Studies of the guinea-pig epididymis. III. Innervation of epididymal segments.

The innervation of the ductuli efferentes and seven zones of the guinea-pig epididymis was investigated using immunohistochemical, histochemical and electron-microscopical techniques. Nerve fibers were localized by use of antibodies against substance P (SP-IR), vasoactive intestinal polypeptide (VIP-IR) and dopamine-beta-hydroxylase (DBH-IR). In the ductuli efferentes and all zones of the epididymal duct, SP-IR is consistently observed in the interstitial tissue and perivascular areas. Histochemistry reveals a significant amount of acetylcholinesterase-containing fibers in the interstitial, perivascular and periductal smooth muscles of the ductuli efferentes and zones V, VI and VII. In contrast to the homogeneous distribution of SP-IR within all zones of the epididymis, VIP-IR is seen only in zones VI and VII. Within these zones, VIP-IR is detected in large amounts in the subepithelial and muscular layers as is a sparse number of SP-IR varicosities. DBH-IR is also seen throughout all zones in the interstitial and perivascular regions with a tendency to increase in zones VI and VII. Transmission electron microscopy (TEM) reveals evidence of a cholinergic (agranular vesicles, AGV), adrenergic (small granular vesicles, SGV) and peptidergic (large granular vesicles, LGV) innervation throughout the interstitial connective tissue of the ductuli efferentes and all epididymal zones. Furthermore AGV are localized in the subepithelial layer, and also co-stored with LGV in the muscular layer of zones VI and VII. No nerve profiles were encountered within the epithelium. A correlation of immunohistochemical findings to TEM counterparts as well as their possible functional role are discussed.