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L. H. Chan, E. J. Lee, A. Ray, B. B. Thomas, M. S. Humayun, J. D. Weiland; Correlation of Morphological and Electrophysiological Changes in Degenerated Rat Retina. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3015. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To determine how morphological changes in the retina of S334ter-line-3 retinal degenerate (RD) rats correlate with superior colliculus responses evoked by epiretinal electrical stimulation.
Epiretinal electrical stimulation was performed in normal pigmented rats (Copenhagen, n=2) and S334ter-line-3 RD rats (n=2, P180; n=2, P300). A bipolar stimulating electrode was inserted through sclerotomy and positioned on the retina. A constant current source was used for electrical stimulation in a range of 1-100 µA with 5 pulse widths (0.1, 0.2, 0.5, 1, 2 ms). Responses to stimulation were recorded from the surface of the SC using a single microelectrode. The threshold of each pulse width was determined when the responses appeared more than 80% of the total number of sweeps (n=50). We also used cell specific immunolabeling to investigate the anatomy of retinal neurons in the RD rat.
Single and multi- unit activities were recorded from the rostral-medial part of the SC corresponding to the temporal-ventral part of the retina. The strength-duration curve was similar between control and P180 RD retinas. However, P300 RD retinas showing elevated threshold, particularly at shorter pulse widths. We showed that anatomical changes in horizontal cells and rod bipolar cells at postnatal-day 21 (P21-only half of the outer nuclear layer (ONL) was left). In P90 retinas (no ONL), cone bipolar cell showed retraction of their dendritic trees. In P180 (cell death in the inner nuclear layer (INL)), displaced amacrine cells were observed. The density of rod bipolar cells and horizontal cells was reduced significantly in RD retinas compared to that of control retinas at P90.
In P180 RD retinas, we observed cell death and displacement of inner neurons in the INL. However, electrical stimulus thresholds in P180 were similar to normal retina. In P300 RD retina, we observed a higher electrical stimulus threshold, suggesting more degeneration in these retinas. These results suggested that severe cell deaths and displacement of cells in INL are needed to cause changes in threshold values.
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