VAGAL AFFERENT TRANSMISSION IN THE NTS MEDIATING REFLEX RESPONSES OF THE RAT ESOPHAGUS

In urethan-anesthetized rats, esophageal distension evoked volume-depe ndent reflex contractions with phase-locked multiunit discharges in th e central subnucleus of the solitary tract complex (NTSC) and the nucl eus ambiguus. During blockade of solitarial, but not peripheral, musca rinic cholinoceptors, the volume-response relationship of reflex contr actions was shifted rightward with a depression in pressure wave ampli tude. Concurrently, premotor NTSC responses were attenuated and nucleu s ambiguus activity was abolished during esophagomotor inhibition. Bot h NTSC discharges and reflex responses were eliminated, or strongly in hibited, during blockade of excitatory amino acid receptors (EAARs) wi th 6-cyano-7-nitroquinoxaline-2,3-dione, gamma-glutamylglycine or 2-am ino-7-phosphonoheptanoate. In brain stem slice preparations, whole cel l recordings in the NTSC region revealed fast excitatory postsynaptic potentials (EPSPs) with spikes in response to electrical stimulation o f the solitary tract. Although spiking was facilitated by muscarine, E PSPs were resistant to cholinoceptor antagonists but sensitive to EAAR blockers. We conclude that esophageal vagal afferents excite ipsilate ral NTSC interneurons via activation of glutamate receptors of the -al pha-amino-3-hydroxy-5-methylisoxazole-propionic acid and N-methyl-D-as partate subtypes. Cholinergic input to the NTSC probably derives from propriobulbar sources and serves to modulate the responsiveness of ref lex interneurons.