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The Journal of Neuroscience, November 10, 2004, 24(45):10159-10166; doi:10.1523/JNEUROSCI.3004-04.2004
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Cellular/Molecular
Increased GABA Release in the Central Amygdala of Ethanol-Dependent Rats
Marisa Roberto,
Samuel G. Madamba,
David G. Stouffer,
Loren H. Parsons, and
George Robert Siggins
Department of Neuropharmacology, The Scripps Research Institute, La Jolla, California 92037
The central nucleus of amygdala (CeA) is important in regulating alcohol consumption and plays a major role in the anxiogenic response to ethanol withdrawal. We showed previously that acute ethanol augments GABAA receptor-mediated IPSPs and IPSCs, possibly by a presynaptic mechanism. Here, we have examined the interaction of acute ethanol with the GABAergic system in chronic ethanol-treated (CET) rats using an in vitro CeA slice preparation and in vivo brain microdialysis. We found that in CeA slices from CET rats, the baseline evoked IPSP and IPSC amplitudes were increased, and paired-pulse facilitation ratios were lower than in naive rats, suggesting an increased GABAergic transmission after chronic ethanol treatment. Interestingly, acute ethanol (5-66 mM) significantly enhanced IPSPs and IPSCs equally in CET and naive rats, indicating a lack of tolerance for this effect of acute ethanol. Analysis of miniature IPSC frequency suggests that the increased GABAergic transmission by both acute and chronic ethanol arises from a presynaptic mechanism involving enhanced vesicular release of GABA. These data are supported by microdialysis studies showing that CET rats presented a fourfold increase in baseline GABA dialysate content compared with naive rats. In vivo administration of ethanol (0.1, 0.3, and 1.0 M) produced a dose-dependent increase in GABA release in the CeA dialysate in both CET and naive rats. These combined findings suggest that acute and chronic ethanol increases GABA release in CeA and support previous reports that the behavioral actions of ethanol are mediated, in part, by increased GABAergic transmission in the CeA.
Key words: alcohol; acute ethanol; chronic ethanol treatment; inhibition; microdialysis; electrophysiology
Received July 22, 2004;
revised August 27, 2004;
accepted September 14, 2004.
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