Role of Nitric Oxide in the Epileptogenesis of EL Mice

Abstract

Summary:Purpose: To understand the role of nitric oxide (NO) in the regulation of seizures, we measured the extracellular levels of the NO metabolites nitrite and nitrate as indices of NO generation in the parietal cortex, hippocampus, and temporal cortex of EL mice. Furthermore, alterations of neuronal, endothelial, and inducible nitric oxide synthetase (nNOS, eNOS, and iNOS, respectively) were observed to correlate them with epileptogenesis.Methods: EL mice of 20 weeks and 30 weeks of age (before and after the establishment of epileptogenesis, respectively) were used. Nitrite was quantified using the specific absorbancy of diazo dye. NOS isoenzymes (nNOS, iNOS, and eNOS) were also investigated in the hippocampus during development until mice were 30 weeks old. Samples (total protein, 8.33 to 8.43 Fg) were separated by sodium dodecyl sulfate-polyacrylamide geI electrophoresis and identified by immunoblotting.Results: EL mice that experienced repetitive seizures showed a remarkable increase in nitrite in the hippocampus at 30 weeks of age compared with EL mice that had no experience of seizures. nNOS and iNOS were major and minor components, respectively, and both increased in parallel with the development of epileptogenesis. eNOS was not detectable.Conclusions: Excess iNOS (and subsequent increase in harmful NO) and deficient eNOS (and subsequent decrease in NO identified as an endothelium-derived relaxing factor) may work together to form a focus complex. Key Words: Epileptic mutant-EL mouse-Nitric oxide (NO)-Nitric oxide synthetase (NOS)-Abnormal plasticity-Epileptogenesis.The EL mouse is an inbred mutant strain that has been used as an animal model of secondarily generalized seizures (1,2). Several lines of evidence indicate that seizure discharges are initiated in the parietal area and then generalized through the hippocampus (3). These findings have been substantiated by histochemical and biochemical analyses of glucose utilization (4) and inhibitory neurotransmissions by aminobutyric acid (5). The developmental formation of the focus complex, which consists mainly of the parietal cortex and the hippocampus, has been hypothesized to be key to epileptogenesis in EL mice.In our recent studies, allopurinol, a xanthine oxidase inhibitor, exerted an antiepileptic action on EL mice (6), and the drug ameliorated abnormalities in the activities of the free radical scavenger superoxide dismutase isoenzymes, which are present in the hippocampus (7). Furthermore, DNA fragmentation was found in the hippocampal CA1 region and the parietal cortex in EL mice, presumably as a consequence of the production of free radicals attributable to decreased Cu,Zn-superoxide dismutase (7). Nitric oxide (NO) has been identified as a source of free radical oxidants with special relevance to pathological conditions in the brain, and reactive nitrogen intermediates could damage DNA as an important target (8). In addition, NO, identified as an endothelium-derived relaxing factor (9), is a potent vasodilator that regulates cerebral blo...

Involvement of Nitric Oxide in Spatial Memory Deficits in Status Epilepticus Rats

“…In the nervous system, nNOS is largely responsible for NO production, while iNOS has been implicated in some important central processes [51]. Since the activity of iNOS increased after seizure, which is accordant to the previous reports [41,52], it is valuable to examine the probable contribution of iNOS in SE-induced memory deficits. In this study, we used AG, which is an irreversible specific inhibitor of iNOS [53].…”

“…In fact, several in vivo studies using 7-NI support a role of neuron-deirved NO in the excitotoxicity-related activity [39,40].According to previous reports, 7-NI not only reduces NO generation but also prevents the delayed death of hippocampal neurons [30,41], while the effects produced by 7-NI can be attributed to its ability to inhibit nNOS activity directly. According to Mackenzie et al [42], 7-NI produced the maximal effects at 0.5 h post-infection and recovery at 24 h (i.p.…”

Posttraumatic Epilepsy: Hemorrhage, Free Radicals and the Molecular Regulation of Glutamate

“…Synthesis and release of NO occurs with stimulation of NMDA receptors [47,48]. Nitric oxide has pro-convulsant effects in seizures induced under various experimental conditions including pentylenetetrazole [PTZ] [49] and in El-mice [50]. However, NO has had anticonvulsant effects in kainate induced seizures, [51] in a-guanidinogultaric acid induced seizures [52], and with NMDA induced seizures [53].…”

Opposite caudal versus rostral brain nitric oxide synthase response to generalized seizures in a novel rodent model of reflex epilepsy

“…To that effect, we employed animals of the GASH:Sal strain (Generalized Audiogenic Seizure Hamster, University of Salamanca, Spain), examining areas across the brain rostro-caudal axis. We studied constitutive NOS (cNOS) activity and the expression of the two cNOS isoforms (nNOS and eNOS) based on previous studies showing a more prominent role of cNOS over iNOS in epileptic crises (Murashima et al, 2000;González-Hernández et al, 2000;Tutka et al, 2007;Itoh and Watanabe, 2009;Kovács et al, 2009;Bahremand et al, 2010). The present work shows a differential activation and expression of nNOS in the caudal versus the rostral areas of the epileptic brain after 10 crises.…”