Changes in Light Intensity and Duration Alter the Metabolic Status of Dopamine in Mouse Retina

Abstract

Purpose: : Dopamine regulates various cellular and neurological functions in the retina and is involved in refractive development of the eye. This study investigated levels of retinal dopamine and the associated metabolite under different diurnal light intensities.

Methods: : This study included two experiments using C57BL/6L mice (age of 12 days). In Experiment 1, the animals were treated with different light intensities (n=5 for 125 lux; n=6 for 250 lux and 375 lux respectively) in lighting cycle of 12-h light/12-h dark for two weeks. In Experiment 2, the animals were treated with different lighting duration (n=11 for 6/18 (light/dark in hour); n=7 for 12/12; n=9 for 18/6) under illumination of 250 lux for 2 weeks. The lighting phase started at 9:00 daily for the 2 experiments. Retinal samples were collected at 19:00 for Experiment 1 and at 24:00 for Experiment 2 at the end of the experiment. The retinal dopamine and its metabolite (3,4-dihydroxyphenylacetic acid, DOPAC) were then measured by HPLC with electrochemical detection.

Results: : At 2 weeks of experiment, retinal dopamine level was 0.46±0.11 (Mean±SD, ng/mg wet retina) in 125 lux, 0.36±0.06 in 250 lux and 0.38±0.03 in 375 lux (p≤0.017 between different light intensities) and retinal DOPAC level was 0.03±0.01 (Mean±SD, ng/mg wet retina) in 125 lux, 0.03±0.01 in 250 lux and 0.05±0.02 in 375 lux (p≤0.04 between different light intensities) . However, the value of DA/DOPAC was 13.80±2.39, 10.78±0.84 and 8.89±2.18 in 125 lux, 250 lux and 375 lux respectively (p≤0.019 between 125 lux and 250 lux or 375 lux). The retinal dopamine level in both the 18/6 and 12/12 groups (0.50±0.05 vs 0.53±0.06) was similar but significantly higher than in the 6/18 group (0.37±0.05, p< 0.001 between 18/6 or 12/12 group and 6/18 group) and the DOPAC level in the 18/6 group (0.05±0.01) was higher than in both the 12/12 (0.02±0.01) and 6/18 (0.01±0.01) groups (p<0.001 between 18/6 and 12/12 or 6/18 groups). In contrast, the value of DA/DOPAC in the 18/6 group was lowest (10.53±1.66), followed by the 12/12 group (28.90±4.27) and finally the 6/18 group (42.67±6.34) (p<0.001 between 18/6 and 12/12 or 6/18 groups).

Conclusions: : Dopamine activities in the retina appear to increase with an increase in intensity or duration of the ambient lighting. These results suggest that dopamine may play a role in the development of refractive errors associated with an interrupted normal lighting-cycle (12/12hs).

Keywords: myopia • dopamine