AJP - Regulatory, Integrative and Comparative Physiology, Vol 255, Issue 3 485-R491, Copyright © 1988 by American Physiological Society
Orthodromic field potentials and recurrent inhibition during anoxia in turtle brain
Z. C. Feng, T. J. Sick and M. Rosenthal
Department of Neurology, University of Miami School of Medicine, Florida 33101.
Recent evidence suggests that suppression of electrical activity, with the
likely reduction of energy use, provides a necessary strategy for prolonged
anoxic tolerance of turtle brain. The present study was aimed toward
defining mechanisms underlying anoxia-induced suppression of electrical
activity in turtle brain. Goals were to determine whether effects of anoxia
were selective to excitatory or inhibitory processes and to test the
hypothesis that enhanced inhibition underlies suppression of orthodromic
field potentials in olfactory bulb. Amplitudes of "conditioning" and "test"
responses, provoked by pairs of stimulus pulses to the olfactory nerve,
were evaluated before, during, and after anoxic insults in the brains of
turtles anesthetized with pentobarbital sodium. Suppression of conditioning
responses was proportionally greater than that of test responses,
indicating that inhibition was decreased and that enhanced inhibitory
activity is not responsible for suppression of field potentials in turtle
olfactory bulb during anoxia. When normoxia was restored, conditioning
responses recovered but test responses remained suppressed. These data
confirm that the inhibitory effect of a conditioning pulse on responses to
a second pulse of stimulation results from a recurrent circuit and suggest
that anoxia-induced changes in field potentials are independent of this
recurrent circuit. Enhanced inhibition during the early period of recovery
after anoxic insults may provide advantages for restoring energy status and
cell physiology by suppressing electrical activity and energy use.
