Effect of electrolytic lesions of the medullary inspiratory region in rats.

The medulla oblongatas of 48 anesthetized rats were explored by electrical stimulation. The pneumotachogram and in some, the arterial blood pressure as well, were recorded. The inspiratory area was located in the ventral reticular formation from the obex to 1.8 mm rostral to the obex. It occupied about 2.2 mm3 on each side of the midline. The expiratory reactive points were scattered in a region which was dorsal and caudal to the inspiratory area. Unilateral and midline lesions produced by 3, 5 and 8 ma direct current did not stop rhythmic respiration. There was an initial increase in the respiratory rate followed by diminution to below that of the prelesion time. The respiratory air flow was decreased. The changes in respiratory rate and air flow were not statistically significant in majority of the above groups. Bilateral lesions produced by 3 or 5 ma stopped breathing. Continuation of thythmic respiration after destruction of a number of inspiratory neurons and/or fibers in the midline or one side of the medulla indicates that all the inspiratory neurons and fibers are not essential for the maintenance of respiration. Cessation of thythmic respiration after destruction of all or most of inspiratory neurons on both sides of the midline indicates the essential role of the medulla-oblongata for genesis or maintenance of rhythmic respiration.