Neuroendocrine mechanisms underlying the intergenerational transmission of maternal behavior and infant abuse in rhesus macaques

Parenting style in rhesus macaques (Macaca mulatta) can vary dramatically among individuals along the two orthogonal dimensions of maternal protectiveness and maternal rejection. High rates of maternal rejection can be accompanied by infant abuse. We investigated the effects of exposure to variable parenting styles on offspring behavioral and neuroendocrine development to identify the possible mechanisms underlying the intergenerational transmission of maternal behavior and infant abuse. Forty-three non-crossfostered male and female infants and 16 crossfostered female infants were followed through their first three years of life or until they reproduced for the first time. Half of the infants were reared by abusive mothers and half by nonabusive controls. Cerebral spinal fluid (CSF) concentrations of the serotonin metabolite, 5-HIAA, were measured at six-month intervals. Abused infants were rejected more by their mothers than controls, and infants exposed to higher rates of maternal rejection had significantly lower CSF 5-HIAA in the first three years of life. When the crossfostered females gave birth for the first time, their rates of maternal rejection matched those of their foster mothers and were negatively correlated with CSF 5-HIAA. Approximately half of the females reared by the abusive mothers exhibited abusive parenting, whereas none of the females reared by controls did. The abused females who became abusive mothers had lower CSF 5-HIAA than the abused females who did not. These findings provide evidence that maternal rejection and infant abuse are transmitted across generations and suggest that experience-induced, long-term alterations in brain serotonergic function may play an important role in the intergen e rational transmission of normal and abnormal parenting.