Fig. 4.

Protection against the ventilatory-depressant effects of 0.178 mg/kg fentanyl by MCAM (left) and naloxone (right). The preceding day, rats received 0.178 mg/kg fentanyl intravenously followed by intravenous MCAM or naloxone. On the (next) test day shown in this figure, rats received an intravenous infusion of fentanyl at minute “0” and an infusion of vehicle intravenously at “5” minutes. The gray bar represents the 95% CI for minute volume under control conditions (saline followed by vehicle). Insets represent the area under the curve (AUC) for MCAM or naloxone curves compared with vehicle curves. Asterisks indicate that AUC obtained after the administration of an antagonist was significantly different from AUC after vehicle, P < 0.05. Ordinates: minute volume plotted as percent of control and averaged among eight rats ± 1 S.E.M. Abscissae: time in minutes. CI, confidence interval.