Effect Of Electro-Acupuncture On Cortical Potential Evoked By Stimulation Of Saphenous Nerve

Acupuncture Anesthesia Research Group Zhongshan Medical College

Experiments were performed on cats anesthetized with chloralose. The saphenous nerve was stimulated with the rectangular wave pulses of different strength. They induced the excitation of different kinds of nerve fibers. The cortical evoked potentials were recorded with a silver ball electrode on the surface of contralateral somato-sensory area I, in order to study the relationship between the component of evoked-potential and the fiber excitation and the pain. At last, the effect of electro-acupuncture was examinated.

1. The cortical evoked potential during excitation of A-fiber: When the saphenous nerve was stimulated by weak pulse current, the A-fibers excited alone. At this time, a biphasic positive-negative evoked potential appeared on the contralateral cortical somatosensory area I, Its latency was short (11-14 mSec), The positive  phase was larger than the negative. The amplitude was 350 -- 1000µV. The duration was 23 -- 35 mSec. It was a rapid component.

2. The cortical evoked potential during excitation of A- and C-fibers: When the sapheneous nerve was stimulated by more intense pulse current, both A- and C-fibers were excited. At this time, the cortical evoked potential expressed a rapid component with short latency and a slow component with long latency (150-250m Sec.). The slow component was a positive or negative wave, the amplitude was 150-500 µV. Its duration was 17-50mSec.

3. The cortical evoked potential during excitation of C-fiber: After the A-fiber was blocked by galvanic anode, the impulses of the C-fiber transmitted to the central nervous system only, when the intensive stimulation was given, the cortical evoked potential expressed only a slow component with long latency, its amplitude increased. This demonstrated that the rapid component was induced by A-fiber, while the slow one by C-fiber and the slow component might be inhibited by A-fiber.

4. The effect of analgesics (Dolantin) on the cortical evoked potential: After 10mg Dolantin was injected iv., the saphenous nerve was stimulated with intense pulse current. When the A- and C-fibers were excited, the cortical evoked potential expressed only the rapid compoment, the slow component was absent, and then recovered after 30 minutes. This demonstrated that the slow component was related with the pain.

5. The effect of electro-acupuncture on the cortical evoked potential: When the point near the saphenous nerve was stimulated by electro-acupuncture, the two components of the cortical evoked potential were both inhibited. After acupuncture was stopped, the rapid component recovered first, and then the slow one.