Adrenergic, nitrergic and peptidergic innervation of the urethral muscle in the boar.

In this study, the innervation of the urethral muscle in adult male pigs was investigated using combined NADPH-diaphorase (NADPH-d) histochemistry and immunocytochemistry. Nerve fibres supplying the urethral muscle were found to show NADPH-d activity and they also expressed immunoreactivity to catecholamine synthesising enzymes including tyrosine hydoxylase (TH) and dopamine-beta-hydroxylase (DbetaH) as well as to: vasoactive intestinal polypeptide (VIP) and neuropeptide Y (NPY). Different subpopulations of the nerve fibres (NADPH-d positive, TH-, DbetaH-, VIP- and NPY-immunoreactive (IR), but also NADPH-d/VIP- and NADPH-d/NPY-IR) were disclosed. These nerve fibres were observed not only to run among muscle fibres of the urethral muscle, but also within extrinsic nerve trunks. Moreover, in the organ studied, numerous ganglia were found. The intramural ganglia, composed of a few to 30 neurons were located in the proximal, middle and distal regions of the pelvic urethra. In the vicinity of the urethral muscle, there were mainly small ganglia containing two to several neurons, but also larger ganglia consisting of up to tens neurons were encountered in the connective tissue surrounding the pelvic urethra. In the ganglia observed in the neighbourhood of the urethral muscle, different subpopulations of nerve cells were found, namely: catecholaminergic, nitrergic, VIP-IR, NPY-IR and also NADPH-d/DbetaH-, NADPH-d/VIP- and NADPH-d/NPY-positive. Possible sources of the innervation for this muscle were also discussed.