Fig. 5. The effect of approximately 1.25 mm (3.57 minimum alveolar concentration [MAC]) sevoflurane on the activities of inspiratory (Insp; A ), preinspiratory (Pre-I; B ), expiratory (Exp; C ), and phrenic motor neurons (Phr; D ). Simultaneous recordings of the integrated C4 activity (∫C4) are also provided. After the control recording, the control artificial cerebrospinal fluid was changed to artificial cerebrospinal fluid containing approximately 1.25 mm (3.57 MAC) sevoflurane for approximately 3–6 min, followed by a 10- to 20-min washout period using control artificial cerebrospinal fluid. In inspiratory neurons, sevoflurane did not affect the intraburst firing frequency or the resting membrane potential. The depolarizing cycle rate reduced by sevoflurane was synchronized with C4 burst rate. In preinspiratory and expiratory neurons, sevoflurane induced a decrease in the intraburst firing frequencies but did not affect the resting membrane potentials. In preinspiratory neurons, the depolarization of both preinspiratory and postinspiratory phases became smaller and seemed to be phase locked during superfusion of sevoflurane, although C4 burst was maintained. In phrenic motor neurons, sevoflurane induced hyperpolarization of the resting membrane potential and decreased the intraburst firing frequency.