Effect of dextromethorphan on antinociception and tolerance induced by swim-stress in the formalin test.

BACKGROUND: In the present study, the effect of dextromethorphan on antinociception and tolerance induced by water swim-stress in the formalin test was investigated. METHODS: Swim-stress at 8 masculineC induces antinociception in both phases of the formalin test. Intraperitoneal administration of dextromethorphan (60 mg/kg) also induces antinociception in the second phase of the formalin test. The lower doses of dextromethorphan (1.25, 2.5, and 5 mg/kg) which did not induce antinociception alone, but did so in combination with swim- stress (40 second), showed antinociceptive effect in both phases of the test. Exposure to water swimming stress with a period of 20 sec, once daily for three days, altered swim- stress- induced antinociception in the formalin test, when tested on the fourth day. RESULTS: In these animals, exposure to either water swimming stress alone or water swimming stress in combination with dextromethorphan showed potentiation of antinociception induced by swim- stress up to 20 second and decreased the response induced by 40 and 60 second swim- stress, indicating a tolerance induction. Dextromethorphan (20 mg/kg) did not alter the changes induced by three days exposure to swim- stress. CONCLUSION: The results may indicate a possible involvement of n-methyl-d-aspartate receptor mechanism in the antinociception but not tolerance induced by swim- stress at 8 masculineC.

Effect of lithium on swim stress-induced antinociception in naive mice and mice with subchronic administration of morphine or swim stress in formalin test.

BACKGROUND: Lithium has been shown to relieve mania and induce antinociception. In the present study, swim stress at 8C induced antinociception in both phases of the formalin test. Intraperitoneal administration of lithium chloride (LiCl) (0.05, 0.25, and 0.5 mg/kg) also induced antinociception in both phases of the formalin test. METHODS: Antinociception was assessed by the formalin test method. Swim stress was achieved in the 8C water in a container 5 cm in diameter and 20 cm tall filled with water do a depth of 11 cm. RESULTS: The drug (0.5 and 5 mg/kg) potentiated swim stress-induced antinociception in the second phase of the test. Repeated exposure to water swimming stress with a period of 40 sec, once daily for three days, in combination with lithium chloride did not alter stress-induced antinociception in either phases of the formalin test, when swim stress-induced antinociception was tested on the fourth day. Subchronic treatment with morphine (25 mg/kg), once daily for three days, in the presence or absence of lithium chloride (5 mg/kg) did not alter swim stress-induced antinociception, either, when swim stress-induced antinociception was tested on the fourth day. CONCLUSION: It may be concluded that lithium chloride potentiates swim stress-induced antinociception, but the drug has no influence on the response of subchronic administration swim stress or morphine.