Sex Differences in the Circadian and Ultradian Rhythms of Mice

Biological rhythms in behavior and physiology are pervasive and provide temporal structure to an organism's basic biological functions. Circadian rhythms are generated by a cellular transcriptional-translational feedback loop consisting of 'clock genes' and their protein products, interacting in a 24 h loop. But biological timekeeping happens over many timescales. Circadian rhythms occur on a daily timescale (~24 h e.g., sleep, activity, metabolism), whereas ultradian rhythms persist at sub-daily timescales (~1-6 h e.g., sleep stages, activity bouts, meal patterns). Understanding how circadian and ultradian rhythms work in isolation, and perhaps more importantly, how they interact, holds the potential for deeper insights into behavior and physiology. Females are historically underrepresented in behavioral neuroscience, and this bias extends to the study of biological rhythms (chronobiology). Although sex differences have been reported in rhythmic aspects of humans and non-human behavior, clock-driven behaviors, and clock-dependent pathology, the assumption that females and males rely on the same molecular mechanisms, to the same degree, to generate circadian rhythms has not been rigorously examined. Ultradian rhythms, while ubiquitous, have garnered far less empirical study as compared to circadian rhythms, and females are similarly neglected in this domain. I conducted several experiments to interrogate sex differences in circadian and ultradian rhythms, and their regulation by environmental and epigenetic processes.