INTRATHECAL PREADMINISTRATION OF L-NAME REDUCING FORMALIN-EVOKED C-FOS EXPRESSION IN SPINAL DORSAL HORN OF RATS

Objective:To observe the effects of intrathecal preadministration of L-NAME,a non-selective NOS inhibitor,on the formalin-evoked c-fos expression in the spinal dorsal horn of rats.Methods:Sixty female SD rats weighing 220～310 g,showing no signs of neurological deficiency after intrathecal catheterization,received subcutaneous injection of formalin 40 μl in the plantar surface of the left hindpaw to establish the inflammatory pain model.15 minutes before formalin test,L-NAME 250 μg or 0.9% normal saline,all in volume of 10 μl,were intrathecally injected through previously inserted catheter.The survival time of animals were 1,4,8,12 and 24 hours after operation,with 6 rats for each manipulation at each time point.In addition,4 other rats were sacrificed 4 hours following subcutaneous injection of normal saline 40 μl and served as control.The c-fos expression in ipsilateral spinal dorsal horn was detected by immunohistochemistry technique.Results:There appeared a rapid and persistent enhancement of c-fos expression in the spinal dorsal horn after subcutaneous injection of formalin.Furthermore,with the time passing by,the increase in the number of fos-like immunoreactivity(FLI) neurons seemed more obvious in the deep laminae of spinal dorsal horn.As compared to FN group,the number of FLI neurons was decreased by 23.1%～51.8% in the superficial laminae and 46.3%～58.3% in the deep laminae of spinal dorsal horn,respectively.Conclusion:Intrathecal preadministration of L-NAME can effectively inhibit formalin-induced c-fos expression in the spinal dorsal horn of rats,especially in the deep laminae.