterocomplex and its potential implication in schizophrenia and antipsychotic drug action. This article is part of the Special Issue on "The receptor-receptor interaction as a new target for therapy".

Reduced alcohol preference and intake after fecal transplant in patients with alcohol use disorder is transmissible to germ-free mice.

Alcohol use disorder is a major cause of morbidity, which requires newer treatment approaches. We previously showed in a randomized clinical trial that alcohol craving and consumption reduces after fecal transplantation. Here, to determine if this could be transmitted through microbial transfer, germ-free male C57BL/6 mice received stool or sterile supernatants collected from the trial participants pre-/post-fecal transplant. We found that mice colonized with post-fecal transplant stool but not supernatants reduced ethanol acceptance, intake and preference versus pre-fecal transplant colonized mice. Microbial taxa that were higher in post-fecal transplant humans were also associated with lower murine alcohol intake and preference. A majority of the differentially expressed genes (immune response, inflammation, oxidative stress response, and epithelial cell proliferation) occurred in the intestine rather than the liver and prefrontal cortex. These findings suggest a potential for therapeutically targeting gut microbiota and the microbial-intestinal interface to alter gut-liver-brain axis and reduce alcohol consumption in humans.

Glucocorticoid receptor dysregulation underlies 5-HT2AR-dependent synaptic and behavioral deficits in a mouse neurodevelopmental disorder model.

Prenatal environmental insults increase the risk of neurodevelopmental psychiatric conditions in the offspring. Structural modifications of dendritic spines are central to brain development and plasticity. Using maternal immune activation (MIA) as a rodent model of prenatal environmental insult, previous results have reported dendritic structural deficits in the frontal cortex. However, very little is known about the molecular mechanism underlying MIA-induced synaptic structural alterations in the offspring. Using prenatal (E12.5) injection with polyinosinic-polycytidylic acid potassium salt as a mouse MIA model, we show here that upregulation of the serotonin 5-HT2A receptor (5-HT2AR) is at least in part responsible for some of the effects of prenatal insults on frontal cortex dendritic spine structure and sensorimotor gating processes. Mechanistically, we report that this upregulation of frontal cortex 5-HT2AR expression is associated with MIA-induced reduction of nuclear translocation of the glucocorticoid receptor (GR) and, consequently, a decrease in the enrichment of GR at the 5-HT2AR promoter. The translational significance of these preclinical findings is supported by data in postmortem human brain samples suggesting dysregulation of GR translocation in frontal cortex of schizophrenia subjects. We also found that repeated corticosterone administration augmented frontal cortex 5-HT2AR expression and reduced GR binding to the 5-HT2AR promoter. However, virally (adeno-associated virus) mediated augmentation of GR function reduced frontal cortex 5-HT2AR expression and improved sensorimotor gating processes via 5-HT2AR. Together, these data support a negative regulatory relationship between GR signaling and 5-HT2AR expression in the mouse frontal cortex that may carry implications for the pathophysiology underlying 5-HT2AR dysregulation in neurodevelopmental psychiatric disorders.

Differences across sexes on head-twitch behavior and 5-HT2A receptor signaling in C57BL/6J mice.

Psychedelics, also known as classical hallucinogens, affect processes related to perception, cognition and sensory processing mostly via the serotonin 5-HT2A receptor (5-HT2AR). This class of psychoactive substances, which includes lysergic acid diethylamide (LSD), psilocybin, mescaline and the substituted amphetamine 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), is receiving renewed attention for their potential therapeutic properties as it relates to psychiatric conditions such as depression and substance use disorders. Current studies focused on the potentially clinical effects of psychedelics on human subjects tend to exclude sex as a biological variable. Much of the understanding of psychedelic pharmacology is derived from rodent models, but most of this preclinical research has only focused on male mice. Here we tested the effects of DOI on head-twitch behavior (HTR) - a mouse behavioral proxy of human psychedelic potential - in male and female mice. DOI elicited more HTR in female as compared to male C57BL/6J mice, a sex-specific exacerbated behavior that was not observed in 129S6/SvEv animals. Volinanserin (or M100907) - a 5-HT2AR antagonist - fully prevented DOI-induced HTR in male and female C57BL/6J mice. Accumulation of inositol monophosphate (IP1) in the frontal cortex upon DOI administration showed no sex-related effect in C57BL/6J mice. However, the pharmacokinetic properties of DOI differed among sexes - brain and plasma concentrations of DOI were lower 30 and 60 min after drug administration in female as compared to male C57BL/6J mice. Together, these results suggest strain-dependent and sex-related differences in the behavioral and pharmacokinetic profiles of the 5-HT2AR agonist DOI in C57BL/6J mice, and support the importance of studying sex as a biological variable in preclinical psychedelic research.

Tolerance and Cross-Tolerance among Psychedelic and Nonpsychedelic 5-HT2A Receptor Agonists in Mice.

Classical psychedelics represent a subgroup of serotonergic psychoactive substances characterized by their distinct subjective effects on the human psyche. Another unique attribute of this drug class is that such effects become less apparent after repeated exposure within a short time span. The classification of psychedelics as a subgroup within the serotonergic drug family and the tolerance to their effects are replicated by the murine head twitch response (HTR) behavioral paradigm. Here, we aimed to assess tolerance and cross-tolerance to HTR elicited by psychedelic and nonpsychedelic serotonin 2A receptor (5-HT2AR) agonists in mice. We show that repeated (4 days) administration of the psychedelic 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) induced a progressive decrease in HTR behavior. Tolerance to DOI-induced HTR was also observed 24 h after a single administration of this psychedelic. Pretreatment with the 5-HT2AR antagonist M100907 reduced not only the acute manifestation of DOI-induced HTR, but also the development of tolerance to HTR. Additionally, cross-tolerance became apparent between the psychedelics DOI and lysergic acid diethylamide (LSD), whereas repeated administration of the nonpsychedelic 5-HT2AR agonist lisuride did not affect the ability of these two psychedelics to induce HTR. At the molecular level, DOI administration led to down-regulation of 5-HT2AR density in mouse frontal cortex membrane preparations. However, development of tolerance to the effect of DOI on HTR remained unchanged in ß-arrestin-2 knockout mice. Together, these data suggest that tolerance to HTR induced by psychedelics involves activation of the 5-HT2AR, is not observable upon repeated administration of nonpsychedelic 5-HT2AR agonists, and occurs via a signaling mechanism independent of ß-arrestin-2.

Nanobody-based sensors reveal a high proportion of mGlu heterodimers in the brain.

Membrane proteins, including ion channels, receptors and transporters, are often composed of multiple subunits and can form large complexes. Their specific composition in native tissues is difficult to determine and remains largely unknown. In this study, we developed a method for determining the subunit composition of endogenous cell surface protein complexes from isolated native tissues. Our method relies on nanobody-based sensors, which enable proximity detection between subunits in time-resolved Förster resonance energy transfer (FRET) measurements. Additionally, given conformation-specific nanobodies, the activation of these complexes can be recorded in native brain tissue. Applied to the metabotropic glutamate receptors in different brain regions, this approach revealed the clear existence of functional metabotropic glutamate (mGlu)2-mGlu4 heterodimers in addition to mGlu2 and mGlu4 homodimers. Strikingly, the mGlu4 subunits appear to be mainly heterodimers in the brain. Overall, these versatile biosensors can determine the presence and activity of endogenous membrane proteins in native tissues with high fidelity and convenience.

Effects of the 5-HT2A receptor antagonist volinanserin on head-twitch response and intracranial self-stimulation depression induced by different structural classes of psychedelics in rodents.

BACKGROUND: Clinical studies suggest that psychedelics exert robust therapeutic benefits in a number of psychiatric conditions including substance use disorder. Preclinical studies focused on safety and efficacy of these compounds are necessary to determine the full range of psychedelics' effects. OBJECTIVES: The present study explores the behavioral pharmacology of structurally distinct psychedelics in paradigms associated with serotonin 2A receptor (5-HT2AR) activation and behavioral disruption in two rodent models. Utilizing the selective 5-HT2AR antagonist volinanserin, we aimed to provide further pharmacological assessment of psychedelic effects in rodents. METHODS: We compared volinanserin (0.0001-0.1 mg/kg) antagonism of the phenethylamine 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI, 1.0 mg/kg) and the ergoline lysergic acid diethylamide (LSD, 0.32 mg/kg) in preclinical assays predictive of hallucinations (head-twitch response or HTR in mice) and behavioral disruption (intracranial self-stimulation or ICSS in rats). Volinanserin antagonism of the phenethylamine mescaline, the tryptamine psilocybin, and the k-opioid receptor agonist salvinorin A was also evaluated in the rat ICSS assay. RESULTS: Volinanserin had similar potency, effectiveness, and time-course to attenuate DOI-induced HTR in mice and ICSS depression in rats. Volinanserin completely blocked LSD-induced HTR in mice, but not LSD-induced ICSS depression in rats. Volinanserin also reversed ICSS depression by mescaline, but it was only partially effective to reduce the effects of psilocybin, and it exacerbated ICSS depression by salvinorin A. CONCLUSION: Although hallucination-related HTR behavior induced by phenethylamine, ergoline, and tryptamine psychedelics appears to be 5-HT2AR-mediated, the receptor(s) responsible for behavioral disruptive effects may differ among these three structural classes.

Sex-specific role for serotonin 5-HT2A receptor in modulation of opioid-induced antinociception and reward in mice.

Opioids are among the most effective analgesics and the mainstay of pain management. However, concerns about safety and abuse liability have challenged their widespread use by the medical community. Opioid-sparing therapies include drugs that in combination with opioids have the ability to enhance analgesia while decreasing opioid requirement as well as their side effects. Sex differences in antinociceptive responses to opioids have received increasing attention in recent years. However, the molecular mechanisms underlying sex differences related to opioid-sparing adjuncts remain largely unexplored. Using warm water tail-withdrawal as a mouse model of acute thermal nociception, our data suggest that adjunctive administration of the serotonin 5-HT2A receptor (5-HT2AR) antagonist volinanserin dose-dependently enhanced potency of the opioid analgesic oxycodone in male, but not female, mice. This antinociceptive-like response induced by oxycodone was also augmented in 5-HT2AR knockout (5-HT2AR-/-) male, but not female mice; an effect that was reversed by Cre-loxP-mediated selective expression of 5-HT2AR in dorsal root ganglion (DRG) neurons of 5-HT2AR-/- littermates. Pharmacological inhibition with volinanserin or genetic deletion in 5-HT2AR-/- animals potentiated the ability of oxycodone to reduce DRG excitability in male mice. Adjunctive volinanserin did not affect oxycodone-induced conditioned place preference (CPP), whereas it reduced oxycodone-induced locomotor sensitization in male and female mice. Together, these results suggest that adjunctive volinanserin augments opioid-induced antinociception, but not abuse-related behavior, through a sex-specific signaling crosstalk mechanism that requires 5-HT2AR expression in mouse DRG neurons. Ultimately, our results may pave the way for the clinical evaluation of volinanserin as a potential sex-specific opioid adjuvant.

Molecular targets of psychedelic-induced plasticity.

Psychedelic research across different disciplines and biological levels is growing at a remarkably fast pace. In the prospect of a psychedelic drug becoming again an approved treatment, much of these efforts have been oriented toward exploring the relationship between the actual psychedelic effects and those manifestations of therapeutic interest. Considering the central role of the serotonin 5-HT2A receptor in the distinct effects of psychedelics in human psyche, neuropharmacology sits at the center of this debate and exploratory continuum. Here we discuss some of the most recent findings in human studies and contextualize them considering previous preclinical models studying phenomena related to synaptic plasticity. A special emphasis is placed on knowledge gaps, challenges, and limitations to evaluate the underpinnings of psychedelics' potential antidepressant action.

G protein-coupled receptor-effector macromolecular membrane assemblies (GEMMAs).

G protein-coupled receptors (GPCRs) are the largest group of receptors involved in cellular signaling across the plasma membrane and a major class of drug targets. The canonical model for GPCR signaling involves three components - the GPCR, a heterotrimeric G protein and a proximal plasma membrane effector - that have been generally thought to be freely mobile molecules able to interact by 'collision coupling'. Here, we synthesize evidence that supports the existence of GPCR-effector macromolecular membrane assemblies (GEMMAs) comprised of specific GPCRs, G proteins, plasma membrane effector molecules and other associated transmembrane proteins that are pre-assembled prior to receptor activation by agonists, which then leads to subsequent rearrangement of the GEMMA components. The GEMMA concept offers an alternative and complementary model to the canonical collision-coupling model, allowing more efficient interactions between specific signaling components, as well as the integration of the concept of GPCR oligomerization as well as GPCR interactions with orphan receptors, truncated GPCRs and other membrane-localized GPCR-associated proteins. Collision-coupling and pre-assembled mechanisms are not exclusive and likely both operate in the cell, providing a spectrum of signaling modalities which explains the differential properties of a multitude of GPCRs in their different cellular environments. Here, we explore the unique pharmacological characteristics of individual GEMMAs, which could provide new opportunities to therapeutically modulate GPCR signaling.