SYNAPTIC TRANSMISSION FROM RODS TO ROD-DOMINATED BIPOLAR CELLS IN THE TIGER SALAMANDER RETINA

Synaptic transmission between photoreceptors and bipolar cells was studied in dark-adapted tiger salamander retinas. Based on the relative light sensitivity, bipolar cells, either depolarizing (DBC) or hyperpolarizing (HBC), fell into two groups: one receives inputs primarily from rods (rod-dominated bipolar cells, DBC(R) and HBC(R)) and the other receives inputs primarily from cones (cone-dominated bipolar cells, DBC(C) and HBC(C)). The input-output relations of the rod-DBC(R) and rod-HBC(R) synapses were determined by plotting the voltage responses of the rod and DBC(R) (or HBC(R)) to dim 500-nm light steps, which polarizes only the rods but not the cones. The slope gains of both synapses were the highest near the dark rod voltage (-2.5 for the rod-DBC(R) Synapse and 4.0 for the rod-HBC(R) synapse), and they (the absolute values) became progressively smaller at more hyperpolarized rod voltages.