Myelin's a Basal Characteristic of Neurons, More Derved Have Less

Harvard neuroscientists have made a discovery that turns 160 years of neuroanatomy on its head.

Myelin, the electrical insulating material long known to be essential for the fast transmission of impulses along the axons of nerve cells, is not as ubiquitous as thought, according to a new work lead by Professor Paola Arlotta of the Harvard Stem Cell Institute (HSCI) and the University's Department of Stem Cell and Regenerative Biology, in collaboration with Professor Jeff Lichtman, of Harvard's Department of Molecular and Cellular Biology.

"Myelin is a relatively recent invention during evolution," says Arlotta. "It's thought that myelin allowed the brain to communicate really fast to the far reaches of the body, and that it has endowed the brain with the capacity to compute higher level functions." In fact, loss of myelin is a feature of a number of devastating diseases, including multiple sclerosis and schizophrenia.

But the new research shows that despite myelin essential roles in the brain, "some of the most evolved, most complex neurons of the nervous system have less myelin than older, more ancestral ones" Arlotta, co-director of the HSCI neuroscience program, says.

What this means, Arlotta says, is that the higher in the cerebral cortex one looks – the closer to the top of the brain, which is its most evolved region - the less myelin one finds. Not only that, but "neurons in this part of the brain display a brand new way of positioning myelin along their axons that has not been previously seen. They have 'intermittent myelin' with long axon tracts that lack myelin interspersed among myelin-rich segments.

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