N-METHYL-D-ASPARTATE RECEPTORS ARE EXPRESSED BY INTRINSIC NEURONS OF RAT LARYNX AND ESOPHAGUS

Overactivation of N-methyl-D-aspartate receptors (NMDAR), a mechanism of central neurotoxicity, has recently been shown to increase airway r esponsiveness in rat lungs. NMDAR have not been localized in the airwa ys, but neurons of the myenteric plexus in the rat express mRNA for NM DAR. Furthermore, a population of glutamate-containing cell bodies in the nucleus ambiguus projects to the rat larynx. On this basis, we hyp othesized that some postganglionic parasympathetic neurons of the lary nx, trachea and esophagus may express NMDAR. Sections of rat larynx, t rachea and esophagus were immunocytochemically labeled for NMDAR subty pe 2B using a specific antibody. NMDAR immunoreactivity was observed i n cell bodies of individual neurons located in the submucosa and on th e external surface of skeletal muscle in the larynx and also in neuron s of the esophageal plexus. AII NMDAR-positive nerve cell bodies also contained immunoreactivity for vasoactive intestinal peptide (VIP) and some were immunoreactive for nitric oxide synthase (NOS). None of the cell bodies of the tracheal plexus contained NMDAR immunoreactivity. The findings demonstrate that NMDAR are expressed in neurons of the ra t larynx and esophagus and their activation may be associate with VIP or NO release. (C) 1998 Published by Elsevier Science Ireland Ltd.