Neurite extension from rod bipolar cells in retinal cell and explant cultures

One of the key requirements for the success of a subretinal prosthesis or photoreceptor transplant is the formation of an effective interface with the remaining neural retina. An optimal interface would be one where specific and highly efficient contacts were made with retinal neurons, presumably bipolar cells. Although the properties of neurite (particularly axonal) outgrowth have been extensively studied in retinal ganglion cells, comparatively little work has been done with other retinal neurons. The goal of the present research is to explore the survival and neurite outgrowth properties of a specific type of retinal cell, the rod bipolar cell (RBC), using in vitro culture preparations. RBCs are the most numerous of the several classes of bipolar cells in mammals, and would be a likely target of stimulation by any subretinal implant. We report here that RBCs in short term culture - as isolated cells or within retinal explants - extend their dendrites, and that these are often decorated with varicosities and smaller spine-like extensions. This response is similar to remodeling of RBCs observed in cat models of retinal detachment, and suggests it might be possible to manipulate RBCs with appropriate growth and guidance cues to form an optimal interface with subretinal devices or transplants.