Cholecystokinin-octapeptide (CCK-8) receptors in the hippocampal region: a comparative in vitro autoradiographic study in the rat, monkey and the postmortem human brain.

Quantitative in vitro receptor autoradiography of 125I-CCK-8 was used to study the regional distribution of CCK-8 receptors in the primate hippocampal region. In the monkey, specific 125I-CCK-8 binding sites were enriched in layer 2 of the presubiculum, layers 1, 2, and 4 of the entorhinal area and in the inner two-thirds of the molecular layer of the area dentata. Moderate to low densities were detected in layer 3 of the entorhinal area, the deep layers of the presubiculum, all layers of subiculum and subfields CA1 and CA3 of Ammon's horn. In the human brain, the highest densities of 125I-CCK-8 binding sites were detected in layer 2 of the presubiculum and layer 2 of the lateral entorhinal area. Moderate to low levels were detected in the Ammon's horn and area dentata. This pattern of receptor distribution overlaps only partly with that found in the rat and indicates phylogenetic differences in the localization of CCK-8 receptors within the hippocampal region.