The Effects of a Single Injection of Monosodium Glutamate on the Reproductive Neuroendocrine Axis of the Female Hamster

Abstract

A lesion of the arcuate nucleus of the hypothalamus was induced by a single subcutaneous injection of monosodium glutamate (8 mg/gm) given to hamsters on Days 6, 7 or 8 of the neonatal period. When MSG was given on Days 9 or 10 the lesion was still prominent but less severe than that seen on previous days.

Adult female hamsters, previously treated with MSG on Day 8, did not exhibit postovulatory vaginal discharges while saline treated animals appeared to have had regular estrous cycles. Organ and body weights were significantly lower in the MSG-treated animals and histological evaluation of the ovaries from these animals suggested that there was an inhibition of follicular maturation. This inhibition of normal follicular maturation may have been due to altered levels of FSH and LH that were found in the plasma of treated animals. Alterations in the levels of LH and FSH would be expected due to the destruction of the arcuate nucleus caused by MSG administration. The axons of this nucleus comprise a major portion of the tubero-infundibular catecholaminergic pathway which effects the secretion of LHRH from the median eminence. Partial destruction of this pathway by MSG treatment was confirmed using the Falk-Hillarp histofluorescence technique. The strong green fluorescence normally seen in the external layer of the median eminence was greatly reduced in MSG-treated animals.