Elevated shock threshold in sexually receptive female rats

Previous studies have found cyclic differences in wheel running, extinction of conditioned avoidance responses, and open field behavior as a function of the estrous cycle in rodents. The purpose of this study was to investigate possible sensory changes associated with estrus in rodents. Female rats were monitored for behavioral and physiological changes related to the estrous cycle. Using the method of constant stimuli and foot shock, jump thresholds were determined during the estrous cycle stages of sexual receptivity (proestrus) and non-receptivity (metestrus). A significantly higher jump threshold was demonstrated by animals during proestrus as compared to metestrus. Possible explanations for the failure of previous investigators to find attenuated sensitivity as a function of the estrous cycle are discussed.