Student Prize Award Abstract 1996 Poster Paper Honorable Mention
REARING CONDITION AND PLASMA CORTISOL IN RHESUS MONKEY
INFANTS
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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