Brain free magnesium concentration is predictive of motor outcome following traumatic axonal brain injury in rats

A number of studies have supported a role for brain free magnesium as an im portant secondary injury factor in the development of neurologic deficits f ollowing traumatic brain injury. Despite this, few studies have characteris ed free magnesium changes in diffuse models of brain injury relevant to cli nical trauma, and none have critically examined the association between bra in free magnesium concentration and degree of neurologic deficit following graded trauma. In the present study, a combination of nuclear magnetic reso nance spectroscopy and rotarod motor function tests were used to characteri se the relationship between brain free magnesium concentration and neurolog ic motor function following graded traumatic axonal brain injury in rats. I nduction of moderate or severe impact-acceleration induced traumatic brain injury resulted in a profound decline (p < 0.01) in brain free magnesium co ncentration that persisted for a minimum of 4 days postrauma in both injury groups. Posttraumatic rotarod deficits assessed on a daily basis after inj ury were linearly correlated with brain free magnesium concentration measur ed in the same animals immediately after the motor tests were performed (r = 0.87; p < 0.001). These results suggest that brain free magnesium decline s following graded diffuse axonal brain injury and that the concentration o f the ion after trauma may be a prognostic indicator of motor outcome follo wing.