Dopaminergic Loss Research Articles

The status of olfactory function and the striatal dopaminergic system in drug-induced parkinsonism

Olfactory impairment has been reported in drug-induced parkinsonism (DIP), but the relationship between dopaminergic dysfunction and smell deficits in DIP patients has not been characterized. To this end, we studied 16 DIP patients and 13 patients affected by Parkinson's disease (PD) using the "Sniffin' Sticks" test and [(123)I] FP-CIT SPECT (single-photon emission computed tomography). DIP patients were divided based on normal (n=9) and abnormal (n=7) putamen dopamine transporter binding. Nineteen healthy age- and sex-matched subjects served as controls of smell function. Patients with DIP and pathological putamen uptake had abnormal olfactory function. In this group of patients, olfactory TDI scores (odor threshold, discrimination and identification) correlated significantly with putamen uptake values, as observed in PD patients. By contrast, DIP patients with normal putamen uptake showed odor functions-with the exception of the threshold subtest-similar to control subjects. In this group of patients, no significant correlation was observed between olfactory TDI scores and putamen uptake values. The results of our study suggest that the presence of smell deficits in DIP patients might be more associated with dopaminergic loss rather than with a drug-mediated dopamine receptor blockade. These preliminary results might have prognostic and therapeutic implications, as abnormalities in these individuals may be suggestive of an underlying PD-like neurodegenerative process.

Neuroprotective effects of an herbal medicine, Yi-Gan San on MPP +/MPTP-induced cytotoxicity in vitro and in vivo

Ethnopharmacological relevance A traditional herb, Yi-Gan San, has been widely used for the management of neurodegenerative disorders in traditional East Asian Medicine. Aim of the study The present study investigated the neuroprotective effects of Yi-Gan San in 1-methyl-4-phenylpyridine/1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced cytotoxicity in vitro and in vivo and sought to clarify its underlying mechanisms. Materials and methods The effect of Yi-Gan San on 1-methyl-4-phenylpyridine was measured in terms of 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assays, caspase-3 activity, and western blot analysis of phosphorylated Akt, one of the survival-related signaling proteins in SH-SY5Y cells. The effects of Yi-Gan San were also confirmed in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Parkinsonian mouse model using a rotarod test and tyrosine hydroxylase-immunohistochemistry. Results Pretreatment of Yi-Gan San with 1-methyl-4-phenylpyridine showed a significant protective effect on SH-SY5Y cells and significantly decreased the level of caspase-3 activity compared to the values for the 1-methyl-4-phenylpyridine-treated cells. This process increased the protein expressions of phosphorylated Akt, and an inhibitor of phosphatidylinositol 3-kinase (PI3K)/Akt, LY294002, significantly decreased this protective effect of Yi-Gan San. In the mouse Parkinson's disease model, treatment with Yi-Gan San also significantly improved motor functioning and prevented dopaminergic loss related to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine challenge. Conclusion Using both in vitro and in vivo methods, this study revealed that Yi-Gan San has neuroprotective effects and rescues dopaminergic neurons from 1-methyl-4-phenylpyridine/1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine toxicity, possibly via the PI3K/Akt pathway.

Cardiac sympathetic denervation precedes nigrostriatal loss in the E46K mutation of the α-synuclein gene (SNCA)

Here we report the case of an asymptomatic carrier of the E46K substitution in alpha-synuclein gene where we have documented that cardiac sympathetic denervation precedes nigrostriatal dopaminergic loss. She has been followed up regularly with standard neurological examination, UPDRS, neuropsychological formal testing, parkinson disease sleep scale-PDSS, Epworth scale, Hamilton-D scale, SCOPA Aut, orthostatic hypotension test, brief smell identification test, polysomnography, cerebral 123-I-FP-CIT SPECT, and, 123I-MIBG cardiac scintigraphy. She shows no presence of orthostatic hypotension. Olfactory test results demonstrate normal limits. In the PSG the nocturnal sleep shows mild abnormalities although the sleep efficiency and stage proportion remain under normal limits. The 123-I-FP-CIT SPECT is normal; in contrast, the 123I-MIBG cardiac scintigraphy shows a complete lack of isotopic uptake compatible with a severe sympathetic myocardial denervation. This example of monogenic autosomal dominant parkinsonism due to an alpha-synuclein mutation favours the hypothesis that peripheral autonomous nervous system involvement occurs earlier than the CNS degeneration.

Imaging essential tremor

To investigate over time changes in striatal dopamine transporter (DAT), we performed two sequential N-omega-fluoropropyl-2beta-carbomethoxy-3beta-(4-iodophenyl) tropane single photon computed tomography (SPECT) scans in 20 subjects with essential tremor (ET), in 13 with Parkinson disease (PD) and in 23 healthy controls (HC, one scan only). We also performed an [(99m)Tc]ethyl cysteinate dimer bicisate SPECT exam for regional brain network analysis in 9 ET, in a second group of 18 PD (9 with tremor, tPD and 9 akinetic-rigid dominant, arPD) and in 8 HC. PD subjects had a reduced DAT binding in comparison to ET and HC with an annual decline rate of 7.3% in the contralateral putamen. There were no mean uptake differences between ET and HC at baseline and no uptake loss over time in ET. A discriminant analysis grouped 30% (first scan) and 5% (second scan) of ET as PD and a partition analysis showed overlap between ET and PD for caudate nucleus uptake. Spatial covariance analysis revealed that the expression of the PD-related regional pattern separated both tPD and arPD from ET and HC. In conclusion, PD and ET do not share a common pattern of dopaminergic loss over time. However, mild impairment of dopamine transporter in the caudate nucleus may contribute to tremor onset in ET.

Melatonin reduces striatal dopaminergic and mitochondrial deficits associated with chronic Parkinson's disorder

Neuronal oxidative stress and mitochondrial dysfunction have been implicated in Parkinson's disease (PD). We have recently correlated striatal dopaminergic (DA) neurodegeneration with mitochondrial deficit in a chronic mouse model of PD (MPD) induced by 10 injections of 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine and probenecid over 5 weeks. Melatonin is a natural antioxidant and free radical scavenger, which has been shown to reduce cellular oxidative stress, protect mitochondria, and slow aging. In this study, we examined the effect of long‐term melatonin treatment (5 mg/kg/day, i.p., 5 days/week for 18 weeks) on mitochondrial and DA neuronal functions in the striatum of the chronic MPD. Melatonin alone did not alter the normal neuronal, mitochondrial and motor functions as seen in the saline‐treated control mice. The chronic MPD exhibited marked loss of DA, reduction of mitochondrial respiration and ATP level in the striatum, and impaired motor performance on the challenging beam. Interestingly, melatonin treatment for 18 weeks significantly reduced DA loss and motor impairment and prevented mitochondrial deficit as detected in the chronic MPD. This study demonstrates that long‐term melatonin is not only mitochondria‐protective but also neuroprotective in the chronic MPD supporting the hypothesis that melatonin may slow the progression of PD neurodegeneration. Supported by NINDS R01 NS47920.

Time-dependent striatal dopamine depletion after injection of 6-hydroxydopamine in the rat. Comparison of single bilateral and double bilateral lesions.

For future investigation of possible perturbation of circadian rhythm in animal models of Parkinson's disease we needed an animal model providing lasting 80-100% striatal dopaminergic depletion in rats, but without induced mortality. We have thus compared the effects of a single hydroxydopamine bilateral striatal lesion (SB-hydroxydopamine) with those of a double hydroxydopamine bilateral lesion (DB-hydroxydopamine) at the same dose (16 microg/striatum) by HPLC determination of dopamine and 3,4-dihydrophenylacetic acid (dopac) levels in the striatum. Two weeks after neurosurgery, SB-hydroxydopamine and DB-hydroxydopamine induced dopaminergic depletion of at least 81% compared with control groups. After eight weeks striatal dopaminergic depletion was only 60.97% in SB-hydroxydopamine rats, suggesting a compensatory phenomenon, whereas in DB-hydroxydopamine rats dopaminergic loss was stable at 88%. For the DB-hydroxydopamine group the dopac/dopamine ratio was significantly increased at week 2 only, whereas no significant change was observed for other groups. This increase might be explained by increased dopamine turnover. We have demonstrated that striatal DB-hydroxydopamine injection induces lasting 80-100% neuronal loss, close to that observed in the disease in man, without induced mortality, and provides a tool which meets our experimental requirements.

Clinically reported heterozygous mutations in the PINK1 kinase domain exert a gene dosage effect

Mutations in the gene encoding phosphatase and tensin homolog (PTEN)-induced kinase 1 (PINK1) have been associated with the loss of dopaminergic neurons characteristic of familial and sporadic Parkinson disease. We developed an in vitro system of stable human dopaminergic neuronal cell lines coexpressing an equivalent copy of normal and mutant PINK1 to simulate "heterozygous" and "homozygous" states in patients. Mutants in the N-terminus, C-terminus, and kinase domain were generated and cloned into a two-gene mammalian expression vector to generate stable mammalian expression cell lines producing an equivalent copy number of wild-type/mutant PINK1. The cell lines were subjected to oxidative stress and the rate of apoptosis and change in mitochondrial membrane potential (DeltaPsi(m)) were assessed. Cell lines expressing kinase and C-terminus mutants exhibited a greater rate of apoptosis and decrease in DeltaPsi(m), and increased time-dependent cell loss when subjected to oxidative stress compared to the wild-type. Cell lines expressing two copies of kinase mutants exhibited a greater apoptosis rate and DeltaPsi(m) decrease than those expressing one copy of the mutant. In time-dependent experiments, there was a significant difference between "homozygous," "heterozygous," and wild-type cell lines, with decreasing cell survival in cell lines expressing mutant copies of PINK1 compared to the wild-type. We provided the first experimental evidence that clinically reported PINK1 heterozygous mutations exert a gene dosage effect, suggesting that haploinsufficiency of PINK1 is the most likely mechanism that increased the susceptibility to dopaminergic cellular loss.

The Nigrostriatal Pathway in Creutzfeldt-Jakob Disease

Parkinsonism, chorea, and dystonia are well-known clinical manifestations of Creutzfeldt-Jakob disease (CJD), but lesions of the nigrostriatal pathway have never been thoroughly studied. We performed a detailed neuropathologic study of the nigrostriatal pathway in 15 sporadic CJD and 2 variant CJD cases that included clinical correlations and assessment of neuron subtype loss, distribution of prion protein, alpha-synuclein, ubiquitin, and 14-3-3 aggregation. We found evidence of nigrostriatal pathway damage in these CJD cases. Dopaminergic neurons and striatal outflow neurons were markedly affected in sporadic CJD, whereas cholinergic interneurons were spared. In cases of CJD with chorea or myoclonus, there was less presynaptic dopaminergic loss than in cases of CJD with parkinsonism. The 2 variant CJD cases with parkinsonism or chorea showed severe cholinergic interneuron loss in the caudate and putamen, a pattern that differed from that found in sporadic CJD. alpha-Synuclein, ubiquitin, and 14-3-3 aggregation coexisted with prion protein aggregation, thereby generating mixed pathological features. These findings suggest a possible pathophysiological overlap of abnormal protein aggregation in CJD and Parkinson disease.

In vitro dopaminergic neuroprotective and in vivo antiparkinsonian-like effects of Delta 3,2-hydroxybakuchiol isolated from Psoralea corylifolia (L.).

Cocktail recipes containing Psoralea corylifolia seeds (PCS) are used to empirically treat Parkinson disease. A PCS isolate Delta(3),2-hydroxybakuchiol (BU) can inhibit dopamine uptake in dopamine transporter (DAT) transfected Chinese hamster ovary (CHO) cells, and dopamine reuptake blockade may provide an alternative approach for ameliorating parkinsonism. Here, we assessed the potential dopaminergic neuroprotective, and antiparkinsonian-like activity of BU. BU sample size was increased by using a scale-up extraction paradigm. Pharmacologically, BU significantly protected SK-N-SH cells from 1-methyl-4-phenylpyridinium (MPP(+)) insult, produced striking inhibitory actions on dopamine/norepinephrine uptake and WIN35,428 binding in synaptosomes on in vivo administration, and significantly preventing poor performance on rotarod and dopaminergic loss in substantia nigra in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mice. BU acts by protecting dopaminergic neurons from MPP(+) injury and preventing against MPTP-induced behavioral and histological lesions in the Parkinson's disease (PD) model, possibly by inhibiting monoamine transporters. These findings suggest that BU could be meaningful in PD treatment.

Prefrontal cortical D1 dopamine receptors modulate subcortical D2 dopamine receptor-mediated stress responsiveness

Increased responsiveness to stress plays an important role in the manifestation of schizophrenia symptoms. Evidence indicates that the prefrontal cortex (PFC), and dopamine neurotransmission in the PFC in particular, is involved in the modulation of stress responsiveness. Decreased dopaminergic activity and loss of dopamine fibres have been reported in PFC in schizophrenia patients. Consequently, it was hypothesized that depletion of dopamine in PFC may facilitate increased stress responsiveness. Adult Sprague-Dawley rats received injections of 6-hydroxydopamine or saline bilaterally into the medial PFC (mPFC) following desipramine pretreatment to selectively deplete dopaminergic fibres. Following a 3-wk recovery period, the lesioned and control rats received injections of a D1 or D2 dopamine receptor agonist or vehicle into the mPFC and were immediately subjected to forced swimming as a stressor. Results showed that frequency of locomotion and rearing, behavioural measures indicative of increased dopaminergic activity in the nucleus accumbens (NAc), were significantly increased following stress in prefrontal cortical dopamine-depleted rats. This effect was significantly ameliorated by infusions of a D1 dopamine receptor agonist directly into the mPFC in a dose-dependent manner but not by infusion of a D2 dopamine receptor agonist. In addition, stress-induced behavioural changes in prefrontal cortical dopamine-depleted rats were significantly reduced following selective discrete infusions of a D2 dopamine receptor antagonist into the NAc shell. The results suggest that dopaminergic transmission via D1 receptors in the mPFC modulates D2 dopamine receptor-mediated stress responsiveness in the NAc, a feature that may be disrupted in schizophrenia patients.

Parkinson-Linked Genes and Toxins That Affect Neuronal Cell Death Through the Bcl-2 Family

Parkinson's disease (PD) results from the death of specific neuronal populations in the CNS. Potential causative factors include environmental toxins and gene mutations that can combine to dysregulate the processing and degradation of alpha-synuclein. Oxidative stress induced by the neurotoxins MPTP, paraquat, maneb, and rotenone causes lipid peroxidation and protein misfolding that affects cell death through members of the Bcl-2 family. Sufficient activation of Bax and Bak facilitates mitochondrial outer-membrane permeabilization, which releases death-inducing factors that cause apoptotic and nonapoptotic programmed cell death. The formation of alpha-synuclein aggregates is a defining pathologic feature of PD and is induced by these neurotoxins as well as several Parkinson-linked familial mutations. Of the familial mutations identified thus far, two of the loci encode proteins associated with ubiquitin-proteasome degradation of misfolded proteins (Parkin and Uch-L1), and two encode proteins associated with mitochondria and oxidative stress (DJ-1 and PINK1). Both gene and toxin findings indicate that dopaminergic neuron losses in PD are the result of oxidative stress affecting mitochondria function and ubiquitin-proteasome activity. Here we describe how related cell death mechanisms are involved in the pathophysiology of Parkinson's disease.

An Optimized Method for Histological Detection of Dopaminergic Neurons in Drosophila melanogaster

Parkinson's disease (PD) affects >1 million Americans and is marked by the loss of dopaminergic neurons in the substantia nigra. PD has been linked to two causative factors: genetic risks (hereditary PD) and environmental toxins (idiopathic PD). In recent years, considerable effort has been devoted to the development of a Drosophila model of human PD that might be useful for examining the cellular mechanisms of PD pathology by genetic screening. In 2000, Feany and Bender reported a Drosophila model of PD in which transgenic flies expressing human mutant alpha-synuclein exhibited shortened life spans, dopaminergic losses, Parkinsonian behaviors, and Lewy bodies in surviving dopaminergic neurons. Since then, a number of studies have been published that validate the model or build on it; conversely, a number report an inability to replicate the results and suggest that most protocols for dopaminergic histology underreport the actual numbers of dopaminergic neurons in the insect brain. Here we report the optimization of dopaminergic histology in Drosophila and identification of new dopaminergic neurons, show the remarkable dendritic complexity of these neurons, and provide an updated count of these neurons in adult brains. This manuscript contains online supplemental material at http://www.jhc.org. Please visit this article online to view these materials.

MAO-B Elevation in Mouse Brain Astrocytes Results in Parkinson's Pathology

Age-related increases in monoamine oxidase B (MAO-B) may contribute to neurodegeneration associated with Parkinson's disease (PD). The MAO-B inhibitor deprenyl, a long-standing antiparkinsonian therapy, is currently used clinically in concert with the dopamine precursor L-DOPA. Clinical studies suggesting that deprenyl treatment alone is not protective against PD associated mortality were targeted to symptomatic patients. However, dopamine loss is at least 60% by the time PD is symptomatically detectable, therefore lack of effect of MAO-B inhibition in these patients does not negate a role for MAO-B in pre-symptomatic dopaminergic loss. In order to directly evaluate the role of age-related elevations in astroglial MAO-B in the early initiation or progression of PD, we created genetically engineered transgenic mice in which MAO-B levels could be specifically induced within astroglia in adult animals. Elevated astrocytic MAO-B mimicking age related increase resulted in specific, selective and progressive loss of dopaminergic neurons in the substantia nigra (SN), the same subset of neurons primarily impacted in the human condition. This was accompanied by other PD-related alterations including selective decreases in mitochondrial complex I activity and increased mitochondrial oxidative stress. Along with a global astrogliosis, we observed local microglial activation within the SN. These pathologies correlated with decreased locomotor activity. Importantly, these events occurred even in the absence of the PD-inducing neurotoxin MPTP. Our data demonstrates that elevation of murine astrocytic MAO-B by itself can induce several phenotypes of PD, signifying that MAO-B could be directly involved in multiple aspects of disease neuropathology. Mechanistically this may involve increases in membrane permeant H2O2 which can oxidize dopamine within dopaminergic neurons to dopaminochrome which, via interaction with mitochondrial complex I, can result in increased mitochondrial superoxide. Our inducible astrocytic MAO-B transgenic provides a novel model for exploring pathways involved in initiation and progression of several key features associated with PD pathology and for therapeutic drug testing.

Role of imaging techniques in the diagnosis of dementia

Dementia is a common and growing problem, affecting 5% of the over 65 s and 20% of the over 80s. The recent availability of new treatments for dementia, as well as the importance of subtype-specific management, has renewed interest in the use of brain imaging techniques that can assist in the accurate recognition of Alzheimer's disease (AD), dementia with Lewy bodies (DLB), vascular dementia (VaD) and frontotemporal dementia (FTD). Structural imaging, historically used to exclude an intracerebral lesion as a cause for dementia, is increasingly playing a role in "ruling in" diagnoses, with atrophy of the hippocampus and entorhinal cortex an early and sensitive marker for AD, and cortical and subcortical infarcts and white matter lesions characteristic of VaD. Regionally distinct patterns of hypoperfusion on single-photon emission computed tomography (SPECT) or hypometabolism on positron emission tomography (PET) can help differentiate FTD, AD and VaD, and dopaminergic loss in the basal ganglia can differentiate DLB from AD. Newer techniques show great promise to detect specific neuroreceptor changes as well as pathological underpinnings of dementia, such as amyloid and tau pathology.

Generation of a α-synuclein-based rat model of Parkinson's disease

Two missense mutations (A30P and A53T) in the gene for alpha-synuclein (α-syn) cause familial Parkinson's disease (PD) in a small cohort. There is increasing evidence to propose that abnormal metabolism and accumulation of α-syn in dopaminergic neurons play a role in the development of familial as well as sporadic PD. The complexity of the mechanisms underlying α-syn-induced neurotoxicity, however, has made difficult the development of animal models that faithfully reproduce human PD pathology. We now describe and characterize such a model, which is based on the stereotaxic injection into rat right substantia nigra pars compacta of the A30P mutated form of α-syn fused to a protein transduction domain (TAT). The TAT sequence allows diffusion of the fusion protein across the neuronal plasma membrane and results in a localized dopaminergic loss. Dopaminergic cell loss was evaluated both by tyrosine hydroxylase immunohistochemistry and by HPLC analysis of dopamine and its catabolite 3,4 dihydroxyphenylacetic acid. Infusion of TAT-α-synA30P induced a significant 26% loss in dopaminergic neurons. This dopaminergic loss was accompanied by a time-dependent impairment in motor function, evaluated utilizing the rotarod and footprint tests. In comparison to chemical neurotoxin-based (e.g. 6-hyroxydopamine, MPTP) animal models of PD, the α-syn-based PD animal model offers the advantage of mimicking the early stages and slow development of the human disease and should prove valuable in assessing specific aspects of PD pathogenesis in vivo and in developing new therapeutic strategies.

Striatal dopaminergic denervation and gait in healthy adults

Parkinsonian-like motor impairments are common in the elderly. The etiology of these symptoms in the absence of clinically diagnosable Parkinson's disease (PD) is unknown. The aim of this study was to evaluate associations between striatal dopaminergic neuron losses that occur with aging and gait in healthy adults. Forty healthy subjects aged 21-85 years old underwent [(11)C]-beta-CFT dopamine transporter (DAT) positron emission tomography (PET). Subjects were also asked to walk in a gait laboratory at their own pace. Gait variables of interest included average general spatiotemporal characteristics of walking patterns and their standard deviation reflecting gait variability. Segmented nonlinear models were used to investigate the relationship between striatal DAT activity and gait while controlling for age. Gait speed, cadence, and single and double support durations were significantly slower than age-based predictions in adults with lower striatal DAT activity (P < 0.05). After controlling for age, striatal DAT activity was not significantly associated with average step length and step width and with gait variability. We conclude that dopaminergic physiology influences certain aspects of gait independent of age-related changes. The findings of this study may augur novel therapeutic approaches to treating gait disorders in the elderly.

Mutual enhancement of central neurotoxicity induced by ketamine followed by methamphetamine

We hereby report that repeated administration of ketamine (350 mg/kg in total) and methamphetamine (30 mg/kg in total) causes specific glutamatergic and dopaminergic neuron deficits, respectively, in adult mouse brain. Acute ketamine did not affect basal body temperature or the later methamphetamine-induced hyperthermia. However, pretreatment with repeated doses of ketamine aggravated methamphetamine-induced dopaminergic terminal loss as evidenced by a drastic decrease in the levels of dopamine, 3,4-dihydroxyphenylacetic acid, and dopamine transporter density as well as poor gait balance performance. In contrast, methamphetamine-induced serotonergic depletion was not altered by ketamine pretreatment. Likewise, the subsequent treatment with methamphetamine exacerbated the ketamine-induced glutamatergic damage as indicated by reduced levels of the vesicular glutamate transporter in hippocampus and striatum and poor memory performance in the Morris water maze. Finally, since activation of the D1 and AMPA/kainate receptors has been known to be involved in the release of glutamate and dopamine, we examined the effects of co-administration of SCH23390, a D1 antagonist, and CNQX, an AMPA/kainate antagonist. Intraventricular CNQX infusion abolished ketamine's potentiation of methamphetamine-induced dopamine neurotoxicity, while systemic SCH23390 mitigated methamphetamine's potentiation of ketamine-induced glutamatergic toxicity. We conclude that repeated doses of ketamine potentiate methamphetamine-induced dopamine neurotoxicity via AMPA/kainate activation and that conjunctive use of methamphetamine aggravates ketamine-induced glutamatergic neurotoxicity possibly via D1 receptor activation.

The rationale for continuous dopaminergic stimulation in advanced Parkinson's disease

Control of movement depends on the continuous release of dopamine by neurons in the basal ganglia of the brain. The degeneration of these neurons in Parkinson's disease (PD) interferes with the flow of dopamine, leading to classic motor symptoms. In early PD, enough dopaminergic neurons remain to store dopamine provided by periodic dosing with oral levodopa and relatively normal, tonic levels of dopamine release are maintained. PD progression leads to degeneration of remaining dopaminergic terminals and loss of buffering capacity for exogenous levodopa. As a result, there are supraphysiological levels of dopamine after dosing and troughs when the available dopamine has been depleted. These divergent levels are associated with dyskinesia and ‘off’ states, respectively. Treatment strategies that provide a continuous flow of dopamine and can thus mimic normal physiological dopamine stimulation have potential to improve motor control for patients with advanced PD.

Short-Term Supplementation with Plant Extracts Rich in Flavonoids Protect Nigrostriatal Dopaminergic Neurons in a Rat Model of Parkinson's Disease

Objective: Antioxidants from plants were known to reduce the oxidative stress by scavenging free radicals, chelating metal ions and reducing inflammation. As increased oxidative stress was implicated in the nigrostriatal dopaminergic neuronal loss in Parkinson's disease (PD), we have assessed whether the plant extracts protects the nigrostriatal dopaminergic neurons in the animal model of PD.Methods: Male adult Sprague-Dawley rats were treated orally between 10am–11am each day with the extracts from tangerine peel, grape seeds, cocoa and red clover for four days. One hour after the final dosing, the left medial forebrain bundle was lesioned by infusing the dopaminergic neurotoxin 6-hydroxydopamine (6-OHDA; 12μg) under anaesthesia. Seven days post-lesion, the number of dopaminergic cells in the substantia nigra pars compacta and the levels of dopamine and its metabolites 3, 4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the striata were quantified and compared with the vehicle-treated groups.Results: Compared to the unlesioned side, 6-OHDA lesions significantly reduced the number of dopaminergic cells and the levels of dopamine and its metabolites DOPAC and HVA in the vehicle-treated animals. Pretreatment of animals with extracts of tangerine peel (rich in polymethoxylated flavones; 35 mg/kg/day), cocoa-2 (rich in procyanidins; 100 mg/kg/day) and red clover (rich in isoflavones; 200 mg/kg/day) significantly attenuated the 6-OHDA-induced dopaminergic loss. However, no significant protection was seen in animals supplemented with red and white grape seeds (rich in catechins; 100 mg/kg/day), and cocoa-1 (rich in catechins; 100 mg/kg/day).Conclusions: Pre-treatment of plant extracts rich in polymethoxylated flavones, procyanidins and isoflavones but not catechins protected the nigrostriatal dopaminergic neurons in the rat model of PD.

Treadmill exercise suppresses nigrostriatal dopaminergic neuronal loss in 6-hydroxydopamine-induced Parkinson's rats

In Parkinson's disease, the progressive loss of dopaminergic neurons in the pars compacta of the substantia nigra leads to debilitating motor dysfunction. In the present study, we investigated the effects of treadmill exercise on the dopaminergic neuronal cell death in the substantia nigra and on the dopaminergic fiber loss in the striatum of Parkinson's rats. Parkinson's rats were made by injecting 6-hydroxydopamine into the striatum with using a stereotaxic instrument. The rats in the exercise groups were put on the treadmill to run for 30 min once a day for 14 consecutive days after 6-hydroxydopamine administration into the striatum. Two weeks after the intrastriatal injection of 6-hydroxydopamine, the rats without treadmill exercise displayed rotational asymmetry following injection of apomorphine (0.5 mg/kg, s.c.). In contrast, the rats undergoing treadmill exercise showed a significant reduction of rotational asymmetry. Analysis via immunohistochemistry for the tyrosine hydroxylase expression revealed a substantial loss of cell bodies in the substantia nigra and their projected fibers in the striatum ipsilateral to the lesion following 6-hydroxydapamine injection into the striatum. However, treadmill running enhanced the survival of dopaminergic neurons in the substantia nigra and also their fibers projecting into the striatum. The results of the present study show that treadmill exercise may provide therapeutic value for the treatment of Parkinson's disease patients.