5-HT receptors in mammalian brain: receptor autoradiography andin situ hybridization studies of new ligands and newly identified receptors
In recent years the family of mammalian serotonin receptors has grown to 14 different subtypes, characterized by pharmacological or molecular biological techniques. In parallel, new ligand molecules have been developed for their study. However, selective ligands are not yet available to study every one of them. In addition the degree of selectivity of ligands, hitherto regarded as specific for a particular receptor subtype has been called in question by their affinities for newly discovered receptors. Consequently, a re-evaluation of past ligand receptor autoradiography work is necessary in view of the redefined receptor profiles of these ligands, and the introduction of newly developed ligands. A further difficulty for the characterization of these receptors is the absence of selective antagonist ligands which, for some of the subtypes, have become available only recently. In an attempt to overcome these difficulties we have combinedin situ hybridization histochemistry and receptor ligand autoradiography to study the regional and cellular localization of several serotonin receptors in the rodent brain. In addition, for some receptors, we have expanded these studies to primates, including humans.
We have found that the distribution of 5-HT1A receptors in monkey brain, labelled with the agonist3H-8-OH-DPAT and the antagonist3H-WAY 100635 was very similar at the levels examined, and corresponded well with that observed for the cells containing mRNA coding for this receptor, confirming the somatodendritic localization of 5-HT1A receptors in monkey brain. The labelling conditions to visualize 5-HT1F receptors in guinea pig brain, namely3H-sumatriptan in the presence of 10−8m 5-CT to block 5-HT1D receptors, are suitable for visualizing this receptor, since the results agreed with those observed byin situ hybridization. By using3H-ketanserin and3H-mesulergine in parallel within situ hybridization using the corresponding oligonucleotides, we were able to show that these ligands label respectively 5-HT2A and 5-HT2C binding sites in monkey brain. 5-HT4 receptors were localized in the brain of several species including humans by using125I-SB 207710.In situ hybridization experiments performed in guinea pig confirmed that 5-HT4 receptors are localized on the terminals of the striatopallidal and striatonigral projections. 5-HT7 binding sites were labelled in rat and guinea pig brains by incubating with3H-5-CT in the presence of 100 μm WAY 100135 and 250 μm GR 127935; the distribution obtained in both species agreed, in general, with that of the corresponding mRNA coding for them. These results are an illustration of the understanding of our current knowledge of the chemical neuroanatomy of the mammalian 5-HT system.
KeywordsSerotonin Receptor Monkey Brain Molecular Biological Technique Receptor Profile Receptor Autoradiography
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- Adham, N., Kao, H.-T., Schechter, L. E., Bard, J., Olsen, M., Urquhart, D., Durkin, M., Hartig, P. R., Weinshank, R. L. &Branchek, T. A. (1993) Cloning of another human serotonin (5-HT1F): a fifth 5-HT1 receptor subtype coupled to the inhibition of adenylate cyclase.Proc. Natl. Acad. Sci. USA 90, 408–12.PubMedGoogle Scholar
- Brown, A. M., Young, T. J., Patch, T. L., Cheung, C. W., Kaumann, A. J., Gaster, L. & King, F. D. (1993) [125I]-SB 207710, a potent, selective radioligand for 5-HT4 receptors.Br. J. Pharmacol. 110, 10P.Google Scholar
- Foguet, M., Hoyer, D., Pardo, L. A., Parekh, A., Kluxen, F. W., Kalkman, H. O., Stühmer, W. &Lübbert, H. (1992a) Cloning and functional characterization of the rat stomach fundus serotonin receptor.EMBO J. 9, 3481–7.Google Scholar
- Gerald, C., Adham, N., Hung-Teh, K., Olsen, M. A., Laz, T. M., Schechter, L. E., Bard, J. A., Vaysse, P. J.-J., Hartig, P. R., Branchek, T. A. &Weinshank, R. L. (1995) The 5-HT4 receptor: molecular cloning and pharmacological characterization of two splice variants.EMBO J. 14, 2806–15.PubMedGoogle Scholar
- Lovenberg, T. W., Baron, B. M., De Lecea, L., Miller, J. D., Prosser, R. A., Rea, M. A., Foye, P. E., Racke, M., Slone, A. L., Siegel, B. W., Danielson, P. E., Sutcliffe, J. G. &Erlander, M. G. (1993a) A novel adenylyl cyclase-activating serotonin receptor (5-HT7) implicated in the regulation of mammalian circadian rhythms.Neuron 11, 449–58.CrossRefPubMedGoogle Scholar
- Lovenberg, T. W., Erlander, M. G., Baron, B. M., Racke, M., Slone, A. L., Siegel, B. W., Craft, C. M., Burns, J. E., Danielson, P. E. &Sutcliffe, J. G. (1993b) Molecular cloning and functional expression of 5-HT1E-like rat and human 5-hydroxytryptamine receptor genes.Proc. Natl. Acad. Sci. USA 90, 2184–8.PubMedGoogle Scholar
- Matthes, H., Boschert, U., Amlaiky, N., Grailhe, R., Plassat, J. L., Muscatelli, F., Mattei, M. G. &Hen, R. (1992) Mouse 5-hydroxytryptamine5A and 5-hydroxytryptamine5B receptors define a new family of serotonin receptors: cloning, functional expression, and chromosomal localization.Mol. Pharmacol. 43, 313–19.Google Scholar
- Mengod, G., Le, H., Nguyen, H., Lübbert, H., Waeber, C. &Palacios, J. M. (1990) The distribution and cellular localization of the mRNA for the 5-HT1C receptor in the rodent brain examined by in situ hybridization. Comparison with receptor binding distribution.Neuroscience 35, 577–91.CrossRefPubMedGoogle Scholar
- Palacios, J.M., Mengod, G. &Hoyer, D. (1993) Brain serotonin receptor subtypes: radioligand binding, second messengers, ligand autoradiography, andin situ hybridization histochemistry.Meth. Neurosci. 12, 238–60.Google Scholar
- Palacios, J. M., Raurich, A., Mengod, G., Hurt, S. D. &Cortés, R. (1996) Autoradiographic analysis of 5-HT receptor subtypes labeled by3H-5-CT (3H-5-carboxamidotryptamine).Behav. Brain Res. 295, 271–4.Google Scholar
- Vilaró, M. T., Wiederhold, K.-H., Palacios, J. M. &Mengod, G. (1992) Muscarinic M2 receptor mRNA expression and receptor binding in cholinergic and non-cholinergic cells in the rat brain: A correlative study using in situ hybridization histochemistry and receptor autoradiography.Neuroscience 47, 367–93.CrossRefPubMedGoogle Scholar
- Vilaró, M. T., Cortés, R., Gerald, C., Branchek, T. A., Palacios, J. M. & Mengod, G. Localization of 5-HT4 receptor mRNA in rat brain by in situ hybridization histochemistry.Mol. Brain Res. In press.Google Scholar