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<p><b>OBJECTIVE</b>To observe descending inhibition of cardiac nociception induced by microinjection of endomorphin-1 (EM1) in the ventrolateral periaqueductal gray (VLPAG) in rats effect and explore the role of μ-opioid receptor in mediating this effect.</p><p><b>METHODS</b>Male SD rats were randomized into electromyography (EMG) group and c-Fos group, both of which were further divided into 5 subgroups, namely 0.9% NaCl group, bradykinin (BK) group, BK+EM1 group, BK+CTOP group, and BK+CTOP+EM1 group. Rat models of cardiac nociception were established by intrapericardial injection of BK. The changes of cardiaosomatic motor reflex induced by BK were observed by assessing EMG responses of the dorsal spinotrapezius muscle; c-Fos expression in the spinal dorsal horn at levels T-T was tested.</p><p><b>RESULTS</b>Compared with 0.9% NaCl, intrapericardial BK injection induced obvious EMG activities and significantly increased c-Fos expression in the spinal dorsal horn at T-T ( < 0.05). Compared with BK injection, microinjection of EM1 in the VLPAG dose-dependently inhibited EMG activities and significantly decreased c-Fos expression ( < 0.05); microinjection of CTOP in the VLPAG produced no significant effect on EMG or c-Fos expression ( > 0.05). Microinjection of CTOP obviously reversed EM1-induced inhibition of EMG activities and c-Fos expression ( < 0.05).</p><p><b>CONCLUSIONS</b>Microinjection of EM1 in the VLPAG produces descending inhibition of cardiac nociception in rats by activating μ-opioid receptor.</p>
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Aim To observe the effect of endomorphin-1 (EM-1 )on TLR2 and TLR4 expressions of dendritic cells (DC)from human peripheral blood.Methods Monocytes isolated from human peripheral blood mono-nuclear cells were cultured in medium containing re-combinant human interleukin-4 and recombinant hu-man granulocyte macrophage colony stimulating factor. After six days of culture,the immature dendritic cells (imDC ) were divided into four groups,the control group (BLA group),EM-1 group,LPS group and LPS+EM-1 group.After 2 days of culture,the expres-sions of TLR2 and TLR4 were determined by fluores-cence activated cell sorter(FACS).The expressions of TLR2 and TLR4 at mRNA level in DC were detected by RT-PCR.Results The FACS results showed that the expressions of TLR2 and TLR4 in imDC were high-er,and their expressions were decreased with the mat-uration of DC.Compared with BLA group,the expres-sions of TLR2 and TLR4 in DC were down-regulated in EM-1 group (P0.05 ).mR-NA expressions of TLR2 and TLR4 on DC in LPS +EM-1 group were lower than those in LPS group (P<0.05 ).Conclusions EM-1 enables the down-regula-tion of the expressions of TLR2 and TLR4 on DC sur-face,the effects of EM-1 on immune function may be associated with TLR2 and TLR4 expressions on DC surface.
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The enzymatic synthesis of endomorphins were carried out by immobilized papain on sodium alginate-chitosan (IPSAC). The reaction has been carried out in two steps. First, Trp-Phe-NH2 was obtained by Boc-Trp-OH coupling with Phe-NH2 using IPSAC catalyst in microaqueous acetonitrile system with a 27.8 % yielding as determined by high performance liquid chromatography (HPLC). The catalytic properties of IPSAC were examined by studying the dependence of pH, ionic strength, solution content, reaction temperature,enzyme loading and reaction time over the yields. The results of orthogonal experiments indicated that pH was the most significant factor that influenced this synthesis. Second, Boc-Tyr-Pro-OMe and Trp-Phe-NH2 were suspended into the microaqueous acetonitrile to produce Tyr-Pro-Trp-Phe-NH2 (endomorphin-1) with a 35.2% yield.
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The present investigation was designed to study, whether endogenous antinociceptive system is effective on mirror-image pain induced by peripheral inflammation. After Complete Freund's adjuvant (CFA) was subcutaneously injected into one hindpaw, besides heat hyperalgesia and mechanical allodynia from 1 h to 72 h at the injured site, contralateral mechanical allodynia was also induced at 1 h and significantly lasted for 24 h after injection, which was called mirror-image pain. To explore the effects of endogenous antinociceptive system on mirror-image pain, endomorphin (EM) 2 was intrathecally administered at doses of 0.2 μg, 2 μg, 20 μg and EM1 was given at the maximum dose of 20 μg by the same way, respectively, 10 min prior to CFA injection. The present results showed that three doses of EM2could reverse the decreased contralateral mechanical threshold from 48.03 ± 9.07 mN ( pre-treatment with vehicle) to 200.49 ± 53.68mN, 247.63 ± 49.43 mN and 250.57 ± 55.34 mN ( pre-treatments with EM2 ), respectively, but not in a significantly dose-dependent manner. On the other hand, intrathecal pre-treatment with EM1, the contralateral mechanical threshold was 51.24 ± 12.59 mN after CFA injection, which was similar to that pre-treatment with vehicle. It indicates that spinal EM1 did not have remarkable effect on mirror-image pain behavior. The present results provide evidence for that spinal EM2, but not EM1, mainly originated from the endogenous antinociceptive system might play an inhibitory role in mirror-image mechanical allodynia induced by peripheral tissue inflammation.
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Effects of endomorphin-1 (EM-1) and endomorphin-2 (EM-2) on synaptic transmission were investigated on neurons in substantia gelatinosa (SG) of the spinal dorsal horn by whole-cell voltage clamp recording. Both EM-1 (1 μmol/L) and EM-2 (1 μmol/L)remarkably reduced the frequency but not the amplitude of miniature excitatory postsynaptic currents (mEPSCs) and miniature inhibitory postsynaptic currents (mIPSCs). These effects were antagonized by 3-funaltrexamine ( β-FNA, 10 μmol/L), a selective μ-opioid receptor antagonist. Noticeably, EM-1 showed higher potency in decreasing the frequency of mEPSCs and mIPSCs than that of EM-2. These results indicate that EMs suppress both excitatory and inhibitory synaptic transmission by activating presynaptic μ-opioid receptors in the SG and EM-1, compared with EM-2, might be a more potent endogenous analgesic at the spinal cord level.
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This study was performed to test whether endomorphin-1 has analgesic effect, when locally administrated into inflamed peripheral tissue. Carrageenan suspension (0.5%) was injected intraplantarly into the right paw of Sprague-Dawley male rats, and the rats were subjected to a series of mechanical stimuli with von Frei filaments before and after the injection. Carrageenan-injected rats showed typical inflammatory hyperalgesic signs and decrease of withdrawal threshold, peaked at 3 to 6 hours after the injection and lasted more than 3 days. Endomorphin-1 was intraplantarly injected with carrageenan, simultaneously or 3~4 hours after carrageenan. Simultaneous injection of endomorphin-1 with carrageenan significantly reduced hyperalgesia and thd analgesic effect was prolonged up to 8 hours. The delivery of endomorphin-1 (50 microgram) into the inflamed area after 3 to 4 hours of carrageenan injection significantly increased the threshold of hyperalgesic mechanical withdrawal response, but only partially. Intrathecal treatment of endomorphin-1 completely reversed carrageenan-induced hyperalgesia. This report is the first to show that peripherally delivered endomorphin-1 relieved inflammatory hyperalgesia. But a control through peripheral mu-opioid receptors appears to be not sufficient for complete pain treatment.
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Animales , Humanos , Masculino , Ratas , Carragenina , Hiperalgesia , Inflamación , Ratas Sprague-DawleyRESUMEN
Objective: To observe the effects of OFQ on endomorphin-1 in pain modulation. Methods: OFQ and endomorphin-1 were microinjected intracerebroventricularly or intrathecally in rats. The pain thresholds were measured by tail-flick test and acetic-acid induced twitching test, and the changes of antinociceptive effects induced by endomorphin-1 were observed. Results: OFQ antagonizing endomorphin-1 antinociception at the supraspinal level, while enhancing at the spinal level were observed. Conclusion: OFQ has functional effects on endomorphin-1 in pain modulation,both in the brain and the spinal cord. The mechanisms of its effect may be different.
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Objective:To observe the development of tolerance and dependence to endomorphin 1(EM 1) and its regulation on ? opioid receptor(MOR) in rat brain,providing references for the mechanism of the EM 1 dependence. Methods: Totally 60 SD rats were randomly divided into saline, acute EM 1 treatment and chronic EM 1 treatment groups. For acute EM 1 treatment, rats were injected intracerebroventricularly with 10 ?g/kg EM 1 30 min prior to sacrifice. The chronic group were treated with EM 1 daily administration at 8:00 and 15:00 starting with 10 ?g/kg on day 1 to 50 ?g/kg on day 9. After chronic EM 1 treatment on day 1, 3, 6 and 9, the antinociceptive AD 50 or catatonic ED 50 values were determined by modified Dixon's method. The B max and K d values of 3H DAMGO saturation binding to MOR were measured by Scatchard analysis. The gene expression of MOR was appraised by RT PCR. Results:(1) EM 1 chronic treatment produced a high degree of tolerance to the antinociceptic and catatonic effects on the 3rd day (3.1 fold and 1.9 fold) and the 9th day (28.4 fold and 8.5 fold). The jumping times, weight lost and withdrawal score of rats were significantly higher than that of the control group after 9 d chronic EM 1 treatment. (2) After 9 d of administration with EM 1, the specific binding capacity and mRNA expression of MOR in rat cortex, midbrain and striatum were all decreased compared with those of the control and acute treatment groups, but the K d values were not significantly altered. Conclusion:Endomorphin 1 has the tolerant and dependent potent. For long term chronic treatment, Endomorphin 1 induces downregulation of the binding capacity and mRNA of MOR, which may be related to the dependence development.
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Objective To investigate the synaptic connections between endomorphin-immunoreactive(ir) terminals and ? opioid receptor-ir neurons in the superficial layers(laminae Ⅰ and Ⅱ) of the rat spinal dorsal horn. Methods The double-labeling immunohistochemical electron microscopic technique,i.e.pre-embedding immunohistochemical detection of endomorphin combin with pre-embedding immuno-gold particles labeling technique to identify ? opioid receptor-immunoreactivity,was used in the present study. Results ? opioid receptor-ir neuronal cell bodies,fibers as well as axon terminals were observed in laminae Ⅰ and Ⅱ of the spinal dorsal horn,meanwhile dense endomorphin-ir axon terminals were located mainly within the same region.Under electron microscope,the synaptic connections formed by endomorphin-ir axon terminals labeled with diaminobenzidine(DAB) reaction products and ? opioid receptor-ir neuronal cell bodies and dendritic profiles labeled with immuno-gold particles were observed.The principle synaptic type was asymmetric synapse.There were more axon-dendritic synapses than axon-somatic ones as encountered in the present study.Conclusion The distribution patterns of endomorphin-ir and ? opioid receptor-ir structures match with each other in the superficial laminae of the spinal dorsal horn,that provides morphological base for the antinociceptive effects of endomorphin and ? opioid receptor in the processing of nociceptive information transmission.
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Objective To observe whether endomorphin-2-immunoreactive(EM2-ir) neurons in the trigeminal ganglion(TG) project to the medullary dorsal horn(MDH) in the rat. Methods Fluoro-gold(FG) retrograde tracing and immunofluorescent histochemical staining for EM2 were applied. Results After FG was injected into the MDH,many FG labeled neurons with small,medium and large diameters were observed in the TG.There were also aboundant EM2-ir neurons with different diameters in the TG.The majority of FG labeled neurons in the TG showed EM2-immunoreactivities.Almost all of the EM2/FG double-labeled neurons were medium and small in size.Conclusion EM2-ir neurons in the TG project to the MDH in the rat.