Amazing stuff! Function follows form or vice versa. Could be a breakthrough.
"... Their findings ... contrast with the classical view of tubular axons. ...
“... To see nanoscale structures with standard electron microscopy, we fix and dehydrate the tissues, but freezing them retains their shape — similar to freezing a grape rather than dehydrating it into a raisin,” ...
The researchers studied three types of mouse neurons: ones grown in the lab, those taken from adult mice and those taken from mouse embryos. The neurons were nonmyelinated (they were without the myelin insulating cover that surrounds the axon).
The researchers found the bubbly, pear shape of axons among all of the tens of thousands of images taken of the tissue samples.
The scientists named the pearl-like structures in which the axon swells “non-synaptic varicosities.”
“These findings challenge a century of understanding about axon structure,” ...
The scientists also used mathematical modeling to see if the axon membrane influenced the shape or presence of the pearl on a string structure. They found that simple mechanical models could be used to explain these structures very effectively. ..."
From the abstract:
"Axons are ultrathin membrane cables that are specialized for the conduction of action potentials. Although their diameter is variable along their length, how their morphology is determined is unclear.
Here, we demonstrate that unmyelinated axons of the mouse central nervous system have nonsynaptic, nanoscopic varicosities ~200 nm in diameter repeatedly along their length interspersed with a thin cable ~60 nm in diameter like pearls-on-a-string.
In silico modeling suggests that this axon nanopearling can be explained by membrane mechanical properties.
Treatments disrupting membrane properties, such as hyper- or hypotonic solutions, cholesterol removal and nonmuscle myosin II inhibition, alter axon nanopearling, confirming the role of membrane mechanics in determining axon morphology.
Furthermore, neuronal activity modulates plasma membrane cholesterol concentration, leading to changes in axon nanopearls and causing slowing of action potential conduction velocity. These data reveal that biophysical forces dictate axon morphology and function, and modulation of membrane mechanics likely underlies unmyelinated axonal plasticity."
Study May Reverse Century-Old Understanding of The Shape of ‘Arms’ on Mammals’ Brain Cells (original news release)
Fig. 1: Axons are pearled, not tubular, under homeostatic conditions.
Fig. 2: Membrane mechanics dictate axon nanopearling.
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