X-Message-Number: 1418
Date: 10 Dec 92 05:48:36 EST
From: Mike Darwin <>
Subject: CRYONICS Re: DMSO vs Glycerol

From: Mike Darwin
Date: 9 December, 1992
Re: DMSO vs. Glycerol

     I  have  realized  that in responding to Ben  Best  I  failed  to 
mention  another  very powerful reason that glycerol was  chosen  over 
DMSO,  namely that Isamu Suda perfused cat brains with both  DMSO  and 
glycerol  and found glycerol to be superior (Brain Research  70:527-31 
(1974)).

     I  also neglected to mention that when Fahy attempted to  vitrify 
dog  brains using his DMSO-propylene glycol(PG)-formamide  mixture  he 
was  successful in vitrifying only the gray matter.  The white  matter 
was  extensively  (perhaps  uniformly)  frozen.   Why?   Because   the 
myelinated tracts are not well penetrated by cryoprotectant.   Perhaps 
they are only not well penetrated by the formamide and PG.  Additional 
research needs to be done to answer this question.  

     The  point is that it is not just the blood brain  barrier  (BBB) 
that  needs  to  be overcome, but the barrier  represented  by  myelin 
sheathing  as well.  There are openings in the sheath - the  nodes  of 
ranvier - however their "infrequent" intervals and the long  diffusion 
times "down the pipe" limit their utility in mass exchange.

     The BBB can be opened osmotically, however overcoming the problem 
of getting cryoprotectant into the white matter may be very difficult.  
It was interesting to observe that in the ischemic animals we did  not 
observe  any dehydration of axons.  This is probably because  membrane 
integrity was so degraded that relatively big molecules like  glycerol 
(MW=90) could breeze right through.  Not a good sign.

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