衰老大鼠嗅觉障碍与嗅球神经元内线粒体的变化(英文)

Olfactory disturbance in aged rats in association with mitochondrial changes in the olfactory bulb neurons

背景:机体衰老时,各组织尤其是中枢神经组织中线粒体DNA发生突变,氧化磷酸化基因受损致线粒体功能下降已被证实,形态学上也会发生相应的改变。目的:对衰老和年轻大鼠嗅球内神经元的线粒体超微结构进行对比观察,分析衰老大鼠嗅觉障碍与嗅球内神经细胞线粒体改变的关系。设计:随机对照实验。单位:承德医学院附属医院内科,承德医学院电镜室。材料:实验于2002-04／12在承德医学院电镜室完成。雄性Wistar大鼠 16只,老龄组(>24个月)8只,体质量300-350 g;年轻组(6个月)8只, 体质量180-220 g。方法:两组大鼠给予质量浓度为10 g／L的乌拉坦1 g／kg腹腔内注射．麻醉后开胸,升主动脉插管,戊二醛与多聚甲醛混合固定液200 mL灌流固定,取嗅球,振荡切片,锇酸后固定,平板包埋,光镜下选取嗅球各层,制备超薄切片,透射电镜下对比观察。主要观察指标:①两组大鼠嗅球的分层。②两组嗅球主要神经元内的线粒体超微结构变化。结果:实验纳入大鼠16只,全部进入结果分析。①两组大鼠嗅球的分层:两组大鼠的嗅球分层均无明显改变,自外向内分别为嗅神经纤维层、团伞层、外丛状层、僧帽细胞层、内丛状层和嗅束神经纤维层。②两组嗅球主要神经元内的线粒体超微结构变化:老龄组刷状细胞线粒体较多,杆状或椭圆形,线粒体嵴不规则,局部排列紊乱,有的嵴断裂分解成细粒状,形成电子密度很高的固缩小体,少数线粒体成为不规则或同心圆形的髓鞘样小体。年轻组所有神经元的线粒体多为椭圆形,内、外层膜清晰可辨,线粒体嵴排列较均匀,不规则者偶见。结论:老龄大鼠的嗅球分层与年轻大鼠基本一致,但其嗅球内主要神经元的线粒体超微结构发生了明显变化,这与线粒体氧化磷酸化功能下降相一致,可能是导致老年嗅觉障碍的主要原因之一。

BACKGROUND： Mutation of the mitochondrial DNA may occur during the aging process of organisms, which is especially likely in the central nervous system. Evidences have been obtained that mitochondrial dysfunction may ensue from genetic impairment involved in oxidative phosphorylation, which is accompanied by corresponding morphological changes.OBJECTIVE： To investigate the association between olfactory disturbance and ultrastructural mitochondrial changes in olfactory bulb neurons of aged rats in comparison with young rats.DESIGN： Randomized controlled experiment.SETTING： Department of Internal Medicine, Affiliated Hospital of Chende Medical College and Department of Electron Microscopy of Chende Medical College.MATERIALS： This experiment was conducted in the Department of Electron Microscopy of Chende Medical College between April and December 2002. Sixteen male Wistar rats were divided equally into aged group （＞ 24 months） with body mass of 300-350 g and young group （6 months） with body mass of 180-220 g.METHODS： The rats in the two groups were anaesthetized by intraperitoneal injection of 10 g/L urethane （1 g/kg） and the chest was opened to insert a tube into the ascending aorta for perfusion with 200 mL of the mixture containing glutaric dialdehyde and paraformaldehyde for fixation.The olfactory bulb was then obtained and sliced, fixed in perosmic acid and embedded. Each layer of the olfactory bulb was observed under optical microscope and ultra-thin sections were prepared for observation under transmission electron microscope.MAIN OUTCOME MEASURES： The stratification of rat olfactory bulb and ultrastructural changes of the mitochondria in the major neurons in the olfactory bulb.REULSTS： No obvious changes were found in the stratification of the olfactory bulb in the two groups. From the exterior to the interior of the olfactory bulb, the olfactory nerve fiber layer, glomerular layer, external plexiform layer, mitral cell lalyer, internal plexiform layer and olfactory bundle nerve fiber layer were observed. Ultrastructurally, the mitochondria were more numerous in the brush cells in aged rat olfactory bulb, appearing rodshaped or ovoid with irregular cristae which were arranged in local disorder and some fragmented into small granules to form small bodies of high electron density. A few mitochondria became myeliuoid body with irregular or concentric circular morphologies. In the younger rats, most of the mitochondria in the neurons were ovoid with distinct outer and inner membrane and regular arrangement of the mitochondrial cristae, and irregular arrangement of the cristae was seen only in rare cases.CONCLUSION： The stratification of the olfactory bulb is basically the same in aged and young rats, but the ultrastructural changes in the mitochondria in the major neurons in aged rat olfactory bulb can be obvious,which is consistent with the reduced mitochondrial oxidative phosphorylation function. This might be one of the major causes for olfactory disturbance related to aging.