The brain has always been a bit mysterious. How does it all work so that a human being can live, breathe and talk. The brain is composed of two broad classes of cells: neurons and glia. These two types are equally numerous in the brain as a whole, although glial cells outnumber neurons roughly 4 to 1 in the cerebral cortex. Glia come in several types, which perform a number of critical functions, including structural support, metabolic support, insulation, and guidance of development. Astrocytes (brain cells named after their characteristic star-shape) that were previously thought to act only as the glue between neurons have a central role in the regulation of breathing.
The finding provides a new dimension for research into fundamental principles of brain organization and function and may be relevant for understanding causes of respiratory failure such as Sudden Infant Death Syndrome.
The research was carried out by Dr Alexander Gourine and colleagues at University College London, and Professor Sergey Kasparov and colleagues in Bristol University's Department of Physiology and Pharmacology. They demonstrate that brain astrocytes are able to sense the levels of carbon dioxide in the blood. They then activate brain neuronal respiratory networks to increase our breathing in accord with prevailing metabolism and activity.
Astrocytes are a subtype of a group of brain cells known as glia (which means â€˜glueâ€™ in Greek). Glial cells are the most abundant cells in the human brain â€“ outnumbering neurons by a factor of ten to one. Until very recently, glial cells have been thought to be the less exciting sisters of neurons, merely providing them with structural and nutritional support.
The four traditional functions of glial cells are to surround neurons and hold them in place, to supply nutrients and oxygen to neurons, to insulate one neuron from another, and to destroy pathogens and remove dead neurons.
Astrocytes perform many functions, including biochemical support of endothelial cells which form the blood brain barrier, provision of nutrients to the nervous tissue, maintenance of extracellular ion balance, and a principal role in the repair and scarring process of the brain and spinal cord following traumatic injuries. They have now been found to have a unique ability to sense the composition of arterial blood entering the brain by sensing increases in arterial levels of carbon dioxide. When activated they release a chemical messenger called ATP which stimulates brain respiratory centers to increase breathing rates in order for extra carbon dioxide to be removed from the blood and exhaled.
This observation places astrocytes as a key automatic role for respiratory adjustment due to changing conditions. Normally no one thinks to breathe more rapidly. This may be the way the brain makes that adjustment.
This newly realized brain cell function may be critical to understanding and then treating certain respiratory diseases such as Sudden Infant Death Syndrome and Ondine's curse (a sleep disorder where the body stops breathing for a moment.
For further information: http://www.bristol.ac.uk/news/2010/7133.html