Effects of intrathecal morphine on substance P expression in the dorsal horn of spinal cord in a rat model of incisional pain / 中华麻醉学杂志

ABSTRACT

Objective Substance P and its 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) morphine on substance P expression in the dorsal horn of spinal cord in a rat model of incisional pain Methods Sixteen male SD rats weighing 250 300g were randomly divided into four groups of 4 animal each in group Ⅰ (sham operation) 30 min after IT normal saline(NS) 20 ?l 1 4% isoflurane was inhaled for 5 min but no incision was made; in group Ⅱ (control group) 30 min before incision NS 20 ?l was given IT; in group Ⅲ (postoperative analgesia group) morphine 5 ?g (10 ?l) was given IT 30 min after incision; group Ⅳ ( preemptive analgesia group) morphine 5 ?g (10 ?l) was given IT 30 min before incision The animals were anesthetized with intraperitoneal pentobarbital sodium 40 mg?kg -1 PE 10 catheter was inserted intrathecally to the lumbar region according to method of Yaksh 5 days later incision of 1 cm long 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 a cumulative pain score Immuno histochemistry technique was used to measure the expression of substance P Results IT morphine given either before or after incision decreased the cumulative pain scores Incision made in the plantar region of left hindpaw increased substance P expression in the ipsilateral dorsal horn of spinal cord (0 62?0 07 vs 0 40?0 09) In group Ⅳ increase in substance P expression in the dorsal horn of spinal cord was inhibited Conclusions The analgesia provided by preemptive IT morphine is possibly mediated via the decrease in substance P in the dorsal horn of spinal cord