Spontaneous reconstruction of the canine hypogastric nerve over a long period after removing half of its length

Spontaneous reconstruction of the sympathetic pathway projecting to the seminal tract after serious injury has not been well understood. Multiple cross-innervation mechanisms from the spinal cord via the hypogastric nerve to the seminal tract have been demonstrated currently. This study was undertaken to explore long-term spontaneous reconstruction of the canine hypogastric nerve (HGN), which controls ejaculation, after removing half of its length. Further, the study tried to identify the crossed-pathway(s) reconstructed. Responses of the vas deferens/epididymis and bladder neck to electrical stimulation of the lumbar splanchnic nerve (LSN) or the HGN were examined. In six dogs whose hypogastric nerve was injured bilaterally as described above 4 years before, corresponding to more than 20 years in human, nine (43%) and 13 (57%) of the 21 LSNs stimulated elicited elevation of vasal and bladder neck pressure, respectively. By combining re-transection of a HGN, the following pathways to the vas deferens/epididymis were identified to have been reconstructed: (1) to the ipsilateral vas deferens/epididymis without crossing to the other side; (2) to the contralateral vas deferens/epididymis by crossing to the other side at the caudal mesenteric plexus (CMP); (3) to the contralateral vas deferens/epididymis by crossing to the other side from the ipsilateral HGN at the commissural branches between the right and left pelvic plexuses (CBPP); and (4) to the ipsilateral vas deferens/epididymis by crossing twice at the CMP to the other side and at the CBPP again from the contralateral HGN to the ipsilateral side. The similar patterns of reconstruction were also observed in the bladder neck. The above results indicate that the sympathetic pathways via the HGN to the canine seminal tract can be reconstructed spontaneously in a high rate over a long period after serious injuries and that their cross-innervation system can be repaired.