Human serotonin 1D receptor is encoded by a subfamily of two distinct genes: 5-HT1D alpha and 5-HT1D beta

Migraine drugs

According to recent studies, migraine affects more than 1 billion people worldwide, making it one of the world’s most prevalent diseases. Although this highly debilitating illness has been known since ancient times, the first therapeutic drugs to treat migraine, ergotamine (Gynergen) and dihydroergotamine (Dihydergot), did not appear on the market until 1921 and 1946, respectively. Both drugs originated from Sandoz, the world’s leading pharmaceutical company in ergot alkaloid research at the time. Historically, ergot alkaloids had been primarily used in obstetrics, but with methysergide (1-methyl-lysergic acid 1′-hydroxy-butyl-(2S)-amide), it became apparent that they also held some potential in migraine treatment. Methysergide was the first effective prophylactic drug developed specifically to prevent migraine attacks in 1959. On the basis of significantly improved knowledge of migraine pathophysiology and the discovery of serotonin and its receptors, Glaxo was able to launch sumatriptan in 1992. It was the first member from the class of triptans, which are selective 5-HT1B/1D receptor agonists. Recent innovations in acute and preventive migraine therapy include lasmiditan, a selective 5-HT1F receptor agonist from Eli Lilly, the gepants, which are calcitonin gene-related peptide (CGRP) receptor antagonists discovered at Merck & Co and BMS, and anti-CGRP/receptor monoclonal antibodies from Amgen, Pfizer, Eli Lilly, and others.

Graphical abstract

Deficiency of Intellectual Disability-Related Gene Brpf1 Attenuated Hippocampal Excitatory Synaptic Transmission and Impaired Spatial Learning and Memory Ability

Patients with monoallelic bromodomain and PHD finger-containing protein 1 (BRPF1) mutations showed intellectual disability. The hippocampus has essential roles in learning and memory. Our previous work indicated that Brpf1 was specifically and strongly expressed in the hippocampus from the perinatal period to adulthood. We hypothesized that mouse Brpf1 plays critical roles in the morphology and function of hippocampal neurons, and its deficiency leads to learning and memory deficits. To test this, we performed immunofluorescence, whole-cell patch clamp, and mRNA-Seq on shBrpf1-infected primary cultured hippocampal neurons to study the effect of Brpf1 knockdown on neuronal morphology, electrophysiological characteristics, and gene regulation. In addition, we performed stereotactic injection into adult mouse hippocampus to knock down Brpf1 in vivo and examined the learning and memory ability by Morris water maze. We found that mild knockdown of Brpf1 reduced mEPSC frequency of cultured hippocampal neurons, before any significant changes of dendritic morphology showed. We also found that Brpf1 mild knockdown in the hippocampus showed a decreasing trend on the spatial learning and memory ability of mice. Finally, mRNA-Seq analyses showed that genes related to learning, memory, and synaptic transmission (such as C1ql1, Gpr17, Htr1d, Glra1, Cxcl10, and Grin2a) were dysregulated upon Brpf1 knockdown. Our results showed that Brpf1 mild knockdown attenuated hippocampal excitatory synaptic transmission and reduced spatial learning and memory ability, which helps explain the symptoms of patients with BRPF1 mutations.

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.

Serotonergic modulation across sensory modalities

The serotonergic system has been widely studied across animal taxa and different functional networks. This modulatory system is therefore well positioned to compare the consequences of neuromodulation for sensory processing across species and modalities at multiple levels of sensory organization. Serotonergic neurons that innervate sensory networks often bidirectionally exchange information with these networks but also receive input representative of motor events or motivational state. This convergence of information supports serotonin's capacity for contextualizing sensory information according to the animal's physiological state and external events. At the level of sensory circuitry, serotonin can have variable effects due to differential projections across specific sensory subregions, as well as differential serotonin receptor type expression within those subregions. Functionally, this infrastructure may gate or filter sensory inputs to emphasize specific stimulus features or select among different streams of information. The near-ubiquitous presence of serotonin and other neuromodulators within sensory regions, coupled with their strong effects on stimulus representation, suggests that these signaling pathways should be considered integral components of sensory systems.

Serotonin discovery and stepwise disclosure of 5-HT receptor complexity over four decades. Part II. Some contributions of Manfred Göthert

About 40% of the papers within the scientific oeuvre of Manfred Göthert (1939-2019) were dedicated to serotonin (5-hydroxytryptamine, 5-HT). He was not only the witness of the gradual definition of the fourteen 5-HT receptor subtypes but also was involved directly by identifying 5-HT_1B, 5-HT_1D and 5-HT₃ receptors. Moreover, he identified presynaptic 5-HT receptors on central and/or peripheral serotoninergic, noradrenergic and/or cholinergic neurones. Two inhibitory (5-HT_1B, 5-HT_1D) and two facilitatory (5-HT₃, 5-HT₄) receptors were found, the 5-HT_1B receptor representing a possible target for antidepressant drugs. Ten years earlier than electrophysiologists, he identified ligand-gated receptors like the 5-HT₃ and the nicotinic acetylcholine (nACh) receptor as targets of halothane. Simultaneously with, but independent of, other authors he found that ethanol allosterically inhibits N-methyl-D-aspartate (NMDA) receptors, which are affected at an even lower concentration than 5-HT₃ and nACh receptors. The latter two receptors were shown to be subject to allosteric inhibition also by cannabinoids via a mechanism unrelated to cannabinoid CB₁ or CB₂ receptors; cannabinoid inhibition of 5-HT₃ receptors may represent a new target for the treatment of neuropathic pain.

Pharmacologic assessment of bovine ruminal and mesenteric vascular serotonin receptor populations

Prior work using a contractility bioassay determined that the serotonin (5-HT) receptor subtype 5-HT2A is present in bovine lateral saphenous veins and plays a role in ergot alkaloid (EA)-induced vascular contraction in steers grazing endophyte-infected (Epichloë coenophiala) tall fescue (Lolium arundinaceum). Ergot alkaloids have also been shown to be vasoactive in bovine gut vasculature. To determine what 5-HT receptors are involved in vasoconstriction of gut vasculature, contractility of ruminal and mesenteric arteries and veins collected from cattle was evaluated in the presence of agonists selective for 5-HT1B (CP 93129), 5-HT1D (L-694, 247), 5-HT2A (TCB-2), 5-HT2B (BW 723C86), 5-HT4 (BIMU-8), and 5-HT7 (LP 44) receptors. Segments of ruminal and mesenteric veins and arteries were collected and suspended in a multimyograph containing continuously oxygenated Krebs-Henseleit buffer. Blood vessels were exposed to increasing concentrations of 5-HT agonists every 15 min and contractile response data were normalized as a percentage of the maximum contractile response induced by 120 mM KCl. Analysis of variance was evaluated using mixed models procedure of SAS for effects of agonist concentration for each vessel type. Receptor agonists for 5-HT2B, 5-HT1D, and 5-HT7 did not induce a contractile response for ruminal or mesenteric vasculature (P > 0.05). However, when exposed to agonists for 5-HT2B or 5-HT1D, mesenteric veins relaxed below zero (P < 0.05). Exposure of all 4 blood vessel types to 5-HT2A agonist induced contractile responses (P < 0.05). The findings of this study indicate that 5-HT1D and 5-HT2B are present in mesenteric veins and may play a role in vasorelaxation. Further, 5-HT2A is present in ruminal and mesenteric vasculature, plays a role in vasoconstriction of these vessels, and could be influenced by EA exposure as has been demonstrated in peripheral blood vessels.

Chronic 5-HT2 receptor blockade unmasks the role of 5-HT1F receptors in the inhibition of rat cardioaccelerator sympathetic outflow

Serotonin (5-hydroxytryptamine; 5-HT) inhibits the rat cardioaccelerator sympathetic outflow by 5-HT1B/1D/5 receptors. Because chronic blockade of sympatho-excitatory 5-HT2 receptors is beneficial in several cardiovascular pathologies, this study investigated whether sarpogrelate (a 5-HT2 receptor antagonist) alters the pharmacological profile of the above sympatho-inhibition. Rats were pretreated for 2 weeks with sarpogrelate in drinking water (30 mg/kg per day; sarpogrelate-treated group) or equivalent volumes of drinking water (control group). Animals were pithed and prepared for spinal stimulation (C7-T1) of the cardioaccelerator sympathetic outflow or for intravenous (i.v.) bolus injections of noradrenaline. Both procedures produced tachycardic responses remaining unaltered after saline. Continuous i.v. infusions of 5-HT induced a cardiac sympatho-inhibition that was mimicked by the 5-HT receptor agonists 5-carboxamidotryptamine (5-CT; 5-HT1/5A), CP 93,129 (5-HT1B), or PNU 142633 (5-HT1D), but not by indorenate (5-HT1A) in both groups; whereas LY344864 (5-HT1F) mimicked 5-HT only in sarpogrelate-treated rats. In sarpogrelate-treated animals, i.v. GR 127935 (310 μg/kg; 5-HT1B/1D/1F receptor antagonist) attenuated 5-CT-induced sympatho-inhibition and abolished LY344864-induced sympatho-inhibition; while GR 127935 plus SB 699551 (1 mg/kg; 5-HT5A receptor antagonist) abolished 5-CT-induced inhibition. These results confirm the cardiac sympatho-inhibitory role of 5-HT1B, 5-HT1D, and 5-HT5A receptors in both groups; nevertheless, sarpogrelate treatment specifically unmasked a cardiac sympatho-inhibition mediated by 5-HT1F receptors.

Crystal structure of the human 5-HT1B serotonin receptor bound to an inverse agonist

5-hydroxytryptamine (5-HT, also known as serotonin) regulates many physiological processes through the 5-HT receptor family. Here we report the crystal structure of 5-HT1B subtype receptor (5-HT1BR) bound to the psychotropic serotonin receptor inverse agonist methiothepin (MT). Crystallization was facilitated by replacing ICL3 with a novel optimized variant of BRIL (OB1) that enhances the formation of intermolecular polar interactions, making OB1 a potential useful tool for structural studies of membrane proteins. Unlike the agonist ergotamine (ERG), MT occupies only the conserved orthosteric binding pocket, explaining the wide spectrum effect of MT on serotonin receptors. Compared with ERG, MT shifts toward TM6 and sterically pushes residues W3276.48, F3306.50 and F3316.51 from inside the orthosteric binding pocket, leading to an outward movement of the extracellular end and a corresponding inward shift of the intracellular end of TM6, a feature shared by other reported inactive G protein-coupled receptor (GPCR) structures. Together with the previous agonist-bound serotonin receptor structures, the inverse agonist-bound 5-HT1BR structure identifies a basis for the ligand-mediated switch of 5-HT1BR activity and provides a structural understanding of the inactivation mechanism of 5-HT1BR and some other class A GPCRs, characterized by ligand-induced outward movement of the extracellular end of TM6 that is coupled with inward movement of the cytoplasmic end of this helix.

The 5-HT1B receptor - a potential target for antidepressant treatment

Major depressive disorder (MDD) is the leading cause of disability worldwide. The serotonin hypothesis may be the model of MDD pathophysiology with the most support. The majority of antidepressants enhance synaptic serotonin levels quickly, while it usually takes weeks to discern MDD treatment effect. It has been hypothesized that the time lag between serotonin increase and reduction of MDD symptoms is due to downregulation of inhibitory receptors such as the serotonin 1B receptor (5-HT1BR). The research on 5-HT1BR has previously been hampered by a lack of selective ligands for the receptor. The last extensive review of 5-HT1BR in the pathophysiology of depression was published 2009, and based mainly on findings from animal studies. Since then, selective radioligands for in vivo quantification of brain 5-HT1BR binding with positron emission tomography has been developed, providing new knowledge on the role of 5-HT1BR in MDD and its treatment. The main focus of this review is the role of 5-HT1BR in relation to MDD and its treatment, although studies of 5-HT1BR in obsessive-compulsive disorder, alcohol dependence, and cocaine dependence are also reviewed. The evidence outlined range from animal models of disease, effects of 5-HT1B receptor agonists and antagonists, case-control studies of 5-HT1B receptor binding postmortem and in vivo, with positron emission tomography, to clinical studies of 5-HT1B receptor effects of established treatments for MDD. Low 5-HT1BR binding in limbic regions has been found in MDD patients. When 5-HT1BR ligands are administered to animals, 5-HT1BR agonists most consistently display antidepressant-like properties, though it is not yet clear how 5-HT1BR is best approached for optimal MDD treatment.

5-HT Receptor Nomenclature: Naming Names, Does It Matter? A Tribute to Maurice Rapport

The naming of 5-HT receptors has been challenging, especially in the early days when the concept of multiple receptors for a single neurotransmitter was considered to be unrealistic at best. Yet pharmacological (rank orders of potency in functional or biochemical settings) and transductional evidence (second messengers, electrophysiology) clearly indicated the existence of receptor families and subfamilies. The genetic revolution, with the cloning and study of recombinantly expressed receptors, and eventually the cloning of the human and other genomes have made such reservations obsolete. Further, the advances in structural biology, with the possibility to study ligand receptor complexes as crystals and/or using solution NMR have largely confirmed the complexity of the 5-HT receptor system: species differences, existence of multiple receptor active and inactive states, splice variants, editing variants, complexes with multiple interacting proteins and transduction bias. This is a short personal history on how advances in biochemistry, molecular biology, biophysics, imaging and medicinal chemistry, some lateral thinking, and a decent amount of collaborative spirit within the 5-HT receptor nomenclature committee and the 5-HT community at large have helped to better define the pharmacology of the 5-HT receptor family.

Development of Flashplate™ Technology to Measure [35S]GTPyS Binding to Chinese Hamster Ovary Cell Membranes Expressing the Cloned Human 5-HTIB Receptor

With the exponential rate at which proposed drugs are being produced for disease therapy, it is now essential to automate assays used to screen these compounds and increase throughput. This has been rapidly adopted for simple radioligand binding assays but is less amenable for certain functional screens. [35S]GTPγS binding represents a convenient method for screening ligands that bind to G protein-coupled receptors and, ultimately, stimulate G-protein activation. In this study we have investigated the use of 96-well FlashPlates™ (NEN DuPont, Stevenage, England) to measure [35S]GTPγS binding to human 5-HT1B receptors expressed in Chinese hamster ovary cells. The cells were added to the individual wells of the FlashPlate and incubated with [35S]GTPγS in the presence or absence of test drug and bound radioactivity measured in a 96-well spectrometer. 5-HT produced a stimulation of basal [35S]GTPγS binding, which was robust within and between experiments, with pEC50= 8.1. The 5-HT1Bpartial agonist GR127935 (2′n-methyl-4′-5-methyl-1,2,4 oxadiazol-3-yl)-biphenyl-4-carboxylic acid [4-methoxy-3-(4-methyl-piperazin-1-yl)-phenyl]-amide) caused a partial stimulation (pEC5o = 8.3, intrinsic activity = 0.7), and the selective 5-HTIB receptor antagonist SB-224289 (2,3,6,7-tetrahydro-1′-methyl-5-{2′-methyl-4′-[(5-methyl-1,2,4-oxadiazole-3-yl)biphenyl-4-yl]carbonyl}furo[2,3-flindole-3-spiro-4′-piperidine oxalate) displayed inverse agonism with pEC50 = 7.6. These results are similar to those obtained using the conventional filtration method and indicate that FlashPlate technology can provide a rapid method for measuring [35S]GTPγS binding.

The Multiplicity of Serotonin Receptors: Uselessly Diverse Molecules or an Embarrassment of Riches?

A large number of 5-HT receptors (>15) have been identified by molecular cloning technology over the past 10 years. This review briefly summarizes available information regarding the functional and therapeutic implications of serotonin receptor diversity for neurology and psychiatry. 5-HT receptors are divided into seven main families: 5-HT1, 5-HT2, 5-HT3, 5-HT4, 5-HT5, 5-HT6, and 5-HT7. Several families (e.g., 5-HT1 family) have many members (e.g., 5-HT1A, 5-HT1B, 5-HT1D, 5-HT1E, 5-HT1F), each of which is encoded by a distinct gene product. In addition to the genomic diversity of 5-HT receptors, splice variants and editing isoforms exist for many of the 5-HT receptors, making the family even more diverse. Evidence that is summarized in this review suggests that 5-HT receptors represent novel therapeutic targets for a number of neurologic and psychiatric diseases including migraine headaches, chronic pain conditions, schizophrenia, anxiety, depression, eating disorders, obsessive compulsive disorder, pervasive developmental disorders, and obesity-related conditions (Type II diabetes, hypertension, obesity syndromes). It is possible that sub-type-selective serotonergic agents may revolutionize the treatment for a number of medical, psychiatric, and neurological disorders.

Structure and function of serotonin G protein-coupled receptors

Serotonin receptors are prevalent throughout the nervous system and the periphery, and remain one of the most lucrative and promising drug discovery targets for disorders ranging from migraine headaches to neuropsychiatric disorders such as schizophrenia and depression. There are 14 distinct serotonin receptors, of which 13 are G protein-coupled receptors (GPCRs), which are targets for approximately 40% of the approved medicines. Recent crystallographic and biochemical evidence has provided a converging understanding of the basic structure and functional mechanics of GPCR activation. Currently, two GPCR crystal structures exist for the serotonin family, the 5-HT1B and 5-HT2B receptor, with the antimigraine and valvulopathic drug ergotamine bound. The first serotonin crystal structures not only provide the first evidence of serotonin receptor topography but also provide mechanistic explanations into functional selectivity or biased agonism. This review will detail the findings of these crystal structures from a molecular and mutagenesis perspective for driving rational drug design for novel therapeutics incorporating biased signaling.

Application of quantitative structure-activity relationship models of 5-HT1A receptor binding to virtual screening identifies novel and potent 5-HT1A ligands

The 5-hydroxytryptamine 1A (5-HT_1A) serotonin receptor has been an attractive target for treating mood and anxiety disorders such as schizophrenia. We have developed binary classification quantitative structure–activity relationship (QSAR) models of 5-HT_1A receptor binding activity using data retrieved from the PDSP K_i database. The prediction accuracy of these models was estimated by external 5-fold cross-validation as well as using an additional validation set comprising 66 structurally distinct compounds from the World of Molecular Bioactivity database. These validated models were then used to mine three major types of chemical screening libraries, i.e., drug-like libraries, GPCR targeted libraries, and diversity libraries, to identify novel computational hits. The five best hits from each class of libraries were chosen for further experimental testing in radioligand binding assays, and nine of the 15 hits were confirmed to be active experimentally with binding affinity better than 10 μM. The most active compound, Lysergol, from the diversity library showed very high binding affinity (K_i) of 2.3 nM against 5-HT_1A receptor. The novel 5-HT_1A actives identified with the QSAR-based virtual screening approach could be potentially developed as novel anxiolytics or potential antischizophrenic drugs.

Serotonin receptors and their role in the pathophysiology and therapy of irritable bowel syndrome

BACKGROUND

Irritable bowel syndrome (IBS) is a functional disorder of the gastrointestinal tract characterized by abdominal discomfort, pain and changes in bowel habits, often associated with psychological/psychiatric disorders. It has been suggested that the development of IBS may be related to the body's response to stress, which is one of the main factors that can modulate motility and visceral perception through the interaction between brain and gut (brain-gut axis). The present review will examine and discuss the role of serotonin (5-hydroxytryptamine, 5-HT) receptor subtypes in the pathophysiology and therapy of IBS.

METHODS

Search of the literature published in English using the PubMed database.

RESULTS

Several lines of evidence indicate that 5-HT and its receptor subtypes are likely to have a central role in the pathophysiology of IBS. 5-HT released from enterochromaffin cells regulates sensory, motor and secretory functions of the digestive system through the interaction with different receptor subtypes. It has been suggested that pain signals originate in intrinsic primary afferent neurons and are transmitted by extrinsic primary afferent neurons. Moreover, IBS is associated with abnormal activation of central stress circuits, which results in altered perception during visceral stimulation.

CONCLUSIONS

Altered 5-HT signaling in the central nervous system and in the gut contributes to hypersensitivity in IBS. The therapeutic effects of 5-HT agonists/antagonists in IBS are likely to be due also to the ability to modulate visceral nociception in the central stress circuits. Further studies are needed in order to develop an optimal treatment.

The Concise Guide to PHARMACOLOGY 2013/14: G protein-coupled receptors

The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. G protein-coupled receptors are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, nuclear hormone receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.

Functional topography of serotonergic systems supports the Deakin/Graeff hypothesis of anxiety and affective disorders

Over 20 years ago, Deakin and Graeff hypothesized about the role of different serotonergic pathways in controlling the behavioral and physiologic responses to aversive stimuli, and how compromise of these pathways could lead to specific symptoms of anxiety and affective disorders. A growing body of evidence suggests these serotonergic pathways arise from topographically organized subpopulations of serotonergic neurons located in the dorsal and median raphe nuclei. We argue that serotonergic neurons in the dorsal/caudal parts of the dorsal raphe nucleus project to forebrain limbic regions involved in stress/conflict anxiety-related processes, which may be relevant for anxiety and affective disorders. Serotonergic neurons in the "lateral wings" of the dorsal raphe nucleus provide inhibitory control over structures controlling fight-or-flight responses. Dysfunction of this pathway could be relevant for panic disorder. Finally, serotonergic neurons in the median raphe nucleus, and the developmentally and functionally-related interfascicular part of the dorsal raphe nucleus, give rise to forebrain limbic projections that are involved in tolerance and coping with aversive stimuli, which could be important for affective disorders like depression. Elucidating the mechanisms through which stress activates these topographically and functionally distinct serotonergic pathways, and how dysfunction of these pathways leads to symptoms of neuropsychiatric disorders, may lead to the development of novel approaches to both the prevention and treatment of anxiety and affective disorders.

Vasoconstrictor 5-HT receptors in the smooth muscle of the rat middle cerebral artery

Serotonin (5-HT) can constrict cerebral arteries via activation of 5-HT(1B) and 5-HT(2A) receptors. Our goal was to reveal the importance and relative contribution of the two 5-HT receptor subtypes to the serotonin-induced vasoconstriction in the rat middle cerebral artery. The vasoconstrictor effects of 5-carboxamidotryptamine, sumatriptan and 5-HT were measured without and with pre-treatment with SB 216641 (5-HT(1B) antagonist), or ritanserin, (5-HT(2A) antagonist), in endothelium-denuded arteries, in vitro. All agonists caused vasoconstrictions. The order of potency (EC(50)) of the compounds was: 5-carboxamidotryptamine (14±3 nM)>5-HT (270±30 nM)>sumatriptan (5.8±1.9 μM). The concentration-response curve of 5-carboxamidotryptamine resembled the sum of two sigmoid curves (EC(50) 14±3 nM and 15±7 μM), and SB 216641 and ritanserin antagonized its low and high concentration components, respectively. Vasoconstrictions evoked by 5-HT at low and high concentrations were also fully antagonized by SB 216641 and ritanserin, respectively. Sumatriptan constricted the middle cerebral artery exclusively via 5-HT(1B) receptors. The efficacy of 5-carboxamidotryptamine and sumatriptan was low in comparison to the maximum contractile force elicited by 120 mmol/l KCl, reaching only 18-23% for 5-HT(1B) and 14% for 5-HT(2A) receptor activation. In conclusion, 5-HT produced small vasoconstrictions in the rat middle cerebral artery that were mediated by 5-HT(1B) receptors with high potency and by 5-HT(2A) receptors with low potency. Thus, 5-HT may have a minor physiological role in blood flow regulation via 5-HT(1B) receptor activation while 5-HT(2A) receptors seem to have a pathophysiological role in this vessel.

Serotonin receptors in hippocampus

Serotonin is an ancient molecular signal and a recognized neurotransmitter brainwide distributed with particular presence in hippocampus. Almost all serotonin receptor subtypes are expressed in hippocampus, which implicates an intricate modulating system, considering that they can be localized as autosynaptic, presynaptic, and postsynaptic receptors, even colocalized within the same cell and being target of homo- and heterodimerization. Neurons and glia, including immune cells, integrate a functional network that uses several serotonin receptors to regulate their roles in this particular part of the limbic system.

The serotonergic system in Parkinson's disease

Although the cardinal manifestations of Parkinson's disease (PD) are attributed to a decline in dopamine levels in the striatum, a breadth of non-motor features and treatment-related complications in which the serotonergic system plays a pivotal role are increasingly recognised. Serotonin (5-HT)-mediated neurotransmission is altered in PD and the roles of the different 5-HT receptor subtypes in disease manifestations have been investigated. The aims of this article are to summarise and discuss all published preclinical and clinical studies that have investigated the serotonergic system in PD and related animal models, in order to recapitulate the state of the current knowledge and to identify areas that need further research and understanding.

Association between the 5-HTR1B gene polymorphisms and alcohol dependence in a Han Chinese population

The human serotonin receptor 1B (HRT1B) plays an important role in regulating serotonin release. Previous research has suggested that the genetic variation of the HTR1B gene may confer susceptibility to alcoholism or some subtypes of alcohol dependence, but the evidence has been inconsistent. The aim of the present study is to examine whether polymorphic variants of the HTR1B gene are associated with alcohol dependence subtypes or drinking-related behaviors in Chinese Han population. Alcohol-dependent (AD) male patients (n=135) and controls (n=143) were genotyped for two polymorphisms: A161T in the promoter region and the synonymous variation G861C in the coding region of HTR1B. The results showed that the A161T polymorphism was associated with alcohol dependence (T vs. A allele: p=0.002; OR=2.18, 95% CI: 1.32-3.60). This association was strengthened in those with positive family history (OR=3.12, 95% CI: 1.71-5.70) and/or early onset (OR=4.53, 95% CI: 2.18-9.44) of alcohol dependence. The A161T variant was also significantly associated with age of onset of alcoholism (p=0.001). Furthermore, there was a significant difference of haplotypic frequencies between patients and controls (χ(2)=14.84, df=3, p=0.002), with one common haplotype AG of being significantly underrepresented among the patient group compared to the control group (34% vs. 47.7%, permutation p=0.0034; OR=0.56; 95% CI: 0.39-0.79). These findings confirm HTR1B as a susceptibility gene for alcohol dependence in the sample of Chinese Han population. The HTR1B A-161T polymorphism may be particularly valuable as a functional genetic marker for alcoholism and merits additional study.

Pharmacological facilitation of fear extinction and the search for adjunct treatments for anxiety disorders--the case of yohimbine

There is current interest in identifying drugs that facilitate fear extinction, as this form of learning is the basis of certain cognitive therapies for anxiety disorders. Following an initial report several years ago that the alpha2-adrenoreceptor antagonist yohimbine facilitated extinction in mice, more recent studies have shown mixed effects or even impairment. It has become clear that the effect of yohimbine on extinction depends on a number of factors, including genetic background, contextual variables and the presence of competing behaviors. To what extent theses effects of yohimbine are mediated through the alpha2-adrenoreceptor, as opposed to other sites of action, is also uncertain. More work is needed before this drug can be approved as a pharmacological adjunct for extinction-based therapies. More generally, the case of yohimbine may serve as a model for the development of other extinction facilitators.

Serotonin pharmacology in the gastrointestinal tract: a review

Serotonin (5-hydroxytryptamine or 5-HT) plays a critical physiological role in the regulation of gastrointestinal (GI) function. 5-HT dysfunction may also be involved in the pathophysiology of a number of functional GI disorders, such as chronic constipation, irritable bowel syndrome and functional dyspepsia. This article describes the role of 5-HT in the enteric nervous system (ENS) of the mammalian GI tract and the receptors with which it interacts. Existing serotonergic therapies that have proven effective in the treatment of GI functional disorders and the potential of drugs currently in development are also highlighted. Advances in our understanding of the physiological and pathophysiological roles of 5-HT in the ENS and the identification of selective receptor ligands bodes well for the future development of more efficacious therapies for patients with functional GI disorders.

Stimulation of growth hormone release by 5-hydroxytryptamine (5-HT) in cultured rat anterior pituitary cell aggregates: evidence for mediation by 5-HT2B, 5-HT7, 5-HT1B, and ketanserin-sensitive receptors

5-Hydroxytryptamine (5-HT) promotes the release of GH by a hypothalamic site of action. The present study explores a putative pituitary action in a perifused rat anterior pituitary aggregate cell culture system. In aggregates cultured with 1 nM estradiol for expression of the 5-HT4, -5, and -6 receptor (R), 5-HT promptly stimulated GH secretion with a dose dependency between 1 and 10 nM. The effect of 5-HT was partially blocked by methiothepin and methysergide; by SB-206553, a 5-HTR2B/C antagonist; SB-269970, a 5-HTR7/5A antagonist; and SB-224289, a 5-HTR1B antagonist. The GH response was fully blocked by combined administration of SB-206553+SB-269970 and SB-206553+ketanserin but not by SB-206553+spiperone. Culturing the aggregates without estradiol diminished the magnitude of the GH response to 5-HT as well as the impact of 5-HTR7/5 blockade on the response. Basal GH release was stimulated by the 5-HTR2 agonists 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane, m-chlorophenyl piperazine, and alpha-methyl 5-HT; 5-carboxytryptamine (agonist at 5-HTR1, -5, and -7); tryptamine (preferential 5-HTR7 agonist); and the selective 5-HTR1B agonist CP93129 but not the 5-HTR1A agonists 7-(dipropylamino)tetralin-1-ol-8-hydroxy-2-(di-n-propylamino)tetralin and the 5-HTR1B/D agonist sumatriptan. The selective 5-HTR2B agonist BW 723C86 stimulated GH release, and the selective 5-HTR2B antagonist SB-204741 attenuated the GH response to 5-HT. The present data suggest that 5-HT may release GH through a pituitary site of action, and that the 5-HTR2B, 5-HTR7 and 5-HTR1B mediate this response, with possibly an inhibitory component of the 5-HTR1D. The relative contribution of these receptors may be modulated by estrogen.

Vasoactive peptides in cardiovascular (patho)physiology

Numerous vasoactive agents play an important physiological role in regulating vascular tone, reactivity and structure. In pathological conditions, alterations in the regulation of vasoactive peptides result in endothelial dysfunction, vascular remodeling and vascular inflammation, which are important processes underlying vascular damage in cardiovascular disease. Among the many vasoactive agents implicated in vascular (patho)biology, angiotensin II (Ang II), endothelin (ET), serotonin and natriuretic peptides appear to be particularly important because of their many pleiotropic actions and because they have been identified as potential therapeutic targets in cardiovascular disease. Ang II, ET-1, serotonin and natriuretic peptides mediate effects via specific receptors, which belong to the group of G-protein-coupled receptors. ET, serotonin and Ang II are primarily vasoconstrictors with growth-promoting actions, whereas natriuretic peptides, specifically atrial, brain and C-type natriuretic peptides, are vasodilators with natriuretic effects. Inhibition of vasoconstrictor actions with drugs that block peptide receptors, compounds that inhibit enzymes that generate vasoactive peptides or agents that increase levels of natriuretic peptides are potentially valuable therapeutic tools in the management of cardiovascular diseases. This review focuses on ET, natriuretic peptides and serotonin. The properties and distribution of these vasoactive agents and their receptors, mechanisms of action and implications in cardiovascular (patho)physiology will be discussed.

Pharmacologic mechanisms of serotonergic regulation of dopamine neurotransmission

The neurotransmitter dopamine (DA) has a long association with normal functions such as motor control, cognition, and reward, as well as a number of syndromes including drug abuse, schizophrenia, and Parkinson's disease. Studies show that serotonin (5-HT) acts through several 5-HT receptors in the brain to modulate DA neurons in all 3 major dopaminergic pathways. There are at least fourteen 5-HT receptor subtypes, many of which have been shown to play some role in mediating 5-HT/DA interactions. Several subtypes, including the 5-HT1A, 5-HT1B, 5-HT2A, 5-HT3 and 5-HT4 receptors, act to facilitate DA release, while the 5-HT2C receptor mediates an inhibitory effect of 5-HT on DA release. Most 5-HT receptor subtypes only modulate DA release when 5-HT and/or DA neurons are stimulated, but the 5-HT2C receptor, characterized by high levels of constitutive activity, inhibits tonic as well as evoked DA release. This review summarizes the anatomical evidence for the presence of each 5-HT receptor subtype in dopaminergic regions of the brain and the neuropharmacological evidence demonstrating regulation of each DA pathway. The relevance of 5-HT receptor modulation of DA systems to the development of therapeutics used to treat schizophrenia, depression, and drug abuse is discussed. Lastly, areas are highlighted in which future research would be maximally beneficial to the treatment of these disorders.

Functional Pharmacology in Human Brain

Most neurological and psychiatric disorders involve selective or preferential impairments of neurotransmitter systems. Therefore, studies of functional transmitter pathophysiology in human brain are of unique importance in view of the development of effective, mechanism-based, therapeutic modalities. It is well known that central nervous system functional proteins, including receptors, transporters, ion channels, and enzymes, can exhibit high heterogeneity in terms of structure, function, and pharmacological profile. If the existence of types and subtypes of functional proteins amplifies the possibility of developing selective drugs, such heterogeneity certainly increases the likelihood of interspecies differences. It is therefore essential, before choosing animal models to be used in preclinical pharmacology experimentation, to establish whether functionally corresponding proteins in men and animals also display identical pharmacological profiles. Because of evidence that scaffolding proteins, trafficking between plasma membrane and intracellular pools, phosphorylation and allosteric modulators can affect the function of receptors and transporters, experiments with human clones expressed in host cells where the environment of native receptors is rarely reproduced should be interpreted with caution. Thus, the use of neurosurgically removed fresh human brain tissue samples in which receptors, transporters, ion channels, and enzymes essentially retain their natural environment represents a unique experimental approach to enlarge our understanding of human brain processes and to help in the choice of appropriate animal models. Using this experimental approach, many human brain functional proteins, in particular transmitter receptors, have been characterized in terms of localization, function, and pharmacological properties.

Synthesis of potent and selective serotonin 5-HT1B receptor ligands

A series of serotonin 5-HT1B ligands were synthesized and evaluated for their potency and selectivity against other 5-HT receptor subtypes. Many of these new compounds displayed high affinity and selectivity for the 5-HT1B receptor and compound 6c was found to have the in vitro binding profile necessary for development as a PET radioligand.

In vitro profile of the antidepressant candidate OPC-14523 at rat and human 5-HT1A receptors

This study determined the in vitro functional profile of 1-[3-[4-(3-chlorophenyl)-1-piperazinyl]propyl]-5-methoxy-3,4-dihydro-2-quinolinone monomethanesulfonate (OPC-14523) at rat and human serotonin (5-HT) 5-HT1A receptors and binding affinity of OPC-14523 at human frontocortical 5-HT1A receptors. OPC-14523 (1 microM) increased guanosine-5'-O-(3-[35S]thio)-triphosphate ([35S]GTPgammaS) binding to 5-HT1A receptor-containing regions of rat brain tissue sections (approximately 53% of the effect of 1 microM (+)8-hydroxy-2-(di-n-propylamino)tetralin ((+)8-OH-DPAT) that were blocked by the selective 5-HT1A receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinylcyclohexanecarboxamide (WAY-100635). OPC-14523 also behaved as a partial agonist in its stimulation of [35S]GTPgammaS binding to membranes from rat hippocampus (pEC50=7.60+/-0.23, Emax=41.1% of the effect of 10 microM (+)8-OH-DPAT), human frontal cortex (pEC50=7.89+/-0.08; Emax=64% of the effect of 10 microM (+)8-OH-DPAT), and Chinese Hamster Ovary cells expressing cloned human 5-HT1A receptors (pEC50=8.0+/-0.11; Emax=85.5% of the effect of 10 microM 5-HT), and all of these effects of OPC-14523 were blocked by WAY-100635. Taken together, these data support the development of OPC-14523 as an antidepressant whose mechanism of action involves potent partial agonist activity at 5-HT1A receptors.

[Lack of association between the G681C polimorphism in the 5-HT1D(beta) autoreceptor gene and schizophrenia]

A major role of the serotonergic system has been hypothesized in the pathogenesis of schizophrenia, mostly based on the evidence of action of atypical antipsychotics. Disturbances of serotonergic pathways have been implicated in the etiology of schizophrenia. The aim of this study was to investigate the association between schizophrenia and the G861C polymorphism in the 5-HT1D(beta) autoreceptor gene. There was conducted a case-control analysis in a sample of 196 schizophrenic patients and 143 gender, age and ethnic matched controls. No statistically differences were found in allelic or genotypic distributions between cases and controls. Thus, the results do not support an association of the G861C polymorphism in the 5-HT1D(beta) autoreceptor gene with schizophrenia in the studied sample.

Design, synthesis and evaluation of bicyclic benzamides as novel 5-HT1F receptor agonists

Several fused bicyclic systems have been investigated to serve as the core structure of potent and selective 5-HT1F receptor agonists. Replacement of the indole nucleus in 2 with indazole and 'inverted' indazole provided more potent and selective 5-HT1F receptor ligands. Indoline and 1,2-benzisoxazole systems also provided potent 5-HT1F receptor agonists, and the 5-HT1A receptor selectivity of the indoline- and 1,2-benzisoxazole-based 5-HT1F receptor agonists could be improved with modification of the benzoyl moiety of the benzamides. Through these studies, we found that the inherent geometries of the templates, not the nature of hybridization of the linking atom, were important for the 5-HT1F receptor recognition.

Advances toward new antidepressants beyond SSRIs: 1-aryloxy-3-piperidinylpropan-2-ols with dual 5-HT1A receptor antagonism/SSRI activities. Part 3

A series of 1-aryloxy-3-piperidinylpropan-2-ols possessing potent dual 5-HT(1A) receptor antagonism and serotonin reuptake inhibition was discovered. Modification of potential metabolic sites of 1-(1H-indol-4-yloxy)-3-(4-benzo[b]thiophen-2-ylpiperidinyl)propan-2-ols further improved the in vitro binding affinities and functional antagonism.

Lack of association or linkage disequilibrium between schizophrenia and polymorphisms in the 5-HT1Dalpha and 5-HT1Dbeta autoreceptor genes: family-based association study

Genetic factors play a major role in the etiology of schizophrenia and disturbances of serotonergic pathways have been implicated in this disorder. The aim of the present study was to examine genetic association between schizophrenia and polymorphisms in the 5-HT1Dalpha (TaqI) and 5-HT1Dbeta (T261G and G861C) autoreceptor genes in ninety trios from Portugal. No association or linkage disequilibrium was obtained between schizophrenia and 5-HT1Dalpha and 5-HT1Dbeta autoreceptor genes with both haplotype relative risk (HRR) and transmission disequilibrium test (TDT). Concerning 5-HT1Dbeta autoreceptor gene, also negative results was obtained in the analysis of the haplotypes with transmit. Thus, our data provide no support for the hypothesis that polymorphisms at 5-HT1Dalpha (TaqI) and 5-HT1Dbeta (T261G and G861C) genes contributes to susceptibility to schizophrenia in the Portuguese population.

Advances toward new antidepressants beyond SSRIs: 1-aryloxy-3-piperidinylpropan-2-ols with dual 5-HT1A receptor antagonism/SSRI activities. Part 4

A series of 1-(1H-indol-4-yloxy)-3-(4-arylpiperidinyl)propan-2-ols possessing potent dual 5-HT(1A) receptor antagonism and serotonin reuptake inhibition was discovered. The fused aryl ring moiety contributed to the robust dual activities irrespective of the regiochemistry associated with its connectivity to the piperidine central ring.

Serotonin 5-HT1A, 5-HT1B, and 5-HT2A receptor mRNA expression in subjects with major depression, bipolar disorder, and schizophrenia

BACKGROUND

Alterations of serotonin neurotransmission are implicated in both mood disorders and schizophrenia. Specific serotonin-receptor-based abnormalities in these psychiatric illnesses have been intensively studied; however, it has been difficult to draw any conclusions because of a lack of consensus. These inconsistencies have most likely arisen from the unavailability of selective ligands.

METHODS

Our study used in situ hybridization to quantify 5-HT(1A), 5-HT(1B), and 5-HT(2A) mRNA levels in the hippocampus (HC) and 5-HT(1A) and 5-HT(2A) mRNA levels in the dorsolateral prefrontal cortex (DLPFC) of subjects with a history of major depression disorder (MDD), bipolar disorder (BPD), schizophrenia, and a normal comparison group (15 subjects per group).

RESULTS

In the DLPFC, there is a significant decrease in 5-HT(1A) mRNA of subjects with MDD and in 5-HT(2A) mRNA of subjects with BPD. Subjects with MDD have a significant decrease in 5-HT(1A) mRNA in the HC; subjects with BPD and schizophrenia had increased 5-HT(1B) mRNA levels and a significant decrease in 5-HT(2A) mRNA levels in the hippocampal formation.

CONCLUSIONS

Alterations in 5-HT(1A,) 5-HT(1B), and 5-HT(2A) mRNA levels in the brains of subjects with both mood disorders and schizophrenia add further support for hypothesis of dysregulation of the serotonergic system in these psychiatric disorders.

Substituted furo[3,2-b]pyridines: novel bioisosteres of 5-HT 1F receptor agonists

Synthesis and evaluation of a series of 2,3,5- and 3,5-substituted furo[3,2-b]pyridines were undertaken in order to investigate their utility as bioisosteres of 5-HT(1F) receptor agonist indole analogues, 1-3. The replacement proved to be effective, providing compounds with similar 5-HT(1F) receptor affinity and improved selectivity when compared with the indole analogues. Through these studies we identified 4-fluoro-N-[3-(1-methyl-piperidin-4-yl)-furo[3,2-b]pyridin-5-yl]-benzamide (5), a potent and selective 5-HT(1F) receptor agonist with the potential to treat acute migraine.

5-HT1F receptor agonists in acute migraine treatment: a hypothesis

Serotonin-1F receptor (5-HT1F) agonists may relieve acute migraine without vasoconstriction. We conducted a review of preclinical and clinical data that assessed the potential link between migraine and 5-HT1F activation. (i) A high correlation exists between the potency of various 5-HT1 receptor agonists in the guinea pig dural plasma protein extravasation assay and their 5-HT1F receptor binding affinity. (ii) 5-HT1F receptors are on the trigeminal system, and may participate in blocking migraine pain transmission through the trigeminal ganglion and nucleus caudalis. (iii) 5-HT1F receptors are located on glutamate-containing neurones and their activation might inhibit glutamate release; glutamate excess may play a role in migraine. (iv) Selective 5-HT1F receptor agonists (LY334370; LY344864) are effective in preclinical migraine models and are non-vasoconstrictive. (v) LY334370 is effective in acute migraine, and does not cause any symptoms/signs of coronary vasoconstriction. Preclinical experiments and clinical observations argue for a role of selective 5-HT1F agonists in migraine.