Delayed delivery of AAV-GDNF prevents nigral neurodegeneration and promotes functional recovery in a rat model of Parkinson's disease

Glial cell line-derived neurotrophic factor (GDNF) is a strong candidate agent in the neuroprotective treatment of Parkinson's disease (PD). We investigated whether adeno-associated viral (AAV) vector-mediated delivery of a GDNF gene in a delayed manner could prevent progressive degeneration of dopaminergic (DA) neurons, while preserving a functional nigrostriatal pathway. Four weeks after a unilateral intrastriatal injection of 6-hydroxydopamine (6-OHDA), rats received injection of AAV vectors expressing GDNF tagged with FLAG peptide (AAV-GDNFflag) or beta-galactosidase (AAV-LacZ) into the lesioned striatum. Immunostaining for FLAG demonstrated retrograde transport of GDNFflag to the substantia nigra (SN). The density of tyrosine hydroxylase (TH)-positive DA fibers in the striatum and the number of TH-positive or cholera toxin subunit B (CTB, neuronal tracer)-labeled neurons in the SN were significantly greater in the AAV-GDNFflag group than in the AAV-LacZ group. Dopamine levels and those of its metabolites in the striatum were remarkably higher in the AAV-GDNFflag group compared with the control group. Consistent with anatomical and biochemical changes, significant behavioral recovery was observed from 4-20 weeks following AAV-GDNFflag injection. These data indicate that a delayed delivery of GDNF gene using AAV vector is efficacious even 4 weeks after the onset of progressive degeneration in a rat model of PD.     

高压氧对帕金森病大鼠多巴胺神经元保护作用的研究

目的探讨高压氧对帕金森病大鼠多巴胺神经元的保护作用。方法将68只雌性Sprague—Dawley大鼠随机分成5组：注射生理盐水高压氧处理组（A组，n=7）、全程高压氧处理模型组（B组，n=18）、未经高压氧处理模型组（C组，n=7）、造模后高压氧处理组（D组，n=18）、造模前高压氧处理组（E组，n=18）。在实验第1天至第7天给予A组、B组和E组大鼠高压氧治疗；而在实验第8天时，分别向B组、C组、D组及E组大鼠单侧脑黑质内定位注射6-羟基多巴胺以制作偏侧帕金森病大鼠模型，给予A组等量生理盐水定位注射。从实验第8天至结束，分别给予A组、B组及D组大鼠高压氧处理；并于造模后第9天，16天及21天每组各处死6只大鼠，取其纹状体用分光光度计测定超氧化物歧化酶（SOD）、丙二醛（MDA）和谷胱甘肽过氧化物酶（GSH—Px）含量，选用免疫组织化学方法测定黑质区域内酪氨酸羟化酶（TH）阳性细胞数量及胶质纤维酸性蛋白（GFAP）的表达。结果与C组比较，B、D、E组大鼠病变侧纹状体内SOD及GSH—Px活性显著增高，MDA含量及GFAP表达明显降低，6-羟基多巴胺毁损黑质区残存的TH阳性细胞数目明显增加。结论高压氧治疗可以显著提高机体抗自由基损伤功能、减弱胶质细胞效应发挥，从而有效保护脑黑质区多巴胺（DA）能神经元功能。     

3-硝基丙酸预处理阻止黑质多巴胺神经元细胞凋亡

目的:观察3 硝基丙酸(3 NP)预处理时黑质多巴胺(DA)神经元细胞凋亡改变的作用机制及5 羟癸 酸(5 HD)对3 NP效果的影响。方法:25只雄性SD大鼠随机分为5组各5只。右侧黑质内立体定向注射6 羟多 巴胺(6 OHDA)建立帕金森病(PD)模型组,对照组大鼠立体定向和腹腔注射生理盐水,3 NP组在对照组的基础上 腹腔注射3 NP(20mg/kg),预处理组(CPC组)造模前24h给予3 NP(20mg/kg),5 HD组于造模前10min侧脑 室内给予5 HD(5mg/kg)。采用缺口末端标记原位检测法及免疫组化法检测黑质DA神经元细胞凋亡率及酪氨 酸羟化酶(TH)阳性细胞数。结果:PD组、CPC组及5 HD组与对照组和3 NP组比较细胞凋亡率均明显增高,损 毁侧TH阳性细胞数显著降低(P<0.01或P<0.05);CPC组与PD组比较细胞凋亡率降低,TH阳性细胞数增多 (P<0.05);5 HD组与PD组比较则差异无显著性意义(P>0.05)。结论:3 NP预处理可抑制细胞凋亡,而5 HD 可阻断3 NP预处理保护效应。线粒体ATP敏感性钾通道激活参与3 NP预处理神经元保护作用。     

Differential effects of glial cell line-derived neurotrophic factor (GDNF) in the striatum and substantia nigra of the aged Parkinsonian rat

Injection of an adenoviral (Ad) vector encoding human glial cell line-derived neurotrophic factor (GDNF) protects dopaminergic (DA) neurons in the substantia nigra (SN) of young rats. As Parkinson's disease occurs primarily in aged populations, we examined whether chronic biosynthesis of GDNF, achieved by adenovirus-mediated delivery of a GDNF gene (AdGDNF), can protect DA neurons and improve DA-dependent behavioral function in aged (20 months) rats with progressive 6-OHDA lesions of the nigrostriatal projection. Furthermore, the differential effects of injecting AdGDNF either near DA cell bodies in the SN or at DA terminals in the striatum were compared. AdGDNF or control vector was injected unilaterally into either the striatum or SN. One week later, rats received a unilateral intrastriatal injection of 6-OHDA on the same side as the vector injection. AdGDNF injection into either the striatum or SN significantly reduced the loss of FG labelled DA neurons 5 weeks after lesion (P 相似文献   

帕金森病模型大鼠行为学评价与黑质神经元凋亡的相关研究

目的检测帕金森病(PD)模型大鼠行为学及黑质神经元凋亡的相关指标。方法将6-羟基多巴胺(6-OHDA)通过立体定位仪注入大鼠右侧纹状体制备PD模型,5周后检测行为学指标;酪氨酸羟化酶(TH)组化染色观察各组大鼠右侧黑质神经元形态,Hoechst 33258染色了解其凋亡情况,Western blotting方法检测黑质内caspase-3蛋白表达。结果成功筛选的15只PD模型大鼠在露台Morris水迷宫实验中,与正常对照组及假手术组同侧相比,其寻台速度下降,时间延长(P<0-05);在平衡杆实验中,其潜伏期和过杆时间增加(P<0-05);模型组右侧黑质TH阳性神经元明显减少,该区域凋亡细胞明显增多,且caspase-3蛋白表达显著增高。结论6-OHDA诱导黑质内多巴胺(DA)神经元凋亡与其胞内caspase-3表达增高相关,模型大鼠在露台Morris水迷宫和平衡杆实验中行为学改变与TH免疫组化染色及Hoechst 33258染色结果吻合。     

Iron accumulation in the substantia nigra in rats visualized by ultrasound.

In recent studies, we have found a marked increase in substantia nigra (SN) echogenicity in patients with Parkinson's disease (PD) using transcranial ultrasound. Because a substantial body of evidence has accumulated indicating a selective elevation of iron in the SN from patients with PD, we set out to test the hypothesis that trace metals like iron could lead to the observed increase of SN echogenicity in PD. Rat brains were scanned after stereotactic injection of iron in different concentrations into the SN and after injecting ferritin, zinc and 6-OHDA alone, and after the addition of desferrioxamine. The amount of iron in the SN was measured spectroscopically. For iron, and partly for 6-OHDA, in different concentrations, a dose-dependent increase of SN echogenicity could be visualized, corresponding to an increase of iron measured by spectroscopy. No increase of echogenicity was visualized after the injection of ferritin and the addition of desferrioxamine to 6-OHDA, though an increase of iron was measured by spectroscopy. Therefore, we conclude that iron not bound to these proteins may lead to an increase of echogenicity of the SN.     

颈动脉体球细胞块移植治疗帕金森病大鼠行为学的实验研究

探讨帕金森病（ＰＤ）大鼠颈动脉体球细胞块移植后其行为学的变化。采用６－羟多巴胺（６－ＯＨＤＡ）损毁大鼠一侧黑质细胞制成ＰＤ样大鼠模型。在右侧纹状体内分别移植入胚胎黑质和自、异体颈动脉体球细胞块。在移植后２、４、８和１２周记录阿朴吗啡诱发大鼠的旋转行为,同步分析存活酪氨酸羟化酶（ＴＨ）阳性细胞数目。结果：在１２周时与胚胎中脑组织移植相比较,自、异体颈动脉体球细胞移植组大鼠旋转行为改善更为明显。存活ＴＨ＾＋细胞显著增多（分别Ｐ〈０．０５）,但自、异体颈动脉体球细胞移植组间比较差异无显著性,提示：颈动脉体球细胞块移植后ＰＤ大鼠行为学显著改善。效果优于胚胎中脑组织块的移植。     

Assessing nigrostriatal dysfunctions by pharmacological MRI in parkinsonian rhesus macaques

New imaging techniques are needed to longitudinally monitor the development, progression and treatment of Parkinson's disease. The present study was designed to test whether the blood oxygenation level-dependent (BOLD) response to dopaminergic stimulation as measured by pharmacological MRI (phMRI) correlated to specific histological and behavioral features of the parkinsonian state. Nine adult rhesus monkeys were rendered hemiparkinsonian by intracarotid administration of MPTP. Three months after MPTP treatment, the trained, MRI-adapted awake animals were scanned with a phMRI technique while being administered a presynaptic (D-amphetamine) or postsynaptic (apomorphine) dopamine stimulating agents. The primary findings were (1) the putamen and substantia nigra (SN) but not the caudate nucleus displayed significant BOLD responses to these dopaminergic drugs; (2) a significant relationship was found between amphetamine-evoked activation and the number of surviving dopamine neurons in the SN, which was also correlated with bradykinesia; and (3) inverse relationships were seen in response to apomorphine and amphetamine stimulation between the MPTP-lesioned and unlesioned putamen and SN. The results suggest that phMRI may prove useful for longitudinally monitoring the progression and treatment of PD.     

Effects of benserazide on L-DOPA-derived extracellular dopamine levels and aromatic L-amino acid decarboxylase activity in the striatum of 6-hydroxydopamine-lesioned rats

Benserazide is commonly used for Parkinson's disease in combination with L-DOPA as a peripheral aromatic L-amino acid decarboxylase (AADC) inhibitor. However, recent studies using intact animals indicate that benserazide acts also in the central nervous system. We determined the influence of benserazide on the central AADC activity in rats with dopaminergic denervation and observed changes in extracellular dopamine (DA) levels after benserazide and L-DOPA administration. First, using in vivo microdialysis technique, we measured extracellular DA levels in the striatum of 6-hydroxydopamine (6-OHDA)-lesioned rats treated with benserazide and L-DOPA. Second, we measured AADC activity in the striatal tissues after benserazide administration. Although administration of 5, 10 and 50 mg/kg benserazide to 6-OHDA-lesioned rats showed an identical increase in exogenous L-DOPA-derived extracellular DA levels, the time to reach the peak DA levels were significantly prolonged by benserazide dose-dependently. The AADC activity in the denervated striatal tissues showed a significant decrease by 10 mg/kg and 50 mg/kg benserazide. These results suggest that benserazide reduces the central AADC activity in the striatum of rats with nigrostriatal denervation, which leads to changes in the metabolism of exogenous L-DOPA. Central activity of AADC inhibitors should be taken into consideration when they are used both in experimental and clinical studies on Parkinson's disease.     

帕金森病大鼠模型的行为学及神经元形态学评价

背景由于黑质致密部体积狭小,应用6-羟基多巴胺(6-Hydroxydopamine,6-OHDA)损毁黑质多巴胺神经元(Nigral dopaminergic neuron,NDN)制作帕金森病大鼠模型的成功率较低,一般仅为30%～40%左右.目的探讨帕金森病大鼠模型建立后的行为学及神经元形态学改变.设计完全随机的实验研究.地点和材料安徽省药物研究所,SD大鼠,6-OHDA,阿朴吗啡,兔抗TH血清,SR-6N大鼠脑立体定向仪等.干预将6-OHDA立体定向注射于90只SD大鼠的左侧黑质区及黑质纹状体通路,观察大鼠行为及多巴胺神经元形态学变化.主要观察指标旋转行为,震颤及其他异常行为,免疫组织化学观察,电镜观察.结果经阿朴吗啡诱导共筛选出64只成功大鼠模型(占71%);免疫组化观察发现注射侧黑质区NDN较对侧明显减少,电镜观察发现其普遍存在凋亡及坏死样改变.结论本方法是建立帕金森病大鼠模型的有效方法,在行为学和神经元形态学等方面同帕金森病人有许多相似之处.     

烟草成份保护多巴胺神经元作用的研究

目的：探讨烟草成份保护多巴胺神经元对抗6－羟基多巴胺（6－OHDA）的神经毒性作用。方法：采用大鼠脑内立体注射6－OHDA建立帕金森病模型，连续观察术前4周开始分别给予被动吸烟和腹腔注射尼古丁（每次0.1mg/kg或0.4mg/kg,bid，持续6周）对阿朴吗啡诱发的旋转行为，纹状体多巴胺（dopamine,DA)的含量和黑质酪氨酸羟化酶（Tyrosine Hydroxylase,TH）阳性神经细胞数目的影响。结果：被动吸烟和腹腔注射尼古丁的大鼠旋转行为明显减少，受损侧纹状体DA含量和黑质TH阳性神经元的数目较对照组增高（P＜0．01），高剂量尼古丁作为更为显著。结论：烟草成份可减轻6－OHDA对黑质DA神经元的损伤。     

6- 羟基多巴不同部位毁损大鼠帕金森氏病模型的建立及比较

目的比较 6- OHDA毁损黑质 , 黑质 + 内侧前脑束 , 纹状体而制作 PD模型的异同及可靠性 . 方法在脑立体定位技术下 , 将 20 μ g 6- OHDA分两点注入大鼠上述脑区 , 术后不同时间用阿扑吗啡诱发大鼠异常旋转行为 , 并进行检测比较 . 结果 6- OHDA毁损黑质及黑质 + 内侧前脑束 , PD鼠于术后一周即出现稳定旋转行为 , 两部位模型成功率均为 50% ; 纹状体毁损后一周 PD鼠可出现轻微旋转 , 逐渐增强 , 模型成功率可达 80% . 结论 6- OHDA毁损大鼠黑质 , 黑质 + 内侧前脑束 , 纹状体均可制作成功的 PD模型 .     

Selective activation of group III metabotropic glutamate receptors by L-(+)-2-amino-4-phosphonobutryic acid protects the nigrostriatal system against 6-hydroxydopamine toxicity in vivo

Evidence from several studies suggests that the progressive degeneration of dopaminergic (DA) neurones of the substantia nigra pars compacta (SNc) in Parkinson's disease (PD) may in part be due to excessive release of glutamate from subthalamic projections onto nigral DA neurones. Previous in vitro studies have demonstrated that selective activation of Group III metabotropic glutamate receptors (mGluR) negatively modulates excitatory transmission in the SNc and is neuroprotective against glutamate-mediated toxicity. Consistent with this, we have reported preliminary data indicating that the selective group III mGluR agonist l-(+)-2-amino-4-phosphonobutyric acid (l-AP4) can also protect the nigrostriatal system against 6-hydroxydopamine (6-OHDA) toxicity in vivo. We have now extended these preliminary studies in this model and report here that both acute and subchronic intranigral injections of l-AP4 provide significant protection of the nigrostriatal system against 6-OHDA toxicity. This neuroprotection displays a bell-shaped profile with a clear concentration-dependent relationship. In contrast, when administered to animals 7 days post-6-OHDA lesioning, l-AP4 significantly protects the functionality but not the integrity of the nigrostriatal system. We further demonstrate that neuroprotection by l-AP4 in vivo is reversed by coadministration of the selective Group III mGluR antagonist (RS)-alpha-methylserine-O-phosphate, confirming a receptor-mediated mechanism of action. These data provide further compelling evidence that selective activation of Group III mGluR is neuroprotective in an in vivo experimental model of PD, a finding that may have important implications for the future treatment of this disease.     

Quantitative [(123)I]FP-CIT pinhole SPECT imaging predicts striatal dopamine levels, but not number of nigral neurons in different mouse models of Parkinson's disease

Single photon emission computed tomography (SPECT) using [(123)I]FP-CIT as radioligand for the dopamine transporter has become a widely used tool to monitor the integrity of the nigrostriatal dopaminergic projection in Parkinson's disease (PD). Previous studies with pinhole SPECT in small animals have demonstrated that the striatal [(123)I]FP-CIT binding indeed correlates with the striatal dopamine transporter protein level. It is unclear, however, if there is a stable relationship between the striatal [(123)I]FP-CIT binding and other functionally important parameters of the nigrostriatal system, such as the striatal dopamine levels and the number of dopaminergic neurons in the substantia nigra. To assess this question experimentally, we studied two different mouse models of PD, namely a mild 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine intoxication paradigm, to model mild nigrostriatal damage and the intrastriatal 6-hydroxydopamine paradigm to model more advanced nigrostriatal damage. Our data demonstrate that the striatal [(123)I]FP-CIT binding measured by SPECT in vivo precisely predicts the striatal dopamine concentrations, but does not necessarily correlate with the nigral dopaminergic cell number. Thus, the present work underscores that FP-CIT SPECT does only allow judging the integrity of the striatal dopaminergic nerve terminals, but not the nigral dopaminergic cells in PD. This finding may have significant impact on the use of [(123)I]FP-CIT SPECT as a surrogate marker for clinical trials aimed at measuring neuroprotection.     

Zentrale Schmerzverarbeitung bei Morbus Parkinson

Parkinson??s disease (PD) is caused by degeneration of the dopaminergic neurons in the substantia nigra (SN) and a resulting dysfunction of the nigrostriatal pathways including the basal ganglia. Beside motor symptoms, different types of pain (e.g., dystonic musculoskeletal pain or central pain) occur in a considerable number of patients. In addition, abnormalities in pain processing have been observed in PD patients, which may present as increased pain sensitivity. The pathophysiological mechanisms involved in disturbed pain processing of PD, however, are still poorly understood. The present article gives an overview of the relevant experimental studies, investigating the abnormalities of pain processing in PD by means of electrophysiological [electroencephalography (EEG), sympathetic skin response (SSR)] and psychophysical methods [quantitative sensory testing (QST), RIII reflex threshold]. Based on a review of the literature, it is postulated that dysfunction in endogenous pain inhibition caused by dopaminergic deficiency in the basal ganglia, especially in the striatum, but also in mesolimbic areas is a main pathophysiological mechanism involved in nociceptive abnormalities in PD.     

Anterograde Axonal Transport of AAV2-GDNF in Rat Basal Ganglia

We elucidated the effects of parkinsonian degeneration on trafficking of AAV2-GDNF in the nigro-striatum (nigro-ST) of unilaterally 6-hydroxydopamine (6-OHDA)-lesioned rats. Vector infused into striatum (ST) was transported to substantia nigra (SN), both pars compacta (SNc), and pars reticulata (SNr). In the lesioned hemisphere, glial cell line–derived neurotrophic factor (GDNF) immunoreactivity was only found in SNr consistent with elimination of SNc dopaminergic (DA) neurons by 6-OHDA. Further analysis showed that striatal delivery of AAV2-GDNF resulted in GDNF expression in globus pallidus (GP), entopeduncular nucleus (EPN), and subthalamic nucleus (STN) in both lesioned and unlesioned hemispheres. Injection of vector into SN, covering both SNc and SNr, resulted in striatal expression of GDNF in the unlesioned hemisphere but not in the lesioned hemisphere. No expression was seen in GP or EPN. We conclude that adeno-associated virus serotype 2 (AAV2) is transported throughout the nigro-ST exclusively by anterograde transport. This transport phenomenon directs GDNF expression throughout the basal ganglia in regions that are adversely affected in Parkinson''s disease (PD) in addition to SNc. Delivery of vector to SN, however, does not direct expression of GDNF in ST, EPN, or GP. On this basis, we believe that striatal delivery of AAV2-GDNF is the preferred course of action for trophic rescue of DA function.     

Striatal pleiotrophin overexpression provides functional and morphological neuroprotection in the 6-hydroxydopamine model

Neurotrophic factors are integrally involved in the development of the nigrostriatal system and in combination with gene therapy, possess great therapeutic potential for Parkinson's disease (PD). Pleiotrophin (PTN) is involved in the development, maintenance, and repair of the nigrostriatal dopamine (DA) system. The present study examined the ability of striatal PTN overexpression, delivered via psueudotyped recombinant adeno-associated virus type 2/1 (rAAV2/1), to provide neuroprotection and functional restoration from 6-hydroxydopamine (6-OHDA). Striatal PTN overexpression led to significant neuroprotection of tyrosine hydroxylase immunoreactive (THir) neurons in the substantia nigra pars compacta (SNpc) and THir neurite density in the striatum, with long-term PTN overexpression producing recovery from 6-OHDA-induced deficits in contralateral forelimb use. Transduced striatal PTN levels were increased threefold compared to adult striatal PTN expression and approximated peak endogenous developmental levels (P1). rAAV2/1 vector exclusively transduced neurons within the striatum and SNpc with approximately half the total striatal volume routinely transduced using our injection parameters. Our results indicate that striatal PTN overexpression can provide neuroprotection for the 6-OHDA lesioned nigrostriatal system based upon morphological and functional measures and that striatal PTN levels similar in magnitude to those expressed in the striatum during development are sufficient to provide neuroprotection from Parkinsonian insult.     

Delayed Dominant-Negative TNF Gene Therapy Halts Progressive Loss of Nigral Dopaminergic Neurons in a Rat Model of Parkinson's Disease

Parkinson''s disease (PD) is a progressive neurodegenerative disorder typified by the loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc). Recent evidence indicates that neuroinflammation may play a critical role in the pathogenesis of PD, particularly tumor necrosis factor (TNF). We have previously shown that soluble TNF (solTNF) is required to mediate robust degeneration induced by 6-hydroxydopamine (6-OHDA) or lipopolysaccharide. What remains unknown is whether TNF inhibition can attenuate the delayed and progressive phase of neurodegeneration. To test this, rats were injected in the SNpc with lentivirus encoding dominant-negative TNF (lenti-DN-TNF) 2 weeks after receiving a 6-OHDA lesion. Remarkably, when examined 5 weeks after the initial 6-OHDA lesion, no further loss of nigral DA neurons was observed. Lenti-DN-TNF also attenuated microglial activation. Together, these data suggest that TNF is likely a critical mediator of nigral DA neuron death during the delayed and progressive phase of neurodegeneration, and that microglia may be the principal cell type involved. These promising findings provide compelling reasons to perform DN-TNF gene transfer studies in nonhuman primates with the long-term goal of using it in the clinic to prevent the delayed and progressive degeneration of DA neurons that gives rise to motor symptoms in PD.     

消旋-3-正丁基苯酞对帕金森病大鼠脑组织Bax、Caspase-8和TH表达的影响

目的观察消旋-3-正丁基苯酞(丁苯酞)对帕金森病(PD)模型鼠黑质Bax、Caspase-8、TH表达的影响,进一步明确丁苯酞对PD模型鼠脑保护作用及其机制。方法 90只SD大鼠随机分为三组,模型PD对照组30只:采用立体定向注入6-羟多巴法造模;消旋-3-正丁基苯酞组30只:立体定向注入6-羟多巴,对模型鼠进行丁苯酞灌胃4周;正常对照组30只:立体定向注入抗坏血酸生理盐水。各组动物处死后行脑组织快速冰冻切片并采用免疫组化法分别检测黑质的Bax、Caspase-8、TH阳性细胞数,用原位杂交法分别检测Bax mRNA、Caspase-8 mRNA、TH mRNA的阳性细胞数。结果 NBP组免疫组化法分别检测黑质的Bax、Caspase-8、TH阳性细胞数分别为35.1±6.4,21.4±5.7,95.8±9.4;原位杂交法分别检测Bax mRNA、Caspase-8 mRNA、TH mRNA的阳性细胞数分别为23.7±6.3,16.9±7.3,48.8±7.5。与PD组相比,消旋-3-正丁基苯酞组免疫组化和原位杂交均显示术侧黑质Bax、Caspase-8阳性神经元数量较PD组均明显降低。而TH阳性神经元数量较PD组明显增多。结论正丁苯酞对PD模型鼠脑有保护作用且可能与降低Bax、Caspase-8的表达,增加TH的表达有关。     

AAV transduction of dopamine neurons with constitutively active Rheb protects from neurodegeneration and mediates axon regrowth

There are currently no therapies that provide either protection or restoration of neuronal function for adult-onset neurodegenerative diseases such as Parkinson's disease (PD). Many clinical efforts to provide such benefits by infusion of neurotrophic factors have failed, in spite of robust effects in preclinical assessments. One important reason for these failures is the difficulty, due to diffusion limits, of providing these protein molecules in sufficient amounts to the intended cellular targets in the central nervous system. This challenge suggests an alternative approach, that of viral vector transduction to directly activate the intracellular signaling pathways that mediate neurotrophic effects. To this end we have investigated the ability of a constitutively active form of the GTPase Rheb, an important activator of mammalian target of rapamycin (mTor) signaling, to mediate neurotrophic effects in dopamine neurons of the substantia nigra (SN), a population of neurons affected in PD. We find that constitutively active hRheb(S16H) induces many neurotrophic effects in mice, including abilities to both preserve and restore the nigrostriatal dopaminergic axonal projections in a highly destructive neurotoxin model. We conclude that direct viral vector transduction of vulnerable neuronal populations to activate intracellular neurotrophic signaling pathways offers promise for the treatment of neurodegenerative disease.