Differential serotonergic mediation of aggression in roosters bred for resistance and susceptibility to Marek's disease

1. Serotonin (5-HT) is a primary regulating neurotransmitter involved in aggressive and impulsive behaviours in mammals. Previous studies have also demonstrated that the function of the serotonergic system in regulating aggression is affected by both genetic and environmental factors. The serotonergic system may display similar functions in chickens.2. Our objective was to investigate the aggressive and impulsive behavioural response to antagonism of the 5-HT1A and 1B receptors in cocks bred for susceptibility and resistance to Marek's disease (i.e. strain 7(2) and 6(3), respectively).3. Cocks from strain 7(2) exhibited increased aggressive behaviours and lower brain 5-HT concentrations compared to strain 6(3) cocks.4. Antagonism of 5-HT1A receptors increased aggressiveness and reduced serotonin turnover in strain 7(2), but not strain 6(3) cocks. 5-HT1B receptor antagonism had no effect on aggression or serotonin turnover in either strain.5. Levels of the serotonin metabolite 5-HIAA, but not absolute central 5-HT levels, were altered in both strains following 5-HT1B antagonism, but only in strain 7(2) cocks following 5-HT1A antagonism.6. The data suggest that 5-HT1A and 1B regulate aggression differently in high and low aggressive strains.