THE PRESENT INVENTION RELATES TO ETHYNYL DERIVATIVES OF FORMULA I WHEREIN X IS N OR CH； G IS N OR CH； WITH THE PROVISO THAT MAXIMUM ONE OF X OR G CAN BE NITROGEN； R1 IS PHENYL OR PYRIDYL, WHICH ARE OPTIONALLY SUBSTITUTED BY HALOGEN, LOWER ALKYL OR LOWER ALKOXY； R2 IS HYDROGEN, LOWER ALKYL OR MAY FORM TOGETHER WITH R4 A C3-C6-CYCLOALKYL； R3/R3’/R4/R4’ ARE INDEPENDENTLY FROM EACH OTHER HYDROGEN, LOWER ALKYL OR CF3； OR TO A PHARMACEUTICALLY ACCEPTABLE ACID ADDITION SALT, TO A RACEMIC MIXTURE, OR TO ITS CORRESPONDING ENANTIOMER AND/OR OPTICAL ISOMER AND/OR STEREOISOMER THEREOF. IT HAS NOW SURPRISINGLY BEEN FOUND THAT THE COMPOUNDS OF GENERAL FORMULA I ARE POSITIVE ALLOSTERIC MODULATORS (PAM) OF THE METABOTROPIC GLUTAMATE RECEPTOR SUBTYPE 5 (MGLUR5). (NO SUITABLE FIGURE)
