In response to harmful stresses, cells induce programmed cell death (PCD) or apoptosis.
Seizures can induce neural damage and activate biochemical pathways associated with PCD. Since
seizures trigger intracellular
calcium overload, it has been presumed that the intrinsic cell death pathway mediated by
mitochondrial dysfunction would modulate cell death following
seizures. However, previous work suggests that the extrinsic cell death pathway may initiate the damage program. Here we investigate intrinsic versus extrinsic cell death pathway activation using
caspase cleavage as a marker for activation of these pathways in a rat in vitro model of
seizures. Hippocampal cells, chronically treated with
kynurenic acid, had
kynurenic acid withdrawn to induce seizure-like activity for 40 min. Subjecting rat hippocampal cultures to
seizures increased cell death and apoptosis-like DNA fragmentation using TUNEL staining. Seizure-induced cell death was blocked by both
MK801 (10 microM) and
CNQX (40 microM), which suggests multiple
glutamate receptors regulate seizure-induced cell death. Cleavage of the
initiator caspases,
caspase 8 and 12 were increased 4h following seizure, and cleavage of the quintessential executioner
caspase,
caspase 3 was increased 4h following seizure. In contrast,
caspase 9 cleavage only increased 24h following seizure. Using an affinity labeling approach to trap activated
caspases in situ, we show that
caspase 8 is the apical
caspase activated following
seizures. Finally, we show that the
caspase 8 inhibitor Ac-IETD-CHO was more effective at blocking seizure-induced cell death than the
caspase 9 inhibitor
Ac-LEHD-CHO. Taken together, our data suggests the extrinsic cell death pathway-associated
caspase 8 is activated following
seizures in vitro.