Localization of Spontaneous Respiratory Neuronal Activities in the Medulla Oblongata of the Cat: A New Location of the Expiratory Center

Abstract

Medulla oblongata of 80 vagotomized cats was explored with microelectrodes. Spontaneous respiratory neuronal activities and chest movements were recorded simultaneously with a twin beam cathode ray oscilloscope. It was found that inspiratory discharges are concentrated in the reticular formation between 3 mm rostral and 1 mm caudal to the level of the obex, which corresponds approximately to the inspiratory region of Pitts, Magoun and Ranson. On the other hand, expiratory discharges are not obtained in Pitts' expiratory area, but are found in a circumscribed region in the reticular formation from the level of the obex to 3 mm caudally. Electric stimulation of this region has been found recently by Ngai and Wang to yield marked expiratory spasm. It is concluded that the expiratory center is located caudally to the inspiratory center in the cat. The spontaneous respiratory neuronal discharges continue with no alterations of pattern of firing during drug-induced respiratory paralysis, and are increased both in number and in frequency during CO₂ inhalation. Stimulation of the vagus nerve with 50 shocks/sec. reduces inspiratory discharges and prolongs the duration of expiratory discharges.