LOCALIZATION OF 5-HT1B, 5-HT1D-ALPHA, 5-HT1E AND 5-HT1F, RECEPTOR MESSENGER-RNA IN RODENT AND PRIMATE BRAIN

In situ hybridization histochemistry (ISHH) was used to study the dist ribution of various 5-HT1 receptor messenger RNAs (mRNA) in the mammal ian nervous system. Since the cDNAs encoding the different 5-HT1 recep tors, have not been cloned in one single species, brains of the specie s appropriate for the 5-HT1 receptor messenger RNA (mRNA) have been us ed. Thus, 5-HT1B and 5-HT1D alpha mRNA were determined in rat and mous e brain, while 5-HT1E and 5-HT1F mRNA were studied in human (and monke y) and guinea-pig brain, respectively. 5-HT1B and 5-HT1D alpha hybridi zation signals were predominantly present in caudate-putamen and corti cal areas; in addition, 5-HT1B mRNA was also detected in hippocampus, cerebellum and cerebral arteries. In general, the distribution of 5-HT 1B mRNA was characterized by high densities, whereas 5-HT1D alpha mRNA was expressed at very low levels. Comparison of the localization of t he mRNAs to the regional distributions of the 5-HT1B and 5-HT1D bindin g sites in rat brain (described in a previous study), revealed that bo th receptor subtypes could be putative presynaptic heteroreceptors, mo dulating the release of various neurotransmitters in the central nervo us system. The mRNA encoding the recently cloned 5-HT1E receptor, whic h has low affinity for the 5-HT1 receptor ligand 5-carboxamidotryptami ne (5-CT), was localized in human brain. It was found to be present in cortical areas, caudate, putamen and amygdala, areas known to contain 5-CT insensitive 5-HT1 binding sites. The regional distribution of th e 5-HT1F mRNA was determined in guinea-pig brain: high densities were observed in various cortical areas, the hippocampal formation and clau strum, which are regions known to contain 5-CT insensitive 5-HT1, or n on 5-HT1A/1B/1C/1D [H-3]5-HT binding sites. Altogether, this ISHH stud y describes the distribution of mRNAs of recently cloned 5-HT1 recepto rs in rodent and primate brain and compares these results to the distr ibution of the heterogeneous population of 5-HT1 binding sites.