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      Leptin Immunoreactivity Is Localized to Neurons in Rat Brain

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          Abstract

          Leptin is secreted from adipocytes and is thought to enter the brain to regulate and coordinate metabolism, feeding behaviour, energy balance and reproduction. It is now clear that there are many additional sites of leptin production, including human placenta, ovary, stomach, skeletal muscle, mammary gland, pituitary gland and brain. In the present work, we employed double-label immunofluorescent histochemistry to establish the neuronal localization of leptin immunoreactivity (IR). To accomplish this, we used the neuron-specific marker NeuN to label cells in the arcuate nucleus (ARC), piriform cortex and hippocampus. In the supraoptic nucleus (SON) and paraventricular nucleus (PVN), we used antisera to oxytocin and vasopressin as neuronal markers. Double labelling revealed leptin IR in neurons of the ARC and piriform cortex. Leptin IR was confined to the nucleus and to distinct perinuclear sites. In contrast, neurons in the CA 2/CA 3 region of the hippocampus showed little nuclear staining. Leptin IR was clustered around the nucleus in these cells. Neurons of the dentate gyrus exhibited both nuclear and perinuclear localization of leptin IR. In the SON/PVN, most oxytocin- and vasopressin-IR neurons also contained leptin IR, often in perinuclear sites. In conclusion, the neuronal, perinuclear localization of leptin IR in rat brain corresponds closely to that of leptin receptor (OB-R) IR, which has also been detected intracellularly. Our observation of leptin IR associated with cell nuclei suggests the existence of an OB-R distinct from the well-described membrane forms.

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          Most cited references 17

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          Leptin.

          The discovery of the adipose-derived hormone leptin has generated enormous interest in the interaction between peripheral signals and brain targets involved in the regulation of feeding and energy balance. Plasma leptin levels correlate with fat stores and respond to changes in energy balance. It was initially proposed that leptin serves a primary role as an anti-obesity hormone, but this role is commonly thwarted by leptin resistance. Leptin also serves as a mediator of the adaptation to fasting, and this role may be the primary function for which the molecule evolved. There is increasing evidence that leptin has systemic effects apart from those related to energy homeostasis, including regulation of neuroendocrine and immune function and a role in development.
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            The stomach is a source of leptin.

            The circulating peptide leptin, which is the product of the ob gene, provides feedback information on the size of fat stores to central Ob receptors that control food intake and body-weight homeostasis. Leptin has so far been reported to be secreted only by adipocytes and the placenta. Here we show that leptin messenger RNA and leptin protein are present in rat gastric epithelium, and that cells in the glands of the gastric fundic mucosa are immunoreactive for leptin. The physiological function of this previously unsuspected source of leptin is unknown. However, both feeding and administration of CCK-8 (the biologically active carboxy-terminal end of cholecystokinin) result in a rapid and large decrease in both leptin cell immunoreactivity and the leptin content of the fundic epithelium, with a concomitant increase in the concentration of leptin in the plasma. These results indicate that gastric leptin may be involved in early CCK-mediated effects activated by food intake, possibly including satiety.
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              Divergent signaling capacities of the long and short isoforms of the leptin receptor.

              Leptin receptors include a long form (OBRl) with 302 cytoplasmic residues that is presumed to mediate most or all of leptins signaling, and several short forms, including one (OBRs) that has 34 cytoplasmic residues, is widely expressed, and is presumed not to signal but to mediate transport or clearance of leptin. We studied the abilities of these two receptor isoforms to mediate signaling in transfected cells. In response to leptin, OBRl, but not OBRs, underwent tyrosine phosphorylation that was enhanced by co-expression with JAK2. In cells expressing receptors and JAK2, both OBRs and OBRl mediated leptin-dependent tyrosine phosphorylation of JAK2, and this was abolished with OBRs when the Box 1 motif was mutated. In cells expressing receptors, JAK2 and IRS-1, leptin induced tyrosine phosphorylation of IRS-1 through OBRs and OBRl. In COS cells expressing hemagglutinin-ERK1 and receptors, leptin increased ERK1 kinase activity through OBRl, with the magnitude increased by co-expression of JAK1 or JAK2, and to a lesser degree through OBRs, despite greater receptor expression. In stable Chinese hamster ovary cell lines expressing OBRs or OBRl, leptin stimulated endogenous ERK2 phosphorylation. Whereas leptin stimulated tyrosine phosphorylation of hemagglutinin-STAT3 and induction of a c-fos luciferase reporter plasmid through OBRl, OBRs was without effect in these assays. In conclusion, OBRl is capable of signaling to IRS-1 and mitogen-activated protein kinase via JAK, in addition to activating STAT pathways. Although substantially weaker than OBRl, OBRs is capable of mediating signal transduction via JAK, but these activities are of as yet unknown significance for leptin biology in vivo.
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                Author and article information

                Journal
                NEN
                Neuroendocrinology
                10.1159/issn.0028-3835
                Neuroendocrinology
                S. Karger AG
                0028-3835
                1423-0194
                2002
                April 2002
                17 April 2002
                : 75
                : 4
                : 264-272
                Affiliations
                aDivision of Endocrinology, Departments of bObstetrics and Gynaecology and cPhysiology and Biophysics, Faculty of Medicine, Dalhousie University, Halifax, N.S., Canada
                Article
                54718 Neuroendocrinology 2002;75:264–272
                10.1159/000054718
                11979057
                © 2002 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: 3, References: 66, Pages: 9
                Categories
                Leptin and Food Intake Behaviour

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