A POTASSIUM CURRENT CONTROLS BURST TERMINATION IN RAT NEOCORTICAL NEURONS AFTER GABA WITHDRAWAL

Bursting activities were investigated under conditions of reduced outward K+ currents in neocortical slices obtained from rats presenting the gamma-aminobutyric acid (GABA)-withdrawal syndrome (GWS), a focal epilepsy consecutive to the interruption of a chronic intracortical GABA infusion into the somatomotor cortex. These bursts were induced by intracellular depolarizing current injection and/or by white matter stimulation. Tetraethyiammonium (TEA) at doses which did not change input resistance, spike duration or first interspike time interval abolished the burst terminating process and induced plateau-like potentials (up to 500 ms) which were tetrodotoxin-resistant and blocked by Ca2+ antagonists Cd2+ and Co2+. Therefore, it appears that bursts during GWS are generated by Ca2+-dependent plateau potentials which are terminated by a K+ current highly sensitive to TEA.