Transient potassium current shapes the firing profile. A: Modulation of the firing profile following the application of 4-AP, a blocker of transient K+ currents (IA), in three different lamina II neurons. B: Firing profile changes exhibited by a phasic neuron (left panels, standard protocol) submitted to conditioning hyperpolarizing (middle panels) or depolarizing prepulse (right panels) aimed at maximizing or minimizing IA current, respectively. In these three conditions, the effect of TGOT application (bottom traces) is compared to the control situation (upper trace). Black arrowheads indicate the accommodation in spike frequency. White arrowheads show the delay time before obtaining the first action potential. C: Effect of 4-AP on a neuron exhibiting a delayed firing profile after a conditioning hyperpolarizing prepulse producing a large IA current. Dashed lines represent -60 mV.