Effects of anterior hypothalamic deafferentation and arcuate nucleus lesions on the feedback actions of estradiol benzoate on luteinizing hormone and follicle-stimulating hormone secretion in the female hamster.

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This investigation studied theeffectsof anterior hypothalamic deafferentation (EFC), a monosodium glutamate (MSG)-induced lesion of the arcuate nucleus (ARC), or a combination of these two procedures on the regulation of luteinizing hormone (LU) and follicle-stimulating hormone (FSH) secretion in the chronically ovariectomized hamster given estradiol benzoate (EB) or oil. MSG-treated or control animals were ovariectomized and subjected to EFC or sham deafferentation (SFC) at 2-3 months of age. Three weeks later, animals were given a single injection of 50 �ig of EB or oil and the inhibitory and stimulatory actions of EB were determined by measuring LH and FSH by radioimmunoassay (RIA) of plasma obtained at 0900 h (AM) and 1600 h (PM) 3 days later. The tonic secretion of LH in SFC hamsters given oil was significantly reduced by EFC or MSG-induced lesions of the ARC. EFC in combination with these lesions did not further reduce LH levels in these animals. EB suppressed AM levels of LU in SFC animals and induced a PM surge which was prevented by EFC. Although EB did not further suppress AM levels of LH in the MSGtreated animals, a PM elevation was apparent and was prevented by EFC. In contrast to oil-treated animals, MSG-treated hamsters with EFC and given EB had significantly reduced levels of LH in both the AM and PM when compared to all other treatment groups. In contrast to LH, plasma FSH levels were not altered by EFC in control animals given oil, whereas FSH was reduced in MSG-treated animals with or without EFC. EB did not suppress AM levels of FSH in either control or MSG-treated animals, but did induce a significant surge of FSH in the PM in both groups of animals that was prevented by EFC. These results suggest that in the ovariectomized hamster, the ARC and anterior hypothalamus (AH) act as a functional unit in regulating the tonic secretion of LH, whereas the AH has little role in regulating tonic FSH secretion. The results also confirm previous reports suggesting that the ARC is involved in the tonic regulation of FSH secretion and that the AH is necessary for the stimulatory effects of estrogen on gonadotropin secretion.