Dejerine-Sottas

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Nerve signal discovery backs Nobel winner’s theory

October 13, 2012

from R&D Magazine:

Scientists have proved a 60-year-old theory about how nerve signals are sent around the body at varying speeds as electrical impulses.

Researchers tested how these signals are transmitted through nerve fibres, which enables us to move and recognise sensations such as touch and smell.

The findings from the University of Edinburgh have validated an idea first proposed by Nobel laureate Sir Andrew Huxley.

It has been known for many years that an insulating layer—known as myelin—which surrounds nerve fibres is crucial in determining how quickly these signals are sent.

This insulating myelin is interrupted at regular intervals along the nerve by gaps called nodes.

Scientists, whose work was funded by the Wellcome Trust, have now proved that the longer the distance between nodes, the quicker the nerve fibres send signals down the nerves.

The theory that the distance between these gaps might affect the speed of electrical signals was first proposed by Sir Andrew Huxley, who won the Nobel Prize in 1963 for his work on electrical signalling in the nervous system, and who died earlier this year.

The study, published in the journal Current Biology, will help provide insight into what happens in people with nerve damage. It will also shed light on how nerves develop before and after birth.

Professor Peter Brophy, Director of the University of Edinburgh’s Centre for Neuroregeneration, said: “The study gives us greater insight into how the central and peripheral nervous systems work and what happens after nerves become injured. We know that peripheral nerves have the capacity to repair, but shorter lengths of insulation around the nerve fibres after repair affect the speed with which impulses are sent around the body.”

The researchers found that when the myelin reached a certain length, the speed with which nerves impulses were conducted reached a peak.

The study, carried out in mice, also confirmed that a protein—periaxin—plays a key role in regulating the length of myelin layers around nerve fibers.

Turning Back The Clock For Schwann Cells

May 20, 2008

Myelin-making Schwann cells have an ability every aging Hollywood star would envy: they can become young again. According to a study appearing in the May 19 issue of the Journal of Cell Biology, David B. Parkinson (University College London, London, UK) and collogues have pinned down a protein that returns the cells to their youth, a finding that might help researchers understand why myelin production falters in some diseases.

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Developmental loss of NT-3 in vivo results in reduced levels of myelin-specific proteins

February 1, 2008

Glia. 2008 Feb;56(3):306-17.
Developmental loss of NT-3 in vivo results in reduced levels of myelin-specific proteins, a reduced extent of myelination and increased apoptosis of Schwann cells.
Woolley AG, Tait KJ, Hurren BJ, Fisher L, Sheard PW, Duxson MJ.
Department of Pathology, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand.
This work investigates the role of NT-3 in peripheral myelination. Recent articles, based in vitro, propose that NT-3 acting through its high-affinity receptor TrkC may act to inhibit myelin formation by enhancing Schwann cell motility and/or migration. Here, we investigate this hypothesis in vivo by examining myelination formation in NT-3 mutant mice. On the day of birth, soon after the onset of myelination, axons showed normal ensheathment by Schwann cells, no change in the proportion of axons which had begun to myelinate, and no change in either myelin thickness or number of myelin lamellae. However in postnatal day 21 mice, when myelination is substantially complete, we observed an unexpected reduction in mRNA and protein levels for MAG and P(0), and in myelin thickness. This is the opposite result to that predicted from previous in vitro studies, where removal of an inhibitory NT-3 signal would have been expected to enhance myelination. These results suggest that, in vivo, the importance of NT-3 as a major support factor for Schwann cells (Meier et al., (1999) J Neurosci 19:3847-3859) over-rides its potential role as an myelin inhibitor, with the net effect that loss of NT-3 results in degradation of Schwann cell functions, including myelination. In support of this idea, Schwann cells of NT-3 null mutants showed increased expression of activated caspase-3. Finally, we observed significant reduction in width of the Schwann cell periaxonal collar in NT-3 mutant animals suggesting that loss of NT-3 and resulting reduction in MAG levels may alter signaling at the axon-glial interface.

1996 article from New York Times archives explains P0 mutation in Dejerine-Sottas

December 2, 2007

The New York Times recently digitized its pre-Internet archives and opened them to the public, so today I ran a search and found a single mention of Dejerine-Sottas disease. It’s an interesting article on the use of x-ray crystallography to shed some light on the proteins created by the P0 mutation, one of the mutations that causes Dejerine-Sottas.

Protein Linked to 3 Nerve Ailments

IN two papers representing the work of 19 researchers, scientists reported last week that they had seen, at a molecular level, the damage to an important protein that is the cause of three genetic nerve disorders. Dr. Thomas Bird, a professor at the University of Washington and chief of neurology at the Veterans Affairs hospital in Seattle, who is not associated with the groups who made the reports, said that the papers are examples of where medicine has arrived: at the molecular detail of human disease.

Read more of Protein Linked to 3 Nerve Ailments

Key Nerve Navigation Pathway Identified

November 27, 2007

Newly launched nerve cells in a growing embryo must chart their course to distant destinations, and many of the means they use to navigate have yet to surface. In a study published in the current issue of the journal Neuron, scientists at the Salk Institute for Biological Studies have recovered a key signal that guides motor neurons — the nascent cells that extend from the spinal cord and must find their way down the length of limbs such as arms, wings and legs.
The Salk study, led by Samuel Pfaff, Ph.D, a professor in the Gene Expression Laboratory, identifies a mutation they christened Magellan, after the Portuguese mariner whose ship Victoria was first to circumnavigate the globe. The Magellan mutation occurs in a gene that normally pilots motor neurons on the correct course employing a newly discovered mechanism, their results demonstrate.
Read the rest of Key Nerve Navigation Pathway Identified

Critical Knowledge About The Nervous System Uncovered By Rutgers Scientists

November 8, 2007

Uncover the neural communication links involved in myelination, the process of protecting a nerve’s axon, and it may become possible to reverse the breakdown of the nervous system’s electrical transmissions in such disorders as multiple sclerosis, spinal cord injuries, diabetes and cancers of the nervous system.
With $697,065 in grants from the New Jersey Commission on Spinal Cord Injury and the New Jersey Commission on Brain Injury Research, Haesun Kim of Teaneck, NJ, assistant professor of biological sciences at Rutgers University in Newark, is working on gaining a better understanding of those links.
Specifically, her work focuses on Schwann cells within the peripheral nervous system and their communication links with the axons they myelinate by enwrapping them in myelin. Axons are the long fibrous part of neurons that carry the nerve’s electrical signals. A fatty substance, myelin covers those axons both to protect them and to provide a conduit for the fast conduction of electrical signals within the nervous system. Once that myelin is lost,the electrical signal breaks down and eventually the neuron dies — like a cell phone that loses its signal.

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Movies Reveal That the Process of Insulating Nerves Is Surprisingly Dynamic

November 15, 2006

The first time lapse movies of the initial stage of the process that wraps nerve fibers with an outer, insulating layer, published online on Nov. 12 in the journal Nature Neuroscience, are shedding new light on this complex process and should aid in the design of new therapies to promote this protective layer following disease or injury.
RedGreenOPCs_jpeg.jpgAn image of the spinal cord of a living zebrafish embryo captures two oligodendrocyte progenitor cells, labeled in red and green fluorescent protein, during the period in development when they are spacing themselves along newly formed axons.
Much like the electrical wiring in your house, the nerves in your body need to be completely covered by a layer of insulation to work properly.
Instead of red, white or black plastic, however, the wiring in the nervous system is protected by layers of an insulating protein called myelin. These layers increase the speed that nerve impulses travel throughout the brain and the body. The critical role they play is dramatically illustrated by the symptoms of multiple sclerosis, which is caused by lesions that destroy myelin. These include: blindness, muscle weakness and paralysis, loss of coordination, stuttering, pain and burning sensations, impotence, memory loss, depression and dementia.
The formation of myelin sheaths during development requires a complex choreography generally considered to be one of nature’s most spectacular examples of the interaction between different kinds of cells. Now, a group of Vanderbilt researchers has successfully produced movies that provide the first direct view of the initial stage of this process: the period when the cells that ultimately produce the myelin sheathing spread throughout the developing nervous system. The results were published online in the journal Nature Neuroscience on Nov. 12 and should aid in the design of new therapies to promote the repair of this protective layer following disease or injury.

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USC Researchers Closer To Cure For Multiple Sclerosis And Other Myelin-Related Diseases

November 5, 2006

Los Angeles – A breakthrough finding on the mechanism of myelin formation by Jonah Chan, assistant professor of cell and neurobiology at the Keck School of Medicine of the University of Southern California, could have a major impact on the treatment of diseases such as multiple sclerosis and demyelination as a result of spinal cord injuries.
Myelin, the white matter that coats all nerves, allows long-distance communication in the nervous system. “It plays a vital role in the overall health and function of the nervous system, and its degeneration plays a role in a number of diseases, such as multiple sclerosis, peripheral neuropathies, and even in spinal cord injury,” Chan explained.

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Researchers Find Protein Determines Nerve’s Fate

October 26, 2005

Researchers at the Skirball Institute of Biomolecular Medicine, New York University (NYU) School of Medicine, have found that a protein (neuregulin-1 type III, or NRG1-III) essential for the protective wrapping around a nerve’s central wiring, or axons, also determines its fate.
Just as plastic coatings insulate electrical wires, myelin coats nerve fibers. This fatty substance also accelerates message-carrying impulses that travel along the nerve fibers and frees them from interference. For more than a decade, scientists have known that nerve cells make neuregulins, growth proteins that promote glial cell growth. However, the delicate interaction between nerve cells and the glial cells (Schwann cells) that produce them remain a mystery.
It has been shown that growth factor protein NRG1-III triggers glial cells to make myelin. This knowledge should lead researchers to develop more effective treatments for several neurological diseases, including peripheral neuropathy. [Read more]

Developing nervous system sculpted by opposing chemical messengers

June 4, 2005

From Medical News Today: A newborn baby moves, breathes and cries in part because a network of nerves called motor neurons carry signals from the infant’s brain and spinal cord to muscles throughout its body.
Thanks to new research by scientists at the Salk Institute for Biological Studies, we are closer to understanding how these complicated network connections are wired up during embryonic development. Salk researchers have discovered that the same chemicals (called neurotransmitters) that are responsible for nerve signals are also involved in the wiring of synapses, the network’s crucial contact points between nerves, or between nerves and muscle cells.
The study, published in the May issue of the journal Neuron, showed that as the motor neurons grow from their home base in the spinal cord towards muscles throughout the body, they release two opposing chemical signals. These signals act to preserve synapses that link a motor neuron to its correct muscle cell. ‘Spare’ sites for potential synapses that fail to team up with a motor neuron are dismantled.
“Our study provides the first evidence in a living animal system that the neurotransmitters themselves are sculpturing the developing nervous system,” said Kuo-Fen Lee, Associate Professor at the Salk, who heads the research team reporting its results in Neuron.

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