Glutamate, aging and enriched environment after dopamine loss

描述（由申请人提供）： 如在帕金森病中所观察到的，由于神经毒素1-甲基-4-苯基-1，2，3，6-四氢吡啶（MPTP），啮齿动物中黑质纹状体通路内多巴胺（DA）的损失导致纹状体和黑质（SN）的谷氨酸输入的改变。MPTP后，纹状体中的基础谷氨酸水平降低，SN增加56，84。谷氨酸受体拮抗剂减少与纹状体DA的损失相关的运动缺陷。暴露于富集环境（EE）的小鼠2个月前给药的MPTP的结果在减少损失的酪氨酸羟化酶（TH）免疫标记的神经元在黑质pars延髓（SN-PC）相比，MPTP处理的动物暴露于标准环境（SE）6。我们是第一个报告，1周后，亚慢性MPTP，连续暴露于EE为未来21天，继续MPTP管理，部分恢复TH标记的神经元的损失相比，在SN-PC的MPTP/SE组。这也导致运动功能的改善。在年轻小鼠中，亚慢性MPTP给药导致SN-PC中TH标记的神经元损失50%，并且当在圆柱体中饲养时（即壁辅助与无辅助的后部），它们对垂直支撑的依赖性增加30%。在老年小鼠中，亚慢性MPTP导致SN-PC中TH标记细胞损失45%，并且壁辅助与无辅助的后部数量增加近60%。比较老年小鼠与年轻小鼠，仅暴露于EE后，有1。细胞外纹状体谷氨酸的基础水平增加25%（在年轻小鼠中约95%），2.）神经末梢谷氨酸免疫金标密度无变化（幼鼠减少25%），3.）胶质蛋白、GFAP的纹状体蛋白水平没有变化（在年轻小鼠中增加65%），和4.）谷氨酸转运蛋白GLT-1的蛋白水平增加29%（年轻小鼠增加10%）。在年轻和老年小鼠中，EE后多巴胺转运蛋白有增加的趋势。因此，增加纹状体谷氨酸可能是EE减少SN-PC中TH标记神经元损失并促进运动恢复的机制。我们将测试的另一种可能的机制是EE是否直接影响SN中的谷氨酸和γ-氨基丁酸（GABA）突触。 本提案的总体目标是研究亚慢性MPTP、年龄和暴露于EE对纹状体和SN中谷氨酸改变的影响。还将测量SN中的GABA水平。该提议的首要假设是，MPTP对纹状体和SN谷氨酸的影响将通过暴露于EE而部分逆转，导致运动行为、纹状体中的DA水平的部分恢复以及SN-PC中TH标记细胞的部分恢复。这种逆转将发生在老年小鼠中，但与老年小鼠相比，它在年轻小鼠中的作用更大。 本提案的具体目标是：（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标记细胞和MPTP亚慢性给药1周后运动行为变化的影响，随后连续暴露于EE，2.）确定在暴露于EE 2或6小时/天后，亚慢性MPTP诱导的纹状体谷氨酸、SN-PC中TH标记细胞和运动行为变化的影响，和3.）确定MPTP的亚慢性给药，随后连续暴露于EE，对年轻小鼠与老年小鼠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MPTP后增加纹状体谷氨酸是否都能模拟暴露于EE的影响。 公共卫生相关性： 运动障碍的调查，尤其是帕金森氏病，是退伍军人事务部的一个高优先级研究领域。由于这种疾病在50岁以上的普通人群中的发病率很高，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越来越多的退伍军人。由于至少在非帕金森病患者和该疾病的动物模型中暴露于丰富的环境似乎在增强运动和认知行为方面是有效的，因此这种类型的非药物方法需要进一步研究。该项目的结果可能对退伍军人事务部照顾的人群具有重要意义，并且目前资助了六个帕金森病研究，教育和护理中心（PADRECs）（其中一个在波特兰VA医疗中心），以开展临床研究项目，重点是帕金森病。

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.