FCAP shortens the protraction duration of CBI-2-elicited motor programs in a concentration-dependent manner partly through its actions on interneuron B20. (a1–4), FCAP shortens protraction duration of CBI-2-elicited programs, representative examples; a single cycle of a motor program was elicited by stimulating CBI-2 at 10 Hz until the end of the protraction phase, detected by the onset of the sharp synaptic inhibition of CPG neuron B34 and the abrupt ending of I2 nerve activity. Protraction phase (open bar) is defined by the activity in the I2 nerve. Retraction phase (filled bar) is defined by a period of hyperpolarization of B34 after the protraction phase is terminated. Upon wash, protraction duration returns to its control value. (a5), group data on protraction duration. In contrast, FCAP has no significant effect on the duration of retraction (a6). (b), FCAP increases B20 excitability in a concentration-dependent manner. (b1), a representative example, (b2), group data. Recordings in (a) were made in ASW, whereas recordings in (b) were made in high divalent saline. *, p < 0.05; **, p < 0.01; ***, p < 0.001 (Bonferroni post hoc tests). Error bars, S.E.