PERIPHERAL STIMULATION IN MICE INDUCES SHORT-DURATION ANALGESIA PREVENTABLE BY NALOXONE

Peripheral stimulation was applied to mice by mild caudal electrostimulation, by mechanical pressure or by footshock for 30 s, before testing on a 52.degree. C hot plate. Reaction times to paw lick and to escape from the hot plate were recorded. Analgesia could be elicited and measured by these procedures. It was of short duration, declining in 1 min, and was antagonized by low doses of naloxone. The analgesia measured by the escape reaction time could be elicited after multiple caudal electrostimulation and in morphine-tolerant mice, and it could still be reversed by naloxone. An opioid link is involved in the phenomenon, which supports the notion of more than 1 opioid pathway existing in the brain. The short period of analgesic cover afforded in the face of noxious stimuli would permit aversive action to be taken in nature and thus might represent the prime functional role of enkephalins in the brain.