Immunohistochemical characteristics of neurons supplying the porcine bulbourethral gland

In the male pig, the bulbourethral gland (BG) is a particulary well developed accessory genital gland (AGG) which produces complex secretion contributing to the fluid component of semen. The secretory and motor function of AGGs is thought to be under the autonomic nervous system control. Although relatively much is known about the innervation of the prostate gland and, to a lesser degree, of the seminal vesicle, the paucity of data dealing with the innervation of BG is striking. Therefore, combined retrograde tracing and double-labelling immunofluorescence have been used to investigate the distribution and immunohistochemical properties of autonomic and primary afferent neurons projecting to this gland in the pig. BG-projecting neurons were found in some ipsilateral (I) and contralateral (C) sympathetic chain ganglia (SChG), the caudal mesenteric ganglion (CaMG), pelvic ganglia (PG) and some dorsal root ganglia (DRG). Immunohistochemistry revealed that the vast majority of CaMG and SChG BG-projecting neurons contained tyrosine hydroxylase (TH) and dopaminebeta-hydroxylase (DbetaH), and some neuropeptides including neuropeptide Y (NPY), somatostatin (SOM) and galanin (GAL). Three subpopulations of PG neurons supplying BG could be distinguished: 1) cholinergic neurons vesicular acetylcholine transporter (VAChT)-positive] which also contained vasoactive intestinal polypeptide (VIP), nitric oxide synthase (NOS), SOM and NPY, 2) adrenergic neurons (TH-positive) which also stained for NPY, GAL or leu5-enkephalin (LEU), and 3) non-adrenergic, non-cholinergic neurons (NANC). DRG BG-projecting neurons contained mostly substance P (SP) and/or calcitonin gene-related peptide (CGRP) which sometimes colocalized with GAL. The possible functional significance of the substances found within the neurons is discussed.