nPKCϵ and NMDA Receptors Participate in Neuroprotection Induced by Morphine Pretreatment

Morphine pretreatment induces ischemic tolerance in neurons, but it remains uncertain whether novel protein kinase C epsilon isoform (nPKCepsilon) and N-methyl-D-aspartate (NMDA) receptors are involved in this neuroprotection. The present study examined this issue. Hippocampal slices from adult BALB/C mice were incubated with morphine at 0.1-10.0 muM in the presence or absence of various antagonists for 30 minutes and then kept in morphine- and antagonist-free buffer for 30 minutes before being subjected to oxygen-glucose deprivation for 20 minutes. After recovery in oxygenated artificial fluid for 5 hours, assessment of slice injury was done by determination of the intensity of slice stain after they were incubated with 2% 2,3,5-triphenyltetrazolium chloride for 30 minutes and extracted by organic solvent for 24 hours. At designated periods, slices were preserved for immunoblot analysis to observe effects of morphine pretreatment on membrane translocation and total protein expression of nPKCepsilon and phosphorylation of NR1 subunits of NMDA receptors. The neuroprotection induced by morphine pretreatment was partially blocked by chelerythrine (a nonselective PKC blocker), epsilonv(1-2) (a selective nPKCepsilon antagonist), MK-801 (a noncompetitive NMDA receptor blocker), chelerythrine combined with MK-801, and epsilonv(1-2) with MK-801. Morphine pretreatment significantly inhibited nPKCepsilon membrane translocation and phosphorylation of NR1 subunits of NMDA receptors during reperfusion injury. However, epsilonv(1-2) blocked these effects induced by morphine pretreatment. These findings suggested that nPKCepsilon and NMDA receptors might participate in neuroprotection induced by morphine pretreatment, and NMDA receptors might be downstream targets of nPKCepsilon.