Systemic administration of cholecystokinin (CCK) inhibits a sub-population of RVLM presympathetic vasomotor neurons. This study was designed to determine whether this effect involved sub-diaphragmatic vagal afferents and/or central N-methyl-D-aspartic acid (NMDA) receptors. Recordings were made from CCK-sensitive RVLM presympathetic vasomotor neurons in halothane-anesthetized, paralysed male Sprague-Dawley rats. The responses of the neurons to CCK (2 and 4 µg/kg, i.v), phenylephrine (PE; 5 µg/kg, i.v.) and phenylbiguanide (PBG; 5 µg/kg, i.v.) were tested before and after application of the local anesthetic lidocaine (2% w/v gel; 1 ml) to the sub-diaphragmatic vagi at the level of the oesophagus. In 7 separate experiments, lidocaine markedly reduced the inhibitory effects of CCK on RVLM presympathetic neuronal discharge rate. In other experiments, the effect of systemic administration of dizocilpine (MK-801; 1 mg/kg, i.v.), a non-competitive antagonist at N-methyl-D-aspartate (NMDA) receptor ion channels, on the RVLM presympathetic neuronal responses to CCK, PBG and PE was tested. In all cases (n = 6 neurons in 6 individual rats), dizocilpine inhibited the effects of CCK, PBG and PE on RVLM presympathetic neuronal discharge. These results suggest that the effects of systemic CCK on the discharge of RVLM presympathetic neurons is mediated via an action on receptors located on sub-diaphragmatic vagal afferents. Furthermore, the data suggest that the CCK activates a central pathway involving NMDA receptors to produce inhibition of RVLM presympathetic neuronal discharge.