Clonidine preconditioning alleviated focal cerebral ischemic insult in rats via up-regulating p-NMDAR1 and down-regulating NMDAR2A / p-NMDAR2B

A brain ischemia rat model was established by middle cerebral artery occlusion (MCAO) for 2 h and reperfusion for 4 h to investigate the underlying mechanism of the neuroprotection action of clonidine, a classical alpha-2 adrenergic agonist, on cerebral ischemia. Clonidine and yohimbine were intraperitoneally given to the rats each day for a week before ischemia. Neurological deficits evaluations were carried out at 6 h after operation. TTC staining method was used to measure the volume of brain infarction. Expression levels of NMDAR1, NMDAR2A, NMDAR2B were assayed by western blotting. Our data demonstrated that clonidine pretreatment significantly improved the neurological deficit scores and reduced the brain infarct volumes of the rats. Furthermore, protein expression level of p-NMDAR2B in cortex was significantly up-regulated whereas that of p-NMDAR1 was decreased when compared with the sham-operated rats. Remarkably, clonidine treatment led to significant down-regulation of p-NMDAR2B and NMDAR2A in addition to enhancement of the expression level of p-NMDAR1 in cortex. This is the first report illustrating the neuroprotective role of clonidine may be mediated through modulation of the expression levels of p-NMDAR2B, NMDAR2A and p-NMDAR1 during cerebral ischemia.