[Effects of hypothalamic deafferentation and estrogen on the distribution and content of hypothalamic LHRH (author's...

Anterior (AHD), or complete (CHD) hypothalamic deafferentation was performed in female rats to ascertain the origin of LHRH in the arcuate median eminence region (ARC-ME). Furthermore, effects of estrogen on the distribution and content of hypothalamic LHRH in AHD castrated rats were examined to elucidate the mechanism of feedback action of estrogen. Hypothalamic tissues were sectioned serially at 220 micrometers in thickness in the frontal plane and LHRH activity in each section was measured by RIA. AHD induced a significant reduction of LHRH in the ARC-ME. The reduction of LHRH was more prominent in CHD rats. In control castrated rats, serum LH significantly decreased 24 hr and 48 hr after estrogen treatment, and subsequently increased, accompanied with reciprocal change of LHRH in the ARC-ME. Conversely, estrogen caused continuous suppression of serum LH with elevated LHRH content in the ARC-ME of AHD rats. In conclusion, considerable amount of LHRH in the ARC-ME is synthesized in the preoptic area (POA) and transported to the ARC-ME, and some part of LHRH in the ARC-ME is produced in the ARC-ME itself. Axonal transport of LHRH from the POA to the ARC-ME is essential for positive feedback action of estrogen. Moreover, estrogen is suggested to act on the hypothalamus, initially by inhibiting the release of LHRH, which results in subsequent release of LHRH after the disappearance of this temporary inhibition.