Effect on airway caliber of stimulation of the hypothalamic locomotor region.

Airway dilation is one of the many autonomic responses to exercise. Two neural mechanisms are believed to evoke these responses: central command and the muscle reflex. Previously, we found that activation of central command, evoked by electrical and chemical stimulation of the mesencephalic locomotor region, constricted the airways rather than dilated them. In the present study we examined in decerebrate paralyzed cats the role played by the hypothalamic locomotor region, the activation of which also evokes central command, in causing the airway dilator response to exercise. We found that activation of the hypothalamic locomotor region by electrical and chemical stimuli evoked fictive locomotion and, for the most part, airway constriction. Fictive locomotion also occurred spontaneously, and this too, for the most part, was accompanied by airway constriction. We conclude that central command plays a minor role in the airway dilator response to exercise.