We generated a mouse line harboring an autosomal-dominant nocturnal frontal lobe epilepsy (ADNFLE) mutation: the ␣4 nicotinic receptor S248F knock-in strain. In this mouse, modest nicotine doses (1-2 mg/kg) elicit a novel behavior termed the dystonic arousal complex (DAC). The DAC includes stereotypical head movements, body jerking, and forelimb dystonia; these behaviors resemble some core features of ADNFLE. A marked Straub tail is an additional component of the DAC. Similar to attacks in ADNFLE, the DAC can be partially suppressed by the sodium channel blocker carbamazepine or by pre-exposure to a very low dose of nicotine (0.1 mg/kg). The DAC is centrally mediated, genetically highly penetrant, and, surprisingly, not associated with overt ictal electrical activity as assessed by (1) epidural or frontal lobe depth-electrode electroencephalography or (2) hippocampal c-fos-regulated gene expression. Heterozygous knock-in mice are partially protected from nicotine-induced seizures. The noncompetitive antagonist mecamylamine does not suppress the DAC, although it suppresses high-dose nicotine-induced wild-type-like seizures. Experiments on agonist-induced 86 Rb ϩ and neurotransmitter efflux from synaptosomes and on ␣4S248F2 receptors expressed in oocytes confirm that the S248F mutation confers resistance to mecamylamine blockade. Genetic background, gender, and mutant gene expression levels modulate expression of the DAC phenotype in mice. The S248F mouse thus appears to provide a model for the paroxysmal dystonic element of ADNFLE semiology. Our model complements what is seen in other ADNFLE animal models. Together, these mice cover the spectrum of behavioral and electrographic events seen in the human condition.Key words: nicotine; epilepsy; ADNFLE; dystonia; mecamylamine; synaptosome
IntroductionNocturnal frontal lobe epilepsy (NFLE) is characterized by clusters of stereotypic episodes of arousal from sleep associated with dystonic neck, limb, and trunk movements that occur during stages 2-4 of non-rapid eye movement (REM) sleep (Montagna, 1992;Plazzi et al., 1995;Provini et al., 1999;Provini et al., 2000).Less commonly, there are prolonged ballistic limb and trunk movements, resulting in injury Combi et al., 2004). Autosomal-dominant NFLE (ADNFLE) , a familial subtype of NFLE, was initially associated with a missense (S248F) mutation in the ␣4 nicotinic acetylcholine receptor subunit (␣4-nAChR) gene (Steinlein et al., 1995) at position 6Ј in the M2 transmembrane region. Subsequently, in other ADNFLE pedigrees, additional mutations were discovered at the ␣4 M2-10Ј (Steinlein et al., 1997;Hirose et al., 1999), M2-17Ј (Steinlein et al., 1997;Hirose et al., 1999), and 2 subunit M2-22Ј positions and one at the 2 M3 position that contacts M2 in most structural models (De Fusco et al., 2000;Phillips et al., 2001;Bertrand et al., 2005). A mutation in ␣2 (Aridon et al., 2006) was identified in a pedigree with atypical nocturnal epilepsy.Electrophysiological analyses of heterologously expressed ADNFLE alleles sugge...
