Fig. 8. Responses to opioid receptor agonists of inspiratory neuron after blockade of ongoing synaptic activity by tetrodotoxin (TTX). The application of 0.5 μm tetrodotoxin abolished C4 and inspiratory neuron discharges. Resting membrane potential shifted by −4 mV. After the application of 1 μm DAGO with 0.5 μm tetrodotoxin, membrane potential hyperpolarized farther by 6 mV, and input membrane resistance decreased 48% (315 to 164 MΩ) in a naloxone-reversible manner. (A ) Continuous recording of membrane potential with injecting hyperpolarizing current pulse (40 pA, 0.2 Hz, 500 ms). Current pulses with different intensity were injected into the neuron to examine current–voltage relation at the three time intervals denoted by bars above the neuron tracing. (B ) The injected hyperpolarizing and depolarizing current pulses and the generated electronic potentials. (C ) Reversal potential was −71 mV according to the current–voltage relation.