Presynaptic mechanisms of motor fluctuations in Parkinson’s disease: a probabilistic model

The effect of peripheral enzyme inhibitors on levodopa concentrations in blood and CSF

Levodopa combined with a dopa-decarboxylase inhibitor, such as carbidopa, shifts the metabolism to the COMT pathway. Adding the peripheral acting COMT inhibitor entacapone provides improvement for patients with PD suffering from motor fluctuations. We studied the effects of the enzyme inhibitors entacapone and carbidopa on the levodopa concentrations in CSF and in blood. Five PD patients with wearing-off underwent lumbar drainage and intravenous microdialysis. Samples were taken 12 h daily for 3 days. Day 1; intravenous levodopa was given, day 2; additional oral entacapone 200 mg tid, day 3; additional oral entacapone 200 mg tid and carbidopa 25 mg bid. Levodopa in CSF and in dialysates was analysed. The AUC for levodopa increased both in blood and CSF when additional entacapone was given alone and in combination with carbidopa. The C(max) of levodopa in both CSF and blood increased significantly. Additional entacapone to levodopa therapy gives an increase of C(max) in CSF and in blood. The increase is more evident when entacapone is combined with carbidopa.

Homeostatic mechanisms in dopamine synthesis and release: a mathematical model

BACKGROUND

Dopamine is a catecholamine that is used as a neurotransmitter both in the periphery and in the central nervous system. Dysfunction in various dopaminergic systems is known to be associated with various disorders, including schizophrenia, Parkinson's disease, and Tourette's syndrome. Furthermore, microdialysis studies have shown that addictive drugs increase extracellular dopamine and brain imaging has shown a correlation between euphoria and psycho-stimulant-induced increases in extracellular dopamine 1. These consequences of dopamine dysfunction indicate the importance of maintaining dopamine functionality through homeostatic mechanisms that have been attributed to the delicate balance between synthesis, storage, release, metabolism, and reuptake.

METHODS

We construct a mathematical model of dopamine synthesis, release, and reuptake and use it to study homeostasis in single dopaminergic neuron terminals. We investigate the substrate inhibition of tyrosine hydroxylase by tyrosine, the consequences of the rapid uptake of extracellular dopamine by the dopamine transporters, and the effects of the autoreceoptors on dopaminergic function. The main focus is to understand the regulation and control of synthesis and release and to explicate and interpret experimental findings.

RESULTS

We show that the substrate inhibition of tyrosine hydroxylase by tyrosine stabilizes cytosolic and vesicular dopamine against changes in tyrosine availability due to meals. We find that the autoreceptors dampen the fluctuations in extracellular dopamine caused by changes in tyrosine hydroxylase expression and changes in the rate of firing. We show that short bursts of action potentials create significant dopamine signals against the background of tonic firing. We explain the observed time courses of extracellular dopamine responses to stimulation in wild type mice and mice that have genetically altered dopamine transporter densities and the observed half-lives of extracellular dopamine under various treatment protocols.

CONCLUSION

Dopaminergic systems must respond robustly to important biological signals such as bursts, while at the same time maintaining homeostasis in the face of normal biological fluctuations in inputs, expression levels, and firing rates. This is accomplished through the cooperative effect of many different homeostatic mechanisms including special properties of tyrosine hydroxylase, the dopamine transporters, and the dopamine autoreceptors.

The duration of the motor response to apomorphine boluses is conditioned by the length of a prior infusion in Parkinson's disease

"Pulsatile" administration of levodopa has been invocated a relevant factor for motor fluctuations in Parkinson's disease (PD). We studied dopaminergic sensitivity to apomorphine in 10 parkinsonian patients with motor fluctuations. Patients were tested as follows: the minimal effective dose of apomorphine (MED-1) was administered in the morning to induce an on response. Fifteen minutes after this motor response had disappeared, an apomorphine infusion was initiated and maintained to ensure on periods of three different durations on different days. Infusion lasted for approximately 30, 60 and 90 minutes. Subsequently, the infusion was stopped, and after 15 minutes in the off state, a second bolus of apomorphine (MED-2) was given. The mean infusion doses were 49.2 +/- 5.4, 108.4 +/- 10.3, and 150 +/- 8.2 mg. These elicited on periods of 48.2 +/- 4.1, 110 +/- 4.5, and 195 +/- 3.8 minutes. The MED-2 elicited on responses with a duration of 30 +/- 4.5, 18.4 +/- 3.2, and 11.2 +/- 4.1 minutes. The duration of the on response induced by the apomorphine infusions correlated inversely (P < 0.01) with the on induced by the MED-2 of apomorphine. Our findings indicate that a continuous dopaminergic stimulus may induce pharmacodynamic changes associated with tolerance in PD patients.

Dopamine transporter relation to levodopa-derived synaptic dopamine in a rat model of Parkinson's: an in vivo imaging study

Studies showed that the dopamine (DA) transporter (DAT) modulates changes in levodopa-derived synaptic dopamine levels (Delta(DA)) in Parkinson's disease (PD). Here we evaluate the relationship between DAT and Delta(DA) in the 6-hydroxydopamine model of Parkinson's disease to investigate these mechanisms as a function of dopaminergic denervation and in relation to other denervation-induced regulatory changes. 27 rats with a unilateral 6-hydroxydopamine lesion (denervation approximately 20-97%) were imaged with (11)C-dihydrotetrabenazine (VMAT2 marker), (11)C-methylphenidate (DAT marker) and (11)C-raclopride (D2-type receptor marker). For denervation <75%Delta(DA) was significantly correlated with a combination of relatively preserved terminal density and lower DAT. For denervation <90%, Delta(DA) was significantly negatively correlated with DAT with a weaker dependence on VMAT2. For the entire data set, no dependence on pre-synaptic markers was observed; Delta(DA) was significantly positively correlated with (11)C-raclopride binding-derived estimates of DA loss. These findings parallel observations in humans, and show that (i) regulatory changes attempt to normalize synaptic DA levels (ii) a lesion-induced functional dependence of Delta(DA) on DAT occurs up to approximately 90% denervation (iii) for denervation < 75% relative lower DAT levels may relate to effective compensation; for higher denervation, lower DAT levels likely contribute to oscillations in synaptic DA associated with dyskinesias.

Impact of grafted serotonin and dopamine neurons on development of L-DOPA-induced dyskinesias in parkinsonian rats is determined by the extent of dopamine neuron degeneration

Previous studies have shown that serotonin neurons play an important role in the induction and maintenance of L-DOPA-induced dyskinesia in animals with lesion of the nigrostriatal dopamine system. Patients with Parkinson's disease that receive transplants of foetal ventral mesencephalic tissue, the graft cell preparation is likely to contain, in addition to dopamine neurons, serotonin neurons that will vary in number depending on the landmarks used for dissection. Here, we have studied the impact of grafted serotonin neurons--alone or mixed with dopamine neurons--on the development of L-DOPA-induced dyskinesia in rats with a partial 6-hydroxydopamine lesion of the host nigrostriatal projection. In these rats, which showed only low-level dyskinesia at the time of transplantation, serotonin grafts induced a worsening in the severity of dyskinesia that developed during continued L-DOPA treatment, while the dopamine-rich graft had the opposite, dampening effect. The detrimental effect seen in animals with serotonin neuron grafts was dramatically increased when the residual dopamine innervation in the striatum was removed by a second 6-hydroxydopamine lesion. Interestingly, rats with grafts that contained a mixture of dopamine and serotonin neurons (in approximately 2:1) showed a marked reduction in L-DOPA-induced dyskinesia over time, and the appearance of severe dyskinesia induced by the removal of the residual dopamine innervation, seen in the animals with transplants of serotonin neurons alone, was blocked. FosB expression in the striatal projection neurons, which is associated with dyskinesias, was also normalized by the dopamine-rich grafts, but not by the serotonin neuron grafts. These data indicate that as long as a sufficient portion, some 10-20%, of the dopamine innervation still remains, the increased host serotonin innervation generated by the grafted serotonin neurons will have limited effect on the development or severity of L-DOPA-induced dyskinesias. At more advanced stages of the disease, when the dopamine innervation of the putamen is reduced below this critical threshold, grafted serotonin neurons are likely to aggravate l-DOPA-induced dyskinesia in those cases where the dopamine re-innervation derived from the grafted neurons is insufficient in magnitude or do not cover the critical dyskinesia-inducing sub-regions of the grafted putamen. We conclude that it is not the absolute number of serotonin neurons in the grafts, but the relative densities of dopamine and serotonin innervations in the grafted striatum that is the critical factor in determining the long-term effect of foetal tissue graft, beneficial or detrimental, on dyskinesia in grafted Parkinson's disease patients.

Involvement of the serotonin system in L-dopa-induced dyskinesias

The ability of L-dopa to relieve the motor impairments in Parkinson's disease patients declines over time, and side-effects, such as dyskinesias, appear--limiting the use of the drug in the advanced stage of the disease. Serotonergic neurons are able to convert L-dopa to dopamine and to store this neurotransmitter in synaptic vesicles. This peculiarity might be very important in the advanced disease, when most of the dopaminergic neurons have degenerated. Indeed, an increasing body of evidence points to dopamine released as a false neurotransmitter from the serotonin terminals as the main pre-synaptic determinant of L-dopa-induced dyskinesias in animal models of Parkinson's disease. These findings make the serotonin system an intriguing target for anti-dyskinetic therapies.

Motor complications in Parkinson disease: Clinical manifestations and management

Long-term dopaminomimetic therapy, not limited to levodopa, is complicated by the emergence of variations of motor response in a majority of Parkinson disease (PD) patients. These variations can occur in different forms, as early wearing off during the initial stage of motor complications, dyskinesias in the intermediate stage, and complex fluctuations in the advanced stage. Considered to be a major source of disability in advanced PD patients, recognition of these complications is critical in order to develop different strategies designed not only to treat these problems when they develop, but also to prevent troublesome complications associated with potential risk factors. In this article, authors classify a wide clinical spectrum of motor complications into different stages as the disease progresses through the treatment. A number of strategies are proposed in order to manage these complications as well as to avoid them. Better understanding of these potential complications will result in better management of these problems and lessen the disability associated with advanced PD.

Young onset Parkinson's disease. Practical management of medical issues

Young Onset Parkinson's disease (YOPD) is defined as Parkinson's disease diagnosed between the ages of 21 and 40 years. Problems faced by this group are different from those faced by older subjects because they face decades with the illness. This article reviews current literature and offers suggestions for intervention when appropriate and practical suggestions in the areas of drug treatment, rehabilitation, nutrition, sexuality, pregnancy, menstruation and menopause. The suggestions are not exclusively restricted to the management of YOPD, but emphasis is placed on items where people with YOPD have either had particular difficulties or where they can proactively self-manage their illness.

Norepinephrine loss produces more profound motor deficits than MPTP treatment in mice

Although Parkinson's disease (PD) is characterized primarily by loss of nigrostriatal dopaminergic neurons, there is a concomitant loss of norepinephrine (NE) neurons in the locus coeruleus. Dopaminergic lesions induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) are commonly used to model PD, and although MPTP effectively mimics the dopaminergic neuropathology of PD in mice, it fails to produce PD-like motor deficits. We hypothesized that MPTP is unable to recapitulate the motor abnormalities of PD either because the behavioral paradigms used to measure coordinated behavior in mice are not sensitive enough or because MPTP in the absence of NE loss is insufficient to impair motor control. We tested both possibilities by developing a battery of coordinated movement tests and examining motor deficits in dopamine beta-hydroxylase knockout (Dbh-/-) mice that lack NE altogether. We detected no motor abnormalities in MPTP-treated control mice, despite an 80% loss of striatal dopamine (DA) terminals. Dbh-/- mice, on the other hand, were impaired in most tests and also displayed spontaneous dyskinesias, despite their normal striatal DA content. A subset of these impairments was recapitulated in control mice with 80% NE lesions and reversed in Dbh-/- mice, either by restoration of NE or treatment with a DA agonist. MPTP did not exacerbate baseline motor deficits in Dbh-/- mice. Finally, striatal levels of phospho-ERK-1/2 and DeltaFosB/FosB, proteins which are associated with PD and dyskinesias, were elevated in Dbh-/- mice. These results suggest that loss of locus coeruleus neurons contributes to motor dysfunction in PD.

Blood pressure and heart rate in parkinsonian patients with and without wearing-off

Our study aimed to investigate the cardiovascular autonomic regulation related to the wearing-off phenomenon in Parkinson's disease (PD). We measured blood pressure (BP) and heart rate (HR) at rest and during orthostatic test in 16 patients with PD with wearing-off and in 15 patients with PD without wearing-off both before (baseline) and repetitively at 1-h intervals for up to 4 h after the morning PD medication dose. The patients with wearing-off had fluctuation of BP during the observation period, BP increasing when the motor performance worsened and vice versa. The mean supine BP was at its highest at the baseline measurement (patients with wearing-off, 145 +/- 18 mmHg; patients without wearing-off, 138 +/- 17 mmHg), fell during the first hour (patients with wearing-off, 119 +/- 17 mmHg; patients without wearing-off, 126 +/- 18 mmHg), and then rose again toward the end of the observation period (patients with wearing-off, 136 +/- 15 mmHg; patients without wearing-off, 138 +/- 18 mmHg). This BP change was statistically significant only in PD patients with wearing-off (P < 0.001). In conclusion, BP seems to fluctuate with motor impairment in PD patients with wearing-off. This fluctuation may represent autonomic dysfunction caused by the PD process itself, the effect of PD medication, or both.

Norepinephrine: The redheaded stepchild of Parkinson's disease

Parkinson's disease (PD) affects approximately 1% of the world's aging population. Despite its prevalence and rigorous research in both humans and animal models, the etiology remains unknown. PD is most often characterized by the degeneration of dopamine (DA) neurons in the substantia nigra pars compacta (SNc), and models of PD generally attempt to mimic this deficit. However, PD is a true multisystem disorder marked by a profound but less appreciated loss of cells in the locus coeruleus (LC), which contains the major group of noradrenergic neurons in the brain. Historic and more recent experiments exploring the role of norepinephrine (NE) in PD will be analyzed in this review. First, we examine the evidence that NE is neuroprotective and that LC degeneration sensitizes DA neurons to damage. The second part of this review focuses on the potential contribution of NE loss to the behavioral symptoms associated with PD. We propose that LC loss represents a crucial turning point in PD progression and that pharmacotherapies aimed at restoring NE have important therapeutic potential.

Dopamine transporter relation to dopamine turnover in Parkinson's disease: a positron emission tomography study

OBJECTIVE

To investigate the role of the dopamine transporter (DAT) in the regulation of synaptic dopamine (DA) levels in Parkinson's disease and its role in the preservation of DA in presynaptic terminals.

METHODS

Ten Parkinson's disease patients (age, 62.9 +/- 9.5 years; Unified Parkinson's Disease Rating Scale motor score in "off" state, 28.5 +/- 8.2) underwent positron emission tomography with (11)C-methylphenidate (MP, a DAT marker), (11)C-dihydrotetrabenazine (a vesicular monoamine transporter 2 marker), and (18)F-fluorodopa, leading to the determination of the MP and (11)C-dihydrotetrabenazine binding potentials (BPs) and the effective distribution volume for (18)F-fluorodopa, the inverse of DA turnover. Seven patients also underwent positron emission tomography with (11)C-raclopride before and 1 hour after levodopa administration to estimate levodopa-induced changes in synaptic DA concentration.

RESULTS

We found a significant positive correlation between effective distribution volume and BP(MP) (r = 0.93; p < 0.001) and a significant negative correlation between changes in synaptic DA concentration and BP(MP) (r = -0.93; p = 0.04), independent of disease severity and duration.

INTERPRETATION

These data show that in Parkinson's disease, greater DAT levels are directly associated with lower DA turnover and lower changes in synaptic DA concentration. This implies that an important functional role of DAT is to maintain relatively constant synaptic DA levels and to preserve DA in nerve terminals. A decrease in DAT, although potentially serving as a compensatory mechanism in early disease, may ultimately result in increased DA turnover and higher oscillations in synaptic DA concentration, thereby possibly predisposing toward the occurrence of motor complications as disease progresses.

End-of-dose deterioration in non ergolinic dopamine agonist monotherapy of Parkinson’s disease

The study was designed to investigate the possible occurrence of "wearing-off" (WO) during dopamine agonist (DA) monotherapy. Sixty patients with "de novo" idiopathic PD were randomised into one of two DA monotherapy branches to receive oral ropinirole at 15 mg per day, or pramipexole at 2.1 mg per day. DA doses could be increased in the following two years but levodopa could not be added until the study ended. WO was assessed by self-evaluation charts confirmed by a blinded observation of a 30% or greater deterioration in the Unified Parkinson's Disease Rating Scale (UPDRS) motor score. Proc Mixed and Kaplan-Meier curves evaluated treatment variables as a function of time. T-tests were used to compare post-hoc variables reclassified according to WO occurrence. Thirty patients received ropinirole, and 30 pramipexole monotherapy. Eighteen patients (30%) experienced "wearing-off" 15-21 months after beginning monotherapy. No differences were observed between treatments. WO phenomena was observed 3.4+/-0.3 hours after intake of the morning or afternoon dose and consisted of UPDRS score worsening by 11.1+/-2.1 points (69-111% more than "on" score). Statistical evaluation gave evidence of differences between patients who experienced WO and those who did not: UPDRS motor scores obtained at admission to the study were higher (by 3.4+/-0.2 points, p=0.01 t-test) and DA doses at 6-12 months were higher in fluctuating patients. UPDRS motor scores deteriorated, however. similarly and there were no differences, in UPDRS scores recorded in ON conditions, between fluctuating and non-fluctuating patients at the end of the study. Our findings provide evidence of WO phenomena in patients with early PD receiving non-ergolinic DA monotherapy.

Less is more: pathophysiology of dopaminergic-therapy-related augmentation in restless legs syndrome

Therapy-related augmentation of the symptoms of restless legs syndrome (RLS) is an important clinical problem reported in up to 60% of patients treated with levodopa and, to a lesser extent, with dopamine agonists. The efficacy of low-dose dopaminergic drugs for RLS has been established, but the mode of action is unknown. Here, we review the existing data and conclude that augmentation is a syndrome characterised by a severely increased dopamine concentration in the CNS; overstimulation of the dopamine D1 receptors compared with D2 receptors in the spinal cord may lead to D1-related pain and generate periodic limb movements; iron deficiency may be a main predisposing factor of augmentation, probably caused by a reduced function of the dopamine transporter; therapy with levodopa or dopamine agonists should remain at low doses and; iron supplementation and opiates are the therapy of choice to counter augmentation.

Treatment of drug-induced psychosis in Parkinson's disease with ziprasidone can induce severe dose-dependent off-periods and pathological laughing

"Atypical anti-psychotics" are substances of choice in treating drug-induced psychosis (DP) in Parkinson's disease (PD). We report on four patients with DP who received treatment with ziprasidone after previously applied clozapine and quetiapine had failed. Three patients showed a significant improvement of DP, without deterioration of motor function. In one case, ziprasidone considerably increased decline in off-periods. Two patients developed pathological laughing as a possible side-effect of ziprasidone. Ziprasidone may serve as an additional "atypical anti-psychotic" for the treatment of DP in PD but can also induce deterioration of motor function.

Post- versus presynaptic plasticity in L-DOPA-induced dyskinesia

L-3,4-dihydroxyphenylalanine (L-DOPA) remains the most efficacious drug for the treatment of Parkinson's disease (PD), but causes adverse effects that limit its utility. L-DOPA-induced dyskinesia (abnormal involuntary movements) is a significant clinical problem that attracts growing scientific interest. Current notions attribute the development of dyskinesia to two main factors, viz. the loss of nigrostriatal dopamine (DA) projections and the maladaptive changes produced by L-DOPA at sites postsynaptic to the nigrostriatal neuron. Basic research in the past 15 years has placed a lot of emphasis on the postsynaptic plasticity associated with dyskinesia, but recent experimental work shows that also some presynaptic factors, involving the regulation of L-DOPA/DA release and metabolism in the brain, may show plasticity during treatment. This review summarizes significant studies of L-DOPA-induced dyskinesia in patients and animal models, and outlines directions for future experiments addressing mechanisms of presynaptic plasticity. These investigations may uncover clues to the varying susceptibility to L-DOPA-induced dyskinesia among PD patients, paving the way for tailor-made treatments.

Visual hallucinations in Parkinson's disease: clues to separate origins

Our paper discusses two experimental studies suggesting that Visual Hallucinations (VH) in Parkinson's Disease (PD) may have separate origins. The first is a prospective 8years study evaluating the appearance of VH, visual abnormalities assessed by Visual Evoked Potentials (VEPs) and REM sleep Behaviour Disorder (RBD), in 80 PD patients treated with l-Dopa and Dopaminoagonists (DA). In chronically treated, cognitively unimpaired, PD patients VH were statistically related (p=0.001) to RBD occurrence and high DA doses. Visual abnormalities were significantly reduced by l-Dopa or DA intake, and were statistically unrelated to VH. The second study involved PD patients placed in a Virtual Reality Environment, to decontextualize visual input. When motor symptoms worsened and VEP abnormalities developed patients consistently described hallucinatory dysperceptions of the virtual environment. The two studies therefore show that VH can occur in two seemingly distinct conditions, one is related to chronic treatment and to a sleep disorder frequently observed in PD, the other is probably related to a hypodopaminergic state. Our studies support a recently proposed integrative model of VH, and show that the neural circuits purported to explain VH must include the retinal dopaminergic system and the REM sleep regulatory system.

New ideas on the origin of L-dopa-induced dyskinesias: age, genes and neural plasticity

More than 50% of Parkinson's disease (PD) patients treated with L-dopa develop L-dopa-induced dyskinesias (LIDs) in the long term. Some patients exhibit severe dyskinesias soon after starting low doses of L-dopa, whereas other patients remain free of this disabling complication despite treatment with L-dopa. Avoiding or delaying the appearance of LIDs is one of the main objectives of the management of PD. Plasticity of the brain to adapt to a progressive disease, together with a non-physiological treatment strategy, might be the key physiopathological element that underlies LIDs. Neural plasticity varies among patients according to age and genetics. Thus, I propose that this variation explains the observed differences in the occurrence of LIDs in PD patients. Furthermore, I suggest that denervation and L-dopa treatment act as modulating and triggering factors of LIDs, respectively. In this article, the practical implications of these ideas and the role of pharmacogenetics in PD treatment are discussed. Treatment decisions are likely to rely on this information, challenging the relevance of current 'hot' debates about how to start treatment in PD.

Age-related differences in levodopa dynamics in Parkinson's: implications for motor complications

Treatment-related motor complications in Parkinson's disease have been previously linked to disease-induced pre-synaptic alterations: dopaminergic denervation and changes in dopamine (DA) release patterns. The occurrence of such complications is also known to be partly dependent on the age of disease onset, occurring more frequently in patients with disease onset at a younger age. Using positron emission tomography (PET) and 4-h-long 18F-fluorodopa (FD) scans we have investigated in vivo an age dependence of disease-induced changes in DA turnover as a possible contributing factor to the age-related differences in treatment-related motor complications. We evaluated the relative changes in DA turnover (measured by its direct inverse, effective DA distribution volume--EDV) and DA synthesis and vesicular storage capacity (quantified by the plasma input uptake rate constant Ki) in Parkinson's disease patients as a function of age (n = 27, age range 38-79 years). After correcting for disease severity, a significant negative correlation was found between age and magnitude of disease-induced decrease in EDV and in Ki in the putamen (P < 0.001, P = 0.02, respectively). However, the difference between the disease-induced decrease in EDV and that in Ki also exhibited an age dependence (P < 0.001), indicating a relatively higher disease-induced increase in DA turnover (inverse of EDV) compared with the decrease in DA synthesis and storage rate in patients of younger age compared with older patients. This finding implies that DA turnover in younger-onset patients undergoes a relatively greater alteration and thus likely contributes to a greater imbalance between DA synthesis, storage and release, which could lead to larger swings in synaptic DA levels. It has indeed been suggested on theoretical grounds that such imbalance may contribute to the greater propensity for motor fluctuations. These results provide one possible explanation for the age-dependent occurrence of complications and support the existence of a pre-synaptic contribution to the occurrence of motor complications.

Lifestyle regularity measured by the social rhythm metric in Parkinson's disease

Parkinson's disease (PD) is a chronic progressive motor disorder that may present with a spectrum of symptoms and disease severity. Therapy is frequently associated with motor fluctuations and dyskinesias; therefore, monitoring of motor fluctuations and daily abilities is important for adequate management. The Social Rhythm Metric (SRM) is a diary-like questionnaire that quantifies the extent to which a person's life is regular vs. irregular on a daily basis with respect to event timing. Lifestyle regularity has been assessed by the SRM in other clinical situations. The aim of this study was to evaluate lifestyle regularity in a population with PD using the SRM and its relationship to clinical and therapeutic factors. Twenty-eight consecutive patients with PD and 14 control subjects were studied. Severity of motor dysfunction was evaluated with the Unified Parkinson's Disease Rating Scale (UPDRS). Depressive symptoms were assessed with the Montgomery Asberg Depressive Rating Scale (MADRS), sleep quality with the Pittsburgh Sleep Quality Index (PSQI), and subjective daytime sleepiness with the Epworth sleepiness scale. Daily lifestyle regularity was assessed by the SRM for 2 weeks. Patients with PD had lower SRM scores than controls, and those with motor fluctuations had even lower scores (p=0.04). Patients with motor fluctuations showed more clinical disability (p=0.01), a worse quality of sleep (p=0.02), and more depressive symptoms (p=0.02). SRM results were correlated with PSQI values (p=0.016). Our findings show that the regularity of daily activities as measured by the SRM is disorganized in patients with PD and that this irregularity is related to sleep quality.

Modeling the Parkinson's tremor and its treatments

In this paper, we discuss modeling issues of the Parkinson's tremor. Through the work we have employed physiological structure as well as functioning of the parts in brain that are involved in the disease. To obtain more practical similarity, random behaviors of the connection paths are also considered. Medication or treatment of the disease both by drug prescription and electrical signal stimulation are modeled based on the same model introduced for the disease itself. Two new medication strategies are proposed based on the model to reduce the side effects caused by the present drug prescription.