Calcium imaging reveals a network of intrinsically light-sensitive inner-retinal neurons.
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.
Sekaran
Sumathi
S
Department of Integrative and Molecular Neuroscience, Division of Neuroscience and Psychological Medicine, Imperial College London, Charing Cross Hospital, London, United Kingdom.
Foster
Russell G
RG
Lucas
Robert J
RJ
Hankins
Mark W
MW
D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D016257:Fura-2 / Q000378:metabolism; D007150:Immunohistochemistry; D017136:Ion Transport; D051379:Mice; D008856:Microscopy, Fluorescence; D010775:Photic Stimulation; D020419:Photoreceptor Cells, Vertebrate / Q000378:metabolism* / Q000502:physiology*; D012165:Retinal Ganglion Cells / Q000502:physiology*; D017299:Rod Opsins / Q000378:metabolism; D000099210:Melanopsin
D002118:Calcium; D016257:Fura-2; D017299:Rod Opsins; D000099210:Melanopsin