This is a remarkable time to study the vertebrate retina, either as a model for the brain or to understand the first steps in vison. We have known about the diversity of retinal neurons and glia for more than one hundred years, and we are now extending these findings and making new discoveries about retinal cell types by analyzing gene expression in single cells. We have made significant progress toward our ultimate goals of describing the neural circuits in the retinas at the level of connections between identified populations of neurons and understanding neuronal and glial cell function at the molecular level. We have also made great strides toward understanding retinal development and the etiology of retinal diseases. Physiologists are now using more realistic stimuli and modern analytical methods to analyze the mechanisms underlying light responses of retinal neurons, and this has led to more accurate computational models of neural circuits in the retina. My colleague at the McGovern Medical School in Houston, Steve Massey, has made many important contributions to this field, both as a researcher and as a mentor, and he is planning his retirement. Judith Ogilvie, Christophe Ribelayga, Chai-an Mao and I will dedicate this issue to him and plan to publish some of his latest work. This Research Topic will include mini-reviews and brief communications about neurons and neural circuits in vertebrate retinas. The scope will be very broad, including anatomical, physiological, psychophysical and computational approaches to this topic. Potential topics include, but are not restricted to: • Development. morphology and synaptic connections of neuronal types • Light responses, spontaneous activity and membrane properties of retinal neurons • Gene expression and other aspects of cell biology of identified retinal neurons • Release of neurotransmitters and modulators and their effects in the retina • Structure and function of electrical synapses in the retina • Neural circuits that mediate responses to color, contrast and movement • Roles of neuroglia in retinal development, homeostasis and light responses • Contributions of neural circuits in the retina to visual perception • Evolution of neuronal types and neural circuits in the retina • Novel techniques for analyzing retinal neurons and neural circuits • Non-invasive methods to analyze retinal structure and function • Etiology of retinal diseases and potential new therapies • Directions for future research on the vertebrate retina

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.