Bispecific sigma-1 receptor antagonism and mu-opioid receptor partial agonism: WLB-73502, an analgesic with improved efficacy and safety profile compared to strong opioids

Opioids are the most effective painkillers, but their benefit-risk balance often hinder their therapeutic use. WLB-73502 is a dual, bispecific compound that binds sigma-1 (S1R) and mu-opioid (MOR) receptors. WLB-73502 is an antagonist at the S1R. It behaved as a partial MOR agonist at the G-protein pathway and produced no/unsignificant β-arrestin-2 recruitment, thus demonstrating low intrinsic efficacy on MOR at both signalling pathways. Despite its partial MOR agonism, WLB-73502 exerted full antinociceptive efficacy, with potency superior to morphine and similar to oxycodone against nociceptive, inflammatory and osteoarthritis pain, and superior to both morphine and oxycodone against neuropathic pain. WLB-73502 crosses the blood-brain barrier and binds brain S1R and MOR to an extent consistent with its antinociceptive effect. Contrary to morphine and oxycodone, tolerance to its antinociceptive effect did not develop after repeated 4-week administration. Also, contrary to opioid comparators, WLB-73502 did not inhibit gastrointestinal transit or respiratory function in rats at doses inducing full efficacy, and it was devoid of proemetic effect (retching and vomiting) in ferrets at potentially effective doses. WLB-73502 benefits from its bivalent S1R antagonist and partial MOR agonist nature to provide an improved antinociceptive and safety profile respect to strong opioid therapy.

Research progress on analgesic effect and adverse drug reactions of opioid receptor agonist-antagonists / 中国药房

Opioid receptor agonist-antagonists are a class of drugs which have both agonistic and antagonistic effects on opioid receptors. These drugs already on the market mainly include pentazocine， butorphanol， nalbuphine， buprenorphine， dezocine and so on. Compared with pure opioid receptor agonists such as morphine and fentanyl， these drugs have strong analgesic effects， less addictive， and less side effects such as cough， itching and respiratory depression. Due to the different tendentious effects of opioid receptor agonists-antagonists among different endogenous opioid receptors （μ， κ， δ， etc.）， different receptors of subtypes can exhibit different or even opposite effects in terms of affecting emotions and drug dependence. Therefore， the rational use of these drugs can effectively reduce the occurrence of adverse reactions and drug abuse caused by opioid drugs. With the deepening of research on various endogenous opioid receptor subtypes and related drugs in the academic community， opioid receptor agonists- antagonists have broad application space and prospects in improving adverse reactions to opioid drugs and enhancing patient drug compliance.

Antinociception Induced by Moringa Stenopetela (Baker f.) Cufod. Leaves Extract and Possible Mechanisms of Action

Moringa stenopetala (Baker f.) Cufod., is an endemic species growing in the south of Ethiopia. M. stenopetala is often consumed as food and used in traditional medicine and it has also been traditionally used for relieving of pain in Ethiopia. This study aimed to investigate the antinociceptive effect and mechanisms of action of M. stenopetala leaves methanol extract in mice. The per-oral doses of 50, 100, and 200 mg/kg of M. stenopetala extract were tested for antinociceptive action by using hot-plate, tail-immersion, and writhing tests. The possible mechanisms of in the antinociceptive action were investigated by pre-treatment with 5 mg/kg naloxone (non-selective opioid antagonist), 1 mg/kg ketanserin (5-HT2A/2C receptor antagonist), and 1 mg/kg yohimbine (α2 adrenoceptor antagonist). The methanol extract of M. stenopetala showed antinociceptive effect in all tests. The significant involvement of 5-HT2A/2C receptors and α2 adrenoceptors in antinociception induced by M. stenopetala extract in the hot-plate and tail-immersion tests, as well as significant contribution of opioid receptors and α2 adrenoceptors in writhing test, were identified. In conclusion, these findings demonstrate that the methanol extract of M. stenopetala has potential in pain management. Thisstudywillcontributetonewtherapeuticapproachesandprovideguidancefornewdrug development studies.

Electroacupuncture Attenuates Surgical Stress-Induced Reduction of T Lymphocytes through Modulation of Peripheral Opioid System / 中国结合医学杂志

OBJECTIVE@#To investigate the action mechanisms of electroacupuncture (EA) on postoperative immunosuppression.@*METHODS@#Male C57BL/6 mice (5`-7 weeks old) were randomly divided into: the sham injury group, the surgical trauma stressed group, the EA group [surgery + 2/100 Hz EA at Neiguan (PC 6)], and the EA+ Nal (surgery + EA + intraperitoneal injection of naloxone). Abdominal surgical trauma stress mice model was established. EA was performed on bilateral PC 6 acupoints by an EA apparatus (2/100 Hz) for 20 min once a day for 3 days. The mRNA expressions of MOR, DOR, and KOR in thymus and L3`-L5 dorsal root ganglions (DRG) were determined by quantitative real-time polymerase chain reaction (qRT-PCR) and the protein expressions of MOR, DOR, and KOR in thymus were measured by Western blot. Flow cytometry assay was used to detect the levels of T lymphocyte subtypes in the peripheral blood.@*RESULTS@#Surgical trauma induced decreased the mRNA expression level of MOR in both thymus (P0.05). Furthermore, T lymphocyte population of CD3@*CONCLUSION@#EA may improve postoperative immunosuppression through the peripheral opioid system.

Mu-Opioid Receptors Expressed in Glutamatergic Neurons are Essential for Morphine Withdrawal / 神经科学通报·英文版

Although opioids still remain the most powerful pain-killers, the chronic use of opioid analgesics is largely limited by their numerous side-effects, including opioid dependence. However, the mechanism underlying this dependence is largely unknown. In this study, we used the withdrawal symptoms precipitated by naloxone to characterize opioid dependence in mice. We determined the functional role of mu-opioid receptors (MORs) expressed in different subpopulations of neurons in the development of morphine withdrawal. We found that conditional deletion of MORs from glutamatergic neurons expressing vesicular glutamate transporter 2 (Vglut2) largely eliminated the naloxone-precipitated withdrawal symptoms. In contrast, conditional deletion of MORs expressed in GABAergic neurons had a limited effect on morphine withdrawal. Consistently, mice with MORs deleted from Vglut2 glutamatergic neurons also showed no morphine-induced locomotor hyperactivity. Furthermore, morphine withdrawal and morphine-induced hyperactivity were not significantly affected by conditional knockout of MORs from dorsal spinal neurons. Taken together, our data indicate that the development of morphine withdrawal is largely mediated by MORs expressed in Vglut2 glutamatergic neurons.

Mu-Opioid Receptors Expressed in Glutamatergic Neurons are Essential for Morphine Withdrawal / 神经科学通报·英文版

Although opioids still remain the most powerful pain-killers, the chronic use of opioid analgesics is largely limited by their numerous side-effects, including opioid dependence. However, the mechanism underlying this dependence is largely unknown. In this study, we used the withdrawal symptoms precipitated by naloxone to characterize opioid dependence in mice. We determined the functional role of mu-opioid receptors (MORs) expressed in different subpopulations of neurons in the development of morphine withdrawal. We found that conditional deletion of MORs from glutamatergic neurons expressing vesicular glutamate transporter 2 (Vglut2) largely eliminated the naloxone-precipitated withdrawal symptoms. In contrast, conditional deletion of MORs expressed in GABAergic neurons had a limited effect on morphine withdrawal. Consistently, mice with MORs deleted from Vglut2 glutamatergic neurons also showed no morphine-induced locomotor hyperactivity. Furthermore, morphine withdrawal and morphine-induced hyperactivity were not significantly affected by conditional knockout of MORs from dorsal spinal neurons. Taken together, our data indicate that the development of morphine withdrawal is largely mediated by MORs expressed in Vglut2 glutamatergic neurons.

Mu-opioid receptors in the paraventricular nucleus regulate ejaculatory behaviors via the sympathetic nerve system in male rats / 中华男科学杂志

Objective@#To explore the effects of the mu-opioid receptor (MOR) in the paraventricular nucleus (PVN) on the ejaculatory behaviors of male rats and its potential mechanisms.@*METHODS@#Male SD rats with normal ejaculation ability were mated with female ones in hormone-induced estrus. After bilateral PVN microinjection of D-Ala-2-Me-Phe-4-Gly-ol enkephalin (DAGO) or D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2 (CTAP) with an inserted catheter, the male animals were observed for mount latency (ML), mount frequency (MF), intromission latency (IL), intromission frequency (IF), ejaculation latency (EL), ejaculation frequency (EF), post-ejaculation interval (PEI), and intromission ratio (IR). The lumbar sympathetic nerve activity (LSNA) of the rats was recorded using the PowerLab data acquisition hardware device, and the levels of norepinephrine (NE) in the peripheral plasma were measured by ELISA following microinjection of saline or different doses of DAGO or CTAP.@*RESULTS@#Neither CTAP nor DGAO significantly affected the ML of the male rats (P > 0.05). DGAO remarkably increased IF (P < 0.01) and MF (P < 0.01), prolonged IL (P < 0.01), EL (P < 0.01) and PEI (P < 0.01), and reduced EF (P <0.01) and IR (P < 0.05). On the contrary, CTAP markedly decreased IF (P < 0.01) and MF (P < 0.01), shortened IL (P < 0.01), EL (P < 0.01) and PFI (P < 0.01), and elevated EF (P < 0.01) and IR (P < 0.01). Additionally, DAGO decreased LSNA in a dose-dependent manner and reduced the NE level in the peripheral plasma. CTAP, however, not only offset the effects of DAGO on LSNA, but also significantly increased LSNA.@*CONCLUSIONS@#MOR in PVN inhibits ejaculatory behaviors in male rats by weakening LSNA, which has provided some theoretical evidence for the use of highly selective opioids in the treatment of premature ejaculation.

Anti-nociceptive effect of patchouli alcohol: Involving attenuation of cyclooxygenase 2 and modulation of mu-opioid receptor / 中国结合医学杂志

OBJECTIVE@#To explore the anti-nociceptive effect of patchouli alcohol (PA), the essential oil isolated from Pogostemon cablin (Blanco) Bent, and determine the mechanism in molecular levels.@*METHODS@#The acetic acid-induced writhing test and formalin-induced plantar injection test in mice were employed to confirm the effect in vivo. Intracellular calcium ion was imaged to verify PA on mu-opioid receptor (MOR). Cyclooxygenase 2 (COX2) and MOR of mouse brain were expressed for determination of PA's target. Cellular experiments were carried out to find out COX2 and MOR expression induced by PA.@*RESULTS@#PA significantly reduced latency period of visceral pain and writhing induced by acetic acid saline solution (P<0.01) and allodynia after intra-plantar formalin (P<0.01) in mice. PA also up-regulated COX2 mRNA and protein (P<0.05) with a down-regulation of MOR (P<0.05) both in in vivo and in vitro experiments, which devote to the analgesic effect of PA. A decrease in the intracellular calcium level (P<0.05) induced by PA may play an important role in its anti-nociceptive effect. PA showed the characters of enhancing the MOR expression and reducing the intracellular calcium ion similar to opioid effect.@*CONCLUSIONS@#Both COX2 and MOR are involved in the mechanism of PA's anti-nociceptive effect, and the up-regulation of the receptor expression and the inhibition of intracellular calcium are a new perspective to PA's effect on MOR.

Role of ZHX2 in regulating dorsal root ganglion μ-opioid receptor expression in mice with peripheral nerve injuryinduced pain hypersensitivity / 南方医科大学学报

OBJECTIVE@#To investigate the role of zinc-fingers and homeoboxes 2 (ZHX2) in regulating μ-opioid receptor expression in the dorsal root ganglion (DRG) in mice with peripheral nerve injury-induced pain hypersensitivity.@*METHODS@#Forty-eight male adult C57BL6J mice were randomized into 4 groups and subjected to chronic constriction injury (CCI) of the sciatic nerve or sham operation followed by microinjection of a specific small interfering RNA (siRNA) of ZHX2 or a negative control siRNA sequence (siNC) into the DRG. Seven days later, the mice were examined for changes in the hind paw withdrawal frequency (PWF), after which the DRG tissue was collected for detecting the expressions of μ-opioid receptor at the mRNA and protein levels using RT-qPCR and Western blotting. In another experiment, the DRG tissues were collected from 6 mice (21-day-old) for primary culture of the DRG neurons, which were transfected with ZHX2 siRNA or the siNC to observe the changes in the expressions of ZHX2 and μ-pioid receptor.@*RESULTS@#Microinjection of ZHX2 siRNA into the ipsilateral L3 and L4 DRGs significantly reversed CCI-induced μ-pioid receptor downregulation in the injured DRG and alleviated CCI-induced mechanical allodynia in the mice. In the cell experiment, ZHX2 knockdown obviously upregulated the mRNA and protein expressions of opioid receptor in the primary cultured DRG neurons.@*CONCLUSIONS@#ZHX2 knockdown in the DRG reverses CCI-induced down-regulation of μ opioid receptor to alleviate periphery nerve injury-induced pain hypersensitivity in mice.

Antitussive effect and mechanism study of effective fractions from Sauropus rostratus / 中草药

Objective: To study the antitussive effect of Sauropus spatulifolius, screen the active part of its antitussive effect, and study its antitussive mechanism. Methods The acute toxicity of different extraction sites of S. spatulifolius were studied by modified Karber’s method; The model was made with ammonia liquor to induce cough. The spray time that caused half of the mice to cough was calculated by sequential method with aim to screen the active sites. Capsaicin was used to induce cough, and the mechanism of action of extracts from various parts of S. spatulifolius on opioid receptor and ATP-sensitive potassium channel (KATP) of mice was explored. Results The LD50 of 75% ethanol, ethyl acetate, n-butanol, and 95% ethanol extracts was 7.30, 17.00, 69.68, and 75.88 g/kg, respectively; The maximum tolerance dose (MTD) of petroleum ether extracts was 117.71 g/kg; Extracts from 75% ethanol and ethyl acetate had antitussive effects, and its antitussive effect was related to opioid receptor and KATP pathway. Conclusion The fractions from 75% ethanol and ethyl acetate are the active parts of S. spatulifolius for relieving cough, and its antitussive mechanism is related to the KATP pathway and opioid receptors in the excited central system.

Progress in evaluation methods and mechanisms of opioid receptor-mediated side effects / 中国药理学通报

K opioid receptor agonists produce potent antinociception without morphine-like side effects. However, selective K opioid receptor agonists exhibit severe dysphoria, limiting their clinical use. Developing new K agonists with less CNS side effects appears to offer some advantages over u, agonist for the treatment of pain. In this review, we summarize the representative analgesics targeting K opioid receptors in the clinic and introducethe latest progress of methodology and underlying mechanism of K receptor-mediated dysphoria.

Electroacupuncture intervention relieves pain possibly by promoting MOR endocytosis in locus coeruleus in bone cancer pain rats with morphine tolerance / 针刺研究

OBJECTIVE: To observe the effect of electroacupuncture (EA) on pain behavior and expression of µ-opioid receptor (MOR) and Rab5 (an important protein molecule for internalization of MOR) in the locus coeruleus (LC) region in bone cancer pain (BCP) rats with morphine tolerance (MT), so as to explore its mechanisms underlying improvement of BCP and MT. METHODS: The present study included two parts. In the first part, 23 female SD rats were randomized into sham BCP (n＝6), BCP (n＝9) and BCP＋MT (n＝8) groups, and in the second part, 61 female SD rats were randomized into 5 groups: sham BCP (n＝11), BCP (n＝11), BCP＋MT (n＝13), BCP＋MT＋EA (n＝13) and BCP＋MT＋sham EA (n＝13). The BCP morphine tolerance (BCP＋MT) model was established by injection of 10 µL of human Walker 256 breast cancer cells (MRMT-1 breast cancer cells, 1 x104 cells/µL) into the bone marrow cavity at the upper part of the left tibia and intraperitoneal injection of morphine hydrochloride (10 mg/kg, once per 12 h, for 11 successive days). On day 21 after inoculation, EA (2 Hz/100 Hz, 0.5－1.5 mA, increasing 0.5 mA every 10 min) was began to applied to bilateral "Zusanli" (ST30) and "Kunlun" (BL60) immediately after the first intraperitoneal injection of morphine. The treatment was performed for 30 min every time, once daily for 7 successive days. The paw withdrawal threshold (PWT) was detected before and 10, 11, 21, 22, 24, 26 and 28 days after inoculation. The immunoactivity of MOR and Rab5 proteins in the LC region was detected by immunofluorescence histochemistry. RESULTS: In the first part of the study, at the 10th day after inoculation of cancer cells, the PWT of the BCP and BCP＋MT groups was significantly lower than that of the sham BCP group (P0.05) but significantly lower than that of the sham BCP group (P0.05). CONCLUSION: EA intervention can relieve pain and MT in bone cancer pain rats with MT, which may be related to its effects in increasing MOR expression and promoting endocytosis of MOR in LC region.

Role of On-cells and Off-cells in the rostral ventromedial medulla in pain modulation / 上海交通大学学报（医学版）

The rostral ventromedial medulla is one of the key structures in descending pain modulation system. It receives inputs from the thalamus, the periaqueductal gray, and parabrachial nucleus, and sends descending projections through the dorsolateral funiculus and ventrolateral funiculus to the spinal dorsal horns. The rostral ventromedial medulla is thought to be the final relay in descending modulation of pain. The neurons in this region can be classified into On-cells, Off-cells and Neutral cells according to the changes in the firing activity before tail flick. This review mainly focuses on pain modulation functions and potential analgesia mechanisms of On-cells and Off-cells.

Differential expression of spinal γ-aminobutyric acid and opioid receptors modulates the analgesic effects of intrathecal curcumin on postoperative/inflammatory pain in rats

BACKGROUND: Curcumin is traditionally used as an herbal medicine. We explored the efficacy of intrathecal curcumin in relieving both postoperative and inflammatory pain and elucidated the mechanisms of action of curcumin interacting with γ-aminobutyric acid (GABA) and opioid receptors at the spinal level. METHODS: Experimental pain was induced in male Sprague-Dawley rats via paw incision or injection of intraplantar carrageenan. After examination of the effects of intrathecal curcumin on the pain, GABA and opioid receptor antagonists were intrathecally administered to explore the involvement of GABA or opioid receptors on the effect of curcumin. Additionally, the expression levels of the GABA and opioid receptors were assessed. RESULTS: Intrathecal curcumin reduced the withdrawal threshold of both incisional surgery- and carrageenan injection-induced nociception. Intrathecal GABA and opioid receptor antagonists reversed the curcumin-mediated antinociception. Incisional surgery decreased the levels of the GABA receptors mRNA, but little changed the levels of the opioid receptors mRNA. Carrageenan injection increased the levels of the opioid receptors mRNA, but not the GABA receptors mRNA levels. Intrathecal curcumin increased or decreased the levels of GABA receptors mRNA and opioid receptors mRNA in the spinal cords of incised or carrageenan-injected rats, respectively. CONCLUSIONS: Intrathecal curcumin was effective to postoperative and inflammatory pain and such antinociception of curcumin was antagonized by both GABA and opioid receptor antagonists. Also, intrathecal curcumin altered the levels of GABA and opioid receptors. Thus, spinal GABA and opioid receptors may, respectively, be directly or indirectly involved when curcumin alleviates postoperative and inflammatory pain.

Can oliceridine (TRV130), an ideal novel µ receptor G protein pathway selective (µ-GPS) modulator, provide analgesia without opioid-related adverse reactions?

All drugs have both favorable therapeutic and untoward adverse effects. Conventional opioid analgesics possess both analgesia and adverse reactions, such as nausea, vomiting, and respiratory depression. The opioid ligand binds to µ opioid receptor and non-selectively activates two intracellular signaling pathways: the G protein pathway induce analgesia, while the β-arrestin pathway is responsible for the opioid-related adverse reactions. An ideal opioid should activate the G protein pathway while deactivating the β-arrestin pathway. Oliceridine (TRV130) has a novel characteristic mechanism on the action of the µ receptor G protein pathway selective (µ-GPS) modulation. Even though adverse reactions (ADRs) are significantly attenuated, while the analgesic effect is augmented, the some residual ADRs persist. Consequently, a G protein biased µ opioid ligand, oliceridine, improves the therapeutic index owing to increased analgesia with decreased adverse events. This review article provides a brief history, mechanism of action, pharmacokinetics, pharmacodynamics, and ADRs of oliceridine.

Stable co-expression of human kappa opioid receptor and PKAcat-EGFP in CHO cells and functional identification / 中国药理学通报

Aim To establish a cell model which stably co-ex-press human kappa opioid receptor (hKOR) and enhanced green fluorescent protein ( EGFP) labeled catalytic domain of cAMP-dependent protein kinase A(PKAcat) fusion protein (PKAcat-EGFP) in Chinese hamster ovary(CHO) cells, laying the foun-dation for the high-throughput screening of hKOR drugs and drug molecular mechanisms in vitro. Methods Hygromycin B resist-ant hKOR recombinant plasmid [ pcDNA3.1/Hygro ( + ) -hKOR] was transfected into CHO cells stably expressing PKA-cat-EGFP by a lipofectin based method. Transfected cells were selected in culture medium containing hygromycin B. The posi-tive clones were selected by PKA redistribution assay. Z’ factor was used for evaluation and validation the reliability of the cell model. PKA redistribution assay and LANCE cAMP 384 Kit were used to test the function of the receptors in selected clone. Results CHO-PKAcat-EGFP/hKOR-13 cell model exhibited stable response in PKA redistribution assay and LANCE cAMP 384 Kit. Treated with 100 nmol·L-1U-50488 for 30 min, the average value of Z’ factor was 0.596, proving the reliability of the cell model. The hKOR expression in cell model remained stable after a few generations. Conclusion The CHO-PKAcat-EGFP/hKOR-13 cell model with stable co-expression of hKOR and PKAcat-EGFP has been successfully established.

Expression of µ-Opioid Receptor in CA1 Hippocampal Astrocytes

µ-opioid receptor (MOR) is a class of opioid receptors with a high affinity for enkephalins and beta-endorphin. In hippocampus, activation of MOR is known to enhance the neuronal excitability of pyramidal neurons, which has been mainly attributed to a disinhibition of pyramidal neurons via activating Gαi subunit to suppress the presynaptic release of GABA in hippocampal interneurons. In contrast, the potential role of MOR in hippocampal astrocytes, the most abundant cell type in the brain, has remained unexplored. Here, we determine the cellular and subcellular distribution of MOR in different cell types of the hippocampus by utilizing MOR-mCherry mice and two different antibodies against MOR. Consistent with previous findings, we demonstrate that MOR expression in the CA1 pyramidal layer is co-localized with axon terminals from GABAergic inhibitory neurons but not with soma of pyramidal neurons. More importantly, we demonstrate that MOR is highly expressed in CA1 hippocampal astrocytes. The ultrastructural analysis further demonstrates that the astrocytic MOR is localized in soma and processes, but not in microdomains near synapses. Lastly, we demonstrate that astrocytes in ventral tegmental area and nucleus accumbens also express MOR. Our results provide the unprecedented evidence for the presence of MOR in astrocytes, implicating potential roles of astrocytic MOR in addictive behaviors.

Advances of Butorphanol in Clinical Research / 中国医师进修杂志

Pain is a common and crucial problem in clinical practice, because it has a profound influence on patients in perioperative period. Butorphanol, among plenty of analgesics, is widely used in clinical trials for its various advantages and better analgesic effects. As a typical agonist-antagonist opioid analgesic agent, butorphanol, however, shows different clinical manifestations with different affinity for opioid receptors 25∶4∶1 (κ∶μ∶δ). Besides, butorphanol provides remarkable analgesic and sedative effect in preemptive analgesia, induction and recovery period in general anesthesia, and postoperative analgesia And it could be as a adjuvant to local anaesthesia either. Compared with other opioid drugs, butorphanol is less likely to have side effect on respiratory depression. In addition, its physical dependence is extremely low.

New thoughts in mechanism research of acupuncture for myocardial stunning from κ-opioid receptor signaling pathway / 中国针灸

By reviewing the literature regarding the development mechanism of myocardial stunning, effects of acupuncture on myocardial ischemic injury, and correlation between acupuncture and κ-opioid receptor, it was suggested that acupuncture was highly likely to act on κ-opioid receptor in myocardial cells, and directly treated myocardial malfunction induced by myocardial stunning through κ-opioid receptor and its signaling pathway. In addition, acupuncture could inhabit the signaling pathway of adrenoceptor β1, one of the main functional receptors, to indirectly improve myocardial ischemic injury. From κ-opioid receptor signaling pathway, the action mechanism of acupuncture for prevention and treatment of myocardial stunning was discussed in this paper, hoping to provide new ideas for possible mechanism of acupuncture for myocardial ischemic injury.

Effects of electroacupuncture on expression of μ-opioid receptor in nucleus ceruleus in rats with bone cancer pain-morphine tolerance / 中国针灸

<p><b>OBJECTIVE</b>To observe the effects of electroacupuncture (EA) on pain behavior in rats with bone cancer pain and morphine tolerance, and to explore partial action mechanism.</p><p><b>METHODS</b>Forty-two SD healthy female rats were randomly divided into a sham operation group (7 rats), a bone cancer pain group (8 rats), a morphine tolerance group (9 rats), an EA group (9 rats) and a sham EA group (9 rats). The rats in the sham operation group were treated with injection of phosphate buffer saline at medullary cavity of left-side tibia, and the rats in the remaining groups were injected with MRMT-1 breast cancer cells. After operation, no treatment was given to rats in the sham operation group and bone cancer pain group. 11 days after operation, rats in the morphine tole-rance group, EA group and sham EA group were treated with intraperitoneal injection of morphine hydrochloride, once every 12 hours, for 11 days to establish the model of bone cancer pain and morphine tolerance. One day after the establishment of this bone cancer pain model, the rats in the morphine tolerance group were injected with morphine, once every 12 hours (9:00 a.m. and 9:00 p.m.) for 7 days; the rats in the EA group and sham EA group were injected with morphine at 9:00 a.m., and treated with EA (2 Hz/100 Hz) and sham EA (only injected into the subcutaneous tissue) at bilateral "Zusanli" (ST 36) and "Kunlun" (BL 60), 30 min per treatment, once a day for 7 days. One day before cancer cell injection, 6 days, 8 days, 10 days after operation, after 30 min on 1 days, 5 days, 9 days, 11 days of morphine injection, and after 30 min on 1 days, 3 days, 5 days, 7 days of EA treatment, the paw withdrawal threshold (PWT) was measured in each group. On 11 day of morphine injection, HE staining was applied to observe the morphology and structure change of tibia in the sham operation group, bone cancer pain group and morphine tolerance group, random 2 rats in each group. On 7 days of EA treatment, fluorescent immunohistochemical method was applied to observe the expression of μ-opioid receptor positive cells in nucleus ceruleus in each group, random 4 rats in each one.</p><p><b>RESULTS</b>After 10 days of the cancer cells injection, the PWT of 28 rats of bone cancer pain model (8 rats in the bone cancer pain group, 8 rats in the morphine tolerance group, 6 rats in the EA group and 6 rats in the sham EA group) was significantly lower than that of 7 rats in the sham operation group (<0.01). After one day of morphine injection, the PWT of the morphine tolerance group, EA group and sham EA group was higher than that of the bone cancer pain group (all<0.01); on 11 d of morphine injection, the PWT of the morphine tolerance group, EA group and sham EA group was not significantly different from that of the bone cancer pain group (all>0.05). On 11 d of morphine injection, the tumor induced by cancer cells was observed in upper 1/3 tibia in the bone cancer pain group and morphine tolerance group, and the marrow cavity was filled with MRMT-1 cancer cells; no abnormal change was observed in the sham operation group. On 1 d, 3 d, 5 d and 7 d of EA treatment, the PWT of the cancer pain group, morphine tolerance group and sham EA group was lower than that of the EA group (all<0.01). On 7 d of EA treatment, the positive expression of MOR in nucleus ceruleus in the cancer pain group, morphine tolerance group, EA group and sham EA group was lower than that in the sham operation group (<0.01,<0.05), and that in the cancer pain group, morphine tolerance group and sham EA group was lower than that in the EA group (all<0.01).</p><p><b>CONCLUSIONS</b>EA can improve mechanical pain threshold in rats with bone cancer pain-morphine tolerance, and improve the abnormal pain, which is likely to be involved with improvement of the MOR positive cells expression in nucleus ceruleus by EA.</p>