Abstracts

Rationale: Growing evidence suggests that metabolic dysfunction plays an important role in the pathophysiology of epilepsy. However, little is known regarding the changes in gene expression and activity of metabolic enzymes that are involved in glycolysis, citric acid cycle (CAC) and anaplerosis during seizure development in chronic mouse pilocarpine model.Methods: Male CD1 mice (30-35g) were injected with methyscopolamine (2.5mg/kg, i.p.) 15 minutes prior to pilocarpine injection (315-345mg/kg, s.c.). Seizures were terminated after 90 minutes using sodium pentobarbitone (30mg/kg, i.p.). Spontaneous recurrent seizures only develop in mice that experienced pilocarpine-induced status epilepticus (SE), but not in mice that did not experience SE (no SE mice; Borges et al., 2003, Exp Neurol., 182, 21). Mice were sacrificed either three days or three weeks post-SE. One half of the forebrain was subjected to gene expression analysis using quantitative real time-PCR while the other half was subjected to enzyme activity analysis. Changes in the expression and activity of metabolic enzymes were analysed using unpaired two-tailed t-test (n= 8-13 per group).Results: The gene expression of enzymes involved in glycolysis, CAC and anaplerosis was significantly reduced in SE mice in comparison to no SE mice three days post-SE. Specifically, we found lower mRNA levels of pyruvate dehydrogenase (PDH, 38%), succinate dehydrogenase (SDHA, 21%), propionyl-CoA carboxylase subunit (PCC , 45%), propionyl-CoA carboxylase subunit (PCC , 44%), methylmalonyl-CoA mutase (MCM, 44%) and pyruvate carboxylase (PC, 32%) in SE mice compared to no SE mice (all enzymes p<0.001). Similarly, the enzyme activity of PDH and PC was reduced by 23% (p<0.05) and 28% (p<0.05) respectively in SE mice three days post-SE. No significant changes in gene expression and enzyme activity were observed three weeks post-SE between SE and no SE mice. However, our group has recently shown that the levels of several neurotransmitters, including glutamate and glutamine produced through the PDH and PC pathways are reduced three weeks after pilocarpine-induced SE (Smeland et al. 2013, JCBFM, doi: 10.1038/jcbfm.2013.54), indicating impairment of mitochondrial metabolism in epileptic tissue. Therefore we are currently assessing the expression and activity of enzymes involved in glucose metabolism such as hexokinase, phosphofructokinase and pyruvate kinase as well as glutamate dehydrogenase and glutamine synthase, which are involved in neurotransmitter synthesis, in mice three weeks after the induction of SE. Conclusions: Reduction in gene expression and activity of metabolic enzymes involved in glycolysis, CAC and anaplerosis indicates that metabolic dysfunction occurs during seizure development (three days post-SE) in the mouse pilocarpine model. However, both the activity and expression of the investigated metabolic enzymes are restored three weeks post-SE. Further work is necessary to determine the enzymes involved in the changes of glutamate and glutamine levels that have previously been reported in this model.