Caffeine interferes with morphine-induced hyperactivity but not analgesia.
In C57BL/6 mice caffeine antagonized morphine-induced hyperactivity. This effect was most evident when caffeine was used in doses that slightly increased locomotor activity. Given at the same dose caffeine did not affect morphine-induced analgesia. Two possibilities of explanation of this effect are discussed: action of caffeine on dopaminergic mechanisms responsible for morphine-induced running fit through its effect on cyclic AMP level, and a direct action of caffeine on delta opiate receptors involved in the stimulatory effect of morphine.
D000700:Analgesics; D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009020:Morphine / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D009043:Motor Activity / Q000187:drug effects*
D000700:Analgesics; D002110:Caffeine; D009020:Morphine