Circadian rhythms are fundamental biological processes in mammals that synchronize the hormonal, metabolic and physiological activities of the organism into a twenty-four hour cycle. The primary circadian pacemaker, also called the biological clock, is found in a collection of neurons located in the suprachiasmatic nuclei at the base of the hypothalamus in the brain. This pacemaker receives input from the eye to convey information about the light/dark cycle of a solar day that is used to set the time of the clock, but the pacemaker also receives input from other brain regions whose function is unclear. This project aims to determine the role of one of these inputs, from the intergeniculate leaflet of the thalamus, on the timekeeping properties of the biological clock in hamsters. This project will use behavioral and anatomical approaches to study the role of the intergeniculate leaflet in circadian activity rhythms. This project is expected to demonstrate that the input from the intergeniculate leaflet to the clock is tonically inhibitory at night, and that when this input is blocked, the pacemaker is capable of a much more rapid resetting of time in response to changes in daylength. This project will also demonstrate how organisms are able to prevent low levels of light from stars and the moon from shifting the timing of the pacemaker. The results of this project are very important for our understanding of how organisms adapt to seasonal daylight changes in their environment. Finally, this project will provide crucial training in the sciences to undergraduate and graduate students, many of whom will be female and underrepresented minorities.
