New research in mice has identified the brain circuitry involved in the learning of maternal behaviors. The findings could be a first step toward treatments for conditions such as postpartum depression and postpartum psychosis.
The study, led by a team at the Medical University of Vienna, Austria, analyzed the behavior of female mice that had never been pregnant when they were exposed to newborn pups. The mice were able to learn parental behaviors, such as grooming the pups and carrying them to the nest, and over time were able to replicate these behaviors at the same levels as are seen in mice that have given birth.
"Our observations have demonstrated that, through repeated experience with pups, the virgin females are capable of learning maternal behaviour that fully resembles those of mothers after delivery," explained project leader Dr Daniela Pollak in a statement.
A variety of behavioral tests were conducted with the mice, to see how they would respond to pups that they had not given birth to.
In one experiment, virgin females were presented with either three pups, or three Lego blocks as a control, which were placed in the cage on the opposite side to the nest. These mice were compared with foster mothers – mice who had been pregnant, but who were being presented with pups that were not their own – and biological mothers.
Maternal female mice will typically retrieve newborns that have strayed from the nest. After three days, the virgin female mice were able to perform retrieval as quickly as the biological and foster mothers.
Further research revealed that this learned behavior appears to be controlled by activation in a brain region called the anterior cingulate cortex (ACC). This region, located in the prefrontal cortex, is associated with the development of emotional and social awareness.
When the virgin female mice were first exposed to the pups, the researchers found that the ACC was activated. As they learned to care for the pups, the ACC controlled the behavior of the mice via an excitatory feedback loop involving another brain region, the thalamus.
While there has been extensive research into the neural processes underlying instinctive maternal behavior, this new study has uncovered a brain circuit that is activated in mice that have not given birth but have learned through experience to care for their young.
While this research is so far limited to mice, future expansion of the work could be of considerable clinical relevance to humans. Adoptive parents are able to learn parental behaviors towards children that they have not given birth to; by contrast, mothers experiencing conditions like postpartum depression or postpartum psychosis may be unable to develop a bond with their child in the usual way. Studies such as this one offer hope for potential treatments for these conditions in the future.
"By showing that maternal behaviours can be acquired and identifying the underlying neuronal circuits in the brain that control this acquisition, we are creating a potential basis for developing therapeutic options for these clinical situations," said Dr Pollak.
The study is published in The EMBO Journal.