Afferent nerve characteristics during acupuncture stimulation

Abstract

A number of studies have provided evidence that acupuncture or acupuncture-like stimulation increases pain threshold in humans. According to traditional Chinese theory, there is a specific point called meridian point to treat a specific symptom. For example, if a needle was inserted into Ho-Ku point, and this point was stimulated electrically or manually, oro-facial pain, especially tooth pain, is fairly diminished. To clarify peripheral mechanisms of acupuncture effects and to reveal the nature of meridian points scientifically, characteristics of afferent nerve information evoked by acupuncture stimulation were investigated in Wistar albino rats. The magnitude of the jaw opening reflex induced by stimulation of the lower incisor tooth pulp was estimated as an indicator of the acupuncture effect. Acupuncture needling was given at one meridian point of Ho-Ku and two nonmeridian points in the forepaw. Compound action potentials of ulnar, median and radial nerves elicited by electroacupuncture stimulation (0.1 ms duration at 45 Hz for 15 min) were recorded from the brachial plexus. Electroacupuncture stimulation applied to the Ho-Ku point showed a greater suppressive effect than that to the two nonmeridian points. The threshold current intensity for producing the compound action potentials was the lowest at Ho-Ku. There was a significant correlation between the amplitude of A-beta fibers in the compound action potentials elicited by electroacupuncture stimulation and the degree of suppression of the jaw opening reflex. The results of the present study are in good agreement with the traditional view that stimulation of the meridian point is an important factor for obtaining excellent acupuncture effects. Moreover, we propose that A-beta component plays a leading role in producing acupuncture effects (A-beta theory). Activation of A-delta or C components may play a supplemental role in detecting the magnitude of the A-beta activities, and relate to the “Tokki”, which is reported to be dull, warm or tingling sensation. At the central terminal site of the primary nociceptive afferent, three inhibitory mechanisms were observed in the spinal trigeminal nucleus.