Dose responses of a panel of opioid ligands in SH-SY5Y cells. (a) Dose dependent responses of opioid ligands obtained using DMR agonist assays. The maximal amplitudes were plotted as a function of agonist doses. (b) Dose-dependent inhibition of the DMR of 64 nM DAMGO by opioid ligands. The maximal amplitudes of the DAMGO DMR were plotted as a function of ligand doses. For (a) and (b) data represents the mean ± s.d. for 2 independent measurements, each in duplicate (n = 4).