Visualization of Müller (retinal glial) cells by bulk filling with procion yellow

A method is presented that allows for an easy and reliable demonstration of retinal glial (Müller) cell morphology. When a 3% solution of the fluorescent dye Procion Yellow (reactive yellow, Sigma) is placed on isolated living retinae for 2 hrs, many Müller cells take up the dye. In paraffin sections, the cells can be observed by confocal microscopy in great detail. As the cells are filled throughout their length, the method has advantages over most immunocytochemical methods which label only parts of the cells. The method was applied to retinae of frogs, rats, guinea pigs, and rabbits. The vitread trunks of the cells differed in diameter. Those of frogs and rats were thin (less than 1 to 2 microns diameter) whereas those of guinea pigs and rabbits were thicker (2 to 5 microns). In all species studied the following rule was found. In thick central regions of the retina, Müller cells were long with slender trunks whereas in the thin retinal periphery, the Müller cells had thick short trunks. There was an inverse relationship between length and diameter of Müller cell trunks. Mammalian Müller cells were densely packed and had rather cylindrical endfeet. In the frog retina, Müller cells were more sparsely distributed, and the endfeet formed wide, flat funnels. It is concluded that the higher metabolic rate of mammalian retinae requires more densely packed Müller cells than occur in the amphibian retina.