Fig. 6. CX717 counters fentanyl-induced depression of respiratory frequency and amplitude generated by perfused heart  in situ preparations. (  A ) Recording of raw and integrated phrenic nerve discharge in a postnatal day (P)23 rat. (  B ) Population data (n = 5) showing the relative effects (compared with control) of fentanyl and CX717 (in the continued presence of fentanyl) on amplitude and frequency of integrated phrenic nerve discharge. Control values normalized to one.  Open bars = frequency;  solid bars = amplitude. *  P < 0.05, significant difference.