Estrous cycle variation of afferent fibers supplying reproductive organs in the female rat.

Multi-unit afferent nerve activity was recorded from branches of the hypogastric and pelvic nerves in virgin female rats on different days of the estrous cycle. In each rat, the response of hypogastric nerve fibers to uterine distension and the response of pelvic nerve fibers to vaginal distension was tested. The minimal pressure necessary to evoke a response was highest in diestrus for both the hypogastric and pelvic nerve fibers. For the hypogastric nerve, the minimal necessary pressures were significantly lower during both proestrus and estrus, whereas for the pelvic nerve, the pressure was significantly lower only on the day of proestrus. These results suggest that the overall response sensitivity of afferent fibers in the pelvic and hypogastric nerves are differentially affected by hormonal variations occurring across the estrous cycle in a manner that would enhance reproduction.