Study On The Mechanism Of The Antinociception Of Intrathecal Neostigmine In The Formalin Test In Rats

OBJECTIVE and BACKGROUND: Nitric oxide, a cell messengerand neurotransmitter in the central neri'ous system, plays animportant role in the modulation of the nociception in the spinalcord.The protein product of c-fos gene expression isFos.Nociceptive inputs have been reported to produce increasedexpression of Fos.Fos expression has been used as a molecularmarker fOr neuronal activity in the nociceptive transmission. It wassuggested that c-fOs gene expression in the CNS was related to themodulation of nociception.Noxious stimulation can activate Fosexpression.Recently,it was suggested that noxious stimulationcould promote spinal fOs expression via activation of spinal NOSexpression.But it was also suggested that intravenous morphineincreased release of nitric oxide from spinal cord by a cholinergicmechanism.Neostigmine can increase Ach indirect1y and possessantinociceptive effect.But there has no report on whetherintrathecal neostigmine has antinociceptive effect in the formalintest and whether NO and Fos is involved in theantinociception.The aim of the present stUdy is to assess the effectof intrathecal neostigmine and its possible mechanism in theformalin test by histochemical and behavioral study.3MATERJAL and METHOD: ll2healthy male rats u'ere distributed inrandom fashion into control groups (group NS, F ) and test group(group LaF, LnF, NeF, LaNeF, LnNeF) with correpondingnumbers.Group NS sersyed as normal control.Group F was treatedwith 5%formalin 100 ll l,s.c.Group LaF, LnF, NeF, LaNeF, LnNeFwere treated respectively with L-Arg4.7 ll mol ith,L-NAME370nmol ith, Neol0 ll g ith, L-Arg4.7 u mol+ Neo l0 llg ith, L-NAME370nmol+ Neol0 P g ith before recei1Iing5%f Ormalin l00 ll l,s.c like group F.l/2h after formalin treatmentfOr No. 1~56 rats,the L3~4 spinal cord segments were removed forexpression of NOS. No.57~1l2 rats' flinch and licking time wasmeasured and their spinal cord segments were removed fOrexpression of Fos.RESULT: l. The flinch and licking time in phase 1 and 2 of group NeFwas shorter than that of group F. Pretreatment of L-Arg orL-NAME potentiated or reduced neostigmine-induced inhibitionof the formlin response.2.NOS expression of grouP NeF was stronger than that of group F.Pretreatment of L-Arg or L-NAME potentiated or reducedneostigmine-induced increased expression of NOS.3. Fos expression of group NeF was weaker than that of group F.Pretreatmeat of L-Arg or L-NAME potentiated or reducedneostigmine-induced reduced expression of Fos.4. The flinch and licking time in phase l and 2 of group F waslonger than that of group NS. Pretreatment of L-Arg or L-NANtE4potentiated or reduced formalin-induced behavior response. 5.NOS expression of group F was higher than that of group NS. Pretreatment of L-Arg or L-NAME potentiated or reduced formalin-induced increased expression of NOS.6. Fos expression of group F is stronger than that of group NS. Pretreatment of L-Arg or L-NAME potentiated or reduced formalin-induced increased expression of Fos.CONCLUSION: 1. It might be one of the nociception mechanisms in the formalin test that Fos expression in the spinal cord was induced by spinal nitric oxide release,2 . Intrathecal neostigmine could reduce both phases of formalin-induced behavioral nociception in the rats,indicating its antinociception.3. Intrathecal neostigmine could supress Fos expression induced by nitric oxide release in the spinal cord,as might be one of the antinociception mechanisms of intrathecal neostigmine in the formalin test.More studies about the mechanism are needed.