The dissociation of the antinociceptive effect of clonidine from supraspinal structures.

The tail flick assay was used to assess the antinociceptive effects of morphine and clonidine in control and T₆-T₈ spinally transected mice. In spinalized mice the morphine ED₅₀ was increased 4–7 fold while the clonidine ED₅₀ was not significantly altered. These results indicate a clear separation of the principle sites for the antinociceptive activity of morphine and clonidine in this test.