Abstracts

Rationale: Metabolic dysfunction is emerging as an important mechanism in the pathogenesis of temporal lobe epilepsy (TLE). TLE is the most common form of acquired epilepsy in which injury leads to epilepsy development by a process known as epileptogenesis. Epileptogenesis is the process whereby a precipitating injury activates a series of cellular and molecular changes that ultimately lead to the development of a hyper-excitable state in which spontaneous recurrent seizures are observed. Understanding how mitochondrial and glycolytic dysfunction occurs during epileptogenesis could lead to new metabolic approaches to the treatment of TLE.Methods: To determine the relative contributions of mitochondrial respiration and glycolysis during epileptogenesis, real-time analysis of oxygen consumption and glycolytic rates were assessed in isolated synaptosomes from the hippocampus of rats at various times (3h, 8h, 16h, 48h, 1wk, 3wk and 6wk) after kainate administration using an extracellular flux analyzer (Seahorse Bioscience, North Billerica, MA, USA). Animals in the 3 and 6-week time points were video monitored for behavioral seizures. Results observed in the kainate model were verified in the pilocarpine model. In addition, brain bioenergetic functions of manganese superoxide dismutase (MnSOD) knockout mice, a model of mitochondrial oxidative stress and epilepsy, were assessed. Ouabain and 4-aminopyridine (4-AP) were used as to provide an additional ATP demand to further test mitochondrial and glycolytic function.Results: In the kainate model, overall respiratory capacity and ATP-linked respiration were decreased at the 48-hour time-point and returned to control levels at the 1-week time point. This deficit returns at the 3 and 6-week chronic time points. Baseline rates of glycolysis were unchanged compared to controls. However, treatment with the mitochondrial uncoupler FCCP resulted in a time-dependent decrease in glycolytic rates that recovered at the 1-week time-point in kainate treated rats. Synaptosomes from epileptic MnSOD knockout mice demonstrated a severe decline in respiratory capacity in response to physiological stress induced by uncoupling. Additionally, hippocampal synaptosomes from kainate-treated rats challenged with 4-AP or ouabain were unable to compensate for the additional ATP demand. Results obtained in the kainate model were also observed in hippocampal synaptosomes of pilocarpine-treated rats.Conclusions: These data demonstrate profound deficits in mitochondrial oxygen consumption and glycolytic rates in animal models of TLE that coincide with increases in indices of mitochondrial oxidative stress previously shown in the laboratory. This study provides further evidence of metabolic dysfunction in experimental TLE, and demonstrates an accurate and reliable method for analyzing metabolic dysfunction in specific areas of the brain pertinent to epilepsy.