Membrane and synaptic activity during anoxia in the isolated turtle cerebellum

Electrical depression in the turtle brain during anoxia has been suggested as a strategy for sparing energy and promoting the extraordinary survival capacity of this tissue. The present study was aimed toward defining the changes in membrane properties during anoxia that may underlie such electrical depression. Studies were conducted in isolated cerebellum from turtle brain. Anoxia caused transmembrane potentials (TMP) to become relatively less polarized in most Purkinje cells. In no cell, however, was TMP depolarized to levels associated with the complete loss of transmembrane ion gradients produced by tissue superfusion with iodoacetate during anoxia. 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 needed for ion transport and perhaps other functions that may be directly related to cell survival.