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According to the Center for Disease Control’s (CDC) report to the Congress, there are 2.2 million emergency department visits; 80,000 hospitalizations; and 50,000 deaths each year due to traumatic brain injury. Adults 65 years and older account substantially for the majority of the hospitalization and deaths. Over 70% of the traumatic brain injuries of the older adults are classified as mild to moderate; however, even with these milder injuries, older adults present with a significantly higher morbidity and mortality compared to all other age groups (LeBlanc et al., 2006). With that in mind, it seems essential to develop a deeper understanding of the causes behind higher mortality and morbidity of traumatic brain injury in the elder population. It is well documented that increased age is accompanied by increased CNS inflammation. Recently, our laboratory showed that inflammation drives brain pathology. Specifically, we reported that the axon initial segment of cortical neurons was structurally and functionally compromised in an inflamed CNS environment. With this in mind, we proposed that age-related inflammation predisposes that brain to exacerbated pathologic consequence. To test this hypothesis, we administered a mild to moderate central fluid percussion brain injury in aged and young adult mice. Using immunocytochemical labeling against the axon initial segment protein ankyrinG combined with laser scanning confocal microscopy, we quantitatively compared axon initial segment number and length between age groups and within age groups with and without injury. Additionally, we also quantified global axonal pathology by immunolabeling for amyloid precursor protein (APP) positive swelling as an indicator of compromised axonal transport. We proposed that ankyrinG labeling will be both reduced in the aged injured mice compared against aged uninjured, young adult injured and young adult non-injured. We observed a significant increase in APP accumulations due to injury independent of aging, and due to aging independent of injury. No significant changes in the effect of injury between young and aged injured mice were observed. Although AIS length was not altered between age groups following injury, our results demonstrate that the elderly population presents with significantly shorter initial segments. The consequence of this shortening is not clear but may reflect compensatory changes in the brain to maintain homeostasis. |
