Mapping retinal degeneration and loss-of-function in Rd-FTL mice.

PURPOSE Retinitis pigmentosa (RP) is a blinding disease caused by the degeneration of photoreceptors. To further understand the process of degeneration in RP, the authors have traced activation patterns associated with rod and cone photoreceptor degeneration in a mouse model of RP METHODS: The authors used a double-mutant mouse, Rd-FTL, which contains a natural mutation, rd1, affecting the rod photoreceptors and an axon-targeted beta-galactosidase reporter system, which is under the regulation of the promoter of the c-fos gene. These mice allowed the authors to trace degeneration-related activity that corresponded to rod and cone death. RESULTS The authors traced cell death-associated activation in both rods and cones, allowing them to accurately determine the time course of cone degeneration in these mice. In the analysis of downstream activation patterns in the inner retina, they found that amacrine and ganglion cells maintain their photopic light-related activation until at least the initiation of cone degeneration. These cell populations then show increased activity during the peak time of cone cell degeneration. The authors also examined light-regulated functional activation of a subclass of amacrine cells, the dopaminergic amacrine cells. These cells showed light-induced functional activation after rod photoreceptor death and until the period of cone photoreceptor death, suggesting that they can be regulated by cone photoreceptors alone. CONCLUSIONS These findings have helped to accurately trace the periods of photoreceptor degeneration in this model of RP and show that correct light-regulated inner retinal activation is maintained until the time of cone degeneration.