Müller cells in adult rabbit retinae: Morphology, distribution and implications for function and development

Abstract

We describe the morphology and distribution of Müller cells in wholemounts of rabbit retinae labelled with either monoclonal antibodies (anti-Vimentin, 3H3, 4D6, and 4H11), or intracellular horseradish peroxidase. Several new features of Müller cell organization are noted. First, Müller cells appear to compose a single morphological class and their morphology varies systematically with retinal thickness. Second, in contrast to other retinal glia, Müller cells have a neuronlike distribution, with a peak density of 10,700-15,000 cells per mm2 at the visual streak and a minimum density of 4,400-6,000 per mm2 at both the superior and inferior retinal edges. There are 4.2 +/- 0.5 x 10(6) Müller cells per retina. Third, unlike in other species, rabbit Müller cells do not contact blood vessels, suggesting that they do not participate in the transfer of metabolites or in the blood:retinal barrier. Fourth, each Müller cell has a vitread endfoot about 20-40 microns in diameter composed of numerous fimbriae. The fimbriae from a single Müller cell generally contact several axon fascicles in the nerve fibre layer, and at each point along its length each fascicle is enclosed by the overlapping fimbriae from several Müller cells. Fifth, in the inner and outer plexiform layers, numerous filamentous branchlets extend 20 microns or more from the radial trunk, interweaving with branchlets from nearby Müller cells to form dense and continuous strata. In the ganglion cell layer and outer nuclear layer, Müller cell processes completely wrap neuronal somata, whereas in the inner nuclear layer they partially wrap somata. We discuss the functional and developmental implications of these observations.

AE3 anion exchanger isoforms in the vertebrate retina: developmental regulation and differential expression in neurons and glia

“…Consistent with this role, MC elaborate fine processes that invest neurons in all retinal layers, particularly in regions of high synaptic density such as the plexiform layers (Robinson and Dreher, 1990). MC are the only cell type to span the entire thickness of the retina; apical processes at the outer limiting membrane surround the photoreceptor inner segments and basal "end feet" contact vitreous humor and blood vessels (Robinson and Dreher, 1990).…”

“…5B, arrows). These radial processes are characteristic of Miiller cell staining (Drgger et al, 1984;Bjijrklund et al, 1985;Robinson and Dreher, 1990). AE3 (AP-3 antibody) staining in the same section, observed sequentially (to avoid any fluorescent "spillover" between rhodamine and fluorescein channels) in the confocal microscope, was present in the OPL and in only the radially projecting subset of GFAP-positive fibers.…”

The organization of the inner nuclear layer of the rabbit retina

“…5B). The situation for Mtiller cells was slightly different, because the absolute density of Mtiller cells does not rise as much as the density of neurons in the visual streak (Robinson and Dreher, 1990;Jeon and Masland, 1993). Outside the visual streak, Mtiller cells represented on average 26% of the cell bodies that make up the INL.…”

“…Discussion A striking feature of our results was the limited variability between different eyes and different animals, once the data were expressed as fractions of the different cell classes rather than absolute densities (Table 1). Among individual rabbits (indeed, among individuals of all mammalian species) there is substantial variation in the density of retinal cells (Repka and Quigley, 1989;Curcio and Allen, 1990;Robinson and Dreher, 1990;Masland et al, 1993). In addition, spurious variability is introduced during tissue preparation.…”

Contribution of Müller cells toward the regulation of photoreceptor outer segment assembly

“…Increasing evidence also documents that glial cells may regulate synapto-genesis (Ullian et al, 2001;Ullian et al, 2004) and neuronal processing (Newman, 2004) through bidirectional communication (Araque and Perea, 2004). During development, Müller cells, photoreceptors and a subset of inner retinal neurons descend from a single retinal progenitor cell and arrange themselves in a columnar fashion (Turner and Cepko, 1987;Reichenbach et al, 1993) in which Müller cells surround photoreceptors from the synaptic terminals to the inner segments (Robinson and Dreher, 1990) where the two cells are joined via the adherens junctions that comprise the outer limiting membrane (reviewed in Ervin, 2000 andTepass, 2002). In addition, Müller cells express voltage-gated ion channels, neurotransmitter receptors and various uptake carrier systems, which enable them to modulate the activity of retinal neurons (Reichenbach et al, 1997;Lin and Bergles, 2004).…”