Effects of chemical and surgical lesions on levels of chromatographically identified enkephalin-like peptides in rat hippocampus

Proenkephalin and prodynorphin related neuropeptides in the cochlea

Dynorphin B (rimorphin), a proenkephalin B (prodynorphin)-derived peptide, and met-enkephalin-Arg6, Gly7, Leu8 (met-enkephalin octapeptide), a proenkephalin A-derived peptide, were identified in the mammalian cochlea by specific radioimmunoassays. The antisera are directed against unique sequences in the peptides, and this immunoreactivity cannot be ascribed to cross-reaction with any other known opioid peptides. Met-enkephalin octapeptide and dynorphin B can for this reason serve as reliable markers for the proenkephalin A- and proenkephalin B-derived peptides, respectively. Lesion studies in the cochlea indicate that dynorphin B is confined to olivocochlear efferents. It has not been determined if the dynorphin-containing neurons are the same as those known to contain enkephalin-related peptides, or if they may be cholinergic. Different, presumably inhibitory, neurotransmitters or modulators in the olivocochlear fibers create the possibility of separately modulating the effects of inner or outer hair cells on auditory nerve activity, and so becoming able to study their individual actions in audition. The olivocochlear fiber-hair cell-eighth nerve interaction may provide a valuable model for a complex multi-transmitter synaptic junction.

Localization and quantitation of dynorphin B in the rat hippocampus

The present study measures the content of dynorphin B in the rat hippocampus, and localizes the dynorphins within the intrinsic hippocampal neuronal circuitry. The level of dynorphin B, which is representative of the prodynorphin-derived peptides, was markedly depleted by intrahippocampal injection of colchicine, which destroyed the great majority of the hippocampal granule cells and the associated mossy fiber pathway. The hippocampus contralateral to the injection demonstrated a slight, non-significant rise in dynorphin B levels after colchicine. Entorhinal cortical lesions ablating the perforant pathway input to the hippocampus did not significantly alter dynorphin B 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 unlesioned side, but neither side was significantly different from control.