MU-OPIOID VS DELTA-OPIOID INFLUENCE ON RESPIRATORY AND SLEEP BEHAVIORDURING DEVELOPMENT

The role of mu- vs. delta-opioid receptors in modulating cardiorespira tory and sleep/wake behavior was studied in sixteen 4- to 11-, and 26- to 33-day-old chronically instrumented piglets. Each underwent 1.5-h recordings of sleep/wake state, diaphragmatic and posterior cricoaryte noid electromyogram (EMGdi, EMGpca), heart rate, and arterial pressure , pH, and gas tensions, before and after either naltrexone (2 mg/kg iv ), a predominantly mu antagonist, or naltrindole (4 mg/kg iv), a speci fic delta antagonist. In younger piglets, 1) naltrindole, but not nalt rexone, decreased percent of time spent in active and quiet sleep and increased that in wakefulness, and 2) naltrexone, but not naltrindole, increased respiratory frequency, decreased the duration of EMGdi and EMGpca activity, and increased initial summed EMGdi activity, all inde pendently of state. Older piglets exhibited 1) increased arousal with both drugs and 2) weaker stimulation of respiratory timing and no stim ulation of EMGdi or EMGpca with naltrexone and enhanced EMGpca activit y with naltrindole during transitional sleep only. Thus, in early neon atal life, delta-opioid systems modulate sleep/wake behavior, whereas mu systems modulate respiration. With age, these influences change and become less specific.