Depression-like Behavior Induced By Altering GDNA Methylation State In Lateral Habenula Of Rats And Its Related Mechanism

Depression is a mood disorder with high prevalence, and the pathogensis is really complex, but it is thought to be result from the lack of serotonin in the central nervous system. The lateral habenula(LHb) is an epithalamic region with close connections to the midbrain dorsal raphe nucleus(DRN), which is the principal source of cerebral serotonin. The efferent connections from LHb to DRN play a crucial role in regulation of serotonin synthesis. Epigenetic studies have point that environmental factor can induce depressive-like behavior in rats by altering DNA methylation state of hippocampus and orbitofrontal cortex. Our previous study has confirmed that there are a plenty of DNA methyltransferase(DNMTs) in the LHb of rats, but it is not clear that whether DNMTs in LHb can influence and how to influence animal’s behavior and physiological functions. This study focused on the behavior changes induced by intra-LHb administration of 5-aza-2’-deoxycytidine(5-aza D), a DNMTs inhibitor, and its related mechanism in rats.Firstly, bilateral intra-LHb administration of 5-aza D significantly reduced DNA methylation level in LHb and increased depressive-like behavior in rats. Compared to the vehicle group, the rats received intra-LHb administration of 5-aza D showed remarkably decreased locomotor acitivity and frequency of rearing in open field test, and increased immobility time in forced swimming test.Secondly, high performance liquid chromatography was used to detect the level of serotonin in DRN, which is thought to be important in the development of depression. The results confirmed a lower level of serotonin in DRN of rats received intra-LHb administration of 5-aza D than those of rats received vehicle. Some studies have shown that DRN was inhibited when LHb become hyperactive, and a reduction of serotonin in DRN was found on this occasion. Our data suggested that LHb might become hyperactive after administration of 5-aza D, and then reduced the level of serotonin in DRN, which induced depressive-like behavior in rats.Finally, we tested whether the expression of DNMTs in LHb of depression rats is different from the normal rats. Depression rats were prepared through chronic unpredictable mild stress(CUMS) procedure. With significant lower sucrose preference, longer immobility time, shorter climbing time in those rats undergone CUMS procedure, our behavioral data demonstrated that the depression model has been successfully established. The expression of Dnmt1 m RNA, but not Dnmt3 a and Dnmt3 b m RNA, was notably decreased in LHb of depressive rats induced by CUMS. Accordingly, the expression of DNMT1 protein detected by western blot was also significantly decreased.These findings suggested that intra-LHb administration of DNMTs inhibitor 5-aza D reduced DNA methylation in LHb, and decreased the level of serotonin in DRN, and then induced depressive-like behavior in rats. On the other hand, the decreased expression of Dnmt1 m RNA and protein in LHb in depression rats induced by CUMS also indicated a relationship between DNA methylation in LHb and depressive-like behavior in rats. This study revealed that altering g DNA methylation state in LHb is involved in the pathology of depression.