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Beyond Neurotransmission - P. Katz (Oxford, 1999) WW PDF

406 Pages·1999·23.35 MB·English
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Beyond Neurotransmission This page intentionally left blank Beyond Neurotransmission Neuromodulation and its Importance for Information Processing Edited by Paul S. Katz Department of Biology Georgia State University OXFORD UNIVERSITY PRESS Oxford University Press, Great Clarendon Street, Oxford OX2 6DP Oxford New York Athens Auckland Bangkok Bogota Bombay Buenos Aires Calcutta Cape Town Chennai Dar es Salaam Delhi Florence Hong Kong Istanbul Karachi Kuala Lumpur Madrid Melbourne Mexico City Mumbai Nairobi Paris Sao Paulo Singapore Taipei Tokyo Toronto Warsaw and associated companies in Berlin Ibadan Oxford is a trade mark of Oxford University Press Published in the United States by Oxford University Press Inc., New York © Oxford University Press, 1999 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, without the prior permission in writing of Oxford University Press. Within the UK, exceptions are allowed in respect of any fair dealing for the purpose of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act, 1988, or in the case of reprographic reproduction in accordance with the terms of licences issued by the Copyright Licensing Agency. Enquiries concerning reproduction outside those terms and in other countries should be sent to the Rights Department, Oxford University Press, at the address above. This book is sold subject to the condition that it shall not, by way of trade or otherwise, be lent, re-sold, hired out, or otherwise circulated without the publisher's prior consent in any form of binding or cover other than that in which it is published and without a similar condition including this condition being imposed on the subsequent purchaser. A catalogue record for this book is available from the British Library Library of Congress Cataloging in Publication Data Beyond neurotransmission : neuromodulation and its importance for information processing / edited by Paul S. Katz. Includes bibliographical references and index. 1. Neural transmission - Regulation. I. Katz, Paul S. [DNLM: 1. Neurotransmitters - physiology. 2. Neurons - physiology. 3. Mental Processes - physiology. QV 126B573 1999] QP364.5.B49 1999 573.8'54 - dc21 DNLM/DLC for Library of Congress 98-39256 CIP ISBN 0 19 852424 2 Typeset by Technical Typesetting Ireland in Belfast Printed in Great Britain by Bookcraft Ltd., Midsomer Norton, Avon Foreword by Ronald M. Harris-Warrick It wasn't very long ago that most neuroscientists thought the brain was a black and white world: all chemical communication in the nervous system was mediated by either rapid excitatory or rapid inhibitory synaptic poten- tials, and the major role of neurons was to algebraically summate synaptic input and decide whether or not to spike. That time is now gone, as this fine introduction to neuromodulation makes abundantly clear. We now know that there is a huge diversity of non-traditional modes of neuronal communi- cation, grouped under the general name of neuromodulation, which creates a multicolored rainbow of varied ways for neurons to be affected and to affect one another. Paul Katz, one of the most innovative leaders in this field, has selected an international group of experts to bring together a superb summary of the cutting edge of research spanning the full range of this growing and exciting field, from biochemical mechanisms of receptors and second messengers to behavioral analyses of neuromodulation during learning. Since neuromodula- tion is ubiquitous and affects every part of nervous system function, neurosci- entists of all stripes can benefit from reading this book; it should provoke new research in a number of areas. Scientists studying molecular and cellular aspects of nervous system function will deepen their understanding of the complexities of molecular modulation. Systems neuroscientists working at higher levels will also see how neuromodulation permeates their field: it is no longer possible to discuss sensory processing or motor coordination without a full recognition of the many roles that non-traditional forms of neuronal activity and communication play. Behavioral pharmacologists who work with neuromodulators such as amines and peptides will recognize that the terms 'excitatory' and 'inhibitory' only hint at the complex functions that compound such as dopamine and serotonin play in affecting higher level functions. Even high-level modelers and neurophilosophers will find useful reminders of the fractal nature of the real nervous system in which each neuron is an independent microprocessor, with variable baseline states and variable non-linear input/output functions that are controlled by the modu- latory milieu. For all of us who study the brain, the moment-to-moment plasticity of properties of neurons and their connections is central to all higher order cognitive function, and cannot be ignored. By giving an accessible yet thorough survey of the field of modulation, Katz and his colleagues are showing all of us a better view of the machinery of the real brain. The reader should be prepared to accept a quantum leap in their perception of the complexity of neural function. Thanks to the actions of neuromodulators, the number of possible interactions and states of activity vi Foreword in the brain is inconceivably greater than was previously thought. This revelation is delightful and exciting, and gives us a glimmer of understanding into how magnificent human brains could have created Hamlet and The Art of the Fugue. Preface As neuroscientists, our goal is to understand how nervous systems process information. What steps occur in the brain during decision making? How do animals perceive their environment? How do animals learn? One problem that we face is that we don't know all of the forms that information takes in the nervous system, nor how it is communicated. Often there is an underlying assumption that information is transferred through the nervous system in the form of neurotransmission consisting of fast excitatory postsynaptic poten- tials (EPSPs) and fast inhibitory postsynaptic potentials (IPSPs); all other neuronal actions, such as neuromodulation, are usually considered secondary and not really involved in active information transfer. This view of informa- tion flow dismisses what may be some of the brain's most important computational capabilities. The aim of this book is to explore these other mechanisms of transferring information through the nervous system. The title of this book, Beyond Neurotransmission, is not meant to imply that we already understand all the implications of neurotransmission. In fact, it can be said that we may be misled by the apparent simplicity of neurotransmission. Rather, the point that we are making is that there are many other forms of neuronal communi- cation that also need to be considered when trying to understand how nervous systems process information. Although the term neuromodulation has been in common usage for more than 20 years, there is still a great deal of disagreement about what it means, as I found when I conducted an informal survey of my colleagues working in the field. I asked them to label particular situations as either: A) Neurotransmission, B) Neuromodulation, C) Neither, D) Both, or E) Cannot be determined from this information. Here are the responses that I received from three of the situations: Situation 1) Slow EPSPs such as peptidergic, muscarinic, or aminergic input to sympathetic ganglia. Responses: 33% of the respondents said it was an example of neurotransmission because the inputs caused a depolarization, 33% said it was neuromodulation because these inputs have slow actions, and 33% said it was both neurotransmission and neuromodulation. viii Preface Situation 2) A morphologically defined synapse that uses G protein-coupled receptors (i.e. metabotropic receptors). Responses: 25% of the respondents said that this would be considered neurotransmis- sion because it was a morphologically defined synapse, 25% said neuromodulation because anything with a metabotropic receptor is modulatory, 25% said it was both neurotransmission and neuromodulation, and 25% said that it can't be determined from this information. Situation 3) Presynaptic inhibition (e.g. GABA inputs onto axonal terminals). Responses: 40% said neurotransmission because it involves morphologically defined synapses and ionotropic receptors and 60% said this would be neuromodulation because the presynaptic inhibition alters the strengths of synapses. This informal poll convinced me that the book needed to begin by addressing what neuromodulation is. It is of little use to again attempt to strictly define neuromodulation or coin new terms. This just leads to more disagreements over semantics. The important point here is that, regardless of what we call them, there are more modes for communication of information in the nervous system. In this case, neuromodulation is as good a term as any. This book seeks to examine neuromodulation and its functional role in information flow and neural circuit flexibility. It has three functional divi- sions: 1. The first section of the book deals with the mechanisms of neuromodula- tion. It is intended to provide a basis for systems physiologists to catch up with some of the latest cellular concepts in neuromodulation. It takes a large volume of current literature and synthesizes some fundamental principles for neuromodulation and cellular signaling. • Chapter 1 begins by exploring some of the alternate forms of neuronal communication and why they are important for understanding how the brain works. • Chapter 2 discusses the roles that intercellular messengers play in both neurotransmission and neuromodulation. It defines how neurons commu- nicate information and the roles that neurotransmitters and receptors play in defining the message. • Chapter 3 reviews our current knowledge of intracellular second messen- ger processes involved in neuromodulation. This is a review of how modulatory signals are translated into cellular actions. Preface ix • Chapter 4 examines how neurons change their behavior in response to neuromodulatory signals. The control of neuronal properties is what really defines neuromodulatory communication. • Chapter 5 discusses the concept of metaplasticity where plasticity itself can be altered. This chapter offers a slightly different perspective on the importance of heterosynaptic versus homosynaptic mechanisms in the control of synaptic plasticity. 2. In order to understand the roles played by neuromodulation in vivo., it is necessary to look at how systems of neurons use neuromodulation to process information. Therefore, the second section of the book focuses on the use and control of neuromodulation. These chapters provide useful examples from many different systems. They serve to illustrate the impor- tance of neuromodulatory signaling in information flow in the nervous system. I hope these chapters will also inspire systems physiologists to consider how neuromodulation might be operating in their own experi- mental systems. • Beginning with information entering the nervous system, Chapter 6 ex- plores how neuromodulation affects sensory processing. It shows that neuromodulation has effects at every stage of sensory processing. • Chapter 7 looks at the output of the nervous system by examining how neuromodulation alters neuromuscular transmission and what role that alteration plays in the production of muscular movements. This chapter also gives a more general look at the role that neuromodulation plays in matching input/output properties of senders and receivers. • Chapter 8 examines how neuromodulation enables the nervous system to generate different patterns of activity which are translated into move- ments. Here the actions of neuromodulators on the basic mechanisms of motor pattern generation are shown to enable neuronal circuits to pro- duce flexible outputs. • Neuromodulation also plays many important roles in learning, memory, and attention, as is discussed in Chapter 9. This chapter is important because it stresses the need for mechanisms that go beyond long-term potentiation (LTP) in models of associative learning. 3. Finally, the last section of the book deals with the next level of complex- ity, modulation of modulation or metamodulation. Chapter 10 investi- gates the various ways that neuromodulation itself is controlled. I feel that this is the next direction for work in the field. To answer questions about information processing in the nervous system, researchers begin by asking how individual systems of neurons operate to produce particular forms of behavior. For example, one may study how the neurons in the abdominal nerve cord in a crayfish communicate with each

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