The Effect Of Altered Lighting Hours On Depression-related Behaviors In Rats

IntroductionDepression is a public health problem affecting large adult population and results in huge social loss.However,the cause,the pathology of depression remains to be understood.The efficacy of long term treatment remains to be achieved. Epidemiologic research has revealed that the insufficient of social activity is one of the major risk factors.It is believed that serotonergic deficiency is the key in the pathology of depression and most antidepressants are affecting on 5-HT ergic system by either extending the acting time of 5-HT or increasing extracellular concentration of 5-HT.These include drugs that act through both 5-HT reuptake inhibition,known as selective serotonin receptor inhibitors(SSRI),and monoamine oxidase inhibitors (MOI).More and more literature reported that deficiency in multiple cells signaling pathway,including brain derived neurotrophic factors(BDNF),MAPK signaling pathway and calcium signaling pathway,and neuronal growth are also critically involved in the pathology and the treatment of depression.Deficiency in multiple components of MAPK signaling pathway including phosphorylation of Ras, extracellular signal-regulated kinase1/2(ERK1/2) and Creb has been confirmed in human depressive suicide victims and in our rat model of depression.In human, running exercise significantly increased ERK phosphorylation in skeletal muscles and improves depressive symptoms.This evidence supports that deficiency in MAPK signaling pathway is a biomarker of depression and suicide.In addition,we found that rats chronically expose to running wheel highly induced brain level ofcalsequestrin 2, one of the most abundant calcium binding proteins,in the frontal cortex and hippocampus.Surprisingly,we also found that rats stopped wheel running in days that lights were accidently kept on 24 hr/day for a week.This evidence implicated that constant lighting or extended lighting time may promote depressive pathology by affecting on locomotors activities.In the following studies,we report results from multiple behavior testing and brain levels of pERK and calsequestrin in rats exposed to normal,extended and reduced daily lighting time.ObjectivesThe objectives were to determine how shorter daily lighting time and longer lighting time affect depressive measurements in behavioral test and brain levels of biomarkers associated with depression.Methods1.Experimental design:5 weeks old male Sprague Dawley rats were divided as five groups:control group,short time light group,long time light group,short time light reversal group,long time light reversal group.These groups were treated with different daily lighting hours for eight weeks.The control group was treated with 12 hours light on and 12 hours light off,the short time light group was treated with 8 hours light on and 16 hours light off and the long time light group was treated with 16 hours light on and 8 hours light off.Behavioral tests in short time light group and long time light group began immediately after the end of the treatment,while tests in short time light reversal group and long time light reversal group were conducted after one week after recovery from a lighting phase reversal at the end of the lighting treatment.2.Behavioral test:Recording first 5 minutes behavior in rats' forced swimming test (FST),analyzing their climbing,swimming and immobility time,in order to determine their depression degree.Recording different judgment frequency and time of rats' learning and memory in Y-maze test,so that we can determine their learning and memory ability.3.Protein immunoblotting:Rats were sacrificed in the next day of FST and Y-maze test.Brain tissue of HIP,PFC,FC,HT were dissected.Tissue contains of pERK and calsequestrin2(CASQ2) in multiple brain regions were determined by Western blot. All tests were done between 8:00 am and 12:00 am.4.Statistic analysis:One-way ANOVA analysis was used to analyze each interclass mean difference,and chi square test was used to analyze each interelass percentage difference.Results1.The results of FSTBefore light reverted,compared with control group rats,each experimental group rats was different in locomotery and immobility in FST and the difference was statistical significant,so did after light reverted.Among them,whenever before or after light reverted,compared with control group rats,the movement time was longer and the immobility time was shorter in short time light group;whereas,the long time light group had the opposite results.2.The results of Y-maze testBefore light reverted,compared with control group rats,each experimental group rats was different in learning and memory in Y-maze test and the difference was statistical significant,so did after light reverted.Among them,whenever before or after light reverted,compared with control group rats,the total frequency,the error frequency and the cumulative time in learning and memory all reduced significantly in short time light group;whereas,the long time light group had the opposite results.3.The results of Western blotBefore light reverted,compared with control group rats,experimental group rats were different in pERK1/2 level of the four brain regions,but the difference had no statistical significance,nor did after light reverted.Among them,whenever before or after light reverted,compared with control group rats,the pERK1/2 level of the four brain regions increased in short time light group;whereas,the long time light group had the opposite results.But compared with the long time light group,the protein level of pERK1/2 in the short time light group increased significantly and the difference had statistical significance.Before light reverted,compared with control group rats,each experimental group rats was different in CASQ2 level of the four brain regions,and the difference had statistical significance,so did after light reverted.Among them,whenever before or after light reverted,compared with control group rats,the protein level of CASQ2 increased significantly in short time light group;whereas,the long time light group had the opposite results.Conclusion1.To alter lighting hours would have an effect on the behaviors in FST and in Y-maze test and the protein levels of pERK1/2,which suggests that altered lighting hours is an important factor to affect rats' emotion.2.Treated with different lighting hours would affect the protein levels CASQ2,which imply that to alert lighting hours is an important factor to affect rats' basic activity.3.To change lighting hours would have an effect on behaviors and biomarkers in brain of rats,furthermore,the effect would not be reverted by given normal lighting hours.4.Altered lighting hours might change rats' emotion by changing their basic activity.