Localization of 5-HT(7) receptors in rat brain by immunocytochemistry, in situ hybridization, and agonist stimulated cFos expression.

5-HT(7) receptors are recently identified members of the serotonin receptor family that have moderate to high affinity for several important psychotropic drugs. However, the lack of selective ligands has impeded the study of the brain distribution of these receptors. In this report, we describe the localization of 5-HT(7) receptor in rat forebrain by immunocytochemistry, in situ hybridization of 5-HT(7) mRNA, and functional stimulation of cFOS expression by 5-HT(7) receptor activation. The anatomical localization of 5-HT(7) mRNA in situ hybridization signal. Prominent immunostaining was apparent in numerous sites within the cerebral cortex, hippocampal formation, tenia tecta, thalamus and hypothalamus. 5-HT(7) receptors were detected in suprachiasmatic nucleus by both immunocytochemistry and in situ hybridization. At a microscopic level, both cell bodies and proximal fibers were strongly stained in these regions, suggesting a somatodendritic subcellular distribution. 5-HT(7) receptor-like immunoreactivity was further compared with 5-HT(7) mediated biological function by administering 8-OH-DPAT intracerebroventricular injection (icv)with WAY 100135 (to block 5-HT(1A) receptors) followed by double immunostaining localization of cFos activation and 5-HT(7) receptors. In all regions examined, cFos stimulation and 5-HT(7)-like immunoreactivity colocalized to the same neurons. Furthermore, cFos activation by 8-OH-DPAT was blocked by pimozide--a 5-HT(7) antagonist. Therefore, by using multiple strategies, we were able to localize 5-HT(7) receptors in rat brain unequivocally. The distribution of these receptors is consistent with their involvement in the control of circadian activity and the action of anti-depressants and atypical neuroleptics.