Early signs of neuronal apoptosis in the substantia nigra pars compacta of the progressive neurodegenerative mouse 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/probenecid model of Parkinson’s disease

HIV-1 gp120 neurotoxicity proximally and at a distance from the point of exposure: protection by rSV40 delivery of antioxidant enzymes

Toxicity of HIV-1 envelope glycoprotein (gp120) for substantia nigra (SN) neurons may contribute to the Parkinsonian manifestations often seen in HIV-1-associated dementia (HAD). We studied the neurotoxicity of gp120 for dopaminergic neurons and potential neuroprotection by antioxidant gene delivery. Rats were injected stereotaxically into their caudate-putamen (CP); CP and (substantia nigra) SN neuron loss was quantified. The area of neuron loss extended several millimeters from the injection site, approximately 35% of the CP area. SN neurons, outside of this area of direct neurotoxicity, were also severely affected. Dopaminergic SN neurons (expressing tyrosine hydroxylase, TH, in the SN and dopamine transporter, DAT, in the CP) were mostly affected: intra-CP gp120 caused approximately 50% DAT+ SN neuron loss. Prior intra-CP gene delivery of Cu/Zn superoxide dismutase (SOD1) or glutathione peroxidase (GPx1) protected SN neurons from intra-CP gp120. Thus, SN dopaminergic neurons are highly sensitive to HIV-1 gp120-induced neurotoxicity, and antioxidant gene delivery, even at a distance, is protective.

Restorative effect of endurance exercise on behavioral deficits in the chronic mouse model of Parkinson's disease with severe neurodegeneration

BACKGROUND

Animal models of Parkinson's disease have been widely used for investigating the mechanisms of neurodegenerative process and for discovering alternative strategies for treating the disease. Following 10 injections with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, 25 mg/kg) and probenecid (250 mg/kg) over 5 weeks in mice, we have established and characterized a chronic mouse model of Parkinson's disease (MPD), which displays severe long-term neurological and pathological defects resembling that of the human Parkinson's disease in the advanced stage. The behavioral manifestations in this chronic mouse model of Parkinson's syndrome remain uninvestigated. The health benefit of exercise in aging and in neurodegenerative disorders including the Parkinson's disease has been implicated; however, clinical and laboratory studies in this area are limited. In this research with the chronic MPD, we first conducted a series of behavioral tests and then investigated the impact of endurance exercise on the identified Parkinsonian behavioral deficits.

RESULTS

We report here that the severe chronic MPD mice showed significant deficits in their gait pattern consistency and in learning the cued version of the Morris water maze. Their performances on the challenging beam and walking grid were considerably attenuated suggesting the lack of balance and motor coordination. Furthermore, their spontaneous and amphetamine-stimulated locomotor activities in the open field were significantly suppressed. The behavioral deficits in the chronic MPD lasted for at least 8 weeks after MPTP/probenecid treatment. When the chronic MPD mice were exercise-trained on a motorized treadmill 1 week before, 5 weeks during, and 8-12 weeks after MPTP/probenecid treatment, the behavioral deficits in gait pattern, spontaneous ambulatory movement, and balance performance were reversed; whereas neuronal loss and impairment in cognitive skill, motor coordination, and amphetamine-stimulated locomotor activity were not altered when compared to the sedentary chronic MPD animals.

CONCLUSION

This study indicates that in spite of the drastic loss of dopaminergic neurons and depletion of dopamine in the severe chronic MPD, endurance exercise training effectively reverses the Parkinson's like behavioral deficits related to regular movement, balance and gait performance.

Reactive oxygen species production and MAPK activation are implicated in tetrahydrobiopterin-induced SH-SY5Y cell death

Tetrahydrobiopterin (BH4), an obligatory cofactor for dopamine (DA) synthesis, has been shown to produce reactive oxygen species (ROS) upon its autoxidation and induce selective dopaminergic cell death in many in vivo and in vitro models of Parkinson's disease (PD). The precise molecular mechanisms underlying neuronal death upon BH4 exposure, however, have not yet been well elucidated. The present study aims to examine the intracellular ROS production and the signal transduction pathways underlying the toxic effects of BH4 on human dopaminergic SH-SY5Y cells. The results show that BH4 treatment at concentrations ranging from 50microM to 400microM induces neuronal death in a dose-dependent manner. In concomitant with the elevation of intracellular ROS formation, BH4-induced activation of MAPK, p38 and ERK1/2 in SH-SY5Y cells is attenuated by pretreatment with MAPK inhibitors, SB203580 or PD98059. These data indicate that MAPK activation and oxidative stress are involved in BH4-induced dopaminergic cell death, possibly through the autoxidation of BH4 and subsequent ROS production.

A diet for dopaminergic neurons?

Parkinson's disease (PD) is the second most common neurodegenerative disease, which unfortunately is still fatal. Since the discovery of dopamine (DA) neuronal cell loss within the substantia nigra in PD, the past decades have seen the understanding of the pathophysiological mechanisms underlying the degenerative process advance at a very impressive rate. Nevertheless, there is at present no cure for PD. Although there are no proven therapies for prevention, a large body of evidence from animal studies has highlighted the paramount role of dietary factors in counteracting DA degeneration. Consistently, associations between the risk of developing PD and the intake of nutrients, individual foods, and dietary patterns have been recently shown. Therefore, promoting healthy lifestyle choices such as a Mediterranean diet might be the key to reducing the risk of PD.

Effects of endurance exercise on ventral tegmental area neurons in the chronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and probenecid-treated mice

Loss of dopaminergic neurons in the substantia nigra (A9 cells) and ventral tegmental area (VTA) (A10 cells) has been reported in Parkinson's disease with reference to causing motor and non-motor deficits, although clinical and laboratory animal studies on the degeneration of VTA neurons are less emphasized comparative to the degeneration of substantia nigra neurons. In the present study, we examined the VTA dopaminergic neurons in a chronic mouse model of Parkinson's disease induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and probenecid at a level showing moderate neurodegeneration and studied the impact of endurance exercise on VTA neurons in this model. In comparison to the normal control animals, the chronic mouse model of Parkinson's disease with moderate neurodegeneration demonstrated a significant reduction of VTA neurons (52% loss), when these animals were kept sedentary throughout the study. Morphologically, the VTA dopaminergic neurons in this model displayed a decrease in cell volume and showed irregular or disparaging axonal and dendritic projections. When the chronic Parkinsonian mice were exercised on a motorized rodent treadmill up to 15m/min, 40 min/day, 5 days/week for 10 and 18 weeks, the total number of VTA dopaminergic neurons were significantly higher than the sedentary Parkinsonian animals. Especially noted with the 18-week exercised Parkinsonian mice, the number of VTA neurons returned to normal range and the cells were densely populated and displayed distinctive axons and dendritic arborization. These results demonstrate that prolonged exercise training is neuroprotective to the dopaminergic neurons in the VTA of the chronic mouse model of Parkinson's disease with moderate neurodegeneration.

Neurotoxicity of MPTP to migrating neuroblasts: studies in acute and subacute mouse models of Parkinson's disease

The acute or subacute administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) has been widely used in C57BL/6 mice to develop models of Parkinson's disease (PD). The loss of dopaminergic neurons is suggested to be mediated by a mechanism of nonapoptotic cell death or by apoptosis. In recent years, the notion that the neurotoxicity of MPTP is restricted to dopaminergic neurons in the substantia nigra (SN) has been challenged. Here, we provide evidence of rapid cell death in the subventricular zone (SVZ) and rostral migratory stream (RMS) in the adult C57BL/6 mouse brain in response to acute or subacute treatment with MPTP. Significant terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) of fragmented DNA was observed at 24 h (or 1 day) after the last injection in the acute model or after the first injection in the subacute model. Ultrastructural analysis confirmed that dying cells displayed an apoptotic morphology. Using a double labeling method, we demonstrated that the phenotype of the cells undergoing apoptosis is that of migrating neuroblasts. This is further supported by evidence of a subsequent loss of migrating neuroblasts. The results raise the possibility that migrating neuroblasts in the SVZ and RMS may be more vulnerable to MPTP than nigrostriatal dopaminergic neurons in the SN, and the death of migrating neuroblasts may be a primary event in the mouse model of PD. Furthermore, our data suggests that the death and subsequent loss of migrating neuroblasts in the acute or subacute model probably lead to a decreased potential for neurogenesis to some extent.

Endurance exercise promotes cardiorespiratory rehabilitation without neurorestoration in the chronic mouse model of parkinsonism with severe neurodegeneration

Physical rehabilitation with endurance exercise for patients with Parkinson's disease has not been well established, although some clinical and laboratory reports suggest that exercise may produce a neuroprotective effect and restore dopaminergic and motor functions. In this study, we used a chronic mouse model of Parkinsonism, which was induced by injecting male C57BL/6 mice with 10 doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (25 mg/kg) and probenecid (250 mg/kg) over 5 weeks. This chronic parkinsonian model displays a severe and persistent loss of nigrostriatal neurons, resulting in robust dopamine depletion and locomotor impairment in mice. Following the induction of Parkinsonism, these mice were able to sustain an exercise training program on a motorized rodent treadmill at a speed of 18 m/min, 0 degrees of inclination, 40 min/day, 5 days/week for 4 weeks. At the end of exercise training, we examined and compared their cardiorespiratory capacity, behavior, and neurochemical changes with that of the probenecid-treated control and sedentary parkinsonian mice. The resting heart rate after 4 weeks of exercise in the chronic parkinsonian mice was significantly lower than the rate before exercise, whereas the resting heart rate at the beginning and 4 weeks afterward in the control or sedentary parkinsonian mice was unchanged. Exercised parkinsonian mice also recovered from elevated electrocardiogram R-wave amplitude that was detected in the parkinsonian mice without exercise for 4 weeks. The values of oxygen consumption, carbon dioxide production, and body heat generation in the exercised parkinsonian mice before and during the Bruce maximal exercise challenge test were all significantly lower than that of their sedentary counterparts. Furthermore, the exercised parkinsonian mice demonstrated a greater mass in the left ventricle of the heart and an increased level of citrate synthase activity in the skeletal muscles. The amphetamine-induced, dopamine release-dependent locomotor activity was markedly inhibited in the sedentary parkinsonian mice and was also inhibited in the exercised parkinsonian mice. Finally, neuronal recovery from the loss of nigrostriatal tyrosine hydroxylase expression and dopamine levels in the severe parkinsonian mice after exercise was not evident. Taken all together, these data suggest that 4 weeks of treadmill exercise promoted physical endurance, resulting in cardiorespiratory and metabolic adaptations in the chronic parkinsonian mice with severe neurodegeneration without demonstrating a restorative potential for the nigrostriatal dopaminergic function.

A chronic mouse model of Parkinson's disease has a reduced gait pattern certainty

The purpose of this investigation was to determine if a chronic Parkinson's disease mouse model will display less certainty in its gait pattern due to basal ganglia dysfunction. A chronic Parkinson's disease mouse model was induced by injecting male C57/BL mice with 10 doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (25mg/kg) (MPTP) and probenecid (250 mg/kg) (P) over 5 weeks. This chronic model produces a severe and persistent loss of nigrostriatal neurons resulting in dopamine depletion and locomotor impairment. The control mice were treated with probenecid alone. Fifteen weeks after the last MPTP/P treatment, the mice were videotaped in the sagittal plane with a digital camera (60 Hz) as they ran on a motorized treadmill at a speed of 10 m/min. The indices of gait and gait variability were calculated. Stride length was significantly (p=0.016) more variable in the chronic MPTP/P mice. Additionally, the chronic MPTP/P mice had a statistically less certain gait pattern when compared to the control mice (p=0.02). These results suggest that variability in the gait pattern can be used to evaluate changes in neural function. Additionally, our results imply that disorder of the basal ganglia results in less certainty in modulating the descending motor command that controls the gait pattern.

Differential nigral expression of bcl-2 protein family in the pure and common forms of Dementia with Lewy bodies: relevance for dopaminergic neuronal vulnerability

We investigated whether bcl-2 protein family is involved in the pathogenesis of the dopaminergic neurodegeneration that occurs in Dementia with Lewy bodies (DLB). The expression of the proapoptotic protein bax and the antiapoptotic proteins bcl-2 and bcl-xL was investigated by Western blot in the pars compacta of the substantia nigra of pure and common DLB forms. No changes in the nigral expression levels of bax, bcl-2 and bcl-xL proteins were found between control and DLB pure cases. In the common DLB forms, nigral bcl-xL and bcl-2 proteins levels were significantly decreased in the DLB cases associated with a concomitant severe AD pathology (p < 0.05). An increase in nigral bcl-2 protein expression was observed in the DLB cases with a mild AD-associated pathology (p < 0.05). The present results are in agreement with previous observations indicating that DLB cases with severe AD pathology tend to show severe Lewy pathology suggesting that AD pathology might exacerbate Lewy pathology.

Mechanism of cell death caused by complex I defects in a rat dopaminergic cell line

Defects in the proton-translocating NADH-quinone oxidoreductase (complex I) of mammalian mitochondria are linked to neurodegenerative disorders. The mechanism leading to cell death elicited by complex I deficiency remains elusive. We have shown that expression of a rotenone-insensitive yeast NADH-quinone oxidoreductase (Ndi1) can rescue mammalian cells from complex I dysfunction. By using the Ndi1 enzyme, we have investigated the key events in the process of cell death using a rat dopaminergic cell line, PC12. We found that complex I inhibition provokes the following events: 1) activation of specific kinase pathways; 2) release of mitochondrial proapoptotic factors, apoptosis inducing factor, and endonuclease G. AS601245, a kinase inhibitor, exhibited significant protection against these apoptotic events. The traditional caspase pathway does not seems to be involved because caspase 3 activation was not observed. Our data suggest that overproduction of reactive oxygen species (ROS) caused by complex I inhibition is responsible for triggering the kinase activation, for the release of the proapoptotic factors, and then for cell death. Nearly perfect prevention of apoptotic cell death by Ndi1 agrees with our earlier observation that the presence of Ndi1 diminishes rotenone-induced ROS generation from complex I. In fact, this study demonstrated that Ndi1 keeps the redox potential high even in the presence of rotenone. Under these conditions, ROS formation by complex I is known to be minimal. Possible use of our cellular model is discussed with regard to development of therapeutic strategies for neurodegenerative diseases caused by complex I defects.

Apoptotic neuronal death in Parkinson's disease: Involvement of nitric oxide

Apoptosis of nigral dopaminergic neurons by various mechanisms is an emerging phenomenon involved in the degeneration of dopaminergic neurons in Parkinson's disease (PD). Both extrinsic and intrinsic pathways seems to be involved in death of nigral neurons, intrinsic pathway however, seems to be more important due to the energy crisis. Apoptosis by intrinsic pathway is executed by several initiators and effector caspases, which have been found activated in PD patients, experimental models as well as in neuronal cultures. Nitric oxide (NO) seems to be a central molecule due to its ability to modulate both pro and antiapoptotic phenomenon. The review focuses on the diverse extrinsic and intrinsic factors, signaling pathways and their modulation by NO leading to the death of dopaminergic neurons.

Bergmann glia as putative stem cells of the mature cerebellum

The adult brain is known to retain a population of stem cells with self-renewing and differentiation ability, which have been identified in two main regions. Recent reports now suggest the presence of such cells in the cerebellum, a part of the CNS which was not formerly thought to harbour stem cells. The precise nature and localisation of these potential new stem cells within the tissue remains unclear, as they have primarily been described at early postnatal stages, before completion of the extensive cell migration accompanying cerebellum maturation. We have shown that a discrete cell population of the cerebellar cortex, the Bergmann glia, shares the expression of key molecular markers with neural stem cells. We examine the hypothesis that the Bergmann glia may represent a novel and abundant stem cell population in the mature cerebellum.

Non-steroidal anti-inflammatory drugs in Parkinson's disease

Parkinson's disease (PD) is known to be a chronic and progressive neurodegenerative disease caused by a selective degeneration of dopaminergic (DAergic) neurons in the substantia nigra pars compacta (SNc). A large body of experimental evidence indicates that the factors involved in the pathogenesis of this disease are several, occurring inside and outside the DAergic neuron. Recently, the role of the neuron-glia interaction and the inflammatory process, in particular, has been the object of intense study by the research community. It seems to represent a new therapeutic approach opportunity for this neurological disorder. Indeed, it has been demonstrated that the cyclooxygenase type 2 (COX-2) is up-regulated in SNc DAergic neurons in both PD patients and animal models of PD and, furthermore, non-steroidal anti-inflammatory drugs (NSAIDs) pre-treatment protects against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or 6 hydroxydopamine (6-OHDA)-induced nigro-striatal dopamine degeneration. Moreover, recent epidemiological studies have revealed that the risk of developing PD is reduced in humans who make therapeutical use of NSAIDs. Consequently, it is hypothesized that they might delay or prevent the onset of PD. However, whether or not these common drugs may also be of benefit to those individuals who already have Parkinson's disease has not as yet been shown. In this paper, evidence relating to the protective effects of aspirin or other NSAIDs on DAergic neurons in animal models of Parkinson's disease will be discussed. In addition, the pharmacological mechanisms by which these molecules can exert their neuroprotective effects will be reviewed. Finally, epidemiological data exploring the effectiveness of NSAIDs in the prevention of PD and their possible use as adjuvants in the therapy of this neurodegenerative disease will also be examined.

Temporal mRNA profiles of inflammatory mediators in the murine 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrimidine model of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). With the exception of a few rare familial forms of the disease, the precise molecular mechanisms underlying PD are unknown. Inflammation is a common finding in the PD brain, but due to the limitation of postmortem analysis its relationship to disease progression cannot be established. However, studies using the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD have also identified inflammatory responses in the nigrostriatal pathway that precede neuronal degeneration in the SNpc. To assess the pathological relevance of these inflammatory responses and to identify candidate genes that might contribute to neuronal vulnerability, we used quantitative reverse-transcription polymerase chain reaction (qRT-PCR) to measure mRNA levels of 11 cytokine and chemokine encoding genes in the striatum of MPTP-sensitive (C57BL/6J) and MPTP-insensitive (Swiss Webster, SWR) mice following administration of MPTP. The mRNA levels of all 11 genes changed following MPTP treatment, indicating the presence of inflammatory responses in both strains. Furthermore, of the 11 genes examined only 3, interleukin 6 (Il-6), macrophage inflammatory protein 1 alpha/CC chemokine ligand 3 (Mip-1alpha/Ccl3) and macrophage inflammatory protein 1 beta/CC chemokine ligand 4 (Mip-1beta/Ccl4), were differentially regulated between C57BL/6J and SWR mice. In both mouse strains, the level of monocyte chemoattractant protein 1/CC chemokine ligand 2 (Mcp-1/Ccl2) mRNA was the first to increase following MPTP administration, and might represent a key initiating component of the inflammatory response. Using Mcp-1/Ccl2 knockout mice backcrossed onto a C57BL/6J background we found that MPTP-stimulated Mip-1alpha/Ccl3 and Mip-1beta/Ccl4 mRNA expression was significantly lower in the knockout mice; suggesting that Mcp-1/Ccl2 contributes to MPTP-enhanced expression of Mip-1alpha/Ccl3 and Mip-1beta/Ccl4. However, stereological analysis of SNpc neuronal loss in Mcp-1/Ccl2 knockout and wild-type mice showed no differences. These findings suggest that it is the ability of dopaminergic SNpc neurons to survive an inflammatory insult, rather than genetically determined differences in the inflammatory response itself, that underlie the molecular basis of MPTP resistance.