A comparative study of aggression related changes in brain serotonin in CBA, C57BL, and DBA mice

Spontaneous aggression was induced in 3 strains of male mice (CBA, C57BL, and DBA) by a new technique of socially intermixing them for 14 days and daily measuring the amount of scarring each received. In all strains, serotonin (5-HT) was lower in the ventromedial (VMH) and supraoptic (SO) hypothalamic areas and amygdala in the more aggressive as compared to the controls or less aggressive animals. The correlation coefficients between the amount of physical scarring and brain 5-HT in these areas ranged from 0.50 to 0.91 (P less than 0.05 to P less than 0.01). Hippocampal (HPC) 5-HT was also lower in the more aggressive animals in CBA mice. Also the most aggressive strain (CBA) tended to have the lowest SO, VMH, and amygdala 5-HT concentration. In all 3 strains the concentration of brain 5-HT from lowest to highest was: frontal cortex less than HPC less than amygdala less than VMH less than SO. The data suggest that there is an inverse relationship between hypothalamic and limbic 5-HT and aggressiveness. Also the data suggest that the technique of intermixing 3 strains of mice successfully induced spontaneous aggression which peaked around 14 days and was reliable and could be quantified.