Effects of capsaicin (CAP) treatment on electro-acupuncture (EA) analgesia were studied by examining, threshold of rats treated CAP in their naonatal and adult periods. Pain threshold of animals were measured as the latency until the occurrence of the hind paw withdrawal in response to heat noxious stimuli by using a hot-plate (HP) method. In control rats, application of EA to the right forepawLI-10, 11), increase the latency to about 160% of the control level (befor the EA application), where as in rats treated with CAP in both neonatal and adult periods, EA application hardly affected the latency.
There results suggests that treatment with CAP in both neonatal and adult period abolishes the EA analgesia in rats.

Effects of local application of capsaicin (CAP) to peripheral nerve on electro-acupuncture (EA) analgesia were examined in rats. Changes in paine thresholds by the EA were examind using tail-flick, hot-plate and Jaw-opening reflex methods. In the tail-flick methods, and hot-plate the latency of responses to heat noxious stimuli were measured in awake rats. In the jaw-opening reflex method, the EMG amplitude of digstric muscle in response to electrical stimulation of the tooth pulp of the incisor was measure in lightly anesthetized rats. Cap was topically treated on the right side of the radial, ulner and medial nerves of the animal's forepaw. The application of the EA to the CAP-untreated left side of the animal's forepaw produced significant changes in the latencies and the EMG amplitude, indicating the abolishment of the EA analgesia by CAP treatment.
These results suggest that CAP-sensitive primaly afferents are responsible for the EA analgesia measured by there different methodes.

The effects of local application of capsaicin (CAP) to peripheral nerves on electroacupuncture (EA) analgesia were behaviorally examined in the rats. Pain threshold, datermined by using a hot-plate and tail-flick methods, increased to 160-180% of the control value after EA, which was applied to the acupuncture points between LI-11 and LI-12 of the rat forepaw. After the local application of CAP to the radial, ulner and median nerves of the animal's right forepaw, the EA, applied to the treated forepaw, did not significantly change the pain threshold. In the same animals, the EA applied to the untreated side increased the threshold as high as that before the CAP treatment. This indecates that the EA became ineffective on the CAP treated side, this ineffectiveness of the EA cont inued until at last 15 days in the case of the single CAP treatment for 15min, on the peripheral nerves. The substance P (SP) concentration in the spinal dolsal horn (C5-7) of these animals, which was measured by radioimmunoassay, was about 40% lower in the CAP treated side than in the untreated side.
These results suggest that SP-containing primary afferents, of which nerve conduction was probably blocked by treatment whth CAP, convey information for EA analgesia.