强啡肽对脊髓原生型与诱生型一氧化氮合成酶活性、分布和基因表达的影响及机制

Effects of Dynorphin A 1 17 on the Activities, Immunoreactivities and mRNA Expression of cNOS and iNOS in Rat Spinal Cord and Their Mechanisms

蛛网膜下腔注射（ｉ．ｔ．）强啡肽Ａ１－１７（Ｄｙｎ）引起剂量依赖性后肢和尾部瘫痪及甩尾甩足抑制。脊髓背角（侧）ＮＭＤＡ受体和ＮＯＳ／ＮＯ功能活性下降可能与Ｄｙｎ镇痛作用有关，脊髓腹角（侧）ＮＭＤＡ受体－Ｃａ２＋－ＮＯＳ／ＮＯ通路过度激活及ｃ－ｆｏｓ高表达可能与Ｄｙｎ致脊髓损伤（ＳＣＩ）作用有关。在Ｄｙｎ致ＳＣＩ机制中，过量ＮＯ（细胞水平）具有神经毒性作用，脑源性ＮＯＳ主要在早期，诱生型ＮＯＳ主要在后期起作用，而内皮细胞源性ＮＯＳ和适量ＮＯ（血管水平）可能具有保护作用。在原代培养脊髓神经元中，高浓度Ｄｙｎ可通过ＮＭＤＡ受体和κ受体直接引起细胞内Ｃａ２＋超负荷。

Intrathecal administration(i.t.) of Dynorphin A 1 17 (Dyn) 1.25～20nmol produced dose dependent paralysis of hindlimbs and tail as well as inhibition of tail flick and foot flinch reflexes. The Dyn spinal neurotoxicity and antinociception involve two differential mechanisms: Enhancement of NMDA Ca 2+ NOS/NO pathway and c fos over expression in the ventral spinal cord for neurotoxicity, and depression of NMDA receptor and NOS activities in the dorsal spinal cord for antinociception. Both brain derived constitutive NOS (predominant at early stage) and inducible NOS(at later stage) are detrimental, but endothelial constitutive NOS might be beneficial to Dyn spinal neurotoxicity. Dyn exerts adualistic modulatory effect on [Ca 2+ ]i of the cultured rat single spinal neurons, inducing sustained overload of intracellular free calcium via both NMDA and κ receptor activation at higher concentrations, and producing significant inhibition of the depolarization evoked calcium influx only via κ receptor activation at lower concentrations. Dyn exposure for 1h produced direct neurotoxicity in the cultured spinal neurons within an optimal range of concentrations.