Title : Time course changes in mood disorders in mice after the systemic administration of lipopolysaccharide
It has been well known that lipopolysaccharide (LPS) induces neuroinflammation in rodents. However, anxiety- and depressive-like symptoms induced by LPS are known to be controversial. In the present study, we performed various mood disorder experiments such as open field test (OFT), elevated plus maze (EPM), and tail suspension test (TST) at different hours to investigate the time course effects of LPS (0.83 mg/kg, i.p.) on behaviors in mice. The LPS-treated group showed a significant reduction in food intake after 6 and 24 h of treatments and water intake only after 24 h of treatment compared with the vehicle group. In addition, changes in body weight were significantly lower than those of vehicle group at 3, 6, and 24 h after LPS treatment. Also, LPS significantly induced hypothermia after 3 and 6 h in mice. However, these anorexia and sickness behaviors were recovered after 1 week. Additionally, LPS significantly increased anxiety-like behaviors at 1, 6, and 24 h after the administration in the OFT and EPM. Moreover, in the TST, treatment with LPS increased depressive-like behaviors in mice. However, all increases in LPS-induced behaviors substantially restored after 24 h. Surprisingly, changes in the TST were relapsed again after 1 week. Taken together, our results demonstrate that LPS causes sickness symptoms, which resulted in several mood disorder behaviors in mice. The effects of LPS were most severe at 1 and 6 h after administration, but recovered generally after 24 h, which remained until 1 week.7.