STIMULATION OF THE NUCLEUS RAPHE OBSCURUS PRODUCES MARKED SEROTONIN RELEASE INTO THE DORSAL MEDULLA OF FED BUT NOT FASTED RATS - GLUTAMATERGIC DEPENDENCE

Serotonin interacts with TRH at the dorsal vagal complex (DVC) to augm ent gastric functional parameters. To ascertain physiologic relevance, patterns of stimulated release at the terminal field were characteriz ed. Stimulation of the nucleus raphe obscurus (nRO) by kainic acid (42 3 pmol/10 nl) produced marked release of serotonin into dorsal medulla ry dialysates containing the DVC in freely fed, but not 24-h fasted ra ts. Probe infusion of kynurenic acid (1 mM), but not acute bilateral c ervical vagotomy attenuated nRO-stimulated serotonin release in fed an imals. The results suggest that the fed state facilitates serotonin re lease into the dorsal medulla by a mechanism mediated by activation of excitatory amino acid receptors in the dorsal medulla. Enhanced serot onergic neurotransmission at the DVC may comprise a heretofore unrecog nized component of the integrated vago-vagal response to a meal.