Brain superoxide anion formation in immature rats during seizures: protection by selected compounds

Abstract

The widely-held assumption was that oxidative stress does not occur during seizures in the immature brain. The major finding of the present study concerns evidence of oxidative stress in the brain of immature rats during seizures induced by DL-homocysteic acid. Seizures were induced in 12-day-old rats by bilateral intracerebroventricular infusion of DL-homocysteic acid (DL-HCA, 600 nmol/side) and oxidative stress was evaluated by in situ detection of superoxide anion (O(2)·(-)). Using hydroethidine (Het) method, the fluorescent signal of the oxidized products of Het (reflecting O(2)·(-) production) significantly increased (by 50%-60%) following 60 min lasting seizures in all the studied structures, namely CA1, CA3 and dentate gyrus of the hippocampus, cerebral cortex and thalamus. The enhanced O(2)·(-) production was substantially attenuated or completely prevented by substances providing an anticonvulsant effect, namely by a competitive NMDA receptor antagonist AP7, a highly selective and potent group II metabotropic glutamate receptor (mGluR) agonist 2R,4R-APDC and highly selective group III mGluR, subtype 8 agonist (S)-3,4-DCPG. Complete protection was achieved by two SOD mimetics Tempol and MnTMPYP which strongly suggest that the increased fluorescent signal reflects O(2)·(-) formation. In addition, both scavengers provided a partial protection against brain damage associated with the present model of seizures. Signs of neuronal degeneration, as evaluated by Fluoro-Jade B staining, were detected at 4h following the onset of seizures. The present findings thus suggest that the increased superoxide generation precedes neuronal degeneration and may thus play a causative role in neuronal injury. Occurrence of oxidative stress in brain of immature rats during seizures, as demonstrated in the present study, can have a clinical relevance for a novel approach to the treatment of epilepsy in children, suggesting that substances with antioxidant properties combined with the conventional therapies might provide a beneficial effect.