Caffeine shakes up growing mouse brains

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Pregnant mice buzzed on caffeine gave birth to pups with brain changes and lasting memory deficits, a new study shows. The results, published August 7 in Science Translational Medicine, leave unclear whether caffeine causes a similar effect in people.

The study convincingly shows that caffeine changes the brains of exposed pups, says child neurologist Barry Kosofsky of Weill Cornell Medical College in New York. But he cautions that mouse and human brains develop very differently, so direct comparisons are impossible. The study has no immediate message for pregnant women, Kosofsky says. “We are totally at a loss about what to say for caffeine.”

For a mouse mother, though, the experiment’s story is clearer: Moderate caffeine intake during pregnancy changes baby brains, and not for the better. While pregnant and later lactating, mice drank water laced with caffeine in an amount comparable to a person drinking three to four cups of coffee a day. In offspring, cells in a memory center in the brain called the hippocampus fired off too many messages, an abnormal behavior that could lead to seizures, Carla Silva, of the French National Institute of Health and Medical Research and the University of Coimbra in Portugal, and colleagues found.

As adults, the caffeine-exposed mice performed worse than nonexposed mice on memory tests. Usually, mice ignore familiar objects and spend lots of time investigating something new. But mice exposed to caffeine while developing weren’t keen on exploring new objects, suggesting that they couldn’t remember which object was new. What’s more, these mice had fewer neurons in parts of the hippocampus than normal mice.

These problems might be explained by another deficit the researchers uncovered. As brains form, some neurons must migrate great distances to reach their final home. This journey, which happens in the second half of pregnancy in mice, was disrupted in pups born to caffeinated mothers: New neurons traveling to part of the hippocampus reached their final destination later in those mice than in mice not exposed to caffeine.

Neurons in monkeys, and probably people, undergo a journey, too, but the timing is very different, Silva says. In primates, the bulk of this migration takes place after birth, which may mean that caffeine exposure during pregnancy might have less of an effect on primate brains.

Much more work needs to be done before scientists understand caffeine’s full effects on the rodent brain, much less a human brain, Silva says. “The purpose of our paper is not to make an alarm or say in a simple way that pregnant women cannot drink coffee.”

Caffeine slows down newborn mouse neurons as they travel to their final destination in the brain (right).
Credit: Inserm/ Christine Métin – Christophe Bernard