Autonomic dysfunction and plasticity in micturition reflexes in human α-synuclein mice

Neuroprotective potential of Mentha piperita extract prevents motor dysfunctions in mouse model of Parkinson's disease through anti-oxidant capacities

Parkinson's disease (PD) is the second most common neurodegenerative disease in the world. Neurodegeneration of the substantia nigra (SN) and diminished release of dopamine are prominent causes of this progressive disease. The current study aims to evaluate the protective potential of ethanolic extract of Mentha piperita (EthMP) against rotenone-mediated PD features, dopaminergic neuronal degeneration, oxidative stress and neuronal survival in a mouse model. Swiss albino male mice were assigned to five groups: control (2.5% DMSO vehicle), PD (rotenone 2.5 mg/kg), EthMP and rotenone (200mg/kg and 2.5mg/kg, respectively), EthMP (200 mg/kg), and Sinemet, reference treatment containing levodopa and carbidopa (20 mg/kg and rotenone 2.5mg/kg). Behavioral tests for motor functional deficit analysis were performed. Anti-oxidant capacity was estimated using standard antioxidant markers. Histopathology of the mid-brain for neurodegeneration estimation was performed. HPLC based dopamine level analysis and modulation of gene expression using quantitative real-time polymerase chain reaction was performed for the selected genes. EthMP administration significantly prevented the rotenone-mediated motor dysfunctions compared to PD group as assessed through open field, beam walk, pole climb down, stepping, tail suspension, and stride length tests. EthMP administration modulated the lipid peroxidation (LPO), reduced glutathione (GSH), and superoxide dismutase (SOD) levels, as well as glutathione-s-transferase (GST) and catalase (CAT) activities in mouse brain. EthMP extract prevented neurodegeneration in the SN of mice and partially maintained dopamine levels. The expression of genes related to dopamine, anti-oxidant potential and synapses were modulated in M. piperita (MP) extract treated mice brains. Current data suggest therapeutic capacities of MP extract and neuroprotective capacities, possibly through antioxidant capacities. Therefore, it may have potential clinical applications for PD management.

Review: Lower urinary tract dysfunction in animal models of Parkinson's disease (PD): Translational aspects for the treatment of PD patients with overactive bladder

Although the loss of dopaminergic neurons in the substantia nigra and consequent motor symptoms are the hallmarks of Parkinson's disease (PD), several non-motor symptoms may appear prior to these typical motor symptoms. While a variety of non-motor symptoms have emerged as the primary predictor of PD patients' quality of life, even though motor symptoms are undoubtedly distressing. According to a study, the prevalence of lower urinary tract symptoms (LUTS) varies between 27% and 64%, suggesting that PD-related lower urinary tract dysfunction may be affected by the disease stage, the presence of concomitant conditions affecting the lower urinary tract, and other autonomic dysfunctions. Animal models can serve as a platform for research into the causes of PD-related dysfunction and the evaluation of cutting-edge therapeutic approaches although the majority of animal research have been directed toward motor symptoms of PD. At present, the cause of lower urinary tract dysfunction in PD has not been fully clarified although the increasing evidence showing the multiple mechanisms underlying PD-related LUTS has emerged. In this chapter we summarize the findings of basic research in the studies of the lower urinary tract dysfunction using with different animal PD models and we try to shed light on the translational aspects for the development of future treatment modalities in PD patients with LUTS.

How Well Do Rodent Models of Parkinson's Disease Recapitulate Early Non-Motor Phenotypes? A Systematic Review

The prodromal phase of Parkinson's disease (PD) is characterised by many non-motor symptoms, and these have recently been posited to be predictive of later diagnosis. Genetic rodent models can develop non-motor phenotypes, providing tools to identify mechanisms underlying the early development of PD. However, it is not yet clear how reproducible non-motor phenotypes are amongst genetic PD rodent models, whether phenotypes are age-dependent, and the translatability of these phenotypes has yet to be explored. A systematic literature search was conducted on studies using genetic PD rodent models to investigate non-motor phenotypes; cognition, anxiety/depressive-like behaviour, gastrointestinal (GI) function, olfaction, circadian rhythm, cardiovascular and urinary function. In total, 51 genetic models of PD across 150 studies were identified. We found outcomes of most phenotypes were inconclusive due to inadequate studies, assessment at different ages, or variation in experimental and environmental factors. GI dysfunction was the most reproducible phenotype across all genetic rodent models. The mouse model harbouring mutant A53T, and the wild-type hα-syn overexpression (OE) model recapitulated the majority of phenotypes, albeit did not reliably produce concurrent motor deficits and nigral cell loss. Furthermore, animal models displayed different phenotypic profiles, reflecting the distinct genetic risk factors and heterogeneity of disease mechanisms. Currently, the inconsistent phenotypes within rodent models pose a challenge in the translatability and usefulness for further biomechanistic investigations. This review highlights opportunities to improve phenotype reproducibility with an emphasis on phenotypic assay choice and robust experimental design.

Animal models of Parkinson's disease: a guide to selecting the optimal model for your research

Parkinson's disease (PD) is a complex, multisystem disorder characterised by α-synuclein (SNCA) pathology, degeneration of nigrostriatal dopaminergic neurons, multifactorial pathogenetic mechanisms and expression of a plethora of motor and non-motor symptoms. Animal models of PD have already been instructive in helping us unravel some of these aspects. However, much remains to be discovered, requiring continued interrogation by the research community. In contrast with the situation for many neurological disorders, PD benefits from of a wide range of available animal models (pharmacological, toxin, genetic and α-synuclein) but this makes selection of the optimal one for a given study difficult. This is especially so when a study demands a model that displays a specific combination of features. While many excellent reviews of animal models already exist, this review takes a different approach with the intention of more readily informing this decision-making process. We have considered each feature of PD in turn - aetiology, pathology, pathogenesis, motor dysfunctions and non-motor symptoms (NMS) - highlighting those animal models that replicate each. By compiling easily accessible tables and a summary figure, we aim to provide the reader with a simple, go-to resource for selecting the optimal animal model of PD to suit their research needs.

Animal Model for Lower Urinary Tract Dysfunction in Parkinson's Disease

Although Parkinson's disease (PD) is characterized by the loss of dopaminergic neurons in the substantia nigra and subsequent motor symptoms, various non-motor symptoms often precede these other symptoms. While motor symptoms are certainly burdensome, a wide range of non-motor symptoms have emerged as the key determinant of the quality of life in PD patients. The prevalence of lower urinary tract symptoms differs according to the study, with ranges between 27% and 63.9%. These can be influenced by the stage of disease, the presence of lower urinary tract-related comorbidities, and parallels with other manifestations of autonomic dysfunction. Animal models can provide a platform for investigating the mechanisms of PD-related dysfunction and for the assessment of novel treatment strategies. Animal research efforts have been primarily focused on PD motor signs and symptoms. However, the etiology of lower urinary tract dysfunction in PD has yet to be definitively clarified. Several animal PD models are available, each of which has a different effect on the autonomic nervous system. In this article, we review the various lower urinary tract dysfunction animal PD models. We additionally discuss techniques for determining the appropriate model for evaluating the development of lower urinary tract dysfunction treatments.

Propagation of Pathological α-Synuclein from the Urogenital Tract to the Brain Initiates MSA-like Syndrome

The neuropathological feature of multiple system atrophy (MSA), a fatal adult-onset disorder without effective therapy, is the accumulation of pathological α-synuclein (α-Syn) in the central nervous system (CNS). Here we show that pathological α-Syn exists in nerve terminals in detrusor and external urethral sphincter (EUS) of patients with MSA. Furthermore, α-Syn-preformed fibrils (PFFs) injected in the EUS or detrusor in TgM83^+/− mice initiated the transmission of pathological α-Syn from the urogenital tract to brain via micturition reflex pathways, and these mice developed widespread phosphorylated α-Syn inclusion pathology together with phenotypes. In addition, urinary dysfunction and denervation-reinnervation of external anal sphincter were detected earlier in the mouse models with α-Syn PFFs inoculation before the behavioral manifestations. These results suggest that pathological α-Syn spreading through the micturition reflex pathways retrogradely from the urogenital tract to CNS may lead to urinary dysfunction in patients with MSA, which is different from the etiology of idiopathic Parkinson disease.

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Pathological α-Syn exhibits in nerve terminals in DET and EUS of patients with MSA

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Propagation of pathological α-Syn from urinary tract to CNS causes MSA-like syndrome

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The mouse models show urinary dysfunction and abnormal EAS EMG before motor deficits

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Lower urinary tract injection of α-Syn PFFs induces autonomic and motor dysfunctions

Autonomic ganglionic injection of α-synuclein fibrils as a model of pure autonomic failure α-synucleinopathy

α-Synucleinopathies are characterized by autonomic dysfunction and motor impairments. In the pure autonomic failure (PAF), α-synuclein (α-Syn) pathology is confined within the autonomic nervous system with no motor features, but mouse models recapitulating PAF without motor dysfunction are lacking. Here, we show that in TgM83+/- mice, inoculation of α-Syn preformed fibrils (PFFs) into the stellate and celiac ganglia induces spreading of α-Syn pathology only through the autonomic pathway to both the central nervous system (CNS) and the autonomic innervation of peripheral organs bidirectionally. In parallel, the mice develop autonomic dysfunction, featured by orthostatic hypotension, constipation, hypohidrosis and hyposmia, without motor dysfunction. Thus, we have generated a mouse model of pure autonomic dysfunction caused by α-Syn pathology. This model may help define the mechanistic link between transmission of pathological α-Syn and the cardinal features of autonomic dysfunction in α-synucleinopathy.

Urodynamic Mechanisms Underlying Overactive Bladder Symptoms in Patients With Parkinson Disease

PURPOSE

To assess the urodynamic findings in patients with Parkinson disease (PD) with overactive bladder symptoms.

METHODS

We performed a retrospective chart review of all PD patients who were seen in an outpatient clinic for lower urinary tract symptoms (LUTS) between 2010 and 2017 in a single-institution. Only patients who complained of overactive bladder (OAB) symptoms and underwent a video-urodynamic study for these symptoms were included. We excluded patients with neurological disorders other than PD and patients with voiding LUTS but without OAB symptoms.

RESULTS

We included 42 patients (29 men, 13 women, 74.5±8.1 years old). Seven patients (16.7%) had a postvoid residual (PVR) bladder volume >100 mL and only one reported incomplete bladder emptying. Detrusor overactivity (DO) was found in all 42 patients (100%) and was terminal in 19 (45.2%) and phasic in 22 patients (52.4%). Eighteen patients had detrusor underactivity (DU) (42.3%). Later age of PD diagnosis was the only parameter associated with DU (P=0.02). Patients with bladder outlet obstruction (BOO) were younger than patients without BOO (70.1 years vs. 76.5 years, P=0.004), had later first sensation of bladder filling (173.5 mL vs. 120.3 mL, P=0.02) and first involuntary detrusor contraction (226.4 mL vs. 130.4 mL, P=0.009).

CONCLUSION

DO is almost universal in all patients with PD complaining of OAB symptoms (97.1%). However, a significant percentage of patients also had BOO (36.8%), DU (47%), and increased PVR (16.7%) indicating that neurogenic DO may not be the only cause of OAB symptoms in PD patients.

Sensory neuropathy and nociception in rodent models of Parkinson's disease

Parkinson's disease (PD) often manifests with prodromal pain and sensory losses whose etiologies are not well understood. Multiple genetic and toxicity-based rodent models of PD partly recapitulate the histopathology and motor function deficits. Although far less studied, there is some evidence that rodents, similar to humans, develop sensory manifestations of the disease, which may precede motor disturbances and help to elucidate the underlying mechanisms of PD-associated pain at the molecular and neuron circuit levels. The present Review summarizes nociception and other sensory functions in frequently used rodent PD models within the context of the complex phenotypes. In terms of mechanisms, it appears that the acute loss of dopaminergic neurons in systemic toxicity models (MPTP, rotenone) primarily causes nociceptive hyperexcitability, presumably owing to a loss of inhibitory control, whereas genetic models primarily result in a progressive loss of heat perception, reflecting sensory fiber neuropathies. At the molecular level, neither α-synuclein deposits alone nor failure of mitophagy alone appear to be strong enough to result in axonal or synaptic pathology of nociceptive neurons that manifest at the behavioral level, and peripheral sensory loss may mask central ‘pain’ in behavioral tests. Hence, allostatic combinations or additional challenges and novel behavioral assessments are needed to better evaluate PD-associated sensory neuropathies and pain in rodents.

Summary: Rodent models of Parkinson's disease partially develop prodromal somatosensory and olfactory dysfunctions reminiscent of sensory neuropathies in patients and reveal mechanistic insight, but data are incomplete and fragmented.

FTY720 Improves Behavior, Increases Brain Derived Neurotrophic Factor Levels and Reduces α-Synuclein Pathology in Parkinsonian GM2+/- Mice

Parkinson's disease (PD) is a progressive aging disorder that affects millions worldwide, thus, disease-modifying-therapies are urgently needed. PD pathology includes α-synuclein (aSyn) accumulation as synucleinopathy. Loss of GM1 gangliosides occurs in PD brain, which is modeled in GM2 synthase transgenic mice. GM2+/- mice have low, not absent GM1 and develop age-onset motor deficits, making them an excellent PD drug testing model. FTY720 (fingolimod) reduces synucleinopathy in A53T aSyn mice and motor dysfunction in 6-OHDA and rotenone PD models, but no one has tested FTY720 in mice that develop age-onset PD-like motor problems. We confirmed that GM2+/-mice had equivalent rotarod, hindlimb reflexes, and adhesive removal functions at 9 mo. From 11 mo, GM2+/- mice received oral FTY720 or vehicle 3x/week to 16 mo. As bladder problems occur in PD, we also assessed GM2+/- bladder function. This allowed us to demonstrate improved motor and bladder function in GM2+/- mice treated with FTY720. By immunoblot, FTY720 reduced levels of proNGF, a biomarker of bladder dysfunction. In humans with PD, arm swing becomes abnormal, and brachial plexus modulates arm swing. Ultrastructure of brachial plexus in wild type and GM2 transgenic mice confirmed abnormal myelination and axons in GM2 transgenics. FTY720 treated GM2+/- brachial plexus sustained myelin associated protein levels and reduced aggregated aSyn and PSer129 aSyn levels. FTY720 increases brain derived neurotrophic factor (BDNF) and we noted increased BDNF in GM2+/- brachial plexus and cerebellum, which contribute to rotarod performance. These findings provide further support for testing low dose FTY720 in patients with PD.

Autonomic dysfunction in Parkinson disease and animal models

Parkinson disease has traditionally been classified as a movement disorder, despite patients' accounts of diverse symptoms stemming from impairments in numerous body systems. Today, Parkinson disease is increasingly recognized by clinicians and scientists as a complex neurodegenerative disorder featuring both motor and nonmotor manifestations concomitant with pathology throughout all major branches of the nervous system. Dysfunction of the autonomic nervous system, or dysautonomia, is a common feature of Parkinson disease. It produces signs and symptoms that severely affect patients' quality of life, such as blood pressure dysregulation, hyperhidrosis, and constipation. Treatment options for dysautonomia are limited to symptom alleviation because the cause of these symptoms and Parkinson disease overall are still unknown. Animal models provide a platform to interrogate mechanisms of Parkinson disease-related autonomic nervous system dysfunction and test novel treatment strategies. Several animal models of Parkinson disease are available, each with different effects on the autonomic nervous system. This review critically analyses key dysautonomia signs and symptoms and associated pathology in Parkinson disease patients and relevant findings in animal models. We focus on the cardiovascular system, adrenal medulla, skin/thermoregulation, bladder, pupils, and gastrointestinal tract, to assess the contribution of animal models to the understanding of Parkinson disease autonomic dysfunction.

Parkinsonian GM2 synthase knockout mice lacking mature gangliosides develop urinary dysfunction and neurogenic bladder

Parkinson's disease is a neurodegenerative disorder that reduces a patients' quality of life by the relentless progression of motor and non-motor symptoms. Among the non-motor symptoms is a condition called neurogenic bladder that is associated with detrusor muscle underactivity or overactivity occurring from neurologic damage. In Parkinson's disease, Lewy-body-like protein aggregation inside neurons typically contributes to pathology. This is associated with dopaminergic neuron loss in substantia nigra pars compacta (SNc) and in ventral tegmental area (VTA), both of which play a role in micturition. GM1 gangliosides are mature glycosphingolipids that enhance normal myelination and are reduced in Parkinson's brain. To explore the role of mature gangliosides in vivo, we obtained GM2 Synthase knockout (KO) mice, which develop parkinsonian pathology including a loss of SNc dopaminergic neurons, which we reconfirmed. However, bladder function and innervation have never been assessed in this model. We compared GM2 Synthase KO and wild type (WT) littermates' urination patterns from 9 to 19 months of age by counting small and large void spots produced during 1 h tests. Because male and female mice had different patterns, we evaluated data by sex and genotype. Small void spots were significantly increased in 12-16 month GM2 Synthase KO females, consistent with overactive bladder. Similarly, at 9-12 month GM2 KO males tended to have more small void spots than WT males. As GM2 Synthase KO mice aged, both females and males had fewer small and large void spots, consistent with detrusor muscle underactivity. Ultrasounds confirmed bladder enlargement in GM2 Synthase KO mice compared to WT mice. Tyrosine hydroxylase (TH) immunohistochemistry revealed significant dopaminergic loss in GM2 Synthase KO VTA and SNc, and a trend toward TH loss in the GM2 KO periaqueductal gray (PAG) micturition centers. Levels of the nerve growth factor precursor, proNGF, were significantly increased in GM2 Synthase KO bladders and transmission electron micrographs showed atypical myelination of pelvic ganglion innervation in GM2 Synthase KO bladders. Cumulatively, our findings provide the first evidence that mature ganglioside loss affects micturition center TH neurons as well as proNGF dysregulation and abnormal innervation of the bladder. Thus, identifying therapies that will counteract these effects should be beneficial for those suffering from Parkinson's disease and related disorders.

PACAP/Receptor System in Urinary Bladder Dysfunction and Pelvic Pain Following Urinary Bladder Inflammation or Stress

Complex organization of CNS and PNS pathways is necessary for the coordinated and reciprocal functions of the urinary bladder, urethra and urethral sphincters. Injury, inflammation, psychogenic stress or diseases that affect these nerve pathways and target organs can produce lower urinary tract (LUT) dysfunction. Numerous neuropeptide/receptor systems are expressed in the neural pathways of the LUT and non-neural components of the LUT (e.g., urothelium) also express peptides. One such neuropeptide receptor system, pituitary adenylate cyclase-activating polypeptide (PACAP; Adcyap1) and its cognate receptor, PAC1 (Adcyap1r1), have tissue-specific distributions in the LUT. Mice with a genetic deletion of PACAP exhibit bladder dysfunction and altered somatic sensation. PACAP and associated receptors are expressed in the LUT and exhibit neuroplastic changes with neural injury, inflammation, and diseases of the LUT as well as psychogenic stress. Blockade of the PACAP/PAC1 receptor system reduces voiding frequency in preclinical animal models and transgenic mouse models that mirror some clinical symptoms of bladder dysfunction. A change in the balance of the expression and resulting function of the PACAP/receptor system in CNS and PNS bladder reflex pathways may underlie LUT dysfunction including symptoms of urinary urgency, increased voiding frequency, and visceral pain. The PACAP/receptor system in micturition pathways may represent a potential target for therapeutic intervention to reduce LUT dysfunction.

Knockdown of α-synuclein in cerebral cortex improves neural behavior associated with apoptotic inhibition and neurotrophin expression in spinal cord transected rats

Spinal cord injury (SCI) often causes severe functional impairment with poor recovery. The treatment, however, is far from satisfaction, and the mechanisms remain unclear. By using proteomics and western blot, we found spinal cord transection (SCT) resulted in a significant down-regulation of α-synuclein (SNCA) in the motor cortex of SCT rats at 3 days post-operation. In order to detect the role of SNCA, we used SNCA-ORF/shRNA lentivirus to upregulate or knockdown SNCA expression. In vivo, SNCA-shRNA lentivirus injection into the cerebral cortex motor area not only inhibited SNCA expression, but also significantly enhanced neurons' survival, and attenuated neuronal apoptosis, as well as promoted motor and sensory function recovery in hind limbs. While, overexpression SNCA exhibited the opposite effects. In vitro, cortical neurons transfected with SNCA-shRNA lentivirus gave rise to an optimal neuronal survival and neurite outgrowth, while it was accompanied by reverse efficiency in SNCA-ORF group. In molecular level, SNCA silence induced the upregulation of Bcl-2 and the downregulation of Bax, and the expression of NGF, BDNF and NT3 was substantially upregulated in cortical neurons. Together, endogenous SNCA play a crucial role in motor and sensory function regulation, in which, the underlying mechanism may be linked to the regulation of apoptosis associated with apoptotic gene (Bax, Bcl2) and neurotrophic factors expression (NGF, BDNF and NT3). These finds provide novel insights to understand the role of SNCA in cerebral cortex after SCT, and it may be as a novel treatment target for SCI repair in future clinic trials.

Investigation of Urination Disorder in Parkinson's disease

BACKGROUND

Urination disorders are common in Parkinson's disease (PD) and respond poorly to medication. This study aimed to analyze the risk factors for urination disorders in PD.

METHODS

Ninety-one patients with PD (aged 34-83 years old) were recruited. Patients were assessed with the Unified PD Rating Scale (UPDRS), Hoehn and Yahr stage, Pittsburgh Sleep Quality Index (PSQI), Hamilton Depression Rating Scale (HAMD), and Hamilton Anxiety Scale (HAMA). Micturition number was recorded, and Type B ultrasound was used to evaluate residual urine. Statistics was performed using binary logistic regression, bivariate correlations, and Chi-square and t-tests.

RESULTS

Of 91 patients, urinary dysfunction occurred in 55.0%. Among these, 49.5% suffered with nocturia, 47.3% with pollakiuria. Nocturia number had a positive linear relationship with HAMA score (odds ratio [OR] = 0.340, P = 0.001), HAMD score (OR = 0.323, P = 0.002), duration of L-dopa medication (OR = 0.328, P = 0.001), dose of L-dopa (OR = 0.273, P = 0.009), UPDRS-II (OR = 0.402, P = 0.000), UPDRS-III score (OR = 0.291, P = 0.005), and PSQI score (OR = 0.249, P = 0.017). Micturition number over 24 h was positively associated with HAMA (OR = 0.303, P = 0.004) and UPDRS-II scores (OR = 0.306, P = 0.003). Of patients with residual urine, 79.3% had a volume of residual urine <50 ml. Residual urine was present in 44.4% of the patients with nocturia, 46.5% of the patients with pollakiuria, and 80.0% of the patients with dysuria. More men than women had residual urine (35.2% male vs. 13.3% female; P = 0.002).

CONCLUSIONS

Nocturia and pollakiuria were common micturition symptoms in our participants with PD. Nocturia was associated with depression, anxiety, sleep problems, and severity of PD. Pollakiuria was associated with anxiety and severity of PD. Male patients were more prone to residual urine and pollakiuria.

Bladder dysfunction in a transgenic mouse model of multiple system atrophy

Multiple system atrophy (MSA) is an adult-onset neurodegenerative disorder presenting with motor impairment and autonomic dysfunction. Urological function is altered in the majority of MSA patients, and urological symptoms often precede the motor syndrome. To date, bladder function and structure have never been investigated in MSA models. We aimed to test bladder function in a transgenic MSA mouse featuring oligodendroglial α-synucleinopathy and define its applicability as a preclinical model to study urological failure in MSA. Experiments were performed in proteolipid protein (PLP)-human α-synuclein (hαSyn) transgenic and control wild-type mice. Diuresis, urodynamics, and detrusor strip contractility were assessed to characterize the urological phenotype. Bladder morphology and neuropathology of the lumbosacral intermediolateral column and the pontine micturition center (PMC) were analyzed in young and aged mice. Urodynamic analysis revealed a less efficient and unstable bladder in MSA mice with increased voiding contraction amplitude, higher frequency of nonvoiding contractions, and increased postvoid residual volume. MSA mice bladder walls showed early detrusor hypertrophy and age-related urothelium hypertrophy. Transgenic hαSyn expression was detected in Schwann cells ensheathing the local nerve fibers in the lamina propria and muscularis of MSA bladders. Early loss of parasympathetic outflow neurons and delayed degeneration of the PMC accompanied the urological deficits in MSA mice. PLP-hαSyn mice recapitulate major urological symptoms of human MSA that may be linked to αSyn-related central and peripheral neuropathology and can be further used as a preclinical model to decipher pathomechanisms of MSA.

Parkinson's disease

Parkinson's disease (PD) is the most common age-related motoric neurodegenerative disease initially described in the 1800's by James Parkinson as the 'Shaking Palsy'. Loss of the neurotransmitter dopamine was recognized as underlying the pathophysiology of the motor dysfunction; subsequently discovery of dopamine replacement therapies brought substantial symptomatic benefit to PD patients. However, these therapies do not fully treat the clinical syndrome nor do they alter the natural history of this disorder motivating clinicians and researchers to further investigate the clinical phenotype, pathophysiology/pathobiology and etiology of this devastating disease. Although the exact cause of sporadic PD remains enigmatic studies of familial and rare toxicant forms of this disorder have laid the foundation for genome wide explorations and environmental studies. The combination of methodical clinical evaluation, systematic pathological studies and detailed genetic analyses have revealed that PD is a multifaceted disorder with a wide-range of clinical symptoms and pathology that include regions outside the dopamine system. One common thread in PD is the presence of intracytoplasmic inclusions that contain the protein, α-synuclein. The presence of toxic aggregated forms of α-synuclein (e.g., amyloid structures) are purported to be a harbinger of subsequent pathology. In fact, PD is both a cerebral amyloid disease and the most common synucleinopathy, that is, diseases that display accumulations of α-synuclein. Here we present our current understanding of PD etiology, pathology, clinical symptoms and therapeutic approaches with an emphasis on misfolded α-synuclein.