5-HT Receptors and Temperature Homeostasis.

The present review summarizes the data concerning the influence of serotonin (5-HT) receptors on body temperature in warm-blooded animals and on processes associated with its maintenance. This review includes the most important part of investigations from the first studies to the latest ones. The established results on the pharmacological activation of 5-HT1A, 5-HT3, 5-HT7 and 5-HT2 receptor types are discussed. Such activation of the first 3 type of receptors causes a decrease in body temperature, whereas the 5-HT2 activation causes its increase. Physiological mechanisms leading to changes in body temperature as a result of 5-HT receptors' activation are discussed. In case of 5-HT1A receptor, they include an inhibition of shivering and non-shivering thermogenesis, as well simultaneous increase of peripheral blood flow, i.e., the processes of heat production and heat loss. The physiological processes mediated by 5-HT2 receptor are opposite to those of the 5-HT1A receptor. Mechanisms of 5-HT3 and 5-HT7 receptor participation in these processes are yet to be studied in more detail. Some facts indicating that in natural conditions, without pharmacological impact, these 5-HT receptors are important links in the system of temperature homeostasis, are also discussed.

Recent Developments on Future Antidepressant-related Serotonin Receptors.

Conventional serotonin-enhancing antidepressants including selective serotonin reuptake inhibitors (SSRIs) and serotonin and norepinephrine reuptake inhibitors (SNRIs) have shown effectiveness in the treatment of major depression, but their significant limitations such as slowness of action have led to intensive research efforts to develop new antidepressants. Increased synaptic neurotransmission of serotonin (5-hdroxytryptamine; 5-HT) through orchestration of stimulation and blockade of various subtypes of 5-HT receptors is involved in the mechanisms of action of SSRIs. Agonists at the 5-HT1A, 5-HT1B, 5-HT2C, 5-HT4, and 5-HT6 receptors and antagonists at the 5-HT1A, 5-HT2A, 5-HT2C, 5-HT3, 5- HT6, and 5-HT7 receptors have shown antidepressant properties in clinical and preclinical studies. However, paradoxical antidepressant-like effects of both agonists and antagonists at particular 5-HT receptors suggest the need to consider the neurochemical mechanisms of each 5-HT receptor subtype. Therefore, better knowledge of the involvement of individual 5-HT receptors in the mechanisms of action of currently used antidepressants as well as antidepressant effects of selective ligands of 5- HT receptor subtypes will provide opportunities for the development of future antidepressants with more rapid onset of action, fewer side effects, and better efficacy than SSRIs.

Antidepressant-like activity of aroxyalkyl derivatives of 2-methoxyphenylpiperazine and evidence for the involvement of serotonin receptor subtypes in their mechanism of action.

Since serotonin (5-HT) is strongly involved in the etiology and pathophysiology of depression, the development of new antidepressants is still based on the serotonergic system. The complexity of serotonergic system provides an opportunity for the development of compounds with multiple and complementary mechanism of action. This study describes serotonin receptor profile, functional characterization, and pharmacological in vivo evaluation of new aroxyalkyl derivatives of 2-methoxyphenylpiperazine. The obtained results allowed for the identification of compound 3, (1-[3-(2,6-dimethylphenoxy)propyl]-4-(2-methoxyphenyl)piperazine hydrochloride), a partial 5-HT1A receptor agonist, and 5-HT2A receptor antagonist, with high affinity toward 5-HT7 receptors, showing antidepressant- and anxiolytic-like properties. Moreover, 5-HT1A receptor activation is crucial for the antidepressant-like activity of compound 3. The rest of the compounds (except compounds 1 and 9) showed antidepressant but not anxiolytic-like properties, which did not result from 5-HT1A receptors activation. Furthermore, the compounds are 5-HT1A and weak 5-HT3 receptors antagonists, and some of them 5-HT2A antagonists. Moreover, none of the studied compounds impaired motor coordination at antidepressant-like doses. Since the studied compounds exhibited activity in behavioral assays and interacted with various receptors, the results of our experiments are very promising and require further studies.

Regulatory Effects of 5-Hydroxytryptamine Receptors on Voiding Function.

UNLABELLED: A growing body of evidence suggests that 5-hydroxytryptamine (5-HT; serotonin) has both physiological and pathological functions in the lower urinary tract. A wide variety of 5-HT receptor subtypes are variably expressed in different organs, both peripheral and central. On urinary bladder smooth muscle, 5-HT1A, 5-HT2, 5-HT3, and 5-HT7 subtypes could function as postjunctional receptors. Postjunctional 5-HT2 receptors induce detrusor contraction of the bladder body. 5-HT1A is suggested to have a similar effect to 5-HT2, while 5-HT3 might suppress detrusor contraction evoked by direct muscle stimulation. Postjunctional 5-HT7 is reported to induce relaxation of the bladder neck, which might be required for efficient voiding. 5-HT1A, 5-HT2A, 5-HT2C, 5-HT3, 5-HT4, and 5-HT7 subtypes also could act as prejunctional receptors in autonomic excitatory nerve terminals. 5-HT2A, 5-HT2C, 5-HT3, 5-HT4, and 5-HT7 subtypes facilitate the neurogenic contraction of the detrusor by enhancing cholinergic or purinergic transmission, whereas 5-HT1A receptors might inhibit the release of acetylcholine in the detrusor. Furthermore, 5-HT1D could be involved in the suppression of ATP release from the urothelium, aiding visceral sensation of the urinary bladder. In the central pathways controlling the micturition reflex, 5-HT1A, 5-HT2A, and 5-HT7 are involved in regulation of bladder and urethral sphincter activities. Their functions, especially that of 5-HT1A, vary in a species- and site (spinal or supraspinal)- dependent manner. In addition to urinary bladder, 5-HT could be involved in prostate contraction and cell proliferation. Evidence indicates that 5-HT receptor subtypes may be novel therapeutic targets for lower urinary tract symptoms. FUNDING: Grants-in-Aid for Scientific Research (C) (KAKENHI 23590707, 24590722, and 26460694) from the Japan Society for the Promotion of Science.

Expression of 5-Hydroxytryptamine Receptors in Human Urinary Bladders with Benign Prostatic Hyperplasia.

INTRODUCTION: This study investigated the mRNA expression pattern and distribution of 5-hydroxytryptamine (5-HT) receptors 5-HT2A, 5-HT2B, 5-HT3A, 5-HT4, and 5-HT7 within the urothelium and detrusor of normal bladder tissue and in the urothelium of bladders from patients with benign prostatic hyperplasia (BPH). METHODS: Normal urinary bladder specimens were obtained from 13 patients undergoing radical cystectomy due to bladder cancer (normal group) and BPH specimens were obtained from 27 benign prostatic obstruction patients receiving transurethral prostatectomy or retropubic prostatectomy. Receptor subtype mRNA expression was determined by real-time reverse transcription polymerase chain reaction on urothelium, detrusor, and whole mucosal preparations. Receptor distribution was determined by immunohistochemistry. RESULTS: In normal tissues, expressions of 5-HT2B and 5-HT7 receptor mRNAs in the urothelium, detrusor, and whole mucosa were greater than the average expression for all receptor subtype mRNAs. 5-HT2B receptor protein was distributed in the apical urothelium and among the detrusor smooth muscle layers. In contrast, the 5-HT7 receptors were within the urothelium middle cell layers and detrusor smooth muscle cells. The expression pattern of each 5-HT receptor subtype mRNA within the BPH urothelium was similar to that in the normal urothelium. The expression level of 5-HT2A receptor mRNA in the BPH group was significantly lower than the normal group; however, the expressions of both 5-HT3A and 5-HT7 mRNAs were significantly higher. The expressions of both 5-HT2B and 5-HT4 mRNAs were not significantly different between the normal and BPH groups. CONCLUSION: In normal urinary bladders, the expressions of both 5-HT2B and 5-HT7 mRNAs were higher compared to the 5-HT2A, 5-HT3A, and 5-HT4 mRNAs. The distributions of 5-HT2B and 5-HT7 receptors were different in the urothelium and detrusor layers. The 5-HT3A and 5-HT7 receptor mRNAs in the BPH group were significantly higher compared to the normal urothelium, while the 5-HT2A mRNA was significantly lower. FUNDING: Asahi Kasei Pharma Corporation.

Effects of Kaixin Jieyu Decoction () on behavior, monoamine neurotransmitter levels, and serotonin receptor subtype expression in the brain of a rat depression model.

OBJECTIVE: To determine the mechanisms underlying the anti-depressant effects of Kaixin Jieyu Decoction (, KJD) by investigating the effects of KJD on behavior, monoamine neurotransmitter levels, and serotonin (5-HT) receptor subtype expression in the brain in a rat model of depression. METHODS: The rat depression model was established using chronic unpredictable mild stress (CUMS). Forty-eight Sprague Dawley rats were randomly divided into control, depression model (CUMS), CUMS+KJD (7.7 g/kg(-1)·d(-1) of crude drug), and CUMS+fluoxetine (2.4 mg/kg(-1)·d(-1)) groups (n=12 in each group), and the treatments lasted for 21 days. We regularly evaluated body weight, sucrose consumption, and horizontal and vertical activity scores in open-field tests. The content of the monoamine neurotransmitters 5-HT, norepinephrine (NE), and dopamine (DA) and the DA metabolite homovanillic acid in the cerebral cortex, and 5-HT1A and 5-HT2A receptor mRNA in the cerebral cortex and the hippocampus, were determined respectively by high-performance liquid chromatography-coularray electrochemical detector and real-time polymerase chain reaction. RESULTS: Compared with the control group, CUMS rats showed a variety of depression-like behavioral changes, including a significant reduction in body weight, sucrose consumption, and horizontal and vertical activity scores in open-field tests (P<0.05 or P<0.01), and a significant decrease in 5-HT and NE levels and 5-HT2A receptor mRNA expression. In contrast, they showed a significant increase in 5-HT1A receptor mRNA expression in the cerebral cortex. In the hippocampus, 5-HT1A receptor mRNA expression was lower whereas 5-HT2A receptor mRNA expression was higher than in the control group (P<0.05 or P<0.01). Treatment with KJD or fluoxetine partially attenuated these changes (P<0.05 or P<0.01). CONCLUSION: KJD could normalize the levels of 5-HT and NE and adjust the balance of 5-HT1A and 5-HT2A receptor expression in rat cerebrum, and this may be one of mechanisms of antidepressant effects of KJD.

Pharmacology of serotonin and female sexual behavior.

In this review, first a historical perspective of serotonin's (5-HT) involvement in female sexual behavior is presented. Then an overview of studies implicating 5-HT is presented. The effect of drugs that increase or decrease CNS levels of 5-HT is reviewed. Evidence is presented that drugs which increase 5-HT have negative effects on female sexual behavior while a decrease in 5-HT is associated with facilitation of sexual behavior. Studies with compounds that act on 5-HT1, 5-HT2 or 5-HT3 receptors are discussed. Most evidence indicates that 5-HT1A receptor agonists inhibit sexual behavior while 5-HT2 or 5-HT3 receptors may exert a positive influence. There is substantial evidence to support a role for 5-HT in the modulation of female consummatory sexual behavior, but studies on the role of 5-HT in other elements of female sexual behavior (e.g. desire, motivation, sexual appetite) are few. Future studies should be directed at determining if these additional components of female sexual behavior are also modulated by 5-HT.

Serotonin 1A, 1B, and 7 receptors of the rat medial nucleus accumbens differentially regulate feeding, water intake, and locomotor activity.

Serotonin (5-HT) signaling has been widely implicated in the regulation of feeding behaviors in both humans and animal models. Recently, we reported that co-stimulation of 5-HT1&7 receptors of the anterior medial nucleus accumbens with the drug 5-CT caused a dose-dependent decrease in food intake, water intake, and locomotion in rats (Pratt et al., 2009). The current experiments sought to determine which of three serotonin receptor subtypes (5-HT1A, 5-HT1B, or 5-HT7) might be responsible for these consummatory and locomotor effects. Food-deprived rats were given 2-h access to rat chow after stimulation of nucleus accumbens 5-HT1A, 5-HT1B, or 5-HT7 receptors, or blockade of the 5-HT1A or 5-HT1B receptors. Stimulation of 5-HT1A receptors with 8-OH-DPAT (at 0.0, 2.0, 4.0, and 8.0 µg/0.5 µl/side) caused a dose-dependent decrease in food and water intake, and reduced rearing behavior but not ambulation. In contrast, rats that received the 5-HT1B agonist CP 93129 (at 0.0, 1.0, 2.0 and 4.0 µg/0.5 µl/side) showed a significant dose-dependent decrease in water intake only; stimulation of 5-HT7 receptors (AS 19; at 0.0, 1.0, and 5.0 µg/0.5 µl/side) decreased ambulatory activity but did not affect food or water consumption. Blockade of 5-HT1A or 5-HT1B receptors had no lasting effects on measures of food consumption. These data suggest that the food intake, water intake, and locomotor effects seen after medial nucleus accumbens injections of 5-CT are due to actions on separate serotonin receptor subtypes, and contribute to growing evidence for selective roles of individual serotonin receptors within the nucleus accumbens on motivated behavior.

[Serotonin and its immune and physiological effects].

Now that the neurotransmitter serotonin modulates the immune system cells, and its main sources for antigenpresenting cells and lymphocytes are enterochromaffin cells of the gut, peripheral nerves, platelets and mast cells in case of inflammation. Immune cells uptake serotonin because they express receptors for this monoamine and intracellular serotonin transporters. The dendritic cells have a mechanism to transfer serotonin to T lymphocytes during antigen presentation. The macrophages and T cells have the ability to serotonin synthesis. Serotonin can influence mobility and proliferation of lymphocytes, phagocytosis, cytolytic properties, synthesis of chemokines and cytokines. Diversity of immunomodulating effects of serotonin is determined by heterogeneity of serotoninergic receptors. Immunomodulating action of serotonin is evidence of the close relationship between nervous and immune systems.

Involvement of serotonin receptor subtypes in the antidepressant-like effect of beta receptor agonist Amibegron (SR 58611A): an experimental study.

New therapeutic strategies against depression, with less side effects and thus greater efficacy in larger proportion of depressed patients, are needed. Amibegron (SR58611A) is the first selective ß3 adrenergic agent that has been shown to possess a profile of antidepressant activity in rodents. To investigate the involvement of serotonin receptors in the effects of amibegron, we used the serotonin 5HT1A receptor antagonist WAY-100635 (WAY) or serotonin 5HT2A-2C receptor antagonist ketanserin or serotonin 5HT3 receptor antagonist ondansetron in mice forced swimming test (FST). The locomotor activity was evaluated by measuring the total distance moved in the apparatus and the speed of the animals in the open field test. Imipramine (30mg/kg) significantly reduced immobility time compared to vehicle-treated group while amibegron (5 and 10mg/kg) dose dependently reduced immobility time in the FST. WAY(0.1mg/kg), ondansetron (1mg/kg), ketanserin(5mg/kg) had no effect on immobility time in naive mice while all of the drugs partially and significantly reversed amibegron (10mg/kg) induced decreasement in the immobility time in FST. None of the drugs alter locomotor activity in the open field test. The antidepressant-like effect of amibegron in the FST seems to be mediated by an interaction with serotonin 5-HT1A, serotonin 5-HT2A-2C and serotonin 5-HT3 receptors.

Targeting to 5-HT1F receptor subtype for migraine treatment: lessons from the past, implications for the future.

The effective anti-migraine drugs triptans, all bind with high affinity to three serotonin (5-HT) subtypes, the 5-HT1B, 5-HT1D and 5-HT1F. 5-HT1B mRNA is densely localized within smooth muscle, and less in the endothelium of cerebral blood vessels. This vascular distribution of 5-HT1B receptor has been shown to mediate the vasoconstrictive properties of the triptans, responsible for potential cardiac adverse events. Activation of 5-HT1D subtype, although effective in animal models of migraine, was not enough efficient to attenuate migraine attacks in clinical trials. The 5-HT1F receptor is located both in vessels and within the trigeminal ganglion (TG) and the trigeminal nucleus caudalis (Sp5C), but with the difference that the 5-HT1F receptor lack vasoconstrictive properties, making it an attractive target for new anti-migraine drugs. Selective activation of 5-HT1F receptor potently inhibited markers associated with electrical stimulation of the TG. Thus 5-HT1F receptor represents an ideal target for anti-migraine drugs. So far two selective 5-HT1F agonists have been tested in human trials for migraine: LY334370 and lasmiditan. Both molecules were efficient in attenuating migraine attacks with efficacy in the same range as oral sumatriptan 100mg, the gold standard for triptans. The LY334370 project withdrew because of toxicity in animals, while lasmiditan is still testing. In this review we present all the available preclinical and clinical data on the 5-HT1F agonists as a potential new class of anti-migraine drugs lacking vascular activity and we discuss related issues on the vascular and neuronal aspects of migraine pathogenesis.

Differential distribution of serotonin receptor subtypes in BNST(ALG) neurons: modulation by unpredictable shock stress.

The bed nucleus of the stria terminalis (BNST) plays a critical role in regulating the behavioral response to stress. Stressors that activate the BNST also activate serotonergic (5-HT) systems. Hence, maladaptive changes of 5-HT receptor expression may contribute to stress-induced anxiety disorders. The BNST contains three neuronal types, Type I-III neurons. However, little is known about 5-HT receptor subtypes mRNA expression in these neurons, or whether it can be modulated by stress. Whole-cell patch clamp recording from Type I-III neurons was used in conjunction with single cell reverse transcriptase polymerase chain reaction (RT-PCR) to characterize 5-HT receptor mRNA expression, and examine the effects of stress on this expression. We report that Type I neurons expressed mRNA transcripts predominantly for 5-HT(1A) and 5-HT(7) receptors. Type II neurons expressed transcripts for every 5-HT receptor except the 5-HT(2C) receptor. Type II neurons were divided into three sub-populations: Type IIA in which transcripts for 5-HT(3) and 5-HT(7) receptors predominate, Type IIB that mainly express 5-HT(1B) and 5-HT(4) receptor transcripts, and Type IIC in which transcripts for 5-HT(1A) and 5-HT(2A) receptors predominate. Type III neurons were also subdivided into two sub-populations; one that predominantly expressed transcripts for 5-HT(1A), 5-HT(1B) and 5-HT(2A) receptors, and another that mainly expressed transcripts for 5-HT(2C) receptor. Unpredictable shock stress (USS) caused a long-lasting increase in anxiety-like behavior, and a concomitant decrease in 5-HT(1A) transcript expression in Type I-III neurons, as well as an up-regulation of a transcriptional repressor of 5-HT(1A) gene expression, deformed epidermal autoregulatory factor 1 (Deaf-1). Significantly USS decreased 5-HT(1A) protein level, and increased the level of Deaf-1. USS also increased 5-HT(1B) transcript expression in Type III neurons, as well as 5-HT(7) expression in Type I and II neurons. These data suggest that cell type-specific disruption of 5-HT receptor expression in BNST(ALG) neurons may contribute to stress-induced anxiety disorders.

Identification of alternatively spliced multiple transcripts of 5-hydroxytryptamine receptor in mouse.

5-Hydroxytryptamine receptors (HTRs) are coded by seventeen different genes in mouse. One of them is htr4 that codes for the HTR4 receptor, a G-protein coupled receptor containing seven transmembrane domains. In mouse, the gene is reported to contain 6 exons and 5 introns. Our present study reports the presence of four transcript variants of this gene encoding different N-termini. These transcripts are expressed in neuronal as well as non-neuronal tissues of mouse. We have identified five novel coding exons present at the 5' end of the gene which splice with the published internal exon in an alternative manner making a total of five transcripts, four new transcript variants (T1, T2l, T2s and T3) and one published earlier. All five transcripts encoding different N-termini were expressed in mouse brain. It was interesting to note the expression of only T3 transcript that was also detected in heart muscle and is the only htr4 transcript expressed in heart. For the first time a transcript of htr4 gene was detected in the heart of the mouse which might help us to make use of small laboratory animals to study HTR4 in heart. As this transcript is unique to the heart it can serve as potential therapeutic target for various cardiovascular disorders and dysregulation of heart rate, atrial contraction and atrial relaxation. These variants display heterogeneous properties in terms of the presence of signal peptide, acetylation, phosphorylation and glycosylation. Thus alternative splicing of htr4 producing heterogeneous N-termini increases the diversity of the receptor.

Subtype specific roles of serotonin receptors in the spine formation of cortical neurons in vitro.

Dendritic spines are postsynaptic structures which are formed from filopodia. We examined roles of serotonin (5-HT) receptors in the spine formation. Embryonic rat cortical neurons were cultured for 10 or 14 days and treated by 5-HT receptor agonists for 24 h. At 11 days in vitro, 5-HT(1A) agonist increased filopodia density, whereas 5-HT(2A/2C) agonist increased the density of puncta and spines. At 15 days in vitro, 5-HT(1A) agonist decreased the density of puncta and spines, whereas 5-HT(2A/2C) agonist decreased filopodia density with increase of spines. In conclusion, the present study shows 5-HT receptors have subtype-specific effects on the spine formation.

Multiple subtypes of serotonin receptors in the feeding circuit of a pond snail.

In the central nervous system of the pond snail Lymnaea stagnalis, serotonergic transmission plays an important role in controlling feeding behavior. Recent electrophysiological studies have claimed that only metabotropic serotonin (5-HT(2)) receptors, and not ionotropic (5-HT(3)) receptors, are used in synapses between serotonergic neurons (the cerebral giant cells, CGCs) and the follower buccal motoneurons (the B1 cells). However, these data are inconsistent with previous results. In the present study, we therefore reexamined the serotonin receptors to identify the receptor subtypes functioning in the synapses between the CGCs and the B1 cells by recording the compound excitatory postsynaptic potential (EPSP) of the B1 cells evoked by a train of stimulation to the CGC in the presence of antagonists: cinanserin for 5-HT(2) and/or MDL72222 for 5-HT(3). The compound EPSP amplitude was partially suppressed by the application of these antagonists. The rise time of the compound EPSP was longer in the presence of MDL72222 than in that of cinanserin. These results suggest that these two subtypes of serotonin receptors are involved in the CGC-B1 synapses, and that these receptors contribute to compound EPSP. That is, the fast component of compound EPSP is mediated by 5-HT(3)-like receptors, and the slow component is generated via 5-HT(2)-like receptors.

5-HT receptors mediate lineage-dependent effects of serotonin on adult neurogenesis in Procambarus clarkii.

BACKGROUND: Serotonin (5-HT) is a potent regulator of adult neurogenesis in the crustacean brain, as in the vertebrate brain. However, there are relatively few data regarding the mechanisms of serotonin's action and which precursor cells are targeted. Therefore, we exploited the spatial separation of the neuronal precursor lineage that generates adult-born neurons in the crayfish (Procambarus clarkii) brain to determine which generation(s) is influenced by serotonin, and to identify and localize serotonin receptor subtypes underlying these effects. RESULTS: RT-PCR shows that mRNAs of serotonin receptors homologous to mammalian subtypes 1A and 2B are expressed in P. clarkii brain (referred to here as 5-HT1α and 5-HT2ß). In situ hybridization with antisense riboprobes reveals strong expression of these mRNAs in several brain regions, including cell clusters 9 and 10 where adult-born neurons reside. Antibodies generated against the crustacean forms of these receptors do not bind to the primary neuronal precursors (stem cells) in the neurogenic niche or their daughters as they migrate, but do label these second-generation precursors as they approach the proliferation zones of cell clusters 9 and 10. Like serotonin, administration of the P. clarkii 5-HT1α-specific agonist quipazine maleate salt (QMS) increases the number of bromodeoxyuridine (BrdU)-labeled cells in cluster 10; the P. clarkii 5-HT2ß-specific antagonist methiothepin mesylate salt (MMS) suppresses neurogenesis in this region. However, serotonin, QMS and MMS do not alter the rate of BrdU incorporation into niche precursors or their migratory daughters. CONCLUSION: Our results demonstrate that the influences of serotonin on adult neurogenesis in the crayfish brain are confined to the late second-generation precursors and their descendants. Further, the distribution of 5-HT1α and 5-HT2ß mRNAs and proteins indicate that these serotonergic effects are exerted directly on specific generations of neuronal precursors. Taken together, these results suggest that the influence of serotonin on adult neurogenesis in the crustacean brain is lineage dependent, and that 5-HT1α and 5-HT2ß receptors underlie these effects.

Serotonin receptors - from molecular biology to clinical applications.

Serotonin (5-hydroxytryptamine) is an ubiquitary monoamine acting as one of the neurotransmitters at synapses of nerve cells. Serotonin acts through several receptor types and subtypes. The profusion of 5-HT receptors should eventually allow a better understanding of the different and complex processes in which serotonin is involved. Its role is expected in the etiology of several diseases, including depression, schizophrenia, anxiety and panic disorders, migraine, hypertension, pulmonary hypertension, eating disorders, vomiting and irritable bowel syndromes. In the past 20 years, seven distinct families of 5-HT receptors have been identified and various subpopulations have been described for several of them. Increasing number of 5-HT receptors has made it difficult to unravel the role of 5-HT receptor subpopulations due to the lack of suitable selective agents. The present review describes the different populations and nomenclature of recently discovered 5-HT receptors and their pharmacological relevance.

Role of serotonin in gastrointestinal physiology and pathology.

Serotonin is one of the most abundant molecules in the gastrointestinal tract and it plays a crucial role in the regulation of several physiological functions, such as motility, secretion and visceral sensitivity. Besides this well documented physiological role, increasing evidence supports the concept that 5-HT is directly involved in pathological mechanisms, as well as the modulation of immune/inflammatory responses within the gut. The wide range of pathophysiological actions exerted by 5-HT are mediated by several different serotonergic receptor types and subtypes. Depending on the receptor bound and its localization, 5-HT evokes different and, sometimes, opposite responses. Therapeutic interventions aiming at modulating 5-HT signaling are mainly focused on the development of receptor agonists/antagonists, characterized by high affinity and selectivity for serotonergic receptors in the gut, to avoid the presence of adverse effects in the brain, where 5-HT is important in control mood. This review summarizes the vast current knowledge on 5-HT as a physiological mediator and analyzes the increasing body of literature describing 5-HT signaling abnormalities in functional and inflammatory disorders both in animal models and in humans. Finally, an overview on the therapeutic agents used in clinical practice is provided.

Discovery of 1-(3-{2-[4-(2-methyl-5-quinolinyl)-1-piperazinyl]ethyl}phenyl)-2-imidazolidinone (GSK163090), a Potent, selective, and orally active 5-HT1A/B/D receptor antagonist.

In an effort to identify selective drug like pan-antagonists of the 5-HT1 autoreceptors, studies were conducted to elaborate a previously reported dual acting 5-HT1 antagonist/SSRI structure. A novel series of compounds was identified showing low intrinsic activities and potent affinities across the 5-HT1A, 5-HT1B, and 5-HT1D receptors as well as high selectivity against the serotonin transporter. From among these compounds, 1-(3-{2-[4-(2-methyl-5-quinolinyl)-1-piperazinyl]ethyl}phenyl)-2-imidazolidinone (36) was found to combine potent in vivo activity with a strong preclinical developability profile, and on this basis it was selected as a drug candidate with the aim of assessing its potential as a fast-onset antidepressant/anxiolytic.

Synthesis and SAR of (piperazin-1-yl-phenyl)-arylsulfonamides: a novel series of atypical antipsychotic agents.

(Piperazin-1-yl-phenyl)-arylsulfonamides were synthesized and identified to show high affinities for both 5-HT(2C) and 5-HT(6) receptors. Among them, naphthalene-2-sulfonic acid isopropyl-[3-(4-methyl-piperazin-1-yl)-phenyl]-amide (6b) exhibits the highest affinity towards both 5-HT(2C) (IC(50)=4 nM) and 5-HT(6) receptors (IC(50)=3 nM) with good selectivity over other serotonin (5-HT(1A), 5-HT(2A), and 5-HT(7)) and dopamine (D(2)-D(4)) receptor subtypes. In 5-HT(2C) and 5-HT(6) receptor functional assays, this compound showed considerable antagonistic activity for both receptors.