Positron Emission Tomography Analysis of the Analgesic Effects of Acupuncture in Rhesus Monkeys

Abstract

The purpose of this study was to examine whether pain-induced brain activation was suppressed by acupuncture analgesia. We investigated the suppression of the pain-induced neuronal activation in specific brain areas of three male rhesus monkeys (aged four years old) using positron emission tomography (PET), in which changes in the regional cerebral blood flow (rCBF) were examined as an index of the neuronal activation. The brain areas such as the thalamus, insula and anterior cingulate cortex were activated by heating the tail of monkeys in 47°C water compared to the heating at 37°C. Those activations were suppressed by electroacupuncture (EA) with a 2 sec alteration of the frequency of 4 Hz/60 Hz at the right ST36 (the upper anterior tibial muscle) and the right LI4 (the back palm between the first and second metacarpal) acupoints. Meanwhile, this EA analgesic effect was confirmed by prolonging the tail withdrawal latencies from hot water in the temperature range from 45 to 50°C.These brain areas were corresponded to the pain-related areas as reported in previous studies. In conclusion, we were able to visualize the acupuncture analgesia in the CNS. We also detected the brain areas activated or inactivated by acupuncture. The areas that responded to acupuncture stimulation at 47°C water were different from the regions at 37°C. We consider that this difference in the response to acupuncture may support the variation of the clinical efficacy of acupuncture in patients bearing pain or other disorders.