Cognitive Impairment Induced by Delta9-tetrahydrocannabinol Occurs through Heteromers between Cannabinoid CB1 and Serotonin 5-HT2A Receptors

Bridging the gap: The endocannabinoid system as a functional fulcrum for benzodiazepines in a novel frontier of anxiety pharmacotherapy

While benzodiazepines have been a mainstay of the pharmacotherapy of anxiety disorders, their short-term efficacy and risk of abuse have driven the exploration of alternative treatment approaches. The endocannabinoid (eCB) system has emerged as a key modulator of anxiety-related processes, with evidence suggesting dynamic interactions between the eCB system and the GABAergic system, the primary target of benzodiazepines. According to the existing literature, the activation of the cannabinoid receptors has been shown to exert anxiolytic effects, while their blockade or genetic deletion results in heightened anxiety-like responses. Moreover, studies have provided evidence of interactions between the eCB system and benzodiazepines in anxiety modulation. For instance, the attenuation of benzodiazepine-induced anxiolysis by cannabinoid receptor antagonism or genetic variations in the eCB system components in animal studies, have been associated with variations in benzodiazepine response and susceptibility to anxiety disorders. The combined use of cannabinoid-based medications, such as cannabinoid receptor agonists and benzodiazepine co-administration, has shown promise in augmenting anxiolytic effects and reducing benzodiazepine dosage requirements. This article aims to comprehensively review and discuss the current evidence on the involvement of the eCB system as a key modulator of benzodiazepine-related anxiolytic effects, and further, the possible mechanisms by which the region-specific eCB system-GABAergic connectivity modulates the neuro-endocrine/behavioral stress response, providing an inclusive understanding of the complex interplay between the eCB system and benzodiazepines in the context of anxiety regulation, to inform future research and clinical practice.

Microbiota and social behavior alterations in a mouse model of down syndrome: Modulation by a synbiotic treatment

Sex differences in the composition and functionality of gut microbiota are an emerging field of interest in neurodevelopmental disorders, as they may help in understanding the phenotypic disparities between males and females. This study aimed to characterize sex-related specific alterations in gut microbiota composition in a mouse model of Down syndrome (Ts65Dn mice, TS mice) through the sequencing of the PCR-amplified 16S ribosomal DNA fraction. Moreover, it intended to examine whether the modulation of gut microbiota by the administration of a synbiotic (SYN) treatment would be beneficial for the behavioral alterations observed in male and female TS mice. Our results show that male, but not female, TS mice exhibit alterations in beta diversity compared to their wild-type (WT) littermates. Sex-dependent differences are also observed in the relative abundance of the classes Bacilli and Clostridia. Administering the SYN effectively counteracts hypersociability in females, and normalizes the overall abundance of Bacilli, specifically by increasing Lactobacillaceae. On the contrary, it rescues emotional recognition deficits in male TS mice and increases the relative abundance of the families Lactobacillaceae, Streptococcaceae and Atopobiaceae. In addition, a metagenome KEGG analysis of differentially enriched pathways shows relevant changes in the cofactor biosynthesis and the amino acid synthesis categories. Finally, following SYN treatment, both male and female TS mice exhibit a robust increase in propionic acid levels compared to WT littermates. These findings suggest sex-specific mechanisms that could link gut microbiota composition with behavior in TS mice, and underscore the potential of targeted gut microbiota interventions to modulate social abnormalities in neurodevelopmental disorders.

Design of Small Non-Peptidic Ligands That Alter Heteromerization between Cannabinoid CB1 and Serotonin 5HT2A Receptors

Activation of cannabinoid CB1 receptors (CB1R) by agonists induces analgesia but also induces cognitive impairment through the heteromer formed between CB1R and the serotonin 5HT2A receptor (5HT2AR). This side effect poses a serious drawback in the therapeutic use of cannabis for pain alleviation. Peptides designed from the transmembrane helices of CB1R, which are predicted to bind 5HT2AR and alter the stability of the CB1R-5HT2AR heteromer, have been shown to avert CB1R agonist-induced cognitive impairment while preserving analgesia. Using these peptides as templates, we have now designed nonpeptidic small molecules that prevent CB1R-5HT2AR heteromerization in bimolecular fluorescence complementation assays and the heteromerization-dependent allosteric modulations in cell signaling experiments. These results provide proof-of-principle for the design of optimized ligand-based disruptors of the CB1R-5HT2AR heteromer, opening new perspectives for in vivo studies.

The role of heterodimers formed by histamine H3 receptors and dopamine D1 receptors on the methamphetamine-induced conditioned place preference

RATIONALE

The rewarding effect of Methamphetamine (METH) is commonly believed to play an important role in METH use disorder. The altered expression of dopamine D1 receptor (D1R) has been suggested to be essential to the rewarding effect of METH. Notably, D1R could interact with histamine H3 receptors (H3R) by forming a H3R-D1R heteromer (H3R-D1R).

OBJECTIVES

This study was designed to specifically investigate the involvement of H3R-D1R in the rewarding effect of METH.

METHODS

C57BL/6 mice were treated with intraperitoneal injections of a selective H3R antagonist (Thioperamide, THIO; 20 mg/kg), an H1R antagonist (Pyrilamine, PYRI; 10 mg/kg), or microinjections of cytomegalovirus (CMV)-transmembrane domain 5 (TM5) into the nucleus accumbens (NAc). The animal model of Conditioned Place Preference (CPP) was applied to determine the impact of H3R-D1R on the rewarding effect of METH.

RESULTS

METH resulted in a significant preference for the drug-associated chamber, in conjunction with increased H3R and decreased D1R expression in both NAc and the ventral tegmental area (VTA). THIO significantly attenuated the rewarding effect of METH, accompanied by decreased H3R and increased D1R expression. In contrast, pyrilamine failed to produce the similar effects. Moreover, the inhibitory effect of THIO on METH-induced CPP was reversed by SKF38393, a D1R agonist. Furthermore, SCH23390, a D1R antagonist, counteracted the ameliorative effect of SKF38393 on THIO. Co-immunoprecipitation (CO-IP) experiments further demonstrated the specific interaction between H3R and D1R in METH CPP mice. The rewarding effect of METH was also significantly blocked by the interruption of CMV-transmembrane domain 5 (TM5), but not CMV-transmembrane domain 7 (TM7) in NAc.

CONCLUSION

These results suggest that modulating the activity of H3R-D1R complex holds promise for regulating METH use disorder and serves as a potential drug target for its treatment.

Adolescent cannabinoid exposure rescues phencyclidine-induced social deficits through modulation of CA2 transmission

Psychotic disorders entail intricate conditions marked by disruptions in cognition, perception, emotions, and social behavior. Notably, psychotic patients who use cannabis tend to show less severe deficits in social behaviors, such as the misinterpretation of social cues and the inability to interact with others. However, the biological underpinnings of this epidemiological interaction remain unclear. Here, we used the NMDA receptor blocker phencyclidine (PCP) to induce psychotic-like states and to study the impact of adolescent cannabinoid exposure on social behavior deficits and synaptic transmission changes in hippocampal area CA2, a region known to be active during social interactions. In particular, adolescent mice underwent 7 days of subchronic treatment with the synthetic cannabinoid, WIN 55, 212-2 (WIN) followed by one injection of PCP. Using behavioral, biochemical, and electrophysiological approaches, we showed that PCP persistently reduced sociability, decreased GAD67 expression in the hippocampus, and induced GABAergic deficits in proximal inputs from CA3 and distal inputs from the entorhinal cortex (EC) to CA2. Notably, WIN exposure during adolescence specifically restores adult sociability deficits, the expression changes in GAD67, and the GABAergic impairments in the EC-CA2 circuit, but not in the CA3-CA2 circuit. Using a chemogenetic approach to target EC-CA2 projections, we demonstrated the involvement of this specific circuit on sociability deficits. Indeed, enhancing EC-CA2 transmission was sufficient to induce sociability deficits in vehicle-treated mice, but not in animals treated with WIN during adolescence, suggesting a mechanism by which adolescent cannabinoid exposure rescues sociability deficits caused by enhanced EC-CA2 activity in adult mice.

The interaction between cannabinoids and long-term synaptic plasticity: A survey on memory formation and underlying mechanisms

Synaptic plasticity, including long-term potentiation (LTP) and long-term depression (LTD), is an essential phenomenon in memory formation as well as maintenance along with many other cognitive functions, such as those needed for coping with external stimuli. Synaptic plasticity consists of gradual changes in the biochemistry and morphology of pre- and postsynaptic neurons, particularly in the hippocampus. Consuming marijuana as a primary source of exocannabinoids immediately impairs attention and working memory-related tasks. Evidence regarding the effects of cannabinoids on LTP and memory is contradictory. While cannabinoids can affect a variety of specific cannabinoid receptors (CBRs) and nonspecific receptors throughout the body and brain, they exert miscellaneous systemic and local cerebral effects. Given the increasing use of cannabis, mainly among the young population, plus its potential adverse long-term effects on learning and memory processes, it could be a future global health challenge. Indeed, the impact of cannabinoids on memory is multifactorial and depends on the dosage, timing, formula, and route of consumption, plus the background complex interaction of the endocannabinoids system with other cerebral networks. Herein, we review how exogenously administrated organic cannabinoids, CBRs agonists or antagonists, and endocannabinoids can affect LTP and synaptic plasticity through various receptors in interaction with other cerebral pathways and primary neurotransmitters.

Allosterism in the adenosine A2A and cannabinoid CB2 heteromer

BACKGROUND AND PURPOSE

Allosterism is a regulatory mechanism for GPCRs that can be attained by ligand-binding or protein-protein interactions with another GPCR. We have studied the influence of the dimer interface on the allosteric properties of the A2A receptor and CB2 receptor heteromer.

EXPERIMENTAL APPROACH

We have evaluated cAMP production, phosphorylation of signal-regulated kinases (pERK1/2), label-free dynamic mass redistribution, β-arrestin 2 recruitment and bimolecular fluorescence complementation assays in the absence and presence of synthetic peptides that disrupt the formation of the heteromer. Molecular dynamic simulations provided converging evidence that the heteromeric interface influences the allosteric properties of the A2AR-CB2R heteromer.

KEY RESULTS

Apo A2AR blocks agonist-induced signalling of CB2R. The disruptive peptides, with the amino acid sequence of transmembrane (TM) 6 of A2AR or CB2R, facilitate CB2R activation, suggesting that A2AR allosterically prevents the outward movement of TM 6 of CB2R for G protein binding. Significantly, binding of the selective antagonist SCH 58261 to A2AR also facilitated agonist-induced activation of CB2R.

CONCLUSIONS AND IMPLICATIONS

It is proposed that the A2AR-CB2R heteromer contains distinct dimerization interfaces that govern its functional properties. The molecular interface between protomers of the A2AR-CB2R heteromer interconverted from TM 6 for apo or agonist-bound A2AR, blocking CB2R activation, to mainly the TM 1/7 interface for antagonist-bound A2AR, facilitating the independent opening of intracellular cavities for G protein binding. These novel results shed light on a different type of allosteric mechanism and extend the repertoire of GPCR heteromer signalling.

Early biomarkers in the presymptomatic phase of cognitive impairment: changes in the endocannabinoidome and serotonergic pathways in Alzheimer's-prone mice after mTBI

BACKGROUND

Despite extensive studies on the neurobiological correlates of traumatic brain injury (TBI), little is known about its molecular determinants on long-term consequences, such as dementia and Alzheimer's disease (AD).

METHODS

Here, we carried out behavioural studies and an extensive biomolecular analysis, including inflammatory cytokines, gene expression and the combination of LC-HRMS and MALDI-MS Imaging to elucidate the targeted metabolomics and lipidomics spatiotemporal alterations of brains from wild-type and APP-SWE mice, a genetic model of AD, at the presymptomatic stage, subjected to mild TBI.

RESULTS

We found that brain injury does not affect cognitive performance in APP-SWE mice. However, we detected an increase of key hallmarks of AD, including Aβ1-42 levels and BACE1 expression, in the cortices of traumatized transgenic mice. Moreover, significant changes in the expanded endocannabinoid (eCB) system, or endocannabinoidome (eCBome), occurred, including increased levels of the endocannabinoid 2-AG in APP-SWE mice in both the cortex and hippocampus, and N-acylserotonins, detected for the first time in the brain. The gene expression of enzymes for the biosynthesis and inactivation of eCBs and eCB-like mediators, and some of their main molecular targets, also underwent significant changes. We also identified the formation of heteromers between cannabinoid 1 (CB1) and serotonergic 2A (5HT2A) receptors, whose levels increased in the cortex of APP-SWE mTBI mice, possibly contributing to the exacerbated pathophysiology of AD induced by the trauma.

CONCLUSIONS

Mild TBI induces biochemical changes in AD genetically predisposed mice and the eCBome may play a role in the pathogenetic link between brain injury and neurodegenerative disorders also by interacting with the serotonergic system.

Centralizing the Knowledge and Interpretation of Pain in Chemotherapy-Induced Peripheral Neuropathy: A Paradigm Shift towards Brain-Centric Approaches

Chemotherapy-induced peripheral neuropathy (CIPN) is a side effect of cancer treatment, often linked with pain complaints. Patients report mechanical and thermal hypersensitivity that may emerge during chemotherapy treatment and may persist after cancer remission. Whereas the latter situation disturbs the quality of life, life itself may be endangered by the appearance of CIPN during cancer treatment. The causes of CIPN have almost entirely been ascribed to the neurotoxicity of chemotherapeutic drugs in the peripheral nervous system. However, the central consequences of peripheral neuropathy are starting to be unraveled, namely in the supraspinal pain modulatory system. Based on our interests and experience in the field, we undertook a review of the brain-centered alterations that may underpin pain in CIPN. The changes in the descending pain modulation in CIPN models along with the functional and connectivity abnormalities in the brain of CIPN patients are analyzed. A translational analysis of preclinical findings about descending pain regulation during CIPN is reviewed considering the main neurochemical systems (serotoninergic and noradrenergic) targeted in CIPN management in patients, namely by antidepressants. In conclusion, this review highlights the importance of studying supraspinal areas involved in descending pain modulation to understand the pathophysiology of CIPN, which will probably allow a more personalized and effective CIPN treatment in the future.

G protein-specific mechanisms in the serotonin 5-HT2A receptor regulate psychosis-related effects and memory deficits

G protein-coupled receptors (GPCRs) are sophisticated signaling machines able to simultaneously elicit multiple intracellular signaling pathways upon activation. Complete (in)activation of all pathways can be counterproductive for specific therapeutic applications. This is the case for the serotonin 2 A receptor (5-HT2AR), a prominent target for the treatment of schizophrenia. In this study, we elucidate the complex 5-HT2AR coupling signature in response to different signaling probes, and its physiological consequences by combining computational modeling, in vitro and in vivo experiments with human postmortem brain studies. We show how chemical modification of the endogenous agonist serotonin dramatically impacts the G protein coupling profile of the 5-HT2AR and the associated behavioral responses. Importantly, among these responses, we demonstrate that memory deficits are regulated by Gαq protein activation, whereas psychosis-related behavior is modulated through Gαi1 stimulation. These findings emphasize the complexity of GPCR pharmacology and physiology and open the path to designing improved therapeutics for the treatment of stchizophrenia.

Allosteric Modulators of Serotonin Receptors: A Medicinal Chemistry Survey

Serotonin (5-hydroxytryptamine, 5-HT) is a neurotransmitter regulating numerous physiological functions, and its dysregulation is a crucial component of the pathological processes of schizophrenia, depression, migraines, and obesity. 5-HT interacts with 14 different receptors, of which 5-HT1A-1FRs, 5-HT2A-CRs, and 5-HT4-7Rs are G protein-coupled receptors (GPCRs), while 5-HT3R is a ligand-gated ion channel. Over the years, selective orthosteric ligands have been identified for almost all serotonin receptors, yielding several clinically relevant drugs. However, the high degree of homology between 5-HTRs and other GPCRs means that orthosteric ligands can have severe side effects. Thus, there has recently been increased interest in developing safer ligands of GPCRs, which bind to less conserved, more specific sites, distinct from that of the receptor's natural ligand. The present review describes the identification of allosteric ligands of serotonin receptors, which are largely natural compounds (oleamide, cannabidiol, THC, and aporphine alkaloids), complemented by synthetic modulators developed in large part for the 5-HT2C receptor. The latter are positive allosteric modulators sought after for their potential as drugs preferable over the orthosteric agonists as antiobesity agents for their potentially safer profile. When available, details on the interactions between the ligand and allosteric binding site will be provided. An outlook on future research in the field will also be provided.

5-HT2A receptors are involved in the pharmaco-toxicological effects of the synthetic cannabinoids JWH-018 and 5F-PB22: In vivo studies in mice

Over the last years, Synthetic Cannabinoids (SCs) have been among the largest and most frequently seized groups of Novel Psychoactive Substances (NPS). These substances have been frequently detected in biological samples from patients involved in several intoxication and death cases. Their serious adverse effects have been related to their action as potent agonist of cannabinoid CB1 receptors. However, evidence concerning the potential interaction between SCs and serotoninergic mechanisms has emerged. Therefore, this study aims to evaluate the involvement of 5-HT2A receptors in the effects induced by acute systemic administration of 1-pentyl-3-(1-naphthoyl)indole (JWH-018; 1 mg/kg) and quinolin-8-yl 1-pentyfluoro-1H-indole-3-8-carboxylate (5F-PB22; 1 mg/kg). Sensorimotor (visual, acoustic, and tactile) responses, pain threshold (acute mechanical and thermal nociception), core temperature, breath rate and motor performance (stepping activity) have been assessed in CD-1 male mice. The present results pointed out that both substances deeply alter sensorimotor responses, nociceptive threshold, core temperature, breath rate and motor activity in mice. Noteworthy, pretreatment with the selective 5-HT2A receptors antagonist MDL100907 (0.1 mg/kg) at least partially prevented sensorimotor disruption, antinociception and hypothermic effects. Conversely, the respiratory and motor impairment was not prevented. Thus, it states the relevance of serotoninergic 5-HT2A mechanisms on pharmaco-toxicological effects induced by SCs.

The CB1 receptor interacts with cereblon and drives cereblon deficiency-associated memory shortfalls

Cereblon/CRBN is a substrate-recognition component of the Cullin4A-DDB1-Roc1 E3 ubiquitin ligase complex. Destabilizing mutations in the human CRBN gene cause a form of autosomal recessive non-syndromic intellectual disability (ARNSID) that is modelled by knocking-out the mouse Crbn gene. A reduction in excitatory neurotransmission has been proposed as an underlying mechanism of the disease. However, the precise factors eliciting this impairment remain mostly unknown. Here we report that CRBN molecules selectively located on glutamatergic neurons are necessary for proper memory function. Combining various in vivo approaches, we show that the cannabinoid CB1 receptor (CB1R), a key suppressor of synaptic transmission, is overactivated in CRBN deficiency-linked ARNSID mouse models, and that the memory deficits observed in these animals can be rescued by acute CB1R-selective pharmacological antagonism. Molecular studies demonstrated that CRBN interacts physically with CB1R and impairs the CB1R-Gi/o-cAMP-PKA pathway in a ubiquitin ligase-independent manner. Taken together, these findings unveil that CB1R overactivation is a driving mechanism of CRBN deficiency-linked ARNSID and anticipate that the antagonism of CB1R could constitute a new therapy for this orphan disease.

Modulation of DOM-Induced Head-Twitch Response by mGluR2 Agonist/Inverse Agonist is Associated with 5-HT2AR-Mediated Gs Signaling Pathway

Hallucinogenic 5-HT2A receptor (5-HT2AR) agonists-induced head-twitch response (HTR) is regulated by Gs signaling pathway. Formation of heterodimers between 5-HT2AR and metabotropic glutamate mGlu2 receptor (mGluR2) is essential for the hallucinogenic 5-HT2AR agonist-induced HTR. In order to investigate the effects of mGluR2 agonists and inverse agonists on hallucinogenic 5-HT2AR agonists DOM-induced HTR, C57BL/6 mice were pretreated with mGluR2 agonists (LY379268, LY354740, LY404039) or the inverse agonist LY341495, and the HTR was manually counted after administering DOM immediately. IP-One (IP1) HTRF assay and cAMP assay were performed to evaluate the effect of LY341495 or LY354740 on DOM-induced Gq and Gs activation in Human Embryonic Kidney-293 (HEK-293) T-type cells co-expressing 5-HT2AR and mGluR2. The results showed that DOM-induced HTR in mice was dose-dependently inhibited by LY379268, LY354740, and LY404039, while it was dose-dependently enhanced by LY341495. Moreover, LY341495 reversed the inhibitory effect of LY354740 on DOM-induced HTR. In HEK-293T cells co-expressing 5-HT2AR and mGluR2, DOM-induced cAMP level was decreased by LY354740 and increased by LY341495, but DOM-induced IP1 level was not regulated by LY354740 or LY341495. The regulation of DOM-induced HTR by mGluR2 agonists and inverse agonists is closely related to 5-HT2AR-mediated Gs signaling pathway. In HEK-293T cells co-expressing 5-HT2AR and mGluR2 A677S/A681P/A685G mutant (mGluR2 3 A mutant), DOM-induced cAMP level was not regulated by LY354740, but was significantly enhanced by LY341495. The 5-HT2AR/mGluR2 heterodimers is critical for DOM-induced HTR and cAMP level, both of which are inhibited by mGluR2 agonists and enhanced by mGluR2 inverse agonists.

The Effects of Psychedelics on Neuronal Physiology

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

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

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

The psychedelic effects of cannabis: A review of the literature

Cannabis and classic psychedelics are controlled substances with emerging evidence of efficacy in the treatment of a variety of psychiatric illnesses. Cannabis has largely not been regarded as having psychedelic effects in contemporary literature, despite many examples of historical use along with classic psychedelics to attain altered states of consciousness. Research into the "psychedelic" effects of cannabis, and delta-9-tetrahydrocannabinol (THC) in particular, could prove helpful for assessing potential therapeutic indications and elucidating the mechanism of action of both cannabis and classic psychedelics. This review aggregates and evaluates the literature assessing the capacity of cannabis to yield the perceptual changes, aversiveness, and mystical experiences more typically associated with classic psychedelics such as psilocybin. This review also provides a brief contrast of neuroimaging findings associated with the acute effects of cannabis and psychedelics. The available evidence suggests that high-THC cannabis may be able to elicit psychedelic effects, but that these effects may not have been observed in recent controlled research studies due to the doses, set, and settings commonly used. Research is needed to investigate the effects of high doses of THC in the context utilized in therapeutic studies of psychedelics aimed to occasion psychedelic and/or therapeutic experiences. If cannabis can reliably generate psychedelic experiences under these conditions, high-THC dose cannabis treatments should be explored as potential adjunctive treatments for psychiatric disorders and be considered as an active comparator in clinical trials involving traditional psychedelic medications.

The Basic Science of Cannabinoids

The cannabis plant has been used for centuries to manage the symptoms of various ailments including pain. Hundreds of chemical compounds have been identified and isolated from the plant and elicit a variety of physiological responses by binding to specific receptors and interacting with numerous other proteins. In addition, the body makes its own cannabinoid-like compounds that are integrally involved in modulating normal and pathophysiological processes. As the legal cannabis landscape continues to evolve within the United States and throughout the world, it is important to understand the rich science behind the effects of the plant and the implications for providers and patients. This narrative review aims to provide an overview of the basic science of the cannabinoids by describing the discovery and function of the endocannabinoid system, pharmacology of cannabinoids, and areas for future research and therapeutic development as they relate to perioperative and chronic pain medicine.

Functional Dimerization of Serotonin Receptors: Role in Health and Depressive Disorders

Understanding the neurobiological underpinnings of depressive disorder constitutes a pressing challenge in the fields of psychiatry and neurobiology. Depression represents one of the most prevalent forms of mental and behavioral disorders globally. Alterations in dimerization capacity can influence the functional characteristics of serotonin receptors and may constitute a contributing factor to the onset of depressive disorders. The objective of this review is to consolidate the current understanding of interactions within the 5-HT receptor family and between 5-HT receptors and members of other receptor families. Furthermore, it aims to elucidate the role of such complexes in depressive disorders and delineate the mechanisms through which antidepressants exert their effects.

Cortical structural differences following repeated ayahuasca use hold molecular signatures

Introduction

Serotonergic psychedelics such as ayahuasca are reported to promote both structural and functional neural plasticity via partial 5-HT2A agonism. However, little is known about how these molecular mechanisms may extend to repeated psychedelic administration in humans, let alone neuroanatomy. While early evidence suggests localised changes to cortical thickness in long-term ayahuasca users, it is unknown how such findings may be reflected by large-scale anatomical brain networks comprising cytoarchitecturally complex regions.

Methods

Here, we examined the relationship between cortical gene expression markers of psychedelic action and brain morphometric change following repeated ayahuasca usage, using high-field 7 Tesla neuroimaging data derived from 24 members of an ayahuasca-using church (Santo Daime) and case-matched controls.

Results

Using a morphometric similarity network (MSN) analysis, repeated ayahuasca use was associated with a spatially distributed cortical patterning of both structural differentiation in sensorimotor areas and de-differentiation in transmodal areas. Cortical MSN remodelling was found to be spatially correlated with dysregulation of 5-HT2A gene expression as well as a broader set of genes encoding target receptors pertinent to ayahuasca's effects. Furthermore, these associations were similarly interrelated with altered gene expression of specific transcriptional factors and immediate early genes previously identified in preclinical assays as relevant to psychedelic-induced neuroplasticity.

Conclusion

Taken together, these findings provide preliminary evidence that the molecular mechanisms of psychedelic action may scale up to a macroscale level of brain organisation in vivo. Closer attention to the role of cortical transcriptomics in structural-functional coupling may help account for the behavioural differences observed in experienced psychedelic users.

Endocannabinoid signaling in adult hippocampal neurogenesis: A mechanistic and integrated perspective

Dentate gyrus of the hippocampus continuously gives rise to new neurons, namely, adult-born granule cells, which contribute to conferring plasticity to the mature brain throughout life. Within this neurogenic region, the fate and behavior of neural stem cells (NSCs) and their progeny result from a complex balance and integration of a variety of cell-autonomous and cell-to-cell-interaction signals and underlying pathways. Among these structurally and functionally diverse signals, there are endocannabinoids (eCBs), the main brain retrograde messengers. These pleiotropic bioactive lipids can directly and/or indirectly influence adult hippocampal neurogenesis (AHN) by modulating, both positively and negatively, multiple molecular and cellular processes in the hippocampal niche, depending on the cell type or stage of differentiation. Firstly, eCBs act directly as cell-intrinsic factors, cell-autonomously produced by NSCs following their stimulation. Secondly, in many, if not all, niche-associated cells, including some local neuronal and nonneuronal elements, the eCB system indirectly modulates the neurogenesis, linking neuronal and glial activity to regulating distinct stages of AHN. Herein, we discuss the crosstalk of the eCB system with other neurogenesis-relevant signal pathways and speculate how the hippocampus-dependent neurobehavioral effects elicited by (endo)cannabinergic medications are interpretable in light of the key regulatory role that eCBs play on AHN.

Cognitive Alterations in Addictive Disorders: A Translational Approach

The cognitive decline in people with substance use disorders is well known and can be found during both the dependence and drug abstinence phases. At the clinical level, cognitive decline impairs the response to addiction treatment and increases dropout rates. It can be irreversible, even after the end of drug abuse consumption. Improving our understanding of the molecular and cellular alterations associated with cognitive decline could be essential to developing specific therapeutic strategies for its treatment. Developing animal models to simulate drug abuse-induced learning and memory alterations is critical to continue exploring this clinical situation. The main aim of this review is to summarize the most recent evidence on cognitive impairment and the associated biological markers in patients addicted to some of the most consumed drugs of abuse and in animal models simulating this clinical situation. The available information suggests the need to develop more studies to further explore the molecular alterations associated with cognitive impairment, with the ultimate goal of developing new potential therapeutic strategies.

Control of a hippocampal recurrent excitatory circuit by cannabinoid receptor-interacting protein Gap43

The type-1 cannabinoid receptor (CB₁R) is widely expressed in excitatory and inhibitory nerve terminals, and by suppressing neurotransmitter release, its activation modulates neural circuits and brain function. While the interaction of CB₁R with various intracellular proteins is thought to alter receptor signaling, the identity and role of these proteins are poorly understood. Using a high-throughput proteomic analysis complemented with an array of in vitro and in vivo approaches in the mouse brain, we report that the C-terminal, intracellular domain of CB₁R interacts specifically with growth-associated protein of 43 kDa (GAP43). The CB₁R-GAP43 interaction occurs selectively at mossy cell axon boutons, which establish excitatory synapses with dentate granule cells in the hippocampus. This interaction impairs CB₁R-mediated suppression of mossy cell to granule cell transmission, thereby inhibiting cannabinoid-mediated anti-convulsant activity in mice. Thus, GAP43 acts as a synapse type-specific regulatory partner of CB₁R that hampers CB₁R-mediated effects on hippocampal circuit function.

The effects of serotonergic psychedelics in synaptic and intrinsic properties of neurons in layer II/III of the orbitofrontal cortex

RATIONALE

Serotonergic psychedelics show promise in the treatment of psychiatric disorders, including obsessive-compulsive disorder. Dysfunction of the orbitofrontal cortex (OFc) has been implicated in the pathophysiology of compulsive behavior, which might be a key region for the efficacy of psychedelics. However, the effects of psychedelics on the neural activities and local excitation/inhibition (E/I) balance in the OFc are unclear.

OBJECTIVES

This study aimed to investigate how 25C-NBOMe, a substituted phenethylamine psychedelic, regulated the synaptic and intrinsic properties of neurons in layer II/III of the OFc.

METHODS

Acute brain slices containing the OFc of adult male Sprague Dawley rats were used for ex vivo whole-cell recording. The synaptic and intrinsic properties of neurons were monitored using voltage and current clamps, respectively. Electrically evoked action potential (eAP) was used to measure synaptic-driven pyramidal activity.

RESULTS

25C-NBOMe enhanced spontaneous neurotransmission at glutamatergic synapses but diminished that in GABAergic synapses through the 5-HT_2A receptor. 25C-NBOMe also increased both evoked excitatory currents and evoked action potentials. Moreover, 25C-NBOMe promoted the excitability of pyramidal neurons but not fast-spiking neurons. Either inhibiting G protein-gated inwardly rectifying potassium channels or activating protein kinase C significantly obstructed the facilitative effect of 25C-NBOMe on the intrinsic excitability of pyramidal neurons.

CONCLUSIONS

This work reveals the multiple roles of 25C-NBOMe in modulating synaptic and neuronal function in the OFc, which collectively promotes local E/I ratios.

The histamine H3 receptor modulates dopamine D2 receptor-dependent signaling pathways and mouse behaviors

The histamine H3 receptor (H3R) is highly enriched in the spiny projection neurons (SPNs) of the striatum, in both the D1 receptor (D1R)-expressing and D2 receptor (D2R)-expressing populations. A crossantagonistic interaction between H3R and D1R has been demonstrated in mice, both at the behavioral level and at the biochemical level. Although interactive behavioral effects have been described upon coactivation of H3R and D2R, the molecular mechanisms underlying this interaction are poorly understood. Here, we show that activation of H3R with the selective agonist R-(-)-α-methylhistamine dihydrobromide mitigates D2R agonist-induced locomotor activity and stereotypic behavior. Using biochemical approaches and the proximity ligation assay, we demonstrated the existence of an H3R-D2R complex in the mouse striatum. In addition, we examined consequences of simultaneous H3R-D2R agonism on the phosphorylation levels of several signaling molecules using immunohistochemistry. H3R agonist treatment modulated Akt (serine/threonine PKB)-glycogen synthase kinase 3 beta signaling in response to D2R activation via a β-arrestin 2-dependent mechanism in D2R-SPNs but not in D1R-SPNs. Phosphorylation of mitogen- and stress-activated protein kinase 1 and rpS6 (ribosomal protein S6) was largely unchanged under these conditions. As Akt-glycogen synthase kinase 3 beta signaling has been implicated in several neuropsychiatric disorders, this work may help clarify the role of H3R in modulating D2R function, leading to a better understanding of pathophysiology involving the interaction between histamine and dopamine systems.

Allosteric Regulation of G-Protein-Coupled Receptors: From Diversity of Molecular Mechanisms to Multiple Allosteric Sites and Their Ligands

Allosteric regulation is critical for the functioning of G protein-coupled receptors (GPCRs) and their signaling pathways. Endogenous allosteric regulators of GPCRs are simple ions, various biomolecules, and protein components of GPCR signaling (G proteins and β-arrestins). The stability and functional activity of GPCR complexes is also due to multicenter allosteric interactions between protomers. The complexity of allosteric effects caused by numerous regulators differing in structure, availability, and mechanisms of action predetermines the multiplicity and different topology of allosteric sites in GPCRs. These sites can be localized in extracellular loops; inside the transmembrane tunnel and in its upper and lower vestibules; in cytoplasmic loops; and on the outer, membrane-contacting surface of the transmembrane domain. They are involved in the regulation of basal and orthosteric agonist-stimulated receptor activity, biased agonism, GPCR-complex formation, and endocytosis. They are targets for a large number of synthetic allosteric regulators and modulators, including those constructed using molecular docking. The review is devoted to the principles and mechanisms of GPCRs allosteric regulation, the multiplicity of allosteric sites and their topology, and the endogenous and synthetic allosteric regulators, including autoantibodies and pepducins. The allosteric regulation of chemokine receptors, proteinase-activated receptors, thyroid-stimulating and luteinizing hormone receptors, and beta-adrenergic receptors are described in more detail.

Cannabinoids and the placenta: Receptors, signaling and outcomes

Cannabis use during pregnancy is increasing. The improvement of pregnancy-related symptoms including morning sickness and management of mood and stress are among the most reported reasons for its use. Δ9-tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD) are the most abundant cannabinoids found within the cannabis flower. The concentration of these components has drastically increased in the past 20 years. Additionally, many edibles contain only one cannabinoid and are marketed to achieve a specific goal, meaning there are an increasing number of pregnancies that are exposed to isolated cannabinoids. Both Δ9-THC and CBD cross the placenta and can impact the fetus directly, but the receptors through which cannabinoids act are also expressed throughout the placenta, suggesting that the effects of in-utero cannabinoid exposure may include indirect effects from the placenta. In-utero cannabis research focuses on short and long-term fetal health and development; however, these studies include little to no placenta analysis. Prenatal cannabinoid exposure is linked to small for gestational age and fetal growth-restricted babies. Compromised placental development is also associated with fetal growth restriction and the few studies (clinical and animal models) that included placental analysis, identify changes in placental vasculature and function in these cannabinoid-exposed pregnancies. In vitro studies further support cannabinoid impact on cell function in the different populations that comprise the placenta. In this article, we aim to summarize how phytocannabinoids can impact placental development and function. Specifically, the cannabinoids and their actions at the different receptors are described, with receptor localization throughout the human and murine placenta discussed. Findings from studies that included placental analysis and how cannabinoid signaling may modulate critical developmental processing including cell proliferation, angiogenesis and migration are described. Considering the current research, prenatal cannabinoid exposure may significantly impact placental development, and, as such, identifying windows of placental vulnerability for each cannabinoid will be critical to elucidate the etiology of fetal outcome studies.

THC and CBD: Villain versus Hero? Insights into Adolescent Exposure

Cannabis is the most used drug of abuse worldwide. It is well established that the most abundant phytocannabinoids in this plant are Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD). These two compounds have remarkably similar chemical structures yet vastly different effects in the brain. By binding to the same receptors, THC is psychoactive, while CBD has anxiolytic and antipsychotic properties. Lately, a variety of hemp-based products, including CBD and THC, have become widely available in the food and health industry, and medical and recreational use of cannabis has been legalized in many states/countries. As a result, people, including youths, are consuming CBD because it is considered “safe”. An extensive literature exists evaluating the harmful effects of THC in both adults and adolescents, but little is known about the long-term effects of CBD exposure, especially in adolescence. The aim of this review is to collect preclinical and clinical evidence about the effects of cannabidiol.

Endocannabinoid System and Exogenous Cannabinoids in Depression and Anxiety: A Review

Background: There is a growing liberalization of cannabis-based preparations for medical and recreational use. In multiple instances, anxiety and depression are cited as either a primary or a secondary reason for the use of cannabinoids. Aim: The purpose of this review is to explore the association between depression or anxiety and the dysregulation of the endogenous endocannabinoid system (ECS), as well as the use of phytocannabinoids and synthetic cannabinoids in the remediation of depression/anxiety symptoms. After a brief description of the constituents of cannabis, cannabinoid receptors and the endocannabinoid system, the most important evidence is presented for the involvement of cannabinoids in depression and anxiety both in human and from animal models of depression and anxiety. Finally, evidence is presented for the clinical use of cannabinoids to treat depression and anxiety. Conclusions: Although the common belief that cannabinoids, including cannabis, its main studied components-tetrahydrocannabinol (THC) and cannabidiol (CBD)-or other synthetic derivatives have been suggested to have a therapeutic role for certain mental health conditions, all recent systematic reviews that we report have concluded that the evidence that cannabinoids improve depressive and anxiety disorders is weak, of very-low-quality, and offers no guidance on the use of cannabinoids for mental health conditions within a regulatory framework. There is an urgent need for high-quality studies examining the effects of cannabinoids on mental disorders in general and depression/anxiety in particular, as well as the consequences of long-term use of these preparations due to possible risks such as addiction and even reversal of improvement.

The piperazine analogue para-fluorophenylpiperazine alters timing of the physiological effects of the synthetic cannabinoid receptor agonist AMB-FUBINACA, without changing its discriminative stimulus, signalling effects, or metabolism

AMB-FUBINACA is a synthetic cannabinoid receptor agonist (SCRA), which has been associated with substantial abuse and health harm since 2016 in many countries including New Zealand. A characteristic of AMB-FUBINACA use in New Zealand has included the observation that forensic samples (from autopsies) and drugs seized by police have often been found to contain para-fluorophenylpiperazine (pFPP), a relatively little-characterised piperazine analogue that has been suggested to act through 5HT1a serotonin receptors. In the current study, we aimed to characterise the interactions of these two agents in rat physiological endpoints using plethysmography and telemetry, and to examine whether pFPP altered the subjective effects of AMB-FUBINACA in mice trained to differentiate a cannabinoid (THC) from vehicle. Though pFPP did not alter the ability of AMB-FUBINACA to substitute for THC, it did appear to abate some of the physiological effects of AMB-FUBINACA in rats by delaying the onset of AMB-FUBINACA-mediated hypothermia and shortening duration of bradycardia. In HEK cells stably expressing the CB1 cannabinoid receptor, 5HT1a, or both CB1 and 5HT1a, cAMP signalling was recorded using a BRET biosensor (CAMYEL) to assess possible direct receptor interactions. Although low potency pFPP agonism at 5HT1a was confirmed, little evidence for signalling interactions was detected in these assays: additive or synergistic effects on potency or efficacy were not detected between pFPP and AMB-FUBINACA-mediated cAMP inhibition. Experiments utilising higher potency, classical 5HT1a ligands (agonist 8OH-DPAT and antagonist WAY100635) also failed to reveal evidence for mutual CB1/5HT1a interactions or cross-antagonism. Finally, the ability of pFPP to alter the metabolism of AMB-FUBINACA in rat and human liver microsomes into its primary carboxylic acid metabolite via carboxylesterase-1 was assessed by HPLC; no inhibition was detected. Overall, the effects we have observed do not suggest that increased harm/toxicity would result from the combination of pFPP and AMB-FUBINACA.

Endocannabinoid System: Chemical Characteristics and Biological Activity

The endocannabinoid system (eCB) has been studied to identify the molecular structures present in Cannabis sativa. eCB consists of cannabinoid receptors, endogenous ligands, and the associated enzymatic apparatus responsible for maintaining energy homeostasis and cognitive processes. Several physiological effects of cannabinoids are exerted through interactions with various receptors, such as CB1 and CB2 receptors, vanilloid receptors, and the recently discovered G-protein-coupled receptors (GPR55, GPR3, GPR6, GPR12, and GPR19). Anandamide (AEA) and 2-arachidoylglycerol (2-AG), two small lipids derived from arachidonic acid, showed high-affinity binding to both CB1 and CB2 receptors. eCB plays a critical role in chronic pain and mood disorders and has been extensively studied because of its wide therapeutic potential and because it is a promising target for the development of new drugs. Phytocannabinoids and synthetic cannabinoids have shown varied affinities for eCB and are relevant to the treatment of several neurological diseases. This review provides a description of eCB components and discusses how phytocannabinoids and other exogenous compounds may regulate the eCB balance. Furthermore, we show the hypo- or hyperfunctionality of eCB in the body and how eCB is related to chronic pain and mood disorders, even with integrative and complementary health practices (ICHP) harmonizing the eCB.

Endocannabinoid-Binding Receptors as Drug Targets

Cannabis plant has been used from ancient times with therapeutic purposes for treating human pathologies, but the identification of the cellular and molecular mechanisms underlying the therapeutic properties of the phytocannabinoids, the active compounds in this plant, occurred in the last years of the past century. In the late 1980s and early 1990s, seminal studies demonstrated the existence of cannabinoid receptors and other elements of the so-called endocannabinoid system. These G protein-coupled receptors (GPCRs) are a key element in the functions assigned to endocannabinoids and appear to serve as promising pharmacological targets. They include CB₁, CB₂, and GPR55, but also non-GPCRs can be activated by endocannabinoids, like ionotropic receptor TRPV₁ and even nuclear receptors of the PPAR family. Their activation, inhibition, or simply modulation have been associated with numerous physiological effects at both central and peripheral levels, which may have therapeutic value in different human pathologies, then providing a solid experimental explanation for both the ancient medicinal uses of Cannabis plant and the recent advances in the development of cannabinoid-based specific therapies. This chapter will review the scientific knowledge generated in the last years around the research on the different endocannabinoid-binding receptors and their signaling mechanisms. Our intention is that this knowledge may help readers to understand the relevance of these receptors in health and disease conditions, as well as it may serve as the theoretical basis for the different experimental protocols to investigate these receptors and their signaling mechanisms that will be described in the following chapters.

Role of cyclin-dependent kinase 5 in psychosis and the modulatory effects of cannabinoids

Cyclin-dependent kinase 5 (CDK5) is a serine/threonine kinase that has emerged as a key regulator of neurotransmission in complex cognitive processes. Its expression is altered in treated schizophrenia patients, and cannabinoids modulate CDK5 levels in the brain of rodents. However, the role of this kinase, and its interaction with cannabis use in first-episode psychosis (FEP) patients is still not known. Hence, we studied the expression changes of CDK5 and its signaling partner, postsynaptic density protein 95 (PSD95) in olfactory neuroepithelial (ON) cells of FEP patients with (FEP/c) and without (FEP/nc) prior cannabis use, and in a dual-hit mouse model of psychosis. In this model, adolescent mice were exposed to the cannabinoid receptor 1 agonist (CB1R) WIN-55,212-2 (WIN: 1 mg/kg) during 21 days, and to the N-methyl-d-aspartate receptor (NMDAR) blocker phencyclidine (PCP: 10 mg/kg) during 10 days. FEP/c showed less social functioning deficits, lower CDK5 and higher PSD95 levels than FEP/nc. These changes correlated with social skills, but not cognitive deficits. Consistently, exposure of ON cells from FEP/nc patients to WIN in vitro reduced CDK5 levels. Convergent results were obtained in mice, where PCP by itself induced more sociability deficits, and PSD95/CDK5 alterations in the prefrontal cortex and hippocampus than exposure to PCP-WIN. In addition, central blockade of CDK5 activity with roscovitine in PCP-treated mice restored both sociability impairments and PSD95 levels. We provide translational evidence that increased CDK5 could be an early indicator of psychosis associated with social deficits, and that this biomarker is modulated by prior cannabis use.

Molecular Pathways of the Therapeutic Effects of Ayahuasca, a Botanical Psychedelic and Potential Rapid-Acting Antidepressant

Ayahuasca is a psychoactive brew traditionally used in indigenous and religious rituals and ceremonies in South America for its therapeutic, psychedelic, and entheogenic effects. It is usually prepared by lengthy boiling of the leaves of the bush Psychotria viridis and the mashed stalks of the vine Banisteriopsis caapi in water. The former contains the classical psychedelic N,N-dimethyltryptamine (DMT), which is thought to be the main psychoactive alkaloid present in the brew. The latter serves as a source for β-carbolines, known for their monoamine oxidase-inhibiting (MAOI) properties. Recent preliminary research has provided encouraging results investigating ayahuasca’s therapeutic potential, especially regarding its antidepressant effects. On a molecular level, pre-clinical and clinical evidence points to a complex pharmacological profile conveyed by the brew, including modulation of serotoninergic, glutamatergic, dopaminergic, and endocannabinoid systems. Its substances also interact with the vesicular monoamine transporter (VMAT), trace amine-associated receptor 1 (TAAR1), and sigma-1 receptors. Furthermore, ayahuasca’s components also seem to modulate levels of inflammatory and neurotrophic factors beneficially. On a biological level, this translates into neuroprotective and neuroplastic effects. Here we review the current knowledge regarding these molecular interactions and how they relate to the possible antidepressant effects ayahuasca seems to produce.

Cannabis use selectively modulates circulating biomarkers in the blood of schizophrenia patients

Cannabis use disorder is frequent in schizophrenia patients, and it is associated with an earlier age of onset and poor schizophrenia prognosis. Serotonin 2A receptors (5-HT2AR) have been involved in psychosis and, like Akt kinase, are known to be modulated by THC. Likewise, endocannabinoid system dysregulation has been suggested in schizophrenia. The presence of these molecules in blood makes them interesting targets, as they can be evaluated in patients by a minimally invasive technique. The aim of the present study was to evaluate 5-HT2AR protein expression and the Akt functional status in platelet homogenates of subjects diagnosed with schizophrenia, cannabis use disorder, or both conditions, compared with age- and sex-matched control subjects. Additionally, endocannabinoids and pro-inflammatory interleukin-6 (IL-6) levels were also measured in the plasma of these subjects. Results showed that both platelet 5-HT2AR and the active phospho (Ser473)Akt protein expression were significantly increased in schizophrenia subjects, whereas patients with a dual diagnosis of schizophrenia and cannabis use disorder did not show significant changes. Similarly, plasma concentrations of anandamide and other lipid mediators such as PEA and DEA, as well as the pro-inflammatory IL-6, were significantly increased in schizophrenia, but not in dual subjects. Results demonstrate that schizophrenia subjects show different circulating markers pattern depending on the associated diagnosis of cannabis use disorder, supporting the hypothesis that there could be different underlying mechanisms that may explain clinical differences among these groups. Moreover, they provide the first preliminary evidence of peripherally measurable molecules of interest for bigger prospective studies in these subpopulations.

Class A and C GPCR Dimers in Neurodegenerative Diseases

Neurodegenerative diseases affect over 30 million people worldwide with an ascending trend. Most individuals suffering from these irreversible brain damages belong to the elderly population, with onset between 50 and 60 years. Although the pathophysiology of such diseases is partially known, it remains unclear upon which point a disease turns degenerative. Moreover, current therapeutics can treat some of the symptoms but often have severe side effects and become less effective in long-term treatment. For many neurodegenerative diseases, the involvement of G proteincoupled receptors (GPCRs), which are key players of neuronal transmission and plasticity, has become clearer and holds great promise in elucidating their biological mechanism. With this review, we introduce and summarize class A and class C GPCRs, known to form heterodimers or oligomers to increase their signalling repertoire. Additionally, the examples discussed here were shown to display relevant alterations in brain signalling and had already been associated with the pathophysiology of certain neurodegenerative diseases. Lastly, we classified the heterodimers into two categories of crosstalk, positive or negative, for which there is known evidence.

Regulation of glutamate homeostasis in the nucleus accumbens by astrocytic CB1 receptors and its role in cocaine-motivated behaviors

Cannabinoid type 1 receptors (CB1Rs) orchestrate brain reward circuitry and are prevalent neurobiological targets for endocannabinoids and cannabis in the mammalian brain. Decades of histological and electrophysiological studies have established CB1R as presynaptic G-protein coupled receptors (GPCRs) that inhibit neurotransmitter release through retrograde signaling mechanisms. Recent seminal work demonstrates CB1R expression on astrocytes and the pivotal function of glial cells in endocannabinoid-mediated modulation of neuron-astrocyte signaling. Here, we review key facets of CB1R-mediated astroglia regulation of synaptic glutamate transmission in the nucleus accumbens with a specific emphasis on cocaine-directed behaviors.

The Role of Cannabinoids in CNS Development: Focus on Proliferation and Cell Death

The active principles of Cannabis sativa are potential treatments for several diseases, such as pain, seizures and anorexia. With the increase in the use of cannabis for medicinal purposes, a more careful assessment of the possible impacts on embryonic development becomes necessary. Surveys indicate that approximately 3.9% of pregnant women use cannabis in a recreational and/or medicinal manner. However, although the literature has already described the presence of endocannabinoid system components since the early stages of CNS development, many of their physiological effects during this stage have not yet been established. Moreover, it is still uncertain how the endocannabinoid system can be altered in terms of cell proliferation and cell fate, neural migration, neural differentiation, synaptogenesis and particularly cell death. In relation to cell death in the CNS, knowledge about the effects of cannabinoids is scarce. Thus, the present work aims to review the role of the endocannabinoid system in different aspects of CNS development and discuss possible side effects or even opportunities for treating some conditions in the development of this tissue.

Preferential Gs protein coupling of the galanin Gal1 receptor in the µ-opioid-Gal1 receptor heterotetramer

Recent studies have proposed that heteromers of µ-opioid receptors (MORs) and galanin Gal₁ receptors (Gal₁Rs) localized in the mesencephalon mediate the dopaminergic effects of opioids. The present study reports converging evidence, using a peptide-interfering approach combined with biophysical and biochemical techniques, including total internal reflection fluorescence microscopy, for a predominant homodimeric structure of MOR and Gal₁R when expressed individually, and for their preference to form functional heterotetramers when co-expressed. Results show that a heteromerization-dependent change in the Gal₁R homodimeric interface leads to a switch in G-protein coupling from inhibitory Gi to stimulatory Gs proteins. The MOR-Gal₁R heterotetramer, which is thus bound to Gs via the Gal₁R homodimer and Gi via the MOR homodimer, provides the framework for a canonical Gs-Gi antagonist interaction at the adenylyl cyclase level. These novel results shed light on the intense debate about the oligomeric quaternary structure of G protein-coupled receptors, their predilection for heteromer formation, and the resulting functional significance.

Adolescents are more sensitive than adults to acute behavioral and cognitive effects of THC

Increased cannabis availability has contributed to increased use with concomitant incidence of adverse effects. One risk factor for adverse drug reactions may be age. There is preclinical evidence that acute effects of delta-9-tetrahydrocannabinol (THC), the primary active constituent of cannabis, are greater during adolescence, but this has not been fully studied in humans. The present study sought to determine whether adolescent men and women are more sensitive than adults to acute THC. Adolescents aged 18-20 (N = 12) and adults aged 30-40 (N = 12), with less than 20 total lifetime uses of THC-containing products, received capsules of THC (7.5, 15 mg) and placebo across three study sessions in randomized order under double blind conditions. During each session, subjective, cardiovascular, behavioral, and EEG measures were obtained. Behavioral measures included Simple Reaction Time, Stop Task, Time Production and N-back and EEG measures included P300 amplitudes during an auditory oddball task and eyes-closed resting state. THC affected subjective state and heart rate similarly in both age groups. However, adolescents were more sensitive to performance impairing effects, exhibiting dose-dependent impairments on reaction time, response accuracy, and time perception. On EEG measures, THC dose-dependently decreased P300 amplitude in adolescents but not adults. Adolescents were more sensitive to behavioral and cognitive effects of THC, but not to cardiovascular effects or subjective measures. Thus, at doses that produce comparable ratings of intoxication, adolescents may exhibit greater cognitive impairment and alterations in brain function.

Unmasking allosteric binding sites: Novel targets for GPCR drug discovery

INTRODUCTION

Unexpected non-apparent and hidden allosteric binding sites are non-classical and non-apparent allosteric centers in 3-D X-ray protein structures until orthosteric or allosteric ligands bind to them. The orthosteric center of one protomer that modulates binding centers of the other protomers within an oligomer is also an unexpected allosteric site. Furthermore, another partner protein can also produce these effects, acting as an unexpected allosteric modulator.

AREAS COVERED

This review summarizes both classical and non-classical allosterism. The authors focus on G protein-coupled receptor (GPCR) oligomers as a paradigm of allosteric molecules. Moreover, they show several examples of unexpected allosteric sites such as hidden allosteric sites in a protomer that appear after the interaction with other molecules and the allosterism exerted between orthosteric sites within GPCR oligomer, emphasizing on the allosteric modulations that can occur between binding sites.

EXPERT OPINION

The study of these new non-classical allosteric sites will expand the diversity of allosteric control on the function of orthosteric sites within proteins, whether GPCRs or other receptors, enzymes or transporters. Moreover, the design of new drugs targeting these hidden allosteric sites or already known orthosteric sites acting as allosteric sites in protein homo- or hetero-oligomers will increase the therapeutic potential of allosterism.

The Autism-Psychosis Continuum Conundrum: Exploring the Role of the Endocannabinoid System

Evidence indicates shared physiopathological mechanisms between autism and psychosis. In this regard, the endocannabinoid system has been suggested to modulate neural circuits during the early stage of neurodevelopment, with implications for both autism and psychosis. Nevertheless, such potential common markers of disease have been investigated in both autism and psychosis spectrum disorders, without considering the conundrum of differentiating the two groups of conditions in terms of diagnosis and treatment. Here, we systematically review all human and animal studies examining the endocannabinoid system and its biobehavioral correlates in the association between autism and psychosis. Studies indicate overlapping biobehavioral aberrancies between autism and schizophrenia, subject to correction by modulation of the endocannabinoid system. In addition, common cannabinoid-based pharmacological strategies have been identified, exerting epigenetic effects across genes controlling neural mechanisms shared between autism and schizophrenia. Interestingly, a developmental and transgenerational trajectory between autism and schizophrenia is supported by evidence that exogenous alteration of the endocannabinoid system promotes progression to inheritable psychosis phenotypes in the context of biobehavioral autism vulnerability. However, evidence for a diametral association between autism and psychosis is scant. Several clinical implications follow from evidence of a developmental continuum between autism and psychosis as a function of the endocannabinoid system dysregulation.

Metabolomics and integrated network analysis reveal roles of endocannabinoids and large neutral amino acid balance in the ayahuasca experience

There has been a renewed interest in the potential use of psychedelics for the treatment of psychiatric conditions. Nevertheless, little is known about the mechanism of action and molecular pathways influenced by ayahuasca use in humans. Therefore, for the first time, our study aims to investigate the human metabolomics signature after consumption of a psychedelic, ayahuasca, and its connection with both the psychedelic-induced subjective effects and the plasma concentrations of ayahuasca alkaloids. Plasma samples of 23 individuals were collected both before and after ayahuasca consumption. Samples were analysed through targeted metabolomics and further integrated with subjective ratings of the ayahuasca experience (i.e., using the 5-Dimension Altered States of Consciousness Rating Scale [ASC]), and plasma ayahuasca-alkaloids using integrated network analysis. Metabolic pathways enrichment analysis using diffusion algorithms for specific KEGG modules was performed on the metabolic output. Compared to baseline, the consumption of ayahuasca increased N-acyl-ethanolamine endocannabinoids, decreased 2-acyl-glycerol endocannabinoids, and altered several large-neutral amino acids (LNAAs). Integrated network results indicated that most of the LNAAs were inversely associated with 9 out of the 11 subscales of the ASC, except for tryptophan which was positively associated. Several endocannabinoids and hexosylceramides were directly associated with the ayahuasca alkaloids. Enrichment analysis confirmed dysregulation in several pathways involved in neurotransmission such as serotonin and dopamine synthesis. In conclusion, a crosstalk between the circulating LNAAs and the subjective effects is suggested, which is independent of the alkaloid concentrations and provides insights into the specific metabolic fingerprint and mechanism of action underlying ayahuasca experiences.

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

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

Multimodal MRI data fusion reveals distinct structural, functional and neurochemical correlates of heavy cannabis use

Heavy cannabis use (HCU) is frequently associated with a plethora of cognitive, psychopathological and sensorimotor phenomena. Although HCU is frequent, specific patterns of abnormal brain structure and function underlying HCU in individuals presenting without cannabis-use disorder or other current and life-time major mental disorders are unclear at present. This multimodal magnetic resonance imaging (MRI) study examined resting-state functional MRI (rs-fMRI) and structural MRI (sMRI) data from 24 persons with HCU and 16 controls. Parallel independent component analysis (p-ICA) was used to examine covarying components among grey matter volume (GMV) maps computed from sMRI and intrinsic neural activity (INA), as derived from amplitude of low-frequency fluctuations (ALFF) maps computed from rs-fMRI data. Further, we used JuSpace toolbox for cross-modal correlations between MRI-based modalities with nuclear imaging derived estimates, to examine specific neurotransmitter system changes underlying HCU. We identified two transmodal components, which significantly differed between the HCU and controls (GMV: p = 0.01, ALFF p = 0.03, respectively). The GMV component comprised predominantly cerebello-temporo-thalamic regions, whereas the INA component included fronto-parietal regions. Across HCU, loading parameters of both components were significantly associated with distinct HCU behavior. Finally, significant associations between GMV and the serotonergic system as well as between INA and the serotonergic, dopaminergic and μ-opioid receptor system were detected. This study provides novel multimodal neuromechanistic insights into HCU suggesting co-altered structure/function-interactions in neural systems subserving cognitive and sensorimotor functions.

Biochemical Mechanisms Underlying Psychedelic-Induced Neuroplasticity

In addition to producing profound subjective effects following acute administration, psychedelic compounds can induce beneficial behavioral changes relevant to the treatment of neuropsychiatric disorders that last long after the compounds have been cleared from the body. One hypothesis with the potential to explain the remarkable enduring effects of psychedelics is related to their abilities to promote structural and functional neuroplasticity in the prefrontal cortex (PFC). A hallmark of many stress-related neuropsychiatric diseases, including depression, post-traumatic stress disorder (PTSD), and addiction, is the atrophy of neurons in the PFC. Psychedelics appear to be particularly effective catalysts for the growth of these key neurons, ultimately leading to restoration of synaptic connectivity in this critical brain region. Furthermore, evidence suggests that the hallucinogenic effects of psychedelics are not directly linked to their ability to promote structural and functional neuroplasticity. If we are to develop improved alternatives to psychedelics for treating neuropsychiatric diseases, we must fully characterize the molecular mechanisms that give rise to psychedelic-induced neuroplasticity. Here, I review our current understanding of the biochemical signaling pathways activated by psychedelics and related neuroplasticity-promoting molecules, with an emphasis on key unanswered questions.

Polypharmacological Approaches for CNS Diseases: Focus on Endocannabinoid Degradation Inhibition

Polypharmacology breaks up the classical paradigm of “one-drug, one target, one disease” electing multitarget compounds as potential therapeutic tools suitable for the treatment of complex diseases, such as metabolic syndrome, psychiatric or degenerative central nervous system (CNS) disorders, and cancer. These diseases often require a combination therapy which may result in positive but also negative synergistic effects. The endocannabinoid system (ECS) is emerging as a particularly attractive therapeutic target in CNS disorders and neurodegenerative diseases including Parkinson’s disease (PD), Alzheimer’s disease (AD), Huntington’s disease (HD), multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), stroke, traumatic brain injury (TBI), pain, and epilepsy. ECS is an organized neuromodulatory network, composed by endogenous cannabinoids, cannabinoid receptors type 1 and type 2 (CB₁ and CB₂), and the main catabolic enzymes involved in the endocannabinoid inactivation such as fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL). The multiple connections of the ECS with other signaling pathways in the CNS allows the consideration of the ECS as an optimal source of inspiration in the development of innovative polypharmacological compounds. In this review, we focused our attention on the reported polypharmacological examples in which FAAH and MAGL inhibitors are involved.

Disrupting GPCR Complexes with Smart Drug-like Peptides

G protein-coupled receptors (GPCRs) are a superfamily of proteins classically described as monomeric transmembrane (TM) receptors. However, increasing evidence indicates that many GPCRs form higher-order assemblies made up of monomers pertaining to identical (homo) or to various (hetero) receptors. The formation and structure of these oligomers, their physiological role and possible therapeutic applications raise a variety of issues that are currently being actively explored. In this context, synthetic peptides derived from TM domains stand out as powerful tools that can be predictably targeted to disrupt GPCR oligomers, especially at the interface level, eventually impairing their action. However, despite such potential, TM-derived, GPCR-disrupting peptides often suffer from inadequate pharmacokinetic properties, such as low bioavailability, a short half-life or rapid clearance, which put into question their therapeutic relevance and promise. In this review, we provide a comprehensive overview of GPCR complexes, with an emphasis on current studies using GPCR-disrupting peptides mimicking TM domains involved in multimerization, and we also highlight recent strategies used to achieve drug-like versions of such TM peptide candidates for therapeutic application.

Probing GPCR Dimerization Using Peptides

G protein-coupled receptors (GPCRs) are the largest class of membrane proteins and the most common and extensively studied pharmacological target. Numerous studies over the last decade have confirmed that GPCRs do not only exist and function in their monomeric form but in fact, have the ability to form dimers or higher order oligomers with other GPCRs, as well as other classes of receptors. GPCR oligomers have become increasingly attractive to investigate as they have the ability to modulate the pharmacological responses of the receptors which in turn, could have important functional roles in diseases, such as cancer and several neurological & neuropsychiatric disorders. Despite the growing evidence in the field of GPCR oligomerisation, the lack of structural information, as well as targeting the 'undruggable' protein-protein interactions (PPIs) involved in these complexes, has presented difficulties. Outside the field of GPCRs, targeting PPIs has been widely studied, with a variety of techniques being investigated; from small-molecule inhibitors to disrupting peptides. In this review, we will demonstrate several physiologically relevant GPCR dimers and discuss an array of strategies and techniques that can be employed when targeting these complexes, as well as provide ideas for future development.

Psychedelic experience dose-dependently modulated by cannabis: results of a prospective online survey

RATIONALE

Classic psychedelics are currently being studied as novel treatments for a range of psychiatric disorders. However, research on how psychedelics interact with other psychoactive substances remains scarce.

OBJECTIVES

The current study aimed to explore the subjective effects of psychedelics when used alongside cannabis.

METHODS

Participants (n = 321) completed a set of online surveys at 2 time points: 7 days before, and 1 day after a planned experience with a serotonergic psychedelic. The collected data included demographics, environmental factors (so-called setting) and five validated questionnaires: Mystical Experience Questionnaire (MEQ), visual subscales of Altered States of Consciousness Questionnaire (ASC-Vis), Challenging Experience Questionnaire (CEQ), Ego Dissolution Inventory (EDI) and Emotional Breakthrough Inventory (EBI). Participants were grouped according to whether they had reported using no cannabis (n = 195) or low (n = 53), medium (n = 45) or high (n = 28) dose, directly concomitant with the psychedelic. Multivariate analysis of covariance (MANCOVA) and contrasts was used to analyse differences in subjective effects between groups while controlling for potential confounding contextual 'setting' variables.

RESULTS

The simultaneous use of cannabis together with classic serotonergic psychedelics was associated with more intense psychedelic experience across a range of measures: a linear relationship was found between dose and MEQ, ASC-Vis and EDI scores, while a quadratic relationship was found for CEQ scores. No relationship was found between the dose of cannabis and the EBI.

CONCLUSIONS

Results imply a possible interaction between the cannabis and psychedelic on acute subjective experiences; however, design limitations hamper our ability to draw firm inferences on directions of causality and the clinical implications of any such interactions.