In addition to providing hope for people with serious vision problems, Hattar's findings hint that, in the past, mammals may have used their ipRGCs for sight/image formation, but during the course of evolution, that function was somehow taken over by rods and cones.
The study also concludes that, far from being homogenous, ipRGCs come in five different subtypes, with the possibility that each may have different light-detecting physiological functions.
To conduct the study, the team used a special system to genetically label cells and then "trace" them to the rodents' brains before subjecting the mice to a number of vision tests. In one, mice followed the movements of a rotating drum, a test that assessed the animals' ability to track moving objects. In another, the rodents were placed within a "Y"-shaped maze and challenged to escape by selecting the lever that would let them out. That lever was associated with a certain visual pattern. The mice that were blind -- they lacked rods, cones and ipRGCs -- couldn't find that lever. But those with only ipRGCs could.
"These studies are extremely exciting to me, because they show that even a simple light-detecting system like ipRGCs has incredible diversity and may support low-acuity vision, allowing us to peer into evolution to understand how simple vision may have originally evolved before the introduction of the fancy photoreceptors rods and cones," Hattar said.
|Contact: Lisa DeNike|
Johns Hopkins University