Activation of ventral pallidum-projecting neurons in the nucleus accumbens via 5-HT2C receptor stimulation regulates motivation for wheel running in male mice.

Rodents have a strong motivation for wheel running; however, the neural mechanisms that regulate their motivation remain unknown. We investigated the possible involvement of serotonin (5-HT) systems in regulating motivation for wheel running in male mice. Systemic administration of a 5-HT1A receptor antagonist (WAY100635) increased the number of wheel rotations, whereas administration of a 5-HT2A or 5-HT2C receptor antagonist (volinanserin or SB242084, respectively) decreased it. In the open field test, neither WAY100635 nor volinanserin affected locomotor activity, whereas SB242084 increased locomotor activity. To identify the brain regions on which these antagonists act, we locally injected these into the motivational circuitry, including the nucleus accumbens (NAc), dorsomedial striatum (DM-Str), and medial prefrontal cortex (mPFC). Injection of SB242084 into the NAc, but not the DM-Str or mPFC, reduced the number of wheel rotations without altering locomotor activity. The local administration of WAY100635 or volinanserin to these brain regions did not affect the number of wheel rotations. Immunohistochemical analyses revealed that wheel running increased the number of c-Fos-positive cells in the NAc medial shell (NAc-MS), which was reduced by systemic SB242084 administration. In vitro slice whole-cell recordings showed that bath application of the 5-HT2C receptor agonist lorcaserin increased the frequency of spontaneous excitatory and inhibitory postsynaptic currents in the ventral tegmental area (VTA)-projecting neurons, whereas it only increased the frequency of spontaneous excitatory postsynaptic currents in ventral pallidum (VP)-projecting neurons in the NAc-MS. These findings suggest that the activation of VP-projecting NAc-MS neurons via 5-HT2C receptor stimulation regulates motivation for wheel running.

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

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

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

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

Acute dose-dependent effects of mescaline in a double-blind placebo-controlled study in healthy subjects.

Classic psychedelics have regained interest in research and therapy. Despite the long tradition of the human use of mescaline, modern data on its dose-dependent acute effects and pharmacokinetics are lacking. Additionally, its mechanism of action has not been investigated in humans. We used a randomized, double-blind, placebo-controlled, crossover design in 16 healthy subjects (8 women) who received placebo, mescaline (100, 200, 400, and 800 mg), and 800 mg mescaline together with the serotonin 5-hydroxytryptamine-2A (5-HT2A) receptor antagonist ketanserin (40 mg) to assess subjective effects, autonomic effects, adverse effects, and pharmacokinetics up to 30 h after drug administration. Mescaline at doses >100 mg induced dose-dependent acute subjective effects. Mescaline increased systolic and diastolic blood pressure at doses >100 mg, with no difference between doses of 200-800 mg. Heart rate increased dose-dependently. Pharmacokinetics of mescaline were dose-proportional. Maximal concentrations were reached after approximately 2 h, and the plasma elimination half-life was approximately 3.5 h. The average duration of subjective effects increased from 6.4 to 14 h with increasing doses of 100-800 mg mescaline. Nausea and emesis were frequent adverse effects at the 800 mg dose. Co-administration of ketanserin attenuated and shortened acute effects of 800 mg mescaline to become comparable to the 100 and 200 mg doses. There were no ceiling effects of the subjective response within the investigated dose range, but tolerability was lower at the highest doses. These results may assist with dose finding for future research and suggest that acute effects of mescaline are primarily mediated by 5-HT2A receptors.

Inhibition of HTR2B-mediated serotonin signaling in colorectal cancer suppresses tumor growth through ERK signaling.

Colorectal cancer (CRC) is a leading cause of cancer-related mortality worldwide. Serotonin (5-HT) is a biogenic monoamine that acts as a neurotransmitter in the central nervous system and as a paracrine, exocrine, or endocrine messenger in peripheral tissues. In this study, we hypothesized that inhibition of serotonin signaling using 5-HT receptor 2B (HTR2B) inhibitors could potentially impede the progression of CRC. We treated CT26 and COLO-205 cells with SB204741, an inhibitor of HTR2B, and evaluated CRC cell proliferation and migration. We then evaluated the effects of HTR2B inhibition in a xenograft mouse model of human colorectal cancer. We also evaluated the role of a novel inhibitor, GM-60186, using both in vitro and in vivo models. RNA sequencing analysis was performed to elucidate the underlying mechanism of the anti-tumor effects of pharmacological inhibition of HTR2B on CRC. In both CRC cell lines and xenograft mouse models, we show that pharmacological inhibition of HTR2B with SB204741 and GM-60186 significantly inhibits CRC cell proliferation and migration. HTR2B inhibition leads to the suppression of extracellular signal-regulated kinase (ERK) signaling, a critical pathway in CRC pathogenesis. Notably, transcriptomic analysis reveals distinct gene expression changes associated with HTR2B inhibition, providing insight into its therapeutic potential. In this study, we found that pharmacological inhibition of HTR2B suppressed CRC proliferation via ERK signaling. In addition, we proposed a novel HTR2B inhibitor for the treatment of CRC. This study highlights the potential role of HTR2B signaling in CRC. These inhibitors may contribute to new therapeutics for CRC treatment.

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

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

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

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

[18F]RS-127445 radiosynthesis and evaluation as a 5-HT2B receptor PET radiotracer in rat brain.

Serotonin (5-hydroxytryptamine, 5-HT) is a neurotransmitter involved in many physiological and pathological mechanisms through its numerous receptors. Among these, the 5-HT2B receptor is known to play a key role in multiple brain disorders but remains poorly understood. Positron emission tomography (PET) can contribute to a better understanding of pathophysiological mechanisms regulated by the 5-HT2B receptor. To develop the first PET radiotracer for the 5-HT2B receptor, RS-127445, a well-known 5-HT2B receptor antagonist, was labeled with fluorine-18. [18F]RS-127445 was synthesized in a high radiochemical purity and with a good molar activity and radiochemical yield. Preliminary PET scans in rats showed good brain penetration of [18F]RS-127445. However, competition experiments and in vitro autoradiography showed high non-specific binding, especially to brain white matter.

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

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

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

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

Chronic sarpogrelate treatment improves renal sympathetic hyperactivity in experimental diabetes.

Diabetes and derived complications, especially diabetic nephropathy and neuropathy annually cause great morbimortality worldwide. 5-hydroxytryptamine (5-HT) acts as a modulator of renal sympathetic input and vascular tone. In this line, 5-HT2 receptor blockade has been linked with reduced incidence and progression of diabetic microvascular alterations. In this work, we aimed to determine, in diabetic rats, whether 5-HT2 blockade ameliorates renal function and to characterize the serotonergic modulatory action on renal sympathetic neurotransmission. Diabetes was induced in male Wistar rats by alloxan administration (150 mg/kg, s.c.), and sarpogrelate (30 mg/kg·day, p.o.; 5-HT2 antagonist) was administered for 14 days (DM-S). Normoglycemic and diabetic (DM) animals were maintained as aged-matched controls. At 28th day, DM-S animals were anesthetized and prepared for the in situ autoperfusion of the kidney. Renal vasoconstrictor responses were induced electrically or by i.a. noradrenaline (NA) administration. The role of 5-HT and selective 5-HT agonist/antagonist were studied on these renal vasopressor responses. Sarpogrelate treatment decreased renal sympathetic-induced vasopressor responses, reduced renal hypertrophy and kidney damage markers increased in DM. Intraarterial 5-HT inhibited the sympathetic-induced renal vasoconstrictions, effect reproduced by 5-CT, AS-19, L-694,247 and LY 344864 (5-HT1/5/7, 5-HT7, 5-HT1D and 5-HT1F receptor agonists, respectively). Blocking 5-HT1D/1F/7 receptors completely abolished the 5-CT sympatho-inhibition. NA vasoconstrictions were not altered by any of the 5-HT agonists tested. Thus, in experimental diabetes, chronic sarpogrelate treatment reduces renal damage markers, kidney hypertrophy and renal sympathetic hyperactivity and modifies serotonergic modulation of renal sympathetic neurotransmission, causing a sympatho-inhibition by prejunctional 5-HT1D/1F and 5-HT7 activation.

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 ß-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.

AlphaFold2 structures guide prospective ligand discovery.

AlphaFold2 (AF2) models have had wide impact but mixed success in retrospective ligand recognition. We prospectively docked large libraries against unrefined AF2 models of the σ2 and serotonin 2A (5-HT2A) receptors, testing hundreds of new molecules and comparing results with those obtained from docking against the experimental structures. Hit rates were high and similar for the experimental and AF2 structures, as were affinities. Success in docking against the AF2 models was achieved despite differences between orthosteric residue conformations in the AF2 models and the experimental structures. Determination of the cryo-electron microscopy structure for one of the more potent 5-HT2A ligands from the AF2 docking revealed residue accommodations that resembled the AF2 prediction. AF2 models may sample conformations that differ from experimental structures but remain low energy and relevant for ligand discovery, extending the domain of structure-based drug design.

Metabolism, Disposition, Excretion, and Potential Transporter Inhibition of 7-16, an Improving 5-HT2A Receptor Antagonist and Inverse Agonist for Parkinson's Disease.

Compound 7-16 was designed and synthesized in our previous study and was identified as a more potential selective 5-HT2A receptor antagonist and inverse agonist for treating Parkinson's disease psychosis (PDP). Then, the metabolism, disposition, and excretion properties of 7-16 and its potential inhibition on transporters were investigated in this study to highlight advancements in the understanding of its therapeutic mechanisms. The results indicate that a total of 10 metabolites of 7-16/[14C]7-16 were identified and determined in five species of liver microsomes and in rats using UPLC-Q Exactive high-resolution mass spectrometry combined with radioanalysis. Metabolites formed in human liver microsomes could be covered by animal species. 7-16 is mainly metabolized through mono-oxidation (M470-2) and N-demethylation (M440), and the CYP3A4 isozyme was responsible for both metabolic reactions. Based on the excretion data in bile and urine, the absorption rate of 7-16 was at least 74.7%. 7-16 had weak inhibition on P-glycoprotein and no effect on the transport activity of OATP1B1, OATP1B3, OAT1, OAT3, and OCT2 transporters. The comprehensive pharmacokinetic properties indicate that 7-16 deserves further development as a new treatment drug for PDP.

N-(4-Bromo-2,5-Dimethoxyphenethyl)-6-(4-Phenylbutoxy)Hexan-1-Amine (XOB): A Novel Phenylalkylamine Antagonist of Serotonin 2A Receptors and Voltage-Gated Sodium Channels.

Bipolar disorder impacts millions of patients in the United States but the mechanistic understanding of its pathophysiology and therapeutics is incomplete. Atypical antipsychotic serotonin2A (5-HT2A) receptor antagonists, such as quetiapine and olanzapine, and mood-stabilizing voltage-gated sodium channel (VGSC) blockers, such as lamotrigine, carbamazepine, and valproate, show therapeutic synergy and are often prescribed in combination for the treatment of bipolar disorder. Combination therapy is a complex task for clinicians and patients, often resulting in unexpected difficulties with dosing, drug tolerances, and decreased patient compliance. Thus, an unmet need for bipolar disorder treatment is to develop a therapeutic agent that targets both 5-HT2A receptors and VGSCs. Toward this goal, we developed a novel small molecule that simultaneously antagonizes 5-HT2A receptors and blocks sodium current. The new compound, N-(4-bromo-2,5-dimethoxyphenethyl)-6-(4-phenylbutoxy)hexan-1-amine (XOB) antagonizes 5-HT-stimulated, Gq-mediated, calcium flux at 5-HT2A receptors at low micromolar concentrations while displaying negligible affinity and activity at 5-HT1A, 5-HT2B, and 5-HT2C receptors. At similar concentrations, XOB administration inhibits sodium current in heterologous cells and results in reduced action potential (AP) firing and VGSC-related AP properties in mouse prefrontal cortex layer V pyramidal neurons. Thus, XOB represents a new, proof-of-principle tool that can be used for future preclinical investigations and therapeutic development. This polypharmacology approach of developing a single molecule to act upon two targets, which are currently independently targeted by combination therapies, may lead to safer alternatives for the treatment of psychiatric disorders that are increasingly being found to benefit from the simultaneous targeting of multiple receptors. SIGNIFICANCE STATEMENT: The authors synthesized a novel small molecule (XOB) that simultaneously antagonizes two key therapeutic targets of bipolar disorder, 5-HT2A receptors and voltage-gated sodium channels, in heterologous cells, and inhibits the intrinsic excitability of mouse prefrontal cortex layer V pyramidal neurons in brain slices. XOB represents a valuable new proof-of-principle tool for future preclinical investigations and provides a novel molecular approach to the pharmacological treatment of complex neuropsychiatric disease, which often requires a combination of therapeutics for sufficient patient benefit.

Serotonin 2C receptor in a rat model of temporal lobe epilepsy: From brainstem expression to pharmacological blockade in relation to ventilatory function.

Because of its involvement in breathing control and neuronal excitability, dysregulation of the serotonin (5-HT) 2C receptor (5-HT2C) might play a key role in sudden unexpected death in epilepsy. Seizure-induced respiratory arrest is thus prevented by a 5-HT2B/C agonist in different seizure model. However, the specific contribution of 5-HT2C in chronic epilepsy-related respiratory dysfunction remains unknown. In a rat model of temporal lobe epilepsy (EPI rats), in which we previously reported interictal respiratory dysfunctions and a reduction of brainstem 5-HT tone, quantitative reverse transcriptase polymerase chain reaction showed overexpression of TPH2 (5-HT synthesis enzyme), SERT (5-HT reuptake transporter), and 5-HT2C transcript levels in the brainstem of EPI rats, and of RNA-specific adenosine deaminase (ADAR1, ADAR2) involved in the production of 5-HT2C isoforms. Interictal ventilation was assessed with whole-body plethysmography before and 2 h after administration of SB242084 (2 mg/kg), a specific antagonist of 5-HT2C. As expected, SB242084 administration induced a progressive decrease in ventilatory parameters and an alteration of breathing stability in both control and EPI rats. However, the size of the SB242084 effect was lower in EPI rats than in controls. Increased 5-HT2C gene expression in the brainstem of EPI rats could be part of a compensatory mechanism against epilepsy-related low 5-HT tone and expression of 5-HT2C isoforms for which 5-HT affinity might be lower.

5-HT 2A and 5-HT 2C receptor antagonism differentially modulate reinforcement learning and cognitive flexibility: behavioural and computational evidence.

RATIONALE: Cognitive flexibility, the ability to adapt behaviour in response to a changing environment, is disrupted in several neuropsychiatric disorders, including obsessive-compulsive disorder and major depressive disorder. Evidence suggests that flexibility, which can be operationalised using reversal learning tasks, is modulated by serotonergic transmission. However, how exactly flexible behaviour and associated reinforcement learning (RL) processes are modulated by 5-HT action on specific receptors is unknown. OBJECTIVES: We investigated the effects of 5-HT2A receptor (5-HT2AR) and 5-HT2C receptor (5-HT2CR) antagonism on flexibility and underlying RL mechanisms. METHODS: Thirty-six male Lister hooded rats were trained on a touchscreen visual discrimination and reversal task. We evaluated the effects of systemic treatments with the 5-HT2AR and 5-HT2CR antagonists M100907 and SB-242084, respectively, on reversal learning and performance on probe trials where correct and incorrect stimuli were presented with a third, probabilistically rewarded, stimulus. Computational models were fitted to task choice data to extract RL parameters, including a novel model designed specifically for this task. RESULTS: 5-HT2AR antagonism impaired reversal learning only after an initial perseverative phase, during a period of random choice and then new learning. 5-HT2CR antagonism, on the other hand, impaired learning from positive feedback. RL models further differentiated these effects. 5-HT2AR antagonism decreased punishment learning rate (i.e. negative feedback) at high and low doses. The low dose also decreased reinforcement sensitivity (beta) and increased stimulus and side stickiness (i.e., the tendency to repeat a choice regardless of outcome). 5-HT2CR antagonism also decreased beta, but reduced side stickiness. CONCLUSIONS: These data indicate that 5-HT2A and 5-HT2CRs both modulate different aspects of flexibility, with 5-HT2ARs modulating learning from negative feedback as measured using RL parameters and 5-HT2CRs for learning from positive feedback assessed through conventional measures.

Desloratadine alleviates ALS-like pathology in hSOD1G93A mice via targeting 5HTR2A on activated spinal astrocytes.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease with progressive loss of motor neurons in the spinal cord, cerebral cortex and brain stem. ALS is characterized by gradual muscle atrophy and dyskinesia. The limited knowledge on the pathology of ALS has impeded the development of therapeutics for the disease. Previous studies have shown that autophagy and astrocyte-mediated neuroinflammation are involved in the pathogenesis of ALS, while 5HTR2A participates in the early stage of astrocyte activation, and 5HTR2A antagonism may suppress astrocyte activation. In this study, we evaluated the therapeutic effects of desloratadine (DLT), a selective 5HTR2A antagonist, in human SOD1G93A (hSOD1G93A) ALS model mice, and elucidated the underlying mechanisms. HSOD1G93A mice were administered DLT (20 mg·kg-1·d-1, i.g.) from the age of 8 weeks for 10 weeks or until death. ALS onset time and lifespan were determined using rotarod and righting reflex tests, respectively. We found that astrocyte activation accompanying with serotonin receptor 2 A (5HTR2A) upregulation in the spinal cord was tightly associated with ALS-like pathology, which was effectively attenuated by DLT administration. We showed that DLT administration significantly delayed ALS symptom onset time, prolonged lifespan and ameliorated movement disorders, gastrocnemius injury and spinal motor neuronal loss in hSOD1G93A mice. Spinal cord-specific knockdown of 5HTR2A by intrathecal injection of adeno-associated virus9 (AAV9)-si-5Htr2a also ameliorated ALS pathology in hSOD1G93A mice, and occluded the therapeutic effects of DLT administration. Furthermore, we demonstrated that DLT administration promoted autophagy to reduce mutant hSOD1 levels through 5HTR2A/cAMP/AMPK pathway, suppressed oxidative stress through 5HTR2A/cAMP/AMPK/Nrf2-HO-1/NQO-1 pathway, and inhibited astrocyte neuroinflammation through 5HTR2A/cAMP/AMPK/NF-κB/NLRP3 pathway in the spinal cord of hSOD1G93A mice. In summary, 5HTR2A antagonism shows promise as a therapeutic strategy for ALS, highlighting the potential of DLT in the treatment of the disease. DLT as a 5HTR2A antagonist effectively promoted autophagy to reduce mutant hSOD1 level through 5HTR2A/cAMP/AMPK pathway, suppressed oxidative stress through 5HTR2A/cAMP/AMPK/Nrf2-HO-1/NQO-1 pathway, and inhibited astrocytic neuroinflammation through 5HTR2A/cAMP/AMPK/NF-κB/NLRP3 pathway in the spinal cord of hSOD1G93A mice.

Identification of 5-HT2 Serotonin Receptor Modulators through the Synthesis of a Diverse, Tropane- and Quinuclidine-alkaloid-Inspired Compound Library.

The recombination of natural product (NP) fragments in unprecedented ways has emerged as an important strategy for bioactive compound discovery. In this context, we propose that privileged primary fragments predicted to be enriched in activity against a specific target class can be coupled to diverse secondary fragments to engineer selectivity among closely related targets. Here, we report the synthesis of an alkaloid-inspired compound library enriched in spirocyclic ring fusions, comprising 58 compounds from 12 tropane- or quinuclidine-containing scaffolds, all of which can be considered pseudo-NPs. The library displays excellent predicted drug-like properties including high Fsp3 content and Lipinski's rule-of-five compliance. Targeted screening against selected members of the serotonin and dopamine G protein-coupled receptor family led to the identification of several hits that displayed significant agonist or antagonist activity against 5-HT2A and/or 5-HT2C, and subsequent optimization of one of these delivered a lead dual 5-HT2B/C antagonist with a highly promising selectivity profile.

No trip needed for psychedelics to lift mood?

LSD and psilocin molecules bind to antidepressant drug targets in the brain, study shows.