Ultrastructural identification of vasoactive intestinal polypeptide- and neuropeptide Y-containing nerve fibres in the vas deferens of the guinea-pig.

Vasoactive intestinal polypeptide (VIP)-like and neuropeptide Y (NPY)-like immunoreactive nerve fibres were identified by electron microscopic immunohistochemistry in the guinea-pig vas deferens. Labelled nerve fibres were observed in all layers of the wall. However, the NPY-like immunoreactive nerve fibres were most numerous in the muscle layer, and only a few labelled nerve processes were found in the tunica mucosa. In contrast, many of the VIP-like immunoreactive nerve fibres were found in close relation to the blood vessels, especially in the tunica mucosa. In the muscle layer, most immunoreactive nerve fibres were found in close relation to the smooth muscle cells; in these situations the separation between axon and muscle cell membranes was nearly always less than 100 nm, and in many cases as little as 20 nm. The ratio of large to small vesicles in the VIP-like immunopositive axons was 1:3.1, while in the NPY-like immunoreactive nerve terminals the ratio was 1:6.2. These ultrastructural observations confirm that VIP- and NPY-like immunoreactive nerve fibres exist in vas deferens and provide a morphological basis for the possibility that these fibres may participate in the regulation of smooth muscle activity and may influence blood flow in the vas deferens.