Neurobiology of sex differences in sleep

Though sleep has been extensively studied for many years. Little is known about sex differences in sleep. Some studies on humans and mice have revealed that sleep patterns are different between males and females. It is also known that sexual dimorphism exists in certain brain structures, transmitters and hormones which are involved in the control and regulation of sleep.;In the present work, a series of experiments are conducted in rats to examine whether sleep is differentially regulated in males and females by sex hormones and certain brain mechanisms. The following results are observed: (1) Slow wave sleep (SWS) and total sleep time (TS) are not different between male and female rats. (2) Normal male rats have more paradoxical sleep (PS) and greater percentage of PS in TS than normal female rats. The sex difference in daytime PS is not influenced by estrus cycle and adult ovariectomy; whereas the sex difference in nighttime PS is due to the suppression of PS during proestrus and, to a less extent, estrus in females. The latter sex difference is eliminated by ovariectomy. (3) Neonatal exposure to sex hormones may have some organizational effect on daytime sleep. Neonatal ovariectomy tends to increase daytime PS. This effect is not observed in females received neonatal testosterone treatment. These results need further confirmation. Neonatal castration and testosterone treatment do not significantly influence sleep pattern in males. However, prenatal influences of testosterone on PS mechanisms can not be excluded. (4) Bilateral electrolytic lesions of locus coeruleus (LC) significantly increase PS in female but not male rats. SWS and total sleep time are not influenced by LC lesions. The results suggest that LC is critically involved in the sex differences in PS in rats, probably by exerting stronger inhibitory influences on PS in females than in males.