A Test of Dietary Monosodium Glutamate Developmental Neurotoxicity in Rats: A Reappraisal

In 1979, we tested dietary monosodium glutamate (MSG) for developmental neurotoxicity in rats. The study was recently cited for establishing a No Observable Adverse Effect Level (NOAEL) for MSG as a food additive resulting in a change in the acceptable daily intake (ADI). Therefore, I re-evaluated the study [Vorhees et al.: Toxicol Appl Pharmacol 1979; 50: 267-282]. Sprague-Dawley rats were fed diets containing 0, 1.7, 3.4, or 5.1% MSG prior to conception, throughout gestation and lactation, and the same diets were fed to the offspring until 90 days of age. About 18-20 L were tested per dose with litter and sex factors in data analyses. There were 21 functional tests with 36 dependent variables and 10 body weight and histological outcomes. Of the functional tests, 4 were significant involving 6 effects. Two effects were on swimming ontogeny: one was an improvement and the other an atypical minor delay of no significance. Two effects were on active avoidance: one was a low-dose female-only extinction effect and the other a high-dose male-only acquisition effect, neither providing evidence of consistency. One was on passive avoidance, but was an improvement not a deficit. The last was on open-field rearing in the absence of its normal association with locomotion changes. Thus, it can be concluded, as was done in 1979 and by the U.S. Food and Drug Administration who sponsored the study, that there is no evidence in these data that dietary MSG is developmentally neurotoxic, hence, the study provides no basis for the establishment of a NOAEL and changing the ADI for dietary MSG.