Cholinergic nucleus 4 atrophy and gait impairment in Parkinson's disease

Frontoparietal-Striatal Network and Nucleus Basalis Modulation in Patients With Parkinson Disease and Gait Disturbance

BACKGROUND AND OBJECTIVES

Neural computations underlying gait disorders in Parkinson disease (PD) are multifactorial and involve impaired expression of stereotactic locomotor patterns and compensatory recruitment of cognitive functions. This study aimed to clarify the network mechanisms of cognitive contribution to gait control and its breakdown in patients with PD.

METHODS

Patients with PD were instructed to walk at a comfortable pace on a mat with pressure sensors. The characterization of cognitive-motor interplay was enhanced by using a gait with a secondary cognitive task (dual-task condition) and a gait without additional tasks (single-task condition). Participants were scanned using 3-T MRI and 123I-ioflupane SPECT.

RESULTS

According to gait characteristics, cluster analysis assisted by a nonlinear dimensionality reduction technique, t-distributed stochastic neighbor embedding, categorized 56 patients with PD into 3 subpopulations. The preserved gait (PG) subgroup (n = 23) showed preserved speed and variability during gait, both with and without additional cognitive load. Compared with the PG subgroup, the mildly impaired gait (MIG) subgroup (n = 16) demonstrated deteriorated gait variability with additional cognitive load and impaired speed and gait variability without additional cognitive load. The severely impaired gait (SIG) subgroup (n = 17) revealed the slowest speed and highest gait variability. In addition, group differences were found in attention/working memory and executive function domains, with the lowest performance in the SIG subgroup than in the PG and MIG subgroups. Using resting-state functional MRI, the SIG subgroup demonstrated lower functional connectivity of the left and right frontoparietal network (FPN) with the caudate than the PG subgroup did (left FPN, d = 1.21, p < 0.001; right FPN, d = 1.05, p = 0.004). Cortical thickness in the FPN and 123I-ioflupane uptake in the striatum did not differ among the 3 subgroups. By contrast, the severity of Ch4 density loss was significantly correlated with the level of functional connectivity degradation of the FPN and caudate (left FPN-caudate, r = 0.27, p = 0.04).

DISCUSSION

These findings suggest that the functional connectivity of the FPN with the caudate, as mediated by the cholinergic Ch4 projection system, underlies the compensatory recruitment of attention and executive function for damaged automaticity in gait in patients with PD.

Cholinergic nucleus degeneration and its association with gait impairment in Parkinson's disease

BACKGROUND

The contribution of cholinergic degeneration to gait disturbance in Parkinson's disease (PD) is increasingly recognized, yet its relationship with dopaminergic-resistant gait parameters has been poorly investigated. We investigated the association between comprehensive gait parameters and cholinergic nucleus degeneration in PD.

METHODS

This cross-sectional study enrolled 84 PD patients and 69 controls. All subjects underwent brain structural magnetic resonance imaging to assess the gray matter density (GMD) and volume (GMV) of the cholinergic nuclei (Ch123/Ch4). Gait parameters under single-task (ST) and dual-task (DT) walking tests were acquired using sensor wearables in PD group. We compared cholinergic nucleus morphology and gait performance between groups and examined their association.

RESULTS

PD patients exhibited significantly decreased GMD and GMV of the left Ch4 compared to controls after reaching HY stage > 2. Significant correlations were observed between multiple gait parameters and bilateral Ch123/Ch4. After multiple testing correction, the Ch123/Ch4 degeneration was significantly associated with shorter stride length, lower gait velocity, longer stance phase, smaller ankle toe-off and heel-strike angles under both ST and DT condition. For PD patients with HY stage 1-2, there were no significant degeneration of Ch123/4, and only right side Ch123/Ch4 were corrected with the gait parameters. However, as the disease progressed to HY stage > 2, bilateral Ch123/Ch4 nuclei showed correlations with gait performance, with more extensive significant correlations were observed in the right side.

CONCLUSIONS

Our study demonstrated the progressive association between cholinergic nuclei degeneration and gait impairment across different stages of PD, and highlighting the potential lateralization of the cholinergic nuclei's impact on gait impairment. These findings offer insights for the design and implementation of future clinical trials investigating cholinergic treatments as a promising approach to address gait impairments in PD.

Cholinergic basal forebrain system degeneration underlies postural instability/gait difficulty and attention impairment in Parkinson's disease

BACKGROUND AND PURPOSE

The specific pathophysiological mechanisms underlying postural instability/gait difficulty (PIGD) and cognitive function in Parkinson's disease (PD) remain unclear. Both postural and gait control, as well as cognitive function, are associated with the cholinergic basal forebrain (cBF) system.

METHODS

A total of 84 PD patients and 82 normal controls were enrolled. Each participant underwent motor and cognitive assessments. Diffusion tensor imaging was used to detect structural abnormalities in the cBF system. The cBF was segmented using FreeSurfer, and its fiber tract was traced using probabilistic tractography. To provide information on extracellular water accumulation, free-water fraction (FWf) was quantified. FWf in the cBF and its fiber tract, as well as cortical projection density, were extracted for statistical analyses.

RESULTS

Patients had significantly higher FWf in the cBF (p < 0.001) and fiber tract (p = 0.021) than normal controls, as well as significantly lower cBF projection in the occipital (p < 0.001), parietal (p < 0.001) and prefrontal cortex (p = 0.005). In patients, a higher FWf in the cBF correlated with worse PIGD score (r = 0.306, p = 0.006) and longer Trail Making Test A time (r = 0.303, p = 0.007). Attentional function (Trail Making Test A) partially mediated the association between FWf in the cBF and PIGD score (indirect effect, a*b = 0.071; total effect, c = 0.256; p = 0.006).

CONCLUSIONS

Our findings suggest that degeneration of the cBF system in PD, from the cBF to its fiber tract and cortical projection, plays an important role in cognitive-motor interaction.

Band-Specific Altered Cortical Connectivity in Early Parkinson's Disease and its Clinical Correlates

BACKGROUND

Functional connectivity (FC) has shown promising results in assessing the pathophysiology and identifying early biomarkers of neurodegenerative disorders, such as Parkinson's disease (PD).

OBJECTIVES

In this study, we aimed to assess possible resting-state FC abnormalities in early-stage PD patients using high-density electroencephalography (EEG) and to detect their clinical relationship with motor and non-motor PD symptoms.

METHODS

We enrolled 26 early-stage levodopa naïve PD patients and a group of 20 healthy controls (HC). Data were recorded with 64-channels EEG system and a source-reconstruction method was used to identify brain-region activity. FC was calculated using the weighted phase-lag index in θ, α, and β bands. Additionally, we quantified the unbalancing between β and lower frequencies through a novel index (β-functional ratio [FR]). Statistical analysis was conducted using a network-based statistical approach.

RESULTS

PD patients showed hypoconnected networks in θ and α band, involving prefrontal-limbic-temporal and frontoparietal areas, respectively, and a hyperconnected network in the β frequency band, involving sensorimotor-frontal areas. The θ FC network was negatively related to Non-Motor Symptoms Scale scores and α FC to the Movement Disorder Society-Sponsored Revision of the Unified Parkinson's Disease Rating Scale part III gait subscore, whereas β FC and β-FR network were positively linked to the bradykinesia subscore. Changes in θ FC and β-FR showed substantial reliability and high accuracy, precision, sensitivity, and specificity in discriminating PD and HC.

CONCLUSIONS

Frequency-specific FC changes in PD likely reflect the dysfunction of distinct cortical networks, which occur from the early stage of the disease. These abnormalities are involved in the pathophysiology of specific motor and non-motor PD symptoms, including gait, bradykinesia, mood, and cognition. © 2023 International Parkinson and Movement Disorder Society.

Cholinergic nucleus 4 grey matter density is associated with apathy in Parkinson's disease

Objective: The generation and maintenance of goal-directed behavior is subserved by multiple brain regions that receive cholinergic inputs from the cholinergic nucleus 4 (Ch4). It is unknown if Ch4 degeneration contributes to apathy in Parkinson's disease (PD). Method: We analyzed data from 106 pre-surgical patients with PD who had brain MRIs and completed the Frontal Systems Behavior Scales (FrSBe). Eighty-eight patients also completed the Beck Depression Inventory-2nd Edition. Cholinergic basal forebrain grey matter densities (GMD) were measured by applying probabilistic maps to T1 MPRAGE sequences processed using voxel-based morphometry methods. We used linear and hierarchical regression modelling to examine the association between Ch4 GMD and the FrSBe Apathy subscale scores. We used similar methods to assess the specificity of this association and potential associations between Ch4 target regions and apathy. Results: Ch4 GMD (p = .021) and Ch123 GMD (p = .032) were significantly associated with Apathy subscale scores on univariate analysis. Ch4 GMD, but not Ch123 GMD, remained significantly associated with apathy when adjusting for age, sex, levodopa equivalent doses, and disease duration. Centromedial amygdala GMD, which receives cholinergic inputs from Ch4, was also associated with apathy. Ch4 GMD was not associated with depression or disinhibition, nor was it associated with executive dysfunction when adjusting for clinical and demographic variables. Conclusions: Ch4 GMD is specifically associated with apathy in PD. Ch4 degeneration results in cholinergic denervation of multiple cortical and limbic regions, which may contribute to the cognitive and emotional-affective processing deficits that underlie the behavioral symptoms of apathy.

Reduced Short-Latency Afferent Inhibition in Parkinson's Disease Patients with L-dopa-Unresponsive Freezing of Gait

BACKGROUND

Freezing of gait (FOG) in Parkinson's disease (PD), especially the "L-dopa-unresponsive" subtype, is associated with the dysfunction of non-dopaminergic circuits.

OBJECTIVE

We sought to determine whether cortical sensorimotor inhibition evaluated by short-latency afferent inhibition (SAI) related to cholinergic and gamma-aminobutyric acid (GABA)-ergic activities is impaired in PD patients with L-dopa-unresponsive FOG (ONOFF-FOG).

METHODS

SAI protocol was performed in 28 PD patients with ONOFF-FOG, 15 PD patients with "off" FOG (OFF-FOG), and 25 PD patients without FOG during medication "on" state. Additionally, 10 ONOFF-FOG patients underwent SAI testing during both "off" and "on" states. Twenty healthy controls participated in this study. Gait was measured objectively using a portable Inertial Measurement Unit system, and participants performed 5-meter Timed Up and Go single- and dual-task conditions. Spatiotemporal gait characteristics and their variability were determined. FOG manifestations and cognition were assessed with clinical scales.

RESULTS

Compared to controls, PD patients without FOG and with OFF-FOG, ONOFF-FOG PD patients showed significantly reduced SAI. Further, dopaminergic therapy had no remarkable effect on this SAI alterations in ONOFF-FOG. Meanwhile, OFF-FOG patients presented decreased SAI only relative to controls. PD patients with ONOFF-FOG exhibited decreased gait speed, stride length, and increased gait variability relative to PD patients without FOG and controls under both walking conditions. For ONOFF-FOG patients, significant associations were found between SAI and FOG severity, gait characteristics and variability.

CONCLUSION

Reduced SAI was associated with severe FOG manifestations, impaired gait characteristics and variability in PD patients with ONOFF-FOG, suggesting the impaired thalamocortical cholinergic-GABAergic SAI pathways underlying ONOFF-FOG.

Preclinical and randomized clinical evaluation of the p38α kinase inhibitor neflamapimod for basal forebrain cholinergic degeneration

The endosome-associated GTPase Rab5 is a central player in the molecular mechanisms leading to degeneration of basal forebrain cholinergic neurons (BFCN), a long-standing target for drug development. As p38α is a Rab5 activator, we hypothesized that inhibition of this kinase holds potential as an approach to treat diseases associated with BFCN loss. Herein, we report that neflamapimod (oral small molecule p38α inhibitor) reduces Rab5 activity, reverses endosomal pathology, and restores the numbers and morphology of BFCNs in a mouse model that develops BFCN degeneration. We also report on the results of an exploratory (hypothesis-generating) phase 2a randomized double-blind 16-week placebo-controlled clinical trial (Clinical trial registration: NCT04001517/EudraCT #2019-001566-15) of neflamapimod in mild-to-moderate dementia with Lewy bodies (DLB), a disease in which BFCN degeneration is an important driver of disease expression. A total of 91 participants, all receiving background cholinesterase inhibitor therapy, were randomized 1:1 between neflamapimod 40 mg or matching placebo capsules (taken orally twice-daily if weight <80 kg or thrice-daily if weight >80 kg). Neflamapimod does not show an effect in the clinical study on the primary endpoint, a cognitive-test battery. On two secondary endpoints, a measure of functional mobility and a dementia rating-scale, improvements were seen that are consistent with an effect on BFCN function. Neflamapimod treatment is well-tolerated with no study drug associated treatment discontinuations. The combined preclinical and clinical observations inform on the validity of the Rab5-based pathogenic model of cholinergic degeneration and provide a foundation for confirmatory (hypothesis-testing) clinical evaluation of neflamapimod in DLB.

Alterations of structure and functional connectivity of visual brain network in patients with freezing of gait in Parkinson’s disease

Freezing of gait (FOG) is a disabling gait disorder common in advanced stage of Parkinson’s disease (PD). The gait performance of PD-FOG patients is closely linked with visual processing. Here, we aimed to investigate the structural and functional change of visual network in PD-FOG patients. Seventy-eight PD patients (25 with FOG, 53 without FOG) and 29 healthy controls (HCs) were included. All the participants underwent structural 3D T1-weighted magnetic resonance imaging (MRI) and resting state functional MRI scan. Our results demonstrated a significant decrease of right superior occipital gyrus gray matter density in PD-FOG relative to non-FOG (NFOG) patients and healthy controls (PD-FOG vs. PD-NFOG: 0.33 ± 0.04 vs. 0.37 ± 0.05, p = 0.005; PD-FOG vs. HC: 0.37 ± 0.05 vs. 0.39 ± 0.06, p = 0.002). Functional MRI revealed a significant decrease of connectivity between right superior occipital gyrus and right paracentral lobule in PD-FOG compared to PD-NFOG (p = 0.045). In addition, the connectivity strength was positively correlated with gray matter density of right superior occipital gyrus (r = 0.471, p = 0.027) and negatively associated with freezing of gait questionnaire (FOGQ) score (r = -0.562, p = 0.004). Our study suggests that the structural and functional impairment of visual-motor network might underlie the neural mechanism of FOG in PD.

Cholinergic systems, attentional-motor integration, and cognitive control in Parkinson's disease

Dysfunction and degeneration of CNS cholinergic systems is a significant component of multi-system pathology in Parkinson's disease (PD). We review the basic architecture of human CNS cholinergic systems and the tools available for studying changes in human cholinergic systems. Earlier post-mortem studies implicated abnormalities of basal forebrain corticopetal cholinergic (BFCC) and pedunculopontine-laterodorsal tegmental (PPN-LDT) cholinergic projections in cognitive deficits and gait-balance deficits, respectively. Recent application of imaging methods, particularly molecular imaging, allowed more sophisticated correlation of clinical features with regional cholinergic deficits. BFCC projection deficits correlate with general and domain specific cognitive deficits, particularly for attentional and executive functions. Detailed analyses suggest that cholinergic deficits within the salience and cingulo-opercular task control networks, including both neocortical, thalamic, and striatal nodes, are a significant component of cognitive deficits in non-demented PD subjects. Both BFCC and PPN-LDT cholinergic projection systems, and striatal cholinergic interneuron (SChI), abnormalities are implicated in PD gait-balance disorders. In the context of experimental studies, these results indicate that disrupted attentional functions of BFCC and PPN-LDT cholinergic systems underlie impaired gait-balance functions. SChI dysfunction likely impairs intra-striatal integration of attentional and motor information. Thalamic and entorhinal cortex cholinergic deficits may impair multi-sensory integration. Overt degeneration of CNS systems may be preceded by increased activity of cholinergic neurons compensating for nigrostriatal dopaminergic deficits. Subsequent dysfunction and degeneration of cholinergic systems unmasks and exacerbates functional deficits secondary to dopaminergic denervation. Research on CNS cholinergic systems dysfunctions in PD requires a systems-level approach to understanding PD pathophysiology.

The Cholinergic Brain in Parkinson's Disease

The central cholinergic system includes the basal forebrain nuclei, mainly projecting to the cortex, the mesopontine tegmental nuclei, mainly projecting to the thalamus and subcortical structures, and other groups of projecting neurons and interneurons. This system regulates many functions of human behavior such as cognition, locomotion, and sleep. In Parkinson's disease (PD), disruption of central cholinergic transmission has been associated with cognitive decline, gait problems, freezing of gait (FOG), falls, REM sleep behavior disorder (RBD), neuropsychiatric manifestations, and olfactory dysfunction. Neuropathological and neuroimaging evidence suggests that basal forebrain pathology occurs simultaneously with nigrostriatal denervation, whereas pathology in the pontine nuclei may occur before the onset of motor symptoms. These studies have also detailed the clinical implications of cholinergic dysfunction in PD. Degeneration of basal forebrain nuclei and consequential cortical cholinergic denervation are associated with and may predict the subsequent development of cognitive decline and neuropsychiatric symptoms. Gait problems, FOG, and falls are associated with a complex dysfunction of both pontine and basal forebrain nuclei. Olfactory impairment is associated with cholinergic denervation of the limbic archicortex, specifically hippocampus and amygdala. Available evidence suggests that cholinergic dysfunction, alongside failure of the dopaminergic and other neurotransmitters systems, contributes to the generation of a specific set of clinical manifestations. Therefore, a "cholinergic phenotype" can be identified in people presenting with cognitive decline, falls, and RBD. In this review, we will summarize the organization of the central cholinergic system and the clinical correlates of cholinergic dysfunction in PD.

Altered Cortical Cholinergic Network in Parkinson's Disease at Different Stage: A Resting-State fMRI Study

The cholinergic system is critical in Parkinson’s disease (PD) pathology, which accounts for various clinical symptoms in PD patients. The substantia innominata (SI) provides the main source of cortical cholinergic innervation. Previous studies revealed cholinergic-related dysfunction in PD pathology at early stage. Since PD is a progressive disorder, alterations of cholinergic system function along with the PD progression have yet to be elucidated. Seventy-nine PD patients, including thirty-five early-stage PD patients (PD-E) and forty-four middle-to-late stage PD patients (PD-M), and sixty-four healthy controls (HC) underwent brain magnetic resonance imaging and clinical assessments. We employed seed-based resting-state functional connectivity analysis to explore the cholinergic-related functional alterations. Correlation analysis was used to investigate the relationship between altered functional connectivity and the severity of motor symptoms in PD patients. Results showed that both PD-E and PD-M groups exhibited decreased functional connectivity between left SI and left frontal inferior opercularis areas and increased functional connectivity between left SI and left cingulum middle area as well as right primary motor and sensory areas when comparing with HC. At advanced stages of PD, functional connectivity in the right primary motor and sensory areas was further increased. These altered functional connectivity were also significantly correlated with the Unified Parkinson’s Disease Rating Scale motor scores. In conclusion, this study illustrated that altered cholinergic function plays an important role in the motor disruptions in PD patients both in early stage as well as during the progression of the disease.

Cholinergic Basal Forebrain Volumes Predict Gait Decline in Parkinson's Disease

BACKGROUND

Gait disturbance is an early, disabling feature of Parkinson's disease (PD) that is typically refractory to dopaminergic medication. The cortical cholinergic system, originating in the nucleus basalis of Meynert of the basal forebrain, has been implicated. However, it is not known if degeneration in this region relates to a worsening of disease-specific gait impairment.

OBJECTIVE

To evaluate associations between sub-regional cholinergic basal forebrain volumes and longitudinal progression of gait impairment in PD.

METHODS

99 PD participants and 47 control participants completed gait assessments via an instrumented walkway during 2 minutes of continuous walking, at baseline and for up to 3 years, from which 16 spatiotemporal characteristics were derived. Sub-regional cholinergic basal forebrain volumes were measured at baseline via MRI and a regional map derived from post-mortem histology. Univariate analyses evaluated cross-sectional associations between sub-regional volumes and gait. Linear mixed-effects models assessed whether volumes predicted longitudinal gait changes.

RESULTS

There were no cross-sectional, age-independent relationships between sub-regional volumes and gait. However, nucleus basalis of Meynert volumes predicted longitudinal gait changes unique to PD. Specifically, smaller nucleus basalis of Meynert volume predicted increasing step time variability (P = 0.019) and shortening swing time (P = 0.015); smaller posterior nucleus portions predicted shortening step length (P = 0.007) and increasing step time variability (P = 0.041).

CONCLUSIONS

This is the first study to demonstrate that degeneration of the cortical cholinergic system predicts longitudinal progression of gait impairments in PD. Measures of this degeneration may therefore provide a novel biomarker for identifying future mobility loss and falls. © 2020 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.