Effects of interleukin-1 and endotoxin in the forced swim and tail suspension tests in mice.

Male CD-1 mice were administered interleukin-1beta (IL-1beta) and bacterial endotoxin (lipopolysaccharide, LPS) and subsequently tested in the tail suspension test (TST), the Porsolt forced swim test (FST), and in the open field. IL-1beta (100, 300 and 1000 ng/mouse) injected intraperitoneally (i.p.) 90 min before the test induced a dose-dependent increase in the time spent immobile in the TST and the time spent floating in the FST. These responses were statistically significant only at the higher doses of IL-1beta (300 and 1000 ng). Nevertheless, all three doses of IL-1beta significantly decreased line crossings and rears in the open field and depressed food intake and body weight. Very similar effects were induced by LPS. Doses of 1 and 5 mug i.p. increased immobility time in the TST and floating time in the FST, but the same doses strongly depressed locomotor activity and body weight. These results indicate that both IL-1beta and LPS can induce depression-like effects in the TST and the FST. However, the doses necessary to induce these changes reduced feeding and activity in an open field, so that the effects observed in the FST and TST could be attributed to a general reduction in locomotor activity. Thus the results obtained in these two animal tests commonly used to test antidepressant properties do not provide strong support for an IL-1 hypothesis of depression.