Effects of hypogastric neurectomy on escape responses to uterine distention in the rat

Anatomical data indicate that the rat uterine horn is innervated primarily by afferent fibers in the hypogastric nerves, suggesting that hypogastric n eurectomy, but not pelvic or pudendal neurectomy, should eliminate behavior al responses to uterine horn stimulation. To test this hypothesis, detectio n and escape responses of rats to different volumes of uterine horn distent ion (via an indwelling intrauterine balloon) were compared before and after bilateral hypogastric (n = 9), sham-hypogastric (n = 3), pelvic (n = 3), o r pudendal (n = 2) neurectomies. As predicted, sham-hypogastric, pelvic, an d pudendal neurectomies had no effect on the rats' responses. However, alth ough hypogastric neurectomy completely eliminated responses in five rats wh ose postmortem evaluation revealed no signs that the uterine balloons had e voked any pelvic pathophysiology, the neurectomy had no effect on the respo nses of an additional four rats. Postmortem evaluation of these rats reveal ed gross signs of severe pathology in the vicinity of the balloon in two ra ts, and evidence that the balloon had shifted caudally so that it was stimu lating the cervix rather than the uterine horn in a third. In the fourth ra t, pathophysiology had been deliberately induced by the prior implantation of a small pellet that released similar to 1 mu g/day of prostaglandin PF2 alpha over the uterine hem. Similar findings have been reported in clinical studies on the efficacy of hypogastric ('presacral') neurectomy for dysmen orrhea. Together, the findings support the hypothesis that the major source of afferent innervation of the uterine horn in healthy rats and women is t he hypogastric nerve but that the situation changes under conditions of pel vic pathology. Such changes could include additional activation of afferent fibers in nerves that supply other pelvic organs, activation by the uterin e pathophysiology of latent uterine innervation from afferent fibers in the pelvic, vagus or ovarian plexus nerves, or some form of central sensitizat ion. (C) 1999 International Association for the Study of Pain. Published by Elsevier Science B.V.