Purpose:
To determine the anatomical distribution of individual Müller cells within the retina and their association with other retinal cell types.
Methods:
Three to 6 month old Fischer 344 rats (n=16 eyes) underwent intravitreal injection of an adenovirus vector with the marker gene encoding enhanced green fluorescent protein (eGFP) under control of a CMV promoter. One week after injection the animals were sacrificed, retinas dissected free and lightly fixed. Additional immunohistochemistry (ICC) was performed for retinal neurons, photoreceptor cells, endothelial cells, and microglia. Confocal microscopy along with three–dimensional reconstruction were used to determine the interaction of the individual Müller cell domains and their interaction with other cell types within the retina labeled via ICC.
Results:
Individual Müller cells expressed eGFP throughout their cytoplasm, extending to their finest distal processes. The Müller cells formed individual colums within the retina spanning from the inner limiting membrane to the outer limiting membrane. These columns formed distinct domains within the retina with little overlap of adjacent Müller cell processes. The Müller cell domain was most pronounced in the outer nuclear layer where Müller cell cytoplasm ensheathed mulitple photoreceptor cell nuclei. Domain structure began to breakdown as the ganglion cell layer was approached.
Conclusions:
Müller cells form distinct anatomical domains in the retina. As in recent astrocyte studies within the central nervous system, this has implications for the functional significance of the Müller cell beyond their long known supportive role. Müller cells domains may very well affect neuronal processing. Breakdown of these domains during degeneration could alter neuronal function, possibly contributing to photoreceptor cell death. We are now beginning to image labeled Müller cells in vivo. These initial labeling experiments for the basis for future functional studies.
Keywords: Muller cells • imaging/image analysis: clinical • microscopy: light/fluorescence/immunohistochemistry