X-Message-Number: 14829
Date: Thu, 2 Nov 2000 20:45:28 -0800 (PST)
From: Doug Skrecky <>
Subject: wood frogs can survive freezing to -5  C

  Electrophysiological and ultrastructural correlates of cryoinjury in sciatic
  nerve of the freeze-tolerant wood frog, Rana
  Journal of Comparative Physiology - B, Biochemical, Systemic, & Environmental
  Physiology.  169(4-5):351-9, 1999 Jul.
  We investigated function and ultrastructure of sciatic nerves isolated from
  wood frogs (Rana sylvatica) endemic to the
  Northwest Territories, Canada, following freezing at -2.5 degrees C, -5.0
  degrees C, or -7.5 degrees C. All frogs frozen at -2.5 degrees C, and most
  frogs (71%) frozen at -5.0 degrees C, recovered within 14 h after thawing
  began; however, frogs did not survive exposure to -7.5 degrees C. Sciatic
  nerves isolated from frogs frozen at -7.5 degrees C were refractory to
  electrical stimulation, whereas those obtained from frogs surviving exposure
  to -2.5 degrees C or -5.0 degrees C generally exhibited normal
  characteristics of compound action potentials. Frogs responded to freezing by
  mobilizing hepatic glycogen reserves to synthesize the cryoprotectant
  glucose, which increased 20-fold in the liver and 40-fold in the blood.
  Ultrastructural analyses of nerves harvested from frogs in each treatment
  group revealed that freezing at -2.5 degrees C or -5.0 degrees C had little
  or no effect on tissue and cellular organization, but that (lethal) exposure
  to -7.5 degrees C resulted in marked shrinkage of the axon, degeneration of
  mitochondria within the axoplasm, and extensive delamination of myelin
  sheaths of the surrounding Schwann cells.

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