Figure 1.

Transition from control to quantal pattern of breathing in an 11-day-old vagotomized rat after fentanyl

Top three traces, recordings of tidal volume (V_T), genioglossus muscle electromyographic (EMG_GG) and abdominal muscle electromyographic (EMG_ABD) activity. Bottom, timing bars indicating occurrence of inspiratory airflow (inspiration) and expiratory motor activity (EMG_ABD). A, control recording had all normal (I-E) cycles (i.e. cycles with inspiration and expiration). B, onset of quantal breathing as an occasional sequence of inspiration–expiration–expiration, i.e. E-only cycle (cycle without inspiration), is observed at 9 min after an initial dose of fentanyl (20 μg kg⁻¹s.c.). C, at 4 min after a supplemental dose of fentanyl (10 μg kg⁻¹), there are more E-only cycles. Note split EMG_ABD bursts in I-E cycles, and single EMG_ABD burst in E-only cycles.