[Influence of electric stimulation of the medulla oblongata on the smooth muscle tone of the airway in cats].

Changes in the tracheal smooth muscle tone have been studied in 30 cats anaesthetized with a chloralose-urethane mixture and paralyzed with succinyl choline bromide during electrical stimulation of the medulla oblongata. Constrictor responses were evoked from the regions including the caudal portion of the dorsal motor nucleus of the vagus, nucleus ambiguous and neighbouring structures of the reticular formation. Dilatory responses of the tracheal smooth muscle were observed during stimulation of the reticular formation at the level from 1 mm caudally to 6 mm rostrally of the obex. It is supposed that structures responsible for contractile responses are vagal preganglionic neurons, located in the dorsal motor nucleus of the vagus, in the nucleus ambiguous and in neighbouring regions and axons of these cells, looping through the medial part of the medulla. It is also supposed that dilatory responses are associated with excitation of sympathotonic reticular neurons, inhibitory neurons activated by the input from pulmonary stretch receptors and, possibly, vagal efferent neurons belonging to the nonadrenergic nervous system of the bronchi.