Abstract
Light stimulates dopamine (DA) release in the retina. The purpose of this was to determine the threshold and dose-response relationship between ocular light exposure and retinal DA synthesis in vivo. Groups of dark-adapted rats were exposed to 0, 1, 3, 5, 10, 25, 50, 100 or 1000 microwatts per square centimeter (μW/cm 2 of white light for 15 min. Retinal DA and dihydroxyphenylalanine (DOPA) were subsequently quantified by liquid chromatography with electrochemical detection. Both the DA and DOPA data fit hyperbolic curves significantly ( Pˇ0.01). Exposure to white light at 25 μW/cm 2 or greater appears to elicit the maximum response of these neurons. Threshold irradiance is calculated to be 3–5 μW/cm 2. These results indicate that retinal DA synthesis and presumably DA neuron activity have a graded response to increasing irradiances of white light.
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