Metabotropic glutamate receptor-mediated hetero-synaptic interaction of red- and green-cone inputs to LHC of carp retina.

The role of presynaptic metabotropic glutamate receptor (mGluR) on the interaction of red- and green-cone signals was investigated in luminosity-type horizontal cell (LHC) of isolated carp retina. It was found that a dim red background could enhance LHC's light response to green stimulus, and a dim green background was also able to increase the cell's response to red flash. Such mutual color enhancement was eliminated by application of groups II and III mGluR antagonist (S)-methyl-4-carboxyphenyl-glycine (MCPG). Furthermore, inhibition of glutamate uptake by using D-aspartate (D-Asp) or DL-threo-beta-hydroxy-aspartic acid (THA) completely blocked the mutual enhancement of color signals in LHC. However, the GABAergic feedback pathway in the outer retina was unnecessarily involved.