The dopaminergic amacrine system and its response to light stimulation in rats with inherited retinal dystrophy

In both the RCS mutant strain of rats with hereditary progressive retinal dystrophy and in controls, concentrations of dopamine (DA) and its metabolic DOPAC increased steeply in retina from 14 to 60 days postnatally with no further elevations in older animals indicating normal dopaminergic system evolution in the RCS rats. In 60-, 90-, and 135-day-old but not in younger (14- and 30-day-old) RCS rats killed in the light phase of the light-dark cycle, retinal DA, and more markedly DOPAC levels, were lower than those in age-matched controls. In normal rats aged 24, 35 and 70 days that were dark-adapted for 24 hr, 2-hr light exposure increased DA and mainly DOPAC levels in retina. LIght stimulation after dark adaptation elevated retinal DA and DOPAC only in 24- but not in 35- or 70-day-old RCS rats. In RCS rats with advanced retinal dystrophy, decreases in retinal DA and DOPAC levels and lack of response of DA amacrine cells to light exposure are probably secondary to degeneration or impairment of photoreceptors which are no longer capable of transmitting light stimuli onto DA neurons in retina.