Differential roles of hypogastric and pelvic nerves in the analgesic and motoric effects of vaginocervical stimulation in rats

Bilateral transection of the pelvic and/or hypogastric nerves, which convey afferent activity from the reproductive tract, was performed to ascertain the role of these nerves in the analgesic and motoric effects of vaginocervical mechanostimulation (VS) in rats. Two indices of analgesia were used: tail flick latency to radiant heat (TFL) and vocalization threshold to electrical shock of the tail (Voc-T). Nerve cuts were performed at least one week prior to behavioral testing. Bilateral transection of both the pelvic and hypogastric nerves eliminated the analgesic effects of VS on the TFL and Voc-T tests. Bilateral transection of only the pelvic nerves reduced the number of rats showing maximal VS-induced elevation in TFL, without altering the effect of VS on Voc-T. By contrast, bilateral transection of only the hypogastric nerves attenuated the Voc-T-elevating effect of VS, without reducing the effect of VS on elevating TFL. The effects of VS on producing immobility, hindlimb extension and blockage of hindlimb withdrawal to foot pinch were eliminated by combined bilateral pelvic and hypogastric neurectomy. However, bilateral transection of either nerve alone did not significantly alter the efficacy of VS in producing these effects. These findings indicate that the pelvic and hypogastric nerves contribute to the immobility- and extensor-inducing, and flexor-inhibiting effects of VS, and differentially mediate the analgesia-producing effects of VS.