Effects on mechanical pain thresholds (PPT) in inflamed (a, b) and noninflamed (c, d) hindpaws following i.v. injections of morphine (MOR; a, c, e) or PG-M (b, d, f). Dosages of MOR and PG-M represent the absolute amounts of morphine free base (see Table 1). Bilateral intraplantar (i.pl.) injection of NLXM (50 μg/paw) partially reduced peak PPT elevations occurring at 15 min after MOR (6 mg/kg; e) and completely abolished effects after PG-M (equivalent to 6 mg/kg morphine; f). (a, b, c) *p<0.05, two-way RM-ANOVA and Bonferroni test (compared to controls). (e, f) *p<0.05, paired t-test (BL vs. agonist without/with NLXM); #p<0.05, unpaired t-test (agonist vs. agonist with NLXM). N = 8 rats per group; means ± SEM. PPT increases in a, c (0–12 mg/kg) and b (0–6 mg/kg) were dose-dependent (p<0.05, linear regression ANOVA).