Effects of Cervical Sympathectomy on Mechanical Allodynia and Cold Allodynia in a Rat Model of Neuropathic Pain / 대한마취과학회지

BACKGROUND: The pathophysiologic mechanism of the neuropathic pain is still unclear. We designed this study to evaluate the effect of bilateral cervical sympathectomy on allodynia and the relationship of neuropathic pain with sympathetic nerve system of supraspinal level in rats experiencing neuropathic pain. METHODS: Neuropathic pain was produced by tight ligating the left 5th and 6th lumbar spinal nerves of male Sprague-Dawley rats. Mechanical allodynia was quantified by measuring the foot withdrawal frequency to stimuli with two von Frey filaments of 14.5 mN and 53.9 mN applied to the affected left hind paw, and cold allodynia was quantified with the same manner using 100% acetone. We divided the neuropathic pain models into experimental group (bilateral cervical sympathectomy) and control group (sham operation), and then measured the foot withdrawal frequency 1, 3, 5, 7, 14, 21 and 28 days postoperatively. RESULTS: In experimental group, the foot withdrawal frequency to mechanical stimuli with 14.5 and 53.9 mN of von Frey filament and cold stimuli with 100% acetone was significantly lower than that of control group for all postoperative observation points. Also, the experimental group showed decrease in foot withdrawal frequency compared with preoprative value over the course of the study. CONCLUSIONS: Bilateral cervical sympathectomy reduced mechanical allodynia and cold allodynia in the rat model of neuropathic pain suggesting that neuropathic pain, although the lesions are localized in low extremities, may be correlated with functional disturbance of sympathetic nerve fibers of supraspinal or brain level and help explain the mechanism of neuropathic pain.

Interaction between Neostigmine and Morphine in the Neuropathic Pain Model / 대한마취과학회지

BACKGROUND: Spinally administered neostigmine, but not morphine, has been well known to reverse the mechanical allodynia in human and animal studies. The efficacy of morphine in neuropathic pain state is somewhat controversial. Using an isobolographic analysis, we examine the spinal interaction between neostigmine and morphine in a rat model of neuropathic pain. METHODS: Male Sprague Dawley rats were prepared with tight ligation of left lumbar 5th and 6th spinal nerves and chronic lumbar intrathecal catheter. Intrathecal dose response curves were established for the antiallodynic effect of neostigmine (0.3, 1.0, 3.0, and 10 microgram) and morphine (0.3, 1.0, 3.0, and 10 microgram) alone to obtain the ED50 for each agent. ED50 fractions (1/2, 1/4, 1/8, and 1/16) of drug combination of neostigmine-morphine were administered. Allodynic thresholds for left hindpaw withdrawal to von Frey hairs application were assessed and converted to %MPE. The ED50 of neostigmine-morphine combinations was established and isobolographic analysis of the drug interaction was carried out. RESULTS: Intrathecal neostigmine and morphine alone produced dose-dependent reductions of tactile allodynia. ED50 values are 0.43 microgram (0.21~0.86 microgram) for neostigmine and 0.39 microgram (0.07~2.01 microgram) for morphine. The log dose responses were plotted from the peak effect of %MPE in each group of neostigmine and morphine. The experimental ED50 1.34E-2 microgram (2.1E-4-0.85 microgram) for neostigmine and morphine combination was found to be significantly below the theoretical additive ED50 value 0.41 microgram (P<0.05). CONCLUSION: The results suggest that intrathecal neostigmine and morphine alone produce a dose dependent antagonism on touch evoked allodynia and intrathecal neostigmine is synergistic at the spinal level when combined with intrathecal morphine in a rat model of neuropathy.

The Effect of Selective Muscarinic Receptor Antagonists on Antiallodynic Action in a Rat Model of Neuropathic Pain / 대한마취과학회지

BACKGROUND: Peripheral nerve injury may produce a syndrome consisting of spontaneous pain, allodynia and hyperpathia. In previous study, we examined the antiallodynic action produced by intrathecal (i.t.) cholinesterase inhibitors (ChEi) in a neuropathic pain rat model and the reversal of antiallodynic state by i.t. atropine, muscarinic antagonist, but not by nicotinic antagonist mecamylamine. The purpose of this study was to determine the selective antagonistic action of four subtypes of muscarinic receptor on antiallodynic state by i.t. ChEi in a rat model of neuropathic pain. METHODS: Sprague Dawley rats were prepared with tight ligation of left L5/L6 spinal nerves with 6-0 black silk and chronic lumbar intrathecal catheters. After obtaining the baseline hindpaw withdrawal scores, edrophonium (100 microgram) or neostigmine (10 microgram) was administered intrathecally. Tactile allodynia was measured using von Frey filaments and allodynic threshold was calculated by the up-down method. Allodynic changes were tested at 15, 30, 45, 60, 90, 120 and 180 minutes. To examine the reversal of antiallodynia and to compare the antagonizing action of antiallodynic state produced by i.t. administration of ChEi, non-selective muscarinic receptor antagonists atropine (10 microgram), M1 antagonist pirenzepine (3 microgram), M2 antagonist methoctramine (3 microgram), M3 antagonist 4-DAMP (3 microgram) and M4 antagonist tropicamide (3 microgram) were injected intrathecally respectively 5 minutes prior to the injection of edrophonium or neostigmine. RESULTS: Antiallodynia produced by i.t. edrophonium was reversed by pretreatment with i.t. methoctramine, 4-DAMP, tropicamide and pirenzepine (P<0.05). On the contrary, antiallodynic state made by i.t. neostigmine was not antagonized by methoctramine, 4-DAMP and tropicamide. M1 antagonist pirenzepine had a moderate, statistically significant (P<0.05) effect on reversal of increased allodynic threshold while atropine showed a complete antagonism. CONCLUSION: These experiments suggest that antialllodynic action of cholinesterase inhibitors is likely due to mediation of spinal muscarinic system and M1 receptor subtype is more likely involved in this mechanism.

The Antiallodynic Effect of Edrophonium and Neostigmine in a Neuropathic Pain Model / 대한마취과학회지

BACKGROUND: Peripheral nerve injury may produce a syndrome consisting of spontaneous pain, allodynia and hyperpathia. Cholinesterase inhibitors are known to have an antinociceptive effect in hot plate and tail flick tests and to be mediated by spinal muscarinic system. The purpose of the current study was to determine the effect of intrathecally (i.t.) administered edrophonium and neostigmine on the touch-evoked allodynia and to identify the antagonism of antiallodynia in a rat model of neuropathic pain. METHODS: Sprague Dawley rats were prepared with tight ligation of left L5/L6 spinal nerves with 6~0 black silk and chronic lumbar intrathecal catheters. After obtaining the baseline hindpaw withdrawal scores, edrophonium (3~100ug) or neostigmine (0.3~10ug) was administered intrathecally. Tactile allodynia was measured using von Frey filaments and allodynic threshold was calculated by updown method. Motor dysfunction was assessed by observing righting/stepping reflex responses and abnormal weight bearing. To examine the reversal of antiallod ynia, muscarinic receptor antagonist atropine (10ug) or nicotinic receptor antagonist mecamylamine (10ug) was injected intrathecally 5 min. prior to injection of edrophonium or neostigmine. RESULTS: I.t. edrophonium and i.t. neostigmine produced a dose dependent antagonism of allodynic state but had moderate to severe effect on motor weakness at doses of 3 and 10 g of neostigmine. Pretreatment with i.t. atropine yielded a complete antagonism of antiallodynia in both drugs, but i.t. mecamylamine did not significantly reverse incresed allodynic threshold. CONCLUSIONS: These experiments suggest that i.t. edrophonium or i.t. neostigmine produces a dose dependent antagonism on touch-evoked allodynia at the spinal level and this antagonism is likely due to spinal muscarinic system.