Functional activity of the brain 5-HT2A and 5-HT2C serotonin receptors and expression of 5-HT2A and 5-HT2C genes in Norway rats selectively bred for 60 generations for high level and for a lack of fear-induced aggression towards humans were studied. There were no essential differences between aggressive and tame rats in 5-HT2A receptor mRNA level in the midbrain, hippocampus and frontal cortex as well as in the intensity of head-twitch induced by selective 5-HT2A agonist DOI. At the same time, administration of 5-HT2C receptor selective agonist MK-212 reduced the amplitude of acoustic startle response in tame but not in aggressive animals. The increase in 5-HT2C receptor mRNA level in the frontal cortex and hippocampus of nonaggressive rats compared to aggressive animals was shown. The data indicate involvement of the brain 5-HT2C receptor rather than 5-HT2C receptors in the mechanisms of genetically predetermined suppression of fear-induced aggressive behavior.