Comparative distribution of receptors for amylin and the related peptides calcitonin gene related peptide and calcitonin in rat and monkey brain

The distribution of amylin receptors ( ¹²⁵ I-labelled rat amylin) in brains of rat and monkey were mapped and compared with the distribution of receptors for calcitonin (CT) ( ¹²⁵ I-labelled salmon CT) and calcitonin gene related peptide (CGRP) (rat, ¹²⁵ I-labelled rat CGRPα; monkey, ¹²⁵ I-labelled human CGRPα). In rat, amylin receptors were discretely distributed with the highest receptor densities found in mid-caudal accumbens nucleus, parts of the bed nucleus of the stria terminalis, amygdala, and hypothalamus. Moderate to high densities of binding also occurred in the area postrema, subfornical organ, vascular organ of the lamina terminalis, locus ceruleus, dorsal raphe, and caudal solitary tract nucleus. In monkey, the distribution of amylin binding sites was similar, although the highest densities of receptors were in the hypothalamus, with relatively fewer sites present in the accumbens nucleus. In rat, the distribution of amylin receptors formed a subset of the receptor distributions for ¹²⁵ I-labelled salmon CT and ¹²⁵ I-labelled rat CGRPα. In contrast, in monkey, although the amylin receptors again formed a subset of the binding sites identified with ¹²⁵ I-labelled salmon CT, there was very little overlap with the pattern of CGRP receptor distribution. This suggests that the specificity profile of amylin receptors in primates differs from that of amylin receptors in the rat, with CGRPα having relatively lower affinity for the primate amylin receptors.