The window of opportunity for administration of magnesium therapy following focal brain injury is 24 h but is task dependent in the rat

The present study was conducted to establish the window of opportunity for the administration of a regimen of MgCl₂ pharmacotherapy following focal injury to the brain. Rats were subjected to unilateral electrolytic lesions of the sensorimotor cortex (SMC) and administered a regimen of MgCl₂ (1.0 mmol/kg) or 0.9% saline (1.0 ml/kg) beginning either 15 min, 8 h or 24 h after injury. Subsequent injections were administered 24 and 72 h after the initial treatment. Behavioral testing assessed recovery of function on several sensorimotor behaviors for 24 days following injury. The results of the present study suggest that treatment with a regimen of MgCl₂ significantly facilitated recovery of function on the forelimb→forelimb and vibrissae→forelimb placing tests when administered 15 min, 8 h or 24 h after injury compared with saline-treated rats. Recovery of locomotor placing was significantly facilitated at 15 min and 8 h but not at 24 h compared with saline-treated rats. In addition, the ability of MgCl₂ to limit neuronal loss in the ipsilateral ventral posterior lateral (VPL) nucleus of the thalamus was seen at only the 15-min treatment interval. These results suggest that the window of opportunity for MgCl₂ pharmacotherapy is 24 h, task dependent and is much shorter for protecting neurons in the VPL.