Regulatory mechanism of melatonin on the retinal ganglion cell photoreaction in mice

The study aimed to analyze the regulatory mechanism of melatonin (MLT) on the retinal ganglion cell photoreaction in mice. Forty-eight, 3-week-old healthy ICR mice, regardless of gender, were randomly divided into 4 groups. Group A was exposed to an illumination/dark time of 0 h/24 h, 6 h/18 h in group B, 12 h/12 h in group C and 18 h/6 h in group D, for up to 6 weeks. Four mice in each group were sacrificed at week 1, 3 and 6, respectively, for harvesting of retinal ganglion cells. ELISA was used to detect nocturnal plasma MLT levels at midnight. Immunohistochemistry was used to detect the expression of the retinal MLT receptor and the expression levels of inducible nitric oxide synthase (iNOS) and c-fos protein. The plasma MLT levels, MLT receptor levels and c-fos protein expression levels of group C, after 1, 3 and 6 weeks of light application, were the highest, followed by groups B and D, while group A had the lowest levels. For each illumination time, the iNOS levels of group C were the lowest and group A was the highest. Differences were all statistically significant (P<0.05). In conclusion, appropriate illumination regimens can increase c-fos protein, decrease iNOS activity and regulate the physiological activities of the retinal ganglion cells by regulating the expressions of MLT and its receptor.