Distribution of cholecystokinin receptors in the bovine brain: a quantitative autoradiographic study

Quantitative in vitro receptor autoradiography was used to study the distribution of cholecystokin receptors in the bovine brain. [125I]Bolton-Hunter cholecystokinin octapeptide binding was described in whole hemisphere sagittal and coronal sections using cholecystokinin octapeptide, devazepide and L-365,260 as competitors to identify the subtypes. High levels of cholecystokinin receptors were found in the cortex, where they presented a laminar distribution which varied from area to area. The basal ganglia, the caudate nucleus, nucleus accumbens and putamen presented high to moderate levels of cholecystokinin binding, whereas only very low labelling was found in the globus pallidus. Cholecystokinin binding was present in all portions of the bovine hippocampus; high levels were found in the dentate gyrus, CA1 subfield of Ammon's horn, subiculum and presubiculum. Moderate to high levels were also found in the amygdala, inferior colliculus and olfactory tract, while most of the hypothalamic and thalamic nuclei exhibited very low or no cholecystokinin binding. Low cholecystokinin binding was uniformly distributed across cell layers of the bovine cerebellar cortex. Competition of [125I]Bolton-Hunter cholecystokinin octapeptide binding in the cortex, nucleus accumbens, caudate nucleus, hippocampus, cerebellum and brainstem was much greater in the presence of L-365,260 than devazepide, thereby suggesting that the majority of cholecystokinin receptors in these regions are of the cholecystokinin-B subtype. The results of this study, when compared to distribution profiles in other mammalian species, provide further evidence for species differences in the distribution of cholecystokinin receptors in the brain. The results also support the possible interaction between cholecystokinin and dopaminergic systems in areas of the brain containing dopaminergic terminals, such as the frontal cortex, nucleus accumbens, caudate-putamen and olfactory tubercle.