Fig. 5. Antagonist effect of 5′-guanidinylnaltrindole (GNTI) on the actions of butorphanol against intrathecal morphine–induced scratching (  A ) and antinociception (  B ). Butorphanol (0.032 mg/kg) was administered subcutaneously 45 min after 32 μg intrathecal morphine.  Filled symbols represent the effect of GNTI (1 mg/kg) 1-day pretreatment (PT) on the actions of subcutaneous butorphanol against intrathecal morphine. Each value represents mean ± SEM (n = 6). * Significant difference between experimental conditions, (GNTI +[morphine + butorphanol]) and (morphine + butorphanol). # Significant difference between experimental conditions, (GNTI +[morphine + butorphanol]) and (morphine alone). The effect of GNTI 14-day pretreatment was not shown for the sake of clarity because its effect was similar to that of (morphine + butorphanol). See Results section for other details.