Circadian Systems and Aging in White-Throated Sparrows

Open Access
Author:
Phalen, Mary
Area of Honors:
Animal Sciences
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Paul Allen Bartell, Thesis Supervisor
  • Troy Ott, Honors Advisor
Keywords:
  • circadian
  • MRI
  • aging
  • sparrow
Abstract:
The main objective of my work was to determine how the circadian system responds to aging in White-Throated Sparrows. The study used geriatric sparrows, aged at least 10 years in captivity, and monitored locomotor activity continuously. Birds were held under a 12/12 light dark cycle and then experienced a four hour phase shift forward, followed by a shift back to the original light cycle after entrainment for approximately one month in order to measure their ability to synchronize to new light schedules. The resulting data showed a variety of unique circadian manifestations including arrhythmic, nocturnal, with many birds maintaining their original phase of activity despite a shift in the light cycle. The second was to use MRI to compare the brain structure of three geriatric sparrows to three younger sparrows, aged around 2 years. A 7 Tesla machine was used to perform a series of MRI scans and Avizo 9.0 software was used to calculate volumes of the total brain, ventricles, hippocampus, hypothalamus, and the cerebellum. The older birds exhibited smaller hypothalamic volumes. From the actogram data we propose that the previously reported dawn and dusk oscillators are less coupled and their photic input has been differentially affected in the aged birds. The dawn oscillator correctly shifted and entrained to a new light schedule, while the dusk oscillator had reduced photic input and did not shift accordingly. These results are consistent with the hypothesis that the dusk oscillator relies on circadian time memory instead of reentraining to new light cycles.