INCREASED GABAERGIC INHIBITION THROUGH ACTIVATION OF [alpha]4 nAChR IN FRONTAL LOBE LAYER II/III PYRAMIDAL CELLS OF TWO ADNFLE MUTANT MICE
Abstract number :
2.036
Submission category :
Year :
2005
Submission ID :
5340
Source :
www.aesnet.org
Presentation date :
12/3/2005 12:00:00 AM
Published date :
Dec 2, 2005, 06:00 AM
Authors :
1,3Joseph Glykys, 1Alwin Klaassen, 3Jamie Maguire, 2James Boulter, and 3Istvan Mody
It is not known how mutations in nAChR [alpha]4 subunits result in autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE). To understand the alterations in neuronal excitability in ADNFLE, we made electrophysiological recordings from mice genetically engineered to express one of two known mutations (S252F or +L264) found in the nAChR [alpha]4 subunit of ADNFLE patients. Brain slices (350[mu]m thick) were prepared from wild type (wt), heterozygous, or homozygous mutant male mice. Whole-cell voltage-clamp recordings were obtained at 32-34oC from visually identified frontal cortical layer II/III pyramidal cells (PCs). Spontaneous inhibitory (sIPSCs) and excitatory (sEPSCs) postsynaptic currents were recorded simultaneously or in isolation before and during the perfusion of 1[mu]M nicotine. The average current produced by the synaptic events was measured during 1 s epochs. In simultaneous recordings of inhibition and excitation in PCs of S252F heterozygous mice, the inhibitory component was increased [sim]34-fold by nicotine compared to a [sim]4-fold increase in wt. When recorded alone, sIPSCs were increased [sim]23-fold while a [sim]20-fold increase was observed in +L264 heterozygous mice compared to [sim]3-fold increase in wt. Isolated sEPSC did not change in response to nicotine. The effect of nicotine was blocked by the nAChR [alpha]4 antagonist dihydro-[beta][ndash]erythroidine (10[mu]M) but not by the [alpha]7 blocker methyllycaconitine (50nM). Frequency and kinetics of S252F heterozygous mice mIPSCs were significantly increased by 1 [mu]M nicotine while wt mIPSCs did not. Our results demonstrate that activation of nAChR [alpha]4 significantly increases inhibitory activity in two types of mutant mice carrying human ADNFLE mutations. This suggests that seizures in ADNFLE arise from synchrony in the frontal cortex produced by interneuronal hyperactivity. (Supported by Gonda Fellowship (JG), NIH Molecular and Cellular Neurobiology predoctoral training grant (AK), NS02808 (IM), NIH NIDA, the Milken Family Medical Foundation (JB).)