Figure 7.
Minute ventilation and breathing frequency (means ± SD) in baseline condition and following fentanyl up to 60 mg/kg in control and in β-arr2-deficient mice. In this figure, data after fentanyl were averaged over a 15-min period without consideration for the animal conditions (locomotion or immobility). The periods of immobility in baseline condition are shown in each group (bars with hatch pattern). Note that 1) the effects of fentanyl on breathing control were similar in both groups, 2) minute ventilation and breathing frequency were more depressed when the animals were immobile in baseline conditions than after the lowest doses of fentanyl. At the highest dose (60 mg/kg), data in the surviving animals are shown. Baseline data used to evaluate the effects of 60 mg/kg were different from those used for the lowest dose (see methods). Despite the same level of minute ventilation in the surviving animals, only 60% of animals of β-arr2-deficient mice survived vs. 95% in the control group (see Fig. 10). *P < 0.05 when compared with baseline, $P < 0.05 when compared with the baseline periods of immobility (bars with hatch pattern). Arrb2tm1Rjl, Arrb2 knockout mice; β-arr2, β arrestin 2.