Magnesium treatment and spontaneous mild hypothermia after transient focal cerebral ischemia in the rat

There is evidence from global cerebral ischemia experiments in the rat that the neuroprotection attributable to magnesium treatment depends on the concurrent presence of at least mild hypothermia. We set out to determine to what extent spontaneous hypothermia occurred after transient middle cerebral artery occlusion in the rat, and whether this hypothermia influenced the outcome of magnesium treatment. We found that rectal temperatures from 30 min to 3 h after recovery from anaesthesia/surgery were 1 °C lower than in the period from 4 to 6 h. Striatal infarcts were significantly reduced by 32% in animals treated with 360 μmol/kg MgSO4 intravenously immediately prior to ischemia. A higher magnesium dose of 720 μmol/kg had not effect on infarct volume. Having previously established that these two doses of magnesium are ineffective in normothermic animals using this model, we conclude that the mild spontaneous hypothermia contributed to the observed neuroprotective effect of magnesium in this study, and that previous studies of magnesium in cerebral ischemia have likely been confounded in this way.