Role of Cytokines during Epileptogenesis and in the Transition from the Interictal to the Ictal State in the Epileptic Mutant EL Mouse

Abstract

Purpose: Epileptic mutant EL mice show secondary generalized seizures. Seizure discharges initiate in the parietal cortex and generalize through the hippocampus. We have previously demonstrated an increase in the activity of inducible nitric oxide synthetase (iNOS) as well as a decrease in the activity of superoxide dismutase (SOD) in the hippocampus of EL mice, suggesting that cell toxic free radicals are increased in the brain of EL mice. In parallel with this, neurotrophic factors were signifi cantly increased in the hippocampus of EL mice in earlier developmental stages before exhibiting frequent seizures. These fi ndings were no longer present after frequent seizures, suggesting that these events may trigger ictogenesis. On the other hand, it is reported that limbic seizures rapidly induce cytokines and related infl ammatory mediators. It remains to be seen, however, whether cytokines contribute to the transition from interictal to ictal state. The present study was designed to address this issue using EL mice.Methods: EL mice at the age from 4 to 23 weeks and their control animal, DDY mice at the age of 10 and 20 weeks were used. Seizures were induced in EL mice once every week since 5 weeks. Cytokines, such as interleukin-1 alpha (IL-1a), interleukin 1-beta (IL-1b), IL-6, IL-1 receptor (IL-1r), IL-1 receptor antagonist (IL-ra) and tumor necrosis factor alpha (TNF-a) were examined by Western blotting in the 'focus complex' of brain (namely, in the parietal cortex and hippocampus) of EL mice in the interictal period at different developmental stages. In 15 week old EL mice, which show seizures once a week, these cytokines were similarly determined 5 min, 2 hr, 4 hr, 11 hr, 24 hr, 3 days and 6 days after the last seizure induced. Results:A signifi cant increase in the level of cytokines was observed in the brain of EL mice at any stages during development, compared with the level of cytokines in the brain of control DDY. Cytokines were increased predominantly before experiencing frequent seizures. In EL mice at the age of 15 weeks, the level of cytokines in the hippocampus was highest 6 days after seizures. In the parietal cortex, cytokines were most highly expressed 2 hr after seizures. The results indicate that cytokines were kept up-regulated until next seizures in the hippocampus, whereas they were transiently up-regulated immediately after seizures in the parietal cortex. Conclusion:It is concluded that in the brain of EL mice, pro-infl ammatory cytokines are increased progressively and periodically in association with the development and the seizure activity, respectively. A periodic increase of cytokines prior to the next seizure episode may play a role in triggering the ictal activity. Namely, alteration of region-specifi c cytokines may induce ictal activities from the interictal state. It is conceivable that infl ammatory cytokines may work together with neuronal factors during epileptogenesis and in the transition from interictal to ictal state.

A postnatal peak in microglial development in the mouse hippocampus is correlated with heightened sensitivity to seizure triggers

“…Pro and anti‐inflammatory molecules are upregulated in the brain at the sites of seizure initiation and propagation and may influence seizure susceptibility (Murashima et al. ; Fukuda et al. ; Galic et al.…”

“…Infectious and autoimmune diseases are often accompanied by recurrent seizures (Dalmau et al 2008;Kim et al 2009). Pro and anti-inflammatory molecules are upregulated in the brain at the sites of seizure initiation and propagation and may influence seizure susceptibility (Murashima et al 2008;Fukuda et al 2009;Galic et al 2012;Choy et al 2014;Vezzani 2014). Furthermore, microgliathe resident innate immune cells of the central nervous systemare markedly activated in the brains of individuals with chronic intractable epilepsy and in animal models of seizures (Beach et al 1995;Yang et al 2000;Drage et al 2002;Avignone et al 2008;Choi et al 2009;Somera-Molina et al 2009;Fabene et al 2010).…”

Minocycline attenuates microglia activation and blocks the long-term epileptogenic effects of early-life seizures

“…In addition, pro- and anti-inflammatory molecules are synthesized during seizures in the brain at the sites of seizure initiation and propagation (Murashima et al, 2008). Extensive microglia activation occurs in the brain parenchyma of individuals with chronic intractable epilepsy and in animal models of seizures (Avignone et al, 2008; Beach et al, 1995; Choi et al, 2009; Drage et al, 2002; Fabene et al, 2010; Somera-Molina et al, 2009; Yang et al, 2010).…”

Oral hygiene in children with epilepsy: Effect of interleukin-1β and VEGF levels in gingival crevicular fluid

“…Researchers have found that IL-1β and VEGF production increases in the blood and brain during an epileptic seizure. 9,22 Vezzani et al reported that cytokine levels approximate to the normal values in brain tissue in the next 3-7 days after the seizure. 7 In this study, an increase in biochemical parameters in GCF couldn't be attributed to the epileptic seizures because all the epilepsy cases were seizure-free.…”

“…7,8 It has been found that IL-1β plays a role in the development of a neuronal cell death after traumatic, ischemic, excitotoxic and seizureinduced brain injuries. 8,9 Gingival crevicular fluid (GCF) is an exudate that is originated from gingival crevices or periodontal pockets around teeth with inflamed gingiva. GCF contains a variety of materials, including leukocytes (mainly neutrophils), antibodies, complement proteins, various enzymes, and cytokines.…”