The excitatory amino acid glutamate mediates reflexly increased tracheal blood flow and airway submucosal gland secretion

In six decerebrated and in eight alpha -chloralose anesthetized, paralyzed and mechanically ventilated beagle dogs, we have studied involvement of glu tamate and glutamate receptors in transmission of excitatory inputs from th e airway sensory receptors to the nucleus tractus solitarius and from this site to airway-related vagal preganglionic cells that regulate the tracheal circulation and the submucosal gland secretion. Stimulation of airway sens ory fibers by lung deflation-induced reflex increase in tracheal blood flow and submucosal gland secretion. These responses were diminished by prior a dministration of AMPA/kainate receptor antagonist CNQX into the fourth vent ricle (n=6). Furthermore, topical application or microinjection of AMPA/kai nate receptor blockers, into the region of the ventrolateral medulla, where airway-related vagal preganglionic neurons are located, abolished the refl ex changes in tracheal submucosal gland secretion (n=8); in these dogs muco sal blood flow was not measured). These findings indicate that reflex incre ase in tracheal blood flow and submucosal gland secretions are mediated mai nly via release of glutamate and activation of the AMPA/kainate subtype of glutamate receptors. (C) 2000 Elsevier Science B.V. All rights reserved.