Figure 1.

Salsolinol (SAL) acts as an agonist of μ-opioid receptors. Functional assay of μ-opioid receptor dose-response activation by morphine and racemic (R/S)-SAL. Each ligand was assayed three times in duplicate using concentrations ranged from 1 × 10⁻⁸ M to 1 × 10⁻³ for (R/S)-SAL, and 3 × 10⁻⁹ M to 1 × 10⁻⁴ M for morphine. Values are expressed as the means of cyclic adenosine monophosphate (cAMP) levels (percentage relative de control) ± SEM. The luminescence is proportional to the intracellular cAMP levels (induced by forskolin); therefore, a decrease in cAMP levels signals the activation of the μ-opioid receptor, which is coupled to a inhibitory G protein (Gi). Half-maximal effective concentration (EC₅₀) corresponds to the concentration of ligand eliciting 50% of the maximal response. (R/S)-SAL curve: degrees of freedom, 26 (four points excluded as outliers, at [Ligand](log, M) = −3, −3.5, −7, −7.5); R² = 0.8809. Morphine curve: degrees of freedom, 17; R² = 0.8825.