Investigating the aspect of asymmetry in brain-first versus body-first Parkinson's disease.

Parkinson's disease (PD) is characterized by a progressive loss of dopaminergic neurons in the substantia nigra. Recent literature has proposed two subgroups of PD. The "body-first subtype" is associated with a prodrome of isolated REM-sleep Behavior Disorder (iRBD) and a relatively symmetric brain degeneration. The "brain-first subtype" is suggested to have a more asymmetric degeneration and a prodromal stage without RBD. This study aims to investigate the proposed difference in symmetry of the degeneration pattern in the presumed body and brain-first PD subtypes. We analyzed 123I-FP-CIT (DAT SPECT) and 18F-FDG PET brain imaging in three groups of patients (iRBD, n = 20, de novo PD with prodromal RBD, n = 22, and de novo PD without RBD, n = 16) and evaluated dopaminergic and glucose metabolic symmetry. The RBD status of all patients was confirmed with video-polysomnography. The PD groups did not differ from each other with regard to the relative or absolute asymmetry of DAT uptake in the putamen (p = 1.0 and p = 0.4, respectively). The patient groups also did not differ from each other with regard to the symmetry of expression of the PD-related metabolic pattern (PDRP) in each hemisphere. The PD groups had no difference in symmetry considering mean FDG uptake in left and right regions of interest and generally had the same degree of symmetry as controls, while the iRBD patients had nine regions with abnormal left-right differences (p < 0.001). Our findings do not support the asymmetry aspect of the "body-first" versus "brain-first" hypothesis.

Association between probable REM sleep behavior disorder and increased dermal alpha-synuclein deposition in Parkinson's disease.

INTRODUCTION: Many patients with Parkinson's disease suffer from REM sleep behavior disorder, potentially preceding the onset of motor symptoms. Phospho-alpha-synuclein is detectable in skin biopsies of patients with isolated REM sleep behavior disorder several years prior to the onset of manifest PD, but information on the association between dermal phospho-alpha-synuclein deposition and REM sleep behavior disorder in patients with manifest PD is limited. We therefore aimed to investigate the alpha-synuclein burden in dermal peripheral nerve fibers in patients with Parkinson's disease with and without REM sleep behavior disorder. METHODS: Patients with Parkinson's disease (n = 43) who had undergone skin biopsy for the immunohistochemical detection of phosphorylated alpha-synuclein were screened for REM sleep behavior disorder using RBDSQ and Mayo Sleep Questionnaire. Skin biopsies from 43 patients with isolated polysomnography-confirmed REM sleep behavior disorder were used as comparators. RESULTS: Dermal alpha-synuclein deposition was more frequently found (81.8% vs. 52.4%, p = 0.05) and was more abundant (p = 0.01) in patients with Parkinson's disease suffering from probable REM sleep behavior disorder compared to patients without REM sleep behavior disorder and was similar to patients with isolated REM sleep behavior disorder (79.1%). CONCLUSION: The phenotype of REM sleep behavior disorder is associated with high amounts of dermal alpha-synuclein deposition, demonstrating a strong involvement of peripheral nerves in patients with this non-motor symptom and may argue in favor of REM sleep behavior disorder as an indicator of a "body-predominant" subtype of Parkinson's disease.

Consistent skin α-synuclein positivity in REM sleep behavior disorder - A two center two-to-four-year follow-up study.

OBJECTIVE/METHODS: Phosphorylated alpha-synuclein (p-syn) in dermal nerves of patients with isolated REM sleep behavior disorder (iRBD) is detectable by immunofluorescence-labeling. Skin-biopsy-p-syn-positivity was recently postulated to be a prodromal marker of Parkinson's disease (PD) or related synucleinopathies. Here, we provide two-to four-year clinical and skin biopsy follow-up data of 33 iRBD patients, whose skin biopsy findings at baseline were reported in 2017. RESULTS: Follow-up biopsies were available from 25 patients (18 positive at baseline) and showed consistent findings over time in 24 patients. One patient converted from skin-biopsy-negativity to -positivity. P-syn-positivity was observed in iRBD patients who still had a normal FP-CIT-SPECT two years later. Clinically, five of the 23 at baseline skin-biopsy-positive patients (21.7%) had converted to PD or dementia with Lewy bodies at follow-up, but none of the skin-biopsy-negative patients. CONCLUSIONS: Dermal p-syn in iRBD is most probably an early consistent marker of synucleinopathy and may support other indicators of conversion to manifest disease state.

Socioeconomic impact of restless legs syndrome and inadequate restless legs syndrome management across European settings.

Restless legs syndrome (RLS) is one of the most common neurological disorders. It describes an irresistible urge to move the legs, mostly manifested in the evening and at night, which can lead to severe sleep disturbance. As part of the European Brain Council (EBC)-led Value-of-Treatment project, this study aimed at capturing the socioeconomic impact of RLS related to the inadequate diagnosis and treatment across different European healthcare settings. The economic burden of RLS was estimated using the published EBC framework of analysis in three separate European Union healthcare systems (France, Germany, and Italy). The RLS care pathway was mapped to identify the unmet needs of patients. Based on specific patient stories, the economic impact of correctly diagnosing RLS and changing between inadequate and target treatment was calculated using appropriate scenario analysis. RLS proved to be a significant personal and social burden, when epidemiological data, high prevalence of RLS, and its need for treatment are combined. By looking at the savings emerging from the provision of optimal care management (timely and correct diagnosis, evidence-based therapy, avoidance of therapy-related complications such as augmentation), the authors foresee substantial economic savings with the achievement of adequate diagnosis and treatment of RLS. Education about RLS is urgently needed for all subspecialties involved in RLS patient care as well as the general public. Equally important, the search for new causal treatment strategies should be intensified to reduce suffering and substantial societal cost.

The economic benefit of timely, adequate, and adherence to Parkinson's disease treatment: the Value of Treatment Project 2.

BACKGROUND: Parkinson's disease (PD) is a chronic progressive neurological disorder with a high psychosocial and economic burden. As part of the European Brain Council (EBC)-led Value of Treatment project, this study aimed to capture the economic benefit of timely, adequate, and adherence to PD treatment. METHODS: The EBC Value of Treatment Initiative combined different stakeholders to identify unmet needs in the patients' journey according to Rotterdam methodology. The economic evaluation focused on three major topics identified as major gaps: start of treatment; best treatment for advanced disease; and adherence to treatment. Two separate healthcare systems (Germany and the UK) were chosen. Cost-effectiveness was determined by using decision-analytical modelling approaches. Effectiveness was expressed as quality-adjusted life-years (QALYs) gained and incremental cost-effectiveness ratio (ICER). RESULTS: Treatment intervention in PD was found to be cost-effective regardless of the initial health state of the patient receiving the treatment. Cost savings were between -€1000 and -€5400 with 0.10 QALY gain and -€1800 and -€7600 with 0.10 QALY gain for Germany and the UK, respectively. Treatment remains cost-effective within the National Institute for Health and Care Excellence thresholds. Availability of adequate treatment to more patients was also found to be cost-effective, with an ICER of €15,000-€32,600 across country settings. Achieving the target adherence to treatment would generate cost-savings of €239,000-€576,000 (Germany) and €917,000-€2,980.000 (UK) for every 1,000 patients treated adequately. CONCLUSIONS: The analyses confirmed that timely, adequate, and adherence to PD treatment will not only improve care of the patients but is also cost-effective across healthcare systems. Further studies with a distinct identification of gaps in care are necessary to develop better and affordable care.

[The role of the gut microbiome in idiopathic Parkinson's disease]. / Die Rolle des Darmmikrobioms beim idiopathischen Parkinson-Syndrom.

BACKGROUND: In recent years studies have provided increasing evidence suggesting an association between the (gut) microbiome and idiopathic Parkinson's disease (IPD). OBJECTIVE: The aim of this article is to summarize and evaluate existing evidence with respect to the relevance of the (gut) microbiome for IPD. MATERIAL AND METHODS: An analysis and critical review of studies in the field of IPD and (gut) microbiome were carried out. The resulting potential perspectives and therapeutic strategies are discussed. RESULTS: Despite partially divergent results between different studies (potentially due to the applied methods and variance in the composition of the investigated cohorts), there is an overlap between studies indicating an association between IPD, the microbiome and microbial metabolites. Nevertheless, the cause-effect relationship between IPD and the microbiome has still not been clarified. Taken together, existing evidence supports a potentially relevant role for the microbiome with respect to typical disease symptoms and pathogenesis of the disease. CONCLUSION: Over the past 5 years there has been an enormous increase in the evidence with respect to the relevance of the microbiome for IPD. While early work in this field was mainly descriptive, new diagnostic methods provide evidence for the underlying mechanisms and the complex interactions between man as the host, the human immune system, the enteric nervous system, gut microbiota and microbial metabolites. A relatively novel and clinically relevant field of research is how the gut microbiome can influence the success of oral pharmacotherapy and whether substitution of specific microbiome components might be used either for future therapeutic or prophylactic strategies.

Abnormal α-synuclein deposits in skin nerves: intra- and inter-laboratory reproducibility.

BACKGROUND AND PURPOSE: Visualization of phosphorylated α-synuclein at serine 129 (p-syn) in skin nerves is a promising test for the in vivo diagnosis of synucleinopathies. Here the aim was to establish the intra- and inter-laboratory reproducibility of measurement of intraneural p-syn immunoreactivity in two laboratories with major expertise (Würzburg and Bologna). METHODS: In total, 43 patients affected by Parkinson's disease (PD 21 patients), dementia with Lewy bodies (DLB 1), rapid eye movement sleep behaviour disorder (RBD 11), multiple system atrophy (MSA-P 4) and small fibre neuropathy (SFN 6) were enrolled. Skin biopsy was performed at the C7 paravertebral spine region and distal skin sites (thigh or leg). The analysis was standardized in both laboratories and carried out blinded on a single skin section double stained with antibodies to p-syn and the pan-axonal marker protein gene product 9.5. Fifty skin sections were randomly selected for the analysis: 25 from C7 and 25 from distal sites. Differently classified sections were re-evaluated to understand the reasons for the discrepancy. RESULTS: The intra-laboratory analysis showed an excellent reproducibility both in Würzburg (concordance of classification 100% of sections; K = 1; P < 0.001) and Bologna (96% of sections; K = 0.92; P < 0.001). Inter-laboratory analysis showed reproducibility in 45 sections (90%; K = 0.8; P < 0.001) and a different classification in five sections, which was mainly due to fragmented skin samples or weak fluorescent signals. CONCLUSIONS: Analysis of p-syn showed excellent inter- and intra-laboratory reproducibility supporting the reliability of this technique. The few ascertained discordances were important to further improve the standardization of this technique.

Basic clinical features do not predict dopamine transporter binding in idiopathic REM behavior disorder.

REM sleep behavior disorder (RBD) is strongly associated with development of Parkinson's Disease and other α-synuclein-related disorders. Dopamine transporter (DAT) binding deficit predicts conversion to α-synuclein-related disorders in individuals with RBD. In turn, identifying which individuals with RBD have the highest likelihood of having abnormal DAT binding would be useful. The objective of this analysis was to examine if there are basic clinical predictors of DAT deficit in RBD. Participants referred for inclusion in the RBD cohort of the Parkinson Progression Markers Initiative were included. Assessments at the screening visit including DAT SPECT imaging, physical examination, cognitive function screen, and questionnaire-based non-motor assessment. The group with DAT binding deficit (n = 49) was compared to those without (n = 26). There were no significant differences in demographic or clinical features between the two groups. When recruiting RBD cohorts enriched for high risk of neurodegenerative disorders, our data support the need for objective biomarker assessments.

Validation of semiautomatic scoring of REM sleep without atonia in patients with RBD.

OBJECTIVE/BACKGROUND: To evaluate REM sleep without atonia (RSWA) in REM sleep behavior disorder (RBD) several automatic algorithms have been developed. We aimed to validate our algorithm (Mayer et al., 2008) in order to assess the following: (1). capability of the algorithm to differentiate between RBD, night terror (NT), somnambulism (SW), Restless legs syndrome (RLS), and obstructive sleep apnea (OSA), (2). the cut-off values for short (SMI) and long muscle activity (LMI), (3). which muscles qualify best for differential diagnosis, and (4). the comparability of RSWA and registered movements between automatic and visual analysis of videometry. PATIENTS/METHODS: RSWA was automatically scored according to Mayer et al., 2008 in polysomnographies of 20 RBD, 10 SW/NT, 10 RLS and 10 OSA patients. Receiver operating characteristic (ROC) curves were used to determine the sensitivity and specificity of SMI and LMI. Independent samples were calculated with t-tests. Boxplots were used for group comparison. The comparison between motor events by manual scoring and automatic analysis were performed with "Visual Basic for Applications" (VBA) for every hundredth second. RESULTS: Our method discriminates RBD from SW/NT, OSA and RLS with a sensitivity of 72.5% and a specificity of 86.7%. Automatic scoring identifies more movements than visual video scoring. Mentalis muscle discriminates the sleep disorders best, followed by FDS, which was only recorded in SW/NT. Cut-off values for RSWA are comparable to those found by other groups. CONCLUSION: The semi-automatic RSWA scoring method is capable to confirm RBD and to discriminate it with moderate sensitivity from other sleep disorders.

[Pharmacotherapy of Parkinson's disease : Aspects of drug safety]. / Pharmakotherapie des Morbus Parkinson : Aspekte der Arzneimitteltherapiesicherheit.

BACKGROUND: This overview focuses on the aspects of the pharmacotherapy of Parkinson's disease, which is one of the most common disorders of the nervous system. This article presents the complexity of the pharmacotherapy of geriatric patients with neurological diseases. OBJECTIVES: Information about the potential risk factors and aspects of drug safety in the pharmacotherapy of Parkinson's disease. MATERIALS AND METHODS: Selective literature search using PubMed and the scientific-clinical experience of the authors. RESULTS: Patients with Parkinson's disease are usually geriatric patients with concomitant diseases. As a result they are often treated with comedication which leads to a complex medication regime with more than five drugs. Such polypharmacy increases the risk of adverse drug events due to the rising number of possible interactions and contraindications. To control this risk and maintain a safe therapy, certain measures should be considered. This implies additional need for educational work in order to create awareness regarding potential adverse drug events. In certain cases of diagnosed comorbidities or relevant drug prescriptions in the medication regime, follow-up examinations should be conducted. CONCLUSION: Specific parameters of Parkinson's disease, the health-related quality of life of affected patients and the quality of pharmacotherapeutic drug safety can be improved by targeted monitoring of the medication regime. As a result, the overall drug safety can be increased.

[Wearable Technique for the Assessment of Parkinson Symptoms: What's the Future?]. / Tragbare und aktiv vom Parkinson-Patienten genutzte Technologie im häuslichen Umfeld: Was bringt die Zukunft?

Parkinson's disease (PD) is a multisystem disorder with a plethora of symptoms affecting the quality of life of patients in the home environment. Due to the rapid development of wearable technique in the health and fitness sector, an increasing number of such wearable devices are available to complement diagnostic strategies of PD symptoms not only in the clinical but also in the home environment. This development has clear advantages over clinical evaluation, as the latter is relatively subjective, time-consuming and costly, and provides only a snapshot of the condition. First results about the use of such technology for the assessment of PD symptoms (including bradykinesia, dyskinesia, tremor, daily activity and sleep behavior) in the home environment are promising. They suggest that these techniques can provide complementary information about the symptoms of PD patients, and have the potential to be included in future diagnostic workup concepts of routine care in PD. The use of such technique provides also the opportunity to more actively include patients into medical decision-making processes.

Longitudinal changes in cognition in early Parkinson's disease patients with REM sleep behavior disorder.

INTRODUCTION: Cognitive decline is common in Parkinson's disease (PD), and identifying patients at highest risk for it is essential. We aimed to examine the effect of possible REM sleep behavior disorder (pRBD) on rate of cognitive decline in early PD, for both global cognition and in specific cognitive domains. METHODS: Parkinson's Progression Markers Initiative (PPMI) is a multi-site, international study of PD patients untreated at enrollment. pRBD was assessed with the REM sleep behavior disorder questionnaire (RBDSQ). Global cognition was assessed at baseline and annually using the Montreal Cognitive Assessment (MoCA) and a cognitive battery. Linear mixed effects models were used to examine the relationship between pRBD (RBDSQ≥6) and rate of change in cognitive variables. Age, sex, years of education, and baseline motor and cognitive scores were included as covariates. RESULTS: The baseline sample consisted of 423 individuals with PD, mean age 61.7 years and 65.5% male. Data was available on 389, 366, and 196 participants at 1-year, 2-year, and 3-year follow-up respectively. Possible RBD occurred in 108 (25.5%) at baseline. In multivariate analyses, baseline RBD was associated with greater annual rate of decline in MoCA score (ß = -0.34, 95%CI -0.54, -0.13, p < 0.001), Symbol Digit Modalities Test (ß = -0.69, 95%CI -1.3, -0.09, p = 0.024), and Hopkins Verbal Learning Test-Revised, delayed free recall (ß = -0.21, 95%CI -0.41, -0.013, p = 0.037). CONCLUSIONS: Possible RBD is common in early PD and predicts future cognitive decline, particularly in attention and memory domains.

Experimental pain sensitivity in multiple system atrophy and Parkinson's disease at an early stage.

BACKGROUND: Chronic spontaneous pain is a clinically relevant non-motor symptom in multiple system atrophy (MSA) and Parkinson's disease (PD). Experimental pain sensitivity, reflecting the mechanisms of nociception and pain perception leading to clinical pain, is known to be enhanced in both diseases at advanced stages. Also, this study aimed at investigating experimental pain sensitivity already at an early stage (i.e. symptom duration ≤5 years). METHODS: Experimental pain sensitivity was assessed by investigating the nociceptive flexion reflex (NFR, reflecting spinal nociception) and heat and electrical pain thresholds. 'Off-drug' MSA (n = 11) and PD (n = 14) patients selected at an early stage of the disease were compared to healthy controls (HC, n = 27). MSA patients had either parkinsonian (MSA-P, n = 5) or cerebellar (MSA-C, n = 6) subtypes. RESULTS: Compared to HC, MSA patients had lower heat pain sensitivity, whereas PD patients had reduced NFR threshold. MSA and PD patients did not differ from HC regarding other variables. MSA-P and MSA-C patients did not differ, either. CONCLUSIONS: Impaired sensory discrimination and attention deficits could contribute to the reduced perception of heat pain in MSA, whereas in PD, local changes in spinal excitability or a diminished dopaminergic descending inhibition might impact on the motor efference of the NFR to reduce its threshold to nociceptive afferent information. WHAT DOES THIS STUDY ADD?: This study investigated experimental pain sensitivity at an early stage in MSA and PD.

The frontal assessment battery is not useful to discriminate progressive supranuclear palsy from frontotemporal dementias.

BACKGROUND: The frontal assessment battery (FAB) has been suggested as a useful tool in the differential diagnosis of progressive supranuclear palsy (PSP) from Parkinson's disease (PD) and multiple system atrophy with parkinsonism (MSA-P). However, the utility of the FAB in the differential diagnosis of PSP from frontotemporal dementia (FTD) phenotypes is still under research. METHODS: We performed the FAB, in a multi-centre cohort of 70 PSP, 103 FTD (N = 84 behavioral variant FTD, N = 10 semantic dementia, N = 9 progressive non-fluent aphasia), 26 PD and 11 MSA-P patients, diagnosed according to established criteria. Patients were also rated with the mini mental state examination and motor scales. RESULTS: The FAB total score showed a poor discriminatory power between PSP and FTD as a group [area under the curve (AUC) = 0.523]. Moreover, the FAB score showed no correlation with disease duration in PSP (r = 0.05) or FTD group (r = 0.04). In contrast, we confirmed that the FAB is clinically useful to differentiate PSP from PD and MSA-P (AUC = 0.927). In fact, the sum of two FAB subscores together (verbal fluency and Luria motor series) were as good as the total score in differentiating PSP from PD and MSA-P (AUC = 0.957). CONCLUSIONS: The FAB may not be a useful tool to differentiate PSP from FTDs, and shows no correlation with disease duration in these disorders. On the other hand, the essential information to differentiate PSP from PD and MSA-P is contained in the sum of only two FAB subscores. This should be taken into consideration in both clinical practice and the planning of clinical trials.

Effects of rotigotine transdermal patch in patients with Parkinson's disease presenting with non-motor symptoms - results of a double-blind, randomized, placebo-controlled trial.

BACKGROUND AND PURPOSE: Non-motor symptoms (NMS) of Parkinson's disease (PD) have a major impact on health-related quality of life. This is the first randomized controlled trial to use the NMS Scale (NMSS) as a primary outcome to assess treatment effects on NMS in PD. METHODS: In this double-blind trial (NCT01300819), patients with PD and a total NMSS score ≥40 were randomized (2:1) to rotigotine or placebo, titrated over 1-7 weeks to optimal dose (≤8 mg/24 h for patients not receiving levodopa, ≤16 mg/24 h for patients receiving levodopa), maintained for 12 weeks. The primary outcome was change in NMSS total score from baseline to end of maintenance. Secondary outcomes were the nine NMSS domains, Unified Parkinson's Disease Rating Scale (UPDRS) III (motor) and the 39-item Parkinson's Disease Questionnaire (PDQ-39). RESULTS: In total, 283/349 (81.1%) randomized patients completed the trial; 211 rotigotine and 122 placebo were included in the full analysis set. The NMSS total score decreased by 23 (rotigotine) and 19 (placebo) points; the treatment difference was not statistically significant (-3.58; 95% confidence interval -8.43, 1.26; P = 0.147). Numerically greater than placebo improvements were detected in the 'mood/apathy' and 'miscellaneous' NMSS domains (P < 0.05). Treatment differences in UPDRS III (-2.60; -4.27, -0.92; P = 0.002) and PDQ-39 (-2.79; -5.21, -0.37; P = 0.024) favoured rotigotine. Adverse events reported more frequently with rotigotine were nausea, application site reactions, somnolence and headache. CONCLUSIONS: Rotigotine improvement in the multi-domain NMSS total score was not superior to placebo. A different sensitivity of individual NMSS domains to dopaminergic therapy and a large placebo effect may have contributed to these findings.

Striatal tyrosine hydroxylase-positive neurons are associated with L-DOPA-induced dyskinesia in hemiparkinsonian mice.

L-3,4-Dihydroxyphenylalanine (L-DOPA) is the therapeutic gold standard in Parkinson's disease. However, long-term treatment is complicated by the induction of debilitating abnormal involuntary movements termed L-DOPA-induced dyskinesias (LIDs). Until today the underlying mechanisms of LID pathogenesis are not fully understood. The aim of this study was to reveal new factors, which may be involved in the induction of LID. We have focused on the expression of striatal tyrosine hydroxylase-positive (TH+) neurons, which are capable of producing either L-DOPA or dopamine (DA) in target areas of ventral midbrain DAergic neurons. To address this issue, a daily L-DOPA dose was administered over the course of 15 days to mice with unilateral 6-hydroxydopamine-induced lesions of the medial forebrain bundle and LIDs were evaluated. Remarkably, the number of striatal TH+ neurons strongly correlated with both induction and severity of LID as well as ΔFosB expression as an established molecular marker for LID. Furthermore, dyskinetic mice showed a marked augmentation of serotonergic fiber innervation in the striatum, enabling the decarboxylation of L-DOPA to DA. Axial, limb and orolingual dyskinesias were predominantly associated with TH+ neurons in the lateral striatum, whereas medially located TH+ neurons triggered locomotive rotations. In contrast, identified accumbal and cortical TH+ cells did not contribute to the generation of LID. Thus, striatal TH+ cells and serotonergic terminals may cooperatively synthesize DA and subsequently contribute to supraphysiological synaptic DA concentrations, an accepted cause in LID pathogenesis.

Long-term treatment with L-DOPA or pramipexole affects adult neurogenesis and corresponding non-motor behavior in a mouse model of Parkinson's disease.

Non-motor symptoms such as hyposmia and depression are often observed in Parkinson's disease (PD) and can precede the onset of motor symptoms for years. The underlying pathological alterations in the brain are not fully understood so far. Dysregulation of adult neurogenesis in the dentate gyrus of the hippocampus and the olfactory bulb has been recently suggested to be implicated in non-motor symptoms of PD. However, there is so far no direct evidence to support the relationship of non-motor symptoms and the modulation of adult neurogenesis following dopamine depletion and/or dopamine replacement. In this study, we investigated the long-term effects of l-DOPA and pramipexole, a dopamine agonist, in a mouse model of bilateral intranigral 6-OHDA lesion, in order to assess the impact of adult neurogenesis on non-motor behavior. We found that l-DOPA and pramipexole can normalize decreased neurogenesis in the hippocampal dentate gyrus and the periglomerular layer of the olfactory bulb caused by a 6-OHDA lesion. Interestingly, pramipexole showed an antidepressant and anxiolytic effect in the forced swim test and social interaction test. However, there was no significant change in learning and memory function after dopamine depletion and dopamine replacement, respectively.