“School of Cognitive Sciences”
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| Paper IPM / Cognitive Sciences / 8966 |
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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�C 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 swimstress, 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�C.
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