Expression of at_1A and at_1B angiotensin II receptor messenger RNA in forebrain of 2-wk-old rats

-The gene expression of angio-tensin II receptor subtypes AT_1A and AT_1B was localized in theforebrain of 2-wk-old rats by in situ hybridization histochemistry and compared with [¹²⁵I]Sar1-angiotensin II binding patterns. AT_1A and AT_1B receptor mRNA was expressed in circumventricular organs, in hypothalamic nuclei like the paraventricular nucleus, in the lateral olfactory tract, in the basolateral amygdaloid and anterior olfactory nuclei, and in the piriform cortex. No AT_1A and AT_1B receptor mRNA was detected in these areas. AT_1A and AT_1B receptor mRNA was detected in the hippocampus, cingulate cortex, and choroid plexus. No forebrain area studied expressed AT_1B receptor mRNA exclusively. Most often, a good match for receptor mRNA and binding was found. In some areas, apparent mismatches suggested receptor formation elsewhere (median eminence) or receptor presence in local neuronal circuits (hippocampus, cingulate, and piriform cortex). Our results support the hypothesis that AT_1A receptors are involved in the classical central functions of angiotensin II. Both AT_1A and AT_1B receptors may play roles in cortical and limbic system function, particularly early in development.