THE ROLE OF EXCITATORY AMINO-ACIDS IN AIRWAY REFLEX RESPONSES IN ANESTHETIZED DOGS

In these studies we examined the role of excitatory amino acids (EAAs) neurotransmission in communicating sensory inputs to the airway-relat ed vagal preganglionic neurons, by examining the effects of either NMD A or AMPA/kainate receptor blockade on reflex and chemical responses o f tracheal smooth muscle. Experiments were performed in chloralose ane sthetized, paralyzed and mechanically ventilated beagle dogs (n = 18), under hyperoxic, normocapnic, and normohydric conditions. Topical app lication or microinjection of NMDA receptor blockers, into the region of the ventrolateral medulla where airway-related vagal preganglionic neurons are located, insignificantly decreased the reflex changes in t racheal tone. However, topical application or microinjection of AMPA/k ainate subtype of glutamate receptor selective antagonists markedly re duced reflex increase in tracheal tone induced by (1) lung deflation, (2) stimulation of laryngeal cold receptors, and (3) activation of per ipheral or central chemoreceptors. These effects were potentiated by p rior NMDA receptor blockade. Findings indicate that an increase in cen tral cholinergic outflow to the airways by a variety of excitatory aff erent inputs is mediated via activation of EAA receptors, mainly AMPA/ kainate subtype of glutamate receptors. (C) 1997 Elsevier Science B.V.