Analgesia is produced by uterocervical mechanostimulation in rats: roles of afferent nerves and implications for analgesia of pregnancy and parturition.

Afferent activity from the reproductive tract activates intrinsic pain attenuating processes. For example, analgesia results from vaginocervical mechano-stimulation in nonpregnant rats and occurs during pregnancy and parturition. In the present study, the effect of uterocervical mechanostimulation on pain thresholds was investigated in order to determine whether direct stimulation of the uterine cervix could play a role in the analgesia of pregnancy. Uterocervical mechanostimulation was applied to nonpregnant rats via a silastic disc implanted in the uterus. The disc abutted against the cervix and was attached to a thread externalized through the vaginal orifice. Application of a force of 150 g, but not 100 g, produced a significant increase in tail flick latency (110.4 +/- 40.6%, P less than 0.03). This effect was abolished by pelvic neurectomy, but was not altered by hypogastric neurectomy. Stimulation of the uterine cervix in combined pelvic and hypogastric neurectomy rats produced a decrease in tail flick latency. These results indicate that the analgesia that occurs during pregnancy and/or parturition may result, at least in part, from the uterocervical mechanostimulation that occurs during this condition.