The possible antinociceptive effect of a Rho-kinase inhibitor, (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide dihydrochloride monohydrate (Y-27632), was investigated in mice by using the hot-plate and abdominal constriction response (writhing) tests. In addition, the expression of Rho-kinase protein (ROCK-2) was studied in the mouse brain and spinal cord by Western blotting. Male balb/c mice (n = 8, for each group) were used in the experiment. Hot-plate latency and the number of writhes were recorded in control and in Y-27632-treated (1-5 mg/ kg, i.p.) groups. Y-27632 (I mg/kg) did not affect hot-plate latency; however, it considerably diminished the number of writhes, from 89 +/- 12 in controlto 30 +/- 6 in the mice treated with 1 mg/kgY-27632 (P=0.001). Atahigherdose(5 mg/kg), Y-27632 prolonged the hot-plate latency from 8.7 +/- 1.0 s to 14.4 +/- 1.7 s (P=0.005) and decreased the number of writhes from 80 +/- 8 to 24 +/- 7 (P=0.002). Western blot analysis revealed that mouse spinal cord and brain homogenates expressed ROCK-2 protein. These results indicate that Rho-kinase may be involved in nociception and that its inhibitors, such as Y-27632, may represent a new type of antinociceptive drug. (c) 2006 Elsevier B.V All rights reserved.