[ExI] cryonics vs. chemopreservation

Eugen Leitl eugen at leitl.org
Tue Jan 15 09:21:26 UTC 2013


On Mon, Jan 14, 2013 at 12:26:50PM -0800, Joshua Job wrote:
> It is really hard to slice a glass or ice into micron thick sheets without
> fracturing, and that's a necessary step when tracing the connectome. That,

This is incorrect. Ion milling and serial block scanning microscopy
(if stained with heavy metals for contrast, for anything else
you'd need a different imaging modality, still surface, though)
work well enough.

> and they also have to dye the brain tissue before putting it under the
> microscope, and you can't do that with a frozen brain. Cyropreservation

The jury is out whether you can combine perfusion and staining
in one step, using the vascular system which still intact (so you'll 
probably have to hit the animal while still alive).
I'm skeptical, but ready to be convinced by evidence.

> probably also changes the morphology of the neurons a good deal too (either
> due to ice crystal formation or dehydration) whih would make figuring out

There is no ice crystal formation with vitrification. Shrinking 
might indeed be a problem with at least some cryoprotectants, 
it is not known yet.

> the connectome harder (though obviously not impossible), and it's already a
> hard enough task.

Notice that it *might* be possible to do room temperature vitrification,
which would obviate need for refrigeration yet leave tissue potentially
viable (at least, not a total brick). It will probably wreck the cell
membranes rather soon, though, unless you can do some selective magic there.



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