CHARACTERIZATION OF (2S,2'R,3'R)-2-(2',3'-[H-3]-DICARBOXYCYCLOPROPYL)GLYCINE BINDING IN RAT-BRAIN

[(2S,2'R,3'R)-2-(2',3'-[H-3] Dicarboxycyclopropyl)glycine ([H-3] DCG I V) binding was characterized in vitro in rat brain cortex homogenates and rat brain sections. In cortex homogenates, the binding was saturab le and the saturation isotherm indicated the presence of a single bind ing site with a K-D value of 180 +/- 33 nM and a B-max of 780 +/- 70 f mol/mg of protein. The nonspecific binding, measured using 100 mu M LY 354740, was <30%. NMDA, AMPA, kainate, L(-)-threo-3-hydroxyaspartic ac id, and (S)-3,5-dihydroxyphenylglycine were all inactive in [3H]DCG IV binding up to 1 mM. However, several compounds inhibited [3H]DCG IV b inding in a concentration-dependent manner with the following rank ord er of potency: LY341495 = LY354740 > DCG IV = (2S,1 'S,2'S)-2-(2-carbo xycyclopropyl)glycine > (1S,3R)-1-amino-cyclopentane-1,3-dicarboxylic acid > (2S,1'S,2'S)-2-methyl-2-(2-carboxycyclopropyl) glycine > L-glut amate = ibotenate > quisqualate > (RS)-alpha-methyl-4-phosphonophenylg lycine = L(+)-2-amino-3-phosphonopropionic acid > (S)-alpha-methyl-4-c arboxyphenylglycine > (2S)-alpha-ethylglutamic acid > L(+)-2-amino-4-p hosphonobutyric acid. N-Acetyl-L-aspartyl-L-glutamic acid inhibited th e binding in a biphasic manner with an IC50 Of 0.2 mu M for the high-a ffinity component. The binding was also affected by GTP gamma S, reduc ing agents, and CdCl2. In parasagittal sections of rat brain, a high d ensity of specific binding was observed in the accessory olfactory bul b, cortical regions (layers 1,3, and 4 > 2, 5, and 6), caudate putamen , molecular layers of the hippocampus and dentate gyrus, subiculum, pr esubiculum, retrosplenial cortex, anteroventral thalamic nuclei, and c erebellar granular layer, reflecting its preferential (perhaps not exc lusive) affinity for pre- and postsynaptic metabotropic glutamate mGlu 2 receptors. Thus, the pharmacology, tissue distribution, and sensitiv ity to GTP gamma S show that [H-3]DCG IV binding is probably to group II metabotropic glutamate receptors in rat brain.