STABILITY OF INTERINDIVIDUAL DIFFERENCES IN SEROTONIN FUNCTION AND ITS RELATIONSHIP TO SEVERE AGGRESSION AND COMPETENT SOCIAL-BEHAVIOR IN RHESUS MACAQUE FEMALES

Few studies have investigated longitudinally interindividual stability of cerebrospinal fluid (CSF) 5-hydroxyindoleacetic acid (5-HIAA) conc entrations in adult nonhuman primates across time and between baseline and stressful conditions. Furthermore, whereas studies with male maca ques consistently have reported a significant, negative correlation be tween CSF 5-HIAA and rates of spontaneous aggression, wounding, and se vere aggression, very few studies have examined this relationship in a dult female nonhuman primates. Even fewer studies have investigated co rrelations between CSF 5-HIAA and competent social behavior, such as s ocial dominance, in female monkeys. In the present study, two social g roups of adult rhesus monkeys (Macaca mulatta) were formed by placing 16 females (aged 42 to 180 months, mean age: 68 months) in one of two indoor-outdoor enclosures with one or two adult males. CSF norepinephr ine (NE), monoamine metabolites, and behavioral data were collected sy stematically over a 24-week period. In week 5 of the study, one additi onal female, not familiar to any of the other subjects, was added to e ach social group. Thereafter the groups were left undisturbed, and dat a characterizing spontaneous aggressive wounding and severe wound inju ries in the females were collected for an additional year The results showed that both group introduction and the addition of a new subject into each group resulted in increased monoamine turnover in the animal s within the social groups. Interindividual differences in CSF concent rations of each of the monoamine metabolites and NE were highly stable from the baseline period to the stress samplings, and between stress samplings. Females with low CSF 5-HIAA exhibited higher rates of spont aneous aggressive wounding, and they were more likely to be removed fr om their social groups for aggressive wounding and/or treatment of inj uries. CSF NE concentrations also were negatively correlated with rate s of spontaneous aggression. In contrast, competitive aggression, i.e. noninjurious aggression used to maintain social dominance ranking, wa s not correlated with CSF 5-HIAA or NE. Females with above average CSF 5-HIAA prior to and following group formation were more likely to att ain and maintain a high social dominance ranking within their social g roup than females with below average CSF 5-HIAA. The present findings indicate that CNS monoamine functioning in adult female rhesus macaque s is traitlike, showing a high degree of interindividual stability acr oss time and setting. These findings also suggest a role for serotonin in controlling impulses that regulate aggression and that competent s ocial behavior among nonhuman primates may require average or above av erage serotonin functioning.