Effect Of Methylene Blue On Depression-and Anxiety-like Behaviors In Mice

Objective: Depression is a chronic neuropsychiatric disease with high prevalence rate,high recurrence rate,high disability rate and high suicide rate,often accompanied with anxiety,cognitive impairment and other behavioral defects.There is growing evidence of interactions between oxidative stress,inflammation,hippocampus and depression,with elevated levels of proinflammatory cytokines associated with depression-related symptoms that can be reversed with antidepressant treatment.Some studies have suggested that the caudate nucleus,prefrontal cortex,hippocampus and other brain regions are closely related to depression,and the hippocampus has always been an important brain region for depression research.Studies from basic and clinical have shown that methylene blue(MB)has significant anti-inflammatory and anti-oxidant effects,and it can promote cortical neurogenesis and provides neuroprotection against various brain disorders,including bipolar disorder.However,the potential antidepressant anxiety effects of MB have not been fully investigated.This study investigated the effects of MB pretreatment on behavior defects and their underlying mechanisms in LPS-induced depression mouse models.Methods:1.40 ICR mice were randomly divided into four groups: normal saline+ normal saline group(Sal+Sal),normal saline + LPS group(Sal+LPS),MB(5mg/kg)+ LPS group(MB5+LPS),MB(20mg/kg)+ LPS group(MB20+LPS).30 minutes before LPS injected and each test,mice were intraperitoneally injected into Sal,Sal,MB(5mg/kg)and MB(20mg/kg)respectively.Behavioral tests were administrated 24 hours after the LPS(800?g/kg)intraperitoneally injection,and behavioral testing mainly includes: the opening test(OFT),novelty suppressed bean test(NSF),sucrose preference test(SPT),tail suspension test(TST).One type of behavioral tests was conducted everyday.2.40 ICR mice were randomly divided into four groups: Sal+Sal,Sal+LPS,MB5+LPS and MB20+LPS.MB intraperitoneally injected and training every day,LPS(800?g/kg)was injected in the third day and novel object recognition task(NOR)was performed in the fourth day.MB was injected 30 minutes before the training,the short-term memory was tested 1.5 hours after the training,and the long-term memory was tested 24 hours after the training.At the end of the test,the eyeball was taken for blood.3.40 ICR mice were surgically implanted with cannula according to the brain map through the stereotaxic brain locator,and after 7 days' recovery,randomly divided into three groups: Sal+Sal,Sal+LPS and MB+LPS.Behavioral tests were administrated after the LPS(800?g/kg)injection 24 hours.Before the test,the MB+LPS group was injected with MB(5?g/side/0.4?L),injecting for 2 minutes,and stopped for 2 minutes.The OFT was conducted 0-5 minutes after the first administration,TST was followed.OFT.FST was followed by another injection which was 6 hours after the last injection.4.Enzyme-linked immune-sorbent assay(ELISA): blood sample of mice was collected through extracting eyeballs after the last behavioral test.The contents of heme oxygenase-1(HO-1)were detected according to the instructions of ELISA kit.Results:1.The body weight curve of mice showed that MB system treatment had no effect on the weight loss induced by LPS(P > 0.05).2.In the NSF,there was no inter-group difference in feeding latency and total intake(P > 0.05,P > 0.05)and in the OFT,there was no inter-group difference in total distance(P > 0.05).3.In the FST,MB system treatment can significantly reverse the LPS-induced prolong of floating time(P < 0.01,P < 0.01)and reduce of latency to floating(P < 0.01,P < 0.05).In the TST,MB system treatment can significantly reverse the LPS-induced prolong of immobility time(P < 0.005,P < 0.01),MB system treatment has no effect in reduce of latency to immobility.In the SPT,MB system treatment can significantly reverse the LPS-induced decrease in sugar water preference(P < 0.05,P < 0.01),MB system treatment has no effect in total intake.4.In the NOR,MB system treatment can significantly reverse the LPS-induced long-term memory damage in mice(P < 0.05,P < 0.01).5.ELISA results showed that the decrease of HO-1 level in peripheral blood of mice induced by LPS could be significantly reversed by MB treatment(P < 0.05,P < 0.01).6.In the OFT,MB nuclear treatment can significantly reverse the LPS-induced reduction in central residence time(P < 0.01)and the reduction in total distance of activity(P < 0.01).7.In the FST,MB nuclear treatment can significantly reverse the LPS-induced prolong of floating time(P < 0.01)and reduce of latency to floating(P < 0.01).In the TST,MB nuclear treatment can significantly reverse the LPS-induced prolong of immobility time(P < 0.05)and reduce of latency to immobility(P < 0.01).Conclusion:1.Methylene blue has significant anti-depression and anti-anxiety activities.2.The nerve regulatory effect of methylene blue may be related to the regulation of HO-1 in serum.3.DG in the hippocampus may be a target brain region where methylene blue exerts anti-depressant effects.