For many animals, it doesn’t seem to matter if a mother is neglectful or even if she gets violent with her kids; her young ones will bond with her despite those bad tendencies. Now a new study shows that the neurotransmitter dopamine seems to control this behavior in rats—potentially shedding light on the effects of abusive child-parent relationships in people.
Researchers led by Regina Sullivan of New York University had previously found that 8-day-old rat pups are drawn to odors around them, which normally leads them to bond with the smell of their mother. This occurred even if the odors were paired with painful electrical shocks. But 12-day-old rats—which are emerging from the rat equivalent of infancy—quickly came to flee the smell associated with shock. Something seemed to change within the rats’ brains during this period.
In the Sept. 27 in the journal Nature Neuroscience, the scientists argue that dopamine is the key. The team found that the younger rats had significantly reduced levels of the neurotransmitter dopamine in their amygdalas, the brain region associated with fear responses. Injecting the rats with dopamine successfully got them to avoid the odors; injecting them with corticosterone, a stress hormone, caused dopamine levels to rise and led to the same avoidance.
On the other hand, the 12-day-old pups showed elevated levels of dopamine in their amygdalas when they were exposed to shocks. Blocking the dopamine caused them to shift gears and stick around. “It’s pretty amazing, to see different reaction in the same animal in the exact same conditions,” Sullivan says.
According to the researchers, this overwhelming drive to bond may be a hardwired mechanism to ensure survival during the period immediately following birth, when animals are still developing and are unable to move around on their own. Since humans go through a similar period, this mechanism might also serve as an animal model for abusive human caretaker-infant relationships. Human infants often show the same strong attachment to their mothers even in the face of abuse and neglect during their first few years of life.
“We always have to be very cautious relating other species to humans,” Sullivan says. “We have no idea if the results will be the same in rats as human infants, but it does tell us some things about normal brain development ... People like to assume we know a great deal about brain development, but we don’t. Animals can give us great insights into general patterns of brain development, and from there we can go on to pathology.”
-Aalok Mehta
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