Sexual cyclicity and diurnal corticosterone secretion in rats given hypothalamic transection at two days of age

Female rats given neural transection between suprachiasmatic and arcuate nuclei at 2 days of age showed regular sexual cyclicity and had ovarian corpora lutea. Thus, the ovarian activity seemed identical to that of intact or sham-operated control rats. However, the diurnal rhythm of the blood corticosterone concentration of the neonatally transected rats was not evident at 22 days of age, while it was already evident in controls. At 30 and 50 days of age, they had clear adrenal rhythms although the peak values were significantly lower than those of controls. Thus, the anterior connections of the medial basal hypothalamus, which are necessary for both cyclic gonadotropin discharge and diurnal corticosterone secretion, are still plastic and not yet established at 2 days of age.