Metabotropic glutamate mGlu2 receptor is necessary for the pharmacological and behavioral effects induced by hallucinogenic 5-HT2A receptor agonists

Catalysts for change: the cellular neurobiology of psychedelics

The resurgence of interest in the therapeutic potential of psychedelics for treating psychiatric disorders has rekindled efforts to elucidate their mechanism of action. In this Perspective, we focus on the ability of psychedelics to promote neural plasticity, postulated to be central to their therapeutic activity. We begin with a brief overview of the history and behavioral effects of the classical psychedelics. We then summarize our current understanding of the cellular and subcellular mechanisms underlying these drugs' behavioral effects, their effects on neural plasticity, and the roles of stress and inflammation in the acute and long-term effects of psychedelics. The signaling pathways activated by psychedelics couple to numerous potential mechanisms for producing long-term structural changes in the brain, a complexity that has barely begun to be disentangled. This complexity is mirrored by that of the neural mechanisms underlying psychiatric disorders and the transformations of consciousness, mood, and behavior that psychedelics promote in health and disease. Thus, beyond changes in the brain, psychedelics catalyze changes in our understanding of the neural basis of psychiatric disorders, as well as consciousness and human behavior.

The Role of G Protein-Coupled Receptors (GPCRs) and Calcium Signaling in Schizophrenia. Focus on GPCRs Activated by Neurotransmitters and Chemokines

Schizophrenia is a common debilitating disease characterized by continuous or relapsing episodes of psychosis. Although the molecular mechanisms underlying this psychiatric illness remain incompletely understood, a growing body of clinical, pharmacological, and genetic evidence suggests that G protein-coupled receptors (GPCRs) play a critical role in disease development, progression, and treatment. This pivotal role is further highlighted by the fact that GPCRs are the most common targets for antipsychotic drugs. The GPCRs activation evokes slow synaptic transmission through several downstream pathways, many of them engaging intracellular Ca²⁺ mobilization. Dysfunctions of the neurotransmitter systems involving the action of GPCRs in the frontal and limbic-related regions are likely to underly the complex picture that includes the whole spectrum of positive and negative schizophrenia symptoms. Therefore, the progress in our understanding of GPCRs function in the control of brain cognitive functions is expected to open new avenues for selective drug development. In this paper, we review and synthesize the recent data regarding the contribution of neurotransmitter-GPCRs signaling to schizophrenia symptomology.

The G Protein-Coupled Glutamate Receptors as Novel Molecular Targets in Schizophrenia Treatment-A Narrative Review

Schizophrenia is a severe neuropsychiatric disease with an unknown etiology. The research into the neurobiology of this disease led to several models aimed at explaining the link between perturbations in brain function and the manifestation of psychotic symptoms. The glutamatergic hypothesis postulates that disrupted glutamate neurotransmission may mediate cognitive and psychosocial impairments by affecting the connections between the cortex and the thalamus. In this regard, the greatest attention has been given to ionotropic NMDA receptor hypofunction. However, converging data indicates metabotropic glutamate receptors as crucial for cognitive and psychomotor function. The distribution of these receptors in the brain regions related to schizophrenia and their regulatory role in glutamate release make them promising molecular targets for novel antipsychotics. This article reviews the progress in the research on the role of metabotropic glutamate receptors in schizophrenia etiopathology.

Neurochemical and Behavioral Effects of a New Hallucinogenic Compound 25B-NBOMe in Rats

4-Bromo-2,5-dimethoxy-N-(2-methoxybenzyl)phenethylamine (25B-NBOMe) is a hallucinogen exhibiting high binding affinity for 5-HT2A/C serotonin receptors. In the present work, we investigated its effect on dopamine (DA), serotonin (5-HT), acetylcholine (ACh), and glutamate release in the rat frontal cortex, striatum, and nucleus accumbens. Hallucinogenic activity, impact on cognitive and motor functions, and anxiogenic/anxiolytic properties of this compound were also tested. The release of DA, 5-HT, ACh, and glutamate was studied using microdialysis in freely moving animals. Hallucinogenic activity was investigated using head and body twitch response (WDS), cognitive functions were examined with the novel object recognition test (NOR), locomotor activity was studied in the open field (OF), while anxiogenic/anxiolytic effect was tested using the light/dark box (LDB). Neurotoxicity was evaluated with the comet assay. 25B-NBOMe increased DA, 5-HT, and glutamate release in all studied brain regions, induced hallucinogenic activity, and lowered the recognition index (Ri) vs. control in the NOR test. It also decreased locomotor activity of rats in the OF test. The effect of 25B-NBOMe in the NOR test was inhibited by scopolamine. In the LDB test, the time spent in the dark zone was longer in comparison to control and was dose-dependent. In contrast to MDMA, 25B-NBOMe showed subtle genotoxic effect observed in the comet assay.Our findings indicate that 25B-NBOMe shows hallucinogenic activity in the wide range of doses. The changes in neurotransmitter levels may be related to 25B-NBOMe affinity for 5-HT2A receptor. Alterations in the NOR, OF, and LDB indicate that 25B-NBOMe impacts short-term memory, locomotion, and may be anxiogenic.

Cortical influences of serotonin and glutamate on layer V pyramidal neurons

Layer V pyramidal neurons constitute principle output neurons of the medial prefrontal cortex (mPFC)/neocortex to subcortical regions including the intralaminar/midline thalamic nuclei, amygdala, basal ganglia, brainstem nuclei and the spinal cord. The effects of 5-hydroxytryptamine (5-HT) on layer V pyramidal cells primarily reflect a range of excitatory influences through 5-HT_2A receptors and inhibitory influences through non-5-HT_2A receptors, including 5-HT_1A receptors. While the 5-HT_2A receptor is primarily a postsynaptic receptor on throughout the apical dendritic field of 5-HT_2A receptors, activation of a minority of 5-HT_2A receptors also appears to increase spontaneous excitatory postsynaptic currents/potentials (EPSCs/EPSPs) via a presynaptic effect on thalamocortical terminals arising from the midline and intralaminar thalamic nuclei. Activation of 5-HT_2A receptors by the phenethylamine hallucinogen also appears to increase asynchronous release of glutamate upon the layer V pyramidal dendritic field, an effect that is suppressed by 5-HT itself through non-5-HT_2A receptors. Serotonergic hallucinogens acting on 5-HT_2A receptors also appears to increase gene expression of immediate early genes (iEG) and other receptors appearing to induce an iEG-like response like BDNF. Psychedelic hallucinogens acting on 5-HT_2A receptors also induce head twitches in rodents that appear related to induction of glutamate release. These electrophysiological, biochemical and behavioral effects of serotonergic hallucinogens appear to be related to modulating glutamatergic thalamocortical neurotransmission and/or shifting the balance toward 5-HT_2A receptor activation and away from non-5-HT_2A receptor activation. These 5-HT_2A receptor induced responses are modulated by feedback homeostatic mechanisms through mGlu₂, mGlu₄, and mGlu₈ presynaptic receptors on thalamocortical terminals. These 5-HT_2A receptor and glutamatergic interactions also appear to play a role on higher cortical functions of the mPFC such as motoric impulsivity and antidepressant-like behavioral responses on the differential-reinforcement-of low rate 72-s (DRL 72-s schedule). These mutually opposing effects between 5-HT_2A receptor and mGlu autoreceptor activation (e.g., blocking 5-HT_2A receptors and enhancing activity at mGlu₂ receptors) may play a clinical role with respect to currently prescribed or novel antidepressant drugs. Thus, there is an important balance between 5-HT_2A receptor activation and activation of mGlu autoreceptors on prefrontal cortical layer V pyramidal cells with respect to the electrophysiological, biochemical and behavioral effects serotonergic hallucinogenic drugs.

G Protein-Coupled Receptor Heteromers as Putative Pharmacotherapeutic Targets in Autism

A major challenge in the development of pharmacotherapies for autism is the failure to identify pathophysiological mechanisms that could be targetable. The majority of developing strategies mainly aim at restoring the brain excitatory/inhibitory imbalance described in autism, by targeting glutamate or GABA receptors. Other neurotransmitter systems are critical for the fine-tuning of the brain excitation/inhibition balance. Among these, the dopaminergic, oxytocinergic, serotonergic, and cannabinoid systems have also been implicated in autism and thus represent putative therapeutic targets. One of the latest breakthroughs in pharmacology has been the discovery of G protein-coupled receptor (GPCR) oligomerization. GPCR heteromers are macromolecular complexes composed of at least two different receptors, with biochemical properties that differ from those of their individual components, leading to the activation of different cellular signaling pathways. Interestingly, heteromers of the above-mentioned neurotransmitter receptors have been described (e.g., mGlu2-5HT2A, mGlu5-D2-A2A, D2-OXT, CB1-D2, D2-5HT2A, D1-D2, D2-D3, and OXT-5HT2A). We hypothesize that differences in the GPCR interactome may underlie the etiology/pathophysiology of autism and could drive different treatment responses, as has already been suggested for other brain disorders such as schizophrenia. Targeting GPCR complexes instead of monomers represents a new order of biased agonism/antagonism that may potentially enhance the efficacy of future pharmacotherapies. Here, we present an overview of the crosstalk of the different GPCRs involved in autism and discuss current advances in pharmacological approaches targeting them.

Efficacy of psychedelic treatments on depressive symptoms: A meta-analysis

BACKGROUND

Psychedelic drugs have shown an efficacy in some psychiatric disorders and have an original mechanism of action with a 5-HT_2A agonism.

AIM

The aim of this meta-analysis was to assess by a quantitative analysis the putative efficacy of psychedelic drugs on depressive symptoms and to investigate the kinetic of this efficacy.

METHODS

We searched the MEDLINE and PsycINFO databases through April 2019, without limits on year of publication. Means and standard deviations were extracted to calculate standardized mean differences (SMD). Scores of depressive symptoms were compared with baseline scores at days 7, 14, and 21; weeks 4-5 and 6-8; and months 3 and 6.

RESULTS

Eight studies were included in this meta-analysis. A significant decrease of depressive symptoms was found from day 1 (n = 5 studies; SMD = ‒1.4, 95% confidence interval (CI): ‒2.33 to ‒0.48, p = 0.003) to 6 months (n = 4 studies; SMD = ‒1.07, 95% CI: ‒1.44 to ‒0.7, p < 0.001) after psychedelic sessions. No serious adverse effect was reported in all included studies. A transient increase of the heart rate, blood systolic, and diastolic pressure were found after psychedelics compared with placebo.

CONCLUSION

This meta-analysis shows that psychedelic treatments were safe and could contribute to a rapid improvement of depressive symptoms.

Increased behavioral and neuronal responses to a hallucinogenic drug after adolescent toluene exposure in mice: Effects of antipsychotic treatment

Toluene has been characterized as a non-classical hallucinogen drug through activation of 5-HT_2A receptors and antagonism of NMDA receptors. It remains unclear whether psychotic symptoms after long-term and intense toluene exposure are associated with abnormalities in 5-HT_2A receptor function. The present study examined whether the responses to a hallucinogenic 5-HT_2A receptor agonist 2,5-dimethoxy-4-iodoamphetamine (DOI) were altered in a mouse model of toluene psychosis. Male NMRI mice were subchronically treated with toluene during adolescence. Reciprocal social interaction test and novel object recognition test were conducted to confirm the persistent behavioral deficits in adulthood. Subsequently, DOI-induced head twitch, c-Fos and Egr-2 expression, field potentials in the medial prefrontal cortex (mPFC), and the levels of 5-HT_2A, 5-HT_1A and mGlu2 receptors in the mPFC were monitored. Toluene exposure during adolescence produced social and memory impairments and enhanced DOI-induced behavioral, molecular and electrophysiological responses, but did not change the levels of 5-HT_2A, 5-HT_1A or mGlu2 receptors in the mPFC. Moreover, the effects of haloperidol and risperidone on the behavioral deficits and hyper-responsiveness to DOI after adolescent toluene exposure were compared. When administered after adolescent toluene exposure, risperidone could reverse social withdrawal, cognitive impairment and hypersensitivity to DOI, whereas haloperidol was only beneficial for social withdrawal. These findings suggest that increased functionality of 5-HT_2A receptors may play a critical role in solvent-induced psychosis and recommend the antipsychotics with more selective 5-HT_2A receptor antagonism as the first-line treatment for solvent-induced psychosis.

Targeting Serotonin 5-HT2A Receptors to Better Treat Schizophrenia: Rationale and Current Approaches

Schizophrenia is a major mental illness associated with profound disability. Current treatments for schizophrenia (antipsychotics) all have a similar mechanism of action and are primarily dopamine type 2 receptor (D₂R) antagonists. Antipsychotics are not fully effective for the majority of schizophrenia patients, suggesting the need for alternative approaches. The primary focus of this review is to assess the evidence for the role of the serotonin type 2A receptor (5-HT_2AR) in schizophrenia. Topics include an overview of 5-HT_2AR physiology and pathophysiology in schizophrenia, 5-HT_2AR interaction with other neurotransmitter systems, including the glutamatergic system, a review of the 5-HT_2AR/d-lysergic acid diethylamide (LSD) model of schizophrenia, a contrast of the 5-HT_2AR and glutamatergic models of schizophrenia, and finally, a review of Food and Drug Administration (FDA)-approved and investigational 5-HT_2AR-modulating compounds. Recent studies with lumeteperone, pimavanserin, and roluperidone are highlighted.

Acute Low Dose of Trazodone Recovers Glutamate Release Efficiency and mGlu2/3 Autoreceptor Impairments in the Spinal Cord of Rats Suffering From Chronic Sciatic Ligation

We investigated whether chronic sciatic ligation modifies the glutamate release in spinal cord nerve endings (synaptosomes) as well as the expression and the function of presynaptic release-regulating mGlu2/3 autoreceptors and 5-HT_2A heteroreceptors in these particles. Synaptosomes were from the spinal cord of animals suffering from the sciatic ligation that developed on day 6 post-surgery a significant decrease of the force inducing paw-withdrawal in the lesioned paw. The exocytosis of glutamate (quantified as release of preloaded [³H]D-aspartate, [³H]D-Asp) elicited by a mild depolarizing stimulus (15 mM KCl) was significantly increased in synaptosomes from injured rats when compared to controls (uninjured rats). The mGlu2/3 agonist LY379268 (1000 pM) significantly inhibited the 15 mM KCl-evoked [³H]D-Asp overflow from control synaptosomes, but not in terminals isolated from injured animals. Differently, a low concentration (10 nM) of (±) DOI, unable to modify the 15 mM KCl-evoked [³H]D-Asp overflow in control spinal cord synaptosomes, significantly reduced the glutamate exocytosis in nerve endings isolated from the injured rats. Acute oral trazodone (TZD, 0.3 mg/kg on day 7 post-surgery) efficiently recovered glutamate exocytosis as well as the efficiency of LY379268 in inhibiting this event in spinal cord synaptosomes from injured animals. The sciatic ligation significantly reduced the expression of mGlu2/3, but not of 5-HT_2A, receptor proteins in spinal cord synaptosomal lysates. Acute TZD recovered this parameter. Our results support the use of 5-HT_2A antagonists for restoring altered spinal cord glutamate plasticity in rats suffering from sciatic ligation.

Understanding the neurobiological effects of drug abuse: Lessons from zebrafish models

Drug abuse and brain disorders related to drug comsumption are public health problems with harmful individual and social consequences. The identification of therapeutic targets and precise pharmacological treatments to these neuropsychiatric conditions associated with drug abuse are urgently needed. Understanding the link between neurobiological mechanisms and behavior is a key aspect of elucidating drug abuse-related targets. Due to various molecular, biochemical, pharmacological, and physiological features, the zebrafish (Danio rerio) has been considered a suitable vertebrate for modeling complex processes involved in drug abuse responses. In this review, we discuss how the zebrafish has been successfully used for modeling neurobehavioral phenotypes related to drug abuse and review the effects of opioids, cannabinoids, alcohol, nicotine, and psychedelic drugs on the central nervous system (CNS). Moreover, we summarize recent advances in zebrafish-based studies and outline potential advantages and limitations of the existing zebrafish models to explore the neurochemical bases of drug abuse and addiction. Finally, we discuss how the use of zebrafish models may present fruitful approaches to provide valuable clinically translatable data.

G-protein signaling is required for increasing germline stem cell division frequency in response to mating in Drosophila males

Adult stem cells divide to renew the stem cell pool and replenish specialized cells that are lost due to death or usage. However, little is known about the mechanisms regulating how stem cells adjust to a demand for specialized cells. A failure of the stem cells to respond to this demand can have serious consequences, such as tissue loss, or prolonged recovery post injury. Here, we challenge the male germline stem cells (GSCs) of Drosophila melanogaster for the production of specialized cells, sperm cells, using mating experiments. We show that repeated mating reduced the sperm pool and increased the percentage of GSCs in M- and S-phase of the cell cycle. The increase in dividing GSCs depended on the activity of the highly conserved G-proteins. Germline expression of RNA-Interference (RNA-i) constructs against G-proteins, or a dominant negative G-protein eliminated the increase in GSC division frequency in mated males. Consistent with a role for the G-proteins in regulating GSC division frequency, RNA-i against seven out of 35 G-protein coupled receptors (GPCRs) within the germline cells also eliminated the capability of males to increase the numbers of dividing GSCs in response to mating.

Psychedelic treatment of functional neurological disorder: a systematic review

Functional neurological disorder (FND), formerly known as conversion disorder, causes a high burden of disability and distress, and is amongst the most commonly encountered conditions in neurology clinics and neuropsychiatric services, yet the therapeutic evidence base is somewhat limited. There has been recent interest in the therapeutic potential of psychedelics such as psilocybin and lysergic acid diethylamide (LSD), and in recent studies psychedelics have shown promise in treating a range of neuropsychiatric conditions. Modification of neural circuits associated with self-representation is thought to underlie some of this effect, and as some contemporary theories of FND focus on aberrant somatic self-representation, psychedelics may therefore represent an unexplored treatment option for FND. We systematically reviewed studies involving the use of psychedelics in FND. Nine studies published between 1954 and 1967, with a total of 26 patients, were identified. Due to restriction of licencing of psychedelic drugs since this period, no modern studies were identified. In most cases, patients received a course of psychotherapy with variable adjunctive administration of psychedelics (in a combination known as 'psycholytic therapy'), with protocols varying between studies. Of those treated, 69% (n = 18) were found to have made at least some recovery on heterogeneous and subjective clinician-rated criteria. Adverse events were mostly mild and transient; however, at least one patient terminated the study due to distressing effects. All included studies were of low quality, often lacking control groups and valid outcome measures. Although no conclusions on efficacy may be drawn from these data, further research may help to determine whether psychedelics offer a feasible, safe and effective treatment for FND.

Classical psychedelics for the treatment of depression and anxiety: A systematic review

BACKGROUND

Depression and anxiety are prevalent psychiatric disorders that carry significant morbidity. Pharmacological and psychosocial interventions are used to manage these conditions, but their efficacy is limited. Recent interest into the use of psychedelic-assisted therapy using ayahuasca, psilocybin or lysergic acid diethylamide (LSD) may be a promising alternative for patients unresponsive to traditional treatments. This review aims to determine the efficacy and tolerability of psychedelics in the management of resistant depression.

METHODS

Clinical trials investigating psychedelics in patients with depression and/or anxiety were searched via MEDLINE, EMBASE and PsychINFO. Efficacy was assessed by measuring symptom improvement from baseline, and tolerability was evaluated by noting the incidence and type of adverse effects reported. Risk of bias was assessed.

RESULTS

Seven studies, with 130 patients, were analysed in this review. Three were conducted in patients with depression, two in patients with anxiety and two in patients with both. In a supportive setting, ayahuasca, psilocybin, and LSD consistently produced immediate and significant anti-depressant and anxiolytic effects that were endured for several months. Psychedelics were well-tolerated. The most common adverse effects were transient anxiety, short-lived headaches, nausea and mild increases in heart rate and blood pressure.

LIMITATIONS

At present, the number of studies on this subject is very limited; and the number of participating patients within these is also limited as the treatment under investigations is a relatively novel concept.

CONCLUSIONS

Though further evidence is required, psychedelics appear to be effective in significantly reducing symptoms of depression and anxiety and are well-tolerated.

5-HT2A receptor-dependent phosphorylation of mGlu2 receptor at Serine 843 promotes mGlu2 receptor-operated Gi/o signaling

The serotonin 5-HT_2A and glutamate mGlu₂ receptors continue to attract particular attention, given their implication in psychosis associated with schizophrenia and the mechanism of action of atypical antipsychotics and a new class of antipsychotics, respectively. A large body of evidence indicates a functional crosstalk between both receptors in the brain, but the underlying mechanisms are not entirely elucidated. Here, we have explored the influence of 5-HT_2A receptor upon the phosphorylation pattern of mGlu₂ receptor in light of the importance of specific phosphorylation events in regulating G protein-coupled receptor signaling and physiological outcomes. Among the five mGlu₂ receptor-phosphorylated residues identified in HEK-293 cells, the phosphorylation of Ser⁸⁴³ was enhanced upon mGlu₂ receptor stimulation by the orthosteric agonist LY379268 only in cells co-expressing the 5-HT_2A receptor. Likewise, administration of LY379268 increased mGlu₂ receptor phosphorylation at Ser⁸⁴³ in prefrontal cortex of wild-type mice but not 5-HT_2A^-/- mice. Exposure of HEK-293 cells co-expressing mGlu₂ and 5-HT_2A receptors to 5-HT also increased Ser⁸⁴³ phosphorylation state to a magnitude similar to that measured in LY379268-treated cells. In both HEK-293 cells and prefrontal cortex, Ser⁸⁴³ phosphorylation elicited by 5-HT_2A receptor stimulation was prevented by the mGlu₂ receptor antagonist LY341495, while the LY379268-induced effect was abolished by the 5-HT_2A receptor antagonist M100907. Mutation of Ser⁸⁴³ into alanine strongly reduced G_i/o signaling elicited by mGlu₂ or 5-HT_2A receptor stimulation in cells co-expressing both receptors. Collectively, these findings identify mGlu₂ receptor phosphorylation at Ser⁸⁴³ as a key molecular event that underlies the functional crosstalk between both receptors.

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-HT_2A receptor (5-HT_2AR) 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-HT_2AR-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-HT_2AR 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-HT_2AR's pharmacology and its characteristic behavioral outputs in rodents.

Schizophrenia Plasma Autoantibodies Promote 'Biased Agonism' at the 5-Hydroxytryptamine 2A Receptor: Neurotoxicity is Positively Modulated by Metabotropic Glutamate 2/3 Receptor Agonism

AIMS

To test whether neurite-inhibitory plasma autoantibodies in chronic schizophrenia activate Gq/11- and Gi- coupled signaling pathways downstream of 5-hydroxytryptamine 2A receptor activation; and for modulation of serotonergic signaling by the metabotropic 2/3 receptor agonist LY379268.

METHODS

Plasma from five older adults with chronic schizophrenia and eight age-matched patients having another neuropsychiatric, immune or metabolic disorder was subjected to Protein-A affinity chromatography to obtain IgG autoantibodies. Mean neurite retraction (5 minutes) or cell survival (24 hours) was determined in mouse N2A neuroblastoma cells incubated with autoantibodies in the presence or absence of specific antagonists of the Gq/11/PLC/IP3R signaling pathway, Gi-coupled, beta-arrestin2-directed pathways, or LY379268.

RESULTS

Chronic schizophrenia plasma autoantibodies- mediated dose- and time-dependent acute N2A neurite retraction was completely prevented by M100907, a selective 5-hydroxytryptamine 2A receptor antagonist. LY379268 promoted autoantibody-induced neurite retraction causing a shift-to-the-left in the dose-response curve. Antagonists of the RhoA/Rho kinase and Gq/11/PLC/IP3R signaling pathways blocked autoantibody-mediated neurite retraction. Chronic schizophrenia plasma autoantibodies mediated increased N2A cell survival which was blocked by LY379268, pertussis toxin, and antagonists of PI3-kinase- mediated survival signaling.

CONCLUSION

Schizophrenia plasma autoantibodies activate the 5-hydroxytryptamine 2A receptor positively coupled to Gq/11/PLC/IP3R pathway and RhoA/Rho kinase signaling activation in promoting acute N2A cell neurite retraction. Autoantibodies in a subset of patients experiencing hallucinations promoted increased N2A cell survival mediated (in part) via a pertussis-toxin sensitive, Gi-coupled, PI3-kinase-dependent mechanism. Positive modulation of 5-HT2AR-mediated neurite retraction by LY379268 suggests the autoantibodies may target (in part) the 5-HT2AR/mGlu2R heteromer.

Classic psychedelics: the special role of the visual system

Here, we briefly overview the various aspects of classic serotonergic hallucinogens reported by a number of studies. One of the key hypotheses of our paper is that the visual effects of psychedelics might play a key role in resetting fears. Namely, we especially focus on visual processes because they are among the most prominent features of hallucinogen-induced hallucinations. We hypothesize that our brain has an ancient visual-based (preverbal) intrinsic cognitive process that, during the transient inhibition of top-down convergent and abstract thinking (mediated by the prefrontal cortex) by psychedelics, can neutralize emotional fears of unconscious and conscious life experiences from the past. In these processes, the decreased functional integrity of the self-referencing processes of the default mode network, the modified multisensory integration (linked to bodily self-consciousness and self-awareness), and the modified amygdala activity may also play key roles. Moreover, the emotional reset (elimination of stress-related emotions) by psychedelics may induce psychological changes and overwrite the stress-related neuroepigenetic information of past unconscious and conscious emotional fears.

Serotonin and Glutamate Interactions in Preclinical Schizophrenia Models

The serotonergic and glutamatergic neurotransmitter systems have both been implicated in the pathophysiology of schizophrenia, and there are multiple lines of evidence to demonstrate that they can interact in a functionally relevant manner. Particularly, it has been demonstrated that serotonin (5-hydroxytryptamine) 2A (5-HT_2A) receptors and metabotropic glutamate type 2 (mGlu2) receptors can assemble into a functional heteromeric complex and modulate each other's function. This heteromeric complex has been implicated in the mechanism of action of hallucinogens as well as antipsychotic agents, and its role has been demonstrated in both in vitro and in vivo systems. Additionally, the difference in the changes in G_i/o and G_q/11 protein activity when a ligand binds to the heteromeric complex can be used as an index to predict the pro- or antipsychotic properties of an agent. Signaling via the heteromer is dysregulated in postmortem human brain samples of schizophrenia subjects, which may be linked to altered cortical functions. Alternative routes for the functional crosstalk between mGlu2 and 5-HT_2A receptors include synaptic and epigenetic mechanisms. This Review highlights the advances made over the past few years in elucidating the structural and functional mechanisms underlying crosstalk between 5-HT_2A and mGlu2 receptors in preclinical models of schizophrenia.

Serotonergic Psychedelics: Experimental Approaches for Assessing Mechanisms of Action

Recent, well-controlled - albeit small-scale - clinical trials show that serotonergic psychedelics, including psilocybin and lysergic acid diethylamide, possess great promise for treating psychiatric disorders, including treatment-resistant depression. Additionally, fresh results from a deluge of clinical neuroimaging studies are unveiling the dynamic effects of serotonergic psychedelics on functional activity within, and connectivity across, discrete neural systems. These observations have led to testable hypotheses regarding neural processing mechanisms that contribute to psychedelic effects and therapeutic benefits. Despite these advances and a plethora of preclinical and clinical observations supporting a central role for brain serotonin 5-HT2A receptors in producing serotonergic psychedelic effects, lingering and new questions about mechanisms abound. These chiefly pertain to molecular neuropharmacology. This chapter is devoted to illuminating and discussing such questions in the context of preclinical experimental approaches for studying mechanisms of action of serotonergic psychedelics, classic and new.

Dopamine requires unique residues to signal via the serotonin 2A receptor

Serotonin is an important neurotransmitter and neuromodulator. Disruption of the serotonergic system has been implicated in various psychiatric disorders such as schizophrenia and bipolar disorder. Most of the drugs targeting these neurotransmitter systems are classified primarily as agonists or inverse agonists/antagonists, with their described function being limited to activating the canonical signaling pathway(s), or inhibiting the pathway(s) respectively. Previous work with the human 5-HT_2A has shown the receptor to be activated by dopamine, also an endogenous ligand. Dopamine is the cognate ligand of the dopaminergic system, which significantly overlaps with the serotonergic system in the brain. The two systems innervate many of the same brain areas, and the central serotonergic systems also regulate dopamine functions. Our aim was to investigate the downstream signaling set up by the receptor on being activated by dopamine. We show that dopamine is a functionally selective ligand at 5-HT_2A and have examined dopamine as a ligand with respect to some receptor-dependent phenotypes. Our results show that dopamine acts as an agonist at the human serotonin 2A receptor and brings about its activation and internalization. Using in vitro assays, we have established differences in the signaling pathways set up by dopamine as compared to serotonin. Using site-specific mutagenesis we have identified residues important for this functional selectivity, shown by dopamine at this receptor. Our identification of specific residues important in the functional selectivity of dopamine at 5-HT_2A could have far reaching implications for the field of GPCR signaling and drug-design. This article is part of a Special Issue entitled: Honoring Ricardo Miledi - outstanding neuroscientist of XX-XXI centuries.

Chronic treatment with a metabotropic mGlu2/3 receptor agonist diminishes behavioral response to a phenethylamine hallucinogen

BACKGROUND

There is evidence that mGlu2/3 receptors regulate 5-HT_2A signaling, interactions that have been theorized to play a role in the antipsychotic-like effects of mGlu2/3 agonists as well as the hallucinogenic effects of 5-HT_2A agonists. One approach to unraveling this interaction is through the chronic administration of agonists at the two receptors, which should influence the functional properties of the targeted receptor due to receptor downregulation or desensitization and thereby alter crosstalk between the two receptors. In this study, we investigated whether chronic treatment with the mGlu2/3 agonist LY379268 would alter the behavioral response to a phenethylamine hallucinogen, 25CN-NBOH, which acts as a selective 5-HT_2A agonist.

METHODS

We first conducted a dose response of 25CN-NBOH (0.1, 0.3, 1, 3, or 10 mg/kg) to confirm the effects on head-twitch response (HTR) and then blockade studies with either the M100907 (0.1 mg/kg) or SB242084 (0.1, 0.3, or 1 mg/kg) to determine the contribution of 5-HT2A and 5-HT2C to 25CN-NBOH-induced HTR, respectively. To determine whether an mGlu2/3 agonist could block 25CN-NBOH-induced HTR, mice were pretreated with vehicle or LY379268 (0.1, 1, or 10 mg/kg) prior to 25CN-NBOH, and HTR was assessed. The effects of chronic LY379268 on 5-HT2A agonist-induced HTR were evaluated by treating mice with either vehicle or LY379268 (10 mg/kg) for 21 days and measuring 25CN-NBOH-induced HTR 48 h after the final LY379268 treatment. The following day (72 h after the final LY379268 treatment), the ability of acute LY379268 to block PCP-induced locomotor activity was assessed.

RESULTS

25CN-NBOH dose-dependently increased the HTR, a 5-HT_2A-mediated behavior, in mice. The selective 5-HT_2A antagonist M100907 completely blocked the HTR induced by 25CN-NBOH, whereas the selective 5-HT_2C antagonist SB242084 had no effect on the HTR. Administration of LY379268 (10 mg/kg SC) attenuated the HTR induced by 1 mg/kg 25CN-NBOH by ~ 50%. Chronic treatment (21 days) with LY379268 also attenuated the HTR response to 25CN-NBOH when tested 48 h after the last dose of LY379268. In locomotor tests, acute LY379268 significantly attenuated PCP-induced locomotor activity in the chronic vehicle treatment group; by contrast, there was only a trend for an overall interaction in the chronic LY379268 group, with LY379268 blocking the locomotor-stimulating effects of PCP only during the last 20 min.

CONCLUSIONS

These data are consistent with a functional interaction between mGlu2/3 and 5-HT_2A receptors, although the specific mechanism for the interaction is not known. These data support the hypothesis that mGlu2/3 receptors play a prominent role in modulating the behavioral response to 5-HT_2A receptor activation.

The multidimensional brain

Brain activity takes place in three spatial-plus time dimensions. This rather obvious claim has been recently questioned by papers that, taking into account the big data outburst and novel available computational tools, are starting to unveil a more intricate state of affairs. Indeed, various brain activities and their correlated mental functions can be assessed in terms of trajectories embedded in phase spaces of dimensions higher than the canonical ones. In this review, I show how further dimensions may not just represent a convenient methodological tool that allows a better mathematical treatment of otherwise elusive cortical activities, but may also reflect genuine functional or anatomical relationships among real nervous functions. I then describe how to extract hidden multidimensional information from real or artificial neurodata series, and make clear how our mind dilutes, rather than concentrates as currently believed, inputs coming from the environment. Finally, I argue that the principle "the higher the dimension, the greater the information" may explain the occurrence of mental activities and elucidate the mechanisms of human diseases associated with dimensionality reduction.

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-HT_2A 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.

Chronic methamphetamine self-administration dysregulates 5-HT2A and mGlu2 receptor expression in the rat prefrontal and perirhinal cortex: Comparison to chronic phencyclidine and MK-801

Chronic methamphetamine (meth) abuse often turns into a compulsive drug-taking disorder accompanied by persistent cognitive deficits and re-occurring psychosis. Possible common neurobiological substrates underlying meth-induced deficits and schizophrenia remain poorly understood. Serotonin 2A (5-HT2A) and metabotropic glutamate 2 (mGlu2) receptors co-regulate psychosis-like behaviors and cognitive function in animals. Therefore, in the present study we examined the effects of chronic exposure to three different drugs known to produce persistent deficits in sensorimotor gating and cognition [meth, phencyclidine (PCP) and MK-801] on the expression of 5-HT2A and mGlu2 within the rat medial prefrontal cortex (mPFC), dorsal hippocampus (dHPC) and perirhinal cortex (PRh). Adult male rats underwent 14 days of: (a) meth self-administration (6 h/day), (b) phencyclidine (PCP; 5 mg/kg, twice/day) administration, or (c) MK-801 (0.3 mg/kg, twice/day) administration. Seven days after the discontinuation of drug administration, tissues of interest were collected for protein expression analysis. We found that despite different pharmacological mechanism of action, chronic meth, PCP, and MK-801 similarly dysregulated 5-HT2A and mGlu2, as indicated by an increase in the 5-HT2A/mGlu2 expression ratio in the mPFC (all three tested drugs), PRh (meth and PCP), and dHPC (MK-801 only). Complementary changes in G-protein expression (increase in Gαq and decrease in Gαi) were also observed in the mPFC of meth animals. Finally, we found that 5-HT2A/mGlu2 cooperation can be mediated in part by the formation of the receptor heteromer in some, but not all cortical regions. In summary, these data suggest that a shift towards increased availability (and G-protein coupling) of cortical 5-HT2A vs. mGlu2 receptors may represent a common neurobiological mechanism underlying the emergence of psychosis and cognitive deficits observed in subjects with meth use disorder and schizophrenia.

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.

G protein-coupled receptor heteromers are key players in substance use disorder

G protein-coupled receptors (GPCR) represent the largest family of membrane proteins in the human genome. Physical association between two different GPCRs is linked to functional interactions which generates a novel entity, called heteromer, with specific ligand binding and signaling properties. Heteromerization is increasingly recognized to take place in the mesocorticolimbic pathway and to contribute to various aspects related to substance use disorder. This review focuses on heteromers identified in brain areas relevant to drug addiction. We report changes at the molecular and cellular levels that establish specific functional impact and highlight behavioral outcome in preclinical models. Finally, we briefly discuss selective targeting of native heteromers as an innovative therapeutic option.

Interactions of Hallucinogens with the Glutamatergic System: Permissive Network Effects Mediated Through Cortical Layer V Pyramidal Neurons

Recordings made from layer V (L5) pyramidal cells of the prefrontal cortex (PFC) and neocortex in rodent slice preparations have shown that serotonin (5-hydroxytryptamine, 5-HT) and serotonergic hallucinogens induce an increase in the frequency of spontaneous excitatory postsynaptic currents (EPSCs) in the apical dendritic field by activating 5-HT_2A receptors. Serotonergic hallucinogens induce late EPSCs and increase recurrent network activity when subcortical or mid-cortical regions are stimulated at low frequencies (e.g., 0.1 Hz). A range of agonists or positive allosteric modulators (PAMs) for mostly G_i/o-coupled receptors, including metabotropic glutamate₂ (mGlu₂), adenosine A₁, or μ-opioid receptors, suppress these effects of 5-HT_2A receptor stimulation. Furthermore, a range of mostly G_q/11-coupled receptors (including orexin₂ [OX₂]; α₁-adrenergic, and mGlu₅ receptors) similarly induce glutamate (Glu) release onto L5 pyramidal cells. Evidence implicates a number of brain regions in mediating these effects of serotonergic hallucinogens and G_q/11-coupled receptors including the midline and intralaminar thalamic nuclei, claustrum, and neurons in deep PFC. These effects on 5-HT_2A receptors and related GPCRs appear to play a major role in the behavioral effects of serotonergic hallucinogens, such as head twitches in rodents and higher order behaviors such as rodent lever pressing on the differential-reinforcement-of-low rate 72-s (DRL 72-s) schedule. This implies that the effects of 5-HT_2A receptor activation on the activity of L5 pyramidal cells may be responsible for mediating a range of behaviors linked to limbic circuitry with connectivity between the PFC, striatum, thalamus, claustrum, striatum, amygdala, and the hippocampal formation.

Pharmacokinetics of Escalating Doses of Oral Psilocybin in Healthy Adults

INTRODUCTION

Psilocybin is a psychedelic tryptamine that has shown promise in recent clinical trials for the treatment of depression and substance use disorders. This open-label study of the pharmacokinetics of psilocybin was performed to describe the pharmacokinetics and safety profile of psilocybin in sequential, escalating oral doses of 0.3, 0.45, and 0.6 mg/kg in 12 healthy adults.

METHODS

Eligible healthy adults received 6-8 h of preparatory counseling in anticipation of the first dose of psilocybin. The escalating oral psilocybin doses were administered at approximately monthly intervals in a controlled setting and subjects were monitored for 24 h. Blood and urine samples were collected over 24 h and assayed by a validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for psilocybin and psilocin, the active metabolite. The pharmacokinetics of psilocin were determined using both compartmental (NONMEM) and noncompartmental (WinNonlin) methods.

RESULTS

No psilocybin was found in plasma or urine, and renal clearance of intact psilocin accounted for less than 2% of the total clearance. The pharmacokinetics of psilocin were linear within the twofold range of doses, and the elimination half-life of psilocin was 3 h (standard deviation 1.1). An extended elimination phase in some subjects suggests hydrolysis of the psilocin glucuronide metabolite. Variation in psilocin clearance was not predicted by body weight, and no serious adverse events occurred in the subjects studied.

CONCLUSIONS

The small amount of psilocin renally excreted suggests that no dose reduction is needed for subjects with mild-moderate renal impairment. Simulation of fixed doses using the pharmacokinetic parameters suggest that an oral dose of 25 mg should approximate the drug exposure of a 0.3 mg/kg oral dose of psilocybin. Although doses of 0.6 mg/kg are in excess of likely therapeutic doses, no serious physical or psychological events occurred during or within 30 days of any dose.

CLINICAL TRIALS IDENTIFIER

NCT02163707.

Behavioral and Serotonergic Changes in the Frontal Cortex Following Methamphetamine Self-Administration

BACKGROUND

Methamphetamine use is associated with a variety of negative health outcomes, including psychosis. The frontal cortex serotonin receptors are thought to contribute to psychosis-like behaviors. This study investigated changes in serotonergic markers in the frontal cortex following methamphetamine self-administration and hallucinogenic drug-induced behavior.

METHODS

Consistent with previously published studies, freely cycling male and female rats were allowed to self-administer methamphetamine (males: 0.12 mg/infusion; females: 0.09 mg/infusion) or saline (10 µL) for 7 days. On the day following self-administration or following 10 days of extinction training, animals were given the serotonin 2A/2C agonist, 1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (2 mg/kg, i.p.), and head twitches were analyzed. Autoradiography was also used to assess serotonin receptors and transporters in the frontal cortex following self-administration.

RESULTS

Methamphetamine self-administration led to an increase in DOI-induced head-twitch behavior compared to saline only on the day following self-administration. Increases in serotonin receptors in the orbitofrontal cortex and decreases in serotonin transporters in the orbitofrontal cortex and infralimbic cortex were observed following methamphetamine self-administration as assessed by autoradiography.

CONCLUSIONS

Methamphetamine self-administration was associated with serotonergic alterations in the frontal cortex, which may underlie behavioral changes related to methamphetamine-associated psychosis.

Evaluation of Neurotransmitter Alterations in Four Distinct Brain Regions After Rapid Eye Movement Sleep Deprivation (REMSD) Induced Mania-Like Behaviour in Swiss Albino Mice

A number of neurotransmitter systems have been implicated in contributing to the pathology of mood disorders, including those of dopamine (DA), serotonin (5-HT), norepinephrine (NE) and γ-aminobutyric acid (GABA). Rapid eye movement sleep deprivation (REMSD) alters most of the neurotransmitters, which may have adverse behavioural changes and other health consequences like mania and other psychiatric disorders. The exact role of REMSD altered neurotransmitter levels and the manner in which emerging consequences lead to mania-like behaviour is poorly understood. Thus, we sought to verify the levels of neurotransmitter changes after 48, 72 and 96 h of REMSD induced mania-like behaviour in mice. We performed modified multiple platform (MMP) method of depriving the REM sleep and one group maintained as a control. To measure the hyperactivity through locomotion, exploration and behavioural despair, we performed the Open Field Test (OFT) and the Forced Swim Test (FST). Quantitative determinations of DA, 5-HT, NE and GABA concentrations in four distinct brain regions (cerebral cortex, hippocampus, midbrain, and pons) were determined by the spectrofluorimetric method. These experiments showed higher locomotion and increased swimming, struggling/climbing and decreased mobility among REMSD animals as well as disrupted concentrations of the majority of the studied neurotransmitters during REMSD. Our study indicated that REMSD results in mania-like behaviour in mice and associated disruption to neurotransmitter levels, although the exact mechanisms by which these take place remain to be determined.

Metabotropic Glutamate2 Receptors Play a Key Role in Modulating Head Twitches Induced by a Serotonergic Hallucinogen in Mice

There is substantial evidence that glutamate can modulate the effects of 5-hydroxytryptamine_2A (5-HT_2A) receptor activation through stimulation of metabotropic glutamate_2/3 (mGlu_2/3) receptors in the prefrontal cortex. Here we show that constitutive deletion of the mGlu₂ gene profoundly attenuates an effect of 5-HT_2A receptor activation using the mouse head twitch response (HTR). MGlu₂ and mGlu₃ receptor knockout (KO) as well as age-matched ICR (CD-1) wild type (WT) mice were administered (±)1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and observed for head twitch activity. DOI failed to produce significant head twitches in mGlu₂ receptor KO mice at a dose 10-fold higher than the peak effective dose in WT or mGlu₃ receptor KO mice. In addition, the mGlu_2/3 receptor agonist LY379268, and the mGlu₂ receptor positive allosteric modulator (PAM) CBiPES, potently blocked the HTR to DOI in WT and mGlu₃ receptor KO mice. Conversely, the mGlu_2/3 receptor antagonist LY341495 (10 mg/kg) increased the HTR produced by DOI (3 mg/kg) in mGlu₃ receptor KO mice. Finally, the mGlu₂ receptor potentiator CBiPES was able to attenuate the increase in the HTR produced by LY341495 in mGlu₃ receptor KO mice. Taken together, all of these results are consistent with the hypothesis that that DOI-induced head twitches are modulated by mGlu₂ receptor activation. These results also are in keeping with a critical autoreceptor function for mGlu₂ receptors in the prefrontal cortex with differential effects of acute vs. chronic perturbation (e.g., constitutive mGlu₂ receptor KO mice). The robust attenuation of DOI-induced head twitches in the mGlu₂ receptor KO mice appears to reflect the critical role of glutamate in ongoing regulation of 5-HT_2A receptors in the prefrontal cortex. Future experiments with inducible knockouts for the mGlu₂ receptor and/or selective mGlu₃ receptor agonists/PAMs/antagonists could provide an important tools in understanding glutamatergic modulation of prefrontal cortical 5-HT_2A receptor function.

β2-Adrenergic Receptor Activation Suppresses the Rat Phenethylamine Hallucinogen-Induced Head Twitch Response: Hallucinogen-Induced Excitatory Post-synaptic Potentials as a Potential Substrate

5-Hydroxytryptamine2A (5-HT2A) receptors are enriched in layers I and Va of the rat prefrontal cortex and neocortex and their activation increases the frequency of glutamatergic excitatory post-synaptic potentials/currents (EPSP/Cs) onto layer V pyramidal cells. A number of other G-protein coupled receptors (GPCRs) are also enriched in cortical layers I and Va and either induce (α1-adrenergic and orexin2) or suppress (metabotropic glutamate2 [mGlu2], adenosine A1, μ-opioid) both 5-HT-induced EPSCs and head twitches or head shakes induced by the phenethylamine hallucinogen 2,5-dimethoxy-4-iodoamphetamine (DOI). Another neurotransmitter receptor also localized to apparent thalamocortical afferents to layers I and Va of the rat prefrontal cortex and neocortex is the β2-adrenergic receptor. Therefore, we conducted preliminary electrophysiological experiments with rat brain slices examining the effects of epinephrine on electrically-evoked EPSPs following bath application of DOI (3 μM). Epinephrine (0.3-10 μM) suppressed the late EPSPs produced by electrical stimulation and DOI. The selective β2-adrenergic receptor antagonist ICI-118,551 (300 nM) resulted in a rightward shift of the epinephrine concentration-response relationship. We also tested the selective β2-adrenergic receptor agonist clenbuterol and the antagonist ICI-118,551 on DOI-induced head twitches. Clenbuterol (0.3-3 mg/kg, i.p.) suppressed DOI (1.25 mg/kg, i.p.)-induced head twitches. This clenbuterol effect appeared to be at least partially reversed by the selective β2-adrenergic receptor antagonist ICI-118,553 (0.01-1 mg/kg, i.p.), with significant reversal at doses of 0.1 and 1 mg/kg. Thus, β2-adrenergic receptor activation reverses the effects of phenethylamine hallucinogens in the rat prefrontal cortex. While Gi/Go-coupled GPCRs have previously been shown to suppress both the electrophysiological and behavioral effects of 5-HT2A receptor activation in the mPFC, the present work appears to extend this suppressant action to a Gs-coupled GPCR. Furthermore, the modulation of 5-HT2A receptor activation-induced glutamate release onto mPFC layer V pyramidal neurons apical dendrites by a range GPCRs in rat brain slices appears to results in behaviorally salient effects of relevance when screening for novel CNS therapeutic drugs.

Double-blind comparison of the two hallucinogens psilocybin and dextromethorphan: similarities and differences in subjective experiences

RATIONALE

Although psilocybin and dextromethorphan (DXM) are hallucinogens, they have different receptor mechanisms of action and have not been directly compared.

OBJECTIVE

This study compared subjective, behavioral, and physiological effects of psilocybin and dextromethorphan under conditions that minimized expectancy effects.

METHODS

Single, acute oral doses of psilocybin (10, 20, 30 mg/70 kg), DXM (400 mg/70 kg), and placebo were administered under double-blind conditions to 20 healthy participants with histories of hallucinogen use. Instructions to participants and staff minimized expectancy effects. Various subjective, behavioral, and physiological effects were assessed after drug administration.

RESULTS

High doses of both drugs produced similar increases in participant ratings of peak overall drug effect strength, with similar times to maximal effect and time-course. Psilocybin produced orderly dose-related increases on most participant-rated subjective measures previously shown sensitive to hallucinogens. DXM produced increases on most of these same measures. However, the high dose of psilocybin produced significantly greater and more diverse visual effects than DXM including greater movement and more frequent, brighter, distinctive, and complex (including textured and kaleidoscopic) images and visions. Compared to DXM, psilocybin also produced significantly greater mystical-type and psychologically insightful experiences and greater absorption in music. In contrast, DXM produced larger effects than psilocybin on measures of disembodiment, nausea/emesis, and light-headedness. Both drugs increased systolic blood pressure, heart rate, and pupil dilation and decreased psychomotor performance and balance.

CONCLUSIONS

Psilocybin and DXM produced similar profiles of subjective experiences, with psilocybin producing relatively greater visual, mystical-type, insightful, and musical experiences, and DXM producing greater disembodiment.

Effect of Hallucinogens on Unconditioned Behavior

Because of the ethical and regulatory hurdles associated with human studies, much of what is known about the psychopharmacology of hallucinogens has been derived from animal models. However, developing reliable animal models has proven to be a challenging task due to the complexity and variability of hallucinogen effects in humans. This chapter focuses on three animal models that are frequently used to test the effects of hallucinogens on unconditioned behavior: head twitch response (HTR), prepulse inhibition of startle (PPI), and exploratory behavior. The HTR has demonstrated considerable utility in the neurochemical actions of hallucinogens. However, the latter two models have clearer conceptual bridges to human phenomenology. Consistent with the known mechanism of action of hallucinogens in humans, the behavioral effects of hallucinogens in rodents are mediated primarily by activation of 5-HT2A receptors. There is evidence, however, that other receptors may play secondary roles. The structure-activity relationships (SAR) of hallucinogens are reviewed in relation to each model, with a focus on the HTR in rats and mice.

The Role of Sigma-1 Receptor, an Intracellular Chaperone in Neurodegenerative Diseases

BACKGROUND

Widespread protein aggregation occurs in the living system under stress or during aging, owing to disturbance of endoplasmic reticulum (ER) proteostasis. Many neurodegenerative diseases may have a common mechanism: the failure of protein homeostasis. Perturbation of ER results in unfolded protein response (UPR). Prolonged chronical UPR may activate apoptotic pathways and cause cell death.

METHODS

Research articles on Sigma-1 receptor were reviewed.

RESULTS

ER is associated to mitochondria by the mitochondria-associated ER-membrane, MAM. The sigma-1 receptor (Sig-1R), a well-known ER-chaperone localizes in the MAM. It serves for Ca2+-signaling between the ER and mitochondria, involved in ion channel activities and especially important during neuronal differentiation. Sig-1R acts as central modulator in inter-organelle signaling. Sig-1R helps cell survival by attenuating ER-stress. According to sequence based predictions Sig-1R is a 223 amino acid protein with two transmembrane (2TM) domains. The X-ray structure of the Sig-1R [1] showed a membrane-bound trimeric assembly with one transmembrane (1TM) region. Despite the in vitro determined assembly, the results of in vivo studies are rather consistent with the 2TM structure. The receptor has unique and versatile pharmacological profile. Dimethyl tryptamine (DMT) and neuroactive steroids are endogenous ligands that activate Sig-1R. The receptor has a plethora of interacting client proteins. Sig-1R exists in oligomeric structures (dimer-trimer-octamer-multimer) and this fact may explain interaction with diverse proteins.

CONCLUSION

Sig-1R agonists have been used in the treatment of different neurodegenerative diseases, e.g. Alzheimer's and Parkinson's diseases (AD and PD) and amyotrophic lateral sclerosis. Utilization of Sig-1R agents early in AD and similar other diseases has remained an overlooked therapeutic opportunity.

Psychedelic Drugs in Biomedicine

Psychedelic drugs, such as lysergic acid diethylamide (LSD), mescaline, and psilocybin, exert profound effects on brain and behavior. After decades of difficulties in studying these compounds, psychedelics are again being tested as potential treatments for intractable biomedical disorders. Preclinical research of psychedelics complements human neuroimaging studies and pilot clinical trials, suggesting these compounds as promising treatments for addiction, depression, anxiety, and other conditions. However, many questions regarding the mechanisms of action, safety, and efficacy of psychedelics remain. Here, we summarize recent preclinical and clinical data in this field, discuss their pharmacological mechanisms of action, and outline critical areas for future studies of psychedelic drugs, with the goal of maximizing the potential benefits of translational psychedelic biomedicine to patients.

Assessing the Psychedelic "After-Glow" in Ayahuasca Users: Post-Acute Neurometabolic and Functional Connectivity Changes Are Associated with Enhanced Mindfulness Capacities

Background

Ayahuasca is a plant tea containing the psychedelic 5-HT2A agonist N,N-dimethyltryptamine and harmala monoamine-oxidase inhibitors. Acute administration leads to neurophysiological modifications in brain regions of the default mode network, purportedly through a glutamatergic mechanism. Post-acutely, ayahuasca potentiates mindfulness capacities in volunteers and induces rapid and sustained antidepressant effects in treatment-resistant patients. However, the mechanisms underlying these fast and maintained effects are poorly understood. Here, we investigated in an open-label uncontrolled study in 16 healthy volunteers ayahuasca-induced post-acute neurometabolic and connectivity modifications and their association with mindfulness measures.

Methods

Using 1H-magnetic resonance spectroscopy and functional connectivity, we compared baseline and post-acute neurometabolites and seed-to-voxel connectivity in the posterior and anterior cingulate cortex after a single ayahuasca dose.

Results

Magnetic resonance spectroscopy showed post-acute reductions in glutamate+glutamine, creatine, and N-acetylaspartate+N-acetylaspartylglutamate in the posterior cingulate cortex. Connectivity was increased between the posterior cingulate cortex and the anterior cingulate cortex, and between the anterior cingulate cortex and limbic structures in the right medial temporal lobe. Glutamate+glutamine reductions correlated with increases in the "nonjudging" subscale of the Five Facets Mindfulness Questionnaire. Increased anterior cingulate cortex-medial temporal lobe connectivity correlated with increased scores on the self-compassion questionnaire. Post-acute neural changes predicted sustained elevations in nonjudging 2 months later.

Conclusions

These results support the involvement of glutamate neurotransmission in the effects of psychedelics in humans. They further suggest that neurometabolic changes in the posterior cingulate cortex, a key region within the default mode network, and increased connectivity between the anterior cingulate cortex and medial temporal lobe structures involved in emotion and memory potentially underlie the post-acute psychological effects of ayahuasca.

Cross-compartmental Modulation of Dendritic Signals for Retinal Direction Selectivity

Compartmentalized signaling in dendritic subdomains is critical for the function of many central neurons. In the retina, individual dendritic sectors of a starburst amacrine cell (SAC) are preferentially activated by different directions of linear motion, indicating limited signal propagation between the sectors. However, the mechanism that regulates this propagation is poorly understood. Here, we find that metabotropic glutamate receptor 2 (mGluR2) signaling, which acts on voltage-gated calcium channels in SACs, selectively restricts cross-sector signal propagation in SACs, but does not affect local dendritic computation within individual sectors. mGluR2 signaling ensures sufficient electrotonic isolation of dendritic sectors to prevent their depolarization during non-preferred motion, yet enables controlled multicompartmental signal integration that enhances responses to preferred motion. Furthermore, mGluR2-mediated dendritic compartmentalization in SACs is important for the functional output of direction-selective ganglion cells (DSGCs). Therefore, our results directly link modulation of dendritic compartmentalization to circuit-level encoding of motion direction in the retina.

A Single Dose of LSD Does Not Alter Gene Expression of the Serotonin 2A Receptor Gene (HTR2A) or Early Growth Response Genes (EGR1-3) in Healthy Subjects

Rationale: Renewed interest has been seen in the use of lysergic acid diethylamide (LSD) in psychiatric research and practice. The repeated use of LSD leads to tolerance that is believed to result from serotonin (5-HT) 5-HT_2A receptor downregulation. In rats, daily LSD administration for 4 days decreased frontal cortex 5-HT_2A receptor binding. Additionally, a single dose of LSD acutely increased expression of the early growth response genes EGR1 and EGR2 in rat and mouse brains through 5-HT_2A receptor stimulation. No human data on the effects of LSD on gene expression has been reported. Therefore, we investigated the effects of single-dose LSD administration on the expression of the 5-HT_2A receptor gene (HTR2A) and EGR1-3 genes.

Methods: mRNA expression levels were analyzed in whole blood as a peripheral biomarker in 15 healthy subjects before and 1.5 and 24 h after the administration of LSD (100 μg) and placebo in a randomized, double-blind, placebo-controlled, cross-over study.

Results: LSD did not alter the expression of the HTR2A or EGR1-3 genes 1.5 and 24 h after administration compared with placebo.

Conclusion: No changes were observed in the gene expression of LSD’s primary target receptor gene or genes that are implicated in its downstream effects. Remaining unclear is whether chronic LSD administration alters gene expression in humans.

Ayahuasca, dimethyltryptamine, and psychosis: a systematic review of human studies

Ayahuasca is a hallucinogen brew traditionally used for ritual and therapeutic purposes in Northwestern Amazon. It is rich in the tryptamine hallucinogens dimethyltryptamine (DMT), which acts as a serotonin 5-HT_2A agonist. This mechanism of action is similar to other compounds such as lysergic acid diethylamide (LSD) and psilocybin. The controlled use of LSD and psilocybin in experimental settings is associated with a low incidence of psychotic episodes, and population studies corroborate these findings. Both the controlled use of DMT in experimental settings and the use of ayahuasca in experimental and ritual settings are not usually associated with psychotic episodes, but little is known regarding ayahuasca or DMT use outside these controlled contexts. Thus, we performed a systematic review of the published case reports describing psychotic episodes associated with ayahuasca and DMT intake. We found three case series and two case reports describing psychotic episodes associated with ayahuasca intake, and three case reports describing psychotic episodes associated with DMT. Several reports describe subjects with a personal and possibly a family history of psychosis (including schizophrenia, schizophreniform disorders, psychotic mania, psychotic depression), nonpsychotic mania, or concomitant use of other drugs. However, some cases also described psychotic episodes in subjects without these previous characteristics. Overall, the incidence of such episodes appears to be rare in both the ritual and the recreational/noncontrolled settings. Performance of a psychiatric screening before administration of these drugs, and other hallucinogens, in controlled settings seems to significantly reduce the possibility of adverse reactions with psychotic symptomatology. Individuals with a personal or family history of any psychotic illness or nonpsychotic mania should avoid hallucinogen intake.

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-HT_2A) 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-HT_2A 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-HT_2A, 5-HT_1A, and mGlu2 mRNA and [³H]ketanserin binding levels were measured in brain homogenates. As expected, 5-HT_2A binding was significantly increased in PFC in the RHA-I rats, while no difference in binding was observed in STR. Surprisingly, 5-HT_2A 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-HT_1A 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 GSK3β at tyrosine 216 and increased β-catenin levels in the PFC of the RHA-I rats. These results reveal region-specific regulation of the 5-HT_2A receptor in the RHA-I rats probably due to absence of mGlu2 receptor that may result in differential regulation of downstream pathways.

Elucidation of molecular kinetic schemes from macroscopic traces using system identification

Overall cellular responses to biologically-relevant stimuli are mediated by networks of simpler lower-level processes. Although information about some of these processes can now be obtained by visualizing and recording events at the molecular level, this is still possible only in especially favorable cases. Therefore the development of methods to extract the dynamics and relationships between the different lower-level (microscopic) processes from the overall (macroscopic) response remains a crucial challenge in the understanding of many aspects of physiology. Here we have devised a hybrid computational-analytical method to accomplish this task, the SYStems-based MOLecular kinetic scheme Extractor (SYSMOLE). SYSMOLE utilizes system-identification input-output analysis to obtain a transfer function between the stimulus and the overall cellular response in the Laplace-transformed domain. It then derives a Markov-chain state molecular kinetic scheme uniquely associated with the transfer function by means of a classification procedure and an analytical step that imposes general biological constraints. We first tested SYSMOLE with synthetic data and evaluated its performance in terms of its rate of convergence to the correct molecular kinetic scheme and its robustness to noise. We then examined its performance on real experimental traces by analyzing macroscopic calcium-current traces elicited by membrane depolarization. SYSMOLE derived the correct, previously known molecular kinetic scheme describing the activation and inactivation of the underlying calcium channels and correctly identified the accepted mechanism of action of nifedipine, a calcium-channel blocker clinically used in patients with cardiovascular disease. Finally, we applied SYSMOLE to study the pharmacology of a new class of glutamate antipsychotic drugs and their crosstalk mechanism through a heteromeric complex of G protein-coupled receptors. Our results indicate that our methodology can be successfully applied to accurately derive molecular kinetic schemes from experimental macroscopic traces, and we anticipate that it may be useful in the study of a wide variety of biological systems.

Unraveling the lower-level (microscopic) processes underlying the overall (macroscopic) cell response to a given stimulus is a challenging problem in cell physiology. This has been a classic problem in biophysics, where the ability to record the activity of single ion channels that generate a macroscopic ion current has allowed a measure of direct access to the underlying microscopic processes. These classic studies have demonstrated that very different groupings of the microscopic processes can yield extremely similar macroscopic responses. Biologists in fields other than biophysics are frequently confronted with the same macroscopic-to-microscopic problem, usually, however, without any direct access to the microscopic processes. Thus, the development of computational methods to deduce from the available macroscopic measurements the nature of the underlying microscopic processes can be expected to substantially advance the study of many areas of cell physiology. Toward that aim, here we have derived and tested a hybrid computational-analytical method to extract information about the microscopic processes that is hidden in macroscopic experimental traces. Our method is independent of the particular system under study, and thus can be applied to new as well as previously-recorded macroscopic traces obtained in a wide variety of biological systems.

The Effects of Hallucinogens on Gene Expression

The classic serotonergic hallucinogens, or psychedelics, have the ability to profoundly alter perception and behavior. These can include visual distortions, hallucinations, detachment from reality, and mystical experiences. Some psychedelics, like LSD, are able to produce these effects with remarkably low doses of drug. Others, like psilocybin, have recently been demonstrated to have significant clinical efficacy in the treatment of depression, anxiety, and addiction that persist for at least several months after only a single therapeutic session. How does this occur? Much work has recently been published from imaging studies showing that psychedelics alter brain network connectivity. They facilitate a disintegration of the default mode network, producing a hyperconnectivity between brain regions that allow centers that do not normally communicate with each other to do so. The immediate and acute effects on both behaviors and network connectivity are likely mediated by effector pathways downstream of serotonin 5-HT2A receptor activation. These acute molecular processes also influence gene expression changes, which likely influence synaptic plasticity and facilitate more long-term changes in brain neurochemistry ultimately underlying the therapeutic efficacy of a single administration to achieve long-lasting effects. In this review, we summarize what is currently known about the molecular genetic responses to psychedelics within the brain and discuss how gene expression changes may contribute to altered cellular physiology and behaviors.

Hallucinogens in Drug Discrimination

Hallucinogens comprise a diverse collection of chemicals with multifarious receptor actions in the central nervous system. Preclinical drug screening methods have proven invaluable in the evaluation and characterization of hallucinogen psychopharmacology. Used in concert with structural chemistry and receptor pharmacology methods, preclinical drug discrimination research has informed our current understanding of hallucinogens and the neurochemical receptor mechanisms responsible for their interoceptive stimulus effects. This chapter summarizes the strengths and limitations of drug discrimination as an in vivo drug detection method and offers a brief review of historical and contemporary drug discrimination research with classical hallucinogens.