Resiniferatoxin reduces the spontaneous activity of dorsal horn neurons and precludes conditioned place preference to dermorphin [D-Arg2, Lys4] (1–4) amide (DALDA) in nerve-injured rats. (A) The spontaneous activity rates of wide-dynamic range (WDR) neurons in vehicle-pretreated spinal nerve ligation rats were significantly decreased by DALDA (10 mg/kg, subcutaneous). The baseline spontaneous activity rates were significantly lower in spinal nerve ligation rats that received resiniferatoxin pretreatment (0.1 mg/kg, intraperitoneal, n = 7) than in those that received vehicle (n = 6). Two-way mixed model ANOVA with Bonferroni post hoc test, *P < 0.05, **P < 0.01 versus baseline; #P < 0.05 versus the indicated group. (B) Spinal nerve ligation rats pretreated with vehicle (n = 7), but not resiniferatoxin (0.1 mg/kg, intraperitoneal, n = 11), spent more time in the DALDA-paired chamber (10 mg/kg, subcutaneous) after conditioning, than they did during the preconditioning test period. (C) The difference scores. Two-way repeated measures ANOVA with Bonferroni post hoc test, **P < 0.01 versus the indicated group or the saline-paired chamber. Data are expressed as mean ± SD. APs = action potentials.