Abstracts

Rationale: Linkage analysis and both case-control and family-based association analysis show strong evidence that malic enzyme 2 (ME2) is a gene linked to idiopathic generalized epilepsy (IGE) on chromosome 18q. ME2 is a genome-coded enzyme localized in the mitochondria. In neurons, it reversibly catalyzes the carboxylation of pyruvate to malate and is also implicated in neuronal synthesis of the transmitters, γ-aminobutryic acid (GABA) and glutamate. In order to test what effect ME2 has on neurotransmission, we investigated the effect of the malic enzyme inhibitor, Tartronic Acid (TA), on synaptic glutamate transmission in neurons from mouse brain slices.Methods: Neurons within the basolateral amygdala of acute brain slices from C57BL/6J mice were recorded with whole-cell voltage clamp configuration. Brain slices obtained from P16-P20 mice were kept at room temperature in oxygenated, artificial cerebrospinal fluid (aCSF) for at least one hour prior to electrophysiological recordings. To assess miniature synaptic activity (mPSCs), 1µM Tetradotoxin (TTX) was added to aCSF to inhibit voltage-sensitive sodium channels contributing to action potentials. Bicuculine was added to aCSF in some experiments to block GABA A-receptor mediated transmission so that glutamate-receptor (GluR)-mediated activity was predominantly glutamatergic synaptic transmission. Spontaneous synaptic activity-in such slices-was initially monitored for 10-60 minutes followed by the perfusion of 1mM TA.Results: The frequency but not the amplitude of mPSCs was reduced in 6 of 8 neuronal samples recorded. Furthermore, we observed the same reduced activity in three neurons recorded devoid of any prior TTX, suggesting the inhibition of malic enzyme activity may have a profound effect on overall glutamate transmission. Conclusions: Our data suggests the inhibition of malic enzyme by TA reduces the baseline synaptic activity generated by glutamate transmission. These results are consistent with the hypothesis that changes in ME2 activity affect neural transmission and support the finding that variation in ME2 activity may affect seizure susceptibility in humans.