A comprehensive study on the putative δ-opioid receptor (sub)types using the highly selective δ-antagonist, Tyr-Tic-(2S,3R)-β-MePhe-Phe-OH

► Selective ligands are needed for identifying receptors and their functions. ► Tyr-Tic-(2S,3R)-β-MePhe-Phe-OH is a highly potent and selective δ-opioid antagonist in murine brain and DOR-CHO cells. ► It behaved as a δ1-opioid receptor antagonist in the antinociception assay in mouse after i.t. administration. ► Subtypes of δ-opioid receptors were not detected in vitro in ligand binding, receptor autoradiography and functional assays.