Autoradiographic localization of [3H]neurotensin-binding sites in the hippocampal region of the rat and primate brain.

The distribution of binding sites for the neuropeptide neurotensin was studied in the hippocampal region of the rat, monkey and human brain by using the method of in vitro receptor autoradiography. Biochemical studies of [3H]neurotensin binding to homogenates or sections of the rat hippocampal region showed it to be saturable, reversible and of high specificity. Displacement studies showed that neurotensin-(1-13) and neurotensin-(8-13) were active, while neurotensin-(1-6) and (1-8) were inactive in blocking the specific binding of [3H]neurotensin to hippocampal sections. The autoradiographic studies showed a highly heterogeneous pattern of [3H]neurotensin binding in the hippocampal region: the highest density was present in the entorhinal area while little binding was found in the Ammon's horn. In the rat most of the [3H]neurotensin binding was found in layer II of the medial entorhinal area and in the parasubiculum, while the lateral entorhinal area contained fewer [3H]neurotensin-binding sites. The laminar distribution of binding remained the same throughout the longitudinal axis of the entorhinal area. The pattern of [3H]neurotensin binding in the monkey resembled that seen in the rat inasmuch as the medial was rich and the lateral entorhinal area was poor in [3H]neurotensin-binding sites. In the medial entorhinal area most binding was found in layers I-IV. Unlike in the rat, the hilus of the monkey contained moderate and the molecular layer of the area dentata few [3H]neurotensin-binding sites. In the human brain the outer three layers of both the medial and the lateral entorhinal area contained binding sites for [3H]neurotensin. Binding sites for [3H]neurotensin were found also in the parasubiculum and in the molecular layer of the area dentata of the human brain. The present autoradiographic studies show that the hippocampal region of the rat and primate brain is rich in binding sites for [3H]neurotensin, that a majority of these are situated in the entorhinal area and that despite some differences in the regional distribution of these binding sites within the hippocampal region, some principal similarities may exist between these species.