Opiate-induced depression of inspiratory rhythm. A, In a mPBC[500/−0.77] W-P2 slice, bath application of the μ-opiate receptor agonist DAMGO depressed frequency, but not amplitude of inspiratory VRC bursting. Rhythm recovered partially after 25 min of washout. B, In a mPBC[600/−0.80] W-P3 slice, DAMGO abolished rhythm, which was reactivated within 5 min of simultaneously washing out DAMGO while washing in (bath application) of the opiate receptor antagonist naloxone. C, D, Bar graphs show effects of DAMGO on frequency and the recovery of rhythm after washout of DAMGO alone (C) and in the presence of naloxone (D). The bars represent means ± SEM; values indicate the number of slices tested.