Immature retinal neurons spontaneously generate correlated activity in the form of waves of action potentials that sweep across the retinal ganglion cell layer. These retinal waves occur during the developmental period when functional circuits within the retina are emerging and retinal projections to the brain are undergoing a tremendous amount of refinement. Though significant progress in elucidating the circuits that mediate these waves has been achieved, the mechanisms that underlie the reliable generation of retinal waves is not fully understood. Here we explore the circuits that robustly generate retinal waves. Retinal waves are mediated by different circuits at different stages of development. In the first postnatal week, a circuit consisting of cholinergic interneurons, called starburst amacrine cells (SACs), mediates waves. During the second postnatal week, glutamatergic interneurons called bipolar cells mediate waves. Although cholinergic and glutamatergic waves are mediated by distinct circuits, they share one characteristic: the depolarization propagates across cells that do not have direct synaptic connections. Using two-photon calcium imaging and state-of-art optical sensors that measure[?] extrasynaptic release of ACh and glutamate, we will test the hypothesis that these waves propagate via volume transmission. In addition, we will study the influence of intrinsically photosensitive retinal ganglion cells (ipRGCs) on retinal waves. While ipRGCs do modulate waves in WT mice, they more dramatically modulate the compensatory waves found in knockout mice lacking the ?2 subunit of the nicotinic acetylcholine receptor (?2KO). ?2KO mice exhibit significantly different patterns of spontaneous activity than WT mice, and therefore have served as a primary model system for understanding the role of retinal waves in visual system development. We propose using multielectrode and targeted recordings from WT and ?2KO mice expressing GFP in ipRGCs to explore the novel hypothesis that ipRGCs regulate firing patterns in the developing retina by altering the dopamine level. This work will address the principles of general organization that are responsible for generating the activity patterns that drive activity-dependent developmental processes. It should also elucidate the principles that govern the normal development of the human nervous system, thus making it possible to understand the origin of neurological birth defects and to devise strategies that enable the nervous system to regenerate functioning neural circuits after injury.
Retinal waves are highly correlated spontaneous firing patterns detected in the developing retina prior to maturation of visual responses and they are critical source of activity to drive the refinement of connections throughout the developing visual system. Retinal waves are a robust phenomenon detected in many vertebrate species and persisting through the changing circuits of the developing retina. Our work will determine what the features of developing retinal circuits that are responsible for this robustness. Developing a detailed understanding of the organizing principles that govern the normal development of the circuits may make it possible to understand the origin of neurological birth defects.
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