Researchers at Ohio State University say that long-term exposure to air pollution can lead to physical changes in the brain, as well as learning and memory problems--even depression! A study on mice published online this week in the journal Molecular Psychiatry
shows damaging effects of air pollution on the brain, in much the same way that long-term studies have revealed similar effects on heart and lungs.
The scientists--continuing a collaboration through Ohio State's Department of Neuroscience and the university's Davis Heart and Lung Research Institute--previously demonstrated that fine particles in the air cause widespread inflammation in the body, which can be linked to high blood pressure, diabetes, and obesity.
In the new study, mice were exposed to either filtered air or polluted air. The polluted air contained fine particulate matter, the kind of pollution created by cars, factories, and natural dust. After breathing the air six hours a day, five days a week for 10 months--nearly half the lifespan of the mice--the animals were given a variety of behavioral tests.
In a learning and memory test, mice were placed in the middle of a brightly lit arena and given two minutes to find an escape hole leading to a dark box where they feel more comfortable. They were given five days of training, but the mice who breathed the polluted air took longer to learn the location of the escape hole. They were also less likely to remember the site of the escape hole when tested later.
In another experiment, mice exposed to the polluted air showed more depressive-like behaviors than did the mice that breathed the filtered air. The polluted-air mice also showed signs of higher levels of anxiety in one test, but not in another.
The hippocampus, which lies deep within the brain, is important to learning, memory, and mood.
How might air pollution lead to these changes? The researchers studied the hippocampal area of the mice brains looking for answers. "We wanted to look carefully at the hippocampus because it is associated with learning, memory, and depression," said Laura Fonken, lead author of the study and a doctoral student in neuroscience at Ohio State University.
The researchers looked specifically at branches, called dendrites, that grow from nerve cells. Dendrites have small projections growing off them called spines, which transmit signals from one neuron to another. The researchers found that the mice that breathed polluted air had shorter dendrites, fewer spines, and overall reduced cell complexity compared to the clean-air mice.
A and B are dendrites. Notice the small spines.
The differences may be a result of inflammation. "The hippocampus is particularly sensitive to damage caused by inflammation," Fonken said. "We suspect that the systemic inflammation caused by breathing polluted air is being communicated to the central nervous system. . . . This could have important and troubling implications for people who live and work in polluted urban areas around the world."
For More Information
L K Fonken, X Xu, Z M Weil, G Chen, Q Sun, S Rajagopalan and R J Nelson.
Air pollution impairs cognition, provokes depressive-like behaviors and alters hippocampal cytokine expression and morphology. Mol Psychiatry advance online publication, July 5, 2011.
Dentrite/spine photo by Grazyna Gorny from Terry E. Robinson's University of Michigan website.