Activation of Spinal Anti-analgesic System Following Electroacupuncture Stimulation in Rats

The Roles of Imaging Biomarkers in the Management of Chronic Neuropathic Pain

Chronic neuropathic pain (CNP) affects around 10% of the general population and has a significant social, emotional, and economic impact. Current diagnosis techniques rely mainly on patient-reported outcomes and symptoms, which leads to significant diagnostic heterogeneity and subsequent challenges in management and assessment of outcomes. As such, it is necessary to review the approach to a pathology that occurs so frequently, with such burdensome and complex implications. Recent research has shown that imaging methods can detect subtle neuroplastic changes in the central and peripheral nervous system, which can be correlated with neuropathic symptoms and may serve as potential markers. The aim of this paper is to review available imaging methods used for diagnosing and assessing therapeutic efficacy in CNP for both the preclinical and clinical setting. Of course, further research is required to standardize and improve detection accuracy, but available data indicate that imaging is a valuable tool that can impact the management of CNP.

Acupuncture/Electroacupuncture as an Alternative in Current Opioid Crisis

Opioid drugs are the first line of defense in severe pain but the adverse effects associated with opioids are considered as a serious issue worldwide. Acupuncture/electroacupuncture is a type of Chinese medicine therapy which is an effective analgesic therapy, well documented in animals and human studies. Electroacupuncture stimulation could release endogenous opioid peptides causing analgesia in a variety of pain models. It can be used as an alternative therapy to control the opioid crisis.

The effect of electrical stimulation on impairment of the painful post-stroke shoulder

Background: Transcutaneous electrical nerve stimulation (TENS) and transcutaneous neuromuscular electrical stimulation (t-NMES) are commonly used therapies in the treatment of chronic hemiplegic shoulder pain. These treatments are often utilized during physical or occupational therapy sessions, yet research into the acute analgesic effects of TENS and t-NMES on hemiplegic shoulder pain and use during therapy is limited. Objective: To compare the acute effects of transcutaneous electrical nerve stimulation (TENS), transcutaneous neuromuscular electrical stimulation (t-NMES), and no stimulation on pain-free passive range of motion of the shoulder in subjects with hemiplegic shoulder pain. Methods: Prospective cohort study of 10 subjects randomly treated with t-NMES, TENS, and one non-stimulation experimental condition. Pain-free passive external rotation and abduction range of motion of the affected shoulder were measured during stimulation. Results: There was not a significant within-subject difference in pain-free range of motion for external rotation or abduction. Subject to subject differences explained the majority of the variability in pain-free range of motion. Conclusion: This pilot study is the first to measure pain-free passive range of motion during electrical stimulation. Our findings demonstrate the lack of an acute effect of TENS and t-NMES on pain reduction.

Spinal p38 activity and analgesic effect after low- and high-intensity electroacupuncture stimulation in a plantar incision rat model

AIMS

Postoperative pain is a major problem. Electroacupuncture (EA) has been accepted as a useful and low-risk complementary therapy for post-operative pain. Animal studies indicate that surgical incision activates p38 MAPK in the spinal microglia, which critically contributes to post-incisional nociceptive development. How EA affects incision-induced p38 activation is important but yet to be fully elucidated.

METHODS

Male adult rats received plantar incision (PI) at the right hind paw followed by 30-min EA of 4-Hz, one of two intensities (3 and 10mA), and at right ST36 (Zusanli) acupoint immediately after PI and for 3 successive days. EA analgesia was evaluated by von Frey fibers and Hargreaves' tests. Spinal p38 activation was examined by immunostaining. In separate groups, SB203580, a p38 inhibitor, was intrathecally injected alone or with EA to test the combining effect on nociception and spinal phospho-p38.

KEY FINDINGS

EA of 10-mA significantly ameliorated mechanical allodynia, but 3-mA did not. None of them altered thermal hyperalgesia. Repeated EA could not inhibit phospho-p38 in the PI rats, contrarily, EA per se significantly induced phospho-p38 in the normal rats. Intrathecal SB203580 injection dose-dependently prevented PI-induced allodynia. Combination of low-dose SB203580 and 3-mA EA, which were ineffective individually, profoundly reduce post-PI allodynia.

SIGNIFICANCE

We demonstrated that 10-mA EA exerts a significant inhibition against post-PI mechanical hypersensitivity via a p38-independent pathway. Importantly, co-treatment with low-dose p38 inhibitor and 3-mA EA can counteract spinal phospho-p38 to exert strong analgesic effect. Our finding suggests a novel strategy to improve EA analgesic quality.

Telemetry monitoring for non-invasive assessment of changes in core temperature after spinal drug administration in freely moving rats

INTRODUCTION

There are no data available about the effects of spinally administered drugs on thermoregulation in freely moving animals. The first goal of the present study was to throw light on the consequences of intrathecally administered saline as a vehicle on core temperature and motor activity in unrestrained conditions. The second goal was to characterize the effects of morphine on these parameters as a widely used antinociceptive drug in spinal anesthesia, and reveal the potential role of the N-methyl-d-aspartate (NMDA) receptors in these processes.

METHODS

For these purposes, male Wistar rats were catheterized intrathecally, and E-Mitter battery-free transponders were implanted intraabdominally to continuously monitor core temperature and locomotor activity.

RESULTS

Saline induced a short-lasting hyperactivity accompanied by significant and prolonged hyperthermia that was blunted by systemic paracetamol administration. Morphine had no impact on motor activity; however, it caused high but equivalent degree hyperthermia in a wide dose range (1-15 μg), suggesting that it reached its peak effect. In the highest applied dose (25 μg), the NMDA receptor antagonist kynurenic acid blunted the saline-induced hyperthermia, and all doses caused higher hyperactivity compared to vehicle or morphine injections. In combination, kynurenic acid significantly inhibited the morphine-induced hyperthermia.

DISCUSSION

These data suggest that this method might be a valuable tool for investigating the thermoregulatory and locomotor effects of different drugs at spinal level; however, the prolonged effects of intrathecal vehicle injections should also be considered. The results point out that morphine is a very potent hyperthermic drug that may act primarily on the efferent limb of thermoregulation, at least partially, via an indirect NMDA-receptor mediated action mechanism.

Comparison of electroacupuncture and morphine-mediated analgesic patterns in a plantar incision-induced pain model

Electroacupuncture (EA) is a complementary therapy to improve morphine analgesia for postoperative pain, but underlying mechanism is not well-known. Herein, we investigated EA-induced analgesic effect in a plantar incision (PI) model in male Sprague-Dawley rats. PI was performed at the left hind paw. EA of 4 Hz and high intensity or sham needling was conducted at right ST36 prior to PI and repeated for another 2 days. Behavioral responses to mechanical and thermal stimuli, spinal phospho-ERK, and Fos expression were all analyzed. In additional groups, naloxone and morphine were administered to elucidate involvement of opioid receptors and for comparison with EA. EA pretreatment significantly reduced post-PI tactile allodynia for over 1 day; repeated treatments maintained analgesic effect. Intraperitoneal naloxone could reverse EA analgesia. Low-dose subcutaneous morphine (1 mg/kg) had stronger inhibitory effect on PI-induced allodynia than EA for 1 h. However, analgesic tolerance appeared after repeated morphine injections. Both EA and morphine could equally inhibit PI-induced p-ERK and Fos inductions. We conclude that though EA and morphine attenuate postincision pain through opioid receptor activations, daily EA treatments result in analgesic accumulation whereas daily morphine injections develop analgesic tolerance. Discrepant pathways and mechanisms underlying two analgesic means may account for the results.

Antinociception of Heterotopic Electro-Acupuncture Mediated by the Dorsolateral Funiculus

We investigated the inhibitory pathways that mediate the antinociceptive effects of heterotopic electro-acupuncture (EA) on formalin injection-induced pain in rats. EA (2 ms, 10 Hz, 3 mA) was delivered to heterotopic acupoints HT7 and PC7 for 30 min; this was followed immediately by subcutaneous injection of formalin into the left hind paw of rats. Naltrexone (10 mg/kg, i.p.), an opioid receptor antagonist, was administered to evaluate the involvement of endogenous opioids. The dorsolateral funiculus (DLF), which is a descending pathway that inhibits pain, was transected at the ipsilateral T10–11 level of the thoracic spinal cord. EA inhibited behavioral responses to formalin injection-induced pain and prevented the pain-induced increase in cFos expression in the lumbar spinal cord. Pretreatment with naltrexone did not inhibit the antinociceptive effects of EA on formalin injection-induced pain. Transection of the DLF ipsilateral to the acupuncture site eliminated the antinociceptive effects of EA. These results suggest that the antinociceptive effects of heterotopic EA are mediated by the DLF and not by endogenous opioids.

Blood fluidity enhancement by electrical acupuncture stimulation is related to an adrenergic mechanism

We have reported that electrical acupuncture stimulation (ACU) increases blood fluidity by decreasing platelet aggregation. In this study, we investigated the mechanism causing the increase of blood fluidity. The effects of ACU on blood fluidity and platelet adhesion were examined using a Micro Channel Array Flow Analyzer (MC-FAN) and a laser scattering platelet aggregometer (PA-20). Male Wistar rats (7-8 weeks old) were used in the study. ACU (1 or 100 Hz, 3-5 V), which causes slight muscle twitching, was applied to the ZuSanli (ST-36) acupoint for 15 or 60 minutes once/day. Blood samples were collected from the inferior vena cava. ACU applied to ST-36 revealed significant increases in blood fluidity, while platelet adhesion activity decreased, regardless of the difference of stimulus time. The acupuncture had an immediate effect. Even if naloxone was administered during acupuncture stimulus, the blood flow time shortened in a similar way, as in the only acupuncture stimulus group. In addition, the effect of acupuncture on blood fluidity was inhibited by a β-antagonist. The results indicate that ACU affects blood fluidity depending on the acupoints, and that the effect of ACU might involve an endogenous adrenergic mechanism.

L-364,718 potentiates electroacupuncture analgesia through cck-a receptor of pain-related neurons in the nucleus parafascicularis

Electroacupuncture (EA) has been successfully used to alleviate pain produced by various noxious stimulus. Cholecystokinin-8 (CCK-8) is a neuropeptide involved in the mediation of pain. We have previously shown that CCK-8 could antagonize the analgesic effects of EA on pain-excited neurons (PENs) and pain-inhibited neurons (PINs) in the nucleus parafascicularis (nPf). However, its mechanism of action is not clear. In the present study, we applied behavioral and neuroelectrophysiological methods to determine whether the mechanisms of CCK-8 antagonism to EA analgesia are mediated through the CCK-A receptors of PENs and PINs in the nPf of rats. We found that focusing radiant heat on the tail of rats caused a simultaneous increase in the evoked discharge of PENs or a decrease in the evoked discharge of PINs in the nPf and the tail-flick reflex. This showed that radiant heat could induce pain. EA stimulation at the bilateral ST 36 acupoints in rats for 15 min resulted in an inhibition of the electrical activity of PEN, potentiation of the electrical activity of PIN, and prolongation in tail-flick latency (TFL), i.e. EA stimulation produced an analgesic effect. The analgesic effect of EA was antagonized when CCK-8 was injected into the intracerebral ventricle of rats. The antagonistic effect of CCK-8 on EA analgesia was reversed by an injection of CCK-A receptor antagonist L-364,718 (100 ng/μl) into the nPf of rats. Our results suggest that the pain-related neurons in the nPf have an important role in mediating EA analgesia. L-364,718 potentiates EA analgesia through the CCK-A receptor of PENs and PINs in the nPf.

Cholecystokinin-8 antagonizes electroacupuncture analgesia through its B receptor in the caudate nucleus

OBJECTIVES

  The analgesic effect of electroacupuncture (EA) stimulation has been proved. However, its mechanism of action is not clear. It has been well-known that cholecystokinin-8 (CCK-8) is a neuropeptide which is mainly related to the mediation of pain. The caudate nucleus was selected to determine if the release of CCK and the neural activity in this nucleus were involved in producing EA analgesia.

MATERIALS AND METHODS

  Radiant heat focused on the rat-tail was used as the noxious stimulus. The pain threshold of rats was measured by tail-flick latency (TFL). EA stimulation at the bilateral Zusanli (ST 36) acupoints of rats was used to investigate the effects of EA analgesia. The electrical activities of pain-excited neurons (PEN) and pain-inhibited neurons (PIN) in the caudate nucleus were recorded with a glass microelectrode. The present study examined the antagonistic effects of the intracerebral ventricular injection of CCK-8 on EA analgesia and reversing effects of CCK-B receptor antagonist (L-365,260) injection into the caudate nucleus on CCK-8.

RESULTS

  The radiant heat focused on the tail of rats caused an increase in the evoked discharge of PEN and a reduction in the evoked discharge of PIN. EA stimulation at the bilateral ST 36 acupoints of rats resulted in the inhibition of PEN, the potentiation of PIN, and prolongation of TFL. The analgesic effect of EA was antagonized when CCK-8 was injected into the intracerebral ventricle of rats. The antagonistic effect of CCK-8 on EA analgesia was reversed by injection of CCK-B receptor antagonist (L-365,260) into the caudate nucleus of rats.

CONCLUSIONS

  Our results suggest that CCK-8 antagonize EA analgesia through its B receptor.

EFNS guidelines on neurostimulation therapy for neuropathic pain

Pharmacological relief of neuropathic pain is often insufficient. Electrical neurostimulation is efficacious in chronic neuropathic pain and other neurological diseases. European Federation of Neurological Societies (EFNS) launched a Task Force to evaluate the evidence for these techniques and to produce relevant recommendations. We searched the literature from 1968 to 2006, looking for neurostimulation in neuropathic pain conditions, and classified the trials according to the EFNS scheme of evidence for therapeutic interventions. Spinal cord stimulation (SCS) is efficacious in failed back surgery syndrome (FBSS) and complex regional pain syndrome (CRPS) type I (level B recommendation). High-frequency transcutaneous electrical nerve stimulation (TENS) may be better than placebo (level C) although worse than electro-acupuncture (level B). One kind of repetitive transcranial magnetic stimulation (rTMS) has transient efficacy in central and peripheral neuropathic pains (level B). Motor cortex stimulation (MCS) is efficacious in central post-stroke and facial pain (level C). Deep brain stimulation (DBS) should only be performed in experienced centres. Evidence for implanted peripheral stimulations is inadequate. TENS and r-TMS are non-invasive and suitable as preliminary or add-on therapies. Further controlled trials are warranted for SCS in conditions other than failed back surgery syndrome and CRPS and for MCS and DBS in general. These chronically implanted techniques provide satisfactory pain relief in many patients, including those resistant to medication or other means.

Morphine-induced antinociception in the formalin test: sensitization and interactions with D1 and D2 dopamine receptors and nitric oxide agents

In this study, the effects of dopamine receptor antagonists and nitric oxide agents on morphine-induced sensitization in the formalin test in mice have been investigated. Repeated daily intraperitoneal administration of morphine (30 mg/kg for 3 days) followed by a 11-day wash out period increased morphine-induced antinociception in the formalin test, which may be due to sensitization. The antinociceptive response to higher doses of morphine (6 and 9 mg/kg) but not 3 mg/kg was significantly increased in sensitized animals compared with control groups. Pretreatment of animals with an opioid receptor antagonist, naloxone (4 mg/kg), during repeated administration of morphine, attenuated the morphine-induced sensitization. In the second part of the study, the animals received SCH23390 (D1 receptor antagonist), sulpiride (D2 receptor antagonist), L-Arg (nitric oxide precursor) and NG-nitro-L-Arg methylester (nitric oxide synthase inhibitor) during repeated morphine administration, to evaluate the role of dopamine receptor antagonists and nitric oxide agents in this phenomenon. Pretreatment of animals with NG-nitro-L-Arg methylester (20 mg/kg) and sulpiride (100 mg/kg) during morphine sensitization decreased the antinociceptive response to higher doses of morphine in the formalin test. It is concluded that D2 dopamine receptor and nitric oxide mechanisms may be involved at least partly in morphine-induced sensitization in the formalin test.

Activation of spinal cholecystokinin and neurokinin-1 receptors is associated with the attenuation of intrathecal morphine analgesia following electroacupuncture stimulation in rats

We previously demonstrated that electroacupuncture (EA) stimulation both produced antinociception and attenuated intrathecal (i.t.) morphine analgesia, suggesting that EA is capable of inducing two opposing systems, that is, opioid and anti-opioid mechanisms. This study examined the involvement of cholecystokinin (CCK) in the anti-opioid effects following EA in the spinal cord. EA was applied to commonly used acupoints for antinociception, ST-36 located 5-mm lateral to the anterior tubercle of the tibia, and analgesia was assessed by the hind-paw pressure test in male Sprague-Dawley rats. I.t. administration of CCK (0.01 - 10 microg) attenuated i.t. morphine analgesia (10 microg) dose-dependently. The attenuation of morphine analgesia following EA was reversed by i.t. proglumide, a CCK-receptor antagonist (0.01 microg). CCK-like immunoreactivity was increased in lamina I and II in the dorsal horn, and expression of spinal CCK mRNA increased after EA. Moreover, i.t. pretreatment with the neurokinin-1 (NK1)-receptor antagonist L-703,606 (18 microg) reversed both EA- and CCK-induced attenuation of morphine analgesia. These results suggest that CCK-mediated neural systems in the spinal cord may be involved in the attenuation of morphine analgesia following EA and that substance P-induced activation of NK1 receptors may be responsible for the downstream neuronal transmission of the CCK-mediated neuronal system.

Endogenous opiates and behavior: 2005

This paper is the 28th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2005 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity, neurophysiology and transmitter release (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); immunological responses (Section 17).