Lipopolysaccharide-mediated immobility in mice: reversal by cyclooxygenase enzyme inhibitors.

Endotoxin (lipopolysaccharide, LPS) is known to activate the hypothalamo-pituitary adrenocortical axis, as well as norepinephrine and indolamine metabolism. In the present study we examined the effects of systemically administered LPS on forced swimming-induced despair behavior in mice. LPS (50 micrograms/mouse i.p.) time-dependently enhanced the forced swimming-induced immobility period. The increase in immobility time was highest after 2 h of LPS administration. Desipramine (10 mg/kg), a tricycle antidepressant, or fluoxetine (10 mg/kg), a serotonin reuptake inhibitor, significantly reversed the LPS-induced increase in immobility time. Cyclooxygenase inhibitors nimesulide (1, 2 and 5 mg/kg), naproxen (10 mg/kg) and rofecoxib (2 mg/kg) did not alter the despair behavior per se. Nimesulide (10 mg/kg) did reverse reserpine-induced immobility. Nimesulide (2 mg/kg), naproxen (10 mg/kg) and rofecoxib (2 mg/kg) significantly reversed LPS-mediated despair behavior. The present study demonstrated that LPS-induced inflammatory responses in the brain may cause despair behavior. Reversal with a cyclooxygenase inhibitor indicates the role of prostaglandins in despair behavior.