Evaluation of the Analgesic Effect of Dextromethorphan and its Interaction With Nitric Oxide on Sciatic Nerve Ligated Rats

The additive effect between bupropion and citicoline upon induction of anti-nociceptive effect in nerve-ligated mice

OBJECTIVES

Bupropion is an atypical antidepressant that shows robust efficacy in the regulation of neuropathic pain. Citicoline is a dietary supplement which is used as a neuroprotective agent for central nervous system (CNS) disorders. The probable interaction between bupropion and citicoline on neuropathic pain was assessed in male mice.

METHODS

Neuropathic pain was induced by sciatic nerve ligation. Neuropathic pain was examined in nerve-ligated mice using tail-flick and hot-plate tests.

RESULTS

The results indicated that intraperitoneal (i.p.) administration of citicoline (50 and 100 mg/kg) induced an anti-nociceptive effect in nerve-ligated animals. Similarly, i.p. injection of bupropion (2.5 and 5 mg/kg) induced anti-nociceptive effects in nerve-ligated mice. Co-administration of different doses of bupropion (2.5 and 5 mg/kg) along with a low dose of citicoline (25 mg/kg) caused an anti-nociceptive effect by enhancement of tail-flick and hot plate latencies. Interestingly, there is an additive effect between bupropion and citicoline upon the induction of the anti-nociceptive effect.

CONCLUSIONS

Based on these results, it can be concluded that there is an interaction between bupropion and citicoline upon induction of an anti-nociceptive effect in nerve-ligated mice.

Effects of luteolin and luteolin-morphine co-administration on acute and chronic pain and sciatic nerve ligated-induced neuropathy in mice

Background Neuropathic pain (NP) is a common condition accompanied by nerve injury. To date, there is no definite treatment approved for this disorder. In addition, many drugs that are used for NP cause adverse reactions. Luteolin is a naturally occurring flavonoid with diverse pharmacological properties such as anti-inflammatory, antioxidant and anticancer. We sought to investigate luteolin effects on chronic, acute and neuropathic pain as well as its potential to increase morphine anti-nociceptive effects in mice. Methods Albino mice (20-25 g) were randomly divided into 14 groups (n=7) including morphine 1 mg/kg body weight +luteolin (5 mg/kg body weight), morphine (9 mg/kg body weight, i.p.), luteolin (2.5, 5 and 10 mg/kg body weight), imipramine 40 mg/kg body weight and normal saline (NS) (0.9 %) as vehicle and subjected to hot plate test. Formalin test was done in the following groups: NS, diclofenac sodium (10 mg/kg body weight, i.p.), morphine (9 mg/kg body weight, i.p.) and luteolin (2.5, 5 and 10 mg/kg body weight). Results Administration of luteolin single dose (5 and 10 mg/kg body weight) significantly reduced neuropathic pain ( p<0.05$\rm{p}<0.05$) in comparison to negative control. Anti-nociceptive effects of luteolin were comparable to imipramine as the standard positive control ( p<0.001$\rm{p}<0.001$). Co-administration of luteolin and morphine potentiated morphine 1 mg/kg body weight painkilling effects ( p<0.001$\rm{p}<0.001$). Conclusions Our results showed that luteolin alone reduces neuropathic pain. Furthermore, when co-administered with morphine 1 mg/kg body weight, luteolin potentiates morphine effects. Therefore, luteolin-morphine co-administration might be a valuable alternative for the conventional treatment.

Anticonvulsant effect of dextrometrophan on pentylenetetrazole-induced seizures in mice: Involvement of nitric oxide and N-methyl-d-aspartate receptors

Dextrometrophan (DM), widely used as an antitussive, has recently generated interest as an anticonvulsant drug. Some effects of dextrometrophan are associated with alterations in several pathways, such as inhibition of nitric oxide synthase (NOS) enzyme and N-methyl d-aspartate (NMDA) receptors. In this study, we aimed to investigate the anticonvulsant effect of acute administration of dextrometrophan on pentylenetetrazole (PTZ)-induced seizures and the probable involvement of the nitric oxide (NO) pathway and NMDA receptors in this effect. For this purpose, seizures were induced by intravenous PTZ infusion. All drugs were administrated by intraperitoneal (i.p.) route before PTZ injection. Our results demonstrate that acute DM treatment (10-100mg/kg) increased the seizure threshold. In addition, the nonselective NOS inhibitor L-NAME (10mg/kg) and the neural NOS inhibitor, 7-nitroindazole (40mg/kg), at doses that had no effect on seizure threshold, augmented the anticonvulsant effect of DM (3mg/kg), while the inducible NOS inhibitor, aminoguanidine (100mg/kg), did not affect the anticonvulsant effect of DM. Moreover, the NOS substrate l-arginine (60mg/kg) blunted the anticonvulsant effect of DM (100mg/kg). Also, NMDA antagonists, ketamine (0.5mg/kg) and MK-801 (0.05mg/kg), augmented the anticonvulsant effect of DM (3mg/kg). In conclusion, we demonstrated that the anticonvulsant effect of DM is mediated by a decline in neural nitric oxide activity and inhibition of NMDA receptors.

The role of NMDA receptor and nitric oxide/cyclic guanosine monophosphate pathway in the antidepressant-like effect of dextromethorphan in mice forced swimming test and tail suspension test

Depression is a devastating disorder which has a high impact on the wellbeing of overall society. As such, need for innovative therapeutic agents are always there. Most of the researchers focused on N-methyl-d-aspartate receptor to explore the antidepressant like activity of new therapeutic agents. Dextromethorphan is a cough suppressant agent with potential antidepressant activity reported in mouse force swimming test. Considering N-methyl-d-aspartate as a forefront in exploring antidepressant agents, here we focused to unpin the antidepressant mechanism of dextromethorphan targeting N-methyl-d-aspartate receptor induced nitric oxide-cyclic guanosine monophosphate signaling. Dextromethorphan administered at a dose of 10 and 30mg/kg i.p significantly reduced the immobility time. Interestingly, this effect of drug (30mg/kg) was inhibited when the animals were pretreated either with N-methyl-d-aspartate (75mg/kg), or l-arginine (750mg/kg) as a nitric oxide precursor and/or sildenafil (5mg/kg) as a phosphodiesterase 5 inhibitor. However, the antidepressant effect of Dextromethorphan subeffective dose (3mg/kg) was augmented when the animals were administered with either L-NG-Nitroarginine methyl ester (10mg/kg) non-specific nitric oxide synthase inhibitor, 7-Nitroindazole (30mg/kg) specific neural nitric oxide synthase inhibitor, MK-801 (0.05mg/kg) an N-methyl-d-aspartate receptor antagonist but not aminoguanidine (50mg/kg) which is specific inducible nitric oxide synthase inhibitor as compared to the drugs when administered alone. No remarkable effect on locomotor activity was observed during open field test when the drugs were administered at the above mentioned doses. Therefore, it is evident that the antidepressant like effect of Dextromethorphan is owed due to its inhibitory effect on N-methyl-d-aspartate receptor and NO- Cyclic guanosine monophosphate pathway.

Antinociceptive and Anti-Inflammatory Activities of Teucrium persicum Boiss. Extract in Mice

Background. Therapeutic properties of Teucrium species as antioxidant, antibacterial, analgesic, anticancer, diuretic, and tonic compounds have been proved earlier. Materials and Methods. In this study, the antinociceptive and anti-inflammatory effects of the aqueous extract of Teucrium persicum on chronic pain, sciatic nerve ligation as a model of neuropathic pain, and inflammatory models were investigated by formalin, hot-plate, and cotton pellet-induced granuloma models in mice, respectively. T. persicum aqueous extracts (100, 200, and 400 mg/kg) were orally gavaged for one week. On 8th day, the time spent and the number of lickings were recorded in formalin test. Morphine and Diclofenac were used intraperitoneally as positive controls. In sciatic nerve ligated animals, as a model of neuropathic pain, doses (100, 200, and 400 mg/kg) of T. persicum extract (TPE) were orally gavaged for 14 consecutive days. The analgesic effect of this extract was examined 14 days after sciatic nerve ligation using the hot-plate test. Controls received saline and Imipramine (40 mg/kg, i.p.) was used a positive control for neuropathic pain model. Results. In the formalin test, a week oral gavage of all TPE doses (100, 200, and 400 mg/kg) caused a significant decrease on the licking response compared to the control negative animals. In the hot-plate test, doses of 200 and 400 mg/kg showed significant analgesic effects in sciatic nerve ligated animals. Oral gavaged of TPE revealed significant analgesic effect on chronic pain in both formalin test and sciatic nerve ligated animals. The TPEs did not have any significant anti-inflammatory effects in cotton pellet-induced granuloma formation in mice. Conclusions. These results suggest that the aqueous extract from T. persicum Boiss. produced antinociceptive effects. Its exact mechanism of action still remains indistinct.

Effects of dextromethorphan and oxycodone on treatment of neuropathic pain in mice

Background

Neuropathic pain is a very troublesome and difficult pain to treat. Although opioids are the best analgesics for cancer and surgical pain in clinic, only oxycodone among opioids shows better efficacy to alleviate neuropathic pain. However, many side effects associated with the use of oxycodone render the continued use of it in neuropathic pain treatment undesirable. Hence, we explored whether dextromethorphan (DM, a known N-methyl-D-aspartate receptor antagonist with neuroprotective properties) could potentiate the anti-allodynic effect of oxycodone and underlying mechanisms regarding to glial cells (astrocytes and microglia) activation and proinflammatory cytokines release in a spinal nerve injury (SNL) mice model.

Results

Oxycodone produced a dose-dependent anti-allodynic effect. Co-administration of DM at a dose of 10 mg/kg (i.p.) (DM10) which had no anti-allodynic effect by itself enhanced the acute oxycodone (1 mg/kg, s.c.) effect. When the chronic anti-allodynic effects were examined, co-administration of DM10 also significantly enhanced the oxycodone effect at 3 mg/kg. Furthermore, oxycodone decreased SNL-induced activation of glial cells (astrocytes and microglia) and plasma levels of proinflammatory cytokines (IL-6, IL-1β and TNF-α). Co-administration of DM10 potentiated these effects of oxycodone.

Conclusion

The combined use of DM with oxycodone may have therapeutic potential for decreasing the effective dose of oxycodone on the treatment of neuropathic pain. Attenuation of the glial activation and proinflammatory cytokines in the spinal cord may be important mechanisms for these effects of DM.

Low doses of dextromethorphan have a beneficial effect in the treatment of neuropathic pain

N-methyl-D-aspartate receptor (NMDAR) antagonists may be given in persistent neuropathic pain, but adverse events especially with ketamine may limit their clinical use. Less central and cognitive adverse events are described with dextromethorphan and memantine. These molecules have been explored in many preclinical and clinical studies, but data are conflicting as regards neuropathic pain alleviation. Dextromethorphan and memantine have been administered to animals after spinal nerve ligation (SNL) to evaluate their antinociceptive/cognitive effects and associated molecular events, including the phosphorylation of several tyrosine (pTyr(1336), pTyr(1472)) residues in the NR2B NMDAR subunit. Spinal nerve ligation and sham animals received dextromethorphan (10 mg/kg, i.p.), memantine (20 mg/kg, i.p.) or saline (1 mL/kg, i.p.). These drugs were administered once symptoms of allodynia and hyperalgesia had developed. Tests were carried out before and after surgery. Tactile allodynia, mechanical hyperalgesia and spatial memory were, respectively, evaluated by von Frey, Randall & Selitto and Y-maze tests and molecular events by Western blot analysis. Spinal nerve-ligated animals displayed nociception and impaired spatial memory. Dextromethorphan, but not memantine, reversed neuropathic pain (NP) symptoms, restored spatial memory integrity and decreased the expression of pTyr(1336)NR2B. Following postoperative administration of dextromethorphan, this study has demonstrated for the first time a concordance between behaviour, cognitive function and molecular events via pTyr(1336)NR2B for neuropathic pain alleviation. Confirmation of these findings in patients would constitute a major step forward in the treatment of neuropathic pain and in the improvement of cognitive function and quality of life.