Direct evidence that the arcuate nucleus-median eminence tuberoinfundibular system is not of primary importance in the feedback regulation of luteinizing hormone and follicle-stimulating hormone secretion in the castrated rat

Adult rats which have received monosodium-L-glutamate (MSG, 4 mg/g BW) on alternate days for the first 10 days of life manifest central nervous system lesions largely restricted to the retina and the arcuate nucleus of the hypothalamus in which nearly 90% of the perikarya are destroyed, leaving axons in passage intact. In animals so treated, concentrations of dopamine within the arcuate nucleus and median eminence of the hypothalamus are reduced 52% and 57%, respectively, in males and 45% and 61% in females, whereas concentrations of norepinephrine in these same two areas are normal. Concentrations of both norepinephrine and dopamine in five other hypothalamic nuclei (dorsal septal, medial preoptic, suprachiasmatic, periventricular, and dorsomedial nuclei) are unchanged. Nevertheless, despite the destruction of the arcuate nucleus cell bodies of MSG-treated rats, postcastration levels of serum FSH and LH in males, and FSH in females were not significantly different from FSH and LH values in castrated controls. Serum LH in castrated, MSG-treated females was slightly but significantly lower than in castrated controls. It is concluded that the arcuate nucleus-median eminence tuberoinfundibular neurons are not of primary importance in the tonic, negative feedback regulation of gonadotropin secretion.