Title

Membrane strategies in the cerebellum to promote survival of the turtle Pseudemis scripta elegans, during diving anoxia

Date of Award

1991

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Marine Biology and Fisheries

First Committee Member

Peter L. Lutz, Committee Chair

Second Committee Member

Myron Rosenthal, Committee Member

Abstract

Intact turtle brain provides a useful model for the study of anoxia since it maintains transmembrane ion gradients and ATP levels during prolonged anoxia.The first study sought to determine effects of anoxia on the isolated turtle cerebellum and to define relationships between anoxia survival and glucose supply. In normoxia, the activity of extracellular potassium ( (K$\sp+$) $\sb{\rm o})$ and evoked potentials were maintained with 5 mM glucose, but 20 mM glucose was required to maintain ATP levels and prevent significant increase in (K$\sp+$) $\sb{\rm o}$ during anoxia.The second study was aimed to determine the metabolic rate of the isolated turtle cerebellum during anoxia. It is reported here that the glycolytic rate is almost doubled from control during the first 30 min of anoxia. But it is reduced approx 30%, concomitant with the reduction of metabolic rate and electrical activity after 2 hrs of anoxia. This study concludes that a Pasteur effect occurs during the transition to anoxia and that a hypometabolic state is reached as anoxia progresses.The third study was aimed toward defining the changes in membrane properties during anoxia that may underlie such electrical depression. Sodium (and likely calcium) spike thresholds were increased, postsynaptic responses from the major afferent input pathways to Purkinje cells were depressed and input resistance decreased significantly during anoxia. These changes likely contribute to the sparing of energy.Goals of fourth study were to test the 'channel arrest' hypothesis. It is reported here that anoxia induced a significant (42%) decline in voltage-gated sodium channel density as determined by studies of the binding of a sodium channel ligand, ($\sp3$H) -brevetoxin. This study demonstrates that sodium channel densities in brain may be regulated by tissue oxygenation.The fifth study was aimed to determine the possible protective role of extracellular adenosine during anoxia in the isolated turtle cerebellum. It is reported here that adenosine is released as observed in intact turtle brain. It is also reported that blockade of the adenosine A$\sb1$ receptor during anoxia causes loss of transmembrane ion gradients and electrical activity.

Keywords

Biology, Neuroscience; Biology, Oceanography

Link to Full Text

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