Role of caudal ventrolateral medulla in reflex and central control of airway caliber

We investigated the role played by the caudal ventrolateral (CVL) medulla in the reflex and central neural control of airway caliber in chloralose- anesthetized dogs. Changes in total lung resistance were evoked by four different stimuli. These changes were compared before and after bilateral injection of either ibotenic acid (75 nl; 100 mM) or cobalt chloride (75 nl; 50 mM) into the CVL medulla. The four stimuli used to change lung resistance were static muscular contraction, electrical stimulation of thin fiber afferents in the sciatic nerve, electrical stimulation of the posterior diencephalon, and hypoxia. The first three stimuli have been shown to decrease total lung resistance, whereas the latter stimulus has been shown to increase resistance. We found that injection of both ibotenic acid, which destroys cell bodies but not fibers of passage, and cobalt, which prevents synaptic transmission, either abolished or greatly attenuated the decrease in total lung resistance evoked by static contraction, by sciatic nerve stimulation, and by posterior diencephalic stimulation. We also found that injection of ibotenic acid and cobalt attenuated the reflex increase in lung resistance evoked by hypoxia. In control experiments, we found that bilateral injection of ibotenic acid into the dorsal medulla had no effect on the changes in total lung resistance evoked by these four stimuli. We conclude that the CVL medulla plays an important role in the reflex and central control of airway caliber.