Effect of water restriction on the development of hypothalamic lesions in weanling rodents given MSG. I. Drinking behaviour and physiological parameters in mice (Mus musculus).

Deprivation of water overnight (ON: 19.00-09.00 h) induced approx. 20% haemoconcentration in weanling ICR strain mice and resulted in avid consumption of fluid offered for 30 min subsequently, with delayed restoration of serum osmolality and sodium to normal levels in those offered 8% w/v monosodium L-glutamate monohydrate (MSG) aqueous solution. Neuronal necrosis of the arcuate nucleus of the hypothalamus was found in 12/180 dehydrated mice deprived ON and subsequently consuming 3.0 g or more MSG/kg body weight offered hypertonic MSG solution as the sole source of drinking water. The lesions were less severe than in mice given MSG s.c. or by forced intubation. Mice deprived ON and subsequently consuming MSG solution with water in a free choice experiment, and those deprived during daytime (DT: 07.00-21.00 h) and subsequently consuming MSG solution, with or without water, developed fewer and less severe lesions than did mice deprived ON and subsequently consuming MSG solution solely. The provision of other nutrients (e.g. glucose, arginine) reduced glutamate-induced hypothalamic lesions and elevation of plasma L-glutamate. The findings are in accord with earlier observations that hypothalamic lesions do not result even in this most susceptible species from the 'voluntary' consumption of MSG by physiologically normal animals. No lesions were produced even in mice deprived of food and water ON and subsequently consuming up to 7.3 g MSG/kg body weight in diet and in soup.