Pain Sensitivity and Behavioral Indices in Mice Exposed to Glutamate Toxicity: Neuroprotective Effects of Vitamin Supplementation

We examined the effects of glutamate toxicity induced by chronic (for 21 days) intraperitoneal (i.p.) introductions of monosodium glutamate (MSG, 4 mg/kg per day) into albino mice. It was found that such treatment significantly ( P < 0.05) decreased the latencies of defensive motor responses in the hot plate and tail withdrawal tests, as compared with the respective indices in the control group (injected with saline). This treatment also led to dramatic decreases ( P < 0.05) in the intensities of locomotor activity and orientational/research phenomena (rearings) in the open field test; the number of grooming episodes also considerably decreased. Glutamate intoxication also provided significant ( P < 0.05) decreases in the time spent in the open arms of the elevated plus maze and in the number of entries in these arms. Introductions of 200 mg/kg vitamin C, as well as of 20 mg/kg vitamin E, into MSG-treated mice significantly ( P < 0.05) increased the response latencies in the hot plate and tail withdrawal tests; the respective values became even greater than those in the norm. Injections of both vitamins also partly normalized the values reflecting the intensity of locomotion and rearings and nearly completely normalized grooming behavior. These vitamins provided also clear trends toward normalization with respect to the anxiety indices in the elevated plus maze test. Thus, glutamate intoxication leads to the development of a hyperalgesic state, significant suppression of behavioral activities, and a significant increase in the anxiety level. Introductions of vitamins C and E known as effective antioxidants considerably moderate these negative shifts.