WASHINGTON, April 4 (Xinhua) -- A new study published on Wednesday in the journal Neuron revealed how a mother's "basic instinct" to grab her wandering offspring and return them to the nest depends on a specific set of brain cell signals.
"Our study shows precisely how a maternal instinct is generated in the mammalian brain," says study senior investigator Lin Dayu, an assistant professor at the Neuroscience Institute at New York University Langone Health.
The researchers monitored brain activity in dozens of female mice as they interacted with their own and others' pups, focusing on a region near the front of the brain called the medial preoptic area (MPOA), which previous work had shown was key to pup retrieval in mother mice.
Tests have shown that among the millions of cells in this brain region, the few have a signaling protein on their surfaces called estrogen receptor alpha expressing (MPOA Esr1) and they are the most active electrically when mothers located and then brought their pups back to the nest. This activity dropped once the pups were returned.
According to the study, chemically stimulating hundreds of thousands of these cells at once triggered mother mice to immediately pick up their pups.
It has shown that even virgin mice would retrieve pups that were not theirs when these cells were artificially turned on, but when activity in those cells are chemically blocked, all retrieval efforts stopped.
Lin told Xinhua, mice mothers did not distinguish between their own pups and others' pups and they would take care any pups that were in the nest.
However, for other species, such as sheep, mothers do bond with their own pups and will reject others' pups, according to Lin.
"The rationale is that mouse pups have low mobility and foreign pups are unlikely to enter the nest while sheep pups are much more likely to be mixed up," she said.
Lin suggested a change in the accessory olfactory bulb in sheep had been implicated in specific pup bonding.
The researchers traced axons of MPOA Esr1 nerve cells to another brain region, the ventral tegmental area (VTA), where dopamine is produced.
Previous research had shown that chemically blocking cells in the VTA impaired retrieval behaviors. In the new study, researchers found that stimulating MPOA Esr1 axons that projected to the VTA of mother mice led to pup retrieval within seconds.
Lin said that because evolution has conserved biochemistry in most mammals, the findings may help to explain human maternal behaviors, such as breastfeeding and rocking a newborn, and could suggest new ways to help new mothers who have trouble nursing or bonding with their infants.
Lin's team plans to study what changes occur in mothers' brains to sensitize them to their pups in the time between pregnancy and lactation, when MPOA Esr1 cells become most active.
They also plan to investigate what if any similar actions occur in the brains of father mice, whose aggressive behavior toward pups is known to cease for a short period of time around birth.
