Total Retinal Volume Research Articles

Relationships between Müller cells and neurons in a primitive tetrapod, the Australian lungfish.

We recently proposed a model of cytogenesis which assumes that primitive ancestral mammals and premammalian vertebrates had a retinal composition that consisted of about seven neurons per Müller cell, comprising 1-2 cone photoreceptors, 1-2 rod photoreceptors, 2-3 bipolar cells, 1-2 amacrine cells, less than 1 ganglion cell, and less than 1 horizontal cell (Reichenbach & Robinson, 1995). The Australian lungfish (Neoceratodus forsteri) closely resembles the lobe-finned ancestors of land vertebrates, and has an extremely plesiomorphic nervous system. The present study, therefore, has examined the relative frequencies of retinal neurons and Müller cells (identified by immunolabelling for glutamine synthetase) in the lungfish retina. It was found that for each Müller cell there is an average of 1.9 cone photoreceptors, 1.7 rod photoreceptors, 3.1 amacrine/bipolar/horizontal cells, and 0.6 ganglion cells; amounting to a ratio of 7.3 neurons per Müller cell. These results support our conjecture that the sequence of cytogenesis in mammals is constrained by a developmental program that predates the evolution of mammals. The study also provides the first detailed morphological descriptions of lungfish Müller cells and their relationship with adjacent neurons. It was found that individual Müller cells in lungfish have a volume (more than 12,000 microns3) that is an order of magnitude higher than in mammals, yet the proportion of total retinal volume occupied by these cells (20%) is very similar.

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.

Quantitative properties of Müller cells in rabbit retina as revealed by histochemical demonstration of NADH-diaphorase activity.

Müller cells in rabbit retina were selectively stained by demonstrating NADH-diaphorase activity. After the sections were measured by light microscopy, the following properties of Müller cells were found: (a) independent of the retinal localization, one Müller cell corresponds with a retinal volume of 15,000 microns 3, i.e., with 11 photoreceptor cells, 2 neurons of the inner nuclear layer, and 0.3-1 ganglion cells; (b) the Müller cell population represents about 6.8% of the total retinal volume; (c) the sorbitol accumulation of Müller cells in diabetic retinopathy is said to be unable to cause osmotic damage.

A morphometric study of the Müller cell in rod and cone retinas with and without retinal vessels

A comparative morphometric study of the Müller cells, their nuclei, and mitochondria was made in the following animals: Rattus norwegicus (albino rat) which has a vascular rod retina, Gecko eublipharis macularis (nocturnal gecko) which has an avascular rod retina, Eutamios sciurus (Korean ground squirrel) which has a vascular cone retina, and Natrix natrix (grass snake) which has an avascular cone retina. The study was restricted to a zone 30° wide, extending 30–60° from the centre, and each retinal layer in this zone was examined separately. The rat retina proved to contain 377 000 Müller cells/mm 3, each having a volume of 260 μm 3 and a surface of 2759 μm 2. The Müller cell cytoplasm made up 8·8% of the total retinal volume, and the mean surface: volume ratio was 114·4 × 10 8 μm 2/mm 3 Müller cell. Mitochondria average 78·2 × 10 6/mm 3 retina and were situated mainly in the vitreal part of the retina. There were 16·4 microvilli/μm 2 at the outer limiting membrane. In the gecko retina there were 154 000 Müller cells/mm 3 retina, each having a volume of 1338 μm 3 and a surface of 20 325 μm 2. The cytoplasmic volume percentage was 19·8%, and the mean surface: volume ratio was 156·9 × 10 8 μm 2/mm 3 Müller cell. There was an average of 44·5 × 10 6 mitochondria/mm 3 retina, situated exclusively in the scleral part of the retina. At the outer limiting membrane there were 43·7 microvilli/μm 2. In the gound squirrel there were 328 000 Müller cells/mm 3 retina, each having a volume of 378 μm 3 and a surface of 2378 μm 2. The cytoplasmic volume percentage was 10·5% and the mean surface: volume ratio 67·8 × 10 8 μm 2/mm 3 Müller cell. The mean mitochondrial content was 29·9 × 10 6 mm 3 retina, with a fairly even distribution in all layers. At the outer limiting membrane there were 49·2 rather short microvilli/μm 2. In the grass snake retina there were 373 000 Müller cells/mm 3 retina, each having a volume of 209 μm 3 and a surface of 2038 μm 2. The cytoplasmic volume percentage made up 5·6% and the mean surface: volume ratio was 106·5 × 10 8 μm 2/mm 3 Müller cell. There was an average of 43·6 × 10 6 mitochondria/mm 3 retina, approximately equally distributed over the entire retina. At the outer limiting membrane there were 27·3 microvilli/μm 2.