Fit moms, brainier babies: exercising mothers provide neurological benefits.

Offspring of mice that jogged each day during pregnancy may have an advantage over pups of sedentary morns, according to a new study. In a part of the brain that contributes to learning and memory, the exercisers' pups have more cells than those of sedentary mice do.

Over the past few years, studies have suggested that exercise provides a host of neurological benefits (SN: 2/25/06, p. 122). However, scientists typically performed these studies on adult animals, notes neuroscientist Gerd Kempermann of the Max Delbriick Center for Molecular Medicine in Berlin. He says that he wondered, "If exercise has this neurological effect during adulthood and in old age, what about the other extreme of life, during the earliest development?"

To explore how a mother's exercise affects very young brains, Kempermann and his colleagues devised a simple experiment. A day after laboratory mice had mated, the researchers put the pregnant animals into standard, individual cages with or without a running wheel.

Kempermann's team compared the brains of the offspring during gestation and after birth. The scientists focused on a particular region called the dentate gyrus, which earlier studies had suggested plays a role in consolidating memories.

Animals with and without access to the running wheel all seemed to progress normally through their pregnancies. However, the researchers began noticing distinct differences in the embryos at 15 days of gestation, a time when brain cells are rapidly dividing. Compared with the dentate gyri in the sedentary animals' embryos, those in the runners' embryos had about 20 percent fewer cells.

Despite this initially slow development, the brains of the runners' offspring seemed to rebound rapidly in the weeks after birth. When the runners' pups were 6 weeks old, their dentate gyri had about 40 percent more cells than those of the inactive animals' offspring did. The researchers report these findings in the March 7 Proceedings of the National Academy of Sciences.

Although previous studies had highlighted several different proteins as contributing to exercise's neurological benefits in adults, Kempermann says that the effect in embryos probably doesn't result from a simple transfer of these proteins across the placenta. That scenario can't explain why development in the dentate gyrus was delayed, then bounced back.

In future studies, Kempermann and his team plan to look for the underlying mechanism. They are also curious whether the extra cells in the dentate gyrus have any effect on learning and memory.

Says Henriette van Praag, a neuroscientist at the Salk Institute in San Diego, "It would be interesting to find out how these animals behave over the long term, whether [exercise] could give them a better start in life"

Only after analyzing the results of such research might scientists recommend heavy exercise during pregnancy, notes Fernando Gomez-Pinilla, who studies exercise's neurological effects at the University of California, Los Angeles. "We cannot say that this has a beneficial effect for the brain," he cautions.