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Vol. 293, Issue 2, 654-661, May 2000
-Aminobutyric Acid Responses in a
Subpopulation of Nucleus Accumbens Neurons: Role of Metabotropic
Glutamate Receptors1
The Scripps Research Institute, Department of Neuropharmacology and
Alcohol Research Center, La Jolla, California
The nucleus accumbens (NAcc) may be a key area in the rewarding effects
of abused drugs. We previously showed that low ethanol concentrations
decreased both N-methyl-D-aspartate
(NMDA)-induced and kainate-induced currents in NAcc core neurons (Nie
et al., 1994). To explore the effects of ethanol on
-aminobutyric
acid (GABA) responses in NAcc, we used intracellular voltage-clamp recordings and locally applied GABA in a slice preparation containing the NAcc. Ethanol (11-200 mM) had no effect on resting membrane properties, but 11, 22, 44, 100, and 200 mM ethanol increased GABA
currents in 17, 33, 45, 50, and 22% of cells, respectively. Superfusion of low glutamate concentrations that had no direct effect
on membrane properties enhanced ethanol potentiation of GABA currents
in more than half the NAcc cells. Neither
-amino-3-hydroxy-5-methylisoxazole-4-propionic acid/kainate receptor
nor NMDA receptor antagonists affected the percentage of cells showing
ethanol enhancement of GABA responses or the degree of ethanol
enhancement of GABA currents in NAcc neurons. However, in
ethanol-sensitive cells, the metabotropic receptor antagonist
-methyl-4-carboxyphenylglycine (MCPG) blocked the ethanol
enhancement of GABA currents. In addition, the metabotropic receptor
agonist trans-1-aminocyclopentane-1,3-dicarboxylic acid enhanced GABA responses in 50% of cells tested, an effect blocked by
MCPG. These data suggest that NAcc core neurons possess both ethanol-sensitive and -insensitive GABA receptors and that glutamate can mimic and enhance the ethanol potentiation of GABA currents in many
of these neurons. Furthermore, the ethanol potentiation of GABA
currents may involve metabotropic glutamate receptors, perhaps via a
phosphorylation mechanism that regulates ethanol sensitivity of GABA
receptors in some NAcc neurons.
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