Effects of dopamine, isoproterenol, and lobeline on cranial and phrenic motoneurons.

Recent studies have suggested that the upper airway muscles receive a substantial portion of their excitatory input from the peripheral chemoreceptors. We examined the responses of the phrenic, hypoglossal, and recurrent laryngeal nerves to agents that are known to modify carotid body activity. Dopamine, an inhibitor, and isoproterenol and lobeline, two stimulators of carotid body activity, were administered into the lingual arteries of 14 anesthetized, paralyzed cats artificially ventilated with 100% O2. Dopamine decreased the activity of all three nerves (P less than 0.001) but inhibited the hypoglossal nerve more than the phrenic and recurrent laryngeal nerves (P less than 0.001). Isoproterenol and lobeline increased the activity of all three nerves (P less than 0.001) but stimulated the hypoglossal nerve more than the phrenic and recurrent laryngeal nerves (P less than 0.001). These relatively greater effects of all three agents on the hypoglossal nerve compared with the phrenic and the recurrent laryngeal nerves persisted under both hypoxic and hypercapnic conditions. After midcervical vagotomy, the responses of the hypoglossal to all three drugs remained larger than those of the phrenic nerve. After combined vagotomy and carotid sinus nerve section, the stimulatory effects of lobeline and the inhibitory effects of dopamine were no longer apparent. We conclude that it is possible to preferentially alter respiratory-related activity of the hypoglossal nerve compared with that of the phrenic nerve using agents that modify peripheral chemoreceptor activity.