[show abstract][hide abstract] ABSTRACT: In a phenotype-driven mutagenesis screen, a novel, dominant mouse mutation, Nmf350, caused low seizure threshold, sporadic tonic-clonic seizures, brain enlargement and ectopic neurons in the dentate hilus and molecular layer of the hippocampus. Genetic mapping implicated Akt3, one of four candidates within the critical interval. Sequencing analysis revealed that mutants have a missense mutation in Akt3 (encoding one of three AKT/protein kinase B molecules), leading to a non-synonymous amino acid substitution in the highly conserved protein kinase domain. Previous knockout studies showed that Akt3 is pivotal in postnatal brain development, including a smaller brain, although seizures were not observed. In contrast to Akt3(Nmf350), we find that Akt3 null mice exhibit an elevated seizure threshold. An in vitro kinase assay revealed that Akt3(Nmf350) confers higher enzymatic activity, suggesting that Akt3(Nmf350) might enhance AKT signaling in the brain. In the dentate gyrus of Akt3(Nmf350) homozygotes, we also observed a modest increase in immunoreactivity of phosphorylated ribosomal protein S6, an AKT pathway downstream target. Together these findings suggest that Akt3(Nmf350) confers an increase of AKT3 activity in specific neuronal populations in the brain, and a unique dominant phenotype. Akt3(Nmf350) mice provide a new tool for studying physiological roles of AKT signaling in the brain, and potentially novel mechanisms for epilepsy.
Human Molecular Genetics 03/2011; 20(5):988-99. · 7.69 Impact Factor
[show abstract][hide abstract] ABSTRACT: The rat demyelination (dmy) mutation serves as a unique model system to investigate the maintenance of myelin, because it provokes severe myelin breakdown in the central nervous system (CNS) after normal postnatal completion of myelination. Here, we report the molecular characterization of this mutation and discuss the possible pathomechanisms underlying demyelination. By positional cloning, we found that a G-to-A transition, 177 bp downstream of exon 3 of the Mrs2 (MRS2 magnesium homeostasis factor (Saccharomyces cerevisiae)) gene, generated a novel splice acceptor site which resulted in functional inactivation of the mutant allele. Transgenic rescue with wild-type Mrs2-cDNA validated our findings. Mrs2 encodes an essential component of the major Mg²+ influx system in mitochondria of yeast as well as human cells. We showed that the dmy/dmy rats have major mitochondrial deficits with a markedly elevated lactic acid concentration in the cerebrospinal fluid, a 60% reduction in ATP, and increased numbers of mitochondria in the swollen cytoplasm of oligodendrocytes. MRS2-GFP recombinant BAC transgenic rats showed that MRS2 was dominantly expressed in neurons rather than oligodendrocytes and was ultrastructurally observed in the inner membrane of mitochondria. Our observations led to the conclusion that dmy/dmy rats suffer from a mitochondrial disease and that the maintenance of myelin has a different mechanism from its initial production. They also established that Mg²+ homeostasis in CNS mitochondria is essential for the maintenance of myelin.
[show abstract][hide abstract] ABSTRACT: Levetiracetam (LEV) is known to inhibit convulsive seizures and is clinically used for treating both partial and generalized seizures. The study was performed to determine whether LEV possesses an inhibitory effect on absence seizures in a novel genetic animal model of absence epilepsy, Groggy (GRY) rats. Single injections of LEV at doses ranging from 20 to 160 mg/kg i.p. markedly inhibited absence seizures in GRY rats. The anti-absence action of LEV was potent and the cumulative duration of spike and wave discharges (SWD) in GRY rats was almost completely suppressed even at 20 mg/kg (i.p.). When the time-course of the inhibitory action of LEV (80 mg/kg i.p.) was examined up to 24 h after the treatment, the appearance of SWD was suppressed for over 6 h after injection of LEV in contrast to the action of sodium valproate (200 mg/kg i.p.) which had a very short effect (< 2 h). The maximum level of blood concentration of LEV was attained within 2 h after administration, and the drug disappeared from the blood in 24 h with T(¹/₂) of 2.7 h. These results revealed that LEV displays potent and relatively long-lasting inhibitory effects on absence seizures in GRY rats.
Brain research 11/2010; 1359:298-303. · 2.46 Impact Factor
[show abstract][hide abstract] ABSTRACT: Absence epilepsy is a common form of idiopathic generalized epilepsy whose etiology is poorly understood because of genetic and phenotypic heterogeneity. The inbred mouse strain C3H/He exhibits spontaneous absence seizures characterized by spike and wave discharges (SWD) on the electroencephalogram concomitant with behavioral arrest. Previous studies using the C3H/HeJ (HeJ) substrain identified a mutation in the Gria4 gene as a major susceptibility locus. In the present study, we found that two closely related substrains C3H/HeOuJ (OuJ) and C3H/HeSnJ, which have a similar SWD incidence as HeJ, do not contain the Gria4 mutation. Further analysis of backcross mice segregating OuJ and C57BL/6J alleles shows that, unlike the HeJ substrain, OuJ does not have a major locus for SWD but has suggestive loci at best that would explain only a fraction of the phenotypic variance. These results illustrate how the genetic etiology of a common neurological disorder can differ between substrains with similar phenotypes. We infer that all C3H strains are sensitized to SWD and that additional mutations affecting SWD arose or were fixed independently in the years since the substrains diverged.
Genes Brain and Behavior 01/2009; 8(3):283-9. · 3.60 Impact Factor
[show abstract][hide abstract] ABSTRACT: The groggy rat (strain name; GRY) exhibits ataxia, an unstable gait, and paroxysmal severe extension of the entire body. Adults show a reduction in size of the cerebellum and presynaptic and axon terminal abnormalities of Purkinje cells. These neurological abnormalities are inherited in an autosomal recessive manner, and the causative mutation has been named groggy (gry). In this study, we mapped gry on rat chromosome 19 and found a nonconservative missense (M251K) mutation in the alpha(1A) subunit of the P/Q-type voltage-gated Ca(2+) channel gene (Cacna1a) within the gry-critical region. This mutation was located at a highly conserved site close to the ion-selective pore and led to the shortening of the inactivation phase of the Ca(2+) channel current without a change of peak current density or current-voltage relationship in whole cell patch recordings of the recombinant Ca(2+) channel expressed in HEK cells. It has been well established that mice with a mutation at Cacna1a such as tottering and leaner show absence seizures. The Cacna1a-mutant GRY rat also exhibited absence-like seizures from 6 to 8 weeks of age, which were characterized by bilateral and synchronous 7-8 Hz spike-and-wave discharges concomitant with sudden immobility and staring, on cortical and hippocampal EEGs. The pharmacological profile of the seizures was similar to that of human absence epilepsy: the seizures were inhibited by ethosuximide and valproic acid but not phenytoin. Thus, the GRY rat with P/Q-type Ca(2+) channel disorders is a useful model for studying absence epilepsy and Cacna1a-related diseases.
Brain Research 03/2007; 1133(1):168-77. · 2.88 Impact Factor
[show abstract][hide abstract] ABSTRACT: The demyelination (dmy) rat is a unique mutant exhibiting severe myelin breakdown in the central nervous system (CNS). In this study, we conducted immunohistochemical and morphometrical investigations in the dmy rat. From around 6 weeks of age, the affected rats developed ataxia especially in the hindlimbs. Afterwards, ataxia worsened rapidly, resulting in complete paralysis of the hindlimbs and recumbency. Histopathology at 7 to 10 weeks of age revealed myelin destruction throughout the white matter of the CNS in the dmy rats. The most severely affected lesions were distributed in the corpus callosum, capsula interna, striatum, subcortical white matter, cerebellar peduncle, and ventral and lateral parts of the spinal cord. Immunohistochemistry demonstrated prominent astrogliosis and many ED-1 positive macrophages in the myelin-destructed areas. Until the 4th week, no significant differences in myelin thickness and fiber diameter were found between dmy and control rats. However, from 5 weeks of age, myelin thickness of residual myelinated fibers in dmy rats became significantly less than that in controls. These data indicated that the dmy phenotype shows a prolonged period of myelin destruction, suggesting that dmy mutation affects the adequate maintenance of myelin.
Brain Research 11/2004; 1022(1-2):110-6. · 2.88 Impact Factor
[show abstract][hide abstract] ABSTRACT: Rat myelin vacuolation mutation at the Attractin locus (Atrn(mv)) is a genomic deletion including the whole exon 1 of the Atrn gene. The precise size and location of the deleted region has not yet been identified because of poor information on genomic organization of the rat Atrn gene. Here, we identified the breakpoints of the Atrn(mv) mutation, using a draft sequence of the rat genome. In the Atrn(mv/mv) rat, a 6,914-bp genomic region was deleted. Primers flanked 5'- and 3'- breakpoints amplified the Atrn(mv) allele but not the wild-type allele. This primer set enables us to distinguish Atrn(mv/+) heterozygous rats from Atrn(+/+) rats, and will contribute to the efficient production of Atrn(mv/mv) rats.