Scientists Debunk 100-Year-Old Theory of Brain Cell Structure

The MICrONS encephalon representation with 500 cardinal neural connections. Credit: Birth Into Being / CC BY-NC-SA 2.0

For much than a century, scientists assumed the bladed extensions of brain cells that transportation electrical signals, known arsenic axons, were smooth, tube-shaped structures. A caller survey debunks that long-standing presumption of encephalon compartment structure, showing that axons alternatively signifier a repeated pearl-like signifier nether near-natural conditions. This signifier straight controls however accelerated signals question done the brain.

The findings, published successful Nature Neuroscience, travel from researchers astatine Johns Hopkins University School of Medicine. Lead writer Jacqueline M. Griswold and her squad discovered that unmyelinated axons transportation repeated tiny swellings astir 200 nanometers (0.0000079 inches) wide.

These swellings are connected by ultra-thin segments astir 60 nanometers (0.0000024 inches) successful diameter. The researchers called this signifier “nanopearling,” distinguishing it from the larger deformations seen successful dying oregon degenerating neurons.

Johns Hopkins squad uncovers the existent signifier of axons

The crushed earlier studies missed this was the preservation method they used. Chemical-based fixation, the modular attack for decades, distorted good membrane structures and made axons look cylindrical. Griswold’s squad utilized high-pressure freezing instead, a method that preserves insubstantial successful a near-natural state.

When applied to 3 antithetic rodent encephalon preparations, including freshly extracted brain tissue, organotypic portion cultures, and dissociated hippocampal cultures, the pearl signifier appeared consistently crossed each of them. Live-cell imaging confirmed the pearls were stable, did not determination oregon merge, and were not synapses.

To explicate what drives this shape, the researchers built a machine exemplary based connected membrane physics. The exemplary showed that the pearl signifier arises from the carnal properties of the membrane itself, peculiarly its tension.

Human encephalon cells. Credit: Michael / CC BY-NC 2.0 / Flickr

When the squad exposed neurons to solutions of varying concentration, the pearl size changed precisely arsenic the exemplary predicted. Doubling the osmolarity shrank the swellings by 45 percent successful width, portion halving it caused them to grow by the aforesaid margin.

Scientists debunk 100-year-old encephalon compartment operation theory

Cholesterol besides played a cardinal role. Removing it from the membrane utilizing a compound called “MβCD” reduced pearl magnitude and slowed electrical awesome conduction velocity by astir 28 percent.

Blocking a centrifugal macromolecule called nonmuscle myosin II widened the connector regions betwixt pearls and accrued conduction velocity by 19 percent. Disrupting the periodic actin ringing operation of the axon, however, did not meaningfully change the pearl shape.

This pointed to membrane mechanics, alternatively than the cytoskeleton, arsenic the superior operator of the pearl shape.

The study besides recovered that high-frequency electrical stimulation caused pearls to turn larger, with the width expanding by 17 percent. At the aforesaid time, membrane cholesterin dropped by astir 45 percent. This structural alteration slowed awesome conduction velocity and persisted for astatine slightest 60 minutes aft stimulation.

When researchers artificially depleted cholesterol earlier stimulation, structural changes inactive occurred, but conduction velocity nary longer slowed. This suggested cholesterin question is specifically needed to trigger that functional shift.

Cholesterol mobilization triggers changes successful awesome conduction speed

Griswold and her colleagues besides noted that this pearl-like morphology appears successful neurons of simpler organisms, including roundworms and comb jellies. This suggests it is an past and conserved diagnostic of nervus cells alternatively than thing unsocial to mammals.

Researchers accidental the findings reframe however the encephalon encodes and transmits information, showing that the carnal signifier of axons is actively tuned by the cell’s ain membrane chemistry.