Early adverse rearing experiences alter sleep–wake patterns and plasma cortisol levels in juvenile rhesus monkeys

Summary 

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 sleep–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 sleep–wake patterns in juvenile nursery- and mother-reared rhesus macaques (Macaca mulatta, 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 sleep, earlier morning waking, and longer periods of sleep 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 sleep efficiency in the two groups. A strong positive relationship (r²>0.8) was found between mean cortisol levels and sleep 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.

Keywords: Circadian, Sleep, Sleep–wake cycle, Cortisol, Hypothalamic–pituitary–adrenal axis, Rearing, Mood, Development