Behavioral, inflammatory and neurochemical disturbances in LPS and UCMS-induced mouse models of depression

The immuno-inflammatory activation triggered by various stresses play an important role in pathophysiology of depression. The immune responses display differential pathological characters in different stresses. However, comparative data and analysis on behavioural, inflammatory and neurochemical changes in different stress induced depression is limited. To imitate different stressful situations, in this study, mice were subjected to a single injection of LPS (0.5 mg/kg, i.p.) and UCMS (4 week period), respectively. LPS-stressed mice showed more immobility time in FST and TST, as well as more time in periphery in OFT than UCMS-stressed mice. Further, LPS-stressed mice showed robuster expression and release of TNF-alpha, IL-1 beta and IL-6 in serum and depression related brain areas (prefrontal cortex, hippocampus and striatum) as compared to UCMS-stressed mice. The ELISA results showed that IDO expression was significantly increased following LPS and UCMS stresses, but more increased IDO expression was observed in prefrontal cortex and hippocampus of LPS-stressed mice. The decrease of 5-HT and BDNF was detected only in hippocampus of LPS-stressed mice, but in overall all the brain areas assessed in UCMS-stressed mice as compared to control. The data indicate that LPS induced more severe depressive-like behaviours and robuster immune activation than UCMS. Our study strongly imply that hippocampus is relatively more vulnerable to acute inflammatory challenge in depression, while chronic psychological stress is more likely to cause the multidimensional symptoms of clinical depression. Our findings provide more insight into pathophysiology in various stress-induced depression and also implicate a potential suitability of different stress models.