Differential localization of³H-[Pro⁹]SP binding sites in the guinea pig and rat brain

Abstract

Due to the existence of differences in the pharmacological properties of tachykinin NK-1 receptors in the rat and the guinea pig, the autoradiographic distribution of NK-1 binding sites was compared in the brain of the two species using the selective NK-1 ligand³H-[Pro⁹]SP. If a good similarity in the distribution of NK-1 binding sites could be seen in basal ganglia, a relative absence of correlation was observed between the estimated optical densities in other brain structures of the two species. For instance, the interpeduncular nucleus, the lateral habenular nucleus and the deep layers of the cerebral cortex were labeled in the guinea pig but not in the rat while the reverse was observed for the columns of the vermis lobules 9–10, the dorsal raphe nucleus, the medial habenular nucleus, the superficial cortical layers and the dorsal hippocampus. Furthermore, the high similarity found in the localization of¹²⁵I-BHSP (a non selective ligand) and³H-[Pro⁹]SP binding sites, does not suggest the existence of NK-1 binding site subtypes in the guinea pig brain.