Macaca mulatta retinas were superfused,
in vitro, to measure the efflux of dopamine. Steady
light, in the low photopic range, stimulated dopamine release
slightly. Flashing light (3 Hz) superimposed over the steady
background increased dopamine efflux significantly. This
increase was completely blocked by the addition of
d,l-2-amino-4-phosphonobutyric acid (d,l-APB,
10–100 μM) to the superfusion medium, but not
by the addition of the inactive enantiomer d-APB
(10 μM). The results suggest that ON bipolar cells
provide the excitatory drive to dopaminergic amacrine cells
in primates, as in other species.