Examples of Na+ currents recorded in a cortical slice from a pyramidal neuron in layer V (A), and from a dissociated cortical pyramidal neuron, identified based on morphology (B). The inset contains I–V curves obtained from neurons in slices (mean values and s.d., n = 20, black plots) and from dissociated neurons (n = 8, red plots). These traces were recorded with internal solutions containing 13 mM Na+. The traces in (A) used TTX-subtraction to isolate sodium current. In (B), sodium current was isolated by leak-subtraction using the P/n protocol.