The effects of changing retinal ganglion cell (RGC) density and availability of presynaptic sites on the development of RGC dendritic arbor in the developing chick retina were contrasted. Visual form deprivation was used to induce ocular enlargement and expanded retinal area resulting in a 20–30% decrease in RGC density. In these retinas, RGC dendritic arbors increased in a compensatory manner to maintain the inner nuclear layer to RGC convergence ratio in a way that is consistent with simple stretching; RGC dendritic arbors become larger with increased branch lengths, but without change in the total number of branches. In the second manipulation, partial optic nerve section was used to produce areas of RGC depletion of approximately 60% in the central retina. This reduction in density is comparable to the density of locations in the normal peripheral retina. In RGC-depleted retinas, dendritic arbor areas of RGCs in the central retina grow to match the size of normal peripheral arbors. In contrast to the expanded case, two measures of intrinsic arbor structure are changed in RGC-depleted retinas; the branch density of RGC dendrites is greater, and the relative areas of the two arbors of bistratified cells are altered. We discuss the potential roles of retinal growth, local RGC density, and availability of presynaptic terminals in the developmental control of RGC dendritic arbor.

This study presents a morphological and quantitative analysis of displaced ganglion cells performed in the chick retina at different stages of development (E11, E17, & P2). The lipophilic dye DiI inserted into the optic nerve provided a complete staining of displaced ganglion cell population and of their dendritic trees. From 11 days of incubation (E11) all neurons present a uniform morphology and are unmistakably recognizable by the dimensions of their cell body and by the presence of the axon. Their dendritic arborizations shape a complex network through the retina. Cell bodies are randomly distributed but dendritic trees of neighboring cells constantly present two levels of dendritic overlap: about 50% of the cells present a high degree of overlap, more than the 30% up to 95% of their total area, while the other half overlaps less than 20%. The high degree of overlap identifies a cluster, which is regularly formed by three and more rarely by four neurons starting from 17 days of incubation (E17) onward and after birth. From E17 onward, 94% of clusters is constantly formed by three cells and 6% of the clusters by four neurons. The distribution and the spatial arrangement of clusters are very regular, forming a mosaic that gives rise to a precise retinal coverage. The nearest-neighbor analysis unequivocally demonstrated that the mosaic of clusters is the most regular array so far described. This exact arrangement starts from 11 days of incubation and is maintained and refined through the following stages of development and after birth.