MK801对幼鼠脊髓背角LTP的抑制作用

Inhibitory Effect of MK801 on LTP in Cornu Dorsale Medullae Spinal of Young Rats

目的观察NMDA受体的非竞争性阻断剂MK801对幼鼠脊髓背角浅层诱发场电位长时程增强(LTP)现象的反应,分析痛觉传入信息在未成熟大鼠脊髓背角浅层的表现特征。方法选50例雄性SD大鼠,分为新生期组、幼年组,每组动物随机分空白对照组、生理盐水对照组、MK801低剂量组、中剂量组及高剂量组5组。分离左侧坐骨神经,给予12 V,0.5 ms的单个方波刺激,记录同侧胸13~腰1脊髓背角浅层的诱发场电位,脊髓局部注射不同剂量MK801、生理盐水20μL,而后给予高频高强度强直电刺激(35 V,0.5 ms,100 Hz,串长1 s,串间隔10 s的4串电刺激)后观察场电位的变化。结果电刺激坐骨神经可在脊髓背角浅层记录到诱发场电位,强直刺激作用于坐骨神经可诱导各组脊髓背角浅层诱发场电位产生了LTP(P<0.01),新生期组场电位体现为A类神经纤维诱发的特点,幼年组场电位体现在C类神经纤维诱发的特点。MK801低剂量组对脊髓背角LTP场电位幅度没有抑制效应,强直刺激前后平均潜伏期缩减有显著差异(P<0.01);MK801高剂量组对脊髓背角LTP完全抑制;强直刺激后场电位幅度同强直前相比差别无显著性意义(P>0.05),强直刺激前后平均潜伏期缩减无明显差异(P>0.05);MK801中剂量组场电位幅值同对照组相比,差别有显著意义(P<0.05),强直刺激前后平均潜伏期缩减无明显差异(P>0.05)。结论幼鼠在单刺激和条件刺激后引起诱发场电位有不同特点;MK801脊髓注射对幼鼠脊髓背角区LTP均有抑制作用,对脊髓背角LTP抑制是其记忆损伤作用的机制之一,且致场电位潜伏期程度不等的缩减与幅度的变化无相关性。

Objective To observe the inhibitory effect of MK - 801 （ NMDA receptor） on long - term potentiation（ LTP） of evoked field potential at superficial layer of cornu dorsale medullae spinal in young rats and analyze manifestations of pain conduction information at superficial lay- ers of cornu dorsale medullae spinal in immature rats. Methods：Based on their birthdays,male rats were divided into neonate group （17 -20 days old,weighing 40 -52 g,n =25）,infant group （40-50 days old, weighing 82- l l0 g, n = 25）, rats of every group were random divided into blank control group（ n = 5） ,normal saline control group（ n = 5 ） ,low dosage MKSOI group（ n = 5）,middling dosage MKS01 group（n =5）and high dosage MKS01 group（n =5）. Left sciatic nerve was separated and stimulated with single square wave （I2V,0.5ms）, Meanwhile, e- voked field potential was recorded at superficial layers of lateral TI3 - LI cornu dorsale medullae spinal after injected the different dosage MKS01 and normal saline 20μL in spinal cord,and then stimulated with high - frequent and high - intensive tetanizing current（35 V,0.5ms, 100 Hz, 1 s per bundle,10s in bundle interval） four times. After the operation,onset of LTP was observed; meanwhile,amplitude changes and latency of field potential were analyzed. Results Electric stimulation at sciatic nerve with high -frequent and high -intensive tetanizing current could in- duce LTP at superficial layers of cornu dorsale medullae spinal （P 〈0.01）. LTP in the naenon- ate group manifested the amplitude characteristics of A - kind never fiber and there was signifi- cant difference （P 〈 0.01 ）, the infant group manifested the amplitude characteristics of C - kind never fiber and there was significant difference （P 〈 0.0! ）, otherwise, latencies were all shortened. Compare blank control group and 0.9% sodium chloride injection group. Average amplitude of the low dosage MK80! group was no significant difference after high - frequent and high -intensive electric stimulation （P 〉0.05）, but the average latency reduction was sig- nificantly different before and after high -frequent and high -intensive electric stimulation（P 〈 0.01）; Average amplitude and average latencies reduction of the high dosage MKS0] group was no significant difference （P 〉 0.05） ; Average amplitude of the middling dosage MKS0] group was significant difference after high - frequent and high - intensive electric stimulation （P 〈0.05）, but Average latencies reduction was no significant difference before and after high - frequent and high - intensive electric stimulation （ P 〉 0.05 ）. Cend^ien Evoked field potential at superficial layer of cornu dorsale medullae spinal can be recorded through electric stimulation at sciatic nerve, Single stimulation and tetanizing electric stimulation can cause different charac- teristics of evoked field potential in the naenonate and infant rats. After injected the differ dos- age MKS0! in spinal cord,The inhibitory effect of electric stimulation at sciatic nerve on LTP of evoked field potential at superficial layer of cornu dorsale medullae spinal in the young rats, which may probably be one of its mechanisms of memory dysfunction. There is no correlation between the increased amplitude and the latencies reduction