Calcium imaging reveals a network of intrinsically light-sensitive inner-retinal neurons

Curr Biol. 2003 Aug 5;13(15):1290-8. doi: 10.1016/s0960-9822(03)00510-4.


Background: Mice lacking rod and cone photoreceptors (rd/rd cl) are still able to regulate a range of responses to light, including circadian photoentrainment, the pupillary light reflex, and suppression of pineal melatonin by light. These data are consistent with the presence of a novel inner-retinal photoreceptor mediating non-image-forming irradiance detection.

Results: We have examined the nature and extent of intrinsic light sensitivity in rd/rd cl retinae by monitoring the effect of light stimulation (470 nm) on intracellular Ca(2+) via FURA-2 imaging. Using this approach, which does not rely on pharmacological or surgical isolation of ganglion cells from the rod and cone photoreceptors, we identified a population of light-sensitive neurons in the ganglion cell layer (GCL). Retinal illumination induced an increase of intracellular Ca(2+) in approximately 2.7% of the neurons. The light-evoked Ca(2+) fluxes were dependent on the intensity and duration of the light stimulus. The light-responsive units formed an extensive network that could be uncoupled by application of the gap junction blocker carbenoxolone. Three types of light-evoked Ca(2+) influx were observed: sustained, transient, and repetitive, which are suggestive of distinct functional classes of GCL photoreceptors.

Conclusions: Collectively, our data reveal a heterogeneous syncytium of intrinsically photosensitive neurons in the GCL coupled to a secondary population of light-driven cells, in the absence of rod and cone inputs.

Publication types

  • Comparative Study

MeSH terms

  • Animals
  • Biological Transport, Active
  • Calcium / metabolism*
  • Fura-2 / metabolism
  • Immunohistochemistry
  • Ion Transport
  • Mice
  • Microscopy, Fluorescence
  • Photic Stimulation
  • Photoreceptor Cells, Vertebrate / metabolism*
  • Photoreceptor Cells, Vertebrate / physiology*
  • Retinal Ganglion Cells / physiology*
  • Rod Opsins / metabolism


  • Rod Opsins
  • melanopsin
  • Calcium
  • Fura-2