Evidence for a Medullary Inspiratory Pacemaker

Functional Concept of Central Regulation of Respiration

¹ From the Department of Pharmacology, University of Utah College of Medicine, Salt Lake City, Utah

Experiments on central respiratory regulation were performed with unanesthetized cats which were both decerebrated and decerebellated. Electrical stimulation of a circumscribed area in the floor of the fourth ventricle in the medullary preparation consistently produced an increase in the rate of gasping. In the decerebrate animal, stimulation of this area converted the respiration into a gasping form of breathing which varied in rate and amplitude according to changes in stimulus parameters. Electrical stimulation of the medial reticular formation in the medullary animal revealed a functional separation of gasping and sustained inspiratory responses. Cauterization of the medullary tegmentum in the decerebrate preparation produced gasping. In the medullary preparation it was necessary to destroy the dorsal half of the medulla in order to abolish gasping. Surface cauterization of the medullary tegmentum prevented the rate-stimulating effect of cyanide which is regularly evocable in the animal with intact medulla. Because of the increasing need for revised terminology in central respiratory physiology, a new set of terms, namely, oscillator, modulator, integrator, and pacemaker, was incorporated in a functional concept of the central control of respiration.