PT  - JOURNAL ARTICLE
AU  - Zheng-Xiong Xi
AU  - David A. Baker
AU  - Hui Shen
AU  - Daniel S. Carson
AU  - Peter W. Kalivas
TI  - Group II Metabotropic Glutamate Receptors Modulate Extracellular Glutamate in the Nucleus Accumbens
AID  - 10.1124/jpet.300.1.162
DP  - 2002 Jan 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 162--171
VI  - 300
IP  - 1
4099  - http://jpet.aspetjournals.org/content/300/1/162.short
4100  - http://jpet.aspetjournals.org/content/300/1/162.full
SO  - J Pharmacol Exp Ther2002 Jan 01; 300
AB  - The regulation of extracellular glutamate in the nucleus accumbens by group II metabotropic glutamate receptors (mGluR2/3) was examined in vivo. Stimulation of mGluR2/3 with 2R,4R-4-aminopyrrolidine-2,4-dicarboxylate (APDC) or N-acetylaspartylglutamate reduced extracellular glutamate levels. Conversely, blockade of mGluR2/3 by LY143495 or (RS)-1-amino-5-phosphonoindan-1-carboxylic acid (APICA) increased extracellular glutamate, an effect antagonized by the coadministration of APDC. These effects likely involve both vesicular and nonvesicular glutamate, because the increase in glutamate by APICA or the decrease by APDC was prevented by blocking N-type calcium channels and the release of glutamate after potassium-induced membrane depolarization was antagonized by APDC. In addition, blockade of the cystine-glutamate exchange, a major nonvesicular source of extracellular glutamate, by (S)-4-carboxyphenylglycine blocked the effects induced by either APDC or APICA. However, blockade of Na+ channels by tetrodotoxin or Na+-dependent glutamate transporters bydl-threo-β-benzyloxyaspartate failed to affect the alterations in extracellular glutamate by APICA or APDC, respectively. Group II mGluRs are Gi-coupled and coperfusion with the cAMP-dependent protein kinase (PKA) activator Sp-cAMPS blocked the reduction in glutamate by APDC and the PKA inhibitor Rp-cAMPS prevented the elevation in glutamate by APICA. Taken together, these data support three conclusions: 1) group II mGluRs regulate both vesicular and nonvesicular release of glutamate in the nucleus accumbens, 2) there is tonic in vivo stimulation of mGluR2/3 by endogenous glutamate, and 3) modulation of group II mGluRs of extracellular glutamate is Ca2+- and PKA-dependent. mGluRsmetabotropic glutamate receptorsAPDC(2R,4R)-4-aminopyrrolidine-2,4-dicarboxylateNAAG N-acetylaspartylglutamate2-PMPA2-(phosphonomethyl) pentanedioic acidAPICA(RS)-amino-5-phosphonoindan-1-carboxylic acid(S)-4CPG(S)-4-carboxyphenylglycineTTXtetrodotoxinTBOA dl-threo-β-benyloxyaspartateSp-/Rp-cAMPSSp-/Rp-adenosine 3′5′-cyclic monophosphothioate triethylaminePKAcAMP-dependent protein kinaseANOVAanalysis of variancePLSDprotected least significant differenceNAccnucleus accumbensNMDA N-methyl-d-aspartate