Involvement of descending inhibition in the effect of acupuncture on the splanchnically evoked potential in the orbital cortex of cat.

The possible involvement of descending inhibition in the effect of acupuncture on the transmission of visceral afferent impulses has been investigated. Averaged splanchnically evoked potentials were recorded in the orbital cortex of the unanesthetized immobilized cat. The evoked orbital potentials could be inhibited by electroacupuncture. Section of the descending inhibitory pathway which is known to be located in the dorsolateral funiculi of the spinal cord produced marked diminution of the acupuncture inhibitory effect on the evoked cortical potentials with needles either inserted in the hindlimb or in the forelimb. Since the afferent impulses from the forelimb entered the cord above the level of section (T3-4), the ascending pathway for acupuncture signals to the supraspinal structure was thus left intact. Destruction of the pontobulbar reticular formation including mainly the nucleus raphe magnus produced the same diminution of the acupuncture effect. The results indicate that the ascending visceral afferent impulses are blocked at the level of the spinal cord by the acupuncture-induced descending impulses from the supraspinal center, probably the nucleus raphe magnus.