Cytokine variations within brain structures in rats selected for differences in aggression

The present study examined the content of cytokines (IL-1β IL-2, IL-6, IL-10) in the brain structures (the hypothalamus, striatum, frontal cortex, and hippocampus) in two rat lines selected for differences in fear-induced aggression at 2, 4, and 24 h after a peripheral injection of saline or lipopolysaccharide (LPS, 250 μg/kg). LPS stimulation elevated cytokine activity above baseline levels in both aggressive and nonaggressive rats, but the pattern, time course of cytokine changes, and their regional characteristics varied according to the animal aggressiveness. After LPS administration, aggressive rats showed increased levels of IL-1β in the hypothalamus at 2 and 4 h and in the frontal cortex at 4 and 24 h compared to LPS-treated nonaggressive line. IL-2 was increased in the frontal cortex and striatum of aggressive rats within 24 h, while IL-6 elevation in the hypothalamus was found at 4 h and in the frontal cortex at 2 and 4 h. In the hippocampus, the levels of IL-1β IL-2, and IL-6 were lower in LPS-treated aggressive rats than in nonaggressive animals. The levels of anti-inflammatory cytokine IL-10 were also decreased in all brain structures of aggressive rats receiving LPS. The results indicate that genetic predisposition to increased aggression is associated with a time and region-dependent changes in the levels of pro- and anti-inflammatory cytokines.