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TW Kraft, DE Allen; Cone Physiology in a Model of Retinal Degeneration . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3757.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Retinitis pigmentosa is a disease which often has origins in rods, yet causes a delayed cell death in the cone photoreceptor population as well. We wished to document the signaling ability of the cones at various stages of degeneration. Methods: Our model was a transgenic pig with rhodopsin mutations of the proline in position 347. The suction electrode technique was used to record single cone photocurrents isolated from dark-adapted transgenic animals with either the P347L or P347S mutant gene. Recordings were obtained from 37 cones (32 L-cones, 5 S-cones) from eight P347L animals from 5 to 33 weeks-old. In five P347S animals from 8 to 20 weeks-old, results were obtained from 16 cones (12 L-cones, 4 S-cones). Results: Disease related changes in cone function were observed. During the period of rapid rod loss, cone sensitivity was reduced (I1/2 elevated). The retinal degeneration (loss of rod cells) proceeds quickly in the P347L mutant, by 11 weeks of age over 80% of the rods are gone. Recordings from cones, well after the time of rapid rod loss, at 29 and 33 weeks-of-age, showed a recovery of sensitivity. The retinal degeneration in the P347S animal was more variable. Changes in rod sensitivity followed the number of surviving rods, that is, there was a degeneration dependant acceleration and desensitization of the rod responses. Cone sensitivity in this animal was elevated over the more extended period of rod cell loss. The dominant time constant of the cones was measured, and did not change in the presence of background light. However, the dominant time constant of the cones did change with retinal degeneration, following the sensitivity changes. Conclusion: Retinal degeneration produces significant changes in the signaling ability of rods and cones throughout the degenerative process. The changes may reflect changes in the subretinal environment or adaptation within the photoreceptors themselves.
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