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Microglia are important cells involved in the regulation of neuropathic pain (NPP) and morphine tolerance. Information on their plasticity and polarity has been elucidated after determining their physiological structure, but there is still much to learn about the role of this type of cell in NPP and morphine tolerance. Microglia mediate multiple functions in health and disease by controlling damage in the central nervous system (CNS) and endogenous immune responses to disease. Microglial activation can result in altered opioid system activity, and NPP is characterized by resistance to morphine. Here we investigate the regulatory mechanisms of microglia and review the potential of microglial inhibitors for modulating NPP and morphine tolerance. Targeted inhibition of glial activation is a clinically promising approach to the treatment of NPP and the prevention of morphine tolerance. Finally, we suggest directions for future research on microglial inhibitors.
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Humans , Calcitonin Gene-Related Peptide/antagonists & inhibitors , Drug Tolerance , Hypoglycemic Agents/pharmacology , Microglia/physiology , MicroRNAs/physiology , Minocycline/pharmacology , Morphine/pharmacology , Neuralgia/etiology , Plant Extracts/pharmacology , Signal Transduction/physiologyABSTRACT
OBJECTIVE: To observe the effect of bone-edge electroacupuncture (EA) intervention on mechanical pain threshold (PT) and expression of G protein-coupled receptor kinase (GRK5), β-arrestin 2, total and phosphorylated PKC alpha (p-PKCα) proteins in the locus coeruleus (LC) of rats with bone cancer pain induced morphine tolerance, so as to reveal its partial central mechanisms underlying pain relief. METHODS: Forty SD rats were randomly divided into 5 groups, namely sham bone cancer, bone cancer pain, morphine tolerance, bone-edge EA, and sham EA (n＝ 8 rats in each group). The bone cancer with morphine tolerance model was established by intramedullary injection of MRMT-1 cells into the tibial cavity, and then intraperitoneal injection of morphine hydrochloride injection. After successful establishment of morphine tolerance model, the bone-edge EA (2 Hz/100 Hz，0.5－1.5 mA) was applied to bilateral "Zusanli" (ST36) and "Kunlun" (BL60) for 30 min, once a day for 7 days, after inserting the needle-tip to the tibial bone surface. The ipsilateral mechanical paw withdrawal thresholds (PWTs) were detected dynamically. The expression levels of GRK5, β-arrestin 2, PKCα and p-PKCα in the LC area were measured by Western blot. RESULTS: The PWTs of bone cancer pain rats were decreased on day 10 after inoculation of cancer cells (P0.05). The PWTs were significantly increased in the bone-edge EA intervention group (P0.05). In comparison with the sham bone cancer group, the expression of GRK5 protein in morphine tolerance group was significantly decreased (P<0.01); compared with morphine tolerance group, the expression of GRK5 protein in bone-edge EA group was increased(P<0.01). In comparison with the sham bone cancer group, the expression of β-arrestin 2 and p-PKCα in bone cancer group significantly increased (P<0.01). After the intervention, the increased β-arrestin 2 and p-PKCα expressions were reversed in the bone-edge EA group (P<0.01); compared with morphine tolerance group and sham EA group, the expression of PKCα protein was decreased(P<0.01). CONCLUSION: Bone-edge EA can effectively relieve morphine tolerance in bone cancer pain rats, which may be related to its functions in up-regulating GRK5 protein and down-regulating β-arrestin 2, PKCα and p-PKCα proteins in LC. .
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OBJECTIVE@#To observe the effect of early intervention of bone-nearby acupuncture (BNA) combined with electroacupuncture (EA) on the expression of histone deacetylase1(HDAC1), histone deacetylase 2 (HDAC2) andμ-opioid recepter (MOR) in dorsal root ganglia (DRG) of bone cancer pain-morphine tolerance (BCP-MT) rats, and to explore its possible mechanism.@*METHODS@#A total of 35 SD rats were randomized into a sham BCP group (=6), a BCP group (=7), a MT group (=7), a BNA+EA group (=8) and a shame BNA group (=7). Except of the sham BCP group, cancer cell inoculation operation at left tibia was given in the other 4 groups to establish the bone cancer pain model. In the MT group, the BNA+EA group and the shame BNA group, intraperitoneal injection of morphine hydrochloride was given to establish the morphine tolerance model. After the operation, bone-nearby acupuncture combined with electroacupuncture was applied at "Zusanli" (ST 36) and "Kunlun" (BL 60) in the BNA+EA group, with dilatational wave, 2 Hz/100 Hz in frequency, 0.5 to 1.5 mA in intensity. Intervention in the shame BNA group was applied at the same time and acupoints as those in the BNA+EA group, the needles were pierced the skin without any electrical stimulation. The needles were retained for 30 min, once a day for continuous 7 days in both BNA+EA and shame BNA groups. Before and 10, 11, 15, 22 days after the operation, the left paw withdrawal threshold (PWT) was measured in the 5 groups. The levels of HDAC1, HDAC2 and MOR in DRG were detected by Western blot.@*RESULTS@#Ten days after the cancer cell inoculation operation, the PWT of the BCP, MT, BNA+EA and sham BNA groups was decreased compared with the sham BCP group (0.05); the PWT of the BNA+EA group was increased compared with the MT and sham BNA group (<0.01). In the BCP group, the DRG levels of HDAC1 and HDCA2 were increased, while the level of MOR was decreased compared with the sham BCP group (<0.05, <0.01). In the MT group, the DRG level of HDAC1 was increased compared with the BCP group (<0.05). In the BNA+EA group, the DRG level of HDAC1 was decreased compared with the MT group and the sham BNA group (<0.01, <0.05), while the level of MOR was increased (<0.01).@*CONCLUSION@#Early intervention of bone-nearby acupuncture combined with electroacupuncture can relieve the morphine tolerance in bone cancer pain rats, it may relate to down-regulating the expression of HDAC1 and up-regulating the expression of MOR in the dorsal root ganglia.
Subject(s)
Animals , Rats , Acupuncture Points , Bone Neoplasms , Cancer Pain , Therapeutics , Drug Tolerance , Electroacupuncture , Ganglia, Spinal , Metabolism , Histone Deacetylases , Metabolism , Morphine , Random Allocation , Rats, Sprague-Dawley , Receptors, Opioid, mu , MetabolismABSTRACT
Microglia are important cells involved in the regulation of neuropathic pain (NPP) and morphine tolerance. Information on their plasticity and polarity has been elucidated after determining their physiological structure, but there is still much to learn about the role of this type of cell in NPP and morphine tolerance. Microglia mediate multiple functions in health and disease by controlling damage in the central nervous system (CNS) and endogenous immune responses to disease. Microglial activation can result in altered opioid system activity, and NPP is characterized by resistance to morphine. Here we investigate the regulatory mechanisms of microglia and review the potential of microglial inhibitors for modulating NPP and morphine tolerance. Targeted inhibition of glial activation is a clinically promising approach to the treatment of NPP and the prevention of morphine tolerance. Finally, we suggest directions for future research on microglial inhibitors.
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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.
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The ATP-gated ionotropic P2X7 receptor has been widely concerned in recent years. Upon activation by ATP and its derivatives, P2X7 receptor induces a series of responses such as activation of PANX1 and release of IL-lg. Elucidation of the role and mechanism of P2X7 receptor in pain would provide ideas for the development of new and effective analgesic drugs. This review discusses the recent progress of P2X7 receptor in inflammatory pain, neuropathic pain, cancer pain, and morphine tol-erance , and summarizes the possible mechanism of P2X7 receptor involved in the modulation of pain.
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<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>
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Honey has been used as a supplement nutrient in human for centuries. It exerts antibacterial, anticancer, anti-inflammatory properties as well as analgesic activity. But not many studies have been done to analyze effect of honey on morphine tolerance. Hence, this review is targeting on analgesic effect of honey bioactive compounds and their potential in morphine tolerance study.
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Objective: To evaluate the effect of down-regulation of Nav1.7 on the activation of astrocytes and microglia in DRG of rats with cancer pain, and explore the transmission of the nociceptive information. Methods: Lentiviral vector harboring RNAi sequence targeting the Nav1.7 gene was constructed, and Walker 256 breast cancer cell and morphine was injected to build the bone cancer pain model and morphine tolerance model in rats. Lentiviral vector was injected. Rats in each model were divided into 4 groups: model group, PBS group, vehicle group and LV-Nav1.7 group. The expression levels of GFAP and OX42 in dorsal root ganglia (DRG) were measured. Results: After the animal model was built, the level of Nav1.7, GFAP and OX42 was improved obviously with the time prolonged, which was statistically significant (P<0.05). The expression level of GFAP and OX42 in the DRG in the LV-Nav1.7 group declined obviously compared to the model group, PBS group and vehicle group (P<0.05). Conclusions: Intrathecal injection of Navl.7 shRNA lentiviral vector can reduce the expression of Nav1.7 and inhibit the activation of astrocytes and microglia in DRG. The effort is also effective in morphine tolerance bone cancer pain model rats.
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OBJECTIVE@#To evaluate the effect of down-regulation of Nav1.7 on the activation of astrocytes and microglia in DRG of rats with cancer pain, and explore the transmission of the nociceptive information.@*METHODS@#Lentiviral vector harboring RNAi sequence targeting the Nav1.7 gene was constructed, and Walker 256 breast cancer cell and morphine was injected to build the bone cancer pain model and morphine tolerance model in rats. Lentiviral vector was injected. Rats in each model were divided into 4 groups: model group, PBS group, vehicle group and LV-Nav1.7 group. The expression levels of GFAP and OX42 in dorsal root ganglia (DRG) were measured.@*RESULTS@#After the animal model was built, the level of Nav1.7, GFAP and OX42 was improved obviously with the time prolonged, which was statistically significant (P<0.05). The expression level of GFAP and OX42 in the DRG in the LV-Nav1.7 group declined obviously compared to the model group, PBS group and vehicle group (P<0.05).@*CONCLUSIONS@#Intrathecal injection of Navl.7 shRNA lentiviral vector can reduce the expression of Nav1.7 and inhibit the activation of astrocytes and microglia in DRG. The effort is also effective in morphine tolerance bone cancer pain model rats.
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Objective:To evaluate the effect of down-regulation of Nav1.7 on the activation of astrocytes and microglia in DRG of rats with cancer pain, and explore the transmission of the nociceptive information.Methods:Lentiviral vector harboring RNAi sequence targeting theNav1.7gene was constructed, and Walker 256 breast cancer cell and morphine was injected to build the bone cancer pain model and morphine tolerance model in rats. Lentiviral vector was injected. Rats in each model were divided into 4 groups: model group, PBS group, vehicle group and LV-Nav1.7 group. The expression levels of GFAP and OX42 in dorsal root ganglia (DRG) were measured.Results: After the animal model was built,the level of Nav1.7, GFAP and OX42 was improved obviously with the time prolonged, which was statistically significant (P<0.05). The expression level of GFAP and OX42 in the DRG in the LV-Nav1.7 group declined obviously compared to the model group, PBS group and vehicle group (P<0.05).Conclusions:Intrathecal injection of Navl.7 shRNA lentiviral vector can reduce the expression of Nav1.7 and inhibit the activation of astrocytes and microglia in DRG. The effort is also effective in morphine tolerance bone cancer pain model rats.
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Aim To explore the effect of knockdown spinal cord LCN2 by RNAi on the development of mor-phine tolerance in normal rats.Methods After suc-cessful intrathecal implantation, fourty-eight male Sprague-Dawley rats weighing 1 80 -220 grams were randomly divided into 4 groups (n =1 2):group I:control group,group II:morphine tolerance group, group Ⅲ:mismatch siRNA group,group IV:LCN2 siRNA group.The sixth day after intrathecal implanta-tion,rats were tested to ensure the position of cathe-ters,and it was recorded as d 0.On d 2 -8,rats were subcutaneously (s.c)injected of normal saline (NS) (group I)or morphine (group Ⅱ,Ⅲ,Ⅳ)1 0 μg· g -1 twice a day at 8:00 and 1 6:00.Before everyday s. c injection,rats were intrathecally injected of 1 0 μL DEPC solution (group Ⅰ,Ⅱ),1 0 μL DEPC solution containing 4 μg mismatch siRNA (group III)and 4 μg LCN2 siRNA solution (group IV).Paw withdrawal la-tencies to thermal stimuli (PWTL)were tested before morphine injection and 45 minutes after morphine in-jection on d 1 and d 9.The percentage of maximal pos-sible effect (% MPE)was calculated later.Animals were sacrificed on d 9 after the behavioral test and the lumbar enlargement segments of the spinal cord were removed for detecting the expression of phosphorylated-p38 mitogen-activated protein kinase (p-p38 MAPK) and LCN2 by Western blot and microglia marker Iba1 by immunofluorecence.Results On d 1 ,there was no significant difference in %MPE among four groups. On d 9,compared to group Ⅰ,%MPE was signifi-cantly reduced (P <0.05)while p-p38MAPK,LCN2 and Iba1 were markedly up-regulated in group Ⅱ andⅢ (P <0.05 ).On d 9,compared to group Ⅱ,%MPE was significantly increased while p-p38MAPK, LCN2 and Iba1 were markedly reduced in group IV (P<0.05).Conclusion Using LCN2 siRNA to knock-down spinal LCN2 relieves the development of mor-phine tolerance in normal rats possibly through inhibi-ting the activation of microglia and p38 MAPK in the spinal cord.
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Objective To observe the effect of intrathecal agmatine(AG) at the spinal cord level on morphine tolerance. Methods (1) Twenty-four SD rats were divided into four groups: control group, pure intrathecal injection(i.t.) of saline(15 μL); morphine group, i.t. morphine(15 μg/15 μL); AG group, i.t. AG (12.5 μg/15 μL); and morphine+AG group, i.t. morphine (15 μg/5 μg) and AG (12.5 μg/10 μL). Rats of the four groups were injected with 0.2 mg bee venom subcutaneously in the plantar 5 min after i.t, and the numbers of spontaneous paw withdrawal reflex were recorded within 1 hour. (2) Twenty-four SD rats were divided into three groups: control group, pure intrathecal saline(15 μL); morphine tolerance group, i.t. morphine(15 μg/5 μL) twice a day for 4 consecutive days; and morphine tolerance+AG group, i.t. morphine(15 μg/5 μL)twice a day for 4 consecutive days, on the fourth day the rats also received AG(12.5 μg/10 μL). Half of the rats were examined for thermal paw withdrawal latency and mechanical withdrawal threshold after i.t, and the other half was injected with 0.2 mg bee venom subcutaneously in the plantar 10 min after last dose; the number of spontaneous paw withdrawal reflex were recorded within 1 hour. Results (1)Compared with the control group, the numbers of flinches of intrathecal morphine and AG groups were significantly reduced(P<0.05). (2) In intrathecal morphine tolerance model, the thermal paw withdrawal latency and mechanical withdrawal threshold were significantly increased in the morphine tolerance+AG group compared with the control group (P<0.05);morphine tolerance + AG group had significantly stronger inhibitory effect against spontaneous s.c. BV-induced pain, with the number of spontaneous flinches within 1 hour decreased significantly in the morphine tolerance + AG group(P<0.05). Conclusion Intrathecal AG has synergistic effect with morphine in pain relieving, and it can also reverse the morphine tolerance induced by repeated i.t. injection.
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Objective To explore the efficacy of electroacupuncture treatment in cancer induced bone pain (CIBP)-morphine tolerance rat model and the expression of calcitonin-gene related peptide(CGRP) immunohistochemisty in dorsal root ganglion (DRG).Methods Forty SD rats were divided into four groups:sham group,CIBP + morphine tolerance group (BM),CIBP + electroacupuncture group (BE),and CIBP + morphine tolerance + electroacupuncture group (BME).BM,BE and BME groups were prepared CIBP model by carcinoma cell tibia implanted.After six days,the three CIBP groups accepted treatment of morphine,electroacupuncture,and morphine combined electroacupuncture,separately,nine days continuously.Acupoints were selected Zusanli (ST36) and Sanyinjiao (SP6).50％ mechanical withdraw threshold was evaluated by mechanical stimulation.CGRP expression in dorsal root ganglion was detected by immunohistochemisty.Results After five days of electroacupuncture treatment,pain threshold was (10.9 ± 0.8) g in BME group,(8.7 ± 0.6) g in BM group and (6.2 ± 0.9) g in BE group.The results had significant statistic differences (P ＜ 0.01,separately).IOD value of CGRP expression in dorsal root ganglion was 9026.5 ± 1827.4 in BME group,compared with 14803.1 ± 2086.7 in BM group and 15730.6 ± 2712.5 in BE group (P ＜ 0.01,separately).Results Electroacupuncture can relieve CIBP-morphine tolerance rat pain behavior.The mechanism is related to inhibiting CGRP overdue expression in DRG.
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Objective To explore the role of excitatory amino acid carrier 1 (EAAC1)in dorsal root ganglion (DRG) in the mechanism of developing morphine tolerance. Methods Thirty male SD rats were implanted intrathecal catheters and randomized into 6 groups with 5 rats each. The rats of 4 groups were made into the model of adjuvant-induced arthritis in the left hind limb and were administered intrathecally, morphine 10 μg(group M_(10)), morphine 20μg(group M_(20)), morphine 20 μg plus naloxone 10 μg(group MN) ,or saline(group C) respectively. The other 2 groups without were administered intrathecally saline (group C_0) or morphine 20 μg (group M0). The drugs were administered twice daily for 7 days. Mechanical withdrawl threshold(MWT) of the left hind limb was examined to evaluate the behavior. Immunohistochemistry was used to detect the expression of EAAC1 in the left L_(3-4) and L_(4-5) DRG. Results Morphine tolerance was formmed stably in the arthritis rats of group M_(10) and group M_(20) after administering morphine for 7 days. The expression of EAAC1 in DRG was downregulated. Conclusion DRG EAAC1 may be involved in the mechanism of developing morphine tolerance in rats with inflammatory pain.
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The MAPKs activation pathway consists of three protein kinases in activation sequence:MAPKs kinase kinases (MKKKs)→,MAPKs kinases (MKKs)→MAPKs and four pathways:extracellular signal-regulated kinase (MAPK~(ERK)),C-JUN N-terminal kinase (MAPK~(JNK)),MAPK~(P38) and MKKS/MAPK~(ERK5) activation pathways.It has been proved that MAPKs(ERK,JNK and P38) are acvtivated in the progress of morphine tolerance.Inhibitors of any element of MAPKs activation pathway may function as a potential clinical medicine for morphine tolerance.
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ObjectiveTo study the distribution and expression of NMDA receptor subunit 2A in the spinal cord of morphine tolerant rats. MethodsTwelve Sprague-Dawley rats were randomly divided into two groups with 6 rats each: control group (C) were intrathecally administrated 0.9% NaCl 10μl and morphine group(M) received 10μg morphine (i.t.). Drugs were administrated twice daily for 7 consecutive days. Tail flick latency (TFL) in the hot water immersion test was used to evaluate changes of thermal hyperalgesia latency of each group before and 30min after administration every morning. Rats were killed the day after last administration and L4～5 segment of the spinal cord was removed for determination the expression of NR2A by immunofluorescence method. ResultsTFL of group M was decreased gradually after chronic administration of morphine intrathecally. There was no significant difference between group M[(3.25±0.93)s] and group C[(2.66±0.27)s] on the 7th day (P＞0.05). A morphine tolerant model was established successfully. NR2A was distributed throughout the rat spinal cord. The expression of NR2A in group M(OD:9617±1233) was increased compared with group C(OD:2.66±0.93) (t=3.133,P＜0.05).ConclusionThe expression of NR2A was upregulated after repeated administration of morphine intrathecally in the superficial dorsal horn of spinal cord of morphine tolerant rats,which may be part of the mechanisms of morphine tolerance.
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0.05) in tail flick test.MPE% in group MK was always higher than group M and descended more slowly than group M,especially from the d4 to d8(P0.05). Conclusion Ketamine could block the development of morphine tolerance partly due to its inhibition effect on pCREB protein.
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AIMTo further elucidate the role of agmatine on the pharmacological effects of opioids. METHODSThe effect of L-arginine and L-arginine decarboxylase(L-ADC) antibodies on pain threshold, morphine ntinociception and tolerance were investigated in mouse acetic acid writhing test, mouse radiant heat tail flick test and mouse hot plate test. RESULTSIn mouse acetic acid writhing test, intracerebroventricular injection of L-arginine dose-ependently inhibited the writhing of mice compared with saline control. L-arginine did not influence the tail flick latency itself in mouse radiant heat tail flick test, but enhanced antinociceptive effect of morphine in a dose-dependent manner. The possible maximal analgesia percentage of morphine 2.5 mg*kg-1 was increased from 23% to 71%. Furthermore, L-arginine inhibited acute tolerance induced by morphine 100 mg*kg-1in mouse radiant heat tail flick test. The effect of L-arginine as mentioned above could be antagonized by idazoxan (3 mg*kg-1, ip), which is a selective antagonist of imidazoline receptors. L-ADC specific antibodies inhibited morphine antinociception and promoted the development of tolerance to morphine in mouse radiant heat tail flick test and 55℃ hot plate test. CONCLUSIONL-Arginine and L-ADC play important roles in the formation of pain threshold, morphine antinociception and tolerance.
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In the present study, we first examined whether the changes in the DNA binding activities of the transcription factors, cAMP response element binding protein (CREB) and activator protein-1 (AP-1) mediate the long-term effects of morphine in differentiated SH-SY5Y human neuroblastoma cells. The increases in CREB and AP-1 DNA binding activities were time-dependent up to 6 days of morphine treatment (1, 4, and 6 days). However, the significant reduction in the DNA binding activities of CREB and AP-1 was observed after 10 days of chronic morphine (10 muM) administration. Secondly, we examined whether the changes of CREB and AP-1 DNA binding activities could be modulated by dopamine and haloperidol. Dopamine cotreatment moderately increased the levels of the CREB and AP-1 DNA binding activities induced by 10 days of chronic morphine treatment, and haloperidol cotreatment also resulted in a moderate increase of the CREB and AP-1 DNA binding activities. However, dopamine or haloperidol only treatment showed a significant increase or decrease of the CREB and AP-1 DNA binding activities, respectively. In the case of acute morphine treatment, the CREB and AP-1 DNA binding activities were shown to decrease in a time-dependent manner (30, 60, 90, and 120 min). Taken these together, in differentiated SH-SY5Y cells, morphine tolerance seems to involve simultaneous changes of the CREB and AP-1 DNA binding activities. Our data also suggest the possible involvement of haloperidol in prevention or reversal of morphine tolerance at the transcriptional level.