Astrocytes, traditionally thought to be support cells for neurons, have an important role in modulating motor circuits, according to new research that found that silencing astrocytes in the brain's breathing center caused rats to breathe at a lower rate and tire out on a treadmill earlier than normal.
"For decades we thought that breathing was exclusively controlled by neurons in the brain. Our results suggest that astrocytes actively help control the rhythm of breathing," said Jeffrey C. Smith, senior investigator at the NIH's National Institute of Neurological Disorders and Stroke (NINDS) and a senior author of the study published last month in Nature Communications. "These results add to the growing body of evidence that is changing the way we think about astrocytes and how the brain works."
In this study, the scientists tested the role of astrocytes in breathing by genetically modifying the ability of astrocytes in the preBötzinger complex to release transmitters. When they hushed the astrocytes in rats by reducing transmitter release, the rats breathed and sighed at a lower rate than normal. In contrast, if they made the astrocytes chattier by increasing transmission, the rats breathed at higher resting rates and sighed more often.
The team also tested how silencing astrocytes affected the rats' responses to changes in oxygen and carbon dioxide levels. Although the rats' breathing rate increased when oxygen levels were lower or carbon dioxide levels higher, it was still lower than normal. Silencing astrocytes also decreased the rate at which the rats sighed under lower oxygen levels. Moreover, the rats became exhausted much earlier than normal. They could only run half the distance that normal rats could run on a treadmill before tiring out.
"Our results expand our understanding of how the brain controls breathing under normal and disease conditions," said Dr. Smith. "We plan to follow this path to understand how astrocytes help control other aspects of breathing."
Image: NIH study in rats shows that astrocytes (red) may play an active role in breathing. Image courtesy of Jeffrey C. Smith lab, NIH/NINDS.