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The soft mechanical signature of glial scars in the central nervous system

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  • Ref The soft mechanical signature of glial scars in the central nervous system

    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5364386/
    "Injury to the central nervous system (CNS) alters the molecular and cellular composition of neural tissue and leads to glial scarring, which inhibits the regrowth of damaged axons. Mammalian glial scars supposedly form a chemical and mechanical barrier to neuronal regeneration. While tremendous effort has been devoted to identifying molecular characteristics of the scar, very little is known about its mechanical properties. Here we characterize spatiotemporal changes of the elastic stiffness of the injured rat neocortex and spinal cord at 1.5 and three weeks post-injury using atomic force microscopy. In contrast to scars in other mammalian tissues, CNS tissue significantly softens after injury. Expression levels of glial intermediate filaments (GFAP, vimentin) and extracellular matrix components (laminin, collagen IV) correlate with tissue softening. As tissue stiffness is a regulator of neuronal growth, our results may help to understand why mammalian neurons do not regenerate after injury".

  • #2
    This made me think of the late Chicago neurologist Karold Klawans, who noted in his book Why Michael Jordan Couldn't Hit--And Other Tales of Neurology in Sport that Muhammad Ali suffered from trauma to his substantia nigra.

    "Each hard blow to the head of a boxer causes a sudden movement of the brain, a displacement. Each time the head is snapped back, the brain is sent sailing back and forth within the spinal fluid. Acceleration and deceleration. Once. Twice. Hundreds of times. And in Ali thousands of times. Each displacement, each acceleration and deceleration, leaves its trace in the axons that cross from the brain stem to the brain. The process is much like breaking off a length of wire to hang a picture. A single bending of the wire, no matter how sudden or vigorous, leaves the wire still intact. Small, repetitive bends back and forth do the trick, but only if you bend it often enough. Some fibers break quickly, others far more slowly, but eventually all become weakened and frayed and then snap.

    This is what happened to Muhamad Ali."

    By why Ali and not other boxers?

    According to Klawans, "Ali had just enough trauma to cause a mild reduction in nigral robustness, but not enough to limit his athletic prowess in any way. Just enough to set him up for traumatic parkinsonism. His wires were thinner than the average wire. Thick enough to do their job, but so thin that they were more easily frayed and fractured than those of some others. It took fewer bends and twists to break them."

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