EFFECT OF PHOTOPERIOD ON NEURAL ESTROGEN AND PROGESTIN RECEPTOR IMMUNOREACTIVITY IN FEMALE SYRIAN-HAMSTERS

This study explored the possibility that reduced behavioral responsive ness to estradiol and progesterone in female Syrian hamsters exposed t o a short photoperiod is associated with a reduction in the concentrat ion of neural steroid receptors. The effects of long and short photope riod (LP; SP) exposure on steroid receptor immunoreactivity were exami ned in the ventromedial hypothalamus (VMH), medial tuberal region (mTu ), medial preoptic area (mPOA), medial nucleus of the amygdala (mAMYG) , and the arcuate nucleus (ARC) of ovariectomized hamsters. In Experim ent 1, exposure to SP for ten weeks attenuated the lordosis response f ollowing sequential treatment with estradiol and progesterone. In a se parate group of animals not given hormones, SP decreased the staining intensity of estrogen receptor immunoreactive (ERIR) cells in the mPOA while increasing the number of detectable ERIR cells in part of the m AMYG. In Experiment 2, SP diminished the lordosis response as it did i n Experiment 1. One week later, the same females were administered est radiol systemically to induce progestin receptors (PR). Animals housed in SP showed significantly reduced progestin receptor immunoreactivit y (PRIR) in the VMH, mTu, mPOA, mAMYG, and ARC. Experiment 3 examined whether the results of Experiment 2 might have been influenced by phot operiodic effects on peripheral metabolism of estradiol, Among hamster s housed in LP or SP, PRs were induced by estradiol implanted unilater ally in the medial basal hypothalamus, thus bypassing possible photope riodic effects on peripheral estradiol availability. This treatment re sulted in significantly fewer cells with detectable PRIR in the VMH an d mPOA of SP females, suggesting that the photoperiodic influences on PR induction observed in Experiment 2 do not depend on alterations in the peripheral availability of estradiol. (C) 1998 Elsevier Science B. V. All rights reserved.