Detecting dopaminergic neuronal degeneration using diffusion tensor imaging in a rotenone-induced rat model of Parkinson's disease: fractional anisotropy and mean diffusivity values

Dopamine content in the basal ganglia is strongly associated with the degree of dopaminergic neuron loss in the substantia nigra pars com-pacta. Symptoms of Parkinson's disease might not arise until more than 50% of the substantia nigra pars compacta is lost and the dopamine content in the basal ganglia is reduced by more than 80%. Greater diagnostic sensitivity and specificity would allow earlier detection of Parkinson's disease. Diffusion tensor imaging is a recently developed magnetic resonance imaging technique that measures mean diffusiv-ity and fractional anisotropy, and responds to changes in brain microstructure. When the microscopic barrier (including cell membranes, microtubules and other structures that interfere with the free diffusion of water) is destroyed and extracellular fluid volume accumulates, the mean diffusivity value increases; when the integrity of the microstructure (such as myelin) is destroyed, fractional anisotropy value decreases. However, there is no consensus as to whether these changes can reflect the early pathological alterations in Parkinson's disease. Here, we established a rat model of Parkinson's disease by injecting rotenone (or sunflower oil in controls) into the right substantia nigra. Diffusion tensor imaging results revealed that in the stages of disease, at 1, 2, 4, and 6 weeks after rotenone injection, fractional anisotropy value decreased, but mean diffusivity values increased in the right substantia nigra in the experimental group. Fractional anisotropy values were lower at 4 weeks than at 6 weeks in the right substantia nigra of rats from the experimental group. Mean diffusivity values were mark-edly greater at 1 week than at 6 weeks in the right corpus striatum of rats from the experimental group. These findings suggest that mean diffusivity and fractional anisotropy values in the brain of rat models of Parkinson's disease 4 weeks after model establishment can reflect early degeneration of dopaminergic neurons. The change in fractional anisotropy values after destruction of myelin integrity is likely to be of greater early diagnostic significance than the change in mean diffusivity values.     

鱼藤酮致大鼠脑内α-突触核蛋白的表达分布变化

目的 研究鱼藤酮所致的帕金森病大鼠的脑内α-突触核蛋白（α—synuclein,ASN）分布。方法 Wistar大鼠随机分成两组,分别给予鱼藤酮和／或溶剂（对照组）皮下注射,4周后取脑组织,对黑质部位HE染色,光镜下观察Lewy小体形态;对黑质、海马、纹状体等脑区进行酪氨酸羟化酶（tyrosine hydroxylase,TH）、ASN免疫组织化学染色。结果 在对照组大鼠脑内,ASN广泛分布于各脑区,尤其在皮质、纹状体、海马等纤维投射丰富的区域。鱼藤酮处理的大鼠脑中,黑质TH阳性多巴胺能神经元数目减少、纹状体区TH阳性纤维脱失,黑质部位可见Lewy小体样结构;ASN阳性染色在各个脑区均有增强但各个脑区增强程度不一,黑质部位神经元胞浆和胞核内均有ASN明显聚集,纹状体可见ASN聚集围绕在细胞周围。海马部位偶见ASN在胞浆中点状聚集,胞核中无明显改变。结论 在鱼藤酮皮下注射导致的帕金森病大鼠的脑内,ASN在多个脑区中表达增加,而在黑质纹状体部位聚集最为明显,蛋白分布由多巴胺能神经元的突触末端向胞浆和胞核扩展。     

Isatin decreases Bax protein expression in the substantia nigra of a mouse model of Parkinson’s disease

The present study observed the action of 1H-indole-2, 3-dione (isatin) on Bax protein expression in the substantia nigra of a Parkinson’s disease animal model. Parkinson’s disease-like behaviors were induced in C57BL/6J mice treated with 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP). Bax protein expression was significantly reduced in isatin (100, 200 mg/kg)-pretreated mice. Results demonstrate that isatin plays a neuroprotective role in mice treated with MPTP by down-regulating Bax protein express...     

Gastrodin inhibits neuroinflammation in rotenone-induced Parkinson's disease model rats

The present study showed that the latency of rats moving on a vertical grid was significantly prolonged,and the number of rats sliding down from the declined plane was increased remarkably,in rotenone-induced Parkinson’s disease model rats compared with control rats.The moving latency recovered to normal levels,but the number of slides was significantly increased at 28 days after model establishment.The slope test is a meaningful approach to evaluate the symptoms of Parkinson’s disease model rats treated with rotenone.In addition,loss of substantia nigral dopaminergic neurons in model rats was observed at 1 day after the model was established,and continued gradually at 14 and 28 days.The expression of tyrosine hydroxylase-positive cells was significantly increased in gastrodin-treated rats at 14 days.Significant numbers of activated microglia cells were observed in model rats at 14 and 28 days;treatment of rats with Madopar at 28 days suppressed microglial activation.Treatment of rats with gastrodin or Madopar at 28 days significantly reduced interleukin-1β expression.The loss of substantia nigral dopaminergic neurons paralleled the microglial activation in Parkinson’s disease model rats treated with rotenone.The inflammatory factors tumor necrosis factor-α and interleukin-1β are involved in the substantia nigral damage.Gastrodin could protect dopaminergic neurons via inhibition of interleukin-1β expression and neuroinflammation in the substantia nigra.     

Neuroprotective role of (Val8)GLP-1-Glu-PAL in an in vitro model of Parkinson's disease

The growth factor glucagon-like peptide-1(GLP-1) is neuroprotective in several animal models of neurodegeneration. Here, we analyzed the neuroprotective effects of a novel protease-resistant GLP-1 analogue,(Val~8)GLP-1-Glu-PAL, which has advantages over older analogues, such as improvement of hippocampal neurogenesis, glucose homeostasis, and insulin secretion. We established an in vitro model of Parkinson's disease using the mitochondrial stressor rotenone in primary cultured mouse neurons pretreated with(Val~8)GLP-1-Glu-PAL.(Val~8)GLP-1-Glu-PAL alone did not affect neuronal viability, but prevented the rotenone-induced reduction in cell viability in a dose-dependent manner. In addition,(Val~8)GLP-1-Glu-PAL pretreatment prevented rotenone-induced proapoptotic changes manifesting as downregulation of procaspase-3 and Bcl-2 and upregulation of cleaved caspase-3. These results demonstrate that the novel agent(Val~8)GLP-1-GluPAL shows promise as a drug treatment for Parkinson's disease.     

Parkinson's disease: depletion of substantia nigra neurotensin receptors

Neurotensin receptor autoradiography reveals dense binding in normal human substantia nigra. In nigra from patients with Parkinson's disease, nigral receptor binding is only about one-third of control values. ‘Saturation’ analysis suggests that these changes result from receptor loss. These results support a neurotensin-domapine interaction in human nigro-striatal circuits.     

Mitochondrial complex inhibitors preferentially damage substantia nigra dopamine neurons in rat brain slices

Using a rat brain slice preparation, we investigated the role of energy impairment on the selective loss of dopamine neurons in the substantia nigra (SN). Brain slices (400 microm) were incubated at 35 degrees C for 2 h in the presence or absence of mitochondrial complex inhibitors, rotenone, MPP+, 3-nitropropionic acid, and antimycin A. Slices were also incubated in rotenone with excitatory amino acid (EAA) receptor antagonists, MK-801 and CNQX, to determine whether rotenone-induced damage was mediated by EAAs. The slices were then fixed, recut into 30-microm sections, and immunolabeled for tyrosine hydroxylase (TH) to identify catecholamine neurons and to quantify loss of TH-labeled dendrites after treatment. Quantitative comparison was made between SN dopamine neurons, in which rotenone-induced dendrite loss was severe, and hypothalamic A11 dopamine neurons, which were spared. Adjacent sections that were immunolabeled for calbindin or stained with cresyl violet also revealed a striking dendritic degeneration of SN neurons in rotenone-exposed slices, whereas noncatecholamine neurons, such as those in the perifornical nucleus (PeF), were more resistant. Preferential damage to SN dopamine neurons was also evident with other mitochondrial complex inhibitors, MPP+ and antimycin A. EAA receptor antagonists provided partial protection to SN neurons in slices incubated with rotenone (3 microM). The particular vulnerability of SN dopamine neurons in the slice is consistent with the vulnerability of SN in Parkinson's disease. The selective effect of mitochondrial complex inhibition in SN dopamine neurons implies a fundamental deficit in the capacity of these neurons to defend against toxic insult.     

依达拉奉对帕金森病大鼠模型的神经保护作用及黑质纹状体丙二醛和一氧化氮水平的影响

目的 探讨依达拉奉对帕金森病(PD)大鼠的神经保护作用及黑质纹状体丙二醛(MDA)和一氧化氮(NO)水平的影响.方法 将72只SD大鼠随机分为正常对照组(n=12)、生理盐水对照组(NS组,n=12)、依达拉奉治疗组(ED组,n=48),ED组又分为ED 0.3 mg、1 mg、3 mg及3 mg停药后亚组,每个亚组12只大鼠.在大鼠脑内注入6-羟基多巴胺(6-OHDA)制作PD模型,术后各组大鼠分别相应给予NS 1 ml及ED 0.3 mg/kg、1 mg/kg、3 mg/kg腹腔注射,每天2次,连续14 d.对各组大鼠并进行旋转试验;用免疫组化染色检测黑质酪氨酸羟化酶(TH)阳性细胞数,化学比色法检测黑质纹状体MDA和NO水平.结果 正常对照组大鼠旋转圈数与NS组及ED各亚组比较,差异有统计学意义(均P＜0.01).ED 3 mg及ED 3 mg停药后亚组的旋转圈数显著少于NS组及ED 0.3 mg、1 mg亚组(均P＜0.05).NS组及各ED亚组左侧黑质TH阳性神经元显著少于正常对照组及右侧(均P ＜0.05).ED 3 mg及ED 3 mg停药后亚组左侧黑质TH阳性神经元显著多于NS组和ED 0.3 mg、1 mg亚组(均P＜0.05).与正常对照组比较,NS组和各ED亚组黑质、纹状体NO和MDA水平显著升高(均P＜0.01).ED 3 mg及ED 3 mg停药后亚组黑质、纹状体NO和MDA水平较NS组和ED 0.3 mg、1 mg亚组显著降低(均P＜0.05).结论 依达拉奉对PD大鼠的神经保护作用呈剂量依赖性;其能抑制过氧化反应,降低PD大鼠黑质纹状体的MDA、NO水平.     

RNA干扰沉默Synphilin-1可提高帕金森病大鼠黑质超氧化物歧化酶表达：一种假设的验证？

目的 研究灵芝孢子对帕金森病（PD）动物模型黑质神经细胞凋亡的影响,以探讨灵芝孢子对帕金森病的脑保护作用。方法 120只SD大鼠随机分为三组, PD组：向黑质部立体定向注入6－羟多巴,术后一周腹腔注入阿朴吗啡观察30分钟大鼠旋转的次数,连续至第四周每分钟大于6次者为成功的帕金森模型;灵芝孢子组：先用灵芝孢子粉灌胃三天,立体定向注入6－羟多巴, 继续灌胃4周,直至处死;正常对照组：向黑质部立体定向注入抗坏血酸生理盐水。处死后制作快速冰冻切片用免疫组化检测Caspase 3阳性细胞数,用原位杂交法检测Caspase 3 mRNA的阳性细胞数,用Western blot检测Caspase 3的半定量变化。结果 免疫组化显示灵芝组术侧黑质Caspase 3阳性神经元数量较PD组明显降低,原位杂交显示灵芝组术侧黑质Caspase 3 mRNA阳性神经元数量较PD组明显降低,Western blot显示Caspase 3蛋白灵芝组较PD组显著降低。结论 灵芝孢子能够降低Caspase 3的表达,对PD有脑保护作用。     

Alterations in the distribution of glutathione in the substantia nigra in Parkinson's disease

Summary Depletion of reduced glutathione occurs in the substantia nigra in Parkinson's disease and in incidental Lewy body disease (presymptomatic Parkinson's disease) which may implicate oxidative stress in the neurode-generative process. In this study mercury orange fluorescent staining and immunostaining with an antibody to reduced glutathione have been used to determine the distribution of reduced glutathione in the substantia nigra in Parkinson's disease compared with normal individuals.Mercury orange staining showed moderate background levels of fluorescence in the neuropil in both control and Parkinson's disease substantia nigra and localised reduced glutathione to the somata of melanized nigral neurons and glial elements of the neuropil. Neuronal nuclei revealed a relative lack of fluorescence after mercury orange staining. There was a significant depletion of reduced glutathione in surviving neurons in Parkinson's disease compared to nerve cell populations in control tissue. Mercury orange fluorescence indicated a high concentration of reduced glutathione in a subpopulation of non-neuronal cells, most likely astrocytes or microglia.Immunohistochemical examination of nigral tissue from the same Parkinson's disease and control patients with an antibody to glutathione showed staining in neuronal perikarya and axonodendritic processes of melanized nigral neurons which was generally most intense in control neurons. Moderately intense staining of the background neuropil, most prominent in control nigras, and staining of capillary walls was also detected. Intense staining was seen in cells with the morphological features of glial cells in both control and PD nigra.These data show a significant presence of reduced glutathione in the cell bodies and axons of nigral neurons. They are in agreement with biochemical studies showing depletion of reduced glutathione in substantia nigra in Parkinson's disease, and indicate a significant loss of neuronal reduced glutathione in surviving nigral neurons in Parkinson's disease.Abbreviations GFAP glial fibrillary acidic protein - GSH reduced glutathione - GSSG oxidized glutathione - ILBD incidental Lewy body disease - PBS phosphate-buffered saline - PD Parkinson's disease     

Mean volume of pigmented neurons in the substantia nigra in Parkinson's disease

A new unbiased stereological estimator, the rotator, was used to estimate the mean volume of pigmented substantia nigra (SN) neurons in three Parkinson's disease (PD) brains and agematched controls. Average pigmented neuron volume was 31300 μm³ (5200) in controls and 28900 μm³ (120) in patients. Estimating the absolute size distribution, revealed that PD patients had ≈ 80% less total SN pigmented volume than controls. Compared with biased methods, in addition to dramatic improvements in efficiency and accuracy, results obtained by the unbiased rotator suggest that primarily the largest pigmented neurons in SN are lost in PD.     

Is Parkinson's disease a progressive siderosis of substantia nigra resulting in iron and melanin induced neurodegeneration?

Abstract– Razor sharp and high iron deposits are present in the substantia nigra (SN). Although the function of such high iron content is not known, the homeostatis of brain iron is important for normal brain function. The participation of free tissue iron in oxidative stress (OS), resulting in the formation of cytotoxic hydroxyl radical (·OH) from H₂O₂ (Fenton reaction) and promotion of membrane lipid peroxides by ·OH can no longer be questioned as a biological phenomenon. The highly selective increase of Fe²⁺ and Fe³⁺ and lipid peroxidation observed in parkinsonian SN points to OS in such brains. Lipid peroxidation proceeds with either Fe²⁺ or Fe³⁺ provided a mechanism exists to facilitate the interconversion of iron between its redox states. Indeed H₂O₂ derived from MAO B reaction and autooxidation of dopamine to melanin in the SN can drive the iron dependent Fenton reaction. Furthermore, interaction of iron with melanin may be even more important considering that melanin avidly binds Fe³⁺ and reduce it to Fe²⁺, resulting in ·OH generation. Thus, without evoking environmental neurotoxins, the excessive accumulation of free iron in the SN and "melanintrap'could be the trigger for accelerated cell death and Parkinsonism.     

Echogenicity of the substantia nigra in Parkinson's disease and its relation to clinical findings

Recently an increased echogenicity of the substantia nigra (SN) in patients with Parkinson's disease (PD) was demonstrated by transcranial ultrasound (TCS). In this study we set out to compare SN echogenicitiy with disease characteristics (time of onset, duration, toxin exposure) in a large patients sample. Patients' history and exposure to toxins were recorded from 112 PD patients who underwent a thorough neurological examination including assessment of disease stage according to Hoehn and Yahr and CURS (Columbia University Rating Scale). Personality was assessed according to the Freiburg Personality Inventory. In all patients the area of SN echogenicity was encircled and measured by TCS. All except 9 patients had hyperechogenic SN areas exceeding the mean plus standard deviation values of an age matched control group (0.19cm²). The age of disease onset was lower in patients who displayed an area of SN echogenicity above this value. The area of SN echogenicity was larger contralateral to the side with more severe symptoms. None of the other characteristics correlated with ultrasound findings. We conclude that SN hyperechogenicity is a typical finding in PD. The cause of hyperechogenicity is so far unknown. Investigation of the underlying reason might disclose a pathogenic factor in PD. Received: 13 November 2000 / Received in revised form: 24 January 2001 / Accepted: 19 February 2001     

Neuroprotective effects of subthalamic nucleus high-frequency stimulation on substantia nigra neurons in a Parkinson''s disease rat model

BACKGROUND: Deep-brain stimulation has proven to be beneficial in the treatment of Parkinson's disease (PD) patients. OBJECTIVE: To investigate the effects of high-frequency stimulation (HFS) to the subthalamic nucleus (STN) on neuronal apoptosis and apoptosis-related gene expression in the substantia nigra pars compacta, and to analyze the neuroprotective effect of HFS-STN. DESIGN, TIME AND SETTING: Neuronal morphology experiments were performed in the Beijing Nearosurgical Institute from May to December in 2005. MATERIALS: Forty healthy, adult, Sprague Dawley rats were used to establish a PD model with a unilateral microinjection of 6-hydroxydopamine into two target areas of the right medial forebrain bundle. 6-hydroxydopamine was purchased from Sigma (USA); high-frequency electrical stimulator was produced by World Precision Instruments (USA); Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) kit was a product of Nanjing Jiancheng Technology Co., Ltd. (China); and Bcl-2 and Bax protein assay kit were purchased from Wuhan Boster Bioengineering Co., Ltd. (China). METHODS: Forty rats were randomly divided into three groups. The stimulation group (n = 15) received HFS-STN on the day of PD modeling. The PD model group (n = 15) was used to establish the PD model. The control group (n = 1 0) was injected with normal saline containing 0.2 g/L ascorbic acid into two areas of the right medial forebrain bundle. MAIN OUTCOME MEASURES: Survival of dopaminergic neurons in the substantia nigra pars compacta was determined using Nissl staining. Apoptosis of dopaminergic neurons was detected using TUNEL techniques. Expression of anti-apoptotic protein, Bcl-2, and pro-apoptotic protein, Bax, were assayed by immunohistochemistry. RESULTS: Following 6-hydroxydopamine injection, the number of substantia nigra pars compacta neurons was reduced in the stimulation and PD model groups, compared to the control group. At 2 and 4 weeks post-surgery, the grey value of Nissl stained images was significantly less in the PD model and stimulation groups (P < 0.05), and the stimulation group exhibited greater grey values compared to the model group (P < 0.05). At 2 and 4 weeks post-surgery, the number of apoptotic neurons was significantly less in the stimulation group compared to the model group (P < 0.05). In addition, Bcl-2 and Bax expression, as well as the Bcl-2/Bax ratio, was much higher in the stimulation group compared to the model group (P < 0.05). CONCLUSION: HFS-STN has a neuroprotective effect on dopaminergic neurons in the substantia nigra pars eompacta of PD rats by promoting Bcl-2 expression, inhibiting Bax expression, and reducing the number of apoptotic dopaminergic neurons.     

Protective effects of kidney-tonifying Chinese herbal preparation on substantia nigra neurons in a mouse model of Parkinson’s disease

The Chinese herbs Herba Epimedii, Fructus Ligustri Lucidi and Rhizoma Polygonati were injected into Parkinson’s disease mice established via intraperitoneal injection of 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine hydrochloride. The selective monoamine oxidase B inhibitor selegiline was used as a positive control drug. After successive administration for 4 weeks, Herba Epimedii could downregulate the expression of caspase-3 and increase the brain-derived neurotrophic factor level, as well as increase tyrosine hydroxylase activity in the substantia nigra of Parkinson’s disease mouse models. Rhizoma Polygonati could downregulate the expression of caspase-3 and FasL, and increase neural growth factor and brain-derived neurotrophic factor levels. Fructus Ligustri Lucidi could downregulate caspase-3 expression. Rhizoma Polygonati and Fructus Ligustri Lucidi did not produce obvious effects on tyrosine hydroxylase activity. Herba Epimedii and Fructus Ligustri Lucidi yielded similar effects on apoptosis-promoting factors to those elicited by selegiline. Herba Epimedii and Rhizoma Polygonati significantly increased the levels of neurotrophic factors compared with selegiline. Herba Epimedii significantly increased tyrosine hydroxylase activity compared with selegiline. It is indicated that the kidney-tonifying Chinese herbal preparation can downregulate the expression of apoptosis-promoting factors, increase neurotrophic factors levels in the substantia nigra and striatum, as well as increase tyrosine hydroxylase activity in the substantia nigra of Parkinson’s disease mouse models, thereby exerting a stronger or similar neuroprotective effects compared with selegiline.     

Loss of insulin receptor immunoreactivity from the substantia nigra pars compacta neurons in Parkinson's disease

Immunohistochemistry using both a newly developed polyclonal, and a commercially available monoclonal, anti-insulin receptor antibody was done on the midbrain from cases of idiopathic Parkinson's disease (PD), Alzheimer's disease, amyotrophic lateral sclerosis, vascular parkinsonism and non-neurological controls. Both antibodies gave indentical patterns of neuronal staining. The neurons of the oculomotor nucleus were immunopositive in all the brains. However, the neurons in the pars compacta of the substantia nigra, paranigral nucleus, parabrachial pigmental nucleus, tegmental pedunculopontine nucleus, supratrocheal nucleus, cuneiform nucleus, subcuneiform nucleus and lemniscus medialis, which were positive in other diseases and in non-neurological controls, were not stained by these antibodies in PD brains. These results suggest that, in PD, a dysfunction of the insulin/insulin receptor system may precede death of the dopaminergic neurons.The work in the Kinsmen Laboratory was supported by the MRC of Canada and the Parkinson Society of Canada     

Involvement of GABAergic pathway on inhibition of subthalamic nucleus high-frequency stimulation of spontaneous firing activity in substantia nigra pars reticulata neurons in a rat model of Parkinson's disease

BACKGROUND： Subthalamic nucleus-high frequency stimulation （STN-HFS） plays an important role in the treatment of Parkinson＇s disease, but the mechanisms underlying STN-HFS remain unclear. Some studies have demonstrated that STN stimulation inhibits the firing activity of substantia nigra pars reticulata neurons. OBJECTIVE： To investigate the effects of different-frequency STN stimulation and microiontophoresis of gamma-aminobutyric acid （GABA） and its antagonist, bicuculline, on spontaneous firing activity in a rat model of Parkinson＇s disease, and to analyze the action pathway of high frequency stimulation in firing activity inhibition of substantia nigra pars reticulata neurons. DESIGN, TIME AND SETTING： This neuroelectrophysiological, animal experiment was performed at the Electrophysiology Laboratory of Liaoning Medical University, China from March to August 2008. MATERIALS： 6-hydroxydopamine （6-OHDA） （Sigma, USA）, A320R isolated stimulus and DAM80 preamplifier （World Precision Instruments, USA）, 6400A microiontophoresis apparatus （Dagan, USA）, and Spike 2 biological signal acquisition system （CED, UK） were used in this study. METHODS： A total of 20 Sprague Dawley rats were used to establish a Parkinson＇s disease model via injection of 6-OHDA into the right striatum. Electrical stimulation （0.06-ms width, 0.4-mA intensity 20-200-Hz frequency, 5-second train duration） was delivered to the subthalamic nucleus. Peripheral channels were separately filled with GABA （pH 3.5, 0.2 mol/L）, bicuculline （pH 4.0, 0.01 mol/L）, and NaCI （pH 7.0, 3 mol/L）. The electrode was positioned with a WK-2 microelectrode propulsion device, and was slowly inserted into the substantia nigra pars reticulata to record spontaneous firing activity of substantia nigra pars reticulata neurons. MAIN OUTCOME MEASURES： The number and firing rate of substantia nigra pars reticulata neurons which were either inhibited or excited were measured. RESULTS： Substantia nigra pars reticulata neurons were inhibited by STN stimulation. The proportion of inhibited substantia nigra pars reticulata neurons increased with increasing stimulation frequency. GABA had a tonic inhibitory effect on substantia nigra pars reticulata neurons. Microiontophoresis of bicuculline suppressed the inhibitory effect of STN-HFS on 67% （4/6） of substantia nigra pars reticulata neurons. CONCLUSION： STN-HFS ameliorated abnormal activity in substantia nigra pars reticulata neurons via the inhibitory effect of GABA treatment in a rat model of Parkinson＇s disease.     

APP knockout attenuates microglial activation and enhances neuron survival in substantia nigra compacta after axotomy

Focal microglial activation and progressive dopaminergic neurodegeneration in substantia nigra compacta (SNc) have characterized Parkinson's disease (PD). We have hypothesized that the microglial response may be provoked by molecular signals from chronically stressed SNc neurons. To test whether amyloid precursor protein (APP) could serve as such a signal, we evaluated microglial activation in SN after unilateral transection of the medial forebrain bundle (MFB) in mice either wild-type (WT) or null (KO) for APP. WT and KO mice displayed comparable microglial response at the MFB transection site. In WT mice microglial activation was first apparent in the ipsilateral SN at 3 days postlesion (dpl), marked by morphological change and increased isolectin immunoreactivity. The microglial response intensified at 7 dpl and persisted in the medial nigra through 14 dpl. In contrast, in KO mice activated microglia appeared predominantly at 7 dpl, with little activation at 3 dpl and none at 14 dpl. Neuron number in affected WT SNc at 14 dpl was significantly reduced compared with loss in affected KO SNc. The delayed and limited local microglial activation and increased neuron survival in response to distal axotomy of SNc neurons in APP KO mice are consistent with the important role APP in neuronal stress responses in vivo.     

Melatonin treatment potentiates neurodegeneration in a rat rotenone Parkinson's disease model

Parkinson's disease (PD) is characterized pathologically by progressive neurodegeneration of the nigrostriatal dopamine (DA) system. Currently, the cause of the disease is unknown, except for a small percentage of familial cases (<10% of total). The rat rotenone model reproduces many of the pathological features of the human disease, including apomorphine‐responsive behavioral deficits, DA depletion, loss of striatal DA terminals and nigral dopaminergic neurons, and α‐synuclein/polyubiquitin‐positive cytoplasmic inclusions reminiscent of Lewy bodies. Therefore, this model is well‐suited to examine potential neuroprotective agents. Melatonin is produced mainly by the pineal gland and is known primarily for regulating circadian rhythms. It also has potent free radical scavenging and antiinflammatory properties. Melatonin has been reported to be neuroprotective in the 6‐hydroxydopamine (6‐OHDA) and 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) models of PD. However, there are conflicting reports suggesting that melatonin does not provide neuroprotection in these models. Melatonin elicits significant functional changes in the nigrostriatal DA system that may affect 6‐OHDA and MPTP entry into cells. Therefore, rotenone is an ideal model for assessing protection, because it does not rely on the dopamine transporter uptake to exert neurotoxicity. In this study, the neuroprotective potential of melatonin in the rotenone PD model was assessed. Melatonin potentiated striatal catecholamine depletion, striatal terminal loss, and nigral DA cell loss. Indeed, melatonin alone elicited alterations in striatal catecholamine content. Our findings indicate that melatonin is not neuroprotective in the rotenone model of PD and may exacerbate neurodegeneration. © 2009 Wiley‐Liss, Inc.