**4.3 T-type Cav**

T-type channels, widely distributed in the thalamus, are important for the repetitive firing of APs in rhythmically firing cells, which could be activated and inactivated more rapidly at more negative membrane potentials than other VGCCs [90]. Three subtypes of T-type channels have been identified, designated as Cav3.1, Cav3.2, and Cav3.3; they correspond to complexes containing the pore-forming α1 subunits, α1G, α1H, and α1I, respectively [91]. It has long been suggested that generalized absence seizures are accompanied by hyperexcitable oscillatory activities in the thalamocortical network [92]. The evidence that succinimide and related anticonvulsants could block thalamic T-type channels make researchers speculate that T-type Ca2+ channels might be related to the pathogenesis of spike-and-wave discharges (SWDs) in generalized absence seizures [93]. In the kainate epilepsy model, Cav3.1<sup>−</sup>/<sup>−</sup> mice display significantly reduced duration of seizures compared to wild type, but the frequency of seizures increased slightly [94]. In the WAG/Rij model, the expression of Cav3.1 may be related to age, and blocking Cav3.1 can reduce the onset of epilepsy [94, 95] which suggested that decrease in Cav3.1 channel expression and Ca2+ current component that they carry in thalamocortical relay neurons serves as a protective measure against early onset of SWD and absence seizures [96]. Notably, Cav3.1<sup>−</sup>/<sup>−</sup> mice are resistant to SWD seizures specifically induced by γ-GABABR agonists. Simultaneously, the γ-GABABR agonists induced only very weak and intermittent SWDs in Cav3.1<sup>−</sup>/<sup>−</sup> mice [97]. Cav3.2 single nucleotide mutation has been reported in patients with childhood absence epilepsy and other types of idiopathic generalized epilepsies [98, 99]. Gain-of-function mutations (C456S) in Cav3.2 channels increase seizure susceptibility by directly altering neuronal electrical properties and indirectly by changing gene expression [100].
