Low-voltage-activated calcium channel subunit expression in a genetic model of absence epilepsy in the rat

The Genetic Absence Epilepsy Rats from Strasbourg (GAERS) are an inbred strain of rats that display many of the characteristics of human absence epilepsy. In these rats, reciprocal thalamocortical projections play a critical role in the generation of spike-and-wave discharges that characterize absence seizures. When compared to those of the non-epileptic control strain, juvenile animals of the GAERS strain reportedly possess higher-amplitude T-type calcium currents in neurons of the thalamic reticular nucleus (nRt). We hypothesized that differences in calcium currents seen between GAERS and controls result from differences in expression of genes for low-voltage-activated calcium channels. Quantitative in situ hybridization was used to compare expression of α1G, α1H, α1I, and α1E calcium channel subunit mRNAs from adult and juvenile animals of the two strains. We found higher levels of α1H mRNA expression in nRt neurons of juvenile animals (34.9±2.3 vs. 28.4±1.8 grains/10 3 pixels, p