Possible involvement of opioid peptides of caudate nucleus in acupuncture analgesia.

Rabbits chronically implanted with permanent cannulae were used in brain perfusion and microinjection experiments. Potassium iontophoresis applied to the rabbits' ear skin served as a noxious stimulus and the electric current used to elicit the defense response was taken as the pain threshold. The brain perfusate was analysed by radioreceptor assay and the level of endogenous opioid peptides (EOP) was expressed as competition rate.