Localization and neurochemical features of the sympathetic trunk ganglia neurons projecting to the urethral muscle. An experimental study in a porcine animal model.

The striated perineal urethral muscle (UM) is involved in the voluntary control of the micturition requiring complex interactions between afferent and efferent (autonomic and somatic) pathways to store and periodically eliminate urine. Our aim was to define the site, cross sectional area and phenotype of sympathetic trunk ganglia (STG) neurons projecting to the porcine UM, combining retrograde neuronal tracer Fast Blue (FB) and double immunohistochemical labelling methods. The research was carried out on 3 male intact pigs, in which we counted a total number of 4992.67 ± 834.35 (mean ± S.E.M., n = 3) FB+ neurons distributed in the bilateral T12-S3 STG. These neurons were significantly larger in lumbar STG than in the sacral ones. Moreover we highlighted the presence of Dopamine β hydroxylase (DβH), Vesicular Acetylcholine Transporter (VAChT), neuronal Nitric Oxyde Sinthase (n-NOS), Calcitonine Gene Related Peptide (CGRP), Leu-Enkephaline (LENK), Neuropeptide Y (NPY), Substance P (SP), Vasoactive Intestinal Polypeptide (VIP) and Somatostatine (SOM) and their eventual co-existence with Tyrosine Hydroxylase(TH) in both lumbar and sacral FB+ neurons. In particular, lumbar and sacral STG neurons expressed similar percentages of immunoreactivity for TH, SP and CGRP, but showed significantly different levels of immunoreactivity for NPY, VIP, VAChT, LENK, nNOS, DβH and SOM. Taken together, these data indicate a different contribution of lumbar and sacral pathways in the sympathetic transmission to the boar UM.