Abstract
In most mammals, retinal ganglion cell axons from each retina project to both sides of the brain. The segregation of ipsi and contralateral projections into eye-specific territories in their main brain targets—the dorsolateral geniculate nucleus and the superior colliculus—is critical for the processing of visual information. The investigation of the developmental mechanisms contributing to the wiring of this binocular map in mammals identified competitive mechanisms between axons from each retina while interactions between axons from the same eye were challenging to explore. Studies in vertebrates lacking ipsilateral retinal projections demonstrated that competitive mechanisms also exist between axons from the same eye. The development of a genetic approach enabling the differential manipulation and labeling of neighboring retinal ganglion cells in a single mouse retina revealed that binocular map development does not only rely on axon competition but also involves a cooperative interplay between axons to stabilize their terminal branches. These recent insights into the developmental mechanisms shaping retinal axon connectivity in the brain will be discussed here.
Highlights
The accurate processing of visual information relies on the precise tuning of visual system connectivity
We provide a brief overview of the inter-eye competitive mechanisms and further describe the studies that explored the interplay between axons from the same eye, including those conducted in vertebrate species lacking ipsilateral retinal ganglion cells (RGCs)
Whether retinal waves play a permissive or instructive role in the formation of binocular maps remained to be clarified. This controversy was elegantly solved by studying transgenic mice in which spontaneous cholinergic waves were spatially reduced without affecting the overall activity of RGCs (Xu et al, 2011). This slight alteration of the structural properties of spontaneous activity is sufficient to impair the segregation of eye-specific territories in the superior colliculus (SC) and dorsolateral geniculate nucleus (dLGN), suggesting that retinal activity is not sufficient to shape binocular maps and that structured and correlated activity between neighboring RGC axons is required to fine-tune visual map connectivity (Xu et al, 2011)
Summary
The accurate processing of visual information relies on the precise tuning of visual system connectivity. This slight alteration of the structural properties of spontaneous activity is sufficient to impair the segregation of eye-specific territories in the SC and dLGN, suggesting that retinal activity is not sufficient to shape binocular maps and that structured and correlated activity between neighboring RGC axons is required to fine-tune visual map connectivity (Xu et al, 2011). Investigations in tadpoles highlight that Hebbian and Stentian mechanisms control the dynamic remodeling of axonal branches, influencing the activity-based competitive interplay required for the segregation of retinal axons in eye-specific territories.
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