Search

Background Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by impairments in social interaction and repetitive stereotyped behaviors. Previous studies have reported an association of serotonin or 5-hydroxytryptamine (5-HT) with ASD, but the specific receptors and neurons by which serotonin modulates autistic behaviors have not been fully elucidated. Methods RNAi-mediated knockdown was done to destroy the function of tryptophan hydroxylase (Trh) and all the five serotonin receptors. Given that ubiquitous knockdown of 5-HT2B showed significant defects in social behaviors, we applied the CRISPR/Cas9 system to knock out the 5-HT2B receptor gene. Social space assays and grooming assays were the major methods used to understand the role of serotonin and related specific receptors in autism-like behaviors of Drosophila melanogaster. Results A close relationship was identified between serotonin and autism-like behaviors reflected by increased social space distance and high-frequency repetitive behavior in Drosophila. We further utilized the binary expression system to knock down all the five 5-HT receptors, and observed the 5-HT2B receptor as the main receptor responsible for the normal social space and repetitive behavior in Drosophila for the specific serotonin receptors underlying the regulation of these two behaviors. Our data also showed that neurons in the dorsal fan-shaped body (dFB), which expressed 5-HT2B, were functionally essential for the social behaviors of Drosophila. Conclusions Collectively, our data suggest that serotonin levels and the 5-HT2B receptor are closely related to the social interaction and repetitive behavior of Drosophila. Of all the 5 serotonin receptors, 5-HT2B receptor in dFB neurons is mainly responsible for serotonin-mediated regulation of autism-like behaviors.

The circadian clock programs daily rhythms and coordinates multiple behavioural processes, including micturition. Partial bladder outlet obstruction (pBOO) in mice produces hyperactive voiding. However, long-term effects of pBOO on bladder function have not been clarified. In this study, we investigated micturition under conditions of impaired circadian bladder function by inducing long-term pBOO by tying the proximal urethra. Micturition behavior was evaluated at 1, 3, 6 and 12 months after surgery. We used automated voided stain on paper method for a precise micturition recording for mice. And quantitative assessment of gene expression was performed at 24 months after pBOO surgery using qRT-PCR procedure. The micturition frequencies in the pBOO group were significantly decreased at 3, 6, and 12 months compared to those at 1 month after operation in the same group (p

Previous research has implicated the serotonin-2B (5-HT(2B)) receptor as a possible contributor to the antidepressant-like response. Aripiprazole has been successfully used in combination with selective serotonin reuptake inhibitors (SSRIs) in treatment-resistant depression and it, among all receptors, exhibits the highest affinity for the 5-HT(2B) receptor. However, the potential contribution of such an antagonistic action on 5-HT(2B) receptors in the context of adjunct therapy is not known. In vivo electrophysiological recordings of ventral tegmental area (VTA) dopamine (DA) neurons, dorsal raphe nucleus (DRN) 5-HT neurons and pyramidal neurons in the medial prefrontal cortex (mPFC), and the hippocampus were conducted in anaesthetized Sprague-Dawley rats after the administration of 5-HT(2B) receptor ligands alone or in combination with the SSRI escitalopram. An escitalopram-induced decrease in DA, but not 5-HT firing activity, was rescued by 2-day co-administration of the selective 5-HT(2B) receptor antagonist LY266097. In the mPFC, 14-day escitalopram administration alone had no effect on pyramidal neuron firing and burst activity, whereas, aripiprazole administered alone or in combination with escitalopram for 14 days increased pyramidal neuron firing and burst activity. Likewise, the administration of LY266097 alone or its addition on the last 3 days of a 14-day escitalopram regimen increased pyramidal neuron firing and burst activity. These results indicated that 5-HT(2B) receptors play, at least in part, a role in this enhancement. In the hippocampus, 5-HT(2B) receptor activation by BW723c86 decreased escitalopram-induced inhibition of 5-HT reuptake, which was reversed by a 5-HT(2B) receptor antagonist. Altogether, these results put into evidence the possibility that 5-HT(2B) receptor blockade contributes to the therapeutic effect of aripiprazole addition to SSRIs in depression.

Insulin resistance is a cornerstone of obesity-related complications such as type 2 diabetes, metabolic syndrome, and nonalcoholic fatty liver disease. A high rate of lipolysis is known to be associated with insulin resistance, and inhibiting adipose tissue lipolysis improves obesity-related insulin resistance. Here, we demonstrate that inhibition of serotonin (5-hydroxytryptamine [5-HT]) signaling through serotonin receptor 2B (HTR2B) in adipose tissues ameliorates insulin resistance by reducing lipolysis in visceral adipocytes. Chronic high-fat diet (HFD) feeding increased Htr2b expression in epididymal white adipose tissue, resulting in increased HTR2B signaling in visceral white adipose tissue. Moreover, HTR2B expression in white adipose tissue was increased in obese humans and positively correlated with metabolic parameters. We further found that adipocyte-specific Htr2b-knockout mice are resistant to HFD-induced insulin resistance, visceral adipose tissue inflammation, and hepatic steatosis. Enhanced 5-HT signaling through HTR2B directly activated lipolysis through phosphorylation of hormone-sensitive lipase in visceral adipocytes. Moreover, treatment with a selective HTR2B antagonist attenuated HFD-induced insulin resistance, visceral adipose tissue inflammation, and hepatic steatosis. Thus, adipose HTR2B signaling could be a potential therapeutic target for treatment of obesity-related insulin resistance.

Background Stress has emerged as an important risk factor for heart disease in women. Stress levels have been shown to correlate with delayed recovery and increased mortality after a myocardial infarction. Therefore, we sought to investigate if the observed sex‐specific effects of stress in myocardial infarction may be partly attributed to genomic interactions between the female sex hormones, estrogen (E2), and the primary stress hormones glucocorticoids. Methods and Results Genomewide studies show that glucocorticoids inhibit estrogen‐mediated regulation of genes with established roles in cardiomyocyte homeostasis. These include 5‐HT2BR (cardiac serotonin receptor 2B), the expression of which is critical to prevent cardiomyocyte death in the adult heart. Using siRNA, gene expression, and chromatin immunoprecipitation assays, we found that 5‐HT2BR is a primary target of the glucocorticoid receptor and the estrogen receptor α at the level of transcription. The glucocorticoid receptor blocks the recruitment of estrogen receptor α to the promoter of the 5‐HT2BR gene, which may contribute to the adverse effects of stress in the heart of premenopausal women. Using immunoblotting, TUNEL (terminal deoxynucleotidal transferase–mediated biotin–deoxyuridine triphosphate nick‐end labeling), and flow cytometry, we demonstrate that estrogen decreases cardiomyocyte death by a mechanism relying on 5‐HT2BR expression. In vitro and in vivo experiments show that glucocorticoids inhibit estrogen cardioprotection in response to hypoxia/reoxygenation injury and exacerbate the size of the infarct areas in myocardial infarction. Conclusions These results established a novel mechanism underlying the deleterious effects of stress on female cardiac health in the setting of ischemia/reperfusion.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Degeneration of brainstem serotonin neurons has been demonstrated in ALS patients and mouse models and was found responsible for the development of spasticity. Consistent with involvement of central serotonin pathways, 5-HT2B receptor (5-HT2BR) was upregulated in microglia of ALS mice. Its deletion worsened disease outcome in the Sod1G86R mouse model and led to microglial degeneration. In ALS patients, a polymorphism in HTR2B gene leading to higher receptor expression in CNS, was associated with increased survival in patients as well as prevention of microglial degeneration. Thus, the aim of our study was to determine the effect of a 5-HT2BR agonist : BW723C86 (BW), in the Sod1G86R mouse model. Despite good pharmacokinetic and pharmacological profiles, BW did not ameliorate disease outcome or motor neuron degeneration in a fast progressing mouse model of ALS despite evidence of modulation of microglial gene expression.

International audience; The serotonin 2B (5-HT2B) receptor coupled to Gq-protein contributes to the control of neuronal excitability and is implicated in various psychiatric disorders. The mechanisms underlying its brain function are not fully described. Using peptide affinity chromatography combined with mass spectrometry, we found that the PDZ binding motif of the 5-HT2B receptor located at its C-terminal end interacts with the scaffolding protein channel interacting PDZ protein (CIPP). We then showed, in COS-7 cells, that the association of the 5-HT2B receptor to CIPP enhanced receptor-operated inositol phosphate (IP) production without affecting its cell surface and intracellular levels. Co-immunoprecipitation experiments revealed that CIPP, the 5-HT2B receptor, and the NR1 subunit of the NMDA receptor form a macromolecular complex. CIPP increased 5-HT2B receptor clustering at the surface of primary cultured hippocampal neurons and prevented receptor dispersion following agonist stimulation, thus potentiating IP production and intracellular calcium mobilization in dendrites. CIPP or 5-HT2B receptor stimulation in turn dispersed NR1 clusters colocalized with 5-HT2B receptors and increased the density and maturation of dendritic spines. Collectively, our results suggest that the 5-HT2B receptor, the NMDA receptor, and CIPP may form a signaling platform by which serotonin can influence structural plasticity of excitatory glutamatergic synapses.

G protein-coupled receptors are linked to various intracellular transducers, each pathway associated with different physiological effects. Biased ligands, capable of activating one pathway over another, are gaining attention for their therapeutic potential, as they could selectively activate beneficial pathways whilst avoiding those responsible for adverse effects. We performed molecular dynamics simulations with known &beta, arrestin-biased ligands like lysergic acid diethylamide and ergotamine in complex with the 5-HT2B receptor and discovered that the extent of ligand bias is directly connected with the degree of closure of the extracellular loop region. Given a loose allosteric coupling of extracellular and intracellular receptor regions, we delineate a concept for biased signaling at serotonin receptors, by which conformational interference with binding pocket closure restricts the signaling repertoire of the receptor. Molecular docking studies of biased ligands gathered from the BiasDB demonstrate that larger ligands only show plausible docking poses in the ergotamine-bound structure, highlighting the conformational constraints associated with bias. This emphasizes the importance of selecting the appropriate receptor conformation on which to base virtual screening workflows in structure-based drug design of biased ligands. As this mechanism of ligand bias has also been observed for muscarinic receptors, our studies provide a general mechanism of signaling bias transferable between aminergic receptors.

International audience; Serotonin2B receptor (5-HT2BR) antagonists inhibit cocaine-induced hyperlocomotion independently of changes of accumbal dopamine (DA) release. Given the tight relationship between accumbal DA activity and locomotion, and the inhibitory role of medial prefrontal cortex (mPFC) DA on subcortical DA neurotransmission and DA-dependent behaviors, it has been suggested that the suppressive effect of 5-HT2BR antagonists on cocaine-induced hyperlocomotion may result from an activation of mPFC DA outflow which would subsequently inhibit accumbal DA neurotransmission. Here, we tested this hypothesis by means of the two selective 5-HT2BR antagonists, RS 127445 and LY 266097, using a combination of neurochemical, behavioral and cellular approaches in male rats. The intraperitoneal (i.p.) administration of RS 127445 (0.16 mg/kg) or LY 266097 (0.63 mg/kg) potentiated cocaine (10 mg/kg, i.p.)-induced mPFC DA outflow. The suppressant effect of RS 127445 on cocaine-induced hyperlocomotion was no longer observed in rats with local 6-OHDA lesions in the mPFC. Also, RS 127445 blocked cocaine-induced changes of accumbal glycogen synthase kinase (GSK) 3β phosphorylation, a postsynaptic cellular marker of DA neurotransmission. Finally, in keeping with the location of 5-HT2BRs on GABAergic interneurons in the dorsal raphe nucleus (DRN), the intra-DRN perfusion of the GABAAR antagonist bicuculline (100 μM) prevented the effect of the systemic or local (1 μM, intra-DRN) administration of RS 127445 on cocaine-induced mPFC DA outflow. Likewise, intra-DRN bicuculline injection (0.1 μg/0.2 μl) prevented the effect of the systemic RS 127445 administration on cocaine-induced hyperlocomotion and GSK3β phosphorylation. These results show that DRN 5-HT2BR blockade suppresses cocaine-induced hyperlocomotion by potentiation of cocaine-induced DA outflow in the mPFC and the subsequent inhibition of accumbal DA neurotransmission.

Interstitial lung disease (ILD) encompasses a heterogeneous group of more than 200 conditions, of which primarily idiopathic pulmonary fibrosis (IPF), idiopathic nonspecific interstitial pneumonia, hypersensitivity pneumonitis, ILD associated with autoimmune diseases and sarcoidosis may present a progressive fibrosing (PF) phenotype. Despite different aetiology and histopathological patterns, the PF-ILDs have similarities regarding disease mechanisms with self-sustaining fibrosis, which suggests that the diseases may share common pathogenetic pathways. Previous studies show an enhanced activation of serotonergic signaling in pulmonary fibrosis, and the serotonin (5-HT)2 receptors have been implicated to have important roles in observed profibrotic actions. Our research findings in support by others, demonstrate antifibrotic effects with 5-HT2B receptor antagonists, alleviating several key events common for the fibrotic diseases such as myofibroblast differentiation and connective tissue deposition. In this review, we will address the potential role of 5-HT and in particular the 5-HT2B receptors in three PF-ILDs: ILD associated with systemic sclerosis (SSc-ILD), ILD associated with rheumatoid arthritis (RA-ILD) and IPF. Highlighting the converging pathways in these diseases discloses the 5-HT2B receptor as a potential disease target for PF-ILDs, which today have an urgent unmet need for therapeutic strategies.

The βHere, we aim to investigate the potential cardioprotective effect of βUsing pharmacological, genetic and biophysical protein-protein interaction approaches, we studied the cardioprotective effect of the βThese data demonstrate that the β

Calcific aortic valve disease (CAVD) is a deadly disease that is rising in prevalence due to population aging. While the disease is complex and poorly understood, one well-documented driver of valvulopathy is serotonin agonism. Both serotonin overexpression, as seen with carcinoid tumors and drug-related agonism, such as with Fenfluramine use, are linked with various diseases of the valves. Thus, the objective of this study was to determine if genetic ablation or pharmacological antagonism of the 5-HT2Bserotonin receptor (gene:Htr2b) could improve the hemodynamic and histological progression of calcific aortic valve disease.Htr2bmutant mice were crossed withNotch1+/-mice, an established small animal model of CAVD, to determine if genetic ablation affects CAVD progression. To assess the effect of pharmacological inhibition on CAVD progression,Notch1+/-mice were treated with the 5-HT2Breceptor antagonist SB204741. Mice were analyzed using echocardiography, histology, immunofluorescence, and real-time quantitative polymerase chain reaction.Htr2bmutant mice showed lower aortic valve peak velocity and mean pressure gradient–classical hemodynamic indicators of aortic valve stenosis–without concurrent left ventricle change. 5-HT2Breceptor antagonism, however, did not affect hemodynamic progression. Leaflet thickness, collagen density, and CAVD-associated transcriptional markers were not significantly different in any group. This study reveals that genetic ablation ofHtr2battenuates hemodynamic development of CAVD in theNotch1+/-mice, but pharmacological antagonism may require high doses or long-term treatment to slow progression.

International audience; Severe peripheral infections induce an adaptive sickness behavior and an innate immune reaction in various organs including the brain. On the long term, persistent alteration of microglia, the brain innate immune cells, is associated with an increased risk of psychiatric disorders. It is thus critical to identify genes and mechanisms controlling the intensity and duration of the neuroinflammation induced by peripheral immune challenges. We tested the hypothesis that the 5-HT2B receptor, the main serotonin receptor expressed by microglia, might represent a valuable candidate. First, we observed that Htr2b-/- mice, knock-out for the 5-HT2B receptor gene, developed, when exposed to a peripheral lipopolysaccharide (LPS) challenge, a stronger weight loss compared to wild-type mice; in addition, comparison of inflammatory markers in brain, 4 and 24 hr after LPS injection, showed that Htr2b deficiency leads to a prolonged neuroinflammation. Second, to assess the specific contribution of the microglial 5-HT2B receptor, we investigated the response to LPS of conditional knock-out mice invalidated for Htr2b in microglia only. We found that deletion of Htr2b in microglia since birth is sufficient to cause enhanced weight loss and increased neuroinflammatory response upon LPS injection at adult stage. In contrast, mice deleted for microglial Htr2b in adulthood responded normally to LPS, revealing a neonatal developmental effect. These results highlight the role of microglia in the response to a peripheral immune challenge and suggest the existence of a developmental, neonatal period, during which instruction of microglia through 5-HT2B receptors is necessary to prevent microglia overreactivity in adulthood.

Colorectal cancer (CRC) is a heterogeneous disease with different genetic and molecular backgrounds, leading to a diverse patient prognosis and treatment response. Four consensus molecular subtypes (CMS 1–4) have recently been proposed based on transcriptome profiling. A clinically practical immunohistochemistry (IHC) based CMS classifier consisting of the four markers FRMD6, ZEB1, HTR2B, and CDX2 was then demonstrated. However, the IHC-CMS classifier did not distinguish between CMS2 and CMS3 tumours. In this study, we have applied the proposed transcriptome based and IHC-based CMS classifiers in a CRC cohort of 65 patients and found a concordance of 77.5 %. Further, we modified the IHC-CMS classifier by analysing the differentially expressed genes between CMS2 and CMS3 tumours using RNA-sequencing data from the TCGA dataset. The result showed that WNT signalling was among the most upregulated pathways in CMS2 tumours, and the expression level of CTNNB1 (encoding β-catenin), a WNT pathway hallmark, was significantly upregulated (P = 1.15 × 10−6). We therefore introduced nuclear β-catenin staining to the IHC-CMS classifier. Using the modified classifier in our cohort, we found a 71.4 % concordance between the IHC and RNA-sequencing based CMS classifiers. Moreover, β-catenin staining could classify 16 out of the 19 CMS2/3 tumours into CMS2 or CMS3, thereby showing an 84.2 % concordance with the RNA-sequencing-based classifier. In conclusion, we evaluated CMS classifiers based on transcriptome and IHC analysis. We present a modified IHC panel that categorizes CRC tumours into the four CMS groups. To our knowledge, this is the first study using IHC to identify all four CMS groups.

Chronic loss of sleep damages health and disturbs the quality of life. Long-lasting sleep deprivation (SD) as well as sleep abnormalities are substantial risk factors for major depressive disorder, although the underlying mechanisms are not clear. Here, we showed that chronic SD in mice promotes a gradual elevation of extracellular ATP, which activates astroglial P2X(7) receptors (P2X(7)Rs). Activated P2X(7)Rs, in turn, selectively down-regulated the expression of 5-HT(2B) receptors (5-HT(2B)Rs) in astrocytes. Stimulation of P2X(7)Rs induced by SD selectively suppressed the phosphorylation of AKT and FoxO3a in astrocytes, but not in neurons. The over-expression of FoxO3a in astrocytes inhibited the expression of 5-HT(2B)Rs. Down-regulation of 5-HT(2Bs)Rs instigated by SD suppressed the activation of STAT3 and relieved the inhibition of Ca(2+)-dependent phospholipase A2. This latter cascade promoted the release of arachidonic acid and prostaglandin E2. The depression-like behaviors induced by SD were alleviated in P2X(7)R-KO mice. Our study reveals the mechanism underlying chronic SD-induced depression-like behaviors and suggests 5-HT(2B)Rs as a key target for exploring therapeutic strategies aimed at the depression evoked by sleep disorders.

Applying serotonergic (5-HT) agonists or grafting of fetal serotonergic cells into the spinal cord improves locomotion after spinal cord injury. Little is known about the role of 5-HT receptors in the control of voluntary locomotion, so we administered inverse agonists of 5-HT2 (Cyproheptadine; Cypr), 5-HT2A neutral antagonist (Volinanserin; Volin), 5-HT2C neutral antagonist (SB 242084), and 5-HT2B/2C inverse agonist (SB 206553) receptors intrathecally in intact rats and monitored their effects on unrestrained locomotion. An intrathecal cannula was introduced at the low thoracic level and pushed caudally until the tip reached the L2/L3 or L5/L6 spinal segments. Locomotor performance was evaluated using EMG activity of hindlimb muscles during locomotion on a 2 m long runway. Motoneuron excitability was estimated using EMG recordings during dorsi- and plantar flexion at the ankle. Locomotion was dramatically impaired after the blockage of 5-HT2A receptors. The effect of Cypr was more pronounced than that of Volin since in the L5/L6 rats Cypr (but not Volin) induced significant alteration of the strength of interlimb coordination followed by total paralysis. These agents significantly decreased locomotor EMG amplitude and abolished or substantially decreased stretch reflexes. Blocking 5-HT2B/2C receptors had no effect either on locomotion or reflexes. We suggest that in intact rats serotonin controls timing and amplitude of muscle activity by acting on 5-HT2A receptors on both CPG interneurons and motoneurons, while 5-HT2B/2C receptors are not involved in control of the locomotor pattern in lumbar spinal cord.

Calcification, fibrosis, and chronic inflammation are the predominant features of calcific aortic valve disease, a life-threatening condition. Drugs that induce serotonin (5-hydroxytryptamine [5-HT]) are known to damage valves, and activated platelets, which carry peripheral serotonin, are known to promote calcific aortic valve stenosis. However, the role of 5-HT in valve leaflet pathology is not known. We tested whether serotonin mediates inflammation-induced matrix mineralization in valve cells. Real-time reverse transcription-polymerase chain reaction analysis showed that murine aortic valve interstitial cells (VICs) expressed both serotonin receptor types 2A and 2B (Htr2a and Htr2b). Although Htr2a expression was greater at baseline, Htr2b expression was induced several-fold more than Htr2a in response to the pro-calcific tumor necrosis factor-α (TNF-α) treatment. 5-HT also augmented TNF-α-induced osteoblastic differentiation and matrix mineralization of VIC, but 5-HT alone had no effects. Inhibition of serotonin receptor type 2B, using specific inhibitors or lentiviral knockdown in VIC, attenuated 5-HT effects on TNF-α-induced osteoblastic differentiation and mineralization. 5-HT treatment also augmented TNF-α-induced matrix metalloproteinase-3 expression, which was also attenuated by Htr2b knockdown. Htr2b expression in aortic roots and serum levels of peripheral 5-HT were also greater in the hyperlipidemic Apoe-/- mice than in control normolipemic mice. These findings suggest a new role for serotonin signaling in inflammation-induced calcific valvulopathy.

Ethenzamide (ETZ), an antipyretic analgesic categorized as a non-steroidal anti-inflammatory drug (NSAID), is widely used as an OTC drug in combination with other NSAIDs. However, its site of action and mechanism underlying its analgesic action have not yet been fully elucidated. In this study, we performed in vitro pharmacological assays to identify the mechanism underlying the analgesic action of ETZ, and also conducted the rat formalin test to investigate its analgesic effect and site of action. Of the 85 receptors, ion channels, transporters and enzymes tested, we found that ETZ binds to the 5-hydroxytryptamine (5HT)

Despite respiratory motor neuron death, ventilation is preserved in SOD1(G93A) rats. Compensatory respiratory plasticity may counterbalance the loss of these neurons. Phrenic long-term facilitation (pLTF; a form of respiratory plasticity) in naïve rats is 5-HT(2) and NADPH oxidase-dependent. Furthermore, 5-HT(2A), not 5-HT(2B), receptor-induced phrenic motor facilitation is NADPH oxidase-independent in naïve rats. pLTF is NADPH oxidase-dependent in pre-symptomatic, but not end-stage, SOD1(G93A) rats. Here, we hypothesized that in the putative phrenic motor nucleus (PMN) of SOD1(G93A) rats vs. wild-type littermates: 1) pre-symptomatic rats would have greater 5-HT(2B) receptor expression that decreases at end-stage; and 2) 5-HT(2A) receptor expression would increase from pre-symptomatic to end-stage. Putative PMN 5-HT(2A) receptor expression was reduced when comparing across (but not within) pre-symptomatic vs. end-stage groups (p

BACKGROUND AND AIMS: Serotonin (5HT) is a neuroendocrine hormone synthetized in the central nervous system (CNS) as well as enterochromaffin cells of the gastrointestinal tract. Tryptophan hydroxylase (TPH1) and monoamine oxidase (MAO-A) are the key enzymes for the synthesis and catabolism of 5HT, respectively. Previous studies demonstrated that 5-hydroxytryptamine receptor (5HTR)1A/1B receptor agonists inhibit biliary hyperplasia in bile-duct ligated (BDL) rats, whereas 5HTR2B receptor antagonists attenuate liver fibrosis (LF) in mice. Our aim was to evaluate the role of 5HTR2A/2B/2C agonists/antagonists in cholestatic models. APPROACH AND RESULTS: While in vivo studies were performed in BDL rats and the multidrug resistance gene 2 knockout (Mdr2(−/−)) mouse model of PSC, in vitro studies were performed in cell lines of cholangiocytes and hepatic stellate cells (HSCs). 5HTR2A/2B/2C and MAO-A/TPH1 are expressed in cholangiocytes and HSCs from BDL rats and Mdr2(−/−) mice. Ductular reaction, LF, as well as the mRNA expression of proinflammatory genes increased in normal, BDL rats, and Mdr2(−/−) mice following treatment 5HTR2A/2B/2C agonists, but decreased when BDL rats and Mdr2(−/−) mice were treated with 5HTR2A/2B/2C antagonists compared to BDL rats and Mdr2(−/−) mice, respectively. 5HT levels increase in Mdr2(−/−) mice and in PSC human patients compared to their controls and decrease in serum of Mdr2(−/−) mice treated with 5HTR2A/2B/2C antagonists compared to untreated Mdr2(−/−) mice. In vitro, cell lines of murine cholangiocytes and human HSCs express 5HTR2A/2B/2C and MAO-A/TPH1; treatment of these cell lines with 5HTR2A/2B/2C antagonists or TPH1 inhibitor decreased 5HT levels as well as expression of fibrosis and inflammation genes compared to controls. CONCLUSIONS: Modulation of the TPH1/MAO-A/5HT/5HTR2A/2B/2C axis may represent a therapeutic approach for management of cholangiopathies, including PSC.

G Protein-Coupled Receptors (GPCRs) mediate intracellular signaling in response to extracellular ligand binding and are the target of one-third of approved drugs. Ligand binding modulates the GPCR molecular free energy landscape by preferentially stabilizing active or inactive conformations that dictate intracellular protein recruitment and downstream signaling. We perform enhanced sampling molecular dynamics simulations to recover the free energy surfaces of a thermostable mutant of the GPCR serotonin receptor 5-HT2B in the unliganded form and bound to a lysergic acid diethylamide (LSD) agonist and lisuride antagonist. LSD binding imparts a ∼110 kJ/mol driving force for conformational rearrangement into an active state. The lisuride-bound form is structurally similar to the apo form and only ∼24 kJ/mol more stable. This work quantifies ligand-induced conformational specificity and functional selectivity of 5-HT2B and presents a platform for high-throughput virtual screening of ligands and rational engineering of the ligand-bound molecular free energy landscape.

Activation of hepatic stellate cells (HSC) plays a crucial role in the liver disease progression from liver fibrosis/cirrhosis to cancer. Here, we found a rapid change of microenvironment after kras V12 -induction in zebrafish liver with progressively increased stromal cell number and enlarged liver size. Neutrophils and macrophages exhibited a faster response than HSCs. By manipulating the numbers of neutrophils and macrophages through morpholino knockdown, we found that macrophages contributed to both HSC survival and activation while neutrophils appear to be only required for HSC activation. Serotonin, which is essential for HSC survival and activation, was found up-regulated in hepatocytes and macrophages, but not in neutrophils after kras V12 induction. Serotonin receptor was highly expressed in HSCs; increase of the receptor activity by an agonist stimulated HSCs and oncogenic growth of the liver while an opposite effect was observed with an antagonist. Activated HSCs promoted the pro-tumorigenesis functions of neutrophils and macrophages through secretion of Tgfb1. Overall, these observations elucidated a cellular interaction in microenvironment where that upregulated serotonin in hepatocytes and macrophages activated HSCs. Since the microenvironment crosstalk plays a vital role in manipulation of liver carcinogenesis, the underlying mechanism may provide potential therapeutic targets for liver diseases.

Caffeoylserotonin (CaS), one derivative of serotonin (5-HT), is a secondary metabolite produced in pepper fruits with strong antioxidant activities. In this study, we investigated the effect of CaS on proliferation and migration of human keratinocyte HaCaT cells compared to that of 5-HT. CaS enhanced keratinocyte proliferation even under serum deficient condition. This effect of CaS was mediated by serotonin 2B receptor (5-HT2BR) related to the cell proliferation effect of 5-HT. We also confirmed that both CaS and 5-HT induced G1 progression via 5-HT2BR/ERK pathway in HaCaT cells. However, Akt pathway was additionally involved in upregulated expression levels of cyclin D1 and cyclin E induced by CaS by activating 5-HT2BR. Moreover, CaS and 5-HT induced cell migration in HaCaT cells via 5-HT2BR. However, 5-HT regulated cell migration only through ERK/AP-1/MMP9 pathway while additional Akt/NF-κB/MMP9 pathway was involved in the cell migration effect of CaS. These results suggest that CaS can enhance keratinocyte proliferation and migration. It might have potential as a reagent beneficial for wound closing and cell regeneration. [BMB Reports 2018; 51(4): 188-193].

The community-wide blind prediction of G-protein coupled receptor (GPCR) structures and ligand docking has been conducted three times and the quality of the models was primarily assessed by the accuracy of ligand binding modes. The seven transmembrane (TM) helices of the receptors were taken as a whole; thus the model quality within the 7TM domains has not been evaluated. Here we evaluate the 7TM domain structures in the models submitted for the last round of prediction - GPCR Dock 2013. Applying the 7 x 7 RMSD matrix analysis described in our prior work, we show that the models vary widely in prediction accuracy of the 7TM structures, exhibiting diverse structural differences from the targets. For the prediction of the 5-hydroxytryptamine receptors, the top 7TM models are rather close to the targets, which however are not ranked top by ligand-docking. On the other hand, notable deviations of the TMs are found in in the previously identified top docking models that closely resemble other receptors. We further reveal reasons of success and failure in ligand docking for the models. This current assessment not only complements the previous assessment, but also provides important insights into the current status of GPCR modelling and ligand docking.

Serotonin is a neurotransmitter involved in many psychiatric diseases. In humans, a lack of 5-HT2B receptors is associated with serotonin-dependent phenotypes, including impulsivity and suicidality. A lack of 5-HT2B receptors in mice eliminates the effects of molecules that directly target serotonergic neurons including amphetamine derivative serotonin releasers, and selective serotonin reuptake inhibitor antidepressants. In this work, we tested the hypothesis that 5-HT2B receptors directly and positively regulate raphe serotonin neuron activity. By ex vivo electrophysiological recordings, we report that stimulation by the 5-HT2B receptor agonist, BW723C86, increased the firing frequency of serotonin Pet1-positive neurons. Viral overexpression of 5-HT2B receptors in these neurons increased their excitability. Furthermore, in vivo 5-HT2B-receptor stimulation by BW723C86 counteracted 5-HT1A autoreceptor-dependent reduction in firing rate and hypothermic response in wild-type mice. By a conditional genetic ablation that eliminates 5-HT2B receptor expression specifically and exclusively from Pet1-positive serotonin neurons (Htr2b 5-HTKO mice), we demonstrated that behavioral and sensitizing effects of MDMA (3,4-methylenedioxy-methamphetamine), as well as acute behavioral and chronic neurogenic effects of the antidepressant fluoxetine, require 5-HT2B receptor expression in serotonergic neurons. In Htr2b 5-HTKO mice, dorsal raphe serotonin neurons displayed a lower firing frequency compared to control Htr2b lox/lox mice as assessed by in vivo extracellular recordings and a stronger hypothermic effect of 5-HT1A-autoreceptor stimulation was observed. The increase in head-twitch response to DOI (2,5-dimethoxy-4-iodoamphetamine) further confirmed the lower serotonergic tone resulting from the absence of 5-HT2B receptors in serotonin neurons. Together, these observations indicate that the 5-HT2B receptor acts as a direct positive modulator of serotonin Pet1-positive neurons in an opposite way as the known 5-HT1A-negative autoreceptor. Fil: Belmer, Arnauld. Universite Paris Sorbonne - Paris Iv; Francia. Inserm; Francia. Queensland University of Technology; Australia Fil: Quentin, Emily. Universite Paris Sorbonne - Paris Iv; Francia. Inserm; Francia Fil: Diaz, Silvina Laura. Inserm; Francia. Universidad de Morón; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Biología Celular y Neurociencia "Prof. Eduardo de Robertis". Universidad de Buenos Aires. Facultad de Medicina. Instituto de Biología Celular y Neurociencia; Argentina Fil: Guiard, Bruno P.. Université Paul Sabatier; Francia Fil: Fernandez, Sebastian P.. Inserm; Francia. Universite Paris Sorbonne - Paris Iv; Francia Fil: Doly, Stéphane. Inserm; Francia. Universite Paris Sorbonne - Paris Iv; Francia Fil: Banas, Sophie M.. Inserm; Francia. Universite Paris Sorbonne - Paris Iv; Francia Fil: Pitychoutis, Pothitos M.. Inserm; Francia. Universite Paris Sorbonne - Paris Iv; Francia Fil: Moutkine, Imane. Inserm; Francia. Universite Paris Sorbonne - Paris Iv; Francia Fil: Muzerelle, Aude. Universite Paris Sorbonne - Paris Iv; Francia. Inserm; Francia Fil: Tchenio, Anna. Universite de Lausanne; Suiza. Inserm; Francia Fil: Roumier, Anne. Inserm; Francia. Universite Paris Sorbonne - Paris Iv; Francia Fil: Mameli, Manuel. Universite de Lausanne; Suiza. Universite Paris Sorbonne - Paris Iv; Francia. Inserm; Francia Fil: Maroteaux, Luc. Inserm; Francia. Universite Paris Sorbonne - Paris Iv; Francia

Serotonin (5-hydroxytryptamine) has repeatedly been associated with the development of fibrotic disorders such as pulmonary fibrosis. By blocking the binding of 5-HT to 5-HT2B receptors with receptor antagonists, several pro-fibrotic mechanisms can be inhibited. Bleomycin-induced pulmonary fibrosis is a model used to evaluate pathological mechanisms and pharmacological interventions. Previously we have shown attenuated fibrosis in systemic bleomycin-treated mice following treatment with two 5-HT2B receptor antagonists (EXT5 and EXT9). Our aim is to further identify cellular effects and signaling pathways associated with the anti-fibrotic effects of EXT5/9. Gene expressions in lung tissues from systemic bleomycin-treated mice were examined, revealing significant increased expression of Cdkn1α (a gene coding for p21), particularly in distal regions of the lung. In vitro studies in human lung fibroblasts revealed increased levels of p21 (p = 0.0032) and pAkt (p = 0.12) following treatment with 5-HT (10 µM). The induction of p21 and pAkt appears to be regulated by 5-HT2B receptors, with diminished protein levels following EXT9-treatment (p21 p = 0.0024, pAkt p = 0.15). Additionally, 5-HT induced fibroblast proliferation, an event significantly reduced by EXT5 (10 µM) and EXT9 (10 µM). In conclusion, our results suggest that 5-HT2B receptor antagonism attenuates pulmonary fibrosis in part by anti-proliferative effects, associated with inhibited pAkt/p21 signaling pathway.

Background: Psychocardiological researches have suggested a central role of 5-hydroxytryptamine (5-HT) on psychocardiological mechanism. This study aimed to further explore the central role of 5-HT and pretreatment effects of XinLingWan on rats with myocardial infarction (MI) and/or depression. Methods: Ninety Sprague-Dawley rats were randomly divided into three groups: MI group, depression group, and MI + depression group (n = 30 in each group). Each group was then divided into three subgroups (n = 10 in each subgroup): a negative control subgroup (NCS), a Western medicine subgroup (WMS), and a traditional Chinese medicine subgroup (TCMS), which were received pretreatment once a day for 4 weeks by saline, 20 mg/kg sertraline mixed with 2 ml saline, and 40 mg/kg XingLingWan mixed with 2 ml saline, respectively. Different rat models were established after different pretreatments. Rats were then sacrificed for detection of serum 5-HT, platelet 5-HT, 5-HT2A receptors (5-HT2AR), and serotonin transporter (SERT). Data were analyzed by one-way analysis of variance (ANOVA) and least-significant difference (LSD) testing. Results: MI group: compared with NCS, there was a significant increase in WMS and TCMS of serum 5-HT (176.15 ± 11.32 pg/ml vs. 334.50 ± 29.09 pg/ml and 474.04 ± 10.86 pg/ml, respectively, both P = 0.000), platelet 5-HT (129.74 ± 27.17 pg/ml vs. 322.24 ± 11.60 pg/ml and 340.4 5 ± 17.99 pg/ml, respectively, both P = 0.000); depression group: compared with NCS, there was a significant increase in WMS and TCMS of serum 5-HT (194.69 ± 5.09 pg/ml vs. 326.21 ± 39.98 pg/ml and 456.33 ± 23.12 pg/ml, respectively, both P = 0.000), platelet 5-HT (175.15 ± 4.07 pg/ml vs. 204.56 ± 18.59 pg/ml and 252.03 ± 22.26 pg/ml, respectively, P = 0.004 and P = 0.000, respectively); MI + depression group: compared with NCS, there was a significant increase in both WMS and TCMS of serum 5-HT (182.50 ± 10.23 pg/ml vs. 372.55 ± 52.23 pg/ml and 441.76 ± 23.38 pg/ml, respectively, both P = 0.000) and platelet 5-HT (180.83 ± 11.08 pg/ml vs. 221.12 ± 22.23 pg/ml and 265.37 ± 29.49 pg/ml, respectively, P = 0.011 and P = 0.000, respectively). Conclusions: By elevating the amount of 5-HT and modulating 5-HT2AR and SERT levels in serum and platelets, XinLingWan and sertraline were found to exert pretreatment effect on rat models of MI and/or depression. Key words: 5-Hydroxytryptamine; Depression; Myocardial Infarction; Selective Serotonin Reuptake Inhibitors; Traditional Chinese Medicine

Purpose: 5-HT 2A R exists in high and low affinity states. Agonist PET tracers measure binding to the active high affinity site and thus provide a functionally relevant measure of the receptor. Limited in vivo data have been reported so far for a comparison of agonist versus antagonist tracers for 5-HT 2A R used as a proof of principle for measurement of high and low affinity states of this receptor. We compared the in vivo binding of [ 11 C]CIMBI-5, a 5-HT 2A R agonist, and of the antagonist [ 11 C]M100907, in monkeys and baboons. Methods: [ 11 C]CIMBI-5 and [ 11 C]M100907 baseline PET scans were performed in anesthetized male baboons (n=2) and male vervet monkeys (n=2) with an ECAT EXACT HR+ and GE 64-slice PET/CT Discovery VCT scanners. Blocking studies were performed in vervet monkeys by pretreatment with MDL100907 (0.5 mg/kg, i.v.) 60 minutes prior to the scan. Regional distribution volumes and binding potentials were calculated for each ROI using the likelihood estimation in graphical analysis and Logan plot, with either plasma input function or reference region as input, and simplified reference tissue model approaches. Results: PET imaging of [ 11 C]CIMBI-5 in baboons and monkeys showed the highest binding in 5-HT 2A R-rich cortical regions, while the lowest binding was observed in cerebellum, consistent with the expected distribution of 5-HT 2A R. Very low free fractions and rapid metabolism were observed for [ 11 C]CIMBI-5 in baboon plasma. Binding potential values for [ 11 C]CIMBI-5 were 25-33% lower than those for [ 11 C]MDL100907 in the considered brain regions. Conclusion: The lower binding potential of [ 11 C]CIMBI-5 in comparison to [ 11 C]MDL100907 is likely due to the preferential binding of the former to the high affinity site in vivo in contrast to the antagonist, [ 11 C]MDL100907, which binds to both high and low affinity sites.

Despite the ubiquity of cholesterol within the cell membrane, the mechanism by which it influences embedded proteins remains elusive. Numerous G-protein coupled receptors exhibit dramatic responses to membrane cholesterol with regard to the ligand-binding affinity and functional properties, including the 5-HT receptor family. Here, we use over 25 μs of unbiased atomistic molecular dynamics simulations to identify cholesterol interaction sites in the 5-HT 1B and 5-HT 2B receptors and evaluate their impact on receptor structure. Susceptibility to membrane cholesterol is shown to be subtype dependent and determined by the quality of interactions between the extracellular loops. Charged residues are essential for maintaining the arrangement of the extracellular surface in 5-HT 2B ; in the absence of such interactions, the extracellular surface of the 5-HT 1B is malleable, populating a number of distinct conformations. Elevated cholesterol density near transmembrane helix 4 is considered to be conducive to the conformation of extracellular loop 2. Occupation of this site is also shown to be stereospecific, illustrated by differential behavior of nat-cholesterol isomers, ent- and epi-cholesterol. In simulations containing the endogenous agonist, serotonin, cholesterol binding at transmembrane helix 4 biases bound serotonin molecules toward an unexpected binding mode in the extended binding pocket. The results highlight the capability of membrane cholesterol to influence the mobility of the extracellular surface in the 5-HT 1 receptor family and manipulate the architecture of the extracellular ligand-binding pocket.

Serotonin (5-hydroxytryptamine; 5-HT) can induce hepatocyte DNA synthesis and proliferation by autocrine secretion of transforming growth factor (TGF)-α through 5-HT

Hydrogen peroxide, formed in the endothelium, acts as a factor contributing to the relaxation of blood vessels. The reason for this vasodilatory effect could be modulation by H2O2 of calcium metabolism, since mobilization of calcium ions in endothelial cells is a trigger of endothelium-dependent relaxation. The aim of this work was to investigate the influence of H2O2 on the effects of Ca2+-mobilizing agonists in human umbilical vein endothelial cells (HUVEC). We have found that H2O2 in concentration range 10-100 μM increases the rise of [Ca2+]i induced by 5-hydroxytryptamine (5-HT) and carbachol and does not affect the calcium signals of ATP, agonist of type 1 protease-activated receptor SFLLRN, histamine and bradykinin. Using specific agonists of 5-HT1B and 5-HT2B receptors CGS12066B and BW723C86, we have demonstrated that H2O2 potentiates the effects mediated by these types of 5-HT receptors. Potentiation of the effect of BW723C86 can be produced by the induction of endogenous oxidative stress in HUVEC. We have shown that the activation of 5-HT2B receptor by BW723C86 causes production of reactive oxygen species (ROS). Inhibitor of NADPH oxidases VAS2870 suppressed formation of ROS and partially inhibited [Ca2+]i rise induced by BW723C86. Thus, it can be assumed that vasorelaxation induced by endogenous H2O2 in endothelial cells partially occurs due to the potentiation of the agonist-induced calcium signaling.

Endocannabinoids (eCBs) and serotonin (5-HT) play a neuromodulatory role in the central nervous system. Both eCBs and 5-HT regulate neuronal excitability and their pharmacological potentiation has been shown to control seizures in pre-clinical and human studies. Compelling evidence indicates that eCB and 5-HT systems interact to modulate several physiological and pathological brain functions, such as food intake, pain, drug addiction, depression, and anxiety. Nevertheless, there is no evidence of an eCB/5-HT interaction in experimental and human epilepsies, including status epilepticus (SE). Here, we performed video-EEG recording in behaving rats treated with the pro-convulsant agent pilocarpine (PILO), in order to study the effect of the activation of CB1/5-HT2 receptors and their interaction on SE. Synthetic cannabinoid agonist WIN55,212–2 (WIN) decreased behavioral seizure severity of PILO-induced SE at 2 mg/kg (but not at 1 and 5 mg/kg, i.p.), while 5-HT2B/2C receptor agonist RO60–0175 (RO; 1, 3, 10 mg/kg, i.p.) was devoid of any effect. RO 3 mg/kg was instead capable of potentiating the effect of WIN 2 mg/kg on the Racine scale score. Surprisingly, neither WIN 2 mg/kg nor RO 3 mg/kg had any effect on the incidence and the intensity of EEG seizures when administered alone. However, WIN+RO co-administration reduced the incidence and the severity of EEG SE and increased the latency to SE onset after PILO injection. WIN+RO effects were blocked by the selective CB1R antagonist AM251 and the 5-HT2BR antagonist RS127445, but not by the 5-HT2CR antagonist SB242084 or the 5-HT2AR antagonist MDL11,939. These data revealed a synergistic interaction between CB1R/5-HT2BR in the expression of PILO-induced SE.

Rationale: Pulmonary arterial hypertension is a deadly disease of the pulmonary vasculature for which no disease-modifying therapies exist. Small-vessel stiffening and remodeling are fundamental pathological features of pulmonary arterial hypertension that occur early and drive further endovascular cell dysfunction. Bone marrow (BM)–derived proangiogenic cells (PACs), a specialized heterogeneous subpopulation of myeloid lineage cells, are thought to play an important role in pathogenesis. Objective: To determine whether BM-derived PACs directly contributed to experimental pulmonary hypertension (PH) by promoting small-vessel stiffening through 5-HT 2B (serotonin 2B receptor)–mediated signaling. Methods and Results: We performed BM transplants using transgenic donor animals expressing diphtheria toxin secondary to activation of an endothelial-specific tamoxifen-inducible Cre and induced experimental PH using hypoxia with SU5416 to enhance endovascular injury and ablated BM-derived PACs, after which we measured right ventricular systolic pressures in a closed-chest procedure. BM-derived PAC lineage tracing was accomplished by transplanting BM from transgenic donor animals with fluorescently labeled hematopoietic cells and treating mice with a 5-HT 2B antagonist. BM-derived PAC ablation both prevented and reversed experimental PH with SU5416-enhanced endovascular injury, reducing the number of muscularized pulmonary arterioles and normalizing arteriole stiffness as measured by atomic force microscopy. Similarly, treatment with a pharmacological antagonist of 5-HT 2B also prevented experimental PH, reducing the number and stiffness of muscularized pulmonary arterioles. PACs accelerated pulmonary microvascular endothelial cell injury response in vitro, and the presence of BM-derived PACs significantly correlated with stiffer pulmonary arterioles in pulmonary arterial hypertension patients and mice with experimental PH. RNA sequencing of BM-derived PACs showed that 5-HT 2B antagonism significantly altered biologic pathways regulating cell proliferation, locomotion and migration, and cytokine production and response to cytokine stimulus. Conclusions: Together, our findings illustrate that BM-derived PACs directly contribute to experimental PH with SU5416-enhanced endovascular injury by mediating small-vessel stiffening and remodeling in a 5-HT 2B signaling–dependent manner.

International audience; Cannabis use is increasing in the United States, as are its adverse effects. We investigated the genetics of an adverse consequence of cannabis use: cannabis-related aggression (CRA) using a genome-wide association study (GWAS) design. Our GWAS sample included 3269 African Americans (AAs) and 2546 European Americans (EAs). An additional 89 AA subjects from the Grady Trauma Project (GTP) were also examined using a proxy-phenotype replication approach. We identified genome-wide significant risk loci contributing to CRA in AAs at the serotonin receptor 2B receptor gene (HTR2B), and the lead SNP, HTR2B*rs17440378, showed nominal association to aggression in the GTP cohort of cannabis-exposed subjects. A priori evidence linked HTR2B to impulsivity/aggression but not to cannabis response. Human functional data regarding the HTR2B variant further supported our finding. Treating an Htr2b-/- knockout mouse with THC resulted in increased aggressive behavior, whereas wild-type mice following THC administration showed decreased aggression in the resident-intruder paradigm, demonstrating that HTR2B variation moderates the effects of cannabis on aggression. These concordant findings in mice and humans implicate HTR2B as a major locus associated with cannabis-induced aggression.

Anecdotal reports suggest that abused synthetic cannabinoids produce cannabis-like “highs,” but some of their effects may also differ from traditional cannabinoids such as Δ9-tetrahydrocannabinol (THC). This study examined the binding affinities of first-generation indole-derived synthetic cannabinoids at cannabinoid and noncannabinoid receptors and their effects in a functional observational battery (FOB) and drug discrimination in mice. All seven compounds, except JWH-391, had favorable affinity (≤159 nM) for both cannabinoid receptors. In contrast, binding at noncannabinoid receptors was absent or weak. In the FOB, THC and the six active compounds disrupted behaviors in CNS activation and muscle tone/equilibrium domains. Unlike THC, however, synthetic cannabinoids impaired behavior across a wider dose and domain range, producing autonomic effects and signs of CNS excitability and sensorimotor reactivity. In addition, mice acquired JWH-018 discrimination, and THC and JWH-073 produced full substitution whereas the 5-HT2B antagonist mianserin did not substitute in mice trained to discriminate JWH-018 or THC. Urinary metabolite analysis showed that the compounds were extensively metabolized, with metabolites that could contribute to their in vivo effects. Together, these results show that, while first-generation synthetic cannabinoids shared some effects that were similar to those of THC, they also possessed effects that differed from traditional cannabinoids. The high nanomolar (or absent) affinities of these compounds at receptors for most major neurotransmitters suggests that these divergent effects may be related to the greater potencies and/or efficacies at CB1 receptors; however, action(s) at noncannabinoid receptors yet to be assessed or via different signaling pathways cannot be ruled out.

Herein, we examined insulin resistance (IR), insulin sensitivity (IS), beta cell activity, and glucose metabolism in subjects with antisocial personality disorder (ASPD), and whether the serotonin 2B (5-HT2B) receptor and testosterone have a role in energy metabolism. A cohort of subjects belonging to a founder population that included 98 ASPD males, aged 25-30, was divided into groups based on the presence of a heterozygous 5-HT2B receptor loss-of-function gene mutation (HTR2B Q20*; n = 9) or not (n = 89). Serum glucose and insulin levels were measured in a 5 h oral glucose tolerance test (75 g) and indices describing IR, IS, and beta cell activity were calculated. Body mass index (BMI) was also determined. Concentrations of the serotonin metabolite 5-hydroxyindoleacetic acid were measured in cerebrospinal fluid, and testosterone levels from serum. An IR-like state comprising high IR, low IS, and high beta cell activity indices was observed among ASPD subjects without the HTR2B Q20* allele. By contrast, being an ASPD HTR2B Q20* carrier appeared to be preventive of these pathophysiologies. The HTR2B Q20* allele and testosterone predicted lower BMI independently, but an interaction between HTR2B Q20* and testosterone lead to increased insulin sensitivity among HTR2B Q20* carriers with low testosterone levels. The HTR2B Q20* allele also predicted reduced beta cell activity and enhanced glucose metabolism. Reduced 5-HT2B receptor function at low or normal testosterone levels may be protective of obesity. Results were observed among Finnish males having an antisocial personality disorder, which limits the generality. (C) 2016 Elsevier Ltd. All rights reserved.

The present study investigated interactions between the novel psychoactive tryptamines DiPT, 4-OH-DiPT, 4-OH-MET, 5-MeO-AMT, and 5-MeO-MiPT at monoamine receptors and transporters compared with the classic hallucinogens lysergic acid diethylamide (LSD), psilocin, N,N-dimethyltryptamine (DMT), and mescaline. We investigated binding affinities at human monoamine receptors and determined functional serotonin (5-hydroxytryptamine [5-HT]) 5-HT2A and 5-HT2B receptor activation. Binding at and the inhibition of human monoamine uptake transporters and transporter-mediated monoamine release were also determined. All of the novel tryptamines interacted with 5-HT2A receptors and were partial or full 5-HT2A agonists. Binding affinity to the 5-HT2A receptor was lower for all of the tryptamines, including psilocin and DMT, compared with LSD and correlated with the reported psychoactive doses in humans. Several tryptamines, including psilocin, DMT, DiPT, 4-OH-DiPT, and 4-OH-MET, interacted with the serotonin transporter and partially the norepinephrine transporter, similar to 3,4-methylenedioxymethamphetamine but in contrast to LSD and mescaline. LSD but not the tryptamines interacted with adrenergic and dopaminergic receptors. In conclusion, the receptor interaction profiles of the tryptamines predict hallucinogenic effects that are similar to classic serotonergic hallucinogens but also MDMA-like psychoactive properties.

Serotonin regulates many intestinal motor and sensory functions. Altered serotonergic metabolism has been described in human gastrointestinal diseases. The objective of our study was to compare expression of several components of the serotonergic system [serotonin (5-HT), serotonin reuptake transporter protein (SERT), tryptophan hydroxylase-1 (TPH-1), 5-HT receptor2B (5-HT2B)] and the enterochromaffin cell marker chromogranin-A (CgA) in the intestinal mucosa between dogs with chronic enteropathy and healthy controls. Serotonin and CgA expression were determined by immunohistochemistry using banked and prospectively obtained, paraffin-embedded canine gastrointestinal biopsies ( n = 11), and compared to a control group of canine small intestinal sections ( n = 10). Expression of SERT, TPH-1, and 5-HT2B were determined via real-time reverse transcription (qRT)-PCR using prospectively collected endoscopic duodenal biopsies ( n = 10) and compared to an additional control group of control duodenal biopsies ( n = 8, control group 2) showing no evidence of intestinal inflammation. Dogs with chronic enteropathies showed strong staining for both 5-HT and CgA. Mean positive cells per high power field (HPF) were significantly increased for both compounds in dogs with chronic enteropathies ( p < 0.001 for 5-HT; p < 0.05 for CgA). The number of 5-HT–positive and CgA-positive cells/HPF showed significant correlation in the entire group of dogs, including both diseased and healthy individuals (Pearson r2 = 0.2433, p = 0.016). No significant differences were observed for SERT, TPH-1, or 5-HT2B expression; however, dogs with chronic enteropathy showed greater variability in expression of TPH-1 and 5-HT2B. We conclude that components of the neuroendocrine system show altered expression in the intestinal mucosa of dogs with chronic enteropathy. These changes may contribute to nociception and clinical signs in these patients.

Despite the fact that a high proportion of elderly stroke patients develop mood disorders, the mechanisms underlying late-onset neuropsychiatric and neurocognitive symptoms have so far received little attention in the field of neurobiology. In rodents, aged animals display depressive symptoms following stroke, whereas young animals recover fairly well. This finding has prompted us to investigate the expression of serotonin receptors 2A and 2B, which are directly linked to depression, in the brains of aged and young rats following stroke. Although the development of the infarct was more rapid in aged rats in the first 3 days after stroke, by day 14 the cortical infarcts were similar in size in both age groups i.e. 45% of total cortical volume in young rats and 55.7% in aged rats. We also found that the expression of serotonin receptor type B mRNA was markedly increased in the perilesional area of aged rats as compared to the younger counterparts. Furthermore, histologically, HTR2B protein expression in degenerating neurons was closely associated with activated microglia both in aged rats and human subjects. Treatment with fluoxetine attenuated the expression of Htr2B mRNA, stimulated post-stroke neurogenesis in the subventricular zone and was associated with an improved anhedonic behavior and an increased activity in the forced swim test in aged animals. We hypothesize that HTR2B expression in the infarcted territory may render degenerating neurons susceptible to attack by activated microglia and thus aggravate the consequences of stroke.

The Gq-coupled 5-hydroxytryptamine 2B (5-HT2B) receptor is known to regulate the proliferation of islet beta cells during pregnancy. However, the role of serotonin in the control of insulin release is still controversial. The aim of the present study was to explore the role of the 5-HT2B receptor in the regulation of insulin secretion in mouse and human islets, as well as in clonal INS-1(832/13) cells.Expression of HTR2B mRNA and 5-HT2B protein was examined with quantitative real-time PCR, RNA sequencing and immunohistochemistry. α-Methyl serotonin maleate salt (AMS), a serotonin receptor agonist, was employed for robust 5-HT2B receptor activation. Htr2b was silenced with small interfering RNA in INS-1(832/13) cells. Insulin secretion, Ca(2+) response and oxygen consumption rate were determined.Immunohistochemistry revealed that 5-HT2B is expressed in human and mouse islet beta cells. Activation of 5-HT2B receptors by AMS enhanced glucose-stimulated insulin secretion (GSIS) in human and mouse islets as well as in INS-1(832/13) cells. Silencing Htr2b in INS-1(832/13) cells led to a 30% reduction in GSIS. 5-HT2B receptor activation produced robust, regular and sustained Ca(2+) oscillations in mouse islets with an increase in both peak distance (period) and time in the active phase as compared with control. Enhanced insulin secretion and Ca(2+) changes induced by AMS coincided with an increase in oxygen consumption in INS-1(832/13) cells.Activation of 5-HT2B receptors stimulates GSIS in beta cells by triggering downstream changes in cellular Ca(2+) flux that enhance mitochondrial metabolism. Our findings suggest that serotonin and the 5-HT2B receptor stimulate insulin release.

The mechanism of serotonin 5-HT2 receptor subtype-stimulated DNA synthesis and proliferation was investigated in primary cultures of adult rat hepatocytes to elucidate the intracellular signal transduction pathways. DNA synthesis and proliferation were detected in hepatocyte parenchymal cells grown in serum-free, defined medium containing 5-HT (10−6 M) or the selective 5-HT2B receptor agonist BW723C86 (10−6 M). In addition, exogenous transforming growth factor (TGF)-α (1.0 ng/mL) significantly increased hepatocyte DNA synthesis and proliferation, which reached plateau after 4 h of culture. Use of blocking monoclonal antibodies demonstrated that TGF-α, but not insulin-like growth factor-I, was involved in hepatocyte proliferation mediated by 5-HT or BW723C86. TGF-α levels in the culture medium increased significantly versus baseline within 5 min in response to 5-HT (10−6 M) or BW723C86 (10−6 M), and the maximum TGF-α level (30 pg/mL) was reached 10 min after 5-HT or BW723C86 stimulation. Secretion of TGF-α into the culture medium was inhibited by addition of the selective phospholipase C (PLC) inhibitor, U-73122 (10−6 M), or somatostatin (10−7 M). These results indicate that the proliferative mechanism of action of 5-HT is mediated mainly through a 5-HT2B receptor/Gq/PLC-stimulated increase in autocrine secretion of TGF-α from primary cultured hepatocytes., Regular Articles

Background: Our previous studies have demonstrated that the levels of 5-hydroxytryptamine (5-HT) and 5-HT 2A receptor (5-HT2AR) in serum and platelet were associated with depression and myocardial infarction (MI), and pretreatment with ginseng fruit saponins (GFS) before MI and depression had an effect on the 5-HT system. In this study, the effects of GFS on the 5-HT system in the Sprague-Dawley (SD) rats with MI, depression, and MI + depression were evaluated. Methods: A total of eighty SD rats were allocated to four groups: MI, depression, MI + depression, and control groups (n = 20 in each group). Each group included two subgroups (n = 10 in each subgroup): Saline treatment subgroup and GFS treatment subgroup. The levels of 5-HT, 5-HT2AR, and serotonin transporter (SERT) were quantified in serum, platelet lysate, and brain tissue through the enzyme-linked immunosorbent assay method, respectively. Results: Compared with those in the saline treatment subgroups, the levels of 5-HT in serum and platelet lysate statistically significantly increased in the GFS treatment subgroups of MI, depression, and MI + depression groups (serum: all P = 0.000; platelet lysate: P = 0.002, 0.000, 0.000, respectively). However, the 5-HT levels in brain homogenate significantly decreased in the GFS treatment subgroups compared with those in the saline treatment subgroups in MI and depression groups (P = 0.025 and 0.044 respectively), and no significant difference was observed between saline and GFS treatment subgroups in MI + depression group (P = 0.663). Compared with that in GFS treatment subgroup of control group, the 5-HT2AR levels in the platelet lysate significantly decreased in GFS treatment subgroups of MI, depression, and MI + depression groups (all P = 0.000). Compared to those in the saline treatment subgroups, the serum SERT levels significantly decreased in the GFS treatment subgroups in MI, depression, and MI + depression groups (P = 0.009, 0.038, and P = 0.001, respectively), while the SERT levels of platelet lysate significantly decreased in GFS treatment subgroup of MI group (P = 0.000), significantly increased in GFS treatment subgroup of depression group (P = 0.019), and slightly changed in GFS treatment subgroup of MI + depression group (P = 0.219). No significant changes for SERT levels in brain homogenate could be found between the saline and GFS treatment subgroups in MI, depression, and MI + depression groups (P = 0.421, 0.076 and P = 0.642). Conclusions: This study indicated that GFS might inhibit the reuptake of 5-HT from serum to platelet according to decreased 5-HT2AR in platelet and SERT in serum and platelet. The change of 5-HT in serum after GFS treatment was inconsistent with that in the brain. It seemed that GFS could not pass through the blood-brain barrier to affect the central serotonergic system. Key words: 5-hydroxytryptamine 2A Receptor; Depression; Ginseng Fruit Saponins; 5-hydroxytryptamine; Myocardial Infarction; Serotonin Transporter

Serotonin [5-hydroxytryptamine (5-HT)], an inflammatory mediator, contributes to inflammatory pain. The presence of multiple 5-HT subtype receptors on peripheral and central nociceptors complicates the role of 5-HT in pain. Previously, we found that 5-HT2B/2C antagonist could block 5-HT-induced mechanical hyperalgesia. However, the types of neurons or circuits underlying this effect remained unsolved. Here, we demonstrate that the Gq/11-phospholipase Cβ-protein kinase Ce (PKCe) pathway mediated by 5-HT2B is involved in 5-HT-induced mechanical hyperalgesia in mice. Administration of a transient receptor potential vanilloid 1 (TRPV1) antagonist inhibited the 5-HT-induced mechanical hyperalgesia. 5-HT injection enhanced 5-HT- and capsaicin-evoked calcium signals specifically in isolectin B4 (IB4)-negative neurons; signals were inhibited by a 5-HT2B/2C antagonist and PKCe blocker. Thus, 5-HT2B mediates 5-HT-induced mechanical hyperalgesia by regulating TRPV1 function.

The neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) has been linked to multiple aspects of cognition. For example, in rodents, discrimination and reversal learning are altered by experimentally induced changes in brain serotonin levels, and reduced expression of the 5-HT(2B) receptor subtype in mice and humans is associated with decreased serotonergic tone and increased behavioral impulsivity. Serotonin modulates cognitive flexibility as well as fear and anxiety, but the specific contributions of 5-HT(2B) receptors to these behaviors is unknown. The current study assessed mice with partial Htr2b deletion for performance on a touchscreen-based pairwise visual discrimination and reversal learning task followed by a test of cued fear learning. Male Htr2b heterozygous mice (+/−) and littermate controls (+/+) were trained to discriminate between two visual stimuli presented on a touch-sensitive screen, one which predicted delivery of a 14-mg food pellet and the other which was not rewarded. Once discrimination performance criterion was attained, the stimulus-reward contingencies were reversed. Htr2b +/− mice were faster to reach discrimination criterion than +/+ controls, and made fewer errors. Htr2b +/− mice were also slower to make responses and collect rewards. Conversely, measures of reversal learning were not different between genotypes. Pavlovian cued fear conditioning was also normal in Htr2b +/−mice. These data demonstrate a selective improvement in touchscreen-based discrimination learning in mice with partial deletion of the 5-HT(2B) receptor, and provide further insight into the role of the 5-HT(2B) receptor in cognition.

Endocannabinoids (eCBs) and serotonin (5-HT) play a neuromodulatory role in the central nervous system. Both eCBs and 5-HT regulate neuronal excitability and their pharmacological potentiation has been shown to control seizures in pre-clinical and human studies. Compelling evidence indicates that eCB and 5-HT systems interact to modulate several physiological and pathological brain functions, such as food intake, pain, drug addiction, depression, and anxiety. Nevertheless, there is no evidence of an eCB/5-HT interaction in experimental and human epilepsies, including status epilepticus (SE). Here, we performed video-EEG recording in behaving rats treated with the pro-convulsant agent pilocarpine (PILO), in order to study the effect of the activation of CB