HYPOXIA, SLEEP AND RESPIRATION IN RELATION TO OPIOIDS IN DEVELOPING SWINE

To test the role of mu and delta opioid systems in neonates during hyp oxia, a total of sixteen, 4-11 (n = 7) and 26-33-day-old piglets (n = 9) were instrumented aseptically for assessment of sleep/wake states ( S/W), electromyographic activities of the diaphragm and posterior cric oarytenoid muscles (EMG(di), EMG(pca), respectively), heart rate, and arterial pressures, pH and gas tensions. During daily sessions for 5 c onsecutive days, the piglets inhaled 10% O2/90% N2 for 10 min twice pe r session, first before any drug, then after either naltrexone (2 mg.k g-1 i.v.), a predominantly mu opioid antagonist, or naltrindole (4 mg. kg-1 i.v.), a specific delta opioid antagonist. During hypoxia, young, in contrast to older piglets, spent more time asleep, and increased s leep during the second half of the hypoxic exposure before, but not af ter each antagonist. They also exhibited, overall, higher breathing fr equency, and lower slope, amplitude, area and initial area of EMG(di) and EMG(pca) activity than older piglets. Naltrindole stimulated EMG(p ca) activity in both age groups, and naltrexone increased the breathin g frequency and slope of EMG(di) in the older group. We conclude that hypoxia enhances the activation of central mu and delta opioid systems which influence S/W and respiration.