Hypothermic preconditioning increases survival of Purkinje neurons in rat cerebellar slices after an in vitro simulated ischemia

Background: A period of hypothermia before ischemia (hypothermic preconditioning) induces a delayed phase of ischemic tolerance in rat brain. However, whether hypothermic preconditioning induces an acute phase (within a few hours after the hypothermia) of ischemic tolerance remains unknown. This study was designed to determine the time window of the hypothermic preconditioning-induced acute phase of neuroprotection, which is useful information for situations during surgery with anticipated ischemic episodes, and its involved mechanisms. Methods: Survival of Purkinje cells in rat cerebellar slices was evaluated after a 20-min oxygen-glucose deprivation (OGD, in vitro simulated ischemia) followed by a 4-h recovery. Mild hypothermia (33degreesC) for 20 min was applied at various times before the OGD. Results: The hypothermia applied immediately to 3 h before the OGD equally effectively reduced OGD-induced Purkinje cell death/injury. Glibenclamide, a selective K-ATP channel blocker; 8-cyclopentyl-1,3-dipropylxanthine, a selective adenosine A, receptor antagonist; and farnesyl protein transferase inhibitor III, a selective inhibitor to reduce Ras farnesylation, abolished bypothermic preconditioning-induced neuroprotection when applied during the hypothermia. OGD increased the expression of high-mobility group I(Y) proteins, which are nuclear transcription factors to enhance the expression of putatively damaging proteins such as cyclooxygenase-2, in cerebellar slices. This increase was attenuated by hypothermic preconditioning. Conclusions: Hypothermic preconditioning induces an acute phase of neuroprotection. This neuroprotection depends on activation of the signaling molecules, adenosine A, receptors, K-ATP channels, and Ras. Inhibition of putatively damaging proteins via the effects of hypothermic preconditioning on high-mobility group I(Y) expression may also be involved in hypothermic preconditioning-induced neuroprotection.