Analgesic and anti-inflammatory effects of modafinil in a mouse model of neuropathic pain: A role for nitrergic and serotonergic pathways

Analgesic effect of a cholinergic agonist (carbachol) in a sural nerve ligation-induced hypersensitivity mouse model

OBJECTIVES

Neuropathic pain is characterized by long-lasting, intractable pain. Sciatic nerve ligation is often used as an animal model of neuropathic pain, and the spared nerve injury (SNI) model, in which the common peroneal nerve (CPN) and tibial nerve (TN) are ligated, is widely used. In the present study, we evaluated the analgesic effect of a cholinergic agonist, carbachol, on a neuropathic pain model prepared by sural nerve (SN) ligation in mice.

METHODS

The SN was tightly ligated as a branch of the sciatic nerve. Mechanical and thermal allodynia, and hyperalgesia were assessed using von Frey filaments and heat from a hot plate. The analgesic effects of intracerebroventricularly-administered morphine and carbachol were compared.

RESULTS

SN ligation resulted in a significant decrease in pain threshold for mechanical stimulation 1 day after ligation. In response to thermal stimulation, allodynia was observed at 50°C and hyperalgesia at 53 and 56°C 3 days after ligation. Content of thiobarbituric acid reactive substances (TBARS) in the spinal cord increased significantly at 6 and 12 h after ligation. Acetylcholine content of the spinal cord also increased at 5 and 7 days after ligation. Intracerebroventricular administration of carbachol at 7 days after ligation produced a marked analgesic effect against mechanical and thermal stimuli, which was stronger and longer-lasting than morphine at all experimental time points.

CONCLUSION

These findings suggest that cholinergic nerves are involved in allodynia and hyperalgesia of the SN ligation neuropathic pain model.

The Possible Role of Nitric Oxide signaling and NMDA Receptors in Allopurinol effect on Maximal Electroshock- and Pentylenetetrazol-Induced Seizures in Mice

Allopurinol, a uric-acid-lowering medication, has shown its efficacy in several studies suggesting that allopurinol can be prescribed as adjunctive cure meant for intractable epilepsy. The exact mechanism of allopurinol is still unknown. This study evaluates allopurinol's effect on seizure threshold, seizure incidence, and mortality rate in mice models. Moreover, the possible involvement of nitric oxide (NO) pathway and N-methyl-D-aspartate (NMDA) receptors are investigated. To evaluate the effect of allopurinol on seizure, we used the pentylenetetrazole (PTZ)-induced seizure along with maximal electroshock (MES)-induced seizure. To assess the underlying mechanism behind the allopurinol activity, we used nitric oxide synthase (NOS) substrate (L-arginine), NOS inhibitors (L-NAME, aminoguanidine, 7-nitroindazole), and NMDA receptor antagonist (MK-801). Intraperitoneal allopurinol administration at a dose of 50 mg/kg in mice showed a significant (p<0.001) anti-convulsant activity in the PTZ-induced seizure. Even though pre-treatment with L-Arginine (60 mg/kg) potentiates allopurinol's anti-convulsant effect in the PTZ-induced seizure, pre-treatment with L-NAME (10 mg/kg), aminoguanidine (100 mg/kg), and 7-nitroindazole (30 mg/kg) reversed the anti-convulsant effect of allopurinol in the PTZ-induced seizure. In addition, pre-treatment with MK-801 also decreased the anti-convulsant effect of allopurinol in the PTZ-induced seizure. While allopurinol at a dose of 50 mg/kg and 100 mg/kg did not induce protection against seizure incidence in the MES-induced seizure, it revealed a remarkable effect in reducing the mortality rate in the MES-induced seizure. Allopurinol increases the seizure threshold in PTZ-induced seizure and enhances the survival rate in MES-induced seizure. Allopurinol exerts its anti-convulsant effect, possibly through targeting NO pathway and NMDA receptors.