Date of Award


Document Type


Degree Name

Master of Science (MS)



First Advisor

Christina L. Ruby

Second Advisor

Robert J. Major

Third Advisor

Robert D. Hinrichsen


Humans are constantly engaging in behaviors that may affect SCN-mediated circadian (daily, 24-hour) rhythms and negatively impact health. Here, we examined the effect of both chronic and acute caffeine exposure as well as social stress on photic regulation of circadian activity rhythms in mice. We found that entrainment to a standard 12-hour light, 12-hour dark (LD) photocycle was delayed during self-administration of caffeine. Both acute, high-dose caffeine and chronic, oral caffeine exposure potentiated photic phase-delays in mice. Similar results were seen when mice were injected with an adenosine A1 antagonist, suggesting a possible mechanism by which caffeine affects the SCN. Social defeat experiments that mimic stressful social situations in humans resulted in a greater phase-delay response in mice compared to controls that did not experience social defeat. Our results support the hypothesis that caffeine and stressful experiences interferes with the ability of the circadian clock to entrain normally to light.