[Intrathecal injection of ketamine and clonidine for chronic neuropathic pain model in rats].

OBJECTIVE: To observe the effect of intrathecal injection of ketamine and clonidine for chronic constriction injury (CCI) in rats. METHODS: Thirty-two SD male rats weighing 220-280 g were anesthetized with intraperitoneal chloral hydrate 300 mg/kg. A catheter was implanted in the subarachnoid space at the lumbal region and CCI rat models were made successfully. On the 4th day after the surgery, the rats were randomly divided into 4 group: a control group,injecting 0.9%NS 20 microL intrathecally; a ketamine group, injecting ketamine 1 mg/kg(20 microL) intrathecally; a clonidine group (CL), injecting clonidine 20 microg/kg (20 microL) intrathecally; a combined ketamine and clonidine group, injecting ketamine 0.5mg/kg and clonidine 10 g/kg (20 microL) intrathecally, once a day for 1 week. BME-410A Plantar Analgesia Tester was used to measured pain threshold before the administration and 30 min after the administration. The rats were killed after the test was finished. And then we detected the nitric oxide synthase (NOS) activity and the NO production in the spinal cord. RESULTS: The combined injection of ketamine (0.5mg/kg)and clonidine(10 g/kg) produced significantly more potent analgesia than the injection of ketamine (1 mg/ kg) or clonidine (20 microg/ kg)alone. The NOS activity and the production of NO in the combined injection group were significantly lower than those of the single injection group (P<0.05). The weight of rats post-administration increased obviously in the 4 groups (P<0.05). CONCLUSION: The combined injection of ketamine and clonidine can produce synergistic ab-irritation without obvious side effects.