The mature vertebrate retina is a highly complicated array of several kinds of cells, capable of receiving light impulses, transforming them into neuronal membrane currents, and transmitting these in a meaningful way to central processing. Before it starts to develop, it is a small sheet of unconspicuous cells, which do not differ from other cells of the central nervous system. The chain of events which lead to the trans formation from this stage into that of highly specialized cells ready to fulfll a specific task, is usually called "differentiation. " Originally, this word indicated firstly the proc ess of divergence from other cells which were previously alike, and secondly, the change from an earlier stage of the same cello lt has become widespread practice to imply by the word "differentiation" also the acquisition of specific properties and capacities which are characteristic of a mature, Le. , specifically active, cello Every cell is active at any stage of development, but certain activities are shared by most cells (e. g. , the activities of preparing and accomplishing proliferation, that of initiating development, that of maintaining a certain level of metabolism), while there are others which are shared by only a small number of - originally relate- cells. In most cases these latter activities are acquired by the fmal steps of cellular development, the terminal "differentiation. " In the context of the present paper, the word "function" will refer to this latter type of specific activity.

The vertebrate retina has a form that is closely and clearly linked to its func tion. Though its fundamental cellular architecture is conserved across verte brates, the retinas of individual species show variations that are also of clear and direct functional utility. Its accessibility, readily identifiable neuronal types, and specialized neuronal connectivity and morphology have made it a model system for researchers interested in the general questions of the genet ic, molecular, and developmental control of cell type and shape. Thus, the questions asked of the retina span virtually every domain of neuroscientific inquiry-molecular, genetic, developmental, behavioral, and evolutionary. Nowhere have the interactions of these levels of analysis been more apparent and borne more fruit than in the last several years of study of the develop ment of the vertebrate retina. Fields of investigation have a natural evolution, rdoving through periods of initial excitement, of framing of questions and controversy, to periods of synthesis and restatement of questions. The study of the development of the vertebrate retina appeared to us to have reached such a point of synthesis. Descriptive questions of how neurons are generated and deployed, and ques tions of mechanism about the factors that control the retinal neuron's type and distribution and the conformation of its processes have been posed, and in good part answered. Moreover, the integration of cellular accounts of development with genetic, molecular, and whole-eye and behavioral accounts has begun.

"Who would believe that so small a space could contain the images of all the universe?" Leonardo da Vinci The last years of the 20th century have found the discipline of Developmental Biology returning to its original position at the forefront of biological re search. This progress can be attributed to the burgeoning knowledge base on molecules and gene families, and to the power of the molecular genetic ap proach. Topping the list of organ systems which have provided the most significant advances would have to be the eye. The vertebrate eye was one of the classic embryologic models, used to demonstrate many important prin ciples, including the concepts of inductive tissue interactions first put forth in the early 1900s. Within the last decade of this century, a return to some of the old questions with the new approaches has put eye development back into the limelight. I find this a highly appropriate topic for a book which aims to spark research for the new millennium. We begin with a chapter that discusses the anatomy of eye development, providing the basic reference information for the chapters that follow. A novel aspect of this introduction is the connection made between develop mental strategies and the eye's optical function. What also emerges from this chapter is the number of important eye structures that have barely been touched by the modern developmental biologist. Work on cornea and ante rior chamber development has lagged behind lens and retina.

Synapse Development and Maturation, the latest release in the Comprehensive Developmental Neuroscience series, presents the latest information on the genetic, molecular and cellular mechanisms of neural development. The book provides a much-needed update that underscores the latest research in this rapidly evolving field, with new section editors discussing the technological advances that are enabling the pursuit of new research on brain development. This volume focuses on the synaptogenesis and developmental sequences in the maturation of intrinsic and synapse-driven patterns. Features leading experts in various subfields as section editors and article authors Presents articles that have been peer reviewed to ensure accuracy, thoroughness and scholarship Includes coverage of mechanisms which regulate synapse formation and maintenance during development Covers neural activity, from cell-intrinsic maturation, to early correlated patterns of activity

This book provides a series of comprehensive views on various important aspects of vertebrate photoreceptors. The vertebrate retina is a tissue that provides unique experimental advantages to neuroscientists. Photoreceptor neurons are abundant in this tissue and they are readily identifiable and easily isolated. These features make them an outstanding model for studying neuronal mechanisms of signal transduction, adaptation, synaptic transmission, development, differentiation, diseases and regeneration. Thanks to recent advances in genetic analysis, it also is possible to link biochemical and physiological investigations to understand the molecular mechanisms of vertebrate photoreceptors within a functioning retina in a living animal. Photoreceptors are the most deeply studied sensory receptor cells, but readers will find that many important questions remain. We still do not know how photoreceptors, visual pigments and their signaling pathways evolved, how they were generated and how they are maintained. This book will make clear what is known and what is not known. The chapters are selected from fields of studies that have contributed to a broad understanding of the birth, development, structure, function and death of photoreceptor neurons. The underlying common word in all of the chapters that is used to describe these mechanisms is “molecule”. Only with this word can we understand how these highly specific neurons function and survive. It is challenging for even the foremost researchers to cover all aspects of the subject. Understanding photoreceptors from several different points of view that share a molecular perspective will provide readers with a useful interdisciplinary perspective.