Detailed analysis of estrous-related changes in wheel running and self-stimulation

Previous studies have demonstrated that a number of behaviors change their probability of occurrence during the estrous cycle. Wheel running is known to show estrous-related changes while reports upon intracranial reinforcement (self-stimulation, ICS) have been equivocal. The present studies examined both behaviors to further resolve the underlying behavioral determinants of these estrous effects. Data for wheel running and intracranial self-stimulation behaviors of adult female Holtzman rats were collected nightly on a minute by minute basis across the estrous cycle. It was found that: (a) both behaviors showed significant estrous-related changes in frequency; (b) the two behaviors occurred in discontinuous episodes (bursts) during the dark phase of the diurnal cycle; and (c) of three burst parameters (number/session, average length, rate of response), number proved the best predictor of estrous-related behavioral change. Burst number may reflect an important motivational parameter underlying estrous-related changes in behavior.