CEREBELLAR CONTROL OF EXPIRATORY ACTIVITIES OF MEDULLARY NEURONS AND SPINAL NERVES

Expiratory-related activities of spinal nerves are augmented after sti mulation of the infracerebellar nucleus of the cerebellum. These stimu lations alter neither inspiratory spinal neural activities nor inspira tory and expiratory laryngeal neural activities. It was hypothesized t hat efferents from the infracerebellar nucleus impinge on spinal moton eurons by a pathway that bypasses the medulla. In decerebrate, paralyz ed, and vagotomized cats, phrenic and expiratory triangularis sterni a ctivities and activities of medullary respiratory neurons were recorde d. During infracerebellar stimulation, activities increased for expira tory bulbospinal neurons and neurons with tonic discharge patterns. Af ter unilateral ablation of the infracerebellar nucleus by kainic acid, triangularis sterni discharge was eliminated and activities of expira tory bulbospinal neurons continued at reduced frequencies. Stimulation s of the anterior interposed nucleus caused both inspiratory and expir atory activities to increase, whereas no systematic changes followed s timulations of the vermis. Results establish that at least a portion o f the changes in expiratory activities of spinal motoneurons after per turbations of the infracerebellar nucleus occurs secondarily to change s in activities of medullary neurons. The possibility of separate cere bellar projections to medullary and spinal neurons is discussed.