SB-243213; a selective 5-HT2C receptor inverse agonist with improved anxiolytic profile: lack of tolerance and withdrawal anxiety

Treadmill Exercise Improves Behavioral and Neurobiological Alterations in Restraint-Stressed Rats

Stress is a state that is known to impact an organism's physiological and psychological balance as well as the morphology and functionality of certain brain areas. In the present work, chronic restraint stress (CRS) model rats treated with treadmill exercise were used to examine anomalies associated to emotion and mood as well as molecular changes in the brain. Forty male Sprague-Dawley rats were divided into control, stress, exercise, and stress+exercise groups. CRS were exposed to stress group rats and exercise group underwent a chronic treadmill exercise. Depressive-like behavior was evaluated with the forced swim test (FST) and tail suspension test (TST). For assessing anxiety-like behavior, the light-dark test (LDT) and the open field test (OFT) were used. The Morris water maze test (MWMT) was used for testing memory and learning. Brain's monoamine level and the expression of genes related to stress were measured. It was discovered that CRS lengthens latency in the MWMT, increases immobility in the FST and TST, decreases time in the light compartment, and causes hypoactivity in the OFT. CRS reduced the dopamine levels in the nucleus accumbens(NAc). Brain-derived neurotrophic factor (BDNF), dopamine receptors, and serotonin receptor (HTR2A) gene expression in the prefrontal cortex, corpus striatum, and hypothalamus were decreased by CRS. Exercise on a treadmill leads to increase NAc's dopamine and noradrenaline levels and prevented behavioral alterations. Exercise increased the alterations of BDNF expressions in the brain in addition to improving behavior. As a result, CRS-induced behavioral impairments were effectively reversed by chronic treadmill exercise with molecular alterations in the brain.

Evaluation of the 5-HT2C receptor drugs RO 60-0175, WAY 161503 and mirtazepine in a preclinical model of comorbidity of depression and cocaine addiction

BACKGROUND

Epidemiological data indicate a high rate of comorbidity of depression and cocaine use disorder (CUD). The role of serotonin 2C (5-HT_2C) receptors in the mechanisms responsible for the coexistence of depression and CUD was not investigated.

METHODS

We combined bilateral olfactory bulbectomy (OBX), an animal model of depression, with intravenous cocaine self-administration and extinction/reinstatement in male rats to investigate two 5-HT_2C receptor agonists (Ro 60-0175 (RO) and WAY 161503 (WAY)) and the 5-HT_2C-receptor preferring antagonist mirtazapine (MIR; an antidepressant), with the goal of determining whether these drugs alter cocaine-induced reinforcement and seeking behaviors. Additionally, neurochemical analyses were performed following cocaine self-administration and its abstinence period in the brain structures in OBX rats and SHAM-operated controls.

RESULTS

Acute administration of RO reduced, while WAY non-significantly attenuated cocaine reinforcement in both rat phenotypes. Moreover, RO or WAY protected against cocaine-seeking behavior after acute or after repeated drug administration during extinction training in OBX and SHAM rats. By contrast, acutely administered MIR did not alter cocaine reinforcement in both rat phenotypes, while it's acute (but not repeated) pretreatment reduced cocaine-seeking in OBX and SHAM rats. In neurochemical analyses, cocaine reinforcement increased 5-HT_2C receptor levels in the ventral hippocampus; a preexisting depression-like phenotype enhanced this effect. The 10-daily cocaine abstinence reduced 5-HT_2C receptor expression in the dorsolateral striatum, while the coexistence of depression and CUD enhanced local receptor expression.

CONCLUSION

The results support a key role of 5-HT_2C receptors for treating CUD and comorbid depression and CUD. They may be backs the further research of pharmacological strategies with drug targeting receptors.

"Selective" serotonin 5-HT2A receptor antagonists

Blockade of the serotonin 5-HT_2A G protein-coupled receptor (5-HT_2AR) is a fundamental pharmacological characteristic of numerous antipsychotic medications, which are FDA-approved to treat schizophrenia, bipolar disorder, and as adjunctive therapies in major depressive disorder. Meanwhile, activation of the 5-HT_2AR by serotonergic psychedelics may be useful in treating neuropsychiatric indications, including major depressive and substance use disorders. Serotonergic psychedelics and other 5-HT_2AR agonists, however, often bind other receptors, and standard 5-HT_2AR antagonists lack sufficient selectivity to make well-founded mechanistic conclusions about the 5-HT_2AR-dependent effects of these compounds and the general neurobiological function of 5-HT_2ARs. This review discusses the limitations and strengths of currently available "selective" 5-HT_2AR antagonists, the molecular determinants of antagonist selectivity at 5-HT_2ARs, and the utility of molecular pharmacological and computational methods in guiding the discovery of novel unambiguously selective 5-HT_2AR antagonists.

Agomelatine for the treatment of generalized anxiety disorder: focus on its distinctive mechanism of action

Generalized anxiety disorder (GAD), the most frequently diagnosed form of anxiety, is usually treated by cognitive-behavioural approaches or medication; in particular, benzodiazepines (acutely) and serotonin or serotonin/noradrenaline reuptake inhibitors (long term). Efficacy, compliance, and acceptability are, however, far from ideal, reinforcing interest in alternative options. Agomelatine, clinically employed in the treatment of major depression, expresses anxiolytic properties in rodents and was effective in the treatment of GAD (including severely ill patients) in several double-blind, short-term (12 weeks) and relapse-prevention (6 months) studies. At active doses, the incidence of adverse effects was no higher than for placebo. Agomelatine possesses a unique binding profile, behaving as a melatonin (MT₁/MT₂) receptor agonist and 5-HT_2C receptor antagonist, yet recognizing neither monoamine transporters nor GABA_A receptors. Extensive evidence supports a role for 5-HT_2C receptors in the induction of anxious states, and their blockade likely plays a primary role in mediating the anxiolytic actions of agomelatine, including populations in the amygdala and bed nucleus of stria terminalis, as well as the hippocampus. Recruitment of MT receptors in the suprachiasmatic nucleus, thalamic reticular nucleus, and hippocampus appears to fulfil a complimentary role. Downstream of 5-HT_2C and MT receptors, modulation of stress-sensitive glutamatergic circuits and altered release of the anxiogenic neuropeptides, corticotrophin-releasing factor, and vasopressin, may be implicated in the actions of agomelatine. To summarize, agomelatine exerts its anxiolytic actions by mechanisms clearly distinct from those of other agents currently employed for the management of GAD.

PLAIN LANGUAGE SUMMARY

How agomelatine helps in the treatment of anxiety disorders.

INTRODUCTION

• Anxiety disorders have a significant negative impact on quality of life.• The most common type of anxiety disorder, called generalized anxiety disorder (GAD), is associated with nervousness and excessive worry.• These symptoms can lead to additional symptoms like tiredness, sleeplessness, irritability, and poor attention.• GAD is generally treated through either cognitive-behavioural therapy or medication. However, widely used drugs like benzodiazepines and serotonin reuptake inhibitors have adverse effects.• Agomelatine, a well-established antidepressant drug, has shown anxiety-lowering ('anxiolytic') properties in rats and has been shown to effectively treat GAD with minimal side effects.• However, exactly how it acts on the brain to manage GAD is not yet clear.• Thus, this review aims to shed light on agomelatine's mechanism of action in treating GAD.

METHODS

• The authors reviewed studies on how agomelatine treats anxiety in animals.• They also looked at clinical studies on the effects of agomelatine in people with GAD.

RESULTS

• The study showed that agomelatine 'blocks' a receptor in nerve cells, which plays a role in causing anxiety, called the 5-HT_2C receptor.• Blocking this receptor, especially in specific brain regions such as nerve cells of the amygdala, bed nucleus of stria terminalis, and hippocampus, produced the anxiety reduction seen during agomelatine treatment.• Agomelatine also activates the melatonin (MT) receptor, which is known to keep anxiety in check, promote sleep, and maintain the sleep cycle.• Agomelatine should thus tackle sleep disturbances commonly seen in patients with GAD.• Beyond 5-HT_2C and MT receptors, signalling molecules in nerve cells that are known to be involved in anxiety disorders (called 'neurotransmitters' and 'neuropeptides') are also affected by agomelatine.

CONCLUSION

• Agomelatine's anxiolytic effects are caused by mechanisms that are distinct from those of other medications currently used to treat GAD.• This explains its therapeutic success and minimal adverse side effects.

International Union of Basic and Clinical Pharmacology. CX. Classification of Receptors for 5-hydroxytryptamine; Pharmacology and Function

5-HT receptors expressed throughout the human body are targets for established therapeutics and various drugs in development. Their diversity of structure and function reflects the important role 5-HT receptors play in physiologic and pathophysiological processes. The present review offers a framework for the official receptor nomenclature and a detailed understanding of each of the 14 5-HT receptor subtypes, their roles in the systems of the body, and, where appropriate, the (potential) utility of therapeutics targeting these receptors. SIGNIFICANCE STATEMENT: This review provides a comprehensive account of the classification and function of 5-hydroxytryptamine receptors, including how they are targeted for therapeutic benefit.

A Subset of Purposeless Oral Movements Triggered by Dopaminergic Agonists Is Modulated by 5-HT2C Receptors in Rats: Implication of the Subthalamic Nucleus

Dopaminergic medication for Parkinson’s disease is associated with troubling dystonia and dyskinesia and, in rodents, dopaminergic agonists likewise induce a variety of orofacial motor responses, certain of which are mimicked by serotonin2C (5-HT_2C) receptor agonists. However, the neural substrates underlying these communalities and their interrelationship remain unclear. In Sprague-Dawley rats, the dopaminergic agonist, apomorphine (0.03–0.3 mg/kg) and the preferential D2/3 receptor agonist quinpirole (0.2–0.5 mg/kg), induced purposeless oral movements (chewing, jaw tremor, tongue darting). The 5-HT_2C receptor antagonist 5-methyl-1-[[2-[(2-methyl-3-pyridyl)oxyl]-5-pyridyl]carbamoyl]-6-trifluoromethylindone (SB 243213) (1 mg/kg) reduced the oral responses elicited by specific doses of both agonists (0.1 mg/kg apomorphine; 0.5 mg/kg quinpirole). After having confirmed that the oral bouts induced by quinpirole 0.5 mg/kg were blocked by another 5-HT_2C antagonist (6-chloro-5-methyl-1-[6-(2-methylpiridin-3-yloxy)pyridine-3-yl carbamoyl] indoline (SB 242084), 1 mg/kg), we mapped the changes in neuronal activity in numerous sub-territories of the basal ganglia using c-Fos expression. We found a marked increase of c-Fos expression in the subthalamic nucleus (STN) in combining quinpirole (0.5 mg/kg) with either SB 243213 or SB 242084. In a parallel set of electrophysiological experiments, the same combination of SB 243213/quinpirole produced an irregular pattern of discharge and an increase in the firing rate of STN neurons. Finally, it was shown that upon the electrical stimulation of the anterior cingulate cortex, quinpirole (0.5 mg/kg) increased the response of substantia nigra pars reticulata neurons corresponding to activation of the “hyperdirect” (cortico-subthalamonigral) pathway. This effect of quinpirole was abolished by the two 5-HT_2C antagonists. Collectively, these results suggest that induction of orofacial motor responses by D2/3 receptor stimulation involves 5-HT_2C receptor-mediated activation of the STN by recruitment of the hyperdirect (cortico-subthalamonigral) pathway.

Serotonin receptors in depression and anxiety: Insights from animal studies

Serotonin regulates many physiological processes including sleep, appetite, and mood. Thus, serotonergic system is an important target in the treatment of psychiatric disorders, such as major depression and anxiety. This natural neurotransmitter interacts with 7 families of its receptors (5-HT1-7), which cause a variety of pharmacological effects. Using genetically modified animals and selective or preferential agonists and antagonist, numerous studies demonstrated the involvement of almost all serotonin receptor subtypes in antidepressant- or anxiolytic-like effects. In this review, based on animal studies, we discuss the possible involvement of serotonin receptor subtypes in depression and anxiety.

Utilization of an Active Site Mutant Receptor for the Identification of Potent and Selective Atypical 5-HT2C Receptor Agonists

Agonism of the 5-HT_2C receptor represents one of the most well-studied and clinically proven mechanisms for pharmacological weight reduction. Selectivity over the closely related 5-HT_2A and 5-HT_2B receptors is critical as their activation has been shown to lead to undesirable side effects and major safety concerns. In this communication, we report the development of a new screening paradigm that utilizes an active site mutant D134A (D3.32) 5-HT_2C receptor to identify atypical agonist structures. We additionally report the discovery and optimization of a novel class of nonbasic heterocyclic amide agonists of 5-HT_2C. SAR investigations around the screening hits provided a diverse set of potent agonists at 5-HT_2C with high selectivity over the related 5-HT_2A and 5-HT_2B receptor subtypes. Further optimization through replacement of the amide with a variety of five- and six-membered heterocycles led to the identification of 6-(1-ethyl-3-(quinolin-8-yl)-1H-pyrazol-5-yl)pyridazin-3-amine (69). Oral administration of 69 to rats reduced food intake in an ad libitum feeding model, which could be completely reversed by a selective 5-HT_2C antagonist.

A short history of the 5-HT2C receptor: from the choroid plexus to depression, obesity and addiction treatment

This paper is a personal account on the discovery and characterization of the 5-HT_2C receptor (first known as the 5-HT_1C receptor) over 30 years ago and how it translated into a number of unsuspected features for a G protein-coupled receptor (GPCR) and a diversity of clinical applications. The 5-HT_2C receptor is one of the most intriguing members of the GPCR superfamily. Initially referred to as 5-HT_1CR, the 5-HT_2CR was discovered while studying the pharmacological features and the distribution of [³H]mesulergine-labelled sites, primarily in the brain using radioligand binding and slice autoradiography. Mesulergine (SDZ CU-085), was, at the time, best defined as a ligand with serotonergic and dopaminergic properties. Autoradiographic studies showed remarkably strong [³H]mesulergine-labelling to the rat choroid plexus. [³H]mesulergine-labelled sites had pharmacological properties different from, at the time, known or purported 5-HT receptors. In spite of similarities with 5-HT₂ binding, the new binding site was called 5-HT_1C because of its very high affinity for 5-HT itself. Within the following 10 years, the 5-HT_1CR (later named 5-HT_2C) was extensively characterised pharmacologically, anatomically and functionally: it was one of the first 5-HT receptors to be sequenced and cloned. The 5-HT_2CR is a GPCR, with a very complex gene structure. It constitutes a rarity in the GPCR family: many 5-HT_2CR variants exist, especially in humans, due to RNA editing, in addition to a few 5-HT_2CR splice variants. Intense research led to therapeutically active 5-HT_2C receptor ligands, both antagonists (or inverse agonists) and agonists: keeping in mind that a number of antidepressants and antipsychotics are 5-HT_2CR antagonists/inverse agonists. Agomelatine, a 5-HT_2CR antagonist is registered for the treatment of major depression. The agonist Lorcaserin is registered for the treatment of aspects of obesity and has further potential in addiction, especially nicotine/ smoking. There is good evidence that the 5-HT_2CR is involved in spinal cord injury-induced spasms of the lower limbs, which can be treated with 5-HT_2CR antagonists/inverse agonists such as cyproheptadine or SB206553. The 5-HT_2CR may play a role in schizophrenia and epilepsy. Vabicaserin, a 5-HT_2CR agonist has been in development for the treatment of schizophrenia and obesity, but was stopped. As is common, there is potential for further indications for 5-HT_2CR ligands, as suggested by a number of preclinical and/or genome-wide association studies (GWAS) on depression, suicide, sexual dysfunction, addictions and obesity. The 5-HT_2CR is clearly affected by a number of established antidepressants/antipsychotics and may be one of the culprits in antipsychotic-induced weight gain.

New therapeutic opportunities for 5-HT2C receptor ligands in neuropsychiatric disorders

The 5-HT2C receptor (R) displays a widespread distribution in the CNS and is involved in the action of 5-HT in all brain areas. Knowledge of its functional role in the CNS pathophysiology has been impaired for many years due to the lack of drugs capable of discriminating among 5-HT2R subtypes, and to a lesser extent to the 5-HT1B, 5-HT5, 5-HT6 and 5-HT7Rs. The situation has changed since the mid-90s due to the increased availability of new and selective synthesized compounds, the creation of 5-HT2C knock out mice, and the progress made in molecular biology. Many pharmacological classes of drugs including antipsychotics, antidepressants and anxiolytics display affinities toward 5-HT2CRs and new 5-HT2C ligands have been developed for various neuropsychiatric disorders. The 5-HT2CR is presumed to mediate tonic/constitutive and phasic controls on the activity of different central neurobiological networks. Preclinical data illustrate this complexity to a point that pharmaceutical companies developed either agonists or antagonists for the same disease. In order to better comprehend this complexity, this review will briefly describe the molecular pharmacology of 5-HT2CRs, as well as their cellular impacts in general, before addressing its central distribution in the mammalian brain. Thereafter, we review the preclinical efficacy of 5-HT2C ligands in numerous behavioral tests modeling human diseases, highlighting the multiple and competing actions of the 5-HT2CRs in neurobiological networks and monoaminergic systems. Notably, we will focus this evidence in the context of the physiopathology of psychiatric and neurological disorders including Parkinson's disease, levodopa-induced dyskinesia, and epilepsy.

Ethanol induced adaptations in 5-HT2c receptor signaling in the bed nucleus of the stria terminalis: implications for anxiety during ethanol withdrawal

One of the hallmarks of alcohol dependence is the presence of a withdrawal syndrome during abstinence, which manifests as physical craving for alcohol accompanied by subjective feelings of anxiety. Using a model of chronic intermittent ethanol (CIE) vapor in mice, we investigated the role of serotonin2c receptor (5HT2c-R) signaling in the BNST as a neural substrate underlying ethanol-induced anxiety during withdrawal. Mice were subjected to a 5-day CIE regimen of 16 h of ethanol vapor exposure followed by an 8 h "withdrawal" period between exposures. After the 5th and final exposure, mice were withdrawn for 24 h or 1 week before experiments began. Anxiety-like behavior was assessed in the social approach, light dark, and open field tests with mice showing deficits in social, but not general anxiety-like behavior that was alleviated by pretreatment with the 5HT2c-R antagonist SB 242,084 (3 mg/kg, i.p.) 24 h and 1 week post-CIE. Using immunohistochemistry and whole cell patch clamp electrophysiology, we also found that CIE increased FOS-IR and enhanced neuronal excitability in the ventral BNST (vBNST) 24 h into withdrawal in a 5HT2c-R dependent manner. This enhanced excitability persisted for 1 week post-CIE. We also found that mCPP, a 5HT2c/b agonist, induced a more robust depolarization in cells of the vBNST in CIE mice, confirming that 5HT2c-R signaling is upregulated in the vBNST following CIE. Taken together, these results suggest that CIE upregulates 5HT2c-R signaling in the vBNST, leading to increased excitability. This enhanced excitability of the vBNST may drive increased anxiety-like behavior during ethanol withdrawal.

Controversies on the role of 5-HT(2C) receptors in the mechanisms of action of antidepressant drugs

Evidence from the various sources indicates alterations in 5-HT2C receptor functions in anxiety, depression and suicide, and other stress-related disorders treated with antidepressant drugs. Although the notion of a 5-HT2C receptor desensitization following antidepressant treatments is rather well anchored in the literature, this concept is mainly based on in vitro assays and/or behavioral assays (hypolocomotion, hyperthermia) that have poor relevance to anxio-depressive disorders. Our objective herein is to provide a comprehensive overview of the studies that have assessed the effects of antidepressant drugs on 5-HT2C receptors. Relevant molecular (second messengers, editing), neurochemical (receptor binding and mRNA levels), physiological (5-HT2C receptor-induced hyperthermia and hormone release), behavioral (5-HT2C receptor-induced changes in feeding, anxiety, defense and motor activity) data are summarized and discussed. Setting the record straight about drug-induced changes in 5-HT2C receptor function in specific brain regions should help to determine which pharmacotherapeutic strategy is best for affective and anxiety disorders.

Serotonin2C Receptors and the Motor Control of Oral Activity

Data from many experiments has shown that serotonin2C (5-HT2C) receptor plays a role in the control of orofacial activity in rodents. Purposeless oral movements can be elicited either by agonists or inverse agonists implying a tight control exerted by the receptor upon oral activity. The effects of agonists has been related to an action of these drugs in the subthalamic nucleus and the striatum, the two input structures for cortical efferents to the basal ganglia, a group of subcortical structures involved in the control of motor behaviors. The oral effects of agonists are dramatically enhanced in case of chronic blockade of central dopaminergic transmission induced by neuroleptics or massive destruction of dopamine neurons. The mechanisms involved in the hypersensitized oral responses to 5-HT2C agonists are not clear and deserve additional studies. Indeed, while the oral behavior triggered by 5-HT2C drugs would barely correspond to the dyskinesia observed in humans, the clinical data have consistently postulated that 5-HT2C receptors could be involved in these aberrant motor manifestations.

Multiple controls exerted by 5-HT2C receptors upon basal ganglia function: from physiology to pathophysiology

Serotonin2C (5-HT2C) receptors are expressed in the basal ganglia, a group of subcortical structures involved in the control of motor behaviour, mood and cognition. These receptors are mediating the effects of 5-HT throughout different brain areas via projections originating from midbrain raphe nuclei. A growing interest has been focusing on the function of 5-HT2C receptors in the basal ganglia because they may be involved in various diseases of basal ganglia function notably those associated with chronic impairment of dopaminergic transmission. 5-HT2C receptors act on numerous types of neurons in the basal ganglia, including dopaminergic, GABAergic, glutamatergic or cholinergic cells. Perhaps inherent to their peculiar molecular properties, the modality of controls exerted by 5-HT2C receptors over these cell populations can be phasic, tonic (dependent on the 5-HT tone) or constitutive (a spontaneous activity without the presence of the ligand). These controls are functionally organized in the basal ganglia: they are mainly localized in the input structures and preferentially distributed in the limbic/associative territories of the basal ganglia. The nature of these controls is modified in neuropsychiatric conditions such as Parkinson's disease, tardive dyskinesia or addiction. Most of the available data indicate that the function of 5-HT2C receptor is enhanced in cases of chronic alterations of dopamine neurotransmission. The review illustrates that 5-HT2C receptors play a role in maintaining continuous controls over the basal ganglia via multiple diverse actions. We will discuss their interest for treatments aimed at ameliorating current pharmacotherapies in schizophrenia, Parkinson's disease or drugs abuse.

Serotonin2C ligands exhibiting full negative and positive intrinsic activity elicit purposeless oral movements in rats: distinct effects of agonists and inverse agonists in a rat model of Parkinson's disease

This study examined in naive or hemiparkinsonian rats the effect of various serotonin 2C (5-HT(2C)) receptor ligands differing in their intrinsic activity at 5-HT(2C) receptors on purposeless oral movements, a motor response integrated in the basal ganglia. Intraperitoneal administration of a non-selective [meta-chlorophenylpiperazine (m-CPP) 0.1-3 mg/kg], preferential [S-2-(6-chloro-5-fluoroindol-1-yl)-1-methylethylamine, Ro60-0175, 0.1-3 mg/kg] or selective [(7bR,10aR)-1,2,3,4,8,9,10,10a-octahydro-7bH-cyclopenta-[b][1,4]diazepino[6,7,1hi]indole, WAY163909, 0.3-10 mg/kg] 5-HT(2C) agonists enhanced oral bouts in naive rats. The 5-HT(2C) inverse agonists SB206553 [1-20 mg/kg; 5-methyl-1-(3-pyridylcarbamoyl)-1,2,3,5-tetrahydropyrrolo[2,3-f]indole] and S32006 [1-20 mg/kg; N-pyridin-3-yl-1,2-dihydro-3H-benzo[e]indole-3-carboxamide], but not the 5-HT(2C) antagonist SB243213 [1-10 mg/kg; 5-methyl-1-[[2-[(2-methyl-3-pyridyl)oxy]-5-pyridyl]carbamoyl]-6-trifluoromethylindoline], likewise dose-dependently enhanced oral movements. The effects induced by preferential 5-HT(2C) agonists and inverse agonists, but not by the cholinomimetic drug pilocarpine (5 mg/kg), were abolished by SB243213 underpinning its specificity. S32006-induced oral bouts was unaffected by the 5,7-dihydroxytryptamine lesions of 5-HT neurons. Nigrostriatal dopaminergic lesions potentiated oral effects induced by the agonists Ro60-0175 (3 mg/kg) and WAY163909 (1 mg/kg), but not by the inverse agonist SB206553 (10 mg/kg). The effect of Ro60-0175 in dopamine-lesioned rats was suppressed by SB243213. These data show that 5-HT(2C) agonists and full inverse agonists (but not neutral antagonists) perturb oral activity in rodents, paralleling studies of common antidepressant, anxiolytic and antipsychotic properties. The differential sensitivity of their actions to depletion of dopamine suggests recruitment of different contrasting neural mechanisms in the basal ganglia.

Blonanserin reverses the phencyclidine (PCP)-induced impairment in novel object recognition (NOR) in rats: role of indirect 5-HT(1A) partial agonism

Blonanserin is an atypical antipsychotic drug (APD) which, compared to other atypical APDs, is a relatively selective serotonin (5-HT)2A and dopamine D2 antagonist. Comparing blonanserin with more broadly acting atypical APDs could be useful to test the contributions of actions at other monoamine receptors, e.g. 5-HT1A receptors, to the reversal of PCP-induced novel object recognition (NOR) deficit. In this study, we tested the effect of blonanserin alone, and in combination with 5-HT1A agents, on NOR deficit induced by subchronic treatment with the N-methyl-D-aspartate (NMDA) receptor antagonist, phencyclidine (PCP; 2 mg/kg), b.i.d., for 7 days. Blonanserin, 1mg/kg, but not 0.3mg/kg, improved the PCP-induced NOR deficit. However, at 1mg/kg, object exploration was diminished. Co-administration of sub-effective doses of blonanserin (0.3 mg/kg) and the 5-HT1A partial agonist, tandospirone (0.2 mg/kg), significantly reversed the NOR deficit without diminishing activity during the acquisition or retention periods. The combination of WAY100635 (0.6 mg/kg), a 5-HT1A antagonist, and blonanserin (1 mg/kg), also diminished object exploration which prevented assessment of the effect of this combination on NOR. WAY100635 (0.6 mg/kg) blocked the ameliorating effect of risperidone (0.1 mg/kg), another atypical APD with low affinity for 5-HT1A receptors, but did not impair exploration. These results suggest that blonansein and risperidone, atypical APDs which lack a direct action on 5-HT1A receptors require 5-HT1A receptor stimulation to reverse the subchronic PCP-induced NOR deficit and provide a support for clinical trial of blonanserin in combination with tandospirone to ameliorate cognitive impairment in schizophrenia and to have fewer side effects.

Synthesis and evaluation of a series of 2-substituted-5-thiopropylpiperazine (piperidine)-1,3,4-oxadiazoles derivatives as atypical antipsychotics

Background

It is important to develop novel antipsychotics that can effectively treat schizophrenia with minor side-effects. The aim of our work is to develop novel antipsychotics that act on dopamine D₂ and D₃, serotonin 5-HT_1A and 5-HT_2A receptors with low affinity for the serotonin 5-HT_2C and H₁ receptors, which can effectively cure positive symptoms, negative symptoms and cognitive impairment without the weight gain side-effect.

Methodology/Principal Findings

A series of 2-substituted-5-thiopropylpiperazine (piperidine) -1,3,4-oxadiazoles derivatives have been synthesized and the target compounds were evaluated for binding affinities to D₂, 5-HT_1A and 5-HT_2A receptors. Preliminary results indicated that compounds 14, 16 and 22 exhibited high affinities to D₂, 5-HT_1A and 5-HT_2A receptors among these compounds. Further binding tests showed that compound 22 had high affinity for D₃ receptor, and low affinity for serotonin 5-HT_2C and H₁ receptors. In addition, compound 22 inhibited apomorphine-induced climbing behavior and MK-801-induced hyperactivity with no extrapyramidal symptoms liability in mice. Moreover, compound 22 exhibited acceptable pharmacokinetic properties.

Conclusions/Significance

Compound 22 showed an atypical antipsychotic activity without liability for extrapyramidal symptoms. We anticipate compound 22 to be useful for developing a novel class of drug for the treatment of schizophrenia.

Pharmacological and genetic interventions in serotonin (5-HT)(2C) receptors to alter drug abuse and dependence processes

The present review provides an overview on serotonin (5-hydroxytryptamine; 5-HT)(2C) receptors and their relationship to drug dependence. We have focused our discussion on the impact of 5-HT(2C) receptors on the effects of different classes of addictive drugs, illustrated by reference to data using pharmacological and genetic tools. The neurochemical mechanism of the interaction between 5-HT(2C) receptors, with focus on the mesocorticolimbic dopaminergic system, and drugs of abuse (using cocaine as an example) is discussed. Finally, we integrate recent nonclinical and clinical research and information with marketed products possessing 5-HT(2C) receptor binding affinities. Accordingly, available nonclinical data and some clinical observations targeting 5-HT(2C) receptors may offer innovative translational strategies for combating drug dependence.This article is part of a Special Issue entitled: Brain Integration.

Stimulation of serotonin2C receptors elicits abnormal oral movements by acting on pathways other than the sensorimotor one in the rat basal ganglia

Serotonin2C (5-HT(2C)) receptors act in the basal ganglia, a group of sub-cortical structures involved in motor behavior, where they are thought to modulate oral activity and participate in iatrogenic motor side-effects in Parkinson's disease and Schizophrenia. Whether abnormal movements initiated by 5-HT(2C) receptors are directly consequent to dysfunctions of the motor circuit is uncertain. In the present study, we combined behavioral, immunohistochemical and extracellular single-cell recordings approaches in rats to investigate the effect of the 5-HT(2C) agonist Ro-60-0175 respectively on orofacial dyskinesia, the expression of the marker of neuronal activity c-Fos in basal ganglia and the electrophysiological activity of substantia nigra pars reticulata (SNr) neuron connected to the orofacial motor cortex (OfMC) or the medial prefrontal cortex (mPFC). The results show that Ro-60-0175 (1 mg/kg) caused bouts of orofacial movements that were suppressed by the 5-HT(2C) antagonist SB-243213 (1 mg/kg). Ro-60-0175 (0.3, 1, 3 mg/kg) dose-dependently enhanced Fos expression in the striatum and the nucleus accumbens. At the highest dose, it enhanced Fos expression in the subthalamic nucleus, the SNr and the entopeduncular nucleus but not in the external globus pallidus. However, the effect of Ro-60-0175 was mainly associated with associative/limbic regions of basal ganglia whereas subregions of basal ganglia corresponding to sensorimotor territories were devoid of Fos labeling. Ro-60-0175 (1-3 mg/kg) did not affect the electrophysiological activity of SNr neurons connected to the OfMC nor their excitatory-inhibitory-excitatory responses to the OfMC electrical stimulation. Conversely, Ro-60-0175 (1 mg/kg) enhanced the late excitatory response of SNr neurons evoked by the mPFC electrical stimulation. These results suggest that oral dyskinesia induced by 5-HT(2C) agonists are not restricted to aberrant signalling in the orofacial motor circuit and demonstrate discrete modifications in associative territories.

Antagonism at serotonin 5-HT(2A) receptors modulates functional activity of frontohippocampal circuit

RATIONALE

Several second-generation antipsychotics are characterised by a significant antagonistic effect at serotonin 5-HT(2A) receptors (5-HT(2A)R), a feature that has been associated with lower incidence of extra-pyramidal symptoms and a putative amelioration of positive and negative symptoms experienced by schizophrenic patients. However, the neurofunctional substrate of 5-HT(2A) antagonism and its exact contribution to the complex pharmacological profile of these drugs remain to be elucidated.

OBJECTIVES

Here, we used pharmacological magnetic resonance imaging to map the modulatory effects of the selective 5-HT(2A)R antagonist Ml00907 on the spatiotemporal patterns of brain activity elicited by acute phencyclidine (PCP) challenge in the rat. PCP is a non-competitive NMDA receptor antagonist that induces dysregulation of corticolimbic glutamatergic neurotransmission and produces cognitive impairment and psychotic-like symptoms reminiscent of those observed in schizophrenia.

RESULTS

Pre-administration of M100907 produced focal and region-dependent attenuation of PCP-induced response in frontoseptohippocampal areas. As early studies highlighted a permissive role of 5-HT(2A)R on frontal dopamine release, the role of post-synaptic dopamine D(1) receptors on PCP-induced response was examined by using the potent antagonist SCH23390. Interestingly, SCH23390 did not affect PCP's response in any of the regions examined. This finding rules out a significant contribution of dopamine in the functional changes mapped and, indirectly, the inhibitory effect of M100907, in favour of a glutamatergic origin.

CONCLUSIONS

Our data expand recent evidence suggesting a key role of 5-HT(2A)R in modulating glutamate-mediated cognitive performance in the prefrontal cortex and highlight the whole frontoseptohippocampal circuit as a key functional substrate of 5-HT(2A)R antagonism in normal and disease states.

The modified Geller-Seifter test in rats was insensitive to GABAB receptor positive modulation or blockade, or 5-HT1A receptor activation

RATIONALE

Both the GABA(B) receptor positive modulator GS39783 and the GABA(B) receptor antagonist CGP46381 exhibit anxiolytic-like properties in animal models. In the present studies, the effects of GS39783 and CGP46381 in the modified Geller-Seifter task were assessed. First, the predictive validity of the task was confirmed by assessing the effects of multiple anxiolytic and non-anxiolytic compounds on punished and unpunished responding.

METHODS

Rats were trained in the modified Geller-Seifter task. After successful acquisition of the task, chlordiazepoxide, diazepam, MPEP, haloperidol, GS39783, 8-OH-DPAT, alprazolam and CGP46381 were tested consecutively. For each test compound, doses were administered in a randomized, counter-balanced, within-subjects design. Drug tests were performed only when rats exhibited baseline performance (the punished and time-out response rates were less than 10% of the unpunished response rate).

RESULTS

Chlordiazepoxide, diazepam, alprazolam and MPEP released punished responding with variable effects on unpunished responding. Haloperidol had a small but significant effect on punished responding at an intermediate dose, and decreased unpunished responding at the highest dose tested. In contrast, administration of the GABA(B) receptor positive modulator GS398783 or the GABA(B) receptor antagonist CGP46381 at doses up to 30 mg/kg had no effects on either punished or unpunished responding. The 5-HT(1A) agonist 8-OH-DPAT did not release punished responding, but significantly decreased unpunished responding at the highest dose tested.

SUMMARY

The modified Geller-Seifter task generally exhibits good predictive validity for anxiolytic-like compounds. Neither GABA(B) receptor positive allosteric modulation nor blockade exhibited anxiolytic-like properties in the modified Geller-Seifter task. The 5-HT(1A) partial agonist buspirone was similarly ineffective.

Olanzapine-induced weight gain in the rat: role of 5-HT2C and histamine H1 receptors

INTRODUCTION

Substantial increases in body weight can be induced by several antipsychotic drugs, most notably olanzapine and clozapine. Antagonism at certain receptors, particularly 5-HT2C and histamine H1 receptors, is implicated in this effect.

MATERIALS AND METHODS

We have investigated the contribution of effects at these receptors to olanzapine-induced weight gain occurring over 5 days following daily intraperitoneal drug injections in groups of eight female rats.

RESULTS

Olanzapine (2 mg/kg) and the 5-HT2C antagonist SB 243213 (1 mg/kg), but not the histamine H1 antagonist mepyramine (1 mg/kg), produced significant increases in percentage body weight above vehicle; olanzapine showed a significantly greater effect than SB 243213. Haloperidol (0.1 mg/kg) alone or with mepyramine had no significant effects on weight gain, while with SB 243213 and with both SB 243213 and mepyramine, it showed olanzapine-like increases in weight.

CONCLUSION

These results suggest that 5-HT2C receptor antagonism or inverse agonism, in the presence of D2 receptor antagonism, may contribute to olanzapine-induced weight gain.

Role of 5-HT receptor mechanisms in sub-chronic PCP-induced reversal learning deficits in the rat

RATIONALE

5-HT receptor mechanisms have been suggested to mediate improvements in cognition in schizophrenia.

AIM

The aim of this study was to investigate the involvement of 5-HT receptor mechanisms in sub-chronic phencyclidine (PCP)-induced reversal learning deficits in female rats, a task of relevance to schizophrenia.

METHODS

Adult female hooded Lister rats were trained to perform an operant reversal learning task and then received sub-chronic PCP (2 mg/kg) or vehicle intraperitoneally (i.p.) twice daily for 7 days, followed by 7-day washout. Rats then received an acute dose of the 5-HT(7) receptor antagonist SB-269970A (1.0, 3.0, and 10.0 mg/kg, i.p.) or vehicle. In experiment 2, PCP-treated rats received the selective 5-HT(2C) receptor antagonist, SB-243213A acutely (1.0, 3.0, and 10.0 mg/kg, i.p.) or vehicle. In experiment 3, PCP-treated rats received the 5-HT(1A) receptor partial agonist, buspirone (0.15625, 0.3125, and 0.625 mg/kg, i.p.) in combination with the selective 5-HT(1A) receptor antagonist WAY-100635 (0.3 and 1.0 mg/kg).

RESULTS

In all experiments, sub-chronic PCP significantly impaired reversal phase performance (P < 0.01-0.001), with no effect in the initial phase. SB-269970A at 3.0 and 10.0 mg/kg significantly improved the PCP-induced deficit (P < 0.05). SB-243213A also significantly attenuated the deficit at 10 mg/kg (P < 0.05). In experiment 3, buspirone attenuated the deficit with significant effects at 0.3125 and 0.625 mg/kg (P < 0.05). WAY-100635 at 0.3 and 1.0 mg/kg produced a partial attenuation of buspirone's effect as buspirone (0.3125 mg/kg) in the presence of WAY-100635 did not significantly reverse the PCP-induced deficit.

CONCLUSIONS

These studies implicate the role of 5-HT(7), 5-HT(2C), and 5-HT(1A) receptors in the improvement of cognitive dysfunction of relevance to schizophrenia.

Mechanisms contributing to the phase-dependent regulation of neurogenesis by the novel antidepressant, agomelatine, in the adult rat hippocampus

Agomelatine is a novel antidepressant acting as a melatonergic receptor agonist and serotonergic (5-HT(2C)) receptor antagonist. In adult rats, chronic agomelatine treatment enhanced cell proliferation and neurogenesis in the ventral hippocampus (VH), a region pertinent to mood disorders. This study compared the effects of agomelatine on cell proliferation, maturation, and survival and investigated the cellular mechanisms underlying these effects. Agomelatine increased the ratio of mature vs immature neurons and enhanced neurite outgrowth of granular cells, suggesting an acceleration of maturation. The influence of agomelatine on maturation and survival was accompanied by a selective increase in the levels of BDNF (brain-derived neurotrophic factor) vs those of VEGF (vascular endothelial factor) and IGF-1 (insulin-like growth factor 1), which were not affected. Agomelatine also activated several cellular signals (extracellular signal-regulated kinase1/2, protein kinase B, and glycogen synthase kinase 3beta) known to be modulated by antidepressants and implicated in the control of proliferation/survival. Furthermore, as agomelatine possesses both melatonergic agonist and serotonergic (5-HT(2C)) antagonist properties, we determined whether melatonin and 5-HT(2C) receptor antagonists similarly influence cell proliferation and survival. Only the 5-HT(2C) receptor antagonists, SB243,213 or S32006, but not melatonin, mimicked the effects of agomelatine on cell proliferation in VH. The promoting effect of agomelatine on survival was not reproduced by the 5-HT(2C) receptor antagonists or melatonin alone. However, it was blocked by a melatonin antagonist, S22153. These results show that agomelatine treatment facilitates all stages of neurogenesis and suggest that a joint effect of melatonin agonism and 5HT(2C) antagonism may be involved in promotion by agomelatine of survival in the hippocampus.

Lack of tolerance to anxiolysis and withdrawal symptoms in mice repeatedly treated with AC-5216, a selective TSPO ligand

AC-5216, a ligand for the translocator protein (18 kDa) (TSPO), produces anxiolytic-like effects in animal models of anxiety without causing the side effects normally associated with conventional benzodiazepines. This study aimed to investigate whether repeated administration of AC-5216 induces tolerance to anxiolytic-like effects of AC-5216 and produces withdrawal on abrupt cessation, and compare the results with those of diazepam. In the tolerance experiment, AC-5216 (0.1 mg/kg, p.o.) produced significant anxiolytic-like effects in both groups of mice pretreated with the vehicle and AC-5216 twice daily for 14 days. Diazepam (0.1 mg/kg, p.o.) also retained its anxiolytic effects in mice repeatedly treated with diazepam. In the withdrawal experiment, mice were orally treated with either AC-5216 (0.1, 1 or 10 mg/kg; twice daily) or diazepam (0.1, 1 or 10 mg/kg; twice daily) for 14 days, and examined, during a treatment withdrawal period, for anxiogenic-like effects in the social interaction test, and for body weight loss as indices of emotional and somatic withdrawal symptoms, respectively. In AC-5216-treated groups, neither anxiogenic-like effects nor body weight loss was observed upon treatment withdrawal at any of the doses tested. In contrast, in diazepam 1 mg/kg- and 10 mg/kg-treated groups, treatment withdrawal not only induced anxiogenic-like effects on the second day of the withdrawal period, but also decreased body weight gain and brought about body weight loss in mice. These findings indicate that AC-5216 when repeatedly administered does not induce tolerance to its anxiolytic-like effects or withdrawal symptoms.

Discriminative stimulus properties of the atypical antidepressant, mirtazapine, in rats: a pharmacological characterization

RATIONALE

Though interoceptive properties of antidepressants have been described, discriminative stimulus (DS) properties of mirtazapine, which does not affect monoamine reuptake, remain uncharacterized.

OBJECTIVES

The objectives of the study are to train rats to recognize a mirtazapine DS, then perform substitution studies with other antidepressants and drugs acting at sites occupied by mirtazapine.

MATERIALS AND METHODS

Using a two-lever, fixed-ratio 10 schedule, rats were trained to discriminate mirtazapine (2.5 mg/kg, i.p.) from saline.

RESULTS

Sessions, 63 +/- 8, were necessary to reach the criterion for 14 rats that all subsequently recognized (100%) mirtazapine at the training dose. Mirtazapine blocks serotonin (5-HT)(2C) receptors, and the 5-HT(2C) antagonists, SB242,084, SB243,213 and S32006, revealed dose-dependent and full (> or =80%) substitution at doses of 2.5, 2.5, and 0.63 mg/kg, respectively. By contrast, the 5-HT(2A) antagonists, MDL100,907 and SR46349-B, the 5-HT(2B) antagonist, SB204,741, and the 5-HT(3) antagonist, ondansetron, showed no significant substitution. Though mirtazapine indirectly recruits 5-HT(1A) receptors, the 5-HT(1A) agonists, buspirone and 8-OH-DPAT, did not substitute. Mirtazapine blocks alpha(2)-adrenoceptors, but several alpha(2)-adrenoceptor antagonists (yohimbine, RX821,002 and atipamezole) failed to substitute. Despite blockade by mirtazapine of histamine H(1) receptors, no substitution was seen with the selective H(1) antagonist, pyrilamine. Finally, the selective noradrenaline reuptake inhibitor, reboxetine (0.16), fully substituted for mirtazapine, whereas the 5-HT/noradrenaline reuptake inhibitors, duloxetine and S33005, several 5-HT reuptake inhibitors (citalopram, fluvoxamine, and paroxetine) and the dopamine reuptake inhibitors, bupropion and GBR12,935, did not substitute.

CONCLUSION

Mirtazapine elicits a DS in rats for which selective antagonists at 5-HT(2C) receptors display dose-dependent substitution, whereas drugs acting at other sites recognized by mirtazapine are ineffective.

Serotonin2C receptors in the medial prefrontal cortex facilitate cocaine-induced dopamine release in the rat nucleus accumbens

A functional balance between excitatory and inhibitory control over dopamine (DA)-dependent behavioral and neurochemical effects of cocaine is afforded by the serotonin(2C) receptor (5-HT(2C)R) located within the ventral tegmental area and the nucleus accumbens (NAc). The 5-HT(2C)R located in the medial prefrontal cortex (mPFC) has also been shown to inhibit cocaine-induced behaviors perhaps through inhibition of DA function in the NAc. Using in vivo microdialysis in halothane-anesthetized rats, we tested this hypothesis by assessing the influence of mPFC 5-HT(2C)Rs on cocaine-induced DA outflow in the NAc shell. Intra-mPFC injection of the 5-HT(2C)R agonist Ro 60-0175 at 5 microg/0.2 microl, but not 1 microg/0.2 microl, potentiated the increase in accumbal DA outflow induced by the intraperitoneal administration of 10 mg/kg of cocaine. Conversely, cocaine-induced accumbal DA outflow was significantly reduced by the intra-mPFC injection of the selective 5-HT(2C)R antagonist SB 242084 (0.5 microg/0.2 microl) or SB 243213 (0.5 and 1 microg/0.2 microl). These results show that mPFC 5-HT(2C)Rs exert a positive control over cocaine-induced accumbal DA outflow. Observations further support the idea that the overall action of central 5-HT(2C)Rs on accumbal DA output is dependent on the functional balance among different 5-HT(2C)R populations located within the mesocorticoaccumbens system, and that 5-HT(2C)Rs can modulate DA-dependent behaviors independently of changes of accumbal DA release itself.

Animal models of anxiety and anxiolytic drug action

Animal models of anxiety attempt to represent some aspect of the etiology, symptomatology, or treatment of human anxiety disorders, in order to facilitate their scientific study. Within this context, animal models of anxiolytic drug action can be viewed as treatment models relevant to the pharmacological control of human anxiety. A major purpose of these models is to identify novel anxiolytic compounds and to study the mechanisms whereby these compounds produce their anxiolytic effects. After a critical analysis of "face," "construct," and "predictive" validity, the biological context in which animal models of anxiety are to be evaluated is specified. We then review the models in terms of their general pharmacological profiles, with particular attention to their sensitivity to 5-HTIA agonists and antidepressant compounds. Although there are important exceptions, most of these models are sensitive to one or perhaps two classes of anxiolytic compounds, limiting their pharmacological generality somewhat, but allowing in depth analysis of individual mechanisms of anxiolytic drug action (e.g., GABAA agonism). We end with a discussion of possible sources of variability between models in response to 5-HTIA agonists and antidepressant drugs.

Current status of inverse agonism at serotonin2A (5-HT2A) and 5-HT2C receptors

Contemporary receptor theory was developed to account for the existence of constitutive activity, as defined by the presence of receptor signaling in the absence of any ligand. Thus, ligands acting at a constitutively active receptor, can act as agonists, antagonists, and inverse agonists. In vitro studies have also revealed the complexity of ligand/receptor interactions including agonist-directed stimulus trafficking, a finding that has led to multi-active state models of receptor function. Studies with a variety of cell types have established that the serotonin 5-HT(2A) and 5-HT(2C) receptors also demonstrate constitutive activity and inverse agonism. However, until recently, there has been no evidence to suggest that these receptors also demonstrate constitutive activity and hence reveal inverse agonist properties of ligands in vivo. This paper describes our current knowledge of constitutive activity in vitro and then examines the evidence for constitutive activity in vivo. Both the serotonin 5-HT(2A) and 5-HT(2C) receptors are involved in a number of physiological and behavioral functions and are the targets for treatment of schizophrenia, anxiety, weight control, Parkinsonism, and other disorders. The existence of constitutive activity at these receptors in vivo, along with the possibility of inverse agonism, provides new avenues for drug development.

S32006, a novel 5-HT2C receptor antagonist displaying broad-based antidepressant and anxiolytic properties in rodent models

RATIONALE

Serotonin (5-HT)(2C) receptors are implicated in the control of mood, and their blockade is of potential interest for the management of anxiodepressive states.

OBJECTIVES

Herein, we characterized the in vitro and in vivo pharmacological profile of the novel benzourea derivative, S32006.

MATERIALS AND METHODS

Standard cellular, electrophysiological, neurochemical, and behavioral procedures were used.

RESULTS

S32006 displayed high affinity for human (h)5-HT(2C) and h5-HT(2B) receptors (pK (i)s, 8.4 and 8.0, respectively). By contrast, it had negligible (100-fold lower) affinity for h5-HT(2A) receptors and all other sites examined. In measures of Gq-protein coupling/phospholipase C activation, S32006 displayed potent antagonist properties at h5-HT(2C) receptors (pK (B) values, 8.8/8.2) and h5-HT(2B) receptors (7.8/7.7). In vivo, S32006 dose-dependently (2.5-40.0 mg/kg, i.p. and p.o.) abolished the induction of penile erections and a discriminative stimulus by the 5-HT(2C) receptor agonist, Ro60,0175, in rats. It elevated dialysis levels of noradrenaline and dopamine in the frontal cortex of freely moving rats, and accelerated the firing rate of ventrotegmental dopaminergic and locus ceruleus adrenergic neurons. At similar doses, S32006 decreased immobility in a forced-swim test in rats, reduced the motor depression elicited by 5-HT(2C) and alpha(2)-adrenoceptor agonists, and inhibited both aggressive and marble-burying behavior in mice. Supporting antidepressant properties, chronic (2-5 weeks) administration of S32006 suppressed "anhedonia" in a chronic mild stress procedure and increased both expression of BDNF and cell proliferation in rat dentate gyrus. Finally, S32006 (0.63-40 mg/kg, i.p. and p.o) displayed anxiolytic properties in Vogel conflict and social interaction tests in rats.

CONCLUSION

S32006 is a potent 5-HT(2C) receptor antagonist, and possesses antidepressant and anxiolytic properties in diverse rodent models.

Comparison of the effects of deramciclane, ritanserin and buspirone on extracellular dopamine and its metabolites in striatum and nucleus accumbens of freely moving rats

In the present study, we assessed the effect of single graded doses of a putative anxiolytic compound, the 5-HT(2A/C )antagonist, deramciclane fumarate (EGIS-3886), on the dopamine efflux and metabolism in nucleus accumbens and striatum and thus evaluated the dose window for deramciclane to cause adverse effects related to the brain dopaminergic system. Dual probe in vivo microdialysis in freely moving rats was used to compare the effects of graded doses of deramciclane fumarate (3, 10 and 30 mg/kg), 5-HT(2A/C )antagonist ritanserin (1 mg/kg) and a partial 5-HT(1A) agonist buspirone hydrochloride (5 mg/kg) on the extracellular levels of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in nucleus accumbens and striatum assayed by high performance liquid chromatography with electrochemical detection. The indirect dopamine agonist, D-amphetamine sulfate (2 mg/kg), was used as a positive control. Ritanserin, buspirone and deramciclane 3 and 10 mg/kg had no significant effects on the extracellular dopamine levels in either brain area but deramciclane 30 mg/kg significantly increased accumbal dopamine as well as DOPAC and HVA in both brain areas. As expected, the positive control D-amphetamine significantly increased both striatal and accumbal dopamine levels. The effects of buspirone or the highest deramciclane dose and D-amphetamine on DOPAC and HVA levels were opposite; buspirone and deramciclane increased while D-amphetamine decreased the metabolite levels in both brain areas. The results indicate that a single high dose of deramciclane has the neuroleptic- or buspirone-like effect, particularly in mesolimbic regions. There is at least a 5-fold margin between the anxiolytic and neuroleptic doses of deramciclane in the rat.

SB-649915-B, a novel 5-HT1A/B autoreceptor antagonist and serotonin reuptake inhibitor, is anxiolytic and displays fast onset activity in the rat high light social interaction test

Preclinically, the combination of an SSRI and 5-HT autoreceptor antagonist has been shown to reduce the time to onset of anxiolytic activity compared to an SSRI alone. In accordance with this, clinical data suggest the coadministration of an SSRI and (+/-) pindolol can decrease the time to onset of anxiolytic/antidepressant activity. Thus, the dual-acting novel SSRI and 5-HT(1A/B) receptor antagonist, SB-649915-B, has been assessed in acute and chronic preclinical models of anxiolysis. SB-649915-B (0.1-1.0 mg/kg, i.p.) significantly reduced ultrasonic vocalization in male rat pups separated from their mothers (ED(50) of 0.17 mg/kg). In the marmoset human threat test SB-649915-B (3.0 and 10 mg/kg, s.c.) significantly reduced the number of postures with no effect on locomotion. In the rat high light social interaction (SI), SB-649915-B (1.0-7.5 mg/kg, t.i.d.) and paroxetine (3.0 mg/kg, once daily) were orally administered for 4, 7, and 21 days. Ex vivo inhibition of [(3)H]5-HT uptake was also measured following SI. SB-649915-B and paroxetine had no effect on SI after 4 days. In contrast to paroxetine, SB-649915-B (1.0 and 3.0 mg/kg, p.o., t.i.d.) significantly (p<0.05) increased SI time with no effect on locomotion, indicative of an anxiolytic-like profile on day 7. Anxiolysis was maintained after chronic (21 days) administration by which time paroxetine also increased SI significantly. 5-HT uptake was inhibited by SB-649915-B at all time points to a similar magnitude as that seen with paroxetine. In conclusion, SB-649915-B is acutely anxiolytic and reduces the latency to onset of anxiolytic behavior compared to paroxetine in the SI model.

The expression and functional significance of the serotonin(2C) receptor in murine contact allergy

Serotonin (5-hydroxytryptamine, 5-HT) was proposed to modulate murine contact allergy by binding to 5-HT(1A/2A) receptors (R). We examined the expression of 5-HT(2C)R in the skin of mice with contact allergy, as well as the effects of an agonist and antagonist of this receptor on the elicitation phase of this type of allergy. Immunohistochemistry revealed the presence of 5-HT(2C)R on epidermal dendritic cells, and in the inflamed skin the cells expressing this antigen were increased in number (P < 0.01) and exhibited longer dendrites than in the control tissue. Furthermore, the majority of these cells also stained positively for I-A, a specific marker for Langerhans cells (LCs). Treatment of the skin of sensitized mice in vivo with RO60-0175 (0.5 and 1.0 mg/kg, once daily for 3 days prior to the challenge with antigen), an agonist for 5-HT(2C)R, enhanced the degree of contact eczema (P < 0.05 and P < 0.01 for the two doses respectively), as indicated by ear thickness. This enhancement could be prevented (P < 0.001) by the 5-HT(2C)R antagonist SB 242084 at 3 mg/kg. Addition of 5 x 10(-5) mol/l RO60-0175 to murine XS52 cells, which resembles LCs, potentiated their secretion of interleukin (IL)-1beta (P < 0.05); whereas 10(-10) mol/l attenuated this secretion (P < 0.05). Under the same conditions, the level of IL-1beta mRNA in these cells (as assessed by RT-PCR) was unaltered suggesting that this agonist may exert its effect on IL-1beta secretion at the post-transcriptional or even at the secretory level. In conclusion, our findings indicate that the 5-HT(2C)R is involved in modulating contact allergy in mice.

Pharmacological, but not genetic, disruptions in 5-HT(2C) receptor function attenuate LPS anorexia in mice

Peripheral administration of bacterial lipopolysaccharide (LPS) elicits anorexia in several species, including rats and mice. There is strong evidence that antagonism of serotonergic activity at 2C receptors (5-HT(2C)R) attenuates LPS anorexia in rats. Here we used pharmacological and genetic approaches to examine the role of the 5-HT(2C)R in LPS anorexia in mice. In Experiment 1, SB 242084, a potent and selective 5-HT(2C) antagonist (0.3 mg/kg) was injected intraperitoneally 15 min before intraperitoneal LPS (2 microg/kg) injections just prior to dark onset in c57BL/6 mice. Food intake was recorded 1, 2 and 4 h after LPS administration. In Experiment 2, we recorded 2, 4 and 24 h food intake following dark onset intraperitoneal LPS (0.125, 0.25, 0.5, 1 and 2 microg/kg) injections in mice with a genetic deletion of 5-HT(2C)R and their WT controls. Our pharmacological results suggest that at least part of the anorexia following peripheral LPS administration is mediated by an increase in 5-HT-ergic activity at the 5-HT(2C)R. Our genetic data, in contrast, suggest that 5-HT(2C)R is not a necessary part of LPS anorexia.

Isoindolone derivatives, a new class of 5-HT2C antagonists: Synthesis and biological evaluation

Two independent approaches resulted in the identification of a series of isoindolone derivatives as potent and selective 5-HT2C antagonists. From a Medicinal Chemistry perspective this template was considered interesting as it allowed the incorporation of the carbon-carbon double bond of an earlier dihydropyrrolone series in an aromatic system within a comparatively simple and compact motif. Additionally an in silico screening approach of the corporate database using a 5-HT2C pharmacophore model resulted in the identification of a related structure containing this template. The strategy used to optimise potency at the target receptor and to improve the pharmacokinetic profile is described, resulting in molecules combining high potency with good selectivity and oral bioavailability.

Anxiolytic activity of a novel potent serotonin 5-HT2C receptor antagonist FR260010: A comparison with diazepam and buspirone

Hyperfunction of brain 5-hydroxytryptamine(2C) (5-HT(2C)) receptor is suggested to be involved in anxiety as evidenced by the fact that a putative 5-HT(2C) receptor agonist 1-(m-chlorophenyl)-piperazine (m-CPP) causes anxiety in humans. We have recently identified FR260010 (N-[3-(4-methyl-1H-imidazol-1-yl)phenyl]-5,6-dihydrobenzo[h]quinazolin-4-amine dimethanesulfonate) as novel 5-HT(2C) receptor antagonist from diaryl amine derivatives, and here characterized in vitro and in vivo profiles of the compound. FR260010 showed high affinity for human 5-HT(2C) receptor (K(i): 1.10 nM) and high selectivity over 5-hydroxytryptamine(2A) (5-HT(2A)) receptor (K(i): 386 nM) and many other transmitter receptors. FR260010 showed antagonist activity at human 5-HT(2C) receptor in an intracellular calcium assay and showed no detectable intrinsic activity. The compound dose-dependently inhibited the hypolocomotion (ID(50): 1.89 mg/kg, p.o.) and hypophagia (ID(50): 2.84 mg/kg, p.o.) in rats induced by m-CPP, putative indices of brain 5-HT(2C) receptor antagonist activity. We then compared the effects of FR260010 with those of two other anxiolytics belonging to different classes, diazepam and buspirone, in anxiety models in rats and mice and adverse effect tests in mice. FR260010 (0.1-3.2 mg/kg, p.o.) and diazepam (1-10 mg/kg, p.o.) decreased behavioral indices of anxiety in all models, whereas buspirone (0.32-10 mg/kg, p.o.) did not significantly affect them in any models. In adverse effect tests, FR260010 and buspirone showed modest effects, whereas diazepam showed significant effects in all tests. These results suggest that FR260010 is a novel, potent, orally active and brain penetrable antagonist of 5-HT(2C) receptor, and may have therapeutic potential for treatment of anxiety, with more desirable profiles than benzodiazepines or 5-hydroxytryptamine(1A) (5-HT(1A)) receptor agonists.