The effects of a single injection of monosodium glutamate on the reproductive neuroendocrine axis of the female hamster.

Abstract

Monosodium glutamate (MSG) was injected into the neonatal hamster to determine whether it was possible to produce a discrete lesion of the accurate nucleus to study the effects of this lesion on ovarian histology hypothalamic neurohistochemistry and plasma and pituitary levels of gonadotropins and to study the response of the hypothalamo-pituitary axis to ovariectomy. MSG was administered in a dose of 8 mg/gm body weight on Day 6 7 8 9 or 10 of the neonatal period and decapitated 6 or 12 hours later. The brains were prepared for histological study. A lesion of the arcuate nucleus o fteh hypothalamus was induced by injection of MSG on Days 6-8. When injection was performed on Day 9 or 10 the lesion was still prominent but less severe. Animals treated on Day 8 of the neonatal period were examined beginning on Day 30 for postovulatory vaginal discharge. Plasma luteinizing hormone (LH) and follicle stimulating hormone (FSH) were measured. Histochemical study of catecholamines was performed on a small piece of the diencephalon. Ovaries and uteri were removed and weighed. A 2nd group of hamsters treated on Day 8 with either saline or MSG were ovariectomized on Day 60. 7 days later the pituitary was removed and gonadotropin determinations made. Postovulatory vaginal discharges in MSG-treated hamsters were absent. Organ and body weights were significantly lower in the treated hamsters and histological evaluation of the ovaries suggested inhibition of follicular maturation. This may have been due to altered levels of LH and FSH found in the plasma of treated animals. Partial destruction of the tubero-infundibular catecholaminergic pathway was confirmed by histofluorescence technique.