Ingestion of a meal results in gastrointestinal hyperaemia and is associated with the systemic and paracrine release of a number of peptide hormones, including cholecystokinin (CCK), and 5-hydroxytryptamine (5-HT). Systemic administration of CCK-octapeptide inhibits a subset of presympathetic neurons of the rostroventrolateral medulla (RVLM) that may be responsible for driving the sympathetic vasomotor tone to the gastrointestinal viscera. The aim of this study was to determine whether endogenous release of CCK and/or 5-HT also inhibits CCK-sensitive RVLM neurons. The effects of intraduodenal administration of secretagogues sodium oleate (SO)/soybean trypsin inhibitor (SBTI) on circulating levels of CCK and 5-HT were examined. In separate experiments, the discharge rates of barosensitive, medullospinal, CCK-sensitive RVLM presympathetic vasomotor neurons were recorded following rapid intraduodenal infusion of SO/SBTI or water. Alternatively, animals were pre-treated with CCK₁ receptor antagonists devazepide or lorglumide or the 5-HT₃ antagonist MDL-72222, before SO/SBTI administration. Secretagogue infusion significantly increased the level of circulating CCK, but not 5-HT. SO/SBTI produced a significant decrease (58%) in the neuronal firing rate of CCK-sensitive RVLM neurons when compared to water (5%). CCK₁ receptor antagonists did not reverse SO/SBTI-induced neuronal inhibition (58%) whereas the 5-HT₃ antagonist significantly attenuated the effect (22%). This study demonstrates a functional relationship between a subset of RVLM presympathetic vasomotor neurons and meal-related signals arising from the gastrointestinal tract. It is likely that endogenously-released 5-HT acts in a paracrine fashion on gastrointestinal 5-HT₃ receptors to initiate the reflex inhibition of these neurons, resulting in gastrointestinal vasodilatation by withdrawal of sympathetic tone.