The effects of glucose and O2 deprivation (OGD) on the survival of cortical and cerebellar neurons were examined to characterize the biochemical mechanisms involved in OGD and OGD followed by reoxygenation. To this aim, neurons were kept for different time periods in a hypoxic chamber with a controlled atmosphere of 95% N(2) and 5% CO2 in a glucose-free medium. After OGD, reoxygenation was achieved by exposing the cells to normal O2 and glucose levels. Neither MTT, an index of mitochondrial oxidative phosphorylation, nor malondialdehyde (MDA) production, a parameter measuring lipid peroxidation, were affected by 1 hr of OGD in cortical neurons. When OGD was followed by 24 hr of reoxygenation, MTT levels were reduced by 40% and MDA was significantly increased, whereas cellular ATP content did not change. Cerebellar granule cells, on the other hand, did not show any reduction of mitochondrial activity after exposure to 1 hr OGD or to 1 hr OGD plus 24 hr of reoxygenation. When OGD was prolonged for 2 hr, a significant reduction of the mitochondrial activity and of cellular ATP content occurred, coupled to a significant MDA increase in cerebellar granule cells, whereas in cortical neurons a reduction of MTT levels after 2 hr OGD was not accompanied by a decrease of cellular ATP content nor by an increase of MDA production. Moreover, 24 hr of reoxygenation further reinforced lipid peroxidation, LDH release, propidium iodide positive neurons and the reduction of ATP content in cerebellar granule cells. The results of the present study collectively show that cortical and cerebellar neurons display different levels of vulnerability to reoxygenation followed by OGD. Furthermore, the impairment of mitochondrial activity and the consequent overproduction of free radicals in neurons were observed for the first time occurring not only during the reoxygenation phase, but already beginning during the OGD phase.
Copyright 2001 Wiley-Liss, Inc.