Conditioning heat stress reduces excitotoxic and apoptotic components of oxygen-glucose deprivation-induced neuronal death in vitro

We investigated the effects of sublethal heat stress in murine cortical cell cultures exposed to combined oxygen and glucose deprivation. Pretreatment with sublethal heat stress mildly attenuated the widespread neuronal death induced a day later by 30-60 min of oxygen-glucose deprivation. Heat stress also blunted the increase in extracellular glutamate concentrations induced by the oxygen-glucose deprivation, as well as the neuronal death and ⁴⁵Ca²⁺ uptake induced by exogenous addition of NMDA, although no reduction was seen in neuronal death caused by exogenous kainate or in NMDA-induced whole-cell currents. However, arguing against the idea that the neuroprotective effect of heat stress against neuronal death was exclusively due to reduction of excitotoxicity was the finding that heat stress also reduced the neuronal apoptosis induced by oxygen-glucose deprivation in the presence of glutamate antagonists. This antiapoptotic effect was specific in that heat stress did not reduce neuronal vulnerability to staurosporine-induced apoptosis. Whereas heat stress transiently suppressed protein synthesis, achieving comparable protein synthesis inhibition with cycloheximide did not reproduce the neuroprotective effects of heat stress. These studies suggest that a conditioning heat stress is able to attenuate both the excitotoxic and the apoptotic components of oxygen- glucose deprivation-induced neuronal death in vitro, by mechanisms independent of protein synthesis reduction.