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      Effects of Hypophysectomy on Galaninergic Neurons in the Rat Hypothalamus

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          Abstract

          To understand better the relationship between hypothalamic galaninergic neurons and the pituitary gland, we studied the effects of hypophysectomy on hypothalamic galanin (GAL) content and distribution by radioimmunoassay and immunohistochemistry, and on GAL mRNA by Northern blot analysis. Three weeks after hypophysectomy, performed at 5 or 8 weeks of age, the hypothalamic concentrations of GAL and GAL mRNA were reduced by 30-50% in both male and female rats, compared to age- and sex-matched controls. Similar reverse-phase HPLC retention times of hypothalamic GAL were observed in intact and hypophysectomized rats. The reduction of hypothalamic GAL concentration following hypophysectomy was time-dependent, as peptide levels were unaffected one week after surgery. Immunohistochemistry showed regional differences in the effect of hypophysectomy on galaninergic neurons. In the hypophysiotropic hypothalamus, the scarce GAL immunoreactivity normally observed in the arcuate nuclei was no longer detectable in hypophysectomized rats, and the intense GAL immunoreactivity of the external zone of the median eminence progressively decreased and completely disappeared 3 and 6 weeks after hypophysectomy. In contrast, in the neurohypophyseal system, there was an increase of GAL labelling of the perikarya and emerging axons in the supraoptic and lateral-paraventricular nuclei, 1 and 3 weeks after hypophysectomy, that disappeared 6 weeks after hypophysectomy. An increase of GAL immunoreactivity was also observed in the internal zone of the median eminence 1 week but not 3 weeks after hypophysectomy. We conclude that hypophysectomy reduces the content of GAL and GAL mRNA in the rat hypothalamus. These changes are time-dependent and clearly detected after 3 weeks. The neurohypophyseal and hypophysiotropic galaninergic systems respond differently to hypophysectomy. In the neurohypophyseal system, the transient increase of GAL immunoreactivity could be related to axonal injury, diabetes insipidus or decreased neurosecretion. In contrast, the marked decrease of the GAL immunoreactivity found in the hypophysiotropic system, mainly in the external zone of the median eminence, accounts for the overall changes in hypothalamic peptide content and likely results from the loss of feedback up-regulation by pituitary or pituitary-dependent factors.

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          Author and article information

          Journal
          NEN
          Neuroendocrinology
          10.1159/issn.0028-3835
          Neuroendocrinology
          S. Karger AG
          0028-3835
          1423-0194
          1993
          1993
          08 April 2008
          : 58
          : 5
          : 539-547
          Affiliations
          Université Catholique de Louvain, Brussels, Belgium
          Article
          126588 Neuroendocrinology 1993;58:539–547
          10.1159/000126588
          7509464
          © 1993 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: 9
          Categories
          Hypothalamic Gonadal Axis

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