COMPARISON OF IMMUNOHISTOCHEMICAL LOCALIZATION OF [MET5] ENKEPHALIN-ARG6-GLY7-LEU8, VASOACTIVE INTESTINAL POLYPEPTIDE AND TYROSINE-HYDROXYLASE IN THE MAJOR PELVIC GANGLION OF THE RAT

The major pelvic ganglion is an autonomic ganglion containing both sym pathetic and parasympathetic postganglionic neuronal cell bodies. The existence of the proenkephalin A-derived peptide [Met5]enkephalin-Arg6 -Gly7-Leu8 immunoreactivity in the rat major pelvic ganglion has been described quite recently. The aim of this study was to compare the rel ations of [Met5]enkephalin-Arg6-Gly7-Leu8-containing postganglionic ne urons and nerve fibers to noradrenergic (tyrosine hydroxylase-immunore active) and non-noradrenergic (putative cholinergic) neurons of the ra t major pelvic ganglion. Immunohistochemical double staining and eluti on restaining techniques were used to investigate the distribution of [Met5]enkephalin-Arg6-Gly7-Leu8 in correlation with tyrosine hydroxyla se and vasoactive intestinal polypeptide. The major pelvic ganglion co ntained neurons immunoreactive either for tyrosine hydroxylase or vaso active intestinal polypeptide. Many principal neurons, however, were n either immunoreactive for tyrosine hydroxylase nor vasoactive intestin al polypeptide. [Met5]Enkephalin-Arg6-Gly7-Leu8-immunoreactive princip al neurons formed a minor subpopulation in the ganglion and were not i mmunoreactive for tyrosine hydroxylase. The majority of [Met5]enkephal in-Arg6-Gly7-Leu8-immunoreactive principal cells were non-immunoreacti ve for vasoactive intestinal polypeptide, but a few of them also conta ined vasoactive intestinal polypeptide. In contrast to the large [Met5 ]enkephalin-Arg6-Gly7-Leu8-immunoreactive principal neurons, which for med a population of non-noradrenergic (putative cholinergic) cells, th e small [Met5]enkephalin-Arg6-Gly7-Leu8-immunoreactive cells exhibited intense tyrosine hydroxylase immunofluorescence and represented a sub population of small, intensely fluorescent cells. [Met5]Enkephalin-Arg 6-Gly7-Leu8-immunoreactive pericellular fiber plexuses were found arou nd tyrosine hydroxylase- and vasoactive intestinal polypeptide-immunor eactive principal neurons and in association with small intensely fluo rescent cells. [Met5]Enkephalin-Arg6-Gly7-Leu8-immunoreactive varicosi ties occurred around the majority of tyrosine hydroxylase-negative neu rons, regardless of their reactivity for vasoactive intestinal polypep tide or for [Met5]enkephalin-Arg6-Gly7-Leu8. These studies indicate th at a neuronal system containing proenkephalin A-derived opioid peptide s participates in innervation of both noradrenergic and non-noradrener gic (putative cholinergic) neurons, as well as small, intensely fluore scent cells of this ganglion, by dense plexuses of axonal varicosities . [Met5]Enkephalin-Arg6-Gly7-Leu8-immunoreactive principal neurons in the rat major pelvic ganglion do not contain catecholamines and theref ore form a subpopulation of non-noradrenergic (putative cholinergic) n eurons.