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High on nursing. In rats, suckling stimulates the same reward centers in the brain as cocaine.

Motherhood is a Drug

Who needs drugs when nursing can be such a great high? New research shows that brain scans of suckling moms are indistinguishable from those of virgin rats on cocaine, supporting the idea that nature rewards mothers for nurturing their pups. The work, described in 5 January issue of the Journal of Neuroscience, also sets the stage to better understand the mother-child bond in humans.

When given the choice, rats with babies under 8 days of age will choose suckling their pups over cocaine. Researchers believe this strong motivation to nurse has evolved to help mothers bond with their offspring. Previous work involving damaging parts of the brain or blocking neurotransmitters has shown that the reward system of the brain is involved both in suckling and in drug stimulation. But no one had imaged the brain of a conscious rat for these studies.

To address this, Craig Ferris of the University of Massachusetts Medical School in Worcester and colleagues monitored the effect of suckling and cocaine use in wide-awake mother rats using magnetic resonance imaging (MRI) of the entire brain. When the team compared the MRIs of suckling mother rats to virgin rats given cocaine, it found that the same areas of the brain lit up in both groups. If the mother rats received injections of cocaine, the reward system in their brains dipped in activity below the lactation high, suggesting that lactation somehow interferes with the rewarding effects of cocaine.

This work will allow scientists to bridge what we know about rats to humans, says neuroscientist Joan Morrell at Rutgers University in Newark, New Jersey. "And it's a good overview of the systems that get turned on during suckling and drug use."

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