Novel localizations of central- and peripheral-type cholecystokinin binding sites in Syrian hamster brain as determined by autoradiography.

Neuronal cholecystokinin (CCK) binding sites were studied in the Syrian hamster, a species with unique CNS localizations of CCK immunoreactivity. Preliminary studies of hamster forebrain sections using 125I-Bolton-Hunter-(BH)-CCK-8 indicated that radioligand binding kinetics and receptor selectivity for various unlabelled CCK peptides were similar to those reported for other species. Autoradiographic visualization of CCK binding sites revealed that the highest binding densities were distributed in the cerebral cortex, olfactory bulb, dorsal vagal complex, raphe obscurus and cochlear nuclei. Moderate binding densities were present in the amygdala, hippocampus, hypothalamus, thalamus, central grey and medial vestibular nucleus. Comparison of autoradiograms generated from adjacent sections incubated in 125I-BH-CCK-8 with unlabelled sulfated or desulfated CCK-8 confirmed the presence of peripheral-type CCK binding sites (i.e. at which desulfated CCK-8 has weak displacing activity) in the hamster dorsal vagal complex. Peripheral-type CCK binding sites were also distributed in regions of the hypothalamus (e.g. the magnocellular cell groups) where similar receptor selectivity had not been previously demonstrated. These observations provide further evidence of species differences in CCK receptor distribution and specificity, which may account for species differences in responsiveness to intracranial administration of CCK peptides.