CNS Opioids and Maternal Behavior

The rapid, reliable onset of maternal behavior in mammals involves a complex and dramatic change in neurochemical, endocrinological, and sensory factors at delivery. These are orchestrated and timed so that the maternal behavior and the object of the behavior (the infant) "emerge" almost simultaneously at delivery. Important for the emergence of maternal behavior and for the suppression of some of the pain of delivery are changes in the brain's own opioid activity. Ingestion of the afterbirth by the mother, a feature of delivery in almost all nonhuman mammals, significantly and rapidly modifies this opioid-based pregnancy mediated analgesia. This project seeks to determine whether afterbirth ingestion also modifies opioid-mediated influences on maternal behavior. Opioid activation at the end of pregnancy and during delivery has a complex effect on maternal behavior best described by focusing on two brain sites of opioid action: increased opioid activity in the ventral tegmental area facilitates the onset of maternal behavior, but in the medial preoptic area disrupts maternal behavior. The hypothesis tested will be to determine whether afterbirth ingestion modifies specific opioid-receptor systems in these discrete brain regions to optimize the onset of maternal behavior: enhancing the facilitative effect of opioids in the ventral tegmental area, and attenuating the disruptive effects of opioids in the medial preoptic area. These studies will facilitate the development of a comprehensive model of the biobehavioral/neurochemical basis of maternal behavior featuring afterbirth ingestion, opioid activity of two of the key areas of the brain, and the internal hormonal environment at the time of delivery. As many as four graduate students and six undergraduates, some funded by this proposal, will be trained in the context of this research project. As a training experience, this research will be used to exemplify problem-oriented, multilevel analytical research into the integration of internal and external stimuli in the natural regulation of a complex constellation of behaviors in a key element of reproduction in mammals - parturition.