Development of a Porcine Model to Study the Aortic Plexus and Innervation to the Internal Urethral Sphincter: Implications for Preventing Retrograde Ejaculation

Abstract

INTRODUCTIONThe sympathetic nerves and ganglia overlying the abdominal aorta in humans are symmetrically organized into a bilateral network called the aortic plexus that must be spared during retroperitoneal surgery in order to maintain antegrade ejaculation. It is well established that complete resection of the aortic plexus causes retrograde ejaculation (RE) that results from de‐innervation of the internal urethral sphincter (IUS). At present, however, it remains uncertain which specific nerves of the aortic plexus control the IUS, and thus, which nerves are important for ejaculation.To ultimately determine which nerves are imperative to maintain ejaculation, the present study aimed to first establish the pig as a comparable model of the human aortic plexus in both structure and function. It was our working hypothesis that the pig exhibits comparable anatomy in terms of gross organization, number of infrarenal splanchnic nerves and constituent ganglia, and that stimulation of the left and right hypogastric nerves (homologous to the human superior hypogastric plexus) would evoke contraction of the IUS.METHODSThe porcine aortic plexus was examined in 18 boars by gross dissection followed by a histological examination to differentiate ganglia from nerve. Innervation of the IUS was examined using a lesion‐and‐test method, in which stimulation with a bipolar electrode was used to excite the hypogastric nerves distal to the caudal mesenteric ganglia before and after transection (n=5).RESULTSAs predicted, the anatomy of the porcine aortic plexus appeared comparable to humans, exhibiting two bilateral cords that were supplied by two or more infrarenal lumbar splanchnic nerves. Right and left caudal mesenteric and spermatic ganglia were invariably observed adjacent to their respective arteries, and given their topography within the plexus, they appear homologous to the prehypogastric, inferior mesenteric and spermatic ganglia in humans, respectively. At the junction of the upper infrarenal lumbar splanchnic nerves, two additional ganglia were observed within the cords of the porcine aortic plexus (prevalenceright = 4/8; prevalenceleft = 3/8); these structures have not been reported in humans. Electrostimulation of each hypogastric nerve evoked bladder neck contraction (ΔPright = 6.2 ± 2.2 mmHg, ΔPleft = 4.5 ± 2.2 mmHg), which was abolished following transection.CONCLUSIONSCollectively, our results confirm that the pig represents an effective preclinical model for studying not only the structure and normal function of the aortic plexus, but also the implications of unintended surgical trauma on the delicate nerves controlling ejaculation.Support or Funding InformationThis work is supported by CIHR