Heroin induces changes in mother-infant monkey communication and subsequent disruption of their dyadic interaction

Heroin was given in a single, low dose (0.2 mg/kg i.v.) to the mother monkey of mother-infant pairs, living in a stable community of 30 individuals (Macaca fascicularis; six pairs treated plus six controls, in experiments repeated twice). The drug did not induce alterations in the response of the mother to the infant's calling signals when they were placed in a new environment denoting a potentially dangerous situation. However, after being returned to the community cage, the treated mother rarely responded to the infant's calling (non-alarming, non-vocal) signals (P less than 0.02). This behaviour was followed by an increased latency of the infant-to-mother approach, by a diminution of the reciprocal ventroventral clasping as well as a diminution of the overall duration of clasping, and by an increase in nipple suckling (unusual for the age), as compared to saline-treated controls (P less than 0.05, P less than 0.02, P less than 0.025, and P less than 0.05, respectively). Analysis of behavioural sequences strongly confirmed this relationship among data (P less than 0.01 and P less than 0.025). Even short lasting, pharmacologically induced failure in the non-vocal communication of a mother monkey may in itself constitute a pathogenetic mechanism. This is an important cause of the disruption of her dyadic interaction with the infant which consequently upsets the infant's behaviour.