Morphology of intrinsically photosensitive retinal ganglion cells: distinct photoreceptors from rod/cone photoreceptors

Objective

This study was to observe the morphology of live intrinsically photosensitive retinal ganglion cells (ipRGCs) at cellular level, and to explore their three-dimensional structure and responses to light in curved retina and the relationship with rod/cone photoreceptors.

Methods

ipRGCs were identified according to the enhanced green fluorescent potein (EGFP) markers.Two hundred and sixty-three ipRGCs were videoed in mouse whole-mounted retina after strengthening with Lucifer Yellow from patch clamp electrodes.The dendrites and cell bodies were analyzed according to their sublayer-specific localization in inner plexiform layer and ganglion cell layer of curved retina.The relationship with rod/cone system was reconstructed and their functions were speculated.The animal feeding and use was in accordance with the standards set by the ARVO, and the experiment was approved by the Ethic Committee for Experimental Animal of Hubei University of Science and Technology.

Results

The ipRGCs had strictly sublayer-specific localization in three sublayers of retinal inner plexiform layer.Each sublayer occupies full retina and form photosensitive surface, without any intermediate photosensitive dentric distribution between sublayers.Each ipRGC had randomly dentric distributions among the three sublayer curves, without the specific ON/OFF stratification.The photosensitive sublayers had absolutely perpendicular assignment related to cone/rod photoreceptors.The expression of melanopsin and spike-producing Ca²⁺ /Na⁺ channels were randomly distributed in M1, M2 and M3 cells.M4 and M5 cells shared the characteristic properties of conventional ganglion cells.

Conclusions

In contrast to the rod/cone photoreceptors, ipRGCs form multiple-sublayer photosensitive curved surface, which are perpendicular to rod/cone photoreceptors, their photosensitive melanopsin and intrinsic spike-producing channels randomly occupy these specific sublayers, which suggest their distinct functions from rod/cone photoreceptors.

Intrinsically photosensitive retinal ganglion cells; Three-deminsion morphology; Melanopsin; Retina; Photoreceptor