A new US study finds that depriving adult mice of social contact
reduces production of myelin, the protein sheath that surrounds the
fibers or axons
that convey electrical signals between nerve cells. The researchers also
found socially isolated mice had lower levels of myelin-forming cells
in the part of the
brain that is important for complex emotion and thinking, and suggest
reduced myelin production may play a role in the development of mental
illness.
The good news is myelin production appears to be restored once social contact resumes.
Senior investigator Patrizia Casaccia, from the Graduate School of
Biomedical Sciences at Mount Sinai School of Medicine in New York, and
colleagues, write
about their work in the 11 November online issue of Nature Neuroscience.
Casaccia, a professor of neuroscience, genetics and genomics, and also of neurology at Mount Sinai, says in a statement released on Friday:
"We knew that a lack of social interaction early in life impacted
myelination in young animals but were unsure if these changes would
persist in
adulthood."
"Social isolation of adult mice causes behavioral and structural changes
in neurons, but this is the first study to show that it causes myelin
dysfunction as well,"
she adds.
Myelin Production
Myelin is a protein that forms the protective sheath that insulates
nerve fibers in the brain, spinal cord and eyes and preserves the vital
electrical signals they
carry.
When myelin is destroyed, the electrical signals can't travel, and the result is diseases like
multiple sclerosis (MS), symptoms of which range from mild limb
numbness to paralysis or blindness.
In the case of MS, the cause of myelin loss is attack by the immune
system, which mistakenly treats the tissue as alien. Another study
reported recently in
Nature Biotechnology, describes how, using nanoparticles, scientists were able to
trick the immune system to stop attacking myelin in mice with MS.
Another way myelin loss occurs is if new myelin production ceases. This
is what Casaccia, who is also Chief of the Center of Excellence for
Myelin Repair at the
Friedman Brain Institute at Mount Sinai, and her team investigated.
New myelin is produced by nerve cells called oligodendrocytes. These
work both during development when new nerve cells are being made, and
also in
adulthood to repair damage, such as that caused by the immune system in
people with MS.
The Study
Casaccia's team found after 8 weeks of isolation, adult mice showed signs of social withdrawal.
When they analyzed the mice's brain tissue and compared it to mice that had not been isolated, the
isolated mice had lower levels of myelin-forming
oligodendrocytes in the prefrontal cortex, but not in other areas of the brain. The prefrontal cortex is responsible for complex emotional and cognitive
behavior.
The team also identified changes in chromatin, the packing material for
DNA, which prevented the oligodendrocytes being available for gene
expression. (This
presumably further reduced capacity to produce myelin).
The team then re-introduced the socially isolated mice back into a
social group. After four weeks, their social withdrawal symptoms had
gone, and the
tissue analysis showed the gene expression changes had reversed.
Implications
The researchers conclude their findings suggest myelin formation "acts
as a form of adult plasticity", and that formation of new
oligodendrocytes is affected by
environmental changes.
"Our study demonstrates that oligodendrocytes generate new myelin as a
way to respond to environmental stimuli, and that myelin production is
significantly
reduced in social isolation," says Casaccia.
The study supports other emerging evidence that abnormal myelin
contributes to a range of psychiatric disorders, including anxiety,
autism, schizophrenia
and depression, as Casaccia explains:
"Abnormalities occur in people with psychiatric conditions characterized
by social withdrawal. Other disorders characterized by myelin loss,
such as MS, often are
associated with
depression."
"Our research emphasizes the importance of maintaining a socially stimulating environment in these instances," she adds.
Casaccia's lab at Mount Sinai is now looking more closely at
oligodendrocyte formation to see if there might be some suitable targets
for drug development.
They are testing candidate compounds in rodent and human brain cells,
for their effect on new myelin production.
Funds from the National Multiple Sclerosis Society, and the National
Institute of Neurological Disorders and Stroke, a division of the
National Institutes of Health,
helped finance the study.
Written by Catharine Paddock PhD
Source:
Medical News Today
