Mild traumatic brain injury (MTBI) leads to spatial learning deficits

Primary objective: The aim of this study was to investigate the effect of mild and severe TBI on young male Wistar rats' spatial learning. Research design: Randomized repeated measure experimental design was used to examine spatial learning in three independent animal groups. Methods and procedures: Twenty-four (severe n = 9, mild n = 8, sham n = 7) male rats were included in the study. Animals received controlled mild (1.5 mm), severe (2.5 mm) cortical impact injury or sham surgery. Spatial learning was assessed daily using a modified Morris water maze test, 20 days post-trauma, for 5 consecutive days. Percentage time travelled within each quadrant and escape latency were calculated. All animals' hippocampal brain regions were examined post-injury using neuron (MAP2) and pre-synaptic protein (Synaptophysin) biomarkers. Main outcomes and results: It took the animals with mild injury until day 3 to reach the platform; and animals with mild and severe injury spent significantly less time in the target quadrant than the sham. The hippocampal neuron numbers differed proportionately between animals with severe and mild injury, but the percentage of synaptophysin density was significantly less in the dentate gyrus of both animals with mild and severe injury than sham group. Conclusion: Persistent spatial learning deficits exist after mild TBI; these deficits appear equivalent to deficits exhibited after a more severe injury.