The role of microglia in spinal cord in painful diabetic rats

Objective The purpose of this present study was to observe the analgesic effect and response of microglia in spinal cord in painful diabetic rats undergoing systemic administration of propentofylline. Methods 20 painful diabetic sprngue-dawley rata induced by streptozotocine(STZ) intraperitoneal injection were randomly allocated to diabetic group (group Ⅱ, n=10) and propentofylline group (group Ⅲ, n = 10), meanwhile 10 other normal age-matched rata were chosen as control group (group Ⅰ, n = 10). The rats in group Ⅲ were received daily intraperitoneal propentofylline 28 d-35 d after STZ injection. The blood samples were collected from vena caudalis to assess the value of blood sugar before STZ injection and at 2 d,7 d,14 d,21 d,28 d,35 d after STZ injection, respectively. The body weight was measured at the same point. Response to the mechanical stimulus was measured with yon Frey filament, and 50% mechanical withdraw threshold (MWT)was recorded before and at 7 d,14 d,21 d,28 d,35 d after STZ injection. The animals were sacrificed and lumbar segment of spinal cord was removed for determination of complement receptor 3 (CR3) in the microglia in spinal cord by immuno-histochemical assay. 35 d after STZ injection. Results The level of blood sugar increased dramatically after STZ injection in both groups Ⅱ and Ⅲ while the body weight started decreasing(P <0.01). The MWT in groups Ⅱ and Ⅲ decreased significantly as compared to that in group Ⅰ at 28 d,35 d after STZ injection(P<0.01), and the rata of group Ⅲ showed lower MWT than these of group Ⅱ after daily intraperitoneal propentofylline at 35 d after STZ injection (P < 0.05). Immuno-histochemical assay demonstrated that CR3 positive in the microglia in the dorsal horn significantly increased in both groups Ⅱ and Ⅲ 35 d after STZ injection compared with that in group Ⅰ(P <0.01). There weresignificantly increasing CR3 positive in the microglia in the dorsal horn in group Ⅱ compared with group Ⅲ (P < 0.01). Conclusion Activation of microglia in spinal cord is involved in the mechanism of diabetic peripheral neuropathy. Daily intraperitoneal propentofylline has the potency to alleviate hyperalgesia in painful diabetic rats, and the mechanism responsible for the analgesic effect may be due to the reduction of microglia activation in spinal cord. Key words: Diabetic neuropathy;  Neuralgia;  Spinal cord;  Microglia;  Propentofylline