|Electrical Impulses Foster Insulation of Brain Cells, Speeding
Electrical impulses foster myelination, the insulation process that speeds
communication among brain cells, report researchers at two institutes of the
National Institutes of Health.
“This finding provides important information that may lead to a greater understanding
of disorders such as multiple sclerosis that affect myelin, as well as a greater
understanding of the learning process,” said Duane Alexander, M.D., Director
of the NICHD.
The study appears in the March 16 Neuron and was conducted by researchers at
the National Institute of Child Health and Human Development and the National
Neurons — specialized cells of the brain and nervous system — communicate via a
relay system of electrical impulses and specialized molecules called neurotransmitters,
explained the study’s senior author, R. Douglas Fields, Ph.D., Head of NICHD’s
Nervous System Development and Plasticity Section.
A neuron generates an electrical impulse, causing the cell to release its neurotransmitters,
he said. The neurotransmitters, in turn, bind to nearby neurons. The recipient
neurons then generate their own electrical impulses and release their own neurotransmitters,
triggering the process in still more neurons, and so on.
Neurons conduct electrical impulses more efficiently if they are covered with
an insulating material known as myelin, Dr. Fields added. Layers of myelin are
wrapped around the fiber-like projections of neurons like electrical tape wrapped
spiral-fashion around an electrical cable. Human beings are born with comparatively
little myelin, and neurons become coated with the material as they develop. Moreover,
mental activity appears to influence myelination, Dr Fields said. For example,
neglected children have less myelin in certain brain regions than do other children.
However, raising animals in stimulating environments increases their myelin
production. Also, mastering an activity, such as learning to play the piano,
fosters myelination, and myelin is decreased in several mental disorders, including
schizophrenia and bipolar disorder.
Dr. Fields said that these phenomena implied that the cells forming myelin must
somehow sense electrical impulse activity in neurons and regulate myelination
To conduct their study, Dr. Fields and his coworkers isolated neurons from mouse
brains and grew them in laboratory cultures with two other kinds of brain cells,
oligodendrocytes and astrocytes. Previous studies had determined that oligodendrocytes
deposit myelin on neurons, but how electrical impulse activity might stimulate
them to do so was unknown.
In their laboratory cultures, the researchers stimulated the neurons by passing
an electrical current through them. This electrical stimulation was designed
to mimic the normal activity that takes place in the brain when neurons communicate
with each other.
The researchers found that the electrical stimulation caused the neurons to
release adenosine triphosphate (ATP), a high-energy molecule essential to many
biological processes. In this instance, however, the ATP bound to special sites,
or receptors, on the surface of the astrocytes, causing them to release a substance
known as leukemia inhibitory factor (LIF). LIF, in turn, bound to the oligodendrocytes,
stimulating those cells to deposit myelin around the neurons.
Dr. Fields explained that the finding has implications for disorders affecting
myelination, such as Alexander disease, which is a fatal neurological disorder
of childhood caused by a genetic defect in astrocytes. The brains of children
who have Alexander disease also have severe myelin defects. The finding that
astrocytes indirectly relay signals from neurons to oligodendrocytes provides
a possible explanation for the lack of myelin characteristic of the disorder.
Researchers may be able to provide treatment for demylinating diseases, such
as multiple sclerosis, by developing drugs that mimic the actions of ATP and
LIF on their target cells. Similarly, an understanding of how myelination takes
place may offer insight into the learning process.
Other authors of the study are: Tomoko Ishibashi, Kelly A. Dakin, Beth Stevens
and Philip R. Lee, of the NICHD; and Serguei V. Kozlov and Colin L. Stewart of
The NICHD sponsors research on development, before and after birth; maternal,
child, and family health; reproductive biology and population issues; and medical
rehabilitation. For more information, visit the Web site at http://www.nichd.nih.gov/.
The National Institutes of Health (NIH) — The Nation's Medical Research
Agency — includes 27 Institutes and Centers and is a component of
the U.S. Department of Health and Human Services. It is the primary federal
agency for conducting and supporting basic, clinical and translational medical
research, and it investigates the causes, treatments, and cures for both common
and rare diseases. For more information about NIH and its programs, visit http://www.nih.gov.