Distribution of [3H]cholecystokinin octapeptide binding sites in the hippocampal region of the rat brain as shown by in vitro receptor autoradiography.

The distribution of binding sites for the neuropeptide cholecystokinin octapeptide in the rat hippocampal region was studied by using quantitative in vitro receptor autoradiography. Biochemical analysis of [3H]cholecystokinin octapeptide binding to tissue sections of the hippocampal region showed it to be of high affinity, to be saturable and approximately 50% specific at saturating concentrations. The binding of [3H]cholecystokinin octapeptide to hippocampal sections was dose-dependently blocked by cholecystokinin octapeptide, cholecystokinin and by pentagastrin. The autoradiographic analysis showed high densities of [3H]cholecystokinin octapeptide binding sites in the hilus of the area dentata, the outer three layers of the retrosplenial area and the presubiculum, layer 3 of the medial, but not the lateral, entorhinal area and the deep and superficial parts of layer 1 and 2, respectively of both the medial and the lateral entorhinal area. Medium binding densities were found in the parasubiculum and remaining layers of the entorhinal area and low densities occurred in the subiculum and in all subfields of Ammon's horn. The angular bundle and fornix-fimbria lacked specific [3H] cholecystokinin octapeptide binding sites. A very similar pattern of binding densities was found for [3H]pentagastrin. Comparisons of the cholecystokinin octapeptide receptor distribution with the cholecystokinin octapeptide innervation of the hippocampal region suggest that there exists a relatively good concordance in some hippocampal subfields such as the presubiculum and the entorhinal area between binding sites for [3H]cholecystokinin octapeptide and cholecystokinin-immunoreactive afferent input.