Chronobiology and Neuroendocrinology lab research examines the neural and behavioral features of circadian rhythms in the day-active Octodon degus, an animal model with circadian properties similar to humans. Currently,the lab is particularly interested in the interaction between stress and the circadian system, development of sex differences in the use of photic and non-photic entraining cues, and the anatomical system which supports the use of both types of entraining signals. The lab has recently begun a new line of research exploring the role of prenatal steroid hormones on the development of gender-specific behavior and physiology across the lifespan, using sheep as the animal model.

• the function of the circadian clock just before and early during puberty in the diurnal degu
• the circadian rhythms of rats exposed to stress during the last trimester of gestation and then were either allowed to self-administer cocaine or exposed to acute stressors (in collaboration with Dr. Jill Becker and Dr. Seema Bhatnagar
• the effect of adolescent exposure to drugs of abuse on circadian rhythms
• the development of sex differences in the rat circadian function
• the effect of developmental disruptions like stress or cocaine exposure on reproductive function of female rats (in collaboration with Dr. Robert Thompson)
• the circadian control over reproduction in the diurnal degu (in collaboration with Dr. Megan Mahoney)
• the attention control of circadian entrainment (in collaboration with Dr. Martin Sarter)
• the similarities and differences in male and female diurnal sleep, how it is altered by jet lag treatments, and whether sleep in juvenile animals without a mature circadian system is different from that of adults
• the effects of endocrine disruptors on dominance and reproductive behaviors over the lifespan (in collaboration with Reproductive Sciences)
• the behavior of inter-sex individuals (in collaboration with Reproductive Sciences)

The slowly maturing, long-lived rodent Octodon degus (degu) provides a unique opportunity to examine the development of the circadian system during adolescence. These studies characterize entrained and free-running activity rhythms in gonadally intact and prepubertally gonadectomized male and female degus across the first year of life to clarify the impact of sex and gonadal hormones on the circadian system during adolescence.

Gonadally intact degus exhibited a delay in the phase angle of activity onset (Psi(on)) during puberty, which reversed as animals became reproductively competent. Gonadectomy before puberty prevented this phase delay. However, the effect of gonadal hormones during puberty on Psi(on) does not result from changes in the period of the underlying circadian pacemaker. A sex difference in Psi(on) and free-running period (tau) emerged several months after puberty; these developmental changes are not likely to be related, since the sex difference in Psi(on) emerged before the sex difference in tau. Changes in the levels of circulating hormones cannot explain the emergence of these sex differences, since there is a rather lengthy delay between the age at which degus reach sexual maturity and the age at which Psi(on) and tau become sexually dimorphic. However, postnatal exposure to gonadal hormones is required for sexual differentiation of Psi(on) and tau, since these sex differences were absent in prepubertally gonadectomized degus.

These data suggest that gonadal hormones modulate the circadian system during adolescent development and provide a new model for postpubertal sexual differentiation of a central nervous system structure.
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