目的：观察小剂量氯胺酮鞘内注射对癌痛大鼠吗啡镇痛耐受大鼠模型镇痛效果的影响，并对其作用机制进行研究。方法：71只雌性Sprague Dawley大鼠，体重230~250g，制备胫骨癌痛模型成功大鼠连续皮下注射盐酸吗啡注射液，建立癌痛大鼠吗啡耐受模型，通过胫骨X线检查，苏木精-伊红（hematoxylin-eosin, HE）染色及疼痛行为学检测，选取胫骨癌痛模型构建成功的大鼠作为实验对象。将癌痛吗啡大鼠随机分为4组：对照组(C组)、氯胺酮组(K组)、吗啡组(M组)和氯胺酮联合吗啡组(K+M组)。采用检测患肢足底热辐射痛阈值作为疼痛行为学指标，采用免疫细胞化学技术和酶联免疫法测定（enzyme linked immunosorbent assay, ELISA）脊髓P物质(substance-P，SP)及缓激肽(BK)含量。结果1 胫骨癌痛大鼠连续9天皮下注射盐酸吗啡注射液（10mg/kg, 2次/d）可成功建立胫骨癌痛大鼠吗啡耐受模型。2 连续7天鞘内注射小剂量盐酸氯胺酮注射液（25μg, 1次/d）联合皮下注射盐酸吗啡注射液致吗啡耐受大鼠热辐射痛阈值较各对照组明显上升（p﹤0.05）。3 鞘内注射小剂量盐酸氯胺酮注射液联合皮下注射盐酸吗啡注射液致吗啡镇痛耐受大鼠脊髓SP和缓激肽水平明显低于对照组（p﹤0.05）。结论：本研究通过对小剂量氯胺酮鞘内注射干预癌痛大鼠吗啡镇痛耐受模型痛阈值及行为学观察再次证实了小剂量氯胺酮的应用可加强吗啡的镇痛效果，同时可一定程度减轻吗啡镇痛耐受的发生。我们研究也表明传导通路中脊髓P物质及缓激肽含量变化是小剂量氯胺酮参与调节吗啡镇痛耐受的机制之一。

Objective: to observe the analgesic effect of intrathecal small dose ketamine injection on morphine tolerance in rat model of cancer pain and to investigate the related mechanism. Methods: 72 female SD rats, weighing 220-260g, were prepared the model of tibial cancer pain, and morphine tolerance model was established by continuous subcutaneous injection of morphine. The successful establishment of the model of tibial cancer pain was confirmed by X-ray film, HE staining and pain behavior determination. The successful morphine tolerance model of cancer pain was randomly divided into four groups: control group (Con), ketamine group (Ket), morphine group (Mor) and ketamine combined morphine group (Ket+ Mor). As an indicator of pain behavior, substance P (SP) and bradykinin in spinal cord were determined by immunohistochemistry and Elisa. Results: 1. The morphine tolerance model of tibial cancer pain was successfully established by 3 l of tibial bone marrow cavity injection into rat breast cancer cells (4.8×106/ml) and subcutaneous morphine injection (10mg/kg,2 times /d) for 9 consecutive days. 2. The pain threshold of morphine-tolerant rats induced by small intrathecal injection of ketamine (25 g,1 time /d) and subcutaneous injection of morphine (Ket+Mor group) increased significantly (p < 0.05). The level of SP and bradykinin in spinal cord of 3 Ket+Mor group was significantly lower than that of control group (p < 0.05). Conclusion: by observing the pain threshold and behavior of morphine-tolerant rats with intrathecal small dose of ketamine, it is confirmed that small dose of ketamine can enhance morphine analgesic effect and alleviate morphine tolerance and dependence effect to some extent. Our study confirmed that the changes of substance P and bradykinin content in the spinal cord in the conduction pathway are one of the analgesic mechanisms of low-dose ketamine in patients with morphine tolerance to cancer pain.