Cardiovascular dysautonomia and cognitive impairment in Parkinson's disease (Review)

Cognitive impairment is a prevalent non-motor symptom of Parkinson's disease (PD), which can result in significant disability and distress for patients and caregivers. There is a marked variation in the timing, characteristics and rate at which cognitive decline occurs in patients with PD. This decline can vary from normal cognition to mild cognitive impairment and dementia. Cognitive impairment is associated with several pathophysiological mechanisms, including the accumulation of β-amyloid and tau in the brain, oxidative stress and neuroinflammation. Cardiovascular autonomic dysfunctions are commonly observed in patients with PD. These dysfunctions play a role in the progression of cognitive impairment, the incidents of falls and even in mortality. The majority of symptoms of dysautonomia arise from changes in the peripheral autonomic nervous system, including both the sympathetic and parasympathetic nervous systems. Cardiovascular changes, including orthostatic hypotension, supine hypertension and abnormal nocturnal blood pressure (BP), can occur in both the early and advanced stages of PD. These changes tend to increase as the disease advances. The present review aimed to describe the cognitive changes in the setting of cardiovascular dysautonomia and to discuss strategies through which these changes can be modified and managed. It is a multifactorial process usually involving decreased blood flow to the brain, resulting in the development of cerebral ischemic lesions, an increased presence of abnormal white matter signals in the brain, and a potential influence on the process of neurodegeneration in PD. Another possible explanation is this association being independent observations of PD progression. Patients with clinical symptoms of dysautonomia should undergo 24-h ambulatory BP monitoring, as they are frequently subtle and underdiagnosed.

Acupuncture improves neuroendocrine defects in a preclinical rat model of reproductive aging

AIMS

Clinical data supports electroacupuncture (EA) as an effective treatment for female reproductive disorders especially gonadotropin abnormalities. This study aims to detect the mechanism of EA that improves the neuroendocrine defects particularly the luteinizing hormone (LH) surge failure in early reproductive aging females.

MATERIALS AND METHODS

Middle-aged ovariectomized rats primed with hormone were treated by EA at acupoints CV4 and SP6 and undergone LH assay. Morphological experiments detected the activation of Kiss1 cells in the anteroventral periventricular nucleus (AVPV). Using targeted liquid chromatography with tandem mass spectrometry (LC-MS/MS) and RNA-sequencing, we determined the concentrations of neurotransmitter metabolites and transcriptomics in AVPV.

KEY FINDINGS

EA significantly increased c-Fos and c-Fos-positive Kiss1 cells in the middle-aged AVPV as well as the total and peak LH release. Targeted LC-MS/MS and RNA-sequencing of AVPV identified differential neurotransmitters in the middle-aged females including Acetylcholine chloride, 5-Hydroxyindole-3-aceticacid, Kynurenine, Histamine, L-Histidine and L-Glycine, while EA decreased the concentration of Acetylcholine chloride. Totally 1255 differentially expressed genes modulated by EA were strongly implicated in neurotransmitter transport and KEGG pathways involved neuroactive ligand-receptor interaction, glutamatergic and gamma-aminobutyric acid-mediated synapse. Specifically, the mRNAs associated with the LH surge such as hormone receptor Pgr, adrenoceptor Adra1a, neurotransmitter transporters Slc17a6 and Slc32a1, glutamate decarboxylase Gad2 and Kiss1 were markedly altered by EA.

SIGNIFICANCE

These findings showed that the age-related reduction of LH surge occurred via differential neurotransmitter metabolisms and altered transcriptions in AVPV, which proposed EA-based therapy for improving responsiveness of the hypothalamus to hormone in women with advanced age.

Rest Tremor in Parkinson's Disease Is Associated with Ipsilateral Striatal Dopamine Transporter Binding

BACKGROUND

The cardinal motor symptoms of Parkinson's disease (PD) include rigidity, bradykinesia, and rest tremor. Rigidity and bradykinesia correlate with contralateral nigrostriatal degeneration and striatal dopamine deficit, but association between striatal dopamine function and rest tremor has remained unclear.

OBJECTIVE

The aim of this study was to investigate the possible link between dopamine function and rest tremor using Parkinson's Progression Markers Initiative dataset, the largest prospective neuroimaging cohort of patients with PD.

METHODS

Clinical, [123I]N-ω-fluoropropyl-2β-carbomethoxy-3β-(4-iodophenyl)nortropane ([123I]FP-CIT) single photon emission computed tomography (SPECT), and structural magnetic resonance imaging data from 354 early PD patients and 166 healthy controls were included in this study. We employed a novel approach allowing nonlinear registration of individual scans accurately to a standard space and voxelwise analyses of the association between motor symptoms and striatal dopamine transporter (DAT) binding.

RESULTS

Severity of both rigidity and bradykinesia was negatively associated with contralateral striatal DAT binding (PFWE < 0.05 [FWE, family-wise error corrected]). However, rest tremor amplitude was positively associated with increased ipsilateral DAT binding (PFWE < 0.05). The association between rest tremor and binding remained the same controlling for Hoehn & Yahr stage, Movement Disorder Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS) part III score, bradykinesia-rigidity score, or motor phenotype. The association between rest tremor and binding was independent of bradykinesia-rigidity and replicated using 2-year follow-up data (PFWE < 0.05).

CONCLUSION

In agreement with the existing literature, we did not find a consistent association between rest tremor and contralateral dopamine defect. However, our results demonstrate a link between rest tremor and increased or less decreased ipsilateral DAT binding. Our findings provide novel information about the association between dopaminergic function and parkinsonian rest tremor. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Establishing connectivity through microdissections of midbrain stimulation-related neural circuits

Comprehensive understanding of the neural circuits involving the ventral tegmental area is essential for elucidating the anatomofunctional mechanisms governing human behaviour, in addition to the therapeutic and adverse effects of deep brain stimulation for neuropsychiatric diseases. Although the ventral tegmental area has been targeted successfully with deep brain stimulation for different neuropsychiatric diseases, the axonal connectivity of the region is not fully understood. Here, using fibre microdissections in human cadaveric hemispheres, population-based high-definition fibre tractography and previously reported deep brain stimulation hotspots, we find that the ventral tegmental area participates in an intricate network involving the serotonergic pontine nuclei, basal ganglia, limbic system, basal forebrain and prefrontal cortex, which is implicated in the treatment of obsessive-compulsive disorder, major depressive disorder, Alzheimer's disease, cluster headaches and aggressive behaviours.

Associations of cerebrospinal fluid monoamine metabolites with striatal dopamine transporter binding and 123I-meta-iodobenzylguanidine cardiac scintigraphy in Parkinson's disease: Multivariate analyses

Cerebrospinal fluid (CSF) homovanillic acid (HVA) and 5-hydroxyindole acetic acid (5-HIAA), dopamine and serotonin metabolites, are decreased in Parkinson's disease (PD). Although some reported associations between HVA and striatal dopamine transporter (DAT) or 5-HIAA and cardiac 123I-meta-iodobenzylguanidine (MIBG) findings, respectively, whether these are direct associations remained unknown. We retrospectively reviewed 57 drug-naïve patients with PD who underwent CSF analyses and DAT and cardiac MIBG imaging. Z-score of striatal DAT specific binding ratio (Z-SBR) was measured, and the positivity of MIBG abnormalities were judged by an expert. The mean age was 75.5 ± 8.7 years. Thirty-three were MIBG-positive and 24 were MIBG-negative. 5-HIAA levels were significantly lower in the MIBG-positive group. Logistic regression analysis showed that MIBG positivity was associated with 5-HIAA level (odds ratio = 0.751, p = 0.006) but not with age, sex, and HVA. DAT Z-SBR correlated with both HVA and 5-HIAA. Multiple regression analysis showed that HVA was the only significant variable associated with Z-SBR (t = 3.510, p < 0.001). We confirmed direct associations between 5-HIAA and cardiac MIBG, and between HVA and striatal DAT binding.

Exploring Analysis Approaches for Using the Dopamine Transporter Striatal Binding Ratio in Early- to Mid-Stage Parkinson's Disease Modification Trials

BACKGROUND

The dopamine transporter striatal binding ratio (DAT SBR) has been used as an outcome measure in Parkinson's disease (PD) trials of potential disease-modifying therapies; however, both patient characteristics and analysis approach potentially complicate its interpretation.

OBJECTIVE

The aim was to explore how well DAT SBR reflects PD motor severity across different striatal subregions and the relationship to disease duration, and side of onset.

METHODS

DAT SBR for the anterior and posterior putamen and caudate in both hemispheres was obtained using validated automated quantitative software on baseline scans of 132 patients recruited for the Exenatide PD2 and PD3 trials. Associations between mean and lateralized SBR subregions (posterior and anterior putamen and caudate) and summed and lateralized motor characteristics were explored using regression analysis. Analyses were repeated considering disease duration and limiting analysis to the less-affected hemisphere.

RESULTS

Lateralized bradykinesia was most consistently associated with the loss of DAT uptake in the contralateral anterior putamen. There was much higher variance in the posterior putamen, and in all regions in those with longer duration disease, although bradykinesia remained robustly associated with anterior putaminal DAT uptake even in longer-duration patients. Restricting analyses to the less-affected side did not usefully reduce the variance compared to the overall cohort.

CONCLUSION

These data suggest that DAT SBR could be a useful biomarker in disease-modifying trials, but a focus on anterior striatal subregions and incorporating disease duration into analyses may improve its utility.

Multimodal neuroimaging to characterize symptom-specific networks in movement disorders

Movement disorders, such as Parkinson's disease, essential tremor, and dystonia, are characterized by their predominant motor symptoms, yet diseases causing abnormal movement also encompass several other symptoms, including non-motor symptoms. Here we review recent advances from studies of brain lesions, neuroimaging, and neuromodulation that provide converging evidence on symptom-specific brain networks in movement disorders. Although movement disorders have traditionally been conceptualized as disorders of the basal ganglia, cumulative data from brain lesions causing parkinsonism, tremor and dystonia have now demonstrated that this view is incomplete. Several recent studies have shown that lesions causing a given movement disorder occur in heterogeneous brain locations, but disrupt common brain networks, which appear to be specific to each motor phenotype. In addition, findings from structural and functional neuroimaging in movement disorders have demonstrated that brain abnormalities extend far beyond the brain networks associated with the motor symptoms. In fact, neuroimaging findings in each movement disorder are strongly influenced by the constellation of patients' symptoms that also seem to map to specific networks rather than individual anatomical structures or single neurotransmitters. Finally, observations from deep brain stimulation have demonstrated that clinical changes, including both symptom improvement and side effects, are dependent on the modulation of large-scale networks instead of purely local effects of the neuromodulation. Combined, this multimodal evidence suggests that symptoms in movement disorders arise from distinct brain networks, encouraging multimodal imaging studies to better characterize the underlying symptom-specific mechanisms and individually tailor treatment approaches.

The raphe nuclei are the early lesion site of gastric α-synuclein propagation to the substantia nigra

Parkinson's disease (PD) is a neurodegeneration disease with α-synuclein accumulated in the substantia nigra pars compacta (SNpc) and most of the dopaminergic neurons are lost in SNpc while patients are diagnosed with PD. Exploring the pathology at an early stage contributes to the development of the disease-modifying strategy. Although the "gut-brain" hypothesis is proposed to explain the underlying mechanism, where the earlier lesioned site in the brain of gastric α-synuclein and how α-synuclein further spreads are not fully understood. Here we report that caudal raphe nuclei (CRN) are the early lesion site of gastric α-synuclein propagating through the spinal cord, while locus coeruleus (LC) and substantia nigra pars compacta (SNpc) were further affected over a time frame of 7 months. Pathological α-synuclein propagation via CRN leads to neuron loss and disordered neuron activity, accompanied by abnormal motor and non-motor behavior. Potential neuron circuits are observed among CRN, LC, and SNpc, which contribute to the venerability of dopaminergic neurons in SNpc. These results show that CRN is the key region for the gastric α-synuclein spread to the midbrain. Our study provides valuable details for the "gut-brain" hypothesis and proposes a valuable PD model for future research on early PD intervention.

Dose-Ranging Effects of the Intracerebral Administration of Atsttrin in Experimental Model of Parkinson's Disease Induced by 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in Mice

Parkinson's disease is one of the most common neurodegenerative disorders characterized by a multitude of motor and non-motor clinical symptoms resulting from the progressive and long-lasting abnormal loss of nigrostriatal dopaminergic neurons. Currently, the available treatments for patients with Parkinson's disease are limited and exert only symptomatic effects, without adequate signs of delaying or stopping the progression of the disease. Atsttrin constitutes the bioengineered protein which ultrastructure is based on the polypeptide chain frame of the progranulin (PGRN), which exerts anti-inflammatory effects through the inhibition of TNFα. The conducted preclinical studies suggest that the therapeutic implementation of Atsttrin may be potentially effective in the treatment of neurodegenerative diseases that are associated with the occurrence of neuroinflammatory processes. The aim of the proposed study was to investigate the effect of direct bilateral intracerebral administration of Atsttrin using stereotactic methods in the preclinical C57BL/6 mouse model of Parkinson's disease inducted by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) intoxication. The analysis of the dose dependency effects of the increasing doses of Atsttrin has covered a number of parameters and markers regarding neurodegenerative processes and inflammatory responses including IL-1α, TNFα, IL-6, TH, and TG2 mRNA expressions. Accordingly, the evaluation of the changes in the neurochemical profile included DA, DOPAC, 3-MT, HVA, NA, MHPG, 5-HT, and 5-HIAA concentration levels. The intracerebral administration of Atsttrin into the striatum effectively attenuated the neuroinflammatory reaction in evaluated neuroanatomical structures. Furthermore, the partial restoration of monoamine content and its metabolic turnover were observed. In this case, taking into account the previously described pharmacokinetic profile and extrapolated bioavailability as well as the stability characteristics of Atsttrin, an attempt was made to describe as precisely as possible the quantitative and qualitative effects of increasing doses of the compound within the brain tissue microenvironment in the presented preclinical model of the disease. Collectively, this findings demonstrated that the intracerebral administration of Atsttrin may represent a potential novel therapeutic method for the treatment of Parkinson's disease.

The role of the nucleus basalis of Meynert in neuromodulation therapy: a systematic review from the perspective of neural network oscillations

As a crucial component of the cerebral cholinergic system and the Papez circuit in the basal forebrain, dysfunction of the nucleus basalis of Meynert (NBM) is associated with various neurodegenerative disorders. However, no drugs, including existing cholinesterase inhibitors, have been shown to reverse this dysfunction. Due to advancements in neuromodulation technology, researchers are exploring the use of deep brain stimulation (DBS) therapy targeting the NBM (NBM-DBS) to treat mental and neurological disorders as well as the related mechanisms. Herein, we provided an update on the research progress on cognition-related neural network oscillations and complex anatomical and projective relationships between the NBM and other cognitive structures and circuits. Furthermore, we reviewed previous animal studies of NBM lesions, NBM-DBS models, and clinical case studies to summarize the important functions of the NBM in neuromodulation. In addition to elucidating the mechanism of the NBM neural network, future research should focus on to other types of neurons in the NBM, despite the fact that cholinergic neurons are still the key target for cell type-specific activation by DBS.

Short term effects of contralateral tendon vibration on motor unit discharge rate variability and force steadiness in people with Parkinson's disease

Background

Vibration of one limb affects motor performance of the contralateral limb, and this may have clinical implications for people with lateralized motor impairments through vibration-induced increase in cortical activation, descending neural drive, or spinal excitability.

Objective

The objective of this study was to evaluate the effects of acute biceps brachii tendon vibration on force steadiness and motor unit activity in the contralateral limb of persons with Parkinson's disease.

Methods

Ten participants with mild to moderate Parkinson's disease severity performed a ramp, hold and de-ramp isometric elbow flexion at 5% of maximum voluntary contraction with the more-affected arm while vibration was applied to the distal biceps brachii tendon on the contralateral, less-affected arm. Using intramuscular fine wire electrodes, 33 MUs in the biceps brachii were recorded across three conditions (baseline, vibration, and post-vibration). Motor unit recruitment & derecruitment thresholds, discharge rates & variability, and elbow flexion force steadiness were compared between conditions with and without vibration.

Results

Coefficient of variation of force and discharge rate variability decreased 37 and 17%, respectively in post-vibration compared with baseline and vibration conditions. Although the motor unit discharge rates did not differ between conditions the total number of motor units active at rest after de-ramp were fewer in the post-vibration condition.

Conclusion

Contralateral tendon vibration reduces MU discharge rate variability and enhances force control on the more affected side in persons with Parkinson's disease.

Olfactory dysfunction and its related molecular mechanisms in Parkinson's disease

Changes in olfactory function are considered to be early biomarkers of Parkinson's disease. Olfactory dysfunction is one of the earliest non-motor features of Parkinson's disease, appearing in about 90% of patients with early-stage Parkinson's disease, and can often predate the diagnosis by years. Therefore, olfactory dysfunction should be considered a reliable marker of the disease. However, the mechanisms responsible for olfactory dysfunction are currently unknown. In this article, we clearly explain the pathology and medical definition of olfactory function as a biomarker for early-stage Parkinson's disease. On the basis of the findings of clinical olfactory function tests and animal model experiments as well as neurotransmitter expression levels, we further characterize the relationship between olfactory dysfunction and neurodegenerative diseases as well as the molecular mechanisms underlying olfactory dysfunction in the pathology of early-stage Parkinson's disease. The findings highlighted in this review suggest that olfactory dysfunction is an important biomarker for preclinical-stage Parkinson's disease. Therefore, therapeutic drugs targeting non-motor symptoms such as olfactory dysfunction in the early stage of Parkinson's disease may prevent or delay dopaminergic neurodegeneration and reduce motor symptoms, highlighting the potential of identifying effective targets for treating Parkinson's disease by inhibiting the deterioration of olfactory dysfunction.

Correlations between serotonin impairments and clinical indices in multiple system atrophy

BACKGROUND AND PURPOSE

Multiple system atrophy (MSA) is a neurodegenerative disease with characteristic motor and autonomic symptoms. Impaired brain serotonergic innervation can be associated with various clinical indices of MSA; however, the relationship between clinical symptoms and cerebrospinal fluid (CSF) levels of 5-hydroxyindole acetic acid (5-HIAA), a main serotonin metabolite, has not been fully elucidated.

METHODS

To compare CSF 5-HIAA levels between patients with MSA and healthy controls, we included 33 controls and 69 MSA patients with either predominant parkinsonian or cerebellar ataxia subtypes. CSF 5-HIAA levels were measured using high-performance liquid chromatography. Additionally, we investigated correlations between CSF 5-HIAA and various clinical indices in 34 MSA patients.

RESULTS

CSF 5-HIAA levels were significantly lower in MSA patients than in controls (p < 0.0001). Probable MSA patients had lower CSF 5-HIAA levels than possible MSA patients (p < 0.001). In MSA patients, CSF 5-HIAA levels were inversely correlated with scores in Parts 1, 2, and 4 of the Unified Multiple System Atrophy Rating Scale, and with systolic and diastolic blood pressure in Part 3. Structural equation modeling revealed significant paths between serotonin and clinical symptoms, and significance was highest for activities of daily living, walking, and body sway.

CONCLUSIONS

Serotonin dysfunction, as assessed by CSF 5-HIAA levels, may implicate greater MSA severity.

Sex-specific pleiotropic changes in emotional behavior and alcohol consumption in human α-synuclein A53T transgenic mice during early adulthood

Point mutations in the α-synuclein coding gene may lead to the development of Parkinson's disease (PD). PD is often accompanied by other psychiatric conditions, such as anxiety, depression, and drug use disorders, which typically emerge in adulthood. Some of these point mutations, such as SNCA and A30T, have been linked to behavioral effects that are not commonly associated with PD, especially regarding alcohol consumption patterns. In this study, we investigated whether the familial PD point mutation A53T is associated with changes in alcohol consumption behavior and emotional states at ages not yet characterized by α-synuclein accumulation. The affective and alcohol-drinking phenotypes remained unaltered in female PDGF-hA53T-synuclein-transgenic (A53T) mice during both early and late adulthood. Brain region-specific activation of ceramide-producing enzymes, acid sphingomyelinase (ASM), and neutral sphingomyelinase (NSM), known for their neuroprotective properties, was observed during early adulthood but not in late adulthood. In males, the A53T mutation was linked to a reduction in alcohol consumption in both early and late adulthood. However, male A53T mice displayed increased anxiety- and depression-like behaviors during both early and late adulthood. Enhanced ASM activity in the dorsal mesencephalon and ventral hippocampus may potentially contribute to these adverse behavioral effects of the mutation in males during late adulthood. In summary, the A53T gene mutation was associated with diverse changes in emotional states and alcohol consumption behavior long before the onset of PD, and these effects varied by sex. These alterations in behavior may be linked to changes in brain ceramide metabolism.

Older adults and individuals with Parkinson's disease control posture along suborthogonal directions that deviate from the traditional anteroposterior and mediolateral directions

A rich and complex temporal structure of variability in postural sway characterizes healthy and adaptable postural control. However, neurodegenerative disorders such as Parkinson's disease, which often manifest as tremors, rigidity, and bradykinesia, disrupt this healthy variability. This study examined postural sway in young and older adults, including individuals with Parkinson's disease, under different upright standing conditions to investigate the potential connection between the temporal structure of variability in postural sway and Parkinsonism. A novel and innovative method called oriented fractal scaling component analysis was employed. This method involves decomposing the two-dimensional center of pressure (CoP) planar trajectories to pinpoint the directions associated with minimal and maximal temporal correlations in postural sway. As a result, it facilitates a comprehensive assessment of the directional characteristics within the temporal structure of sway variability. The results demonstrated that healthy young adults control posture along two orthogonal directions closely aligned with the traditional anatomical anteroposterior (AP) and mediolateral (ML) axes. In contrast, older adults and individuals with Parkinson's disease controlled posture along suborthogonal directions that significantly deviate from the AP and ML axes. These findings suggest that the altered temporal structure of sway variability is evident in individuals with Parkinson's disease and underlies postural deficits, surpassing what can be explained solely by the natural aging process.

Exploring Parkinson's Disease-Associated Depression: Role of Inflammation on the Noradrenergic and Serotonergic Pathways

Parkinson's disease (PD) is a multifactorial disease, with genetic and environmental factors contributing to the disease onset. Classically, PD is a movement disorder characterized by the loss of dopaminergic neurons in the nigrostriatal pathway and intraneuronal aggregates mainly constituted of the protein α-synuclein. However, PD patients also display non-motor symptoms, including depression, which have been linked to functional abnormalities of non-dopaminergic neurons, including serotonergic and noradrenergic ones. Thus, through this comprehensive literature review, we shed light on the noradrenergic and serotonergic impairment linked to depression in PD, focusing on the putative involvement of inflammatory mechanisms.

[Tremor-dominant form of Parkinson's disease]

The article is of a review nature and is devoted to tremor, one of the maladaptive and difficult-to-treat symptoms of Parkinson's disease (PD). Along with the classic rest tremor, patients with PD may experience tremor of other modalities: postural tremor, kinetic tremor, which reflects a multimodal mechanism of tremor formation involving multiple neurotransmitter systems. The unpredictable response to therapeutic options, the ambiguous response to levodopa, also reflects the role of multiple underlying pathophysiological processes. Among the drug methods of tremor correction, preference is given to dopamine receptor agonists - due to the spectrum of their pharmaceutical action, high efficiency in relation to all leading motor and a number of non-motor manifestations. The evidence for advanced neurosurgical, non-invasive modalities is mixed, and there are insufficient comparative studies to assess their efficacy in patients with tremor-dominant forms of PD.

Symmetric and Profound Monoaminergic Degeneration in Parkinson's Disease with Premotor REM Sleep Behavior Disorder

Background

Rapid eye movement sleep behavior disorder (RBD) may precede or follow motor symptoms in Parkinson's disease (PD). While over 70% of idiopathic RBD cases phenoconvert within a decade, a small subset develops PD after a more extended period or remains nonconverted. These heterogeneous manifestations of RBD in PD prompt subtype investigations. Premotor RBD may signify "body-first" PD with bottom-up, symmetric synucleinopathy propagation.

Objective

Explore brainstem and nigrostriatal monoaminergic degeneration pattern differences based on premotor RBD presence and duration in de novo PD patients.

Methods

In a cross-sectional analysis of de novo PD patients (n = 150) undergoing FP-CIT PET and RBD Single-Question Screen, the cohort was categorized into groups with and without premotor RBD (PDRBD +/-), with further classification of PDRBD + based on a 10-year duration of premotor RBD. Analysis of FP-CIT binding in the striatum and pons, striatal asymmetry, and striatum-to-pons ratios compared patterns of nigrostriatal and brainstem monoaminergic degeneration.

Results

PDRBD + exhibited more severe and symmetrical striatal dopaminergic denervation compared to PDRBD-, with the difference in severity accentuated in the least-affected hemisphere. The PDRBD +<10Y subgroup displayed the most prominent striatal symmetry, supporting a more homogeneous "body-first" subtype. Pontine uptakes remained lower in PDRBD + even after adjusting for striatal uptake, suggesting early degeneration of pontine monoaminergic nuclei.

Conclusions

Premotor RBD in PD is associated with severe, symmetrical nigrostriatal and brainstem monoaminergic degeneration, especially in cases with PD onset within 10 years of RBD. This supports the concept of a "widespread, bottom-up" pathophysiological mechanism associated with premotor RBD in PD.

Monoaminergic Degeneration and Ocular Motor Abnormalities in De Novo Parkinson's Disease

BACKGROUND

Evaluating eye movements in Parkinson's disease (PD) provides valuable insights into the underlying pathophysiological changes.

OBJECTIVE

The aim was to investigate the relationship between monoaminergic degeneration and ocular motor abnormalities in de novo PD.

METHODS

Drug-naive PD patients who underwent N-(3-[18 F]fluoropropyl)-2-carbomethoxy-3-(4-iodophenyl) nortropane positron emission tomography scans and video-oculography at diagnosis were eligible. Measurements of saccadic accuracy, latency, and smooth pursuit gain and square wave jerk frequency were collected. Patients underwent Movement Disorders Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) and detailed cognitive tests. We investigated the associations between ocular motor measurements and specific tracer uptake ratios (SUR) in the caudate nucleus, anterior and posterior putamen, thalamus, and dorsal raphe nuclei, along with motor and cognitive symptoms.

RESULTS

One-hundred twenty-four subjects were included in this study. Saccadic accuracy was positively associated with parkinsonian motor severity expressed as Hoehn and Yahr stages, MDS-UPDRS Part III scores, and subscores for bradykinesia and rigidity but not with tremor scores (PFDR  < 0.05). Saccadic accuracy correlated with poor performances in the Rey-Complex-Figure copy, and latency with the Digit Symbol Coding and the Montreal Cognitive Assessment scores (PFDR  < 0.05). Prolonged saccadic latency correlated with reduced thalamic SUR, whereas decreased saccadic accuracy correlated with reduced SUR in the anterior and posterior putamen (PFDR  < 0.05). Reduced smooth pursuit gain showed associations with reduced SUR in the dorsal raphe, a serotonin-predominant region, but did not correlate with parkinsonism severity scores.

CONCLUSION

Defective dopaminergic and nondopaminergic neural systems may discretely influence ocular motor function in de novo PD patients. © 2023 International Parkinson and Movement Disorder Society.

Parkinson's Disease Tremor Differentially Responds to Levodopa and Subthalamic Stimulation

Background

Tremor in Parkinson's disease (PD) has an inconsistent response to levodopa and subthalamic deep brain stimulation (STN-DBS).

Objectives

To identify predictive factors of PD tremor responsiveness to levodopa and STN-DBS.

Material and Methods

PD patients with upper limb tremor who underwent STN-DBS were included. The levodopa responsiveness of tremor (overall, postural, and rest sub-components), was assessed using the relevant Unified Parkinson's Disease Rating Scale-III items performed during the preoperative assessment. Post-surgical outcomes were similarly assessed ON and OFF stimulation. A score for the rest/postural tremor ratio was used to determine the influence of rest and postural tremor severity on STN-DBS outcome. Factors predictive of tremor responsiveness were determined using multiple linear regression modeling. Volume of tissue activated measurement coupled to voxel-based analysis was performed to identify anatomical clusters associated with motor symptoms improvement.

Results

One hundred and sixty five patients were included in this study. Male gender was negatively correlated with tremor responsiveness to levodopa, whereas the ratio of rest/postural tremor was positively correlated with both levodopa responsiveness and STN-DBS tremor outcome. Clusters corresponding to improvement of tremor were in the subthalamic nucleus, the zona incerta and the thalamus, whereas clusters corresponding to improvement for akinesia and rigidity were located within the subthalamic nucleus.

Conclusion

More severe postural tremor and less severe rest tremor were associated with both poorer levodopa and STN-DBS response. The different locations of clusters associated with best correction of tremor and other parkinsonian features suggest that STN-DBS effect on PD symptoms is underpinned by the modulation of different networks.

Integrated PET/MRI With 11C-CFT and 18F-FDG for levodopa response difference in Parkinson's disease

AIM

Parkinson's disease is one of the most common neurodegenerative diseases. Excellent levodopa responsiveness has been proposed as a characteristic supporting feature in substantiating the PD diagnosis. However, a small portion of clinically established PD patients shows poor levodopa response. This study aims to investigate brain function alterations of PD patients with poor levodopa responsiveness by PET/MRI.

METHOD

A total of 46 PD patients were recruited. They all completed 11C-CFT PET/MRI scans and the acute levodopa challenge test. Among these 46 PD patients, 42 participants further underwent 18F-FDG PET/MRI scans. Clinical variables regarding demographic data, disease features and cognition scales were also collected. Based on the improvement rate of UPDRS-III, PD patients were divided into non-responders (improvement rate < 33 %) and responders (improvement rate ≥ 33 %). Statistical parametric zapping was performed to analyze molecular imaging. Dopaminergic uptake and metabolism of 70 brain regions were converted to quantitative values and expressed as standard uptake value (SUV). SUV was further normalized by the cerebellum. The resulting SUV ratios and clinical variables were then compared by SPSS.

RESULTS

The difference between levodopa non-responders (n = 17) and responders (n = 29) in the UPDRS III baseline was statistically significant and the former had a lower UPDRS III baseline (19 (10, 32), p＜0.05). In contrast, no statistical difference between these two groups was found in age, gender, disease duration, cognition, motor subtype and Hoehn-Yahr stage. Dopaminergic uptake differences between levodopa non-responders (n = 17) and responders (n = 29) were shown in the left inferior frontal cortex (1.00 ± 0.09 vs 1.07 ± 0.08, p < 0.05 and FDR < 0.2), the right posterior cingulum (1.10 ± 0.10 vs 1.20 ± 0.13, p < 0.05 and FDR < 0.2) and the right insula (1.21 ± 0.12 vs 1.30 ± 0.10, p < 0.05 and FDR < 0.2). The metabolic alterations between levodopa non-responders (n = 16) and responders (n = 26) were shown in the right supplementary motor area (1.30 (1.18, 1.39) vs 1.41 (1.31, 1.53), p < 0.05 and FDR < 0.2), right precuneus (1.37 ± 0.10 vs 1.47 ± 0.18, p < 0.05 and FDR < 0.2), right parietal cortex (1.14 ± 0.15 vs 1.27 ± 0.21, p < 0.05 and FDR < 0.2), right supramarginal gyrus (1.16 (1.12, 1.26) vs 1.25 (1.14, 1.46), p < 0.05 and FDR < 0.2), right postcentral gyrus (1.15 (1.08, 1.32) vs 1.24 (1.17, 1.39), p < 0.05 and FDR < 0.2), medulla (0.75 ± 0.07 vs 0.80 ± 0.07, p < 0.05 and FDR < 0.2), right rolandic operculum (1.25 (1.18, 1.32) vs 1.33 (1.25, 1.50), p < 0.05 and FDR < 0.2), right olfactory (0.95 (0.91, 1.01) vs 1.01 (0.95, 1.15), p < 0.05 and FDR < 0.2), the right insula (1.15 (1.06, 1.22) vs 1.21 (1.12, 1.35), p < 0.05 and FDR < 0.2) and the left cerebellum crus (0.96 (0.91, 1.01) vs 0.92 (0.86, 0.96), p < 0.05 and FDR < 0.2).

CONCLUSIONS

PD patients with poor response to levodopa showed less severe impairment of baseline motor symptoms, more severe dopaminergic deficits in the left inferior frontal, right posterior cingulate cortex and the right insula, and lower metabolism in the right supplementary motor area, right precuneus, right parietal cortex, right supramarginal gyrus, right postcentral gyrus, medulla, right rolandic operculum, right olfactory, the right insula and higher metabolism in the left cerebellum crus.

The Clinical Profile of Tremor in Parkinson's Disease

Background

Tremor is one of the most troublesome manifestations of Parkinson's Disease (PD) and its response to dopaminergic medication is variable; an evidence-based framework of PD tremor is lacking yet needed to inform future investigations.

Objective

To perform a comprehensive longitudinal analysis on the clinical characteristics, course and response to dopaminergic medication of tremor in de-novo PD.

Methods

Three hundred ninety-seven participants were recruited in the Parkinson Progressive Markers Initiative, a prospective observational cohort study in early de-novo PD. Rest, postural and kinetic tremor scores were extracted from the Movement Disorders Society-Unified Parkinson's Disease Rating Scale. Progression from baseline to 7-year follow-up of rest, postural and kinetic tremor scores, and their response to in-clinic dopaminergic medication were analyzed through linear mixed-effects models adjusted for age, sex and disease duration at enrollment. A sensitivity analysis was conducted through subgroup and imputation analyses.

Results

382 (96.2%) participants showed tremor and 346 (87.2%) showed rest tremor in at least one assessment over 7 years. Off-state rest, postural and kinetic tremor scores increased significantly over time, coupled with a significant effect of dopaminergic medication in reducing tremor scores. However, at each assessment, tremor was unresponsive to in-clinic dopaminergic medication in at least 20% of participants for rest, 30% for postural and 38% for kinetic tremor.

Conclusions

PD tremor is a troublesome manifestation, with increasing severity and variable response to medications. This analysis details the current clinical natural history of tremor in early-to-mid stage PD, outlining an evidence-based framework for future pathophysiological and interventional studies.

Reduced platelet 5-HT content is associated with rest tremor in Parkinson's disease

INTRODUCTION

Parkinson's disease (PD) is highly heterogeneous in manifestations and pathogenesis. Serotonergic neurotransmitter system dysfunction is frequently implicated in PD tremor. Serotonin (5-HT) content in platelets is highly correlated with that in cerebrospinal fluid. In this study, we aimed to understand whether and how platelet 5-HT content reflects tremor in PD.

METHOD

A total of 139 Chinese PD patients met with inclusion criteria were recruited. Motor and non-motor scores, and disease severity were evaluated. Patients were classified into subtypes of tremor-dominant (TD) and non-tremor-dominant (NTD). Peripheral platelets were isolated, and platelet 5-HT levels were measured.

RESULTS

Platelet 5-HT content was lower in PD patients of TD subtype than in NTD subtype. Multifactor risk analysis showed that this lower content was independently associated with the TD phenotype. Platelet 5-HT level was inversely correlated with total tremor score, rest tremor amplitude score, rest tremor constancy score, and index of rest tremor, but not with postural tremor score, and kinetic tremor score.

CONCLUSION

The cross-sectional study demonstrates that reduced platelet 5-HT content is associated with PD rest tremor. Our results support the involvement of serotonergic disturbance in PD rest tremor and indicate that 5-HT reduction can be manifested in peripheral platelets.

Leveraging the regulatory framework to facilitate drug development in Parkinson's disease

There is an exigent need for disease-modifying and symptomatic treatment approaches for Parkinson's disease. A better understanding of Parkinson's disease pathophysiology and new insights in genetics has opened exciting new venues for pharmacological treatment targets. There are, however, many challenges on the path from discovery to drug approval. These challenges revolve around appropriate endpoint selection, the lack of accurate biomarkers, challenges with diagnostic accuracy, and other challenges commonly encountered by drug developers. The regulatory health authorities, however, have provided tools to provide guidance for drug development and to assist with these challenges. The main goal of the Critical Path for Parkinson's Consortium, a nonprofit public-private partnership part of the Critical Path Institute, is to advance these so-called drug development tools for Parkinson's disease trials. The focus of this chapter will be on how the health regulators' tools were successfully leveraged to facilitate drug development in Parkinson's disease and other neurodegenerative diseases.

The challenging quest of neuroimaging: From clinical to molecular-based subtyping of Parkinson disease and atypical parkinsonisms

The current framework of Parkinson disease (PD) focuses on phenotypic classification despite its considerable heterogeneity. We argue that this method of classification has restricted therapeutic advances and therefore limited our ability to develop disease-modifying interventions in PD. Advances in neuroimaging have identified several molecular mechanisms relevant to PD, variation within and between clinical phenotypes, and potential compensatory mechanisms with disease progression. Magnetic resonance imaging (MRI) techniques can detect microstructural changes, disruptions in neural pathways, and metabolic and blood flow alterations. Positron emission tomography (PET) and single-photon emission computed tomography (SPECT) imaging have informed the neurotransmitter, metabolic, and inflammatory dysfunctions that could potentially distinguish disease phenotypes and predict response to therapy and clinical outcomes. However, rapid advancements in imaging techniques make it challenging to assess the significance of newer studies in the context of new theoretical frameworks. As such, there needs to not only be a standardization of practice criteria in molecular imaging but also a rethinking of target approaches. In order to harness precision medicine, a coordinated shift is needed toward divergent rather than convergent diagnostic approaches that account for interindividual differences rather than similarities within an affected population, and focus on predictive patterns rather than already lost neural activity.

The Role of α-Synuclein in the Regulation of Serotonin System: Physiological and Pathological Features

In patients affected by Parkinson's disease (PD), up to 50% of them experience cognitive changes, and psychiatric disturbances, such as anxiety and depression, often precede the onset of motor symptoms and have a negative impact on their quality of life. Pathologically, PD is characterized by the loss of dopamine (DA) neurons in the substantia nigra pars compacta (SNc) and the presence of intracellular inclusions, called Lewy bodies and Lewy neurites, composed mostly of α-synuclein (α-Syn). Much of PD research has focused on the role of α-Syn aggregates in the degeneration of SNc DA neurons due to the impact of striatal DA deficits on classical motor phenotypes. However, abundant Lewy pathology is also found in other brain regions including the midbrain raphe nuclei, which may contribute to non-motor symptoms. Indeed, dysfunction of the serotonergic (5-HT) system, which regulates mood and emotional pathways, occurs during the premotor phase of PD. However, little is known about the functional consequences of α-Syn inclusions in this neuronal population other than DA neurons. Here, we provide an overview of the current knowledge of α-Syn and its role in regulating the 5-HT function in health and disease. Understanding the relative contributions to α-Syn-linked alterations in the 5-HT system may provide a basis for identifying PD patients at risk for developing depression and could lead to a more targeted therapeutic approach.

Astrocytes and Alpha-Synuclein: Friend or Foe?

Despite its devastating disease burden and alarming prevalence, the etiology of Parkinson's disease (PD) remains to be completely elucidated. PD is characterized by the degeneration of dopaminergic neurons in the substantia nigra pars compacta and this correlates with the accumulation of misfolded α-synuclein. While the aggregation of α-synuclein in the form of Lewy bodies or Lewy neurites is a well-established intraneuronal hallmark of the disease process, our understanding of the glial contribution to aberrant α-synuclein proteostasis is lacking. In this regard, restoring astrocyte function during early PD could offer a promising therapeutic avenue and understanding the involvement of astrocytes in handling/mishandling of α-synuclein is of particular interest. Here, we explore the growing body of scientific literature implicating aberrant astrocytic α-synuclein proteostasis with the seemingly inexorable pathological sequelae typifying PD. We also provide a perspective on how heterogeneity in the morphological relationship between astrocytes and neurons will need to be considered in the context of PD pathogenesis.

Pharmacological Treatment of Tremor in Parkinson's Disease Revisited

The pathophysiology of Parkinson's disease (PD) tremor remains incompletely understood and there is a lack of clinical trials specifically addressing its pharmacological treatment. Levodopa is the most efficacious drug for most patients and should be used as primary approach to control troublesome tremor. While the efficacy of oral dopamine agonists on PD tremor has been demonstrated in controlled trials, there is no evidence of greater antitremor efficacy compared to levodopa. The magnitude of the antitremor effect of anticholinergics is generally lower than that of levodopa. Due to their adverse effects, anticholinergics have a limited role in selected young and cognitively intact patients. Propranolol may improve resting and action tremor and may be considered as an adjunct in patients with insufficient tremor response to levodopa and this also applies to clozapine, despite its unfavorable adverse effect profile. Treating motor fluctuations with MAO-B and COMT inhibitors, dopamine agonists, amantadine, or on-demand treatments such as subcutaneous or sublingual apomorphine and inhaled levodopa as well as with continuous infusions of levodopa or apomorphine will improve off period tremor episodes. For patients with drug-refractory PD tremor despite levodopa optimization deep brain stimulation and focused ultrasound are first-line considerations. Surgery can also be highly effective for the treatment medication-refractory tremor in selected patients without motor fluctuations. The present review highlights the clinical essentials of parkinsonian tremor, critically examines available trial data on the effects of medication and surgical approaches and provides guidance for the choice of treatments to control PD tremor in clinical practice.

The pathobiological basis of depression in Parkinson disease: challenges and outlooks

Depression, with an estimated prevalence of about 40% is a most common neuropsychiatric disorder in Parkinson disease (PD), with a negative impact on quality of life, cognitive impairment and functional disability, yet the underlying neurobiology is poorly understood. Depression in PD (DPD), one of its most common non-motor symptoms, can precede the onset of motor symptoms but can occur at any stage of the disease. Although its diagnosis is based on standard criteria, due to overlap with other symptoms related to PD or to side effects of treatment, depression is frequently underdiagnosed and undertreated. DPD has been related to a variety of pathogenic mechanisms associated with the underlying neurodegenerative process, in particular dysfunction of neurotransmitter systems (dopaminergic, serotonergic and noradrenergic), as well as to disturbances of cortico-limbic, striato-thalamic-prefrontal, mediotemporal-limbic networks, with disruption in the topological organization of functional mood-related, motor and other essential brain network connections due to alterations in the blood-oxygen-level-dependent (BOLD) fluctuations in multiple brain areas. Other hypothetic mechanisms involve neuroinflammation, neuroimmune dysregulation, stress hormones, neurotrophic, toxic or metabolic factors. The pathophysiology and pathogenesis of DPD are multifactorial and complex, and its interactions with genetic factors, age-related changes, cognitive disposition and other co-morbidities awaits further elucidation.

Research progress on neuromolecular imaging of REM sleep behavior disorder

Idiopathic rapid eye movement sleep behavior disorder (iRBD) is an important non-motor complication of Parkinson's disease. At the same time, iRBD is considered to be the prodromal stage of α-synucleinopathy. This high risk of conversion suggests that iRBD becomes a nerve It is a window for early research on degenerative diseases and is the best candidate for neuroprotection trials. A wide range of neuroimaging techniques has improved our understanding of iRBD as a prodromal stage of the disease. In addition, neuroimaging of abnormal iRBD is expected to be a potential biomarker for predicting clinical phenotypic transformation. This article reviews the research progress of neuromolecular imaging in patients with iRBD from the perspective of iRBD transforming synucleinopathies.

Tremor in Parkinson's Disease: From Pathophysiology to Advanced Therapies

Background

Tremor is one of the most prevalent symptoms in Parkinson's Disease (PD). The progression and management of tremor in PD can be challenging, as response to dopaminergic agents might be relatively poor, particularly in patients with tremor-dominant PD compared to the akinetic/rigid subtype. In this review, we aim to highlight recent advances in the underlying pathogenesis and treatment modalities for tremor in PD.

Methods

A structured literature search through Embase was conducted using the terms "Parkinson's Disease" AND "tremor" OR "etiology" OR "management" OR "drug resistance" OR "therapy" OR "rehabilitation" OR "surgery." After initial screening, eligible articles were selected with a focus on published literature in the last 10 years.

Discussion

The underlying pathophysiology of tremor in PD remains complex and incompletely understood. Neurodegeneration of dopaminergic neurons in the retrorubral area, in addition to high-power neural oscillations in the cerebello-thalamo-cortical circuit and the basal ganglia, play a major role. Levodopa is the first-line therapeutic option for all motor symptoms, including tremor. The addition of dopamine agonists or anticholinergics can lead to further tremor reduction. Botulinum toxin injection is an effective alternative for patients with pharmacological-resistant tremor who are not seeking advanced therapies. Deep brain stimulation is the most well-established advanced therapy owing to its long-term efficacy, reversibility, and effectiveness in other motor symptoms and fluctuations. Magnetic resonance-guided focused ultrasound is a promising modality, which has the advantage of being incisionless. Cortical and peripheral electrical stimulation are non-invasive innovatory techniques that have demonstrated good efficacy in suppressing intractable tremor.

Levodopa responsiveness in Parkinson's disease: harnessing real-life experience with machine-learning analysis

Responsiveness to levodopa varies greatly among patients with Parkinson's disease (PD). The factors that affect it are ill defined. The aim of the study was to identify factors predictive of long-term response to levodopa. The medical records of 296 patients with PD (mean age of onset, 62.2 ± 9.7 years) were screened for demographics, previous treatments, and clinical phenotypes. All patients were assessed with the Unified PD Rating Scale (UPDRS)-III before and 3 months after levodopa initiation. Regression and machine-learning analyses were used to determine factors that are associated with levodopa responsiveness and might identify patients who will benefit from treatment. The UPDRS-III score improved by ≥ 30% (good response) in 128 patients (43%). On regression analysis, female gender, young age at onset, and early use of dopamine agonists predicted a good response. Time to initiation of levodopa treatment had no effect on responsiveness except in patients older than 72 years, who were less responsive. Machine-learning analysis validated these factors and added several others: symptoms of rigidity and bradykinesia, disease onset in the legs and on the left side, and fewer white vascular ischemic changes, comorbidities, and pre-non-motor symptoms. The main determinants of variations in levodopa responsiveness are gender, age, and clinical phenotype. Early use of dopamine agonists does not hamper levodopa responsiveness. In addition to validating the regression analysis results, machine-learning methods helped to determine the specific clinical phenotype of patients who may benefit from levodopa in terms of comorbidities and pre-motor and non-motor symptoms.

A review on pathology, mechanism, and therapy for cerebellum and tremor in Parkinson's disease

Tremor is one of the core symptoms of Parkinson’s disease (PD), but its mechanism is poorly understood. The cerebellum is a growing focus in PD-related researches and is reported to play an important role in tremor in PD. The cerebellum may participate in the modulation of tremor amplitude via cerebello-thalamo-cortical circuits. The cerebellar excitatory projections to the ventral intermediate nucleus of the thalamus may be enhanced due to PD-related changes, including dopaminergic/non-dopaminergic system abnormality, white matter damage, and deep nuclei impairment, which may contribute to dysregulation and resistance to levodopa of tremor. This review summarized the pathological, structural, and functional changes of the cerebellum in PD and discussed the role of the cerebellum in PD-related tremor, aiming to provide an overview of the cerebellum-related mechanism of tremor in PD.

Depression in Patients with Parkinson's Disease: Current Understanding of its Neurobiology and Implications for Treatment

Depression is one of the most frequent and burdensome non-motor symptoms in Parkinson’s disease (PD), across all stages. Even when its severity is mild, PD depression has a great impact on quality of life for these patients and their caregivers. Accordingly, accurate diagnosis, supported by validated scales, identification of risk factors, and recognition of motor and non-motor symptoms comorbid to depression are critical to understanding the neurobiology of depression, which in turn determines the effectiveness of dopaminergic drugs, antidepressants and non-pharmacological interventions. Recent advances using in vivo functional and structural imaging demonstrate that PD depression is underpinned by dysfunction of limbic networks and monoaminergic systems, depending on the stage of PD and its associated symptoms, including apathy, anxiety, rapid eye movement sleep behavior disorder (RBD), cognitive impairment and dementia. In particular, the evolution of serotonergic, noradrenergic, and dopaminergic dysfunction and abnormalities of limbic circuits across time, involving the anterior cingulate and orbitofrontal cortices, amygdala, thalamus and ventral striatum, help to delineate the variable expression of depression in patients with prodromal, early and advanced PD. Evidence is accumulating to support the use of dual serotonin and noradrenaline reuptake inhibitors (desipramine, nortriptyline, venlafaxine) in patients with PD and moderate to severe depression, while selective serotonin reuptake inhibitors, repetitive transcranial magnetic stimulation and cognitive behavioral therapy may also be considered. In all patients, recent findings advocate that optimization of dopamine replacement therapy and evaluation of deep brain stimulation of the subthalamic nucleus to improve motor symptoms represents an important first step, in addition to physical activity. Overall, this review indicates that increasing understanding of neurobiological changes help to implement a roadmap of tailored interventions for patients with PD and depression, depending on the stage and comorbid symptoms underlying PD subtypes and their prognosis.

Beneficial Effects of Snail Helix aspersa Extract in an Experimental Model of Alzheimer’s Type Dementia

Background: Alzheimer’s disease (AD) is a complex neurodegenerative disease with multifactorial etiology, unsatisfactory treatment, and a necessity for broad-spectrum active substances for cure. The mucus from Helix aspersa snail is a mixture of bioactive molecules with antimicrobial, anti-inflammatory, antioxidant, and anti-apoptotic effects. So far there are no data concerning the capacity of snail extract (SE) to affect neurodegenerative disorders. Objective: The effects of SE from Helix aspersa on learning and memory deficits in Alzheimer’s type dementia (ATD) induced by scopolamine (Sco) in male Wistar rats were examined and some mechanisms of action underlying these effects were evaluated. Methods: SE (0.5 mL/100 g) was applied orally through a food tube for 16 consecutive days: 5 days before and 11 days simultaneously with Sco (2 mg/kg, intraperitoneally). At the end of Sco treatment, using behavioral methods, we evaluated memory performance. Additionally, in cortex and hippocampus the acetylcholinesterase (AChE) activity, acetylcholine and monoamines (dopamine, noradrenaline, and serotonin) content, levels of main oxidative stress markers, and expression of brain-derived neurotrophic factor (BDNF) and cAMP response element-binding protein (CREB) were determined. Results: We demonstrated that, according to all behavioral tests used, SE significantly improved the cognitive deficits induced by Sco. Furthermore, SE possessed AChE inhibitory activity, moderate antioxidant properties and the ability to modulate monoamines content in two brain structures. Moreover, multiple SE applications not only restored the depressed by Sco expression of CREB and BDNF, but significantly upregulated it. Conclusion: Summarizing results, we conclude that complex mechanisms underlie the beneficial effects of SE on impaired memory in Alzheimer’s type dementia.

Role of dopamine and clinical heterogeneity in cognitive dysfunction in Parkinson's disease

Parkinson's disease (PD) is commonly treated with dopaminergic medication, which enhances some, while impairing other cognitive functions. It can even contribute to impulse control disorder and addiction. We describe the history of research supporting the dopamine overdose hypothesis, which accounts for the large within-patient variability in dopaminergic medication effects across different tasks by referring to the spatially non-uniform pattern of dopamine depletion in dorsal versus ventral striatum. However, there is tremendous variability in dopaminergic medication effects not just within patients across distinct tasks, but also across different patients. In the second part of this chapter we review recent studies addressing the large individual variability in the negative side effects of dopaminergic medication on functions that implicate dopamine, such as value-based learning and choice. These studies begin to unravel the mechanisms of dopamine overdosing, thus revising the strict version of the overdose hypothesis. For example, the work shows that the canonical boosting of reward-versus punishment-based choice by medication is greater in patients with depression and a non-tremor phenotype, which both implicate, among other pathology, more rather than less severe dysregulation of the mesolimbic dopamine system. Future longitudinal cohort studies are needed to identify how to optimally combine different clinical, personality, cognitive, neural, genetic and molecular predictors of detrimental medication effects in order to account for as much of the relevant variability as possible. This will provide a useful tool for precision neurology, allowing individual and contextual tailoring of (the dose of) dopaminergic medication in order to maximize its cognitive benefits, yet minimize its side effects.

Motor and non-motor circuit disturbances in early Parkinson disease: which happens first?

For the last two decades, pathogenic concepts in Parkinson disease (PD) have revolved around the toxicity and spread of α-synuclein. Thus, α-synuclein would follow caudo-rostral propagation from the periphery to the central nervous system, first producing non-motor manifestations (such as constipation, sleep disorders and hyposmia), and subsequently impinging upon the mesencephalon to account for the cardinal motor features before reaching the neocortex as the disease evolves towards dementia. This model is the prevailing theory of the principal neurobiological mechanism of disease. Here, we scrutinize the temporal evolution of motor and non-motor manifestations in PD and suggest that, even though the postulated bottom-up mechanisms are likely to be involved, early involvement of the nigrostriatal system is a key and prominent pathophysiological mechanism. Upcoming studies of detailed clinical manifestations with newer neuroimaging techniques will allow us to more closely define, in vivo, the role of α-synuclein aggregates with respect to neuronal loss during the onset and progression of PD.

Etiologies of insomnia in Parkinson's disease - Lessons from human studies and animal models

Sleep disorders are integral to Parkinson's disease (PD). Insomnia, an inability to maintain stable sleep, affects most patients and is widely rated as one of the most debilitating facets of this disease. PD insomnia is often perceived as a multifactorial entity - a consequence of several of the disease symptoms, comorbidities and therapeutic strategies. Yet, this view evolved against a backdrop of a relative scarcity of works trying to directly dissect the underlying neural correlates and mechanisms in animal models. The last years have seen the emergence of a wealth of new evidence regarding the neural underpinnings of insomnia in PD. Here, we review early and recent reports from patients and animal models evaluating the etiology of PD insomnia. We start by outlining the phenomenology of PD insomnia and continue to analyze the evidence supporting insomnia as emanating from four distinct subdivisions of etiologies - the symptoms and comorbidities of the disease, the medical therapy, the degeneration of non-dopaminergic cell groups and subsequent alterations in circadian rhythms, and the degeneration of dopaminergic neurons in the brainstem and its resulting effect on the basal ganglia. Finally, we review emerging neuromodulation-based therapeutic avenues for PD insomnia.

Amantadine Treatment and Delayed Onset of Levodopa-Induced Dyskinesia in Patients with Early Parkinson's Disease

BACKGROUND

Levodopa-induced dyskinesia (LID) is a common motor complication in patients with Parkinson's disease (PD). Although amantadine is indicated LID treatment, it is uncertain whether early treatment with amantadine reduces the risk of LID in patients with PD.

OBJECTIVE

We aimed to evaluate the association between amantadine treatment and LID onset in patients with early-stage PD.

METHODS

This was a hospital-based retrospective cohort study that used electronic medical records from January 1, 2009 to October 31, 2016. The effect of amantadine on LID onset was compared with those of anticholinergics and monoamine oxidase type B inhibitors in patients with PD. Propensity score weighting and landmark analysis were used to reduce potential confounding. The time to LID onset was analyzed using Cox models. Sensitivity analyses were performed to determine the robustness of the results.

RESULTS

The analyses included 807, 661, and 518 patients at 6-, 12-, and 18-month landmark points, respectively. Amantadine use was associated with delayed LID onset in the 6- and 12-month landmark analyses, with adjusted hazard ratios of 0.65 (95% confidence interval [CI] 0.49-0.86) and 0.64 (95% CI 0.47-0.88), respectively. Sensitivity analysis findings were comparable to those of the main analysis.

CONCLUSIONS

Early treatment with amantadine may delay LID onset more than treatment with other symptomatic agents. Further studies are needed to elucidate the mechanism of amantadine in LID onset delay, and to validate our findings.

The Molecular Neuroimaging of Tremor

Purpose of Review

Tremor is a hyperkinetic movement disorder most commonly encountered in essential tremor (ET) and Parkinson’s disease (PD). The purpose of this review is to summarize molecular neuroimaging studies with major implications on pathophysiological and clinical features of tremor.

Recent Findings

Oscillatory brain activity responsible for tremor manifestation is thought to originate in a cerebello-thalamo-cortical network. Molecular neuroimaging has helped clarify metabolic aspects and neurotransmitter influences on the main tremor network. In ET, recent positron emission tomography (PET) studies are built on previous knowledge and highlighted the possibility of investigating metabolic brain changes after treatments, in the attempt to establish therapeutic biomarkers. In PD, molecular neuroimaging has advanced the knowledge of non-dopaminergic determinants of tremor, providing insights into serotonergic and noradrenergic contributions.

Summary

Recent advances have greatly extended the knowledge of tremor pathophysiology and it is now necessary to translate such knowledge in more efficacious treatments for this symptom.

Dopamine Transporter Imaging, Current Status of a Potential Biomarker: A Comprehensive Review

A major goal of current clinical research in Parkinson's disease (PD) is the validation and standardization of biomarkers enabling early diagnosis, predicting outcomes, understanding PD pathophysiology, and demonstrating target engagement in clinical trials. Molecular imaging with specific dopamine-related tracers offers a practical indirect imaging biomarker of PD, serving as a powerful tool to assess the status of presynaptic nigrostriatal terminals. In this review we provide an update on the dopamine transporter (DAT) imaging in PD and translate recent findings to potentially valuable clinical practice applications. The role of DAT imaging as diagnostic, preclinical and predictive biomarker is discussed, especially in view of recent evidence questioning the incontrovertible correlation between striatal DAT binding and nigral cell or axon counts.

The role of neuroimaging in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder that affects millions of people worldwide. Two hallmarks of PD are the accumulation of alpha-synuclein and the loss of dopaminergic neurons in the brain. There is no cure for PD, and all existing treatments focus on alleviating the symptoms. PD diagnosis is also based on the symptoms, such as abnormalities of movement, mood, and cognition observed in the patients. Molecular imaging methods such as magnetic resonance imaging (MRI), single-photon emission computed tomography (SPECT), and positron emission tomography (PET) can detect objective alterations in the neurochemical machinery of the brain and help diagnose and study neurodegenerative diseases. This review addresses the application of functional MRI, PET, and SPECT in PD patients. We provide an overview of the imaging targets, discuss the rationale behind target selection, the agents (tracers) with which the imaging can be performed, and the main findings regarding each target's state in PD. Molecular imaging has proven itself effective in supporting clinical diagnosis of PD and has helped reveal that PD is a heterogeneous disorder, which has important implications for the development of future therapies. However, the application of molecular imaging for early diagnosis of PD or for differentiation between PD and atypical parkinsonisms has remained challenging. The final section of the review is dedicated to new imaging targets with which one can detect the PD-related pathological changes upstream from dopaminergic degeneration. The foremost of those targets is alpha-synuclein. We discuss the progress of tracer development achieved so far and challenges on the path toward alpha-synuclein imaging in humans.

Unexpected (123I)FP-CIT SPECT findings: SWIDD, SWEDD and all DAT

Although the diagnosis of Parkinson's disease (PD) is essentially clinical, the implementation of imaging techniques can improve diagnostic accuracy. While some techniques (e.g. magnetic resonance imaging-MRI, computerized tomography-CT) are used to exclude secondary syndromes, presynaptic dopaminergic imaging including imaging of dopamine transporter (DAT)-can help the Neurologist in the differential diagnosis between neurodegenerative parkinsonian syndromes and parkinsonism without dopamine deficiency. DAT imaging can be useful in cases in which the clinical picture is not univocal, as in case of overlapping clinical features in patients with early disease, atypical syndromes or unsatisfying response to therapy. Currently, (¹²³I)FP-CIT ([123I]N-ω-fluoropropyl-2β-carbomethoxy-3β-(4-iodophenyl)nortropane) (trade name DaTSCAN) is the only agent approved by international regulatory agencies for this purpose. With the increasing use of this technique, some unexpected findings have been reported, including patients clinically diagnosed with PD with a normal SPECT scan [e.g. Scans Without Evidence of Dopaminergic Deficit (SWEDD)]; PD patients with a greater dopaminergic deficit in the striatum ipsilateral to the clinically more affected side [e.g. Scans With Ipsilateral Dopaminergic Deficit (SWIDD)]; as well as some artifacts. Moreover, the neurologist must remember that structural lesions and administration of some drugs might alter the result of DAT imaging. Unexpected findings, artifacts, and misinterpretation of imaging findings can lead to an erroneous diagnosis and inappropriate therapy, neglect of other medical conditions that might explain the clinical picture, and undermine the selection phase in clinical trials. The aim of the present review is to bring clarity on these controversial (and sometimes erroneous) results, in order to inform of these possibilities the clinicians requesting a DaTSCAN in clinical practice.

Serotonergic and Dopaminergic Lesions Underlying Parkinsonian Neuropsychiatric Signs

BACKGROUND

Parkinson's disease (PD) is characterized by heterogeneous motor and nonmotor manifestations related to alterations in monoaminergic neurotransmission systems. Nevertheless, the characterization of concomitant dopaminergic and serotonergic dysfunction after different durations of Parkinson's disease, as well as their respective involvement in the expression and severity of neuropsychiatric signs, has gained little attention so far.

METHODS

To fill this gap, we conducted a cross-sectional study combining clinical and dual-tracer positron emission tomography (PET) neuroimaging approaches, using radioligands of dopamine ([¹¹ C]-N-(3-iodoprop-2E-enyl)-2-beta-carbomethoxy-3-beta-(4-methylphenyl)-nortropane) ([¹¹ C]PE2I) and serotonin ([¹¹ C]-N,N-dimethyl-2-(-2-amino-4-cyanophenylthio)-benzylamine) ([¹¹ C]DASB) reuptake, after different durations of Parkinson's disease (ie, in short-disease duration drug-naive de novo (n = 27, 0-2 years-duration), suffering from apathy (n = 14) or not (n = 13); intermediate-disease duration (n = 15, 4-7 years-duration) and long-disease duration, non-demented (n = 15, 8-10 years-duration) patients). Fifteen age-matched healthy subjects were also enrolled.

RESULTS

The main findings are threefold: (1) both dopaminergic and serotonergic lesions worsen with the duration of Parkinson's disease, spreading from midbrain/subcortical to cortical regions; (2) the presence of apathy at PD onset is associated with more severe cortical and subcortical serotonergic and dopaminergic disruption, similar to the denervation pattern observed in intermediate-disease duration patients; and (3) the severity of parkinsonian apathy, depression, and trait-anxiety appears primarily related to serotonergic alteration within corticostriatal limbic areas.

CONCLUSIONS

Altogether, these findings highlight the prominent role of serotonergic degeneration in the expression of several neuropsychiatric symptoms occurring after different durations of Parkinson's disease. © 2021 International Parkinson and Movement Disorder Society.

Histamine-4 Receptor: Emerging Target for the Treatment of Neurological Diseases

A major challenge in the field of the biogenic amine histamine is the search for new-generation histamine receptor specific drugs. Daniel Bovet and Sir James Black received their Nobel Prizes for Medicine for their work on histamine-1 receptor (H₁R) and H₂R antagonists to treat allergies and gastrointestinal disorders. The first H₃R-targeting drug to reach the market was approved for the treatment of the neurological disorder narcolepsy in 2018. The antagonists for the most recently identified histamine receptor, H₄R, are currently under clinical evaluation for their potential therapeutic effects on inflammatory diseases such as atopic dermatitis and pruritus. In this chapter, we propose that H₄R antagonists are endowed with prominent anti-inflammatory and immune effects, including in the brain. To substantiate this proposition, we combine data from transcriptional analyses of postmortem human neurodegenerative disease brain samples, human genome-wide association studies (GWAS), and translational animal model studies. The results prompt us to suggest the potential involvement of the H₄R in various neurodegenerative diseases and how manipulating the H₄R may create new therapeutic opportunities in central nervous system diseases.

Current Update on Clinically Relevant Sleep Issues in Parkinson's Disease: A Narrative Review

Sleep disturbances are among the common nonmotor symptoms in patients with Parkinson’s disease (PD). Sleep can be disrupted by nocturnal motor and nonmotor symptoms and other comorbid sleep disorders. Rapid eye movement sleep behavior disorder (RBD) causes sleep-related injury, has important clinical implications as a harbinger of PD and predicts a progressive clinical phenotype. Restless legs syndrome (RLS) and its related symptoms can impair sleep initiation. Excessive daytime sleepiness (EDS) is a refractory problem affecting patients’ daytime activities. In particular, during the COVID-19 era, special attention should be paid to monitoring sleep problems, as infection-prevention procedures for COVID-19 can affect patients’ motor symptoms, psychiatric symptoms and sleep. Therefore, screening for and managing sleep problems is important in clinical practice, and the maintenance of good sleep conditions may improve the quality of life of PD patients. This narrative review focused on the literature published in the past 10 years, providing a current update of various sleep disturbances in PD patients and their management, including RBD, RLS, EDS, sleep apnea and circadian abnormalities.

Preserved Extrastriatal 123I-FP-CIT Binding in Scans Without Evidence of Dopaminergic Deficit (SWEDD)

PURPOSE

Scans without evidence of dopaminergic deficit (SWEDD) have been initially described in a minority of subjects with suspected Parkinson's disease (PD). Although a highly controversial entity, longitudinal studies showed that SWEDD cases mostly involve non-degenerative conditions mimicking PD or misattribution of scan images to normal status. Using the Parkinson's Progression Markers Initiative (PPMI) cohort, we undertook a case-controlled analysis of [123I]N-ω-fluoropropyl-2β-carbomethoxy-iodophenyl nortropane ([123I]FP-CIT) single photon emission computed tomography (SPECT) images to measure extrastriatal serotonergic transporter (SERT) density in SWEDD and PD.

PROCEDURES

We included 37 SWEDD cases (mean age 60 years, 33 % female) with available [123I]FP-CIT SPECT imaging and high-resolution T1-weighted magnetic resonance imaging (MRI) for coregistration. Sixty-one controls and 62 similarly aged PD subjects were included for group comparisons. Regional [123I]FP-CIT was extracted with PETPVE12 using geometric transfer matrix and partial volume effect correction.

RESULTS

PD subjects showed significantly lower [123I]FP-CIT binding in both striatal (caudate nucleus and putamen) and extrastriatal regions (pallidum and insula) compared with controls and SWEDD (all between-group p < 0.0001). PD group also showed lower binding in the thalamus relative to controls (p = 0.007). Receiver operating characteristics (ROC) area under the curve (AUC) did not show a significant difference when using extrastriatal region in addition to striatal ROIs for the separation of SWEDD and PD (95 % ROC-AUC for both methods, p = 0.52). In addition, striatal [123I]FP-CIT binding contralateral to the clinically more affected side was usually lower for PD (> 75 %) but not for SWEDD (< 49 %, p < 0.002). No significant difference regarding [123I]FP-CIT binding was observed between SWEDD and controls.

CONCLUSION

These findings corroborate the view that SWEDD cases represent a heterogeneous group of conditions not involving dopaminergic and serotonergic terminals. Further studies are warranted to be assessed whether using extrastriatal [123I]FP-CIT evaluation can be of help in the assessment of degenerative parkinsonism.

Increasing Serotonin to Reduce Parkinsonian Tremor

While current dopamine-based drugs seem to be effective for most Parkinson's disease (PD) motor dysfunctions, they produce variable responsiveness for resting tremor. This lack of consistency could be explained by considering recent evidence suggesting that PD resting tremor can be divided into different partially overlapping phenotypes based on the dopamine response. These phenotypes may be associated with different pathophysiological mechanisms produced by a cortical-subcortical network involving even non-dopaminergic areas traditionally not directly related to PD. In this study, we propose a bio-constrained computational model to study the neural mechanisms underlying a possible type of PD tremor: the one mainly involving the serotoninergic system. The simulations run with the model demonstrate that a physiological serotonin increase can partially recover dopamine levels at the early stages of the disease before the manifestation of overt tremor. This result suggests that monitoring serotonin concentration changes could be critical for early diagnosis. The simulations also show the effectiveness of a new pharmacological treatment for tremor that acts on serotonin to recover dopamine levels. This latter result has been validated by reproducing existing data collected with human patients.