Glutamate, aging and enriched environment after dopamine loss

描述(由申请人提供)： 在帕金森病中观察到，由于神经毒素1-甲基-4-苯基-1，2，3，6-四氢吡啶(MPTP)导致啮齿动物黑质纹状体通路中多巴胺(DA)的丢失，导致纹状体和黑质(SN)谷氨酸输入的改变。MPTP后，纹状体基础谷氨酸水平降低，SN56、84升高。谷氨酸受体拮抗剂可减少与纹状体DA丢失相关的运动缺陷。与暴露于标准环境(SE)6的MPTP处理动物相比，在给予MPTP之前暴露于丰富环境(EE)2个月的小鼠可减少黑质致密部(SN-PC)酪氨酸羟化酶(TH)免疫标记神经元的丢失。我们首次报道，与MPTP/SE组相比，在亚慢性MPTP后1周，连续暴露于EE中接下来的21天，SN-PC中TH标记神经元的丢失部分恢复。这也会导致运动功能的改善。在幼鼠中，亚慢性MPTP给药导致SN-PC中TH标记神经元的50%丢失，在圆柱体中饲养时它们对垂直支撑的依赖增加30%(即辅助墙与不辅助饲养)。在老年小鼠中，亚慢性MPTP导致SN-PC中TH标记细胞的45%丢失，壁辅助与非辅助背部的数量增加近60%。将老年小鼠与年轻小鼠进行比较，仅暴露于EE后，只有1只。)细胞外纹状体谷氨酸基础水平增加25%(幼鼠~95%)，2.神经末梢谷氨酸免疫金标记物密度无变化(幼鼠减少25%)。纹状体中胶质蛋白GFAP的蛋白水平没有变化(幼鼠增加了65%)。谷氨酸转运体GLT-1的蛋白水平增加29%(幼鼠增加10%)。在年轻和老年小鼠中，在EE之后，多巴胺转运蛋白有增加的趋势。因此，纹状体谷氨酸的增加可能是EE减少SN-PC内TH标记神经元丢失和促进运动恢复的机制之一。我们将测试的另一种可能机制是EE是否直接影响SN中的谷氨酸和伽马氨基丁酸(GABA)突触。这项建议的总体目标是调查亚慢性MPTP、年龄和暴露于EE对纹状体和SN中谷氨酸变化的影响。GABA水平也将在SN中进行测量。这一建议的主要假设是，MPTP对纹状体和SN谷氨酸的影响将因暴露于EE而部分逆转，导致运动行为和纹状体DA水平的部分恢复，以及SN-PC中TH标记细胞的部分恢复。这种逆转会发生在老年小鼠身上，但与老年小鼠相比，年轻小鼠的这种情况会更严重。这项建议的具体目标是1.)确定年龄(10周对12个月)和毒素剂量对纹状体谷氨酸、SN-PC中TH标记细胞的变化以及亚慢性给药1周后运动行为的影响，然后继续暴露于EE，2。确定亚慢性MPTP诱导的纹状体谷氨酸、SN-PC中TH标记细胞的变化以及每天暴露于EE 2或6小时后运动行为的影响。确定亚慢性给予MPTP，然后持续暴露在EE中，对青年与老年小鼠SN中谷氨酸和GABA的变化以及运动行为的影响。我们将进一步确定，阻断SN谷氨酸受体或在MPTP后增加纹状体谷氨酸是否都会模拟EE的影响。 公共卫生相关性： 运动障碍的调查，特别是帕金森氏病，是退伍军人事务部内的一个高度优先的研究领域。由于这种疾病在50岁以上的普通人群中发病率很高，而且退伍军人的年龄正在缓慢增加，这种运动障碍正在影响着我们越来越多的退伍军人。由于暴露在丰富的环境中，至少在非帕金森患者和这种疾病的动物模型中，似乎在增强运动和认知行为方面是有效的，这种类型的非药理学方法需要进一步的研究。该项目的结果对退伍军人事务部照顾的人群具有潜在的广泛意义，而且目前有六个帕金森氏病研究、教育和护理中心(PADRECC)(其中一个在波特兰退伍军人医学中心)受到资助，以开展专注于帕金森氏症的临床研究项目。

DESCRIPTION (provided by applicant): As observed in Parkinson's disease, loss of dopamine (DA) within the nigrostriatal pathway in rodents due to the neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), results in alterations in the glutamate input to the striatum and substantia nigra (SN). Following MPTP, there is a decrease in the basal glutamate levels in the striatum and an increase in the SN 56,84. Glutamate receptor antagonists decrease the locomotor deficits associated with the loss of striatal DA. Exposure of mice to an enriched environment (EE) for 2 months prior to the administration of MPTP results in a reduced loss of tyrosine hydroxylase (TH) immunolabeled neurons in the substantia nigra pars compacta (SN-PC) compared to the MPTP-treated animals exposed to the standard environment (SE) 6. We are the first to report that 1 week following subchronic MPTP, continuous exposure to an EE for the next 21 days, with continued MPTP administration, partially restores the loss of TH-labeled neurons in the SN-PC compared to the MPTP/SE group. This also results in improvement in motor function. In young mice, subchronic MPTP administration results in a 50% loss of TH-labeled neurons in the SN-PC and a 30% increase in their dependence upon a vertical support when rearing in a cylinder (ie wall assisted vs unassisted rears). In aged mice, subchronic MPTP results in a 45% loss of TH-labeled cells in the SN-PC and a nearly 60% increase in the number of wall-assisted vs unassisted rears. Comparing aged versus young mice, following exposure to an EE only, there is 1.) a 25% increase in the basal levels of extracellular striatal glutamate (~95% in young mice), 2.) no change in the density of nerve terminal glutamate immuno-gold labeling (25% decrease in young mice), 3.) no change in the striatal protein level for the glial protein, GFAP (65% increase in young mice), and 4.) a 29% increase in the protein levels for the glutamate transporter, GLT-1 (10% increase in young mice). There is a trend towards an increase in the dopamine transporter protein following an EE in both young and aged mice. Therefore, increased striatal glutamate may be a mechanism by which an EE reduces the loss of TH-labeled neurons in the SN-PC and promotes motor recovery. Another possible mechanism we will test is whether an EE is having an affect directly on glutamate and gamma-aminobutyric acid (GABA) synapses in the SN. The overall goal of this proposal is to investigate the effects of subchronic MPTP, age and exposure to an EE on alterations in glutamate in both the striatum and SN. GABA levels will also be measured in the SN. The overarching hypothesis of this proposal is that the effects of MPTP on striatal and SN glutamate will be partially reversed by exposure to an EE, leading to partial recovery of motor behavior, DA levels in the striatum and partial restoration of TH-labeled cells in the SN-PC. This reversal will occur in the aged mice, but it will be greater in younger compared to the aged mice. The specific aims of this proposal are to 1.) determine the effects of age (10 weeks vs 12 months) and dosing of the toxin on changes in striatal glutamate, TH-labeled cells in the SN-PC, and motor behavior after 1 week of subchronic administration of MPTP, followed by continuous exposure to an EE, 2.) determine the effect of subchronic MPTP-induced changes in striatal glutamate, TH-labeled cells in the SN- PC and motor behavior after exposure to an EE for either 2 or 6 hours/day, and 3.) determine the effects of subchronic administration of MPTP, followed by continuous exposure to an EE, on changes in both glutamate and GABA in the SN and motor behavior in young versus aged mice. We will further determine if blockade of SN glutamate receptors or increasing striatal glutamate following MPTP will both mimic the affect of exposure to an EE. PUBLIC HEALTH RELEVANCE: Investigation of movement disorders, especially Parkinson's disease, is a high priority research area within the Department of Veterans Affairs. Because of the high incidence of this disease in the general population over the age of 50 and the fact that the age of the veteran population is slowly increasing, this movement disorder is affecting more and more of our veterans. Since exposure to an enriched environment in at least non-Parkinsonian patients and in an animal model of this disease appears to be effective in terms of augmenting motor and cognitive behavior, this type of non-pharmacological approach needs further investigation. The results from this project have potentially wide implications of great significance to the population cared for by the Department of Veteran Affairs and by the fact that six Parkinson's Disease Research, Education and Care Centers (PADRECCs) currently are funded (one here at the Portland VA Medical Center), to carry out clinical research projects focusing on Parkinson's disease.