Maternal Absence and Stability of Individual Differences in CSF 5-HIAA Concentrations in Rhesus Monkey Infants

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Abstract
Early life events often lead to deficits in CNS serotonin function, which underlie a number of reoccurring psychopathological disorders. Studies using rhesus macaques have demonstrated that early maternal deprivation reduces CNS serotonin turnover, as measured by cisternal CSF 5-HIAA concentrations. In addition, individual differences in CSF 5-HIAA remain stable from the first year of life through adulthood. The purpose of this study was to assess 1) the impact of rearing environment on the early development (<6 months of age) of the serotonin system, and 2) at what stage of early development individual differences in CSF 5-HIAA concentrations stabilize. The subjects were 256 infant rhesus macaques reared in three different conditions (mother-reared, peer-reared, and surrogate/peer-reared). Cisternal CSF was obtained at 14, 30, 60, 90, 120, and 150 days of age. No differences in CSF 5-HIAA concentrations were observed between peer only- and surrogate/peer-reared infants, and these groups combined exhibited lower 5-HIAA concentrations than mother-reared infants throughout early development. CSF 5-HIAA concentrations declined with increasing age regardless of rearing condition. Within each rearing condition, individual differences in CSF 5-HIAA concentrations remained stable from 14 to 150 days of age. Early maternal deprivation reduces CNS serotonin turnover, and individual differences in CSF 5-HIAA concentrations are trait-like and appear to stabilize in infancy.