Effects of dopaminergic agents on antinociception in formalin test

Morphine caused a dose-related antinociception in early phase and late phas e of formalin test in mice. The D-2 dopamine agonist quinpirole, but not th e D-1 dopamine agonist SKF 38393, increased the antinociceptive effect of m orphine in both phases of the test. The antinociceptive effect of quinpirol e also was decreased by sulpiride or domperidone pretreatment in the early phase of test. The D-1 antagonist SCH23390, the D-2 antagonist sulpiride, o r the peripheral D-2 dopamine antagonist domperidone, increased the morphin e effect. Single administration of SKF38393, quinpirole, SCH23390, sulpirid e, and domperidone also induce antinociception. The response of SCH23390, b ut not that of other dopamine agents, was antagonized with naloxone. The ef fects of the drugs alone and in combination with morphine have been discuss ed. (C) 1999 Elsevier Science Inc. All rights reserved.