Can GABAA conductances explain the fast oscillation frequency of absence seizures in rodents ?

Rodent models of absence epilepsy generate spike-and-wave oscillations at relatively fast frequency (5±10 Hz) compared with humans (» 3 Hz). Possible mechanisms for these oscillations were investigated by computational models that included the complex intrinsic ®ring properties of thalamic and cortical neurons, as well as the multiple types of synaptic receptors mediating their interactions. The model indicates that oscillations with spike-and-wave ®eld potentials can be generated by thalamocortical circuits. The frequency of these oscillations critically depended on GABAergic conductances in thalamic relay cells, ranging from 2±4 Hz for strong GABAB conductances to 5±10 Hz when GABAA conductances were dominant. This model therefore suggests that thalamocortical circuits can generate two types of spike-and-wave oscillations, whose frequency is determined by the receptor type mediating inhibition in thalamic relay cells. Experiments are proposed to test this mechanism.