Figure 1.

Number of animals used in each experimental condition. Two different protocols were used: in a first series of tests (protocol 1), a 2-h recording was performed in baseline condition at D0 and data were analyzed for the last hour of recording (see methods for more details). The effects five different dose from 0.1 mg/kg ip to 5 mg/kg ip were investigated on two different days, at D1 and D15–D20. Data were analyzed over the last 15 min after the administration of each dose of fentanyl as well in baseline. Breath-by-breath data were averaged every 5 s, the means and standard deviation data were computed over 15 min, the date presented here consists therefore in 180 data points for each dose. Protocol 2 was performed in two different groups of mice. Ventilation was averaged over the last hour of recording (720 data points).