Evidence for inhibition by brain serotonin of mouse killing behaviour in rats

THERE is some doubt about the role of brain serotonin in aggression. In mice made aggressive by prolonged isolation, there is a decrease in brain serotonin turnover¹, while increased aggressiveness has been noted in cats² and rats³ given p-chlorophenylalanine (PCPA), which inhibits serotonin synthesis⁴, although the experiments with cats² were not confirmed later⁵. Dominguez and Longo ⁶ reported that PCPA attenuates irritability and viciousness in rats with septal lesions, and Welch and Welch⁷ observed decreased aggressiveness in isolated mice given PCPA. The explanation for these contradictory results may be that different models of aggression are not mediated through the same areas of the brain or by the same biochemical mechanisms.