ON CONE BIPOLAR CELLS IN RAT EXPRESS THE METABOTROPIC RECEPTOR MGLUR6

The rod bipolar cell and about five types of ON cone bipolar cells dep olarize to light by employing a sign-reversing metabotropic glutamate receptor. Glutamate responses are similar in both rod bipolar and cone bipolar cells, but the receptor mediating this response (mGluR6) was so far demonstrated only in rod bipolar cells. To test if ON cone bipo lar cells also express mGluR6, we immunoreacted rat retina with an ant ibody specific for mGluR6, and studied the staining from serial ultrat hin sections. We demonstrate that mGluR6 is indeed expressed in the de ndritic tips of cone bipolar cells, the majority of which receive a ri bbon synapse, and thus probably are ON cone bipolar cells. We further show that half of the dendritic tips contacting the cones stain for mG luR6, thus implying that all ON cone bipolar cell types express mGluR6 .