Effects of different light on the ethology and melatonin secretion in depressive rats / 中国职业医学

ABSTRACT

OBJECTIVE: To observe the impact of energy saving light,incandescent light and circadian light on the ethology of depressive rats and explore its possible mechanism on affecting the secretion of melatonin. METHODS: Thirty rats aged 6weeks were randomly selected from 40 specific pathogen free health female SD rats after they adapted to the living environment,depressive rat models were established in the rats by bilateral ovariectomy combined with isolated living and chronic unpredictable mild stress stimulation at the age of 11-14 weeks. Then these 30 ovariectomized rats were randomly divided into 3 intervention groups,including an energy saving light group,an incandescent light group and a circadian light group,with 10 rats in each group. The rats in these 3 groups were given specific experimental light intervention for 3 weeks respectively at the age of 17 weeks. The other 10 rats were raised in conventional environment as the control group. Their body weights were measured at the age of 17,19,20 and 21 weeks. The ethology tests were carried out by sucrose preference test and the open-field test at the age of 7,14 and 20 weeks respectively. The melatonin levels in peripheral blood of 7 time points from 19 30 to 8 30 were measured in the rats at age of 21 weeks. One rat in each group at every time point was randomly selected for examination. RESULTS: At the age of 17 weeks before light-intervention,the body weights of rats in 4 groups showed no significant difference( P > 0. 05). After light-intervention,at the age of 17-20 weeks,the body weights of rats in 3 intervention groups were gradually increased with the increase of age( P < 0. 05).There was no significant difference between body weights of rats at the age of 21 weeks and those at the age of 20 weeks in each group( P > 0. 05). At age of 7 weeks,no significant differences were found in sucrose consumption and standing scores among these 4 groups( P > 0. 05). After the depressive models were established,at the age of 14 weeks before light-intervention,in rats of these 3 intervention groups,the sucrose consumption and standing scores were lower than those of the control group( P < 0. 05),and there was no significant difference found in the above 2 indexes among these 3intervention groups( P > 0. 05). At the age of 20 weeks after light-intervention,the sucrose consumption and standing scores were not significantly different from each other among the 4 groups( P > 0. 05). The peak levels of melatonin in the peripheral blood of rats in these 3 intervention groups were higher than that in the control group. The peak levels onsets of melatonin in peripheral blood of rats in the circadian light group and the energy saving light group were earlier or 2 hours delayed compared to that of control group,while it was similar between the incandescent light group and control group.CONCLUSION: The circadian light,the energy saving light and the incandescent light are similarly effective in improving the behaviors of depressive rats. The circadian light can delay the onset of peak level of melatonin in peripheral blood.