Effect of intrathecal glycine and related amino acids on the allodynia and hyperalgesic action of strychnine or bicuculline in mice / 대한마취과학회지

BACKGROUND: The intrathecal (IT) administration of glycine or GABAA receptor antagonist result in a touch evoked allodynia through disinhibition in the spinal cord. Glycine is an inhibitory neurotransmitter that appears to be important in sensory processing in the spinal cord. This study was aimed to evaluate the effect of glycine-related amino acids on antagonizing the effects of IT strychnine (STR) or bicuculline (BIC) when each amino acid was administered in combination with STR or BIC. METHODS: A total of 174 male ICR mice were randomized to receive an IT injection of equimolar dose of glycine, betaine, beta-alanine, or taurine in combination with STR or BIC. Agitation in response to innocuous stimulation with a von Frey filament after IT injection was assessed. The pain index in hot-plate test were observed after it injection. The effect of it muscimol in combination with str or bic were also observed. RESULTS: The allodynia induced by STR was relieved by high dose of glycine or betaine. But, allodynia induced by BIC was not relieved by any amino acid. Whereas the STR-induced thermal hyperalgesia was only relieved by high dose of taurine at 120 min after IT injection, the BIC-induced one was relieved by not only high dose of taurine at 120 min but also low dose of glycine or betaine at 60 min after IT injection. The BIC-induced allodynia and thermal hyperalgesia was relieved by IT muscimol. CONCLUSIONS: This study suggests that IT glycine and related amino acids can reduce the allodynic and hyperalgesic action of STR or BIC in mice.

Neuropathic Pain Model Induced by Electrical Injury of Sciatic Nerve in Rats

OBJECTIVE: The purpose of this study was to develop a new neuropathic pain model in rat. METHOD: Twenty Sprague-Dawley adult male rats, 10 for control and 10 for experimental, were anesthetized and their sciatic nerves were exposed. In an experimental group, exposed nerve was injured with 10 volts electrical current for 10 seconds. The mechanical and thermal allodynia and pain behavior were evaluated in pre-electrical injury and post-injury 1, 2, 3 days, 1, 2, 3, 4, 6 and 8 weeks. The mechanical allodynia was evaluated by the frequency of response to 5 stimulations of von Frey hairs (4.31 and 4.56) and the thermal allodynia was tested by withdrawal latency to stimulation with radiant heat. Spontaneous pain behavior (paw shaking, paw elevation) was observed for 5 minutes in the cage. RESULTS: The experimental group exhibited significantly higher withdrawal frequency to mechanical stimulation: from post-injury 3 days to 6 weeks for von Frey hair 4.31 and from 2 days to 4 weeks for von Frey hair 4.56 (p<0.05). There was no difference between two groups in withdrawal latency to radiant heat stimulation. The experimental group showed spontaneous pain behavior but control group did not. In electron microscopic finding, prominent myelin destruction and axonal sprouting were observed in experimental group. CONCLUSION: These results suggest that a new neuropathic pain model can be made by 10 volts electrical injury for 10 seconds to rat sciatic nerve.

Development of Neuropathic Pain Model with 1% Phenol Injection in Rat Sciatic Nerve

OBJECTIVE: The purpose of this study is to develop a new neuropathic pain model in the rat. METHOD: Each male adult rat was anesthetized and the sciatic nerve was exposed. Each exposed nerve was injected with 0.03 cc of 1% phenol solution. Normal saline 0.03 cc was injected to the placebo group. Rats were tested for the presence of mechanical allodynia by von Frey hair. Spontaneous pain behavior (paw shaking, paw elevation) was examined for 5 minutes in the cage. RESULTS: Phenol injected group developed allodynia after the second post-injection day for up to 1 month. Allodynia was also observed in the contralateral legs of phenol injected group. The control group did not develop allodynia. Spontaneous pain behavior was not observed in either group. CONCLUSION: Neuropathic pain model was developed by 1% phenol solution injection to the rat sciatic nerve. This study suggests an easier method for making the neuropathic pain model.