Neural Regulation in the Vertebrate Endocrine System: Neuroendocrine Regulation PDF
Preview Neural Regulation in the Vertebrate Endocrine System: Neuroendocrine Regulation
NEURAL REGULATION IN THE VERTEBRATE ENDOCRINE SYSTEM Neuroendocrine Regulation NEURAL REGULATION IN THE VERTEBRATE ENDOCRINE SYSTEM Neuroendocrine Regulation Edited by P. D. Prasada Rao Nagpur University Nagpur; India and Richard E. Peter University of Alberta Edmonton, Alberta, Canada Springer Science+Business Media, LLC Proceedings of Neural Control of the Endocrine System, held November 26-28, 1997, in Nagpur, India ISBN 978-1-4613-7177-9 ISBN 978-1-4615-4805-8 (eBook) DOI 10.1007/978-1-4615-4805-8 ©1999 Springer Science+Business Media New York Originally published by Kluwer Academic/Plenum Publishers in 1999 Softcover reprint of the hardcover 1s t edition 1999 W 9 8 7 6 5 432 1 A C.I.P. record for this book is available from the Library of Congress AlI rights reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted in auy form or by auy meaus, electronic, mechauical, photocopying, microfilming, recording, or otherwise, without written permission from the Publisher PREFACE The objective of this book is to provide recent information on neural regulation in the endocrine system in vertebrates. Classical studies have revealed that certain neurons synthesize and release chemical messengers into the vascular system. These neurons are endocrine devices that link the brain with the endocrine glands and other target organs. In vertebrates, the hypothalamus is the seat for chemical coordination and integration of en vironmental and hormonal cues to modulate function of the pituitary gland, and conse quently, the functions of other endocrine glands. Exciting information generated during the past few decades has resulted in profound alterations in the conceptual fabric of endo crinology. From the wealth of information that emerged on neuropeptides of the central nervous system, and on the other connectivities of various brain centers, its has become clear that several extra-hypothalamic sites are also involved in regulation of hypophysial hormones. The brain has assumed a greater importance in the regulation of the endocrine sys tem. However, recent studies have revealed varying degrees of functional autonomy in hy pophysial hormone secretion, which may be due to intrapituitary cytokines. Although gonadotropin-releasing hormone (GnRH) is a key regulator of gonadotropin secretion, there exists a GnRH receptor diversity in vertebrates such as the receptor presence in can cer cells. Recent studies have demonstrated the multifactorial nature of the neuroendo crine factors involved in growth hormone regulation in fish. On the other hand, in birds, thyrotropin-releasing hormone plays a major role in growth hormone release. In teleosts, the brain hypophysiotropic neurons regulate anterior pituitary hormone release by direct innervation, while in other vertebrates, peptides released in the median eminence are transported to the anterior pituitary by the hypothalamo-hypophysial blood portal system. This book deals with neurons contributing to the pituitary innervation in teleosts, median eminence in vertebrates, brain GnRH and regulation of pituitary and ovarian func tions in fishes, brain control of growth hormone in fish and birds, brain regulation of mammalian luteinizing hormone, functional autonomy of the adenohypophysis, photoperi odic control of GnRH in birds, changes in avian central steroid receptor expression with respect to reproduction and neural control of other endocrines such as pineal organ, endo crine pancreas, and the immune system. It is hoped that this book will prove useful to re searchers, teachers, and students involved in research and teaching in neuroendocrinology and comparative endocrinology. We would like to acknowledge the cooperation and support received form the authors and the publisher. The review papers in the book arose primarily from presenta- v vi Preface tions made at the Symposium on Neural Control of the Endocrine System, held at Nagpur University, Nagpur, India, November 26-28, 1997. This was a Satellite Symposium of the XIII International Congress of Comparative Endocrinology, held in Yokohama, Japan, No vember 17-21, 1997. P. D. Prasada Rao R. E. Peter CONTENTS I. The Median Eminence: A Mediator in the Regulation of the Pituitary by Brain ..................................................... . Hideshi Kobayashi, Yoshimasa Yamaguchi, and Haruko Uemura 2. Hypophysiotropic Neurons in the Brain of Teleosts 23 P. D. Prasada Rao 3. Functional Autonomy of the Adenohypophysis. . . . . . . . . . . . . . . . . . . . . . . . . . . 41 D. R. Naik 4. Brain Regulation of Growth Hormone Secretion and Food Intake in Fish 55 Richard E. Peter and John P. Chang 5. GHRH: A Growth Hormone-Releasing Factor in Birds? . . . . . . . . . . . . . . . . . . . . 69 Stephen Harvey 6. Gonadotropin-Releasing Hormone Neuronal Systems in the Teleostean Brain and Functional Significance ..................................... 85 Koichi Okuzawa and Makito Kobayashi 7. Gonadotropin-Releasing Hormone as a Paracrine Regulator of Ovarian Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IO I Hamid R. Habibi 8. Role of Central Monoamines in Regulation of Gonadotropin-II Secretion: Catfish Model ................................................ III K. P. Joy 9. Opioidergic Regulation of Luteinizing Hormone Secretion and Gonadal Steroidogenesis in Male Rat ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 R. N. Saxena and Poonam A. Kant 10. Photoperiodic Control of Gonadotrophin-Releasing Hormone Secretion in Seasonally Breeding Birds ...................................... 141 Alistair Dawson vii viii Contents 11. Changes in the Expression of Avian Central Steroid Receptors with Respect to the Breeding Cycle ............................................ 161 J. A. Clark, M. D. C. Belle, G. C. Georgiou, and R. W. Lea 12. Neural Elements in Pineal Organs of Vertebrates ......................... 179 Tetsuji Sato, Hiroki Fujieda, and Kenjiro Wake 13. Interactions between the Endocrine and Exocrine Pancreas: Effects ofIslet Hormones, Secretagogues, and Nerve Stimulation ................... 197 Maria Dolores Yago, Ernest Adeghate, and Jaipaul Singh 14. Neuroendocrine Regulation ofImmune Function in Fish 219 Yuwaraj K. Narnaware and Norman Y. S. Woo Index 233 1 THE MEDIAN EMINENCE A Mediator in the Regulation of the Pituitary by Brain Hideshi Kobayashi,1 Yoshimasa Yamaguchi, I and Haruko Uemura2 IResearch Laboratory Zenyaku Kogyo, Co. Ltd. 2-33-70hizumi-machi Nerima-ku, Tokyo 178-0062 2Biological Laboratory Kanagawa Dental College Inaoka-cho, Yokosuka, Kanagawa 238-8580, Japan 1. INTRODUCTION More than thirty different biologically active peptides have been demonstrated, in addition to several classical neurotransmitters, in the median eminence and, unlike neural information, these messenger molecules can be stored in axon endings. Most of these brain peptides seem to be conveyed from the median eminence to the pars distalis of the adenohypophysis via the hypothalamo-hypophysial portal vessels. They appear to control the activities of a large number of adenohypophysial cells, in contrast to the more limited numbers of cells that are controlled by direct innervation in fishes (Vollrath, 1967). Thus, the median eminence is a site for the collection of the various messenger chemicals that are produced in neurons and, upon demand, they are discharged into the hypophysial por tal vessels. The definition of the median eminence will be discussed in the Section 2. Al though regulation of the release of the messenger chemicals from the nerve endings is considered to occur predominantly at the level of cell bodies, the possibility of local regu lation at the level of the median eminence is supported by extensive data that have been accumulated over the course of the past 40 years. However, the regulatory mechanisms at the level of the median eminence have not yet been fully elucidated and are still specula tive. In this review, we shall enumerate the various brain peptides and neurotransmitters in the median eminence and discuss their significance in relation to their release at the level of the median eminence. The involvement of some other substances such as inter leukins, nitric oxide (NO), carbon monoxide (CO), glutamate and gap junctional proteins Neural Regulation in the Vertebrate Endocrine System, edited by Prasada Rao and Peter, Kluwer Academic / Plenum Publishers, New York, 1999. 2 H. Kobayashi et al. in the release of messenger molecules from the median eminence will also be described to some extent. The possible participation of the capillaries of the primary plexus and the portal vessels will be discussed in relation to the transfer of the messenger chemicals from the median eminence to the adenohypophysis. The involvement oftanycytes in the release of the messengers will be discussed. Brain peptides in the adenohypophysis are also con sidered with respect to the functional relationship between the median eminence and the adenohypophysis. 2. DEFINITION OF THE MEDIAN EMINENCE The neurohypophysis consists of the median eminence and the pars nervosa (Figure I). The pars nervosa is a mass that can easily be delineated anatomically, whereas the me dian eminence is difficult to delineate because it is not a simple lobe. It has not been nec essary, for general use, to define the median eminence in detail, and a definition was not completely established until recently. Tilney (1914, 1936) was the first to specify that, in humans, the median eminence is the portion of the tuber cinereum that protuberates from the third ventricle, and that begins to assume prominence immediately behind the optic chiasm, extending backward as far as the cephalic limits of the premammillary area. Diepen (1962) stated that Tilney's median eminence includes only the ventral wall of the neural stalk and that the dorsal wall should also be included (Figures I, 2a). Green (\951) defined the median eminence as that part of the neurohypophysis that receives its blood supply from the hypophysial portal circulation or that shares vascularization with the ade nohypophysis. This definition has physiological implications and is also applicable to the median eminence of lower vertebrates. However, these earlier definitions were based only Figure 1. Sagittal section showing the median eminence of the pigeon. AME, Anterior median eminence; DPME, dorsal posterior median eminence; OC, optic chiasma; PO, pars distal is; PME, posterior median eminence; PN, pars nervosa; PT, pars tuberalis; III, third ventricle; Gomori's aldehyde-fuchsin staining. The Median Eminence 3 on observations of the outer surface of the ventral portion of the tuber cinereum and they do not delineate an inner portion in the basal hypothalamus. In the recent usage of "me dian eminence" by many physiologists, the term seems to include the terminal portions of nerve axons and the processes of tanycytes and glial cells. Details of the structure of the median eminence, including these components, were shown schematically in an earlier re view (Kobayashi et al., 1970). The median eminence is concerned mainly with the release of hypothalamic releas ing hormones (RHs) and inhibiting hormones (IHs) from nerve endings into the capillaries of the primary plexus. Since we considered that tanycytes might be involved in the release of RHs and IHs (Matsui, 1966a, b; Kobayashi and Matsui, 1967; Kobayashi et al., 1970; see also Section 6), we defined the median eminence anatomically as follows: exteriorly it is the basal area of the hypothalamus that is vascularized by the capillaries of the primary plexus, which drain the pars distalis of the adenohypophysis; interiorly it is the portion of the basal hypothalamus delineated by the tanycytes and their processes that terminate at the capillaries of the primary plexus (Kobayashi et al., 1970; Figure 2). This definition is applicable to most vertebrates, but in the case of fishes some modifications are necessary (Kobayashi et al., 1970). In general, the median eminence, when defined as above, in cludes some portion of the arcuate nucleus in mammals (Figure 2) and some portion of the tuberal nucleus or infundibular nucleus in birds, reptiles and certain species of amphibi ans. The median eminence of fishes does not contain the cells of the nucleus tuberis later alis. Therefore, the presence of nerve cells is not a limiting factor in defining the median eminence (Kobayashi et al., 1970). Two types of tanycyte, a and /3, have been distin- a Figure 2. Diagram showing the me b dian eminence, which is clearly de lineated by the processes (P) of tanycytes (T). a, Sagittal section of the median eminence of the pigeon; b, frontal section of the median emi nence of the rat. AME, Anterior me dian eminence; LPC, capillary loops of the primary plexus; N, neuronal perikarya of the arcuate nucleus; OC, optic chiasma, PC, capillaries of the primary plexus; PME, posterior me dian eminence; PN, pars nervosa; PT, pars tuberalis; III, third ventricle (modified from Kobayashi et a!., 1970).
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