DEPLETION OF RETINAL DOPAMINE DOES NOT AFFECT THE ERG B-WAVE INCREMENT THRESHOLD FUNCTION IN GOLDFISH IN-VIVO

Increment threshold functions of the electroretinogram (ERG) b-wave we re obtained from goldfish using an in vivo preparation to study intrar etinal mechanisms underlying the increase in perceived brightness indu ced by depletion of retinal dopamine by 6-hydroxydopamine (6-OHDA). Go ldfish received unilateral intraocular injections of 6-OHDA plus pargy line on successive days. Depletion of retinal dopamine was confirmed b y the absence of tyrosine-hydroxylase immunoreactivity at 2 to 3 weeks postinjection as compared to sham-injected eyes from the same fish. T here was no difference among normal, sham-injected or 6-OHDA-injected eyes with regard to ERG waveform, intensity-response functions or incr ement threshold functions. Dopamine-depleted eyes showed a Purkinje sh ift, that is, a transition from rod-to-cone dominated vision with incr easing levels of adaptation. We conclude (1) dopamine-depleted eyes ar e capable of photopic vision; and (2) the ERG b-wave is not diagnostic for luminosity coding at photopic backgrounds. We also predict that ( 1) dopamine is not required for the transition from scotopic to photop ic vision in goldfish; (2) the ERG b-wave in goldfish is influenced by chromatic interactions; (3) horizontal cell spinules, though correlat ed with photopic mechanisms in the fish retina, are not necessary for the transition from scotopic to photopic vision; and (4) the OFF pathw ay, not the ON pathway, is involved in the action of dopamine on lumin osity coding in the retina.