Central Nervous System Innervation of the Penis, Prostate, and Perineal Muscles: A Transneuronal Tracing Study

The spinal and brain neurons that innervate the male sex organs (penis, perineal muscles, and prostate) were identified using the transneuronal tracing technique. Rats were anesthetized with ketamine/xylazine, and pseudorabies virus (PRV) was injected into either the corpus cavernosum, ventral prostate, or bulbospongiosus or ischiocavernosus muscle. After a 2- to 5-day survival period, rats were perfused transcardially under deep anesthesia, and viral-labeled neurons were identified using immunohistochemistry methods. After a 2- to 3-day survival, prostate or corpus cavernous injections resulted in labeling of sympathetic and parasympathetic preganglionic neurons. Spinal pudendal motoneurons were found to be labeled after perineal muscle injections. Spinal interneurons were found in the medial gray in the dorsal gray commissure and in the lateral gray of T13-S1 after injection at all sites. In the brain, the regions consistently labeled after all injections were the ventrolateral medulla, raphe magnus, raphe pallidus, A5, Barrington¹s nucleus, central gray, and paraventricular nucleus of the hypothalamus. Therefore, there appears to be a large degree of overlap of the spinal and brain circuits that regulate the sex organs.