Participation of pontine structures in the respiratory action of opioids.

The respiratory action of morphine, D-Ala2-D-Leu5-enkephalin, and D-Ala2-Me-Phe4-Met(O)ol5-enkephalin, restrictively applied to the dorso-rostral surface of the pons, was studied in anesthetized cats. Frequency was selectively and dose-dependently depressed, down to apnea, whereas tidal volume and its response to CO2 either remained unchanged or were increased. Similar effects were observed in vagotomized and decerebrate cats. From these and previous (1) results, it can be concluded that the medullary and pontine structures related to respiration are differentially affected by opioids. Pontine nuclei are more sensitive to opioid depression and account for changes in frequency, whereas medullary depression results in reduction of tidal volume and CO2 sensitivity.