Variation in the size and sensitivity of a genital sensory field in relation to the estrous cycle in rats

In rats showing normal estrous cycles, the size and sensitivity of the pudendal nerve's sensory field was determined by recording spike potentials from the pudendal nerve. The overall sensory field area was larger and more sensitive in estrous than in diestrous females. This indicates that the field's characteristics can change within 2 days (the interval between diestrus and estrus), perhaps as a result of the increased estrogen secretion that occurs around the time of mating. One effect of this increased estrogen secretion may be to sensitize and to enlarge the sensory field of the pudendal nerve. In a second experiment, we found that the genital area of the female which the male's penis contacts during an intromittive mount corresponds closely to an area of high sensitivity within the sensory field of the pudendal nerve. We suggest that the male rat's copulatory contact with this region of the female's perineum may facilitate the intensity of her lordosis and/or her orienting for intromission.