Naloxone reverses inhibitory effect of electroacupuncture on sympathetic cardiovascular reflex responses

Effect of Systemic and Auricular Acupuncture with a 2/100 Hz Frequency and Nogier Frequency in Fibromyalgia: a Randomized Clinical Trial, Pilot Study

Background

Fibromyalgia is a syndrome of chronic, generalized muscular pain, accompanied by sleep disturbances, fatigue and cardic autonomic dysfunction that will affect the quality of life. There is currently no gold standard treatment. There are limitations of studies with electroacupuncture in auricular acupuncture.

Objectives

We evaluate the effects of systemic electroacupuncture (EA) with frequencies of 2/100 Hz associated of auricular acupuncture with a Nogier frequency (2.28, 4.56 and 9.12 Hz) for pain intensity, heart rate variability (HRV), and quality of life in fibromyalgia.

Methods

Randomized clinical trial, a pilot study. Eighteen volunteers were randomized into a control group (CG, n = 9) and an experimental group (EG, n = 9). Six systemic EA sessions systemic and auricular were applied in the EG for 20 min, twice a week, for six weeks consecutive. The Numerical Pain Assessment Scale (NPRS), 2010 diagnostic criteria of the American College of Rheumatology (FDC 2010), Fibromyalgia Impact Questionnaire (FIQ) and analysis of HRV were the instruments used. The independent t-test compared to the groups was applied.

Results

There was no statistically significant difference for the primary outcome for NPRS (p > 0.05). In the secondary outcome there was a significant difference in the total score and in some FIQ domains (p = 0.008) and some variables such as pain (p = 0.02) and anxiety (p = 0.006). There was no significant difference for the FDC 2010 and HRV variables (p > 0.05).

Conclusion

2/100 Hz systemic EA associated with the Nogier frequency positively influenced some quality of life variables; however, pain intensity, diagnostic criteria, and HRV variables did not change.

A bibliometric analysis of 100 top-cited journal articles related to acupuncture regulation of the autonomic nervous system

Purpose

Research on the effects of acupuncture on autonomic function has been conducted for several decades, and a few notable studies have emerged in recent years. This study used bibliometric analysis to assess 100 top-cited articles to characterize the current status and research trends over the last three decades.

Methods

The 100 top-cited publications were identified from the Web of Science Core Collection database. The bibliometrix package in R was used for quantitative and qualitative analyses of the publication patterns and the country/region, institution, and author contributions. VOSviewer was used to construct networks based on co-citation analysis of the journals and the keyword co-occurrence.

Results

The 100 top-cited articles were identified with a total of 8,123 citations (range: 37-345). The majority of the articles came from the USA (n = 42), followed by Japan (n = 14) and mainland China (n = 13). Articles from the USA exhibited the largest number of citations (3,582 citations), followed by articles from Japan (1,189 citations), then articles from mainland China (755 citations). Neurosciences/Neurology was the most studied research area (n = 41). The Autonomic Neuroscience: Basic and Clinical published the largest number of papers (n = 14), while Brain Research received the largest number of citations (205 citations). Longhurst JC was the most productive author (10 publications), and Sato A was first among the cited authors (87 citations). The most frequently cited articles that focused on gastrointestinal, cardiovascular, or gynecologic responses to acupuncture regulation of the autonomic nervous system first appeared in the 1990s, peaked in the 2000s, then decreased after 2010. Publication of articles focused on the anti-inflammatory effects of acupuncture associated with autonomic function demonstrated an increasing trend over the last three decades.

Conclusion

From the initial studies focusing on the autonomic mechanism of visceral responses to acupuncture, researchers concentrated on exploring the autonomic mechanism of acupuncture in the control of systemic inflammation. Non-invasive electrical methods that activate somato-autonomic reflexes are current translational directions in clinical practice. Additional investigation of the underlying neuroanatomical basis of somato-autonomic reflexes also is needed.

STAT3 but Not STAT5 Contributes to the Protective Effect of Electroacupuncture Against Myocardial Ischemia/Reperfusion Injury in Mice

Electroacupuncture (EA) can help reduce infarct size and injury resulting from myocardial ischemia/reperfusion (I/R); however, the underlying molecular mechanism remains unknown. We previously reported that STAT5 plays a critical role in the cardioprotective effect of remote ischemic preconditioning (RIPC). Here, we assessed the effects of electroacupuncture pretreatment (EAP) on myocardial I/R injury in the presence and/or absence of Stat5 in mice and investigated whether EAP exerts its cardioprotective effects in a STAT5-dependent manner. Adult Stat5^fl/fl and Stat5-cKO mice were exposed to EAP at Neiguan (PC6) for 7 days before the induction of I/R injury by left anterior descending (LAD) coronary artery ligation. The myocardial infarct size (IS), area at risk, and apoptotic rate of cardiomyocytes were detected. RT-qPCR and western blotting were used to measure gene and protein expression, respectively, in homogenized heart tissues. RNA-seq was used to identify candidate genes and pathways. Our results showed that EAP decreased IS and the rate of cardiomyocyte apoptosis. We further found that STAT5 was activated by EAP in Stat5^fl/fl mice but not in Stat5-cKO mice, whereas the opposite was observed for STAT3. Following EAP, the levels of the antiapoptotic proteins Bcl-xL, Bcl-2, and p-AKT were increased in the presence of Stat5, while that of interleukin 10 (IL-10) was increased in both Stat5^fl/fl and Stat5-cKO. The gene expression profile in heart tissues was different between Stat5^fl/fl and the Stat5-cKO mice with EAP. Importantly, the top 30 DEGs under EAP in the Stat5-cKO mice were enriched in the IL-6/STAT3 signaling pathway. Our results revealed for the first time that the protective effect of EAP following myocardial I/R injury was attributable to, but not dependent on, STAT5. Additionally, we found that EAP could activate STAT3 signaling in the absence of the Stat5 gene, and could also activate antiapoptotic, survival, and anti-inflammatory signaling pathways.

The role of substance P in acupuncture signal transduction and effects

BACKGROUND

Acupuncture has been used to treat a wide variety of diseases, disorders, and conditions for more than 2500 years. While the anatomical structures of acupuncture points (or acupoints) are largely unknown, our previous studies have suggested that many acupoints can be identified as cutaneous neurogenic inflammatory spots (neurogenic spots or Neuro-Sps), arising from the release of neuropeptides from activated small diameter sensory afferents at topographically distinct body surfaces due to the convergence of visceral and somatic afferents. In turn, the neuropeptides released during neurogenic inflammation may play important roles in the effects of acupuncture as well as the formation of active acupoints. Thus, the present study has focused on the role of substance P (SP) in acupuncture signal transduction and effects.

METHODS

Neuro-Sps were detected by using in vivo fluorescence imaging after intravenous injection of Evans blue dye (EBD) and compared with traditional acupoints. Stimulatory effects of the Neuro-Sps were examined in a rat model of immobilization-induced hypertension (IMH). The roles of increased SP in Neuro-Sps were also investigated by using immunohistochemistry, in vivo single-fiber peripheral nerve recordings, and in vivo midbrain extracellular recordings.

RESULTS

Neurogenic inflammation quickly appeared at acupoints on the wrist and was fully developed within 15 min in IMH model. The Neuro-Sps showed an increased release of SP from afferent nerve terminals. Mechanical stimulation of these Neuro-Sps increased cell excitability in the midbrain (rostral ventrolateral medulla) and alleviated the development of hypertension, which was blocked by the local injection of the SP receptor antagonist CP-99994 into Neuro-Sps prior to acupuncture and mimicked by the local injection of capsaicin. Single fiber recordings of peripheral nerves showed that increased SP into the Neuro-Sps elevated the sensitivity of A- and C-fibers in response to acupuncture stimulation. In addition, the discharge rates of spinal wide dynamic response (WDR) neurons significantly increased following SP or acupuncture treatment in Neuro-Sps in normal rats, but decreased following the injection of CP-99994 into Neuro-Sps in IMH rats.

CONCLUSIONS

Our findings suggest that SP released during neurogenic inflammation enhances the responses of sensory afferents to the needling of acupoints and triggers acupuncture signaling to generate acupuncture effects.

Effects of Moxibustion on Stress-Induced Delayed Gastric Emptying via Somatoautonomic Reflex in Rats

Objective: Moxibustion (MOX) is used to treat a wide variety of disorders, including those with gastric symptoms. However, the exact mechanisms underlying the beneficial effects of MOX are unknown. The purpose of this study was to investigate if application of indirect MOX (iMOX) to ST 36 reduces restraint stress (RS)-induced alteration in gastric responses of conscious rats, and if a somatoautonomic reflex mediates gastric emptying (GE). Materials and Methods: One group of rats was fed solid food after 24 hours of fasting. Immediately after food ingestion. These rats were subjected to RS. Ninety minutes after feeding, the rats were euthanized, and their gastric contents were removed to calculate GE. iMOX had been performed at ST 36 bilaterally throughout the stress loading. To investigate if vagal-nerve activity was involved in mediating the stress-induced alterations of GE by iMOX, atropine was intraperitoneally administered to other rats just before initiating RS; bilateral truncal vagotomy had been performed on day 14 before GE measurement. Results: RS delayed GE significantly (42.9 ± 5.8%)in stressed rats, compared to nonstressed rats (68.7 ± 1.8%). iMOX at ST 36 reduced stress-induced inhibition of GE significantly (67.1 ± 2.4%). MOX-mediated reduction of GE disappeared upon atropine injection and vagotomy. Conclusions: RS-induced delayed GE may be ameliorated by iMOX at ST 36. Somatoautonomic, reflex-induced vagal-nerve activity helps mediate the stimulatory effects of iMOX on RS-induced delayed GE. As a complementary and alternative medicine, iMOX may also be advantageous for patients with gastric disorders, such as functional dyspepsia.

Paired mechanical and electrical acupuncture of neurogenic spots induces opioid-mediated suppression of hypertension in rats

While our recent studies have suggested that effective acupoints display neurogenic inflammation and can be identified as neurogenic spots (Neuro-Sps), the optimal stimulation conditions and the underlying mechanisms remain uncharacterized. We developed a combined mechano-electrical acupuncture device (MEA) and examined the effects of acupuncture at Neuro-Sps on systolic blood pressure (BP) in a rat model of immobilization-induced hypertension (IMH) and the mediation of endogenous opioid systems in its effect. Cutaneous neurogenic spots were found mostly in the forelimb. Electrical and mechanical acupuncture of Neuro-Sps increased 22-kHz ultrasonic vocalizations (USVs), c-Fos expression and cell excitability in the midbrain and synergistically alleviated the development of hypertension following immobilization stress, which was prevented by administration of the opioid antagonist naloxone into the rostral ventrolateral medulla (rVLM). These findings suggest that mechanical and electrical stimulation at Neuro-Sps suppresses the development of hypertension via mediation of the endogenous opioid system.

Acupuncture activates a direct pathway from the nucleus tractus solitarii to the rostral ventrolateral medulla

Our previous studies have shown that electroacupuncture (EA) at the Jianshi-Neiguan acupoints (P5-6, overlying the median nerve) attenuates sympathoexcitatory responses through its influence on neuronal activity in the rostral ventrolateral medulla (rVLM). The nucleus tractus solitarii (NTS) receives input from somatic nerve stimulation. Connections between the NTS and the rVLM during EA stimulation have not been investigated and thus were the focus of the present study. Seven to ten days after unilateral microinjection of a rhodamine-conjugated microsphere retrograde tracer (100 nl) into the rVLM, rats were subjected to EA or sham-EA without electrical stimulation. EA was performed for 30 min at the P5-6 acupoints bilaterally. Perikarya containing the microsphere tracer were found in the NTS of both groups. Compared to controls (needle placement without electrical stimulation, n = 7), c-Fos immunoreactivity and neurons double-labeled with c-Fos, an immediate early gene, and the tracer were significantly increased in the NTS of EA-treated rats (all P < 0.05; n = 8), particularly, in the medial and lateral subdivisions of NTS at subpostremal and obex levels. These results suggest that EA at the P5-6 acupoints activates NTS neurons. Furthermore, EA-activated NTS neurons directly project to the rVLM and likely influence the rVLM activity.

Moxibustion Modulates Sympathoexcitatory Cardiovascular Reflex Responses Through Paraventricular Nucleus

Electroacupuncture (EA) point specific (ST36-37) stimulation decreases cardiovascular reflex responses through supraspinal regions such as the hypothalamic paraventricular nucleus (PVN) while mechanical stimulation of acupoints decreases pressor responses through peripheral thermal transient receptor potential vanilloid type-1 (TRPV1). Moxibustion generating heat applied at acupoint in combination with antihypertensive drugs decreases elevated blood pressure. We hypothesized that moxibustion modulates sympathoexcitatory cardiovascular responses through the hypothalamic PVN and peripheral heat sensitive TRPV1 in the absence of antihypertensive drugs. Rats were anesthetized, ventilated, and heart rate and mean blood pressure were monitored. Gastric distention induced consistent pressor reflex responses every 10-min. Thirty-minutes of bilateral moxibustion at the acupoint ST36, overlying the deep peroneal nerves, reduced the gastric distention evoked elevation in blood pressure. Blood pressure reflex responses were not reduced by both EA and moxibustion at G39. The moxibustion inhibition but not EA inhibition of the cardiovascular responses was reversed with blockade of local heat sensitive TRPV1 at ST36. Accordingly, activation of thermal TRPV1 by moxibustion at an average of 44.2°C in contrast to 40°C reduced the pressor responses. Naloxone, an opioid receptor antagonist, microinjected into PVN inhibited transiently the effect of moxibustion. Thus, activation of peripheral heat sensitive TRPV1 mediated the moxibustion-inhibition, but not EA-inhibition, of sympathoexcitatory cardiovascular reflex responses through hypothalamic PVN opioid system.

Chronic median nerve modulation reduces ventricular arrhythmia and improves ventricular function in a postmyocardial infarction rabbit model

AIM

Median nerve stimulation (MNS) is a novel neuromodulation approach for treatment of ventricular arrhythmia, but little is known about its chronic effects. The aim of this study was to investigate the effects of chronic MNS on ventricular arrhythmia and ventricular dysfunction postmyocardial infarction (MI).

METHOD

Two weeks after MI, 12 rabbits were randomly divided into control and MNS groups, and chronic MNS was performed in MNS group for 2 weeks. Ventricular function and arrhythmias; sympathetic innervation and activity; and interleukin-1 β (IL-1 β) and norepinephrine (NE) levels were analyzed.

RESULTS

Both the total number of premature ventricular complex and episodes of ventricular tachycardia were lower in MNS group than in control group (20 560 ± 10 314 beats vs 70 079 ± 37 184 beats, P = .021, and 115 ± 63 episodes vs 307 ± 164 episodes, P = .034, respectively). Compared with control group, MNS decreased the cardiac sympathetic nerve density and level of circulating NE in MNS group (1798.42 ± 644.07 μm² /mm² vs 1003.79 ± 453.00 μm² /mm²_, P = .041, and 20.86 ± 4.54 pg/mL vs 11.07 ± 1.43 pg/mL, P = .002, respectively). MNS also improved the left ventricular ejection fraction (59.07 ± 1.91% vs 49.77 ± 3.47%, P = .003) and inhibited the level of IL-1 β in serum (69.19 ± 4.71 pg/mL vs 85.93 ± 12.80 pg/mL, P = .013).

CONCLUSION

Chronic MNS appears to protect against ventricular arrhythmia and improves ventricular function post-MI, which may be mediated by suppressing cardiac sympathetic activity and anti-inflammatory effects.

Modulation of Neurally Mediated Vasodepression and Bradycardia by Electroacupuncture through Opioids in Nucleus Tractus Solitarius

Stimulation of vagal afferent endings with intravenous phenylbiguanide (PBG) causes both bradycardia and vasodepression, simulating neurally mediated syncope. Activation of µ-opioid receptors in the nucleus tractus solitarius (NTS) increases blood pressure. Electroacupuncture (EA) stimulation of somatosensory nerves underneath acupoints P5–6, ST36–37, LI6–7 or G37–39 selectively but differentially modulates sympathoexcitatory responses. We therefore hypothesized that EA-stimulation at P5–6 or ST36–37, but not LI6–7 or G37–39 acupoints, inhibits the bradycardia and vasodepression through a µ-opioid receptor mechanism in the NTS. We observed that stimulation at acupoints P5–6 and ST36–37 overlying the deep somatosensory nerves and LI6–7 and G37–39 overlying cutaneous nerves differentially evoked NTS neural activity in anesthetized and ventilated animals. Thirty-min of EA-stimulation at P5–6 or ST36–37 reduced the depressor and bradycardia responses to PBG while EA at LI6–7 or G37–39 did not. Congruent with the hemodynamic responses, EA at P5–6 and ST36–37, but not at LI6–7 and G37–39, reduced vagally evoked activity of cardiovascular NTS cells. Finally, opioid receptor blockade in the NTS with naloxone or a specific μ-receptor antagonist reversed P5–6 EA-inhibition of the depressor, bradycardia and vagally evoked NTS activity. These data suggest that point specific EA stimulation inhibits PBG-induced vasodepression and bradycardia responses through a μ-opioid mechanism in the NTS.

Repetitive Electroacupuncture Attenuates Cold-Induced Hypertension through Enkephalin in the Rostral Ventral Lateral Medulla

Acupuncture lowers blood pressure (BP) in hypertension, but mechanisms underlying its action are unclear. To simulate clinical studies, we performed electroacupuncture (EA) in unanesthetized rats with cold-induced hypertension (CIH) induced by six weeks of cold exposure (6 °C). EA (0.1 - 0.4 mA, 2 Hz) was applied at ST36-37 acupoints overlying the deep peroneal nerve for 30 min twice weekly for five weeks while sham-EA was conducted with the same procedures as EA except for no electrical stimulation. Elevated BP was reduced after six sessions of EA treatment and remained low 72 hrs after EA in 18 CIH rats, but not in sham-EA (n = 12) and untreated (n = 6) CIH ones. The mRNA level of preproenkephalin in the rostral ventrolateral medulla (rVLM) 72 hr after EA was increased (n = 9), compared to the sham-EA (n = 6), untreated CIH rats (n = 6) and normotensive control animals (n = 6). Microinjection of ICI 174,864, a δ-opioid receptor antagonist, into the rVLM of EA-treated CIH rats partially reversed EA's effect on elevated BP (n = 4). Stimulation of rVLM of CIH rats treated with sham-EA using a δ-opioid agonist, DADLE, decreased BP (n = 6). These data suggest that increased enkephalin in the rVLM induced by repetitive EA contributes to BP lowering action of EA.

Electroacupuncture pretreatment induces rapid tolerance to bupivacaine cardiotoxicity in rats

BACKGROUND

Evidence suggests that electroacupuncture (EA) protects against arrhythmia and myocardial injury induced by myocardial ischaemia-reperfusion. However, to our knowledge, it remains unknown whether EA could alleviate bupivacaine-induced cardiotoxicity. Therefore, we aimed to explore the effect of EA pretreatment on bupivacaine-induced cardiac arrest and outcomes of cardiopulmonary resuscitation (CPR) in rats.

METHODS

24 adult male Sprague-Dawley rats were randomly divided into two groups: EA (n=12), and minimal acupuncture (MA) (n=12). Rats in both groups were needled at bilateral PC6, ST36, and ST40. Needles in the EA group were electrically stimulated for 60 min. ECG and invasive arterial blood pressure measurements were recorded. Two hours after EA or MA, 10 mg/kg bupivacaine was infused intravenously at a rate of 5 mg/kg/min in all rats. Rats suffering cardiac arrest were immediately subjected to CPR. At the end of the experiment, arterial blood samples were taken from surviving rats for blood gas analysis.

RESULTS

The time from bupivacaine infusion until 20% prolongation of the QRS and QT interval, and the time to cardiac arrest, were notably increased among the rats pretreated with EA. Moreover, EA pretreatment significantly improved mean arterial pressure and heart rate at all monitored points after bupivacaine infusion. The proportion of animals surviving was higher in the EA group (9/12) than the MA group (3/12) at the end of experiment (p=0.039).

CONCLUSIONS

Tolerance to bupivacaine-induced cardiotoxicity appeared to be increased following EA pre-treatment. The mechanism of action underlying the effects of EA on bupivacaine-induced cardiotoxicity requires further investigation.

Paraventricular Nucleus Modulates Excitatory Cardiovascular Reflexes during Electroacupuncture

The paraventricular nucleus (PVN) regulates sympathetic outflow and blood pressure. Somatic afferent stimulation activates neurons in the hypothalamic PVN. Parvocellular PVN neurons project to sympathoexcitatory cardiovascular regions of the rostral ventrolateral medulla (rVLM). Electroacupuncture (EA) stimulates the median nerve (P5-P6) to modulate sympathoexcitatory responses. We hypothesized that the PVN and its projections to the rVLM participate in the EA-modulation of sympathoexcitatory cardiovascular responses. Cats were anesthetized and ventilated. Heart rate and mean blood pressure were monitored. Application of bradykinin every 10-min on the gallbladder induced consistent pressor reflex responses. Thirty-min of bilateral EA stimulation at acupoints P5-P6 reduced the pressor responses for at least 60-min. Inhibition of the PVN with naloxone reversed the EA-inhibition. Responses of cardiovascular barosensitive rVLM neurons evoked by splanchnic nerve stimulation were reduced by EA and then restored with opioid receptor blockade in the PVN. EA at P5-P6 decreased splanchnic evoked activity of cardiovascular barosensitive PVN neurons that also project directly to the rVLM. PVN neurons labeled with retrograde tracer from rVLM were co-labeled with μ-opioid receptors and juxtaposed to endorphinergic fibers. Thus, the PVN and its projection to rVLM are important in processing acupuncture modulation of elevated blood pressure responses through a PVN opioid mechanism.

Electroacupuncture of neiguan (PC 6) inhibits enhanced voltage-gated sodium currents in ischemic ventricular myocytes

OBJECTIVE

To examine the effect of electroacupuncture (EA) at bilateral Neiguan (PC 6) on voltage-gated Na+ currents (I(Na)) and channels (Na(v)) in ischemic ventricular myocytes.

METHODS

EA serum was prepared from six male adult Sprague-Dawley rats that had received EA at bilateral Neiguan (PC 6). Eighteen ventricular myocytes were prepared from six SD rats using an enzymolysis approach. Myocardial ischemia was mimicked by perfusion of ischemic solution. Whole-cell patch-clamping was used to record three currents evoked from isolated cells. The first current was the control, and recorded in absence of ischemic solution current. The second was the ischemic current, and recorded after perfusion of ischemic solution for 5 min, while the EA current was last, and recorded after perfusion of EA serum for 5 min. Na(v) kinetic curves were fitted using related formulas.

RESULTS

Compared with those in controls, in the presence of ischemic solution, peak amplitudes of I(Na) significantly increased from - 40 mV to +30 mV, and half-maximal inactivation potentials of Na(v) increased significantly, while half-maximal activation potentials, slope factors and the recovery time from inactivation to activation of Na(v) were unchanged. Compared with those in the ischemic solution, in the presence of EA serum, peak ischemic current amplitudes significantly reduced from - 40 mV to +40 mV, and half-maximal inactivation potentials were restored, while half-maximal activation potentials, slope factors and the recovery time from inactivation to activation of Na(v) were unchanged.

CONCLUSION

EA at bilateral Neiguan (PC 6) can reduce enhanced I(Na) via restoration of delayed Na(v) inactivation in ischemic ventricular myocytes.

GABA in nucleus tractus solitarius participates in electroacupuncture modulation of cardiopulmonary bradycardia reflex

Phenylbiguanide (PBG) stimulates cardiopulmonary receptors and cardiovascular reflex responses, including decreases in blood pressure and heart rate mediated by the brain stem parasympathetic cardiac neurons in the nucleus ambiguus and nucleus tractus solitarius (NTS). Electroacupuncture (EA) at P5-6 stimulates sensory fibers in the median nerve and modulates these reflex responses. Stimulation of median nerves reverses bradycardia through action of γ-aminobutyric acid (GABA) in the nucleus ambiguus, important in the regulation of heart rate. We do not know whether the NTS or the neurotransmitter mechanisms in this nucleus participate in these modulatory actions by acupuncture. We hypothesized that somatic nerve stimulation during EA (P5-6) modulates cardiopulmonary inhibitory responses through a GABAergic mechanism in the NTS. Anesthetized and ventilated cats were examined during either PBG or direct vagal afferent stimulation while 30 min of EA was applied at P5-6. Reflex heart rate and blood pressure responses and NTS-evoked discharge were recorded. EA reduced the PBG-induced depressor and bradycardia reflexes by 67% and 60%, respectively. Blockade of GABAA receptors in the NTS reversed EA modulation of bradycardia but not the depressor response. During EA, gabazine reversed the vagally evoked discharge activity of cardiovascular NTS neurons. EA modulated the vagal-evoked cardiovascular NTS cellular activity for 60 min. Immunohistochemistry using triple labeling showed GABA immunoreactive fibers juxtaposed to glutamatergic nucleus ambiguus-projecting NTS neurons in rats. These glutamatergic neurons expressed GABAA receptors. These findings suggest that EA inhibits PBG-evoked bradycardia and vagally evoked NTS activity through a GABAergic mechanism, likely involving glutamatergic nucleus ambiguus-projecting NTS neurons.

Electro-acupuncture at Neiguan pretreatment alters genome-wide gene expressions and protects rat myocardium against ischemia-reperfusion

This study investigated genome-wide gene expressions and the cardioprotective effects of electro-acupuncture pretreatment at the PC6 Neiguan acupoint on myocardial ischemia reperfusion (I/R) injury. Male SD rats were randomly divided into four groups: sham operation (SO), I/R, electro-acupuncture at the PC6 Neiguan acupoint pretreatment (EA) and electro-acupuncture at non-acupoint pretreatment (NA). Compared with the I/R group, the survival rate of the EA group was significantly increased, the arrhythmia score, infarction area, serum concentrations of CK, LDH and CK-Mb and plasma level of cTnT were significantly decreased. RNA-seq results showed that 725 genes were up-regulated and 861 genes were down-regulated under I/R conditions compared to the SO group; both EA and NA reversed some of these gene expression levels (592 in EA and 238 in NA group). KEGG pathway analysis indicated that these genes were involved in multiple pathways, including ECM, MAPK signaling, apoptosis, cytokine and leukocyte pathways. In addition, some pathways were uniquely regulated by EA, but not NA pretreatment, such as oxidative stress, cardiac muscle contraction, gap junction, vascular smooth muscle contraction, hypertrophic, NOD-like receptor, and P53 and B-cell receptor pathways. This study was first to reveal the gene expression signatures of acute myocardial I/R injury and electro-acupuncture pretreatment in rats.

Electroacupuncture improves cardiac function and remodeling by inhibition of sympathoexcitation in chronic heart failure rats

Chronic heart failure (CHF) is responsible for significant morbidity and mortality worldwide, mainly as a result of neurohumoral activation. Acupuncture has been used to treat a wide range of diseases and conditions. In this study, we investigated the effects of electroacupuncture (EA) on the sympathetic nerve activity, heart function, and remodeling in CHF rats after ligation of the left anterior descending coronary artery. CHF rats were randomly selected to EA and control groups for acute and chronic experiments. In the acute experiment, both the renal sympathetic nerve activity and cardiac sympathetic afferent reflex elicited by epicardial application of capsaicin were recorded. In the chronic experiment, we performed EA for 30 min once a day for 1 wk to test the long-term EA effects on heart function, remodeling, as well as infarct size in CHF rats. The results show EA significantly decreased the renal sympathetic nerve activity effectively, inhibited cardiac sympathetic afferent reflex, and lowered the blood pressure of CHF rats. Treating CHF rats with EA for 1 wk dramatically increased left ventricular ejection fraction and left ventricular fraction shortening, reversed the enlargement of left ventricular end-systolic dimension and left ventricular end-diastolic dimension, and shrunk the infarct size. In this experiment, we demonstrated EA attenuates sympathetic overactivity. Additionally, long-term EA improves cardiac function and remodeling and reduces infarct size in CHF rats. EA is a novel and potentially useful therapy for treating CHF.

Neuronal Activity Stimulated by Liquid Substrates Injection at Zusanli (ST36) Acupoint: The Possible Mechanism of Aquapuncture

Aquapuncture is a modified acupuncture technique and it is generally accepted that it has a greater therapeutic effect than acupuncture because of the combination of the acupoint stimulation and the pharmacological effect of the drugs. However, to date, the mechanisms underlying the effects of aquapuncture remain unclear. We hypothesized that both the change in the local spatial configuration and the substrate stimulation of aquapuncture would activate neuronal signaling. Thus, bee venom, normal saline, and vitamins B1 and B12 were injected into a Zusanli (ST36) acupoint as substrate of aquapuncture, whereas a dry needle was inserted into ST36 as a control. After aquapuncture, activated neurons expressing Fos protein were mainly observed in the dorsal horn of the spinal cord in lumbar segments L3–5, with the distribution nearly identical among all groups. However, the bee venom injection induced significantly more Fos-expressing neurons than the other substrates. Based on these data, we suggest that changes in the spatial configuration of the acupoint activate neuronal signaling and that bee venom may further strengthen this neuronal activity. In conclusion, the mechanisms for the effects of aquapuncture appear to be the spatial configuration changes occurring within the acupoint and the ability of injected substrates to stimulate neuronal activity.

Electroacupuncture modulation of reflex hypertension in rats: role of cholecystokinin octapeptide

Acupuncture or electroacupuncture (EA) potentially offers a nonpharmacological approach to reduce high blood pressure (BP). However, ~70% of the patients and animal subjects respond to EA, while 30% do not. EA acts, in part, through an opioid mechanism in the rostral ventrolateral medulla (rVLM) to inhibit sympathoexcitatory reflexes induced by gastric distention. CCK-8 opposes the action of opioids during analgesia. Therefore, we hypothesized that CCK-8 in the rVLM antagonizes EA modulation of sympathoexcitatory cardiovascular reflex responses. Male rats anesthetized with ketamine and α-chloralose subjected to repeated gastric distension every 10 min were examined for their responsiveness to EA (2 Hz, 0.5 ms, 1-4 mA) at P5-P6 acupoints overlying median nerve. Repeated gastric distension every 10 min evoked consistent sympathoexcitatory responses. EA at P5-P6 modulated gastric distension-induced responses. Microinjection of CCK-8 in the rVLM reversed the EA effect in seven responders. The CCK1 receptor antagonist devazepide microinjected into the rVLM converted six nonresponders to responders by lowering the reflex response from 21 ± 2.2 to 10 ± 2.9 mmHg (first vs. second application of EA). The EA modulatory action in rats converted to responders with devazepide was reversed with rVLM microinjection of naloxone (n = 6). Microinjection of devazepide in the absence of a second application of EA did not influence the primary pressor reflexes of nonresponders. These data suggest that CCK-8 antagonizes EA modulation of sympathoexcitatory cardiovascular responses through an opioid mechanism and that inhibition of CCK-8 can convert animals that initially are unresponsive to EA to become responsive.

From Acupuncture to Interaction between δ-Opioid Receptors and Na (+) Channels: A Potential Pathway to Inhibit Epileptic Hyperexcitability

Epilepsy is one of the most common neurological disorders affecting about 1% of population. Although the precise mechanism of its pathophysiological changes in the brain is unknown, epilepsy has been recognized as a disorder of brain excitability characterized by recurrent unprovoked seizures that result from the abnormal, excessive, and synchronous activity of clusters of nerve cells in the brain. Currently available therapies, including medical, surgical, and other strategies, such as ketogenic diet and vagus nerve stimulation, are symptomatic with their own limitations and complications. Seeking new strategies to cure this serious disorder still poses a big challenge to the field of medicine. Our recent studies suggest that acupuncture may exert its antiepileptic effects by normalizing the disrupted neuronal and network excitability through several mechanisms, including lowering the overexcited neuronal activity, enhancing the inhibitory system, and attenuating the excitatory system in the brain via regulation of the interaction between δ -opioid receptors (DOR) and Na(+) channels. This paper reviews the progress in this field and summarizes new knowledge based on our work and those of others.

Acupuncture's Cardiovascular Actions: A Mechanistic Perspective

Over the last several decades, there has been an explosion of articles on acupuncture, including studies that have begun to explore mechanisms underlying its analgesic and cardiovascular actions. Modulation of cardiovascular function is most effective during manual and low-frequency, low-intensity electroacupuncture (EA) at a select set of acupoints situated along meridians located over deep somatic nerves on the upper and lower extremities. Stimulation at these acupoints activates underlying sensory neural pathways that project to a number of regions in the central nervous system (CNS) that ultimately regulate autonomic outflow and hence cardiovascular function. A long-loop pathway involving the hypothalamus, midbrain, and medulla underlies EA modulation of reflex increases in blood pressure (BP). Actions of excitatory and inhibitory neurotransmitters in the supraspinal CNS underlie processing of the somatic input and adjustment of autonomic outflow during EA. Acupuncture also decreases elevated blood pressure through actions in the thoracic spinal cord. Reflexes that lower BP likewise are modulated by EA through its actions on sympathetic and parasympathetic nuclei in the medulla. The autonomic influence of acupuncture is slow in onset but prolonged in duration, typically lasting beyond the period of stimulation. Clinical studies suggest that acupuncture can be used to treat cardiac diseases, such as myocardial ischemia and hypertension, associated with overactivity of the sympathetic nervous system.

The Possible Neuronal Mechanism of Acupuncture: Morphological Evidence of the Neuronal Connection between Groin A-Shi Point and Uterus

Somatovisceral reflex suggested that the somatic stimulation could affect visceral function like acupuncture which treats diseases by stimulating acupoints. The neuronal connection between somatic point and visceral organ was not clear. Uterine pain referred to the groin region has long been recognized clinically. Wesselmann, using neurogenic plasma extravasation method, showed that uterine pain was referred to the groin region through a neuronal mechanism (Wesselmann and Lai 1997). This connection could be considered through the somatovisceral reflex pathway. However, the relay center of this pathway is still not clearly identified. In the present study, bee venom was injected in the groin region to induce central Fos expression to map the sensory innervation of groin region. Pseudorabies virus (PrV), a transneuronal tracer, was injected in the uterus to identify the higher motor control of the uterus. Immunohistochemistry staining revealed the Fos expression and PrV-infected double-labeled neurons in the nucleus of solitary tract (NTS), the dorsal motor nucleus of vagus (DMX), and the paraventricular hypothalamic nucleus (PVN). These results suggest a somatoparasympathetic neuronal connection (groin-spinal dorsal horn-NTS/DMX-uterus) and a somatosympathetic neuronal connection (groin-spinal dorsal horn-NTS-PVN-uterus). These two neuronal connections could be the prerequisites to the neuronal basis of the somatovisceral reflex and also the neuronal mechanism of acupuncture.

Medullary GABAergic mechanisms contribute to electroacupuncture modulation of cardiovascular depressor responses during gastric distention in rats

Electroacupuncture (EA) at P5-P6 acupoints overlying the median nerves typically reduces sympathoexcitatory blood pressure (BP) reflex responses in eucapnic rats. Gastric distention in hypercapnic acidotic rats, by activating both vagal and sympathetic afferents, decreases heart rate (HR) and BP through actions in the rostral ventrolateral medulla (rVLM) and nucleus ambiguus (NAmb), leading to sympathetic withdrawal and parasympathetic activation, respectively. A GABAA mechanism in the rVLM mediates the decreased sympathetic outflow. The present study investigated the hypothesis that EA modulates gastric distention-induced hemodynamic depressor and bradycardia responses through nuclei that process parasympathetic and sympathetic outflow. Anesthetized hypercapnic acidotic rats manifested repeatable decreases in BP and HR with gastric distention every 10 min. Bilateral EA at P5-P6 for 30 min reversed the hypotensive response from -26 ± 3 to -6 ± 1 mmHg and the bradycardia from -35 ± 11 to -10 ± 3 beats/min for a period that lasted more than 70 min. Immunohistochemistry and in situ hybridization to detect c-Fos protein and GAD 67 mRNA expression showed that GABAergic caudal ventral lateral medulla (cVLM) neurons were activated by EA. Glutamatergic antagonism of cVLM neurons with kynurenic acid reversed the actions of EA. Gabazine used to block GABAA receptors microinjected into the rVLM or cVLM reversed EA's action on both the reflex depressor and bradycardia responses. EA modulation of the decreased HR was inhibited by microinjection of gabazine into the NAmb. Thus, EA through GABAA receptor mechanisms in the rVLM, cVLM, and NAmb modulates gastric distention-induced reflex sympathoinhibition and vagal excitation.

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.

Repetitive electroacupuncture causes prolonged increased met-enkephalin expression in the rVLM of conscious rats

Enkephalinergic neurons in the rostral ventrolateral medulla (rVLM), an important presympathetic region in the brainstem, are activated by 30 min of low frequency (2 Hz) electroacupuncture (EA) at acupoints P5-P6, which overlie the median nerves. To more closely model the clinical application of acupuncture, we administered EA for 30 min twice over a 72 h period to unsedated conscious rats to examine its prolonged action. We hypothesized that repetitive EA would increase preproenkephalin mRNA and met-enkephalin in the rVLM of unsedated conscious rats. Rats received either EA (1-4 mA, 0.5 ms, 2 Hz) or sham stimulation (needle placement without electrical stimulation) twice at P5-P6 acupoints bilaterally. Preproenkephalin mRNA and its peptide met-enkephalin in the rVLM were measured 24 or 48 h after the final EA or sham procedure. Relative ratios of preproenkephalin mRNA levels (normalized with the 18S housekeeping gene) were almost doubled at 24h compared to sham (6.1 ± 0.79 vs. 3.1 ± 0.47). Met-enkephalin measured in rVLM tissue pooled from several rats exposed to the same treatment was increased by repeated EA by 68% after 24h and 51% after 48h, relative to sham. These findings suggest that repeated application of EA in the conscious rats enhances transcription and translation of enkephalin in rVLM for days. Since opioids in the rVLM contribute importantly to the action of EA on sympathetic outflow, this mechanism may contribute to the prolonged action of acupuncture on elevated blood pressure in patients.

The influence of PC6 on cardiovascular disorders: a review of central neural mechanisms

PC6 is a classic acupuncture point in traditional Chinese medicine. It is considered to be effective when treating cardiovascular disorders. In the present review the authors have focused on the neurophysiological bases of the effects of PC6 stimulation on cardiovascular mechanisms. Experimental studies have shown that the hypothalamic rostral ventrolateral medulla, arcuate nucleus and ventrolateral periaqueductal gray are involved in acupuncture attenuation of sympathoexcitatory cardiovascular reflex responses. This long-loop pathway also appears to contribute to the long-lasting, acupuncture-mediated attenuation of sympathetic premotor outflow and excitatory cardiovascular reflex responses. Acupuncture of PC6 modulates the activity in the cardiovascular system, an effect that may be attributed to attenuation of sympathoexcitatory cardiovascular reflex responses.

Cardioprotection of electroacupuncture against myocardial ischemia-reperfusion injury by modulation of cardiac norepinephrine release

Augmentation of cardiac sympathetic tone during myocardial ischemia has been shown to increase myocardial O(2) demand and infarct size as well as induce arrhythmias. We have previously demonstrated that electroacupuncture (EA) inhibits the visceral sympathoexcitatory cardiovascular reflex. The purpose of this study was to determine the effects of EA on left ventricular (LV) function, O(2) demand, infarct size, arrhythmogenesis, and in vivo cardiac norepinephrine (NE) release in a myocardial ischemia-reperfusion model. Anesthetized rabbits (n = 36) underwent 30 min of left anterior descending coronary artery occlusion followed by 90 min of reperfusion. We evaluated myocardial O(2) demand, infarct size, ventricular arrhythmias, and myocardial NE release using microdialysis under the following experimental conditions: 1) untreated, 2) EA at P5-6 acupoints, 3) sham acupuncture, 4) EA with pretreatment with naloxone (a nonselective opioid receptor antagonist), 5) EA with pretreatment with chelerythrine (a nonselective PKC inhibitor), and 6) EA with pretreatment with both naloxone and chelerythrine. Compared with the untreated and sham acupuncture groups, EA resulted in decreased O(2) demand, myocardial NE concentration, and infarct size. Furthermore, the degree of ST segment elevation and severity of LV dysfunction and ventricular arrhythmias were all significantly decreased (P < 0.05). The cardioprotective effects of EA were partially blocked by pretreatment with naloxone or chelerythrine alone and completely blocked by pretreatment with both naloxone and chelerythrine. These results suggest that the cardioprotective effects of EA against myocardial ischemia-reperfusion are mediated through inhibition of the cardiac sympathetic nervous system as well as opioid and PKC-dependent pathways.

Acupuncture for posttraumatic stress disorder: conceptual, clinical, and biological data support further research

Posttraumatic stress disorder (PTSD) is common, debilitating, and has highly heterogeneous clinical and biological features. With the exception of one published preliminary clinical trial, rationale in support of the efficacy of acupuncture, a modality of Chinese medicine (CM), for PTSD has not been well described. This is a focused review of conceptual and clinical features of PTSD shared by modern western medicine (MWM) and CM, and of biological mechanisms of acupuncture that parallel known PTSD pathology. MWM and CM both recognize individual developmental variables and interactions between external conditions and internal responses in the genesis of PTSD. There is one published and one unpublished clinical trial that preliminarily support the efficacy of acupuncture for PTSD. Although there have been no mechanistic studies of acupuncture in human PTSD, extant research shows that acupuncture has biological effects that are relevant to PTSD pathology. Conceptual, clinical, and biological data support possible efficacy of acupuncture for PTSD. However, further definitive research about simultaneous clinical and biological effects is needed to support the use of acupuncture for PTSD in health care systems.

Activation of reciprocal pathways between arcuate nucleus and ventrolateral periaqueductal gray during electroacupuncture: involvement of VGLUT3

Electroacupuncture (EA) at the Jianshi-Neiguan acupoints (P5-P6, overlying the median nerve) attenuates sympathoexcitatory responses through activation of the arcuate nucleus (ARC) and ventrolateral periaqueductal gray (vlPAG). Activation of the ARC or vlPAG respectively leads to neuronal excitation of the both nuclei during EA. However, direct projections between these two nuclei that could participate in central neural processing during EA have not been identified. The vesicular glutamate transporter 3 (VGLUT3) marks glutamatergic neurons. Thus, the present study evaluated direct neuronal projections between the ARC and vlPAG during EA, focusing on neurons containing VGLUT3. Seven to ten days after unilateral microinjection of a rodamine-conjugated microsphere retrograde tracer (100nl) into the vlPAG or ARC, rats were subjected to EA or served as a sham-operated control. Low frequency (2Hz) EA was performed bilaterally for 30min at the P5-P6 acupoints. Perikarya containing the microsphere tracer were found in the ARC and vlPAG of both groups. Compared to controls (needle placement without electrical stimulation), c-Fos immunoreactivity and neurons double-labeled with c-Fos, an immediate early gene and the tracer were increased significantly in the ARC and vlPAG of EA-treated rats (both P<0.01). Moreover, some neurons were triple-labeled with c-Fos, the retrograde tracer and VGLUT3 in the two nuclei following EA stimulation (P<0.01, both nuclei). These results suggest that direct reciprocal projections between the ARC and vlPAG are available to participate in prolonged modulation by EA of sympathetic activity and that VGLUT3-containing neurons are an important neuronal phenotype involved in this process.

Nucleus raphe pallidus participates in midbrain-medullary cardiovascular sympathoinhibition during electroacupuncture

We have shown that electroacupuncture (EA) inhibits sympathoexcitatory rostral ventrolateral medulla (rVLM) neurons and reflex responses following activation of a long-loop pathway in the arcuate nucleus and ventrolateral periaqueductal gray (vlPAG). Additionally, EA at P 5-6 acupoints (overlying the median nerve) activates serotonin-containing neurons in the nucleus raphé pallidus (NRP), which, in turn, inhibit rVLM neurons. Although direct projections from the vlPAG to the rVLM exist, it is uncertain whether an indirect pathway through the NRP serves an important role in vlPAG-rVLM cardiovascular modulation. Therefore, the splanchnic nerve (SN) was stimulated to induce cardiovascular sympathoexcitatory reflexes, and EA was applied at P 5-6 acupoints in α-chloralose-anesthetized cats. A single-barreled recording electrode was inserted into the NRP or rVLM. Microinjection of DL-homocysteic acid (DLH) into the vlPAG increased the NRP neuronal response to SN stimulation (5 ± 1 to 12 ± 2 spikes/30 stim). Likewise, EA at P 5-6 for 30 min increased the NRP response to SN stimulation (3 ± 1 to 10 ± 2 spikes/30 stim), an effect that could be blocked by microinjection of kynurenic acid (KYN) into the caudal vlPAG. Furthermore, the reflex increase in blood pressure induced by application of bradykinin to the gallbladder and the rVLM cardiovascular presympathetic neuronal response to SN stimulation was inhibited by injection of DLH into the vlPAG, a response that was reversed by injection of KYN into the NRP. These results indicate that EA activates the vlPAG, which excites the NRP to, in turn, inhibit rVLM presympathetic neurons and reflex cardiovascular sympathoexcitatory responses.

Serotonergic projection from nucleus raphe pallidus to rostral ventrolateral medulla modulates cardiovascular reflex responses during acupuncture

We have demonstrated that stimulation of somatic afferents during electroacupuncture (EA) inhibits sympathoexcitatory cardiovascular rostral ventrolateral medulla (rVLM) neurons and reflex responses. Furthermore, EA at P5-P6 acupoints over the median nerve on the forelimb activate serotonin (5-HT)-containing neurons in the nucleus raphe pallidus (NRP). The present study, therefore, examined the role of the NRP and its synaptic input to neurons in the rVLM during the modulatory influence of EA. Since serotonergic neurons in the NRP project to the rVLM, we hypothesized that the NRP facilitates EA inhibition of the cardiovascular sympathoexcitatory reflex response through activation of 5-HT1A receptors in the rVLM. Animals were anesthetized and ventilated, and heart rate and blood pressure were monitored. We then inserted microinjection and recording electrodes in the rVLM and NRP. Application of bradykinin (10 microg/ml) on the gallbladder every 10 min induced consistent excitatory cardiovascular reflex responses. Stimulation with EA at P5-P6 acupoints reduced the increase in blood pressure from 41+/-4 to 22+/-4 mmHg for more than 70 min. Inactivation of NRP with 50 nl of kainic acid (1 mM) reversed the EA-related inhibition of the cardiovascular reflex response. Similarly, blockade of 5-HT1A receptors with the antagonist WAY-100635 (1 mM, 75 nl) microinjected into the rVLM reversed the EA-evoked inhibition. In the absence of EA, NRP microinjection of dl-homocysteic acid (4 nM, 50 nl), to mimic EA, reduced the cardiovascular and rVLM neuronal excitatory reflex response during stimulation of the gallbladder and splanchnic nerve, respectively. Blockade of 5-HT1A receptors in the rVLM reversed the NRP dl-homocysteic acid inhibition of the cardiovascular and neuronal reflex responses. Thus activation of the NRP, through a mechanism involving serotonergic neurons and 5-HT1A receptors in the rVLM during somatic stimulation with EA, attenuates sympathoexcitatory cardiovascular reflexes.

Electroacupuncture enhances preproenkephalin mRNA expression in rostral ventrolateral medulla of rats

Electroacupuncture (EA) causes prolonged suppression of reflex elevations in blood pressure for at least 60min in anesthetized preparations. Thus, EA can modify sympathetic outflow and elevated blood pressure through actions in a number of hind brain regions, including the rostral ventrolateral medulla (rVLM). Since our previous data show that the opioid system plays a role in EA-related prolonged inhibition of presympathetic neuronal activity in the rVLM, we postulated that EA increases preproenkephalin (PPE) mRNA in this region, possibly for prolonged periods of time. Under alpha-chloralose anesthesia, rats received EA (1-2mA, 2Hz, 0.5ms) at P5-P6 acupoints (overlying median nerves) or sham (needle placement without electrical stimulation) for 30min. PPE mRNA in the rVLM also was evaluated in control rats that received surgery but no EA, or sham treatment. 20min, 1.5h or 4h following EA or sham treatment, PPE mRNA in the rVLM was analyzed by reverse transcription and quantitative real-time PCR. Relative ratios of PPE mRNA levels (normalized with 18s house keeping gene) were increased 1.5h after EA stimulation (7.77+/-1.39, n=6) relative to sham (2.84+/-0.37, n=5) but were unchanged both 20min and 4h after EA, compared to the sham or surgery groups at the same time points. Thus, 30min of EA transiently stimulates the production of enkephalin in a region of the brain that importantly regulates sympathetic outflow suggesting that even a single brief acupuncture treatment can increase the expression of this modulatory neuropeptide.

Chinese medicine and biomodulation in cancer patients--Part one

Traditional Chinese Medicine (tcm) may be integrated with conventional Western medicine to enhance the care of patients with cancer. Although tcm is normally implemented as a whole system, recent reductionist research suggests mechanisms for the effects of acupuncture, herbs, and nutrition within the scientific model of biomedicine. The health model of Chinese medicine accommodates physical and pharmacologic interventions within the framework of a body–mind network. A Cartesian split does not occur within this model, but to allow for scientific exploration within the restrictions of positivism, reductionism, and controls for confounding factors, the components must necessarily be separated. Still, whole-systems research is important to evaluate effectiveness when applying the full model in clinical practice. Scientific analysis provides a mechanistic understanding of the processes that will improve the design of clinical studies and enhance safety. Enough preliminary evidence is available to encourage quality clinical trials to evaluate the efficacy of integrating tcm into Western cancer care.

Spinal nociceptin mediates electroacupuncture-related modulation of visceral sympathoexcitatory reflex responses in rats

The role of nociceptin and its spinal cord neural pathways in electroacupuncture (EA)-related inhibition of visceral excitatory reflexes is not clear. Nociceptin/orphanin FQ (N/OFQ) is an endogenous ligand for a G protein-coupled receptor, called the N/OFQ peptide (NOP) receptor, which has been found to be distributed in the spinal cord. The present study investigated the importance of this system in visceral-cardiovascular reflex modulation during EA. Cardiovascular pressor reflex responses were induced by gastric distension in Sprague-Dawley rats anesthetized by ketamine and xylazine. An intrathecal injection of nociceptin (10 nM) at T1-2 attenuated the pressor responses by 35%, similar to the influence of EA at P 5-6 (42% decrease). An intrathecal injection of the NOP antagonist, [N-Phe(1)]nociceptin(1-13) NH(2), partially reversed the EA response. Pretreatment with the opioid receptor antagonist naloxone did not alter the EA-like inhibitory effect of nociceptin on the pressor reflex, whereas a combination of nociceptin receptor antagonist with naloxone completely abolished the EA response. An intrathecal injection of nociceptin attenuated the pressor responses to the electrical stimulation of the rostral ventrolateral medulla by 46%, suggesting that nociceptin can regulate sympathetic outflow. Furthermore, a bilateral microinjection of NOP antagonist into either the dorsal horn or the intermediolateral column at T1 partially reversed the EA inhibitory effect. These results suggest that nociceptin in the spinal cord mediates part of the EA-related modulation of visceral reflex responses.

Low-frequency electroacupuncture and physical exercise decrease high muscle sympathetic nerve activity in polycystic ovary syndrome

We have recently shown that polycystic ovary syndrome (PCOS) is associated with high muscle sympathetic nerve activity (MSNA). Animal studies support the concept that low-frequency electroacupuncture (EA) and physical exercise, via stimulation of ergoreceptors and somatic afferents in the muscles, may modulate the activity of the sympathetic nervous system. The aim of the present study was to investigate the effect of these interventions on sympathetic nerve activity in women with PCOS. In a randomized controlled trial, 20 women with PCOS were randomly allocated to one of three groups: low-frequency EA (n = 9), physical exercise (n = 5), or untreated control (n = 6) during 16 wk. Direct recordings of multiunit efferent postganglionic MSNA in a muscle fascicle of the peroneal nerve before and following 16 wk of treatment. Biometric, hemodynamic, endocrine, and metabolic parameters were measured. Low-frequency EA (P = 0.036) and physical exercise (P = 0.030) decreased MSNA burst frequency compared with the untreated control group. The low-frequency EA group reduced sagittal diameter (P = 0.001), while the physical exercise group reduced body weight (P = 0.004) and body mass index (P = 0.004) compared with the untreated control group. Sagittal diameter was related to MSNA burst frequency (Rs = 0.58, P < 0.005) in the EA group. No correlation was found for body mass index and MSNA in the exercise group. There were no differences between the groups in hemodynamic, endocrine, and metabolic variables. For the first time we demonstrate that low-frequency EA and physical exercise lowers high sympathetic nerve activity in women with PCOS. Thus, treatment with low-frequency EA or physical exercise with the aim to reduce MSNA may be of importance for women with PCOS.

Processing cardiovascular information in the vlPAG during electroacupuncture in rats: roles of endocannabinoids and GABA

A long-loop pathway, involving the hypothalamic arcuate nucleus (ARC), ventrolateral periaqueductal gray (vlPAG), and the rostral ventrolateral medulla (rVLM), is essential in electroacupuncture (EA) attenuation of sympathoexcitatory cardiovascular reflex responses. The ARC provides excitatory input to the vlPAG, which, in turn, inhibits neuronal activity in the rVLM. Although previous studies have shown that endocannabinoid CB(1) receptor activation modulates gamma-aminobutyric acid (GABA)-ergic and glutamatergic neurotransmission in the dorsolateral PAG in stress-induced analgesia, an important role for endocannabinoids in the vlPAG has not yet been observed. We recently have shown (Fu LW, Longhurst JC. J Appl Physiol; doi:10.1152/japplphysiol.91648.2008) that EA reduces the local vlPAG concentration of GABA, but not glutamate, as measured with high-performance liquid chromatography from extracellular samples collected by microdialysis. We, therefore, hypothesized that, during EA, endocannabinoids, acting through CB(1) receptors, presynaptically inhibit GABA release to disinhibit the vlPAG and ultimately modulate excitatory reflex blood pressure responses. Rats were anesthetized, ventilated, and instrumented to measure heart rate and blood pressure. Gastric distention-induced blood pressure responses of 18 +/- 5 mmHg were reduced to 6 +/- 1 mmHg by 30 min of low-current, low-frequency EA applied bilaterally at pericardial P 5-6 acupoints overlying the median nerves. Like EA, microinjection of the fatty acid amide hydrolase inhibitor URB597 (0.1 nmol, 50 nl) into the vlPAG to increase endocannabinoids locally reduced the gastric distention cardiovascular reflex response from 21 +/- 5 to 3 +/- 4 mmHg. This inhibition was reversed by pretreatment with the GABA(A) antagonist gabazine (27 mM, 50 nl), suggesting that endocannabinoids exert their action through a GABAergic receptor mechanism in the vlPAG. The EA-related inhibition from 18 +/- 3 to 8 +/- 2 mmHg was reversed to 14 +/- 2 mmHg by microinjection of the CB(1) receptor antagonist AM251 (2 nmol, 50 nl) into the vlPAG. Pretreatment with gabazine eliminated reversal following CB(1)-receptor blockade. Thus EA releases endocannabinoids and activates presynaptic CB(1) receptors to inhibit GABA release in the vlPAG. Reduction of GABA release disinhibits vlPAG cells, which, in turn, modulate the activity of rVLM neurons to attenuate the sympathoexcitatory reflex responses.

Electroacupuncture modulates vlPAG release of GABA through presynaptic cannabinoid CB1 receptors

Previous studies have demonstrated that electroacupuncture (EA) attenuates sympathoexcitatory reflex responses by activating a long-loop pathway involving the hypothalamic arcuate nucleus (ARC), midbrain ventrolateral periaqueductal gray (vlPAG), and rostral ventrolateral medulla (rVLM). Neurons in the ARC provide excitatory input to the vlPAG, whereas the vlPAG inhibits neuronal activity in the rVLM. gamma-Aminobutyric acid (GABA) and glutamate (Glu) have been identified in the vlPAG. Endocannabinoids (ECs), acting as atypical neurotransmitters, inhibit the release of both neurotransmitters in the hypothalamus and midbrain through a presynaptic cannabinoid type 1 (CB(1)) receptor mechanism. The EC system has been observed in the dorsal but not in the vlPAG. Since it is uncertain whether ECs influence GABA and Glu in the vlPAG, the present study tested the hypothesis that EA modulates the release of these neurotransmitters in the vlPAG through a presynaptic CB(1) receptor mechanism. We measured the release of GABA and Glu simultaneously by using HPLC to assess samples collected with microdialysis probes inserted unilaterally into the vlPAG of intact anesthetized rats. Twenty-eight min of EA (2 Hz, 2-4 mA, 0.5 ms) at the P5-6 acupoints reduced the release of GABA by 39% during EA and by 44% 15 min after EA. Thirty-five minutes after EA, GABA concentrations returned to pre-EA levels. In contrast, sham EA did not change the vlPAG GABA concentration. Blockade of CB(1) receptors with AM251, a selective CB(1) receptor antagonist, reversed the EA-modulated changes in GABA concentration, whereas microinjection of vehicle into the vlPAG did not alter EA-modulated GABA changes. In addition, we observed no changes in the vlPAG Glu concentrations during EA, although the baseline concentration of Glu was much higher than that of GABA (3,541 +/- 373 vs. 33.8 +/- 8.7 nM, Glu vs. GABA). These results suggest that EA modulates the sympathoexcitatory reflex responses by decreasing the release of GABA, but not Glu, in the vlPAG, most likely through a presynaptic CB(1) receptor mechanism.

Long-loop pathways in cardiovascular electroacupuncture responses

We have shown that electroacupuncture (EA) at P 5-6 (overlying median nerves) activates arcuate (ARC) neurons, which excite the ventrolateral periaqueductal gray (vlPAG) and inhibit cardiovascular sympathoexcitatory neurons in the rostral ventrolateral medulla (rVLM). To investigate whether the ARC inhibits rVLM activity directly or indirectly, we stimulated the splanchnic nerve to activate rVLM neurons. Micropipettes were inserted in the rVLM, vlPAG, and ARC for neural recording or injection. Microinjection of kainic acid (KA; 1 mM, 50 nl) in the ARC blocked EA inhibition of the splanchnic nerve stimulation-induced reflex increases in rVLM neuronal activity. Microinjection of d,l-homocysteic acid (4 nM, 50 nl) in the ARC, like EA, inhibited reflex increases in the rVLM neuronal discharge. The vlPAG neurons receive convergent input from the ARC, splanchnic nerve, P 5-6, and other acupoints. Microinjection of KA bilaterally into the rostral vlPAG partially reversed rVLM neuronal responses and cardiovascular inhibition during d,l-homocysteic acid stimulation of the ARC. On the other hand, injection of KA into the caudal vlPAG completely reversed these responses. We also observed that ARC neurons could be antidromically activated by stimulating the rVLM, and that ARC perikarya was labeled with retrograde tracer that had been microinjected into the rVLM. These neurons frequently contained beta-endorphin and c-Fos, activated by EA stimulation. Therefore, the vlPAG, particularly, the caudal vlPAG, is required for ARC inhibition of rVLM neuronal activation and subsequent EA-related cardiovascular activation. Direct projections from the ARC to the rVLM, which serve as an important source of beta-endorphin, appear also to exist.

The status and future of acupuncture mechanism research

On November 8-9, 2007, the Society for Acupuncture Research (SAR) hosted an international conference to mark the tenth anniversary of the landmark NIH [National Institutes of Health] Consensus Development Conference on Acupuncture. More than 300 acupuncture researchers, practitioners, students, funding agency personnel, and health policy analysts from 20 countries attended the SAR meeting held at the University of Maryland School of Medicine, Baltimore, MD. This paper summarizes important invited lectures in the area of basic and translational acupuncture research. Specific areas include the scientific assessment of acupuncture points and meridians, the neural mechanisms of cardiovascular regulation by acupuncture, mechanisms for electroacupuncture applied to persistent inflammation and pain, basic and translational research on acupuncture in gynecologic applications, the application of functional neuroimaging to acupuncture research with specific application to carpal-tunnel syndrome and fibromyalgia, and the association of the connective tissue system to acupuncture research. In summary, mechanistic models for acupuncture effects that have been investigated experimentally have focused on the effects of acupuncture needle stimulation on the nervous system, muscles, and connective tissue. These mechanistic models are not mutually exclusive. Iterative testing, expanding, and perhaps merging of such models will potentially lead to an incremental understanding of the effects of manual and electrical stimulation of acupuncture needles that is solidly rooted in physiology.

Role of medullary GABA, opioids, and nociceptin in prolonged inhibition of cardiovascular sympathoexcitatory reflexes during electroacupuncture in cats

Electroacupuncture (EA) causes prolonged suppression of reflex elevations in blood pressure for 1-2 h in anesthetized preparations. A long-loop pathway involving the arcuate nucleus (ARC), ventrolateral periaqueductal gray, and rostral ventrolateral medulla (rVLM) is involved in sympathoinhibitory cardiovascular EA effects. However, the mechanisms and locations of the prolonged EA inhibition are unknown. We hypothesized that this effect is mediated through a long-loop pathway involving opioid, nociceptin, and gamma-aminobutyric acid (GABA) receptor activation in the rVLM. In anesthetized, ventilated cats application of bradykinin to the gallbladder every 10 min induced consistent reflex increases in blood pressure. Bilateral EA stimulation at the cardiovascular acupoints P5-6 overlying the median nerves reduced the reflex responses for at least 80 min. Bilateral blockade with kynurenic acid in the ARC 60 min after onset of EA inhibition reversed the cardiovascular response, suggesting a role for the ARC in the long-loop pathway during the prolonged inhibitory response. Unilateral microinjection with either an opioid or a GABA(A) antagonist in rVLM 50-60 min after the beginning of the EA response reversed EA inhibition of the cardiovascular excitatory reflex. Gabazine also reversed EA inhibition of cardiovascular premotor sympathetic rVLM neurons. Conversely, microinjection of a nociceptin/orphanin FQ peptide antagonist did not affect the prolonged inhibitory effect. Thus the ARC, an important component in the long-loop pathway in the EA cardiovascular response, is required for prolonged suppression of reflex cardiovascular excitatory responses by EA. Furthermore, in the rVLM, opioids and GABA, but not nociceptin, participate in the long-term EA-related inhibition of sympathoexcitatory cardiovascular responses.

Role of glutamate in the rostral ventrolateral medulla in acupuncture-related modulation of visceral reflex sympathoexcitation

Visceral sympathoexcitatory reflexes induced by stimulation of the gallbladder with bradykinin (BK) are attenuated by electroacupuncture (EA) at Neiguan-Jianshi (P5-6) acupoints located over the median nerve. Previous studies have shown that neurons in the rostral ventrolateral medulla (rVLM) receive convergent input from visceral organs and somatic nerves (activated by EA). Glutamate (Glu), an important excitatory neurotransmitter in the rVLM, processes visceral sympathoexcitatory cardiovascular reflexes. In the present study, we determined the relation between EA-mediated opioidergic modulation of visceral cardiovascular responses and Glu. Reflex cardiovascular responses were evoked by application of BK to the gallbladder before and after EA in anesthetized cats. Glu concentrations ([Glu]) were measured by HPLC from samples collected by microdialysis probe(s) inserted unilaterally or bilaterally into the rVLM. BK-induced reflex responses and [Glu] were attenuated by 45% and 70%, respectively, after 30 min of EA ( n = 6). EA alone did not change [Glu] in the rVLM ( n = 6, P > 0.05). However, microdialysis of naloxone (100 mM) into the rVLM reversed EA-related inhibition of blood pressure and [Glu] ( n = 5). Immunohistochemical visualization showed that δ-opioid receptors colocalized with, and were in close apposition to, vesicular Glu transporter 3- and c-Fos-double-labeled perikarya and processes of rVLM neurons after gallbladder stimulation with BK. These data suggest that EA attenuates BK-induced visceral sympathoexcitatory reflexes through opioid-mediated inhibition of Glu's action in the rVLM.

Electroacupuncture decreases the susceptibility to ventricular tachycardia in conscious rats by reducing cardiac metabolic demand

Reperfusion after a brief period of cardiac ischemia can lead to potentially lethal arrhythmias. Clinical observations and experimental work with animals suggest that acupuncture may have therapeutic effects for individuals with coronary heart disease, certain arrhythmias, and myocardial ischemia. Therefore, we tested the hypothesis that electroacupuncture reduces the susceptibility to ischemia-reperfusion-mediated ventricular tachyarrhythmias. To test this hypothesis, we measured the susceptibility to ventricular tachyarrhythmias produced by 3 min of occlusion and reperfusion of the left main coronary artery in conscious rats under two experimental conditions: 1) control and 2) with electroacupuncture. Acupuncture was simulated by electrically stimulating the median nerves, corresponding to the Jianshi-Neiguan [pericardial meridian (P) 5-6] acupoints. Results document a significantly lower incidence of ventricular tachyarrhythmias with electroacupuncture (2 of 8, 25%) relative to control (14 of 14, 100%) rats. The decreased susceptibility to tachyarrhythmias with electroacupuncture was associated with a reduced cardiac metabolic demand (lower rate-pressure product and ST-segment elevation) during ischemia.

Midbrain vlPAG inhibits rVLM cardiovascular sympathoexcitatory responses during electroacupuncture

The periaqueductal gray (PAG) is an important integrative region in the regulation of autonomic outflow and cardiovascular function and may serve as a regulatory center as part of a long-loop pathway during somatic afferent stimulation with acupuncture. Because the ventrolateral PAG (vlPAG) provides input to the rostral ventrolateral medulla (rVLM), an important area for electroacupuncture (EA) regulation of sympathetic outflow, we hypothesized that the vlPAG plays a role in the EA-related modulation of rVLM premotor sympathetic neurons activated during visceral afferent stimulation and autonomic excitatory reflexes. Cats were anesthetized and ventilated, and heart rate and mean blood pressure were monitored. Stimulation of the splanchnic nerve by a pledget of filter paper soaked in bradykinin (BK, 10 μg/ml) every 10 min on the gallbladder induced consistent cardiovascular reflex responses. Bilateral stimulation with EA at acupoints over the pericardial meridian (P5-6) situated over the median nerve reduced the increases in blood pressure from 34 ± 3 to 18 ± 5 mmHg for a period of time that lasted for 60 min or more. Unilateral inactivation of neuronal activity in the vlPAG with 50–75 nl of kainic acid (KA, 1 mM) restored the blood pressure responses from 18 ± 3 to 36 ± 5 mmHg during BK-induced gallbladder stimulation, an effect that lasted for 30 min. In the absence of EA, unilateral microinjection of the excitatory amino acid dl-homocysteic acid (DLH, 4 nM) in the vlPAG mimicked the effect of EA and reduced the reflex blood pressure responses from 35 ± 6 to 14 ± 5 mmHg. Responses of 21 cardiovascular sympathoexcitatory rVLM neurons, including 12 that were identified as premotor neurons, paralleled the cardiovascular responses. Thus splanchnic nerve-evoked neuronal discharge of 32 ± 4 spikes/30 stimuli in six neurons was reduced to 10 ± 2 spikes/30 stimuli by EA, which was restored rapidly to 28 ± 4 spikes/30 stimuli by unilateral injection of 50 nl KA into the vlPAG. Conversely, 50 nl of DLH in the vlPAG reduced the number of action potentials of 5 rVLM neurons from 30 ± 4 to 18 ± 4 spikes/30 stimuli. We conclude that the inhibitory influence of EA involves vlPAG stimulation, which, in turn, inhibits rVLM neurons in the EA-related attenuation of the cardiovascular excitatory response during visceral afferent stimulation.

Excitatory projections from arcuate nucleus to ventrolateral periaqueductal gray in electroacupuncture inhibition of cardiovascular reflexes

We have shown that the modulatory effect of electroacupuncture (EA) on the blood pressure (BP) response induced by visceral organ stimulation is related to inhibition of cardiovascular neurons in the rostral ventrolateral medulla (rVLM) through a mechanism that involves opioids. This effect is long lasting and may involve a long-loop neural supraspinal pathway, including the arcuate nucleus (ARC), which is an important site of opioid neurotransmitter synthesis. Therefore, we evaluated the role of the hypothalamic ARC and its interaction with the midbrain ventrolateral periaqueductal gray (vlPAG) in the EA-BP response. The gallbladder of α-chloralose-anesthetized cats was stimulated to test for the influence of EA on splanchnic afferent-induced cardiovascular reflexes. Electrodes were placed around the splanchnic nerve (SN), and acupuncture needles were applied at P5-6 acupoints overlying the median nerve (MN). Electrophysiological recordings showed that spontaneous activity of ARC and vlPAG neurons was low (1.3 ± 0.5 and 2.0 ± 0.5 spikes/s, respectively). We observed a gradation of responses of ARC neurons to the stimulation of different acupoints, ranging from uniform responses of all neurons during stimulation of the P5-6, LI4-11, H5-6, and St2-G2 located over deep nerves to fewer responses during stimulation of LI6-7 and G37-39 located over superficial nerves. Microinjection of the excitatory amino acid dl-homocysteic acid (DLH 4 nM, 50 nl) into the ARC augmented the responses of vlPAG neurons, whereas microinjection of kainic acid (KA 1 mM, 50 nl) to deactivate neurons in the ARC decreased vlPAG responses to SN stimulation. Thirty minutes of EA at P5-6 increased the SN-evoked discharge of vlPAG neurons (7.0 ± 1.2 to 14.3 ± 3.0 spikes/30 stimuli), a response that was blocked by microinjection of KA into the ARC. Microinjection of DLH into the ARC, like EA, inhibited (30 min) the reflex increase in BP induced by application of bradykinin (BK) to the gallbladder, whereas microinjection of KA into the ARC blocked the inhibitory influence of EA at P5-6 on the BK-induced BP response. These results suggest that excitatory projections from the ARC to the vlPAG are essential to the EA inhibition of the reflex increase in BP induced by SN or gallbladder visceral afferent stimulation.

Role of glutamate in a visceral sympathoexcitatory reflex in rostral ventrolateral medulla of cats

The rostral ventrolateral medulla (rVLM) is involved in processing visceral sympathetic reflexes. However, there is little information on specific neurotransmitters in this brain stem region involved in this reflex. The present study investigated the importance of glutamate and glutamatergic receptors in the rVLM during gallbladder stimulation with bradykinin (BK), because glutamate is thought to function as an excitatory neurotransmitter in this region. Stimulation of visceral afferents activated glutamatergic neurons in the rVLM, as noted by double-labeling with c-Fos and the cellular vesicular glutamate transporter 3 (VGLUT3). Visceral reflex activation significantly increased arterial blood pressure as well as extracellular glutamate concentrations in the rVLM as determined by microdialysis. Barodenervation did not alter the release of glutamate in the rVLM evoked by visceral reflex stimulation. Iontophoresis of glutamate into the rVLM enhanced the activity of sympathetic premotor cardiovascular rVLM neurons. Also, the responses of these neurons to visceral afferent stimulation with BK were attenuated significantly (70%) by blockade of glutamatergic receptors with kynurenic acid. Microinjection of either an N-methyl-D-aspartate (NMDA) receptor antagonist 2-amino-5-phosphonopentanate (25 mM, 30 nl) or an dl-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (2 mM, 30 nl) into the rVLM significantly attenuated the visceral sympathoexcitatory reflex responses. These results suggest that glutamate in the rVLM serves as an excitatory neurotransmitter through a baroreflex-independent mechanism and that both NMDA and AMPA receptors mediate the visceral sympathoexcitatory reflex responses.

Short-term electroacupuncture at Zusanli resets the arterial baroreflex neural arc toward lower sympathetic nerve activity

Although electroacupuncture reduces sympathetic nerve activity (SNA) and arterial pressure (AP), the effects of electroacupuncture on the arterial baroreflex remain to be systematically analyzed. We investigated the effects of electroacupuncture of Zusanli on the arterial baroreflex using an equilibrium diagram comprised of neural and peripheral arcs. In anesthetized, vagotomized, and aortic-denervated rabbits, we isolated carotid sinuses and changed intra-carotid sinus pressure (CSP) from 40 to 160 mmHg in increments of 20 mmHg/min while recording cardiac SNA and AP. Electroacupuncture of Zusanli was applied with a pulse duration of 5 ms and a frequency of 1 Hz. An electric current 10 times the minimal threshold current required for visible muscle twitches was used and was determined to be 4.8 +/- 0.3 mA. Electroacupuncture for 8 min decreased SNA and AP (n = 6). It shifted the neural arc (i.e., CSP-SNA relationship) to lower SNA but did not affect the peripheral arc (i.e., SNA-AP relationship) (n = 8). SNA and AP at the closed-loop operating point, determined by the intersection of the neural and peripheral arcs, decreased from 100 +/- 4 to 80 +/- 9 arbitrary units and from 108 +/- 9 to 99 +/- 8 mmHg (each P < 0.005), respectively. Peroneal denervation eliminated the shift of neural arc by electroacupuncture (n = 6). Decreasing the pulse duration to <2.5 ms eliminated the effects of SNA and AP reduction. In conclusion, short-term electroacupuncture resets the neural arc to lower SNA, which moves the operating point toward lower AP and SNA under baroreflex closed-loop conditions.

Modulation of cardiovascular excitatory responses in rats by transcutaneous magnetic stimulation: role of the spinal cord

This study investigated the efficacy of magnetic stimulation on the reflex cardiovascular responses induced by gastric distension in anesthetized rats and compared these responses to those influenced by electroacupuncture (EA). Unilateral magnetic stimulation (30% intensity, 2 Hz) at the Jianshi-Neiguan acupoints (pericardial meridian, P 5-6) overlying the median nerve on the forelimb for 24 min significantly decreased the reflex pressor response by 32%. This effect was noticeable by 20 min of magnetic stimulation and continued for 24 min. Median nerve denervation abolished the inhibitory effect of magnetic stimulation, indicating the importance of somatic afferent input. Unilateral EA (0.3-0.5 mA, 2 Hz) at P 5-6 using similar durations of stimulation similarly inhibited the response (35%). The inhibitory effects of EA occurred earlier and were marginally longer (20 min) than magnetic stimulation. Magnetic stimulation at Guangming-Xuanzhong acupoints (gallbladder meridian, GB 37-39) overlying the superficial peroneal nerve on the hindlimb did not attenuate the reflex. Intravenous naloxone immediately after termination of magnetic stimulation reversed inhibition of the cardiovascular reflex, suggesting involvement of the opioid system. Also, intrathecal injection of delta- and kappa-opioid receptors antagonists, ICI174,864 (n=7) and nor-binaltorphimine (n=6) immediately after termination of magnetic stimulation reversed inhibition of the cardiovascular reflex. In contrast, the mu-opioid antagonist CTOP (n=7) failed to alter the cardiovascular reflex. The endogenous neurotransmitters for delta- and kappa-opioid receptors, enkephalins and dynorphin but not beta-endorphin, therefore appear to play significant roles in the spinal cord in mediating magnetic stimulation-induced modulation of cardiovascular reflex responses.