1,1'-Diethyl-2,2'-cyanine Iodide is a potent inhibitor of potent extraneuronal monoamine transporter EMT. It inhibits 1-Methyl-4-phenylpyridinium (MPP+), toxic metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine that induces apoptosis in cerebellar granule neurons (CGNs). Dyes and metabolites.