CGRP increases neuronal excitability and induces direct membrane currents. A, B, Current-clamp recordings of action potentials (spikes) generated in an SG neuron by direct intracellular injections of depolarizing current pulses of increasing magnitude (0 to 250 pA; 500 ms) before (A) and during CGRP (10 nM, B). C, CGRP increased input-output function by significantly increasing spike frequency (n = 5 neurons; P < 0.05–0.01, two-way ANOVA followed by Bonferroni posttests). For the measurement of action potential firing in current-clamp, neurons were recorded at -60 mV. D, CGRP (10 nM) also decreased spike thresholds (membrane potentials at which action potential firing started) significantly (n = 5; P < 0.01, paired t-test). * P < 0.05, ** P < 0.01.