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. 1987 Jun 23;414(1):155-7.
doi: 10.1016/0006-8993(87)91338-2.

Paradoxical hyperalgesic effect of exceedingly low doses of systemic morphine in an animal model of persistent pain (Freund's adjuvant-induced arthritic rats)

V Kayser, J M Besson, G Guilbaud

Paradoxical hyperalgesic effect of exceedingly low doses of systemic morphine in an animal model of persistent pain (Freund's adjuvant-induced arthritic rats)

V Kayser et al. Brain Res. .

Abstract

The effects of exceedingly low doses of morphine (3-50 micrograms/kg i.v.) were studied upon the vocalization threshold induced by paw pressure in rats with Freund's adjuvant-induced arthritis. The highest dose used (50 micrograms/kg i.v.) clearly induced an analgesic effect. No significant modification of the vocalization threshold was observed with 30 micrograms/kg. By contrast, a significant hyperalgesic effect resulted with doses of 10 down to 3 micrograms/kg. Maximum hyperalgesia was observed with 6 micrograms/kg.

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