The brain’s pituitary gland produces prolactin, which is the hormone best known for enabling mothers to produce milk.
Researchers in the laboratory of Rosemary Brown and Dave Grattan discovered a previously unknown function of prolactin.
It limited new mammalian mothers’ aggressive behaviour and focused them instead on protecting their babies from danger, Dr Brown said.
"Prolactin is very high during pregnancy and lactation, so we initially thought it induces protective behaviour.
"However, we learned prolactin restrains aggressive behaviour, so mothers can better concentrate on caring for their offspring," Dr Brown said.
Without prolactin, a new mother might risk her own health and expend too much time and energy dealing with perceived threats, Dr Brown said.
Prolactin limited the investment in unnecessary protective behaviour and instead shifted it to focusing on her infants, Dr Brown said.
"She will protect her babies, but do so in a controlled and focused manner," Dr Brown said.
Prolactin acted on cells in the brain’s ventromedial hypothalamic nucleus, which regulated aggressive behaviour, Dr. Brown said.
Researchers used rodent models, and by removing prolactin receptors in specific regions of the brain were able pinpoint where and how prolactin influenced aggression modulation, Dr Brown said.
"We found that the cells active during protective behaviour respond to prolactin, and prolactin powerfully acts on these cells to restrict the amount of aggressive and protective behaviour in mothers," she said.
Dr Brown’s fellow researcher Teodora Georgescu, of the university’s department of anatomy, described the finding as significant.
‘‘Up to one in five new mothers struggle with some form of mood disorder.
"We hope that by understanding how hormones change behaviour in mothers, we can develop effective ways of helping them," Dr Georgescu said.
Dr Brown and her fellow University of Otago researchers, Dr Grattan, Dr Georgescu and Zin Khant Aung, revealed their findings in an article published in the Proceedings of the National Academy of Sciences.
