Shifting the balance of neuronal apoptosis and necrosis in the cerebral cortex is neuroprotective following traumatic brain injury

Studies have shown that both apoptotic and necrotic neuronal cell death occur in the cortex following human and experimental traumatic brain injury (TBI). In this study we used a Fluoro-Jade (FJ) and TUNEL double labeling technique to identify and quantify necrotic neurons, apoptotic neurons, and apoptotic non-neuronal cells (glia) in the cerebral cortex 24 hr following varying magnitudes of lateral fluid percussion (LFP) brain injury (1.0 atm--2.4 atm) in rats. As injury magnitude increased there was a significant increase in the number of necrotic neurons. However, over a large range of injury magnitudes (1.0 atm--2.2 atm) the ratio of apoptotic to necrotic neurons remained relatively constant. This indicates a relationship between traumatic brain injury magnitude and cell death phenotype that is dissimilar to what has been reported following ischemic and toxic insults to the nervous system. The caspase inhibitors Z-VAD-FMK and Q-VD-OPH were injected i.c.v. immediately following LFP injury to test for histological and behavioral neuroprotection. Z-VAD-FMK reduced total neuronal cell death by reducing apoptosis without increasing necrosis, suggesting an increase in neuronal survival. In addition, Z-VAD-FMK reduced the volume of the FJ-positive injury area and reduced the number of TUNEL positive non-neuronal (glial) cells. Z-VAD-FMK and Q-VD-OPH improved motor outcome on the inclined plane and cognitive outcome in the Morris water maze. Z-VAD-FMK also improved working memory on the radial arm maze. This study suggests that inhibiting apoptosis through caspase inhibitors is histologically and behaviorally neuroprotective.