MATERNAL NURSING INSTINCT FOUND TO BE MORE BIOLOGICALLY REWARDING THAN INGESTING COCAINE IN A STUDY OF ANIMALS
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MATERNAL NURSING INSTINCT FOUND TO BE MORE BIOLOGICALLY REWARDING THAN INGESTING COCAINE IN A STUDY OF ANIMALS
WASHINGTON, DC December 21 , 2004 – Given the choice, female rats prefer the pleasure of nursing their offspring rather than stimulation with cocaine—at least when the pups are very young, according to a study published in the January 5, 2004, issue of The Journal of Neuroscience.
Craig Ferris, PhD, at the University of Massachusetts Medical School in Worcester, and colleagues found that for maternal rats, both nursing their pups and ingesting cocaine activate the same area of the brain—the pleasure circuit.
“These are fascinating findings that verify what any mother who has breastfed knows: that it is a truly rewarding experience,” said Tracey Shors, PhD, of Rutgers University in Piscataway, New Jersey. “It makes sense that a system would evolve to keep a new mother focused on feeding her infants, because it is so critical for survival.”
The scientists used functional magnetic resonance imaging to analyze brain responses to stimuli for virgin rats and lactating mother rats. The results led the authors to determine not only that nursing and cocaine stimulate the same “reward circuit” but also that maternal rats have a preference for nursing over cocaine. Rats who had never given birth appeared to derive extreme reward—analogous to pleasure in humans—from cocaine ingestion. However, when lactating mothers were treated with cocaine, the pleasure pathways were not activated—in fact, the pathways appeared to be somewhat repressed. These findings indicate that natural selection may have preserved the integrity of the bond between mother and child, giving the bond higher priority than other potential pleasure sources, Ferris says.
As the pups got older, the mothers' preferences changed. Whereas the pleasure from nursing their young remained strong and most sought after for about the first week after birth, the mothers chose to get their brain kicks from cocaine stimulation by about the 10th day after birth.
Citing previous work, Ferris's study posits that oxytocin, a chemical released in the rat brain during birthing and lactating, could account for this maternal preference for bonding with their offspring. The authors note that the evidence for oxytocin's role in instigating maternal behavior, social memory, pair bonding, and affiliative behavior is substantial. The release of oxytocin, the authors conclude, may well account for not only the onset of mother–child bonding but also the lactating mother's reduced sensitivity to and appetite for cocaine's stimulating and rewarding effects on the brain. Yet to be addressed: Would the maternal bond be compromised in cocaine-addicted female rats who then become pregnant?
The Journal of Neuroscience is published by the Society for Neuroscience, an organization of more than 36,000 basic scientists and clinicians who study the brain and nervous system. Ferris can be reached at (508) 856-5530 or craig.ferris@umassmed.edu.
