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Steven Walston, Eun-Jin Lee, Mark Humayun, James Weiland; Comparison of Ankyrin-G Labeling of Axon Initial Segments on Ganglion Cells in Normal and Degenerate Rat Retina. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1055.
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© ARVO (1962-2015); The Authors (2016-present)
To compare the position and length of the axon initial segment (AIS) on retinal ganglion cells (RGCs) as it relates to activation thresholds in normal and degenerate retina.
Immunohistochemistry was used to label the AIS and the corresponding RGCs. Studies were conducted on normal Long-Evans, and heterozygous S334ter-line-3 rat retina. Antibodies against ankryin-G, calretinin, and Brn3 were used to label the AIS, RGC somas and axons, and confirm RGC identify, respectively. The length of the AIS and its distance from the soma was acquired using fluorescence microscopy and measured using ImageJ.
RGCs and their corresponding AIS are identified in the ganglion cell and nerve fiber layer with fluorescence microscopy. The average length of the AIS is 1.8μm shorter in degenerate retina when compared to normal (p=0.022, Student t-test). The mean AIS length is 21.1 ± 7.17μm (mean ± std) (n=173) in normal retina and 19.3 ± 6.09μm (n=122) in degenerate retina. The distance between the soma and proximal edge of the AIS along the axon is not significantly different between normal and degenerate retina (p=0.183). The mean position of the AIS is 13.4 ± 8.97μm (n=173) in normal retina and 12.1 ± 7.21μm (n=122) in degenerate retina.
Based on population statistics, the average length of the AIS is statistically shorter in degenerate retina than in normal retina. Although there is significant overlap of the data, this decrease in length may, in theory, increase the threshold at which the neuron fires action potentials. Further study is necessary to determine if there are differences within individual ganglion cell subtypes for normal and degenerate retina.
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