Nelotanserin, a selective 5-HT2A receptor inverse agonist, attenuates aspects of nicotine withdrawal but not reward in mice

Nicotine smoking contributes to many preventable disabilities, diseases and deaths. Targeting nicotine reward and withdrawal is a basis for the majority of smoking cessation pharmacotherapies. Due to the emergence of interest in 5-HT2A receptor modulators for numerous psychiatric disorders, we investigated the effect of nelotanserin, a 5-HT2A receptor inverse agonist, on nicotine reward and withdrawal in ICR mice. In nicotine-dependent mice, nelotanserin dose-dependently reduced somatic signs of nicotine withdrawal and thermal hyperalgesia as measured in the hot plate test. However, nelotanserin had no effect on anxiety-like behavior and failed to reduce nicotine reward as measured in the conditioned place preference test. Our results suggest that inverse agonism of the 5-HT2A receptor may be a feasible novel mechanism for smoking cessation by reducing both physical withdrawal and thermal hyperalgesia associated with nicotine abstinence but may require complementary pharmacotherapies targeting affective and reward-associated decrements to improve cessation outcomes.

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.

Pharmacologic profile of ITI-333: a novel molecule for treatment of substance use disorders

RATIONALE

Medications are urgently needed to treat symptoms of drug withdrawal and mitigate dysphoria and psychiatric comorbidities that drive opioid abuse and relapse. ITI-333 is a novel molecule in development for treatment of substance use disorders, psychiatric comorbidities, and pain.

OBJECTIVE

Characterize the preclinical profile of ITI-333 using pharmacological, behavioral, and physiological assays.

METHODS

Cell-based assays were used to measure receptor binding and intrinsic efficacy of ITI-333; animal models were employed to assess effects on opioid reinstatement, precipitated oxycodone withdrawal, and drug abuse liability.

RESULTS

In vitro, ITI-333 is a potent 5-HT2A receptor antagonist (Ki = 8 nM) and a biased, partial agonist at μ-opioid (MOP) receptors (Ki = 11 nM; lacking β-arrestin agonism) with lesser antagonist activity at adrenergic α1A (Ki = 28 nM) and dopamine D1 (Ki = 50 nM) receptors. In vivo, ITI-333 blocks 5-HT2A receptor-mediated head twitch and MOP receptor-mediated effects on motor hyperactivity in mice. ITI-333 alone is a naloxone-sensitive analgesic (mice) which suppresses somatic signs of naloxone-precipitated oxycodone withdrawal (mice) and heroin cue-induced reinstatement responding without apparent tolerance or physical dependence after chronic dosing (rats). ITI-333 did not acutely impair gastrointestinal or pulmonary function (rats) and was not intravenously self-administered by heroin-maintained rats or rhesus monkeys.

CONCLUSIONS

ITI-333 acts as a potent 5-HT2A receptor antagonist, as well a biased MOP receptor partial agonist with low intrinsic efficacy. ITI-333 mitigates opioid withdrawal/reinstatement, supporting its potential utility as a treatment for OUD.

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.

A Blood Test for the Diagnosis of Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune chronic disease characterized by inflammation and demyelination of the central nervous system (CNS). Despite numerous studies conducted, valid biomarkers enabling a definitive diagnosis of MS are not yet available. The aim of our study was to identify a marker from a blood sample to ease the diagnosis of MS. In this study, since there is evidence connecting the serotonin pathway to MS, we used an ELISA (Enzyme-Linked Immunosorbent Assay) to detect serum MS-specific auto-antibodies (auto-Ab) against the extracellular loop 1 (ECL-1) of the 5-hydroxytryptamine (5-HT) receptor subtype 2A (5-HT2A). We utilized an ELISA format employing poly-D-lysine as a pre-coating agent. The binding of 208 serum samples from controls, both healthy and pathological, and of 104 serum samples from relapsing-remitting MS (RRMS) patients was tested. We observed that the serum-binding activity in control cohort sera, including those with autoimmune and neurological diseases, was ten times lower compared to the RRMS patient cohort (p = 1.2 × 10-47), with a sensitivity and a specificity of 98% and 100%, respectively. These results show that in the serum of patients with MS there are auto-Ab against the serotonin receptor type 2A which can be successfully used in the diagnosis of MS due to their high sensitivity and specificity.

An Overview on the Hallucinogenic Peyote and Its Alkaloid Mescaline: The Importance of Context, Ceremony and Culture

Peyote (Lophophora williamsii) is a cactus that contains various biologically active alkaloids-such as pellotine, anhalonidine, hordenine and mescaline. Here, mescaline induces the psychoactive effects of peyote through the activation of the serotonin 5-HT2A receptor and the subsequent release of calcium (Ca2+) from the endoplasmic reticulum (ER). Moreover, an evaluation of the therapeutic benefits of mescaline is also currently the subject of research. It is important to consider that the outcome of taking a psychedelic drug strongly depends on the mindset of the recipient and the context (set and setting principle), including ceremonies and culture. This overview serves to summarise the current state of the knowledge of the metabolism, mechanism of action and clinical application studies of peyote and mescaline. Furthermore, the benefits of the potential of peyote and mescaline are presented in a new light, setting an example for combining a form of treatment embedded in nature and ritually enriched with our current highly innovative Western medicine.

Psychedelics action and schizophrenia

Psychedelics are compounds acting by serotonin 5-hydroxytryptamine (5-HT)2A receptor activation and induce several behavioral responses. They are of special interest because of their positive effects on neuropsychiatric disorders (depression and posttraumatic stress disorder). However, several findings revealed that some psychedelic actions are similar to symptoms observed in schizophrenia (psychosis, sensorimotor gating impairments, attention, and working memory deficits) which might limit their clinical applications. Psychedelics activate some neurotransmitters, i.e., serotonergic, and glutamatergic, that are also impaired in schizophrenia. Therefore, the neurobiological background of psychedelics and schizophrenia is partially similar. Another important aspect to discuss is the perspective of using psychedelics in schizophrenia therapy. Postmortem studies showed a loss of synapses in schizophrenia, and the positive effects of psychedelics on neuroplasticity (synaptogenesis, neurogenesis, and neuritogenesis) might be essential in the context of schizophrenia therapy. However, because of psychedelics' psychotic action, the recommended doses of psychedelics in schizophrenia treatment are not established, and subpsychedelic dosing or microdosing are considered. Exploratory studies are needed to determine the tolerability of treatment and appropriate dosing regimen. Another therapeutic option is using non-hallucinogenic psychedelic analogs that also induce neuroplastic outcomes but do not have psychotogenic effects. Further preclinical and clinical studies are needed to recognize the potential effectiveness of 5-HT2A agonists in schizophrenia therapy.

In Vivo Serotonin 5-HT2A Receptor Availability and Its Relationship with Aggression Traits in Healthy Individuals: A Positron Emission Tomography Study with C-11 MDL100907

Serotonergic neurotransmission has been associated with aggression in several psychiatric disorders. Human aggression is a continuum of traits, ranging from normal to pathological phenomena. However, the individual differences in serotonergic neurotransmission and their relationships with aggression traits in healthy individuals remain unclear. In this study, we explored the relationship between 5-HT2A receptor availability in vivo and aggression traits in healthy participants. Thirty-three healthy participants underwent 3-Tesla magnetic resonance imaging and positron emission tomography (PET) with [11C]MDL100907, a selective radioligand for 5-HT2A receptors. To quantify 5-HT2A receptor availability, the binding potential (BPND) was derived using the basis function implementation of the simplified reference tissue model, with the cerebellum as the reference region. The participants' aggression levels were assessed using the Buss-Perry Aggression Questionnaire. The voxel-based correlation analysis with age and sex as covariates revealed that the total aggression score was significantly positively correlated with [11C]MDL100907 BPND in the right middle temporal gyrus (MTG) pole, left fusiform gyrus (FUSI), right parahippocampal gyrus, and right hippocampus. The physical aggression subscale score had significant positive correlations with [11C]MDL100907 BPND in the left olfactory cortex, left orbital superior frontal gyrus (SFG), right anterior cingulate and paracingulate gyri, left orbitomedial SFG, left gyrus rectus, left MTG, left inferior temporal gyrus, and left angular gyrus. The verbal aggression subscale score showed significant positive correlations with [11C]MDL100907 BPND in the bilateral SFG, right medial SFG, left FUSI, and right MTG pole. Overall, our findings suggest the possibility of positive correlations between aggression traits and in vivo 5-HT2A receptor availability in healthy individuals. Future research should incorporate multimodal neuroimaging to investigate the downstream effects of 5-HT2A receptor-mediated signaling and integrate molecular and systems-level information in relation to aggression traits.

Effects of Chronic Combined Treatment with Ketanserin and Fluoxetine in B6.CBA-D13Mit76C Recombinant Mice with Abnormal 5-HT1A Receptor Functional Activity

The recombinant B6.CBA-D13Mit76C mouse strain is characterized by an altered sensitivity of 5-HT1A receptors and upregulated 5-HT1A gene transcription. Recently, we found that in B6.CBA-D13Mit76C mice, chronic fluoxetine treatment produced the pro-depressive effect in a forced swim test. Since 5-HT2A receptor blockade may be beneficial in treatment-resistant depression, we investigated the influence of chronic treatment (14 days, intraperitoneally) with selective 5-HT2A antagonist ketanserin (0.5 mg/kg), fluoxetine (20 mg/kg), or fluoxetine + ketanserin on the behavior, functional activity of 5-HT1A and 5-HT2A receptors, serotonin turnover, and transcription of principal genes of the serotonin system in the brain of B6.CBA-D13Mit76C mice. Ketanserin did not reverse the pro-depressive effect of fluoxetine, while fluoxetine, ketanserin, and fluoxetine + ketanserin decreased the functional activity of 5-HT1A receptors and Htr1a gene transcription in the midbrain and hippocampus. All tested drug regimens decreased the mRNA levels of Slc6a4 and Maoa in the midbrain. These changes were not accompanied by a significant shift in the levels of serotonin and its metabolite 5-HIAA. Notably, ketanserin upregulated enzymatic activity of tryptophan hydroxylase 2 (TPH2). Thus, despite some benefits (reduced Htr1a, Slc6a4, and Maoa transcription and increased TPH2 activity), prolonged blockade of 5-HT2A receptors failed to ameliorate the adverse effect of fluoxetine in the case of abnormal functioning of 5-HT1A receptors.

Cortical Correlates of Psychedelic-Induced Shaking Behavior Revealed by Voltage Imaging

(1) From mouse to man, shaking behavior (head twitches and/or wet dog shakes) is a reliable readout of psychedelic drug action. Shaking behavior like psychedelia is thought to be mediated by serotonin 2A receptors on cortical pyramidal cells. The involvement of pyramidal cells in psychedelic-induced shaking behavior remains hypothetical, though, as experimental in vivo evidence is limited. (2) Here, we use cell type-specific voltage imaging in awake mice to address this issue. We intersectionally express the genetically encoded voltage indicator VSFP Butterfly 1.2 in layer 2/3 pyramidal neurons. We simultaneously capture cortical hemodynamics and cell type-specific voltage activity while mice display psychedelic shaking behavior. (3) Shaking behavior is preceded by high-frequency oscillations and overlaps with low-frequency oscillations in the motor cortex. Oscillations spectrally mirror the rhythmics of shaking behavior and reflect layer 2/3 pyramidal cell activity complemented by hemodynamics. (4) Our results reveal a clear cortical fingerprint of serotonin-2A-receptor-mediated shaking behavior and open a promising methodological avenue relating a cross-mammalian psychedelic effect to cell-type specific brain dynamics.

Profile of 5-HT2A receptor involved in signaling cascades associated to intracellular inflammation and apoptosis in hepatocytes and its role in carbon tetrachloride-induced hepatotoxicity

Previously, we found that the 5-HT_2A receptor plays a key role in cell injury. However, the mechanism by which the 5-HT_2A receptor mediates intracellular processes remains unclear. In this study, we aimed to clarify this intracellular process in hepatocyte LO2 cells and evaluate its role in CCl₄-induced hepatotoxicity in mice. In vitro, both the agonist and overexpression of 5-HT_2A receptor could promote 5-HT degradation by upregulating the expression of 5-HT synthases and monoamine oxidase-A (MAO-A) to cause overproduction of ROS in mitochondria. We refer to this as the activation of the 5-HT degradation system (5DS) axis, which leads to the phosphorylation of JNK, p38 MAPK, STAT3, and NF-κB; upregulation of Bax, cleaved-caspase3, and cleaved-caspase9; and downregulation of Bcl-2, followed by apoptosis and oversecretion of TNF-α and IL-1β in cells. This phenomenon could be markedly blocked by the 5-HT_2A receptor antagonist, MAO-A inhibitor, or gene-silencing MAO-A. Through protein kinases C epsilon (PKCε) agonist treatment and gene silencing of the PKCε and 5-HT_2A receptor, we demonstrated that the 5-HT_2A receptor controls 5-HT synthases and MAO-A expression via the PKCε pathway in cells. Unexpectedly, we discovered that PKCε-mediated phosphorylation of the AKT/mTOR pathway is also a consequence of the activation of the 5DS axis. Furthermore, we confirmed that the inhibition of the 5DS axis using the 5-HT_2A receptor antagonist could prevent hepatotoxicity induced by CCl₄ both in vitro and in vivo, inhibiting the aforementioned signaling cascades, inflammation, and apoptosis, and that the 5DS activation area overlapped the necrotic area of mouse liver. Taken together, we revealed a 5DS axis in hepatocytes that controls the signaling cascades associated with inflammation and apoptosis and confirmed its role in CCl₄-induced hepatotoxicity.

25X-NBOMe compounds - chemistry, pharmacology and toxicology. A comprehensive review

Recently, a growing number of reports have indicated a positive effect of hallucinogenic-based therapies in different neuropsychiatric disorders. However, hallucinogens belonging to the group of new psychoactive substances (NPS) may produce high toxicity. NPS, due to their multi-receptors affinity, are extremely dangerous for the human body and mental health. An example of hallucinogens that have been lately responsible for many severe intoxications and deaths are 25X-NBOMes - N-(2-methoxybenzyl)-2,5-dimethoxy-4-substituted phenethylamines, synthetic compounds with strong hallucinogenic properties. 25X-NBOMes exhibit a high binding affinity to serotonin receptors but also to dopamine, adrenergic and histamine receptors. Apart from their influence on perception, many case reports point out systemic and neurological poisoning with these compounds. In humans, the most frequent side effects are tachycardia, anxiety, hypertension and seizures. Moreover, preclinical studies confirm that 25X-NBOMes cause developmental impairments, cytotoxicity, cardiovascular toxicity and changes in behavior of animals. Metabolism of NBOMes seems to be very complex and involves many metabolic pathways. This fact may explain the observed high toxicity. In addition, many analytical methods have been applied in order to identify these compounds and their metabolites. The presented review summarized the current knowledge about 25X-NBOMes, especially in the context of toxicity.

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.

5-HT2ARs Mediate Therapeutic Behavioral Effects of Psychedelic Tryptamines

Psychedelic compounds have displayed antidepressant potential in both humans and rodents. Despite their promise, psychedelics can induce undesired effects that pose safety concerns and limit their clinical scalability. The rational development of optimized psychedelic-related medicines will require a full mechanistic understanding of how these molecules produce therapeutic effects. While the hallucinogenic properties of psychedelics are generally attributed to activation of serotonin 2A receptors (5-HT2ARs), it is currently unclear if these receptors also mediate their antidepressant effects as several nonhallucinogenic analogues of psychedelics with antidepressant-like properties have been developed. Moreover, many psychedelics exhibit promiscuous pharmacology, making it challenging to identify their primary therapeutic target(s). Here, we use a combination of pharmacological and genetic tools to demonstrate that activation of 5-HT2A receptors is essential for tryptamine-based psychedelics to produce antidepressant-like effects in rodents. Our results suggest that psychedelic tryptamines can induce hallucinogenic and therapeutic effects through activation of the same receptor.

Effects of low-doses of methamphetamine on d-fenfluramine-induced head-twitch response (HTR) in mice during ageing and c-fos expression in the prefrontal cortex

BACKGROUND

The head-twitch response (HTR) in mice is considered a behavioral model for hallucinogens and serotonin 5-HT_2A receptor function, as well as Tourette syndrome in humans. It is mediated by 5-HT_2A receptor agonists such as ( ±)- 2,5-dimethoxy-4-iodoamphetamine (DOI) in the prefrontal cortex (PFC). The 5-HT_2A antagonist EMD 281014, can prevent both DOI-induced HTR during ageing and c-fos expression in different regions of PFC. Moreover, the nonselective monoamine releaser methamphetamine (MA) suppressed DOI-induced HTR through ageing via concomitant activation of inhibitory 5-HT_1A receptors, but enhanced DOI-evoked c-fos expression. d-Fenfluramine is a selective 5-HT releaser and induces HTR in mice, whereas MA does not. Currently, we investigated whether EMD 281014 or MA would alter: (1) d-fenfluramine-induced HTR frequency in 20-, 30- and 60-day old mice, (2) d-fenfluramine-evoked c-fos expression in PFC, and (3) whether blockade of inhibitory serotonergic 5-HT_1A- or adrenergic ɑ₂-receptors would prevent suppressive effect of MA on d-fenfluramine-induced HTR.

RESULTS

EMD 281014 (0.001-0.05 mg/kg) or MA (0.1-5 mg/kg) blocked d-fenfluramine-induced HTR dose-dependently during ageing. The 5-HT_1A antagonist WAY 100635 countered the inhibitory effect of MA on d-fenfluramine-induced HTR in 30-day old mice, whereas the adrenergic ɑ₂ antagonist RS 79948 reversed MA's inhibitory effect in both 20- and 30- day old mice. d-Fenfluramine significantly increased c-fos expressions in PFC regions. MA (1 mg/kg) pretreatment significantly increased d-fenfluramine-evoked c-fos expression in different regions of PFC. EMD 281014 (0.05 mg/kg) failed to prevent d-fenfluramine-induced c-fos expression, but significantly increased it in one PFC region (PrL at - 2.68 mm).

CONCLUSION

EMD 281014 suppressed d-fenfluramine-induced HTR but failed to prevent d-fenfluramine-evoked c-fos expression which suggest involvement of additional serotonergic receptors in the mediation of evoked c-fos. The suppressive effect of MA on d-fenfluramine-evoked HTR is due to well-recognized functional interactions between stimulatory 5-HT_2A- and the inhibitory 5-HT_1A- and ɑ₂-receptors. MA-evoked increases in c-fos expression in PFC regions are due to the activation of diverse monoaminergic receptors through increased synaptic concentrations of 5-HT, NE and/or DA, which may also account for the additive effect of MA on d-fenfluramine-evoked changes in c-fos expression. Our findings suggest potential drug receptor functional interaction during development when used in combination.

Disturbed relationship between glucocorticoid receptor and 5-HT1AR/5-HT2AR in ADHD rats: A correlation study

Objective

This work is to investigate the alterations of the central 5-hydroxytryptamine (5-HT) system in spontaneously hypertensive rats (SHR) and the correlation with the behaviors of SHR, and to explore the effects of glucocorticoid intervention on the central 5-HT system and SHR behaviors.

Materials and methods

Three weeks old SHR were chosen as the attention-deficit hyperactivity disorder (ADHD) model and treated with glucocorticoid receptor (GR) agonist or inhibitor, whereas Wista Kyoto rats (WKY) were chosen as the normal control group. Open-field test and Làt maze test were used to evaluate the spontaneous activities and non-selective attention. The levels of 5-HT in the extracellular fluid specimens of the prefrontal cortex of rats were analyzed by high-performance liquid chromatography. The expressions of GR, 5-HT1A receptor (5-HT1AR), and 5-HT2A receptor (5-HT2AR) in the prefrontal cortex were analyzed through immunohistochemistry.

Results

Our study demonstrated that the 5-HT level was lower in the prefrontal cortex of SHR compared to that of WKY. The Open-field test and Làt maze test showed that GR agonist (dexamethasone, DEX) intervention ameliorated attention deficit and hyperactive behavior, whereas GR inhibitor (RU486) aggravated the disorders. With DEX, the expression levels of 5-HT and 5-HT2AR in the prefrontal cortex of SHR were significantly higher than those in the control group, whereas the expression level of 5-HT1AR was lower. However, the expression levels of 5-HT and 5-HT2AR were significantly decreased after the intervention with RU486, while the expression level of 5-HT1AR increased. Results showed that glucocorticoid was negatively correlated with 5-HT1AR and positively correlated with 5-HT2AR.

Conclusion

In the prefrontal cortex of ADHD rats, the down-regulation of 5-HT and 5-HT2AR expressions and the up-regulation of 5-HT1AR, compared with WYK rats, suggested a dysfunctional central 5-HT system in ADHD rats. The GR agonist can upregulate the expression of 5-HT and 5-HT2AR and downregulate the expression of 5-HT1AR in the prefrontal cortex of SHR as well as reduce the hyperactivity and attention deficit behavior in SHR, while the opposite was true for the GR inhibitor. It is suggested that the dysfunction of the 5-HT system in ADHD rats is closely related to glucocorticoid receptor activity.

Preferential Modulatory Action of 5-HT(2A) Receptors on the Dynamic Regulation of Basal Ganglia Circuits

In rodents, cortical information is transferred to the substantia nigra pars reticulata (SNr) through motor and medial prefrontal (mPF) basal ganglia (BG) circuits implicated in motor and cognitive/motivational behaviors, respectively. The serotonergic 5-HT_2A receptors are located in both of these neuronal networks, displaying topographical differences with a high expression in the associative/limbic territories, and a very low expression in the subthalamic nucleus. This study investigated whether the stimulation of 5-HT_2A receptors could have a specific signature on the dynamic regulation of BG circuits, preferentially modulating the mPF information processing through trans-striatal pathways. We performed in vivo single-unit extracellular recordings to assess the effect of the 5-HT_2A agonist TCB-2 on the spontaneous and cortically evoked activity of lateral and medial SNr neurons in male rats (involved in motor and mPF circuits, respectively). TCB-2 (50-200 µg/kg, i.v.) increased the basal firing rate and enhanced the cortically evoked inhibitory response of medial SNr neurons (transmission through the direct striato-nigral pathway). A prior administration of the preferential 5-HT_2A receptor antagonist MDL11939 (200 µg/kg, i.v.) did not modify any electrophysiological parameter, but occluded TCB-2-induced effects. In animals treated with the 5-HT synthesis inhibitor pCPA (4-chloro-dl-phenylalanine methyl ester hydrochloride), TCB-2 failed to induce the above-mentioned effects, thus suggesting the contribution of endogenous 5-HT. However, the mobilization of 5-HT induced by the acute administration of fluoxetine (10 mg/kg, i.p.) did not mimic the effects triggered by TCB-2. Overall, these data suggest that 5-HT_2A receptors have a preferential modulatory action on the dynamic regulation of BG circuitry.SIGNIFICANCE STATEMENT Motor and medial prefrontal (mPF) basal ganglia (BG) circuits play an important role in integrative brain functions like movement control or cognitive/motivational behavior, respectively. Although these neuronal networks express 5-HT_2A receptors, the expression is higher in associative/limbic structures than in the motor ones. We show a topographical-dependent dissociation in the effects triggered by the 5HT_2A agonist TCB-2, which specifically increases the medial substantia nigra pars reticulata neuron activity and has a preferential action on mPF information processing through the striato-nigral direct pathway. These are very likely to be 5-HT_2A receptor-mediated effects that require mobilization of the endogenous 5-HT system. These findings provide evidence about the specific signature of 5-HT_2A receptors on the dynamic regulation of BG circuits.

Recent Studies on Serotonin 5-HT2A Receptor Antagonists in Medicinal Chemistry: A Last Decades Survey

In the last decades, much attention has been paid to the functioning of receptors to understand better how they work with various chemical motifs. Among different families, G-proteincoupled receptor (GPCR) families have drawn much attention in the twenty-first century. They are the most prominent signal transducer across the cell membrane, comprising thousand-odd proteins. One of the members of GPCRs is the serotonin 2A (5-HT2A) receptor, which has been associated with complex etiological mental illnesses. In this survey, we collected data on 5-HT2A, i.e., the role of 5- HT2A receptors in human and animal analogy, various binding site functionalities, advanced effects, and synthetic aspects.

Use of the head-twitch response to investigate the structure-activity relationships of 4-thio-substituted 2,5-dimethoxyphenylalkylamines

RATIONALE

4-Thio-substituted phenylalkylamines such as 2,5-dimethoxy-4-ethylthiophenethylamine (2C-T-2) and 2,5-dimethoxy-4-n-propylthiophenethylamine (2C-T-7) produce psychedelic effects in humans and have been distributed as recreational drugs.

OBJECTIVES

The present studies were conducted to examine the structure-activity relationships (SAR) of a series of 4-thio-substituted phenylalkylamines using the head twitch response (HTR), a 5-HT_2A receptor-mediated behavior induced by psychedelic drugs in mice. The HTR is commonly used as a behavioral proxy in rodents for human psychedelic effects and can be used to discriminate hallucinogenic and non-hallucinogenic 5-HT_2A agonists.

METHODS

HTR dose-response studies with twelve different 4-thio-substituted phenylalkylamines were conducted in male C57BL/6 J mice. To detect the HTR, head movement was recorded electronically using a magnetometer coil and then head twitches were identified in the recordings using a validated method based on artificial intelligence.

RESULTS

2C-T, the parent compound of this series, had relatively low potency in the HTR paradigm, but adding an α-methyl group increased potency fivefold. Potency was also increased when the 4-methylthio group was extended by one to three methylene units. Fluorination of the 4-position alkylthio chain, however, was detrimental for activity, as was the presence of a 4-allylthio substituent versus a propylthio group. 2C-T analogs containing a 4-benzylthio group showed little or no effect in the HTR paradigm, which is consistent with evidence that bulky 4-substituents can dampen agonist efficacy at the 5-HT_2A receptor. Binding and functional studies confirmed that the compounds have nanomolar affinity for 5-HT₂ receptor subtypes and act as partial agonists at 5-HT_2A.

CONCLUSIONS

In general, there were close parallels between the HTR data and the known SAR governing activity of phenylalkylamines at the 5-HT_2A receptor. These findings further support the classification of 2C-T compounds as psychedelic drugs.

Ayahuasca's therapeutic potential: What we know - and what not

The therapeutic potential of the psychedelic brew ayahuasca has been investigated in preclinical and clinical studies. Currently, the most consistent evidence refers to depression. However, various studies suggest that ayahuasca may comprise therapeutic benefits in other health conditions. This narrative review provides a comprehensive, up-to-date overview of ayahuasca's therapeutic effects in diverse clinical conditions in human (clinical, cross-sectional, observational, and qualitative) and preclinical (animal and in vitro) studies. In addition to summarizing and discussing the most commonly studied conditions, such as depression, anxiety, and substance use disorders (SUD), we also examine less frequently studied psychiatric, neurological, and physical conditions. Moreover, we discuss evidence from epidemiological studies on the impact of regular, long-term ayahuasca use on health and psychosocial outcomes. Overall, evidence for depression and SUD is more consistent, with numerous and diverse studies. However, a growing body of evidence suggests that other conditions equally relevant to public health might be promising targets for ayahuasca's therapeutic effects. This includes preliminary studies indicating potential for grief, eating disorders, posttraumatic stress disorder, personality disorders, Parkinson's and Alzheimer's disease, and severe physical illnesses (e.g., cancer, chronic conditions). Moreover, preliminary evidence in long-term ayahuasca users does not suggest detrimental effects but possible benefits for individual and collective health. In light of the emerging evidence of psychedelic drugs as therapeutic agents, it is essential to further investigate in rigorous designs the therapeutic potential of ayahuasca in conditions other than depression.

Rearing behaviour in the mouse behavioural pattern monitor distinguishes the effects of psychedelics from those of lisuride and TBG

Psychedelics alter consciousness and may have potential for drug development. As psychedelics are likely therapeutically active, it is important to study their effects and mechanisms using preclinical models. Here, we examined the effects of phenylalkylamine and indoleamine psychedelics on locomotor activity and exploratory behaviour using the mouse Behavioural Pattern Monitor (BPM). DOM, mescaline, and psilocin reduced locomotor activity at high doses and influenced rearings, an exploratory behaviour, in a characteristic inverted U-shaped dose-response function. Pretreatment with the selective 5-HT_2A antagonist M100907 reversed the drug-induced alterations in locomotor activity, rearings, and jumps after systemic administration of DOM at low doses. However, holepoking at the full range of doses tested was not blocked by M100907. Administration of the hallucinogenic 5-HT_2A agonist 25CN-NBOH induced striking similarities in response to that to psychedelics; these alterations were significantly diminished by M100907, whereas the putatively non-hallucinogenic 5-HT_2A agonist TBG did not affect locomotor activity, rearings, or jumps at the most effective doses. The nonhallucinogenic 5-HT_2A agonist lisuride failed to increase rearing. The results of these experiments provide strong evidence that DOM-elicited increases in rearing are due to mediation by the 5-HT_2A receptor. Finally, discriminant analysis was able to distinguish all four psychedelics from lisuride and TBG based on behavioural performance alone. Thus, increased rearing in mice could provide additional evidence of behavioural differences between hallucinogenic and nonhallucinogenic 5-HT_2A agonists.

Age-Related Changes in Central Nervous System 5-Hydroxytryptamine Signalling and Its Potential Effects on the Regulation of Lifespan

Serotonin or 5-hydroxytryptamine (5-HT) is an important neurotransmitter in the central nervous system and the periphery. Most 5-HT (~99%) is found in the periphery where it regulates the function of the gastrointestinal (GI) tract and is an important regulator of platelet aggregation. However, the remaining 1% that is found in the central nervous system (CNS) can regulate a range of physiological processes such as learning and memory formation, mood, food intake, sleep, temperature and pain perception. More recent work on the CNS of invertebrate model systems has shown that 5-HT can directly regulate lifespan.This chapter will focus on detailing how CNS 5-HT signalling is altered with increasing age and the potential consequences this has on its ability to regulate lifespan.

Analytical profile, in vitro metabolism and behavioral properties of the lysergamide 1P-AL-LAD

Lysergic acid diethylamide (LSD) is known to induce powerful psychoactive effects in humans, which cemented its status as an important tool for clinical research. A range of analogues and derivatives has been investigated over the years, including those classified as new psychoactive substances. This study presents the characterization of the novel lysergamide N,N-diethyl-1-propanoyl-6-(prop-2-en-1-yl)-9,10-didehydroergoline-8β-carboxamide (1P-AL-LAD) using various mass spectrometric, gas- and liquid chromatographic and spectroscopic methods. In vitro metabolism studies using pooled human liver microsomes (pHLM) confirmed that 1P-AL-LAD converted to AL-LAD as the most abundant metabolite consistent with the hypothesis that 1P-AL-LAD may act as a prodrug. Fourteen metabolites were detected in total; metabolic reactions included hydroxylation of the core lysergamide ring structure or the N⁶ -allyl group, formation of dihydrodiol metabolites, N-dealkylation, N¹ -deacylation, dehydrogenation, and combinations thereof. The in vivo behavioral activity of 1P-AL-LAD was evaluated using the mouse head twitch response (HTR), a 5-HT_2A -mediated head movement that serves as a behavioral proxy in rodents for human hallucinogenic effects. 1P-AL-LAD induced a dose-dependent increase in HTR counts with an inverted U-shaped dose-response function, similar to lysergic acid diethylamide (LSD), psilocybin, and other psychedelics. Following intraperitoneal injection, the median effective dose (ED₅₀ ) for 1P-AL-LAD was 491 nmol/kg, making it almost three times less potent than AL-LAD (174.9 nmol/kg). Previous studies have shown that N¹ -substitution disrupts the ability of lysergamides to activate the 5-HT_2A receptor; based on the in vitro metabolism data, 1P-AL-LAD may induce the HTR because it acts as a prodrug and is metabolized to AL-LAD after administration to mice.

Return of the lysergamides. Part VII: Analytical and behavioural characterization of 1-valeroyl-d-lysergic acid diethylamide (1V-LSD)

The psychopharmacological properties of the psychedelic drug lysergic acid diethylamide (LSD) have attracted the interest of several generations of scientists. While further explorations involving novel LSD-type compounds are needed to assess their potential as medicinal drugs, the emergence of novel derivatives as recreational drugs has also been observed. 1-Valeroyl-LSD (also known as 1-valeryl-LSD, 1-pentanoyl-LSD, 1V-LSD, or "Valerie") is a new N¹ -acylated LSD derivative that recently appeared on the online market, and it could be viewed as a higher homolog of ALD-52, 1P-LSD, and 1B-LSD. The present study included the analytical characterization and involved various methods of mass spectrometry (MS), gas and liquid chromatography (GC and LC), nuclear magnetic resonance (NMR) spectroscopy, GC-solid-state infrared (GC-sIR) analysis, and Raman spectroscopy. The in vivo activity of 1V-LSD was assessed using the mouse head-twitch response (HTR), a 5-HT_2A -mediated head movement that serves as a behavioral proxy in rodents for human hallucinogenic effects. Similar to LSD and other psychedelic drugs, the HTR induced by 1V-LSD was dose dependent, and the median effective dose for 1V-LSD was 373 nmol/kg, which was about a third of the potency of LSD (ED₅₀  = 132.8 nmol/kg). Lysergamides containing the N¹ -substituent typically act as weak partial agonists at the 5-HT_2A receptor and are believed to serve as prodrugs for LSD. 1V-LSD is also likely to be hydrolyzed to LSD and serve as a prodrug, but studies to assess the biotransformation and receptor pharmacology of 1V-LSD should be performed to fully elucidate its mechanism of action.

Spinal 5-HT2A Receptor is Involved in Electroacupuncture Inhibition of Chronic Pain

Knee osteoarthritis (KOA) is a highly prevalent, chronic joint disorder, and it is a typical disease which can develop chronic pain. Our previous study has proved that endocannabinoid (2-AG)-CB1R-GABA-5-HT pathway is involved in electroacupuncture (EA) mediated inhibition of chronic pain. However, it is still unclear which among the 5-HT receptor subtype is involved in EA evoked 5-HT mediated inhibition of chronic pain in the dorsal spinal cord. 5-HT_2A is a G protein-coupled receptor and it is involved in 5-HT descending pain modulation system. We found that EA treatment at frequency of 2 Hz +1 mA significantly increased the expression of 5-HT_2A receptor in the dorsal spinal cord and intrathecal injection of 5-HT_2A receptor antagonist or agonist reversed or mimicked the analgesic effect of EA in each case respectively. Intrathecal injection of a selective GABA_A receptor antagonist Bicuculline also reversed the EA effect on pain hypersensitivity. Additionally, EA treatment reversed the reduced expression of GABA_A receptor and KCC2 in the dorsal spinal cord of KOA mice. Furthermore, we demonstrated that intrathecal 5-HT_2A receptor antagonist/agonist reversed or mimicked the effect of EA up-regulate of KCC2 expression, respectively. Similarly, intrathecal injection of PLC and PKC inhibitors prevented both anti-allodynic effect and up-regulation of KCC2 expression by EA treatment. Our data suggest that EA treatment up-regulated KCC2 expression through activating 5-HT_2A-Gq-PLC-PKC pathway and enhanced the inhibitory function of GABA_A receptor, thereby inhibiting chronic pain in a mouse model of KOA.

The Hallucinogenic Serotonin2A Receptor Agonist, 2,5-Dimethoxy-4-Iodoamphetamine, Promotes cAMP Response Element Binding Protein-Dependent Gene Expression of Specific Plasticity-Associated Genes in the Rodent Neocortex

Psychedelic compounds that target the 5-HT_2A receptor are reported to evoke psychoplastogenic effects, including enhanced dendritic arborization and synaptogenesis. Transcriptional regulation of neuronal plasticity-associated genes is implicated in the cytoarchitectural effects of serotonergic psychedelics, however, the transcription factors that drive this regulation are poorly elucidated. Here, we addressed the contribution of the transcription factor cyclic adenosine monophosphate (cAMP)-response element binding protein (CREB) in the regulation of neuronal plasticity-associated genes by the hallucinogenic 5-HT_2A receptor agonist, 2,5-dimethoxy-4-iodoamphetamine (DOI). In vitro studies with rat cortical neurons indicated that DOI enhances the phosphorylation of CREB (pCREB) through mitogen-activated protein (MAP) kinase and calcium/calmodulin dependent kinase II (CaMKII) pathways, with both cascades contributing to the DOI-evoked upregulation of Arc, Bdnf1, Cebpb, and Egr2 expression, whilst the upregulation of Egr1 and cFos mRNA involved the MAP kinase and CaMKII pathway respectively. We observed a robust DOI-evoked increase in the expression of several neuronal plasticity-associated genes in the rat neocortex in vivo. This DOI-evoked upregulation of neuronal plasticity-associated genes was completely blocked by the 5-HT_2A receptor antagonist MDL100,907 in vitro and was also abrogated in the neocortex of 5-HT_2A receptor deficient mice. Further, 5-HT_2A receptor stimulation enhanced pCREB enrichment at putative cAMP response element (CRE) binding sites in the Arc, Bdnf1, Cebpb, cFos, but not Egr1 and Egr2, promoters in the rodent neocortex. The DOI-mediated transcriptional induction of Arc, cFos and Cebpb was significantly attenuated in the neocortex of CREB deficient/knockout (CREBαδ KO) mice. Collectively, these results indicate that the hallucinogenic 5-HT_2A receptor agonist DOI leads to a rapid transcriptional upregulation of several neuronal plasticity-associated genes, with a subset of them exhibiting a CREB-dependent regulation. Our findings raise the intriguing possibility that similar to slow-acting classical antidepressants, rapid-action serotonergic psychedelics that target the 5-HT_2A receptor may also recruit the transcription factor CREB to enhance the expression of neuronal plasticity-associated genes in the neocortex, which could in turn contribute to the rapid psychoplastogenic changes evoked by these compounds.

An ontogenic study of receptor mechanisms by which acute administration of low-doses of methamphetamine suppresses DOI-induced 5-HT2A-receptor mediated head-twitch response in mice

BACKGROUND

Methamphetamine (MA) is a non-selective monoamine releaser and thus releases serotonin (5-HT), norepinephrine (NE) and dopamine (DA) from corresponding nerve terminals into synapses. DOI ((±)-2, 5-dimethoxy-4-iodoamphetamine) is a direct-acting serotonergic 5-HT_2A/C receptor agonist and induces the head-twitch response (HTR) via stimulation of 5-HT_2A receptor in mice. While more selective serotonin releasers such as d-fenfluramine evoke the HTR, monoamine reuptake blockers (e.g., cocaine) suppress the DOI-evoked HTR via indirect stimulation of serotonergic 5-HT_1A- and adrenergic ɑ₂-receptors. Since the induction of HTR by DOI is age-dependent, we investigated whether: (1) during development MA can evoke the HTR by itself, and (2) acute pretreatment with either the selective 5-HT_2A receptor antagonist EMD 281014 or low-doses of MA can: (i) modulate the DOI-induced HTR in mice across postnatal days 20, 30 and 60, and (ii) alter the DOI-induced c-fos expression in mice prefrontal cortex (PFC). To further explore the possible modulatory effect of MA on DOI-induced HTR, we investigated whether blockade of inhibitory serotonergic 5-HT_1A- or adrenergic ɑ₂-receptors by corresponding selective antagonists (WAY 100635 or RS 79948, respectively), can prevent the effect of MA on DOI-induced HTR during aging.

RESULTS

Although neither EMD 281014 nor MA by themselves could evoke the HTR, acute pretreatment with either EMD 281014 (0.01, 0.05 and 0.1 mg/kg, i.p.) or MA (1, 2.5, 5 mg/kg, i.p.), dose-dependently suppressed the DOI-induced HTR across ages. While WAY 100635 significantly reversed the inhibitory effect of MA in 20- and 30-day old mice, RS 79948 failed to significantly counter MA's inhibitory effect. Moreover, DOI significantly increased c-fos expressions in several PFC regions. EMD 281014 prevented the DOI-induced increases in c-fos expression. Despite the inhibitory effect of MA on DOI-induced HTR, MA alone or in combination with DOI, significantly increased c-fos expression in several regions of the PFC.

CONCLUSION

The suppressive effect of MA on the DOI-evoked HTR appears to be mainly due to functional interactions between the HTR-inducing 5-HT_2A receptor and the inhibitory 5-HT_1A receptor. The MA-induced increase in c-fos expression in different PFC regions may be due to MA-evoked increases in synaptic concentrations of 5-HT, NE and/or DA.

The Selective Serotonin 2A Receptor Antagonist Sarpogrelate Prevents Cardiac Hypertrophy and Systolic Dysfunction via Inhibition of the ERK1/2-GATA4 Signaling Pathway

Drug repositioning has recently emerged as a strategy for developing new treatments at low cost. In this study, we used a library of approved drugs to screen for compounds that suppress cardiomyocyte hypertrophy. We identified the antiplatelet drug sarpogrelate, a selective serotonin-2A (5-HT_2A) receptor antagonist, and investigated the drug's anti-hypertrophic effect in cultured cardiomyocytes and its effect on heart failure in vivo. Primary cultured cardiomyocytes pretreated with sarpogrelate were stimulated with angiotensin II, endothelin-1, or phenylephrine. Immunofluorescence staining showed that sarpogrelate suppressed the cardiomyocyte hypertrophy induced by each of the stimuli. Western blotting analysis revealed that 5-HT_2A receptor level was not changed by phenylephrine, and that sarpogrelate suppressed phenylephrine-induced phosphorylation of ERK1/2 and GATA4. C57BL/6J male mice were subjected to transverse aortic constriction (TAC) surgery followed by daily oral administration of sarpogrelate for 8 weeks. Echocardiography showed that 5 mg/kg of sarpogrelate suppressed TAC-induced cardiac hypertrophy and systolic dysfunction. Western blotting revealed that sarpogrelate suppressed TAC-induced phosphorylation of ERK1/2 and GATA4. These results indicate that sarpogrelate suppresses the development of heart failure and that it does so at least in part by inhibiting the ERK1/2-GATA4 signaling pathway.

Influence of 5-HT(2A) receptor function on anxiety-like behavior induced by a combination treatment with doxorubicin and cyclophosphamide in rats

Anxiety-like behavior induced by a combination of doxorubicin and cyclophosphamide may be mediated by serotonin (5-HT)_2A receptor hyperactivity. The anxiolytic effects of fluoxetine may be inhibited by this combination. The present study examined the mechanisms underlying anxiety-like behavior induced by the combination doxorubicin and cyclophosphamide in rats. Anxiety-like behavior was induced during a light-dark test by the doxorubicin and cyclophosphamide treatment (once a week for 2 weeks). 5-HT_2A receptor and 5-HT_2A receptor-mediated extracellular signal-related kinase (ERK)1/2 levels were measured using Western blotting. 5-HT reuptake activity in fluoxetine-treated rats was also examined using microdialysis. ( ±)-1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane, a 5-HT_2A receptor agonist, induced anxiety-like behavior. The fluoxetine treatment increased extracellular 5-HT concentrations in the hippocampus of vehicle- and doxorubicin and cyclophosphamide-treated rats. 5-HT transporter levels in the hippocampus were not affected by chemotherapy. The doxorubicin and cyclophosphamide treatment did not alter 5-HT_2A receptor levels in the frontal cortex. However, chemotherapy increased 5-HT_2A receptor-mediated ERK1/2 phosphorylation levels significantly more than the vehicle treatment. The present results suggest that anxiety-like behavior induced by the combination of doxorubicin and cyclophosphamide is mediated by 5-HT_2A receptor hyperactivity without an increase in 5-HT_2A receptor levels in rats.

Glucosylsphingosine evokes pruritus via activation of 5-HT2A receptor and TRPV4 in sensory neurons

BACKGROUND AND PURPOSE

Glucosylsphingosine (GS), an endogenous sphingolipid, is highly accumulated in the epidermis of patients with atopic dermatitis (AD) due to abnormal ceramide metabolism. More importantly, GS can evoke scratching behaviors. However, the precise molecular mechanism by which GS induces pruritus has been elusive. Thus, the present study aimed to elucidate the molecular signaling pathway of GS, especially at the peripheral sensory neuronal levels.

EXPERIMENTAL APPROACH

Calcium imaging was used to investigate the responses of HEK293T cells or mouse dorsal root ganglion (DRG) neurons to application of GS. Scratching behavior tests were also performed with wild-type and Trpv4 knockout mice.

KEY RESULTS

GS activated DRG neurons in a manner involving both the 5-HT_2A receptor and TRPV4. Furthermore, GS-induced responses were significantly suppressed by various inhibitors, including ketanserin (5-HT_2A receptor antagonist), YM254890 (Gα_q/11 inhibitor), gallein (Gβγ complex inhibitor), U73122 (phospholipase C inhibitor), bisindolylmaleimide I (PKC inhibitor), and HC067047 (TRPV4 antagonist). Moreover, DRG neurons from Trpv4 knockout mice exhibited significantly reduced responses to GS. Additionally, GS-evoked scratching behaviors were greatly decreased by pretreatment with inhibitors of either 5-HT_2A receptor or TRPV4. As expected, GS-evoked scratching behavior was also significantly decreased in Trpv4 knockout mice.

CONCLUSION AND IMPLICATIONS

Overall, the present study provides evidence for a novel molecular signaling pathway for GS-evoked pruritus, which utilizes both 5-HT_2A receptor and TRPV4 in mouse sensory neurons. Considering the high accumulation of GS in the epidermis of patients with AD, GS could be another pruritogen in patients with AD.

Molecular targets of psychedelic-induced plasticity

Psychedelic research across different disciplines and biological levels is growing at a remarkably fast pace. In the prospect of a psychedelic drug becoming again an approved treatment, much of these efforts have been oriented toward exploring the relationship between the actual psychedelic effects and those manifestations of therapeutic interest. Considering the central role of the serotonin 5-HT_2A receptor in the distinct effects of psychedelics in human psyche, neuropharmacology sits at the center of this debate and exploratory continuum. Here we discuss some of the most recent findings in human studies and contextualize them considering previous preclinical models studying phenomena related to synaptic plasticity. A special emphasis is placed on knowledge gaps, challenges, and limitations to evaluate the underpinnings of psychedelics' potential antidepressant action.

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

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

5-HT2A receptor-mediated Gαq/11 activation in psychiatric disorders: A postmortem study

OBJECTIVES

Serotonin-2A (5-HT_2A) receptors play an important role in the regulation of many brain functions that are disturbed in patients with such psychiatric diseases as mood disorders and schizophrenia. The objective of this study was to evaluate 5-HT_2A receptor-mediated signalling pathway through Gα_q/11 activation in psychiatric patients by using post-mortem brain samples.

METHODS

Functional activation of Gα_q/11 proteins coupled to 5-HT_2A receptors was determined by means of [³⁵S]GTPγS binding/immunoprecipitation assay in post-mortem prefrontal cortex of psychiatric patients diagnosed as bipolar disorder (BP), major depressive disorder (MDD), and schizophrenia, and individually matched controls. The effects of antipsychotic treatment as well as suicide were also analysed.

RESULTS

There was no significant difference in maximum percent increase (%E_max) or slope factor among the four groups. The negative logarithm of concentration eliciting the half-maximal effect (pEC₅₀) was significantly reduced in BP and schizophrenia patients as compared to controls. These alterations were attributable to antipsychotic medication. The pEC₅₀ values in 'non-suicide' group of schizophrenia, but not in 'suicide' group, were significantly reduced as compared with controls.

CONCLUSIONS

Altered 5-HT_2A receptor-mediated signalling pathway through Gα_q/11 proteins in prefrontal cortex might be apparently involved in pathophysiology and pharmacotherapy of BP and schizophrenia. In schizophrenic patients, these alterations as a result of successful treatment with antipsychotic agents may help in prevention of suicidal behaviour.

Serotonergic Modulation of Nigrostriatal and Mesolimbic Dopamine and Motor/Exploratory Behaviors in the Rat

Purpose: The 5-HT_2A receptor (R) is known to modulate dopamine (DA) release in the mammalian brain. Altanserin (ALT) and 2,5-dimethoxy-4-iodoamphetamine (DOI) act as 5-HT_2AR antagonist and agonist, respectively. In the present study, we assessed the effects of ALT and DOI on motor and exploratory behaviors and on D_2/3R binding in the rat brain with in vivo imaging methods.

Methods: D_2/3R binding was determined after systemic application of ALT (10 mg/kg) or DOI (0.5 mg/kg) and the respective vehicles [dimethyl sulfoxide (DMSO) and 0.9% saline (SAL)] with [¹²³I]IBZM as a single-photon emission computed tomography (SPECT) radioligand. Anatomical information for the delineation of the target regions was obtained with dedicated small animal MRI. Immediately after 5-HT_2AR antagonistic or agonistic treatment, motor/exploratory behaviors were assessed for 45 (ALT) or 30 min (DOI) in an open field. Additional rats underwent behavioral measurements after injection of DMSO or SAL.

Results: ALT increased D_2/3R binding in the ventral hippocampus relative to vehicle, while DOI augmented D_2/3R binding in caudate putamen, frontal cortex, motor cortex, and ventral hippocampus. The 5-HT_2AR agonist as well as antagonist decreased parameters of motor activity and active exploration. However, ALT, in contrast to DOI, decreased explorative head–shoulder motility and increased sitting.

Conclusions: The regional increases of D_2/3R binding after ALT and DOI (90 and 75 min post-challenge) may be conceived to reflect decreases of synaptic DA. The reductions of motor/exploratory activities (min 1–45 and min 1–30 after challenge with ALT and DOI, respectively) contrast the regional reductions of D_2/3R binding, as they indicate elevated DA levels at the time of behavioral measurements. It may be concluded that ALT and DOI modulate DA in the individual regions of the nigrostriatal and mesolimbocortical pathways differentially and in a time-dependent fashion.

Role of the 5-HT2A Receptor in Acute Effects of LSD on Empathy and Circulating Oxytocin

The psychedelic lysergic acid diethylamide (LSD) has experienced a revival in research, including clinical trials that evaluate LSD-assisted psychotherapy. LSD induces perceptual alterations and influences emotion processing in ways that may support psychotherapy. Here, we investigated the effects of LSD on emotional empathy and mediating role of the serotonin 5-hydroxytryptamine-2A (5-HT_2A) receptor by administering 25, 50, 100, and 200 µg LSD alone and 200 µg LSD combined with pretreatment with the 5-HT_2A receptor antagonist ketanserin (40 mg) using a placebo-controlled, double-blind, random-order, crossover design in 16 healthy subjects. The Multifaceted Empathy Test (MET) was used to assess the effects of LSD on emotional empathy. Plasma oxytocin levels were also measured. LSD dose-dependently increased implicit and explicit emotional empathy, with the highest 200 µg LSD dose having a significant effect compared with placebo. The 200 µg dose of LSD also moderately increased plasma oxytocin levels compared with placebo. Ketanserin reduced the LSD-induced elevations of oxytocin but not the LSD-induced increases in emotional empathy. These findings confirm that LSD enhances empathy, and this effect may be partially independent of its primary action on 5-HT_2A receptors to induce subjective psychedelic effects. In contrast, LSD-induced oxytocin release may depend on 5-HT_2A receptor stimulation, which is consistent with the psychedelic effect of LSD. Further studies are needed to investigate whether LSD may also enhance empathy and potentially produce therapeutic effects in patients who have deficits in empathy and impairments in social functioning.

A Complex Impact of Systemically Administered 5-HT2A Receptor Ligands on Conditioned Fear

BACKGROUND

Though drugs binding to serotonergic 5-HT2A receptors have long been claimed to influence human anxiety, it remains unclear if this receptor subtype is best described as anxiety promoting or anxiety dampening. Whereas conditioned fear expressed as freezing in rats is modified by application of 5-HT2A-acting drugs locally into different brain regions, reports on the effect of systemic administration of 5-HT2A receptor agonists and 5-HT2A antagonists or inverse agonists on this behavior remain sparse.

METHODS

We assessed the possible impact of systemic administration of 5-HT2A receptor agonists, 5-HT2A receptor inverse agonists, and a selective serotonin reuptake inhibitor (SSRI)-per se or in combination-on the freezing displayed by male rats when re-exposed to a conditioning chamber in which they received foot shocks 7 days earlier.

RESULTS

The 5-HT2A receptor agonists psilocybin and 25CN-NBOH induced a reduction in conditioned fear that was countered by pretreatment with 5-HT2A receptor inverse agonist MDL 100907. While both MDL 100907 and another 5-HT2A receptor inverse agonist, pimavanserin, failed to impact freezing per se, both compounds unmasked a robust fear-reducing effect of an SSRI, escitalopram, which by itself exerted no such effect.

CONCLUSIONS

The results indicate that 5-HT2A receptor activation is not a prerequisite for normal conditioned freezing in rats but that this receptor subtype, when selectively over-activated prior to expression, exerts a marked fear-reducing influence. However, in the presence of an SSRI, the 5-HT2A receptor, on the contrary, appears to counter an anti-freezing effect of the enhanced extracellular serotonin levels following reuptake inhibition.

Pharmacological characterization of MT-1207, a novel multitarget antihypertensive agent

Hypertension is a serious public health problem worldwide. MT-1207, chemically named 3-(4-(4-(1H-benzotriazole-1-yl)butyl)piperazine-1-yl) benzisothiazole hydrochloride, is a new chemical entity that has entered into clinical trial as antihypertensive agent in China. In this paper we report the pharmacological profile of MT-1207 regarding its acute, subacute, and long-term effects on hypertensive animal models, and its actions on isolated organs in vitro as well as its molecular targets. Blood pressure (BP) was measured in conscious animals; amlodipine was taken as a positive control drug. We showed that both single dose of MT-1207 (1.25-20 mg/kg, ig) in spontaneously hypertensive rats (SHR) and MT-1207 (0.25-6 mg/kg, ig) in two-kidney one-clip (2K1C) dogs dose-dependently decreased BP. MT-1207 quickly decreased BP within 5 min after administration; the hypotensive effect lasted for 8 and 12 h, respectively, in SHR and 2K1C dogs without reflex increase in heart rate. Multiple doses of MT-1207 (5 mg · kg-1 · d-1 in SHR; 2 mg · kg-1 · d-1 in 2K1C dogs, for 7 days) significantly decreased BP, slightly reduced heart rate, and both of them recovered after withdrawal. Long-term administration of MT-1207 (10 mg · kg-1 · d-1 for 4 months or more time) produced a stable BP reduction, improved baroreflex sensitivity, reduced renal and cardiovascular damage in SHR, and delayed stroke occurrence and death in stroke-prone SHR. In isolated rat aortic rings precontracted by adrenaline, KCl, noradrenaline or 5-hydroxytryptamine (5-HT), MT-1207 (10-9-10-4 M) caused concentration-dependent relaxation. In a panel of enzyme activity or radioligand binding assays of 87 molecular targets, MT-1207 potently inhibited adrenergic α1A, α1B, α1D, and 5-HT2A receptors with Ki < 1 nM. The antagonism of MT-1207 against these receptors was confirmed in isolated rabbit arteries. We conclude that MT-1207 is a novel and promising single-molecule multitarget agent for hypertension treatment to reduce hypertensive organ damage and stroke mortality.

Living-Cell Diffracted X-ray Tracking Analysis Confirmed Internal Salt Bridge Is Critical for Ligand-Induced Twisting Motion of Serotonin Receptors

Serotonin receptors play important roles in neuronal excitation, emotion, platelet aggregation, and vasoconstriction. The serotonin receptor subtype 2A (5-HT_2AR) is a Gq-coupled GPCR, which activate phospholipase C. Although the structures and functions of 5-HT_2ARs have been well studied, little has been known about their real-time dynamics. In this study, we analyzed the intramolecular motion of the 5-HT_2AR in living cells using the diffracted X-ray tracking (DXT) technique. The DXT is a very precise single-molecular analytical technique, which tracks diffraction spots from the gold nanocrystals labeled on the protein surface. Trajectory analysis provides insight into protein dynamics. The 5-HT_2ARs were transiently expressed in HEK 293 cells, and the gold nanocrystals were attached to the N-terminal introduced FLAG-tag via anti-FLAG antibodies. The motions were recorded with a frame rate of 100 μs per frame. A lifetime filtering technique demonstrated that the unliganded receptors contain high mobility population with clockwise twisting. This rotation was, however, abolished by either a full agonist α-methylserotonin or an inverse agonist ketanserin. Mutation analysis revealed that the “ionic lock” between the DRY motif in the third transmembrane segment and a negatively charged residue of the sixth transmembrane segment is essential for the torsional motion at the N-terminus of the receptor.

Guanosine ameliorates positive symptoms of schizophrenia via modulating 5-HT1A and 5-HT2A receptors

Schizophrenia is a serious mental disorder characterized by hallucinations, delusions, and extremely disordered thinking and behavior. There are several hypotheses of pathogenesis in schizophrenia: dopaminergic, glutamatergic, or serotonergic hyperfunction. Guanosine reportedly protects the central nervous system by modulating the glutamatergic system. Thus, we assumed that guanosine may exert a positive effect on the pathophysiology of schizophrenia. Herein, we demonstrated that guanosine significantly reduced MK-801-induced hyperlocomotion and stereotyped behaviors, but showed no effect on hyperlocomotion induced by d-amphetamine, indicating that guanosine may directly affect the glutamatergic system. Guanosine dose-dependently reduced 5-HTP-induced wet dog shakes (WDS) and other serotonin syndromes (SS) behaviors, indicating that it might block serotonin 5-HT_1A or 5-HT_2A receptors. Finally, we confirm that that guanosine modulates serotonin 5-HT_1A and 5-HT_2A receptors and it might be anti-schizophrenic partly through pertussis toxin-sensitive G_i/o-coupled PI3K/Akt signaling. Collectively, this study provides possible compounds and mechanisms for therapeutic effects on schizophrenia.

Knowledge-Based Design of Long-Chain Arylpiperazine Derivatives Targeting Multiple Serotonin Receptors as Potential Candidates for Treatment of Autism Spectrum Disorder

Autism spectrum disorder (ASD) includes a group of neurodevelopmental disorders characterized by core symptoms such as impaired social interaction and communication, repetitive and stereotyped behaviors, and restricted interests. To date, there are no effective treatments for these core symptoms. Several studies have shown that the brain serotonin (5-HT) neurotransmission system is altered in both ASD patients and animal models of the disease. Multiple pieces of evidence suggest that targeting 5-HT receptors may treat the core symptoms of ASD and associated intellectual disabilities. In fact, stimulation of the 5-HT_1A receptor reduces repetitive and restricted behaviors; blockade of the 5-HT_2A receptor reduces both learning deficits and repetitive behavior, and activation of the 5-HT₇ receptor improves cognitive performances and reduces repetitive behavior. On such a basis, we have designed novel arylpiperazine derivatives pursuing unprecedently reported activity profiles: dual 5-HT₇/5-HT_1A receptor agonist properties and mixed 5-HT₇ agonist/5-HT_1A agonist/5-HT_2A antagonist properties. Seventeen new compounds were synthesized and tested in radioligand binding assay at the target receptors. We have identified the dual 5-HT_1AR/5-HT₇R agonists 8c and 29 and the mixed 5-HT_1AR agonist/5-HT₇R agonist/5-HT_2AR antagonist 20b. These compounds are metabolically stable in vitro and have suitable central nervous system druglike properties.

Hallucinogenic/psychedelic 5HT2A receptor agonists as rapid antidepressant therapeutics: Evidence and mechanisms of action

Major depressive disorder (MDD) is among the most prevalent mental health disorders worldwide, and it is associated with a reduced quality of life and enormous costs to health care systems. Available drug treatments show low-to-moderate response in most patients, with almost a third of patients being non-responders (treatment-resistant). Furthermore, most currently available medications need several weeks to achieve therapeutic effects, and the long-term use of these drugs is often associated with significant unwanted side effects and resultant reductions in treatment compliance. Therefore, more effective, safer, and faster-acting antidepressants with enduring effects are needed. Together with ketamine, psychedelics (or classic or serotoninergic hallucinogens) such as lysergic acid diethylamide (LSD), psilocybin, and ayahuasca are among the few compounds with recent human evidence of fast-acting antidepressant effects. Several studies in the 1950s to 1970s reported antidepressive and anxiolytic effects of these drugs, which are being confirmed by modern trials (LSD, one trial; psilocybin, five trials; ayahuasca, two trials). The effects of these drugs appear to be produced primarily by their agonism at serotonin (5-hydroxytryptamine, 5-HT) receptors, especially the 5-HT_2A receptor. Considering the overall burden of MDD and the necessity of new therapeutic options, the promising (but currently limited) evidence of safety and efficacy of psychedelics has encouraged the scientific community to explore more fully their beneficial effects in MDD.

5-HT2A Receptor and 5-HT Degradation Play a Crucial Role in Atherosclerosis by Modulating Macrophage Foam Cell Formation, Vascular Endothelial Cell Inflammation, and Hepatic Steatosis

Aim: Previously, we found that diabetes-related liver dysfunction is due to activation of the 5-HT _2A receptor (5-HT _2A R) and increased synthesis and degradation of 5-HT. Here, we investigated the role of 5-HT in the development of atherosclerosis.

Methods: The study was conducted using high-fat diet-fed male ApoE ^−/− mice, THP-1 cell-derived macrophages, and HUVECs. Protein expression and biochemical indexes were determined by Western blotting and quantitative analysis kit, respectively. The following staining methods were used: oil red O staining (showing atherosclerotic plaques and intracellular lipid droplets), immunohistochemistry (showing the expression of 5-HT _2A R, 5-HT synthase, and CD68 in the aortic wall), and fluorescent probe staining (showing intracellular ROS).

Results: In addition to improving hepatic steatosis, insulin resistance, and dyslipidemia, co-treatment with a 5-HT synthesis inhibitor and a 5-HT _2A R antagonist significantly suppressed the formation of atherosclerotic plaques and macrophage infiltration in the aorta of ApoE ^−/− mice in a synergistic manner. Macrophages and HUVECs exposed to oxLDL or palmitic acid in vitro showed that activated 5-HT _2A R regulated TG synthesis and oxLDL uptake by activating PKCε, resulting in formation of lipid droplets and even foam cells; ROS production was due to the increase of both intracellular 5-HT synthesis and mitochondrial MAO-A-catalyzed 5-HT degradation, which leads to the activation of NF-κB and the release of the inflammatory cytokines TNF-α and IL-1β from macrophages and HUVECs as well as MCP-1 release from HUVECs.

Conclusion: Similar to hepatic steatosis, the pathogenesis of lipid-induced atherosclerosis is associated with activation of intracellular 5-HT _2A R, 5-HT synthesis, and 5-HT degradation.

5-HT2A and 5-HT2C receptors as potential targets for the treatment of nicotine use and dependence

Nicotine use and dependence, typically achieved through cigarette smoking, but increasingly through vape products, is the leading cause of preventable death today. Despite a recognition that many current smokers would like to quit, the success rate at doing so is low and indicative of the persistent nature of nicotine dependence and the high urge to relapse. There are currently three main forms of pharmacotherapy approved as aids to treat nicotine dependence: a variety of nicotine replacement products (NRT's), the mixed NA/DA reuptake inhibitor bupropion (Zyban®), and the preferential nicotinic α4β2 receptor agonist drug, varenicline (Chantix®); the latter being generally recognized to be the most effective. However, each of these approaches afford only limited efficacy, and various other pharmacological approaches are being explored. This chapter focusses on approaches targeted to the serotonin (5-HT) system, namely, selective serotonin reuptake inhibitors (SSRI's) which served a pioneer role in the investigation of serotoninergic modulators in human smoking cessation trials; and secondly drugs selectively interacting with the 5-HT2A and 5-HT2C receptor systems. From an efficacy perspective, measured as smoking abstinence, the 5-HT2A agonist psychedelics, namely psilocybin, seem to show the most promise; although as the article highlights, these findings are both preliminary and there are significant challenges to the route to approval, and therapeutic use of this class should they reach approval status. Additional avenues include 5-HT2C receptor agonists, which until recently was pioneered by lorcaserin, and 5-HT2A receptor antagonists represented by pimavanserin. Each of these approaches has distinct profiles across preclinical tests of nicotine dependence, and may have therapeutic potential. It is anticipated as diagnostic and predictive biomarkers emerge, they may provide opportunities for subject stratification and opportunities for personalizing smoking cessation treatment. The clinical assessment of SSRI, 5-HT2A and/or 5-HT2C receptor-based treatments may be best served by this process.

mRNA Levels of MAOA and 5-HT 2 A Receptor in Patients With Pathological Internet Use: Correlations With Comorbid Symptoms

Objective: Uncontrolled internet use may lead to the emergence of pathological internet use (PIU). PIU has become a global public health concern that can cause a range of psychotic symptoms, including anxiety, depression, and impulse control disorder. To date, we know very little about the principal biological factors related to PIU. Monoamine oxidase type A (MAOA) and serotonin (5-HT) 5-HT_2A receptor (5-HT_2AR) play critical roles in the development of behavioural and drug addictions. Thus, the aim of this study was to measure the relative expression of mRNA of MAOA and 5-HT_2AR in peripheral blood mononuclear cells (PBMCs) of patients with PIU and to determine the correlations between these biological indicators and the comorbid symptoms of patients with PIU. Methods: In this study, the mRNA of MAOA and 5-HT_2AR was detected using real-time PCR in PBMCs of the patients with PIU (n = 24) and healthy controls (HCs, n = 25). The relationship between the mRNA levels of MAOA and 5-HT_2AR and clinical symptoms in patients with PIU was further investigated. Results: MAOA mRNA in PBMCs was significantly upregulated in patients with PIU compared with that in HCs. mRNA levels of 5-HT_2AR were not found to differ significantly between HCs and patients with PIU. Correlation analyses further revealed a significant positive correlation between the relative expression of MAOA mRNA in PBMCs of patients with PIU and the Young's Internet Addiction Test and Self-Rating Depression Scale scores. Conclusion: The present study revealed upregulated expression of MAOA mRNA in patients with PIU and an association between the expression of MAOA mRNA and clinical symptoms of PIU, suggesting that the neurobiological changes may be similar between PIU and substance addiction. Additionally, this study demonstrated a potential association between comorbid symptoms and mRNA levels of MAOA.

Effects of M-1, a Major Metabolite of Sarpogrelate, on 5-HT-Induced Constriction of Isolated Human Internal Thoracic Artery

Sarpogrelate, a selective 5-hydroxytryptamine (5-HT)_2A receptor antagonist, inhibits 5-HT-induced platelet aggregation and vasoconstriction. It improves ischemic symptoms in patients with arteriosclerosis obliterans. M-1 is a major metabolite of sarpogrelate, and has been reported to show a higher affinity for the 5-HT_2A receptor on platelets than sarpogrelate. However, the effects of M-1 on 5-HT-induced constrictive response in human blood vessels have not been investigated. The internal thoracic artery (ITA) is the key conduit for coronary artery bypass grafting (CABG). 5-HT has been implicated as playing an important role in the pathogenesis of vasospasm. Thus, in the present study, the effects of M-1 on 5-HT-induced vasoconstriction were examined in isolated human endothelium denuded ITA. M-1 inhibited 5-HT-induced vasoconstriction in a concentration-dependent manner. At the highest concentration, M-1 almost completely inhibited the 5-HT-induced vasoconstriction. Expression of 5-HT_2A and 5-HT_1B receptor proteins in the membrane fraction of ITA smooth muscle cells was confirmed by Western blot analysis. Individually, supramaximal concentrations of sarpogrelate and SB224289, a selective 5-HT_1B receptor antagonist, only partially inhibited the 5-HT-induced vasoconstriction. However, simultaneous pretreatment with both these antagonists almost completely inhibited the 5-HT-induced vasoconstriction. The inhibitory effect of M-1 pretreatment mimicked the inhibitory effect of simultaneous pretreatment with sarpogrelate and SB224289. These results suggest that M-1 has antagonistic effects not only on the 5-HT_2A receptor but also on the 5-HT_1B receptor in human ITA smooth muscle cells. M-1 may be useful as a lead compound for the development of drugs for the treatment of 5-HT-induced vasospasms in CABG.

LSD acutely impairs working memory, executive functions, and cognitive flexibility, but not risk-based decision-making

BACKGROUND

Psychiatric and neurodegenerative illnesses are characterized by cognitive impairments, in particular deficits in working memory, decision-making, and executive functions including cognitive flexibility. However, the neuropharmacology of these cognitive functions is poorly understood. The serotonin (5-HT) 2A receptor might be a promising candidate for the modulation of cognitive processes. However, pharmacological studies investigating the role of this receptor system in humans are rare. Recent evidence demonstrates that the effects of Lysergic acid diethylamide (LSD) are mediated via agonistic action at the 5-HT2A receptor. Yet, the effects of LSD on specific cognitive domains using standardized neuropsychological test have not been studied.

METHODS

We examined the acute effects of LSD (100 µg) alone and in combination with the 5-HT2A antagonist ketanserin (40 mg) on cognition, employing a double-blind, randomized, placebo-controlled, within-subject design in 25 healthy participants. Executive functions, cognitive flexibility, spatial working memory, and risk-based decision-making were examined by the Intra/Extra-Dimensional shift task (IED), Spatial Working Memory task (SWM), and Cambridge Gambling Task (CGT) of the Cambridge Neuropsychological Test Automated Battery.

RESULTS

Compared to placebo, LSD significantly impaired executive functions, cognitive flexibility, and working memory on the IED and SWM, but did not influence the quality of decision-making and risk taking on the CGT. Pretreatment with the 5-HT2A antagonist ketanserin normalized all LSD-induced cognitive deficits.

CONCLUSIONS

The present findings highlight the role of the 5-HT2A receptor system in executive functions and working memory and suggest that specific 5-HT2A antagonists may be relevant for improving cognitive dysfunctions in psychiatric disorders.

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

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

Gene expression of serotonergic markers in peripheral blood mononuclear cells of patients with late-onset Alzheimer's disease

Serotonin or 5-hydroxytryptamine (5-HT) is primarily involved in the regulation of learning and memory. Pathological changes in metabolism or functional imbalance of 5-HT has been associated with Alzheimer's disease (AD). The hypothesis tested is that in peripheral blood, markers of the serotonergic pathway can be used as a diagnostic tool for AD. The current study measured the relative expression of 5-HT receptors (5-HTR2A and 5-HTR3A) as well as the 5-HT catalytic enzyme, Monoamine oxidase A (MAO-A) mRNA in Peripheral Blood Mononuclear Cells (PBMCs) of patients with late-onset Alzheimer's disease (LOAD) and age-matched controls. 5-HTR2A, 5-HTR3A, and MAO-A mRNA expressions were examined in PBMCs of 30 patients with LOAD and 30 control individuals. Real-time quantitative PCR was used to measure mRNA expression. The dementia status of patients in this study was assessed using a Mini-Mental State Examination (MMSE). Mean data of relative mRNA expression of 5-HTR2A, 5-HTR3A and MAO-A were significantly lower in PBMCs of patients with LOAD compared with controls. Based on the down-regulation of serotonergic markers in PBMCs, our findings may be another claim to the systemic nature of LOAD. The role of peripheral serotonergic downregulation, in the pathogenesis of AD, needs to be further studied. Given the extremely convenient access to PBMCs, these molecular events may represent more complete dimensions of AD neuropathophysiology or possibly lead to a new direction in studies focused on blood-based markers.

Effects of combined 5-HT(2A) and cannabinoid receptor modulation on a schizophrenia-related prepulse inhibition deficit in mice

RATIONALE

Prepulse inhibition of the startle reflex (PPI) is disrupted in several psychiatric disorders including schizophrenia. Understanding PPI pharmacology may help elucidate the pathophysiology of these disorders and lead to better treatments. Given the advantages of multi-target approaches for complex mental illnesses treatment, we have investigated the interaction between receptors known to modulate PPI (5-HT_1A and 5-HT_2A) and the neuromodulatory endocannabinoid system.

OBJECTIVES

To investigate serotonin and cannabinoid receptor (CBR) co-modulation in a model of PPI disruption relevant to schizophrenia METHODS: Male Swiss mice were pretreated with WIN 55,212-2 (CBR agonist), rimonabant (CB1R inverse agonist), 8-OH-DPAT (5-HT_1A/7 agonist), and volinanserin (5-HT_2A antagonist) or with a combination of a cannabinoid and a serotonergic drug. PPI disruption was induced by acute administration of MK-801.

RESULTS

WIN 55,212-2 and rimonabant did not change PPI nor block MK-801-induced deficits. 8-OH-DPAT increased PPI in control mice and, in a higher dose, inhibited MK-801-induced impairments. Volinanserin also increased PPI in control and MK-801-treated mice, presenting an inverted U-shaped dose-response curve. Co-administration of either cannabinoid ligand with 8-OH-DPAT did not change PPI; however, the combination of volinanserin with rimonabant increased PPI in both control and MK-801-exposed mice.

CONCLUSIONS

WIN 55,212-2 and rimonabant had similar effects in PPI. Moreover, serotonin and cannabinoid receptors interact to modulate PPI. While co-modulation of CBR and 5-HT_1A receptors did not change PPI, a beneficial effect of 5-HT_2A and CB1R antagonist combination was detected, possibly mediated through potentiation of 5-HT_2A blockade effects by concomitant CB1R blockade.

Revealing the interaction modes of 5-HT2A receptor antagonists and the Structure-Based virtual screening from FDA and TCMNP database

5-hydroxytryptamine 2A (5-HT2A) receptor is emerging as an important target for numerous psychoactive drugs due to its imperative roles in psychological diseases. In fact, multiple 5-HT2A receptor antagonists were developed to treat numerous psychiatric disorders, however, their clinical outcome was far from ideal probably due to a blurry information of the exact interaction modes between the receptor and its antagonists. Impressively, with a recent release of its crystal structure, we carefully analyzed the receptor-ligand interactions with Protein Contacts Atlas, structure-based pharmacophore models, and molecular dynamics (MD) simulations to sum up the chemical features for antagonists interacting with 5-HT2A receptor. Moreover, the molecular docking-based virtual screening was applied to discover potential 5-HT2A receptor antagonists from FDA and TCMNP databases. Intriguingly, after a systematic assessment of the docking scores, binding modes and free energies, as well as their MD simulations performances, three compounds in TCMNP database were highlighted to be potential 5-HT2A receptor antagonists. Fascinatedly, these three hits also exhibited highly binding affinities with dopamine D2 receptor (D2R) due to the similarity of the ligand binding pockets of the receptors, indicating them to be promising dual target molecules that are of great benefit for anti-psychotic-drug research and development. In addition, ADME/Tox predictions were conducted for a primary evaluation of their developing potential. Together, this study not only revealed the exact interaction modes between 5-HT2A receptor and its antagonists, which shed a light on a better access for developing its novel antagonists, but also provided promising dual D2 and 5-HT2A receptor antagonists.Communicated by Ramaswamy H. Sarma.