RESPIRATORY RESPONSES TO STIMULATION OF SPINAL OR MEDULLARY LOCOMOTORSTRUCTURES IN DECEREBRATE CATS

Respiratory and locomotor EMG activity was recorded in cats after a pr ecollicular post-mamillary decerebration. Locomotion was induced by st imulating either the dorsolateral funiculus (DLF) in the cervical spin al cord or the medullary locomotor strip (MLS). At the onset of locomo tion, both ventilation and blood pressure were enhanced. During locomo tion, the activity of external intercostal muscles decreased but that of the internal intercostal muscles increased. The respiratory pattern changed with the onset of stimulation. The locomotor movements were e voked after a delay. The inspiratory-inhibitory Hering-Breuer reflex w as attenuated. Stimulation of the MLS and DLF evoked similar respirato ry and circulatory effects. Our data resemble the effects observed dur ing stimulation of the subthalamic or mesencephalic locomotor regions. We conclude that respiratory changes are part of an integrated respon se involved in the onset of exercise and are independent of the neuron al site where stimulation evoked locomotion. In contrast to previous r eports, we suggest that the pattern of interaction among respiratory, circulatory, and locomotor systems does not have to be the specialty o f supramedullary structures. Coupling between locomotion and breathing during the post-inspiratory phase suggests that this interaction occu rs at the medullary level.