Continuity and Change in Emotional Reactivity in Rhesus Monkeys Throughout the Prepubertal Period

We examined continuity and change in emotional reactiviy as assessed by hypothalamic–pituitary–adrenal (HPA) activity in rhesus monkeys. Plasma samples were obtained from mother-peer–reared and surrogate-peer–reared monkeys and assayed for cortisol concentrations at 5 time points in infancy. Both plasma and saliva samples were collected for cortisol assay from the same monkeys as 1-, 2-, and 3-year-old juveniles, respectively. Plasma cortisol concentrations increased during the first 5 months of life and decreased from 1 to 3 years of age. Females consistently had higher plasma cortisol concentrations than males. Plasma cortisol concentrations were lower in surrogate-peer–reared than mother-peer–reared monkeys during the first month of life. Juvenile plasma cortisol concentrations were significantly correlated with infant cortisol levels at all but the earliest time point. Analysis of salivary cortisol from a subset of animals showed a similar age-related decline and the presence of a significant rearing effect, with lower concentrations in surrogate-peer–reared juveniles, but no sex difference. Salivary and plasma cortisol concentrations in these animals were significantly correlated.