Fig. 2.

CD38 inhibitors with acute morphine. Drugs that block the CD38–cADPR–ryanodine receptor pathway do not alter acute morphine antinociception. Mice were administered inhibitor intracerebroventricularly and various morphine doses subcutaneously. Antinociception was measured 30 min later, and %MPE was calculated and used to construct dose–response curves for calculation of ED₅₀ values and potency ratios. All three inhibitors, nicotinamide (200 pmol/mouse) (A), ryanodine (1.0 nmol/mouse) (B), and 8-bromo-cADPR (10 nmol/mouse) (C), had no effect on acute morphine antinociception. Each data point represents six mice. ■, inhibitor injected intracerebroventricularly with morphine injected subcutaneously; ●, vehicle injected intracerebroventricularly with morphine injected subcutaneously.