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Lactation hormone helps a mother emotionally attach
Researchers from New Zealand's University of Otago have revealed for the first time the same hormone that stimulates milk production for lactation, also acts in the brain to help establish the nurturing link between mother and baby.
Researchers found that signalling by the hormone prolactin to receptors in a specific brain region, is essential for mothers to show vitally important maternal nurturing behaviour towards their young.
This finding raises the question, is this brain circuitry the "feel good" factor that encourages breast feeding?
Prolactin is best known for its role in enabling milk production in mammals. To test it on emotional attachment, researchers from the University of Otago's Centre for Neuroendocrinology, deleted prolactin receptors in the preoptic brain area of adult female mice.
Study co-author Rosemary Brown says the team observed that these mice without prolactin receptors were able to get pregnant and give birth normally, but abandoned their litters around 24 hours after birth.
The research is newly published in the prestigious international journal Proceedings of the National Academy of Sciences PNAS.
"Our findings establish a critical role for prolactin for more than simply milk production. This work is the first to show this hormone is a literal life saver in that it establishes and maintains the normal parental care that ensures offspring survival. Disruptions in the ability of prolactin to communicate in the brain could lead to problems for mothers establishing a bond with their baby. This may in part explain issues with some animal species abandoning their young."
Prolactin-responsive neurons in the medial preoptic area project widely throughout the brain. After targeted deletion of prolactin receptors in the preoptic area of adult female mice, mice were able to get pregnant and give birth normally. However, mothers lacking prolactin receptors in the medial preoptic area abandoned their litters soon after birth, establishing a critical role for prolactin/placental lactogen action in this area for establishment and maintenance of normal parental care.
Pregnancy hormones, such as prolactin, sensitize neural circuits controlling parental interactions to induce timely activation of maternal behaviors immediately after parturition. While the medial preoptic area (MPOA) is known to be critical for maternal behavior, the specific role of prolactin in this brain region has remained elusive. Here, we evaluated the role of prolactin action in the MPOA using complementary genetic strategies in mice. We characterized prolactin-responsive neurons within the MPOA at different hormonal stages and delineated their projections in the brain. We found that MPOA neurons expressing prolactin receptors (Prlr) form the nexus of a complex prolactin-responsive neural circuit, indicating that changing prolactin levels can act at multiple sites and thus, impinge on the overall activity of a distributed network of neurons. Conditional KO of Prlr from neuronal subpopulations expressing the neurotransmitters GABA or glutamate within this circuit markedly reduced the capacity for prolactin action both in the MPOA and throughout the network. Each of these manipulations, however, produced only subtle impacts on maternal care, suggesting that this distributed circuit is robust with respect to alterations in prolactin signaling. In contrast, acute deletion of Prlr in all MPOA neurons of adult female mice resulted in profound deficits in maternal care soon after birth. All mothers abandoned their pups, showing that prolactin action on MPOA neurons is necessary for the normal expression of postpartum maternal behavior in mice. Our data establish a critical role for prolactin-induced behavioral responses in the maternal brain, ensuring survival of mammalian offspring.
Authors: Rosemary S. E. Browna, Mari Aokic, Sharon R. Ladymana, Hollian R. Phillippsa, Amanda Wyattc, Ulrich Boehmc, and David R. Grattan
Search terms: maternal behavior, prolactin, prolactin receptor, medial preoptic area.
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Mother Jeanne Nursing Her Baby circa 1907 - 1908 Image Credit: by Mary Cassatt thru WikiArt