CSF5-HIAA and aggression in female macaque monkeys: species and interindividual differences

Rationale: While the relationship among CSF 5-HIAA, impulsivity, and aggres sion is well characterized in males, its investigation in females is limite d, and no studies have assessed its generalizability across primates by mak ing simultaneous comparisons between and within closely-related species. Ob jectives: We tested three hypotheses. First, that female rhesus macaques wo uld have lower CSF 5-HIAA concentrations and be more aggressive than would female pigtailed macaques. Second, that females of both macaque species wou ld exhibit an inverse relationship between interindividual differences in C SF 5-HIAA concentrations and rates of severe aggression. Third, that subjec ts with high CSF 5-HIAA concentrations would be higher in social dominance within their respective groups than would subjects with low CSF 5-HIAA conc entrations. Methods: We obtained CSF samples from 61 individually housed fe male primates of two closely related species: rhesus macaques (Macaca mulat ta) and pigtailed macaques (Macaca nemestrina). We later placed subjects in unisex social groups, and correlated interindividual differences in CSF 5- HIAA with aggression, wounding, and acquisition of social dominance rank, R esults: Between-species analyses indicated higher CSF 5-HIAA concentrations in pig-tailed macaques, and higher rates of high-intensity aggression, esc alated aggression, and wounds requiring medical treatment in rhesus macaque s. Within-species analyses indicated that interindividual differences in CS F 5-HIAA concentrations were inversely correlated with escalated aggression and positively correlated with social dominance rank. Conclusions: These f indings show that agonistic and social differences between closely-related species are correlated with CNS serotonin activity, as species that show re latively high rates of severe aggression also tend to have low concentratio ns of CSF 5-HIAA. We conclude that serotonergic functioning plays an import ant role in controlling impulses that regulate severe aggression and social dominance relationships in both male and female primates, and that between -species differences in agonistic temperament can be predicted by species t ypical CNS serotonin functioning.