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This book deals with the mechanism of signal transduction in vertebrate and invertebrate photoreceptors. It contains contributions on the structure and function of rhodopsin or other G-coupled receptors, on the regulation of second messengers by enzyme cascade, the role of Ca2+ in light adaptation, control of ionic channels in photoreceptor cells.

This volume or1g1nates from a NATO Advanced Study Institute on'Photoreceptors'dedicated to M.G.F. Fuortes, held in Erice 1-12 July 1981. The lectures given at the course provided a general review of the photoreceptors functions in both vertebrate and inver­ tebrate eyes. Elaborating on the most recent hypotheses the lec­ tures also added new and interesting details. In order to preserve the novelty and freshness of the subject matter and thus ensure the usefulness of the volume, the authors in their written contributions emphasize more specific findings of their current research rather than the tutorial nature of the lectures actually presented. The contributors of this volume wish to dedicate their papers to the memory of Mike Fuortes, who has been for many of them an inspiring collegue and friend. Five papers that do not strictly pertain to the topics of the course are also included in the volume, the authors could not attend the meeting, but wanted to contribute an article to this memorial volume.

This book collects all the lectures presented during the NATO Advanced Study Institute on'Photoreception and Sensory Transduction in Aneura1 Organisms,'held in Villa Le Pianore (Versi1ia, Italy), September 3-14, 1979. In order to publish the lectures in the shortest possible time, we had to make the decision not to include the free communications, the informal seminars, and the panel discussions, notwithstanding their very high scientific level and interest. Only the final panel discussion has been summarized by Prof. W. Haupt (whose effort we gratefully acknowledge), because it gives a comprehensive view of the state of the art in this field. The ASI was intended to be a high-level course, characterized by an interdisciplinary approach to the problem of photoreception and photosensory physiology in aneural organisms, bringing together scientists from different fields and specializations. We hope that these characteristics are reflected in the content of the book, which is meant to be both an advanced textbook for researchers and students entering the field and a critical overview of the problems of photosensory transduction in aneura1 organisms. The topics pre­ sented range from a phenomenological description of the different photomotile responses in various microorganisms to a discussion of the molecular processes involved in the primary events of photo­ reception as well as in the subsequent steps of the transduction chain.

I see a man's life is a tedious one. Cymbeline, Act III, Sc. 6. It is well known that the best way to learn a subject is to teach it! Along the same lines one might also say that a pleasant way of learning a subject and at the same time getting to know quite a few of the workers active in it, is to arrange and to attend an Advanced Study Institute (ASI) or a workshop lasting about two weeks. This was and is the wisdom behind the NA TO-ASI programme and much as people fear that a fortnight may be too long, before it is over everyone feels that it was too short, especially if the weather had cooperated. Organising this ASI which resulted in this volume has been a very good learning experience. I started my career in research with invertebrates and retained an interest in them over the years due to my teaching a course and working sporadically on various aspects of photoreception in Polychaetes, Crustaceans and Insects. Thus, the thought of organising an ASI on photoreception and vision in invertebrates had been brewing in my mind for the past half a dozen years or so. It was felt that it will be desirable to do a bit of stock taking and discuss possible new approaches to the study of this matter.

The Seventh Symposium on Ocular and Visual Development was held in October, 1982. The aim of the meeting was to develop a broad perspective on visual acuity. The subject was discussed initially in terms of molecular events of photoreception, and the metabolism of the photoreceptor ele­ ments. Subsequent papers presented the development and complexity of the neurocircuitry and transmitter systems in the retina that process the visual information prior to transfer to the brain. The meeting concluded with a series of papers on behavioral and physiological methods of mea­ surement of visual acuity in humans, particularly young children. This volume arose from the papers presented at the meeting. We feel that the juxtaposition of research of broadly differing methodologies will be stim­ ulating, rather than daunting, and will generate an enhanced understand­ ing of this complex subject. We are indebted to our colleagues: Dr. M. Mote from Temple University, and Drs. J. Siegfried, P. Dayhaw-Barker, and L. Press from the Pennsylvania College of Optometry for their expertise and assistance in the organization of the meeting; to the speakers for their presentations and contributions to this volume; and to the reviewers of the manuscripts for their helpful comments. This symposium could not have been held without the generous support of the Temple University College of Arts and Sciences and the Pennsyl­ vania College of Optometry. We also thank Merck, Sharp and Dohme, Inc. for their donation.

This book is based on the lectures given at the NATO Advanced Study Institute on'Sensory Perception and Transduction in Aneural Organisms'held in Volterra (Pisa. Italy) from the third to the fourteenth of September. 1984. The Advanced Study Institute was planned as a high level course dealing with several aspects and problems of sensory perception and transduction of diverse environmental stimuli in aneural organisms. Scientists from different fields and cultural backgrounds were present at the meeting. both as lecturers and as students. The lectures and the discussions that followed represented a well integrated interdisci­ plinary approach to the questions considered. At the end of the Advanced Study Institute course. it was quite clear that. notwith­ standing the apparent heterogeneity of the topics dealt with. unifying concepts and ideas already existed, among the most important being the role of membranes and their physicochemical properties. All this should be reflected in the content of this book. We gratefully acknowledge the financial sponsorship of the Scientific Affairs Division of NATO (Brussels), that made both the Advanced Study Institute on'Sensory Perception and Transduction in Aneural Organisms'and this book possible. Finally. we are also indebted to Ms. Pat Parham Morgan who expertly retyped all the chapters of the book and Ms. Leslie Schmidt of Plenum Publishing Co. provided us valuable advice and suggestions on the preparation of this book. G. Colombetti F. Lenci P. S.

This volume contains the lectures given at the NATO Advanced Study Institute on'Biophysics of Photoreceptors and Photomovements in Microorganisms'held in Tir­ renia (Pisa), Italy, in September 1990. The Institute was sponsored and mainly funded by the Scientific Affairs Division of NATO; the Physical Science Committee and the Institute of Biophysics of National Research Council of Italy also supported the School and substantially contributed to its success. It is our pleasant duty to thank these institu­ tions. Scientists from very different backgrounds contributed to the understanding of this fast developing field of research, which has seen considerable progress during the last years. The areas of expertise ranged from behavioral sciences, supported by sophi­ sticated techniques such as image analysis or laser light scattering, to spectroscopy, ap­ plied, in different time domains, to the study of the primary photoreactions, to electro­ physiology, biochemistry or molecular biology, with the aim of analyzing the various steps of the transduction chains and how they control the motor apparatus of the cells. The organisms studied covered a wide range, from bacteria to algae, fungi and other eukaryotes. Thus, the ASI represented a successful opportunity for carrying on and imple­ menting an interdisciplinary approach to the study of the biophysical basis of photore­ ception and photosensory transduction in aneural organisms, with special attention to the basic phenomena and the underlying molecular events. We hope that this book has caught the spirit in which the ASI was conceived.

'... And the evening and the morning were the third day... And God made two great lights; the greater light to rule the day and the lesser light to rule the night... And the evening and the morning were the fourth day.'The First Book of Moses, called Genesis (1: 13,16,19). There was daytime and nighttime before there was a sun or a moon. An interesting thought: How long were each of those first three days? Without a sun to reckon its length, a day could have been longer or shorter than 24 hours. Animals, says Genesis, appeared on the fifth day and by that time the sun and moon were illuminating the earth, presumably in cyclic fashion and with a period of 24 hours. A good thing, too, as readers of this monograph will as­ certain. The papers collected into this volume are written versions of 45 minute talks given at a symposium on'The Effects of Constant Light on Visual Processes', held at The Florida State University in Tallahassee on April 25-27, 1979. The conference was supported by the Psychobiology Program and handled, logistically, by the Center for Professional Development and Public Services. It was recognized that limitations on time and funds made prohibitive the invitation of others who may be doing interesting and related work. But, our earnest hope is that what is compiled here is a good blend of'true'light-damage and'relevant related'work.

To create a forum for scientists and clinicians interested in degenerative retinal diseases, we began in 1984 to organize a biennial symposium on Retinal Degeneration as a satellite meeting of the International Congress of Eye Research. The timing and varying location of these meetings provides an important assembly for investigators from throughout the world to convene for presentation of their new findings on the causes and potential therapies for degenerative retinal disorders. The VIII International Symposium on Retinal Degeneration was held from July 28-25, 1998, at the Hotel Vier Jahreszeiten in Schluchsee, a small town in the Black Forest of southwestern Germany. Most of the participants in this meeting contributed to this volume, and we are appreciative of the efforts of each author in making this publication possible. The research presented at the meeting, and described in this proceedings volume, reflects a strong emphasis on the molecular genetic approach to understa- ing these disorders. Several of the papers provide important new insights into the mechanism of photoreceptor degeneration and cell death. A number of the studies are targeted at retarding or reversing the degeneration process. Included for the first time are presentations from all the principal laboratories involved in the field of visual prostheses-implant (chip) technology-in which investigations are targeted at restoring vision in eyes that have lost photoreceptor cells. A variety of diagnostic, clinical, histopathological, and physiological assessments of retinal degeneration in patients are also included.

Proceedings of a NATO ARW on Advances in Understanding Visual Processes: Convergence of Neurophysiological and Psychological Evidence, held in Roros, Norway, August 6-10, 1990