Hz Electroacupuncture Research Articles

Relieving effects of electroacupuncture on mechanical allodynia in neuropathic pain model of inferior caudal trunk injury in rat: mediation by spinal opioid receptors

The relieving effects of electroacupuncture (EA) on mechanical allodynia and its mechanism related to the spinal opioid system were investigated in a rat model of neuropathic pain. To produce neuropathic pain in the tail, the right superior caudal trunk was resected between the S1 and S2 spinal nerves. Two weeks after the surgery, EA stimulation (2 or 100 Hz, 0.3 ms, 0.2–0.3 mA) was delivered to Zusanli (ST36) for 30 min. The degree of mechanical allodynia was evaluated quantitatively by touching the tail with von Frey hair (2.0 g) at 10 min intervals. These rats were then subjected to an i.t. injection with one of the three specific opioid agonists in successive ways: the mu agonist (DAMGO 25, 50 and 100 pmol), the delta agonist (DADELT II 0.5, 1 and 2 nmol), and the kappa agonist (U50488H 5, 10 and 20 nmol) separated by 10 min in cumulative doses. During 30 min of EA stimulation, specific opioid antagonists were subjected to i.t. injection: the mu antagonist (β-FNA 5, 10 and 20 nmol), the delta antagonist (naltrindole 5, 10 and 20 nmol), and the kappa antagonist (nor-BNI 3, 6 and 12 nmol) separated by 10 min in cumulative doses. As a result, EA reduced the behavioral signs of mechanical allodynia. Two Hz EA induced a robust and longer lasting effect than 100 Hz. All three opioid agonists also showed relieving effects on mechanical allodynia. However, nor-BNI could not block the EA effects on mechanical allodynia, whereas β-FNA or naltrindole significantly blocked EA effects. These results suggest that the mu and delta, but not kappa, opioid receptors in the spinal cord of the rat, play important roles in mediating relieving effects on mechanical allodynia induced by 2 Hz EA.

Effect of electro-acupuncture on rat joint pathomorphology of chronic adjuvant arthritis model

Objective:To study the effect of electro-acupuncture (EA) on pathomorphological changes of joints in rat model of chronic adjuvant arthritis.Methods: The rat chronic adjuvant arthritis model was established by subcutaneous injection of 0.1 ml of complete Freund’s adjuvant to the left hind sole. Forty Wistar rats were randomly divided into the model group, the low frequency (2 Hz) EA group, the high frequency EA (100 Hz) group and the body acupuncture group. After being modeled except the model group, the other three groups were treated with EA or body acupuncture in Yanglingquan points (bilateral) for 3 weeks, the left ankle joints and metatarsal joints of rats were taken for pathological examination by fixing with 10% formalin and embedding in paraffin, sectioning and staining with HE.Results: Obvious inflammatory cell infiltration, loosened synovial tissue, damage of articular cartilage and proliferation of synovial cells and granulation tissue were observed in the sections of joints in model rats. These pathological changes were significantly improved after treatment, and the effect in the high frequency EA group were significantly superior to that in the low frequency EA and body acupuncture group.Conclusion: High frequency EA could significantly improve the pathomorphological changes of joints in chronic adjuvant arthritis rat models.

Long-term high-frequency electro-acupuncture stimulation prevents neuronal degeneration and up-regulates BDNF mRNA in the substantia nigra and ventral tegmental area following medial forebrain bundle axotomy

Electroacupuncture (EA) has been used in China for many years to treat Parkinson’s disease (PD) with reportedly effective results. However, the physiological and biological mechanism behind its effectiveness is still unknown. In the present study, different frequencies of chronic EA stimulation (0, 2, 100 Hz) were tested in a partially lesioned rat model of PD which was induced by transection of the medial forebrain bundle (MFB). After 24 sessions of EA stimulation (28 days after MFB transection), dopaminergic neurons in the ventral midbrain were examined by immunohistochemical staining, and brain-derived neurotrophic factor (BDNF) mRNA levels in ventral midbrain were measured by in situ hybridization. The results show a marked decrease of dopaminergic neurons on the lesioned side of the substantia nigra (SN) comparing with the unlesioned side. Zero Hz and 2 Hz EA stimulation had no effect on the disappearance of dopaminergic neurons. However, after 100 Hz EA, about 60% of the tyrosine hydroxylase (TH)-positive neurons remained on the lesioned side of the SN. In addition, levels of BDNF mRNA in the SN and ventral tegmental area (VTA) of the lesioned side were significantly increased in the 100 Hz EA group, but unchanged in the 0 and 2 Hz groups. Our results suggest that long-term high-frequency EA is effective in halting the degeneration of dopaminergic neurons in the SN and up-regulating the levels of BDNF mRNA in the subfields of the ventral midbrain. Activation of endogenous neurotrophins by EA may be involved in the regeneration of the injured dopaminergic neurons, which may underlie the effectiveness of EA in the treatment of PD.

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·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·kg −1 was necessary. (4) A positive correlation was observed between analgesia induced by morphine at the dose of 5.0 mg·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.

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

To investigate the involvement of nuclear factor kappa B1 (NF-κB1; p50/p105) in electroacupuncture (EA)-induced analgesia, 2 and 100 Hz EA stimulations were applied at acupoint ST36 (Zusanli) in NF-κB1 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-κB1+/− mice exhibited a 41.8% increase and NF-κB1−/− 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-κB1+/− and a 9.3% increase in NF-κB1−/− mice. The present findings suggest that NF-κB1 may play a crucial role in both low and high frequency EA-induced analgesic effects.

EFFECT OF ELECTROACUPUNCTURE AND TRANSCUTANEOUS ELECTRICAL NERVE STIMULATION AT HEGU (LI.4) ACUPUNCTURE POINT ON THE CUTANEOUS REFLEX

Our previous studies have shown that the cerebral cortex plays a modulator role in the physiological mechanisms of acupuncture and 2Hz electroacupuncture (EA), but either acupuncture or 2Hz EA appeared to have very little effect on spinal cord. However, 2Hz or 100Hz transcutaneous electrical nerve stimulation (TENS) applied to Hegu acupuncture point (LI.4) can increase the amplitude of the H-reflex, whereas manual acupuncture has no similar effect. Therefore, the aim of the present study was to further investigated the effect of 2Hz EA, 2Hz or 100Hz TENS on cutaneous reflex (CR). A total of 13 healthy adult volunteers were studied. CR recordings were obtained on the right first dorsal interosseous muscle by electrical stimulation of the ipsilateral index finger. 2Hz EA, 2Hz or 100Hz TENS was applied to the surface of the left LI.4, and then the changes of CR were observed. The results indicated that CR was characterized by an initial short latency excitatory wave (E1), followed by an inhibitory wave (I1), then a long latency excitatory wave (E2). Both 2Hz EA and 2Hz TENS applied to the surface of the left LI.4 could prolong the latencies of I1 component of CR, whereas 100Hz TENS has no similar effect. In addition, either EA or TENS could not change the latencies of E1, E2 component and the amplitudes of I1, E2 component of CR. In conclusion, 2Hz EA or 2Hz TENS applied to the LI.4 prolonged the latencies of I1 component of CR, suggesting that the action site of 2Hz EA or 2Hz TENS located in the supraspinal, possibly in the subcortical or cortical level. In addition, the electrical stimulation of higher frequency such as 100Hz TENS acting on CR caused habituation easier.

The physiological mechanisms of 2 Hz electroacupuncture: a study using blink and H reflex.

Our previous studies have shown that the cerebral cortex modulates the physiological mechanisms of acupuncture. However, the role of the brain stem and spinal cord in acupuncture remains unclear. The present study investigated the action of the brain stem and spinal cord in acupuncture. A total of eight healthy adult volunteers were studied. Electrical stimulation of the supraorbital nerve in the supraorbital foramen was used to evoke the blink reflex. Electrical stimulation of the posterior tibial nerve in the right popliteal fossa was used to evoke the H reflex. Electroacupuncture (EA) of 2 Hz was applied to the Zusanli acupoint in the right or left leg. The area of the R1 and R2 components of the blink reflex, and the greatest H/M ratio and H-M interval of the H reflex were measured before EA, during EA and at various post-EA periods. These data were analyzed quantitatively by a computerized electromyographic examination system. The results indicate that EA did not change the R1 and ipsilateral R2 components of the blink reflex. EA depressed the contralateral R2 component of the blink reflex 10 minutes and 40 minutes after the start of EA, but not after 5 minutes. EA applied to the Zusanli acupoint did not change the H/M ratio or the H-M interval of the H reflex. The results of this study indicate that 2 Hz EA of the Zusanli acupoint does not change the R1 component of the blink reflex, and the H/M ratio and the H-M interval of the H reflex, suggesting that 2 Hz EA does not change the monosynaptic reflex in the brain stem and spinal cord in humans. We also found that EA at 2 Hz depressed the contralateral but not the ipsilateral R2 component of the blink reflex, suggesting that longer pathways, perhaps including the cerebral cortex, may play a role in the physiological mechanisms responsible for the effectiveness of acupuncture.

The effect of genotype on sensitivity to electroacupuncture analgesia

Individual differences in sensitivity to pain and analgesia are well appreciated, and increasing evidence has pointed towards a role of inherited genetic factors in explaining some proportion of such variability. It has long been known by practitioners of acupuncture, an ancient modality of analgesia, that some patients are ‘responders’ and others ‘non-responders.’ The present research was aimed at defining the inherited genetic influence on acupuncture analgesia in the mouse, using 10 common inbred strains. Two pairs of metallic needles were inserted into acupoints ST 36 and SP 6, fixed in situ and then connected to the output channel of an electric pulse generator. Electroacupuncture (EA) parameters were set as constant current output (intensity: 1.0–1.5–2.0 mA, 10 min each; frequency: 2 or 100 Hz) with alteration of a positive and negative square wave, 0.3 ms in pulse width. Tail-flick latencies evoked by radiant heat were measured before, during and after EA stimulation. Narrow-sense heritability estimates of 2 and 100 Hz EA were 0.37 and 0.16, respectively. We found that the C57BL/10 strain was the most sensitive, and the SM strain was the least sensitive to both 2 and 100 Hz EA. However, the relative sensitivities of other strains to these two EA frequencies suggested some genetic dissociation between them as well. These results demonstrate a role of inherited genetic factors in EA sensitivity in the mouse, although the low-to-moderate heritability estimates suggest that environmental factors may be of greater importance in predicting who will benefit from this analgesic modality.

Endomorphin and μ-opioid receptors in mouse brain mediate the analgesic effect induced by 2 Hz but not 100 Hz electroacupuncture stimulation

This work was designed to examine whether brain endomorphins (EM1 and EM2), the endogenous μ-opioid ligands, are involved in electroacupuncture (EA)-induced analgesia in the mice. C57BL/6J mice were given EA for 30 min and the effect of EA-induced analgesia was assessed by radiant heat tail flick latency (TFL). Intracerebroventricular (i.c.v.) injection of μ-opioid receptor antagonist D-Phe-Cys-Tyr-D-Tyr-Orn-Thr-Pen-Thr-NH 2 (CTOP), or antiserum against EM1 or EM2 was performed to see whether EA analgesia could be blocked. The results showed that: (1) i.c.v. injection of CTOP at 25–100 ng dose-dependently antagonized the analgesia induced by EA of 2 Hz, but not 100 Hz. (2) Intracerebroventricular injection of EM1 antiserum (5 ml, 1:1 or 1:10 dilution) dose-dependently antagonized 2 Hz, but not 100 Hz EA analgesia. (3) EM2 antiserum showed similar effect at 1:1 dilution. The results are interpreted to mean that endogenously released EM1 and EM2 and the cerebral μ-receptors are involved in mediating 2 Hz but not 100 Hz EA analgesia in the mice.

Electroacupuncture potentiates the antinociceptive effect of intrathecal endomorphin-1 in the rat formalin test

Endomorphin-1 is a novel endogenous mu-opioid peptide. In this study, we examined the effects of 2 Hz electroacupuncture in the rat tail flick test and the formalin test (a persistent noxious model). Moreover, we investigated if the electroacupuncture potentiated the effect of intrathecal endomorphin-1. The results demonstrated that electroacupuncture alone produced a significant antinociception in the tail flick test, but not in the formalin test, and that intrathecal endomorphin-1 dose-dependently suppressed the biphasic nociceptive behavior in the formalin test. Electroacupuncture enhanced the antinociceptive effect of intrathecal endomorphin-1 in the formalin test, resulting in a significant leftward shift in the dose-response curves for intrathecal endomorphin-1 antinociception. The enhanced effect was antagonized by intraperitoneal naltrexone. The study suggests that electroacupuncture may potentiate the intrathecal endomorphin-1 antinociception partially mediated by opioid receptors.

Suppression of morphine withdrawal by electroacupuncture in rats: dynorphin and κ-opioid receptor implicated

Our previous work has demonstrated that 100-Hz electroacupuncture (EA) or 100-Hz transcutaneous electrical nerve stimulation (TENS) was very effective in ameliorating the morphine withdrawal syndrome in rats and humans. The mechanism was obscure. (1) Rats were made dependent on morphine by repeated morphine injections (5–140 mg/kg, s.c., twice a day) for eight days. They were then given 100-Hz EA for 30 min 24 h after the last injection of morphine. A marked increase in tail flick latency (TFL) was observed. This effect of 100-Hz EA could be blocked by naloxone (NX) at 20 mg/kg, but not at 1 mg/kg, suggesting that 100-Hz EA-induced analgesia observed in morphine-dependent rats is mediated by κ-opioid receptors. (2) A significant decrease of the concentration of dynorphin A (1–17) immunoreactivity (-ir) was observed in the spinal perfusate in morphine-dependent rats, that could be brought back to normal level by 100-Hz EA. (3) 100-Hz EA was very effective in suppressing NX-precipitated morphine withdrawal syndrome. This effect of EA could be prevented by intrathecal administration of nor-BNI (2.5 μg/20 μl), a κ-opioid receptor antagonist, or dynorphin A (1–13) antibodies (25 μg/20 μl) administered 10 min prior to EA. In conclusion, while the steady-state spinal dynorphin release is low in morphine-dependent rats, it can be activated by 100-Hz EA stimulation, which may be responsible for eliciting an analgesic effect and ameliorating morphine withdrawal syndrome, most probably via interacting with κ-opioid receptor at spinal level.

Endomorphin-1 mediates 2 Hz but not 100 Hz electroacupuncture analgesia in the rat

This work was designed to elucidate the possible involvement of endogenous endomorphin-l (EM1) in analgesia induced by electroacupuncture of low or high frequencies. Taking radiant heat tail flick latency (TFL) as an indication of nociception, rats were subjected to intrathecal (i.t.) injection of 10 μl antiserum against EM1 (EM1-AS) or normal rabbit serum (NRS, as control) and then followed by 2 or 100 Hz electroacupuncture stimulation for 30 min. The analgesia induced by 2 Hz electroacupuncture was attenuated by i.t. injection of EM1-AS at 1:10 and 1:100 but not at 1:1000 dilution. No such suppressive effect was observed for 100 Hz EA analgesia when EM1-AS was injected i.t. at any dilutions. These results indicate that EM1 is involved in 2 Hz but not 100 Hz electroacupuncture analgesia at spinal level.

Randomized Trial of Acupuncture for Nicotine Withdrawal Symptoms

Acupuncture is frequently used for smoking cessation. Positive results from uncontrolled studies have not been supported by meta-analysis of controlled trials. One possible reason for this is that the optimal acupuncture technique was not applied or that the technique was not repeated sufficiently often. A randomized, sham-controlled trial was performed with 2 parallel treatment arms; the participant and the evaluator were unaware of which treatment was received. Seventy-six adults who wanted to stop smoking received either 100-Hz electroacupuncture with needles inserted into the appropriate point in each ear or a sham control procedure over the mastoid bone. Interventions were given on days 1, 3, and 7 of smoking cessation. Nicotine withdrawal symptoms were measured by visual analog scale scores recorded in a daily diary for 14 days; smoking cessation was confirmed objectively. There was no significant difference between the mean reduction of withdrawal symptom scores of the 2 groups from day 1 to day 14. Fifteen participants (39%) who received electroacupuncture and 16 participants (42%) who received a sham procedure were abstinent on day 14. This form of electroacupuncture is no more effective than placebo in reducing nicotine withdrawal symptoms.

CCK B receptors in the periaqueductal grey are involved in electroacupuncture antinociception in the rat cold water tail-flick test

Cholecystokinin octapeptide (CCK-8) (0.25–2.0 ng), the CCK A receptor antagonist L-364,718 (60–100 ng) or the CCK B receptor antagonist L-365,260 (0.3125–1.25 ng) was administered into the periaqueductal grey (PAG) of male SD rats. The antinociceptive effect induced by electroacupuncture (EA) stimulation of different frequencies was then measured by the cold water tail-flick (CWT) test. The results showed that (1) microinjection of CCK-8 into the PAG can significantly block the antinociceptive effect induced by all frequencies of EA stimulation. The effectiveness of the blockade was 100>2 Hz. In addition, CCK-8 blocks the antinociception seen following termination of the electrical stimulation at 100 Hz; (2) microinjection of L-365,260 (1.25 ng) into the PAG significantly increased the 100 Hz EA antinociceptive effect but not the 2 Hz EA antinociceptive effect and microinjection of L-364,718 into PAG did not affect either 2 or 100 Hz EA antinociception. These results demonstrate that CCK-8 in the PAG can antagonize the antinociceptive effect induced by EA stimulation, and the CCK effect is likely to be mediated by the CCK B receptor, but not the CCK A receptor.

Endogenous orphanin FQ: evidence for a role in the modulation of electroacupuncture analgesia and the development of tolerance to analgesia produced by morphine and electroacupuncture.

1. Our previous work has demonstrated that exogenously administered orphanin FQ (OFQ) antagonizes morphine analgesia and electroacupuncture analgesia (EAA) in the brain and potentiates morphine analgesia and EAA in the spinal cord of the rat. In the present study we evaluated the role of endogenously released OFQ in the development of tolerance to morphine and electroacupuncture (EA) and the analgesia produced by electroacupuncture, by use of the IgG fraction of an anti-OFQ antibody (OFQ-Ab) microinjected into the rat central nervous system (CNS). 2. EAA was produced by stimulating rats at a frequency of 100 Hz. Rats were classified as either high responders (HR) or low responders (LR) based on the analgesic effects of EA. LRs could be converted into HRs by the intracerebroventricular (i.c.v.) microinjection of OFQ-Ab at both 1:1 and 1:10 dilutions but not 1:100. HRs could be changed into LRs by the intrathecal (i.t.) injection of OFQ-Ab at both 1:1 and 1:10 dilutions, but not 1:100. 3. Acute morphine tolerance was induced in rats by repeated subcutaneous (s.c.) injections of morphine (5 mg kg, every 2 h) for 16 h. When injected i.c.v. the OFQ-Ab (1:1 dilution) had no effect on the development of acute morphine tolerance. 4. Chronic morphine tolerance was produced in rats by repeated injection of morphine (5-60 mg kg, s.c., 3 x a day) for 6 days. I.c.v. injection of OFQ-Ab (1:1 dilution) reversed this type of morphine tolerance in rats by 50% (P < 0.01). 5. Acute tolerance to the analgesia produced by EA developed after 6 h of continuous (100 Hz, 3 mA) stimulation. This tolerance was almost completely reversed by the i.c.v. injection of OFQ-Ab (1:1 dilution) (P < 0.05). 6. Chronic tolerance to the analgesic effect of EA was produced by repeatedly administering increasing current (1, 2 and 3 mA, each lasting for 10 min, for a total of 30 min) at a frequency of 100 Hz once a day for 6 days. I.c.v. injection of OFQ-Ab (1:1 dilution) reversed this kind of tolerance by 50% (P < 0.01). 7. Together these results suggest that 100 Hz EA may enhance the release of endogenous OFQ in the CNS of the rat, which in turn may act to antagonize EA-produced analgesia in the brain but potentiate EA produced analgesia in the spinal cord. Therefore, OFQ appears to play an important role in the development of tolerance to the analgesic effects produced by EA. 8. The mechanisms underlying the development of acute morphine tolerance and chronic morphine tolerance appear to be different. Central OFQ may play an important role in the development of tolerance after chronic morphine administration.

Involvement of endogenous orphanin FQ in electroacupuncture-induced analgesia.

Recent studies suggest that the novel opioid peptide orphanin FQ (OFQ) is involved in pain modulation. We found that intracerebroventricular (i.c.v.) administration of OFQ in the rat produced a dose-dependent antagonism of the analgesia induced by 100 Hz electroacupuncture (EA) stimulation as measured in the radiant heat tail-flick assay. Antisense oligonucleotides injected i.c.v. potentiated EA analgesia, presumably by interfering with the expression of the OFQ receptor in brain. These results suggest that endogenous OFQ exerts a tonic antagonistic effect on EA-induced analgesia. No such antagonism was observed when OFQ was injected intrathecally (i.t.). Rather, it appears that spinal OFQ produced a marked analgesic effect and enhanced EA-induced analgesia. These findings are consistent with the experimental results obtained in rats where morphine-induced analgesia is antagonized by i.c.v. OFQ and potentiated by i.t. OFQ.

Brain substrates activated by electroacupuncture of different frequencies (I): comparative study on the expression of oncogene c- fos and genes coding for three opioid peptides

Low and high frequency electroacupuncture (EA)-produced analgesia have been shown to be mediated by different brain substrates and different opioid peptides. In this study, Fos-like immunoreactivity (FLI) and in situ hybridization of the three opioid mRNAs were used to examine the effect of low (2 Hz) and high (100 Hz) frequency EA on neuronal activities and the expression of opioid genes. 2 Hz and 100 Hz EA induced a markedly different spatial patterns of Fos expression in the rat brain, suggesting there are distinct neuronal pathways underlying EA of different frequencies. Likewise, 2 Hz and 100 Hz EA exert differential effects on opioid gene expression: while 2 Hz EA induced a more extensive and intensive preproenkephalin (PPE) mRNA expression than 100 Hz EA, it had no effect on preprodynorphin (PPD) mRNA expression which was significantly increased by 100 Hz EA stimulation. In contrast, EA of both frequencies did not affect POMC mRNA expression.

Changes in the content of immunoreactive dynorphin in dorsal and ventral spinal cord of the rat in three different conditions.

Previous study in our group demonstrated that dynorphin exerted a significant analgesic effect in spinal cord, and electroacupuncture (EA) of high frequency (100 Hz) produced analgesia which was mediated by dynorphin released in spinal cord. However, no data are up to nowadays available for demonstrating either from anterior horn or from dorsal horn the dynorphin comes. Using radioimmunoassay, we found in the present study that ir-dynorphin content in dorsal horn was 10 times more than in anterior horn, which were 11.24 +/- 0.91 pmol/10 mg protein and 1.08 +/- 0.20 pmol/10 mg protein, respectively. Stimulation of 100 Hz EA for 30 min produced a significant increase of ir-dynorphin content in dorsal horn, in contrast, no change of ir-dynorphin content was found in anterior horn. For the meanwhile, a significant elevation of ir-dynorphin was induced by 100 Hz EA in cerebrospinal fluid. It is concluded according to these data that EA, as a stimulation in physiological condition, elevates the content of ir-dynorphin only in dorsal horn, and induces release of dynorphin in loci. The released dynorphin acts on dorsal horn to mediate the analgesia of EA.

Effect of electroacupuncture tolerance by different frequencies on the opioid inhibition to cardiovascular activity in the spinal cord of rats

Continuous 2–15 Hz or 2 Hz electroacupuncture (EA) of 6 h applied to rats resulted in electroacupuncture tolerance (ET). The effect of 2–15 Hz ET on the recovery of mean arterial blood pressure (MAP) and heart rate (HR) of rats after hemorrhagic shock, and the effect of intrathecal (i.t.) injection of [D-ala 2, D-leu 5]enkephalin (DADLE) on MAP and HR of 2 Hz ET rats were observed. The results were as follows: 1) there was no dramatic difference between the 2–15 Hz ET group and the control group in the recovery of MAP and HR from hemorrhagic shock; 2) DADLE (25 μg) caused almost the same depressor effect in the 2 Hz ET group as that in the control group. These data suggest that the spinal lateral horn cells (supposed to be involved in regulating blood pressure) are insensitive to EA and cannot be made tolerant to continuous EA, which is different from the dorsal horn cell (supposed to be involved in analgesia).

The distribution of brain-stem and spinal cord nuclei associated with different frequencies of electroacupuncture analgesia

Immunocytochemical localization of the c- fos primary gene protein, Fos, was used to identify spinal cord and brain-stem sites activated by either 4-Hz or 100-Hz electroacupuncture (EA) applied to the Zusanli acupuncture points of both hind limbs in lightly anesthetized Sprague-Dawley rats. The number and distribution of Fos-immunoreactive neurons in the brain stem and spinal cord of 4-Hz and 100-Hz EA-treated rats were compared with these in anesthesia and room control rats. Compared to non-stimulated control rats or rats in which EA was applied to a non-acupuncture point, both 4-Hz and 100-Hz EA-treated groups exhibited a significantly greater number of Fos-labeled neurons in the dorsal horn of the L2 spinal cord segment, lateral parabrachial nucleus, substantia nigra, nucleus raphe pallidus, dorsal raphe, locus coeruleus, posterior pretectal nucleus, and the lateroventral periaqueductal gray. In the 4-Hz-treated group, significant increases in Fos labeling were also observed in the cuneiform nucleus, dorsal and laterodorsal subdivisions of the periaqueductal gray, habenular nucleus, arcuate hypothalamic nucleus, and the lateroventral and lateral hypothalamic nuclei as compared to non-stimulated controls. The only brain-stem nucleus that exhibited significantly increased Fos-immunoreactive neurons in 100-Hz but not 4-Hz EA was the rostolateroventral nucleus of the medulla. These results indicate that many brain-stem regions are activated by both 4-Hz and 100-Hz EA but additional brain-stem regions are selectively activated by 4-Hz EA which may relate to the opiate sensitivity of 4-Hz EA. In sum, these data identify several distinct brain-stem nuclei that may play a role in acupuncture-mediated analgesia.