Early adverse rearing experiences alter steep-wake patterns and plasma cortisol levels in juvenile rhesus monkeys

Monkeys separated from their mothers soon after birth and raised with peers display many disturbances in emotional behavior that are similar to human mood and anxiety disorders. In addition to emotional disturbances, both mood and anxiety disorders are often characterized by disruptions in normal steep-wake cycles, a behavior that has not been well characterized in adversely reared non-human primates. Because polysomnographic measures are difficult to obtain in unrestrained monkeys we used 24-h actigraphy measures to assess probable steep-wake patterns in juvenile nursery- and mother-reared rhesus macaques (Macaca mulatto, N = 16) over several days in the home cage. In addition we assayed plasma cortisol in the morning, afternoon, and evening. Relative to mother-reared (MR) monkeys, actigraphic algorithms indicated that nursery-reared (NR) animals had shorter durations of nocturnal steep, earlier morning waking, and longer periods of steep during the active period, specifically in the mid morning. No shift in diurnal patterns of cortisol was observed, but NR animals displayed an overall elevation in cortisol. Finally a significant interaction was found between cortisol and actigraphic determination of steep efficiency in the two groups. A strong positive relationship (r(2) > 0.8) was found between mean cortisol levels and steep efficiency for the MR monkeys, but a significant negative relationship was found between these same variables for the NR monkeys, indicating a fundamentally different relationship between waking cortisol and actigraphy patterns in these two groups. Published by Elsevier Ltd.