Pao-Luh Tao

Amitriptyline suppresses neuroinflammation and up-regulates glutamate transporters in morphine-tolerant rats.

Abstract The present study was performed to evaluate the effects of the tricyclic antidepressant amitriptyline on morphine tolerance in rats. Male Wistar rats were implanted with two intrathecal (i.t.) catheters with or without a microdialysis probe, then received a continuous i.t. infusion of saline (control) or morphine (15 μg/h) and/or amitriptyline (15 μg/h) for 5 days. The results showed that amitriptyline alone did not produce an antinociceptive effect, while morphine alone induced antinociceptive tolerance and down‐regulation of spinal glutamate transporters (GLAST, GLT‐1, and EAAC1) in the rat spinal cord dorsal horn. Co‐administration of amitriptyline with morphine attenuated morphine tolerance and up‐regulated GLAST and GLT‐1 expression. On day 5, morphine challenge (10 μg/10 μl) resulted in a significant increase in levels of the excitatory amino acids (EAAs), aspartate and glutamate, in CSF dialysates in morphine‐tolerant rats. Amitriptyline co‐infusion not only markedly suppressed this morphine‐evoked EAA release, but also preserved the antinociceptive effect of acute morphine challenge at the end of infusion. Glial cells activation and increased cytokine expression (TNFα, IL‐1β, and IL‐6) in the rat spinal cord were induced by the 5‐day morphine infusion and these neuroimmune responses were also prevented by amitriptyline co‐infusion. These results show that amitriptyline not only attenuates morphine tolerance, but also preserves its antinociceptive effect. The mechanisms involved may include: (a) inhibition of pro‐inflammatory cytokine expression, (b) prevention of glutamate transporter down‐regulation, and even up‐regulation of glial GTs GLAST and GLT‐1 expression, with (c) attenuation of morphine‐evoked EAA release following continuous long‐term morphine infusion.

Pre-incisional epidural ketamine, morphine and bupivacaine combined with epidural and general anaesthesia provides pre-emptive analgesia for upper abdominal surgery.

Background: Previous studies have shown that N‐methyl‐D‐asparate (NMDA) receptor antagonists provide a pre‐emptive analgesic effect in humans. This study investigated the benefits of pre‐emptive analgesia for upper abdominal surgery, using pre‐incisional epidural ketamine + morphine + bupivacaine (K+M+B) treatment for achieving postoperative pain relief.

Decrease in δ-opioid receptor density in rat brain after chronic [d-Ala2,d-Leu5]enkephalin treatment

Chronic treatment of Sprague-Dawley rats with [D-Ala2,D-Leu5]enkephalin (DADLE) resulted in the development of tolerance to the antinociceptive effect of this opioid peptide. When opioid receptor binding was measured, time-dependent decreases in [3H]diprenorphine binding to the P2 membranes prepared from the cortex, midbrain and striatum were observed. Scatchard analysis of the saturation binding data revealed a decrease in Bmax values and no change in the Kd values of [3H]diprenorphine binding to these brain regions, indicative of down-regulation of the receptor. This reduction in the opioid receptor binding activities could be demonstrated to be due to the DADLE effect on the delta-opioid receptors in these brain regions. When [3H]DADLE binding was carried out in the presence of morphiceptin, a significant reduction in the delta-opioid receptor binding was observed in all brain areas tested. mu-Opioid receptor binding decrease was observed only in the striatum after 5 days of DADLE treatment. Additionally, the onset of delta-opioid receptor decrease in the midbrain area was rapid, within 6 h of the initiation of the chronic DADLE treatment. Thus, analogous to previous observations in which chronic etorphine treatment preferentially reduced mu-opioid receptor binding, chronic DADLE treatment preferentially reduced delta-opioid receptor binding activity.

Increasing of intrathecal CSF excitatory amino acids concentration following morphine challenge in morphine-tolerant rats

Excitatory amino acids (EAAs) are involved in the development of opioid tolerance. The present study reveals that an increasing of CSF EAAs concentration might be responsible for the losing of morphines antinociceptive effect in morphine tolerant rats. Male Wistar rats were implanted with two intrathecal (i.t.) catheters and one microdialysis probe, then continuously infused i.t. for 5 days with saline (1 microl/h; control group), morphine (15 micrograms/h), the NMDA antagonist, MK-801 (5 micrograms/h), or morphine (15 micrograms/h) plus MK-801 (5 micrograms/h). Each day, tail-flick responses were measured; in addition, CSF dialysates were collected and CSF amino acids measured by high performance liquid chromatography using a fluorescence detector. Morphine started to lose its analgesic effect on day 2 and this effect was overcome by MK-801. The AD(50) (AD: analgesic dose) was 1.33 micrograms in control animals, 83.83 micrograms in morphine-tolerant rats (a 63-fold shift), and 11.2 micrograms (a 8.4-fold shift) in rats that had received MK-801 plus morphine. No significant differences were observed in CSF amino acid release between the groups from day 1 to day 5. On day 5, after basal dialysate collection, a 10-micrograms challenge of morphine was administered i.t., and CSF samples collected over the next 3 h. After morphine challenge, morphine-tolerant rats showed a significant increase in the release of glutamate and aspartate (131+/-9.5% and 156+/-12% of basal levels, respectively), and no antinociceptive effect in the tail-flick latency test, while MK-801/morphine co-infused rats showed no increase in morphine-induced EAA release and a partial antinociceptive effect (MPE=40%). The present study provides direct evidence for a relationship between EAA release and a lack of an antinociceptive response to morphine, and shows that the NMDA antagonist, MK-801, attenuates both of these effects.

Co-administration of dextromethorphan with morphine attenuates morphine rewarding effect and related dopamine releases at the nucleus accumbens.

Morphine is one of the most effective analgesics in clinic to treat postoperative pain or cancer pain. A major drawback of its continuous use is the development of tolerance and dependence. In our previous study we found that a widely used antitussive agent in clinics, dextromethorphan [(DM); also known as a non-competitive N-methyl-d-aspartate (NMDA) antagonist], could prevent the development of morphine tolerance. In the present study, we further investigated its effect on morphine addiction. Conditioned place preference (CPP) test and behavioral sensitization of locomotor activity were used to investigate the drug-seeking related behaviors, which were in correlation with psychological dependence. Our results showed that co-administered DM was able to abolish completely the CPP effect induced by morphine, but had no effect on morphine-induced behavioral sensitization. By employing the microdialysis technique in free-moving animals, we also determined the extracellular level of dopamine and serotonin metabolites in the shell region of the nucleus accumbens (NAc) in its response to morphine with/without DM. A significant increase in dopamine metabolites following morphine administration was demonstrated in the NAc. This increase by morphine could be attenuated by co-administered DM, whereas DM itself did not show any effect. Based on our results, it is speculated that DM may effectively attenuate morphine-induced psychological dependence. Neurochemical analysis revealed that the effect of DM could be through its action on the dopaminergic mesolimbic pathway, which could be activated by morphine and attributed to the cause of rewarding.

Amitriptyline preserves morphine’s antinociceptive effect by regulating the glutamate transporter GLAST and GLT-1 trafficking and excitatory amino acids concentration in morphine-tolerant rats

Abstract The present study was undertaken to examine the effect of amitriptyline on the antinociceptive effect of morphine and its underlying mechanisms in regulating glutamate transporters trafficking in morphine‐tolerant rats. Long‐term morphine infusion induced antinociceptive tolerance and down‐regulation of glutamate transporters (GTs), GLAST, GLT‐1, and EAAC1, expression in the rat spinal cord dorsal horn. Acute amitriptyline treatment potentiated morphine’s antinociceptive effect, with a 5.3‐fold leftward shift of morphine’s dose–response curve in morphine‐tolerant rats, and this was associated with GLAST and GLT‐1 trafficking onto the cell surface. Similar to our previous studies, morphine challenge (10 μg/10 μl, i.t.) significant by increased the excitatory amino acids (EAAs) aspartate and glutamate level in the CSF dialysates of morphine‐tolerant rats. Acute amitriptyline treatment not only suppressed this morphine‐evoked EAA release, but further reduced the EAA concentration than baseline level. Furthermore, long‐term morphine infusion up‐regulated PKA and PKC protein expression in the spinal cord dorsal horn, while amitriptyline inhibited the increase in expression of phospho‐PKA, PKCα, PKCβII, and PKCγ. In morphine‐tolerant rats, acute treatment with PKA inhibitor H89 and PKC inhibitor Gö6805 attenuated morphine tolerance and the morphine‐induced CSF glutamate and aspartate elevation, and induced trafficking of GLAST and GLT‐1 from cytosol onto the cell surface. These results show that acute amitriptyline treatment preserved morphine’s antinociceptive effect in morphine‐tolerant rats; the mechanisms may be involved in inhibition of phospho‐PKA and PKC expression, and thus inducing the GLAST and GLT‐1 trafficking onto glial cell surface which enhances the EAA uptake from the synaptic cleft and reduces EAA concentration in the spinal CSF.

Amitriptyline suppresses neuroinflammation-dependent interleukin-10-p38 mitogen-activated protein kinase-heme oxygenase-1 signaling pathway in chronic morphine-infused rats.

Background:This study explores the underlying mechanism of the antiinflammatory effect of amitriptyline in chronic morphine-infused rats. Methods:Male Wistar rats were implanted with two intrathecal catheters. One catheter was for the continuous infusion of saline, amitriptyline (15 &mgr;g/h), morphine (15 &mgr;g/h), p38 mitogen-activated protein kinase inhibitor SB203580 (0.5 &mgr;g/h), morphine plus amitriptyline, or morphine plus amitriptyline plus SB203580 for 5 days. The other catheter was used for daily intrathecal injection of anti–interleukin-10 (IL-10) antibody or heme oxygenase-1 inhibitor zinc protoporphyrin for 5 days. Results:Amitriptyline/morphine coinfusion upregulated IL-10 protein expression in microglia; this was not observed in morphine-infused rats. Anti–IL-10 antibody effectively neutralized the amitriptyline-induced IL-10 expression in chronic morphine-infused rats. In addition, coinfusion of amitriptyline restored the antinociceptive effect of morphine (a 4.8-fold right-shift of the morphine dose-response curve compared to a 77.8-fold right-shift in its absence), and the injection of anti–IL-10 antibody or coinfusion of SB203580 partially reversed the effect of amitriptyline on the antinociceptive effect of morphine in morphine-infused rats (a 17.9-fold and 15.1-fold right-shift in morphine dose-response curves). Anti–IL-10 antibody and SB203580 significantly inhibited the amitriptyline-induced p38 mitogen-activated protein kinase and heme oxygenase-1 expression and the associated antiinflammatory effect of amitriptyline. Daily injection of zinc protoporphyrin also demonstrated that it reverses the effect of amitriptyline in morphine’s antinociception and antiinflammation in chronic morphine-infused rats. Conclusions:These results suggest that the antiinflammatory effect of amitriptyline on morphine tolerance, probably acting by increasing IL-10 expression, is mediated by p38 mitogen-activated protein kinase heme oxygenase-1 signal transduction cascade.

Decrease in μ-opioid receptor binding capacity in rat brain after chronic PL017 treatment

In previous studies, we have demonstrated that chronic treatment of rats with either etorphine or D-Ala2, D-Leu5-enkephalin (DADLE) resulted in the reduction of opioid receptor binding activities during the course of tolerance development. In both cases, mu-opioid receptor binding capacity was attenuated together with the delta-opioid receptor binding capacity. Because both etorphine and DADLE are relatively non-specific opioid ligands, interacting with both mu and delta receptors, these studies could not determine whether down-regulation of a specific receptor type is possible. Therefore, in the current studies, animals were rendered tolerant to the mu-opioid receptor-selective ligand PL017 and the receptor binding capacity was measured afterwards. Treating Sprague-Dawley rats with increasing doses of PL017 (2.5-20 micrograms/kg) i.c.v. for 5 days resulted in a 30- to 40-fold increase in the AD50 of the peptide to elicit the antinociceptive response and about 14-fold increase in the ED50 of the peptide to elicit the catatonic effect. When mu- and delta-binding was determined using [3H]diprenorphine in the presence of morphiceptin or DPDPE respectively, a significant decrease (20-30%) in the mu-opioid receptor binding but not in delta-opioid receptor binding was observed in all the brain areas tested after 5 days of PL017 treatment. Scatchard analysis of the [3H]DAMGO saturation binding data revealed a decrease in Bmax values and no change in the Kd values. Hence, mu-opioid receptors can be specifically regulated by ligand in the brain as delta-receptors are in neuroblastoma x glioma NG 108-15 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of nitric oxide in the development of morphine tolerance in rat hippocampal slices.

In the present study, we investigated the effects of a nitric oxide (NO) precursor, L-arginine, on the effect of different drugs, [trans-3, 4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]-benzeneacetamid e hydrochloride] (U-50,488, a kappa-opioid receptor agonist); dPTyr(Me)AVP (a vasopressin receptor antagonist); dizocilpine (MK-801, a N-methyl-D-aspartate (NMDA) receptor antagonist), to block the development of morphine tolerance or NO release in Sprague-Dawley rat hippocampal slices (450 microm). Slices were continuously superfused with artificial cerebrospinal fluid (ACSF) or drugs at 1 ml/min. Nichrome wire electrodes were placed in the Schaffer-collateral pathway and used to deliver biphasic 0.2-ms pulses of 5-30 V (0.033 Hz). A glass microelectrode was placed in the CA1 area to record population spikes. The amount of NO released in the superfusate was measured as nitrite formation. When the slices were superfused with 10 microM morphine, the amplitude of population spikes increased 200%-300% in 30-40 min. However, this effect of morphine decreased, i.e., tolerance developed, after continuous superfusion of morphine for 2-6 h. On the other hand, the nitrite level was increased about 250% of the control level through 6 h of morphine superfusion. Co-superfusion of L-arginine with morphine could further increase the nitrite level and also facilitate the development of morphine tolerance. On the other hand, 3-Br-7-nitroindazole (a neuronal NO synthase inhibitor) decreased the nitrite level significantly and blocked the development of morphine tolerance. When either U-50,488 (200 nM) or dPTyr(Me)AVP (500 pM) or MK-801 (500 pM) was co-superfused with morphine (10 microM), the development of morphine tolerance was blocked significantly and the nitrite level decreased to 100%-150% of the control level. L-arginine (500 nM) significantly reversed the effect of these drugs to block the development of morphine tolerance or to decrease the nitrite level through 6 h of superfusion. These data suggest that NO may play a key role in the development of morphine tolerance. Drugs which suppress the synthesis or release of NO would be expected to block the development of morphine tolerance.

Preincisional dextromethorphan decreases postoperative pain and opioid requirement after modified radical mastectomy.

PurposeTo examine whether preincisional dextromethorphan (DM) improved analgesia after modified radical mastectomy (MRM).MethodsSixty patients (ASA I–II) scheduled for MRM were included and randomly allocated into two groups. Patients in the treatment group (DM) received 40 mg DM and 20 mg chlorpheniramine maleate (CPM) im, and those in the control group received 20 mg CPMim alone 30 min before skin incision. Meperidine, 1 mg·kg−1im, was given for postoperative pain relief as required. The time to first meperidine injection, total meperidine consumption, worst pain score, bed-rest time, and side effects were recorded every 24 hr for 48 hr after surgery by a resident anesthesiologist on a double-blind basis.ResultsA longer time to first meperidine injection (19.2 ± 1.6vs 1.5 ± 0.23 hr,P < 0.001) and lower meperidine consumption (0[10]vs 75[50] mg, median [interquartile range],P < 0.001) were observed in the DM group than in the control group. The bed-rest time was shorter in the DM than in the control group (18.0[4]vs 23.0[19] hr,P < 0.001). No difference was noted in worst VAS pain score. Meperidine-related side effects (nausea, vomiting, pruritus, dizziness, headache) were more frequent in the control (10/30) than in the DM group (3/30,P < 0.05). The number of patients who required meperidine injection for pain relief was lower in the DM (7/30) than in the control group (25/30,P < 0.005). No DM- or CPM-associated side effects were observed.ConclusionPreincisional IM. DM treatment decreased postoperative pain and opioid requirement after MRM surgery.RésuméObjectifDéterminer si l’administration préincision de dextrométhorphane (DM) améliore l’analgésie à la suite d’une mastectomie radicale modifiée (MRM).MéthodeSoixante patientes (ASA I–II) qui devaient subir une MRM ont participé à l’étude et ont été réparties au hasard en deux groupes. Les patientes du groupe de traitement (DM) ont reçu 40 mg de DM et 20 mg de maléate de chlorphéniramine (MCP)im, et celles du groupe témoin ont reçu 20 mg de MCPim seulement, 30 min avant l’incision cutanée. De la mépéridine, 1 mg·kg−1 im, a été administrée sur demande après l’opération pour soulager la douleur. Ont été enregistrés par un anesthésiologiste en service selon un mode à double insu : le temps écoulé avant la première injection de mépéridine, la consommation totale de mépéridine, la douleur la plus intense, le temps de repos au lit et les effets secondaires.RésultatsUn délai plus long avant la première injection de mépéridine (19,2 ± 1,6vs 1,5 ± 0,23 h,P < 0,001) et une plus faible consommation de mépéridine (0[10]vs 75[50] mg, médiane [étendue interquartile],P < 0,001) ont été observés dans le groupe DM comparé au groupe témoin. Le temps de repos au lit a été plus court dans le groupe DM que dans le groupe témoin (18,0[4]vs 23,0[19] h,P < 0,001). Aucune différence n’a toutefois été notée quant à la douleur la plus intense selon I’EVA. Les effets secondaires reliés à la mépéridine (nausées, vomissements, prurit, étourdissements, céphalées) ont été plus fréquents dans le groupe témoin (10/30) que dans le groupe DM (3/30,P < 0,05). Moins de patientes du groupe DM (7/30) que du groupe témoin (25/30) ont demandé une injection de mépéridine pour soulager la douleur,P < 0,005). On n’a pas observé d’effets secondaires associés au DM ou au MCP.ConclusionL’administration préincision et intramusculaire de dextrométhorphane a réduit la douleur et les besoins d’opioïdes postopératoires à la suite d’une mastectomie radicale modifiée.