Magnesium and the N-methyl-D-aspartate receptor antagonist dizocilpine maleate neither increase glucose use nor induce a 72-kilodalton heat shock protein expression in the immature rat brain

Abstract

In adult rats N-methyl-D-aspartate receptor (NMDAR) antagonists increase glucose use and induce a 72-kD heat shock protein (HSP72) expression in limbic system areas that later undergo neuronal necrosis, which have limited the clinical development of these drugs. Dizocilpine maleate (MK-801) and magnesium sulfate (MgSO4) reduce hypoxic-ischemic brain injury in immature animals, but the effects on HSP72 expression and glucose use are unknown. Seven-day-old rats received injections of either vehicle (control), 0.5 or 1.0 mg/kg MK-801, or 2 or 4 mmol/kg MgSO4. Glucose utilization was measured with the deoxyglucose method, 30 min, 48 h, and 4 d after injection. HSP72 immunostaining was evaluated 4 or 24 h after injection. Both doses of MK-801 and 4 mmol/kg MgSO4 induced a temporary decrease in glucose use in the posterior cingulate and retrosplenial cortex, the CA1 and CA3 subfields of the hippocampus, the caudoputamen, and the parietal cortex. Doses of 2 mmol/kg MgSO4 did not affect glucose use in any structure. Neuronal HSP72 expression was not found in any drug-treated rats. In conclusion, neither MK- 801 nor MgSO4 increased glucose use in the limbic system and did not induce HSP72 expression, suggesting that NMDAR antagonists lack direct neurotoxicity in the immature brain.