Year of Publication

2009

Degree Name

Doctor of Philosophy (PhD)

Document Type

Dissertation

College

Medicine

Department

Anatomy and Neurobiology

First Advisor

Dr. Stephen W. Scheff

Abstract

Older individuals sustaining traumatic brain injury (TBI) experience a much higher incidence of morbidity and mortality. This age-related exacerbated response to neurological insult has been demonstrated experimentally in aged animals, which can serve as a model to combat this devastating clinical problem. The reasons for this worse initial response are unknown but may be related to age-related changes in mitochondrial respiration.

Evidence is shown that mitochondrial dysfunction occurs early following traumatic brain injury (TBI), persists long after the initial insult, and is severitydependent. Synaptic and extrasynaptic mitochondrial fractions display distinct respiration capacities, stressing the importance to analyze these fractions separately. Sprague- Dawley and Fischer 344 rats, two commonly used strains used in TBI and aging research, were found to show very similar respiration profiles, indicating respiration data are not strain dependent. Neither synaptic nor extrasynaptic mitochondrial respiration significantly declined with age in naïve animals. Only the synaptic fraction displayed significant age-related increases in oxidative damage, measured by 3-nitrotyrosine (3- NT), 4-hydroxynonenal (4-HNE), and protein carbonyls (PC). Alterations in respiration with age appear to be more subtle than previously thought. Subtle declines in respiration and elevated levels of oxidative damage may not to be sufficient to produce detectable deficits until the system is challenged.

Following TBI, synaptic mitochondria exhibit dysfunction that increased significantly with age at injury, evident in lower respiratory control ratio (RCR) values and declines in ATP production rates. Furthermore, synaptic mitochondria displayed increased levels of oxidative damage with age and injury, while extrasynaptic mitochondria only displayed significant elevations following the insult. Age-related synaptic mitochondrial dysfunction following TBI may contribute to an exacerbated response in the elderly population.

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