Positive Feedback Sites of Estrogen in the Brain on Ovulation : Possible Role of the Bed Nucleus of Stria Terminalis and the Amygdala

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Direct effects of estrogen on the brain inducing ovulation have been studied on the late night of diestrus II in 4-day cyclic rats. Injection of 3mg of progesterone on the evening of diestrus II (23:00) delayed ovulation. However, the inhibitory effect of progesterone was restored by the simultaneous injection of estradiol benzoate (8/10) or bilateral implantation of crystalline estrogen into the medial amygdala (8/12). Implantation of estrogen into the medial preoptic area, the bed nucleus of the stria terminalis and the lateral amygdala resulted in making ovulated rats fewer such as, 1/8, 3/8 and 1/6, respectively. Positive feedback effect of implanted estrogen into the medial amygdal a blocked by chronical transection of the surrounding area of the bed nucleus of the stria terminalis (0/5). Estrogen implantation to the medial amygdala and the bed nucleus of the stria terminalis on the night of diestrus II overcame the inhibitory effect of progesterone on LH release during the critical period of proestrus, while estrogen implantation to the medial preoptic area was relatively ineffective. Thus, estrogen appears to feed back to the medial amygdala and the bed nucleus of the stria terminalis inducing the release of ovulatory hormone.
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