Neurobehavioral Differences in Circadian Rhythms

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

Circadian rhythms are cyclic biological activities that recur at the same time every day. In mammals, a part of the brain called the suprachiasmatic nucleus (SCN) is important for these rhythms, and constitutes part of the biological clock mechanism. These rhythms continue to run under constant conditions, but environmental cues such as timing of daylight can set, or entrain, the timing or phase-shifting of the cycles. Sex differences have been described in the entrained circadian rhythms of most mammals that have been examined, and recent data suggest that steroid hormones can influence the function of the circadian clock biochemistry in the SCN. Most animals used for circadian research are nocturnal rodents, but there are some data on two diurnal species, the human and a rodent called the degu. In the degu, sexually dimorphic circadian effects are seen in responses to free-running periods, light stimuli, and modulation by hormones, among other factors. The sexual dimorphism develops just after puberty, and appears to require changes in both sexes. This project uses biochemical, molecular and behavioral approaches to determine whether sexual differentiation occurs when molecular receptors for estrogen and/or androgen are up-regulated in the SCN, and whether sexual differentiation of circadian rhythms is reflected in changed cycles of the gene expression of key cellular proteins (PER and CRY) that generate the cycles. Results from this project will be important for general biology and psychology as well as neuroendocrinology, for understanding hormonal and genetic mechanisms of circadian rhythms in mammals, for evolutionary comparisons with nocturnal mammals, and potentially for better understanding of how human circadian rhythms develop during adolescence. This project is also in a laboratory with an excellent record of research mentoring.