Regional changes of brain serotonin and its metabolite 5-hydroxyindolacetic Acid and development of immunosuppression in submissive mice.

The production of submissive behavior in C57BL/6J mice during 10 or 20 days of social confrontations resulted in increases in serotonin (5-HT) content in the amygdala, hippocampus, nucleus caudatus, Al1, A10, A9, and hypothalamus. The level of 5-hydroxyindolacetic acid (5-HIAA) was higher in most structures after 20 daily encounters compared to animals tested for 10 days. The ratio 5-HIAA/5-HT was increased in the nucleus raphe, accumbens, A9, and hypothalamus in mice displaying submission during 10 and 20 confrontations. The experience of defeats during 10 days accompanied with 5-HT system activation in a number of brain structures (nucleus raphe, accumbens, and A9) produced immunosuppression. With increasing number of confrontations the ratio 5-HIAA/5-HT was decreased in the same structures and a tendency to the immune response elevation appeared.