Summary: Prolactin, the hormone best known for stimulating milk production, also shifts a mother’s behavioral priorities—reducing excessive aggression and encouraging caregiving and focused interactions with offspring.
Source: University of Otago
Researchers at the University of Otago have identified a previously unrecognized role for prolactin in shaping maternal behavior: rather than promoting aggression, this hormone helps temper aggressive responses so mothers concentrate on caring for their young.
Dr. Rosemary Brown, from the Department of Physiology, explains that one consistent change across mammalian mothers is an increase in protective behavior, which helps them guard infants from real or perceived threats. While mothers can display intense aggression to defend their young, the mechanisms that regulate how and when this protective aggression is expressed were not well understood.
To investigate how hormones influence this behavioral shift, researchers in the laboratories of Dr. Brown and Professor Dave Grattan examined how prolactin acts on specific brain regions. Previous observations showed that prolactin can act on cells in the ventromedial hypothalamic nucleus (VMN), a brain area involved in regulating aggressive behavior in both males and females.
“Because prolactin levels are high during pregnancy and lactation, our initial idea was that it might trigger protective aggression,” Dr. Brown says. “Instead, we found prolactin plays a restraining role—limiting excessive aggression so mothers remain focused on caring for their offspring rather than being distracted by every potential threat.”
Produced by the pituitary gland at the base of the brain, prolactin is primarily known for its role in milk production. However, it also influences many other biological processes. The new findings reveal that prolactin helps balance a mother’s behavioral priorities: it reduces unnecessary or overly risky protective behaviors while promoting direct investment in interactions with pups.
The research team used an animal model and modern neuroscience techniques to selectively block prolactin signaling in target cells of the VMN. They discovered that the neurons active during protective behaviors are responsive to prolactin and that prolactin strongly modulates these neurons to limit the intensity of maternal aggression.
“Prolactin reduces investment in unnecessary protective reactions and encourages mothers to spend more time engaged with their infants,” Dr. Brown explains. “Mothers still protect their young, but do so in a more measured, focused way that avoids unnecessary risk or wasted energy.”
Dr. Teodora Georgescu, from the Department of Anatomy, highlights the clinical and emotional relevance of the findings. “Understanding how hormones influence maternal behavior and mood is highly significant. Up to one in five new mothers experience mood disorders. By clarifying when and how hormones alter maternal behavior, we hope this knowledge will inform future strategies to support women struggling after childbirth,” she says.
About this maternal behavior research news
Author: Press Office, University of Otago
Source: University of Otago
Contact: Press Office – University of Otago
Image: The image is in the public domain
Original Research: Closed access. “Prolactin-mediated restraint of maternal aggression in lactation” by Teodora Georgescu et al., published in PNAS.
Abstract (summary)
Prolactin-mediated restraint of maternal aggression in lactation
Aggressive behavior is uncommon in virgin female mice but becomes pronounced during lactation, where it can serve to protect offspring. Recent work has shown that the hypothalamic ventromedial nucleus (VMN) contributes to aggressive responses in both sexes. In this study, researchers demonstrate that prolactin, acting through its receptor in the VMN, controls the intensity of maternal aggression specifically during lactation.
Removing the prolactin receptor from glutamatergic neurons or selectively from the VMN led to hyperaggressive behavior in lactating females. These animals shifted from investigatory, intruder-directed behaviors toward markedly elevated levels of aggression. Prolactin-sensitive neurons in the VMN were found to project to several other hypothalamic and extrahypothalamic regions—including the medial preoptic area, paraventricular nucleus, and bed nucleus of the stria terminalis—that are part of a broader network regulating maternal behavior.
Within this network, prolactin’s action in the VMN appears to specifically restrain male-directed aggression in lactating females. This modulatory effect likely complements prolactin’s roles in other brain regions, shifting the balance from defense-oriented actions toward pup-directed caregiving behaviors that are essential for offspring survival and development.
These findings clarify a key hormonal mechanism that helps mothers prioritize nurturing behaviors while avoiding excessive or costly defensive responses, offering insight into how maternal mood and behavior are regulated during the postpartum period.