Immunohistochemical characterisation of cholinergic nerve fibres supplying accessory genital glands in the pig

Our previous immunohistochemical investigations revealed three major populations of nerve fibres supplying the porcine accessory genital glands (AGG) including noradrenergic, non-noradrenergic putative cholinergic and sensory nerve terminals (Kaleczyc et al., 1997). However, it is still unclear whether the non-noradrenergic nerve fibres are cholinergic in nature. The knowledge of the population of cholinergic nerve fibres in mammalian AGG based upon vesicular acetylcholine transporter (VAChT) immunohistochemistry is very limited. Therefore, the aim of the present investigation was to disclose the occurrence and colocalization patterns of VAChT, dopamine beta-phydroxylase (D beta H) and some neuropeptides including vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY) and somatostatin (SOM) within nerve fibres supplying the porcine AGG. Double - immunohistochemical labellings showed that VAChT-positive nerve terminals were non-adrenergic (D beta H-negative), however, many of them contained immunoreactivities to VIP, NPY and/or SOM. The coexistence patterns of these biologically active substances in nerve fibres supplying particular glands are similar but the density of cholinergic innervation varies between the organs. The innervation of the seminal vesicle and prostatic body is better developed than that of the disseminated part of the prostate and bulbourethral glands. The majority of cholinergic nerve fibres associated with blood vessels supplying the glands contain VIP and NPY and, to a lesser degree, SOM. The possible function and origin of the cholinergic nerve fibre population are discussed.