Increase of FSH secretion in immature female rats following lesioning of the medial amygdaloid nucleus.

Immature female rats were bilaterally lesioned or sham-lesioned in the anterior part of the medial amygdaloid nucleus (AMN) at 21 days of age, and the serum FSH and LH concentrations were estimated in groups of rats autopsied at daily intervals from day 21 through day 28. Whereas the LH concentration did not differ between lesioned females and the controls, a highly significant elevation of the circulating FSH level was recorded in the lesioned rats from day 22 till day 24. A further experiment demonstrated that similar lesions did not change the FSH and LH-inhibiting effect of estrogen in rats that were ovariectomized on day 22, daily injected with 0.05 microgram estradiol benzoate per 100 g b.w. on days 22 and 23, and sacrificed 24 hr after the last injection. The results suggest that the AMN exerts a restraining influence on the hypophyseal FSH secretion around 21 days of age, and that this inhibitory activity does not depend upon sensitization to the negative feed-back of estrogen.