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      Expression of Glutamate Receptor Subunit mRNAs in Gonadotropin-Releasing Hormone Neurons during the Sexual Maturation of the Female Rat

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          Abstract

          Excitatory amino acids, particularly glutamate, are thought to be important for the maturation of the brain-pituitary-gonadal axis and the induction of puberty in the rat. We have previously shown that, in the female rat, GnRH neurons preferentially express the KA2 and NMDAR2A receptor subunit mRNAs, but not AMPA or NMDAR1 mRNA. The aim of the present study was to determine whether the onset or rate of KA2 and NMDAR2A receptor expression in GnRH neurons is correlated with the onset of puberty. Dual in situ hybridization using digoxigenin-labeled GnRH cRNA probes and <sup>35</sup>S-labeled glutamate receptor subunit probes, followed by autoradiography and image analysis were used to measure the KA2 or NMDAR2A mRNA content in GnRH neurons in 20- to 50-day-old female rats which were sacrificed at 08.00 or 17.00 h. The results show that: (a) the KA2 mRNA content of GnRH neurons and the number of GnRH neurons expressing KA2 mRNA increase progressively in the morning hours between postnatal days 20 and 40; (b) the diurnal pattern of KA2 mRNA levels in GnRH neurons changes between days 40 and 50 from high KA2 levels in the morning hours before day 40 to high KA2 mRNA levels in the afternoon in 45- and 50-day-old animals; (c) while the high levels of KA2 mRNA in GnRH neurons in the morning hours of 20-to 40-day-old animals are paralleled by an overall increase in KA2 expression in the preoptic area, the rise in KA2 mRNA in GnRH neurons in the afternoon of 45- and 50-day-old animals appears to be specific for the GnRH neurons, and (d) no significant differences were detected for the NMDAR2A mRNA content in GnRH neurons among the different age groups and the morning and afternoon values. Since the gradual increase in the KA2 mRNA content in GnRH neurons of animals reaching puberty as well as the reversal of diurnal rhythmicity in KA2 receptor mRNA content of GnRH neurons coincide with the times of vaginal opening and first ovulation, it is suggested that glutamate, acting through KA2 receptors directly on GnRH neurons is, at least in part, an important factor in the excitatory regulation of the postnatal sexual development of the female rat. In contrast, expression of the NMDA-preferring receptor, NMDAR2A, in GnRH neurons appeared to be unchanged during this development.

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          Author and article information

          Journal
          NEN
          Neuroendocrinology
          10.1159/issn.0028-3835
          Neuroendocrinology
          S. Karger AG
          0028-3835
          1423-0194
          1997
          1997
          09 April 2008
          : 66
          : 2
          : 122-129
          Affiliations
          Department of Anatomy and Neurobiology, University of Kentucky College of Medicine, Lexington, Ky., USA
          Article
          127229 Neuroendocrinology 1997;66:122–129
          10.1159/000127229
          9263209
          © 1997 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
          Pages: 8
          Categories
          Hypothalamic Regulation of Gonadotropins

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