The effect of microglial inhibition on the expression of BDNF, KCC2, and GABAA receptor before and after the establishment of CCI-induced neuropathic pain model.

Damage to the peripheral or central nervous system results in neuropathic pain. Based on a complicated mechanism, neuropathic pain has no efficient treatment so far. It has been well-known that the expression of some proteins (BDNF, KCC2, GABA-A) during neuropathic pain changes. Microglial cell activation is considered as a trigger to alter the expression of these proteins. In the current study, the effect of minocycline as a potent microglial activation inhibitor on the gene and protein expression of these neuropathic pain mediators was investigated. This experiment was done in two paradigms, preinjury and postinjury administration of minocycline. In each paradigm, male Wistar rats (weight 150-200 g, n = 6) were allocated to sham, control, and drug groups. Minocycline (30 mg/kg, i.p.) was injected 1 h before or at day seven after nerve injury and continued till day 14 in the preemptive or postinjury part of the study, respectively. After the last injection, the animals were decapitated and the lumbar part of the spinal cord was isolated to assess the expression of genes and proteins of interest. In the preventive study, minocycline increased the expression of KCC2 and GABA-A/γ2 proteins and decreased BDNF expression. On the other hand, the target gene expression and protein expression were not changed when minocycline was administered after nerve injury. It seems that minocycline was able to change the expression of proteins of interest merely when used before nerve damage.

Paroxetine effects on morphine analgesic tolerance in rats.

OBJECTIVES: To alleviate different pain intensities, morphine administration has been extensively used. However, prolonged administration of morphine leads to a progressive decline of its analgesic effect which limits their overall utility. Morphine tolerance is considered as a challenging issue for the treatment of both acute and chronic pain. We conducted this study in rats to investigate the effect of paroxetine on morphine tolerance when used preemptively or after morphine tolerance had developed. METHODS: Male Wistar rats (weight 250-300 g, n=10) were used to evaluate the effects of paroxetine on tolerance to morphine. In order to induce tolerance, daily intraperitoneal injection of morphine (7 mg/kg) was done. After tolerance induction, a group of animals received intraperitoneal injection of 10 mg/kg paroxetine 30 min prior to each morphine dose. In another trial, to investigate the potential of paroxetine to prevent tolerance to morphine, animals were pretreated with 10 mg/kg paroxetine 30 min before morphine administration. In the control groups, 10 mL/kg of saline was injected. The behavioral test (tail-flick test) was done for all groups. RESULTS: Our data showed that paroxetine significantly reversed tolerance to morphine when used after tolerance induction (p<0.001). However, administration of paroxetine before occurrence of tolerance had no effect. CONCLUSIONS: We conclude that paroxetine could decrease tolerance to morphine when used after the occurrence of morphine tolerance, while it was not able to prevent morphine tolerance when administered preemptively. ETHICAL COMMITTEE NUMBER: IRIB.SBMU.MSP.REC.1394.098.

Effect of Paroxetine on the Neuropathic Pain: A Molecular Study.

Background: Neuropathic pain, due to peripheral nerve damage, has influenced millions of people living all over the world. It has been shown that paroxetine can relieve neuropathic pain. Recently, the role of certain proteins like brain-derived neurotrophic factor (BDNF), GABAA receptor, and K+-Cl- cotransporter 2 (KCC2) transporter in the occurrence of neuropathic pain has been documented. In the current study, the expression of these proteins affected by paroxetine was evaluated. Methods: Male Wistar rats were allocated into two main groups of pre- and post-injury. Rats in each main group received paroxetine before nerve injury and at day seven after nerve damage till day 14, respectively. The lumbar spinal cord of animals was extracted to assess the expression of target genes and proteins. Results: In the preventive study, paroxetine decreased BDNF and increased KCC2 and GABAA gene and protein expression, while in the post-injury paradigm, it decreased BDNF and increased KCC2 genes and protein expression. In this regard, an increase in the protein expression of GABAA was observed. Conclusion: It seems that paroxetine with a change in the expression of three significant proteins involved in neuropathic pain could attenuate this type of chronic pain.

The Attenuating Effect of Curcumin on Morphine Dependence in Rats: The Involvement of Spinal Microglial Cells and Inflammatory Cytokines.

New evidence suggests an important role for spinal glial cells in the development of opioid dependence. Curcumin, a component of the Curcuma Longa, has shown to act as a suppressor of microglial cells. The main goal of this study was to explore the attenuating effects of curcumin on morphine dependence with a focus on spinal microglial cells and inflammatory cytokines. In order to induce morphine dependence in male Wistar rats, morphine was administered intraperitoneally (i.p.) once daily for 9 days in an increasing dose of 10, 20, and 40 mg/kg. Curcumin (2.5, 5, and 10 mg/kg, i.p.) was given from the days 10th to 18th. Naloxone-precipitated abstinence syndrome was used to assess the behavioral symptoms of morphine dependence. Immunofluorescence staining of Iba1 and ELISA test were used to measure spinal microglial activity and inflammatory cytokines levels, respectively. The results showed that curcumin (2.5, 5, and 10 mg/kg) significantly decreased jumping, leaning, and diarrhea in morphine-dependent rats. In addition, the spinal concentration of TNF-α and IL-6 was reduced by curcumin (2.5, 5, and 10 mg/kg) significantly. Moreover, curcumin showed a potent attenuating effect on the number of Iba1 positive cells in rats which were subjected to morphine dependence. The results of this study demonstrated that curcumin exerts a remarkable reducing effect on morphine dependence in rats. The findings showed that the therapeutic effect of curcumin on morphine dependence is mediated through the suppression of activated microglial cells and reduction of inflammatory cytokines levels in the spinal cord.

Neuroprotective Effect of Paroxetine on Memory Deficit Induced by Cerebral Ischemia after Transient Bilateral Occlusion of Common Carotid Arteries in Rat.

Memory deficit is the most visible symptom of cerebral ischemia. The hippocampus is sensitive against cerebral ischemia. Oxidative stress and inflammation are involved in the pathological process after cerebral ischemic injury. Paroxetine has anti-oxidative and anti-inflammatory effects. In this study, the effect of paroxetine on memory deficit after cerebral ischemia was investigated. Cerebral ischemia/reperfusion (I/R) injury model was established using the bilateral occlusion of common carotid artery method. Paroxetine (10 mg/kg) was intraperitoneally injected into rats, 24 h before surgery or once a day for 7 days after surgery. Learning and memory were evaluated using the Morris water maze task, then the brain tissue was fixed and hippocampal CA1 pyramidal cells damage was analyzed using the Nissl staining method. In the ischemia group the escape latency time (ELT) and the swimming path length (SPL) were significantly increased and the time spent in target quadrant (TSTQ) was significantly decreased compared with the control group. The ELT and the SPL were significantly shortened and the TSTQ was significantly increased compared with the ischemia group after Pre- or post-ischemic administration of paroxetine. The percentage of viable pyramidal cells in the ischemia group was significantly decreased compared with the control group. The percentage of viable cells was significantly increased following pre-or post-ischemic administration of paroxetine compared with the ischemia group. Memory deficit due to I/R was improved and the percentage of viable cells in CA1 region was increased after administration of paroxetine. Therefore, paroxetine may have a neuroprotective effect against cerebral ischemia.

Carbamazepine effects on pain management and serum IL-6, IL-10 evaluation in addicted patients undergoing surgery.

Postoperative pain control remains an important issue in the field of surgery. Assessing and managing patients with acute pain who are addicted to opioids are often challenging. It has been shown that, addicted patients are less tolerant to pain. There is limited evidence to guide the management of acute pain in these patients. Here we studied the effect of preemptive use of carbamazepine on pain behavior and serum IL-6, IL-10 levels in the addicted patients. 90 male patients (25-45 years, BMI 20-27), were divided into 3 group of 30 patients: 1- control, 2- addicted, 3- addicted patients receiving carbamazepine 400mg before surgery. The visual analog pain scale and serum levels of IL-6 and IL-10 were evaluated at time 0 (before surgery), 1 and 12h postoperatively. Compared with control and carbamazepine groups, addicted patients exhibited exaggerated pain behavior before and after surgery, however, postoperatively, a significant increase in pain behavior was seen in control compared to carbamazepine group. A decrease in serum IL-10 and an increase in IL-6 concentrations were observed in addicted patients. In the morphine abuser, a decrease in pain threshold, an increase in IL-6 and a decrease in IL-10 levels were evident compared with non-abuser subjects. Addition of carbamazepine improved pain sensation and serum IL-6 levels and a reduction in serum IL-10 level in control patients was paralleled to their recovery. It seems that, preemptive use of low dose of carbamazepine can improve postoperative pain and cytokine activities in the addicted patients.

Paradoxical effect of minocycline on established neuropathic pain in rat.

Neuropathic pain occurs after peripheral nerve damage, inflammation or infection. In this situation, microglial cells become activated and play a key role in producing pain. Minocycline (microglia inhibitor), was reported to reduce pain when used preventively. However, it seems that, when used after nerve injury, results in its pain reducing effects are different. In this regard, to assess the pain reducing differences of minocycline, neuropathic pain was induced by the ligation of the sciatic nerve in the rat which is recognized as chronic constriction injury (CCI) and minocycline was administered before and after sciatic nerve injury. Wistar male rats (200-250 g, n=6) were used in these experiments. Rats were distributed in various groups: vehicle-treated CCI (control), sham-operated and minocycline-treated CCI groups. In the first part of the experiment (pre-injury study), minocycline (10, 20, 30 and 40 mg/kg,) was injected one hour before surgery and then daily for two weeks. In the second part (post injury study), minocycline was administered: 1: at day one after nerve damage once a day to day 14, 2: at day seven after surgery and continued daily until day 14. Analgesimeter for thermal hyperalgesia and von Frey hairs for mechanical allodynia were used to evaluate pain behavior. Thermal hyperalgesia and mechanical allodynia were attenuated significantly, when minocycline used before surgery, while it was not able to reduce pain behavior administered after surgery. It seems that, in spite of what some previous studies have reported, here, minocycline is not able to attenuate established neuropathic pain.

Interference-free Determination of Carbamazepine in Human Serum Using High Performance Liquid Chromatography: A Comprehensive Research with Three-way Calibration Methods.

In the present study, a comprehensive and systematic strategy was described to evaluate the performance of several three-way calibration methods on a bio-analytical problem. Parallel factor analysis (PARAFAC), alternating trilinear decomposition (ATLD), self-weighted alternating trilinear decomposition (SWATLD), alternating penalty trilinear decomposition (APTLD), and unfolded partial least squares combined with the residual bilinearization procedure (U-PLS/RBL) were applied on high performance liquid chromatography with photodiode-array detection (HPLC-DAD) data to quantify carbamazepine (CBZ) in different serum samples. Using the proposed approach, successfully quantification of CBZ in human plasma, even in the presence of diverse uncalibrated serious interfering components was achieved. Moreover, the accuracy and precision of each algorithm for analyzing CBZ in serum samples were compared using root mean square error of prediction (RMSEP), the recovery values and figures of merits and reproducibility of the analysis. Satisfying recovery values for the analyte of interest were obtained by HPLC-DAD on a Bonus-RP column using an isocratic mode of elution with acetonitrile/K2HPO4 (pH = 7.5) buffer solution (45:55) coupled with second-order calibrations. Decreas of the analysis time and less solvent consumption are some of the pluses of this method. The analysis of real samples showed that the modeling of complex chromatographic profiles containing CBZ as the target drug using any of the mentioned algorithms can be potentially benefit drug monitoring in therapeutic research.

Role of malate dehydrogenase in facilitating lactate dehydrogenase to support the glycolysis pathway in tumors.

High aerobic glycolysis, as one of the hallmarks of cancer cells, requires nicotinamide adenine dinucleotide (NAD+) as a vital co-factor, to guarantee the flow of glycolysis. Malate dehydrogenase (MDH), as an important enzyme in cancer metabolism, is a source of NAD+ additional to lactate dehydrogenase (LDH). The current study aimed to elucidate the kinetic parameters of MDH in human breast cancer and evaluate its supportive role in the glycolysis pathway. The Michaelis-Menten constant (Km) and maximum velocity (Vmax) of MDH were determined in the crude extracts of human breast tumors and healthy tissue samples, which were obtained directly from the operating theatre. To assess the potential role of MDH in supporting glycolysis, the MDH activity was measured when the LDH activity was inhibited by different concentrations of oxamate, an inhibitor of LDH in breast cancer cell lines. The Km of cancerous MDH (C-MDH) was the same as the healthy MDH, although the Vmax of C-MDH was higher relative to the healthy MDH. Notably, the MDH activity was increased in the MDA-MB-231 cell line, which was treated with the LDH inhibitor (oxamate), but not in the MCF-7 cell line (P<0.05). The higher tendency of C-MDH for NAD+ and malate generation in cancer cells is an effective approach for supporting glycolysis. Increasing MDH activity in the absence of LDH demonstrates the supportive role of MDH in glycolysis. Therefore, decreasing MDH activity and expression in a forward reaction may present as a valid molecular target to abolish its potential effect on tumor metabolism.

Neuroprotective effects of pretreatment with minocycline on memory impairment following cerebral ischemia in rats.

Cerebral ischemia leads to memory impairment that is associated with loss of hippocampal CA1 pyramidal neurons. Neuroinflammation and oxidative stress may be implicated in the pathogenesis of ischemia/reperfusion damage. Minocycline has anti-inflammatory and antioxidant properties. We investigated the neuroprotective effects of minocycline in rats subjected to cerebral ischemia/reperfusion injury. Thirty male rats were divided into three groups: control, sham, and minocycline-pretreated group. Minocycline (40 mg/kg) was injected intraperitoneally immediately before surgery, and then ischemia was induced by occlusion of common carotid arteries for 20 min. Seven days after reperfusion, the Morris water-maze task was used to evaluate memory. Nissl staining was also performed to analyze pyramidal cell damage. We measured the contents of malondialdehyde and proinflammatory cytokines in the hippocampus by the thiobarbituric acid method and enzyme-linked immunosorbent assay, respectively. Microglial activation was also investigated by Iba1 immunostaining. The results showed that pretreatment with minocycline prevented memory impairment induced by cerebral ischemia/reperfusion. Minocycline pretreatment also significantly attenuated ischemia-induced pyramidal cell death and microglial activation in the CA1 region and reduced the levels of malondialdehyde and proinflammatory cytokines (interleukin-1ß and tumor necrosis factor-α) in the hippocampus of ischemic rats. Minocycline showed neuroprotective effects on cerebral ischemia-induced memory deficit probably through its anti-inflammatory and antioxidant activities.

Umbelliprenin is Potentially Toxic Against the HT29, CT26, MCF-7, 4T1, A172, and GL26 Cell Lines, Potentially Harmful Against Bone Marrow-Derived Stem Cells, and Non-Toxic Against Peripheral Blood Mononuclear Cells.

BACKGROUND: Resistance to chemotherapy is a growing concern, thus natural anticancer agents are drawing the attention of many scientists and clinicians. One natural anticancer agent, umbelliprenin, is a coumarin produced by many species of Ferula. OBJECTIVES: We aimed to examine the inhibitory effect of umbelliprenin on human and mouse bone marrow-derived stem cells (BMDSCs), peripheral blood mononuclear cells (PBMCs), and different cancer cell lines. MATERIALS AND METHODS: In this in vitro experimental study, the HT29, CT26, MCF-7, 4T1, A172, and GL26 cancer cells and human and mouse BMDSCs and PBMCs were cultured in RPMI-1640 medium supplemented with 10% fetal bovine serum (FBS), incubated at 37°C for 24 hours in a 5% CO2 atmosphere, and then were treated with different concentrations of umbelliprenin dissolved in dimethyl sulfoxide (DMSO) (3, 6, 12, 25, 50, 100, and 200 µg/mL) for 24, 48, and 72 hours at 37°C. Each experiment was performed in triplicate. Finally, the cell survival rate was assessed by MTT assay. The IC50 values were calculated based on the log values using GraphPad Prism version 5 software for windows (La Jolla CA, USA) and were expressed as mean ± SEM. RESULTS: Umbelliprenin inhibited the cancer cells in a concentration-dependent (P < 0.05) but not time-dependent manner (P > 0.05). The most sensitive and resistant cell lines at the 24-hour incubation time were 4T1 (IC50, 30.9 ± 3.1 µg/mL) and A172 (IC50, 51.9 ± 6.7 µg/mL); at the 48-hour incubation time: 4T1 (IC50, 30.6 ± 2.6 µg/mL) and CT26 (IC50, 53.2 ± 3.6 µg/mL); and at the 72-hour incubation time: HT29 (IC50, 37.1 ± 1.4 µg/mL) and 4T1 (IC50, 62.2 ± 4.8 µg/mL). Both human and mouse BMDSCs showed the highest resistance at the 24-hour incubation time (IC50s, 254.7 ± 21 and 204.4 ± 4.5 µg/mL, respectively) and the highest sensitivity at the 72-hour incubation time (IC50s, 120.4 ± 5 and 159.0 ± 7.3 µg/mL, respectively). The PBMCs of both human and mouse origin revealed very strong resistance to the studied concentrations of umbelliprenin (IC50s ranging from 713.5 ± 499.1 to 6651 ± 3670.7 µg/mL). CONCLUSIONS: Our findings indicate that umbelliprenin exhibits concentration-dependent inhibitory effects on various cell types; it is potentially toxic against the HT29, CT26, MCF-7, 4T1, A172, and GL26 cell lines, potentially harmful against BMDSCs, and non-toxic against PBMCs. Therefore, if our results are approved in the future, umbelliprenin can be an appropriate candidate for developing treatments against different cancers.

Minocycline Effects on IL-6 Concentration in Macrophage and Microglial Cells in a Rat Model of Neuropathic Pain.

BACKGROUND: Evidence indicates that neuropathic pain pathogenesis is not confined to changes in the activity of neuronal systems but involves interactions between neurons, inflammatory immune and immune-like glial cells. Substances released from immune cells during inflammation play an important role in development and maintenance of neuropathic pain. It has been found that minocycline suppresses the development of neuropathic pain. Here, we evaluated the analgesic effect of minocycline in a chronic constriction injury (CCI) model of neuropathic pain in rat and assessed IL-6 concentration from cultured macrophage and microglia cells. METHODS: Male Wistar rat (n=6, 150-200 g) were divided into three different groups: 1) CCI+vehicle, 2) sham+vehicle, and 3) CCI+drug. Minocycline (10, 20, and 40 mg/kg) was injected one hour before surgery and continued daily to day 14 post ligation. Von Frey filaments and acetone, as pain behavioral tests, were used for mechanical allodynia and cold allodynia, respectively. Experiments were performed on day 0 (before surgery) and days 1, 3, 5, 7, 10, and 14 post -injury. At day 14, rats were killed and monocyte-derived macrophage from right ventricle and microglia from lumbar part of the spinal cord were isolated and cultured in RPMI and Leibovitz's media, respectively. IL-6 concentration was evaluated in cell culture supernatant after 24 h. RESULTS: Minocycline (10, 20, and 40 mg/kg) attenuated pain behavior, and a decrease in IL-6 concentration was observed in immune cells compared to CCI vehicle-treated animals. CONCLUSION: Minocycline reduced pain behavior and decreased IL-6 concentration in macrophage and microglial cells.

Comparison of Anticancer Effects of Carbamazepine and Valproic Acid.

BACKGROUND: Valproic acid (VPA) and carbamazepine (CBZ), two widely used antiepileptic drugs, have recently been found to inhibit histone deacetylases (HDAC). HDAC inhibitors (HDACIs) have various effects on cancer cells. OBJECTIVES: The aim of this study was to compare the anticancer activity of these drugs on SW480 colon cancer cell lines. METHODS: In the present experimental study, implemented during 2014 - 2015 in Iran, after incubation of cells into 96-well plates with 5,500 cells/well, the tested drugs were added, and cytotoxic effects were assessed by MTT. Moreover, after incubation of 8×106 cells in 75 cm² flasks to obtain ß-catenin levels and 106 cells in a six-well plate to obtain vascular endothelial growth factor (VEGF) levels , these levels were estimated using enzyme-linked immunosorbent assay (ELISA) analysis. RESULTS: Through MTT assay, we found that the inhibitory concentration of 50% (IC50) values for VPA and CBZ were 2.5 mM and 5 µM, respectively in comparison to controls in terms of total concentration and times evaluated (P < 0.0001). We also found that treatments with these drugs decreased levels of ß-catenin (P < 0.0001) and VEGF (P < 0.0001) significantly more than controls. CONCLUSIONS: VPA and CBZ treatments caused a decrease in ß-Catenin and VEGF levels in SW480 colon cancer cell lines. These results suggest that CBZ can be considered a potential antitumor drug with potencies different from VPA.

The Attenuation of Pain Behavior and Serum COX-2 Concentration by Curcumin in a Rat Model of Neuropathic Pain.

BACKGROUND: Neuropathic pain is generally defined as a chronic pain state resulting from peripheral and/or central nerve injury. There is a lack of effective treatment for neuropathic pain, which may possibly be related to poor understanding of pathological mechanisms at the molecular level. Curcumin, a therapeutic herbal extract, has shown to be effectively capable of reducing chronic pain induced by peripheral administration of inflammatory agents such as formalin. In this study, we aimed to show the effect of curcumin on pain behavior and serum COX-2 level in a Chronic Constriction Injury (CCI) model of neuropathic pain. METHODS: Wistar male rats (150-200 g, n = 8) were divided into three groups: CCI vehicle-treated, sham-operated, and CCI drug-treated group. Curcumin (12.5, 25, 50 mg/kg, IP) was injected 24 h before surgery and continued daily for 7 days post-surgery. Behavioral tests were performed once before and following the days 1, 3, 5, 7 after surgery. The serum COX-2 level was measured on day 7 after the surgery. RESULTS: Curcumin (50 mg/kg) decreased mechanical and cold allodynia (P < 0.001) and produced a decline in serum COX-2 level (P < 0.001). CONCLUSIONS: A considerable decline in pain behavior and serum COX-2 levels was seen in rat following administration of curcumin in CCI model of neuropathic pain. High concentration of Curcumin was able to reduce the chronic neuropathic pain induced by CCI model and the serum level of COX-2.

Paroxetine attenuates the development and existing pain in a rat model of neurophatic pain.

BACKGROUND: P2X4 receptor (P2X4R), a purinoceptor expressed in activated spinal microglia, plays a key role in the pathogenesis of neuropathic pain. Spinal nerve injury induces up-regulation of P2X4R on activated microglia in the spinal cord, and blockade of this receptor can reduce neuropathic pain. The present study was undertaken to determine whether paroxetine, an inhibitor of P2X4R, could attenuate allodynia and hyperalgesia in chronic constriction injury (CCI) model of neuropathic pain when used preemptively or after the sciatic nerve injury. METHODS: Male Wistar rats (150-200 g, n = 6) were divided into 3 different groups: 1- CCI vehicle-treated group, 2- Sham group, and 3- CCI paroxetine-treated group. Paroxetine (10 mg/kg, i.p.) was administered 1 h before surgery and continued daily until day 14. In other part of the study, paroxetine (10 mg/kg, i.p.) was administered at day 7 post injury and continued daily until day 14. von Frey filaments for mechanical allodynia and analgesia meter for thermal hyperalgesia were used to assay pain behavior. RESULTS: In a preventive paradigm, paroxetine significantly attenuated both mechanical allodynia and thermal hyperalgesia (P<0.001). A significant decrease in pain behavior was seen with paroxetine on existing allodynia (P<0.001) and hyperalgesia (P<0.01) when initiated at day 7 post injury. CONCLUSION: It seems that paroxetine can attenuate pain behavior when administered before and also after sciatic nerve injury in CCI model of neuropathic pain.

Enhancement of Antinociception by Co-administrations of Nefopam, Morphine, and Nimesulide in a Rat Model of Neuropathic Pain.

BACKGROUND: Neuropathic pain is a chronic pain due to disorder in the peripheral or central nervous system with different pathophysiological mechanisms. Current treatments are not effective. Analgesic drugs combined can reduce pain intensity and side effects. Here, we studied the analgesic effect of nimesulide, nefopam, and morphine with different mechanisms of action alone and in combination with other drugs in chronic constriction injury (CCI) model of neuropathic pain. METHODS: Male Wistar rats (n = 8) weighing 150-200 g were divided into 3 different groups: 1- Saline-treated CCI group, 2- Saline-treated sham group, and 3- Drug-treated CCI groups. Nimesulide (1.25, 2.5, and 5 mg/kg), nefopam (10, 20, and 30 mg/kg), and morphine (1, 3, and 5 mg/kg) were injected 30 minutes before surgery and continued daily to day 14 post-ligation. In the combination strategy, a nonanalgesic dose of drugs was used in combination such as nefopam + morphine, nefopam + nimesulide, and nimesulide + morphine. Von Frey filaments for mechanical allodynia and acetone test for cold allodynia were, respectively, used as pain behavioral tests. Experiments were performed on day 0 (before surgery) and days 1, 3, 5, 7, 10, and 14 post injury. RESULTS: Nefopam (30 mg/kg) and nimesulide (5 mg/kg) blocked mechanical and thermal allodynia; the analgesic effects of morphine (5 mg/kg) lasted for 7 days. Allodynia was completely inhibited in combination with nonanalgesic doses of nefopam (10 mg/kg), nimesulide (1.25 mg/kg), and morphine (3 mg/kg). CONCLUSIONS: It seems that analgesic drugs used in combination, could effectively reduce pain behavior with reduced adverse effects.

Carbamazepine potentiates morphine analgesia on postoperative pain in morphine-dependent rats.

Postoperative pain and its control remain one of the most important issues in the field of surgery and health care systems. Morphine is a potent and effective analgesic, but substance abuse patients can manifest cross-tolerance to it, making it difficult to satisfy their analgesic/anesthetic requirements. As carbamazepine has shown antinociceptive properties in a variety of experimental and clinical settings, in the present study, we evaluated its potential antiallodynic effects on postoperative pain in naïve and morphine-dependent rats. Male rats were assigned to morphine-dependent and naïve groups and received intraperitoneally drug vehicles as control group, 3mg/kg morphine, 5, 10 or 15 mg/kg carbamazepine or 5mg/kg carbamazepine plus 3mg/kg morphine as a combination therapy 2 and 24h after surgery. Morphine-dependency was induced with multiple doses of morphine administered i.p. and plantar incision was made on the hind paw to simulate the postoperative pain. Paw withdrawal threshold (PWT) was obtained by von Frey filaments every 30 min after drug injection for up to 180 min. Morphine at 3mg/kg exerted antiallodynic effects in naïve rats and a decreased antinociception was observed in morphine-dependent rats. In contrast, 5mg/kg carbamazepine did not significantly alter PWT in naives but it was effective in dependent rats. 10 and 15 mg/kg carbamazepine attenuated allodynia following surgery in both groups. Co-administration of 5mg/kg carbamazepine with 3mg/kg morphine produced higher analgesia in morphine-dependent incised rats and prolonged antinociception as compared to morphine alone (P<0.05). Thus carbamazepine may potentiate the analgesic effect of chronically administered morphine on postoperative pain model in morphine-dependent rats.

Study of the intraplantar injection of lidocaine and morphine on pain perception and the influence of morphine dependence and withdrawal on lidocaine-induced analgesia in rats.

BACKGROUND: Morphine and lidocaine are known to influence the perception of pain. The present study sought to determine the influence of local administration of morphine on lidocaine-induced analgesia in morphine non-dependent (MND), morphine dependent (MD) and morphine withdrawal (MW) animals. METHODS: Adult male Wistar rats were divided into four groups: Control, MND, MD and MW rats. Lidocaine (0.5, 1 and 2%) and morphine (200, 400 and 800 µg) were injected in the plantar surface of the right paw. MD animals received chronic oral morphine (0.1, 0.2, 0.3 and 0.4 mg/ml in their drinking water) for 20 days. Twenty four hours before experiment, the animals in the MW group were deprived of morphine in their drinking water (physical dependence was observed by precipitating an abstinence syndrome with naloxone 2 mg/kg i.p.). Analgesia was assessed using hot-plate apparatus. RESULTS: Morphine (400 µg) and lidocaine (2%) produce local analgesia in MND group. In MND rats, non-analgesic doses of each drug (200 µg morphine and 1% lidocaine) were used in combination and produced analgesia. In MD animals, all doses of lidocaine produced analgesia, while in MW animals, it failed to produce analgesia. In this situation, local administration of morphine could eventually influence the analgesic effect of lidocaine. CONCLUSION: Opioid withdrawal is one of the most common problems in clinic. This study determined the analgesic effect of lidocaine in MW animals in which lidocaine had no analgesic effect. In this regard, local administration of morphine with combination of lidocaine could probably produce an effective analgesia.