

Saturated Reconstruction of a Volume of Neocortex - Someone
http://www.cell.com/cell/abstract/S0092-8674(15)00824-7

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cma
video abstract:
[http://www.cell.com/cms/attachment/2035054472/2050360628/mmc...](http://www.cell.com/cms/attachment/2035054472/2050360628/mmc18.mp4)

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twic
From the materials and methods:

"An anesthetized adult mouse was perfused transcardially with a fixative
solution containing glutaraldehyde, paraformaldehyde, and CaCl2 in cacodylate
buffer. The brain was removed and maintained overnight at 4°C in the same
fixative solution."

I don't know much about neurobiology. But i know that in two other fields of
cell biology - cell motility and vesicle trafficking - something that became
clear in the last decade is that the way you fix samples for electron
microscopy has a huge impact on what you see. Cells are made of highly dynamic
structures that exist in fine-tuned environments; soaking them in formaldehyde
and some random buffer salts is pretty much guaranteed to disrupt those
environments, and let the structures drift away from the states they have in
live cells over the time it takes to fix them, even if it's only fractions of
a second.

The gold standard for fixation is now extremely fast freezing, achieved by
plunging a sample into liquid nitrogen under very high pressure, so that the
water solidifies as a glass rather than growing crystals, which would disrupt
structures inside the cell:

[http://www.biotechniques.com/BiotechniquesJournal/2006/Augus...](http://www.biotechniques.com/BiotechniquesJournal/2006/August/High-
Pressure-Freezing-Cellular-Tomography-and-Structural-Cell-
Biology/biotechniques-40054.html)

In my old field, cell motility, when someone finally tried this, they found
that a thing called the lamellipodium, which has been an object of intense
study for decades, had a rather different structure to what everyone had
thought:

[http://www.ncbi.nlm.nih.gov/pubmed/20418872](http://www.ncbi.nlm.nih.gov/pubmed/20418872)

As a result, it turns out that the prevailing model of how this thing worked
was complete fantasy. Since numerous successful professors have built their
careers on that model, this discovery has not yet really been taken on board
by the field, but it's inevitable that it will.

Which is a very roundabout way of saying that when the authors of this brain
paper write:

"For example, by tracing the trajectories of all excitatory axons and noting
their juxtapositions, both synaptic and non-synaptic, with every dendritic
spine we refute the idea that physical proximity is sufficient to predict
synaptic connectivity (the so-called Peters’ rule)."

I am skeptical, because they are looking at the positions of the spines and
synapses in their formaldehyde-soaked sample, not live tissue, or tissue
prepared in such a way as to preserve the structure of live tissue.

Still a cool paper though.

