Regulation of the bladder neck closure by lumbar splanchnic nerves at ejaculation in the dog

To clarify the role of canine thoracolumbar splanchnic nerves for bladder neck closure during ejaculation, these nerves of adult male mongrel dogs were exposed under anesthesia using ketamine hydrochloride and pentobarbital, and electrical stimulation and anatomical dissection studies were performed. Bladder neck closure by the stimulation of each sympathetic nerve was monitored with a 10 Fr silicon catheter equipped with pressure-sensitive rubber balloon placed at the bladder neck. The dissection study revealed that canine thoracolumbar splanchnic nerves consisted of two nerve groups: one branching from the sympathetic trunks at thoracic and L1 ganglia, reaching caudal mesenteric plexus (CMP) through the anterior wall of the aorta, the other branching from the sympathetic trunks at level L2-L5 ganglia, reaching CMP through the posterior side of the bilateral spermatic arteries. The former were designated intermesenteric splanchnic nerves, the latter lumbar splanchnic nerves. No bladder neck closure was observed by electrical stimulation of the distal end of severed intermesenteric splanchnic nerves or of the sympathetic trunks at the lumbopelvic level among 10 dogs examined. At least one lumbar splanchnic nerve generated the closure in all 10 dogs and generally, a few lumbar splanchnic nerves, generated the closure. The results indicate that bladder neck closure during ejaculation is generated by lumbar splanchnic nerves regardless of their branching levels from lumbar sympathetic ganglia, but not by either intermesenteric splanchnic nerves or pelvic sympathetic trunks.