Regeneration: New Neurons Wire Up Pamela A. Raymond  Current Biology  Volume 26, Issue 17, Pages R794-R796 (September 2016) DOI: 10.1016/j.cub.2016.07.026 Copyright © 2016 Elsevier Ltd Terms and Conditions

Figure 1 Regenerated retinal neurons re-establish neural circuits. The structure of the eye is remarkably similar across vertebrate species, including humans (schematic at upper left). The retina is a hemispheric sheet of neural tissue lining the back of the eye, connected to the brain through the optic nerve. The upper right panel is a cross-sectional view of the neural retina and retinal pigmented epithelium in zebrafish, and again, the basic features are characteristic of all vertebrates. Photoreceptors in zebrafish include rods and four cone subtypes with distinct spectral absorption curves that peak at different wavelengths — red, green, blue, and ultraviolet (UV). The most direct pathway of information flow in the retina is vertical (radial in the eye): light is converted to neural signals by photoreceptors, which relay neural information to interneurons (bipolar cells), which in turn signal to the projection neurons (retinal ganglion cells) whose axons (the optic nerve) transmit neural information to higher order visual centers in the brain. Other classes of interneurons (horizontal and amacrine cells) are involved in the lateral flow of information and additional neural processing. For example, starburst amacrine cells exhibit direction-selectivity in their responses to visual stimuli, a feature important for motion detection. Interneurons in the inner nuclear layer and retinal ganglion cells respond differentially to increases (ON) and decreases (OFF) in illumination, and the dendritic and axonal processes of ON and OFF neurons are segregated in ‘On’ and ‘Off’ sublaminae in the synaptic plexus. The response of zebrafish to ablation of retinal neurons (e.g., bipolar cells) is illustrated in the lower right panel: Müller glial cells divide asymmetrically and give rise to retinal progenitor cells (magenta). The lower left panel shows regenerated bipolar cells (magenta), which largely re-establish their stereotyped neural connections. AC, amacrine cell; BC, bipolar cell; C, cone; GC, ganglion cell; GCL, ganglion cell layer; HC, horizontal cell; ILM, inner limiting membrane; INL, inner nuclear layer; MG, Müller glia; OLM, outer limiting membrane; ONL, outer nuclear layer; SAC, starburst amacrine cell; RPE, retinal pigmented epithelium; R, rod; RPC, retinal progenitor cell. Current Biology 2016 26, R794-R796DOI: (10.1016/j.cub.2016.07.026) Copyright © 2016 Elsevier Ltd Terms and Conditions