Evidence for altered monoamine activity and emotional and cognitive disturbance in marmoset monkeys exposed to early life stress.

In common marmoset monkeys (Callithrix jacchus, order Primates), infants aged 2-28 days were deprived of parental care for 30-120 min/day in order to investigate the long-term effects of this neglect-stress model on affect and cognition in a primate species. Basal morning levels of urinary cortisol across the first year of life were unaffected in early deprived marmosets relative to their sibling controls. Basal morning levels of urinary dopamine were chronically increased. This peripheral increase in dopamine activity could represent a marker for central dopamine hyperactivity. Certainly, subadult early deprived marmosets exhibited performance deficits in two dopamine-regulated neuropsychological tasks. They demonstrated: (1) impaired behavioral inhibition in an object reaching with detour task, exhibiting significantly more nonreinforced forward reaches to a reward visible inside a cube that could only be retrieved through an opening to the side of the cube; and (2) impaired reversal learning in a two-way discrimination task based on visual icons presented on a touch-sensitive computer screen. These findings provide further evidence for the relevance of this novel primate model of parent-infant neglect to the environmental causes and mechanisms of human developmental psychopathology.