氯胺酮对甲醛致痛诱导大鼠脊髓背角神经元兴奋性的抑制

背景:氯胺酮是否可通过影响脊髓水平的伤害性信息的传递而发挥抗伤害作用尚不清楚;一氧化氮在脊髓水平主要参与痛觉过敏的形成和发展,可诱导Fos表达,但其是否参与了氯胺酮对痛信号的转导或调控的机制不明。目的:观察大鼠脊髓对甲醛痛刺激的反应及氯胺酮的影响。设计:均衡随机的动物实验。单位:徐州医学院附属医院麻醉科和江苏省麻醉学重点实验室。材料:实验于2000-01/03在徐州医学院江苏省麻醉学重点实验室进行。取SD大鼠30只,用均衡随机方法分为6组熏甲醛组6只,甲醛 氯胺酮组6只,氯胺酮 甲醛组6只,氯胺酮组6只,甲醛 生理盐水组3只,生理盐水组3只,各组雌雄比例相同。方法:①甲醛组:体积分数为0.05的甲醛200μL一侧前爪掌心皮下注射,刺激1h。②甲醛 氯胺酮组:甲醛痛刺激10min后腹腔注射100mg/kg氯胺酮1h。③氯胺酮 甲醛组:腹腔注射氯胺酮10min后再行甲醛痛刺激1h。④氯胺酮组:腹腔注射同等剂量氯胺酮1h。⑤甲醛 生理盐水组:甲醛痛刺激10min后腹腔注射等容(10mL/kg)的生理盐水1h。⑥生理盐水组:腹腔注射等容生理盐水1h。主要观察指标:①各组大鼠行为学表现。②取脊髓切片,用c-fos基因免疫组化法和NADPH-d组化技术染色,观察大鼠脊髓背角4层(Ⅰ～Ⅱ层,Ⅲ～Ⅳ层,Ⅴ～Ⅵ层,Ⅶ～Ⅹ层)切片Fos样免疫阳性神经元(FLI)和FLI/NOS双标记神经元的数目变化。结果:30只大鼠全部进入结果分析。①行为学变化:甲醛组及甲醛 生理盐水组大鼠注射甲醛后,出现痛反应;注射氯胺酮的大鼠,注射后数分钟内翻正反射消失,无明显的痛行为表现,而呈持续睡眠状态,至灌注时翻正反射仍未恢复。②FLI神经元表达:甲醛组及甲醛 生理盐水组大鼠注射侧脊髓背角出现大量FLI阳性神经元,主要分布在脊髓背角Ⅰ～Ⅱ层;氯胺酮 甲醛组、甲醛 氯胺酮组大鼠脊髓FLI细胞的分布与甲醛组及甲醛 生理盐水组基本相似,但FLI阳性细胞数量显著减少(P<0.01);氯胺酮组和生理盐水组大鼠脊髓未见或偶见FLI阳性细胞。③FLI/NOS双标记神经元表达:氯胺酮 甲醛组、甲醛 氯胺酮组脊髓背角Ⅰ～Ⅱ层双标记神经元数目显著少于甲醛组及甲醛 生理盐水组眼(1±1),(1±1),(7±3),(8±3)个/切片,P<0.01演,氯胺酮组和生理盐水组无表达。结论:同侧相应脊髓节段的某些神经元参与了化学性致痛信息的传导和调控,氯胺酮通过抑制这些神经元的活动而产生抗伤害作用;此作用与抑制脊髓内一氧化氮合酶阳性神经元的活性有关。     

异氟醚对甲醛致痛诱发大鼠脊髓背角P物质释放的影响

目的：研究异氟醚对甲醛疼痛模型大鼠脊髓背角P物质(SP)释放的影响。方法：SD大鼠16只，随机数字表法分为4组，每组4只。通过向右侧后肢跖部皮下注射40g／L甲醛150μL建立疼痛模型。A组、B组跖部皮下注射注射生理盐水，C组、D组注射甲醛，B组、D组在皮下注射前10min吸入15g／L异氟醚，并持续60min，A组、C组吸纯氧。麻醉大鼠。取脊髓L3-5，节段。用SP免疫组化方法结合图像分析测定脊髓背角SP样免疫反应阳性(SPLI)纤维及终末的光密度(A)。结果：4组大鼠两侧脊髓背角SPLI的A值无显著差别(P&;gt;0.05，t=1．065)；与A组脊髓背角SPLI的A值比较，B组无明显变化(P&;gt;0.05，t=1．987)，C，D组显著小于A组(P&;lt;0.01，t=14．342，t=7．514)，有明显的纤维和终末脱失趋势；D组SPLI的A值较C组显著增加(P&;lt;0.01，t=8．263)。结论：异氟醚不影响髓背角浅层SP含量，但能明显减轻甲醛引起的疼痛反应和脊髓背角SP的释放，部分阻断脊髓痛觉的传导。     

异氟醚对甲醛致痛诱发大鼠脊髓背角P物质释放的影响

目的:研究异氟醚对甲醛疼痛模型大鼠脊髓背角P物质(SP)释放的影响。方法:SD大鼠16只,随机数字表法分为4组,每组4只。通过向右侧后肢跖部皮下注射40g/L甲醛150μL建立疼痛模型。A组、B组跖部皮下注射注射生理盐水,C组、D组注射甲醛,B组、D组在皮下注射前10min吸入15g/L异氟醚,并持续60min,A组、C组吸纯氧。麻醉大鼠,取脊髓L3～5节段。用SP免疫组化方法结合图像分析测定脊髓背角SP样免疫反应阳性(SPLI)纤维及终末的光密度(A)。结果:4组大鼠两侧脊髓背角SPLI的A值无显著差别(P>0.05,t=1.065);与A组脊髓背角SPLI的A值比较,B组无明显变化(P>0.05,t=1.987),C,D组显著小于A组(P<0.01,t=14.342,t=7.514),有明显的纤维和终末脱失趋势;D组SPLI的A值较C组显著增加(P<0.01,t=8.263)。结论:异氟醚不影响髓背角浅层SP含量,但能明显减轻甲醛引起的疼痛反应和脊髓背角SP的释放,部分阻断脊髓痛觉的传导。     

过度通气对在体大鼠脊髓背角WDR神经元兴奋性影响的实验研究

目的:考察过度通气对大鼠脊髓背角广动力范围(Wide dynamic range,WDR)神经元自发和疼痛诱发放电频率的影响。方法:将25只SD大鼠随机分为N(正常通气)和H(过度通气)两组。两组均在吸入麻醉下行椎板切除,记录与大鼠后足掌部皮肤感觉对应的脊髓背角WDR神经元放电频率百分比。N组正常通气120分钟,旨在排除手术创伤对WDR神经元的影响;H组实施过度通气60分钟后,恢复正常通气继续观察60分钟,目的为考察过度通气对该神经元电活动的影响。结果:(1)N组各采样点间WDR神经元自发和诱发放电频率百分比均无显著性差异。(2)H组过度通气后WDR神经元自发和疼痛诱发放电频率百分比较对照值显著降低,并随正常通气的恢复而恢复。(3)H组过度通气期间WDR神经元自发及诱发放电频率百分比均较N组相应时间点显著降低。结论:过度通气可使大鼠脊髓背角WDR神经元兴奋性降低。     

蛋白激酶C在甲醛复制内脏炎症痛大鼠脊髓背角神经元电活动中的作用

目的：观察蛋白激酶C抑制剂氯丙嗪对甲醛复制的内脏炎症痛大鼠脊髓背角神经元电活动的影响，了解蛋白激酶C在甲醛复制的内脏炎症痛中的作用。 方法：实验于2005-01／1l在泰山医学院基础医学研究所完成。选用24只健康成年Wistar大鼠，数字表法随机分为3组（n=8）：①甲醛组：体积分数为0．05的甲醛100μL直肠黏膜下注射致炎，复制内脏炎症痛模型。②甲醛＋生理盐水组：在脊髓背角找到对直肠刺激敏感的神经元后，腹腔注射生理盐水0．4mlMkg，30min后记录前对照反应。然后行甲醛直肠黏膜下致炎，方法和剂量同甲醛组。③甲醛＋氯丙嗪组：腹腔注射25异／L氯丙嗪0．4mL／kg，其余处理同甲醛＋生理盐水组。记录3组大鼠注射甲醛后120min内脊髓背角神经元放电频率的变化，以15min为一个时间段，共记录8个时间段。以给药前神经元的放电频率为参照，计算给药后反应的相对值（给药后实际反应频率／给药前实际反应频率&;#215;100％）。 结果：24只大鼠全部进入结果分析，共记录到24个单位的反应结果。①甲醛组在给药后0～15min和16-30min时间段的放电频率分别为致炎前基线水平的（283．7&;#177;46．0）％和（254．0&;#177;37．4）％，与致炎前相比均有显著性增加（P〈0．05）。②甲醛＋氯丙嗪组在致炎后0～15min和16～30min两时间段的脊髓背角神经元放电频率分别为基线水平的（124．6&;#177;10．25）％和（105．4&;#177;8．69）％；甲醛＋生理盐水组致炎后同时间段的放电频率为基线水平的（279．7&;#177;37．4）％和（249．2&;#177;38．5）％。甲醛＋氯丙嗪组在致炎后0～15min和16-30min两时间段的放电频率低于其他2组（P〈0．05），另2组比较差异不显著（P〉0．05）。 结论：①甲醛直肠黏膜下注射可稳定复制大鼠炎症性内脏痛模型。②蛋白激酶C抑制剂氯丙嗪可使脊髓背角神经元放电频率减少，提示蛋白激酶C参与甲醛诱导急性炎症引起的痛觉敏感化的形成。     

蛋白激酶C在甲醛复制内脏炎症痛大鼠脊髓背角神经元电活动中的作用

目的:观察蛋白激酶C抑制剂氯丙嗪对甲醛复制的内脏炎症痛大鼠脊髓背角神经元电活动的影响,了解蛋白激酶C在甲醛复制的内脏炎症痛中的作用。方法:实验于2005-01/11在泰山医学院基础医学研究所完成。选用24只健康成年Wistar大鼠,数字表法随机分为3组(n=8):①甲醛组:体积分数为0.05的甲醛100μL直肠黏膜下注射致炎,复制内脏炎症痛模型。②甲醛 生理盐水组:在脊髓背角找到对直肠刺激敏感的神经元后,腹腔注射生理盐水0.4mL/kg,30min后记录前对照反应,然后行甲醛直肠黏膜下致炎,方法和剂量同甲醛组。③甲醛 氯丙嗪组:腹腔注射25g/L氯丙嗪0.4mL/kg,其余处理同甲醛 生理盐水组。记录3组大鼠注射甲醛后120min内脊髓背角神经元放电频率的变化,以15min为一个时间段,共记录8个时间段。以给药前神经元的放电频率为参照,计算给药后反应的相对值(给药后实际反应频率/给药前实际反应频率×100%)。结果:24只大鼠全部进入结果分析,共记录到24个单位的反应结果。①甲醛组在给药后0～15min和16～30min时间段的放电频率分别为致炎前基线水平的(283.7±46.0)%和(254.0±37.4)%,与致炎前相比均有显著性增加(P<0.05)。②甲醛 氯丙嗪组在致炎后0～15min和16～30min两时间段的脊髓背角神经元放电频率分别为基线水平的(124.6±10.25)%和(105.4±8.69)%;甲醛 生理盐水组致炎后同时间段的放电频率为基线水平的(279.7±37.4)%和(249.2±38.5)%。甲醛 氯丙嗪组在致炎后0～15min和16～30min两时间段的放电频率低于其他2组(P<0.05),另2组比较差异不显著(P>0.05)。结论:①甲醛直肠黏膜下注射可稳定复制大鼠炎症性内脏痛模型。②蛋白激酶C抑制剂氯丙嗪可使脊髓背角神经元放电频率减少,提示蛋白激酶C参与甲醛诱导急性炎症引起的痛觉敏感化的形成。     

氯胺酮对甲醛致炎性痛小鼠背根节TrkA受体表达的影响

目的：观察N-甲基-D-天冬氨酸受体非特异性拮抗剂氯胺酮对甲醛致炎小鼠疼痛行为学的影响，以及背根节神经生长因子受体TrkA表达的变化。方法：实验于2005—02／05在华中科技大学同济医学院附属同济医院进行。取成年健康昆明种小鼠24只，随机分为正常对照组、甲醛组和甲醛＋氯胺酮组3组，每组8只。分别于甲醛组和甲醛＋氯胺酮组小鼠右后足底注入体积分数为0．05的甲醛100μL形成急性炎性痛模型。甲醛＋氯胺酮组小鼠在注入甲醛后立即经腹腔注入40mg／kg的氯胺酮。正常对照组小鼠不干预。观察甲醛注射后小鼠疼痛行为学变化，甲醛致炎2h后处死小鼠，免疫组化ABC方法检测背根节TrkA受体表达。结果：经补充后24只小鼠进入结果分析。①疼痛行为学变化：甲醛注射后1h内小鼠均出现明显的摔腿、舔足、跛行、致炎足不能着地等疼痛行为学改变，注射足呈高度肿胀。甲醛＋氯胺酮组小鼠氯胺酮注射后翻正反射立即消失，甲醛致炎后第一时相（注射后0-5min）、第二时相（注射后20-60min）的疼痛行为学反应次数显著少于甲醛组[（6．0&;#177;2．5），（113．0&;#177;9．5）次；（3&;#177;0），（75．0&;#177;4．5）次；P〈0．01]。②背根节TrkA受体阳性神经元平均灰度值：注射侧甲醛组高于甲醛＋氯胺酮组和正常对照组（205．3&;#177;11．9，121．6&;#177;7．9，116．5&;#177;7．7，P〈0．01），甲醛＋氯胺酮组和正常对照组比差异不显著（P〉0．05）。结论：氯胺酮能抑制急性炎性痛时疼痛行为学变化，并减少背根节TrkA受体的表达，这种效应可能与TrkA受体下调后初级伤害性刺激传人减少有关。     

氯胺酮对脊神经结扎大鼠脊髓背角星形胶质细胞的影响

目的：观察腹腔注射氯胺酮（KET）对脊神经结扎（SNL）大鼠脊髓背角星形胶质细胞的影响.方法：雄性SD大鼠42只随机分为五组：SHAM组;KET0组和NS0组结扎后分别腹腔注射KET 10mg/kg和生理盐水（NS）10 ml/kg;KET7组和NS7组,结扎7天后分别腹腔注射KET 10 mg/kg和NS.每组（除SHAM组）给药,每天两次,共7天.结扎后第4、7、14、21、28天行机械性痛敏实验,并用组化方法测定右侧脊髓背角胶质纤维酸性蛋白（GFAP）阳性细胞的变化.结果：与SHAM比较,KET0、NS0组机械痛敏试验的压力阈值（PWPT）下降,二者GFAP阳性细胞染色较SHAM深,GFAP免疫反应阳性产物表达相对面积分别增加45.0%（P＜0.01）和86.7%（P＜0.01）;与NS7比较,KET7组PWPT升高,KET7组GFAP阳性细胞染色较NS7组浅,相对面积（不同时段）分别下降40.3%（P＜0.01）和24.6%（P＜0.01）.结论：低剂量的KET能抑制星形胶质细胞的激活,从而起到治疗神经病理性疼痛的作用.     

氯胺酮对N-甲基-D-天冬氨酸诱导大鼠脊髓背角星形胶质细胞损伤的作用

背景：氯胺酮是临床常用的静脉全麻药，静脉或硬脊膜外腔用药都有镇痛作用，它是N-甲基-D-天冬氨酸受体非竞争性拮抗剂，可拮抗兴奋性氨基酸的毒性作用。 目的：观察氯胺酮对N-甲基-D-天冬氨酸受体过度激活诱导大鼠脊髓背角星形胶质细胞凋亡的影响，探讨其可能的作用机制。 设计：随机对照观察。 单位：郧阳医学院附属太和医院麻醉科。 材料：实验于2003-09／2005-01在郧阳医学院基础医学研究所细胞生物学实验室完成。由武汉大学动物实验中心提供新生两三天Wistar大鼠。 方法：取Wistar大鼠T11～L6脊髓背角星形胶质细胞原代纯化培养。胶质纤维酸性蛋白鉴定星形胶质细胞纯度达98％后用于实验。将培养细胞24孔板随机分为6组（每组9份）：①对照组加Hanks液50μL。（爹N-甲基-D-天冬氨酸组加药浓度为100μmol／L。（爹氯胺酮组加药浓度为1mmol／L。④100μmol／L N-甲基-D-天冬氨酸＋0．1mmol／L氯胺酮组。⑤100μmol／LN-甲基-D-天冬氨酸＋0．5mmol／L氯胺酮组。⑥100μmol／LN-甲基-D-天冬氨酸＋1mmol／L氯胺酮组。1mmol几氯胺酮为临床镇痛剂量。培养24h后检测超氧化物歧化酶活性和丙二醛含量，免疫细胞化学观察Bcl-2蛋白和形态学变化，流式细胞仪检测星形胶质细胞凋亡率。 主要观察指标：①Bcl-2蛋白免疫组织化学苏木精-伊红复染细胞着色及形态学变化。②流式细胞仪检测星形胶质细胞凋亡率。③丙二醛含量和超氧化物歧化酶活性变化。 结果：①Bcl-2平均吸光度值似）作为半定量测量Bcl-2蛋白表达水平：100μmol／LN-甲基-D-天冬氨酸组低于对照组，差异显著[分别为0．0544&;#177;．021，0．108&;#177;0．039，P〈0．01]，100μmol／LN-甲基-D-天冬氨酸＋1mmol／L氯胺酮组高于100μmol／LN-甲基-D-天冬氨酸组，差异显著[分别为0．148&;#177;0．045，0．054&;#177;0．021，P〈0．01]。②流式细胞仪检测星形胶质细胞凋亡率：100μmol／LN-甲基-D-天冬氨酸组高于对照组，差异显著[分别为（25．26&;#177;6．13）％，（5．66&;#177;2．24）％，P〈0．01]，100μmol／LN-甲基-D-天冬氨酸＋1mmol／L氯胺酮组低于100μmol／LN-甲基-D-天冬氨酸组，差异显著[分别为（24．41&;#177;4．82）％，（25．26&;#177;6．13）％，P〈0．01]。③丙二醛含量和超氧化物歧化酶活性变化：100μmol／LN-甲基-D-天冬氨酸使星形胶质细胞内丙二醛含量显著升高，而超氧化物歧化酶活性明显降低；1mmol／L氯胺酮明显降低丙二醛含量，显著增强超氧化物歧化酶活性，该效应在临床镇痛剂量以内有明显量效关系，与N-甲基-D-天冬氨酸组相比差异显著（P〈0．01）。1mmol／L氯胺酮组与对照组相比、100μmol／LN-甲基-D-天冬氨酸＋0．1mmol/L几氯胺酮组与N-甲基-D。天冬氨酸组相比差异均无显著性。 结论：N-甲基-D-天冬氨酸受体过度激活可诱导大鼠脊髓背角星形胶质细胞大量凋亡，适量氯胺酮显著抑制细胞凋亡，其机制可能增强星形胶质细胞Bcl-2蛋白表达，同时抑制自由基的产生和增强超氧化物歧化酶活性。     

新生时辣椒素处理大鼠的炎症和痛敏：对脊髓背角伤害性神经元的影响

新生时辣椒素处理大鼠的炎症和痛敏──对脊髓背角伤害性神经元的影响已知，脊髓中有两类伤害性神经元：一类是伤害特异性（ＮＳ）神经元，只对伤害性刺激起反应，接受Ｃ纤维和Ａδ纤维的传入冲动；另一类是广动力范围（ＷＤＲ）神经元，对伤害性和非伤害性刺激均起反应，...     

Nitrous oxide inhibits glutamatergic transmission in spinal dorsal horn neurons

The effects of nitrous oxide (N2O) are thought to be mediated by several pharmacological pathways at different levels of the central nervous system. Here, we focus on excitatory glutamatergic transmission in the superficial dorsal horn of the spinal cord with respect to its importance for the nociceptive processing. The effects of 50% N2O on electrically evoked and spontaneous excitatory glutamatergic transmission and on the response to exogenous administration of N-methyl-d-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionic acid (AMPA) receptor agonists were examined in lamina II neurons of adult rat spinal cord slices using the whole-cell patch-clamp technique. Peak amplitudes of Adelta- and C-fiber evoked monosynaptic NMDA- and AMPA-receptor-mediated excitatory postsynaptic currents (EPSCs) were decreased in the presence of N2O. N2O reduced the peak amplitude and integrated area of exogenous NMDA- and AMPA-induced currents. Moreover N2O changed the distribution of miniature EPSC amplitude, but not frequency distribution in most neurons. N2O inhibits glutamatergic transmission in the superficial dorsal horn by modulating the NMDA- and AMPA-receptors. Our findings raise the possibility that the antinociceptive effect of N2O may be directly mediated at the level of the spinal cord.     

Blockade of spinal N- and P-type,but not L-type,calcium channels inhibits the excitability of rat dorsal horn neurones produced by subcutaneous formalin inflammation

The effects of the intrathecal (i.t.) administration of different voltage-sensitive calcium channel (VSCC) blockers were studied in the formalin model of inflammation. The responses of convergent dorsal horn neurones after the subcutaneous injection of formalin (5% formaldehyde, 50 μl volume) were recorded extracellularly in rats under halothane anaesthesia. Administration of the L-type calcium channel blocker verapamil, 5 and 50 μg, before formalin injection had no effect on either the first or second phase of the formalin response. Pre-treatment with the N-type calcium channel blocker ω-Conotoxin-GVIA, 0.1 and 0.4 μg, reduced both phases of the formalin response. The low dose of ω-Conotoxin-GVIA significantly inhibited the first phase response whereas the high dose significantly reduced the second phase. Pre-treatment with the P-type calcium channel blocker ω-Agatoxin-IVA, 0.125 and 0.5 μg, did not cause a significant inhibition of the first phase whereas a marked dose-related reduction in the second phase of formalin response was found with the high dose producing 95% inhibition. These results demonstrate that spinal N- and P-type, but not L-type, VSCCs are involved in the inflammation-evoked hyperexcitability of dorsal horn neurones after peripheral formalin injection. Since selective antagonists for each type of VSCC had differential effects on the formalin response, it is suggested that each type of VSCC could be preferentially regulating or coupled to the release of certain neurotransmitters in the enhanced nociceptive transmission at the spinal level following formalin inflammation.     

Long-lasting enhancement in the intrinsic excitability of deep dorsal horn neurons

Intrinsic excitability (IE) can be defined as an output of action potentials from a given input signal. Changes to the IE of a neuron are an important aspect of the cellular plasticity that underlies learning and memory process. In this study, long-term plastic change in IE of deep dorsal horn neurons (DHNs) was investigated. Associative spike pairing stimulation (PS) induced a long-lasting increase in IE. Buffering intracellular calcium with BAPTA (10mM) prevented the induction of a long-lasting increase in IE. PS failed to induce a long-lasting increase in IE in the presence of either D-APV (50 microM) or cadmium chloride (100 microM). Apamin (100 nM) partially blocked the induction of a long-lasting increase in IE. This intrinsic plasticity requires a rise in postsynaptic Ca(2+) and NMDA receptor activation during the induction period, and this process might be mediated by the down-regulation of small-conductance calcium-dependent potassium (SK) channels. In deep DHNs, PS induced excitatory postsynaptic potential (EPSP)-spike (E-S) potentiation, which increases the firing probability and the number of spikes, by consistent dorsal rootlet stimulation. Under bath application of bicuculline (10 microM) and strychnine (1 microM), PS induced E-S potentiation and long-lasting increases in IE. These results suggest that an increase in IE might underlie E-S potentiation, while a reduction in inhibitory transmission does not contribute to E-S potentiation and long-lasting increases in IE. We conclude that PS enhances the IE of deep DHNs, which may play an important role in spinal processing of nociceptive information.     

Characteristics of spinal dorsal horn neurons after partial chronic deafferentation by dorsal root transection

Unilateral transections of 1-3 lumbar dorsal roots were performed in 13 adult cats to investigate the effect of partial deafferentation on dorsal horn neurons. Eleven to 45 days after deafferentation various parameters of spontaneous and evoked activity of 169 neurons were measured and compared to the data of 168 neurons from previous experiments recorded under identical experimental conditions except that these animals had not been deafferented. Eighty-six of the units encountered were located in the segment of transected dorsal root(s) and 82 in the caudally adjacent segment. No significant differences could be observed in the functional properties of these two samples of units. Most parameters measured indicate that either no change at all in responsiveness or signs of decreased excitability occurred in the partially deafferented neurons compared to units recorded in control animals. Discharges evoked by noxious skin heating indicate a linear relationship between discharge frequency and skin temperature. This kind of encoding curve could also be measured during a reversible cold block of the spinal cord at segment L1. The mean encoding curves before and during spinal blockade were not different in deafferented compared to corresponding curves measured in control animals. The only finding that could be interpreted as an indication for increased excitability of partially deafferented neurons was that the mean frequency of spontaneous discharges of a subsample of heat-sensitive neurons was higher in deafferented compared to control animals. Possible mechanisms are discussed.     

Systemic morphine inhibits dorsal horn projection neurons through spinal cholinergic system independent of descending pathways

Cholinergic circuitry and muscarinic receptors within the spinal cord have been proposed to contribute to the analgesic effects of systemic morphine. In this study, we determined whether the descending pathways are involved in the inhibitory effect of systemic morphine on dorsal horn projection neurons mediated by activation of the spinal cholinergic system. Single-unit activity of dorsal horn projection neurons was recorded in anesthetized rats. The neuronal responses to mechanical stimuli applied to the receptive field were determined before and after intravenous injection of morphine. The inhibitory effect of intravenous morphine on dorsal horn neurons was also tested before and after topical spinal application of the muscarinic antagonist atropine in both intact and spinally transected rats. Intravenous injection of 2.5 mg/kg morphine significantly inhibited the evoked response of dorsal horn neurons in both intact and spinally transected rats. Spinal topical application of the mu opioid antagonist H-d-Phe-Cys-Tyr-d-Trp-Arg-Thr-Pen-Thr-NH(2) (CTAP) completely blocked the effect of morphine on dorsal horn neurons. In addition, spinal application of 10 microM atropine significantly attenuated the effect of systemic morphine. In rats subjected to cervical spinal transection, atropine produced a similar attenuation of the inhibitory effect of systemic morphine on dorsal horn neurons. Data from this electrophysiological study suggest that systemic morphine inhibits ascending dorsal horn neurons through stimulation of spinal mu opioid receptors. Furthermore, activation of the local spinal cholinergic circuitry and muscarinic receptors is involved in the inhibitory effect of systemic morphine on dorsal horn projection neurons independent of descending pathways.     

氯胺酮对N-甲基-D-天冬氨酸诱导大鼠脊髓背角星形胶质细胞损伤的作用

背景氯胺酮是临床常用的静脉全麻药,静脉或硬脊膜外腔用药都有镇痛作用,它是N-甲基-D-天冬氨酸受体非竞争性拮抗剂,可拮抗兴奋性氨基酸的毒性作用.目的观察氯胺酮对N-甲基-D-天冬氨酸受体过度激活诱导大鼠脊髓背角星形胶质细胞凋亡的影响,探讨其可能的作用机制.设计随机对照观察.单位郧阳医学院附属太和医院麻醉科.材料实验于2003-09/2005-01在郧阳医学院基础医学研究所细胞生物学实验室完成.由武汉大学动物实验中心提供新生两三天Wistar大鼠.方法取Wistar大鼠T11～L6脊髓背角星形胶质细胞原代纯化培养.胶质纤维酸性蛋白鉴定星形胶质细胞纯度达98%后用于实验.将培养细胞24孔板随机分为6组(每组9份)①对照组加Hanks液50μL.②N-甲基-D-天冬氨酸组加药浓度为100μmol/L.③氯胺酮组加药浓度为1 mmol/L.④100μmol/L N-甲基-D-天冬氨酸+0.1 mmol/L氯胺酮组.⑤100μmol/L N-甲基-D-天冬氨酸+0.5 mmol/L氯胺酮组.⑥100 μmol/L N-甲基-D-天冬氨酸+1mmol/L氯胺酮组.1 mmol/L氯胺酮为临床镇痛剂量.培养24 h后检测超氧化物歧化酶活性和丙二醛含量,免疫细胞化学观察Bcl-2蛋白和形态学变化,流式细胞仪检测星形胶质细胞凋亡率.主要观察指标①Bcl-2蛋白免疫组织化学苏木精-伊红复染细胞着色及形态学变化.②流式细胞仪检测星形胶质细胞凋亡率.③丙二醛含量和超氧化物歧化酶活性变化.结果①Bcl-2平均吸光度值(A)作为半定量测量Bcl-2蛋白表达水平100 μmol/L N-甲基-D-天冬氨酸组低于对照组,差异显著[分别为0.054±0.021,0.108±0.039,P＜0.01],100 μmol/L N-甲基-D-天冬氨酸+1 mmol/L氯胺酮组高于100 μmol/L N-甲基-D-天冬氨酸组,差异显著[分别为0.148±0.045,0.054±0.021,P＜0.01].②流式细胞仪检测星形胶质细胞凋亡率100 μmol/L N-甲基-D-天冬氨酸组高于对照组,差异显著[分别为(25.26±6.13)%,(5.66±2.24)%,P＜0.01],100μmol/LN-甲基-D-天冬氨酸+1 mmol/L氯胺酮组低于100 μmol/L N-甲基-D-天冬氨酸组,差异显著[分别为(24.41±4.82)%,(25.26±6.13)%,P＜0.01].③丙二醛含量和超氧化物歧化酶活性变化100 μmol/L N-甲基-D-天冬氨酸使星形胶质细胞内丙二醛含量显著升高,而超氧化物歧化酶活性明显降低;1 mmol/L氯胺酮明显降低丙二醛含量,显著增强超氧化物歧化酶活性,该效应在临床镇痛剂量以内有明显量效关系,与N-甲基-D-天冬氨酸组相比差异显著(P＜0.01).1 mmol/L氯胺酮组与对照组相比、100μmol/L N-甲基-D-天冬氨酸+0.1 mmol/L氯胺酮组与N-甲基-D-天冬氨酸组相比差异均无显著性.结论N-甲基-D-天冬氨酸受体过度激活可诱导大鼠脊髓背角星形胶质细胞大量凋亡,适量氯胺酮显著抑制细胞凋亡,其机制可能增强星形胶质细胞Bcl-2蛋白表达,同时抑制自由基的产生和增强超氧化物歧化酶活性.