Brains white matter process information the way grey matter does

A new study has found that nerves in the mammalian brains white matter not only carry information between various brain regions but also process information the way grey matter cells do.

London, May 8 : A new study has found that nerves in the mammalian brain's white matter not only carry information between various brain regions but also process information the way grey matter cells do.

White matter is one of the two main solid components of the central nervous system. It is composed of myelinated nerve cell processes, or axons, which connect various grey matter areas (the locations of nerve cell bodies) of the brain to each other and carry nerve impulses between neurons.

Generally, white matter can be understood as the parts of the brain and spinal cord responsible for information transmission (axons), whereas, grey matter is mainly responsible for information processing (neuron bodies).

The study was conducted by a team of researchers led by Dwight Bergles at Johns Hopkins Medicine.

The research focuses on oligodendrocyte precursor cells (OPCs), whose main role when they mature into oligodendrocytes is to wrap themselves around and insulate nerves with a whitish coat of protective myelin. The immature cells just hang around and slowly divide, before they are stimulated into action.

As part of the study, researchers recorded the activity from individual precursor cells in the mouse brain in the corpus callosum, a region of white matter that connects the two brain hemispheres.

Researchers found that OPCs produced electrical signals by the neurotransmitter glutamate, similar to the signals used as the principle means of cell-to-cell communication and information processing in the gray matter.

The phenomenon was unlikely as in the mouse brain OPCs in the myelin-rich white matter are far from synapses, the points of contact between nerves where glutamate is released.

The researchers studied nearby nerve cells to figure out where the glutamate might be coming from.

By forcing single nerve cells to become excited one at a time, they discovered that as electrical impulses are carried along the nerves, glutamate is released and causes electrical signals in the OPCs. A further microscopic study showed that pools of glutamate were present in the nerve fibres wherever they touched OPCs. All of the nerve cells in the white matter that released glutamate within reach of OPCs, moreover, had something in common, that is they had no myelin insulation.

Myelin is known to speed up electrical impulses. Myelin loss is well known to impair signalling and information processing, causing nerve cells to die and create neurodegenerative conditions as multiple sclerosis.

Researchers feel that this white matter activity may help 'naked' nerve cells signal nearby OPCs and say 'cover me with myelin because we need to replace another cell that has been damaged'.

"We were surprised to see these nerve axons talking to other cells in the white matter," Bergles sid.

The findings of the research were published in the March issue of Nature Neuroscience.

ANI