Undergraduate Honors Theses

Thesis Defended

Fall 2018

Document Type

Thesis

Type of Thesis

Departmental Honors

Department

Psychology & Neuroscience

First Advisor

Dr. Robert Spencer

Second Advisor

Dr. Heidi Day

Third Advisor

Dr. Rolf Norgaard

Abstract

Circadian disruption is a widespread symptom among stress-related mental disorders which indicates an influential relationship between two factors: circadian rhythms and stress. Circadian rhythms throughout the body depend on the suprachiasmatic nucleus (SCN) of the hypothalamus for alignment. The SCN uses an adrenal glucocorticoid hormone, corticosterone (in most rodents; CORT) as a communication device which aligns the peripheral clocks. CORT secretion is controlled by the hypothalamic-pituitary-adrenal (HPA) axis, and displays a daily basal rhythm as well as increases during acute stress. CORT is able to affect the molecular clock through the glucocorticoid response element (GRE). The current experiments examine whether acute CORT, when systemically injected, is able to induce Per1 mRNA expression (a core clock gene) and c-Fos mRNA expression (a marker of general neuronal activation) in various brain regions in male Sprague-Dawley rats. By adrenalectomizing (ADX) all of the subjects, which entails removing both adrenal glands, all endogenous CORT is also removed and provides a method through which acute CORT effects could be isolated. Our data show that administering a saline injection as well as an acute, systemic CORT injection are both able to modulate Per1mRNA through CORT-dependent and CORT-independent mechanisms depending on brain region. They also reveal that c-Fos mRNA expression is brain region-dependent and injection status-dependent. Further exploring a possible CORT-independent mechanism detected in the neocortex, this study investigates the dissimilar results in the hippocampus (HC) compared to prior research done by Conway-Campbell (2011). As a more transient method of analyzing Per1expression, a Per1 hnRNA riboprobe was also created; although, it did not display specific signal. Failure of specific binding of the riboprobe and additional data discrepancies between other studies demonstrate a need for further experimentation.

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