Shin-Ichiro Otsuka

Discrimination of monosodium glutamate and sodium chloride solutions by rats.

Abstract Discrimination of monosodium glutamate (MSG) and sodium chloride (NaCl) solutions by rats was studied in a series of two or three bottle preference tests in free-choice situations. In two bottle preference tests, solutions containing 0.001–0.1 M NaCl or MSG were preferred to deionized water and the peak preference was 0.05 M for both NaCl and MSG-flavored solution. The transition point from preference to aversion was found to be very close to the isotonic point. Total fluid intake of both choices (MSG or NaCl-flavored water and water) was approximately 30% above the consumption of tap water controls when solutions contained 0.1 M NaCl or MSG. However, maximum intake of moles of MSG or NaCl did not exceed approximately 2 × 10 −2 mmoles per gram body weight. In a series of three choice preference tests, MSG (0.005–0.01 M) was preferred to comparable concentration of NaCl and water. Both MSG and NaCl (0.05–0.1 M) were preferred to water. When mixtures of MSG and NaCl (0.05 and 0.1 M) were compared with equimolar solutions of MSG or NaCl, the mixtures were preferred to solutions containing a single taste substance. It is concluded from these results that the rat might recognize MSG solution as a favorable substance, differently from NaCl solution.