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.

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.

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.

Sex-specific effects of psychedelics on prepulse inhibition of startle in 129S6/SvEv mice.

BACKGROUND: Prepulse inhibition (PPI) of startle is a sensorimotor gating phenomenon perturbed in a variety of neuropsychiatric conditions. Psychedelics disrupt PPI in rats and humans, but their effects and involvement of the serotonin 5-HT2A receptor (5-HT2AR) in mice remain unexplored. METHODS: We tested the effect of the psychedelic 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) (0.5 mg/kg, i.p.) on startle amplitude and %PPI in response to acoustic stimuli under up to four different experimental conditions that included changes in background and stimulus intensity, prepulse and pulse duration, and interstimulus interval in male and female 129S6/SvEv mice. We also evaluated the effect of the 5-HT2AR antagonist M100,907 (1 mg/kg, i.p.) on DOI-induced startle amplitude and %PPI, as well as the effect of the psychedelic LSD (0.24 mg/kg, i.p.) and the dopamine agonists apomorphine (5 mg/kg, s.c.) and SKF-82,958 (0.5 mg/kg, i.p.) in male 129S6/SvEv mice. RESULTS: DOI altered startle amplitude with either pulse alone or prepulse + pulse presentations in all PPI conditions, and increased %PPI in three out of four PPI conditions in male mice - an effect that was prevented by M100,907. In female mice, DOI increased %PPI without affecting startle amplitude. %PPI was positively correlated with startle amplitude in males while being negatively correlated in female mice. In male mice, LSD also increased %PPI, although it did not affect startle amplitude, whereas apomorphine and SKF-82,958 induced decreases in %PPI. CONCLUSION: Our findings highlight a distinct effect of the psychedelic DOI on PPI in 129S6/SvEv mice, suggesting 5-HT2AR-dependent PPI improvement in a paradigm-dependent and sex-dependent manner.

Prolonged epigenomic and synaptic plasticity alterations following single exposure to a psychedelic in mice.

Clinical evidence suggests that rapid and sustained antidepressant action can be attained with a single exposure to psychedelics. However, the biological substrates and key mediators of psychedelics' enduring action remain unknown. Here, we show that a single administration of the psychedelic DOI produces fast-acting effects on frontal cortex dendritic spine structure and acceleration of fear extinction via the 5-HT2A receptor. Additionally, a single dose of DOI leads to changes in chromatin organization, particularly at enhancer regions of genes involved in synaptic assembly that stretch for days after the psychedelic exposure. These DOI-induced alterations in the neuronal epigenome overlap with genetic loci associated with schizophrenia, depression, and attention deficit hyperactivity disorder. Together, these data support that epigenomic-driven changes in synaptic plasticity sustain psychedelics' long-lasting antidepressant action but also warn about potential substrate overlap with genetic risks for certain psychiatric conditions.

Psychedelic-like Properties of Quipazine and Its Structural Analogues in Mice.

Known classic psychedelic serotonin 2A receptor (5-HT2AR) agonists retain a tryptamine or phenethylamine at their structural core. However, activation of the 5-HT2AR can be elicited by drugs lacking these fundamental scaffolds. Such is the case of the N-substituted piperazine quipazine. Here, we show that quipazine bound to and activated 5-HT2AR as measured by [3H]ketanserin binding displacement, Ca2+ mobilization, and accumulation of the canonical Gq/11 signaling pathway mediator inositol monophosphate (IP1) in vitro and in vivo. Additionally, quipazine induced via 5-HT2AR an expression pattern of immediate early genes (IEG) in the mouse somatosensory cortex consistent with that of classic psychedelics. In the mouse head-twitch response (HTR) model of psychedelic-like action, quipazine produced a lasting effect with high maximal responses during the peak effect that were successfully blocked by the 5-HT2AR antagonist M100907 and absent in 5-HT2AR knockout (KO) mice. The acute effect of quipazine on HTR appeared to be unaffected by serotonin depletion and was independent from 5-HT3R activation. Interestingly, some of these features were shared by its deaza bioisostere 2-NP, but not by other closely related piperazine congeners, suggesting that quipazine might represent a distinct cluster within the family of psychoactive piperazines. Together, our results add to the mounting evidence that quipazine's profile matches that of classic psychedelic 5-HT2AR agonists at cellular signaling and behavioral pharmacology levels.

Optical control of muscular nicotinic channels with azocuroniums, photoswitchable azobenzenes bearing two N-methyl-N-carbocyclic quaternary ammonium groups.

By linking two N-methyl-N-carbocyclic quaternary ammonium groups to an azobenzene scaffold in meta- or para-positions we generated a series of photoswitchable neuromuscular ligands for which we coined the term "azocuroniums". These compounds switched between the (E)- and (Z)-isomers by light irradiation at 400-450 nm and 335-340 nm, respectively. Meta-azocuroniums were potent nicotinic ligands with a clear selectivity for the muscular nAChRs compared to neuronal α7 and α4ß2 subtypes, showed good solubility in physiologic media, negligible cell toxicity, and would not reach the CNS. Electrophysiological studies in muscle-type nAChRs expressed in Xenopus laevis oocytes showed that (E)-isomers were more potent than (Z)-forms. All meta-azocuroniums were neuromuscular blockers, with the exception of the pyrrolidine derivative that was an agonist. These new meta-azocuroniums, which can be modulated ad libitum by light, could be employed as photoswitchable muscle relaxants with fewer side effects for surgical interventions and as tools to better understand the pharmacology of muscle-type nAChRs.

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.

Fully automated head-twitch detection system for the study of 5-HT2A receptor pharmacology in vivo.

Head-twitch behavior (HTR) is the behavioral signature of psychedelic drugs upon stimulation of the serotonin 5-HT2A receptor (5-HT2AR) in rodents. Following the previous report of a semi-automated detection of HTR based on the dynamics of mouse's head movement, here we present a system for the identification of individual HTR events in a fully automated fashion. The validity of this fully automated HTR detection system was tested with the psychedelic drug DOI in 5-HT2AR-KO mice, and via evaluation of potential sources of false-positive and false-negative HTR events. The increased throughput in data processing achieved via automation afforded the possibility of conducting otherwise time consuming HTR time-course studies. To further assess the versatility of our system, we also explored the pharmacological interactions between 5-HT2AR and the metabotropic glutamate receptor 2 (mGluR2). Our data demonstrate the potentiation effect of the mGluR2/3 antagonist LY341495 on DOI-induced HTR, as well as the HTR-blocking effect of the mGluR2/3 agonist and antipsychotic drug in development LY404039. This fully automated system can contribute to speed up our understanding of 5-HT2AR's pharmacology and its characteristic behavioral outputs in rodents.

Chronic clozapine treatment restrains via HDAC2 the performance of mGlu2 receptor agonism in a rodent model of antipsychotic activity.

Preclinical findings in rodent models pointed toward activation of metabotropic glutamate 2/3 (mGlu2/3) receptors as a new pharmacological approach to treat psychosis. However, more recent studies failed to show clinical efficacy of mGlu2/3 receptor agonism in schizophrenia patients. We previously proposed that long-term antipsychotic medication restricted the therapeutic effects of these glutamatergic agents. However, little is known about the molecular mechanism underlying the potential repercussion of previous antipsychotic exposure on the therapeutic performance of mGlu2/3 receptor agonists. Here we show that this maladaptive effect of antipsychotic treatment is mediated mostly via histone deacetylase 2 (HDAC2). Chronic treatment with the antipsychotic clozapine led to a decrease in mouse frontal cortex mGlu2 mRNA, an effect that required expression of both HDAC2 and the serotonin 5-HT2A receptor. This transcriptional alteration occurred in association with HDAC2-dependent repressive histone modifications at the mGlu2 promoter. We found that chronic clozapine treatment decreased via HDAC2 the capabilities of the mGlu2/3 receptor agonist LY379268 to activate G-proteins in the frontal cortex of mice. Chronic clozapine treatment blunted the antipsychotic-related behavioral effects of LY379268, an effect that was not observed in HDAC2 knockout mice. More importantly, co-administration of the class I and II HDAC inhibitor SAHA (vorinostat) preserved the antipsychotic profile of LY379268 and frontal cortex mGlu2/3 receptor density in wild-type mice. These findings raise concerns on the design of previous clinical studies with mGlu2/3 agonists, providing the rationale for the development of HDAC2 inhibitors as a new epigenetic-based approach to improve the currently limited response to treatment with glutamatergic antipsychotics.

Correction: Chronic clozapine treatment restrains via HDAC2 the performance of mGlu2 receptor agonism in a rodent model of antipsychotic activity.

Following the publication of this article Figs. 3b, c were published incorrectly. Also in sub-panel c of Fig. 4, 'Chronic cloza ine' should read 'Chronic clozapine'.

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

BACKGROUND: Serotonin 5-HT2A 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-HT2A 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-HT2A and mGlu2 receptors in different preclinical models of antipsychotic activity.

HDAC2-dependent Antipsychotic-like Effects of Chronic Treatment with the HDAC Inhibitor SAHA in Mice.

Antipsychotic drugs, including both typical such as haloperidol and atypical such as clozapine, remain the current standard for schizophrenia treatment. These agents are relatively effective in treating hallucinations and delusions. However, cognitive deficits are at present essentially either persistent or exacerbated following chronic antipsychotic drug exposure. This underlines the need of new therapeutic approaches to improve cognition in treated schizophrenia patients. Our previous findings suggested that upregulation of histone deacetylase 2 (HDAC2) expression upon chronic antipsychotic treatment may lead to negative effects on cognition and cortical synaptic structure. Here we tested different phenotypes of psychosis, synaptic plasticity, cognition and antipsychotic drug action in HDAC2 conditional knockout (HDAC2-cKO) mice and controls. Conditional depletion of HDAC2 function in glutamatergic pyramidal neurons led to a protective phenotype against behavior models induced by psychedelic and dissociative drugs, such as DOI and MK801, respectively. Immunoreactivity toward synaptophysin, which labels presynaptic terminals of functional synapses, was decreased in the frontal cortex of control mice chronically treated with clozapine - an opposite effect occurred in HDAC2-cKO mice. Chronic treatment with the class I and class II HDAC inhibitor SAHA prevented via HDAC2 the disruptive effects of MK801 on recognition memory. Additionally, chronic SAHA treatment affected transcription of numerous plasticity-related genes in the frontal cortex of control mice, an effect that was not observed in HDAC2-cKO animals. Together, these findings suggest that HDAC2 may represent a novel target to improve synaptic plasticity and cognition in treated schizophrenia patients.

Cell-type-specific brain methylomes profiled via ultralow-input microfluidics.

Methylomic analyses typically require substantial amounts of DNA, thus hindering studies involving scarce samples. Here, we show that microfluidic diffusion-based reduced representative bisulfite sequencing (MID-RRBS) permits high-quality methylomic profiling with nanogram-to-single-cell quantities of starting DNA. We used the microfluidic device, which allows for efficient bisulfite conversion with high DNA recovery, to analyse genome-wide DNA methylation in cell nuclei isolated from mouse brains and sorted into NeuN+ (primarily neuronal) and NeuN- (primarily glial) fractions, and to establish cell-type-specific methylomes. Genome-wide methylation and methylation in low-CpG-density promoter regions showed distinct patterns for NeuN+ and NeuN- fractions from the mouse cerebellum. The identification of substantial variations in the methylomic landscapes of the NeuN+ fraction of the frontal cortex of mice chronically treated with an atypical antipsychotic drug suggests that this technology can be broadly used for cell-type-specific drug profiling and for the study of drug-methylome interactions.

The Melatonin Analog IQM316 May Induce Adult Hippocampal Neurogenesis and Preserve Recognition Memories in Mice.

Neurogenesis in the adult hippocampus is a unique process in neurobiology that requires functional integration of newly generated neurons, which may disrupt existing hippocampal network connections and consequently loss of established memories. As neurodegenerative diseases characterized by abnormal neurogenesis and memory dysfunctions are increasing, the identification of new anti-aging drugs is required. In adult mice, we found that melatonin, a well-established neurogenic hormone, and the melatonin analog 2-(2-(5-methoxy-1 H-indol-3-yl)ethyl)-5-methyl-1,3,4-oxadiazole (IQM316) were able to induce hippocampal neurogenesis, measured by neuronal nuclei (NeuN) and 5-bromo-2'-deoxyuridine (BrdU) labeling. More importantly, only IQM316 administration was able to induce hippocampal neurogenesis while preserving previously acquired memories, assessed with object recognition tests. In vitro studies with embryonic neural stem cells replicated the finding that both melatonin and IQM316 induce direct differentiation of neural precursors without altering their proliferative activity. Furthermore, IQM316 induces differentiation through a mechanism that is not dependent of melatonergic receptors (MTRs), since the MTR antagonist luzindole could not block the IQM316-induced effects. We also found that IQM316 and melatonin modulate mitochondrial DNA copy number and oxidative phosphorylation proteins, while maintaining mitochondrial function as measured by respiratory assays and enzymatic activity. These results uncover a novel pharmacological agent that may be capable of inducing adult hippocampal neurogenesis at a healthy and sustainable rate that preserves recognition memories.

Differences in 5-HT2A and mGlu2 Receptor Expression Levels and Repressive Epigenetic Modifications at the 5-HT2A Promoter Region in the Roman Low- (RLA-I) and High- (RHA-I) Avoidance Rat Strains.

The serotonin 2A (5-HT2A) and metabotropic glutamate 2 (mGlu2) receptors regulate each other and are associated with schizophrenia. The Roman high- (RHA-I) and the Roman low- (RLA-I) avoidance rat strains present well-differentiated behavioral profiles, with the RHA-I strain emerging as a putative genetic rat model of schizophrenia-related features. The RHA-I strain shows increased 5-HT2A and decreased mGlu2 receptor binding levels in prefrontal cortex (PFC). Here, we looked for differences in gene expression and transcriptional regulation of these receptors. The striatum (STR) was included in the analysis. 5-HT2A, 5-HT1A, and mGlu2 mRNA and [3H]ketanserin binding levels were measured in brain homogenates. As expected, 5-HT2A binding was significantly increased in PFC in the RHA-I rats, while no difference in binding was observed in STR. Surprisingly, 5-HT2A gene expression was unchanged in PFC but significantly decreased in STR. mGlu2 receptor gene expression was significantly decreased in both PFC and STR. No differences were observed for the 5-HT1A receptor. Chromatin immunoprecipitation assay revealed increased trimethylation of histone 3 at lysine 27 (H3K27me3) at the promoter region of the HTR2A gene in the STR. We further looked at the Akt/GSK3 signaling pathway, a downstream point of convergence of the serotonin and glutamate system, and found increased phosphorylation levels of GSK3ß at tyrosine 216 and increased ß-catenin levels in the PFC of the RHA-I rats. These results reveal region-specific regulation of the 5-HT2A receptor in the RHA-I rats probably due to absence of mGlu2 receptor that may result in differential regulation of downstream pathways.

Antipsychotic-induced Hdac2 transcription via NF-κB leads to synaptic and cognitive side effects.

Antipsychotic drugs remain the standard for schizophrenia treatment. Despite their effectiveness in treating hallucinations and delusions, prolonged exposure to antipsychotic medications leads to cognitive deficits in both schizophrenia patients and animal models. The molecular mechanisms underlying these negative effects on cognition remain to be elucidated. Here we demonstrate that chronic antipsychotic drug exposure increases nuclear translocation of NF-κB in both mouse and human frontal cortex, a trafficking event triggered via 5-HT2A-receptor-dependent downregulation of the NF-κB repressor IκBα. This upregulation of NF-κB activity led to its increased binding at the Hdac2 promoter, thereby augmenting Hdac2 transcription. Deletion of HDAC2 in forebrain pyramidal neurons prevented the negative effects of antipsychotic treatment on synaptic remodeling and cognition. Conversely, virally mediated activation of NF-κB signaling decreased cortical synaptic plasticity via HDAC2. Together, these observations may aid in developing therapeutic strategies to improve the outcome of schizophrenia treatment.