Human interferon-alpha increases immobility in the forced swimming test in rats.

We examined the immobility of the forced swimming test induced in an animal model by human interferon (IFN), which has often been reported to induce depression in clinical use. In the present study, we examined the effects of human IFNs on results of the forced swimming test in rats. Single intravenous (IV) administration of human IFN-alpha (6x10(4) IU/kg), but not of human IFN-beta or -gamma, significantly increased immobility time in the forced swimming test in rats. Repeated administration of human IFN-alpha (6x10(3) IU/kg) also significantly increased the immobility time. On the other hand, none of the rat IFNs (rat IFN-alpha, -beta and -gamma, 6x10(4) IU/kg, IV) changed the immobility time. Neither human IFNs nor rat IFNs changed the locomotor activity of rats. These findings suggest that human IFN-alpha has a greater potential for inducing increase of the immobility in the rat forced swimming test than human IFN-beta and -gamma, and that the effect of human IFN-alpha might not be mediated through IFN-alpha/beta receptors.