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Neuroendocrinology |
a Department of Physiology and Pharmacology, West Virginia University, Morgantown, West Virginia 26506
b Department of Anatomy and Structural Biology, University of Otago Medical School, Dunedin, New Zealand
In ewes, anestrus results from a reduction in LH pulsatility due to an increased sensitivity of the hypothalamic estradiol negative feedback system. Considerable evidence has implicated the A15 group of dopaminergic neurons in the retrochiasmatic area in this seasonally dependent estradiol effect. Moreover, estradiol administered to the retrochiasmatic area in ovariectomized anestrous ewes inhibits LH secretion. However, A15 neurons do not appear to contain the classical estrogen receptors (ER
). Therefore, we tested the hypothesis that ß-estrogen receptors mediate the action of estradiol in the retrochiasmatic area by comparing the effects of estradiol and genistein, a selective ERß agonist. We also examined whether there are seasonal changes in response of the retrochiasmatic area to these agonists and if these effects are mediated by dopamine. To test these hypotheses, ovariectomized ewes were implanted with bilateral guide cannulae targeting the retrochiasmatic area. Crystalline agonists were administered via microimplants inserted down the cannulae. Blood samples taken before and 4 days after microimplant insertion were analyzed for LH concentrations, pulse frequency, and amplitude. Genistein treatment produced no significant change in LH levels in either season. Estradiol treatment decreased both mean LH concentrations and pulse frequency in anestrous but not breeding-season ewes. Administration of the dopamine antagonist sulpiride to ovariectomized ewes with estradiol microimplants in the retrochiasmatic area returned LH pulse frequency to levels indistinguishable from controls. From these data, we hypothesize that estradiol acts on local ER-containing neurons in this area to stimulate a dopaminergic pathway that inhibits LH secretion during anestrus.
2 Correspondence: Robert L. Goodman, Department of Physiology and Pharmacology, West Virginia University, P.O. Box 9229, Morgantown, WV 26506-9229. FAX: 304 293 3850; e-mail: bgoodman{at}hsc.wvu.edu
This article has been cited by other articles:
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  A. L. Bogusz, S. L. Hardy, M. N. Lehman, J. M. Connors, S. M. Hileman, J. H. Sliwowska, H. J. Billings, C. J. McManus, M. Valent, S. R. Singh, et al. Evidence that {gamma}-Aminobutyric Acid Is Part of the Neural Circuit Mediating Estradiol Negative Feedback in Anestrous Ewes Endocrinology, June 1, 2008; 149(6): 2762 - 2772. [Abstract] [Full Text] [PDF]
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 C. J McManus, M. Valent, S. L Hardy, and R. L Goodman Does nitric oxide act in the ventromedial preoptic area to mediate oestrogen negative feedback in the seasonally anoestrous ewe? Reproduction, July 1, 2007; 134(1): 137 - 145. [Abstract] [Full Text] [PDF]
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V. L. Adams, R. L. Goodman, A. K. Salm, L. M. Coolen, F. J. Karsch, and M. N. Lehman Morphological Plasticity in the Neural Circuitry Responsible for Seasonal Breeding in the Ewe Endocrinology, October 1, 2006; 147(10): 4843 - 4851. [Abstract] [Full Text] [PDF]
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G. M. Anderson, S. L. Hardy, M. Valent, H. J. Billings, J. M. Connors, and R. L. Goodman Evidence that Thyroid Hormones Act in the Ventromedial Preoptic Area and the Premammillary Region of the Brain to Allow the Termination of the Breeding Season in the Ewe Endocrinology, July 1, 2003; 144(7): 2892 - 2901. [Abstract] [Full Text] [PDF]
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