Effect of long-term, postasphyxial administration of magnesium sulfate on immunostaining of microtubule-associated protein-2 and activated caspase-3 in 7-day-old rat brain

OBJECTIVE: To test whether magnesium inhibits apoptosis during hypoxia-ischemia (HI) in the developing brain, we studied the effect of long-term magnesium treatment on an early marker of neuronal damage (loss of microtubule-associated protein-2; MAP-2) and a marker of apoptosis (activated caspase-3) after HI in newborn rats. METHODS: Seven-day-old rat pups (n = 107) were exposed to unilateral carotid artery ligation and 2 hours of hypoxia (8% oxygen in 92% nitrogen). Magnesium was administered by a micro-osmotic pump implanted in the back, at an infusion rate of 75 mg/kg per hour for 3 days. Neuronal loss in the cerebral cortex and hippocampus was evaluated by loss of MAP-2 at 24 and 48 hours after HI and visually ranked by a semiquantitative, three-point scale (mild, moderate, and severe). Caspase-3 activation was evaluated similarly in an adjacent section. Area and severity of the damaged lesion were compared between the two staining methods and between magnesium and controls, by chi(2) test and Fisher test. RESULTS: Three-day magnesium administration reduced loss of MAP-2 (from 33 of 50 to 21 of 45, P = .06) and activation of caspase-3 (from 34 of 50 to 21 of 45, P = .04) in the cerebral cortex after HI. There was no significant change in these immunostainings in the hippocampal regions. In the hippocampal CA3, the severity ranked by activated caspase-3 staining was significantly less than that of MAP-2 staining. CONCLUSIONS: Long-term, post-HI treatment with magnesium inhibited caspase-3 activation and MAP-2 immunostaining, suggesting that magnesium inhibited apoptotic neuronal death of HI in 7-day-old rats.