GRM6 and congenital stationary night blindness: The pathophysiological role of TRPM1 has been extensively investigated in the context of ON-bipolar neurons, which form synapses with rod, cone, and horizontal cells in the retina,676,755., 756., 757. because LOF mutations in the human TRPM1 gene cause congenital stationary night blindness.757., 758., 759., 760., 761. In the dark, rod cells secrete glutamate, which activates metabotropic glutamate receptor 6 (mGluR6) in postsynaptic ON-bipolar neurons.