Abstracts

Rationale: Leigh syndrome (LS), a progressive neurodegenerative disease, is caused by mitochondrial Complex-I (CI) respiratory chain dysfunction. Loss-of-function mutations in CI-related genes, such as NADH dehydrogenase (ubiquinone) iron sulfur protein 4 (NDUFS4), have been associated with causing LS. _x000D_
Methods: For behavioral experiments, we generated: Ndufs4 ^flx/flx:: Gad2cre^+/- for mutants and Ndufs4^flx/flx: Gad2cre^-/- for controls. PTZ-induced seizures: mice were injected with a single dose (s.c) of PTZ (20 mg/kg) and monitored for 30 minutes using Racine scale 1-5 (Racine 1972). Treadmill-induced seizures: young (P30-45) and old (P46-60) mice were placed on a treadmill and subject to four test trials. Treadmill speed started at 5 m/min then increased by 5 m/min for each trial. Video-EEG-EMG: EEG and EMG electrodes were placed in the mouse and, after recovery, mice were placed in recording chambers for a maximum of 8 hours. We also generated experimental mice with a genetically-mediated Ai14 TdTomato fluorescent marker in GABAergic neurons: Ndufs4 ^flx/flx: Ai14^flx/+ : Gad2cre^+/- for mutants and Ndufs4^+/+:Ai14^flx/+ : Gad2cre^+/- for controls. Cell loss: 50m sections were mounted then imaged using a confocal microscope and cells were counted. In vitro electrophysiology: Hippocampal CA1 Ai14-labeled interneurons were recorded in whole-cell patch clamp configuration. Firing patterns were recorded in response to prolonged depolarization and hyperpolarization currents._x000D_
Results: Gad2-Ndufs4-KO mutants are susceptible to PTZ-induced severe generalized tonic-clonic (GTC) seizures, where mutants showed a ~38% percent incidence. Young and old Gad2-Ndufs4-KO mutants are susceptible to exercise-induced GTCs, where ~80% of young and old mutants showed seizures by the recovery stage. Mutants also show a ~30% interneuron cell loss in key brain regions associated with epilepsy: CA1 hippocampus, central amygdala, and central amygdala nucleus. Mutants show an intrinsic interneuron function impairment, where a subset of mutant CA1 interneurons fail to fire at increased depolarizations. Finally, mutants do not show abnormal EEG oscillation patterns during the interictal period. _x000D_
Conclusions: Selective knockout of Ndufs4 in only GABAergic interneurons causes provoked epileptic seizure susceptibility. Concurrent interneuron cell loss and impaired firing are possible cellular mechanisms underlying the spontaneous and provoked seizure phenotype in these mice. _x000D_
Funding: NIH/NINDS R01NS10279602