Figure 4.

Blockade of distal but not proximal sodium channels disrupts rate enhancement. A, Dendritic voltage records generated by combined somatic and dendritic excitation (top trace; 500 μm from the soma) under control and after local dendritic application of TTX (1 μm). The occurrences of axonal action potentials (APs) are shown as vertical lines. Note that TTX attenuated dendritic electrogenesis and reduced action potential burst firing. B, Summary data showing the action potential firing rate evoked by concerted somatic and apical dendritic excitation under control and after local application of TTX. Note that local application of TTX at proximal dendritic sites (open symbols) failed to alter the action potential firing rate. The line has a slope of 1. C, Pooled data showing the amplitude of the first backpropagating action potential evoked by somatic excitation under control and after local application of TTX. The line has a slope of 1. The inset shows the simultaneous recording of an action potential at the soma and a proximal dendritic site (380 μm from the soma) under control and after local dendritic application of TTX. D, Cumulative probability distribution of action potential instantaneous (Inst.) firing frequency generated by proximal (pooled data from n = 8 neurons) or distal (n = 6 neurons) excitation. Note that local application of TTX at distal dendritic sites dramatically decreased the proportion of action potentials generated at high frequency. Dend, Dendritic.