The Guinea Pig Histamine H2 Receptor: Gene Cloning, Tissue Expression and Chromosomal Localization of Its Human Counterpart

International audienceThe guinea pig is the prototypic animal species for the histamine H2 receptor. Using a strategy based upon nucleotide sequence homology and starting from the sequence of the rat histamine H2 receptor (Ruat et al., Biochem. Biophys. Res. Commun. 1991, 179: 1470-78), we have cloned an intronless highly homologous DNA very likely encoding the guinea pig H2 receptor. The encoded 359 amino acid protein displays 83 to 86% identity with the rat-, human- or dog-H2 receptors. Northern blot analysis identified a single transcript of 4.6 kb in peripheral tissues and brain areas in which the presence of the H2 receptor had been revealed previously by either photoaffinity labeling or binding studies. In brain, the distribution of transcripts, established by either Northern blots or in situ hybridization studies, was consistent with the localization of the H2-receptor. In addition, using Southern analysis of a chromosome mapping panel constructed from human x hamster hybridomas, we assigned the H2 receptor gene to human chromosome 5

A novel rat serotonin (5-HT6) receptor: molecular cloning, localization and stimulation of cAMP accumulation.

International audienceUsing a strategy based upon nucleotide sequence homology and starting from the sequence of the rat histamine H2 receptor (Ruat et al., Biochem. Biophys. Res. Commun. 1991, 179, 1470-1478), we have cloned a rat cDNA encoding a functional serotonin receptor (5-HT6). Its coding sequence corresponds to a glycoprotein of 436 amino acids displaying significant homology with other cloned monoaminergic receptors, e.g., various serotonin receptors. Genomic analysis of its gene indicated the presence of at least one intron. The major transcript of the 5-HT6 receptor gene has a size of approximately 4.1 kb but another minor 3.2 kb transcript was also evidenced. The highest expression, detected by Northern blot analysis as well as by in situ hybridization occurs in various serotoninergic areas of rat or guinea pig brain such as striatum, olfactory tubercle, nucleus accumbens and hippocampus, but a faint expression is also detectable in rat stomach. When transiently expressed in transfected COS-7 cells the 5-HT6 receptor appears to be positively coupled to cyclic AMP production

Molecular cloning, characterization, and localization of a high-affinity serotonin receptor (5-HT7) activating cAMP formation.

By using a strategy based on nucleotide sequence homology, we have cloned a cDNA encoding a functional serotonin (5-HT) receptor. The deduced amino acid sequence of the 5-HT7 receptor displays limited homology with that of other 5-HT receptors. In addition to the seven stretches of hydrophobic amino acids that characterize the superfamily of receptors interacting with guanine nucleotide-binding proteins, the 448-aa sequence of the 5-HT7 receptor contains a hydrophobic domain located at its N-terminal end. Genomic analysis indicated the presence of introns interrupting the coding sequence. The 5-HT7 receptor, stably expressed in transfected CHO cells, bound [3H]5-HT with high affinity (Kd = 1 nM), like receptors of the 5-HT1 subfamily from which, however, it was clearly distinguished by its pharmacology. 5-HT in nanomolar concentrations stimulated cAMP accumulation in these CHO cells by approximately 10-fold, whereas lysergic acid diethylamide displayed low intrinsic agonist activity. These various properties differentiate the 5-HT7 receptor from the four other subfamilies of mammalian 5-HT receptors (i.e., the 5-HT1-, 5-HT2-, 5-HT3-, and 5-HT4-like subfamilies) and, therefore, appear to define another receptor subfamily. Northern blot and in situ hybridization analyses showed the 5-HT7 transcripts to be expressed in discrete areas of the limbic brain (e.g., pyramidal hippocampus cells, tenia tecta, amygdaloid, or mammillary nuclei), suggesting that the receptor mediates serotoninergic controls in functions like mood, learning, or neuroendocrine and vegetative behaviors

Detailed mapping of the histamine H2 receptor and its gene transcripts in guinea-pig brain

International audienceAutoradiographic studies of the distribution of the histamine H2 receptor and its messenger RNAs were performed on serial frontal and a few sagittal sections of guinea-pig brain using [(125)I]iodoaminopotentidine for radioligand binding and a 33P-labelled complementary RNA probe for in situ hybridization, respectively. Both probes were validated by assessing non-specific labelling using non-radioactive competing H2 receptor ligands and a sense probe for binding sites and gene transcripts, respectively. In some areas, e.g., cerebral cortex, hippocampal complex or cerebellum, such studies were completed by identification of neurons expressing the H2 receptor messenger RNAs on emulsion-dipped sections. Nissl-stained sections from comparable levels were used to localize brain structures. In many brain areas, the distribution of the H2 receptor and its messenger RNAs appeared to parallel that known for histaminergic axons. For instance. high levels of both H2 receptor markers were detected in striatal and limbic areas known to receive abundant histaminergic projections. In contrast, in septum, hypothalamic, pontine and several thalamic nuclei, a comparatively low density of both H2 receptor markers was detected, suggesting that histamine actions in these areas are mediated by H1 and/or H3 receptors. Generally, the distribution of H2 receptor messenger RNA correlates well with that of [(125)I]iodoaminopotentidine binding sites, although some differences were observed. In a few regions (e.g., substantia nigra, locus coeruleus) high or moderate densities of binding sites were accompanied by a much more restricted expression of H2 receptor transcripts. Conversely, the mammillary region and the pontine nucleus exhibited higher levels of hybridization than of binding sites. In hippocampus, cerebral and cerebellar cortex there was a selective localization of the H2 receptor messenger RNA in the granule cells of dentate gyrus, pyramidal cells of the Ammon's horn and cerebral cortex, and Purkinje cells of cerebellum, whereas [(125)I]iodoaminopotentidine binding sites were located in layers where the dendritic trees of these messenger RNA-expressing neurons extend. The same discrepancy between messenger RNAs and binding sites suggests that striatonigral endings are endowed with the H2 receptor. The histamine H1 and H2 receptors both appear to be present in several brain areas, in some cases in a way suggesting their potential co-expression by the same neuronal populations, e.g., in granule and pyramidal cells in the hippocampal formation. This co-expression accounts for synergic responses, e.g., on cAMP generation, previously observed upon co-stimulation of both receptor subtypes. The widespread distribution of the H2 receptor, namely in thalamic nuclei or in telencephalic areas such as most layers of the cerebral cortex, together with its excitatory role previously established in electrophysiological studies, support its alleged function in mediating the histamine-driven control of arousal mechanisms. In addition, the detection of H2 receptor expression in brainstem areas from which other monoaminergic pathways involved in the control of states of sleep and wakefulness emanate, e.g., several raphe nuclei, locus coeruleus or substantia innominata, suggests possible interrelationships between all of these systems with highly divergent projections to the thalamus and telencephalon. The present mapping of the H2 receptor and its gene transcripts should facilitate neurochemical, neurophysiological and behavioural studies aimed at clarifying the role of histaminergic systems in brain

A detailed mapping of the histamine H3 receptor and its gene transcripts in rat brain

International audienceThe detailed distribution of histamine H3 receptor mRNAs in rat brain was analyzed by in situ hybridization using a 33P-labelled riboprobe and was combined for the first time with the detailed autoradiographic distribution of the receptor determined in the same animals with [125I]iodoproxyfan, a selective radioligand. The signals generated on adjacent brain sections by each probe were quantified and/or rated and were compared in order to identify neuronal populations expressing the receptor. In addition, the cellular localization of the transcripts within various brain structures was analyzed in sections dipped in a photographic emulsion.In the cerebral cortex, the strong mRNA expression in intermediate and deep layers indicates the presence of H3 receptors on several types of neurons. The binding is dense except in layer V, suggesting that H3 receptors are located on granule cells and apical dendrites of pyramidal cells. In addition to their localization on monoaminergic afferents, the dense binding in layer IV and strong mRNA expression in thalamic nuclei suggest the presence of heteroreceptors on thalamocortical projections. In the hippocampus, the strong mRNA expression but low binding in pyramidal layers of the CA1 and ventral CA3 fields suggest that H3 receptors are abundant on efferent projections of pyramidal cells. In the dentate gyrus, some binding sites in the molecular layer may correspond to H3 receptors synthesized in granule cells and coexpressed with H1 and H2 receptors in their dendrites. In the basal ganglia, H3 receptors are highly expressed in the striatal complex and olfactory tubercles but not in islands of Calleja. Some of the striatal binding sites may correspond to presynaptic receptors present on afferents. The mRNAs in cortical layer V may encode for heteroreceptors on corticostriatal neurons. The presence of mRNAs in the substantia nigra pars compacta suggests that H3 receptors are located upon nigrostriatal afferents. However, the absence of any signal in the ventral tegmental area indicates that some but not all dopaminergic neurons express H3 receptors. In addition, the homogeneous mRNA expression within the caudate putamen and nucleus accumbens suggests that many striatal H3 receptors are present on medium-sized, spiny projection neurons of both the direct and indirect movement pathways. In agreement, a dense binding, but low mRNA expression, is observed in external and internal pallidum and in substantia nigra pars reticulata. In the amygdala, the dense binding and mRNA expression indicate the presence of receptors on both afferents and projections. In the thalamus, the binding in some association nuclei may correspond to receptors present on neurons emanating from the deep cortical layers that strongly express the mRNAs, as well as receptors on the visual systems. However, the low binding and high mRNA expression in most nuclei indicate that many receptors are present upon thalamic projections. In the hypothalamus, the mRNA expression parallels the density of binding sites and is the highest in the tuberomammillary nucleus. Further investigation is needed to know if the dense binding and mRNA expression observed in other nuclei such as the paraventricular, ventromedial and medial tuberal nuclei correspond to pre- and/or postsynaptic receptors. mRNAs are also observed in several areas projecting to the tuberomammillary nucleus, such as the ventrolateral preoptic nucleus. In the lower brainstem, the high mRNA expression and very low binding in the locus coeruleus and raphe nuclei indicate that presynaptic rather than somatodendritic receptors regulate noradrenaline and serotonin release, respectively. A similar pattern in vestibular nuclei suggests that receptors located on projections account for the anti-vertigo properties of H3 receptor antagonists. In the cerebellum, binding is hardly detectable but a strong mRNA expression is found in most, if not all, Purkinje cells as well as in several central cerebellar nuclei, suggesting the presence of H3 receptors on efferent projections.The present study reports the first detailed quantification and/or rating of H3 receptor mRNAs in the brain. The comparison, performed in the same animals, with the distribution of the H3 receptor protein provides evidence for the presence of H3 receptors on many neuronal perikarya, dendrites and projections. Although some localizations, mainly as auto- or heteroreceptors, are consistent with previous functional studies, the physiological role, if any, of most of these presynaptic or postsynaptic receptors remains to be established

Histamine H 3 -receptor-mediated [ 35 S]GTPγ[S] binding: evidence for constitutive activity of the recombinant and native rat and human H 3 receptors

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Acute and chronic effects of methamphetamine on tele-methylhistamine levels in mouse brain: selective involvement of the D(2) and not D(3) receptor.

International audienceWe have explored the role of endogenous dopamine in the control of histaminergic neuron activity in mouse brain regions evaluated by changes in tele-methylhistamine (t-MeHA) levels. In vitro, methamphetamine released [(3)H]noradrenaline but failed to release [(3)H]histamine from synaptosomes. In vivo, methamphetamine enhanced t-MeHA levels by about 2-fold with ED(50) values of approximately 1 mg/kg in caudate putamen, nucleus accumbens, cerebral cortex, and hypothalamus. This response selectively involved the D(2) and not the D(3) receptor as indicated by its blockade by haloperidol and by its persistence after administration of nafadotride, a D(3) receptor preferential ligand, or in (-/-) D(3) receptor-deficient mice. The t-MeHA response to methamphetamine was delayed compared with the locomotor-activating effect of this drug, suggesting that it is of compensatory nature. In agreement, ciproxifan, an inverse agonist known to enhance histamine neuron activity, decreased the hyperlocomotion induced by methamphetamine. Repeated methamphetamine administration resulted in the expected sensitization to the hyperlocomotor effect of the drug but did not modify either the ED(50) or the E(max) regarding t-MeHA levels. However, it resulted in an enhanced basal t-MeHA level (+30-40%), which was sustained for at least 11 days after withdrawal in hypothalamus, striatum, and cerebral cortex and suppressed by haloperidol. Hence, both the acute and chronic administration of methamphetamine enhance histamine neuron activity, presumably in a compensatory manner. Repeated methamphetamine administration also resulted in a modified balance in the opposite influences of dopamine and serotonin on histaminergic neurons as revealed by the enhanced response to haloperidol and abolished response to ketanserin, respectively

MOLECULAR BIOLOGY AND PHARMACOLOGY OF HISTAMINE RECEPTOR SUBTYPES

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