Figure 6.

Naloxone increased f_I/f_E in an 11-day-old rat with intact vagi given fentanyl

A, intervals between successive EMG_ABD bursts (black circles), and between inspirations preceded (blue squares) or not preceded (red squares) by an EMG_ABD burst. A small dose of naloxone (0.03 mg kg⁻¹s.c.) was injected (arrow) and antagonized fentanyl-induced changes in breathing apparent after ∼300 s (double arrow). Note that naloxone had little effect on f_E, but increased f_I to the point where some inspirations (red squares) occurred in between E-bursts. B, quantal breathing after fentanyl but before naloxone. C, ∼300 s after injection of naloxone, ectopic inspiratory bursts were induced.