NMDA receptor activation mediates lipopolysaccharide-induced depressive-like behavior

Abstract

Background : Inflammation associated with cancer and induced by cancer therapy is associated with clinical signs of sickness behavior that can culminate in the development of symptoms of depression. Intraperitoneal administration of lipopolysaccharide to mice induces depressive-like behavior. Lipopolysaccharide-induced depressive-like behavior is mediated by activation of indoleamine 2,3-dioxygenase (IDO) that degrades tryptophan along the kynurenine pathway and produces kynurenine metabolites such as quinolinic acid that acts as a N-Methyl-D-aspartate (NMDA) receptor agonist. The present study was carried out to determine whether the NMDA receptor antagonist ketamine alleviates lipopolysaccharide-induced depressive-like behavior. Methods : Mice were injected intraperitoneally with ketamine or saline immediately before administration of the cytokine inducer lipopolysaccharide or saline via the same route. Their behavior and bodyweight were monitored up to 28 h post-injection. Depressive-like behavior was measured by increased immobility in the forced swim test and decreased sucrose preference for a sucrose solution. Brain, liver and plasma were collected 6 h and 28 h after treatment to measure biomarkers of inflammation. Results : Lipopolysaccharide induced the expression of cytokine, IDO, tryptophan 2,3-dioxygenase (TDO) and heme oxygenase-1 at the periphery and in the brain. This effect was not altered by ketamine pretreatment. Ketamine blocked the development of depressive-like behavior but had no effect on sickness behavior measured by body weight loss, reduced food intake and decreased motor activity. Conclusions : These data indicate that ketamine is able to abrogate inflammation-induced depressive-like behavior by antagonising the activating effects of kynurenine metabolites on NMDA receptors.

Keywords

• lipopolysaccharide
• ketamine
• mouse
• depression
• indoleamine 2,3 dioxygenase
• kynurenine