Experimental and clinical data suggest that
oxygen and/or
glucose deprivation alters electrical transmission in the brain and generates
free radicals, which may mediate neuronal death. We have analyzed the effects of
oxygen and/or
glucose deprivation on both excitatory transmission, by measuring field potential amplitude, and
free radical production, by using electron spin resonance (ESR) spectroscopy, in a corticostriatal slice preparation. Combined
oxygen and/or
glucose deprivation (
ischemia) lasting 10 to 20 minutes induced a long-term depression of field potential amplitude. The
ascorbyl radical could only be detected in brain slices during the reperfusion-phase after 30 minutes of
ischemia. It appeared in the early minutes after the washout of ischemic medium and remained stable throughout the reperfusion phase. This radical was never detected in the external medium.
Ischemia induced only a slight, but progressive, release of
lactate dehydrogenase (LDH) into the external medium during the reperfusion phase. In contrast, exposure of slices to
hypoxia or
hypoglycemia alone resulted in transient depression of field potential amplitude, and no generation of ascorbyl radicals was observed on reperfusion. We propose that the long-lasting loss of electrical signals is the early sign of neuronal damage during
ischemia. On the other hand,
ascorbyl radical formation may be considered an
indicator of neuronal injury after prolonged energy deprivation.