Vasointestinal Polypeptide (VIP)‐Immunoreactive Nerves in the Boar Penis

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Abstract
Vasointestinal polypeptide (VIP)-immunoreactivity was localized at LM-level in cryostat sections using a peroxidase-anti-peroxidase technique, and at EM-level in glutaraldehyde-fixed, resin-embedded sections using an immunogold technique, of samples from the penis of 3 Hampshire boars with a history of normal erection and mating behaviour. One boar of the same breed with an impotence diagnosis was also examined. In the normal animals, VIP-immunoreactivity was localized into nerves associated to blood vessels and non-vascular smooth muscle in the capsular lamina propria and the fibromuscular layers, and intermingled under the penis epithelium. At EM level, the immunogold localization confirmed the above mentioned results, VIP being localized in nerve terminals. Nerve terminals without VIP-reactivity had EM appearance of cholinergic or adrenergic nerve terminals. No obvious differences in VIP innervation were noticed among the normal boars. In the impotent animal, a marked depletion of VIP-immunoreactivity was evident, as well as degenerative changes in the adrenergic and cholinergic nerve profiles. It is concluded that the porcine penis is well innervated, along with adrenergic and cholinergic components, by VIP-containing nerves. The depletion of the scattered VIP-containing nerves in the impotent case suggests its involvement in the mechanisms of penile erection in the boar.