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Thanh T. Tran, Gregoy Y. Bedecarrats, Vivian Choh; The Examination of Retinal Cell Loss in Smoky Joe Chickens. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1817.
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Smoky Joe (SJ) chickens are a genetically blind strain of White Leghorn chickens that show various degrees of blindness at hatch, but by 8 weeks post-hatch, those that are homozygous are completely blind (Salter et al, 1997: J Vet Diagn Invest, 9: 407-9). Additional details pertaining to retinal degeneration in these genetically blind chickens are limited, such as the time course of retinal cell loss and which cell types are affected. The purpose of this project is to determine the characteristics of retinal degeneration in Smoky Joe chickens.
Eyes from sighted (n=3) and blind (n=3) Smoky Joe (SJ) chickens, aged 1 day after hatch, were enucleated and eyecups containing the retina, choroid and sclera were fixed. Eyecups were then prepared for cryosectioning. Cross sections of the retina 12 µm thick were mounted onto glass slides then stained with DAPI (4',6-diamidino-2-phenylindole) to visualize nuclei. Confocal microscopy images at 20x magnification were obtained from the centre of the retina. The number of cells within the three nuclear retinal layers (outer nuclear layer, inner nuclear layer, and ganglion cell layer) was counted to determine the loss of the cells. Cell numbers were only obtained for the left eye of each bird.
In general, the mean number of cells for blind SJ chicks was lower than that in sighted SJ chicks. Comparisons of the means per nuclear layer indicated significantly lower numbers of cells in blind birds in the inner nuclear layer (blind: 323,702 ± 22,547cells per mm², sighted: 411,760 ± 40,712 cells per mm²; p=0.0306), but not in the outer nuclear layer (47,205 ± 702 cells per mm² vs. 51,283 ± 2,941 cells per mm² , respectively; p=0.0797) nor in the ganglion cell layer (27,785 ± 1,158 cells per mm² vs. 31,266 ± 2,724 cells per mm², respectively; p=0.1112).
The number of cells counted in the ganglion cell layer is on the same order of magnitude as previous literature for avian species as are numbers in the outer nuclear layer. The significant difference within the inner nuclear layer between the sighted and blind birds suggests that cells of the inner nuclear layer may be the target for degeneration. As no differentiation between the cell types in the inner nuclear layer was made, it remains unknown whether cell numbers are consistent and which cell are lost.
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