(1) During the past year, our research included studies that investigated neurobiology and behaviors that are correlated with Type II- like excessive alcohol consumption, including aggression, impulsivity, sleep and circadian activity deficits, and reduced affiliative social behavior. In an earlier study we found that adolescent males with low CSF 5-HIAA concentrations were more likely to exhibit violent, impulsive aggression, and as a consequence, to be killed in aggressive encounters. In a recent study, we found that even as adults, males with low CSF 5-HIAA concentrations continued to die at higher rates than subjects with normal and high CSF 5-HIAA concentrations. As in our earlier study of adolescents, the adult males with low CSF 5-HIAA concentrations exhibited high rates of violent, escalated aggression, but in these adults, this appeared to have adaptive consequences, because high rates of escalated aggression resulted in high social dominance ranking. This later finding suggests that reduced serotonin turnover, as measured by low CSF 5-HIAA concentrations in association with physical aggression may be adaptive under certain conditions in some environments.(2) To assess the generalizability of our low CSF 5-HIAA-impulse deficits behavior findings, our rhesus macaques were compared to a closely related, but more peaceful and friendly macaque species (pigtail macaques). Between-species analyses indicated higher concentrations of CSF 5-HIAA in pigtailed macaques, and lower rates of high-intensity aggression, less unrestrained aggression, and fewer wounds in the pigtailed macaques. Within-species analyses indicated that interindividual differences in CSF 5-HIAA concentrations were inversely correlated with escalated aggression and positively correlated with social dominance rank. These findings extend our previous findings and show that our earlier findings have generalizability, i.e., within both species individual subjects that show relatively high rates of excessive aggression also had low concentrations of CSF 5-HIAA.(3) Within the laboratory, long-term studies compared subjects reared in one of three social conditions: In social groups with adults present (A.- Parental-reared) and in one of two social groups without adults present (B.- chronic peer-access i.e., Peer-reared, or (C.- daily exposure to age-matched peers but limited to only a few hours, i.e., Surrogate-peer-reared). All three rearing conditions produced subjects exhibiting a full-range of species-typical behaviors when compared to both parentally deprived groups. Subjects reared with their parents, however, were less likely to show aberrant behaviors. During the first six months of life, the surrogate- peer-reared subjects exhibited more advanced social behaviors relative to the peer-reared monkeys, with the surrogate-peer- reared subjects showing higher levels of social play and less infant-like clinging, when their interactions were limited to only a few hours each day. However when all subjects were placed together in a larger social group, beginning in the second year of life, the surrogate-peer-reared subjects were more likely to exhibit aberrant behavior resulting in clinical intervention. They also failed to acquire high social dominance. On the other hand, over time, the peer-reared subjects eventually equaled the parentally-reared subjects in social dominance ranking, but the surrogate-peer- reared subjects remained low in the social dominance hierarchy, never exceeding any of the peer-reared monkeys or mother-reared monkeys in social dominance ranking.(4) Studies of how monkeys acquire social dominance showed for the first time that high ranking monkeys exhibit accelerated physical development. Subjects that eventually become high and low ranking did not differing in size at the time of group formation, but after one year of being housed in their new social group, subjects acquiring a high social dominance rank showed increased size relative to their lower ranking cohort.(5) Maternal Behavior and Low CSF 5-HIAA concentrations - Previous research has shown that male macaques with low concentrations of CSF 5-HIAA exhibit high rates of aggression, wounds, social ostracism, and impaired impulse control. Therefore, it was hypothesized that infants of females with low concentrations of CSF 5-HIAA would exhibit less socially competent behaviors than infants of females with high concentrations. During the past year, data were analyzed spanning a five year period. Replicating data from previous research, mothers and infants CSF 5-HIAA concentrations were positively correlated. Mother-infant dyads with low levels of CSF 5-HIAA spent significantly more time in ventral and social contact during weaning than did mother-infant dyads with high concentrations, suggesting a less smooth transition from maternal dependency to infant independence in mother-infant dyads with low CSF 5-HIAA concentrations. When compared to dyads with low CSF 5-HIAA concentrations, infants of mothers with high CSF 5-HIAA also spent significantly more time in social interactions with other members of their social group and more time independent, again suggesting a more difficult transition to independence and integration into macaque society for infants from dyads with low CSF 5-HIAA concentrations. We concluded that during the process of weaning, infants of mothers with low concentrations of CSF 5-HIAA exhibit less independent behaviors than infants of mothers with high concentrations. Child Abuse and Aggression in Females-- In as much as studies from the laboratory show that females with low CSF 5-HIAA concentrations exhibit high levels of physical violence, it would not be unreasonable to hypothesize that females with low CSF 5-HIAA concentrations would be more likely to abuse or neglect their infants than the norm. A collaboration was initiated with Dr. Dario Maestripieri, who has maintained large population of females that abuse and kill their offspring at the Yerkes Regional Primate Research Center. Contrary to expectations, females which abused their infants exhibited high CSF 5-HIAA concentrations. One explanation for this unexpected finding is that these females act less out of impulse deficits than high anxiety, similar to humans who exhibit posttraumatic stress disorder. We will further investigate this during the next year.(6) In a recently completed study we examined the relationship among impaired immune functioning, fearful behavior, and left-handedness in female rhesus macaques. We used the percentage of CD4 (T-helper/inducer) and CD8 (T-suppressor/cytotoxic) cells to total T-cell lymphocytes, and the CD4/CD8 ratio as dependent measures of immune functioning. We derived reactivity profiles from fearful and aggressive responses to an invasive threat, and hand preference profiles from a quadrupedal food-reaching test. The results indicated negative correlations between left-handedness and CD4%, CD4/CD8 values, and positive correlations between left-handedness and fearful behavior in response to an invasive threat. The results of this study provide general support for the view that central nervous system functioning is associated primate temperament and immune functioning and indicate that the degree of left-hand bias can be used as a behavioral marker to identify individuals at risk for immunosuppression and fearful temperament. Further analysis of handedness in nonhuman primates showed that adolescents with high cortisol and testosterone were more likely as adults to exhibit left handedness, suggesting a relationship between high cortisol and testosterone early in life and adult right hemisphere specialization in nonhuman primates.
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