Parental care is considered to be partially innate and/or induced after mating. It is also known that, in humans, parental behavior can be learned through experience—illustrated routinely by non-biological parents. However, it is unclear if other species exhibit the same behavior and what neural mechanisms are involved in parental learning. Now, a study that continuously monitored the behavior of female virgin mice co-housed with an experienced mother and litter shows that watching a mother mouse gather her pups into the family’s nest trains other female mice without pups to perform the same parenting task. In addition, these observations lead to the production of oxytocin in the brains of virgin female mice, biochemically shaping their maternal behaviors even before they have pups of their own.
The study is believed to be the first documented observation of “shepherding” in mice and the first time simultaneous recordings were made of oxytocin-producing neurons as maternal behaviors were observed and adopted.
This research is published in Nature in the article, “Oxytocin neurons enable social transmission of maternal behavior.”
The researchers at NYU Grossman School of Medicine filmed the female mice interacting with their newborns as well as with virgin mice around the clock—analyzing nearly 5,000 hours of video footage of several dozen mother mice interacting with their pups and with virgin mice.
The researchers described what they called a never-before-seen behavior in which new mouse mothers would, without prompting, shepherd virgin female mice into the family’s nest along with their pups. Within 24 hours, the virgins began mimicking the maternal behavior of gathering the mom’s pups into the nest even if the mother was not there. Almost as quickly, virgin mice would also start to perform the pup-retrieving task without any direct contact with an experienced mouse mother and after having only “viewed” the mother through a clear plastic window.
“Our study shows that in mice the best way to be a mom is to watch and learn from an experienced mom,” said study senior investigator Robert Froemke, PhD, a professor in the Skirball Institute of Biomolecular Medicine at NYU Langone Health. “Given the evidence, we propose that similar mechanisms operate in human mothers.”
The research team also measured brain electrical activity in virgin mice during shepherding and later when they became mothers on their own. Simultaneous electrical readings were made in several brain regions known to produce oxytocin or thought to be responding to the hormone. They found that both the sight and sound of crying pups moved outside of their nest stimulated oxytocin production in a specific region of the brain, the hypothalamic paraventricular nucleus (PVN). By contrast, chemically blocking any of the visual, auditory, or oxytocin-producing PVN nerve pathways prevented virgin mice from learning to take care of pups.
The research team built on its earlier studies of the so-called pleasure hormone showing that the release of oxytocin is essential not only for the onset of nursing but also for the initiating of other maternal behaviors.
Froemke said the team next plans to examine if the same tutoring relationship exists among dad mice and virgin males.
“This work redefines oxytocin’s role in brain function, broadening its impact to include formidable and complex social networking activities that force the brain to pay attention and adapt to its surroundings at the time, whether it’s reacting to the sound of a pup’s cries or feelings of happiness,” said Froemke.