Figure 3.

A, Effect of naltrindole treatment on naltrexone (NLTRX)-induced analgesia in KI animals (as in Fig. 2C, except that naltrexone-induced analgesia was measured). No significant difference was observed among the three treatment groups; p > 0.06 (Student’s t test). Each dose was tested on at least 8–10 animals. B, Effect of naltrindole treatment on morphine-induced analgesia after tolerance development. WT animals were implanted with a placebo or morphine pellet for 72 h. At 24 h before pellet removal, animals were implanted with an Alzet pump delivering 10 mg · kg⁻¹ · 24 h⁻¹ NTI. Morphine-induced analgesia was measured as described above. *p < 0.05, significant difference between the morphine-plus vehicletreated group and the placebo-treated group; + indicates a significant difference between the morphine plus NTI group and the placebo-treated group (Student’s t test). Each dose was tested on at least 8–10 animals. % MPE, Percentage of maximum possible effect. Error bars represent SEM.