The Effect of Age on Motor and Cognitive Deficits after Traumatic Brain Injury in Rats

Abstract

AGE IS ONE of the most important predictors of outcome after human traumatic brain injury. This study used fluid percussion brain injury to investigate the effects of aging on outcome after brain injury in rats. Three-month-old (n = 8) and 20-month-old (n = 11) rats were injured at a low level (1.7–1.8 atm) of fluid percussion brain injury or received a sham injury (n = 6 for both age groups). Body weight and motor function (beam balance and beam walking) were assessed before injury and for the first 5 days after injury. Cognitive outcome was assessed with the Morris water maze on Days 11 to 15 after injury. Injury did not produce significant weight loss in either age group. At the low level of brain injury used in this study, the 3-month-old rats did not demonstrate any significant motor deficits on the beam-balance or beam-walking tasks. However, the 20-month-old rats displayed significant beam-balance deficits on each of the 5 postinjury test days and significant beam-walking deficits for the first 3 postinjury days. Although Morris water maze performance was impaired in both age groups, the magnitude of impairment was greater in the aged animals. These data demonstrate that traumatic brain injury in the aged animal is marked by increased motor and cognitive deficits, in the absence of pronounced compromise of the animal's general health. Because the rat model of fluid percussion brain injury reproduces the age-related increase in chronic morbidity observed in cases of human brain injury, the fluid percussion model should be useful for studying mechanisms responsible for the age-related increase in vulnerability to brain injury.