THE ROLE OF THE MEDULLARY RAPHE NUCLEI IN REGULATION OF CHOLINERGIC OUTFLOW TO THE AIRWAYS

In these studies we determined the role of the medullary midline nucle i on a cholinergic outflow to the airways by examining the response of tracheal tone and lung resistance to pharmacological stimulation. Stu dies were performed on alpha-chloralose-anesthesized, paralyzed and me chanically ventilated cats, and ferrets. L-glutamate microinjection in to the medullary midline. neurons significantly decreased tracheal ten sion, and reduced lung resistance. These effects were abolished by pri or topical application of methysergide, a broad spectrum serotonin rec eptor antagonist. Stimulation of the medullary raphe nuclei was also a ssociated with a significant increase in the phrenic nerve output, and a decrease in arterial blood pressure. The results indicate that the medullary midline neurons are involved in regulation of cholinergic ou tflow to the airways, and raise the possibility that alterations in th e serotonergic pathways may cause airway dysfunction. (C) 1998 Elsevie r Science B.V. All rights reserved.