Date

5-11-2021

Document Type

Thesis

Abstract

Circadian rhythms, located in all organisms, is an innate natural clock system driving daily cycles in behavior and metabolism. This clock entrains to daily cycles via regular exposure to light:dark cycles. When light exposure is altered, it is known to cause alterations behavior and metabolism because of its role in regulating bodily function. Constant light (LL) is emerging as a predominant circadian disruption due to prolonged exposure to light at night during night-shift work, and the use of TVs and smartphones at night and throughout the night. To understand how different organisms respond to constant light, two comparative studies were performed. In each, two genetically similar strains of mice were used to identify strain differences regarding physiologic and metabolic responses to constant light. The first using two strains of C57BL/6 (C57BL6/J and C57BL6/N) mice to establish differences in response to running wheel (RW) access in LL and the second consisted of two CBA (CBA/J and CBA/CaJ) mouse strains to define differences associated with retinal function in LL. Physiologic and metabolic data were collected through behavioral assays including the open field test, the light-dark box (LD Box), and the novel object test. Metabolic assays including the glucose tolerance test (GTT), and thyroid stimulating hormone (TSH), free thyroxine (fT4), brain-derived neurotrophic factor (BDNF), insulin, liver triglyceride, and testosterone enzyme-linked immunosorbent assays (ELISAs) were used. Several baseline differences in the C57BL/6 strains were established including C57BL6/J mice (B6J) experiencing increased locomotor activity compared to C57BL6/N (B6N) mice. In LL, B6J mice also exhibited greater period lengthening and increased anxiety compared to B6N mice. These results demonstrate strain specific differences in behavioral and physiological responses to LL and RW access. Additionally, baseline differences were observed circadian locomotor activity, behavior, and metabolism in the CBA strains. CBA/CaJ (sighted) mice experienced the effects of LL (period lengthening and weight gain) most severely as the CBA/J (blind) mice responded the same regardless of the photoperiod exposed to. These results suggest a clear photoperiod and retinal function connection.

Department

Biological Sciences

Thesis Comittee

Dr. Joseph Seggio, Thesis Advisor

Dr. Kenneth Adams, Committee Member

Dr. Heather Marella, Committee Member

Copyright and Permissions

Original document was submitted as an Honors Program requirement. Copyright is held by the author.

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