Monosodium glutamate-induced changes of aggression and open-field activity in rats.

Twenty Sprague-Dawley rat pups received injections of 2 mg/g, 4 mg/g monosodium glutamate (MSG) or physiological saline (mean volume) subcutaneous daily for the first 10 days of life. At 70 and 90 days, rats were tested for open-field and aggressive responding, respectively. Body weights were recorded throughout development. When compared to the control group, results indicated: (1) significantly lowered body weights for both MSG-injected groups with the 4 mg/g group showing the greatest weight suppression, (2) a significant decrease in open-field activity for the 2 mg/g MSG group, with the 4 mg/g MSG group not quite reaching a statistically significant decreases, (3) significant decreases in aggressive responding of both MSG groups. The decrease in open-field activity supports the type of MSG-induced behavioral suppression previously reported for rodents, while an MSG-induced decrease in aggression has not been previously documented.