Respiratory responses to stimulation of spinal or medullary locomotor structures in decerebrate cats

Respiratory and locomotor EMG activity was recorded in cats after a precollicular post-mamillary decerebration. Locomotion was induced by stimulating either the dorsolateral funiculus (DLF) in the cervical spinal cord or the medullary locomotor strip (MLS). At the onset of locomotion, both ventilation and blood pressure were enhanced. During locomotion, 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 evoked after a delay. The inspiratory-inhibitory Hering-Breuer reflex was attenuated. Stimulation of the MLS and DLF evoked similar respiratory and circulatory effects. Our data resemble the effects observed during stimulation of the subthalamic or mesencephalic locomotor regions. We conclude that respiratory changes are part of an integrated response involved in the onset of exercise and are independent of the neuronal site where stimulation evoked locomotion. In contrast to previous reports, we suggest that the pattern of interaction among respiratory, circulatory, and locomotor systems does not have to be the specialty of supramedullary structures. Coupling between locomotion and breathing during the post-inspiratory phase suggests that this interaction occurs at the medullary level.