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Student Prize Award Abstract
1996 Poster Paper Honorable Mention


C. Shannon and S. Higley
LCE, NICHD, Poolesville, MD 20837, U.S.A.

Two previous studies have compared cortisol levels of mother-reared and nursery-reared rhesus monkey infants. One study found that on day 14 and day 30 mother-reared infants had lower baseline cortisol than nursery-reared infants. The other study found that from 1-6 months of life there were no rearing effects on baseline cortisol, although under mild stress conditions mother-reared infants had higher cortisol levels than did peer-reared infants. However, in these studies, mother-reared infants were housed in single-cage mother-infant dyads. We attempted to extend these studies to include surrogate-peer reared infants as well as group-housed mother-reared subjects. We also looked at stress conditions longitudinally. The subjects were 145 infant rhesus macaques reared in three different conditions--mother-reared (MR), peer-reared (PR at 30 days old animals were placed in groups of three or four), and surrogate-peer reared (SPR at 30 days old the animals were placed in social groups for two to three hours a day). On days 14 and 30, a 30 minute neonatal assessment was performed. Following the examination blood cortisol was collected. In addition, on days 90, 120, and 150, blood was collected following a 30 minute isolation. On day 60 a baseline blood cortisol sample was collected. MR infants had higher cortisol levels on days 14, 30, and 60 than PR monkeys, and had higher cortisol levels on days 14, 60, 90, 120, and 150 than SPR infants. On day 30 SPR infants had higher cortisol levels than PR infants; however, the opposite was true on days 60, 90, 120, 150. When comparing the values we obtained with previously published baseline cortisol levels, the PR cortisol levels are similar, but MR infants reared in social groups have higher cortisol than those reared in the single-cage dyad condition. This finding indicates that infants reared with their mothers in a social group may not be as buffered by the mother in response to external stimuli and stress as previously proposed. We were able to replicate the findings that under stressful situations MR infants have higher cortisol levels than PR infants.

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