Time-Related Effects of Monosodium Glutamate on the Reproductive Neuroendocrine Axis of the Hamster

Monosodium glutamate (MSG) was used to produce a lesion in the arcuate nucleus (ARC) of the hypothalamus in the neonatal hamster. In Exp I, hamsters were given a single sc injection of saline or 8 mg MSG/g BW on days 1-15 of the neonatal period. The severity of the lesion was measured by studying the percentage of neurons in the ARC that were morphologically intact 6 h after the injection. There was a decline in the percentage of intact neurons from 82% in animals given MSG on day 1 to 14–19% in those injected on days 7–11. There was an increase in the percentage of intact neurons in the ARC to 71% by day 15.

In Exp II, female hamsters were treated with saline or MSG in a similar manner on days 4-15 of the neonatal period. The animals were sacrificed as adults at approximately 2 months of age and the following parameters were studied: the severity of the lesion in the ARC, the occurrence and regularity of estrous cycles, ovarian histology, weights of the anterior pituitary glands, and the concentrations of LH and FSH in the plasma and anterior pituitary glands. There was a decrease in the percentage of intact neurons from 63% in animals given MSG on day 4 to 15% in those injected on day 8. In animals treated with MSG on days 9–15, the values ranged from 28–43%. Only 56–60% of the hamsters that received MSG on day 7 or 8 of the neonatal period had estrous cycles compared to 75–100% of the animals injected with MSG on the other days of the neonatal period. Significant differences in the concentration of plasma and pituitary FSH and the weights of the anterior pituitary glands were found only in animals given MSG on day 7 or 8. All animals given MSG on other days of the neonatal period had gonadotropin levels comparable to control levels. These results suggest that 1) the susceptibility of the ARC neurons to damage by MSG is related to the age of the neonate at the time of injection, and 2) some of the ARC neurons in the hamster may be necessary for adequate FSH secretion. (Endocrinology106: 553, 1980)