Abstracts

NAD(P)H:quinone oxidoreductase 1 (NQO1) is a widely expressed enzyme thought to protect cells from the effects of reactive quinones and their derivatives. NQO1 is part of an oxidative stress-induced cellular defense mechanism that includes induction of gene expression. NQO1 -/- mice have alterations in intracellular redox status and altered glucose and fatty acid metabolism and have been observed to have spontaneous seizures. We compared the responsiveness of the NQO1 -/- mice to kainic acid, pentylenetetrazol (PTZ) and insulin induced seizures to the background strain to try to determine whether there is a change in seizure expression or initiation in the absence of this protein.
Wild-type (C57Bl/6) and NQO1 -/- mice were injected intraperitoneally with either 15 mg/kg kainic acid (n=9 -/-, n=8 +/+) or 30 mg/kg PTZ (n=8 +/+, n=4 -/-). Seizure threshold was tested using PTZ infusion into the tail vein in 10 +/+ mice and 9 -/- mice. Insulin-induced seizures were studied by intraperitoneal injections of 14 IU/kg insulin (n=4 +/+, n=3 -/-). Seizures were monitored until normal baseline behavior returned. In addition, brains from the -/- animals were examined histologically after perfusion with 4% paraformaldehyde. Sections, 35 um, were Nissl stained and stained for GFAP immunoreactivity.
The spontaneous seizures in the NQO1 -/- mice occurred more commonly in older animals, but were still quite rare (once every 3-4 days). The seizures were characterized by tonic extension of the front legs, tension of the tail, salivation, and sometimes loss of righting. Some of the seizures included generalized clonic activity. The seizure threshold determined by the PTZ infusion was not different between the -/- group and the +/+ group. The wild-type animals took 0.29 [plusmn] 0.025 mg/kg PTZ to the first muscle twitch, while the -/- mice took 0.32 [plusmn] 0.02 mg/kg. The seizures induced by intraperitoneal injections of PTZ and kainic acid were not different between the two groups of mice. After injection of insulin, both groups became lethargic by 45 minutes and the first seizure activity occurred between 50 and 65 minutes after the insulin injection. There was no difference in the morphology of the brains from the -/- mice with either the Nissl stain or GFAP immunoreactivity.
The NQO1 -/- mouse is an example of a knockout mouse with spontaneous seizures, but no obvious morphological changes in the brain and no changes in the responses to standard convulsive agents. Additional work has shown that NQO1 in the brain is localized primarily to the oligodendrocytes and a role in myelin formation has been hypothesized. These data, plus the role of NQO1 in metabolism, suggest that the spontaneous seizures in these mice may be due to metabolic abnormalities due to the altered biochemical status of the animals. Further experiments are needed to confirm this hypothesis and to determine whether this animal may be useful in understanding seizures initiated by changes in systemic metabolism.
[Supported by: NS39941 to JLS and ES07943 to AKJ.]