Figure 2. Responses evoked by breathing 8% O₂ in 18N and 18CH rats.

Abbreviations as in Fig. 1. □ and ○ indicate 18N and 18CH rats, respectively; each value is shown as the mean ±s.e.m. Horizontal axes show time before and during the 5 min period of 8% O₂. †† Significant difference between 18N and 18CH for change evoked from baseline (P < 0·01). ***P < 0·001, **P < 0·01, significant difference between baseline values of 18N and 18CH rats. Note that 18N rats were switched from air to 8% O₂ for 5 min, while 18CH rats were switched from 12 to 8% O₂ for 5 min.