Expression of AT(1A) and AT(1B) angiotensin II receptor messenger RNA in forebrain of 2-wk-old rats

The gene expression of angiotensin II receptor subtypes AT(1A) and AT(1B) was localized in the forebrain of 2-wk-old rats by in situ hybridization histochemistry and compared with [I-125]Sar(1)-angiotensin II binding patterns. AT(1A) 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(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.