Prolonged seizure activity impairs mitochondrial bioenergetics and induces cell death

Abstract

The mechanisms underlying neuronal death following excessive activity such as occurs during prolonged seizures are unclear, but mitochondrial dysfunction has been hypothesised to play a role. Here, we tested this with fluorescence imaging techniques in rat glio-neuronal neocortical co-cultures using low Mg(2+) levels to induce seizure-like activity. Glutamate activation of NMDA receptors resulted in Ca(2+) oscillations in neurons and a sustained depolarisation of the mitochondrial membrane potential, which was cyclosporine A sensitive, indicating mitochondrial permeability and transition pore opening. It was also dependent on glutamate release and NMDA receptor activation, because depolarisation was not observed after depleting vesicular glutamate with vacuolar-type H(+)-ATPase concanamycin A or blocking NMDA receptors with APV. Neuronal ATP levels in soma and dendrites decreased significantly during prolonged seizures and correlated with the frequency of the oscillatory Ca(2+) signal, indicative of activity-dependent ATP consumption. Blocking mitochondrial complex I, complex V or uncoupling mitochondrial oxidative phosphorylation under low-Mg(2+) conditions accelerated activity-dependent neuronal ATP consumption. Neuronal death increased after two and 24 hours of low Mg(2+) levels compared with control treatment, and was reduced by supplementation with the mitochondrial complex I substrate pyruvate. These findings demonstrate a crucial role for mitochondrial dysfunction in seizure-activity-induced neuronal death, and that strategies aimed at redressing this are neuroprotective.