Angiotensin II receptor subtype mRNA was localized to selective brain areas by in situ hybridization, to determine the brain sites for receptor formation and to correlate these sites with those of receptor expression by ligand binding and autoradiography. Angiotensin II receptor subtype mRNA was expressed early in development (E12) in peripheral rat tissues. A novel "atypical" angiotensin II receptor subtype was characterized, and its expression was found to be decreased in the gerbil hippocampus after cerebral ischemia. An AT1-like receptor was cloned and sequenced in the gerbil. This receptor has high sequence homology to the rat AT1A receptor, and may correspond to the gerbil hippocampal receptor. Modulation of a novel macrophage non-angiotensin receptor by CGP 42112 was found to enhance macrophage adhesion to fibronectin, indicating that this is a functional, important receptor with a role in macrophage function. Melatonin administration was found to decrease cerebral blood flow, and to selectively affect adenylate cyclase activity.