Age-dependent changes in the hippocampal antioxidant ability of EL mice

The Roles of Dominance of the Nitric Oxide Fractions Nitrate and Nitrite in the Epilepsy-Prone EL Mouse Brain

BACKGROUND

Oxidative stress is thought to be closely related to epileptogenesis. We have previously reported that nitric oxide (NO) levels are higher in epilepsy-prone EL mice between the ages of 3 and 8 weeks than in control mice. However, NO is divided into two fractions, nitrite (NO2) and nitrate (NO3), which appear to play different roles in epileptogenesis.

METHODS

NO2 and NO3 levels were measured, in EL mice and the control mice, in the parietal cortex, which is thought to be the primary epileptogenetic center in EL mice, and measured in the hippocampus, which is thought to be the secondary center.

RESULTS

NO3 levels in the hippocampus and parietal cortex of the immature EL mice (3 to 8 weeks of age) were significantly higher than those in the control mice; NO2 levels were significantly higher in the EL mice throughout the study period. The NO3 levels were significantly higher than the NO2 levels in the immature EL mice, but after the onset of ictogenesis at 10 weeks of age, the relative levels of the two fractions reversed.

CONCLUSION

The reversal of the NO fraction distribution at the onset of seizures that we observed may be related to the developmental process of seizure susceptibility in the neural network of EL mice.

Effects of Edaravone on Hippocampal Antioxidants in EL Mice

BACKGROUND

The role of oxidative stress in susceptibility to seizures has been the focus of several recent studies. The aim of the present study was to evaluate the antiepileptic effects of the free radical scavenger edaravone on EL mice, a strain that is highly susceptible to convulsive seizures.

METHODS

EL mice were treated intraperitoneally with edaravone or saline for 1 week. The levels of reduced glutathione (GSH), oxidized glutathione (GSSG) and 3 isozymes of superoxide dismutase (SOD) (cytoplasmic copper- and zinc-containing SOD, extracellular SOD, and mitochondrial manganese-containing SOD) were measured in the hippocampus, and electroencephalograms (EEGs) were used to evaluate seizure sensitivity.

RESULTS

Hippocampal levels of GSSG were lower in the edaravone group than in the untreated control group, and the GSH/GSSG ratio, Cu/Zn-SOD, and EC-SOD activities were higher in the edaravone group. Edaravone shortened the duration of interictal spike discharges and clinically suppressed epileptic seizures.

CONCLUSION

Edaravone increases antioxidant potency and reduces seizure susceptibility in EL mice, making it a promising novel antiepileptic agent.

Molecular regulation of antioxidant ability in the hippocampus of EL mice

We recently found that the antioxidant ability was remarkably decreased in the hippocampus (Hipp) of EL at 8 weeks of age utilizing ESR spectroscopy. In this study, in addition to evaluating the extracellular glutamate concentration, we tried to determine whether or not changes in the expression of cystine/glutamate exchanger (xCT) and glutamate transporter take place in the Hipp of EL. EL mice and DDY mice at 5, 10, and 20 weeks of age were used for Exp. I and II, respectively. Exp. I: During the interictal state, dialysate was collected from the ventral Hipp using a microdialysis technique, and an extracellular concentration of glutamate ([Glu](o)) was measured with HPLC-ECD. Exp. II: The hippocampal expression of the glutamate transporter and xCT was estimated by Western blots. Exp. I: The level of [Glu](o) at 10 weeks of age was remarkably higher at other ages of EL mice, while [Glu](o) of DDY was unchanged as a result of age. Exp. II: The excitatory amino acid carrier-1 (EAAC-1) and xCT of EL mice at 10 weeks of age decreased more than those of DDY. GLAST and GLT-1 of EL mice at 5 weeks of age decreased more than those of DDY at the same age. No differences were found between EL and DDY for GLAST and GLT-1 at other ages. According to previous studies, the decreased endogenous antioxidant potential observed at 10 weeks of age is a very likely explanation for ictogenesis. The decreased xCT expression at 10 weeks of age could provide the molecular mechanism to explain the depletion of the endogenous antioxidant ability of EL mice during ictogenesis. In addition to the depletion of antioxidant ability, decreased EAAC-1 at this period could be one reason for the collapse of the molecular action of inhibition. These molecular findings support the idea that the elevation of [Glu](o) at 10 weeks of age triggers ictogenesis.