Mechanisms of umami taste preference and aversion in rats

The influence of glutamate intake on growth and appetite, and the mechanism s of preference and aversion for monosodium L-glutamate (MSG) solutions wer e investigated in rats. Food intake, but not weight gain, was reduced signi ficantly in rats fed a glutamate + glutamine (Glx)-deficient diet compared with those fed a control diet. Increase in the voluntary intake of Glx solu tions was more rapid in rats fed the Glx-deficient diet. The preference and aversion for MSG solutions were distinctly different in 14 rat strains tes ted. Brown-Norway rats showed a strong preference for 60 mmol/L MSG and did not show aversive behavior toward solutions containing up to 600 mmol/L MS G. Sprague-Dawley (SD) rats showed a moderate preference for 60 mmol/L MSG; and a weak aversion for MSG concentrations higher than 240 mmol/L; Long-Ev ans Agouti rats showed a moderate preference for 60 mmol/L MSG and a marked aversion for MSG concentrations higher than 120 mmol/L. Aversion was not d ue to nonspecific hyperosmotic effects. After section of gastric branches o f the vagus nerve, MSG became aversive to SD rats. Aversion to 240 mmol/L M SG was reduced by 23-39% when combined with proline, alanine, glycine and g lucose. These results show that the preference and aversion for MSG are det ermined by genetic factors, as well as vagus nerve function, and that the a version to high MSG concentrations is reduced by the presence of other gluc ogenic amino acids and sugars.