| With the acceleration of life rhythm and the increased working pressure,the incidence of depression is simultaneously increased,which severely threatened the human’s health.Varies of factors could involve in the onset of depression,day-night rhythm disturbance,as one of the factors,was focused on recently,especially the sleeping-awareness disturbance,which was list as an important biological sign in the diagnosis of depression.Thus,there will be a great significance for the precaution of depression via the advanced research of the pathogenesis targets at day-night dysrhythmia,as well as the deep understanding of new antidepressant drugs.A recently developed drug that was approved in Europe for the treatment of major depression(agomelatine,S20098)has a unique pharmacological profile.It acts both as an agonist at melatonin MT1 and MT2 receptors and as an antagonist at 5-HT2C receptors.The 5-HT2C receptor and MT play an important role in the onset of depression.It is found that over expression of 5-HT2C receptor in some encephalic region of depression model rats.It is reported that S20098 could improve the cognition and emotion disorders induced by chronic stress,which might result from the blockage of 5-HT2A receptor followed by the functional changes of correlating encephalic region,which showed that the effect of 5-HT2C on anti-depression of the S20098.The other way of anti-depression of S20098 is to improve the day-night dysrhythmia by exciting MT1 and MT2 receptor.It is showed that the MT level in depressive animal and person was decreased and the disorder of sleeping rhythm and emotion could be improved by MT supplement.S20098 could work as melanin-like effect by exciting MT1 and MT2,combined with its antagonistic effect of 5-HT2C,which showed its superiority among the antidepressant drugs and further to be approved.But the direct effect of S20098 on center encephalic neuron activity is unclear.The suprachiasmatic nucleus(SCN)serve as the principal circadian pacemaker in mammals,and is responsible for a variety of biological rhythms,especially the sleep-wake rhythm.Early results showing that the appearance of depressive symptoms was related with disruption of circadian rhythms which were controlled by SCN.It is reported that 5-HT2C receptor and MT1/MT2 receptor distributed in the SCN,S20098 influence the activity of SCN neurons through these two types of receptors.Therefore,SCN was as the research targetin this experiment.First,we investigated the expression of 5-HT2C receptor and melatonin receptor of SCN in depression rats.Second,we used in vitro extracellular discharge recording method to observe the effect of S20098 on SCN neuronal activity and explore whether the effect of S20098 is realized by antagonism of 5-HT2C receptor and activation of melatonin receptor.At the same time,we also compare the effects of S20098 and 5-HT2C receptor antagonist,melatonin receptor agonist on SCN neuronal activity.This experiment focuses on possible mechanisms of antidepressant of S20098 at different levels.1.Effect of S20098 on behavior of depression rats and the role of SCN(1)The results of Sucrose preference and forced swimming test on depression model of rats After 21 days chronic stress,we screened the rats of depression model by sucrose preference test.Sucrose preference results show that sugar consumption ratio of the total liquid consumption significantly decreased in depression rats compared with the control rats which indicated that the rats were anhedonia,the results were consistent with symptoms of depression;forced swimming test(FST)results showed that the immobility time of the depression rats was prolonged and climbing time was significantly reduced compared with the control group,the results showed that the depression rats behavior were obviously despair.The weight test results of 21 day showed that the growth of weight in depression group significantly slowerthan that in control group.The results are consistent with the main clinical manifest of anorexia increase and weight loss in depression patients.All the above results showed that the depression rat model was established successfully.(2)Effect of S20098 on the behavior of depression rats FST results showed that the immobility time in control rats after injection of vehicle(control+veh)group and depression rats after injection of S20098(depression+S20098)group were significantly lower than those in depression rats after injection of vehicle(depression+veh)group,and the climbing time in control+veh group and depression+S20098 group were significantly higher than those in depression+veh group.These results indicated that after the injection of S20098 can significantly improve the depressive behavior of rats.(3)Effect of S20098 on the expression of 5-HT2C receptor and MT1 receptor protein SCN in depression rats Expression of 5-HT2C receptor and MT1 receptor in control+veh group,depression+veh group and depression+S20098 group was examined by Western blot.The results showed that protein of 5-HT2C receptor and MT1 receptor could be detected in SCN of normal rats and depression rats.The expression of 5-HT2C receptor and MT1 receptor in depression rats were significantly higher than those in the normal rats,S20098 can reverse the changes of expression level of those receptors after administration.2.Effects of S20098 on firing rates of SCN neurons and its mechanism(1)Effects of S32006,melatonin and S20098 on SCN neuronal firing ratesWe used in vitro rat slice extracellular recordings technology to observe the effect of 5-HT2C antagonist(S32006),melatonergic agonist(melatonin)and S20098 on firing rates of SCN neurons.The results showed that:S32006 applied to rat SCN cells suppressed firing of neurons,and induced a dose dependent increase in the suppression.There was no significant correlation between the dose of S32006 and the duration of suppression;Melatonin applied to rat SCN cells suppressed firing of neurons,and induced a dose dependent increase in the suppression,the duration of suppression were middling correlated with dose;S20098 applied to rat SCN cells suppressed firing of neurons,and induced a dose dependent increase in the suppression,the duration of suppression were highly correlated with dose;Comparison of the three drugs found that S20098 at high concentrations can achieve similar effects in the inhibitory of S32006,but the longest lasting for S20098.(2)Modulation by Ro60-0175 of effects on firing rates of S32006We first determined observed the 5-HT2C agonist Ro60-0175 affected SCN neuronal firing rates,then perfusing both Ro60-0175 and S32006 together.The results indicate that the addition of Ro60-0175 reduced the effects of S32006 alone,suggesting that S32006 suppressed firing rates of SCN neurons by acting through 5-HT2C receptors.(3)Mechanism of S20098 on firing rates of SCN neuronsThe experimental records were divided into S20098 alone group,combination of S22153 and S20098 group and combination of Ro60-0175 andS20098 group.The effects of perfusion drugs on the firing rates of SCN neurons were observed in each group.The results suggested:Comparing these responses to those obtained with S20098 alone,the addition of S22153 significantly reduced the degree of suppression of firing rates.S22153 reduced the suppressive effects of on SCN neuronal firing,but not completely,affecting both the amplitude and duration of suppression.These results are interpretation that the effects of S20098 on SCN neurons are mediated by its agonist actions on MT1 and MT2 receptors.Comparing result obtained with S20098 alone,the addition of Ro60-0175 significantly reduced the degree of suppression of firing rates,but also not completely.It did not induce significantly reduction in the duration of suppression.These results are the interpretation that the effects of S20098 on SCN neurons are mediated by its antagonist actions on 5-HT2C receptors.Conclusion:1.Up-regulation of MT1 receptor and 5-HT2C receptor in SCN of depression model rats.2.S20098 can improve symptoms of depression model rats,get expression of MT1 receptor and 5-HT2C receptor in SCN of depression model rats back to normal.3.Application of S32006,melatonin and S20098 to rat brain slice could suppresse firing rates of SCN neurons.S20098 had the longest lasting inhibited effect.4.S22153 and Ro60-0175 partially blocked the inhibition effect of S20098 on firing rates of SCN neurons,respectively.These results are consistent with the interpretation that the effects of S20098 on SCN neurons are mediated by its agonist actions on MT1 and MT2 receptors and its antagonist actions on 5-HT2C receptors. |
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