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      Estrogen and Tamoxifen Differentially Regulate Beta-Endorphin and cFos Expression and Neuronal Colocalization in the Arcuate Nucleus of the Rat

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          Abstract

          Estrogen regulates hypothalamic gene expression, synthesis and release of the endogenous opioid peptide β-endorphin (βEND), although a consensus estrogen response element sequence has not been identified in the rat proopiomelanocortin (POMC) gene. POMC gene expression is also regulated by the activation of AP-1 promoter elements, which are known to be estrogen sensitive. The present studies examine whether estrogen modulates the hypothalamic POMC system through a non-classical mechanism involving AP-1 binding proteins such as cFos. Immunohistochemical double-labeling for βEND and cFos was used and immunoreactive (-ir) populations were quantified in the arcuate nucleus and periarcuate area across time using unbiased stereological methods. Ovariectomized rats were injected with 50 µg estradiol (E<sub>2</sub>), 500 µg tamoxifen citrate (TAM) or both (E<sub>2</sub>+TAM) and were perfused 1, 2, 4 or 48 h later. E<sub>2</sub> rapidly increased numbers of cFos-ir, βEND-ir and doubly-labeled cells after 4 h, and the number of βEND-ir cells remained high 48 h later, suggesting that the stimulatory effects of cFos on POMC in the hypothalamus persist after the cFos signal decays. Treatment with TAM alone did not affect the numbers of immunoreactive cells, although E<sub>2</sub>+TAM blocked the E<sub>2</sub>-mediated induction in all immunoreactive populations. Similar effects were seen at the transcriptional level. E<sub>2</sub> increased hypothalamic POMC mRNA after 4 h, while TAM treatment or coadministration of E<sub>2</sub>+TAM did not significantly change the levels of POMC mRNA. Cellular colocalization of βEND-ir and cFos-ir supports a possible intracellular co-regulation of these peptides by an estrogen-dependent mechanism within a subset of hypothalamic neurons. It does not, however, appear that E<sub>2</sub> acts directly through an AP-1 site within the POMC gene.

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          Most cited references 19

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          Comparative distribution of estrogen receptor-? and -? mRNA in the rat central nervous system

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            Differential Ligand Activation of Estrogen Receptors ER and ER at AP1 Sites

             K Paech (1997)
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              Tamoxifen activation of the estrogen receptor/AP-1 pathway: potential origin for the cell-specific estrogen-like effects of antiestrogens

               P. Webb (1995)
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                Author and article information

                Journal
                NEN
                Neuroendocrinology
                10.1159/issn.0028-3835
                Neuroendocrinology
                S. Karger AG
                0028-3835
                1423-0194
                2000
                November 2000
                05 December 2000
                : 72
                : 5
                : 293-305
                Affiliations
                aDepartment of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, Md., and bFishberg Research Center in Neurobiology, Mount Sinai School of Medicine, New York, N.Y., USA
                Article
                54598 Neuroendocrinology 2000;72:293–305
                10.1159/000054598
                11124586
                © 2000 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                Page count
                Figures: 6, References: 70, Pages: 13
                Categories
                Gonadotropin Regulation and Sex Steroid Feedback

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