Fig. 1. Peripheral neurokinin-1 receptor blockade impaired stress-induced opioid-mediated antinociception. Wistar rats were treated with neurokinin-1 receptor antagonists ( A : 20 mg/kg intraperitoneal L-733,060 [n = 6/group]; B : 10 mg/kg intraperitoneal SR140333 [n = 6/group]; C : 0.5 mg/kg intrathecal L-733,060 [control n = 7, drug n = 6]) immediately before and at 12 h after intraplantar injection of complete Freund adjuvant for induction of inflammation. Control animals received complete Freund adjuvant and solvent injections. Paw pressure thresholds were determined 24 h after induction of inflammation before (baseline) and after cold water swim stress (CWS) (* P < 0.05, baseline-CWS [F = 319 for intraperitoneal L-733,060, F = 196 for intraperitoneal SR140333, F = 458 for intrathecal L-733,060], § P < 0.05, drug × baseline-CWS [F = 23.2 for intraperitoneal L-733,060, F = 39.9 for intraperitoneal SR140333], P > 0.05, drug × baseline-CWS for intrathecal L-733,060, two-way repeated-measures analysis of variance). Inflamed (•, ○) and noninflamed contralateral paw (▪, □), neurokinin-1 receptor antagonist (•, ▪), and solvent control (○, □). Data are presented as mean ± SEM.