In mice, child neglect is a product of both nature and nurture, according to a new study.
Writing in the journal PLoS ONE on April 9, researchers from the University of Wisconsin-Madison describe a strain of mice that exhibit unusually high rates of maternal neglect, with approximately one out of every five females failing to care for her offspring. By comparing the good mothers to their less attentive relatives, the group has found that negligent parenting seems to have both genetic and non-genetic influences, and may be linked to dysregulation of the brain signaling chemical dopamine.
As a possible model for human child neglect, these mice offer a valuable opportunity to investigate the biological and behavioral bases of naturally occurring maternal neglect, say UW-Madison zoology professor Stephen Gammie, who led the study, and co-author psychology professor Anthony Auger.
Good mouse mothers suckle, groom, and protect their pups, while their neglectful sisters may start out trying to care for a litter, but fail to follow through. "There seems to be a switch early on. The neglectful mice may nurse for a day or two after birth, but then the parental care ceases," Gammie says.
To separate the effects of genes and environment, the researchers set up a fostering study, in which pups born to previously nurturing mothers and previously neglectful mothers were switched immediately after birth.
Surprisingly, while nurturing moms attentively cared for foster pups born to other nurturing females, some became more neglectful when given foster pups born to a neglectful mother.
"In some cases the previously nurturing mothers would actively scatter the pups away from the nest, suggesting a negative cue from the pups or a lack of a positive cue," Gammie says. The result suggests that the offspring are somehow able to influence females' behavior and shows that maternal care can be affected by non-genetic factors.
In the fostering study, previously neglectful mothers did successfully raise some of the pups born to previously nurturing mothers, but these surviving pups showed lasting effects, including hyperactivity and low adult body weight. Some females neglected as youngsters were also poor mothers as adults, suggesting some aspects of neglect can be transmitted across generations.
The group also found evidence of genetic factors contributing to neglect. For example, virgin females that exhibited poor self-grooming and hyperactive behavior were at greater risk for becoming neglectful mothers.
To identify possible biological differences, the researchers analyzed brains of neglectful and nurturing mothers shortly after birth. In several brain regions - including some implicated in both maternal behaviors and reward responsiveness - they found higher levels of activity as well as signs of abnormal dopamine signaling in the neglectful mothers.