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Keywords:

  • cones;
  • human;
  • melanopsin;
  • rat;
  • retinitis pigmentosa

Abstract

Here we reveal a population of cells that express cone photoreceptor opsins that are located in the inner retina, distant from outer retinal photoreceptors. These cells are present in rodents and human. They also express a range of key proteins critical in the cone phototransduction cascade and make contact with other retinal neurons. Their opsins are not generally confined to cellular specialized regions but are present throughout the plasma membrane, although their nuclear configurations are similar to those of outer retinal cones. This population is distinct from the ganglion cells that contain melanopsin and which are known to be inner retinal irradiance detectors regulating circadian behaviour. Surprisingly, the size of the population of short wavelength opsin positive cells in the ganglion cell layer is plastic. In normal animals their number declines with age. However, their numbers increase significantly in response to outer retinal photoreceptor loss, probably by drawing on a pool of inner retinal cells that express cone specific markers, but not opsins.