Methods: Salivary flow was recorded in humans (n=8) using Lashley cups and cannulae connected to an instantaneous flow meter. Gustatory stimuli were achieved using MSG (0.01 and 0.03M), sucrose (0.1 and 0.5M) and NaCl (0.1 and 0.3M) alone and as mixtures of MSG-sucrose and MSG-NaCl. The mixtures contained the same molar concentrations as those presented singularly. Stimuli were applied for 30s, and repeated following washout and when flows had returned to resting levels. Stimuli were presented as groups of singular solutions of NaCl or sucrose, then singular solutions of MSG, followed by the mixtures. Each group of stimuli was repeated twice and randomly given within the group.
Results: Assuming an additive response, the salivary flows to the single stimuli were added together to give a calculated flow for the mixture. The actual mean salivary flow for all the MSG-sucrose mixtures compared to the calculated flows for these mixtures was significantly different (P<0.001 - Wilcoxon Signed Rank test). The actual salivary flow was, on average, 81.2 % of the calculated flow for the mixtures. The actual mean salivary flow for all the MSG-NaCl mixtures compared to the calculated flows for these mixtures was not significantly different (P=0.247 - Paired t-test). The actual salivary flow was, on average, 95.2% of the calculated flow for the mixtures.
Conclusion: The flow of the mixture did not reach the response additive level calculated from the separate response to the individual tastants for MSG-sucrose suggesting that some degree of interaction is occurring within the gustatory-salivary reflex pathways, whereas the salivary response to MSG-NaCl was not significantly different from the calculated flow suggesting that MSG and NaCl are processed separately within the gustatory-salivary reflex.