Upregulation of the gabaa/benzodiazepine receptor during anoxia in
the freshwater turtle brain.
Lutz, Peter L., and Sandra L. Leone-Kabler.
Florida Atlantic University, Boca Raton, Florida 33431 (USA)
APStracts 2:0050R, 1995.
The freshwater turtle brain survives anoxia by decreasing its energy
expenditure. During this anoxic period there is a sustained release
of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA).
This study investigated if there was a corresponding change in the
binding properties of the GABAA/benzodiazepine receptor. Turtles
(Trachemys scripta) were subjected to a 100% N2 atmosphere for up to
24 h. Following exposure, the cerebral cortex was dissected out, and
saturation binding assays for GABAA/benzodiazepine (GABA/BDZ)
receptors were performed using the radioligand [3H]flunitrazepam.
Control turtles had a dissociation constant (Kd) of 1.97 +/- 0.54 nM
and a receptor density (Bmax) of 2404 +/- 221 fmol/mg protein. The Kd
showed no significant change over 24 h of anoxia. However,
significant increases were seen in Bmax after 12 h (21 %, p<0.05) and
24 h (29 %, p<0.01) anoxia. We suggest that a long term upregulation
of GABAA receptors occurs in the anoxic turtle brain, which acts to
increase the inhibitory effectiveness of the released GABA and
thereby contributes to anoxia survival of the turtle.
Received 20 September 1994; accepted in final form 18 February
1995.
APS Manuscript Number R541-4.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 1 March 1995.