Time course depicting the mean ± SD of the hind paw thermal escape latency (s) versus time in rats prepared with chronic intrathecal (IT) catheters connected to osmotic pumps delivering 0.5 µl/h for 14 days and loaded to deliver: (A) saline (vehicle, 0.5 µl/hr); (B) morphine (33 nmol/h); (C) DMT-DALDA (10 pmol/h) or (D) PZM21 (28 nmol/h). (E) Area under the curve (AUC) (mean ± SD) was calculated from baseline to day 7 for the four treatment groups. For the time course curves, one-way repeated measures ANOVA were performed with Dunnett multiple comparison tests versus day 0 (immediately before implantation). For the AUC data, analysis was by a one-way nonrepeated ANOVA with a Dunnett multiple comparison tests versus saline infusion: *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001. MS, morphine sulfate; NaCl, sodium chloride.