Morphometric parameters of Müller (glial) cells dependent on their topographic localization in the nonmyelinated part of the rabbit retina. A consideration of functional aspects of radial glia.

Morphometric parameters of Müller cells were evaluated by light microscopy both in whole retinae and in enzymatically isolated cells from adult pigmented rabbits. In spite of the marked decrease in cell densities from visual streak to far periphery, a constant glia-neuron ratio of about 1:15 was found in all regions. The volume of individual Müller cells was found to increase strongly when the cells become shorter, i.e. when the retinal centre was compared to the retinal periphery. The contribution of Müller cell volume to the total retinal volume, however, was shown to be constant at about 6%. Long Müller cells have a thin vitreal process and a small vitreal endfoot surface. The consequences of this rule for the proposed function of Müller cells in retinal K+ clearance are discussed with respect to general features of radial glia. It is suggested that foetal radial glial cells too long to perform sufficient K+ clearance are destined to be transformed into 'adult' multipolar glia by mitotic cell division.