Middle age increases tissue vulnerability and impairs sensorimotor and cognitive recovery following traumatic brain injury in the rat.

With increasing age comes an increased risk for sustaining traumatic brain injuries (TBI). However, the effect of age is rarely studied in animal models of TBI. The present study evaluated the effect of increased age on recovery of function following bilateral medial frontal cortex injury. Groups of young (3 months) and middle-aged (14 months) rats received bilateral frontal cortex contusions or sham injuries. The rats were tested on a variety of tests to measure sensorimotor performance (bilateral tactile adhesive removal test), skilled forelimb use (staircase test), and the acquisition of reference and working memory in the Morris water maze. Results indicated that injury produced significant impairments on all behavioral tests compared to sham controls. Middle-aged rats that received cortical contusions were significantly impaired on the bilateral tactile adhesive removal test, acquisition of a reference memory task, and working memory compared to young-injured rats. Histological analysis showed that middle-aged rats developed significantly larger lesion cavities but did not show an increase in the number of glial fibrillary acidic protein (GFAP+) cells compared to young-injured rats. Age alone also significantly impaired function on the bilateral adhesive tactile removal test, skilled forelimb use, the acquisition of a reference memory task, and also increased the number of GFAP+ cells compared to young rats. These results indicate that middle-aged rats respond to brain injury differently than young rats and that age is an important factor to consider in pre-clinical efficacy studies.