乳酸-羟基乙酸共聚物载药纳米粒的制备及体外释药性

摘要 背景：医用纳米粒作为药物传递的新型载体,目前已经成为医药领域研究的重点。 目的：构建以生物可降解材料乳酸-羟基乙酸共聚物为载体,负载抗肿瘤药物5-氟尿嘧啶的载药纳米粒。 方法：利用复乳-溶剂挥发法制备乳酸-羟基乙酸共聚物载药纳米粒。场发射扫描电子显微镜观察纳米粒表面形态;激光粒度分析仪测定粒径分布并计算成球率;紫外分光光度计测定5-氟尿嘧啶载药量、包封率,并对体外释药进行评估。 结果与结论：纳米粒呈球性,平均粒径为(186±14) nm,成球率、载药量和包封率分别为70.8%、6.6%、28.1%,体外释药有突释现象,24 h内5-氟尿嘧啶累积释药量达36.2%,10 d达83.6%。提示成功制备乳酸-羟基乙酸共聚物载药纳米粒,其具有缓释效应。 关键词：乳酸-羟基乙酸共聚物;5-氟尿嘧啶;纳米粒;体外释药;缓释 doi:10.3969/j.issn.1673-8225.2011.16.017     

载多烯紫杉醇聚乳酸-羟基乙酸微球的制备、表征及其药物稳定性*

摘要 背景：目前临床使用的多烯紫杉醇注射液多采用吐温80作为增溶剂,容易导致过敏反应,且全身化疗不良反应大。采用聚乳酸-羟基乙酸包载多烯紫杉醇制备的缓释微球进行肿瘤间质化疗可提高肿瘤局部药物浓度,减轻全身不良反应。 目的：制备一种用于肿瘤间质化疗的载多烯紫杉醇聚乳酸-羟基乙酸缓释微球,并考察其理化性质、体外释放及药物稳定性。 方法：采用溶剂挥发法制备不同投料比载药微球,扫描电镜观察微球的表面形态、粒径,高效液相色谱法检测包封率、载药率及体外药物释放情况。将制备的微球于5,15,25 kGy 60Co 3种剂量辐照灭菌,体外细菌培养观察灭菌效果。 结果与结论：制备的载药微球呈圆球形,表面光滑,分散良好,平均粒径为23.1 µm。聚乳酸-羟基乙酸与多烯紫杉醇的投料比为100 mg/5 mg时可获得最佳的包封率(96.3%)和载药率(4.82%);载药微球体外4周平稳释放药物达81.6%,无明显突释效应,包裹在微球内的多烯紫杉醇结构稳定性明显提高;3种剂量60Co辐照后均未见短小芽孢杆菌生长。说明采用溶剂挥发法可制备粒径及分布适宜、释放周期较理想、药物稳定性好的载多烯紫杉醇聚乳酸-羟基乙酸缓释微球。 关键词：多烯紫杉醇;聚乳酸-羟基乙酸;微球;缓释;生物材料与药物控释 doi:10.3969/j.issn.1673-8225.2010.21.013     

磁性聚乳酸羟基乙酸氧化酚砷纳米微粒的制备及其特性**★

背景：基于纳米技术发展起来的纳米载体介导的磁性载药系统，在外加磁场作用下，能实现位点特异性靶向给药的目的，有利于提高病灶部位的局部药物浓度，从而进一步提高治疗效果，减少全身毒副作用。 目的：研究磁性聚乳酸-羟基乙酸氧化酚砷纳米微粒的制备工艺，评价纳米粒子特性。 设计：首先选择几个可能影响纳米微粒特性的因素进行了单因素实验，然后再根据实验结果，结合统计学中的正交设计，获得了最佳优化处方。 单位：解放军第二军医大学长海医院特诊科。 材料：实验于2005-01/2006-03在解放军第二军医大学药学院药剂教研室完成。实验用氧化酚砷购自美国Sigma公司，聚乳酸-羟基乙酸由山东医疗器械研究所提供，纳米级四氧化三铁购自美国Sigma公司，聚乙烯醇购自北京有机化工厂，二氯甲烷等其他试剂均为分析纯，购于上海国药集团化学试剂有限公司。 方法：运用超声乳化-溶剂挥发法制备磁性聚乳酸-羟基乙酸氧化酚砷纳米微粒，通过透射电镜观察微粒形态，振动样品磁强计确证纳米微粒磁性的存在，激光粒径仪测定纳米粒的粒径大小和分布，高效液相法测定氧化酚砷的载药量及包封率,并计算氧化酚砷体外释放百分率。 主要观察指标：磁性聚乳酸-羟基乙酸氧化酚砷纳米微粒的形态、粒径、载药量、包封率、磁性及体外释放情况。 结果：①微粒包封率和载药量：实验制备的纳米粒平均包封率为34.2%；5批纳米粒载药量分别为3.06%，3.15%，3.18%，3.21%，3.41%，平均载药量为3.20%，批间差异较小，说明工艺稳定性、重现性好。②微粒形态：纳米微粒呈圆形，表面光滑，分布均匀，不粘连，磁性微球中可见非均匀分散的黑色不透光区，为四氧化三铁微粒。③微粒粒径：分布范围窄（140~500 nm）,平均290 nm。④微粒磁性：在不断改变外加磁场的大小与方向的情况下，微粒具有不同的磁化强度，说明氧化酚砷聚乳酸纳米微粒具有一定的磁响应性。⑤体外释放实验：氧化酚砷经过最初的快速释放后，进入缓慢控释阶段，于第8天时达到最终基本稳定的平台期。 结论：实验获得了较满意的磁性聚乳酸-羟基乙酸氧化酚砷纳米微粒制备工艺；该纳米微粒在外加磁场的情况下有较好磁靶向性的作用，同时具备良好药物缓释作用。     

负载紫杉醇壳聚糖纳米粒的制备、表征与释药性能

背景：紫杉醇是一种天然抗肿瘤药物,但其水溶性极低。壳聚糖经接枝改性，生成的共聚物可在液相中生成纳米粒，可用于药物的缓释和控释。 目的：对制备的负载紫杉醇的壳聚糖纳米粒进行表征，分析其体外药物释放能力。 设计、时间及地点：重复测量设计，于2008-01/07在华北煤炭医学院医学系实验室完成。 材料：壳聚糖，平均相对分子质量为2.0×105，脱乙酰度为92%，为浙江省玉环海洋生物化学有限公司产品。紫杉醇，批号082329802，为中国药品生物制品检定所产品。 方法：采用引发接枝效率高、引发反应条件温和的二羟基二过碘酸合镍钾为引发剂，在壳聚糖上接枝醋酸乙烯酯，该聚合物在水溶液中直接生成具有疏水核心、亲水表面的纳米粒，即壳聚糖纳米粒，再利用超声振荡技术将0.5~5.0 mg紫杉醇与上述纳米粒混合制成负载紫杉醇的壳聚糖纳米粒。 主要观察指标：激光粒度分析仪测定纳米颗粒的粒径大小、粒径分布及Zeta电位，透射电镜观察纳米颗粒的外观形态，高效液相色谱法分析负载紫杉醇的壳聚糖纳米粒的包封率、载药量和释药性能。 结果：壳聚糖纳米粒和负载紫杉醇的壳聚糖纳米粒，其粒径分别为196.2 nm和320.8 nm，粒径分布较窄，纳米粒表面均带正电荷，Zeta电位比较差异无显著性意义（F=0.818，F=3.38，P均>0.05）。稳定的纳米粒呈球形，粒径均匀。紫杉醇的加入量可影响纳米粒的包封率，紫杉醇的加入量为纳米粒的量2%时，达到最大包封率93.6%。体外模拟释药结果表明药物释放曲线分为两个阶段，突释阶段微球释药量在24 h内达48.3%，缓释阶段微球释药持续时间长，在175 h时释药量达75.9%，载药纳米粒的药物释放速率持续稳定。 结论：接枝共聚法制备壳聚糖纳米粒简便可靠，负载紫杉醇后纳米粒径明显变大，表面带有正电荷，且纳米粒对紫杉醇有很高的包封率，体外释药具有明显的缓释作用。     

聚乳酸羟基乙酸/纳米羟基磷灰石-5-氟尿嘧啶复合微球的制备及体外释放***◆

背景：由聚乳酸羟基乙酸/纳米羟基磷灰石复合材料制备的微球,在体外磷酸盐缓冲液中能够持续释放药物。 目的：制备聚乳酸羟基乙酸/纳米羟基磷灰石-5-氟尿嘧啶复合微球,探讨纳米羟基磷灰石对复合微球的载药量、包封率和体外释放等性质的影响。 设计、时间及地点：材料学体外观察,于2009-02/2009-07在华南理工大学材料学院实验室完成。 材料：聚乳酸羟基乙酸为济南岱罡生物有限公司产品,纳米羟基磷灰石由华南理工大学特种功能材料教育部重点实验室自制,5-氟尿嘧啶为上海楷洋生物技术有限公司产品。 方法：以水溶性抗癌药物5-氟尿嘧啶作为模型药物,先用纳米羟基磷灰石吸附药物,外包裹生物相容性好且可生物降解的聚乳酸羟基乙酸,采用单乳化溶剂挥发法(S/O/W)制备聚乳酸羟基乙酸/纳米羟基磷灰石-5-氟尿嘧啶复合微球。对载药前后的纳米羟基磷灰石进行透射电子显微镜、扫描电子显微镜观察和FTIR分析。采用扫描电镜、激光粒度仪和紫外分光光度计对微球的理化性质及体外释药性质进行分析。 主要观察指标：纳米羟基磷灰石与5-氟尿嘧啶分子之间的相互作用,微球载药量和包封率,药物体外释放。 结果：FTIR结果表明,纳米羟基磷灰石对5-氟尿嘧啶有较强的吸附作用。聚乳酸羟基乙酸/纳米羟基磷灰石-5-氟尿嘧啶复合微球的载药量和包封率分别为3.83%,86.78%,明显高于单纯的聚乳酸羟基乙酸-5-氟尿嘧啶微球。经过体外释放药物突释后,复合微球比单纯聚乳酸羟基乙酸微球的药物释放慢。在第27天,复合微球和单纯的聚乳酸羟基乙酸微球累积药物释率放分别为84.87%,99.87%。 结论：与单纯的聚乳酸羟基乙酸-5-氟尿嘧啶微球相比,由于纳米羟基磷灰石对5-氟尿嘧啶存在较强的吸附作用,使聚乳酸羟基乙酸/纳米羟基磷灰石-5-氟尿嘧啶复合微球的载药量和包封率得到了较大提高,具有更好的药物缓释效果。 关键词：5-氟尿嘧啶;乳酸-羟基乙酸共聚物;纳米羟基磷灰石;复合微球;药物释放 doi:10.3969/j.issn.1673-8225.2009.47.017     

聚乳酸-羟基乙酸共聚物吗啡微球的制备及其镇痛作用

背景：药物微球因其对特定器官和组织的靶向性及微粒中药物释放的缓释性而成为一种新的给药系统。国内外学者对局麻药缓释给药系统进行了一系列研究,但麻醉性镇痛药的微球制剂未见报道。 目的：制备以聚乳酸-羟基乙酸共聚物为载体的吗啡生物可降解缓释微球制剂,并检测其镇痛作用。 方法：采用溶剂挥发法制备吗啡聚乳酸-羟基乙酸共聚物微球,并计算其载药量及包封率。将雄性健康SD大鼠以数字表法随机分为3组：空白对照组(皮下注射生理盐水),阳性对照组(皮下注射盐酸吗啡注射剂)和吗啡微球组(皮下注射吗啡聚乳酸-羟基乙酸共聚物微球),利用CO2激光为热刺激进行痛阈测定。 结果与结论：制成的吗啡聚乳酸-羟基乙酸共聚物微球为白色粉末,载药量为11.86%,药物包封产率为33%,微球可较明显延长吗啡作用时间至6 h以上。结果说明吗啡聚乳酸-羟基乙酸共聚物微球明显地延长了吗啡释放时间,缓释性好,但未达到预期的理想时间,仍然需要进行改进。     

负载两性霉素B壳聚糖-聚乳酸纳米粒的制备及其释药性能*☆

背景：两性霉素B为治疗深部真菌感染的首选药物,但该药无法通过血脑屏障而对隐球菌性脑膜炎的治疗效果甚微。利用纳米粒子作为药物载体的优势,通过相分离透析技术制备负载两性霉素B的壳聚糖-聚乳酸纳米粒子,有望克服两性霉素B的不足。 目的：对负载两性霉素B的壳聚糖-聚乳酸纳米粒进行表征,分析其体外药物释放能力。 设计、时间及地点：重复测量设计,于 2008-11/2009-04 在国家纳米科学中心纳米医学与生物实验室完成。 材料：壳聚糖,平均相对分子质量为3.4×105,脱乙酰度为93%,为上海卡伯工贸有限公司产品。两性霉素B为Sigma公司产品。 方法：在二甲基亚砜溶液中,在三乙胺存在下,通过壳聚糖和D,L-丙交酯的开环聚合反应能够生成壳聚糖-聚乳酸共聚物。该共聚物由亲水壳聚糖段和疏水聚乳酸段组成,在水中能够组装形成纳米粒子。两性霉素B通过相分离透析技术包载于纳米粒子中。 主要观察指标：激光粒度分析仪测定纳米颗粒的粒径大小、粒径分布,环境扫描电镜观察纳米颗粒的外观形态,紫外光谱分析负载两性霉素B的壳聚糖-聚乳酸纳米粒的包封率、载药量和释药性能。 结果：壳聚糖-聚乳酸纳米粒和负载两性霉素B的壳聚糖-聚乳酸纳米粒,其粒径分别为114 nm和153 nm(当丙交酯与壳聚糖摩尔比为11∶1时)。纳米粒子粒径分布较窄,呈球形。共聚物中丙交酯与壳聚糖摩尔比影响药物的包封率和载药量,随着丙交酯与壳聚糖摩尔比从11∶1到20∶1,包封率从(62.3±3.5)%增加到(90.7±2.8)%,载药量从(7.8±1.2)%增加到(12.3±1.4)%。随着聚乳酸段质量比增加,纳米粒子尺寸、包封率和载药量增加,而药物释放降低。 结论：开环聚合制备壳聚糖-聚乳酸共聚物及用相分离透析方法制备负载两性霉素B纳米粒简便可靠,负载两性霉素B后纳米粒径明显变大,且纳米粒对两性霉素B有很高的包封率,体外释药具有明显的缓释作用。 关键词：两性霉素B;壳聚糖;聚乳酸;纳米粒子;包封率;体外释放     

聚乳酸-羟基乙酸包载眼镜蛇毒细胞毒素缓释微球的表征及体外释放行为

背景：眼镜蛇毒细胞毒素具有强烈的细胞毒活性,但缺乏特异性,全身用药可导致严重毒副作用,而采用缓释载体包载进行间质化疗可达到提高肿瘤局部治疗效应,并且减轻全身毒性。 目的：制备眼镜蛇毒细胞毒素-聚乳酸-羟基乙酸微球,观察其一般性质和体外释药特性。 设计、时间及地点：观察性实验,于2007-12/2008-05在福建医科大学医药生物工程中心完成。 材料：聚乳酸-羟基乙酸、聚乙烯醇由中国科学院成都有机化学有限公司提供,广东产中华眼镜蛇毒。 方法：采用分子筛、离子交换分离,反相疏水高效液相色谱方法纯化细胞毒素,MTT法检测细胞毒活性,复乳-溶剂挥发法制备载药微球。 主要观察指标：扫描电镜观察载药微球的表面形态,激光粒径仪测微球粒径,计算包封率、载药量、体外释放周期。 结果：纯化的眼镜蛇细胞毒素具有明显的细胞毒作用,对HepG2细胞12,24 h的IC50分别为1.43,1.12 mg/L。复乳法制备微球表面光滑圆整,粒径2~8 μm,包封率和载药率分别为(74.10±9.92)%和(0.72±0.09)%,21 d药物累积释放63.3％,释放细胞毒素保持较好的生物学活性。 结论：采用复乳-溶剂挥发法可制备具有较高包封率、良好缓释效果、保持完整生物学活性的眼镜蛇毒细胞毒素-聚乳酸-羟基乙酸微球。     

壳聚糖微球/纳米羟基磷灰石/聚乳酸-羟基乙酸复合支架制备及其蛋白缓释效果：与单纯纳米羟基磷灰石/聚乳酸-羟基乙酸支架、壳聚糖微球的比较

背景：骨组织工程骨构建中如何使生长因子持续高效发挥作用是影响成骨速度和质量的关键,现多以各种材料的微球或支架作为缓释载体,但缓释作用有待提高。 目的：实验拟制备壳聚糖微球,然后复合到纳米羟基磷灰石/聚乳酸-羟基乙酸支架上,形成双重缓释作用,并测量对牛血清白蛋白的释放效果。 方法：以牛血清白蛋白为模型药物,采用乳化交联法制备壳聚糖微球。将微球与纳米羟基磷灰石、聚乳酸-羟基乙酸按一定比例混合,以冰粒子为致孔剂,采用冷冻干燥法制备壳聚糖微球/纳米羟基磷灰石/聚乳酸-羟基乙酸复合支架。利用扫描电镜、激光粒度分析仪、压泵仪和力学性能测试仪检测复合支架的形态性能,考察药物在缓释支架上的体外释放规律。 结果与结论：所制备的壳聚糖微球形态良好,呈规则圆球形,粒径集中分布在20~40 μm,微球药物包封率为86.5%,载药量为0.8%,随牛血清白蛋白初始用量的增加,载药量可升高至2.6%,但包封率下降至74.1%。壳聚糖微球能均匀分布在聚乳酸-羟基乙酸支架上,形成壳聚糖微球/纳米羟基磷灰石/聚乳酸-羟基乙酸复合支架,孔径为100~400 μm,孔隙率> 80%,压缩强度为1.1~2.3 MPa,10周降解率为26.5%。单纯纳米羟基磷灰石/聚乳酸-羟基乙酸支架其牛血清白蛋白在36 h累积释放量达85%以上,壳聚糖微球其牛血清白蛋白10 d累积释放量为33.6%,复合支架其牛血清白蛋白40 d累积释放量为81.5%。结果证实包埋壳聚糖微球的纳米羟基磷灰石/聚乳酸-羟基乙酸支架其压缩强度和降解速率合适,对蛋白类药物具有良好的缓释作用,有望作为组织工程的支架材料和生长因子的缓释载体。 关键词：聚乳酸-羟基乙酸;支架;壳聚糖;缓释载体;骨修复材料,组织工程;生物材料 doi:10.3969/j.issn.1673-8225.2010.03.017     

人转铁蛋白修饰载阿霉素海藻酸钠纳米粒的制备与评价

摘要 背景：对抗肿瘤药物靶向治疗和肿瘤细胞多药耐药产生的问题,载阿霉素海藻酸钠纳米粒经改性,偶联人转铁蛋白,生成的人转铁蛋白修饰载药纳米粒,可用于靶向肿瘤药物载体。 目的：制备人转铁蛋白修饰的载阿霉素海藻酸钠纳米粒并进行表征鉴定,检测其表面蛋白活性。 方法：采用优化的微乳化-离子交联方法制备包覆阿霉素的海藻酸钠复合纳米粒,以水溶性碳二亚胺为交联剂,将载阿霉素海藻酸钠纳米粒与人转铁蛋白连接,制备出人转铁蛋白修饰载阿霉素海藻酸钠纳米粒。透射电镜观察纳米粒的外观大小、形态;高效液相色谱法分析纳米粒的包封率和载药量;流式细胞仪检测其表面人转铁蛋白的活性。 结果与结论：人转铁蛋白修饰载阿霉素海藻酸钠纳米粒呈球形,平均粒径为170 nm。阿霉素的加入量可影响纳米粒的包封率,当阿霉素的加入量为纳米粒的10%时,包封率和包裹量均最佳。每毫克载药纳米粒可与约65 μg人转铁蛋白连接。人转铁蛋白修饰的载药纳米粒在流式细胞仪上除去非特异性吸附后还有67.3%荧光显示,说明人转铁蛋白修饰的载药纳米粒大部分都偶联上了人转铁蛋白抗体并能保持抗体活性,从而为载药纳米粒特异性靶向肿瘤细胞提供了足够的靶向动力。微乳化-离子交联方法制备方法简便可靠,制得的人转铁蛋白修饰载阿霉素海藻酸钠纳米粒有望成为具有潜在价值的一种特异性靶向药物载体。 关键词：海藻酸钠;阿霉素;人转铁蛋白;纳米粒;靶向;生物材料与纳米技术 doi:10.3969/j.issn.1673-8225.2010.21.014     

Subtypes of excitatory amino acid receptors involved in the stimulation of [3H]dopamine release from cell cultures of rat ventral mesencephalon

N-methyl-D-aspartic acid (NMDA), quisqualic acid (QUIS), and kainic acid (KAIN), respective agonists for three excitatory amino acid (EAA) receptor subtypes, stimulated [3H]dopamine ([3H]DA) release from dissociated cell cultures of fetal rat ventral mesencephalon. Release evoked by all three agonists was Ca2(+)-dependent and inhibited by broad-spectrum antagonists (D,L-cis-2,3-piperidine dicarboxylic acid [PDA] and kynurenic acid [KYN]). However, both of these antagonists were more potent against KAIN than against QUIS and only KAIN-evoked release was blocked by gamma-D-glutamyl-aminomethyl sulfonic acid (GAMS, IC50 700 microM). NMDA-stimulated [3H]DA release was selectively inhibited by competitive (3-[2-carboxypiperazine-4-yl]propyl-1-phosphonic acid [CPP] and D,L-2-amino-5-phosphonovaleric acid [APV]) and non-competitive (phencyclidine and MK-801) NMDA receptor antagonists. In 1.2 mM Mg2+, NMDA-stimulated [3H]DA release was Na(+)-dependent and inhibited by tetrodotoxin (TTX, 2 microM) or by the local anaesthetic, lidocaine (200 microM). However, in 0 Mg 2+, NMDA-evoked release was not inhibited by TTX or lidocaine. Thus, TTX-sensitivity of the NMDA response in 1.2 mM Mg2+ apparently occurs because Na(+)-action potentials are required to alleviate a Mg2+ blockade. Neither QUIS- nor KAIN-evoked release was affected by Mg2+ or TTX. When extracellular NaCl was replaced by sucrose or Na2SO4, the QUIS response was increased. KAIN-evoked release was unaffected by the sucrose substitution and was attenuated in the Na2SO4-containing buffer. It is concluded that NMDA and QUIS/KAIN release [3H]DA via separate receptor subtypes.     

海人酸致痫大鼠海马细胞外氨基酸类神经递质的变化

目的 分析海马细胞外氨基酸递质在癫痫发生中的作用,探讨海人酸致痫模型大鼠癫痫发生的机制.方法 应用立体定向方法建立海人酸大鼠颞叶癫痫模型,观察大鼠行为学和电生理变化,应用电镜观察大鼠海马超微结构,应用微透析获取大鼠海马细胞外液,高压液相色谱法测定透析液中的兴奋性氨基酸谷氨酸、抑制性氨基酸牛磺酸及γ-氨基丁酸的含量.结果 海人酸注射后大鼠出现典型的颞叶癫痫发作,皮层脑电显示痫性发作,电镜显示兴奋性神经递质增加,高效液相色谱分析显示海马细胞外谷氨酸、牛磺酸和γ-氨基丁酸含量明显高于对照组(P＜0.05),虽然谷氨酸、γ-氨基丁酸都升高,而谷氨酸升高的更明显.结论 兴奋性氨基酸与抑制性氨基酸的失衡在海人酸致痫大鼠模型的癫痫发生过程中发挥重要作用,是癫痫发生的原因之一.     

Neurotoxic amino acid lesions of the lateral hypothalamus: a parametric comparison of the effects of ibotenate, N-methyl-d,l-aspartate and quisqualate in the rat

Separate groups of rats received unilateral lesions of the lateral hypothalamus by one of the 3 amino-acid neurotoxins, ibotenic acid (IBO), N-methyl-D,L-aspartic acid (NMA) or quisqualic acid (QA). A parametric comparison was made between the toxins on the extent of neuronal cell loss and the specificity of damage, by a systematic variation of both the volume (0.25-1.0 mm3) and concentration (0.03-0.12 M) injected. Neurotoxic potency on hypothalamic neurones varied in the order IBO greater than NMA greater than QA. All 3 toxins spared magnocellular supraoptic and accessory nuclei as well as medial hypothalamic neurones. Extrahypothalamic damage differed between the toxins: ventral thalamic neurones were susceptible to NMA and QA but only slightly to IBO, whereas the medial amygdala was sensitive to IBO but not NMA or QA. All 3 toxins spared ascending monoamine systems passing through the lateral hypothalamus, as assessed by biochemical assays of forebrain dopamine and serotonin. However, IBO induced a bilateral increase in dopamine levels, which was interpreted as an indirect consequence of the loss of lateral hypothalamic efferents projecting to the midbrain.     

Both apoptosis and necrosis occur following intrastriatal administration of excitotoxins

To learn about the mechanisms of excitotoxic cell death in vivo, three different excitatory amino acid receptor agonists (kainic acid, quinolinic acid or quisqualic acid) were injected in the left striatum of adult rats. Brains were examined at 24 and 48 h after injection. Morphological and biochemical studies were performed using conventional stains, histochemistry, in situ labelling of nuclear DNA fragmentation, and agarose gel electrophoresis of extracted DNA. Large numbers of cells with cytoplasmic shrinkage and nuclear condensation or granular degeneration of the chromatin, and fewer cells with apoptotic morphology were distributed at random in the injured areas of the three groups of treated animals but not in rats injected with vehicle alone. A ladder pattern, typical of internucleosomal DNA fragmentation, was observed 24 h after treatment. This was replaced by a smear pattern, consistent with random DNA breakdown, at 48 h. These morphological and biochemical results suggest that prevailing necrosis together with apoptosis occur following intrastriatal injection of different excitotoxins.     

Neuropharmacological actions of kynurenic and quinolinic acids on horizontal cells of the isolated fish retina

We have studied the effects of naturally occurring metabolites of tryptophan, kynurenic and quinolinic acids, on the electrophysiological responses of retinal horizontal cells in the fish (Rutilus rutilus, the roach). Quinolinic acid usually hyperpolarizes the cells and reduces their light evoked responses (S-potentials) but on occasion, it causes a slight depolarization of the membrane potential. These actions are similar to those found with N-methyl-d-aspartate (NMDA) and our results are consistent with the proposal that it acts at NMDA binding sites. Kynurenic acid (1mM) invariably hyperpolarizes horizontal cells to their potassium Nernst equilibrium potential and, more significantly, blocks the depolarizing actions exerted on them by excitatory amino acids, such as kainic and quisqualic acids. We show that this action persists in the presence of the synaptic blocker, cobalt chloride, and thus is not mediated by chemical synaptic activity. Kynurenic acid does not reverse depolarization of horizontal cells by dopamine or γ-aminobutyric acid, thus its inhibitory effects are selective to the actions of excitatory amino acids. Neither xanthurenic acid, a close structural analogue of kynurenic acid, nor quinolinic acid are effective in blocking depolarizations by excitatory aino acids.     

The n-3 polyunsaturated fatty acid/dopamine hypothesis of schizophrenia

The dopamine hypothesis of schizophrenia has been the most influential since the 1970s. Normally, the prefrontal dopamine system suppressively controls the limbic dopamine system. Since the activities of prefrontal dopaminergic neurons are reduced in schizophrenia, the suppressive effect of the prefrontal area on the limbic system is reduced, and activities of the limbic dopamine system are enhanced. Reduced activities of the prefrontal dopamine system contribute to negative symptoms and cognitive disorders, and increased activities of the limbic dopamine system induce positive symptoms. While the dopamine hypothesis explains the relationship between dopamine kinetics and psychiatric symptoms in schizophrenia, it is not a direct explanation of its etiology. The cause of the abnormal activities of dopaminergic neurons in schizophrenia and its resultant symptoms are unknown. Since the late 1980s, it has been revealed that the n-3 fatty acid concentration is reduced in the plasma and erythrocyte membranes of schizophrenic patients and that the administration of n-3 fatty acids may be effective for the treatment of schizophrenia. Whether or not n-3 fatty acid deficiency plays a direct role in schizophrenia etiology, and the mechanisms underlying their therapeutic effect have yet to be clarified. Recently, the dopamine hypothesis and n-3 fatty acid hypothesis have been suggested to represent different aspects of the same pathology of schizophrenia. In schizophrenia, the brain concentrations of certain n-3 fatty acids are decreased. In rodents, n-3 fatty acid deficiency has been shown to cause decreases in dopamine concentration, number of vesicles and D2 receptors at prefrontal presynaptic terminals. The following minireview provides a summary of findings from n-3 fatty acid deficient animal models and their relevance to schizophrenia pathology is discussed.     

Evoked release of aspartate and glutamate: disparities between prelabeling and direct measurement

Slices prepared from hippocampus were dual prelabeled with [14C]L-glutamate and [3H]D-aspartate and superfused in the presence or absence of kainic acid (KA; 1 mM) or KCl (40 mM). Drug-evoked release of radioactivity as well as the endogenous amino acids, glutamate and aspartate were determined. Whereas KCl-induced a Ca2+-dependent release of all compounds, only the release of the endogenous amino acids was stimulated by KA. The results of the present study demonstrate that disparities exist between the Ca2+-dependent drug-evoked release of exogenously supplied and endogenous acidic amino acid neurotransmitters.     

Stimulation-dependent uptake of glutamic acid by hippocampal slices

The activity of human spindle afferents from finger extensor muscles has been studied during voluntary position holding at two finger positions, to disclose any explicit monitoring of muscle length. The results indicate that, taken as groups, neither primary nor secondary afferents show explicit position responses during active position tracking. Thus any contribution from muscle spindle to position sense must be derived from other components in spindle afferent discharge.     

The action of natural and synthetic isomers of quisqualic acid at a well-defined glutamatergic synapse

L-, D- and DL-quisqualic acid have been synthesized and their activities at the glutamatergic locust nerve-muscle junction have been compared with those of natural quisqualic acid and with glutamic acid. Two well-characterised locust nerve-muscle preparations were used in these studies, the retractor unguis nerve-muscle system and the extensor tibiae nerve-muscle system. The amino acids were tested on the whole nerve-muscle system in the former, when reduction in neurally evoked twitch contraction amplitude was the measured parameter, and by ionophoretic application to single excitatory junctional sites in the latter, when amplitude of junctional depolarization was the measured parameter. Synthetic L-quisqualic acid exhibited identical potency to its natural counterpart. However, D-quisqualic acid and DL-quisqualic acid were more active than expected from the known stereospecificity of this glutamatergic system towards D- and L-glutamic acid. The hydantoin analogue of quisqualic acid was inactive. X-ray crystallographic analysis of L-quisqualic acid and the hydantoin analogue showed that the ring junction in the former is pyramidal whereas in the latter it is planar. This may account for the high potency of L-quisqualic acid on a receptor system which identifies a partially folded conformation of L-glutamic acid. A pyramidal configuration of D-quisqualic acid would allow either rapid interconversion between active and inactive configurations at its ring junction or adoption of a trigonal configuration in solution. Either interpretation could explain the unexpected potency of D-quisqualic acid.