The Changes of Neurotransmitters in Central Sensitization after Peripheral Nerve Injury in Rats

Lee, Kyu Yeol; Sohn, Sung Keun; Kim, Dal Hee

Abstract

There has been much interest in the involvement of wind-up in the hyperalgesia and allodynia of chronic pain syndrome. For investigating the hehaviorml parallels of this wind-up phenomenon, it was limed to evaluate the changes of neurotransmitters(aspartate. lutamate, and taurine) in central sensitization after formalin-induced peripheral nerve injurv in the rats. The experiment was divided into two subexperiments; One was the formalin test.;and the other was microdialysis for evaluation of neurotransmitters. In formalin test (n=7), 50 microliter of 5% formalin was injected suhcutaneously in the foot dorsum of the right hind limb with a 30 G neeclle. To cluantify the formilin response. the number of spontaneous t1inches was counted at 1-2 minutes and 5-6 minutes and at 5 minutes intervals during the period 10- 60 minutes after formalin injeclion. In microdialysis study. the experimental animals were divided randomly into two groups. In experimentl group (n=10). the microdialysis catheter was perfused with artificial cerehrospinal fluid by 3 microliter/min for one hour. Then. the two beseline dialysis samples were collected and 50 microliter of 5% formalin was injected .iuhcutaneously in thc plantar surface of the right hind paw with a 30 G needle. Three 10 minutes dialysate samples were collected after formalin injection. In control group(n=10), the normal saline instead of formalin was used. The results were as followed: In formalin test, there was a biphasic pattern of flinchine after formalin injection. The peak in phase I was shown at 2 minutes after formalin injection. The second peak was shown at 35 minutes alter formalin injection during phase II. In microdialysis study, thcre were statistically significant increascs of aspartate and lutamate concentrations, excitatory neuro transmitters, during the first 10 minutes after formalin injection. After lhen, all values of these neurotransmitters were rcturned to baseline values. The concentrations of taurine, an inhihitory neurotransmitter, was shown a tendency of an increase after formalin injection but, it was not statistically significant. From these results, it secms that the excitatory amino acid ncurotransmitter may partly play a role to triqer the central sensitization after peripheral nerve injury.