Brain opioids and mother-infant social motivation.

Brain opioids were the first neurochemical system to be implicated in the elaboration of social-bonding processes. Although a variety of neurochemical systems help elaborate social rewards and specific social behaviors, the role of opioids in the control of maternal behavior remains controversial. Although a great deal of data indicate that intermediate doses of morphine can reduce maternal behavior, the evidence, taken together, suggests that endogenous opioids promote the regulatory control of maternal behavior, probably by providing feedback concerning the satisfaction that can be had from indulging in various maternal behaviors. Thus opioid blockade with naltrexone can reduce maternal competence in animals, while at the same time increasing maternal motivation. Opiate blockade likewise appears to increase the social motivation of rat pups, but reduces the reinforcing quality of interaction with the mother, suggesting that opioids provide feedback concerning the pleasurable qualities of social interaction in both mothers and infants. The clinical implications of this knowledge are not straightforward, but they generally suggest that clinically deficient social bonding might be capable of being strengthened via manipulation of brain opioid systems.