Sleep in female mice: A strain comparison across the estrous cycle

Study Objective: Studying inbred strains of mice has proven useful in uncovering genetic variation in the expression of sleep patterns. However, although genetic influence on many behaviors has been shown to be gender specific, to date, sleep patterns in different strains of female mice have not been reported. In order to perform such studies in female mice, the estrous cycle must be taken into account in view of the effects of reproductive hormones on sleep. The aim of this study was thus to determine sleep patterns in female mice of different inbred strains over the estrous cycle. Design: Three strains of mice were used. Vaginal smears were performed to determine the estrous cycle stage; electroencephalographic and electromyographic activity, as well as body temperature and locomotor activity collected during a full estrous cycle, were analyzed. Measurements and Results: We report a major impact of the genetic background in the regulation of non-rapid eye movement sleep over a 24-hour period and clear strain differences in rapid eye movement sleep distribution over the light-dark cycle. In contrast, the estrous cycle had less influence on non-rapid eye movement sleep and rapid eye movement sleep, and these effects were dependent on the genotype of the mice. Conclusions: Sleep regulation in female mice is influenced primarily by genetic background and, to a lesser extent, by hormonal variations associated with the estrous cycle.