Abstract
Abstract: :
Purpose: To study the shapes and mosaics of ganglion cells in transgenic mice (Brn3b–/– and Math5–/– mice) that contain reduced numbers of ganglion cells. Methods: These tchniques including immunocytochemistry, microinjection, gene gunning and retrograde photodynamics had been used for the present study. Results: We confirm previous reports that there is major loss of retinal ganglion cells in the retinas of Brn3b–/– and Math5–/– mice. In Brn3b–/– mice, where approximately 80% of ganglion cells are lost before their terminal differentiation, the remaining 20% develop to include most or all structural types of retinal ganglion cell. As a consequence, each cell type is present at a lower than normal density. The dendritic arbors of the cells are normal in shape and size despite their wide spacing. Cells of the same type are evenly spaced, indicating that both size and spacing – in this case a regular mosaic that incompletely tiles the retinal surface – can be maintained in the absence of contact between ganglion cells of the same type. An extreme case is encountered in Math5–/– mice, where > 95% of ganglion cells are never formed. The residual ganglion cells in these retinas included examples of the cell types that express melanopsin and the large SMI–32–positive cells. The dendritic arbors of those cells were undistinguishable from normal; they had the same shape and dendritic field size as in the wild type, despite being located millimeters away from the nearest neighboring ganglion cell of the same type. Conclusions: Retinal ganglion cells tile the retinal surface and there is compelling evidence that their spatial arrangement and dendritic shape are controlled by interactions among the dendrites of neighboring cells of the same type. Here we present evidence for the existence of additional mechanisms that are independent of those interactions.