Distribution of neuropeptide-, tyrosine hydroxylase- and nitric oxide synthase containing nerve fibers in the external urethral sphincter of the rat.

The occurrence and distribution of adrenergic, peptidergic and nitrergic nerve fibers were investigated within the part of the rat urethra that corresponds to the external urethral sphincteric mechanism. At this level, the urethral wall was found to be composed of the following layers: mucosa/urothelium, lamina propria, smooth muscle, mixed smooth and striated muscle and striated muscle. Nerve fibers containing immunoreactivity against either nitric oxide synthase (NOS) or any of the following peptides were visualised in various amounts in all three muscle layers of rats of both sexes: neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), calcitonin gene related peptide (CGRP), substance P (SP), cholecystokinin (CCK), gastrin releasing peptide (GRP) and pituitary adenylate cyclase-activating peptide. (PACAP) Tyrosine hydroxylase (TH), marker for nonadrenergic nerves, was only found in nerve fibers of the smooth and mixed muscle layers, while enkephalin 8 (ENK-8) was only found in the striated muscle layer. The great number of putative neuromessengers and different nerve fiber populations suggest a complex innervation pattern of the sphincter area.