CONES CONTRIBUTE TO LIGHT-EVOKED, DOPAMINE-MEDIATED UNCOUPLING OF HORIZONTAL CELLS IN THE MUDPUPPY RETINA

1. The relative effectiveness of adapting lights of different waveleng ths on uncoupling of horizontal cells was measured in dark-adapted mud puppy retinas. Diffuse blue (470 nm) or red (620 nm) adapting stimuli were adjusted in intensity to be equally effective for rods or for con es. Uncoupling of horizontal cells was measured by intracellular recor ding of changes in their responses to spot and annulus stimuli. The in tensities of the adapting light pairs were varied over 3 log units. Th e responses of the horizontal cells indicated that both rods and cones were stimulated by the adapting lights. 2. Relatively dim adapting li ghts did not produce detectable changes in horizontal cell coupling. B righter adapting lights caused uncoupling of horizontal cells. When th e brighter adapting lights were rod matched, the uncoupling effect of the 620-nm light was significantly greater than that of the 470 nm lig ht, indicating that cones contributed to the uncoupling effect. 3. Whe n the adapting lights were cone matched, the effects of the two wavele ngths were not significantly different, but this did not rule out a ro d contribution because the effective adapting lights probably produced maximal or nearly maximal, and hence equal or nearly equal, responses in rods. 4. The results indicate that cones contribute to the light-e voked uncoupling of horizontal cells in mudpuppy, although a contribut ion from rods could not be ruled out. Because it was shown previously that light-evoked uncoupling of horizontal cells in mudpuppy is mediat ed by dopamine, the results also suggest that cones contribute to the light-evoked release of dopamine.