Figure 2.

T-current tunes the transfer function of TC neurons at depolarized membrane potentials. A, The rebound LTS evoked in a TC neuron following a hyperpolarizing current step (CTR) is blocked by TTA-P2 and restored by injection of g_T. B, Voltage traces of a TC neuron injected with a sequence of AMPA conductances (gAMPA) of different amplitudes in control condition (dark blue) and in the presence of TTA-P2. The neuron received the same fluctuating excitatory and inhibitory conductance noise in each condition and displayed a mean membrane potential of −58 mV. The smallest AMPA conductances failed to evoke a spike when the T-current was blocked (red) and the spike probability was restored upon artificial g_T injection (light blue). C, Transfer functions of the neuron presented in B show that the T-current block shifted the input–output curve toward larger AMPA conductances (same color code as in A and B). Recovery was obtained with injection of g_T. D, gAMPA_0.5 values were estimated in the same 12 neurons in control condition and in the presence of TTA-P2 (left graph; filled circles correspond to the neuron illustrated in B). E, Model TC neuron: the gAMPA_0.5 values decreased with increasing T-conductance amplitudes (g_T: left circles, 25, 50, 75, 100, 125 nS from top to bottom, no g_T: right circles).