(A) Effects of 5-HT3 antagonists on clonidine-induced analgesia in spinal nerve ligated (SNL) rats. Animals received intrathecal injection of saline (Sal.), clonidine (Cl, 15 μg/rat), ondansetron (0.3-30 μg/rat), dolasetron (100 μg/rat), or their combination 1 h prior to 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 (Sal.), clonidine (Cl, 3-30 μg/rat), ondansetron (3-30 μg/rat), or their combination 1 h prior to the Randall-Sellitto test. Average of withdrawal threshold in the both paws is presented. N = 8-14. * p < 0.05 versus saline.