TTX sensitivity of sodium currents from neonatal and adult SDH neurons. A. Upper trace shows protocol (repeated 0.5 Hz) applied to neonatal and adult SDH neurons during bath application of 1 μM TTX. Bottom trace shows representative maximum sodium current recorded in an adult SDH neuron (black trace) before and after application of 1 μM TTX for 2 mins (grey trace). Both traces were recorded during the onset of the depolarising step (grey shading in top panel). B. Plots of peak normalized current versus time during application of 1 μM TTX. Sigmoid curves show the onset of TTX block was more rapid in neonates (* p < 0.05), however, the slope of the relationship was similar in neonatal and adult recordings.