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Evidence for direct central nervous inhibition of LH secretion during sexual maturation of female rats.

Intact and ovariectomized female rats were bilaterally lesioned in the anterior part of the medial amygdaloid nucleus (AMN) at 15, 21 or 26 days of age. The onset of puberty and the LH concentration in the peripheral serum on the third day after lesioning, respectively, were recorded. Damage to the AMN on day 15 induced a significant delay of vaginal opening and the first puberal ovulation and suppressed completely the castration-induced increase of LH secretion. In contrast, females lesioned on day 21 showed true precocious puberty and a significant elevation of the LH level as compared to the ovariectomized controls. The LH-inhibiting effect of s.c. administered estradiol benzoate (0.05 micrograms/100 g/day) was not diminished by lesions produced at this age. Neither the onset of puberty nor the LH concentration were influenced by lesioning of the AMN on day 26. Estimation of the LH concentration in untreated female rats revealed a distinct decline between 19 and 23 days of age followed by a significant increase between days 24 and 26. The findings indicate a transient LH-inhibiting activity of the medial amygdala in three-week-old female rats that is not related to the negative estrogen feedback. In other species, too, a temporary inhibitory action of the central nervous system may play a significant role in the prepuberal control of gonadotropin secretion.