Expression of AT1A and AT1B angiotensin II receptor messenger RNA in forebrain of 2-wk-old rats

The gene expression of angiotensin II receptor subtypes AT1A and AT1B was localized in the forebrain of 2-wk-old rats by in situ hybridization histochemistry and compared with [125I]Sar1-angiotensin II binding patterns. AT1A 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 AT1B receptor mRNA was detected in these areas. AT1A and AT1B receptor mRNA was detected in the hippocampus, cingulate cortex, and choroid plexus. No forebrain area studied expressed AT1B 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 AT1A receptors are involved in the classical central functions of angiotensin II. Both AT1A and AT1B receptors may play roles in cortical and limbic system function, particularly early in development.