Figure 1.

Depression of respiration by oxycodone and morphine. Oxycodone (1 and 3 mg·kg⁻¹, i.p.) and morphine (1–10 mg·kg⁻¹, i.p.) dose‐dependently depressed mouse respiration. Saline did not depress respiration. In (A) and (C), data are presented as minute volume whereas in (B) and (D), the level of respiratory depression seen following drug injection is expressed as a percentage change in the pre‐drug minute volume baseline, calculated for each mouse individually before mean data were plotted. In (E) and (F), the effect of oxycodone on respiratory rate and tidal volume is shown. Data are from the same groups of mice as in (A) and (B). In (G), the data in (B) and (D) have been recalculated and plotted as the AUC. The AUC for the percentage change in minute volume has been calculated for each individual animal before the mean AUC has been calculated. The data were analysed using one‐way ANOVA with Bonferroni's comparison (P < 0.05, n = 6 for all groups). In (A–G), data are expressed as mean ± SEM. In (H), raw respiration traces recorded from a single mouse before and after administration of oxycodone (3 mg·kg⁻¹, i.p.) are shown. The thin horizontal line indicates the point of pressure inflexion. On the respiration traces, inspiration is downwards. *P < 0.05; ns, non significant; n = 6 for all groups.