Estrous changes in responses of rat gracile nucleus neurons to stimulationof skin and pelvic viscera

Multi- and single-unit recording was performed in the gracile nucleus in ur ethane-anesthetized rats to examine estrous variations in responses of its neurons to brushing the hindquarters and mechanical stimulation of the uter us, vaginal canal, cervix, and colon. Six rats each were studied in each of the four estrous stages: proestrus (P), estrus (E), metestrus (M), and die strus (D). The magnitude of multi-unit responses to gentle brushing of the perineum, hip, and tail, but not the foot and leg, was significantly greate r during proestrus than during other stages. Of 70 single units responsive to brush, 56 (80%) responded to stimulation of at least one viscus. Althoug h this percentage did not change with estrous stage, the direction and late ncy of some responses did. Pressure on the cervix evoked significantly more inhibitory (vs excitatory) responses in P than in E and M, and the respons e latency was significantly longer in D and P than in E and M. The directio n of response to vaginal distention did not change with estrous stage, but response latency was significantly longer in D than in P and E. Uterine dis tention evoked significantly more inhibitory responses in D than in P, with no estrous changes in latency. Responses to colon distention did not chang e. These variations in both magnitude of response to tactile stimulation an d characteristics of response to stimulation of reproductive organs, but no t the colon, correlate with changes in mating behaviors of the female rat, suggesting that the gracile nucleus is a component of neural systems that c ontrol reproductive behaviors.