Homogeneous 5-HT1D recognition sites in the human substantia nigra identified with a new iodinated radioligand

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

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

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

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

Functions of 5-HT2A receptor and its antagonists in the cardiovascular system

The serotonin (5-hydroxytryptamine, 5-HT) receptors have conventionally been divided into seven subfamilies, most of which have several subtypes. Among them, 5-HT(2A) receptor is associated with the contraction of vascular smooth muscle, platelet aggregation and thrombus formation and coronary artery spasms. Accordingly, selective 5-HT(2A) antagonists may have potential in the treatment of cardiovascular diseases. Sarpogrelate, a selective 5-HT(2A) antagonist, has been introduced clinically as a therapeutic agent for the treatment of ischemic diseases associated with thrombosis. Molecular modeling studies also suggest that sarpogrelate is a 5-HT(2A) selective antagonist and is likely to have pharmacological effects beneficial in the treatment of cardiovascular diseases. This review describes the above findings as well as the signaling linkages of the 5-HT(2A) receptors and the mode of agonist binding to 5-HT(2A) receptor using data derived from molecular modeling and site-directed mutagenesis.

Molecular, pharmacological and functional diversity of 5-HT receptors

Serotonin (5-hydroxytryptamine, 5-HT) is probably unique among the monoamines in that its effects are subserved by as many as 13 distinct heptahelical, G-protein-coupled receptors (GPCRs) and one (presumably a family of) ligand-gated ion channel(s). These receptors are divided into seven distinct classes (5-HT(1) to 5-HT(7)) largely on the basis of their structural and operational characteristics. Whilst this degree of physical diversity clearly underscores the physiological importance of serotonin, evidence for an even greater degree of operational diversity continues to emerge. The challenge for modern 5-HT research has therefore been to define more precisely the properties of the systems that make this incredible diversity possible. Much progress in this regard has been made during the last decade with the realisation that serotonin is possibly the least conservative monoamine transmitter and the cloning of its many receptors. Coupled with the actions of an extremely avid and efficient reuptake system, this array of receptor subtypes provides almost limitless signalling capabilities to the extent that one might even question the need for other transmitter systems. However, the complexity of the system appears endless, since posttranslational modifications, such as alternate splicing and RNA editing, increase the number of proteins, oligomerisation and heteromerisation increase the number of complexes, and multiple G-protein suggest receptor trafficking, allowing phenotypic switching and crosstalk within and possibly between receptor families. Whether all these possibilities are used in vivo under physiological or pathological conditions remains to be firmly established, but in essence, such variety will keep the 5-HT community busy for quite some time. Those who may have predicted that molecular biology would largely simplify the life of pharmacologists have missed the point for 5-HT research in particular and, most probably, for many other transmitters. This chapter is an attempt to summarise very briefly 5-HT receptor diversity. The reward for unravelling this complex array of serotonin receptor--effector systems may be substantial, the ultimate prize being the development of important new drugs in a range of disease areas.

Pharmacological characterization of almotriptan: an indolic 5-HT receptor agonist for the treatment of migraine

Almotriptan (3-[2-(dimethylamino)ethyl]-5-(pyrrolidin-1-ylsulfonylmethyl )-1H-indo le) has been studied in several models predictive of activity and selectivity at 5-HT receptors. Almotriptan showed low nanomolar affinity for the 5-HT(1B) and 5-HT(1D) receptors in several species, including the human, while affinity for 5-HT receptors other than 5-HT(1B/1D) was clearly less. Affinity for 5-HT(7) and 5-HT(1A) receptors was approximately 40 and 60 times lower than that for 5-HT(1B/1D) receptors, respectively. Almotriptan did not exhibit significant affinity for several non-5-HT receptors studied up to 100 microM. Almotriptan inhibited forskolin-stimulated cyclic AMP accumulation in HeLa cells transfected with 5-HT(1B) or 5-HT(1D) human receptors. In this model, almotriptan had the same efficacy as serotonin and an affinity in the low nanomolar range. It induced vasoconstriction in several vessels in which it was compared with sumatriptan. In isolated dog saphenous veins, almotriptan elicited concentration-dependent contractions with an EC(50) of 394 nM. In both these systems, almotriptan behaved as a full agonist. Infusion of almotriptan into the porcine meningeal vasculature induced vasoconstriction. In contrast, in the pig renal and rabbit mesenteric arteries, it had a very low maximal efficacy even at 100 microM, with similar results obtained in the rabbit renal artery. The results suggest that almotriptan is a potent and selective 5-HT(1B/1D) receptor agonist, with selectivity for the cranial vasculature as compared with peripheral vessels.

Multiple serotonin receptors: too many, not enough, or just the right number?

In this manuscript, current knowledge about central nervous system serotonin (5-HT) receptors is discussed with an emphasis toward describing the functional significance of the multiple 5-HT receptors. Five characteristics of 5-HT receptors, which are hypothesized to contribute to this functional significance, are discussed: (a) 5-HT has varying affinity and potency for the different receptor subtypes; (b) multiple transduction pathways are used by the different receptor subtypes; (c) receptor subtypes differ in their susceptibility to agonist-mediated desensitization/downregulation; (d) receptor subtypes interact in mediating cellular responses to the neurotransmitter; and (e) receptor subtypes respond differently to changes in the physiological environment. It is hypothesized that these characteristics of the multiple neurotransmitter receptors provide the nervous system with a capacity for coding and decoding of 5-HT-mediated neuronal transmission that could not take place with a single neurotransmitter receptor. Serotonergic regulation of female reproduction and regulation of glucocorticoid release are used to illustrate the integrative potential deriving from the existence of multiple 5-HT receptors.

5-Hydroxytryptamine-interacting drugs in animal models of anxiety disorders: more than 30 years of research

An overview of the behavioral data arising from the vast literature concerning the involvement of 5-hydroxytryptamine (5-HT) neurotransmission in the regulation of anxiety is presented. More than 1300 experiments were carried out in this area and they provide evidence that: (1) results obtained in ethologically based animal models of anxiety with drugs stimulating 5-HT transmission are most consistent with the classic 5-HT hypothesis of anxiety in that they show an increase in animals' emotional reactivity; (2) no category of anti-anxiety models are selectively sensitive to the anxiolytic-like effects of drugs targetting 5-HT1A, 5-HT2A or 5-HT2C receptor subtypes; (3) anxiolytic-like effects of 5-HT3 receptor antagonists, in the great part, are revealed by models based on spontaneous behaviors. Taken together, these observations lead to the conclusion that different 5-HT mechanisms, mediated by different receptor subtypes, are involved in the genesis of anxiety.

5-Hydroxytryptamine receptor subtypes in vertebrates and invertebrates

In the last few years, molecular biology has led to the cloning and characterization of several 5-HT receptors (serotonin receptors) in vertebrates and in invertebrates. These studies have allowed identification not only of 5-HT receptors already described but also of novel subtypes. The molecular cloning of 13 different mammalian receptor subtypes revealed an unexpected heterogeneity among 5-HT receptors. Except for the 5-HT3 receptors which are ligand-gated ion channel receptors, all the other 5-HT receptors belong to the large family of receptors interacting with G proteins. Based on their amino acid sequence homology and coupling to second messengers these receptors can be divided into distinct families: the 5-HT1 family contains receptors that are negatively coupled to adenylate cyclase: the 5-HT2 family includes receptors that stimulate phospholipase C; the adenylyl cyclase stimulatory receptors are a heterogeneous group including the 5-HT4 receptor which has not yet been cloned, the Drosophila 5-HTdro1 receptor and two mammalian receptors tentatively named 5-HT6 and 5-HT7 receptors. The 5-HT5A and 5-HT5B receptors might constitute a new family of 5-HT receptors whose effectors are unknown. This review focusses on the molecular characteristics of the cloned 5-HT receptors such as their structure, their effector systems and their distribution within the central nervous system. The existence of a large number of receptors with distinct signalling properties and expression patterns might enable a single substance like 5-HT to generate simultaneously a large panel of effects in many brain structures. The availability of the genes encoding these receptors has already allowed a partial characterization of their structure-function relationship and will probably allow in the future a dissection of the contribution of each of these receptor subtypes to physiology and behaviour.

[3H]L-694,247 labels the 5-HT1D beta receptor in pig caudate membranes

This study, carried out in pig caudate membranes, characterises the radioligand binding site labelled with [3H]L-694,247 (2-[5-[3-(4-methylsulphonylamino)benzyl-1,2,4-oxadiazol-5-yl ]-1H-indole-3 - yl]ethylamine). The affinities of 27 standard compounds are consistent with binding to a 5-HT1D recognition site. In addition the results indicate that, under the assay conditions described, [3H]L-694,247 specifically labels the 5-HT1D beta recognition site since ketanserin and ritanserin display a low affinity consistent with their activities at this subtype of the 5-HT1D receptor.

On the nature of the 5-HT receptor subtype inhibiting acetylcholine release in the guinea-pig ileum

1. The nature of the 5-hydroxytryptamine (5-HT) receptor subtype controlling acetylcholine release and contraction induced by stimulation of the neurokinin NK3 receptor has been studied in the longitudinal muscle-myenteric plexus preparation from guinea-pig ileum. 2. In preparations preloaded with [3H]-choline, the selective NK3 agonist, senktide, produced a concentration-dependent increase in tritium overflow, an index of [3H]-acetylcholine release. Low concentrations of neurokinin B, also markedly increased tritium efflux. 3. The senktide-induced acetylcholine release was markedly increased by the same concentration of methysergide and mesulergine. The 5-HT2A/2C agonist DOI (1 microM) inhibited the tritium overflow while 8-OH-DPAT, sumatriptan and ketanserin (1 microM each) were without effect on the senktide-induced tritium efflux. 4. The contractile response to senktide in the guinea-pig ileum was attenuated by atropine, 0.1 microM. Methysergide, a 5-HT1/2 receptor antagonist, and mesulergine, a 5-HT2A/2B/2C receptor antagonist, (1 microM each), enhanced the contractile effect of the NK3 receptor agonist. 5. It is concluded that the acetylcholine release induced by a NK3 receptor agonist is inhibited by stimulation of a 5-HT receptor, possibly of the 5-HT2C or 5-HT2C subtype.

Quantitative autoradiography of 5-HT1D and 5-HT1E binding sites labelled by [3H]5-HT, in frontal cortex and the hippocampal region of the human brain

In human cortex and hippocampus area, [3H]5-HT (5 nM) labels 5-HT1A, 5-HT1D and 5-HT1E sites. After masking 5-HT1A receptors by 0.1 microM 8-OH-DPAT, the binding displaced by 0.1 microM 5-CT presumably represented 5-HT1D sites and the remaining binding 5-HT1E sites. In frontal cortex, 5-HT1A receptors represented the main binding in layers II and VI and a lower fraction in other layers. 5-HT1D and 5-HT1E sites, were more homogeneously distributed in layers II to VI (21-34% of specific [3H]5-HT binding). 5-HT1E sites were of similar affinities (KD close to 6-8 nM) in the cortical layers II to VI. In CA1 field of hippocampus, (pyramidal layer, stratum radiatum, molecular layer), CA2 and dentate gyrus, 5-HT1A receptors represented the major fraction, 5-HT1D sites a significant fraction and 5-HT1E a minor fraction of the specific [3H]5-HT binding. In CA3-CA4 fields, 5-HT1A receptors were less densely present, 5-HT1D sites were predominant and 5-HT1E sites represented a significant fraction (27%). The highest densities of 5-HT1E sites have been measured in subiculum, where 5-HT1A, 5-HT1D and 5-HT1E binding sites were equally represented and in entorhinal cortex where 5-HT1E sites represented the major binding in layer III. They were also present in layers II and IV (29 and 24%) and, to a lesser extent, in layers V and VI. 5-HT1A sites were predominant in layer VI, II and V and were less abundant in other layers. 5-HT1D were homogeneously present in layers II, III, IV and were present in low amounts in other layers. No 5-HT1E were detected in choroid plexus, where [3H]5-HT was dramatically reduced by mesulergine (5-HT2C receptors). No significant displacement of [3H]5-HT by mesulergine was measured in other structures.

The mouse 5-hydroxytryptamine1B receptor is localized predominantly on axon terminals

The 5-hydroxytryptamine1B receptor is a serotonin receptor subtype which is expressed predominantly in the basal ganglia. It has been suggested to play a role in movement and appetite control as well as in certain pathological states such as migraine. The recent cloning of the 5-hydroxytryptamine1B gene as well as the discovery of a radioligand that labels in rodents 5-hydroxytryptamine1B and possibly 5-hydroxytryptamine1D alpha receptors (S-CM-G[125I]TNH2) allowed us to compare the distribution of the messenger RNA and of the protein in mouse brain sections. A high 5-hydroxytryptamine1B messenger RNA level is found in the caudate-putamen in medium spiny neurons that project to the globus pallidus and the substantia nigra. In contrast, no messenger RNA is expressed in the globus pallidus and substantia nigra although these structures reveal the highest level of 5-hydroxytryptamine1B binding sites. In the hippocampus, 5-hydroxytryptamine1B messenger RNA is localized in the cell bodies of pyramidal cells of the CA1 field while the protein is found predominantly in the dorsal subiculum, a projection zone for the CA1 pyramidal neurons. In the cerebellum, 5-hydroxytryptamine1B messenger RNA is expressed in the Purkinje cells, which display no receptor binding sites. Conversely, moderate binding is found in the deep nuclei of the cerebellum, the main projection zone of the Purkinje cells. 5-Hydroxytryptamine1B sites are also detected in the superficial gray layer of the superior colliculus and the lateral geniculate nucleus, brain regions containing the terminals of retinal ganglion cells. The soma of these ganglion cells express high levels of 5-hydroxytryptamine1B messenger RNA while no 5-hydroxytryptamine1B binding sites were found in the retina. This study demonstrates that the main brain regions, expressing 5-hydroxytrypamine1B messenger RNA contain low densities of 5-hydroxytryptamine1B binding sites. Conversely, the major projection areas of these anatomical structures do not express detectable levels of 5-hydroxytryptamine1B messenger RNA, but present a high density of binding sites. In addition, our data suggest that the distribution of the 5-hydroxytryptamine1D alpha binding sites is different from that of the 5-hydroxytryptamine1D alpha messenger RNA. These results together with previous lesion studies, indicate that the 5-hydroxytryptamine1B and possibly the 5-hydroxytryptamine1D alpha receptors are localized predominantly on axon terminals, while their expression is low or absent at the somatodendritic level. The 5-hydroxytryptamine1D alpha proteins might therefore contain an addressing signal allowing their transport toward nerve endings.(ABSTRACT TRUNCATED AT 400 WORDS)

A comparative autoradiographic study of 5-HT1D binding sites in human and guinea-pig brain using different radioligands

Quantitative receptor autoradiography was used to examine the 5-hydroxytryptamine (5-HT, serotonin) binding sites labelled with serotonin-5-O-carboxymethyl-glycyl-[125I]tyrosinamide ([125I]GTI) in human and guinea-pig brain. Competition experiments using 5-carboxamidotryptamine (5-CT), 3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrolo[3,2-b]pyrid-5-one (CP 93129) and sumatriptan revealed monophasic displacement curves in various brain regions, suggesting that a homogeneous population of 5-HT1D binding sites was labelled. Displacement of [3H]5-HT (in the presence of 100 nM 8-hydroxy-2(N-dipropylamino)tetralin (8-OH-DPAT) and 100 nM mesulergine) with unlabelled GTI resulted in monophasic competition curves in substantia nigra, globus pallidus and central gray. In contrast, biphasic displacement was observed in hippocampus, nucleus accumbens, claustrum, caudate-putamen and frontal cortex. The distribution of [125I]GTI sites was compared to that of [3H]5-HT binding sites (under so-called '5-HT1D conditions', i.e. in the presence of 100 nM 8-OH-DPAT and 100 nM mesulergine, in order to block 5-HT1A and 5-HT1C sites, respectively) in human and guinea-pig brain. Qualitative analysis revealed differences in the distributions of [125I]GTI and [3H]5-HT binding sites. Regions such as CA3 and CA4 of the hippocampus, claustrum and putamen showed [3H]5-HT binding (under '5-HT1D conditions') but no [125I]GTI binding sites, indicating that [3H]5-HT labels besides a GTI sensitive (5-HT1D) receptor population, a non-5-HT1A/1B/1C/1D [3H]5-HT binding site in human and guinea-pig brain. The distribution of these non-5-HT1A/1B/1C/1D [3H]5-HT binding sites was studied with [3H]5-HT under conditions where 5-HT1A, 5-HT1C and 5-HT1D [3H]5-HT binding sites were saturated by the presence of 100 nM 8-OH-DPAT, 100 nM mesulergine and 1 microM GTI. Significant densities of these non-5-HT1A/1B/1C/1D sites were observed in cortical areas, hippocampal structures, nucleus accumbens, amygdala, caudate-putamen and claustrum. It is concluded that [125I]GTI does not label the 5-HT1E binding site, since all competition curves obtained with this radioligand were monophasic. By contrast, [3H]5-HT labels non-5-HT1A/1B/1C/1D [3H]5-HT binding sites, but it remains to be established whether these sites represent a single receptor population.

Serotonin-5-O-carboxymethyl-glycyl[125I]tyrosinamide labels the 5-HT1D beta receptor subtype in human cortex

This study, carried out in human cerebral cortical membranes, confirms previous findings in human substantia nigra that serotonin-5-O-carboxymethyl-glycyl[125I]tyrosinamide ([125I]GTI) labels a homogeneous population of recognition sites consistent with a 5-HT1D receptor pharmacology. In addition the results indicate that, under the assay conditions described, [125I]GTI specifically labels the 5-HT1D beta recognition site since ketanserin and ritanserin display a low affinity consistent with their activities at this subtype of the 5-HT1D receptor.

5-HT1 receptors mediating contraction in bovine cerebral arteries: a model for human cerebrovascular '5-HT1D beta' receptors

We report on the pharmacological profile of the 5-HT receptor which induces contraction of the bovine isolated cerebral arteries. Several 5-HT receptor agonists were tested for their ability to induce vasoconstriction in bovine pial arteries and their potencies were compared to that of 5-HT. The rank order of agonist potency can be summarized as 5-carboxamidotryptamine (5-CT) = RU 24969 > or = 5-HT > sumatriptan > alpha-methyl-5-HT > methysergide > 2-methyl-5-HT > ((+-)-2-dipropylamino-8-hydroxy-1,2,3,4-tetrahydronaphthalene (8-OH-DPAT). Only methysergide induced a contraction which was smaller than that elicited by 5-HT. Antagonists with selective affinity at 5-HT1A/1B (propranolol), 5-HT1C (mesulergine), 5-HT2 (ketanserin, mianserin) and 5-HT3 (MDL 72222) sites were inactive to block the 5-HT-induced contraction. In contrast, the 5-HT1/5-HT2 receptor antagonists methiothepin and metergoline inhibited the 5-HT-induced response with relatively high affinity (pA2 = 8.16 +/- 0.26 and 6.73 +/- 0.05, respectively). Overall, this pharmacological profile indicated clearly that a 5-HT1 receptor, most closely related to the 5-HT1D subtype, is responsible for the 5-HT-induced contraction of bovine cerebral arteries. Correlation analysis of the potencies of a series of 5-HT receptor agonists and antagonists in bovine and human cerebrovascular preparations showed a highly significant positive correlation (r = 0.94, P = 0.0051).(ABSTRACT TRUNCATED AT 250 WORDS)

Autoradiographic characterisation and localisation of 5-HT1D compared to 5-HT1B binding sites in rat brain

The regional distribution and the pharmacology of the binding sites labelled with the novel 5-hydroxytryptamine (serotonin) 5-HT1B/1D selective radioligand serotonin-O-carboxy-methyl-glycyl-[125I]tyrosinamide (abbreviated [125I]GTI for the sake of simplicity) was determined using quantitative autoradiography in rat brain. The distribution of [125I]GTI binding sites was largely comparable to that of [125I]iodocyanopindolol ([125I] ICYP) which labels 5-HT1B binding sites (in the presence of 8-OH-DPAT (8-hydroxy-[2N-dipropylamino]tetralin) and isoprenaline, to prevent binding to 5-HT1A and beta-adrenoceptor binding sites), although a detailed analysis revealed differences. The pharmacology of the [125I]GTI binding sites was analysed using compounds known to display high affinity for and/or distinguish between 5-HT1B and 5-HT1D sites: 5-carboxamidotryptamine (5-CT), sumatriptan, CP 93129 (5-hydroxy-3(4-1,2,5,6-tetrahydropyridyl)-4-azaindole), (-)pindolol, PAPP (4[2-[4-[3-(trifluoromethyl)phenyl]-1- piperazinyl]ethyl]benzeneamine), rauwolscine, and 8-OH-DPAT. The displacement of [125I]GTI by 5-CT was monophasic. By contrast, the selective 5-HT1B compound CP 93129 and (-)pindolol produced biphasic curves showing a majority of high affinity sites in the globus pallidus and the substantia nigra, whereas PAPP and sumatriptan (which are somewhat 5-HT1D selective) produced biphasic curves indicating a minority of high affinity sites in these areas. In addition, by blocking the 5-HT1B sites with 100 nM CP 93129, the remaining population of [125I]GTI binding sites could be studied and was found to have high affinity for PAPP, rauwolscine and 8-OH-DPAT. The pharmacological profile of the major binding component was typical of the 5-HT1B type: 5-CT > CP 93129 > or = (-)pindolol > sumatriptan > or = PAPP > rauwolscine. The profile of the minor component of [125I]GTI binding is best characterised as that of a 5-HT1D site: 5-CT > PAPP > or = sumatriptan > rauwolscine > (-)pindolol > or = CP 93129. The localisation of the non 5-HT1B [125I]GTI binding sites was characterised by blocking the 5-HT1B receptors with 100 nM CP 93129. Low densities of the 5-HT1D recognition sites were found to be present in globus pallidus, ventral pallidum, caudate-putamen, subthalamic nucleus, entopeduncular nucleus, substantia nigra (reticular part), nuclei of the (normal and accessory) optic tract, different nuclei of the geniculate body and frontoparietal cortex, although higher densities of 5-HT1B sites were always observed in the same structures.(ABSTRACT TRUNCATED AT 400 WORDS)

5-hydroxytryptamine1 recognition sites in rat brain: heterogeneity of non-5-hydroxytryptamine1A/1C binding sites revealed by quantitative receptor autoradiography

Quantitative in vitro receptor autoradiography was used to characterize the [3H]5-hydroxytryptamine binding sites which are not sensitive to 8-hydroxy-2-(di-N-propylamino)tetralin, mesulergine and serotonin-5-O-carboxy-methyl-glycyl-tyrosinamide, in a non-5-hydroxytryptamine1A/1B/1C/1D receptor population, in rat brain. Displacement of [3H]5-hydroxytryptamine [in the presence of 100 nM 8-hydroxy-2-(di-N-propyl-amino)tetralin and mesulergine, to block 5-hydroxytryptamine1A and 5-hydroxytryptamine1C sites] with (-)pindolol, 5-hydroxy-3(4-1,2,5,6-tetrahydropyridyl)-4-azaindole, sumatriptan and serotonin-5-O-carboxy-methyl-glycyl-tyrosinamide yielded complex competition curves suggesting the presence of 5-hydroxytryptamine1B and 5-hydroxytryptamine1D sites and an additional [3H]5-hydroxytryptamine-sensitive component in rat brain. The non-5-hydroxytryptamine1A/1B/1C/1D binding sites were localized in olfactory tubercle, several nuclei of the amygdala, bed nucleus of the stria terminalis, caudate-putamen, CA3 field of the hippocampus, the frontoparietal cortex (motor area) and parts of the striate cortex. All the drugs used had low affinity for the unknown recognition site, which therefore might be comparable to the [3H]5-hydroxytryptamine binding site reported to display low affinity for sumatriptan and 5-carboxamidotryptamine in the brains of various species, the so-called 5-hydroxytryptamine1E site. A comparison of the density of sites labelled with [125I]serotonin-5-O-carboxy-methyl-glycyl-tyrosinamide (representing 5-hydroxytryptamine1B and 5-hydroxytryptamine1D sites) and [3H]5-hydroxytryptamine (under the conditions mentioned above) showed the density of [3H]5-hydroxytryptamine recognition sites to be higher in some structures.(ABSTRACT TRUNCATED AT 250 WORDS)

Non 5-HT1A/5-HT1C [3H]5-HT binding sites in the hamster, opossum, and rabbit brain show similar regional distribution but different sensitivity to beta-adrenoceptor antagonists

We have used receptor autoradiography to investigate the distribution and pharmacological profile of non 5-HT1A/5-HT1C[3H]5-hydroxytryptamine binding sites in the brain of rabbits, hamsters and opossums. These data were compared to those found under similar conditions in the brain of rats and guinea pigs, species which are known to possess 5-HT1B and 5-HT1D receptors, respectively. In the presence of 100 nM 8-OH-DPAT and mesulergine, the regional distribution of [3H]5-hydroxytryptamine binding sites was very similar in the brain of all species investigated; densest labelling was observed in the globus pallidus, substantia nigra and superior colliculus. In all species, 5-carboxamidotryptamine competed for the labelled sites in a biphasic manner and metergoline displayed a subnanomolar affinity. In contrast, the beta-adrenoceptor blocking agents (-)propranolol, (-)pindolol, and (+/-)SDZ 21009 were potent displacers only in the rat, hamster and opossum brains. These data indicate that non 5-HT1A/5-HT1C[3H]5-HT binding sites display a high affinity for these agents in a particular rodent suborder as well as in opossum, a phylogenetically unrelated species.

"5-HT1R" or 5-HT1D sites? Evidence for 5-HT1D binding sites in rabbit brain

Radioligand binding studies were performed in membranes of rabbit whole brain and striatum using the novel iodinated radioligand for 5-hydroxytryptamine 5-HT1B and 5-HT1D sites, Serotonin-5-O-Carboxymethyl-Glycyl[125I]Tyrosinamide ([125I]GTI). [125I]GTI labelled a finite number of high affinity sites in rabbit brain membranes, Bmax = 191 +/- 47 fmol/mg protein, pKD (-log mol/l) = 8.50 +/- 0.13, n = 5. The pharmacological profile of [125I]GTI binding was fully comparable to that reported previously in human and other brain preparations known to possess 5-HT1D sites (using either [3H]5-HT or [125I]GTI) and displayed a characteristic rank order of affinity: 5-carboxamido-tryptamine greater than 5-HT = dihydroergotamine greater than or equal to ergotamine greater than or equal to sumatriptan greater than or equal to CGS 12066 greater than or equal to metergoline greater than yohimbine greater than or equal to methysergide greater than ICYP greater than 8-OH-DPAT greater than or equal to CP 93129 greater than (-)pindolol greater than ketanserin greater than isamoltane greater than mesulergine greater than corynanthine greater than buspirone greater than MDL 72222. Autoradiographic studies were performed on rabbit brain slices using [3H]5-HT in the presence of 100 nmol/l 8-OH-DPAT and mesulergine (in order to mask 5-HT1A and 5-HT1C binding sites) and [125I]CYP (iodocyanopindolol) in the presence of 3 mumol/l isoprenaline and 100 nmol/l 8-OH-DPAT (in order to mask beta adrenoceptor and 5-HT1A binding sites). There was no detectable specific binding of [125I]CYP through the brain, thus excluding the presence of 5-HT1B sites in rabbit brain.(ABSTRACT TRUNCATED AT 250 WORDS)

5-HT1D binding sites in various species: similar pharmacological profile in dog, monkey, calf, guinea-pig and human brain membranes

Radioligand binding studies were performed in membranes of calf caudate, guinea-pig cortex, dog caudate and whole brain, monkey caudate and whole brain, and human caudate using the novel iodinated radioligand, Serotonin-5-O-Carboxymethyl-Glycyl[125I] Tyrosinamide (abbreviated [125I]GTI for the sake of simplicity), a ligand known to label 5-HT1B and 5-HT1D sites. In all membrane preparations tested, [125I]GTI labelled high affinity sites with the following rank order of affinity: 5-carboxamidotryptamine greater than 5-HT = DHE = ergotamine greater than or equal to sumatriptan greater than or equal to metergoline = CGS 12066 greater than or equal to yohimbine = methysergide greater than or equal to methiothepin greater than 8-OH-DPAT greater than or equal to mianserin greater than or equal to CP 93129 greater than or equal to (-)pindolol = ketanserin greater than or equal to isamoltane = mesulergine greater than or equal to corynanthine = spiperone greater than MDL 72222. The affinity profiles were very similar in the membranes of the different species, especially in dog, monkey and human brain. The pharmacological profile of [125I]GTI binding (determined with up to 25 different drugs) was fully comparable to the binding profile reported previously in human substantia nigra (using [125I]GTI) or in a variety of brain preparations known to contain 5-HT1D sites using [3H]5-HT as a radioligand.(ABSTRACT TRUNCATED AT 250 WORDS)

Direct visualization of serotonin1D receptors in the human brain using a new iodinated radioligand

The development of the new ligand serotonin-5-O-carboxymethyl-glycyl [125I]tyrosinamide (abbreviated [125I]GTI) allows for the direct visualization of serotonin1B and serotonin1D (5-HT1B/1D) sites. Autoradiographic techniques were used to demonstrate the selective binding of this ligand to 5-HT1D sites in human post-mortem brain materials. The distribution of [125I]GTI binding sites was compared to [3H]5-HT sites in the presence of different displacers. The results show the selective binding of [125I]GTI to sites in the basal ganglia and substantia nigra which corresponds to 5-HT1D receptors.