The Analgesic Effect Of Intrathecal Injection Ith Dezocine On The Acute Pain Rat Model

Objective:Substance P, c-FOS protein and their receptor are thought to play an important role in the mechanisms of pain. The purpose of this study was to investigate the effects of intrathecal (IT) dezocine on the expression of substance P and c-FOS protein expression in the dorsal horn of spinal cord in a rat model of acute pain.Methods:Eighty healthy adult male Sprague Dawley (SD) rats weighing220g～250g were randomly divided into five groups (n=16animals each), after intrathecal built pipe:I S group (sham operation group) received intrathecal0.9%NaCl20μl in each time point, Ⅱ C group (control group) received intrathecal0.9%NaCl20μl in each time point, Ⅲ Dl group (intrathecal dezocine25μg group), received intrathecal dezocine25μg in each time point, Ⅳ D2group (intrathecal dezocine50μg group) received intrathecal dezocine50μg in each time point, V D3group (intrathecal dezocine75μg group) received intrathecal dezocine75μg in each time point. The animals were anesthetized with1.4%isoflurane. Catheter was inserted intrathecally to the lumbar region according to method of Storkson. Five days later, a lcm incision was made in the plantar region of left hindpaw parallel to the muscle under isoflurane anesthesia according to the method of Brennan. Pain behavior was assessed by withdrawal threshold to von Frey filament stimulation intensity (0.4g～15g) and response latency of the hindpaw to radiant heat. Expression of rat spinal cord substance P and c-FOS protein at2hours,6hours,24hours,48hours and72hours after incision was tested using immunohistochemical method.Results:MWT and TWL in S group was significantly higher at2hr,6hr,24hr,48hr and72hr after incision compared with the other4groups (P＜0.01). MWT and TWL in C group was significantly lower than D1group, D2group and D3group at2hr,6hr,24hr,48hr and72hr after incision (P＜0.01). MWL and TWL in D2group and D3group compared with D1group, MWL and TWL were significantly higher at2hr,6hr,24hr,48hr and72hr after incision (P＜0.01). MWL and TWL in D3group, compared with D2group, were significantly higher at2hr,6hr after incision(P＜0.05)..Immunohistochemical method shows that S group compared with the other4groups, rat spinal cord substance P and c-FOS protein raised significantly in other4 groups(P＜0.05).Conclusion:Intrathecal dezocine can reduce acute pain in raeffectivelyt, With the increase of the dose, the analgesic effects can be reinforced and capping effect can occur. The analgesic mechanisms are possibly related to the inhibition of the expression of substance P and c-FOS protein in the spinal cord.