TY - JOUR T1 - Group II Metabotropic Glutamate Receptors Modulate Extracellular Glutamate in the Nucleus Accumbens JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 162 LP - 171 DO - 10.1124/jpet.300.1.162 VL - 300 IS - 1 AU - Zheng-Xiong Xi AU - David A. Baker AU - Hui Shen AU - Daniel S. Carson AU - Peter W. Kalivas Y1 - 2002/01/01 UR - http://jpet.aspetjournals.org/content/300/1/162.abstract N2 - 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 ER -