Development and Ageing of the RPE in a Marsupial, the Quokka

Fleming, Patricia A.; Harman, A.M.; Beazley, Lyn

doi:10.1006/exer.1996.0056

Cited by 12 publications

(34 citation statements)

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“…Our present data support these suggestions, there is strong evidence for an increase in retinal area with a concurrent decrease in neuron density, but that neuronal density decreases minimally in the macula. We would suggest that this minimal decrease in density in the macula results, in part, from a minimal retinal areal expansion in this region (Fleming et al, 1996a;Harman et al, 1997;. We have also shown that, even though it is possible that neurons may be lost throughout life from the ganglion cell layer, the loss is not of a particular cell size.…”

Section: Discussionmentioning

confidence: 63%

“…Previously we have suggested, from our examination of the retinal pigment epithelium, that the retina slowly increases in area during adult life and that centro-temporal retina, containing the macular region, undergoes the least areal expansion (Fleming et al, 1996a;Harman et al, 1997). Our present data support these suggestions, there is strong evidence for an increase in retinal area with a concurrent decrease in neuron density, but that neuronal density decreases minimally in the macula.…”

Section: Discussionmentioning

confidence: 74%

“…3). This division allowed statistical comparison of neuronal cell densities in different regions, a method used by us previously (Fleming et al, 1996a,Fleming et al, b, Harman et al, 1997. In this way each region of the retina could be distinguished by a quadrant and eccentricity designation, with ring 1 being centremost and ring 6 indicating the periphery (Fig.…”

Section: Retinal Area Cell Counts and Neuronal Densitymentioning

confidence: 99%

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Neuronal density in the human retinal ganglion cell layer from 16-77 years

et al. 2000

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Section: Discussionmentioning

confidence: 63%

Section: Discussionmentioning

confidence: 74%

Section: Retinal Area Cell Counts and Neuronal Densitymentioning

confidence: 99%

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Neuronal density in the human retinal ganglion cell layer from 16-77 years

et al. 2000

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“…We measured neuron density and calculated total numbers from a systematic 1% sample of the entire surface of each retinal wholemount, as routinely performed by us previously [11][12][13][14]. Analyses were conducted at !1,000 magnification with a light microscope attached to an MDII digitizer (Minnesota Datametrics) and an IBM-compatible PC.…”

Section: Cell Density and Total Cell Numbersmentioning

confidence: 99%

“…Total cell numbers were then calculated from the 1% sample by multiplying by 100. A slight upward correction for complete retinal area (since a retina is not exactly square) was made by dividing the total cell number by the total area analyzed (i.e., the number of counts ÷ the number of mm 2 analyzed) and multiplying by the complete retinal area [11][12][13][14].…”

Section: Cell Density and Total Cell Numbersmentioning

confidence: 99%

Numbers of Neurons in the Retinal Ganglion Cell Layer of the Rat Do Not Change throughout Life

Harman

Macdonald²,

Meyer³

et al. 2003

Gerontology

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Background: There have been many assumptions made about neuronal loss in mammals due to aging. However, when we examined the retinal ganglion cell layer of a marsupial, the quokka, from 0.5 to 13.5 years of age, we found that the total neuron number did not decrease significantly even into extreme old age. The retinal area increased slowly throughout life, leading to a decrease in cell density. Neuronal death in the rat retina has been assumed, since the cell density has been seen to fall with age. However, a similar study to ours in the quokka has never been performed in the laboratory rat, the model for so many experimental investigations. Objective: We decided to test the hypothesis that rats do not lose neurons due to aging and that an increase in retinal area, and not cell death, as previously suggested, might underlie the decreasing cell density seen in aging animals such as rats. Methods: We kept laboratory rats under standard, unvarying conditions throughout the trial, sacrificing 3 animals every 3 months up to 30 months, and examined the retinal ganglion cell layer through adult life. Results: We found that the numbers of neurons did not decrease in this species, even in the oldest rats. We also saw that the retinal area increased slowly with a concomitant slow decrease in mean neuronal density. Soma diameters of neurons gradually increased throughout life. Conclusions: When rats are kept under standard conditions, there is no neuronal loss in the retina during aging, although the cell density does decrease as a result of retinal expansion. It is not sufficient to measure retinal cell density to determine cell loss. In addition, it is important to know that in normal conditions there is no cell loss in the retinal ganglion cell layer as a result of aging. Any loss that is seen must be a result of additional factors.

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Retinal pigment epithelium and photoreceptor maturation in a wallaby, the Quokka

et al. 1996

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Cell generation and the early stages of maturation of the retinal pigment epithelium (RPE) and photoreceptors were examined in a marsupial, the quokka, Setonix brachyurus. Results are presented for animals aged up to postnatal day (P)250. RPE cell generation was studied by analysis of cell number from wholemounted retinae and by tritiated thymidine (3HThy) autoradiography in sectioned material. For 3HThy autoradiography, quokkas aged P1-P200 were injected with 3HThy and killed either 6-20 hours later (pulse-kill) or at P100 or P250 (pulse-leave). The extent of pigmentation of the RPE sheet was examined from sections of embryonic and early postnatal stages. Retinae from animals aged P5 to P160 were also examined at the electron microscope. By P100, RPE cell number is within the range found in adults. New RPE cells are generated in a peripheral band which moves outwards as cells leave the cell cycle in more central locations. RPE cells thus complete their last cell division in a centre-to-periphery wave centred about the optic nerve head. At any given retinal location, RPE cells complete their last cell division earlier than the overlying layers of the neural retina. Cells of the RPE rapidly develop a mature morphology. For example, melanin granules are observed at P5 and Verhoeff's membrane (the terminal bar complex) is evident by P25. By contrast, photoreceptor development in this species is protracted; cone inner segments are observed by P40, whilst the first rod inner segments are observed at P60. Despite being generated earlier, morphological maturation of the cones appears retarded and prolonged compared with that of the rods. The last stages of RPE cell maturation occur late in development, in synchrony with the generation of rods.

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Development and Ageing of the RPE in a Marsupial, the Quokka

Cited by 12 publications

References 0 publications

Neuronal density in the human retinal ganglion cell layer from 16-77 years

Neuronal density in the human retinal ganglion cell layer from 16-77 years

Numbers of Neurons in the Retinal Ganglion Cell Layer of the Rat Do Not Change throughout Life

Retinal pigment epithelium and photoreceptor maturation in a wallaby, the Quokka

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