X-Message-Number: 15577
Date: Wed, 7 Feb 2001 22:34:35 EST
Subject: more viability questions

As previously noted, there are many ways to measure "viability" of tissues 
for various purposes. INC has been using the K/Na ratio, at least in part 
because it appears to be a good predictor of success in transplants of rabbit 

I have suggested that electrophysiology of the brain may be a better 
criterion for cryonics purposes. After all, it is generally believed that we 
"live" in the connections and signals between neurons, with strictly 
housekeeping functions of the cells and tissues secondary and generic. 

(Of course, there is no simple line between "generic" and "individual." If 
you have blood type O, then any healthy type O blood could be substituted for 
yours--more or less. Yet different individuals may have different antibodies 
in their blood, for example, so you might be appreciably different after a 

Anyway, suppose, on the one hand, that the connections between neurons are 
retained but the internal physiological machinery of the cells fails. On the 
other hand, suppose the opposite--the cells "live" but their connections are 
lost. I submit that the latter case is worse from a cryonics viewpoint.

Now let's look at a paper called "The Influence of Postmortem Delay on Evoked 
Hippocampal Field Potentials in the in-Vitro Slice Preparation," by B.W. 
Leonard et al, Experimental Neurology 113, 373-377, 1991. Paraphrasing some 
key sentences:

The "5-minute rule" of neurological practice says irreversible brain damage 
occurs after about 5 minures of in-situ (on site or in the patient) 
anoxia/ischemia. This has led to the "universal" belief that hippocampal 
slices should be prepared and put into the in-vitro environment (test tube or 
culture dish etc) as quickly as possible. However, there is reason to believe 
that the in-situ situation could be worse than that in-vitro, because a 
locally damaged circulatory system can contribute to later damage. (We 
reported this many years ago, Hossman & Sato).

The present study showed that, by a particular electrophysiological 
criterion, for certain types of slices, "viability" was the same for 
postmortem delays of 5 minutes and 30 minutes, and was about half that after 
3 hours. 

"These data also imply that meaningful electrophysiological information about 
postmortem brain conditions may be inferred from nervous system tissue which 
is not available immediately after death."

Another encouraging item, it seems to me.

Robert Ettinger
Cryonics Institute
Immortalist Society

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