Objective: Considerable evidence suggests that low concentrations of 5-hydroxyindoleacetic acid (5-HIAA) in CSF are associated with a history of aggressive behavior in both human and nonhuman primates. The purpose of this investigation was to examine the relationships among CSF 5-HIAA concentration, history of aggressive behavior, and cerebral glucose metabolism in a group of nonhuman primates whose CSF 5-HIAA had been sampled several times over the preceding 2 years and whose social behavior had been observed since birth.
Method: The subjects were nine adult male rhesus monkeys studied under isoflurane anesthesia. Cerebral glucose utilization was measured by [18F]fluorodeoxyglucose positron emission tomography. Aggressiveness ratings were made by a primatologist who had had frequent contact with the animals over several years.
Results: There was a significant negative correlation between ratings of aggressive behavior and CSF 5-HIAA concentrations. There was also a negative correlation between the dose of pentobarbital required to induce anesthesia and level of CSF 5-HIAA. Moreover, there were significant negative correlations between CSF 5-HIAA levels and both whole brain glucose utilization and regional glucose utilization in the orbital-frontal cortex.
Conclusions: These results suggest that both increased aggressiveness and low concentrations of CSF 5-HIAA are associated with higher brain glucose metabolism in rhesus monkeys under standardized anesthesia. Aggressive nonhuman primates with low CSF 5-HIAA concentrations may have "innate" tolerance toward functional gamma-aminobutyric acid A receptor agonists such as pentobarbital, isoflurane, and possibly alcohol.