Prior attenuation of KiSS1/GPR54 signaling in the anteroventral periventricular nucleus is a trigger for the delayed effect induced by neonatal exposure to 17alpha-ethynylestradiol in female rats.

Neonatal exposure to 17alpha-ethynylestradiol (EE) causes delayed effect, a late-occurring irreversible damage to reproductive functions characterized by the early onset of age-matched abnormal estrous cycling. To clarify the involvement of a hypothalamic key cycling regulator KiSS1/GPR54 in the delayed effect, we investigated artificially induced LH surges and KiSS1 mRNA expression in the anteroventral periventricular nucleus (AVPV) of cycling young adult rats neonatally exposed to EE, and compared these parameters to those in about 5 months old middle-aged rats. KiSS1 mRNA expression, the number of KiSS1-positive cells and KiSS1/ERα co-expressing cells in the AVPV decreased in both EE-exposed and middle-aged rats. The peak area and levels of LH surge dose-dependently decreased in EE-exposed rats, and reduction was more evident in middle-aged rats. These results indicate that the prior attenuation of KiSS1 and consequent depression of LH surges plays a key role in the onset of abnormal estrous cycling in the delayed effect.