Dopamine modifies the balance of rod and cone inputs to horizontal cells of the Xenopus retina.

Dopamine (greater than or equal to 2 microM) increased the cone input and suppressed the rod input to axon-bearing horizontal cells of the Xenopus retina. Dopamine (10 microM) also depolarized the horizontal cell by about 9 mV. The D2-dopamine antagonists spiperone and metoclopramide had the opposite action to dopamine, whereas the D1-dopamine antagonist SCH 23390 was without effect. None of the agents tested modified the light-evoked responses of rods.