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Abstract
Using the tail-flick and hot-plate assays, morphine and nefopam were tested for analgesic
activity following intraperitoneal (i.p.), intracranial (i.c.) and intraspinal (i.s.)
injection in mice. By the i.p. route, morphine was equipotent on both analgesic tests.
Nefopam was one-third as potent as morphine on the hot-plate test, but did not affect
the tail-flick. Intracranial morphine was more effective on the hot-plate than on
the tail-flick, but i.s. morphine was most potent on the tail-flick. Naloxone, 0.5
mg/kg i.p., totally reversed morphine's effects on the tail-flick, but only partially
reversed these actions on the hot-plate, suggesting the possibility that morphine's
effects on the mouse hot-plate test may be mediated via multiple receptor types. Nefopam
was more potent by the i.c. route than by the i.p. route, but its was inactive spinally.
Nefopam analgesia was unaffected by naloxone treatment. It is concluded that nefopam
is a novel, centrally acting, non-narcotic analgesic.