Postnatal development of radial glial (Müller) cells of the rabbit retina.

Radial glial (Müller) cells were isolated from postnatal rabbit retinae by enzymatic dissociation in papain-containing solution, air-dried, and submitted to Pappenheim's panoptic stain. Morphometric data of these cells were evaluated by light microscopy. During postnatal development, the cells become substantially thicker and shorter, their nuclei lose the rod shape and move more toward scleral layers, and the nucleus-cytoplasm volume relation decreases. Whereas the cell volume increases from birth on, substantial outgrowth of fine side branches within the plexiform layers fails to occur before electrical activity is established there, i.e. after postnatal day 9. A model is proposed relating the growth of sheath-bearing glial processes to local protein synthesis stimulated by external K+ accumulation due to neuronal activity. Early myelinated nerve fibers are suggested to bear mechanical resistance to growing radial glial processes thus causing a splitting of these processes when they enter developing nerve fiber layers.