Neuroendocrine Determinants of Mating in The Day Versus Night

Michigan State University, East Lansing MI

Investigators

Abstract

Animals have internal biological clocks that enable them to coordinate physiological and behavioral rhythms relative to the time of day, termed circadian rhythms. In mammals, a key part of clock in the brain is the supra-chiasmatic nucleus (SCN) of the hypothalamus. In nocturnal rodents, which are widely used in the laboratory, the SCN is known to be important for the timing of female reproductive behavior and a surge in the luteinizing hormone (LH) that triggers ovulation. However very little is known about diurnal rodents, which have evolved from nocturnal species. This project asks how the neural mechanisms responsible for circadian control of the female reproductive cycle have changed in diurnal compared to nocturnal rodents. The model animal is the unstriped Nile grass rat, which is related to common laboratory rats, but has a virtually complete reversal in the timing of a variety of events associated with female reproduction, including morning instead of evening timing for both mating behavior and for the surge in LH. Cytochemical, anatomical and behavioral approaches will be used to distinguish whether the SCN itself changes signal timing, whether there is instead a change in the timing of receptiveness of target sites to SCN signals, or whether there is a change in the neuroanatomy connecting SCN to different targets in nocturnal and diurnal species. The results will have an impact beyond neuroendocrinology to chronobiology, hypothalamic physiology, and evolutionary physiology. In addition, training of students and researchers at several levels is an important part of the project.