Human interferon-α induces immobility in the mouse forced swimming test: involvement of the opioid system

Abstract

In a previous study, we indicated that human interferon (IFN)-α (IFN-α, 6×0 4 IU/kg, i.v.), but not human IFN-β or -γ, prolonged the immobility time of the forced swimming test in mice. In this study, we investigated the mechanism of the effect of human IFN-α. None of the mouse IFNs tested (IFN-α/β, IFN-β, and IFN-γ, 3×10 5 U/kg, i.v.) changed the immobility time or the spontaneous locomotor activity in mice. Indomethacin (10 mg/kg, s.c.), a cyclooxygenase inhibitor, did not affect the increase in the immobility time induced by human IFN-α (6×10 4 IU/kg, i.v.). However, naloxone (1 mg/kg, s.c.), an opioid receptor antagonist, blocked the increasing caused by human IFN-α in the forced swimming test. These results suggest that the increase in the immobility time caused by human IFN-α in the forced swimming test might be mediated through opioid receptors, but not mouse IFN receptors.