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Melanopsin-expressing retinal ganglion cells (mRGC) are intrinsically photosensitive and combine their melanopsin-based photoresponses with rod and cone signals to convey light information to a subset of retinal brain targets. mRGC axons to non-image forming (NIF) visual centers are essential for the proper functioning of processes like circadian photoentrainment and pupillary light reflex. Surprisingly, mRGCs also send axons to image-forming regions of the brain. It is unknown how mRGCs mediate such diverse functions. Classically, a cell's morphology and location in a biological system is a direct reflection of its synaptic connections and, by definition, their function. mRGCs can be divided into five subtypes (M1-M5) based on morphology and dendritic stratification in the inner plexiform layer. In the classical sense, since M1s send axons to only a subset of mRGC-target regions and are the only subtype that monostratify in the OFF-sublamina, M1s likely serve a distinct function from other subtypes. However, M1s, like all mRGCs, exhibit an ON-response. This reveals a hole in what we understand about intraretinal connectivity and attenuates the weight that should be afforded to stratification in determining function. While the other mRGC subtypes have distinct morphology and branching patterns, it is unknown whether they serve specific functions. Thus, in order to explore the structure-function relationship of mRGC subtypes, we must consider connectivity. Unfortunately, the variable expression of melanopsin protein between subtypes and across the architecture of a single mRGC and the lack of unique markers for up- and downstream interactors has precluded rigorous study of mRGC connectivity in the retina and central targets. We use a correlated light and electron microscopy label and serial blockface scanning electron microscopy to explore the architecture and synaptic partners of mRGCs in an attempt to better understand the connectivity of mRGC subtypes. We show significant differences in the ultrastructure of mRGC axonal terminals in mRGC-recipient brain regions, stratification-specific differences in mRGC dendrites, and catalog the intraretinal connections specific to mRGC subtypes.
Intrinsically photosensitive retinal ganglion cells (ipRGGs) are the most recently discovered photoreceptor class in the human retina. This Element integrates new knowledge and perspectives from visual neuroscience, psychology, sleep science and architecture to discuss how melanopsin-mediated ipRGC functions can be measured and their circuits manipulated. It reveals contemporary and emerging lighting technologies as powerful tools to set mind, brain and behaviour.
Photons are sensed by retinal photoreceptors whose matrix-like distribution underlies the transformation of illumination patterns of the visual scene into photoreceptor activity patterns in a visuotopic fashion. Activity of neighboring photoreceptors then are compared by secondary bipolar cells to decipher information regarding luminosity- and color-contrast. Bipolar cells achieve this by comparing signals received directly from their center receptive field with those come from spatially offset surrounding receptive field areas mediated by inhibitory, sign-inverting horizontal cells. This information is ultimately sent to retinal ganglion cells, the output neurons of the retina. In addition to the excitatory bipolar cell inputs, spatial and temporal features of ganglion cell activation are robustly modified by inner retinal amacrine cells through inhibitory chemical and/or excitatory electrical synaptic inputs. Ganglion cells sample various bipolar cell subtypes in their dendritic field and utilize collected inputs to generate a spike output code on luminosity-contrast, color-contrast, object motion, background motion, motion direction, changes in background illumination in a subtype specific manner. Ganglion cells in each subtype cover the retinal surface economically, thus collective information across the population provide a feature pattern and through time a feature movie to the brain. Some of these movies are utilized for image perception, whereas others are sent to accessory visual brain centers to control eye-movement, pupil contraction or circadian entrainment. A large body of information has been revealed in the past decade regarding this field, however much of the details still remain unknown or even enigmatic, including: (i) the precise description of neural circuits that serve each ganglion cell subtype to generate a specific feature movie; (ii) the estimation of the number of various ganglion cell subtypes that partake in image forming and non-image forming signaling towards the brain; (iii) the description of changes in the inputs, morphology and signaling of retinal ganglion cells when the tissue is under stress or undergoes disease related degenerative processes; (iv) the comparison of ganglion cell classes with those of the human retina and finally, (v) the practical use of all the above information to establish retina inspired visual algorithms to suit computer, drone and/or robotic vision. Therefore, research articles in this issue were collected to touch upon each of these topics and highlight recent advances of the related field.
Across the developing nervous system, immature networks generate spontaneous activity that is highly correlated amongst neighboring cells, which is required for the correct establishment of adult neural circuits. Remarkably, correlated activity persists following disruption of the underlying circuits that mediate it, indicating that plasticity mechanisms exist to ensure correlated activity is maintained. Here, we examine this phenomenon in the developing mouse retina, where correlated activity is mediated by cholinergic transmission and propagates across the retina as a wave. The absence of cholinergic signaling leads to the generation of "recovered" waves that propagate through a distinct, gap junction mediated circuit. Our findings show that stimulation of melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs) facilitates recovery of correlated activity in the absence of cholinergic waves, which results in the emergence of a light-sensitive network. We tested whether pharmacological blockade of cholinergic waves altered retinal light-response properties. We observed an increase in the duration of light-evoked activity and number of light-responsive cells, which arose from signaling via gap junctions. These observations suggest that electrical coupling of ipRGCs increases in the absence of cholinergic input, allowing melanopsin-driven signals to propagate to other neurons. Furthermore, we show that light-sensitive waves are strongly modulated by dopamine signaling--a potent neuromodulator of gap junction coupling. We determine that this light-sensitive wave circuit is present but latent in wild type retina, where it is usually suppressed by a combination of cholinergic and dopaminergic signaling. Our observations indicate that dopamine signaling acts as a switch for network reconfiguration, where high dopamine silences the light-sensitive, gap junction coupled network under cholinergic waves and reduced dopamine activates it in the absence of cholinergic waves. We conclude that the wiring diagram of the developing retina includes several overconnected circuits, in which some circuits are closed and others activated depending on the internal state of the system.
Leading authors review the state-of-the-art in their field of investigation, and provide their views and perspectives for future researchChapters are extensively referenced to provide readers with a comprehensive list of resources on the topics coveredAll chapters include comprehensive background information and are written in a clear form that is also accessible to the non-specialist Leading authors review the state-of-the-art in their field of investigation, and provide their views and perspectives for future research Chapters are extensively referenced to provide readers with a comprehensive list of resources on the topics covered All chapters include comprehensive background information and are written in a clear form that is also accessible to the non-specialist
John Dowling’s The Retina, published in 1987, quickly became the most widely recognized introduction to the structure and function of retinal cells. In this Revised Edition, Dowling draws on twenty-five years of new research to produce an interdisciplinary synthesis focused on how retinal function contributes to our understanding of brain mechanisms. The retina is a part of the brain pushed out into the eye during development. It retains many characteristics of other brain regions and hence has yielded significant insights on brain mechanisms. Visual processing begins there as a result of neuronal interactions in two synaptic layers that initiate an analysis of space, color, and movement. In humans, visual signals from 126 million photoreceptors funnel down to one million ganglion cells that convey at least a dozen representations of a visual scene to higher brain regions. The Revised Edition calls attention to general principles applicable to all vertebrate retinas, while showing how the visual needs of different animals are reflected in their retinal variations. It includes completely new chapters on color vision and retinal degenerations and genetics, as well as sections on retinal development and visual pigment biochemistry, and presents the latest knowledge and theories on how the retina is organized anatomically, physiologically, and pharmacologically. The clarity of writing and illustration that made The Retina a book of choice for a quarter century among graduate students, postdoctoral fellows, vision researchers, and teachers of upper-level courses on vision is retained in Dowling’s new easy-to-read Revised Edition.
This advanced text, first published in 2006, takes a developmental approach to the presentation of our understanding of how vertebrates construct a retina. Written by experts in the field, each of the seventeen chapters covers a specific step in the process, focusing on the underlying molecular, cellular, and physiological mechanisms. There is also a special section on emerging technologies, including genomics, zebrafish genetics, and stem cell biology that are starting to yield important insights into retinal development. Primarily aimed at professionals, both biologists and clinicians working with the retina, this book provides a concise view of vertebrate retinal development. Since the retina is 'an approachable part of the brain', this book will also be attractive to all neuroscientists interested in development, as processes required to build this exquisitely organized system are ultimately relevant to all other parts of the central nervous system.
A comprehensive review of contemporary research in the vision sciences, reflecting the rapid advances of recent years. Visual science is the model system for neuroscience, its findings relevant to all other areas. This essential reference to contemporary visual neuroscience covers the extraordinary range of the field today, from molecules and cell assemblies to systems and therapies. It provides a state-of-the art companion to the earlier book The Visual Neurosciences (MIT Press, 2003). This volume covers the dramatic advances made in the last decade, offering new topics, new authors, and new chapters. The New Visual Neurosciences assembles groundbreaking research, written by international authorities. Many of the 112 chapters treat seminal topics not included in the earlier book. These new topics include retinal feature detection; cortical connectomics; new approaches to mid-level vision and spatiotemporal perception; the latest understanding of how multimodal integration contributes to visual perception; new theoretical work on the role of neural oscillations in information processing; and new molecular and genetic techniques for understanding visual system development. An entirely new section covers invertebrate vision, reflecting the importance of this research in understanding fundamental principles of visual processing. Another new section treats translational visual neuroscience, covering recent progress in novel treatment modalities for optic nerve disorders, macular degeneration, and retinal cell replacement. The New Visual Neurosciences is an indispensable reference for students, teachers, researchers, clinicians, and anyone interested in contemporary neuroscience. Associate Editors Marie Burns, Joy Geng, Mark Goldman, James Handa, Andrew Ishida, George R. Mangun, Kimberley McAllister, Bruno Olshausen, Gregg Recanzone, Mandyam Srinivasan, W.Martin Usrey, Michael Webster, David Whitney Sections Retinal Mechanisms and Processes Organization of Visual Pathways Subcortical Processing Processing in Primary Visual Cortex Brightness and Color Pattern, Surface, and Shape Objects and Scenes Time, Motion, and Depth Eye Movements Cortical Mechanisms of Attention, Cognition, and Multimodal Integration Invertebrate Vision Theoretical Perspectives Molecular and Developmental Processes Translational Visual Neuroscience