The mammalian brain contains a biological clock that generates behavioral and physiological rhythms that are close to, but not exactly 24 hours. For organisms to synchronize these internally generated circadian rhythms to the 24-hour environment, the clock must be adjusted each day through exposure to light. The mechanism through which light is able to adjust the timing of the biological clock is not fully understood. The central aim of this proposal is to test the hypothesis that sustained activation of receptors for ã-aminobutyric acid (GABA) mediates the ability of light to shift the daily rhythms generated by the biological clock. Utilizing an in vivo pharmacological approach in hamsters, small quantities of drugs that either mimic or block GABA activity will be delivered over several hours to the region of the brain that contains the biological clock. The effect of these drugs on circadian rhythms will be determined by measuring the daily activity rhythms of hamsters given access to running wheels. It is expected that long-term administration of GABA-like drugs will shift the daily activity rhythms of hamsters in a manner similar to light, and that the administration of drugs that block the activity of GABA will prevent the ability of light to shift the daily activity rhythms generated by the biological clock. Results from this research will provide insight into a fundamental process by which organisms synchronize or entrain their biological rhythms to a cyclical environment. This research has important implications for understanding how shift work and trans-Atlantic travel alter biological rhythms in humans (e.g., jet lag). Furthermore, the proposed activities will take place at, and involve undergraduates from Morehouse College (a historically black undergraduate institution in Atlanta, Georgia), thus broadening the participation of African American males in biology.
