Know the brain, and its axons, by the clothes they wear

April 18, 2014 by John Hewitt report
This is a computer image of three neurons showing differences in myelin. Credit: Daniel Berger and Giulio Tomassy/Harvard University

(Medical Xpress)—It is widely know that the grey matter of the brain is grey because it is dense with cell bodies and capillaries. The white matter is almost entirely composed of lipid-based myelin, but there is also a little room in the grey matter for a few select axons to be at least partially myelinated. A group of well known researchers, mostly from Harvard and MIT, decided to look for possible patterns in the myelin found in cortical grey matter. Their Science published findings suggest that this dynamic balance struck up by each axon, somewhere between zero and full myelination, does not tip to the benefit of action potential speed alone. Instead, it follows a more subtle give and take between different kinds cells.

In looking down the length of an axon, longitudinally that is, each segment of myelin is separated by a node. The thickness of the myelin coat varies significantly from node to node. Presumably then, so does the speed and reliability of the spike propagated in that segment. The researchers suggest however, that it is more the phase and offset of these nodes that matters. The distance to first node in particular is important because it is here that the spike shape is first initiaillized. As Doug Fields points out in a perspective that accompanies the paper, spike shape (usually inconsequential in computational models) has important functional implications including the amount of transmitter released, the refractory period and the spike frequency.

Within the cortical grey, it is now known that the bare initial segment of the axon is irresistible to other cells. Their synaptic overtures are regularly accepted and also reciprocated by the axon's own transmitter release from bare, noncanonical release sites. The researchers found that the length of the myelin-free axon initial segment had a graded distribution with the more superficially located pyramidal cells in the mouse cortex having longer "open" axon. In layer II/III bare stretches up to o 55 µm were evident.

The technology that makes it possible to reconstruct serial sections of is perhaps the most advanced—and certainly the most industrialized—in neuroscience. It is precisely the same technique used in the recent Brainbow II studies, which incidentally have also yielded some the most celebrated images in science. But I must say, reader, if you are not blown away by the above mentioned details on myelination, you are not alone. That you are still here indicates that you expect something more.

So forgive me, rightfully esteemed authors, if I suggest you have an opportunity here perhaps not yet missed, but rapidly growing stale. Ken, Sebastian, Jeff—Doug, where is the missing myelin mechanics? In the name of all that is Holy, myelination requires a breaking of symmetry, namely it has to wrap in one direction. We have asked previously, in detail, how this constraint is applied in whole brain and nerve, going down an axon, going to immediately adjacent axons, and also to the multiple arms of any one oligodendrocyte.

As myelin undergoes phase transitions in development, does its 3D tubular mesh align like slow motion lipid spin glasses? Is direction imposed individually at each turn, or in bulk transition, perhaps reflective of temperature dependent crystal or magnetic domain formation? More speculatively, can firing axons, simultaneously pulsing mechanically in the radial direction, rectify their continuous cellular substructure into miniscule torques which aid and abet myelination? How does bulk vary across the bilaterally symetric halves of the brain, across the callosum, and down the altogether unique myelin of the nerves units of the body? Now that we clearly have the technology, lets answer these questions and begin to piece this brain together ground up.

The power of the screw and the drill, known to any machinist, is not lost here. The authors own recent incredible work attests to that. They reference their previous discovery of helical substructure in stacked endoplasmic reticulum sheets connected through unique membrane motiffs. Might neurons themselves be chiral, or at least their axons or apical dendrite have a preferred hand? If it is now possible to image effervescent cell organelles, centriolar-defined coordinate systems, the windings of microtubule arrays even down to the tiny symmetry-breaking protein hooks which preferentially adorn them in vs dendrtites, certainly we can now construct geometry on larger scales of the brain.

Explore further: How the brain makes myelination activity-dependent

More information: Paper: Myelin—More than Insulation, Science 18 April 2014: Vol. 344 no. 6181 pp. 264-266. DOI: 10.1126/science.1253851


Related Stories

How the brain makes myelination activity-dependent

January 10, 2014
(Medical Xpress)—A major question regarding how axons acquire a coat of myelin, is the role of spiking activity. It is known that in culture systems oligodendroctyes will at least try to wrap anything that feels like an ...

Fast and reliable: New mechanism for speedy transmission in basket cells discovered

March 24, 2014
In his third major research paper since December 2013, IST Austria Professor Peter Jonas together with his collaborator, postdoc Hua Hu, identifies a new subcellular mechanism for reliable, fast transmission in the so-called ...

Brain electrical activity spurs insulation of brain's wiring

August 11, 2011
(Medical Xpress) -- Researchers at the National Institutes of Health have discovered in mice a molecular trigger that initiates myelination, the process by which brain cell networks are reinforced with an insulating material ...

Schizophrenia: It's in the wiring of the brain

September 16, 2013
Just as wires must be insulated to effectively carry electrical impulses, nerve cells must be insulated by myelin to effectively transmit neural impulses. Using typical magnetic resonance imaging or MRI, one can visually ...

Myelin exploits phase transitions to drive it's assembly

July 19, 2013
The ability to construct complex myelin sheaths around axons is one of the greatest vertebrate inventions since the hinged jaw.

Recommended for you

'Residual echo' of ancient humans in scans may hold clues to mental disorders

July 26, 2017
Researchers at the National Institute of Mental Health (NIMH) have produced the first direct evidence that parts of our brains implicated in mental disorders may be shaped by a "residual echo" from our ancient past. The more ...

Laser used to reawaken lost memories in mice with Alzheimer's disease

July 26, 2017
(Medical Xpress)—A team of researchers at Columbia University has found that applying a laser to the part of a mouse brain used for memory storage caused the mice to recall memories lost due to a mouse version of Alzheimer's ...

Cellular roots of anxiety identified

July 26, 2017
From students stressing over exams to workers facing possible layoffs, worrying about the future is a normal and universal experience. But when people's anticipation of bad things to come starts interfering with daily life, ...

Cognitive cross-training enhances learning, study finds

July 25, 2017
Just as athletes cross-train to improve physical skills, those wanting to enhance cognitive skills can benefit from multiple ways of exercising the brain, according to a comprehensive new study from University of Illinois ...

Brain disease seen in most football players in large report

July 25, 2017
Research on 202 former football players found evidence of a brain disease linked to repeated head blows in nearly all of them, from athletes in the National Football League, college and even high school.

Lutein may counter cognitive aging, study finds

July 25, 2017
Spinach and kale are favorites of those looking to stay physically fit, but they also could keep consumers cognitively fit, according to a new study from University of Illinois researchers.


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.