LOCALIZATION OF THE MEDULLARY RESPIRATORY CENTERS IN THE CAT

Abstract

In a study of the respiratory responses obtained from stimulation of the brain stem of the cat utilizing the Horsley-Clarke technique, the striking character and definite localization of 2 types of response were noted. One of these, a tonicly maintained deep inspiratory apnea which appeared to be in maximal inspiration, was localized to the ventral reticular formation of the medulla immediately overlying the cephalic, 4/5 of the inferior olive extending some 3 mm. to either side of the midline. It thus roughly extended from 2 mm. caudal to the acoustic tubercle to 1 mm. caudal to the obex. The other response which was a maintained expiratory apnea, in some instances in maximal expiration, was localized to the dorsal reticular formation of the medulla, dorsal to, slightly cephalic to, and cupped over the cephalic end of the inspiratory reticular formation. The following evidence was offered that these 2 localized reticular regions constituted the inspiratory and expiratory divisions of the respiratory center. The respiratory responses were well localized within the region which previous workers have vaguely defined as the respiratory center. Responses were coordinated respiratory acts involving both thorax and diaphragm, and were probably not due to stimulation of afferent or efferent fiber tracts but to stimulation of a neuron field closely interrelated synaptically. They were constant responses only quantitatively influenced by strength and frequency of stimulation; they were independent of the anesthetic used and might be obtained in unanesthetized animals with electrodes sealed in the skull. Inspiratory apnea might be maintained till death of the animal in from 3 to 6 mins. Coordinate respiration might be attained by rhythmic stimulation of these centers.