CENTRAL ADMINISTRATION OF IL-1 REDUCES ANXIETY AND INDUCES SICKNESS BEHAVIOR IN RATS

In the present study, we examined the effects of various doses of reco mbinant human interleukin-1 beta on anxiety-like behaviour, on body te mperature, and on behavioural changes typical of sick animals. First, we assessed the behaviour of rats in the elevated plus-maze before and 20 min after intracerebroventricular injection of IL-1 at six doses r anging from 0.001 to 100 ng. After treatment with 0.1 and 100 ng IL-1, animals exhibited different anxiety levels. The dose effect on behavi oural performance in the plus-maze appears to be nonlinear (parabolic function), with the highest effects near a 0.1-ng dose and the lowest near doses of 0.0 and 100 ng. In a second set of experiments, we exami ned the effects of doses of 0.1 and 100 ng IL-1 (which had the most pr onounced effects on performance in the plus-maze) on physical paramete rs over a 24-h period. Using radiotelemetry we measured body temperatu re, locomotor activity, food intake, and water consumption: a) in anim als kept under basal resting conditions, and b) in animals exposed to a novel environment prior to administration of IL-1. Both doses evoked a fever response and reduced locomotor activity, but the increase in body temperature did not correlate with the decrease in locomotor acti vity and both effects did not occur at the time of behavioural testing . Taken together, our data indicate that central administration of IL- 1 has anxiolytic-like properties. (C) 1997 Elsevier Science Inc.