Dr Ji-Sheng Han - 2004

"Acupuncture, Endogenous Opioids and Anti-opioids"
Dr Ji-Sheng Han
Neuroscience Research Center
Beijing Medical University
Beijing, China

Acupuncture and related techniques The acupuncture technique involves the site where to put a needle in, the method of stimulation (manual needling or electroacupuncture, EA) and the parameters of electrical stimulation (frequency and intensity). The intensity of EA should be just enough to excite small myelinated fibers (Aβ/d), as contrast to conventional TENS that only activates large myelinated fibers and "diffuse noxious inhibitory control (DNIC)" that produces full excitation of C fibers, causing "one pain inhibits another pain".

Acupuncture-induced analgesia Acupuncture can elicit an increase of pain threshold in every species tested, from human to mice. A slow onset and slow decay of the analgesic curve suggested a neurochemical mechanism. A searching for classical neurotransmitters accounts for acupuncture-induced analgesia (AA) revealed 5-hydorxytryptamine to be one of the most important candidates. This effort was supplemented by the study of the possible role played by endogenous opioid peptides (EOP) in AA since the discovery of enkephalins in 1975.

Opioid peptides and their mobilization by acupuncture The discovery of EOP in 1970s prompted the question how could we mobilize EOP for medical purpose. Compared to the stress-induced release of EOP observed in experimental animals, acupuncture or EA is a more likely method to be used in human. It is now clear that a differential release of EOP can be achieved by using EA of different frequencies. Thus, low frequency (2-4 Hz) increases the release of enkephalins, endorphins and endomorphins, and high frequency (100 Hz) that of dynorphins. An automatic shifting between low and high frequency (2/100 Hz) each lasting for 3 seconds constitutes the optimal parameter to accelerate the release of all 4 kinds of opioid peptides, resulting in a synergistic effect. It is interesting to find that 2 Hz is optimal for the treatment of neuropathic pain and for the suppression of opiate craving, whereas 100 Hz is best for the treatment of spinal cord injury-induced muscle spastic pain and for the suppression of cocaine-induced conditioned place preference (CPP).

Endogenous inhibitors for opioid peptides Like opioids, there is a whole family of neuropeptides in the CNS playing an anti-opioid role (AOP), among which cholecystokinin, angiotensin II and OFQ (in brain) are the most recognized ones. AOP play important role in the negative feedback control for

morphine analgesia and AA, causing the development of tolerance to morphine and EA. A balance between EOP and AOP determines, among others, the effectiveness of AA (responder vs nonresponder). Supported by NNSF, PRC and NIDA, USA.