Localization of binding sites for calcitonin gene-related peptide in rat brain by in vitro autoradiography

The distribution of binding sites for calcitonin gene-related peptide (CGRP) in rat brain were studied using in vitro autoradiography. In a radioreceptor assay using [125I]human calcitonin gene-related peptide as the radioligand, with cerebellar cortical membranes, rat calcitonin gene-related peptide had a binding affinity constant of 1.16 +/- 0.23 X 10(10) M-1 and a site concentration of 43.4 +/- 3.4 fmol/mg protein. In this system, human calcitonin gene-related peptide had a binding affinity constant of 3.9 +/- 0.7 X 10(9) M-1 whereas salmon calcitonin was very weak with a binding affinity constant of only 6.8 +/- 4.0 X 10(5) M-1. CGRP binding localized by in vitro autoradiography, using [125I]rat calcitonin gene-related peptide, had a characteristic distinct distribution in the rat brain. There were high concentrations of binding found over the accumbens nucleus, the organum vasculosum of the lamina terminalis, ventral caudate putamen, median eminence, the arcuate nucleus, lateral amygdaloid nucleus and lateral mammillary nucleus, the superior and inferior colliculi, pontine nuclei, molecular and Purkinje cell layers of the cerebellar cortex, the nucleus of the solitary tract, the inferior olivary nuclei, hypoglossal complex and the vestibular and cochlear nuclei. The distribution of these binding sites suggests multiple roles for CGRP in the central nervous system including auditory, visual, gustatory and somatosensory processing, and in neuroendocrine control.