A possible effect of dopamine on the temporal resolution of
goldfish was investigated in a behavioral, two-alternative,
forced-choice procedure. Flicker fusion frequency (FFF) was
measured before and after bilateral intravitreal injections
of D1- or D2-dopamine receptor (D1-/D2-R) antagonists, or
after depletion of retinal dopamine by bilateral intravitreal
injections of the dopaminergic neurotoxin 6-hydroxydopamine
(6-OHDA). Prior to drug injections, fish achieved FFFs of
33–39 Hz. A D1-R antagonist, SCH 23390, reduced FFF by
about 12% (P > 0.1), whereas a D2 antagonist,
sulpiride, reduced the relative FFF by 25% (P <
0.03). Depletion of retinal dopamine with 6-OHDA induced a gradual
reduction in the FFF to a maximal reduction of 50% (P
< 0.001) at 2 weeks postinjection. There was recovery to
control levels after 3–4 weeks postinjection. The recovery
of FFF, at least in one animal, was due to the return of retinal
dopamine because FFF could be reduced by intravitreal injections
of sulpiride during the recovery phase. These experiments
demonstrate that retinal dopamine, particularly acting on D2-R,
is important for photopic temporal resolution.