The Human Penis: An Unusual Penetration of Npy-immunoreactive Nerves within the Medial Muscle Coat of the Deep Dorsal Vein

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Abstract
The deep dorsal penile vein was obtained from seven patients undergoing surgery for erectile dysfunction. The veins were studied histologically and immunohistochemically for serotonin, dopamine ^-hydroxylase, vasoactive intestinal polypeptide, neuropeptide Y, substance P, calcitonin gene-related peptide, somatostatin, and [Leu]- and [Met]enkephalin. Histologically, the deep dorsal vein was found to be a large muscular vein with a thin endothelial lining. The tunica media was composed of an inner longitudinally and an outer circularly arranged smooth muscle layer. Numerous vasa vasorum (up to 30 in a single transverse section) were found in the tunica adventitia. The greatest density of nerves supplying the deep dorsal vein and vasa vasorum were neuropeptide Y-immunoreactive nerves followed (in a decreasing order) by vasoactive intestinal polypeptide- and dopamine β-hydroxylase-immunoreactive nerves. Substance P-, calcitonin gene-related peptideand somatostatin-immunoreactive nerves, but not serotonin-, [Leu]- and [Met]enkephalin-immu-noreactive nerves, were occasionally found around the deep dorsal vein. All these nerve fibers were confined to the adventitial-medial border except neuropeptide Y-immunoreactive nerves which in addition penetrated the tunica media to the subendothelial layer of the deep dorsal vein. In contrast, neuropeptide Y-immunoreactive nerves supplying the vasa vasorum were always confined to the adventitial-medial border. The possible function of the medial innervation of the deep dorsal vein by neuropeptide Y-immunoreactive nerves is discussed.