Effects of naloxone on the hering-breuer apnea in sleeping kittens

The modulatory role of endogenous opiates on the Hering -Breuer inflation reflex was examined in 11 newborn kittens, aged 10-31 days, during active and quite sleep. The Hering -Breuer apnea duration was significantly shortened by naloxone (1 mg/kg, intraperitoneally; P less than 0.05). This effect was abolished by 100% O2 breathing. The duration of apnea, and its shortening by naloxone, did not differ significantly in the two sleep states. Hering -Breuer apnea is a result of the inspiratory inhibition and expiratory excitation of medullary neurons in response to lung stretch; the apnea is terminated by the opposing influences of chemoreceptors, which respond to hypercapnia and hypoxia. The results suggest that opioid influences on the Hering -Breuer reflex are due to an opioid modulation of the carotid body discharge in hypoxia, or of its central integration, and that sleep state is not implicated in such modulation in kittens.