Role of interleukin-1 beta in impairment of contextual fear conditioning caused by social isolation

Isolating rats immediately after conditioning impairs contextual but not au ditory-cue fear conditioning. The reported experiments examine the involvem ent of brain interleukin-1 beta (IL-1 beta) in the impairment in contextual fear conditioning caused by social isolation. As measured by the condition ed freezing response, 5 h of social isolation after conditioning, impaired contextual but not auditory-cue fear conditioning in adult male Sprague-Daw ley rats. Social isolation for 1 or 3 h after conditioning also increased I L-1 beta protein in the hippocampus and cerebral cortex. No differences in IL-1 beta protein levels were found in the pituitary or the hypothalamus. I ntracerebroventricular (ICV) IL-1 receptor antagonist (IL-1ra) given after conditioning prevented the impairment in contextual fear conditioning cause d by isolation. ICV IL-1ra had no effect on auditory-cue fear conditioning in these same animals, nor did it affect the level of contextual fear condi tioning displayed by home cage controls. Like isolation, ICV IL-IP (10 or 2 0 ng) after conditioning also impaired contextual but not auditory-cue fear conditioning. These results suggest that increased levels of brain IL-1 be ta play a role in producing the impairment in contextual fear conditioning produced by social isolation. These findings also add to the generality of the idea that stressors induce IL-1 beta activity in the brain and that IL- 1 beta may play physiological roles in the uninjured brain. (C) 1999 Elsevi er Science B.V. All rights reserved.