PT  - JOURNAL ARTICLE
AU  - Anderson, Jeffery J.
AU  - Rao, Sara P.
AU  - Rowe, Blake
AU  - Giracello, Darlene R.
AU  - Holtz, Greg
AU  - Chapman, Deborah F.
AU  - Tehrani, Lida
AU  - Bradbury, Margaret J.
AU  - Cosford, Nicholas D. P.
AU  - Varney, Mark A.
TI  - [<sup>3</sup>H]Methoxymethyl-3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine Binding to Metabotropic Glutamate Receptor Subtype 5 in Rodent Brain: In Vitro and  in Vivo Characterization
AID  - 10.1124/jpet.102.040618
DP  - 2002 Dec 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 1044--1051
VI  - 303
IP  - 3
4099  - http://jpet.aspetjournals.org/content/303/3/1044.short
4100  - http://jpet.aspetjournals.org/content/303/3/1044.full
SO  - J Pharmacol Exp Ther2002 Dec 01; 303
AB  - The binding of [3H]methoxymethyl-3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (methoxymethyl-MTEP), a potent and selective antagonist for metabotropic glutamate (mGlu)5 receptors, was characterized in rat brain both in vitro and in vivo. Nonspecific binding, as defined with 10 μM 2-methyl-6-(phenylethynyl)-pyridine (MPEP), was less than 10% of total binding in rat brain membranes. The binding of [3H]methoxymethyl-MTEP was of high affinity (K d = 20 ± 2.7 nM), saturable (B max = 487 ± 48 fmol/mg protein), and to a single site. The mGlu5 antagonists methoxymethyl-MTEP and MPEP displaced [3H]methoxymethyl-MTEP binding with IC50values of 30 and 15 nM, respectively. In vivo administration of [3H]methoxymethyl-MTEP (50 μCi/kg i.v.) revealed 12-fold higher binding in hippocampus (an area enriched in mGlu5 receptors) relative to cerebellum (an area with few mGlu5 receptors) in rats. Similarly, administration of [3H]methoxymethyl-MTEP to mGlu5-deficient mice demonstrated binding at background levels in forebrain, whereas wild-type littermates exhibited 17-fold higher binding in forebrain relative to cerebellum. Systemic administration of unlabeled mGlu5 antagonists methoxymethyl-MTEP and MPEP to rats reduced the binding of [3H]methoxymethyl-MTEP with ID50 values of 0.8 and 2 mg/kg i.p., respectively, 1 h post-treatment. The mGlu5 agonist 2-chloro-5-hydroxyphenylglycine (CHPG) (0.3, 1, and 3 μmol) dose-dependently increased phosphoinositide (PI) hydrolysis in the hippocampus after i.c.v. administration in rats. CHPG-evoked increases in PI hydrolysis were blocked with MPEP at a dose (10 mg/kg i.p.) that markedly reduced [3H]methoxymethyl-MTEP binding in vivo. These results indicate that [3H]methoxymethyl-MTEP is a selective radioligand for labeling mGlu5 and is useful for studying the binding of mGlu5 receptors in rat brain in vitro and in vivo.