Fig. 5. (A ) Effects of 5-HT3 antagonists on clonidine-induced analgesia in spinal nerve ligated (SNL) rats. Animals received intrathecal injection of saline, clonidine (15 μg/rat), ondansetron (0.3–30 μg/rat), dolasetron (100 μg/rat), or their combination 1 h before the von Frey test. Withdrawal threshold in the paw ipsilateral to SNL is presented. N = 6–8. *P < 0.05 versus  saline. #P < 0.05 versus  clonidine alone. (B ) Effects of ondansetron on clonidine-induced antinociception in normal rats. Animals received intrathecal injection of saline, clonidine (3–30 μg/rat), ondansetron (3–30 μg/rat), or their combination 1 h before the Randall–Sellitto test. Average of withdrawal threshold in the both paws is presented. N = 8–14. *P < 0.05 versus  saline. Cl = clonidine; Sal. = saline.