[The role of the pituitary in the development of electroacupuncture analgesia in rats]

Traditional and Evidence‐Based Acupuncture in Headache Management: Theory, Mechanism, and Practice

Acupuncture, traditional Chinese needle therapy, has become widely used for the relief of headache. The history of the practice of acupuncture in the United States and the theoretical framework for acupuncture in Chinese medicine are reviewed. The basic scientific background and clinical application of acupuncture in the headache management are discussed.

A parametric study of electroacupuncture on persistent hyperalgesia and Fos protein expression in rats

We previously reported the anti-hyperalgesia of electroacupuncture (EA) on persistent inflammatory pain in an unrestrained, unsedated, and conscious rat model. Using this model, induced by injecting complete Freund's adjuvant (CFA) into one hind paw, we systematically evaluated the anti-hyperalgesia of EA stimulation parameters (frequency, intensity, treatment duration, and pulse width). We assessed hyperalgesia by paw withdrawal latency (PWL) to a noxious thermal stimulus and found that 10- and 100-Hz EA frequencies at a current intensity of 3 mA produced the greatest anti-hyperalgesia, when compared to other parameters. Both frequencies significantly increased PWL in the early phases of hyperalgesia (2.5 and 24 h; p < 0.05), and 10 Hz EA also significantly increased PWL in later phases (5 to 7 days; p < 0.05). A sufficient but tolerable intensity of 3 mA was more effective than lower intensities (1-2 mA). A 20-min treatment produced better anti-hyperalgesia than longer and shorter (10 and 30 min) treatments. Acupoint specificity study demonstrated that GB30 produced significant EA anti-hyperalgesia, while Waiguan (TE5) and sham points, an abdominal point and a point at the opposite aspect of GB30, did not. The spinal Fos protein expression study demonstrated that the optimal EA selectively suppressed Fos expression in superficial laminae (I/II) and activated it in deeper laminae (III/IV) of the spinal dorsal horn. The results suggest that the EA anti-hyperalgesia is parameter-dependent and point-specific, and they provide important information for designing further clinical acupuncture research on persistent inflammatory pain.

Differences of electroacupuncture-induced analgesic effect in normal and inflammatory conditions in rats

It has been reported by Stein et al. that the immune system and peripheral opioid receptors are involved in the control of pain accompanying inflammation. Electroacupuncture (EA) is used to relieve various kinds of pain. However, little is known about the effect of electroacupuncture analgesia (EAA) during hyperalgesia elicited by inflammation. The aim of the present study was to compare (1) the individual variation of EAA, (2) the durability of EAA, and (3) the effect of naloxone on EAA between normal rats and rats subjected to acute inflammatory pain. Carrageenan was subcutaneously administered by intraplantar (i.pl.) injection of the left hind paw to induce a nociceptive response. Nociceptive thresholds were measured using the paw pressure threshold (PPT). Rats received EA at 3 Hz in the left anterior tibial muscles for 1 hour after carrageenan injection. Naloxone was administered by intraperitoneal (i.p.) or i.pl. injection just before EA. EAA was elicited in 15 of 29 normal rats. These rats were divided into responders and non-responders. EAA in the responder group was almost completely antagonized by i.p. injection of naloxone. In contrast, in all the rats with carrageenan-induced inflammation, EAA was elicited, lasted for at least 24 hours after carrageenan injection, and was dose-dependently antagonized by i.pl. injection, but not significantly by i.p. injection of naloxone. It seems likely that the EAA in the rats with carrageenan-induced inflammation differs from that in normal rats, and these findings suggest that peripheral opioid receptors are involved in EAA during inflammatory conditions.

Involvement of central opioidergic and nonopioidergic neuroendocrine systems in the suppressive effect of acupuncture on delayed type hypersensitivity in mice

The effect of a single treatment of electroacupuncture (Acu) at early or late stages of the efferent phase on 2, 4, 6-trinitrochlorobenzene (TNCB)-induced delayed type hypersensitivity (DTH) was studied in intact and hypophysectomized (HPX) mice. Acu (2.5 Hz, 15 min) applied to the acu-point equivalent to GV4 at 0, 3, 18 or 21 h after TNCB challenge induced significant suppression (45-73%) of the maximal extent of ear swelling at 24 h after TNCB challenge. An immunosuppressive and antiinflammatory drug, prednisolone 10 mg/kg i.p., also suppressed the DTH to the same extent. Pretreatment with intracisternal injection of naloxone hydrochloride (2 micrograms) significantly blocked the Acu-evoked DTH suppression when Acu treatment was done at 0 or 3 h. On the contrary, naloxone did not block the effect of Acu treatment given at 21 h. In order to examine the potential involvement of the pituitary in the suppression of DTH by Acu, the DTH reaction was examined in HPX mice. Acu failed to produce suppressive response in the HPX mice unless given at 0 h. These findings indicate that Acu treatment at acu-point GV4 during the efferent phase of induced DTH can suppress the DTH through central opioidergic or nonopioidergic systems. The pituitary is apparently pivotal in this immunosuppression and it is suggested that the DTH suppression by Acu may be mediated via activation of the neuroendocrine system.

Electroacupuncture in rats: evidence for naloxone and naltrexone potentiation of analgesia

Low frequency electroacupuncture (EA) analgesia has been thought to be mediated by endogenous opioids. Among other lines of evidence, it has been reported that EA stimulation delivered at 2 and 2-15 Hz in rats could be blocked or partially antagonized by naloxone (NAL) and naltrexone (NTX). In contrast, experiments in one of our laboratories (D.J.M.) showed that NAL did not inhibit 2 Hz, and even potentiated 125 Hz EA analgesia. In an attempt to resolve these discrepancies, we conducted joint experiments in the U.S.A. and in China using the methods which previously yielded NAL reversibility of EA analgesia. In no experiment did opiate antagonists block or reduce EA analgesia. On the contrary, we found that, in most experiments, NAL and NTX potentiated 2 and 2-15 Hz EA analgesia respectively. The potentiation occurred independently of laboratory methods, geographic location of the experiment, strain (Chinese or American), tail temperature, sex, and weight of rats. This potentiation suggests the existence of an opioid anti-analgesic system or that NAL and NTX acquired analgesic properties following EA. These results indicate that EA analgesia in rats is a variable phenomenon even when laboratory methods are rigorously replicated. The EA stimulation may activate multiple conflicting neural circuits which interact and ultimately modulate the analgesic outcome.

Electroacupuncture analgesia in naive rats: effects of brainstem and spinal cord lesions, and role of pituitary-adrenal axis

Recent studies have shown that analgesia is potentiated by naltrexone (NTX) and naloxone (NAL) pretreatment in rats exposed for the first time to electroacupuncture (EA). In the present study, we have investigated the role of the pituitary-adrenal axis and of brainstem and spinal cord structures in EA analgesia and its potentiation by NTX. The pituitary and adrenal glands do not participate in the production of EA analgesia, but may produce a non-opioid substance which interferes with the development of EA analgesia. Spinalization or dorsolateral funiculi lesions blocked EA analgesia, and intrathecal NTX had no effect. These results indicate that supraspinal structures are necessary to produce and potentiate EA analgesia. Contrary to their critical role in morphine and other models of environmentally produced analgesia nucleus raphe alatus and raphe structures dorsal to it are not necessary for the development of EA analgesia. These structures, however, may contain opiate synapses on which NTX may act as an agonist to potentiate analgesia. The various components which appear to participate in the production of EA analgesia imply a complex circuit of pain modulation systems and indicate that an organism can adapt to distinct environmental conditions with versatile means to avoid pain.