Seizures and enhanced cortical GABAergic inhibition in two mouse models of human autosomal dominant nocturnal frontal lobe epilepsy

Selected mutations in the human alpha 4 or beta 2 neuronal nicotinic acetylcholine receptor subunit genes cosegregate with a partial epilepsy syndrome known as autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE). To examine possible mechanisms underlying this inherited epilepsy, we engineered two ADNFLE mutations (Chrna4(S252F) and Chrna4(+L264)) in mice. Heterozygous ADNFLE mutant mice show persistent, abnormal cortical electroencephalograms with prominent delta and theta frequencies, exhibit frequent spontaneous seizures, and show an increased sensitivity to the proconvulsant action of nicotine. Relative to WT, electrophysiological recordings from ADNFLE mouse layer II/III cortical pyramidal cells reveal a > 20-fold increase in nicotine-evoked inhibitory postsynaptic currents with no effect on excitatory postsynaptic currents. i.p. injection of a subthreshold dose of picrotoxin, a use-dependent gamma-aminobutyric acid receptor antagonist, reduces cortical electroencephalogram delta power and transiently inhibits spontaneous seizure activity in ADNFLE mutant mice. Our studies suggest that the mechanism underlying ADNFLE seizures may involve inhibitory synchronization of cortical networks via activation of mutant alpha 4-containing nicotinic acetylcholine receptors located on the presynaptic terminals and somato-dendritic compartments of cortical GABAergic interneurons.