Autoradiographic localization of neuromedin B binding sites in rat brain

The binding properties and autoradiographic distribution of radiolabeled neuromedin B (NMB) to rat brain sections were investigated. 125I-NMB bound with high affinity ( K d = 1 n M) to a single class of sites ( B max = 80 fmol/mg protein) in coronal rat brain sections. Binding was specific, time dependent, and reversible. Structure activity studies indicated that NMB, litorin, ranatensin, bombesin, gastrin releasing peptide (GRP), and GRP 18–27 but not GRP 1–16 inhibited 125I-NMB binding with high affinity. Autoradiographic studies indicated that high 125I-NMB grain densities were present in the olfactory bulb, nucleus accumbens, and central medial thalamic nucleus. Moderate grain densities were present in the septum, stria terminalis, hypothalamus, hippocampus, amygdala, locus coeruleus, dorsal parabrachial nucleus, and superior olive. Grains were absent in the corpus callosum, lateral thalamus, and cerebellum. Because NMB binds with high affinity to discrete brain regions, it may function as a regulatory peptide in the rat central nervous system.