Reduced aggressiveness and low testosterone levels in autoimmune MRL-lpr males.

Autoimmune, lupus-prone MRL-lpr mice float excessively in the forced swim test, explore novel objects and places less, and show blunted responsiveness to palatable stimuli, which is consistent with the hypothesis that the development of chronic autoimmune disease alters emotional reactivity and/or motivation. The present study measures isolation-induced fighting, a model of "affective" aggression, in lupus-prone MRL-lpr and control MRL +/+ males. When compared with controls, autoimmune MRL-lpr mice show reduced aggressiveness, as evidenced by fewer fighting contacts, longer attack latency, shorter fighting episodes and shorter duration of fighting. In addition, reduced testosterone levels accompany serological signs of autoimmunity in the MRL-lpr males. The present results support the hypothesis that affective responsiveness is altered in lupus-prone mice and may suggest limbic system dysfunction during chronic autoimmune/inflammatory disease. The question of whether immune activation alters behavior by a direct effect on the nervous system, or also via the endocrine system, requires further study.