Comparison of immunohistochemical localization of [Met 5] enkephalin-Arg 6-Gly 7-Leu 8, vasoactive intestinal polypeptide and tyrosine hydroxylase in the major pelvic ganglion of the rat

Abstract

The major pelvic ganglion is an autonomic ganglion containing both sympathetic and parasympathetic postganglionic neuronal cell bodies. The existence of the proenkephalin A-derived peptide [Met 5]enkephalin-Arg 6-Gly 7-Leu 8 immunoreactivity in the rat major pelvic ganglion has been described quite recently. The aim of this study was to compare the relations of [Met 5]enkephalin-Arg 6-Gly 7-Leu 8-containing postganglionic neurons and nerve fibers to noradrenergic (tyrosine hydroxylase-immunoreactive) and non-noradrenergic (putative cholinergic) neurons of the rat major pelvic ganglion. Immunohistochemical double staining and elution-restaining techniques were used to investigate the distribution of [Met 5]enkephalin-Arg 6-Gly 7-Leu 8 in correlation with tyrosine hydroxylase and vasoactive intestinal polypeptide. The major pelvic ganglion contained neurons immunoreactive either for tyrosine hydroxylase or vasoactive intestinal polypeptide. Many principal neurons, however, were neither immunoreactive for tyrosine hydroxylase nor vasoactive intestinal polypeptide. [Met 5]Enkephalin-Arg 6-Gly 7-Leu 8-immunoreactive principal neurons formed a minor subpopulation in the ganglion and were not immunoreactive for tyrosine hydroxylase. The majority of [Met 5]enkephalin-Arg 6-Gly 7-Leu 8-immunoreactive principal cells were non-immunoreactive for vasoactive intestinal polypeptide, but a few of them also contained vasoactive intestinal polypeptide. In contrast to the large [Met 5]enkephalin-Arg 6-Gly 7-Leu 8-immunoreactive principal neurons, which formed a population of non-noradrenergic (putative cholinergic) cells, the small [Met 5]enkephalin-Arg 6-Gly 7-Leu 8-immunoreactive cells exhibited intense tyrosine hydroxylase immunofluorescence and represented a subpopulation of small, intensely fluorescent cells. [Met 5]Enkephalin-Arg 6-Gly 7-Leu 8-immunoreactive pericellular fiber plexuses were found around tyrosine hydroxylase- and vasoactive intestinal polypeptide-immunoreactive principal neurons and in association with small intensely fluorescent cells. [Met 5]Enkephalin-Arg 6-Gly 7-Leu 8-immunoreactive varicosities occurred around the majority of tyrosine hydroxylase-negative neurons, regardless of their reactivity for vasoactive intestinal polypeptide or for [Met 5]enkephalin-Arg 6-Gly 7-Leu 8. These studies indicate that a neuronal system containing proenkephalin A-derived opioid peptides participates in innervation of both noradrenergic and non-noradrenergic (putative cholinergic) neurons, as well as small, intensely fluorescent cells of this ganglion, by dense plexuses of axonal varicosities. [Met 5]Enkephalin-Arg 6-Gly 7-Leu 8-immunoreactive principal neurons in the rat major pelvic ganglion do not contain catecholamines and therefore form a subpopulation of non-noradrenergic (putative cholinergic) neurons.