Antinociception And The Interactions Between Intrathecal Neofpam And Neostigmine In A Rat Model Of Postoperative Pain

Objective To observe the effect of intrathecal nefopam and neostigmine on nociceptive behaviors in a rat model of postoperative pain and c-fos protein expression at spinal level. To investigate the mechnism of their antinociception and the drug interactions between nefopam and neostigmine at the spinal level.Methods In a rat of postoperative pain,cumulative pain scores were used to evaluate pain behaviors; Neostigmine and Nefopam were administered to obtain the dose-response curve and the 50% effective dose (ED₅₀); Fractions of ED₅₀ values were administered intrathecally to establish the ED₅₀ s of drug combinations (neostigmine-nefopam);Immunohistochemistry technique was involved in observing c-fos protein expression at spinal level.Results (1) Intrathecal administration of nefopam (50 - 150μg) alone produced a significant dose-dependent antinociception to nociceptive reaction of the postoperative pain rats.According to Fig.1, ED₅₀ of nefopam was calculated to be 82.64ug and 95% confidence intervals were (72.53-94.14) ug. Intrathecal administration of neostigmine (1 -10μg) alone also produced a significant dose-dependent antinociception to nociceptive reaction of the postoperative pain rats. According to Fig.1, ED50 of neostigmine was calculated to be 8.36ug and 95% confidence intervals were (6.68 - 10.70) ug. Intrathecal administration of nefopam combined with neostigmine at the doses of 1/2 ED50, 1/4 ED₅₀,1/8 ED₅₀ and 1/16 ED₅₀ also produced a significant dose-dependent antinociception to to nociceptive reaction of the postoperative pain rats. According to Fig.l,the ED₅₀ of nefopam was calculated to be 10.93μg and 95% confidence intervals were(6.83-17.49)μg,and the ED₅₀ of neostigmine was calculated to be 1.05ug and 95% confidence intervals were(0.66- 1.68)μg ,When the two drugs were used together. (2) The cumulative pain scores of rats in operation group were much higher than those of sham-operation rats.Intrathecal nefopam neostigmine,nefopam add neostigmine either before or after operation decreased cumulative pain scores significantly,but there were no didderences among drug-use groups. (3)According to the Isobologram methods by Tallarida, from the ED₅₀ values of the two drugs used together, Fig.3 was made. From Fig.3, it can be deduced the interaction of nefopam and neostigmine was synergistic.(4)When nefopam and neostigmine were used alone at the dose of ED₅₀ , both of them can significantly repress the expression of c-fos protein. When the two drugs were used together at the dose of 1/2 ED₅₀ , the repression degree was greater . Their functional positions were at the Layerâ… -â…¡andâ…¤-â…¥. (5)At the dose of ED₅₀, nefopam repressed FLI-N of Layerâ… -â…¡at the rate of 41.5% , Layerâ…¤-â…¥34.2 %. At the dose of ED₅₀, neotigmine repressed FLI-N of Layerâ… -â…¡at the rate of 31.9% , Layerâ…¤-â…¥30.6%. At the dose 1/2 ED50, nefopam combined with neostigmine repressed FLI-N layerâ… -â…¡at the rate of 83.4% , Layerâ…¤-â…¥75.5%. According to the methods of Berebaum ,the repression of the two drugs to FLI-N was synergistic. (6) The expression of c-fos is related with behavior response.Conclusion (1)Nefopam at the dose of 50 to 150μg and neostigmine at the dose of 1 to 10μg, both can produce dose-dependant antinociception. (2) The antinociceptive effects of intrathecal nefopam and neostigmine are mediated partly by inhibition of c-fos protein. (3)All analyses of ntinociception and the c-fos repression revealed synergistic interaction for the neotig mine and nefopam at the spinal level.