X-Message-Number: 15331
From: Ettinger
Date: Fri, 12 Jan 2001 14:18:46 EST
Subject: "Viability"

INC had previously reported 53% viability of rat hippocampal slices, using 
the K/Na criterion, after vitrification (near - 130 C?) and rewarming, and 
has now reported 66% viability using a newer cryoprotectant and longer 
equilibration time. Lead scientist Greg Fahy says the 66% refers to each 
individual cell, not an average over all the cells in the specimen.

I'm sure he has good reasons for saying that, but from a general statistical 
point of view it sounds strange. It is extremely rare to find any population 
with variance near zero.  

The term "viability" itself is also subject to interpretation. Ordinarily 
"viability" means "capability of life," but the meaning of that needs to be 
spelled out too.

If we are looking e.g. at a man's semen, to ascertain his ability to father 
children, the usual procedure, as I understand it, is pretty simple. You put 
some under a microscope, count the spermatozoa per cc, and count the number 
of wigglers. The wigglers are assumed capable of doing the job; non-wigglers 
are presumed "dead"--even though they might, in fact, for all we know, still 
retain some internal physiological function. So in this case "50% viability" 
would mean half the individuals alive, not each one half alive.

On the other hand, consider samples of rabbit brain tissue studied for 
coordinated electrical activity after perfusion with glycerol and rewarming 
from liquid nitrogen temperature. Dr. Pichugin did this for CI a couple of 
years ago, with positive results--a first in cryobiology, I believe. 
Arguably, this criterion of "viability"--the coordinated electrical activity 
in nets of neurons--is the most important one for brains. Yet this is no 
guarantee that all of the neurons, or even most of them, retain all the 
normal functions or could support all of the normal brain activity; or that 
the glial cells and vasculature etc were "viable" enough to do their part. 
And my impression is that the K/Na test applied to such specimens would not 
give a good result. My conclusion, tentatively at least, is that the K/Na 
test is not necessarily the best or most important one for brains.  

There are also many other tests for "viability" of biological specimens. One 
of the broad-brush variety is just to culture cells and see if they grow and 
reproduce. Others involve specific chemical/physiological tests, such as 
oxygen uptake, dopamine uptake, glutamate uptake, enzyme activity; presence 
or absence of substances such as neurotransmitters, proteins, lipids, and 
nucleic acids; and many others. I doubt that anyone yet can say which is the 
most important or which are essential for recovery without nanotechnology.

As I have said before, a reasonable degree of assurance of "viability" of 
brain tissue would require good results from studies of structure (histology, 
microscopy), of chemical function (physiology) and of neural nets 
(electrophysiology). 

I'm not looking a gift horse in the mouth. Progress is welcome, even if there 
is still a long way to go. I'm just trying to get some perspective.

Much more extensive background is available on our web site.

Robert Ettinger
Cryonics Institute
Immortalist Society
http://www.cryonics.org

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