Localization and quantitation of proenkephalin-derived neuropeptides in the rat hippocampus.

We have measured the content of met- and leu-enkephalin and dynorphin B in the rat hippocampus, and localized these opioid peptides within the intrinsic hippocampal neuronal circuitry with specific lesions. Several enkephalins, two of which were shown to be met- and leu-enkephalin, were identified in rat hippocampus. The levels of the enkephalin-related peptides were unaffected by intrahippocampal injections of colchicine, which destroyed the great majority of the hippocampal granule cells, while the level of dynorphin B, which serves as a marker for the proenkephalin B-derived peptides, was markedly depleted. Entorhinal cortical lesions ablating the perforant pathway input to the hippocampus did not significantly alter dynorphin B nor enkephalin levels in the hippocampus. Unilateral fimbrial transection caused a small but significant increase in dynorphin B on the side of the lesion relative to the non-lesioned side, although neither side was significantly different from control, while at the same time causing a significant bilateral increase in both met- and leu-enkephalin levels. This may result from loss of a direct or indirect stimulatory input to peptide-containing neurons within the hippocampus. The enkephalins appear to be located in neuronal cell bodies intrinsic to the body of the hippocampus, while the dynorphins are likely to be intrinsic only to the granule cell-mossy fiber system originating in the dentate gyrus.