Sleep patterns in cyclic and pseudopregnant rats

In order to clarify the relationship between sleep and reproductive activities, time-course changes in sleep were analyzed in normal female rats. The state of sleep-wakefulness was continuously monitored for 4 weeks including two-consecutive 4-day estrous cycles, a 12-day pseudopregnant period and a subsequent 4-day cycle. Sleep patterns in estrous cycle were characterized by a marked reduction in nocturnal non-rapid-eye-movement sleep (NREMS) and rapid-eye-movement sleep (REMS) at proestrus. A significant increase in nocturnal NREMS and REMS occurred immediately after the induction of pseudopregnancy by sterile mating, lasting for the whole pseudopregnant period for NREMS and during the early and mid period for REMS. In contrast, diurnal REMS tended to decrease towards the end of pseudopregnancy. The circadian rhythm of brain temperature exhibited no reproductive activity-dependent change. The dynamic changes in sleep may correlate alterations in neuroendocrine activities specific to estrous cycles and pseudopregnancy.