Acute and prolonged alterations in brain free magnesium following fluid percussion-induced brain trauma in rats

Several studies have reported declines in brain total and free magnesium concentration after a traumatic insult to the CNS. Although the evidence suggests that this magnesium decline is associated with eventual neurologic outcome after trauma, the duration of free magnesium decline and its impact on related bioenergetic variables are relatively unknown. The present study has therefore used phosphorus magnetic resonance spectroscopy to determine the length of time that free magnesium remains suppressed after traumatic brain injury in rats. Immediately after the traumatic event, brain intracellular free magnesium declined to <60% of preinjury values and remained significantly depressed (50 +/- 8%; p < 0.001) for 5 days before recovering to preinjury levels by day 8. Cytosolic phosphorylation ratio and mitochondrial oxidative capacity also significantly decreased (p = 0.008) and increased (p = 0.002), respectively, after trauma. However, unlike the time of maximum magnesium change, the maximum changes in these bioenergetic variables occurred at 16-24 h after trauma and thereafter remained stable until after the magnesium had recovered. We conclude that free magnesium decline after trauma precedes changes in bioenergetic variables. Furthermore, therapies targeted at reestablishing magnesium homeostasis after trauma may require administration over a 1-week period.