Investigation Of Spinal Cord Antinociceptive Mechanisms In Rats By Subarachnoid Cannulation

Objective To observe theμtype opioid receptor agonist fentanyl spinal antinociceptive effect after a catheter was inserted into a Wistar rat's subarachnoid space and to study intrathecal ketamine and intraperitoneal combined with intrathecal fentanyl on behavior of rats performance,to investigate the mechanisms of ketamine to enhance analgesic effect of intrathecal opioids in rats.Method A catheter was inserted into 37 male Wistar rat's subarachnoid space through a 27G fine-needle as guidance after ground the lamina thin with a burr under anesthesia.And then,2%lidocaine was injected into subarachnoid space to confirm if cannulation was successfully. Nociceptive test was done after 3 days with rats were divided into 4 groups.GroupⅠ:saline was injected into subarachnoid space,groupⅡ:0.5μg/kg fentanyl was injected into subarachnoid space,groupⅢ: 10mg/kg ketamine was injected intraperitoneally combined with 0.5μg/kg intrathecal fentanyl,groupⅣ:50μg ketamine was injected into subarachnoid space combined with 0.5μg/kg intrathecal fentanyl. Heat plate test,tail flick latency test,tail pressure test,paw pressure test and electric current threshold test were carried out sequentially before test,5 and 10 minutes after injection,then repeated every 10 minutes,lasted for 90 minutes.Drug was given every two days.Each test was repeated 3 times in a time-point.The mean of the 3 values calculated as the result when statistical analysis was performed.Results 32 rats was mockup successfully of all.Lidocaine anesthesia tests positive was used to determine if subarachnoidal cannulated successfully.There were no signs of neurological damages found during drug test cycle.In the drug tests,compared with groupⅠ:the pain threshold was significantly elevated after 5～40 minutes injection in groupⅡ(P＜0.01),after 5～60 minutes in groupⅢ(P＜0.01) and after 5～ 80 minutes in groupⅣ(P＜0.01).There were no significant differences between groupⅠand groupⅢat Electric current threshold test (ECT_n).Compared with groupⅡ:the pain threshold was significantly elevated after 10～60 minutes injection in groupⅢ(P＜0.05) and after 10～80 minutes in groupⅣ(P＜0.05).Compared with groupⅢ:the pain threshold was significantly elevated after 30～70 minutes injection in groupⅣ(P＜0.05).Conclusion①The improved method of subarachnoid catheter can elevation the success rates of models.②Intrathecal fentanyl has significant antinociceptive effect.③Intrathecal and intraperitoneal ketamine can increase the antinociceptive effect of fentanyl.