Figure 4.

Effect of SNC-80 treatment on morphine-induced (A) and naltrexone-induced (B) analgesia in KI animals. KI animals were implanted with a placebo or a naltrexone (NLTRX) pellet and infused with either vehicle or SNC-80 (Alzet pump; 10 mg · kg⁻¹ · 24 h⁻¹) for 72 h; morphine-induced (A) or naltrexone-induced (B) analgesia was then measured. There was a significant difference between the placebo- plus vehicle-treated group and the naltrexone- plus SNC-80-treated group; p < 0.05 (Student’s t test). Each asterisk indicates a significant difference from the placebo-treated group. Each dose was tested on at least 8–10 animals. C, Dose–response effect of SNC-80 infusion on morphine-induced analgesia in KI animals. KI animals were implanted with a naltrexone pellet and infused with either vehicle or varying concentrations of SNC-80 (Alzet pump; 0.1, 1, and 10 mg · kg⁻¹ · 24 h⁻¹) for 72 h; morphine-induced analgesia was then measured. There was a significant difference between the naltrexone- plus vehicle-treated group and the naltrexone- plus 1 mg/kg SNC-80-treated and naltrexone- plus 10 mg/kg SNC-80-treated groups; p < 0.05 (Student’s t test). Each dose was tested on at least 8–10 animals. D, Different durations of SNC-80 exposure on morphine-induced analgesia in KI animals. KI animals were implanted with a naltrexone pellet and infused with either vehicle or SNC-80 (Alzet pump; 10 mg · kg⁻¹ · 24 h⁻¹) for 24, 48, and 72 h; morphine-induced analgesia was then measured. There was a significant difference between the naltrexone- plus vehicle-treated group and the naltrexone plus 72 h SNC-80 group; p < 0.05 (Student’s t test). Each asterisk indicates a significant difference from the naltrexone- plus vehicle-treated group. Each dose was tested on at least 8–10 animals.% MPE, Percentage of maximum possible effect. Error bars represent SEM.