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The molecular biology of serotonin receptors: Therapeutic implications for the interface of mood and psychosis
Abstract
This review summarizes the molecular biology of serotonin (5-HT; 5-hydroxytryptamine) receptors and indicates the potential relevance of this information for the treatment of mood and psychotic disorders. At least 15 separate subtypes of 5-HT receptors have been identified by molecular cloning techniques to be distinct genetic entities. Subtle differences in the primary amino acid sequences of these receptors can yield large differences in ligand selectivity. Additionally, it has recently been discovered that drugs such as atypical antipsychotic drugs and serotonin-selective reuptake inhibitors may interact with a large number of heretofore unknown 5-HT receptors. Thus clozapine, for instance, has high affinity for at least four separate 5-HT receptors, and it is unknown which of these receptors is essential for its unique therapeutic efficacy. One way to approach these questions is to test subtype-selective agents, although there are few of these currently available. Approaches to the design of subtype-selective ligands are described, including structure-based drug design and combinatorial approaches. Modes of regulation of 5-HT receptors are also summarized, and it is emphasized that antipsychotic drugs and antidepressants likely exert their effects via nontranscriptional and posttranslational means. Understanding the cellular mechanisms by which 5-HT receptors are regulated by psychopharmacologic agents is likely to yield novel insights into drug action.
... Furthermore, because of enhanced cancer risk observed during a safety clinical trial along with cardiovascular and other side effects [12,13] this drug was voluntarily withdrawn from the US market [14] in 2020 causing a void for availability of this class of drugs. Besides the cancer risk, the major adverse effects of Lorcaserin could be linked to its subtype selectivity as the agonism of 5-HT 2A and 5-HT 2B may cause hallucination/psychosis [15] and cardiac valvular insufficiency [16,17] respectively. It is therefore necessary to adopt a different strategy for the identification of new chemical entities (NCEs) with effective mechanism of action for 5-HT 2C R agonism. ...
Efforts have been devoted for the discovery and development of positive allosteric modulators (PAMs) of 5-HT2CR because of their potential advantages over the orthosteric agonist like Lorcaserin that was withdrawn from the market. On the other hand, pursuing a positive ago-allosteric modulator (PAAM) is considered as beneficial particularly when an agonist is not capable of affecting the potency of the endogenous agonist sufficiently. In search of a suitable PAAM of 5-HT2CR we adopted an in silico based approach that indicated the potential of the 3-(1-hydroxycycloalkyl) substituted isoquinolin-1-one derivatives against the 5-HT2CR as majority of these molecules interacted with the site other than that of Lorcaserin with superior docking scores. These compounds along with the regioisomeric 3-methyleneisoindolin-1-one derivatives were prepared via the Cu(OAc)2 catalyzed coupling of 2-iodobenzamide with 1-ethynylcycloalkanol under ultrasound irradiation. According to the in vitro studies, most of these compounds were not only found to be potent and selective agonists but also emerged as PAAM of 5-HT2CR whereas Lorcaserin did not show PAAM activities. According to the SAR study the isoquinolin-1(2H)-ones appeared as better PAAM than isoindolin-1-ones whereas the presence of hydroxyl group appeared to be crucial for the activity. With the potent PAAM activity for 5-HT2CR (EC50 = 1 nM) and 107 and 86-fold selectivity towards 5-HT2C over 5-HT2A and 5-HT2B the compound 4i was identified as a hit molecule. The compound showed good stability in male BALB/c mice brain homogenate (∼85 % remaining after 2 h), moderate stability in the presence of rat liver microsomes (42 % remaining after 1 h) and acceptable PK properties with fast reaching in the brain maintaining ∼ 1:1 brain/plasma concentration ratio. The compound at a dose of 50 mg/kg exhibited decreased trend in the food intake starting from day 3 in S.D. rats, which reached significant by 5th day, and the effect was comparable to Lorcaserin (10 mg/kg) on day 5. Thus, being the first example of PAAM of 5-HT2CR the compound 4i is of further medicinal interest.
... However, understanding its beneficial effects becomes quite complex. What is recognized is that abnormal or dysfunctional activity of the 5-HT 2A receptor is linked to several psychiatric disorders and other disorders related to substance use and addiction in humans and animal models [61][62][63][64]. For example, early positron emission tomography binding studies showed decreased 5-HT 2A levels in the hippocampus of patients with major depression [65]. ...
The use of psychedelics as medicines and for overall better brain health is potentially one of the most transformative developments given their immediate and long-lasting therapeutic effects across a plethora of neuropsychiatric disorders and, more recently, some neurodegenerative diseases. The US psychedelic drugs market is forecasted to grow by 16.3% by 2027 due to the increasing prevalence of treatment-resistant depression and mental health disorders. Decades-long restrictions, which date back to when psychedelics were declared controlled substances in 1970, have been lifted to allow researchers to publish on the therapeutic benefits of psychedelics. This review will feature the incredible depth of research underway revealing how psychedelics impact brain structure and function to treat mental health and other neurological disorders.
... 3 In support of this assumption, changes in 5-HT 2A R expression or function have been implicated in the etiology of many neuropsychiatric disorders such as depression, anxiety, or schizophrenia and cognitive disturbances associated with Alzheimer's or Parkinson's disease. 4−7 Based on these findings, pharmacological manipulation of 5-HT 2A Rs has emerged as a promising approach for the treatment of mental or cognitive disorders, as evidenced by various studies on the antidepressant, 8 anxiolytic, 9 and antipsychotic 10 effects of 5-HT 2A R antagonism. ...
Serotonergic 5-HT2A receptors in cortical and forebrain regions are an important substrate for the neuromodulatory actions of serotonin in the brain. They have been implicated in the etiology of many neuropsychiatric disorders and serve as a target for antipsychotic, antidepressant, and anxiolytic drugs. Positron emission tomography imaging using suitable radioligands can be applied for in vivo quantification of receptor densities and receptor occupancy for therapy evaluation. Recently, the radiosynthesis of the selective 5-HT2AR antagonist [18F]R91150 was reported. However, the six-step radiosynthesis is cumbersome and time-consuming with low radiochemical yields (RCYs) of <5%. In this work, [18F]R91150 was prepared using late-stage Cu-mediated radiofluorination to simplify its synthesis. The detailed protocol enabled us to obtain RCYs of 14 ± 1%, and the total synthesis time was reduced to 60 min. In addition, autoradiographic studies with [18F]R91150 in rat brain slices revealed the typical uptake pattern of 5-HT2A receptor ligands.
... This action is thought to counteract the aberrant dopaminergic neurotransmission in SCZ by directly or indirectly increasing 5-HT 1A receptor-mediated neurotransmission and modulating the biosynthesis and release of dopamine, ultimately eliciting antipsychotic activity (Schmidt et al., 1995;Kehne et al., 1996;Rollema et al., 1997;Lieberman et al., 1998;Díaz-Mataix et al., 2005;Meltzer and Huang, 2008;;Meltzer and Massey, 2011). On the other hand, most psychedelics are 5-HT 2A receptor agonists, and this action is thought to mediate their psychedelic, and hallucinogenic, effects (Kroeze and Roth, 1998;Meltzer, 1999;Celada et al., 2004;Nichols, 2016). ...
Mounting evidence suggests safety and efficacy of psychedelic compounds as potential novel therapeutics in psychiatry. Ketamine has been approved by the Food and Drug Administration in a new class of antidepressants, and 3,4-methylenedioxymethamphetamine (MDMA) is undergoing phase III clinical trials for post-traumatic stress disorder. Psilocybin and lysergic acid diethylamide (LSD) are being investigated in several phase II and phase I clinical trials. Hence, the concept of psychedelics as therapeutics may be incorporated into modern society. Here, we discuss the main known neurobiological therapeutic mechanisms of psychedelics, which are thought to be mediated by the effects of these compounds on the serotonergic (via 5-HT2A and 5-HT1A receptors) and glutamatergic [via N-methyl-d-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors] systems. We focus on 1) neuroplasticity mediated by the modulation of mammalian target of rapamycin–, brain-derived neurotrophic factor–, and early growth response–related pathways; 2) immunomodulation via effects on the hypothalamic-pituitary-adrenal axis, nuclear factor ĸB, and cytokines such as tumor necrosis factor-α and interleukin 1, 6, and 10 production and release; and 3) modulation of serotonergic, dopaminergic, glutamatergic, GABAergic, and norepinephrinergic receptors, transporters, and turnover systems. We discuss arising concerns and ways to assess potential neurobiological changes, dependence, and immunosuppression. Although larger cohorts are required to corroborate preliminary findings, the results obtained so far are promising and represent a critical opportunity for improvement of pharmacotherapies in psychiatry, an area that has seen limited therapeutic advancement in the last 20 years. Studies are underway that are trying to decouple the psychedelic effects from the therapeutic effects of these compounds.
Significance Statement
Psychedelic compounds are emerging as potential novel therapeutics in psychiatry. However, understanding of molecular mechanisms mediating improvement remains limited. This paper reviews the available evidence concerning the effects of psychedelic compounds on pathways that modulate neuroplasticity, immunity, and neurotransmitter systems. This work aims to be a reference for psychiatrists who may soon be faced with the possibility of prescribing psychedelic compounds as medications, helping them assess which compound(s) and regimen could be most useful for decreasing specific psychiatric symptoms.
... 5-HT 2A Rs are particularly abundant in the pre-frontal cortex (Fig. 3c;Jakab and Goldman-Rakic 1998;Cornea-Hebert et al. 1999Miner et al. 2003) and are certainly the site of action of hallucinogens, such as LSD (Aghajanian and Marek 1999b), and of some atypical anti-psychotics, such as clozapine and risperidone (Adell et al. 2005). Alterations in 5-HT 2A R function may be a contributing factor to the cognitive impairment in mental disorders such as schizophrenia and depression (Kroeze and Roth 1998). ...
... 5-HTRs contribute to the modulation of various biological processes including sleep-wake cycles, appetite, mood, memory, breathing, cognition and sexual behavior [26]. Serotonin has been the focus of many pharmacological studies for the treatment of neurological disorders with drugs that target either the serotonin receptors or serotonin uptake [19,30]. Examples include SSRIs (serotonin-selective reuptake inhibitors), SNRIs (dual serotonin-norepinephrine reuptake inhibitors) and partial agonists or antagonists for the 5-HTRs. ...
MAGI proteins are Membrane-Associated Guanylate Kinase Inverted proteins that belong to the MAGUK family. They are scaffolding proteins that were shown to mediate the trafficking and signaling of various G protein-coupled receptors (GPCRs). They contain PDZ domains in their structure and most GPCRs interact with these proteins via the PDZ motifs on the carboxyl terminal end of a receptor. In a PDZ overlay assay performed with the carboxyl terminal tail of 5-HT2AR, we were able to detect all three members of the MAGI subfamily, MAGI-1, MAGI-2 and MAGI-3 as interacting PDZ proteins. The PDZ motif of 5-HT2AR consists of three amino acids; serine (S), cysteine (C) and valine (V). In this study, we characterize these 5-HT2AR interactions with MAGI proteins. We first confirm the interaction using co-immunopricipitation and illustrate that the interaction is PDZ motif-dependent in human embryonic kidney (HEK 293) cells. We then assess the effects of overexpression and knockdown of the MAGI proteins on the internalization, trafficking and signaling of 5-HT2AR. We find that knockdown of either MAGI-1 or MAGI-3 using siRNA results in a significant reduction in the internalization of 5-HT2AR. As for signaling, we report here that MAGI proteins can modulate the signaling via the two transduction pathways that 5-HT2AR can activate. We illustrate a significant effect of modulating MAGI proteins expression on 5-HT-stimulated IP formation. We demonstrate an enhancement in 5-HT2AR-stimulated IP formation upon MAGI proteins overexpression. In addition, we show that knockdown of MAGI proteins with siRNA leads to a significant reduction in 5-HT2AR-stimulated IP formation. Furthermore, we illustrate a significant increase in 5-HT-stimulated ERK1/2 phosphorylation upon MAGI proteins overexpression. Interestingly, this effect on ERK1/2 activation is PDZ motif-independent. We also suggest two possible mechanisms of regulation for the effect of MAGI proteins on 5-HT2AR function. One mechanism involves the regulation of cell surface expression since we show that both MAGI-2 and MAGI-3 can enhance receptor trafficking to the plasma membrane when overexpressed in HEK 293 cells. The other mechanism points to regulation of second messengers in the signaling pathways. Specifically, we show that overexpression of any of the three MAGI proteins can enhance the recruitment of PLCβ3 to 5-HT2AR. In addition, we report a negative effect for knocking down MAGI-3 on β-arrestin recruitment to the receptor and this effect is PDZ motif-independent. Taken together, our findings document distinct roles for the three MAGI proteins in regulating 5-HT2AR trafficking and signaling and emphasize the importance of studying PDZ proteins and their interactions with GPCRs to regulate their function.
... NK cells display surface expression of 5-HT 1A and 5-HT 2A-C [21]. These receptors are g-protein coupled receptors [16]. So far little is known about downstream signaling of 5-HT-receptors in NK cells. ...
Increased serotonin (5-HT) levels have been shown to influence natural killer cell (NK cell) function. Acute exercise mobilizes and activates NK cells and further increases serum 5-HT concentrations in a dose-dependent manner. The aim of this study was to investigate the impact of different serum 5-HT concentrations on NK cell migratory potential and cytotoxicity.
The human NK cell line KHYG-1 was assigned to 4 conditions, including 3 physiological concentrations of 5-HT (100, 130 or 170 µg/l 5-HT) and one control condition. NK cells were analyzed regarding cytotoxicity, migratory potential and expression of adhesion molecules.
No treatment effect on NK cell cytotoxicity and expression of integrin subunits was detected. Migratory potential was increased in a dose dependent manner, indicating the highest protease activity in cells that were incubated with 170 µg/l 5-HT (170 µg/l vs. control, p<0.001, 170 µg/l vs. 100 µg/l, p<0.001; 170 µg/l vs. 130 µg/l, p=0.003; 130 µg/l vs. control, p<0.001, 130 µg/l vs. 100 µg/l, p<0.001).
These results suggest that elevated 5-HT serum levels play a mediating role in NK cell function. As exercise has been shown to be involved in NK cell mobilization and redistribution, the influence of 5-HT should be investigated in ex vivo and in vivo experiments.
... Fluoxetine did not produce anxiolytic effect; a study has been demonstrated that acute administration of fluoxetine at a dose of 20 mg/kg might produce anxiogenic effects in elevated plus-maze test; while chronic administration of fluoxetine produced anxiolytic effect [36]. The anxiolytic effect of fluoxetine is due to SSRIs mechanism which has high affinity for at least four 5HT receptor subtypes including 5HT1 A [37]. In the present study fluoxetine did not induce anxiolytic effect, this might be due to that fluoxetine dose and sub-acute administration were not enough to produce significant effect as chronic administration. ...
Depression is a major cause of morbidity worldwide. Fluoxetine is a selective serotonin reuptake inhibitor, and is effective antidepressant medication. Selenium is essential for good health but required only in small amounts.Aim of the study is to investigate the effects of fluxetine alone and in presence of selenium on anxiety, spontaneous motor activity and antidepressant behavior. Also, the study aims to investigate the effects of selenium on spontaneous motor activity, anxiety measure, and antidepressant behavior, using photoelectric cells, elevated plus maze and forced swimming maze.Mice were divided into 5 group (n=6). Group 1 (control), administered 1% tween 80 (5 ml/kg); group 2 administered selenium (200 µg/kg); group 3 received diazepam as a positive control (1 mg/kg); group 4 received fluoxetine (20 mg/kg); while group 5 received combined treatment of fluoxetine and selenium. All drugs injected sub acutely (three doses), mice were intraperitoneally administered at 24, 5, and 1.0 hrs before scoring. All drugs administered as suspension in 1% Tween 80 (T80). It was injected in volume 5ml/kg. Plus maze, photoelectric cells and forced swimming maze models were used.Fluoxetine has no effect on anxiety or locomotor activity; while selenium produced anxiolytic effect without changes on locomotor activity. Fluoxetine has antidepressant activity without any effect on duration of climbing. Selenium induced antidepressant effect with climbing action. Fluoxetine abolish the anxiolytic effect of selenium when administered together, but the combined treatment decreases the locomotor activity. Fluoxetine administration with selenium counteract the antidepressant effect of each other and climbing effect of selenium. Finally, selenium improves anxiety and depression behavior in albino mice, and might be used as an alternative therapy instead of fluoxetine (which treat antidepression only); but it must not be taken in combination with it.
... Apparently, AD is associated with decrements in some 5-HT markers such as the raphe complex, the uptake/ transporter complex, and in the number of 5-HT 1A , 5-HT 1B , 5-HT 1D , 5-HT 2A , 5-HT 2C , 5-HT 4 and 5-HT 6 receptors (Garcia-Alloza et al., 2004Meneses, 2003). It should be noted that receptor numbers could be modified by alterations in transduction, translation, posttranslational processing, and metabolic turnover (see Kroeze and Roth, 1998). ...
... Furthermore, many hallucinogenic drugs exert their psychoactive effects by acting as agonists for 5-HT 2A Rs. Preclinical studies show that 5-HT 2A R blockade has antipsychotic (Meltzer, 1999), antidepressant (Kroeze and Roth, 1998; Roth et al., 1998) and anxiolytic properties (Cohen, 2005). Pharmacological studies indicate that high-affinity antagonists of 5-HT 2A Rs are effective atypical antipsychotics, due to their demonstrated efficacy to reduce both positive and negative symptoms of schizophrenia. ...
Serotonin 5-HT2A receptors (5-HT2ARs) are widely distributed in the central nervous system, especially in brain region essential for learning and cognition. In addition to endogenous 5-HT, several hallucinogens, antipsychotics, and antidepressants function by targeting 5-HT2ARs. Preclinical studies show that 5-HT2AR antagonists have antipsychotic and antidepressant properties, whereas agonist ligands possess cognition-enhancing and hallucinogenic properties. Abnormal 5-HT2AR activity is associated with a number of psychiatric disorders and conditions, including depression, schizophrenia, and drug addiction. In addition to its traditional activity as a G protein-coupled receptor (GPCR), recent studies have defined novel operations of 5-HT2ARs. Here we review progress in the (1) receptor anatomy and biology: distribution, signaling, polymerization and allosteric modulation; and (2) receptor functions: learning and memory, hallucination and spatial cognition, and mental disorders. Based on the recent progress in basic research on the 5-HT2AR, it appears that post-training 5-HT2AR activation enhances non-spatial memory consolidation, while pre-training 5-HT2AR activation facilitates fear extinction. Further, the potential influence that 5-HT2AR-elicited visual hallucinations may have on visual cue (i.e., landmark) guided spatial cognition is discussed. We conclude that the development of selective 5-HT2AR modulators to target distinct signaling pathways and neural circuits represents a new possibility for treating emotional, neuropsychiatric, and neurodegenerative disorders.
... It is also essential in regulating various mental processes including emotion, cognition, perception and consciousness [50]. Abnormalities in the serotonergic nervous system have been related to a number of mental disorders including schizophrenia [51], depression [52], anxiety [53], and obsessive compulsive disorder [54]. These disorders have been associated with either agonistic or antagonistic activation of 5-HT1A and 5-HT2A receptor [55]. ...
Indolealkylamines (IAAs) are biogenic amines and derivatives of 5-hydroxytryptamine, acting primarily on serotonin receptors. IAAs are often considered the most thoroughly investigated group of aromatic amines in the amphibian skin. On the contrary, at present the detailed knowledge of these compounds in lower organisms is still limited and the biogenic amine receptors, mediating hormonal and modulatory functions, are largely unknown in primitive invertebrates. However, some active research is currently underway investigating this class of biogenic amines. Notably, during the last three decades several investigations have demonstrated the biological activity of endogenous biogenic amines in cnidarians, which are known to be the lowest beings equipped with an effective, even though rudimentary, nervous system. Toads, especially those from the Bufonidae family, constitute a significant part of the amphibian family and are an identified source of IAAs. To date fourteen IAAs have been identified in the skins of toad species. All are 5-substituted IAA derivatives acting mainly on the central nervous system (CNS), with most exhibiting some degrees of 5-HT2A receptor selectivity. This selective ability presents potential for their use in the development of treatments for various disorders such as schizophrenia, depression, anxiety, obsessive-compulsive disorders and chronic pain conditions. There are indications that some IAAs may also show subclass selectivity through binding to multiple 5-HT receptor subtypes. Thus, there exists an additional promising platform for the development of therapeutics targeting multiple 5-HT receptors. In this review, IAAs occurring naturally in various species of toad skins, which have been identified and isolated since 1944 are summarized and comparisons are made with similar biogenic amines recognized in cnidarians to date. Such comparisons highlight the potential to utilize existing knowledge gathered from vertebrates, such as toads in order to improve the understanding of the activities of such compounds in lower invertebrates.
... Интерес представляет выявленная связь усталости с аксиальными моторными симптомами БП, которые имеют недофаминергическую природу. В частности, в недавнем исследовании PROMS-PD [8] выявлена связь аксиальных симптомов БП с дисфункцией холинергических путей. Таким образом, результаты нашей работы дают основание для предположения о том, что в биохимических механизмах усталости при паркинсонизме определенную роль играет холинергический дефицит. ...
To study clinical characteristics of fatigue syndrome in patients with Parkinson's disease (PD) and a role of inflammation in its development.
We examined 98 patients with confirmed diagnosis of PD and 18 healthy people. Clinical examination included an analysis of anamnesis and objective somatic symptoms. The unified Parkinson's disease rating scale, The Hoehn and Yahr scale, the Multidimensional Fatigue Inventory (MFI-20) scale, the Modified Fatigue Impact Scale (MFIS), the Hospital Anxiety and Depression Scale (HADS), The Epworth Sleepiness Scale (ESS), Vein's Autonomic Symptoms Questionnaire (VASQ) were used for quantitative assessment. Serum concentrations of IL-6 were measured in 65 patients and 18 controls using ELISA.
In PD patients, fatigue assessed with MFI-20 was recorded in 46 (47%) cases and fatigue as assessed with MFIS in 45 (46%) of cases. High frequency and severity of fatigue syndrome were observed. The most prominent components in the structure of fatigue were physical fatigue, reduced motivation and decreased activity. Signs of fatigue increased with disease progression. Correlation between fatigue and axial motor symptoms of PD is of interest. Patients had higher serum IL-6 levels compared to the controls. Concentrations of IL-6 were correlated with fatigue severity and its main components (general and physical fatigue, decreased activity) and with depression level.
... Los agonistas de este recetor son altamente alucinógenos a bajas dosis, influyendo tanto en la percepción como en los estados de ánimo (Nichols, 2004). La gran mayoría de los antipsicóticos atípicos son antagonistas 5-HT 2A , así como agonistas 5-HT 1A (Kroeze and Roth, 1998;Meltzer, 1999). Así mismo, se han encontrado alteraciones en el receptor 5-HT 2A en trastornos como la depresión clínica y la esquizofrenia (Deutch et al., 1991;Schmidt et al., 1995). ...
... 21 , NO . S6 actions should appear at higher doses (Kroeze and Roth 1998). Data from other laboratories expand these observations. ...
The use of animal models for the study of psychosis and new treatment development is inadequate in assessing target psychotic symptoms because animals lack an ability to use language. Despite this deficiency, new antidopaminergic antipsychotic drugs have still become available. However, even these new antipsychotics, although substantially better than the conventional compounds, do not “cure” psychosis or normalize schizophrenic symptoms. The need for new treatment strategies is apparent. The value of a human model, where language is available to describe target symptoms, is clear. Currently, there is an opportunity to use the mild psychotomimetic symptoms induced by a minimal dose of ketamine in normal humans as a model of psychosis. The mental symptoms in this model resemble some of the symptoms of schizophrenia, suggesting the additional possibility that parallel mechanisms of psychosis may occur in schizophrenia and in a ketamine state, creating a potentially viable psychosis model for pathophysiology. This paper includes arguments in support of this human model's application. Several potential outcome measures that can be used to evaluate potentially novel antipsychotics are described. This model has the potential for identifying novel therapeutics because it does not primarily utilize the dopaminergic system. Further delineation of ketamine pharmacology in humans is pivotal to the eventual application of this ketamine model in drug development.
... The neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) mediates a wide range of physiological functions by interacting with multiple receptors, and these receptors have been implicated for their important roles in certain pathological and psychopathological conditions. In the brain, the function of many 5-HT receptors can now be unequivocally associated with specific physiological responses, ranging from modulation of neuronal activity, and transmitter release to behavioral change [123,124]. ...
Benzodiazepine (BZ or BZD) is a class of gabaminergic psychoactive chemicals used in hypnotics, sedation, in the treatment of anxiety and others CNS disorders. These drugs include alprazolam (Xanax), diazepam (Valium), clonazepam (Klonopin) and others. There are two distinct types of pharmacological binding sites for benzodiazepines in the brain (BZ1 and BZ2) and these sites are on GABA-A receptors and they are classified as short, intermediate and long-acting. Concerning the thienobenzodiazepine class (TBZ), Olanzapine (2-methyl-4-(4-methyl-l-piperazinyl)-10H-thieno[2,3-b][1,5]benzodiazepine) (Zyprexa) an atypical antipsychotic agent, structurally related to clozapine, extensively used for the treatment of schizophrenia, bipolar disorder-associated mania, and the behavioral symptoms of Alzheimer's disease, was used as an example to demonstrate the antagonism of this class of compounds for multiples receptors including: dopamine D1-D5, α-adrenoreceptor, histamine H1, muscarinic M1-M5 and 5-HT2A, 5-HT2B, 5-HT2C, 5-HT3 and 5-HT6 receptors. The functional blockade of these multiple receptors contributes to their wide range of pharmacologic and therapeutic activities, with relatively reduced side effects when compared to other antipsychotics agents, and allow us to characterize them as multi-acting-receptor-targeted-agents. This mini-review discussed about these 2 classes of drugs that act on the central nervous system, the main active compounds used and the various receptors that interact. In addition, we propose 12 olanzapine analogues and generated Random Forest models, from a data set obtained from ChEMBL database, to classify the structures as active or inactive against 5 dopamine receptors (D1, D2, D3, D4, D5 and D6) and dopamine transporter.
... Уменьшение содержания серотонина приводит к ослаблению анальгетического эффекта, снижению болевых порогов, повышению частоты болевых синдромов [6][7][8]. Генетические исследования показали, что структура тромбоцитарного и мозгового серотонинового транспортера кодируется одним и тем же геном, что может быть связано с общим эмбриональным происхождением этих двух различных клеток [9]. Идентичность рецепторов тромбоцитов и серотонинергических нейронов положена в основу теории о сходстве системы «тромбоциты -плазма» и системы «пресинаптические окончания -экстрацеллюлярная жидкость» [10,11]. ...
The indicators of pain and psychological status, the concentrations of serum serotonin and blood platelets, and the levels of brain-derived neurotrophic factor (BDNF) and nerve growth factor were studied in 82 patients with diabetic peripheral neuropathy (DPN). Along with conventional treatment aimed to normalize carbohydrate metabolism, 30 patients with DPN received actovegin in an intravenous, jetwise dose of 10.0 ml for 10 days. Prior to treatment, their pain intensity was 5.94±1.2 and 29.6±6.24 scores according to a visual analogue scale (VAS) and PainDETECT, respectively. The subclinical level of anxiety and depression was noted. The amount of serotonin in the serum (90.39±55.43 ng/ml) and blood platelets (298.13±80.33 ng/ml) was lower than that in the control. The content of serum BDNF in DPN was also substantially lower (419.27±132.7 pg/ml; p<0.04) than that in the control. After treatment, the actovegin group showed a more significant reduction in pain syndrome according to the VAS (3.5±0.6 cm; p=0.005) and PainDETECT (19.4±4.1 scores, p=0.005), a decrease in the degree of anxiety and depression according to the Beck inventory (11.4±1.4 scores; p=0.001), and an increase in BDNF levels up to 979.71±289.9 pg/ml. Serum serotonin and blood platelets increased up to 206.13±78.3 and 477.06±114.45 ng/ml, respectively; which is indicative of the correct choice of the treatment for DPN.
... Antidepressants do more than block uptake of monoamine neurotransmitters. Studies with mammalian cells and mouse brain slices in culture have shown that SSRIs and TCAs bind tightly to several 5-HT receptor subtypes and act as either antagonists or agonists depending on the receptor bound (Ni and Miledi, 1997;Kroeze and Roth, 1998;Eisensamer et al., 2003). Mutations in C. elegans that either eliminate 5-HT, or knock out the 5-HT reuptake transporter, allowed several groups to show that the SSRI fluoxetine and the TCA imipramine can influence behavior independent of 5-HT and 5-HT reuptake (Weinshenker et al., 1995;Choy and Thomas, 1999;Sze et al., 2000;Ranganathan et al., 2001;Dempsey et al., 2005;Kullyev et al., 2010). ...
Many important drugs approved to treat common human diseases were discovered by serendipity, without a firm understanding of their modes of action. As a result, the side effects and interactions of these medications are often unpredictable, and there is limited guidance for improving the design of next-generation drugs. Here, we review the innovative use of simple model organisms, especially Caenorhabditis elegans, to gain fresh insights into the complex biological effects of approved CNS medications. Whereas drug discovery involves the identification of new drug targets and lead compounds/biologics, and drug development spans preclinical testing to FDA approval, drug elucidation refers to the process of understanding the mechanisms of action of marketed drugs by studying their novel effects in model organisms. Drug elucidation studies have revealed new pathways affected by antipsychotic drugs, e.g., the insulin signaling pathway, a trace amine receptor and a nicotinic acetylcholine receptor. Similarly, novel targets of antidepressant drugs and lithium have been identified in C. elegans, including lipid-binding/transport proteins and the SGK-1 signaling pathway, respectively. Elucidation of the mode of action of anesthetic agents has shown that anesthesia can involve mitochondrial targets, leak currents, and gap junctions. The general approach reviewed in this article has advanced our knowledge about important drugs for CNS disorders and can guide future drug discovery efforts.
... 21 , NO . S6 actions should appear at higher doses (Kroeze and Roth 1998). Data from other laboratories expand these observations. ...
The use of animal models for the study of psychosis and new treatment development is inadequate in assessing target psychotic symptoms because animals lack an ability to use language. Despite this deficiency, new antidopaminergic antipsychotic drugs have still become available. However, even these new antipsychotics, although substantially better than the conventional compounds, do not “cure” psychosis or normalize schizophrenic symptoms. The need for new treatment strategies is apparent. The value of a human model, where language is available to describe target symptoms, is clear. Currently, there is an opportunity to use the mild psychotomimetic symptoms induced by a minimal dose of ketamine in normal humans as a model of psychosis. The mental symptoms in this model resemble some of the symptoms of schizophrenia, suggesting the additional possibility that parallel mechanisms of psychosis may occur in schizophrenia and in a ketamine state, creating a potentially viable psychosis model for pathophysiology. This paper includes arguments in support of this human model's application. Several potential outcome measures that can be used to evaluate potentially novel antipsychotics are described. This model has the potential for identifying novel therapeutics because it does not primarily utilize the dopaminergic system. Further delineation of ketamine pharmacology in humans is pivotal to the eventual application of this ketamine model in drug development.
... 1B). In same line, both 5-HT 2A and the 5-HT 3 receptor subtypes (ligand-gated ion channel-receptor) have been found to be highly expressed in apical dendrites of CA1/CA3 pyramidal cells, glial cells and GABAergic interneurons in the hip- pocampus [115,122123124 and which appear to be implicated in the altered activity of distinct neurotransmission systems during depressive illness [125] or decreased in MDD sub- jects [6] or mediate cell loss and hippocampal atrophy during stress-inducing HPA axis hyperactivity and increased glucocorticoid responses in mood-related disorders [23,24] (seeFig. 2). ...
Extensive research studies showed the existing interaction between different systems of the body that maintain the stability of homeostatic processes and which allow species to adapt to its environment in response to stressors. Adaptive responses to stressors activates adaptive-mechanisms, that result in the synthesis and release of several brain neurotransmitters, peptide hormones, proinflammatory cytokines and adrenal steroids from neural, neuroendocrine and immune cells which prepared the organism to alert its systems to adopt the proper behavioral responses against stressful events. Neurotransmitters, peptide hormones and cytokines act through the HPA axis forming a regulatory loop that maintains homeostasis in response to different stressors. One route to understand the interactions between brain transmitters, neurosecretory peptide-hormones, adrenal steroids and immune-borne cytokines, including neurotrophic factors is when body`s systems and chemical communication between cells appear to be disrupted during stressful events as occurs in mood-related disorders and depression. Thus, this review will described the functional interactions between HPA axis activity and the projecting neural pathways (DRN-5HT neurons; LC-NA neurons) and brain neurotransmitters (NE, 5-HT, DA, GLU) that impinge on forebrain-limbic structures (hypothalamus, hippocampus, mPFCx) that drive the release of the CRH and CRH-dependent secretion of ACTH from anterior hypophysis and cortisol from adrenal glands, under stressful conditions. Moreover, interactions between immune-borne cytokines and HPA axis activity, and glucocorticoid receptors have been shown to be extremely important to understand the pathophysiological mechanisms that operate in mood-related disorders and MDD, including the stress-inducing altered changes in brain morphology, neuronal atrophy and neurogenesis in brain areas involved in learning processing and memory functions.
... There is increasing evidence from clinical and pharmacological studies that disturbances in serotonergic (5-HT) neuronal function are involved in the pathogenesis of depression. 1 The serotonin 6 (5-HT6) receptor is one of the newest of several studied serotonin receptors and an important candidate gene for the study of major depressive disorder (MDD) because it is abundant in the limbic system and some antidepressants have a high affinity for it. 2 The 5-HT6 receptor is located on chromosome 1p35-p36 and the density of its mRNA is highest in the olfactory tubercle, striatum, nucleus accumbens, dendate gyrus, and cornu ammonis (CA)1, CA2, and CA3 regions of the hippocampus. ...
Abstract The purpose of the present study was to determine if a 5-HT6 receptor polymorphism is associated with antidepressant treatment response in major depressive disorder (MDD). Ninety-one patients with MDD, compared with 127 normal control subjects, were evaluated after an 8-week treatment period. An association analysis revealed no differences in genotype and allele distribution between patients with MDD and normal control subjects. However, there were significant differences in the treatment response in some Hamilton Depression Rating Scale (HAM-D) scores (sleep, activity, somatic anxiety, and total) between genotypes. Moreover, the heterozygote group (CT genotype) had significantly better treatment response than the homozygote group (CC + TT genotypes), especially in the somatic-anxiety subcategory and the total score of HAM-D. These findings imply that a 5-HT6 receptor polymorphism (C267T) is associated with treatment response in MDD.
... Given the potential relevance of the receptor function there is numerous clues about a role for 5-HT 2A in the pathophysiological function, such as some hallucinogens (e.g. LSD, DOI) are 5-HT 2A agonists and atypical antipsychotics are 5-HT 2A antagonists [51,52]. In recent years, a number of open-label and placebo controlled studies have suggested that atypical antipsychotic drugs and some antidepressants (e.g., mirtazapine and mianserin) augment the clinical response to SSRI's in treatment-resistant patients [53,54]. ...
5-Hydroxytryptamine (5-HT2A) receptors play an important role in several psychiatric disorders. In order to investigate the serotonin (5-HT) receptor in vivo, reliable syntheses are required for positron emission tomography (PET) 5-HT radioligands. Owing to the excellent in vivo properties of [¹⁸F]MDL100907 for PET, there has been great interest to develop a novel synthetic route for [¹⁸F]MDL100907. Here, we report a highly efficient, scalable, and expedient synthesis for [¹⁸F]MDL100907. The radiofluorination was performed on a ¹⁸F-labeling boron pinacol ester precursor, which is synthesized using the Liebeskind–Srogl cross-coupling reaction as a key step. Our method is practically more suitable to employ late-stage Cu-mediated radiofluorination and facilitate the production of the [¹⁸F]MDL100907 radioligand in excellent decay-corrected RCY of 32 ± 10% (n = 7) within 60 min. We prepared [¹⁸F]MDL100907 in high molar activity (2.1 Ci/μmol) and compared it to [¹¹C]MDL100907 in the brain of a nonhuman primate.
A confluence of factors has renewed interest in the scientific understanding and translational potential of psychedelic drugs such as lysergic acid diethylamide (LSD), mescaline, and psilocybin: the desire for additional approaches to mental health care, incremental progress in basic and clinical research, and the reconsideration and relaxation of existing drug policies. With the United States Food and Drug Administration's designation of psilocybin as a “Breakthrough Therapy” for treatment‐resistant depression, a new path has been forged for the conveyance of psychedelics to the clinic. Essential to the further development of such applications, however, is a clearer understanding of how these drugs exert their effects at the molecular level. Here we review the current knowledge regarding the molecular details of psychedelic drug actions and suggest that these discoveries can facilitate new insights into their hallucinogenic and therapeutic mechanisms.
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A series of indole based novel Schiff bases was designed as potential agonists of 5‑HT2C receptor that was supported by docking studies in silico. These compounds were synthesized via Amberlyst-15 catalysed condensation of an appropriate pyrazole based primary amine with the corresponding indole-3-aldehyde under ultrasound irradiation at ambient temperature. A number of target Schiff bases were obtained in good yields (77-87%) under mild conditions within 1 h. Notably, the methodology afforded the corresponding pyrazolo[4,3-d]pyrimidin-7(4H)-one derivatives when the primary amine was replaced by a secondary amine. Several Schiff bases showed agonist activity when tested against human 5-HT2C using luciferase assay in HEK293T cells in vitro. The SAR (Structure-Activity-Relationship) studies suggested that the imine moiety was more favorable over its cyclic form i.e. the corresponding pyrazolopyrimidinone ring. The Schiff bases 3b (EC50 1.8 nM) and 3i (EC50 5.7 nM) were identified as the most active compounds and were comparable with Lorcaserin (EC50 8.5 nM). Also like Lorcaserin, none of these compounds were found to be PAM of 5-HT2C. With ∼24 and ∼150 fold selectivity towards 5-HT2C over 5-HT2A and 5-HT2B respectively the compound 3i that reduced locomotor activity in zebrafish (Danio rerio) larvae model emerged as a promising hit molecule for further study.
This paper presents the results ofa quantitative study ofserotonin in blood platelets in patients in the acute period ofencephalitis. Regardless of the clinical form of infection, in patients, there was revealed a significant decrease in this index 203,7 ± 107,1 ng/ml relatively to control values: 585,4 ± 258,8 ng/ml, respectively (p
A systematic review was implemented according to PRISMA guidelines on Pubmed, Psychinfo, Medline, Embase to fill the existing literature gap on the effectiveness of using Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT) in Anorexia Nervosa (AN), Bulimia Nervosa (BN) and Binge Eating Disorder (BED). Twenty-two articles were included. Four studies reported an increased density in 5-hydroxytryptamine receptor (5-HT1A) in fronto-temporo-parietal regions in both affected and recovered AN as well as in BN. The 5-HT transporter (5-HTT) binding was increased or diminished in different specific cortical areas and in relation to Eating Disorder (ED) subtypes. Some evidences of blunted Dopamine (DA) release in the putamen in BN patients suggest that their DA function might be impaired as in addictive behaviours. Studies estimating the regional Cerebral Blood Flow (rCBF) with SPECT demonstrated that temporal areas seem to play a key role in ED corroborating the hypothesis of a cingulate-temporal cortical dysfunction in AN. In addition, alterations of both parietal and prefrontal cortex provide a possible common neural substrate in AN. Studies included in this review are heterogeneous preventing robust conclusions, however, our findings add knowledge on some of the neurotransmitters involved in ED.
The volume of the International Journal of Pharmacology, Phytochemistry and Ethnomedicine describes the latest scientific investigations concerned with estimation of the effects of fluoxetine alone and in presence of selenium on anxiety, spontaneous motor activity and antidepressant behavior of albino mice as well as assessment of the sedative and antidiarrheal activity of ethanol extract of Commelina appendiculata C.B.Clarke in Swiss albino mice; evaluation of the acute and subchronic oral toxicity of Euphorbia scordifolia Jacq. in mice and rats; carrying out the comparison of the antifungal activity of three Caulerpa species against six human pathogenic yeast and four dermatophytes in order to discover new antifungal metabolites; phytochemical screening of the Common Walnut (Juglans regia L.) leaves as well as biological tests of antioxidant and antimicrobial effects of its aqueous extracts and also identification of the biochemical constitutes and antifungal activity of Psydrax dicoccos (Gaertn) Teys. & Binn. Leaves methanol extracts.
The serotoninergic 5-HT2A receptor is involved in the mechanism of depression and antidepressant drugs action. Earlier we showed that striatal-enriched protein tyrosine phosphatase (STEP) inhibitor – 8-(trifluoromethyl)-1,2,3,4,5-benzopentathiepin-6-amine hydrochloride (TC-2153) affects both the brain serotoninergic system and the brain-derived neurotropic factor that are known to be involved in the psychopathology of depression. In the present study we investigated the effects of chronic TC-2153 administration on behavior in the standard battery of tests as well as the effects of acute and chronic TC-2153 treatment on the brain 5-HT2A receptors in mice. We obtained a prominent antidepressant-like effect of chronic TC-2153 treatment in the forced swim test without any adverse side effects on locomotor activity, anxiety, exploration, motor skill and obsessive–compulsive-like behavior. Moreover, both acute and chronic TC-2153 administration inhibited the functional activity of 5-HT2A receptors estimated by the number of 2,5-dimethoxy-4-iodoamphetamine (DOI, agonist of 5-HT2A receptors)-induced head-twitches. TC-2153 treatment also attenuated the DOI-induced c-fos expression in cortical and hippocampal neurons and reduced the 5-HT2A receptor protein level in the hippocampus and frontal cortex, but not in the striatum. Taken together, our combined data demonstrate that the antidepressant effect of STEP inhibitor TC-2153 could be mediated by its inhibitory properties towards the 5-HT2A receptor-mediated signaling.
Prescription opioid abuse, for example of oxycodone, is a pressing public health issue. This study focuses on how chronic oxycodone self-administration (SA) affects the reward pathways in the mouse brain. In this study, we tested the hypothesis that the expression of reward-related genes in the ventral and dorsal striatum, areas involved in different aspects of opioid addiction models, was altered within 1 hour after chronic oxycodone SA, using transcriptome-wide sequencing (RNA-seq). Based on results from earlier human genetic and rodent studies, we focused on a set of genes that may be associated with the development of addictive diseases and the rewarding effect of drugs of abuse, primarily in the opioid, stress response and classical neurotransmitter systems. We found that 32 transcripts in the ventral striatum, and 7 in the dorsal striatum, were altered significantly in adult mice that had self-administered oxycodone (n=5) for 14 consecutive days (4 hours/day) compared with yoked saline controls (n=5). The following 5 genes in the ventral striatum showed experiment-wise significant changes: proopiomelanocortin (Pomc) and serotonin 5-HT-2A receptor (Htr2a) were upregulated; serotonin receptor 7 (Htr7), galanin receptor1 (Galr1) and glycine receptor 1 (Glra1) were downregulated. Some genes detected by RNA-seq were confirmed by quantitative polymerase chain reaction (qPCR).
Conclusion:
A RNA-seq study shows that chronic oxycodone SA alters the expression of several reward-related genes in the dorsal and ventral striatum. These results suggest potential mechanisms underlying neuronal adaptation to chronic oxycodone self-exposure, of relevance to our mechanistic understanding of prescription opioid abuse.
The 5-HT2CR agonist lorcaserin, clinically approved for the treatment of obesity, causes important side effects mainly related to subtype selectivity. In the search for 5-HT2CR allosteric modulators as safer anti-obesity drugs, a chemical library from Vivia Biotech was screened using ExviTech® platform. Structural modifications of identified hit VA240 in synthesized analogues 6-41 afforded compound 11 (N-[(1-benzyl-1H-indol-3-yl)methyl]pyridin-3-amine, VA012), which exhibited dose-dependent enhancement of serotonin efficacy, no significant off-target activities, and low binding competition with serotonin or other orthosteric ligands. PAM 11 was very active in feeding inhibition in rodents, an effect that was not related to the activation of 5-HT2AR. A combination of 11 with the SSRI sertraline increased the anorectic effect. Subchronic administration of 11 reduced food intake and body weight gain without causing CNS-related malaise. The behaviour of compound 11 identified in this work supports the interest of a serotonin 5-HT2CR PAM as a promising therapeutic approach for obesity.
In an attempt to understand the potential contribution of various neurotransmitter systems to the elaboration of symptoms associated with central nervous systems disorders in humans, we have studied genetically modified animal models. A mouse in which the dopamine transporter gene (DAT-KO) has been inactivated provides a model of hyperdopaminergia. This mouse displays phenotypes of hyperactivity, impaired cognitive tasks, sensorimotor gating, habituation and attention. These behavioral impairments can be corrected by antipsychotic drugs and as such recapitulate some manifestations of psychotic behaviors. However, the potent calming effect of psychostimulants on the hyperlocomotion phenotype of these mice suggests some relevance to symptoms associated with attention deficit hyperactivity disorder (ADHD). In the DAT-KO mice, our results reveal an interplay between the dopamine, glutamate and serotonin systems in controlling these behaviors. A mouse that carries a hypomorphic allele of the NR1 subunit of the NMDA receptor provides a model for a hypofunctioning glutamate system. NR1 mutant mice display behavioral abnormalities that are consistent with other pharmacological models of psychotic disorders (PCP and MK-801 intoxication), and these behaviors can be ameliorated more effectively by atypical rather than by typical antipsychotics. Thus, animals in which specific genes have been genetically modified can provide valuable models that can mimic certain disease symptoms.
The paper presents findings of the quantitative studies of blood serum serotonin in patients in acute period of inflammatory and traumatic brain injuries. The study involved 72 patients with acute traumatic injury (45 patients with brain contusion and 27 with concussion) and 44 patients with tick-borne encephalitis (TBE) at the height of the disease (35 patients with non-paralytic and 9 with paralytic forms). The control group consisted of 15 healthy individuals. The peripheral blood serum serotonin was measured by enzyme-linked immunosorbent assay. Its concentration in patients with brain contusion was 288.63±57.88 ng/ml, which was significantly (p=0.049) higher than in patients with brain concussion and in healthy individuals. Average serum level of serotonin in TBE patients regardless of clinical form of the disease, was 97.2±57.1 ng/ml, significantly lower than in healthy persons (p=0.003). In more severe paralytic form the quantitative serum serotonin levels were significantly lower than in non-paralytic one. Thus, the study of blood serum concentration of serotonin in traumatic and infectious processes allows to define and predict the severity of brain damage.
Serotonin (5-hydroxytryptamine; 5-HT) produces its effects through a variety of membrane-bound receptors both in the central and peripheral nervous system (CNS/PNS) as well as in several non-neuronal tissues (e.g., gastrointestinal tract, cardiovascular system, and blood). The serotoninergic system is one of the oldest neurotransmitter/hormone systems in evolution; this may explain why 5-HT interacts with such a diversity of receptors of both the 7-transmembrane receptors and the ligand-gated ion channels superfamilies, similarly to acetylcholine, GABA, and glutamate, but with a larger number and diversity of receptor subtypes. 5-HT was discovered in the gut in the 1930s and called enteramine, and then rediscovered in the 1940s in the blood and called serotonin, based on its vasoconstrictor features.
The sample of 72 patients with craniocerebral injury of light and medium degree in acute period was used to study the content of serotonin in blood serum and spinal liquor. The increase of the level of serotonin in blood serum depending on degree of severity of trauma was established. This occurrence can be used as a technique of differential diagnostic of concussion and contusion of brain.
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.
Copyright © 2015. Published by Elsevier Inc.
Sixty patients with multiple sclerosis and 12 healthy controls were examined. The fatigue was measured by the Fatigue Severity Scale (FSS). Concentration of platelet serotonin was analyzed with immunoassay techniques («Serotonin ELISA"). The results of the study have shown the primary role of fatigue in multiple sclerosis, with the prevalence of this syndrome reached 57.6%. The patients with multiple sclerosis had low concentration of platelet serotonin that was correlated with clinical features of the disease.
The serotonin subtype 2C (5HT2C) receptor is an emerging and promising drug target to treat several disorders of the human central nervous system. In this current report, two potent and selective 5HT2C full agonists, WAY-163909 (2) and vabicaserin (3) were radiolabeled with carbon-11 via Pictet-Spengler reaction with [11C]formaldehyde and used in positron emission tomography (PET) imaging. Reaction conditions were optimized to exclude the major source of isotope dilution caused by the previously unknown breakdown of N,N-dimethylformamide (DMF) to formaldehyde at high temperature under mildly acid conditions. In vivo PET imaging was utilized to evaluate the pharmacokinetics and distribution of the carbon-11 labeled 5HT2C agonists. Both radiolabeled molecules exhibit high blood brain barrier (BBB) penetration and non-specific binding, which was unaltered by pre-administration of the unlabeled agonist. Our work demonstrates that Pictet-Spengler reactions can be used to label drugs with carbon-11 to study their pharmacokinetics and for evaluation as PET radiotracers.
Serotonin (5-hydroxytryptamine, or 5-HT) receptors mediate a plethora of physiological phenomena in the brain and the periphery. Additionally, serotonergic dysfunction has been implicated in nearly every neuropsychiatric disorder. The effects of serotonin are mediated by fourteen GPCRs. Both the therapeutic actions and side effects of commonly prescribed drugs are frequently due to nonspecific actions on various 5-HT receptor subtypes. For more than 20 years, the search for clinically efficacious drugs that selectively target 5-HT receptor subtypes has been only occasionally successful. This review provides an overview of 5-HT receptor pharmacology and discusses two recent 5-HT receptor subtype-selective drugs, lorcaserin and pimavanserin, which target the 5HT2C and 5HT2A receptors and provide new treatments for obesity and Parkinson's disease psychosis, respectively.
Although St John’s wort has been subjected to extensive scientific studies in the last decade, there are still many open questions about its pharmacology and mechanism of action. Initial biochemical studies reported that St John’s wort is only a weak inhibitor of monoamine oxidase-A and -B activity but that it inhibits the synaptosomal uptake of serotonin, dopamine and noradrenaline (norepinephrine) with approximately equal affinity. However, other in vitro binding assays carried out using St John’s wort extract demonstrated significant affinity for adenosine, GABAa, GABAb and glutamate receptors. In vivo St John’s wort extract leads to a downregulation of β-adrenergic receptors and an upregulation of serotonin 5-HT2 receptors in the rat frontal cortex and causes changes in neurotransmitter concentrations in brain areas that are implicated in depression. In studies using the rat forced swimming test, an animal model of depression, St John’s wort extracts induced a significant reduction of immobility. In other experimental models of depression, including acute and chronic forms of escape deficit induced by Stressors, St John’s wort extract was shown to protect rats from the consequences of unavoidable stress. Recent neuroendocrine studies suggest that St John’s wort is involved in the regulation of genes that control hypothalamic-pituitary-adrenal axis function. With regard to the antidepressant effects of St John’s wort extract, many of the pharmacological activities appear to be attributable to the naphthodianthrone hypericin, the phloroglucinol derivative hyperforin and several flavonoids. This review integrates new findings of possible mechanisms that may underlie the antidepressant action of St John’s wort and its active constituents with a large body of existing literature.
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.
This chapter summarizes the recent advances in identifying potent and selective serotonin receptor ligands. A multitude of non-selective ligands for the various serotonin and other monamine receptors have been identified in the past, some of which have found clinical use. Selective serotonin receptor modulators have been the focus of many research groups. The advances in molecular biology coupled with the advent of high throughput synthesis and progress seen in asymmetric chemistry in the last decade have given rise to a multitude of novel selective serotonin subtype ligands. Utilization of these agents is expected to enable a greater understanding of serotonin's role in the pathophysiology of various disease states. The increased focus on central nervous system (CNS) therapeutics, and serotonin mediated pathways in particular, is expected to fuel the progress of this research. The manifest goal of this effort is to develop selective serotonin therapeutics that holds improvements over current non-selective serotonergic agents with respect to efficacy, side-effect profile and safety margin.
The only bromine and iodine radioisotopes worth using in PET or SPECT in vivo investigations during the development of a new drug are Br-76 and I-123. It is most of the time impossible to isotopically label a drug with Br-76 or I-123 since. the occurrence of drugs having a bromine or an iodine atom within their chemical structure is quite limited. However, by using specific radiobrominated or radioiodinated probes, it is possible to study in vivo the potential interaction of a drug with biochemical processess such as blood flow, glucose consumption, protein synthesis or cell proliferation and neurotransmission. Radiobrominated and radioiodinated probes have been described mainly for assessing cell proliferation. For imaging various classes of specific binding sites involved in neuronal or hormonal transmission, a great number of radiohalogenated ligands have been proposed and validated. The two-steps strategy consists of performing an "in vivo assay" by using first of all, one of these specific radiobrominated / -iodinated ligands (or probes) for targeting specific binding sites (receptor, transporter, enzymes) and in a second step by assessing the interaction of the cold drug on the binding of these probes. This indirect observation of drug-receptor (transporter, enzyme) occupancy allows predicting response, optimum dose and optimum scheduling. The most important radiobrominated and radioiodinated ligands specific for dopaminergic, serotoninergic, cholinergic and gabaergic binding sites and their application in drug development processes are reviewed.
Since being classified as a Schedule I controlled substance, MDMA (3,4-methylenedioxy-N-methylamphetamine; "ecstasy") has been the subject of controversy regarding its potential therapeutic usage, increased use by young people in the "Rave" culture, and issues of potential neurotoxicity. This review article summarizes much of the animal and human studies of the general behavioral effects of MDMA and MDMA-like drugs, as well as studies using specific locomotor activity and startle/prepulse inhibition paradigms. MDMA and related serotonergic drugs produce a unique behavioral profile in both humans and animals. The precise sites of action and mechanisms for these behavioral effects are still being studied. Carefully conducted studies of MDMA and related compounds in animal and human subjects will provide invaluable information that can be used to elucidate mechanisms underlying drug abuse, cognition, arousal, and motor activity, as well as mechanisms of neurotoxicity and the possible therapeutic value of MDMA.
The serotonin (5-HT) system is reviewed starting from the early history of 5-HT. There is a review of the biosynthesis, degradation, and synaptic reuptake of 5-HT as well as the neuroanatomy of the 5-HT system. The roles of these pathways in disease and therapeutic interventions are discussed. The focus of this chapter is on the multiple 5-HT receptors, their history, anatomical and subcellular localization, signaling pathways, and importance in behavior, neuropsychiatric disorders and psychopharmacology.
In the past, there have been many epidemiological and genetic studies of mood disorders, schizophrenia, and alcohol dependence, and in this study, the human serotonin 2A receptor (5-HTR2A) polymorphism was examined in 80 patients with mood disorders, 50 patients with schizophrenia and 41 patients with alcohol dependence. 5-HTR is related to affectivity, regulation, and pharmacologic effects of antidepressant, anti-anxiety and antipsychotic medications. The polymorphism in 5-HTR2A (102T/C, −1438 A/G) was identified by the polymerase chain reaction (PCR), followed by restriction fragment length polymorphism (RFLP). The results suggest that 5-HTR2A (102T/C, −1438G/A) polymorphism might not be associated with susceptibility to schizophrenia or mood disorders, and it might not be a risk factor contributing to alcohol dependency. We found that the 102T/C polymorphism was in linkage disequilibrium with the −1438G/A polymorphism in psychosis (mood disorder, schizophrenia, and alcohol dependence) and in health controls. Further studies are needed to determine whether or not the novel serotonin receptor (5-HTR) polymorphism reflects the pathogenesis of schizophrenia, mood disorders, and alcohol dependence.
IntroductionThe serotonin receptorsPeripheral effects by serotonin on pain transmissionSpinal and supraspinal effects by 5-HT receptorsClinical implicationSummaryReferences
The 5-HT(2C) receptor is an attractive drug target in the quest for new therapeutics to treat a variety of human disorders. We have previously undertaken a structural optimization campaign that has led to some potent and moderately selective 5-HT(2C) receptor agonists. After expanding our structure-function library, we were able to combine our datasets so as to allow the design of compounds of improved selectivity and potency. We disclose herein the structural optimization of our previously reported 5-HT(2B)/5-HT(2C) agonists, which has led to the identification of a highly selective 5-HT(2C) agonist, (+)-trans-[2-(2-cyclopropylmethoxyphenyl)cyclopropyl]methylamine hydrochloride, with an EC(50) of 55 nM and no detectable agonism at the 5-HT(2B) receptor.
The ability of a system to regulate its responsiveness in the presence of a continuous stimulus, often termed desensitization, has been extensively characterized for the beta2-adrenergic receptor (beta2AR). beta2AR signalling is rapidly attenuated through receptor phosphorylation and subsequent binding of the protein beta-arrestin. Ultimately the receptor undergoes internalization, and although the molecular mechanism is unclear, receptor phosphorylation and beta-arrestin binding have been implicated in this processs. Here we report that beta-arrestin and arrestin-3, but not visual arrestin, promote beta2AR internalization and bind with high affinity directly and stoichiometrically to clathrin, the major structural protein of coated pits. Moreover, beta-arrestin/arrestin chimaeras that are defective in either beta2AR or clathrin binding show a reduced ability to promote beta2AR endocytosis. Immunofluorescence microscopy of intact cells indicates an agonist-dependent colocalization of the beta2AR and beta-arrestin with clathrin. These results show that beta-arrestin functions as an adaptor in the receptor-mediated endocytosis pathway, and suggest a general mechanism for regulating the trafficking of G-protein-coupled receptors.
A conserved helix 2 Asp is required for the proper function of many G-protein-coupled receptors. To reveal the structural
basis for the role of this residue, the additive effects of mutations at this locus and at a conserved helix 7 locus were
investigated in the 5-HT2A receptor. All mutant receptors studied retained high affinity agonist and antagonist binding. Whereas an Asp → Asn mutation
in helix 2 eliminated coupling, interchanging the residues at the two positions by a second mutation of Asn → Asp in helix
7 restored receptor function. These data suggest that these residues are adjacent in space and interact. The loss of function
observed with Ala at either position is consistent with each side chain forming hydrogen bonds. Molecular dynamics simulations
were performed on three-dimensional computational models of agonist-receptor complexes of both the wild-type receptor and
the Asp → Asn mutant receptor. Consonant with the lack of coupling observed for the mutant construct, introducing the mutation
into the computational model produced a conformational change in a direction opposite to that seen from computational simulations
of activation of the wild-type receptor model. These results implicate both loci in a common hydrogen-bonding network underlying
receptor activation by agonist.
In [11], an induction principle for processes was given which allows one to apply modelchecking techniques to parameterized families of processes. A limitation of the induction principle is that it does not apply to the case in which one process depends directly upon a parameterized number of processes, which grows without bound. This would seem to preclude its application to families of N processes interconnected in a star topology. Nonetheless, we show that if the dependency can be computed incrementally, then the direct dependency upon the parameterized number of processes may be re-expressed recursively in terms of a linear cascade of processes, yielding in effect a "linearization" of the inter-process dependencies and allowing the induction principle to apply. Keywords: Automatic verification, distributed algorithms, induction, invariant, linearization, model checking, star topology. 1. Introduction Distributed multi-processor systems often are specified as consisting of a fini...
Biogenic amines such as serotonin elicit or modulate a wide range of behaviours by interacting with multiple receptor subtypes. We have isolated cDNA clones encoding three distinct Drosophila serotonin receptors which belong to the G protein-coupled receptor family. When expressed in mammalian cells, these receptors activate different intracellular effector systems. The 5HT-dro1 receptor stimulates adenylate cyclase while the 5HT-dro2A and the 5HT-dro2B receptors inhibit adenylate cyclase and activate phospholipase C. Expression of all three receptors starts in late embryos and is restricted to distinct populations of cells in the central nervous system. The 5HT-dro2A receptor is predominantly expressed in midline motor neurons (VUM neurons) that innervate larval muscles thus suggesting a role for this receptor in motor control.
The 5-hydroxytryptamine1A (5-HT1A) receptor can bind certain beta-adrenergic receptor antagonists, such as pindolol, with high affinity. Such pharmacological cross-reactivity suggests a structural similarity in the ligand binding site between the two receptors. To identify this structural entity, we mutated Asn385 in the seventh transmembrane domain of the human 5-HT1A receptor, based on the observation that this residue is conserved in all 5-HT1A and beta-adrenergic receptors of different species but is absent in all other cloned guanine nucleotide-binding protein-coupled receptors. This single point mutation (Asn385 to valine) causes a highly selective decrease in the affinity of pindolol and other aryloxyalkylamines for the mutant receptor (about 100-fold), while producing only minor changes in the binding of other 5-HT agonists and antagonists. The results provide direct evidence that Asn385 is responsible for the high affinity interaction between 5-HT1A receptors and aryloxyalkylamine beta-adrenergic antagonists but is not required for the binding of other chemical classes of ligands.
Under appropriate conditions, specific double-stranded DNA product was generated after amplification of genomic DNA sequences
in a polymerase chain-like reaction that contained only a single primer. This type of amplification reaction was performed
with a variety of primers and substrate DNAs. In addition to nonspecific heterogeneous products, 5 of 11 primers reproducibly
directed synthesis of double-stranded DNA that corresponded to the region of the template that contained the authentic primer
annealing site. Three of these amplified products were cloned and their ends were sequenced. All three contained a copy of
the primer at both 5′ ends, and the position of one of the primers represented the authentic primer binding site. In each
case, the location of the second copy of the primer Indicated that it had initially hybridized to a partially homologous sequence
In the template DNA. This single primer reaction makes it possible to amplify and clone a DNA region of unknown sequence that
Is adjacent to a known DNA sequence. One of the single primer reaction products described here included sequence to the 5′
side of the coding region of a serotonin receptor gene that contained a functional promoter.
Agonist occupancy of the cloned human serotonin (5-HT)1A receptor expressed in HeLa cells stimulates Na+/K+ ATPase activity as assessed by rubidium uptake. The purpose of the study was to determine which of the receptor-associated signaling mechanisms was responsible for this effect. 5-HT stimulated Na+/K+ ATPase 38% at 2 mM extracellular potassium, an effect characterized by a decrease in apparent K0.5 from 2.8 +/- 0.3 to 1.8 +/- 0.3 mM potassium without a significant change in apparent Vmax. The EC50 for the transport effect was approximately 3 microM 5-HT. The response was pertussis toxin-sensitive but did not involve inhibition of adenylate cyclase, as stimulation of Na+/K+ ATPase by 5-HT was observed in the presence of excess dibutyryl cAMP. Protein kinase C was not required for the response since short-term incubation with the phorbol esters phorbol 12 myristate, 13 acetate (PMA) and phorbol 12,13-dibutyrate (PDBu) did not mimic the 5-HT effect. Moreover, 5-HT increased Na+/K+ ATPase activity after inactivation of protein kinase C by overnight incubation with PMA. 5-HT and the sesquiterpene lactone thapsigargin increased cytosolic calcium in this cell model, and the EC50 for 5-HT corresponded with that for stimulation of Na+/K+ ATPase. Both thapsigargin and A23187, a calcium ionophore, also increased Na+/K+ ATPase activity in a dose-responsive fashion. The response to 5-HT, thapsigargin, and A23187 was blocked by conditions that removed the cytosolic calcium response. By two-dimensional gel electrophoresis, we established evidence for a calcium-sensitive but protein kinase C-independent signaling pathway. We conclude that the 5-HT1A receptor, which we have previously shown to stimulate phosphate uptake via protein kinase C, stimulates Na+/K+ ATPase via a calcium-dependent mechanism. This provides evidence for regulation of two separate transport processes by a single receptor subtype via different signaling mechanisms.
Serotonin is an ancient neurotransmitter. Phylogenetic comparisons suggest that the earliest serotonin receptor may have first appeared over 700 million years ago (Peroutka and Howell 1994). It is released from fiber tracts originating in primitive brainstem regions (the raphe nuclei of the brainstem reticular formation), and is found in species as ancient as Aplysia, Caenorhabditis elegans, and Drosophila. In addition, its synapses and receptors are widely distributed throughout the brain, serving many broad modulatory roles for diverse brain functions. It is not surprising, then, that serotonin receptors are primarily of the G-protein-coupled, 7-transmembrane receptor (7TM) class since these receptors couple to enzymatic and ion channel-modulating second messenger pathways (primarily adenylate cyclase, phosphoinositide turnover, and potassium channel modulation) which exhibit time constants in the second to millisecond range, consistent with broad signal modulation and gain-setting functions in the brain.
The molecular mechanisms by which drugs bind to and regulate G-proteincoupled receptors (GPCR) remains a major unsolved problem for modern molecular biologists, biochemists and structural biologists. Ideally, we would like to ultimately define drug binding at the atomic level. An ideal molecular model would also be able to demonstrate why it is that agonists activate receptors while antagonists, which may or may not bind in overlapping domains, do not activate receptors. A perfect molecular explanation of drug action would elucidate the molecular determinants responsible for cellular regulation processes (e.g. desensitization, internalization and downregulation). At the present time, there are no verifiable models which elucidate these properties for any G-protein-coupled receptor.
We review dystonia treatment results since 1981, including our own findings. Anticholinergics are still the most effective drugs, but less than 50% of patients continue with treatment. The authors recommend a combination of an anticholinergic, a benzodiazepine, and another drug (an antidopaminergic, carbamazepine, or fluperlapine) for the treatment of dystonia.
: 5-Hydroxytryptamine elicits its physiological effects by interacting with a diverse group of receptors. Two of these receptors, the 5-HT1Dβ and the 5-HT1E receptors, are ∼60% identical in the transmembrane domains that presumably form the ligand binding site yet have very different pharmacological properties. Analysis of the pharmacological properties of a series of chimeric 5-HT1Dβ/5-HT1E receptors indicates that sequences in the sixth and seventh transmembrane domains are responsible for the differential affinity of 5-carboxamidotryptamine for these two receptors. More detailed analysis shows that two amino acid differences in the sixth transmembrane domain (Ile333 and Ser334 in the 5-HT1Dβ receptor, corresponding to Lys310 and Glu311 in the 5-HT1E receptor) are largely responsible for the differential affinities of some, but not all, ligands for the 5-HT1Dβ and 5-HT1E receptors. It is likely that these two amino acids subtly determine the overall three-dimensional structure of the receptor rather than interact directly with individual ligands.
In an open multicenter trial 46 schizophrenic patients were treated with fluperlapine for 20 days. A mean daily dosage of 300–400 mg appeared to be an effective antipsychotic treatment in most cases. The marked antipsychotic effect was accompanied by a good improvement of depressive symptoms. Extrapyramidal side effects were extremely rare.Copyright © 1984 S. Karger AG, Basel
Combinatorial libraries are at the forefront of a revolution in basic research and drug discovery. They allow highly active compounds to be selected from hundreds of millions of others on the basis of biological activity.
The electromagnetic field distribution near the surface of a dielectric grating is calculated using a modified beam propagation method under total reflection condition. Results of the image contrast, the polarization dependence and the angular spectrum are given and discussed in the context of near field optical microscopy.
The recently characterized 5-HT2B subfamily of serotonin receptors has now been reported from three different species: human, rat and mouse. Their genomic structures include 2 introns present at identical positions. Despite this similarity, their respective protein sequences show some diversities. In addition, the pharmacology of these receptors is distantly related, and their sites of expression vary amongst species. Thus, it appears difficult at present to unambiguously classify these receptors into the same subfamily, raising the possibility of the existence of other 5-HT2B-like receptors, yet to be discovered.
Pig and rhesus monkey 5-HT2A receptor cDNA clones were isolated. The pig and rhesus monkey clones encode proteins that share a 94% and 95% homology, respectively, with the rat 5-HT2A receptor, and a 97% and > 99% homology, respectively, with the human 5-HT2A receptor. Within the transmembrane regions of the pig and monkey receptors, the deduced amino acid shows only three differences compared to that of the rat and are identical to the human 5-HT2A receptor clone.
The recent cloning of the complementary DNAs and/or genes for several receptors linked to guanine nucleotide regulatory proteins including the adrenergic receptors (alpha 1, alpha 2A, alpha 2B, beta 1, beta 2), several subtypes of the muscarinic cholinergic receptors, and the visual 'receptor' rhodopsin has revealed considerable similarity in the primary structure of these proteins. In addition, all of these proteins contain seven putative transmembrane alpha-helices. We have previously described a genomic clone, G-21, isolated by cross-hybridization at reduced stringency with a full length beta 2-adrenergic receptor probe. This clone contains an intronless gene which, because of its striking sequence resemblance to the adrenergic receptors, is presumed to encode a G-protein-coupled receptor. Previous attempts to identify this putative receptor by expression studies have failed. We now report that the protein product of the genomic clone, G21, transiently expressed in monkey kidney cells has all the typical ligand-binding characteristics of the 5-hydroxytryptamine (5-HT1A) receptor.
Quantitative autoradiography was used to evaluate the effects of adrenalectomy (ADX) and corticosterone (CORT) on binding at 5-HT1A and 5-HT1B receptors in the dorsal hippocampus and cortex of the rat. ADX increased binding of [3H]8-hydroxy-2-(di-n-propylamino)tetralin at 5-HT1A receptors in the oriens and lacunosum moleculare layers of CA2 and CA3, in the lacuno-sum moleculare layer of CA4 region, and in the dentate gyms. In restraint-stressed ADX rats, binding was increased only in the oriens and lacunosum moleculare layers of CA2. Restoration of baseline levels of CORT reversed the effects of ADX on 5-HT1A receptors in the hippocampus, while high levels of CORT decreased binding at 5-HT1A receptors in the dentate gyms. No treatment affected binding at 5-HT1A receptors in the CAl region of the hippocampus or in the cortex. ADX increased binding of [125I]iodocyanopindolol at 5-HT1B receptors in the infrapyramidal dentate, but this effect was not observed in ADX rats that were restrained. CORT treatment in both ADX and SHAM (adrenally intact) rats resulted in binding at 5-HT1B receptors that was lower than that in untreated ADX and SHAM rats in the infrapyramidal dentate, and lower than that in ADX rats in the suprapyramidal dentate and CA4. In ADX and SHAM rats, CORT also reduced binding at 5-HT1B receptors in area 2 of the cortex. It is suggested that decreases in binding at 5-HTA and 5-HT1B/1D receptors resulting from chronic exposure to high levels of CORT may also occur in animals that fail to adapt to chronic severe stress. Such changes in binding may play important roles in the etiology of depression.Copyright © 1992 S. Karger AG, Basel
We have studied the physical and functional linkages of heterologously expressed human 5-HT1A receptors to G protein alpha-subunits in HeLa and CHO-K1 cells. HeLa cells expressed immunoreactivity to G(i) proteins with an apparent rank order of G(ialpha3) (almost-equal-to 1 pmol/mg of protein) >> G(ialpha1) (almost-equal-to 0.1 pmol/mg) >> G(ialpha2) (< 0.02 pmol/mg), whereas CHO-K1 cells expressed immunoreactivity to G(ialpha2) (almost-equal-to 5 pmol/mg) >> G(ialpha3) (almost-equal-to 0.7 pmol/mg), but not to G(ialpha1). Both cell lines expressed large and small forms of G(salpha), but neither expressed detectable G(oalpha). Agonist-promotable physical coupling of the 5-HT1A receptor to G proteins was examined with high-affinity agonist binding and with co-immunoprecipitation using rabbit anti-receptor IgG fractions. Agonist treatment induced coupling of the 5-HT1A receptors to G proteins with an apparent rank order of G(ialpha3) > G(ialpha1), G(ialpha2) in HeLa cells and G(ialpha3) > G(ialpha2) in CHO-K1 cells. Agonist-promotable functional coupling of the 5-HT1A receptors to inhibition of adenylylcyclase was measured in membranes derived from HeLa and CHO-K1 cells expressing approximately 2.5-3 pmol of receptors/mg of protein by preincubation with antisera raised against the carboxyl termini of the G(i) protein alpha-subunits. A noteworthy difference between the two cell types was that antisera against the predominant G protein (G(ialpha2)) were substantially more efficacious than G(ialpha3) antisera at blocking functional coupling to adenylylcyclase inhibition in CHO-K1 cells, whereas in HeLa cells, antisera against nonpredominant G proteins (G(ialpha1)/G(ialpha2)) were equally as effective as those against the predominant G protein (G(ialpha3)). No physical or functional coupling of the 5-HT1A receptor to G(salpha) isoforms was detected in either cell line. These findings suggest that the 5-HT1A receptor can physically couple to multiple distinct G(i) proteins in mammalian cell membranes and that functional coupling to adenylylcyclase inhibition may be mediated by G(ialpha1), G(ialpha2), and G(ialpha3). One factor influencing the relative importance of those G proteins for 5-HT1A receptor-inhibited adenylylcyclase activity appears to be their relative levels of expression. Therefore, these results suggest that the coupling of the 5-HT1A receptor to adenylylcyclase relies in part on factors other than its rank order of affinity for G(i) protein alpha-subunits. It is likely that receptor/G protein molar ratios are important in determining the specificity of G protein coupling of the 5-HT1A receptor.
The serotonin 5-HT1B and 5-HT1A receptors bind certain β-adrenergic antagonists, such as propranolol and pindolol, with high affinity. Other 5-HT1 receptors that display very low affinity for β-adrenergic antagonists, have either a threonine (T) (S-HT1Dα 5-HT1Dβ and 5-HT1E) or an alanine (A) (5-HT1F) residue in the homologous position in the seventh transmembrane domain. In the case of the human 5-HT1Dβ receptor, replacement of this T with asparagine (N), dramatically increases its ability to bind β-adrenergic antagonists. To assess whether other 5-HT1 receptors would behave similarly, we have used site-directed mutagenesis to replace the T or A in 5-HT1Dα, 5-HT1E and 5-HT1F receptors with N. Both the wild-type and mutant genes were expressed transiently in COS-7 cells and radioligand binding studies were performed by using [3H]5-HT and [125I]iodocyanopindolol. Using [3H]5-HT, we found that the affinities of all the mutant receptors for propranolol and pindolol were significantly increased by 100–1000 fold, 5-HT1Dα and 5-HT1F receptors showing the highest and the 5-HT1E receptor displaying the lowest affinity. On the other hand, the affinities for 5-HT were essentially unchanged as compared to the wild-type receptors. All mutant receptors bound [125I]iodocyanopindolol with high affinity. KD values ranging between 0.04nM (mutant 5-HT1Dα) and 0.57 nM (mutant 5-HT1E), whereas the wild-type receptors failed to show any specific binding with this radioligand in the same concentration range used for the mutant receptors.Therefore, the presence of this key asparagine residue confers binding for β -antagonists even in serotoin receptors which differ substantially in molecular structure. Even so, it appears likely that these ligands are recognized by the set of 5-HT1 receptors in a homologous orientation when interacting with the ligand binding pocket.
Previous radioligand binding studies have demonstrated human platelet serotonin2A (5-HT2A) receptor binding sites. Pharmacological similarities between platelet and frontal cortex 5-HT2A receptor binding parameters have been demonstrated. However, it is not clear whether the platelet 5-HT2A receptor primary structure is identical to that of the brain receptor. Three overlapping cDNAs were obtained to span completely the coding region of the 5-HT2A receptor. These clones were sequenced with external and internal primers. The nucleotide sequence of human platelet 5-HT2A cDNA was identical to that reported for the human frontal cortex 5-HT2A receptor, except for nucleotide 102 (T → C), which has been reported to represent a normal DNA polymorphism that does not alter the amino acid sequence. This finding may have implications in the study of neuropsychiatric disorders for which altered platelet 5-HT2A receptor binding has been demonstrated.
A cDNA clone (designated as GP2-7) encoding a novel 5-hydroxytryptamine (5-HT) receptor was isolated from a guinea pig hippocampal library. The receptor shares amino acid homology within the hydrophobic domains with other cloned 5-HT receptor subtypes (34–48%). The sequence of GP2-7 is homologous to that described for a novel receptor previously cloned from a rat brain cDNA library and provisionally designated as 5-HT7. mRNA for GP2-7 was detected in cortical and limbic brain regions. Transiently expressed GP2-7 showed high-affinity binding to [3H]5-HT (pKi = 9.0) with the following rank order of affinities: 5-carboxyamidotryptamine (5-CT) > 5-HT = 5-methoxytryptamine (5-MeOT) > methiothepin > 8-hydroxy-2-(dipropylamino)tetralin (8-OH-DPAT) > spiperone ≫ sumatriptan. Adenylyl cyclase activity in CHO-K1 cells transiently transfected with GP2-7 was stimulated by several analogues of 5-HT with the following order of potency: 5-CT > 5-HT = 5-MeOT > dipropyl-5-CT > 8-OH-DPAT. Methiothepin and spiperone were potent antagonists. Preliminary analysis suggests that GP2-7 closely resembles a receptor in the guinea pig hippocampus that exhibits a high affinity toward 5-CT.
Both glucocorticoid excess and decreased serotoneergic (5-HT) transmission may cause depression. The recently cloned 5-HT6 and 5-HT7 receptors have high affinity for antidepressants. Here, we show that pharmacological adrenalectomy increases 5-HT6 and 5-HT7 receptor mRNA expression in specific hippocampal subfields, effects partly reversed by corticosterone replacement. Increased 5-HT6 and 5-HT7 receptor expression may provide a basis, in part, for the therapeutic actions of adrenal steroid synthesis inhibitors in resistant depression.
The 5-HT2C receptor gene is unique among the members of the 5-HT receptor family by virtue of its genomic organisation. The human 5-HT2C receptor gene, unlike many other genes for guanine nucleotide binding (G)-proteins, contains three introns which interrupt the coding sequence into four exons. The first two introns are at equivalent positions as compared to the intervening sequences previously found in the 5-HT2(A) receptor gene, suggesting a close evolutionary relationship between both genes. Southern blot analysis shows that the 5-HT2C receptor gene is a single copy gene. Furthermore, we report the functional expression of a complementary DNA for the 5-HT2C receptor, cloned from hippocampal RNA. Membranes prepared from NIH 3T3 cells stably expressing the 5-HT2C receptor cDNA, displayed a single population of high affinity sites for the antagonist [3H]mesulergine (Kd = 2.9 ± 0.4 nM, Bmax = 44.3 ± 7.2 pmol/mg protein) as well as for [3H]5-HT (Kd = 9.9 ± 0.7 nM, Bmax = 13.6 ± 1.0 pmol/mg protein). Displacement of [3H]mesulergine and [3H]5HT binding by ligands indicated a pharmacological similarity of these binding sites with porcine and rat choroid plexus 5-HT2C receptors. Furthermore, activation of the 5-HT2C receptor with 5-HT results in an increased phospholipase C activity.
We have recently demonstrated that the LEW/N rat contains lower concentrations of cortical and hippocampal 5-HT1A receptors compared with the F344/N and out-bred HSD rats. To further characterize these strains, we investigated the effect of chronic (8 wk) imipramine administration (5 mg/kg/day) on 5-HT1A and 5-HT2 receptor densities and mRNA in the cortex and hippocampus and 5-HT transporter mRNA in the dorsal raphe of LEW/N, HSD and F344/N rats, using quantitative autoradiography and in situ hybridization histochemistry. After imipramine treatment, a significant increase in the levels of hippocampal 5-HT1A receptors, but not mRNA, was observed in LEW/N rats while the abundance of hippocampal 5-HT1A receptor mRNA, but not 5-HT1A receptor densities, decreased in F344/N rats. Cortical and hippocampal 5-HT2 receptor densities, but not mRNA, significantly decreased after imipramine administration in all three strains. Finally, 5-HT1A receptor densities and the abundance of mRNAs encoding the 5-HT1A receptor and 5-HT transporter in the dorsal raphe remained unaltered after imipramine administration in all three strains. The effects of imipramine on the levels of cortical and hippocampal 5-HT1A and 5-HT2 receptors and their transcripts, therefore, appear to be strain-dependent. The implications of these findings are discussed.
Since most of our knowledge on pharmacological properties of brain 5-HT4 receptors have been discussed for mouse colliculi neurons, we cloned the corresponding receptor using the RT-PCR approach. As expected, the homology with the already cloned rat 5-HT4L receptor was high, revealing only 16 differences at the amino-acid level. One of the differences, proline75 in mouse, alanine75 in the already published rat sequences was not confirmed. Therefore this proline is part of the consensus sequence present in all 5-HT receptor transmembrane domain II (LVMP). Comparing the affinities of 11 agonists and five antagonists for the cloned mouse receptor (5-HT4L) expressed in LLCPK1 and the corresponding receptor in mouse colliculi shows an excellent correlation. The transfected mouse 5-HT4L receptor stimulated cAMP production. When expressed at high density, it exhibited intrinsic activity. In contrast to the previously described distribution, we found that mRNA encoding for both the short (5-HT4S) and the long form (5-HT4L) of 5-HT4 receptors are expressed in all mouse and rat brain areas.
Wild-type and mutant serotonin 1A receptors were transiently expressed in COS-7 cells using the infection-transfection variant of the vaccinia virus/ T7 polymerase vector system. The amino acid substitutions in the transmembrane regions, Asp82→Asn82, Asp116 →Asn116, and Ser198→Ala198 all resulted in a decrease in affinity for 5-HT by 60–100-fold, without affecting the affinity for the antagonist, pindolol. The binding of agonist to the additional mutant, Thr199→Ala199, was too weak to be measured, 5-HT induced GTPase activities for all receptors studied. These findings indicate that the residues mutated play an important role in the binding of the agonist and less critical roles in the binding of the antagonist pindolol.
Serotonin (5-hydroxytryptamine; 5-HT) mediates many central and peripheral nervous system functions by its interaction with specific neuronal receptors. Here we report the genomic structure of the human 5-HT2 receptor. The SacI-EcoRI restriction fragment of rat 5-HT2 receptor cDNA was used as a probe to identify and isolate two positive clones of 8.5 and 7.0 kb from an EcoRI restriction digest of a chromosome 13 specific EcoRI fragment lambda-phage human genomic library. Subcloning and sequencing of these fragments showed the 8.5 kb fragment (designated lambda SE-5) contained the first two exons of the 5-HT2 receptor gene. The 7.0 kb insert (lambda SE-2) contained an incomplete third exon. A HindIII-EcoRI fragment of this insert was used as a probe to isolate a 9.0 kb clone (lambda SH-2), which contained the entire third exon, from a chromosome 13 specific HindIII-fragment lambda-phage human genomic library. The isolation of these three clones (lambda SE-5, lambda SE-2 and lambda SH-2) shows that the human 5-HT2 receptor gene consists of three exons separated by two introns and spans over 20 kb. The deduced amino acid sequence of the human, mouse and rat 5-HT2 receptors are highly conserved and all three share a 90% sequence similarity.
The family of serotonin receptors consists of at least eight distinct subtypes, divided into four classes based on their pharmacological and functional characteristics. Here we report the cloning and expression in Swiss 3T3 cells of the human 5-HT2 and 5-HT1A receptor subtypes. Both genes encode functional receptors for 5-HT, that differ considerably in genomic structure, primary amino acid sequence, pharmacology and signal transduction. The 5-HT1A receptor transfectants displayed a single high affinity site for the agonist [3H](+/-)-8-hydroxy-2-(di-n-propylamino)tetralin HBr ([3H]8-OH-DPAT) and a pharmacological profile specific for the 5-HT1A receptor. In these transfectants, 5-HT mediated a dose-dependent inhibition of forskolin-stimulated cAMP levels. Cells expressing the 5-HT2 receptor exhibited high affinity binding for the antagonist [3H]ketanserin with a 5-HT2 receptor specific pharmacological profile. In these cells 5-HT activated phospholipase C in a dose-dependent manner. The 5-HT2 receptor displayed a genomic organization quite different from the 5-HT1A, 5-HT1B and 5-HT1D receptor subtypes. While these receptors are encoded by one single exon, the 5-HT2 receptor is encoded by three exons separated by two introns. The latter finding adds and additional molecular criterion for receptor classification.
Serotonin (5-hydroxytryptamine, 5-HT) is an important neurotransmitter which mediates numerous physiological functions. Using the SacI-EcoRI restriction fragment of the rat brain 5-HT2 receptor cDNA as a probe, we have screened a mouse brain cDNA library, created by random priming and constructed in SWAJ vectors, and have isolated a cDNA encoding a 1.4 kb open reading frame which codes for a functional mouse 5-HT2 receptor identified from pharmacological binding profiles and coupling of phosphoinositide formation in a stably transfected fibroblast cell line. The deduced amino acid sequence is 97.4% identical to the rat 5-HT2 receptor. Using the same 5-HT2 receptor cDNA probe, ten positive genomic clones were isolated from two mouse genomic libraries constructed in the pWE15 cosmid vector and the EMBL-3 phage vector. Extensive mapping and sequencing of these genomic clones indicate the mouse 5-HT2 receptor coding region spans over 20 kb and is composed of three exons split by two introns. Northern blot analysis shows one band of 5-6 kb in the mouse brain, but not in the heart, lung, liver, or kidney total RNA. Southern analysis of mouse liver genomic DNA shows a simple pattern of digestion by several restriction enzymes, which suggests that one copy of the 5-HT2 receptor gene may exist in the mouse genome.
We determined the affinities of clozapine and 21 other typical and atypical antipsychotic agents for the cloned 5-hydroxytryptamine-1C (5-HT1C) receptor. For these studies, 5-HT1C receptors were transiently expressed in COS-7 cells using the vector pSVK3-5HT1C. We discovered that clozapine and several other putative typical and atypical antipsychotic agents (loxapine greater than tiosperone greater than SCH23390 greater than fluperlapine greater than rilapine greater than chlorpromazine) had relatively high affinities (7-30 nM) for the cloned 5-HT1C receptor. Other antipsychotic agents (risperidone greater than tenilapine greater than mesoridazine greater than thioridazine greater than cis-fluphenthixol) had intermediate affinities (30-100 nM), whereas many other antipsychotics (fluphenazine greater than spiperone greater than amperozide greater than melperone greater than thiothixene greater than haloperidol, metoclopramide, pimozide, domperidone, sulpiride) had low affinities (greater than 500 nM) for the cloned 5-HT1C receptor. The results indicate that although several putative atypical antipsychotic agents have high affinities for the cloned rat 5-HT1C receptor, the spectrum of drug binding does not correlate with the atypical nature of these compounds.
The biogenic amine, 5-hydroxytryptamine (5-HT), was first described in extracts of natural materials almost 30 years ago (see review by Collier, 1957). Twarog and
Page (1953) and Amin et al. (1954) were the first to demonstrate, on pharmacological evidence, the occurence of 5-HT in the central nervous system of the dog which was confirmed by Bogdanski et al. (1956) and
Correale (1956) by physicochemical criteria.
Neuropsychiatric disorders such as anxiety, depression, migraine, vasospasm and epilepsy may involve different subtypes of the 5-hydroxytryptamine (5-HT) receptor. The 1B subtype, which has a unique pharmacology, was first identified in rodent brain. But a similar receptor could not be detected in human brain, suggesting the absence in man of a receptor with equivalent function. Recently a human receptor gene was isolated (designated 5-HT1B receptor, 5-HT1D beta receptor, or S12 receptor) which shares 93% identity of the deduced protein sequence with rodent 5-HT1B receptors. Although this receptor is identical to rodent 5-HT1B receptors in binding to 5-HT, it differs profoundly in binding to many drugs. Here we show that replacement of a single amino acid in the human receptor (threonine at residue 355) with a corresponding asparagine found in rodent 5-HT1B receptors renders the pharmacology of the receptors essentially identical. This demonstrates that the human gene does indeed encode a 1B receptor, which is likely to have the same biological functions as the rodent 5-HT1B receptor. In addition, these findings show that minute sequence differences between homologues of the same receptor from different species can cause large pharmacological variation. Thus, drug-receptor interactions should not be extrapolated from animal to human species without verification.
The signal transduction linkages of the cloned human 5-HT1A receptor as expressed stably in CHO cells were studied. A transfected clonal cell line which expresses 900 +/- 36 fmol 5-HT1A receptor/mg protein (designated CHO-5-HT1A/WT-27) responded to 5-HT and/or 8-OH-DPAT by coupling to several second messenger pathways. The 5-HT1A receptor inhibited, but did not stimulate, membrane adenylyl cyclase activity and whole cell cAMP accumulation in a dose-dependent manner (for 5-HT, IC50 = 146 +/- 27 and 55 +/- 12 nM, respectively). Activation of the receptor was associated with other signal transduction linkages: (i) a 40-50% increase in hydrolysis of inositol phosphates (for 5-HT, EC50 = 1.33 +/- 0.15 microM for 5-HT), (ii) a transient elevation of cytosolic Ca2+ levels (apparent at 1-100 microM 5-HT) which was not affected by chelation of extracellular Ca2+ by EGTA, and (iii) an augmentation of [3H]-arachidonic acid release pharmacologically with the calcium ionophore A23187 or by activation of endogenous thrombin or P2 purinergic receptors (for 5-HT, EC50 = 1.22 +/- 0.17 microM). This pathway may be an amplification mechanism for signaling in anatomic regions with high concentrations of several neuro-transmitters, hormones or autacoids, such as at neuronal junctions or near areas of platelet aggregation. All linkages were sensitive to pertussis toxin pre-treatment (IC50 approximately 0.5-0.6 ng/ml x 4.5 h for all pathways), suggesting the involvement of Gi protein(s) in these signal transduction pathways. Coupling to varied signal transduction pathways in a single cell system may be a common feature of receptors which classically inhibit adenylyl cyclase such as the 5-HT1A receptor.
The human 5-HT1D beta serotonin receptor and its rat homolog (also called the 5-HT1B receptor) share 93% amino acid identity, yet display markedly different pharmacological specificities. Comparison of deduced amino acid sequences among these and other recently cloned receptors suggested that this phenotypic difference might be attributable to a single human threonine355/rat asparagine351 amino acid difference in the putative seventh membrane spanning regions. We now report that Thr355Asn mutagenesis of the human 5-HT1D beta receptor alters the binding characteristics of the recombinant receptor in [3H]5-HT binding assays to a profile very similar to that of the rat 5-HT1B binding site. These results confirm that this single amino acid difference is responsible for the majority of the known pharmacological discrepancies between human and rat observed for 5-HT1D beta (5-HT1B) receptors.
Quantitative autoradiography was used to evaluate the effects of adrenalectomy (ADX) and corticosterone (CORT) on binding at 5-HT1A and 5-HT1B receptors in the dorsal hippocampus and cortex of the rat. ADX increased binding of [3H]8-hydroxy-2-(di-n-propylamino)tetralin at 5-HT1A receptors in the oriens and lacunosum moleculare layers of CA2 and CA3, in the lacunosum moleculare layer of CA4 region, and in the dentate gyrus. In restraint-stressed ADX rats, binding was increased only in the oriens and lacunosum moleculare layers of CA2. Restoration of baseline levels of CORT reversed the effects of ADX on 5-HT1A receptors in the hippocampus, while high levels of CORT decreased binding at 5-HT1A receptors in the dentate gyrus. No treatment affected binding at 5-HT1A receptors in the CA1 region of the hippocampus or in the cortex. ADX increased binding of [125I]iodocyanopindolol at 5-HT1B receptors in the infrapyramidal dentate, but this effect was not observed in ADX rats that were restrained. CORT treatment in both ADX and SHAM (adrenally intact) rats resulted in binding at 5-HT1B receptors that was lower than that in untreated ADX and SHAM rats in the infrapyramidal dentate, and lower than that in ADX rats in the suprapyramidal dentate and CA4. In ADX and SHAM rats, CORT also reduced binding at 5-HT1B receptors in area 2 of the cortex. It is suggested that decreases in binding at 5-HT1A and 5-HT1B/1D receptors resulting from chronic exposure to high levels of CORT may also occur in animals that fail to adapt to chronic severe stress. Such changes in binding may play important roles in the etiology of depression.
Mesulergine displays approximately 50-fold higher affinity for the rat 5-HT2 receptor than for the human receptor. Comparison of the deduced amino acid sequences of cDNA clones encoding the human and rat 5-HT2 receptors reveals only 3 amino acid differences in their transmembrane domains. Only one of these differences (Ser----Ala at position 242 of TM5) is near to regions implicated in ligand binding by G protein-coupled receptors. We investigated the effect of mutating Ser242 of the human 5-HT2 receptor to an Ala residue as is found in the rat clone. Both [3H]mesulergine binding and mesulergine competition of [3H]ketanserin binding showed high affinity for rat membranes and the mutant human clone but low affinity for the native human clone, in agreement with previous studies of human postmortem tissue. These studies suggest that a single naturally occurring amino acid change between the human and the rat 5-HT2 receptors makes a major contribution to their pharmacological differences.
Mutations in the disconnected (disco) gene act to disrupt neural cell patterning in the Drosophila visual system. These mutations also affect adult locomotor activity rhythms, as disco flies are arrhythmic under conditions of constant darkness (DD). To determine the state of the circadian pacemaker in disco mutants, we constructed with pers double mutants (a short period allele of the period gene) and assayed their behavioral rhythms in light-dark cycles (LD), and their biochemical rhythms of period gene expression under both LD and DD conditions. The results demonstrate that disco flies are rhythmic, indicating that they have an active circadian pacemaker that can be entrained by light. They also suggest that disco mutants block or interfere with elements of the circadian system located between the central pacemaker and its outputs that mediate overt rhythms.
The effects of serotonin on pyramidal cells of layer V of the medial prefrontal cortex were examined using intracellular recording techniques in rat brain slices in vitro. Bath administration of serotonin (0.3–100 μM) produced two distinct responses which could be differentiated physiologically and pharmacologically. The first of these responses was a membrane hyperpolarization. This effect of serotonin was associated with a decrease in input resistance and was independent of the transmembrane chloride gradient, suggesting that it was mediated by an increase in potassium conductance. The ability of serotonin to induce a hyperpolarization was mimicked by (±)-8-hydroxy-dipropylaminotetralin hydrobromide and was blocked by BMY 7378 and spiperone but not by ketanserin, indicating that it was mediated by the activation of receptors of the 5-hydroxytryptamine1A subtype.
We investigated the regulation of 5-HT2 and 5-HT1c receptors and their corresponding mRNAs during rat brain development. This study showed that 5-HT2 and 5-HT1c receptors increased markedly during ontogeny. 5-HT2 receptors, measured with [3H]ketanserin or [125I]lysergic acid diethylamide binding, increased 8-fold between embryonic day 17 (E17) and postnatal day 13 (P13). 5-HT2 receptor mRNA levels, quantified by probing Northern blots of total RNA with a synthetic oligonucleotide cDNA probe, multiplied 13-fold between E17 and P5. The developmental pattern of 5-HT2 receptor and mRNA expression appeared to correlate with the serotonergic hyperinnervation of the cortex which occurs between P2 and P17. 5-HT1c receptors, measured with [125I]lysergic acid diethylamide under site-specific conditions, increased 2-fold between E17 and P27, 5-HT1c mRNA increased 5-fold between E17 and P27. Interestingly, the developmentally induced variations in 5-HT1c receptors did not precisely correlate with mRNA alterations. Further study of the factors responsible for these alterations could help to explain the molecular and biochemical mechanisms responsible for modulating receptor levels in vivo.
Both the 5-hydroxytryptamine2 (5-HT2) and 5-HT1c receptors may be regulated by a large number of endogenous and exogenous factors. The 5-HT2 receptors, for example, may be decreased by acute and chronic treatment with many antipsychotic agents, some antidepressants, and receptor-specific agonists. Similar to the 5-HT2 receptor, the 5-HT1c receptors may be decreased by acute and chronic treatment with the antidepressant mianserin. The 5-HT2 receptors appear to increase during perinatal development and are reported to be elevated in the frontal cortex and hippocampus of victims of suicide; the 5-HT1c receptors display supersensitivity following ablation of serotonergic terminals with 5,7-dihydroxytryptamine. The molecular details responsible for these changes remain unknown, though with the recent cloning of the cDNAs for the 5-HT2 and 5-HT1c receptors the occasion is particularly favorable for mechanistic studies aimed at determining how these alterations occur. Preliminary information suggests that developmentally induced alterations in 5-HT2 and 5-HT1c receptors may be due to transcriptional regulation while changes caused by mianserin treatment might be due to posttranslational processes (e.g., proteolysis, internalization, phosphorylation, covalent alterations). Insights into the molecular means by which 5-HT receptors are regulated could have profound influences on our understanding of pharmacologic, developmental, and psychopathologic processes.
In this article we review serotonergic signal transduction mechanisms in the central and peripheral nervous systems and in a variety of target organs. The various classes of pharmacologically defined serotonergic receptors are coupled to three major effector systems: (1) adenylate cyclase; (2) phospholipase C mediated phosphoinositide (PI) hydrolysis and (3) ion channels (K+ and Ca++). Long term occupancy of serotonergic receptors also appears to induce alterations in mRNA and protein synthesis. For all three types of signal transduction there is evidence accumulating which suggests the involvement of guanine nucleotide regulatory proteins. Recent findings suggest that the distinct types of pharmacologically defined serotonergic receptors (5HT1A, 5HT1B, 5HT1c, 5HT2) may be coupled to one or more signal transduction systems. Thus, 5HT1 receptors may both activate and inhibit adenylate cyclase and increase K+-ion conductance in the hippocampus. 5HT2 receptors which activate PI hydrolysis in the brain, both open voltage-gated calcium channels and activate PI metabolism in certain smooth muscle preparations. Thus, each class of serotonergic receptor may be linked to one or more distinct biochemical transduction mechanisms. The possibility is raised that selective agonists and antagonists might be developed which have specific effects on a particular receptor-linked effector system.
The neurohormone 5-hydroxytryptamine (5HT or serotonin) exerts its effects by binding to several distinct receptors. One of these is the M-receptor of Gaddum and Picarelli, now called the 5-HT3 receptor, through which 5-HT acts to excite enteric neurons. Ligand-binding and functional studies have shown that the 5-HT3 receptor is widely distributed in peripheral and central nervous tissue and evidence suggests that the receptor might incorporate an ion channel permeable to cations. We now report the first recordings of currents through single ion channels activated by 5-HT3 receptors, in excised (outside-out) membrane patches from neurons of the guinea pig submucous plexus. Whereas application of acetylcholine activated predominantly a 40-pS channel, 5-HT caused unitary currents apparently through two channels of conductances of 15 and 9 pS, which were reversibly blocked by antagonists of the 5-HT3 receptor. Receptors for amine neurotransmitters, including 5-HT1 and 5-HT2, have previously been thought to transduce their effects through GTP-binding proteins: the direct demonstration that 5-HT3 receptors are ligand-gated ion channels implies a role for 5-HT, and perhaps other amines, as a 'fast' synaptic transmitter.
The pKi values of 13 reference typical and 7 reference atypical antipsychotic drugs (APDs) for rat striatal dopamine D-1 and D-2 receptor binding sites and cortical serotonin (5-HT2) receptor binding sites were determined. The atypical antipsychotics had significantly lower pKi values for the D-2 but not 5-HT2 binding sites. There was a trend for a lower pKi value for the D-1 binding site for the atypical APD. The 5-HT2 and D-1 pKi values were correlated for the typical APD whereas the 5-HT2 and D-2 pKi values were correlated for the atypical APD. A stepwise discriminant function analysis to determine the independent contribution of each pKi value for a given binding site to the classification as a typical or atypical APD entered the D-2 pKi value first, followed by the 5-HT2 pKi value. The D-1 pKi value was not entered. A discriminant function analysis correctly classified 19 of 20 of these compounds plus 14 of 17 additional test compounds as typical or atypical APD for an overall correct classification rate of 89.2%. The major contributors to the discriminant function were the D-2 and 5-HT2 pKi values. A cluster analysis based only on the 5-HT2/D2 ratio grouped 15 of 17 atypical + one typical APD in one cluster and 19 of 20 typical + two atypical APDs in a second cluster, for an overall correct classification rate of 91.9%. When the stepwise discriminant function was repeated for all 37 compounds, only the D-2 and 5-HT2 pKi values were entered into the discriminant function.(ABSTRACT TRUNCATED AT 250 WORDS)