Single-dose Levodopa Administration and Aging Independently Disrupt Time Production

We tested the hypothesis that age-related time production deficits are dopamine-mediated. The experiment was conducted double-blind, and with random assignment of 32 healthy aged and 32 healthy young participants to either inert placebo or levodopa (200 mg) groups. The procedure included training participants to produce two target time intervals (6 and 17 sec) in separate blocks, drug/placebo administration, a 1-hr delay, and then delayed free-recall time production retesting without feedback. Participants also performed a speeded choice reaction time (RT) task, as a control for potential dopaminergic and aging effects on attention and psychomotor speed. Results indicate that during retesting, aged participants show duration-dependent timing errors that are larger than those shown by the young participants. Levodopa administration yielded lengthened time production of both target intervals. The aging and levodopa effects did not interact. Also, aging slowed RT and increased RT variability, but levodopa had no effect on the RT. These results suggest that at this dosage and under these specific conditions, timing is dopamine-mediated but the effect of aging on time production is not. Moreover, the levodopa timing effect cannot be attributed to the effects of dopaminergic function on psychomotor speed

The role of manganese dysregulation in neurological disease: emerging evidence

Manganese is an essential trace metal. The dysregulation of manganese seen in a broad spectrum of neurological disorders reflects its importance in brain development and key neurophysiological processes. Historically, the observation of acquired manganism in miners and people who misuse drugs provided early evidence of brain toxicity related to manganese exposure. The identification of inherited manganese transportopathies, which cause neurodevelopmental and neurodegenerative syndromes, further corroborates the neurotoxic potential of this element. Moreover, manganese dyshomoeostasis is also implicated in Parkinson's disease and other neurodegenerative conditions, such as Alzheimer's disease and Huntington's disease. Ongoing and future research will facilitate the development of better targeted therapeutical strategies than are currently available for manganese-associated neurological disorders

New Insights into Molecular Mechanisms Underlying Neurodegenerative Disorders

Neurodegenerative disorders encompass a broad range of sporadic and/or familial debilitating conditions characterized by the progressive dysfunction and loss of selective neuronal populations, determining different clinical phenotypes. Emerging research data indicate an interplay of genetic factors and epigenetic mechanisms underlying neurodegenerative processes, which lead to increased prevalence of neurodegenerative disorders. In concert with the constant increase in the aging population, neurodegenerative disorders currently represent a major challenge to public health worldwide. Despite recent advances in clinical and preclinical research, the pathogenesis of these disorders still remains poorly understood, without effective treatments being available to halt the neurodegenerative processes, but rather aiming at relieving symptoms. Therefore, a critical evaluation of current research data and in-depth understanding of the molecular mechanisms that lead to neurodegeneration are crucial in order to identify potential therapeutic targets that can pave the way to the development of novel and promising therapies. This Special Issue is focused on novel molecular data in the field of neurodegeneration that associate with the onset and progression of neurodegenerative diseases. We are particularly interested in original articles and reviews that provide new insights into the main molecular pathogenic mechanisms underlying neurodegenerative disorders, aiming to identify potential biomarkers and novel therapeutic strategies

In vivo assessment of non-dopaminergic systems in Parkinson’s disease with Positron Emission Tomography

Parkinson's disease (PD) is characterized by a progressive loss of nigrostriatal dopaminergic neurons. Non-dopaminergic neurotransmission is also impaired. Intraneuronal Lewy bodies, the pathological hallmark of PD, have been observed in serotoninergic, noradrenergic, and cholinergic neurons. Dysfunction of these systems could play a role in the occurrence of non-motor symptoms including fatigue. However, the extent of non-dopaminergic degeneration in PD, rates of its progression, and its contribution to the development of non-motor symptoms is unclear. First, I used 18F-dopa Positron Emission Tomography (PET), a marker of monoaminergic terminal function, to assess the involvement of dopaminergic, noradrenergic, and serotoninergic pathways in PD and in parkin-linked parkinsonism, a genetic form of PD. I found that parkin patients and PD patients have distinct patterns of monoaminergic involvement, with more widespread dysfunction in PD. In a second study, I used serial 18F-dopa PET to assess longitudinal changes in tracer uptake in brain monoaminergic structures over a 3-year period in a group of PD patients. I also assessed the relationship between striatal function decline and dysfunction in extra-striatal areas in the same patients. I found that the degeneration in extrastriatal monoaminergic structures in PD occurs independently from nigrostriatal degeneration and at a slower rate. Brain compensatory mechanisms disappear within the first years of disease. I then used 18F-dopa and 11C-DASB PET to investigate whether fatigue in PD is associated with dysfunction of dopaminergic/serotoninergic innervation. I found that PD patients with fatigue show severe loss of serotoninergic innervation in basal ganglia and limbic areas. Finally, I assessed the relationship between 18F-dopa uptake and measurements of serotonin transporter availability by 11C-DASB PET within brain serotoninergic structures and I provided evidence for the hypothesis that 18F-dopa PET can be used to evaluate the distribution and the function of serotoninergic systems in the brain of PD patients

Emerging Perspectives on Gene Therapy Delivery for Neurodegenerative and Neuromuscular Disorders.

Neurodegenerative disorders (NDDs), such as Alzheimer's disease (AD) and Parkinson's Disease (PD), are a group of heterogeneous diseases that mainly affect central nervous system (CNS) functions. A subset of NDDs exhibit CNS dysfunction and muscle degeneration, as observed in Gangliosidosis 1 (GM1) and late stages of PD. Neuromuscular disorders (NMDs) are a group of diseases in which patients show primary progressive muscle weaknesses, including Duchenne Muscular Dystrophy (DMD), Pompe disease, and Spinal Muscular Atrophy (SMA). NDDs and NMDs typically have a genetic component, which affects the physiological functioning of critical cellular processes, leading to pathogenesis. Currently, there is no cure or efficient treatment for most of these diseases. More than 200 clinical trials have been completed or are currently underway in order to establish safety, tolerability, and efficacy of promising gene therapy approaches. Thus, gene therapy-based therapeutics, including viral or non-viral delivery, are very appealing for the treatment of NDDs and NMDs. In particular, adeno-associated viral vectors (AAV) are an attractive option for gene therapy for NDDs and NMDs. However, limitations have been identified after systemic delivery, including the suboptimal capacity of these therapies to traverse the blood-brain barrier (BBB), degradation of the particles during the delivery, high reactivity of the patient's immune system during the treatment, and the potential need for redosing. To circumvent these limitations, several preclinical and clinical studies have suggested intrathecal (IT) delivery to target the CNS and peripheral organs via cerebrospinal fluid (CSF). CSF administration can vastly improve the delivery of small molecules and drugs to the brain and spinal cord as compared to systemic delivery. Here, we review AAV biology and vector design elements, different therapeutic routes of administration, and highlight CSF delivery as an attractive route of administration. We discuss the different aspects of neuromuscular and neurodegenerative diseases, such as pathogenesis, the landscape of mutations, and the biological processes associated with the disease. We also describe the hallmarks of NDDs and NMDs as well as discuss current therapeutic approaches and clinical progress in viral and non-viral gene therapy and enzyme replacement strategies for those diseases

UN MODELO EN RATA FRL DETERIORO COGNITIVO EN LA ENFERMEDAD DE PARKINSON

Aunque el mal de Parkinson (DP) es considerado clásicamente como undesorden del sistema motor, pueden observarse ligeros deterioros cognitivosaun en las fases iniciales del DP. En este artículo revisamos estudios conductualesy neuroquímicos sobre alteraciones cognitivas observadas en ratastratadas con infusiones intranigrales de la neurotoxina MPTP. El papel críticode la liberación de dopamina en el estriado dorsal y su modulación por losreceptores de adenosina también es revisada como una estrategia potencialpara tratar los deterioros cognitivos en pacientes con desorden de Parkinson(PD) que no mejoran con la terapia de levo dopa. Resultados: La mayoríade de los daños presentados en ratas con infusiones intranigrales de MPTPson similares a los observados en las primeras fases de PD, una pérdidamoderada de neuronas nigrales dopaminérgicas (40-70%) que causa défi -cits sensoriales y motores y poco deterioro motor. Estos animales tambiénmodelan los défi cits de memoria de trabajo y aprendizaje de hábitos, con lamemoria de largo plazo espacial (episódica) mayormente preservada comose observa en los pacientes sin DP. La infusión intranigral de MPTP en ratasa llevado al desarrollo de modelos útiles, ya que no presentan un deterioromotor excesivo que podría de otra manera comprometer la interpretación dede la ejecución de los animales en tareas cognitivas

Regulation of Parkin Protein Levels by L-3,4-dihydroxyphenylalanine

Parkinson's disease (PD) is a debilitating neurodegenerative disorder, affecting roughly 2% of those over the age of 80. Though most cases of PD are "sporadic", arising without a family history, a minority of cases have a clear autosomal dominant or recessive inheritance pattern. The most common known cause of autosomal recessive PD is homozygous inactivation of PARK2, which codes for the E3 ubiquitin ligase parkin. In addition, there is evidence that parkin inactivation may play a role in the pathogenesis of sporadic PD as well. As such, strategies aimed at increasing parkin activity hold therapeutic promise for sporadic PD. Though much work has examined the functions of parkin, and, more recently, the mechanisms by which it is activated, substantially less is known about how parkin levels are regulated in the cell. This is particularly true for activated parkin. Understanding these regulatory mechanisms is critical for the effective development of therapeutic strategies based on upregulation of parkin activity. The work presented in this dissertation provides new insights into these regulatory mechanisms. We show that relatively high doses of the dopamine precursor L-3,4-dihydroxyphenylalanine (L-DOPA) decrease parkin protein levels in vitro, analogously to previous findings using other cellular stressors. Characterizing this effect, we show that L-DOPA increases parkin degradation and that this occurs independently of L-DOPA's conversion to dopamine and of L-DOPA-induced cell death. Furthermore, we define two distinct pathways by which L-DOPA decreases parkin: an oxidative stress-dependent pathway and an oxidative stress-independent pathway. We show that the former overlaps with the previously defined mechanism of PINK1-mediated parkin activation. Specifically, parkin's association with PINK1-generated phosphorylated ubiquitin (phospho-Ub) leads to its proteasomal degradation downstream of oxidative stress, but not via autoubiquitination. Despite the involvement of PINK1 in parkin loss from L-DOPA treatment, we do not observe evidence of mitochondrial parkin activity after L-DOPA treatment, indicating that, surprisingly, parkin loss does not depend on this activity. Additionally, we provide evidence against the involvement of Trib3 and NADPH oxidases in parkin loss from L-DOPA. Finally, we provide preliminary evidence that parkin knockdown does not sensitize cells to L-DOPA-induced death. Taken together, the findings in this dissertation contribute to the understanding of parkin regulation. Our observation that parkin's association with phospho-Ub leads to its degradation following L-DOPA treatment is of particular interest because it may represent the steady-state mechanism by which levels of activated parkin are kept in check. In light of this, an attractive therapeutic strategy may involve uncoupling parkin's activation by phospho-Ub from its phospho-Ub-dependent degradation

Dopamine and oculomotor impulsivity in health and disease.

The role of subcortical pathology in altered cognition is increasingly recognised. However, measurement and monitoring of impairments in motivation and behaviour due to subcortical disease is challenging. Basal ganglia – cortico-thalamo-cortical loops and the neurotransmitter, dopamine, are recognised to be important in modulating both reward learning and oculomotor performance. This thesis considers the use of novel and adapted oculomotor (saccadic) tasks as a means of interrogating these dynamic circuits as measures of rewarded decision-making under risk and time pressure. I first describe a novel rewarded oculomotor task, the Traffic Light Task, which provokes two distributions of saccades – one anticipatory, and one reactive. The balance of these distributions, the number of errors and the reward obtained are used to index oculomotor decision-making. Demonstrated effects of healthy aging include a significant reduction in anticipatory responding and consequent reduction in reward. I then compare behavioural oculomotor task responses in healthy controls with established “self-report” measures of impulsivity, finding significant correlations. Next, I consider a patient with focal lesions of the basal ganglia causing profound apathy. I demonstrate reduced oculomotor anticipatory responding and reward sensitivity. I then show the positive effects of dopaminergic medications (levodopa and ropinirole) upon his oculomotor decision-making in tandem with a clinical improvement in his motivational state. To further qualify this dopaminergic effect, I then assess the effects of two dopaminergic drugs (levodopa and methylphenidate) upon healthy volunteers. Finally, I use oculomotor tasks to compare patients with Parkinson’s Disease, with and without impulse control disorders, with both healthy volunteers and pathological gamblers without neurological disease. The results of these experiments raise questions regarding the development of models of basal ganglia – cortico-thalamo-cortical loops and how best to understand them

The role of the gut and the gastrointestinal microbiome in Parkinson’s disease

INTRODUCTION: Parkinson’s disease (PD) is a disabling and progressive neurodegenerative disorder that is increasing in prevalence with the aging and urbanisation of the global population. The mechanisms underlying PD pathogenesis and progression are incompletely understood. Improved clinical recognition of early and prodromal non-motor symptoms (NMS), namely gastrointestinal (GI) dysfunction, has focused research over the last two decades on the roles of the gut. More recently, the influences of the microbiota-gut-brain-axis (MGBA) in the development and progression of PD have become an intensive area of research. Studies have demonstrated an association between the GM and a variety of PD-related characteristics, identifying important impacts on levodopa metabolism by certain microbiota. Importantly, the effect of device-assisted therapies (DATs) on the GM and the robustness of microbiota compositional differences between PD patients and household controls (HCs) has not been well defined. The aims of this thesis were to 1) investigate GI dysfunction and nutritional patterns in PD, 2) determine if the GM is a biomarker of PD, and 3) investigate the temporal stability of the GM in PD patients receiving standard therapies and those initiating DATs. METHODS: 103 PD patients and 81 HCs were recruited and participants with PD were considered in two sub-cohorts; 1) PD patients initiating DAT; either Deep Brain Stimulation (DBS) (n=10), or levodopa-carbidopa intestinal gel (LCIG) (n=11), who had GM sampling from stool at -2, 0, 2 and 4 weeks around initiation of DAT and baseline, 6 and 12 months following DAT initiation, 2) 82 PD patients receiving standard PD therapies, who had GM sampling from stool at baseline, 6 and 12 months. Validated PD questionnaire metadata ascertaining motor characteristics and NMS, as well as nutritional data in the form of a Food Frequency Questionnaire, were collected for all participants at baseline, 6 and 12 months. Total DNA was isolated from stool before sequencing the V3-V4 region of 16S rRNA. Relative bacterial abundances, diversity measures, compositional differences and clinical-microbiome associations were determined, as well as developing predictive modelling to identify PD patients and assess disease progression. RESULTS: PD patients reported more prevalent and severe GI dysfunction, especially constipation, which was almost three-times more common compared to HC subjects, (78.6% vs 28.4%, p<0.001). PD patients had a higher intake of total carbohydrates (279 g/day vs 232 g/day; p=0.034), which was largely attributable to an increased daily sugar intake (153 g/day vs 119 g/day; p=0.003), particularly of free sugars (61 g/day vs 41 g/day; p=0.001). Significant GM compositional differences across several taxonomic levels were apparent between PD patients and HCs and associated with a number of PD motor and NMS features, as well as certain therapies. Predictive models to distinguish PD from HCs were developed considering global GM profiles, achieving an area under the curve (AUC) of 0.71, which was improved by addition of data on carbohydrate intake (AUC 0.74). Longitudinal analysis demonstrated persistent underrepresentation of known short-chain fatty acid producing bacteria in PD patients, particularly those concerned with butyrate production; Butyricicoccus, Fusicatenibacter, Lachnospiraceae ND3007 group and Erysipelotrichaceae UCG−003. Taxa differences observed over the short-term (four week) sampling period around DAT (DBS and LCIG) initiation, were not sustained at 6 and 12 months. Despite this, persistent longer-term overrepresentation of Prevotella was observed after DBS initiation, and a trend was found that was suggestive of overrepresentation of Roseburia after LCIG initiation. These results suggest that there may be variable shorter and longer-term DBS and LCIG influences on the GM, which are complex and multifactorial. PD progression analysis did not identify distinct persisting GM compositional differences between faster and slower progressing patients, although predictive modelling was strengthened by the consideration of nutritional data, specifically protein intake, and improved the predictive capacity for PD progression. CONCLUSION: This thesis demonstrates that there are numerous clinically significant associations between the gut, GM and PD. GI dysfunction is common, and carbohydrate nutritional intake appears to be different from the general population in PD. Persistent alterations of GM composition in PD compared to HCs were found. These findings provide support for the existence of disturbances of gut homeostatic pathways, which may disrupt intestinal barrier permeability and lead to gut leakiness, in the pathogenesis of PD. This thesis also highlights the potential to use the GM in the identification of PD and the characterisation of disease progression

The Objective Measurement of Sleep-Wake Disturbance in Parkinson's Disease

Parkinson’s disease (PD) is an increasingly prevalent neurodegenerative disease affecting older adults. Motor symptoms, including tremor, rigidity and tremor were classically predominant. However, troublesome non-motor symptomatology are known to impair quality of life for patients with PD and there carers. Sleep-wake disturbances are gaining attention in PD encompassing disturbances of the circadian, homeostatic and ultradian sleep systems. These symptoms have been linked to the troublesome problems of cognitive deficits, mood disturbance and visual hallucinations. Mechanisms exploring the interaction of sleep-wake disturbance and other non-motor symptoms in PD are not well understood. Bidirectional causality between sleep-wake disturbance and concomitant symptoms in PD provide insights into common chemical and neural mechanisms which prior to the development of therapy, must be understood. Furthermore, sleep-wake disorders in PD at present provide a maker of early diagnosis for which future disease modifying treatment can be targeted. However objective and reliable measurement techniques are yet to be devised in this field. This thesis aims to utilise the objective measurement of sleep-wake disturbances across the circadian, homeostatic and ultradian sleep systems in PD through four empiric experiments to help inform our understanding of these critical symptoms. While the usefulness of self-report data is not doubted as a means of engaging the patient and hearing their voice they cannot serve the same identification and measurement uses of objective data. Given our ageing population, the need for diagnostic, predictive and sensitive monitoring biomarkers in Parkinson’s disease has never been greater. Objective, accurate and reliable measurement techniques, as demonstrated in this thesis, underpins further research in this field