Neuropeptides: Regulators of Physiological Processes

Abstract

Since the discovery of the enkephalins and other naturally occurring opioid peptides in the 1970s, there has been intense interest in the neuropeptides as chemical messengers in the nervous system and there have been rapid advances in research in this field. Hastened by the advent of molecular neurobiology techniques there has been a flood of new discoveries of neuropeptides and their associated cellular receptors, and some 50 different vertebrate neuropeptides are now known.Given the complexity and rapid growth of research on neuropeptides it is perhaps not surprising that few texts have attempted to give an overview of this field. We should, therefore, be grateful to Fleur Strand for her well-written and comprehensive monograph. The author is an experienced neuroscientist who has been actively involved in research and teaching on the subject of neuropeptides, and the book is a coherent and readable volume that provides a great deal of valuable information to advanced students and others who are interested in neuropeptides. The book is well prepared with clear illustrations, and a comprehensive bibliography and index.The author provides an easily understood review of the many different experimental approaches needed to study the genes, receptors, distribution, biosynthesis, release and actions of the neuropeptides. These include molecular neurobiology techniques, immunohistochemical-mapping procedures, the use of genetically engineered animals and studies of peptide actions at the cellular and systemic levels, using neurochemical, neurophysiological and behavioural analyses. A section on the relationship between neuropeptides, stress and the immune system is particularly well prepared, as is the explanation of the physiological roles of neuropeptides in the broader context of biology and evolution.Inevitably the largest section of the book is devoted to a series of detailed chapters on individual families of neuropeptides. A large section concerns the hypothalamic releasing hormones, neurohypophyseal and anterior pituitary peptide hormones. An idiosyncrasy of the author is that her definition of ‘neuropeptide’ includes any peptide that has an action in the nervous system, regardless of whether it is secreted by neural or non-neural tissue. Thus, as adrenocorticotrophic hormone has an effect on behaviour that is mediated centrally, it is classified as a ‘neuropeptide’. I found this somewhat confusing and it leads to the inclusion of almost every peptide hormone, including those that originate from the the gut, kidney, heart, parathyroid and thyroid. A more-common definition of a ‘neuropeptide’ would be that it is secreted from a neurone. Students might well be confused to see all the endocrine peptides mixed together with the neuropeptides in the various chapters on peptide families. Nevertheless, there are good reviews of the endogenous opioid peptides; substance P and other tachykinins; and the gut–brain peptides, cholecystokinin, vasoactive intestinal polypeptide, neuropeptide Y, galanin, calcitonin-gene-related peptide and neurotensin.Each chapter concludes with a detailed summary of the conclusions drawn, highlighting the main concepts, which makes for easy review. A concluding section on invertebrate neuropeptides again mixes peptides of neural and non-neural origin but provides a valuable overview of the evolution and biological importance of peptides as chemical signalling molecules.Neuropeptides represents a praiseworthy attempt to review a large and still rapidly changing field in some detail. A monograph is always much preferable to the commoner multi-authored (and often disjointed) works. This monograph has the coherence that comes from the consistency of style and approach to the various different area of the field. However, I must confess to some disappointments. As in other areas of neuroscience, the impact of molecular neurobiology in this field has been immense. It has lead to the rapid discovery of new members of neuropeptide families and hitherto unsuspected neuropeptide-receptor subtypes. The use of genetically engineered animals, especially knockout mice that lack particular neuropeptide receptors or neuropeptides, has become increasingly important. Although these techniques are mentioned, their full impact is lost and there are no descriptions of specific examples such as the opioid-receptor or tachykininreceptor knockouts, which have contributed greatly to new insights in recent years. Another curious omission was information on the many different non-peptide antagonists that act at known neuropeptide receptors. The only reference to such compounds comes in discussions of naloxone and related compounds that act at opiate receptors, and non-peptide antagonists that act at angiotensin receptors. However, the 1990s have seen the discovery of many other nonpeptide antagonist drugs that target receptors for substance P, cholecystokinin, neuropeptide Y, corticotropin releasing factor and many others. Omission of any reference to these important new developments leaves an unfortunate gap in this book. In writing such a heroic monograph, however, it is unlikely that anyone will satisfy all readers and overall this volume does represent a very good resource. [Readers interested in the latest developments in the neuropeptide field might be interested in the symposium ‘Neuropeptides at the Millenium’ to be held in Miami, 21–23 October 1999 (http://www.elsevier.nl/locate/bri99)].