Experience-dependent serotonergic signaling in glia regulates targeted synapse elimination.

The optimization of brain circuit connectivity based on initial environmental input occurs during critical periods characterized by sensory experience-dependent, temporally restricted, and transiently reversible synapse elimination. This precise, targeted synaptic pruning mechanism is mediated by glial phagocytosis. Serotonin signaling has prominent, foundational roles in the brain, but functions in glia, or in experience-dependent brain circuit synaptic connectivity remodeling, have been relatively unknown. Here, we discover that serotonergic signaling between glia is essential for olfactory experience-dependent synaptic glomerulus pruning restricted to a well-defined Drosophila critical period. We find that experience-dependent serotonin signaling is restricted to the critical period, with both (1) serotonin production and (2) 5-HT2A receptors specifically in glia, but not neurons, absolutely required for targeted synaptic glomerulus pruning. We discover that glial 5-HT2A receptor signaling limits the experience-dependent synaptic connectivity pruning in the critical period and that conditional reexpression of 5-HT2A receptors within adult glia reestablishes "critical period-like" experience-dependent synaptic glomerulus pruning at maturity. These results reveal an essential requirement for glial serotonergic signaling mediated by 5-HT2A receptors for experience-dependent synapse elimination.

Molecular Dynamics (MD) Simulations Provide Insights into the Activation Mechanisms of 5-HT2A Receptors.

Recent breakthroughs in the determination of atomic resolution 3-D cryo-electron microscopy structures of membrane proteins present an unprecedented opportunity for drug discovery. Structure-based drug discovery utilizing in silico methods enables the study of dynamic connectivity of stable conformations induced by the drug in achieving its effect. With the ever-expanding computational power, simulations of this type reveal protein dynamics in the nano-, micro-, and even millisecond time scales. In the present study, aiming to characterize the protein dynamics of the 5HT2A receptor stimulated by ligands (agonist/antagonist), we performed 1 µs MD simulations on 5HT2A/DOI (agonist), 5HT2A/GSK215083 (antagonist), and 5HT2A (APO, no ligand) systems. The crystal structure of 5HT2A/zotepine (antagonist) (PDB: 6A94) was used to set up the simulation systems in a lipid bilayer environment. We found the monitoring of the ionic lock residue pair (R3.50-E6.30) of 5HT2A in MD simulations to be a good approximation of the effects of agonists (ionic lock breakage) or antagonists (ionic lock formation) on receptor activation. We further performed analyses of the MD trajectories, including Principal Component Analysis (PCA), hydrogen bond, salt bridge, and hydrophobic interaction network analyses, and correlation between residues to identify key elements of receptor activation. Our results suggest that in order to trigger receptor activation, DOI must interact with 5HT2A through residues V5.39, G5.42, S5.43, and S5.46 on TM5, inducing significant conformational changes in the backbone angles of G5.42 and S5.43. DOI also interacted with residues W6.48 (toggle switch) and F6.51 on TM6, causing major conformational shifts in the backbone angles of F6.44 and V6.45. These structural changes were transmitted to the intracellular ends of TM5, TM6, and ICL3, resulting in the breaking of the ionic lock and subsequent G protein activation. The studies could be helpful in future design of selective agonists/antagonists for various serotonin receptors (5HT1A, 5HT2A, 5HT2B, 5HT2C, and 5HT7) involved in detrimental disorders, such as addiction and schizophrenia.

Photoswitchable TCB-2 for control of the 5-HT2A receptor and analysis of biased agonism.

Therapies that target the serotonin 2A receptor (5-HT2AR) are promising. However, probes are needed to better understand the role of 5-HT2AR. Here, we design and synthesize a photoswitch and photoswitchable 5-HT2AR ligand based on highly potent agonist TCB-2 and arylazopyrazole, which also boasts photoswitchable G protein vs. ß-arrestin pathway bias.

Design, synthesis and biological evaluation of arylpropylamine derivatives as potential multi-target antidepressants.

In this study, a series of novel arylpropylamine derivatives were designed, synthesized and evaluated as potential multi-target antidepressants. Among them, compound (R)-13j displayed unique pharmacological features, exhibiting excellent inhibitory potency against serotonin and noradrenaline transporters (SERT/NET) and high affinity for 5-HT2A/2C receptor, and showing low affinity for histamine H1, adrenergic α1 receptors and hERG channels (to reduce QT interval prolongation). Molecular docking studies provided a rational binding model of (R)-13j in complex with SERT and 5-HT2A/2C receptor. In animal models, compound (R)-13j dose-dependently reduced the immobility time in the tail suspension test (TST) and the forced swimming test (FST) in mice, with higher efficacy when compared to duloxetine, and showed no stimulatory effect on the locomotor activity. Moreover, compound (R)-13j significantly shortened the immobility time in the ACTH-induced rat model of treatment-resistant depression (TRD). Furthermore, compound (R)-13j also exhibited a higher threshold for acute toxicity than duloxetine. In addition, compound (R)-13j possessed a favorable pharmacokinetic profile in mice. Taken together, compound (R)-13j may constitute a novel class of drugs for the treatment of depression.

The psychedelic drug DOI reduces heroin motivation by targeting 5-HT2A receptors in a heroin and alcohol co-use model.

There has been a recent renewed interest in the potential use of psychedelic drugs as therapeutics for certain neuropsychiatric disorders, including substance use disorders. The psychedelic drug 2,5-dimethoxy-4-iodoamphetamine (DOI) has demonstrated therapeutic efficacy in preclinical models of opioid use disorder (OUD). Alcohol is commonly co-used in individuals with OUD, but preclinical models that recapitulate this comorbidity are lacking. We developed a polydrug model wherein male and female rats were allowed to self-administer intravenous heroin and oral alcohol (or saccharin control solution) over weeks of behavioral training, and then we conducted a series of progressive ratio tests to assess the animals' motivational state for heroin and alcohol. In this model, motivation for heroin is higher than alcohol, and DOI (0.4 mg/kg) administered prior to testing significantly reduced heroin motivation measured as the animals' break point, or maximum effort the animal is willing to expend to obtain a single infusion of heroin. The 5-HT2A receptor antagonist MDL 100,907 (0.3 mg/kg), but not the 5-HT2C receptor antagonist SB-242084 (0.5 mg/kg), blocked the therapeutic effect of DOI on heroin motivation. No significant effects on alcohol break points were observed, nor did MDL 100,907 or SB-242084 have any effect on break points on their own. These data support the view that psychedelic drugs like DOI may have therapeutic effects on opioid use in individuals with OUD and comorbid alcohol use, by acting as a 5-HT2A receptor agonist.

Daidzin enhances memory and the antischizophrenia drug olanzapine's effects, possibly through the 5-HT2A and D2 receptor interaction pathways.

Schizophrenia affects identification and disturbs our thinking and motivational capacity. Long-term use of daidzin (DZN) is evident to enhance attention and memory in experimental animals. This study aimed to investigate the effect of DZN on Swiss mice. To check animals' attention, identification, thinking, and motivational ability, we performed behavioral studies using marble burying, dust removal, and trained swimming protocols. For this, a total of 36 male Swiss albino mice were randomly divided into six groups, consisting of 6 animals in each group, as follows: control (vehicle), DZN-1.25, DZN-2.5, DZN-5 mg/kg, olanzapine (OLN)-2, and a combination of DZN-1.25 with OLN-2. Additionally, in silico studies are also performed to understand the possible molecular mechanisms behind this neurological effect. Findings suggest that DZN dose-dependently and significantly (p < .05) increased marble burying and removed dust while reducing the time to reach the target point. DZN-1.25 was found to enhance OLN's effect significantly (p < .05), possibly via agonizing its activity in animals. In silico findings suggest that DZN has strong binding affinities of -10.1 and -10.4 kcal/mol against human serotonin 2 A (5-HT2A) and dopamine 2 (D2) receptors, respectively. Additionally, DZN exhibits favorable pharmacokinetic and toxicity properties. We suppose that DZN may exert its attention- and memory-enhancing abilities by interacting with 5-HT2A and D2 receptors. It may exert a synergistic antischizophrenia-like effect with the standard drug, OLN. Further studies are required to discover the exact molecular mechanism for this neurological function in animals.

Gain control of sensory input across polysynaptic circuitries in mouse visual cortex by a single G protein-coupled receptor type (5-HT2A).

Response gain is a crucial means by which modulatory systems control the impact of sensory input. In the visual cortex, the serotonergic 5-HT2A receptor is key in such modulation. However, due to its expression across different cell types and lack of methods that allow for specific activation, the underlying network mechanisms remain unsolved. Here we optogenetically activate endogenous G protein-coupled receptor (GPCR) signaling of a single receptor subtype in distinct mouse neocortical subpopulations in vivo. We show that photoactivation of the 5-HT2A receptor pathway in pyramidal neurons enhances firing of both excitatory neurons and interneurons, whereas 5-HT2A photoactivation in parvalbumin interneurons produces bidirectional effects. Combined photoactivation in both cell types and cortical network modelling demonstrates a conductance-driven polysynaptic mechanism that controls the gain of visual input without affecting ongoing baseline levels. Our study opens avenues to explore GPCRs neuromodulation and its impact on sensory-driven activity and ongoing neuronal dynamics.

Ketanserin exhibits dose- and concentration-proportional serotonin 2A receptor occupancy in healthy individuals: Relevance for psychedelic research.

The serotonin 2A (5-HT2A) receptor is an important target for drug development and the main receptor through which classical psychedelics elucidate their hallucinogenic effects. The 5-HT2A receptor antagonist ketanserin has frequently been used as a tool to block the receptor. Here, we establish the dose-occupancy relation of ketanserin and the cerebral 5-HT2A receptor in healthy participants by conducting a positron emission tomography (PET) study. 120-min PET scans using the 5-HT2A receptor agonist radiotracer [11C]Cimbi-36 were conducted at baseline and after oral doses of either 10, 20, or 40 mg of ketanserin; each participant underwent one or two scans after ketanserin administration. Occupancy was defined as the percent change in neocortex binding potential (BPND), estimated using the simplified reference tissue model (SRTM) with the cerebellum as reference region. Peroral ketanserin intake resulted in a plasma concentration-related increase in cerebral 5-HT2A receptor occupancy with the highest plasma ketanserin concentrations measured after ∼2 h. The relation between mean plasma ketanserin concentrations and 5-HT2A receptor occupancy conformed to a single-site binding model with an estimated EC50 (95 % CI) of 2.52 (0.75; 8.1) ng/mL, which corresponds to a peroral dose of ketanserin of approximately 10 mg. These data elucidate for the first time in humans the cerebral pharmacodynamics of ketanserin, both benefitting its use as a pharmacological tool for probing brain function and adding to its potential for therapeutic use in rescuing a bad psychedelic experience.

Combining machine learning, molecular dynamics, and free energy analysis for (5HT)-2A receptor modulator classification.

The 5-Hydroxytryptamine (5HT)-2A receptor, a key target in psychoactive drug development, presents significant challenges in the design of selective compounds. Here, we describe the construction, evaluation and validation of two machine learning (ML) models for the classification of bioactivity mechanisms against the (5HT)-2A receptor. Employing neural networks and XGBoost models, we achieved an overall accuracy of around 87 %, which was further enhanced through molecular modelling (MM) (e.g. molecular dynamics simulations) and binding free energy analysis. This ML-MM integration provided insights into the mechanisms of direct modulators and prodrugs. A significant outcome of the current study is the development of a 'binding free energy fingerprint' specific to (5HT)-2A modulators, offering a novel metric for evaluating drug efficacy against this target. Our study demonstrates the prospective of employing a successful workflow combining AI with structural biology, offering a powerful tool for advancing psychoactive drug discovery.

Ultra-low doses of methamphetamine suppress 5-hydroxytryptophan-induced head-twitch response in mice during aging.

The head-twitch response (HTR) in mice is considered a behavioral assay for activation of 5-HT 2A receptors in rodents. It can be evoked by direct-acting 5-HT 2A receptor agonists such as (±)-2,5-dimethoxy-4-iodoamphetamine, 5-hydroxytryptamine precursors [e.g. 5-hydroxytryptophan (5-HTP)], and selective 5-hydroxytryptamine releasers (e.g. d -fenfluramine). The nonselective monoamine releaser methamphetamine by itself does not produce the HTR but can suppress both (±)-2,5-dimethoxy-4-iodoamphetamine- and d -fenfluramine-evoked HTRs across ages via concomitant activation of the inhibitory serotonergic 5-HT 1A or adrenergic α 2 receptors. Currently, we investigated: (1) the ontogenic development of 5-HTP-induced HTR in 20-, 30-, and 60-day-old mice; (2) whether pretreatment with ultra-low doses of methamphetamine (0.1, 0.25, and 0.5 mg/kg, intraperitoneally) can suppress the frequency of 5-HTP-induced HTR at different ages; and (3) whether the inhibitory serotonergic 5-HT 1A or adrenergic α 2 receptors may account for the potential inhibitory effect of methamphetamine on 5-HTP-induced HTR. In the presence of a peripheral decarboxylase inhibitor (carbidopa), 5-HTP produced maximal frequency of HTRs in 20-day-old mice which rapidly subsided during aging. Methamphetamine dose-dependently suppressed 5-HTP-evoked HTR in 20- and 30-day-old mice. The selective 5-HT 1A -receptor antagonist WAY 100635 reversed the inhibitory effect of methamphetamine on 5-HTP-induced HTR in 30-day-old mice, whereas the selective adrenergic α 2 -receptor antagonist RS 79948 failed to reverse methamphetamine's inhibition at any tested age. These findings suggest an ontogenic rationale for methamphetamine's inhibitory 5-HT 1A receptor component of action in its suppressive effect on 5-HTP-induced HTR during development which is not maximally active at a very early age.

The serotonin(5-HT)2A receptor is involved in the hypersensitivity of bladder afferent neurons in cyclophosphamide-induced cystitis.

Interstitial cystitis/bladder pain syndrome (IC/BPS) is a chronic bladder inflammation characterized by the main symptoms of urinary frequency, urgency, and pelvic pain. The hypersensitivity of bladder afferent neurons is considered a significant pathophysiologic mechanism in IC/PBS. Serotonin (5-HT, 5-hydroxytryptamine) receptors are known to be involved in the regulation of the micturition reflex and hyperalgesia, but the effect of 5-HT receptors on cystitis remains unknown. In this study, a rat model of interstitial cystitis induced by intraperitoneal injection of cyclophosphamide (CYP) was used to investigate the role of 5-HT receptors on cystitis. The histology and urodynamics exhibited chronic cystitis and overactive bladder in CYP-treated rats. Notably, among 5-HT1A, 5-HT2A and 5-HT7 receptors, the expression of 5-HT2A receptor was significantly increased in bladder afferent neurons in CYP-treated rats. Intrathecal administration of the 5-HT2A receptor antagonist M100907 could alleviate bladder overactivity and hyperalgesia in CYP-induced cystitis rats. Neuronal calcium imaging of bladder afferent neurons revealed increased calcium influx induced by the 5-HT2A receptor agonist or capsaicin in cystitis rats, which could be inhibited by M100907. Moreover, RNA sequencing indicated that differentially expressed genes were enriched in inflammation-related pathways and cellular calcium homeostasis. These findings suggest that the 5-HT2A receptor is involved in the hypersensitivity of bladder afferent neurons in CYP-induced cystitis, and M100907 could alleviate bladder overactivity and hyperalgesia in CYP-induced cystitis by inhibiting neuronal hypersensitivity in the afferent pathways. The 5-HT2A receptor may be a potential therapeutic target for the treatment of IC/BPS.

Dual 5-HT2A and 5-HT2C Receptor Inverse Agonist That Affords In Vivo Antipsychotic Efficacy with Minimal hERG Inhibition for the Treatment of Dementia-Related Psychosis.

Psychosis is a distressing symptom commonly occurring in people with dementia. To treat Parkinson's disease psychosis, pimavanserin (1), a 5-HT2A receptor inverse agonist having minimal 5-HT2C receptor affinity and no dopamine D2 receptor affinity, was approved in the United States, but not for dementia-related psychosis due to limited efficacy issues. Herein, we report on the identification of a potent and dual 5-HT2A and 5-HT2C receptor inverse agonist 8 having minimal hERG inhibition, after having demonstrated the involvement of both 5-HT2A and 5-HT2C receptors to deliver antipsychotic efficacy in an MK-801-induced locomotor model and having conducted 5-HT2A and 5-HT2C occupancy studies including a surrogate method. The introduction of a spirocyclopropyl group boosting 5-HT2C affinity in 1 followed by further optimization to control lipophilicity resulted in balanced dual potency and metabolic stability, and mitigating hERG inhibition led to 8 that showed significant antipsychotic efficacy due to the involvement of both receptors.

Serotonin (5-HT)2A/2C receptor agonist 2,5-dimethoxy-4-iodophenyl-2-aminopropane hydrochloride improves detrusor sphincter dyssynergia by inhibiting L-type voltage-gated calcium channels in spinal cord injured rats.

AIMS: To explore the role of voltage-gated calcium channels (VGCC) in 5-HT2A/2C receptor agonist 2,5-dimethoxy-4-iodophenyl-2-aminopropane hydrochloride's improvement of spinal cord injury (SCI) induced detrusor sphincter dyssynergia and the expressions of the 5-hydroxy tryptamine (5-HT) 2A receptors and VGCCs in lumbosacral cord after SCI. METHODS: Female Sprague-Dawley rats were randomized into normal control group and SCI group (N = 15 each). Cystometrogram (CMG), simultaneous CMG, and external urethral sphincter electromyography (EUS-EMG) were conducted in all groups under urethane anesthesia. Drugs were administered intrathecally during CMG and EUS-EMG. Rats were euthanized and L6-S1 spinal cord were acquired for immunofluorescence. RESULTS: In SCI rats, intrathecal administration of 2,5-dimethoxy-4-iodophenyl-2-aminopropane hydrochloride or L-type VGCC blocker, nifedipine, could significantly increase voiding volume, voiding efficiency, and the number of high-frequency oscillations. They could also prolong EUS bursting activity duration on EUS-EMG. Moreover, the effect of 2,5-dimethoxy-4-iodophenyl-2-aminopropane hydrochloride can be eliminated with the combined administration of L-type VGCC agonist, (±)-Bay K 8644. No significant differences were observed in CMG after intrathecal administration of T-type VGCC blocker TTA-P2. Additionally, immunofluorescence of the lumbosacral cord in control and SCI rats showed that the 5-HT2A receptor and Cav1.2 immunolabeling-positive neurons in the anterior horn of the lumbosacral cord were increased in SCI rats. CONCLUSIONS: Our study demonstrated that 5-HT2A/2C agonist 2,5-dimethoxy-4-iodophenyl-2-aminopropane hydrochloride may improve SCI-induced DSD by inhibiting the L-type voltage-gated calcium channel in lumbosacral cord motoneurons.

Antidepressant Effect and Mechanism of Picea mariana Essential Oil on Reserpine-Induced Depression Model Mice.

The disturbance of brain biochemical substances serves as a primary cause and aggravating factor of depression. This study aimed to investigate the principal components of Picea mariana and its effect on reserpine-induced depression mice,w ith its relationship with brain central transmitters and related proteins. The main constituents of P. mariana essential oil (PMEO) were analyzed by GC-MS spectrometry. The quiescent time in the tail suspension test (TST) and forced swim test (FST), along with the weight change of the mice was detected. The number of normal neurons was quantified through Nissl staining. Immunohistochemistry was employed to determine the levels of 5HT-1A and 5HT-2A in the brain. Western blotting was utilized to detect 5HT-2A, CRF and TrkB protein levels. RT-qPCR was used to detect the mRNA levels of 5HT-1A, 5HT-2A, TrkB, CRF, and BDNF. The main active ingredients of PMEOs were (-) -bornyl acetate (44.95%), γ-Terpinene (14.17%), and ß-Pinene (10.12%). PMEOs effectively improved the retardation and weight loss due to anorexia in depression-like mice. This improvement was associated with an increase in the number of normal neurons. After administering different doses of PMEOs, the levels of 5HT-1A, 5HT-2A, CRF, and TrkB were found to be increased in brain tissue. RT-qPCR revealed that the mRNA levels of CRF, 5HT-1A, and 5HT-2A were generally upregulated, whereas TrkB and BDNF were downregulated. PMEO can effectively alleviate depression induced by reserpine, which may be attributed to its regulation of 5HT-1A, 5HT-2A, CRF and TrkB protein expression, thus reducing brain nerve injury.

Discovery of MT-1207: A Novel, Potent Multitarget Inhibitor as a Promising Clinical Candidate for the Treatment of Hypertension.

Herein, a series of novel arylpiperazine (piperidine) derivatives were designed, synthesized, and evaluated for mechanisms of action through in vitro and in vivo studies. The most promising compound, II-13 (later named as MT-1207), is a potent α1 and 5-HT2A receptor antagonist with remarkable IC50 in the picomolar level. Importantly, in the in vivo assay, II-13 achieved an effective blood pressure (BP) reduction in the 2K2C rat model without damaging renal function. Compound II-13, with its significant advantages in terms of pharmacological effects, pharmacokinetic parameters, and a large safety window, was extensively investigated. Moreover, data also showed that compound II-13 had fewer side effects in a postural BP assay and could prevent the onset of postural hypotension. Together, these results suggested that compound II-13 is a highly potent antihypertensive drug candidate with multitarget mechanisms of action in preclinical models. Currently, MT-1207 is in phase II hypertensive clinical trials in China.

Sex and Age Differences in Ontogeny of Alloparenting: A Relation to Forebrain DRD1, DRD2, and HTR2A mRNA Expression?

Alloparenting refers to the practice of caring for the young by individuals other than their biological parents. The relationship between the dynamic changes in psychological functions underlying alloparenting and the development of specific neuroreceptors remains unclear. Using a classic 10-day pup sensitization procedure, together with a pup preference and pup retrieval test on the EPM (elevated plus maze), we showed that both male and female adolescent rats (24 days old) had significantly shorter latency than adult rats (65 days old) to be alloparental, and their motivation levels for pups and objects were also significantly higher. In contrast, adult rats retrieved more pups than adolescent rats even though they appeared to be more anxious on the EPM. Analysis of mRNA expression using real-time-PCR revealed a higher dopamine D2 receptor (DRD2) receptor expression in adult hippocampus, amygdala, and ventral striatum, along with higher dopamine D1 receptor (DRD1) receptor expression in ventral striatum compared to adolescent rats. Adult rats also showed significantly higher levels of 5-hydroxytryptamine receptor 2A (HTR2A) receptor expression in the medial prefrontal cortex, amygdala, ventral striatum, and hypothalamus. These results suggest that the faster onset of alloparenting in adolescent rats compared to adult rats, along with the psychological functions involved, may be mediated by varying levels of dopamine DRD1, DRD2, and HTR2A in different forebrain regions.

Pharmacological and behavioural effects of tryptamines present in psilocybin-containing mushrooms.

BACKGROUND AND PURPOSE: Demand for new antidepressants has resulted in a re-evaluation of the therapeutic potential of psychedelic drugs. Several tryptamines found in psilocybin-containing "magic" mushrooms share chemical similarities with psilocybin. Early work suggests they may share biological targets. However, few studies have explored their pharmacological and behavioural effects. EXPERIMENTAL APPROACH: We compared baeocystin, norbaeocystin and aeruginascin with psilocybin to determine if they are metabolized by the same enzymes, similarly penetrate the blood-brain barrier, serve as ligands for similar receptors and modulate behaviour in rodents similarly. We also assessed the stability and optimal storage and handling conditions for each compound. KEY RESULTS: In vitro enzyme kinetics assays found that all compounds had nearly identical rates of dephosphorylation via alkaline phosphatase and metabolism by monoamine oxidase. Further, we found that only the dephosphorylated products of baeocystin and norbaeocystin crossed a blood-brain barrier mimetic to a similar degree as the dephosphorylated form of psilocybin, psilocin. The dephosphorylated form of norbaeocystin was found to activate the 5-HT2A receptor with similar efficacy to psilocin and norpsilocin in in vitro cell imaging assays. Behaviourally, only psilocybin induced head twitch responses in rats, a marker of 5-HT2A-mediated psychedelic effects and hallucinogenic potential. However, like psilocybin, norbaeocystin improved outcomes in the forced swim test. All compounds caused minimal changes to metrics of renal and hepatic health, suggesting innocuous safety profiles. CONCLUSIONS AND IMPLICATIONS: Collectively, this work suggests that other naturally occurring tryptamines, especially norbaeocystin, may share overlapping therapeutic potential with psilocybin, but without causing hallucinations.

Non-hallucinogenic compounds derived from iboga alkaloids alleviate neuropathic and visceral pain in mice through a mechanism involving 5-HT2A receptor activation.

The aim of this study was to determine the anti-hypersensitivity activity of novel non-hallucinogenic compounds derived from iboga alkaloids (i.e., ibogalogs), including tabernanthalog (TBG), ibogainalog (IBG), and ibogaminalog (DM506), using mouse models of neuropathic (Chronic Constriction Injury; CCI) and visceral pain (dextrane sulfate sodium; DSS). Ibogalogs decreased mechanical hyperalgesia and allodynia induced by CCI in a dose- and timeframe-dependent manner, where IBG showed the longest anti-hyperalgesic activity at a comparatively lower dose, whereas DM506 displayed the quickest response. These compounds also decreased hypersensitivity induced by colitis, where DM506 showed the longest activity. To understand the mechanisms involved in these effects, two approaches were utilized: ibogalogs were challenged with the 5-HT2A receptor antagonist ketanserin and the pharmacological activity of these compounds was assessed at the respective 5-HT2A, 5-HT6, and 5-HT7 receptor subtypes. The behavioral results clearly demonstrated that ketanserin abolishes the pain-relieving activity of ibogalogs without inducing any effect per se, supporting the concept that 5-HT2A receptor activation, but not inhibition, is involved in this process. The functional results showed that ibogalogs potently activate the 5-HT2A and 5-HT6 receptor subtypes, whereas they behave as inverse agonists (except TBG) at the 5-HT7 receptor. Considering previous studies showing that 5-HT6 receptor inhibition, but not activation, and 5-HT7 receptor activation, but not inhibition, relieved chronic pain, we can discard these two receptor subtypes as participating in the pain-relieving activity of ibogalogs. The potential involvement of 5-HT2B/2 C receptor subtypes was also ruled out. In conclusion, the anti-hypersensitivity activity of ibogalogs in mice is mediated by a mechanism involving 5-HT2A receptor activation.

5-hydroxytryptamine 2C/1A receptors modulate the biphasic dose response of the head twitch response and locomotor activity induced by DOM in mice.

RATIONALE: The phenylalkylamine hallucinogen (-)-2,5-dimethoxy-4-methylamphetamine (DOM) exhibits an inverted U-shaped dose-response curve for both head twitch response (HTR) and locomotor activity in mice. Accumulated studies suggest that HTR and locomotor hyperactivity induced by DOM are mainly caused by the activation of serotonin 5-hydroxytryptamine 2 A receptor (5-HT2A receptor). However, the mechanisms underlying the biphasic dose response of HTR and locomotor activity induced by DOM, particularly at high doses, remain unclear. OBJECTIVES: The primary objective of this study is to investigate the modulation of 5-HT2A/2C/1A receptors in HTR and locomotor activity, while also exploring the potential receptor mechanisms underlying the biphasic dose response of DOM. METHODS: In this study, we employed pharmacological methods to identify the specific 5-HT receptor subtypes responsible for mediating the biphasic dose-response effects of DOM on HTR and locomotor activity in C57BL/6J mice. RESULTS: The 5-HT2A receptor selective antagonist (R)-[2,3-di(methoxy)phenyl]-[1-[2-(4-fluorophenyl)ethyl]piperidin-4-yl]methanol (M100907) (500 µg/kg, i.p.) fully blocked the HTR at every dose of DOM (0.615-10 mg/kg, i.p.) in C57BL/6J mice. M100907 (50 µg/kg, i.p.) decreased the locomotor hyperactivity induced by a low dose of DOM (0.625, 1.25 mg/kg, i.p.), but had no effect on the locomotor hypoactivity induced by a high dose of DOM (10 mg/kg) in C57BL/6J mice. The 5-HT2C antagonist 6-chloro-5-methyl-1-[(2-[2-methylpyrid-3yloxy]pyrid-5yl)carbamoyl]indoline (SB242084) (0.3, 1 mg/kg, i.p.) reduced the HTR induced by a dose of 2.5 mg/kg DOM, but did not affect the response to other doses. SB242084 (1 mg/kg, i.p.) significantly increased the locomotor activity induced by DOM (0.615-10 mg/kg, i.p.) in mice. The 5-HT1A antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]N-(2-pyridinyl) cyclohexane carboxamide maleate (WAY100635) (1 mg/kg, i.p.) increased both HTR and locomotor activity induced by DOM in mice. The 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) (1 mg/kg, i.p.) significantly reduced both the HTR and locomotor activity induced by DOM in mice. Additionally, pretreatment with the Gαi/o inhibitor PTX (0.25 µg/mouse, i.c.v.) enhanced the HTR induced by DOM and attenuated the effect of DOM on locomotor activity in mice. CONCLUSIONS: Receptor subtypes 5-HT2C and 5-HT1A are implicated in the inverted U-shaped dose-response curves of HTR and locomotor activity induced by DOM in mice. The biphasic dose-response function of HTR and locomotor activity induced by DOM has different mechanisms in mice.

[Up-to-Date on clinical and preclinical studies of psilocybin therapy].

Major Depressive Disorder (MDD) poses a significant global health burden, with 30-40% patients developing resistance to standard clinical antidepressants, such as selective serotonin reuptake inhibitors and tricyclic antidepressants. In 2016, Carhart-Harris and colleagues reported that psilocybin, the hallucinogenic compound derived from magic mushrooms, exhibits rapid and enduring antidepressant effects in patients with treatment-resistant depression. Subsequent clinical studies have found the therapeutic potential of psilocybin in MDD, depressive episode in bipolar disorder, anorexia, and drug addiction. In 2018 and 2019, the U.S. Food and Drug Administration designated psilocybin as a "breakthrough medicine" for treatment-resistant depression and MDD, respectively. Notably, the side effects of psilocybin are limited to transient and mild issues, such as headache and fatigue, suggesting its safety. In 2023, we published a review on the role of serotonin 5-HT2A receptors in the antidepressant effects of serotonergic psychedelics (Nihon Yakurigaku Zasshi, Volume 158, Issue 3, Page 229-232). Here, we present our study alongside the latest clinical and preclinical research on the antidepressant effects of psilocybin and provide an overview of the potential and issues related to psilocybin therapy.