Maternal care by rhesus monkeys of infant monkeys exposed to either lead or 2,3,7,8-tetrachlorodibenzo-p-dioxin

Mother monkeys exposed to psychoactive drugs during gestation and lactation have shown a pattern of decreased ventral-ventral contact and an earlier onset of the negative behaviors which serve to initiate the weaning process. In the studies reported here, the same pattern of increased maternal care was seen when either control mothers or Pb-exposed mothers cared for fostered Pb-exposed infants. Clearly, Pb-exposure of the mother was not necessary to the effect. The similarity of the increased maternal care in the TCDD study suggests that infant exposure to TCDD may have been the determinant of the effects in that study as well. In support of this, the health and behavior of the TCDD-exposed mothers appeared normal. Furthermore, an increase in maternal care is not the expected result if the mothers were debilitated, and there are several reasons for expecting more severe toxicity in the infants than in the mothers. There were no obvious physical effects of either Pb or TCDD exposure on the offspring. The body weights, physical appearance and health of all infants were normal. Also, quantitative observation did not detect abnormal social or nonsocial behavioral patterns in either the Pb- or the TCDD-exposedf infants. That is, exposed infants did not differ from control infants with regard to social or environmental exploration, self-directed behavior, stereotypic behavior or play behavior. These findings suggest that the mothers were responding to very subtle physical or behavioral cues in modifying their care of the Pb- and TCDD-exposed offspring. Overall, these findings demonstrate that altered maternal care may be a very sensitive indicator of toxicant exposure in the monkey. The findings also highlight the need to evaluate the extent to which altered maternal care may mediate later behavioral effects in toxicant exposed offspring. We are not aware of data relating to the effects of increased maternal care, such as was seen in the studies reported here, on later behavior of monkey offspring. However, it seems feasible that increased maternal care may serve to ameliorate the toxic effects of perinatal chemical exposure.