Effects of gonadal steroids on the in vivo binding of [125I]alpha-bungarotoxin to the suprachiasmatic nucleus.
The radioligand [125I]alpha-bungarotoxin (alpha-BTX) has been used to test receptor binding to putative nicotinic cholinergic receptors in the hypothalamus. Using light microscopic autoradiography following third ventricular infusion of the radioligand we have previously demonstrated that in normally cycling rats and in normal males, the suprachiasmatic nucleus (SCN) consistently binds the alpha-neurotoxin. In chronically (5 weeks) oophorectomized female, binding of [125I]alpha-BTX to the SCN is markedly diminished. The present series of experiments were designed to test the effects of gonadal steroids on the binding of [125I]alpha-BTX to the SCN. We first tested whether or not estradiol administered to ovariectomized females could duplicate the presence of the ovary. In females ovariectomized and immediately provided with a constant dose of estradiol-17 beta (E2)--1.0 cm silastic capsules for 5 weeks, (n = 4), the binding of the neurotoxin to the SCN was maintained. In females ovariectomized for 3 weeks and replaced with E2 for 2 weeks (n = 4), the binding of [125I]alpha-BTX to the SCN was restored. In chronically (4 weeks) ovariectomized females receiving E2 for 6 days (n = 2), the binding of the neurotoxin was partially restored. We next tested the effect of chronic (5 weeks) castration (n = 100) and observed that binding of [125I]alpha-BTX to the SCN of castrated males was like that of intact male controls (n = 6).(ABSTRACT TRUNCATED AT 250 WORDS)
D000818:Animals; D000831:Animals, Newborn; D002038:Bungarotoxins / Q000378:metabolism*; D002369:Castration; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D012739:Gonadal Steroid Hormones / Q000502:physiology*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013493:Suprachiasmatic Nucleus / Q000378:metabolism*; D013739:Testosterone / Q000494:pharmacology; D013997:Time Factors
D002038:Bungarotoxins; D012739:Gonadal Steroid Hormones; D013739:Testosterone; D004958:Estradiol