I. Longitudinal Studies of Type 2 Personality In Nonhuman Primates: Follow-up of Middle-Aged Males As an investigation of Type 2 personality in nonhuman primates, beginning in 1989, we initiated a study of 104 rhesus juvenile males with varying CSF 5-HIAA concentrations. Our first samples were taken when the subjects were yearlings, still living with their mothers. Ten years later, in the first study to longitudinally follow male rhesus from childhood through the middle-aged period of life, interesting data have emerged suggesting that the varying life history behavior patterns of individual males consistent across time and are predicted by differences in CNS serotonin functioning early in life. Moreover, interindividual differences in CSF 5-HIAA concentrations were stable across the lifespan. In this year?s assessment, we found that high rates of impulsive aggression early in life predicted a life-long pattern of violent behavior and impulsive aggression. Males with low CSF 5-HIAA concentrations are more likely to die prematurely, often early in life. During the mating season they are less likely to be sought as sexual partners and to inseminate females than subjects with high CSF 5-HIAA concentrations. Last year we reported that males with low CSF 5-HIAA concentrations sired fewer offspring than males with high 5-HIAA. Among the males which successfully sired offspring with high CSF 5-HIAA, sires were likely to be older than their counterparts which failed to sire offspring. As a follow-up of this study, this past year we collected semen samples from macaque males with low and high CSF 5-HIAA concentrations. Analyses revealed that there were no significant relationships between CSF 5-HIAA concentrations and sperm density or motility. These finding suggest that differences in reproductive outcome for males differing in CSF 5-HIAA concentrations could not be explained by variability in sperm quantity or quality. II. Studies of Females with Low CSF 5-HIAA concentrations in Feral Environments To date our naturalistic studies of the phenotypic expression of low concentrations of CSF 5-HIAA have focused mainly on males. To assess the phenotype in females, three years ago, we began to gather a sample of young female macaques with varying levels of CSF 5-HIAA. Replicating what was found in males, we found that females with low CSF 5-HIAA concentrations were more likely to engage in impulsive aggression and to suffer from premature mortality. This finding replicates earlier data from males showing a pattern of Type 2-like impulsive aggression in subjects with low CSF 5-HIAA concentrations. In a second study, a group of 30 juvenile females were removed from the natural environment and moved to the laboratory where they sequentially went through three different housing arrangements: single-cage, small group, gang housing, and finally into the larger social group of all 30 females. CSF 5-HIAA concentrations showed interindividual stability between the natural environment and the single-cage setting, between the single-cage setting and social housing setting, and across the 2 different social housing conditions. This suggests that despite major environmental changes, interindividual differences in CNS serotonin functioning are trait-like, highly stable. This is important for two reasons: First it suggests that individual differences in CSF 5-HIAA concentrations are predictive of the functioning of serotonin system later in other settings. This is important because it shows that measures of serotonin on one day are predictive of measures taken at later occasions. Moreover, to the extent that a behavior is under the control of the serotonin system, knowing the functioning of the serotonin system at earlier periods may predict the behaviors later in life, even in other settings. However the correlation is not perfect, suggesting that if CSF 5-HIAA concentrations is used alone to identify subjects at risk for future psychopathology, some errors in classification will be made. As was found in the natural setting, females with low CSF 5-HIAA concentrations exhibited high rates of impulsive aggression and died at a higher rate than females with high CSF 5-HIAA concentrations. This was not just a result of violence, however. In the laboratory, premature death was typically a result of chronic diarrhea, suggesting that female monkeys with low CSF 5-HIAA concentrations are at risk for illness, as well as violence. Unlike males with low CSF 5-HIAA concentrations, females with low CSF 5-HIAA concentrations produced just as many offspring as females with high CSF 5-HIAA concentrations. The infants from females with low CSF 5-HIAA concentrations, however, were more likely to receive trauma from the other animals in the troop, and their infants were more likely to die during infancy. III. Impaired CNS Hemispheric Specialization A number of studies have shown that alcoholics and alcohol abusers are more likely to show abnormalities of laterality. In the rhesus species there is a bias to left handedness, with subjects varying in their strength of that preference. In our original study reported last year, we found that for adult subjects not showing this typical left bias, they were more likely as juveniles and adolescents to have low CSF 5-HIAA concentrations and high cortisol, suggesting that the atypical right-hand preference was negatively correlated with low CNS serotonin functioning and stress reactivity. In follow-ups this year, we further examined stress-related correlates of hand preference. We found a significant correlation between cortisol levels sampled in juveniles and high use of the right-hand in these same animals during adulthood. Animals with a strong right-hand preference exhibited high stress reactivity. These data are consistent with the view that stress functioning and reactivity are associated with the development of hemispheric specialization in primates. Given the finding of increased illnesses in monkeys with low CSF 5-HIAA concentrations, and higher plasma cortisol levels in monkeys differing handedness, we examined the relationship among handedness, immune functioning, and behavioral reactivity in rhesus macaques. The results indicated a positive correlations between the frequency of right- versus left- hand reaches and the absolute number of CD4+ cells, and between the frequency of right- versus left- hand reaches and the degree of human-directed aggression in response to an invasive threat. These results are consistent with and extend previous findings obtained with rodents to nonhuman primates and provide further support for the view that behavioral lateralization is associated with immune functioning and behavioral reactivity. IV. Reduction of aggression: In an assessment of methods that could be used to reduce aggression when our subjects are formed into social groups, we examined the effects of group formation strategy and corral design on wounding and reproduction rates in rhesus macaques. Specifically, we examined group formation using a staged strategy, in which small groups of animals were introduced incrementally over a period of weeks, and a rapid formation strategy, in which all animals were introduced in one day. We found that incrementally releasing animals in hierarchical subgroups, and using a divided versus undivided housing design, reduced intra-group wounding following formation of rhesus macaque breeding groups.
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