The present study evaluated behavioral and histopathological outcome after controlled cortical impact (CCI) brain injury in mice deficient in tumor necrosis factor [TNF(؊/؊)] and their wild-type (wt) littermates. Mice were subjected to CCI brain injury [TNF(؊/؊), n ‫؍‬ 10; wt, n ‫؍‬ 10] or served as uninjured controls [TNF(؊/؊), n ‫؍‬ 10; wt, n ‫؍‬ 10] and were evaluated for deficits in memory retention at 7 days postinjury. Although both brain-injured wt and TNF(؊/؊) mice exhibited significant memory dysfunction compared to uninjured controls (P < 0.02), the deficits in memory retention in injured TNF(؊/؊) mice were significantly less severe than in injured wt mice (P < 0.02). A second group of mice was subjected to CCI brain injury [TNF(؊/؊), n ‫؍‬ 20; wt, n ‫؍‬ 20] or served as uninjured controls [TNF(؊/؊), n ‫؍‬ 15; wt, n ‫؍‬ 15] and were evaluated over a 4-week period for neurological motor function. In the acute posttraumatic period (48 h postinjury), braininjured TNF(؊/؊) mice were significantly less impaired than injured wt mice on composite neuroscore (P < 0.001), rotarod (P < 0.05), and beam balance (P < 0.02) tests. However, wt mice recovered from brain injury by 2-3 weeks postinjury, whereas TNF(؊/؊) mice continued to demonstrate persistent motor deficits up to 4 weeks postinjury. Histopathological analysis at 2 and 4 weeks postinjury revealed that brain-injured TNF(؊/؊) mice had significantly more cortical tissue loss than wt mice (P < 0.02). Our results suggest that although the presence of TNF in the acute posttraumatic period may be deleterious, this cytokine may play a role in facilitating long-term behavioral recovery and histological repair after brain injury.

Although brain trauma is a risk factor for Alzheimer's disease, no experimental model has been generated to explore this relationship. We developed a model of brain trauma in transgenic mice that overexpress mutant human amyloid precursor protein (PDAPP) leading to the appearance of Alzheimer's disease-like beta-amyloid (Abeta) plaques beginning at 6 months of age. We induced cortical impact brain injury in the PDAPP animals and their wild-type littermates at 4 months of age, ie, before Abeta plaque formation, and evaluated changes in posttraumatic memory function, histopathology, and regional tissue levels of the Abeta peptides Abeta1-40 and Abeta1-42. We found that noninjured PDAPP mice had impaired memory function compared to noninjured wild-type littermates (P < 0.01) and that brain-injured PDAPP mice had more profound memory dysfunction than brain-injured wild-type littermates (P < 0.001). Although no augmentation of Abeta plaque formation was observed in brain-injured PDAPP mice, a substantial exacerbation of neuron death was found in the hippocampus (P < 0.001) in association with an acute threefold increase in Abeta1-40 and sevenfold increase in Abeta1-42 levels selectively in the hippocampus (P < 0.01). These data suggest a mechanistic link between brain trauma and Abeta levels and the death of neurons.