Rods and cones activate different excitatory amino acid receptors on the mudpuppy retinal horizontal cell.

We have studied rod and cone neurotransmission onto horizontal cells (HCs) of the mudpuppy retina by: (1) dual whole-cell recordings from synaptically connected pairs in a superfused retinal slice preparation, and (2) intracellular recordings from HCs in a superfused retina-eyecup preparation. In the presence of relatively weak concentrations of broad spectrum excitatory amino acid antagonists, HC recordings show that cone-mediated responses were significantly more attenuated than those mediated by rods. These observations suggest that the HC postsynaptic receptors for rods and cones are pharmacologically different. One advantage of having distinct rod- and cone-activated receptors on second-order neurons may be to preserve different rod and cone functions under varying levels of light stimulation and provide separate means of regulating rod and cone neurotransmission onto the second-order cells.