Interferon-alpha treatment induces depression-like behaviour accompanied by elevated hippocampal quinolinic acid levels in rats

•One week administration of IFN-α induces depression-like behaviour in the rat forced swim test.•IFN-α treatment alters brain tryptophan levels and downstream kynurenine metabolites.•Imipramine reverses IFN-α-induced depression-like behaviour.•Celecoxib shows potential for antidepressant activity possibly mediated via the tryptophan–kynurenine pathway. Immunotherapy with the cytokine interferon-alpha (IFN-α) can induce symptoms of depression, and it is likely that the tryptophan–kynurenine pathway may be involved in this regard. In this study we investigated the effects of IFN-α on depression-like behaviour and central metabolites of the tryptophan–kynurenine pathway in rats. Secondly, we explored the modulating effects of an antidepressant (imipramine) and anti-inflammatory drug (celecoxib) on IFN-α-induced behavioural and pathophysiological changes in the brain. The following treatment groups were used: Control (saline), IFN-α (6×104IU/kg s.c.), IFN-α+imipramine or IFN-α+celecoxib. Drugs were administered daily for 1 week. IFN-α treatment induced depression-like behaviour by increasing immobility in the forced swim test (FST), and decreased tryptophan levels in the brain. There was a trend for an increased kynurenine/tryptophan ratio, indicative of indoleamine 2,3-dioxygenase (IDO) activation, and increased quinolinic acid in the hippocampus. Imipramine decreased immobility in the FST, but did not reverse the IFN-α-induced changes in the tryptophan–kynurenine pathway. There was a trend for celecoxib to decrease immobility and to reverse the IFN-α-induced increase in the kynurenine/tryptophan ratio. Thus, our study provides further evidence for IFN-α-induced depression-like behaviour through central changes of the tryptophan–kynurenine pathway.