The effect of genotype on sensitivity to electroacupuncture analgesia

The Endocannabinoid System Contributes to Electroacupuncture Analgesia

The extensive involvement of the endocannabinoid system (ECS) in vital physiological and cognitive processes of the human body has inspired many investigations into the role of the ECS and drugs, and therapies that target this system and its receptors. Activation of cannabinoid receptors 1 and 2 (CB₁ and CB₂) by cannabinoid treatments, including synthetic cannabinoids, alleviates behavioral responses to inflammatory and neuropathic pain. An increasing body of scientific evidence details how electroacupuncture (EA) treatments achieve effective analgesia and reduce inflammation by modulating cannabinoid signaling, without the adverse effects resulting from synthetic cannabinoid administration. CB₁ receptors in the ventrolateral area of the periaqueductal gray are critically important for the mechanisms of the EA antinociceptive effect, while peripheral CB₂ receptors are related to the anti-inflammatory effects of EA. This review explores the evidence detailing the endocannabinoid mechanisms involved in EA antinociception.

Neuromodulating Influence of Two Electroacupuncture Treatments on Heart Rate Variability, Stress, and Vagal Activity

Introduction: Although the clinical use of electro-acupuncture is widespread, the neuromodulating influence of various applied frequencies is not well established. Objectives: Heart rate variability (HRV), stress and parasympathetic recovery are closely related to health, longevity and vitality in humans. This study was undertaken to determine the influence of different electro-therapy frequencies on various autonomic nervous system markers when applied to a Battlefield Acupuncture Protocol (BFA). Design: A detailed comparison of autonomic nervous system (ANS) response to low frequency (LF) 2.5 Hz electro-acupuncture and mid-frequency (MF) 15 Hz electro-acupuncture applied by point stimulation to acupuncture points was undertaken on 2 groups of 12 patients. Interventions: Both LFEA and MFEA were applied to Battlefield Acupuncture protocol, consisting of five (5) key acupuncture ear (auricular) points that isolate the autonomic nervous system (ANS) and central nervous system's role in the chronic/acute pain cycle. Evaluations entailed an advanced status of autonomic nervous system (ANS) function through Electro-Cardiogram (ECG) baseline markers reflecting: sympathetic stress (SI); parasympathetic vagal tone (high frequency [HF]) and heart rate variability (HRV = total power). All were repeated subsequent to electro-therapy using 2 separate electro-modalities of low-frequency (2.5 Hz) electro-acupuncture (LFEA) and Mid-Frequency (15 Hz) electro-acupuncture (MFEA). All 24 patients received one (1) elector-acupuncture session. Results: The autonomic nervous system response to LFEA (2.5 Hz) reflected a statistically significant pre-post improvement in three of the markers collected: heart rate variability (HRV) improved by 61% [p = 0.002]; sympathetic stress (SI) reduced 42% [p = 0.002]; and parasympathetic vagal tone (HF) increased 56% [p = 0.017]. In contrast, MFEA (15 Hz) showed positive but non-significant changes in outcomes in all nervous system markers. Conclusions: The autonomic nervous system response with LFEA showed a measurable reduction in sympathetic stress with subsequent improvement in vagal tone, and HRV. This positive sympathetic nervous system deactivation from LFEA application shown in this study could have a major impact on other pathologies related to human health and longevity. Further cohort studies are warranted to determine the validity of these outcomes.

Functional MRI Investigation of Ultrasound Stimulation at ST 36

Background

Clinical and experimental data suggest that ultrasound stimulation (US) at acupoints can produce similar effective treatment compared to manual acupuncture (MA). Although the brain activation to MA at acupoints is investigated by numerous studies, the brain activation to US at acupoints remains unclear.

Methods

In the present work, we employed task state functional magnetic resonance imaging (fMRI) to explore the human brain's activation to US and MA at ST 36 (Zusanli) which is one of the most commonly used acupoints in acupuncture-related studies. 16 healthy subjects underwent US and MA procedures in an interval of more than one week. On-off block design stimulation was used for the recording of fMRI-related brain patterns.

Results

Both US and MA at ST 36 produced activations in somatosensory and limbic/paralimbic regions (postcentral gyrus, insula, middle prefrontal cortex, and anterior cingulate cortex). Only US at ST 36 produced a significant signal increase in the inferior parietal lobule and decrease in the posterior cingulate cortex, whereas MA at ST 36 produced a significant signal increase in the lentiform nucleus and cerebellum.

Conclusions

Our results indicate that US may be a possible noninvasive alternative method to MA due to its similar activation patterns.

A Review of Strain and Sex Differences in Response to Pain and Analgesia in Mice

Pain and its alleviation are currently a highly studied issue in human health. Research on pain and response to analgesia has evolved to include the effects of genetics, heritability, and sex as important components in both humans and animals. The laboratory mouse is the major animal studied in the field of pain and analgesia. Studying the inbred mouse to understand how genetic heritable traits and/or sex influence pain and analgesia has added valuable information to the complex nature of pain as a human disease. In the context of biomedical research, identifying pain and ensuring its control through analgesia in research animals remains one of the hallmark responsibilities of the research community. Advancements in both human and mouse genomic research shed light not only on the need to understand how both strain and sex affect the mouse pain response but also on how these research achievements can be used to improve the humane use of all research animal species. A better understanding of how strain and sex affect the response to pain may allow researchers to improve study design and thereby the reproducibility of animal research studies. The need to use both sexes, along with an improved understanding of how genetic heritability affects nociception and analgesic sensitivity, remains a key priority for pain researchers working with mice. This review summarizes the current literature on how strain and sex alter the response to pain and analgesia in the modern research mouse, and highlights the importance of both strain and sex selection in pain research.

Acupuncture Resolves Persistent Pain and Neuroinflammation in a Mouse Model of Chronic Overlapping Pain Conditions

Patients with chronic overlapping pain conditions have decreased levels of catechol-O-methyltransferase (COMT), an enzyme that metabolizes catecholamines. Consistent with clinical syndromes, we previously demonstrated that COMT inhibition in rodents produces persistent pain and heightened immune responses. Here, we sought to determine the efficacy of manual acupuncture in resolving persistent pain and neuroinflammation in the classic inbred C57BL/6 strain and the rapid-wound healing MRL/MpJ strain. Mice received subcutaneous osmotic minipumps to deliver the COMT inhibitor OR486 or vehicle for 13 days. On day 7 after pump implantation, acupuncture was performed at the Zusanli (ST36) point or a non-acupoint for 6 consecutive days. Behavioral responses to mechanical stimuli were measured throughout the experiment. Immunohistochemical analysis of spinal phosphorylated p38 mitogen-activated protein kinase, a marker of inflammation, and glial fibrillary acidic protein, a marker of astrogliosis, was performed on day 13. Results demonstrated that ST36, but not sham, acupuncture resolved mechanical hypersensitivity and reduced OR486-dependent increases in phosphorylated p38 and glial fibrillary acidic protein in both strains. The magnitude of the analgesic response was greater in MRL/MpJ mice. These findings indicate acupuncture as an effective treatment for persistent pain linked to abnormalities in catecholamine signaling and, furthermore, that analgesic efficacy may be influenced by genetic differences. PERSPECTIVE: Chronic overlapping pain conditions remain ineffectively managed by conventional pharmacotherapies. Here, we demonstrate that acupuncture alleviates persistent pain and neuroinflammation linked to heightened catecholaminergic tone. Mice with superior healing capacity exhibit greater analgesic efficacy. Findings indicate acupuncture as an effective treatment for chronic overlapping pain conditions and provide insight into treatment response variability.

Electroacupuncture Treatment Alleviates the Remifentanil-Induced Hyperalgesia by Regulating the Activities of the Ventral Posterior Lateral Nucleus of the Thalamus Neurons in Rats

Mechanisms underlying remifentanil- (RF-) induced hyperalgesia, a phenomenon that is generally named as opioid-induced hyperalgesia (OIH), still remain elusive. The ventral posterior lateral nucleus (VPL) of the thalamus, a key relay station for the transmission of nociceptive information to the cerebral cortex, is activated by RF infusion. Electroacupuncture (EA) is an effective method for the treatment of pain. This study aimed to explore the role of VPL in the development of OIH and the effect of EA treatment on OIH in rats. RF was administered to rats via the tail vein for OIH induction. Paw withdrawal threshold (PWT) in response to mechanical stimuli and paw withdrawal latency (PWL) to thermal stimulation were tested in rats for the assessment of mechanical allodynia and thermal hyperalgesia, respectively. Spontaneous neuronal activity and local field potential (LFP) in VPL were recorded in freely moving rats using the in vivo multichannel recording technique. EA at 2 Hz frequency (pulse width 0.6 ms, 1-3 mA) was applied to the bilateral acupoints "Zusanli" (ST.36) and "Sanyinjiao" (SP.6) in rats. The results showed that both the PWT and PWL were significantly decreased after RF infusion to rats. Meanwhile, both the spontaneous neuronal firing rate and the theta band oscillation in VPL LFP were increased on day 3 post-RF infusion, indicating that the VPL may promote the development of RF-induced hyperalgesia by regulating the pain-related cortical activity. Moreover, 2 Hz-EA reversed the RF-induced decrease both in PWT and PWL of rats and also abrogated the RF-induced augmentation of the spontaneous neuronal activity and the power spectral density (PSD) of the theta band oscillation in VPL LFP. These results suggested that 2 Hz-EA attenuates the remifentanil-induced hyperalgesia via reducing the excitability of VPL neurons and the low-frequency (theta band) oscillation in VPL LFP.

Does Electroacupuncture Treatment Reduce Pain and Change Quantitative Sensory Testing Responses in Patients with Chronic Nonspecific Low Back Pain? A Randomized Controlled Clinical Trial

Chronic nonspecific low back pain is common and one of the most disabling conditions in the world. There is moderate evidence that chronic low back pain patients present altered functional connectivity in areas related to pain processing. Quantitative sensory testing is a way of clinical measure of these alterations. Although there is not enough evidence, there are some reports that electroacupuncture is supposedly more effective in relieving pain than acupuncture because the addition of electric current could optimize the effects of traditional technique. Thus, the objective of this randomized clinical trial was to verify if electroacupuncture treatment reduces pain and changes quantitative sensory testing responses in patients with chronic nonspecific low back pain. Patients were evaluated before and after 10 sessions regarding pain (11-point numerical rating pain scale) and quantitative sensory testing (pressure pain threshold, temporal summation, and conditioned pain modulation). There were 1 treatment group (electroacupuncture (EA)) and three different control groups (CTR 1, CTR 2, and CTR 3). A total of 69 patients participated in the study. No significant differences were found in pain intensity or quantitative sensory testing responses when comparing electroacupuncture group to the three control groups. There was a significant reduction in both resting and movement pain intensity in groups EA, CTR 1, and CTR3. Although ten sessions of electroacupuncture have diminished pain intensity in both resting and movement, it could not change significantly quantitative sensory testing and diminish central sensitization in patients with chronic nonspecific low back pain. The implications of this study involve the fact that, maybe, in chronic nonspecific low back pain, electroacupuncture should be associated with other treatments that target central sensitization.

Electroacupuncture Ameliorates Propofol-Induced Cognitive Impairment via an Opioid Receptor-Independent Mechanism

While general anesthesia is known to induce cognitive deficits in elderly and pediatric patients, its influence on adults is less well-characterized. The present study was designed to evaluate the influence of propofol on the learning and memory of young adult rats, as well as the potential neuroprotective role of electroacupuncture (EA) in propofol-induced cognitive impairment. Intravenous anesthesia with propofol was administered to young adult male Sprague–Dawley (SD) rats for 6 h, and EA was administered three times before and after anesthesia. The Morris Water Maze (MWM) test was conducted to determine the rat’s cognitive performance following the anesthesia treatment. Our results showed that propofol induced obvious cognitive impairment in young adult rats, which could be ameliorated by multiple EA treatments. Moreover, the decreased level of phosphorylated glycogen synthase kinase 3 β (pGSK-3β) in the CA1 region of the hippocampus accompanying the cognitive impairment was also reversed by EA treatment. Further experiments demonstrated that neither 2 nor 10 mg/kg (I.P.) naloxone blocked the effect of EA, indicating that the neuroprotective effect of EA on propofol-induced cognitive impairment was not mediated via the opioid receptors. The present study suggests that EA could ameliorate the cognitive impairment induced by prolonged anesthesia with propofol in young adult rats, which is likely associated with pGSK-3β levels in the CA1 independently of opioid receptors. These findings imply that EA may be used as a potential neuroprotective therapy for post-operative cognitive dysfunction (POCD).

The Analysis of Normalized Effects on Meridian Current Level After the Photoluminescent Bioceramic Treatment on Acupuncture Points

OBJECTIVE

This study investigated the advantage of photoluminescent bioceramic (PLB) irradiation on meridian channels of abnormal meridian currents, as well as the normalization of meridian current levels that may represent the participants' physiologic conditions.

DESIGN

Statistical analysis of survey data.

PARTICIPANTS

Forty-six patients with abnormal meridian current in the gallbladder (GB).

INTERVENTIONS

The effects on the meridian currents were measured by an electrodermal instrument after PLB irradiation was applied to the GB and other specific acupuncture points. Each meridian was categorized into six physiologic levels to evaluate effectiveness after the PLB irradiation: 1, extremely low; 2, moderately low; 3, normally low; 4, normally high; 5, moderately high; and 6, extremely high level. The positive effect of PLB treatment for each meridian could be defined as the normalized ability of the meridian level from the extreme values (1, 2, 5, or 6) approaching the normal levels (3 or 4).

RESULTS

Participants with higher average meridian current (Amc >36 μA) calculated from the currents of 24 Ryodoraku points could be significantly normalized after the PLB treatment (p=0.0241). A significant positive effect was seen in comparison with the negative effect of PLB on the GB meridian (McNemar test, p=0.00004) (n=46×2 for left and right GB meridians). A patient with benign facial tremor was treated by PLB for 1 month; PLB improved the facial tremor and normalized effects on Amc and meridian current levels at the GB, lung, small intestine, bladder, and kidney.

CONCLUSION

A method was proposed to evaluate the normalization effect of a noninvasive PLB technique on the 12 meridians. PLB acupuncture on the specific meridian points could show the normalization ability of Amc and GB meridian for the participants.

Genomewide analysis of rat periaqueductal gray-dorsal horn reveals time-, region- and frequency-specific mRNA expression changes in response to electroacupuncture stimulation

Electroacupuncture (EA) has been widely applied for illness prevention, treatment or rehabilitation in the clinic, especially for pain management. However, the molecular events that induce these changes remain largely uncharacterized. The periaqueductal gray (PAG) and the spinal dorsal horn (DH) have been verified as two critical regions in the response to EA stimulation in EA analgesia. In this study, a genetic screen was conducted to delineate the gene expression profile in the PAG-DH regions of rats to explore the molecular events of the analgesic effect induced by low-frequency (2-Hz) and high-frequency (100-Hz) EAs. Microarray analysis at two different time points after EA stimulation revealed time-, region- and frequency-specific gene expression changes. These expression differences suggested that modulation of neural-immune interaction in the central nervous system played an important role during EA analgesia. Furthermore, low-frequency EA could regulate gene expression to a greater degree than high-frequency EA. Altogether, the present study offers, for the first time, a characterized transcriptional response pattern in the PAG-DH regions followed by EA stimulation and, thus, provides a solid experimental framework for future in-depth analysis of the mechanisms underlying EA-induced effects.

Safety of Noninvasive Electrical Stimulation of Acupuncture Points During a Routine Neonatal Heel Stick

BACKGROUND

Hospitalized infants may undergo frequent painful procedures with inadequate pain relief. Alternative pain relief interventions are needed.

OBJECTIVE

The aim of this research was to determine the safety of noninvasive electrical stimulation of acupuncture points (NESAP) in neonates who were receiving routine heel sticks.

DESIGN

This was a descriptive study performed to assess the safety of using a transcutaneous electrical nerve stimulation (TENS) unit to deliver NESAP to neonates.

SETTING/SUBJECTS

The subjects were healthy newborn infants<3 days old before hospital discharge.

INTERVENTION

The intervention was NESAP delivered via a TENS unit, administered before, during, and after heel stick. The electrodes of the TENS unit were applied at four acupuncture points. Settings were gradually increased: 6 infants received 1.0 mA, 2 Hz; the second 6 infants received 2.0 mA, 10 Hz; and the last 18 infants received 3.5 mA, 10 Hz.

MAIN OUTCOME MEASURES

THREE MAIN MEASURES WERE USED: (1) skin assessment (2) vital signs; (3) pain scores using the Premature Infant Pain Profile (PIPP).

RESULTS

There were no significant changes in vital signs during and after NESAP. There were no changes in PIPP scores in the first 12 infants after initiation of NESAP. A slight but nonsignificant increase in PIPP scores (from 2.65 to 3.5 on a scale of 0-18) occurred in the last 18 infants. There were no adverse events during or after NESAP.

CONCLUSIONS

NESAP is safe for infants with low settings on a TENS unit.

Modulation of brain electroencephalography oscillations by electroacupuncture in a rat model of postincisional pain

The present study aimed to investigate how ongoing brain rhythmical oscillations changed during the postoperative pain and whether electroacupuncture (EA) regulated these brain oscillations when it relieved pain. We established a postincisional pain model of rats with plantar incision to mimic the clinical pathological pain state, tested the analgesic effects of EA, and recorded electroencephalography (EEG) activities before and after the EA application. By analysis of power spectrum and bicoherence of EEG, we found that in rats with postincisional pain, ongoing activities at the delta-frequency band decreased, while activities at theta-, alpha-, and beta-frequency bands increased. EA treatment on these postincisional pain rats decreased the power at high-frequency bands especially at the beta-frequency band and reversed the enhancement of the cross-frequency coupling strength between the beta band and low-frequency bands. After searching for the PubMed, our study is the first time to describe that brain oscillations are correlated with the processing of spontaneous pain information in postincisional pain model of rats, and EA could regulate these brain rhythmical frequency oscillations, including the power and cross-frequency couplings.

Breathing-controlled Electrical Stimulation (BreEStim) for management of neuropathic pain and spasticity

Electrical stimulation (EStim) refers to the application of electrical current to muscles or nerves in order to achieve functional and therapeutic goals. It has been extensively used in various clinical settings. Based upon recent discoveries related to the systemic effects of voluntary breathing and intrinsic physiological interactions among systems during voluntary breathing, a new EStim protocol, Breathing-controlled Electrical Stimulation (BreEStim), has been developed to augment the effects of electrical stimulation. In BreEStim, a single-pulse electrical stimulus is triggered and delivered to the target area when the airflow rate of an isolated voluntary inspiration reaches the threshold. BreEStim integrates intrinsic physiological interactions that are activated during voluntary breathing and has demonstrated excellent clinical efficacy. Two representative applications of BreEStim are reported with detailed protocols: management of post-stroke finger flexor spasticity and neuropathic pain in spinal cord injury.

History of acupuncture research

The acupuncture has been practiced in China for more than 3000 years and was spread to Europe and American from the sixteenth to the nineteenth century. The history of acupuncture research was initiated in the eighteenth century and developed rapidly since then. In the past, physicians tried hard to apply acupuncture into clinical practice, while scientists were focused on the possible characteristics of acupoints and meridians. In the modern time, scientists have strived hard to evaluate the real effectiveness of acupuncture and the underlying physiological and biological mechanisms of acupuncture. Reviewing research history from past to present, we are delighted to witness this wonderful development. Accumulated evidences that acupuncture is beneficial in various conditions significantly enhanced our understanding the mechanisms of acupuncture treatment. However, there is still no conclusive evidence in acupuncture clinical studies. The clinical research still needs great improving, while the basic research results need to be appropriately transformed into clinical outcomes. Based on current achievements, we believe that although the challenges and difficulties exist, a more collaborative, innovative, and integrated approach will help us to achieve further progress in future acupuncture research.

Differences in neural-immune gene expression response in rat spinal dorsal horn correlates with variations in electroacupuncture analgesia

Background

Electroacupuncture (EA) has been widely used to alleviate diverse pains. Accumulated clinical experiences and experimental observations indicated that significant differences exist in sensitivity to EA analgesia for individuals of patients and model animals. However, the molecular mechanism accounting for this difference remains obscure.

Methodology/Principal Findings

We classified model male rats into high-responder (HR; TFL changes >150) and non-responder (NR; TFL changes ≤0) groups based on changes of their pain threshold detected by tail-flick latency (TFL) before and after 2 Hz or 100 Hz EA treatment. Gene expression analysis of spinal dorsal horn (DH) revealed divergent expression in HR and NR after 2 Hz/100 Hz EA. The expression of the neurotransmitter system related genes was significantly highly regulated in the HR animals while the proinflammation cytokines related genes were up-regulated more significantly in NR than that in HR after 2 Hz and 100 Hz EA stimulation, especially in the case of 2 Hz stimulation.

Conclusions/Significance

Our results suggested that differential regulation and coordination of neural-immune related genes might play an important role for individual variations in analgesic effects responding to EA in DH. It also provided new candidate genes related to EA responsiveness for future investigation.

Electroacupuncture on a Patient with Pacemaker: A Case Report

Electroacupuncture (EA) is commonly used for pain relief, with good results even in persistent chronic pain. However, published reports suggest that EA should not be used in patients who have pacemaker, since there is a theoretical risk of malfunction of the pacemaker. The case is described of a 50-year-old female patient, who has had severe low back pain resistant both to conventional and unconventional treatment methods. The only treatment that seemed to have some positive effect, but of extremely short duration, was acupuncture. Her condition deteriorated considerably, and after due consideration she was treated with EA. Even after the first EA treatment, the patient's condition improved. Since then, she has received many EA courses during the past 2 years without any complications or side effects. The results of this case study suggest that EA might be a safe alternative for patients with a pacemaker, confirming the current recommendations on use. Every patient should be considered with care, individually.

A novel uni-acupoint electroacupuncture stimulation method for pain relief

Electroacupuncture stimulation (EAS) has been demonstrated effective for pain relief and treating other various diseases. However, the conventional way of EAS, the bi-acupoint method, is not suitable for basis study of acupoint specificity. Moreover, its operations are inconvenient and difficult to be persevered, especially for long-term, continuous and even imperative treatments. These disadvantages motivate designs of new EAS methods. We present a novel uni-acupoint electrical stimulation method, which is applied at a single acupoint and quite meets the needs of basis study and simpler clinical application. Its pain relief effect has been evaluated by animal tests of Wistar rats. During the experiments, rats were given 30 min 2/100 Hz uni- and bi-acupoint EAS and their nociceptive thresholds before and after EAS were attained by hot-plate test. The analgesic effect was defined as the change of nociceptive threshold and used to evaluate the effectiveness of uni-acupoint EAS for pain relief. The hot-plate test results indicated that analgesic effect of uni-acupoint group was significantly higher than that of the control group and there was no significant difference of analgesic effects between uni- and bi-acupoint EAS. The results suggested that uni-acupoint method was an effective EAS method and had comparable pain relief effect with bi-acupoint method.

Electroacupuncture restores learning and memory impairment induced by both diabetes mellitus and cerebral ischemia in rats

Previous investigations have demonstrated that electroacupunctural stimulation can ameliorate primary and secondary symptoms such as peripheral neuropathy and diabetic encephalopathy in diabetic rats. In this study, we investigated whether electroacupuncture could improve learning and memory which was typically impaired in diabetic rats with cerebral ischemia. Furthermore, we investigated the mechanisms underlying its effects using passive avoidance test, active avoidance test, Morris water maze and electrophysiology. Electroacupuncture increased the step-down latency in passive avoidance test and accurate rate in active avoidance test, decreased the escape latency in Morris water maze. After electroacupuncture treatment, the long-term potentiation (LTP) impaired by both diabetes and cerebral ischemia was restored significantly. These results suggest that electroacupuncture can ameliorate learning and memory capacity impaired by hyperglycemia and ischemia. LTP plays a very important role in this beneficial effect.

Neural mechanism underlying acupuncture analgesia

Acupuncture has been accepted to effectively treat chronic pain by inserting needles into the specific "acupuncture points" (acupoints) on the patient's body. During the last decades, our understanding of how the brain processes acupuncture analgesia has undergone considerable development. Acupuncture analgesia is manifested only when the intricate feeling (soreness, numbness, heaviness and distension) of acupuncture in patients occurs following acupuncture manipulation. Manual acupuncture (MA) is the insertion of an acupuncture needle into acupoint followed by the twisting of the needle up and down by hand. In MA, all types of afferent fibers (Abeta, Adelta and C) are activated. In electrical acupuncture (EA), a stimulating current via the inserted needle is delivered to acupoints. Electrical current intense enough to excite Abeta- and part of Adelta-fibers can induce an analgesic effect. Acupuncture signals ascend mainly through the spinal ventrolateral funiculus to the brain. Many brain nuclei composing a complicated network are involved in processing acupuncture analgesia, including the nucleus raphe magnus (NRM), periaqueductal grey (PAG), locus coeruleus, arcuate nucleus (Arc), preoptic area, nucleus submedius, habenular nucleus, accumbens nucleus, caudate nucleus, septal area, amygdale, etc. Acupuncture analgesia is essentially a manifestation of integrative processes at different levels in the CNS between afferent impulses from pain regions and impulses from acupoints. In the last decade, profound studies on neural mechanisms underlying acupuncture analgesia predominately focus on cellular and molecular substrate and functional brain imaging and have developed rapidly. Diverse signal molecules contribute to mediating acupuncture analgesia, such as opioid peptides (mu-, delta- and kappa-receptors), glutamate (NMDA and AMPA/KA receptors), 5-hydroxytryptamine, and cholecystokinin octapeptide. Among these, the opioid peptides and their receptors in Arc-PAG-NRM-spinal dorsal horn pathway play a pivotal role in mediating acupuncture analgesia. The release of opioid peptides evoked by electroacupuncture is frequency-dependent. EA at 2 and 100Hz produces release of enkephalin and dynorphin in the spinal cord, respectively. CCK-8 antagonizes acupuncture analgesia. The individual differences of acupuncture analgesia are associated with inherited genetic factors and the density of CCK receptors. The brain regions associated with acupuncture analgesia identified in animal experiments were confirmed and further explored in the human brain by means of functional imaging. EA analgesia is likely associated with its counter-regulation to spinal glial activation. PTX-sesntive Gi/o protein- and MAP kinase-mediated signal pathways as well as the downstream events NF-kappaB, c-fos and c-jun play important roles in EA analgesia.

Long-term synaptic plasticity in the spinal dorsal horn and its modulation by electroacupuncture in rats with neuropathic pain

Our previous study has reported that electroacupuncture (EA) at low frequency of 2 Hz had greater and more prolonged analgesic effects on mechanical allodynia and thermal hyperalgesia than that EA at high frequency of 100 Hz in rats with neuropathic pain. However, how EA at different frequencies produces distinct analgesic effects on neuropathic pain is unclear. Neuronal plastic changes in spinal cord might contribute to the development and maintenance of neuropathic pain. In the present study, we investigated changes of spinal synaptic plasticity in the development of neuropathic pain and its modulation by EA in rats with neuropathic pain. Field potentials of spinal dorsal horn neurons were recorded extracellularly in sham-operated rats and in rats with spinal nerve ligation (SNL). We found for the first time that the threshold for inducing long-term potentiation (LTP) of C-fiber-evoked potentials in dorsal horn was significantly lower in SNL rats than that in sham-operated rats. The threshold for evoking the C-fiber-evoked field potentials was also significantly lower, and the amplitude of the field potentials was higher in SNL rats as compared with those in the control rats. EA at low frequency of 2 Hz applied on acupoints ST 36 and SP 6, which was effective in treatment of neuropathic pain, induced long-term depression (LTD) of the C-fiber-evoked potentials in SNL rats. This effect could be blocked by N-methyl-d-aspartic acid (NMDA) receptor antagonist MK-801 and by opioid receptor antagonist naloxone. In contrast, EA at high frequency of 100 Hz, which was not effective in treatment of neuropathic pain, induced LTP in SNL rats but LTD in sham-operated rats. Unlike the 2 Hz EA-induced LTD in SNL rats, the 100 Hz EA-induced LTD in sham-operated rats was dependent on the endogenous GABAergic and serotonergic inhibitory system. Results from our present study suggest that (1) hyperexcitability in the spinal nociceptive synaptic transmission may occur after nerve injury, which may contribute to the development of neuropathic pain; (2) EA at low or high frequency has a different effect on modulating spinal synaptic plasticities in rats with neuropathic pain. The different modulation on spinal LTD or LTP by low- or high-frequency EA may be a potential mechanism of different analgesic effects of EA on neuropathic pain. LTD of synaptic strength in the spinal dorsal horn in SNL rats may contribute to the long-lasting analgesic effects of EA at 2 Hz.

Analgesic effects by electroacupuncture were decreased in inducible nitric oxide synthase knockout mice

BACKGROUND

This study was designed to investigate the involvement of inducible nitric oxide synthase (iNOS) in electroacupuncture (EA)-induced analgesia.

METHODS

Two and 100 Hz EA stimulation were applied at acupoint ST 36 (Zusanli) in iNOS knockout mice (n = 28). Needles were inserted 5 mm in depth in ST36. After insertion, the needles were fixed in situ with adhesive tape. EA was applied after the basal threshold determination. The EA parameters were set as follows: constant square wave current output (pulse width: 0.6 ms at 2 Hz and 0.2 ms at 100 Hz) and 2 mA intensities. EA was performed for 30 minutes and tail-flick latencies (TFLs) were evaluated every 15 minutes for 1 hour.

RESULTS

In 2 Hz EA stimulation, the tail-flick response (TFR) of wild-type mice for durations of 0, 15, 30, 45 and 60 minutes were 2.70 +/- 0.26, 4.19 +/- 0.37, 4.17 +/- 0.34, 3.57 +/- 0.27 and 3.39 +/- 0.32 seconds of TFLs. Meanwhile, iNOS -/- mice showed 4.10 +/- 0.33, 4.77 +/- 0.24, 5.26 +/- 0.30, 4.48 +/- 0.33 and 5.00 +/- 0.41 seconds of TFLs. In 100 Hz EA stimulation, the TFR of wild-type mice were 3.01 +/- 0.24, 4.67 +/- 0.31, 4.76 +/- 0.25, 4.04 +/- 0.45 and 4.26 +/- 0.30 seconds of TFLs. The iNOS -/- mice were 4.33 +/- 0.16, 5.29 +/- 0.28, 5.06 +/- 0.35, 4.52 +/- 0.17 and 4.80 +/- 0.28 seconds of TFLs. Wild-type mice exhibited 63.9% increase in TFL compared to the baseline after 2 Hz EA, whereas the iNOS knockout mice exhibited 32.9% increase in TFL. The TFL after 100 Hz EA showed similar trends: 66.5% increase in TFL in wildtype mice and 18.3% increase in the iNOS knockout mice.

CONCLUSION

The present findings suggested that iNOS may play a crucial role in both low- and high-frequency EA-induced analgesic effects.

CCK(B) receptor antagonist L365,260 potentiates the efficacy to and reverses chronic tolerance to electroacupuncture-induced analgesia in mice

Cholecystokinin octapeptide (CCK-8) is a physiological antagonist of endogenous opioids in the central nervous system (CNS). Our previous work has shown that CCK-8 plays an important role in the development of tolerance to morphine analgesia and electroacupuncture (EA) analgesia in the rat. The present studies were designed to examine whether the CCK(B) receptor is involved in the modulation of EA analgesia and the development of EA tolerance in mice. The latency to flick the tail in the radiant heat was used as index to assess the efficacy of EA analgesia. Subcutaneous (s.c.) injection of the CCK(B) receptor antagonist L365,260 produced a dose-dependent (0.125-2.0 mg/kg) potentiation of the analgesia induced by 100 Hz EA, with a maximal effect occurred at 0.5 mg/kg. In addition, L365,260 (0.5 mg/kg) significantly reversed chronic tolerance to 100 Hz EA in mice. These results suggest that the CCK(B) receptor might play a role in the tonic inhibition of 100 Hz EA-induced analgesia and in the mediation of chronic tolerance to 100 Hz EA in mice. The results opened a way for further investigation of the function of CCK-8 in pain modulation using inbred strains of mice.

Effects of intensity of electroacupuncture upon experimental pain in healthy human volunteers: a randomized, double-blind, placebo-controlled study

Electroacupuncture is commonly used for pain relief. Despite an extensive evidence-base guiding the selection of stimulation parameters, little methodologically robust research exists regarding the level of intensity required to provide effective doses. This study investigated the hypoalgesic effects of two stimulation intensities compared to placebo on pressure pain thresholds (PPTs) in pain-free humans. Forty-eight acupuncture-naïve volunteers (mean age 23), stratified by gender, were screened for relevant contraindications and randomly allocated to four groups: control, placebo, high-intensity ("to tolerance but sub-noxious") or low-intensity ("strong but comfortable"). True or placebo electroacupuncture, using the Streitberger placebo needle, was administered to acupoints on dominant forearm (LI10, TH5) and ipsilateral leg (GB34, ST38). True needles (30 mm long, 0.3 mm diameter) were inserted 20-25 mm and "de-qi" was elicited from active groups, prior to administering 30 min of 4 Hz, 200 micros electroacupuncture. No electrical stimulation was performed on control and placebo groups, and placebo needles were used. After the intervention period, all needles were removed. Volunteers were monitored for 30 further minutes. Two PPT measurements were taken bilaterally from muscle bellies of first dorsal interosseous by an independent rater, at baseline and at six subsequent 10-min intervals. Square-root transformed data were analysed using repeated-measures ANOVA, with baseline data as covariate. The high-intensity group was significantly different from the placebo group for both measurement sites (p=.020, p=.033). The control group displayed stable PPT readings over time. No significant differences were observed between the placebo and control groups. These findings suggest that high-intensity levels may be important in optimal dose selection.

Mode and site of acupuncture modulation in the human brain: 3D (124-ch) EEG power spectrum mapping and source imaging

This study determined: (a) if acupuncture stimulation at a traditional site might modulate ongoing EEG as compared with stimulation of a control site; (b) if high-frequency vs. low-frequency stimulation could exert differential effects of acupuncture; (c) if the observed effects of acupuncture were specific to certain EEG bands; and (d) if the acupuncture effect could be isolated at a specific scalp field, with its putative underlying intracranial source. Twelve healthy male volunteers (age range 22-35) participated in two experimental sessions separated by 1 week, which involved transcutaneous acupoint stimulation at selected acupoint (Li 4, HeGu) vs. a mock point at the fourth interosseous muscle area on the left hand in high (HF: 100 Hz) vs. low-frequency (LF: 2 Hz) stimulation by counter-balanced order. 124-ch EEG data were used to analyze the Delta, Theta, Alpha-1, Alpha-2, Beta, and Gamma bands. The absolute EEG powers (muv2) at focal maxima across three stages (baseline, stimulation, post) were examined by two-way (condition, stage) repeated measures ANOVA. The activity of the Theta power significantly decreased (P = 0.02), compared with control during HF but not LF stimulation at acupoint stimulation, however, there was no study effect at the mock point. A decreased Theta EEG power was prominent at the frontal midline sites (FCz, Fz) and the contralateral right hemisphere front site (FCC2h). In contrast, the Theta power of low-frequency stimulation showed an increase from the baseline as those in both controlled mock point stimulations. The observed high-frequency acupoint stimulation effects of Theta EEG were only present during, but not after, simulation. The topographic Theta activity was tentatively identified to originate from the intracranial current source in cingulate cortex, likely ACC. It is likely that short-term cortical plasticity occurs during high-frequency but not low-frequency stimulation at the HeGu point, but not mock point. We suggest that HeGu acupuncture stimulation modulates limbic cingulum by a frequency modulation mode, which then may damp nociceptive processing in the brain.

Ectopic discharges from injured nerve fibers are highly correlated with tactile allodynia only in early, but not late, stage in rats with spinal nerve ligation

It is widely accepted that ectopic discharges originated from injured sites and dorsal root ganglion (DRG) neurons after peripheral nerve injury contribute to neuropathic pain. However, it has been recently shown that ectopic discharges were not always necessary for neuropathic pain. In the present study, we aim to further examine the role of ectopic discharges in neuropathic pain in a spinal nerve ligation (SNL) model. With teased fiber recordings in vivo, the characteristics of ectopic discharges were observed over 14 days after SNL, and the correlation between ectopic discharges and tactile allodynia was analyzed. It was observed that ectopic discharges have three firing patterns (tonic, bursting, and irregular) after SNL, and proportions of these three patterns changed dynamically over time. The tonic and bursting types were dominant in the first 24 h following SNL, while the irregular type became the only pattern in the late stage (day 14). The average frequencies of ectopic discharges and the percentage of active filaments also changed over time, reaching the peak 24 h after SNL and then declined gradually. Ectopic discharges were highly correlated with tactile allodynia in the first 24 h following SNL, but surprisingly, not in the late stage of days 1 to 14. These findings suggest that ectopic discharges may be crucial in the triggering of neuropathic pain in the early stage, but their importance become more limited over time.

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.

Analgesic effects of different acupoint stimulation frequencies in humans

Transcutaneous electrical acupoint stimulation (TEAS) provides a convenient and standardized technique for pain treatment. The cold-pressor test is a simple and reliable model in humans for the induction of tonic pain. In this controlled study, the effects of TEAS on cold pressor-induced pain were evaluated in 22 healthy human subjects. Electrical stimulation at 4 Hz and 32 Hz was applied to He-Gu (LI 4) and Nui-Guan (P 6) acupoints for 15 minutes. Pain score ratings were evaluated at four time points from 30-170 seconds during the cold-pressor test. We observed an analgesic effect at both 4 Hz and 32 Hz of stimulation, and pain score rating reductions were statistically significant compared to control (p < 0.01). Our data support the efficacy of TEAS analgesia. However, there was no significant difference between pain scores at 4 Hz and 32 Hz stimulation.

Sex differences in drug- and non-drug-induced analgesia

Historically, biomedical research has been conducted almost exclusively with male subjects. A growing number of studies now demonstrate sex differences in analgesia produced both by drugs and by environmental stimuli. This review summarizes the current literature on sex differences in analgesia produced by opioids, cholinergics and other drugs, and by stress, exercise and other environmental manipulations. A brief overview of the physiological mechanisms underlying sex differences in analgesia is provided, as well as suggestions for future research. It is not yet known whether the development of sex-specific analgesia treatment guidelines is warranted.

Endogenous opiates and behavior: 2001

This paper is the twenty-fourth installment of the annual review of research concerning the opiate system. It summarizes papers published during 2001 that studied the behavioral effects of the opiate peptides and antagonists. The particular topics covered this year include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology(Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Transcutaneous electrical acupoint stimulation potentiates analgesic effect of morphine

Pain is the major complaint of patients who choose acupuncture treatment. Transcutaneous electrical acupoint stimulation (TEAS) provides a safe, standardized technique without needle insertion. TEAS can be tested with the cold-pressor test, a simple, reliable, and widely used model in humansfor the induction of tonic pain. In this controlled study, the effects of TEAS on cold-pressor-induced pain were evaluated in 20 healthy human subjects. Electrical stimulation electrodes were applied to He-Gu (LI 4) and Nui-Guan (P 6) acupoints. The effects of saline plus no TEAS, 15-minute TEAS alone, 0.05 mg/kg morphine alone, and 15-minute TEAS plus morphine were assessed. Pain score ratings were evaluated at four time points from 30 to 170 seconds during the cold-pressor test. The authors observed analgesic effects in both TEAS-alone and morphine-alone sessions, and pain score rating reductions were statistically significant compared to unstimulated control (both p < 0.01). The degree of TEAS analgesia combined with 0.05 mg/kg morphine was significantly higher than TEAS alone (p < 0.01). The results support the efficacy of TEAS analgesia and suggest that combination of TEAS with low-dose morphine can achieve better pain control in a variety of clinical settings.

Characteristics of electroacupuncture-induced analgesia in mice: variation with strain, frequency, intensity and opioid involvement

The present study was conducted to evaluate the characteristics of electroacupuncture (EA)-induced analgesia in mice. Three inbred strains of mice (DBA/2, C57BL/6J, BALB/c) and three outbred strains (ICR, LACA, NIH) were used in the experiment. Two pairs of metallic needles were inserted into acupoints ST 36 and SP 6 connected to an electric pulse generator. EA parameters were set as constant current output with alteration of a positive and negative square wave, 0.6 ms in pulse width for 2 Hz and 0.3 ms for 100 Hz. Tail-flick latencies evoked by radiant heat were measured before, during and after EA stimulation. We found that (1) DBA/2 mice showed a significantly more potent analgesic effect than the other five strains in response to both 100 and 2 Hz EA. In this case, the intensities were 1.0-2.0-2.0 mA, 10 min for each intensity totally 30 min. (2) EA analgesia increased as the intensity of stimulation increased from 0.5 to 2.0 mA, but it remained at this plateau when the intensity further increased from 2.0 to 3.0 mA. (3) 10.0 mg x kg(-1) naloxone was needed to block the analgesic effect induced by 2 Hz EA of 2.0 mA, but to block that by 100 Hz, 25.0 mg x kg(-1) was necessary. (4) A positive correlation was observed between analgesia induced by morphine at the dose of 5.0 mg x kg(-1) and by 100 Hz EA in two tested strains DBA/2 and C57BL/6J. In conclusion, EA induces reliable, strain-dependent analgesia in mice. The naloxone-reversibility of EA, a measure of whether it is opioid or non-opioid mediated, is dependent upon intensity and frequency.

Heritability of nociception. III. Genetic relationships among commonly used assays of nociception and hypersensitivity

We and others have previously demonstrated that nociception in the mouse is heritable. A genetic correlation analysis of 12 common measures of nociception among a common set of inbred strains revealed three major clusters (or 'types') of nociception in this species. In the present study, we re-evaluated the major types of nociception and their interrelatedness using ten additional assays of nociception and hypersensitivity, including: three thermal assays (tail withdrawal from 47.5 degrees C water or -15 degrees C ethanol; tail flick from radiant heat), two chemical assays of spontaneous nociception (bee venom test; capsaicin test) and their subsequent thermal hypersensitivity states (including contralateral hypersensitivity in the bee venom test), a mechanical nociceptive assay (tail-clip test), and a mechanical hypersensitivity assay (intrathecal dynorphin). Confirming our earlier findings, the results demonstrate distinct thermal and chemical nociceptive types. It is now clear that mechanical hypersensitivity and thermal hypersensitivity are genetically dissociable phenomena. Furthermore, we now see at least two distinct types of thermal hypersensitivity: afferent-dependent, featuring a preceding significant period of spontaneous nociceptive behavior associated with afferent neural activity, and non-afferent-dependent. In conclusion, our latest analysis suggests that there are at least five fundamental types of nociception and hypersensitivity: (1) baseline thermal nociception; (2) spontaneous responses to noxious chemical stimuli; (3) thermal hypersensitivity; (4) mechanical hypersensitivity; and (5) afferent input-dependent hypersensitivity.

Decrease of the electroacupuncture-induced analgesic effects in nuclear factor-kappa B1 knockout mice

To investigate the involvement of nuclear factor kappa B1 (NF-kappaB1; p50/p105) in electroacupuncture (EA)-induced analgesia, 2 and 100 Hz EA stimulations were applied at acupoint ST36 (Zusanli) in NF-kappaB1 knockout mice. EA was performed for 30 min and tail-flick latencies (TFLs) were evaluated every 15 min for 1 h. Wild-type mice displayed a 63.3% increase in TFLs compared to baseline after 2 Hz EA, whereas NF-kappaB1+/- mice exhibited a 41.8% increase and NF-kappaB1-/- mice showed only a 3.9% increase of TFLs. The TFLs of 100 Hz EA showed similar trends: a 72.6% increase of TFLs in wild-type, a 38.6% increase in NF-kappaB1+/- and a 9.3% increase in NF-kappaB1-/- mice. The present findings suggest that NF-kappaB1 may play a crucial role in both low and high frequency EA-induced analgesic effects.