| dc.description.abstract | Children under five years of age are at high risk for sustaining traumatic brain injury (TBI) and tend to have poorer outcomes despite greater neuroplasticity in children. Hence, there is a great need to study TBI specifically in models of juvenile injury. Additionally, long chain n-3 polyunsaturated fatty acids (LC-PUFA) are a major component of neural membranes, and accumulate in the brain during late gestation and early childhood. Low dietary content of these essential fatty acids results in decreased n-3 LC-PUFA accumulation in the developing brain. Long-chain n-3 polyunsaturated fatty acids have multiple neuroprotective and anti-inflammatory activities, thus low dietary LC-PUFA content may put children at risk for poorer outcomes after TBI. The first aim established a juvenile TBI model with consistent, measurable deficits, without debilitating injury or mortality. In order to assess functional outcomes including severity of initial injury and the duration of deficits, a qualitative assessment of common sensorimotor behavioral tests in rats of various sizes and developmental stages (postnatal days 16-45, 35-190 g) was performed. Tests were evaluated for their developmental appropriateness, scalability for growth, necessity for extensive pre-training, and throughput capability. The tests evaluated were grid-walk, automated gait analysis (DigiGaitTM), rotarod, beam walk, spontaneous forelimb elevation test, and force-plate actometry. Both the rotarod and grid-walk tests were eliminated on their inability to scale for growth of the animal. Rotarod also required several days of pre-training that young animals were unable to perform. DigiGaitTM was eliminated due to problems associated with development and inadequate throughput. Beam walk, spontaneous forelimb elevation test, and force-plate actometry, however, are simple, complementary tests, each measuring a different aspect of motor function that met the criteria for being adequate behavior tests for use in a rodent model of juvenile TBI and were used in later studies. The second aim investigated the effects of dietary n-3 fatty acid content and, as a consequence, reduced brain fatty acid composition on outcomes of juvenile TBI. Long-Evans rats raised from conception on diets containing adequate n-3 fatty acids (Control) or low in n-3 fatty acids (Deficient), resulting in decreases in brain DHA of 25% and 54%, respectively, were subjected to a controlled cortical impact or sham surgery on postnatal day 17. Rats with decreased brain DHA levels had poorer sensorimotor outcomes, as assessed with force-plate actometry and the spontaneous forelimb elevation test, after TBI. Ccl2, Gfap, and Mmp9 mRNA levels, and MMP-2 and -9 enzymatic activities were increased after TBI regardless of brain DHA level. Lesion volume was also not affected by brain DHA level. In contrast, TBI-induced Timp1 gene expression was lower in rats fed the Deficient diet and was correlated with brain DHA level. These data suggest that decreased brain DHA content contributes to poorer outcomes after TBI through a mechanism involving modulation of Timp1 gene expression. The third aim investigated the use of a high dose oral fish oil dosing regimen on biochemical, blood-brain barrier, and sensorimotor outcomes of TBI in a juvenile rat model. Seventeen-day old Long-Evans rats were given a 15 mL/kG fish oil (2.01 g/kg EPA, 1.34 g/kg DHA) or soybean oil dose via oral gavage thirty minutes prior to being subjected to a controlled cortical impact injury or sham surgery. Doses of oil were then administered for seven days after surgery. Fish oil treatment resulted in improved hindlimb deficits after TBI as assessed with the beam walk test, decreased IgG infiltration into the ipsilateral and contralateral hemispheres, and decreased TBI-induced gene expression of Mmp9 one day after injury. TBI-induced increases in Gfap were also less persistent in rats treated with fish oil. These results indicate that fish oil may improve sensorimotor outcomes after TBI in juveniles by decreasing blood-brain barrier disruption by a mechanism involving decreased gene expression of Mmp9, and also modulating glial activation. In summary, this dissertation established a juvenile model of TBI with persistent, measurable deficits and established three behavioral tools for assessing severity of injury, persistence of deficits, and recovery from TBI. Furthermore, it determined that brain DHA content, not diet, that most influences TBI outcomes and that improved outcomes as a result of greater brain DHA content may be due to increased TBI-induced Timp1 gene expression. Lastly, it determined that acute fish oil dosing improves functional outcomes after TBI by limiting blood-brain barrier damage by preventing TBI-induced gene expression of Mmp9 and faster resolution of astrocytosis. Together, these findings support the use of an LC-PUFA-rich diet during gestation and early neonatal life to provide greater neuroprotection in the event of a TBI as well as support the use of fish oil as a therapy for juvenile TBI. | |
