Add a new issue to the list of concerns about the overuse of antibiotics. Scientists at the Max Delbrück Center for Molecular Medicine in Berlin, Germany have discovered that mice given antibiotics strong enough to wipe out gut bacteria also stopped forming new brain cells in a part of the brain associated with memory.

The researchers also reported that a type of white blood cell appears to be the link between the brain, the immune system, and the gut: the mice who lost their gut bacteria had lower levels of this particular white blood cell, as well as a decline in the formation of new brain cells in a part of the hippocampus, and poor performance on memory tests. At the same time, mice with healthy gut flora and low levels of the white blood cell showed a decline in formation of new brain cells as well as poor memory performance.

When researchers replaced those blood cells, gave the mice antibiotics or had them exercise on a wheel, the mice regained memory and brain cell production improved.