Functional changes of the basal ganglia circuitry in Parkinson's disease

Anticipating social incentives recruits alpha-beta oscillations in the human substantia nigra and invigorates behavior across the life span

Anticipating social and non-social incentives recruits shared brain structures and promotes behavior. However, little is known about possible age-related behavioral changes, and how the human substantia nigra (SN) signals positive and negative social information. Therefore, we recorded intracranial electroencephalography (iEEG) from the SN of Parkinson's Disease (PD) patients (n = 12, intraoperative, OFF medication) in combination with a social incentive delay task including photos of neutral, positive or negative human gestures and mimics as feedback. We also tested a group of non-operated PD patients (n = 24, ON and OFF medication), and a sample of healthy young (n = 51) and older (n = 52) adults with behavioral readouts only. Behaviorally, the anticipation of both positive and negative social feedback equally accelerated response times in contrast to neutral social feedback in healthy young and older adults. Although this effect was not significant in the group of operated PD patients - most likely due to the small sample size - iEEG recordings in their SN showed a significant increase in alpha-beta power (9-20 Hz) from 300 to 600 ms after cue onset again for both positive and negative cues. Finally, in non-operated PD patients, the behavioral effect was not modulated by medication status (ON vs OFF medication) suggesting that other processes than dopaminergic neuromodulation play a role in driving invigoration by social incentives. Together, our findings provide novel and direct evidence for a role of the SN in processing positive and negative social information via specific oscillatory mechanisms in the alpha-beta range, and they suggest that anticipating social value in simple cue-outcome associations is intact in healthy aging and PD.

Parkinson Disease: Translating Insights from Molecular Mechanisms to Neuroprotection

Parkinson disease (PD) used to be considered a nongenetic condition. However, the identification of several autosomal dominant and recessive mutations linked to monogenic PD has changed this view. Clinically manifest PD is then thought to occur through a complex interplay between genetic mutations, many of which have incomplete penetrance, and environmental factors, both neuroprotective and increasing susceptibility, which variably interact to reach a threshold over which PD becomes clinically manifested. Functional studies of PD gene products have identified many cellular and molecular pathways, providing crucial insights into the nature and causes of PD. PD originates from multiple causes and a range of pathogenic processes at play, ultimately culminating in nigral dopaminergic loss and motor dysfunction. An in-depth understanding of these complex and possibly convergent pathways will pave the way for therapeutic approaches to alleviate the disease symptoms and neuroprotective strategies to prevent disease manifestations. This review is aimed at providing a comprehensive understanding of advances made in PD research based on leveraging genetic insights into the pathogenesis of PD. It further discusses novel perspectives to facilitate identification of critical molecular pathways that are central to neurodegeneration that hold the potential to develop neuroprotective and/or neurorestorative therapeutic strategies for PD. SIGNIFICANCE STATEMENT: A comprehensive review of PD pathophysiology is provided on the complex interplay of genetic and environmental factors and biologic processes that contribute to PD pathogenesis. This knowledge identifies new targets that could be leveraged into disease-modifying therapies to prevent or slow neurodegeneration in PD.

Reduced Dopamine Signaling Impacts Pyramidal Neuron Excitability in Mouse Motor Cortex

Dopaminergic modulation is essential for the control of voluntary movement; however, the role of dopamine in regulating the neural excitability of the primary motor cortex (M1) is not well understood. Here, we investigated two modes by which dopamine influences the input/output function of M1 neurons. To test the direct regulation of M1 neurons by dopamine, we performed whole-cell recordings of excitatory neurons and measured excitability before and after local, acute dopamine receptor blockade. We then determined whether chronic depletion of dopaminergic input to the entire motor circuit, via a mouse model of Parkinson's disease, was sufficient to shift M1 neuron excitability. We show that D1 receptor (D1R) and D2R antagonism altered subthreshold and suprathreshold properties of M1 pyramidal neurons in a layer-specific fashion. The effects of D1R antagonism were primarily driven by changes to intrinsic properties, while the excitability shifts following D2R antagonism relied on synaptic transmission. In contrast, chronic depletion of dopamine to the motor circuit with 6-hydroxydopamine induced layer-specific synaptic transmission-dependent shifts in M1 neuron excitability that only partially overlapped with the effects of acute D1R antagonism. These results suggest that while acute and chronic changes in dopamine modulate the input/output function of M1 neurons, the mechanisms engaged are distinct depending on the duration and origin of the manipulation. Our study highlights the broad influence of dopamine on M1 excitability by demonstrating the consequences of local and global dopamine depletion on neuronal input/output function.

Time-Specific Pattern of Iron Deposition in Different Regions in Parkinson's Disease Measured by Quantitative Susceptibility Mapping

Studies have shown the spatial specificity of cranial iron deposition in different regions in Parkinson's disease (PD). However, the time-specific patterns of iron deposition are not yet clear. The purpose of this study was to investigate the time pattern of iron variations and its clinical relevance in multiple gray matter nuclei in PD using quantitative susceptibility mapping (QSM). Thirty controls and 33 PD patients were enrolled, namely, 11 cases of early stage of PD (ESP) and 22 cases of advanced stage of PD (ASP) according to the Hoehn-Yahr stages. The iron content in the subcortical nuclei covering substantia nigra (SN), red nucleus (RN), head of the caudate nucleus (CN), globus pallidus (GP), and putamen (PT) was measured using QSM, and the clinical symptoms of PD were evaluated by various rating scales. The QSM values in SN, RN, GP, and PT significantly increased in PD patients compared with the controls. Further subgroup comparison with the controls indicated that the iron content in SN and GP (paleostriatum) gradually elevated in the whole disease duration and was related to clinical features. While the iron content in RN and PT (neostriatum) only elevated significantly in ESP patients, further iron deposition was not obvious in ASP patients. Our study confirmed that QSM could be used as a disease biomarker and could be suitable for longitudinal monitoring. However, considering the temporal characteristics of iron deposition in neostriatum, iron deposition in the neostriatum should be paid more attention in the early stage of the disease, even in the preclinical stage, in future research.

Dopaminergic Projection from Ventral Tegmental Area to Substantia Nigra Pars Reticulata Mediates Chronic Social Defeat Stress-Induced Hypolocomotion

Numerous human clinical studies have suggested that decreased locomotor activity is a common symptom of major depressive disorder (MDD), as well as other psychiatric diseases. In MDD, the midbrain ventral tegmental area (VTA) dopamine (DA) neurons are closely related to regulate the information processing of reward, motivation, cognition, and aversion. However, the neural circuit mechanism that underlie the relationship between VTA-DA neurons and MDD-related motor impairments, especially hypolocomotion, is still largely unknown. Herein, we investigate how the VTA-DA neurons contribute to the hypolocomotion performance in chronic social defeat stress (CSDS), a mouse model of depression-relevant neurobehavioral states. The results show that CSDS could affect the spontaneous locomotor activity of mice, but not the grip strength and forced locomotor ability. Chemogenetic activation of VTA-DA neurons alleviated CSDS-induced hypolocomotion. Subsequently, quantitative whole-brain mapping revealed decreased projections from VTA-DA neurons to substantia nigra pars reticulata (SNr) after CSDS treatment. Optogenetic activation of dopaminergic projection from VTA to SNr with the stimulation of phasic firing, but not tonic firing, could significantly increase the locomotor activity of mice. Moreover, chemogenetic activation of VTA-SNr dopaminergic circuit in CSDS mice could also rescued the decline of locomotor activity. Taken together, our data suggest that the VTA-SNr dopaminergic projection mediates CSDS-induced hypolocomotion, which provides a theoretical basis and potential therapeutic target for MDD.

Study on the Regulation Effect of Optogenetic Technology on LFP of the Basal Ganglia Nucleus in Rotenone-Treated Rats

Background

Parkinson's disease (PD) is a common neurological degenerative disease that cannot be completely cured, although drugs can improve or alleviate its symptoms. Optogenetic technology, which stimulates or inhibits neurons with excellent spatial and temporal resolution, provides a new idea and approach for the precise treatment of Parkinson's disease. However, the neural mechanism of photogenetic regulation remains unclear.

Objective

In this paper, we want to study the nonlinear features of EEG signals in the striatum and globus pallidus through optogenetic stimulation of the substantia nigra compact part.

Methods

Rotenone was injected stereotactically into the substantia nigra compact area and ventral tegmental area of SD rats to construct rotenone-treated rats. Then, for the optogenetic manipulation, we injected adeno-associated virus expressing channelrhodopsin to stimulate the globus pallidus and the striatum with a 1 mW blue light and collected LFP signals before, during, and after light stimulation. Finally, the collected LFP signals were analyzed by using nonlinear dynamic algorithms.

Results

After observing the behavior and brain morphology, 16 models were finally determined to be successful. LFP results showed that approximate entropy and fractal dimension of rats in the control group were significantly greater than those in the experimental group after light treatment (p < 0.05). The LFP nonlinear features in the globus pallidus and striatum of rotenone-treated rats showed significant statistical differences before and after light stimulation (p < 0.05).

Conclusion

Optogenetic technology can regulate the characteristic value of LFP signals in rotenone-treated rats to a certain extent. Approximate entropy and fractal dimension algorithm can be used as an effective index to study LFP changes in rotenone-treated rats.

The Biology and Pathobiology of Glutamatergic, Cholinergic, and Dopaminergic Signaling in the Aging Brain

The elderly population is growing worldwide, with important health and socioeconomic implications. Clinical and experimental studies on aging have uncovered numerous changes in the brain, such as decreased neurogenesis, increased synaptic defects, greater metabolic stress, and enhanced inflammation. These changes are associated with cognitive decline and neurobehavioral deficits. Although aging is not a disease, it is a significant risk factor for functional worsening, affective impairment, disease exaggeration, dementia, and general disease susceptibility. Conversely, life events related to mental stress and trauma can also lead to accelerated age-associated disorders and dementia. Here, we review human studies and studies on mice and rats, such as those modeling human neurodegenerative diseases, that have helped elucidate (1) the dynamics and mechanisms underlying the biological and pathological aging of the main projecting systems in the brain (glutamatergic, cholinergic, and dopaminergic) and (2) the effect of defective glutamatergic, cholinergic, and dopaminergic projection on disabilities associated with aging and neurodegenerative disorders, such as Alzheimer's and Parkinson's diseases. Detailed knowledge of the mechanisms of age-related diseases can be an important element in the development of effective ways of treatment. In this context, we briefly analyze which adverse changes associated with neurodegenerative diseases in the cholinergic, glutaminergic and dopaminergic systems could be targeted by therapeutic strategies developed as a result of our better understanding of these damaging mechanisms.

How far can I reach? The perception of upper body action capabilities in Parkinson's disease

Successful interaction within the environment is contingent upon one’s ability to accurately perceive the extent over which they can successfully perform actions, known as action boundaries. Healthy young adults are accurate in estimating their action boundaries and can flexibly update them to accommodate stable changes in their action capabilities. However, there are conditions in which motor abilities are subject to variability over time such as in Parkinson’s disease (PD). PD impairs the ability to perform actions and can lead to variability in perceptual-motor experience, but the effect on the perceptions of their action boundaries remains unknown. This study investigated the influence of altered perceptual-motor experience during PD, on the perceptions of action boundaries for reaching, grasping, and aperture passing. Thirty participants with mild-to-moderate idiopathic PD and 26 healthy older adults provided estimates of their reaching, grasping, and aperture-passing ability. Participants’ estimates were compared with their actual capabilities. There was no evidence that individuals with PD’s perceptions were less accurate than those of healthy controls. Furthermore, there was some evidence for more conservative estimates than seen in young healthy adults in reaching (both groups) and aperture passing (PD group). This suggests that the ability to judge action capabilities is preserved in mild to moderate PD.

Glutamic Acid Transporters: Targets for Neuroprotective Therapies in Parkinson's Disease

Parkinson's disease (PD) is a common neurodegenerative disease in middle-aged and elderly individuals. At present, no effective drug has been developed to treat PD. Although a variety of drugs exist for the symptomatic treatment of PD, they all have strong side effects. Most studies on PD mainly focus on dopaminergic neurons. This review highlights the function of glutamic acid transporters (GLTs), including excitatory amino acid transporters (EAATs) and vesicular glutamate transporters (VGLUTs), during the development of PD. In addition, using bioinformatics, we compared the expression of different types of glutamate transporter genes in the cingulate gyrus of PD patients and healthy controls. More importantly, we suggest that the functional roles of glutamate transporters may prove beneficial in the treatment of PD. In summary, VGLUTs and EAATs may be potential targets in the treatment of PD. VGLUTs and EAATs can be used as clinical drug targets to achieve better efficacy. Through this review article, we hope to enable future researchers to improve the condition of PD patients.

Acupuncture for Parkinson's Disease: Efficacy Evaluation and Mechanisms in the Dopaminergic Neural Circuit

Parkinson's disease (PD) is a chronic and progressive neurodegenerative disease caused by degeneration of dopaminergic neurons in the substantia nigra. Existing pharmaceutical treatments offer alleviation of symptoms but cannot delay disease progression and are often associated with significant side effects. Clinical studies have demonstrated that acupuncture may be beneficial for PD treatment, particularly in terms of ameliorating PD symptoms when combined with anti-PD medication, reducing the required dose of medication and associated side effects. During early stages of PD, acupuncture may even be used to replace medication. It has also been found that acupuncture can protect dopaminergic neurons from degeneration via antioxidative stress, anti-inflammatory, and antiapoptotic pathways as well as modulating the neurotransmitter balance in the basal ganglia circuit. Here, we review current studies and reflect on the potential of acupuncture as a novel and effective treatment strategy for PD. We found that particularly during the early stages, acupuncture may reduce neurodegeneration of dopaminergic neurons and regulate the balance of the dopaminergic circuit, thus delaying the progression of the disease. The benefits of acupuncture will need to be further verified through basic and clinical studies.

Explicit motor sequence learning after stroke: a neuropsychological study

Motor learning interacts with and shapes experience-dependent cerebral plasticity. In stroke patients with paresis of the upper limb, motor recovery was proposed to reflect a process of re-learning the lost/impaired skill, which interacts with rehabilitation. However, to what extent stroke patients with hemiparesis may retain the ability of learning with their affected limb remains an unsolved issue, that was addressed by this study. Nineteen patients, with a cerebrovascular lesion affecting the right or the left hemisphere, underwent an explicit motor learning task (finger tapping task, FTT), which was performed with the paretic hand. Eighteen age-matched healthy participants served as controls. Motor performance was assessed during the learning phase (i.e., online learning), as well as immediately at the end of practice, and after 90 min and 24 h (i.e., retention). Results show that overall, as compared to the control group, stroke patients, regardless of the side (left/right) of the hemispheric lesion, do not show a reliable practice-dependent improvement; consequently, no retention could be detected in the long-term (after 90 min and 24 h). The motor learning impairment was associated with subcortical damage, predominantly affecting the basal ganglia; conversely, it was not associated with age, time elapsed from stroke, severity of upper-limb motor and sensory deficits, and the general neurological condition. This evidence expands our understanding regarding the potential of post-stroke motor recovery through motor practice, suggesting a potential key role of basal ganglia, not only in implicit motor learning as previously pointed out, but also in explicit finger tapping motor tasks.

Anatomo-Functional Origins of the Cortical Silent Period: Spotlight on the Basal Ganglia

The so-called cortical silent period (CSP) refers to the temporary interruption of electromyographic signal from a muscle following a motor-evoked potential (MEP) triggered by transcranial magnetic stimulation (TMS) over the primary motor cortex (M1). The neurophysiological origins of the CSP are debated. Previous evidence suggests that both spinal and cortical mechanisms may account for the duration of the CSP. However, contextual factors such as cortical fatigue, experimental procedures, attentional load, as well as neuropathology can also influence the CSP duration. The present paper summarizes the most relevant evidence on the mechanisms underlying the duration of the CSP, with a particular focus on the central role of the basal ganglia in the "direct" (excitatory), "indirect" (inhibitory), and "hyperdirect" cortico-subcortical pathways to manage cortical motor inhibition. We propose new methods of interpretation of the CSP related, at least partially, to the inhibitory hyperdirect and indirect pathways in the basal ganglia. This view may help to explain the respective shortening and lengthening of the CSP in various neurological disorders. Shedding light on the complexity of the CSP's origins, the present review aims at constituting a reference for future work in fundamental research, technological development, and clinical settings.

Exploring the Use of Intracranial and Extracranial (Remote) Photobiomodulation Devices in Parkinson's Disease: A Comparison of Direct and Indirect Systemic Stimulations

In recent times, photobiomodulation has been shown to be beneficial in animal models of Parkinson's disease, improving locomotive behavior and being neuroprotective. Early observations in people with Parkinson's disease have been positive also, with improvements in the non-motor symptoms of the disease being evident most consistently. Although the precise mechanisms behind these improvements are not clear, two have been proposed: direct stimulation, where light reaches and acts directly on the distressed neurons, and remote stimulation, where light influences cells and/or molecules that provide systemic protection, thereby acting indirectly on distressed neurons. In relation to Parkinson's disease, given that the major zone of pathology lies deep in the brain and that light from an extracranial or external photobiomodulation device would not reach these vulnerable regions, stimulating the distressed neurons directly would require intracranial delivery of light using a device implanted close to the vulnerable regions. For indirect systemic stimulation, photobiomodulation could be applied to either the head and scalp, using a transcranial helmet, or to a more remote body part (e.g., abdomen, leg). In this review, we discuss the evidence for both the direct and indirect neuroprotective effects of photobiomodulation in Parkinson's disease and propose that both types of treatment modality, when working together using both intracranial and extracranial devices, provide the best therapeutic option.

Exergaming as Part of the Telerehabilitation Can Be Adequate to the Outpatient Training: Preliminary Findings of a Non-randomized Pilot Study in Parkinson's Disease

Parkinson's disease is a long-term and progressive degenerative disorder of the nervous system, affecting primarily motor coordination, noticeable as a tremor in one hand. Recent studies reported on positive outcomes of intensive physiotherapy of upper extremities. We built a telerehabilitation system with virtual pick and place tasks for small scale hand movements, and designed a pilot study to find whether such exergaming as a telerehabilitation service provides comparable outcomes as an outpatient exergaming service. A non-randomized pilot trial was designed. Hospital outpatients (28/40) with Parkinson's disease were recruited. Those meeting the inclusion criteria were divided into two groups; seven outpatients were assigned to the home (H) group and 21 outpatients to the hospital (URI) group. Both groups received 10 days of exergaming over the course of 2 weeks, each daily session lasting a maximum of 1 h. Primary outcomes were clinical tests; Box and Blocks Test (BBT), Jebsen Hand Function Test (JHFT), and Unified Parkinson's Disease Rating Scale (UPDRS part III) were carried out before and after the study. Secondary outcomes were hand kinematics and exergaming results; number of successfully moved objects and task time. Statistical analysis was carried out to find significant (p < 0.05) differences and Cohen's U3 was used to determine effect sizes. The differences between the groups in gender (p = 0.781), age (p = 0.192), and duration of the disease (p = 0.195) were tested with Bartlett's test and no statistical differences were found with an F test. Both groups demonstrated statistically significant improvements in clinical test UDPRS III (p = 0.006 and p = 0.011) and the hospital group also in BBT (p = 0.002) and JHFT (p = 0.015) and with UDPRS III and JHFT even in favor of the home group (χ² = 5.08, p = 0.024, χ² = 7.76, p = 0.005). Nevertheless, the exergaming results show significant improvement after training (U3 > 0.86). Exergaming has already been suggested as an effective approach in the planning of rehabilitation tasks for persons with Parkinson's disease. We have prepared a pilot study demonstrating that exergaming at home with telerehabilitation support may provide comparable clinical outcomes. The study shall be followed by a randomized study with higher statistical power to provide clinical evidence. Nevertheless, carrying out even part of the rehabilitation program at home is crucial for the development of future telerehabilition clinical services. Clinical Trial Registration: www.ClinicalTrials.gov, identifier: NCT03175107.

Inhibition of striatal dopamine D5 receptor attenuates levodopa-induced dyskinesia in a rat model of Parkinson's disease

Levodopa-induced dyskinesia (LID) is experienced by most patients of Parkinson's disease (PD) upon the long-term use of the dopamine precursor levodopa. Striatal dopaminergic signaling plays a critical role in the pathogenesis of LID through its interactions with dopamine receptors. The specific roles of striatal dopaminergic D5 receptors in the pathophysiological process of LID are still poorly established. In the study, we investigated the role of striatal dopamine D5 receptor in LID by using PD rats with or without dyskinetic symptoms after chronic levodopa administration. The experimental results showed that the expression level of D5 receptors in the sensorimotor striatum of dyskinetic rats is significantly higher than that of the non-dyskinetic controls. The administration of levodopa increased c-Fos expression in a subpopulation of sensorimotor striatum neurons of dyskinetic rats, but not in non-dyskinetic rats. The majority of the c-Fos+ neurons activated by levodopa in the striatum are positive for D5 receptor staining. Intrastriatal injection of D1-like (D1 and D5) dopamine receptor antagonist, SCH-23390, significantly inhibited dyskinetic behavior in dyskinetic rats after the injection of levodopa, meanwhile, intrastriatal administration of SKF-83959, a partial D5 receptor agonist, yielded significant dyskinetic movements in dyskinetic rats without levodopa. In contrast, intrastriatal perfusion of small interfering RNA directed against DRD5 downregulated D5 receptors expression and moderately inhibited dyskinetic behavior of dyskinetic animals. Our data suggested that the striatal dopamine D5 receptor might play a novel role in the pathophysiology of LID.

Ketamine reversed short-term memory impairment and depressive-like behavior in animal model of Parkinson's disease

The most common features of Parkinson's disease (PD) are motor impairments, but many patients also present depression and memory impairment. Ketamine, an N-methyl-d-aspartate (NMDA) receptor antagonist, has been shown to be effective in patients with treatment-resistant major depression. Thus, the present study evaluated the action of ketamine on memory impairment and depressive-like behavior in an animal model of PD. Male Wistar rats received a bilateral infusion of 6 μg/side 6-hydroxydopamine (6-OHDA) into the substantia nigra pars compacta (SNc). Short-term memory was evaluated by the social recognition test, and depressive-like behaviors were evaluated by the sucrose preference and forced swimming tests (FST). Drug treatments included vehicle (i.p., once a week); ketamine (5, 10 and 15 mg/kg, i.p., once a week); and imipramine (20 mg/kg, i.p., daily). The treatments were administered 21 days after the SNc lesion and lasted for 28 days. The SNc lesion impaired short-term social memory, and all ketamine doses reversed the memory impairment and anhedonia (reduction of sucrose preference) induced by 6-OHDA. In the FST, 6-OHDA increased immobility, and all doses of ketamine and imipramine reversed this effect. The anti-immobility effect of ketamine was associated with an increase in swimming but not in climbing, suggesting a serotonergic effect. Ketamine and imipramine did not reverse the 6-OHDA-induced reduction in tyrosine hydroxylase immunohistochemistry in the SNc. In conclusion, ketamine reversed depressive-like behaviors and short-term memory impairment in rats with SNc bilateral lesions, indicating a promising profile for its use in PD patients.

Regularity of kinematic data between single and dual-task treadmill walking in people with Parkinson's disease

BACKGROUND

Regularity, quantified by sample entropy (SampEn), has been extensively used as a gait stability measure. Yet, there is no consensus on the calculation process and variant approaches, e.g. single-scale SampEn with and without incorporating a time delay greater than one, multiscale SampEn, and complexity index, have been used to calculate the regularity of kinematic or kinetic signals. The aim of the present study was to test the discriminatory performance of the abovementioned approaches during single and dual-task walking in people with Parkinson's disease (PD).

METHODS

Seventeen individuals with PD were included in this study. Participants completed two walking trials that included single and dual-task conditions. The secondary task was word searching with twelve words randomly appearing in the participants' visual field. Trunk linear acceleration at sternum level, linear acceleration of the center of gravity, and angular velocity of feet, shanks, and thighs, each in three planes of motion were collected. The regularity of signals was computed using approaches mentioned above for single and dual-task conditions.

RESULTS

Incorporating a time delay greater than one and considering multiple scales helped better distinguish between single and dual-task walking. For all signals, the complexity index, defined as the summary of multiscale SampEn analysis, was the most efficient discriminatory index between single-task walking and dual-tasking in people with Parkinson's disease. Specifically, the complexity index of the trunk linear acceleration of the center of gravity distinguished between the two walking conditions in all three planes of motion.

CONCLUSIONS

The significant results observed across the 24 signals studied in this study are illustrative examples of the complexity index's potential as a gait feature for classifying different walking conditions.

The subthalamic nucleus and the placebo effect in Parkinson's disease

The study of the placebo effect, or response, is related to the investigation of the psychologic component of different therapeutic rituals. The high rate of placebo responses in Parkinson's disease clinical trials provided the impetus for investigating the underlying mechanisms. Ruling out spontaneous remission and regression to the mean through the appropriate experimental designs, genuine psychologic placebo effects have been identified, in which both patients' expectations of therapeutic benefit and learning processes are involved. Specifically, placebo effects are associated with dopamine release in the striatum and changes in neuronal activity in the subthalamic nucleus, substantia nigra pars reticulata, and motor thalamus in Parkinson's disease, as assessed through positron emission tomography and single-neuron recording during deep brain stimulation, respectively. Conversely, verbal suggestions of clinical worsening or drug dose reduction induce nocebo responses in Parkinson's disease, which have been detected at both behavioral and electrophysiologic level. Important implications and applications emerge from this new knowledge. These include better clinical trial designs, whereby patients' expectations should always be assessed, as well as better drug dosage in order to reduce drug intake.

Understanding the Neurophysiological and Molecular Mechanisms of Exercise-Induced Neuroplasticity in Cortical and Descending Motor Pathways: Where Do We Stand?

Exercise is a promising, cost-effective intervention to augment successful aging and neurorehabilitation. Decline of gray and white matter accompanies physiological aging and contributes to motor deficits in older adults. Exercise is believed to reduce atrophy within the motor system and induce neuroplasticity which, in turn, helps preserve motor function during aging and promote re-learning of motor skills, for example after stroke. To fully exploit the benefits of exercise, it is crucial to gain a greater understanding of the neurophysiological and molecular mechanisms underlying exercise-induced brain changes that prime neuroplasticity and thus contribute to postponing, slowing, and ameliorating age- and disease-related impairments in motor function. This knowledge will allow us to develop more effective, personalized exercise protocols that meet individual needs, thereby increasing the utility of exercise strategies in clinical and non-clinical settings. Here, we review findings from studies that investigated neurophysiological and molecular changes associated with acute or long-term exercise in healthy, young adults and in healthy, postmenopausal women.

Restricted Arm Swing in People With Parkinson's Disease Decreases Step Length and Time on Destabilizing Surfaces

Introduction: Fall rates in people with Parkinson's Disease range between 35 and 68% with the majority of falls occurring while walking. Initial evidence suggests that when walking without arm swing, people with Parkinson's Disease adapt their stepping foot placement as a means to preserve dynamic stability. However, it remains unexamined what arm swing's effect has on dynamic stability when walking on destabilizing surfaces.

Methods: Twenty people with Parkinson's Disease (63.78 ± 8.97 years) walked with restricted and unrestricted arm swing on unperturbed, rocky, rolling-hills, and mediolateral translational surfaces. Data were collected on a split-belt treadmill CAREN Extended-System (Motek Medical, Amsterdam, NL). Bilateral averages and coefficient of variations for step time, length, and width; and mediolateral margin of stability were calculated.

Results: Results were examined in three separate analyses that included arm conditions during each of the destabilizing surfaces compared to unperturbed walking (arm-rolling hills, arm-rocky, and arm-mediolateral). Compared to unrestricted arm swing, restricted arm swing reduced average step length (arm-rolling hills) and time (arm-rocky), and increased COV step time (arm-rolling hills). The arm-rolling hills analysis revealed that the most affected leg had a shorter step length than the least affected. The destabilizing surface effects revealed that during the arm-rolling hills and arm-rocky analyses, step time decreased, step width increased, and the COV for step time, length and width increased. No main effects occurred for the arm-mediolateral analysis.

Conclusion: Results indicate that foot placement in response to restricted arm swing, in people with Parkinson's Disease, depends on the encountered destabilizing surface. The arm-rolling hills analysis revealed that participants appropriately reduced step length as compensation to their restricted arm swing. However, the arm-rocky analysis revealed that individuals prioritized forward progression over dynamic stability as they decreased average step time. Additionally, the increased spatiotemporal variability in response to the rocky and rolling hills conditions indicate partial foot placement adaptation to maintain an already existing level of global dynamic stability as no changes in the Margin of Stability occurred. Adaptation is further corroborated by the decreased step time and increased step width. These responses reflect attempts to pass the destabilizing terrains faster while increasing their base of support.

The gut microbiota-brain axis in behaviour and brain disorders

In a striking display of trans-kingdom symbiosis, gut bacteria cooperate with their animal hosts to regulate the development and function of the immune, metabolic and nervous systems through dynamic bidirectional communication along the 'gut-brain axis'. These processes may affect human health, as certain animal behaviours appear to correlate with the composition of gut bacteria, and disruptions in microbial communities have been implicated in several neurological disorders. Most insights about host-microbiota interactions come from animal models, which represent crucial tools for studying the various pathways linking the gut and the brain. However, there are complexities and manifest limitations inherent in translating complex human disease to reductionist animal models. In this Review, we discuss emerging and exciting evidence of intricate and crucial connections between the gut microbiota and the brain involving multiple biological systems, and possible contributions by the gut microbiota to neurological disorders. Continued advances from this frontier of biomedicine may lead to tangible impacts on human health.

The neurobiological reward system in Prolonged Grief Disorder (PGD): A systematic review

Prolonged Grief Disorder (PGD) is a debilitating condition affecting between 7% and 10% of bereaved individuals. Past imaging and psychological studies have proposed links between PGD's characteristic symptoms - in particular, profound yearning - and the neural reward system. We conducted a systematic review to investigate this connection. On December 19, 2019, we searched six bibliographic databases for data on the neurobiology of grief and disordered grief. We excluded studies of the hypothalamic-pituitary-adrenal (HPA) axis, animal studies, and reviews. After abstract and full-text screening, twenty-four studies were included in the final review. We found diverse evidence for the activation of several reward-related regions of the brain in PGD. The data reviewed suggest that compared to normative grief, PGD involves a differential pattern of activity in the amygdala and orbitofrontal cortex (OFC); likely differential activity in the posterior cingulate cortex (PCC), rostral or subgenual anterior cingulate cortex (ACC), and basal ganglia overall, including the nucleus accumbens (NAc); and possible differential activity in the insula. It also appears that oxytocin signaling is altered in PGD, though the exact mechanism is unclear. Our findings appear to be consistent with, though not confirmative of, conceptualizing PGD as a disorder of reward, and identify directions for future research.

The contribution of Parkin, PINK1 and DJ-1 genes to selective neuronal degeneration in Parkinson's disease

Parkinson's disease (PD) is characterised by selective and severe degeneration of the substantia nigra pars compacta and the locus coeruleus (LC), which underlies the most prominent symptoms. Although α-synuclein accumulation has long been established to play a causal role in the disease, it alone cannot explain the selective degenerative pattern. Recent evidence shows that the selective vulnerability could arise due to the large presence of cytosolic catecholamines and Ca2+ ions in the substantia nigra pars compacta and LC specifically that can be aberrantly affected by α-synuclein accumulation. Moreover, each has its own toxic potential, and disturbance of one can exacerbate the toxic effects of the others. This presents a mechanism unique to these areas that can lead to a vicious degenerative cycle. Interestingly, in familial variants of PD, the exact same brain areas are affected, implying the underlying process is likely the same. However, the exact disease mechanisms of many of these genetic variants remain unclear. Here, we review the effects of the PD-related genes Parkin, PINK1 and DJ-1. We establish that these mutant varieties can set in motion the same degenerative process involving α-synuclein, cytosolic catecholamines and Ca2+ . Additionally, we show indications that model organisms might not accurately represent all components of this central mechanism, explaining why Parkin, PINK1 and DJ-1 model organisms often lack a convincing PD-like phenotype.

Activation of transcription factor Nrf2 to counteract mitochondrial dysfunction in Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder, for which no disease-modifying therapies are available to date. Although understanding of the precise aetiology of PD is incomplete, it is clear that age, genetic predisposition and environmental stressors increase the risk. At the cellular level, oxidative stress, chronic neuroinflammation, mitochondrial dysfunction and aberrant protein aggregation have been implicated as contributing factors. These detrimental processes are counteracted by elaborate networks of cellular defence mechanisms, one of which is orchestrated by transcription factor nuclear factor-erythroid 2 p45-related factor 2 (Nrf2; gene name NFE2L2). A wealth of preclinical evidence suggests that Nrf2 activation is beneficial in cellular and animal models of PD. In this review, we summarise the current understanding of mitochondrial dysfunction in PD, the role of Nrf2 in mitochondrial function and explore the potential of Nrf2 as a therapeutic target for mitochondrial dysfunction in PD.

Functional Alteration of Cerebello-Cerebral Coupling in an Experimental Mouse Model of Parkinson's Disease

In Parkinson's disease, the degeneration of the midbrain dopaminergic neurons is consistently associated with modified metabolic activity in the cerebellum. Here we examined the functional reorganization taking place in the cerebello-cerebral circuit in a murine model of Parkinson's disease with 6-OHDA lesion of midbrain dopaminergic neurons. Cerebellar optogenetic stimulations evoked similar movements in control and lesioned mice, suggesting a normal coupling of cerebellum to the motor effectors after the lesion. In freely moving animals, the firing rate in the primary motor cortex was decreased after the lesion, while cerebellar nuclei neurons showed an increased firing rate. This increase may result from reduced inhibitory Purkinje cells inputs, since a population of slow and irregular Purkinje cells was observed in the cerebellar hemispheres of lesioned animals. Moreover, cerebellar stimulations generated smaller electrocortical responses in the motor cortex of lesioned animals suggesting a weaker cerebello-cerebral coupling. Overall these results indicate the presence of functional changes in the cerebello-cerebral circuit, but their ability to correct cortical dysfunction may be limited due to functional uncoupling between the cerebellum and cerebral cortex.

Mutated ATP10B increases Parkinson's disease risk by compromising lysosomal glucosylceramide export

Parkinson’s disease (PD) is a progressive neurodegenerative brain disease presenting with a variety of motor and non-motor symptoms, loss of midbrain dopaminergic neurons in the substantia nigra pars compacta and the occurrence of α-synuclein-positive Lewy bodies in surviving neurons. Here, we performed whole exome sequencing in 52 early-onset PD patients and identified 3 carriers of compound heterozygous mutations in the ATP10B P4-type ATPase gene. Genetic screening of a Belgian PD and dementia with Lewy bodies (DLB) cohort identified 4 additional compound heterozygous mutation carriers (6/617 PD patients, 0.97%; 1/226 DLB patients, 0.44%). We established that ATP10B encodes a late endo-lysosomal lipid flippase that translocates the lipids glucosylceramide (GluCer) and phosphatidylcholine (PC) towards the cytosolic membrane leaflet. The PD associated ATP10B mutants are catalytically inactive and fail to provide cellular protection against the environmental PD risk factors rotenone and manganese. In isolated cortical neurons, loss of ATP10B leads to general lysosomal dysfunction and cell death. Impaired lysosomal functionality and integrity is well known to be implicated in PD pathology and linked to multiple causal PD genes and genetic risk factors. Our results indicate that recessive loss of function mutations in ATP10B increase risk for PD by disturbed lysosomal export of GluCer and PC. Both ATP10B and glucocerebrosidase 1, encoded by the PD risk gene GBA1, reduce lysosomal GluCer levels, emerging lysosomal GluCer accumulation as a potential PD driver.

The Modulation of Pain by Metabotropic Glutamate Receptors 7 and 8 in the Dorsal Striatum

The dorsal striatum, apart from controlling voluntary movement, displays a recently demonstrated pain inhibition. It is connected to the descending pain modulatory system and in particular to the rostral ventromedial medulla through the medullary dorsal reticular nucleus. Diseases of the basal ganglia, such as Parkinson's disease, in addition to being characterized by motor disorders, are associated with pain and hyperactivation of the excitatory transmission. A way to counteract glutamatergic hyperactivation is through the activation of group III metabotropic glutamate receptors (mGluRs), which are located on presynaptic terminals inhibiting neurotransmitter release. So far the mGluRs of group III have been the least investigated, owing to a lack of selective tools. More recently, selective ligands for each mGluR of group III, in particular positive and negative allosteric modulators, have been developed and the role of each subtype is starting to emerge. The neuroprotective potential of group III mGluRs in pathological conditions, such as those characterized by elevate glutamate, has been recently shown. In the dorsal striatum, mGluR7 and mGluR8 are located at glutamatergic corticostriatal terminals and their stimulation inhibits pain in pathological conditions such as neuropathic pain. The two receptors in the dorsal striatum have instead a different role in pain control in normal conditions. This review will discuss recent results focusing on the contribution of mGluR7 and mGluR8 in the dorsal striatal control of pain. The role of mGluR4, whose antiparkinsonian activity is widely reported, will also be addressed.

Absent Arm Swing and Dual Tasking Decreases Trunk Postural Control and Dynamic Balance in People With Parkinson's Disease

Introduction: Falling during walking is a common occurrence in people with Parkinson's disease and is closely associated with severe social and medical consequences. Recent evidence demonstrates that arm swing affects dynamic balance in healthy young adults; however, it remains unexamined what its effect is in people with Parkinson's disease, particularly when combined with a secondary dual task.

Methods: Twenty people with Parkinson's disease (63.78 ± 8.97) walked with two arm swing conditions (absent and normal) with and without a secondary dual task. Data were collected on a split-belt treadmill CAREN Extended-System (Motek Medical, Amsterdam, NL). Average and standard deviations for trunk linear and angular velocity were calculated along with their instantaneous values (during foot strikes) in all three axes. Averages and coefficient of variations for step length, time, and width; margin of stability; and harmonic ratios were also calculated.

Results: Compared with normal arm swing, absent arm swing reduced the least affected leg's average step length and increased its step length coefficient of variation while increasing step time coefficient of variation in the most affected leg. Further, absent arm swing reduced trunk anteroposterior instantaneous angular velocity (least affected leg) and reduced anteroposterior instantaneous linear velocity (bilaterally). For the vertical axis, absent arm swing increased the trunk's average angular velocity but reduced its instantaneous linear velocity and angular velocity standard deviation (least affected leg). Additionally, the margin of stability increased when the arms were absent (least affected leg). Alternatively, dual tasking reduced average step time (most affected leg) and increased the step width coefficient of variation (bilaterally). Additionally, dual tasking increased the mediolateral average angular velocity, instantaneous linear velocity standard deviation (bilaterally), and instantaneous angular velocity standard deviation (least affected leg). For the vertical axis, dual tasking increased average linear and angular velocity standard deviation as well as instantaneous angular velocity standard deviation (bilaterally).

Conclusion: Findings suggest that participants attempted to control extraneous trunk movement (due to absent arm swing) through compensatory responses in both lower and upper extremities. However, participants appeared to predominately compensate on their least affected side. Contrastingly, modifying mediolateral foot placement appeared to be the main means of maintaining walking stability while dual tasking.

Regulation of Protein Synthesis and Apoptosis in Lymphocytes of Parkinson Patients: The Effect of Dopaminergic Treatment

BACKGROUND

Parkinson disease (PD) is a neurodegenerative disorder characterized by progressive degeneration of the dopaminergic neurons in the substantia nigra, presumably due to increased apoptosis. In previous studies, we showed altered expression of proteins involved in mammalian target of rapamycin (mTOR) antiapoptotic and double-stranded RNA-dependent protein kinase (PKR) apoptotic pathways of translational control in experimental cellular and animal models of PD.

RESULTS

In this work, our results showed clear modifications in the expression of kinases involved in mTOR and PKR apoptosis pathways, in lymphocytes of PD patients treated or not with anti-PD treatment (levodopa), which confirmed the role played by apoptosis in the pathogenesis of this disease and the positive effect of treatment with medication on this parameter. Others proteins involved in apo-ptosis were also evaluated in lymphocytes of patients as the expression of the peripheral benzodiazepine receptor and caspase-3.

CONCLUSION

Translational control is altered in PD and hence its evaluation in peripheral blood mononuclear cells may serve as an early marker of apoptosis and indicate the efficacy of the dopaminergic treatment.

Botulinum toxin A injection into the entopeduncular nucleus improves dynamic locomotory parameters in hemiparkinsonian rats

Parkinson’s disease is associated with hyperactivity of the subthalamic nucleus (STN), contributing to motor and gait disturbances. Although deep brain stimulation of the STN alleviates certain motor dysfunction, its specific effect on gait abnormalities remains controversial. This study investigated the long-term changes in locomotion following direct infusions of botulinum toxin-A into the globus pallidus internal segment (GPi) to suppress the flow of information from the STN to the GPi in a hemiparkinsonian rat model. Static and dynamic gait parameters were quantified using a CatWalk apparatus. Interestingly, botulinum toxin-A at 0.5 ng significantly reduced only the dynamic gait parameters of hemiparkinsonian rats at 1 week and 1 month post-infusion, while static gait parameters did not change. This study offers new insights into the complexity of basal ganglia in locomotor control and shows the potential of central infusion of botulinum toxin-A as a novel intervention in the study of experimental hemiparkinson’s disease.

Study on Effect of Striatal mGluR2/3 in Alleviating Motor Dysfunction in Rat PD Model Treated by Exercise Therapy

Background: Exercise therapy has been widely applied in clinical rehabilitation as an important practical and side effect-free adjuvant therapy, with a significant effect in alleviating motor dysfunction of patients with Parkinson's disease (PD) or animal PD models. This study focuses on the effect of exercise therapy in reducing the concentration of extracellular glutamate (Glu) in the striatum in a rat PD model by upregulating the expression of group II metabotropic Glu receptor (mGluR2/3), so as to alleviate motor dysfunction in the rat PD model. Methods: Neurotoxin 6-hydroxydopamine (6-OHDA) was injected into the right medial forebrain bundle (MFB) of the rats to establish the semi-lateral cerebral damage PD model. The sham-operated group was given an equal amount of normal saline at the same site and taken as the control group. The apomorphine (APO)-induced rotational behavior test combined with immunohistochemical staining with tyrosine hydroxylase (TH) in the substantia nigra (SNc) and striatum was performed to assess the reliability of the model. The exercise group was given treadmill exercise intervention for 4 weeks (11 m/min, 30 min/day, 5 days/week) 1 week after the operation. The open field test (OFT) was performed to assess the locomotor activity of the rats; the Western blot technique was used to detect SNc TH and striatal mGluR2/3 protein expressions; real-time polymerase chain reaction (RT-PCR) was applied to detect striatal mGluR2 and mGluR3 mRNA expressions; the microdialysis-high-performance liquid chromatography (HPLC) method was adopted to detect the concentration of extracellular Glu in striatal neurons. Results: Compared with the control group, the number of rotations of each model group at the first week was significantly increased (P < 0.01); compared with the PD group, the number of rotations of the PD + exercise group at the third week and the fifth week was significantly decreased (P < 0.05, P < 0.01). Compared with the control group, the total movement distance, the total movement time, and the mean velocity of each model group at the first week were significantly reduced (P < 0.05); compared with the PD group, the total movement distance, the total movement time, and the mean velocity of the PD + exercise group at the third week and the fifth week were significantly increased (P < 0.01). Compared with the control group, the count of immunopositive cells and protein expression of SNc TH, and the content of immunopositive fiber terminals in the striatal TH of each model group significantly declined (P < 0.01). Compared with the PD group, the striatal mGluR2/3 protein expression of the PD + exercise group significantly rose (P < 0.01). Compared with the control group, the concentration of extracellular Glu in striatal neurons of each model group at the first week significantly grew (P < 0.05); compared with the PD group, the concentration of extracellular Glu in striatal neurons of the PD + exercise group at the third week and the fifth week was significantly decreased (P < 0.01); compared with the PD + exercise group, the concentration of extracellular Glu in striatal neurons of the group injected with mGluR2/3 antagonist (RS)-1-amino-5-phosphonoindan-1-carboxylic acid (APICA) into the striatum at the third week and the fifth week was significantly increased (P < 0.05, P < 0.01). Compared with the control group, the striatal mGluR2/3 protein expression of the PD group was significantly downregulated (P < 0.01); compared with the PD group, the striatal mGluR2/3 protein expression of the PD + exercise group was significantly upregulated (P < 0.05); compared with the control group, the striatal mGluR3 mRNA expression of the PD group was significantly downregulated (P < 0.01); compared with the PD group, the striatal mGluR3 mRNA expression of the PD + exercise group was significantly upregulated (P < 0.01); 6-OHDA damage and exercise intervention had no significant effect on the striatal mGluR2 mRNA expression (P > 0.05). Compared with the PD + exercise group, the total movement distance, the total movement time, and the mean velocity of the PD + exercise + APICA group were significantly decreased (P < 0.05); compared with the PD group, the PD + exercise + APICA group had no significant change in the total movement distance, the total movement time, and the mean velocity (P > 0.05). Conclusion: These data collectively demonstrate that the mGluR2/3-mediated glutamatergic transmission in the striatum is sensitive to dopamine (DA) depletion and may serve as a target of exercise intervention for mediating the therapeutic effect of exercise intervention in a rat model of PD.

Protective effects of β- nicotinamide adenine dinucleotide against motor deficits and dopaminergic neuronal damage in a mouse model of Parkinson's disease

The level of nicotinamide adenine dinucleotide (NAD) decreases in Parkinson's disease (PD), and its reduction has been reported to be involved in many age-associated neurodegenerative pathologies. Thus, we investigated whether NAD replenishment is beneficial in a 6-hydroxydopamine (6-OHDA)-induced mouse model of PD. Preinjection with NAD in the striatum ameliorated motor deficits and dopaminergic neuronal damage in the substantia nigra and striatum of a mouse model of PD. Moreover, preincubation with NAD protected PC12 cells against the loss of cell viability, morphological damage, oxidative stress and mitochondrial dysfunction caused by 6-OHDA. These results add credence to the beneficial role of NAD against parkinsonian neurodegeneration in mouse models of PD, provide evidence for the potential of NAD for the prevention of PD, and suggest that NAD prevents pathological changes in PD via decreasing mitochondrial dysfunctions.

Photobiomodulation as a treatment for neurodegenerative disorders: current and future trends

Photobiomodulation (PBM) is a rapidly growing as an innovative therapeutic modality for various types of diseases in recent years. Neuronal degeneration is irreversible process and it is proven to be difficult to slow down or stop the progression. Pharmacologic approaches to slow neuronal degeneration have been studied, but are limited due to concerns about the side effects. Therefore, it is necessary to develop a new therapeutic approach to stabilize neuronal degeneration and achieve neuronal protection against several neurodegenerative diseases. In this review, we have introduced several previous studies showing the positive effect of PBM over neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease and different types of epilepsy. Despite excellent outcomes of animal researches, not many clinical studies are conducted or showed positive outcome of PBM against neurodegenerative disease. To achieve clinical application of PBM against neurodegenerative disorder, determination of exact mechanism and establishment of effective clinical protocol seems to be necessary.

Combined Assessment of Diffusion Parameters and Cerebral Blood Flow Within Basal Ganglia in Early Parkinson's Disease

Diffusion tensor imaging (DTI) is a sensitive tool for detecting brain tissue microstructural alterations in Parkinson’s disease (PD). Abnormal cerebral perfusion patterns have also been reported in PD patients using arterial spin labeling (ASL) MRI. In this study we aimed to perform a combined DTI and ASL assessment in PD patients within the basal ganglia, in order to test the relationship between microstructural and perfusion alterations. Fifty-two subjects participated in this study. Specifically, 26 PD patients [mean age (SD) = 66.7 (8.9) years, 21 males, median (IQR) Modified Hoehn and Yahr = 1.5 (1–1.6)] and twenty-six healthy controls [HC, mean age (SD) = 65.2 (7.5), 15 males] were scanned with 1.5T MRI. Fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), radial diffusivity (RD) maps were derived from diffusion-weighted images, while cerebral blood flow (CBF) maps were computed from ASL data. After registration to Montreal Neurological Institute standard space, FA, MD, AD, RD and CBF median values were extracted within specific regions of interest: substantia nigra, caudate, putamen, globus pallidus, thalamus, red nucleus and subthalamic nucleus. DTI measures and CBF were compared between the two groups. The relationship between diffusion parameters and CBF was tested with Spearman’s correlations. False discovery rate (FDR)-corrected p-values lower than 0.05 were considered significant, while uncorrected p-values <0.05 were considered a trend. No significant FA, MD and RD differences were observed. AD was significantly increased in PD patients compared with HC in the putamen (p = 0.005, p_FDR = 0.035). No significant CBF differences were found between PD patients and HC. Diffusion parameters were not significantly correlated with CBF in the HC group, while a significant correlation emerged for PD patients in the caudate nucleus, for all DTI measures (with FA: r = 0.543, p_FDR = 0.028; with MD: r = −0.661, p_FDR = 0.002; with AD: r = −0.628, p_FDR = 0.007; with RD: r = −0.635, p_FDR = 0.003). This study showed that DTI is a more sensitive technique than ASL to detect alterations in the basal ganglia in the early phase of PD. Our results suggest that, although DTI and ASL convey different information, a relationship between microstructural integrity and perfusion changes in the caudate may be present.

Defective Tool Embodiment in Body Representation of Individuals Affected by Parkinson's Disease: A Preliminary Study

When efficiently used for action, tools become part of the body, with effect on the spatial-temporal movement parameters and body size perception. Until now, no previous investigation has been reported about tool embodiment in Parkinson’s disease (PD), which is a neurological disease characterized by several sensory and motor symptoms affecting body and action. We enrolled 14 individuals affected by PD and 18 healthy individuals as controls. We studied the spatial-temporal parameters on self-paced free pointing movement task, via an optoelectronic system, before and after a short training in which a 27-cm long rod was used to point toward a far target. Moreover, we investigated changes in estimation of arm length through the Tactile Estimation Task. After the tool-use training, controls showed changes in spatial-temporal parameters: they were slower to perform movements and reported a higher value of deceleration than the baseline. However, such a difference did not emerge in the PD individuals. In the Tactile Discrimination Task, no difference emerged before and after the tool-use training in both groups. Our results were suggestive of possible difficulties of the tool embodiment process in PD. We discussed our results in relation to aberrant multisensory integration as well as in terms of the effect of PD sensory and motor symptoms on body schema plasticity. The present study points at a novel way to conceive PD sensory motor signs and symptoms in terms of their effect on individuals’ body representation.

Sleep-State Dependent Alterations in Brain Functional Connectivity under Urethane Anesthesia in a Rat Model of Early-Stage Parkinson's Disease

Parkinson's disease (PD) is characterized by the gradual degeneration of dopaminergic neurons in the substantia nigra, leading to striatal dopamine depletion. A partial unilateral striatal 6-hydroxydopamine (6-OHDA) lesion causes 40-60% dopamine depletion in the lesioned rat striatum, modeling the early stage of PD. In this study, we explored the connectivity between the brain regions in partially 6-OHDA lesioned male Wistar rats under urethane anesthesia using functional magnetic resonance imaging (fMRI) at 5 weeks after the 6-OHDA infusion. Under urethane anesthesia, the brain fluctuates between the two states, resembling rapid eye movement (REM) and non-REM sleep states. We observed clear urethane-induced sleep-like states in 8/19 lesioned animals and 8/18 control animals. 6-OHDA lesioned animals exhibited significantly lower functional connectivity between the brain regions. However, we observed these differences only during the REM-like sleep state, suggesting the involvement of the nigrostriatal dopaminergic pathway in REM sleep regulation. Corticocortical and corticostriatal connections were decreased in both hemispheres, reflecting the global effect of the lesion. Overall, this study describes a promising model to study PD-related sleep disorders in rats using fMRI.

Quantifying Dynamic Balance in Young, Elderly and Parkinson's Individuals: A Systematic Review

Introduction: Falling is one of the primary concerns for people with Parkinson's Disease and occurs predominately during dynamic movements, such as walking. Several methods have been proposed to quantify dynamic balance and to assess fall risk. However, no consensus has been reached concerning which method is most appropriate for examining walking balance during unperturbed and perturbed conditions, particularly in Parkinson's Disease individuals. Therefore, this systematic review aimed to assess the current literature on quantifying dynamic balance in healthy young, elderly and Parkinson's individuals during unperturbed and perturbed walking. Methods: The PubMed database was searched by title and abstract for publications quantifying dynamic balance during unperturbed and mechanically perturbed walking conditions in elderly adults and PD. Inclusion criteria required publications to be published in English, be available in full-text, and implement a dynamic balance quantification method. Exclusion criteria included clinical dynamic balance measures, non-mechanical perturbations, pathologies other than PD, and dual-tasking conditions. The initial database search yielded 280 articles, however, only 81 articles were included after title, abstract and full-text screening. Methodological quality and data were extracted from publications included in the final synthesis. Results: The dynamic balance articles included 26 Coefficient of Variation of Spatiotemporal Variability, 10 Detrended Fluctuation Analysis, 20 Lyapunov Exponent, 7 Maximum Floquet Multipliers, 17 Extrapolated Center of Mass, 11 Harmonic Ratios, 4 Center of Mass-Center of Pressure Separation, 2 Gait Stability Ratio, 1 Entropy, 3 Spatiotemporal Variables, 2 Center of Gravity and Center of Pressure, and 2 Root Mean Square in the final synthesis. Assessment of methodological quality determined that 58 articles had a low methodological rating, a 22 moderate rating, and 1 having a high rating. Conclusion: Careful consideration must be given when selecting a method to quantify dynamic balance because each method defines balance differently, reflects a unique aspect of neuromuscular stability mechanisms, and is dependent on the walking condition (unperturbed vs. perturbed). Therefore, each method provides distinct information into stability impairment in elderly and PD individuals.

Imaging of Motor Cortex Physiology in Parkinson's Disease

There is abundant evidence that the pathophysiology of Parkinson's disease (PD) is not confined to the nigrostriatal dopaminergic pathway but propagates along the cortico‐basal ganglia‐thalamo‐cortical neural network. A critical node in this functional circuit impacted by PD is the primary motor cortex (M1), which plays a key role in generating neural impulses that regulate movements. The past several decades have lay witness to numerous in vivo neuroimaging techniques that provide a window into the function and structure of M1. A consistent observation from numerous studies is that during voluntary movement, but also at rest, the functional activity of M1 is altered in PD relative to healthy individuals, and it relates to many of the motor signs. Although this abnormal functional activity can be partially restored with acute dopaminergic medication, it continues to deteriorate with disease progression and may predate structural degeneration of M1. The current review discusses the evidence that M1 is fundamental to the pathophysiology of PD, as measured by neuroimaging techniques such as positron emission tomography, single‐photon emission computed tomography, electroencephalography, magnetoencephalography, and functional and structural MRI. Although novel treatments that target the cortex will not cure PD, they could significantly slow down and alter the progressive course of the disease and thus improve clinical care for this degenerative disease. © 2018 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society

Therapeutic strategies for Parkinson disease: beyond dopaminergic drugs

Existing therapeutic strategies for managing Parkinson disease (PD), which focus on addressing the loss of dopamine and dopaminergic function linked with degeneration of dopaminergic neurons, are limited by side effects and lack of long-term efficacy. In recent decades, research into PD pathophysiology and pharmacology has focused on understanding and tackling the neurodegenerative processes and symptomology of PD. In this Review, we discuss the challenges associated with the development of novel therapies for PD, highlighting emerging agents that aim to target cell death, as well as new targets offering a symptomatic approach to managing features and progression of the disease.

An mGlu4-Positive Allosteric Modulator Alleviates Parkinsonism in Primates

BACKGROUND

Levodopa remains the gold-standard treatment for PD. However, it becomes less effective as the disease progresses and produces debilitating side effects, such as motor fluctuations and l-dopa-induced dyskinesia. Modulation of metabotropic glutamate receptor 4 represents a promising antiparkinsonian approach in combination with l-dopa, but it has not been demonstrated in primates.

OBJECTIVE

We studied whether a novel positive allosteric modulator of the metabotropic glutamate receptor 4, PXT002331 (foliglurax), could reduce parkinsonism in primate models.

METHODS

We assessed the therapeutic potential of PXT002331 in three models of MPTP-induced parkinsonism in macaques. These models represent three different stages of disease evolution: early stage and advanced stage with and without l-dopa-induced dyskinesia.

RESULTS

As an adjunct to l-dopa, PXT002331 induced a robust and dose-dependent reversal of parkinsonian motor symptoms in macaques, including bradykinesia, tremor, posture, and mobility. Moreover, PXT002331 strongly decreased dyskinesia severity, thus having therapeutic efficacy on both parkinsonian motor impairment and l-dopa-induced dyskinesia. PXT002331 brain penetration was also assessed using PET imaging in macaques, and pharmacodynamic analyses support target engagement in the therapeutic effects of PXT002331.

CONCLUSIONS

This work provides a demonstration that a positive allosteric modulator of metabotropic glutamate receptor 4 can alleviate the motor symptoms of PD and the motor complications induced by l-dopa in primates. PXT002331 is the first compound of its class to enter phase IIa clinical trials. © 2018 International Parkinson and Movement Disorder Society.

Modulation of CaMKIIa-GluN2B interaction in levodopa-induced dyskinesia in 6-OHDA-lesioned Parkinson's rats

Long-term treatment with L-dopa leads to involuntary aimless movements called L-dopa-induced dyskinesia (LID) has hindered its use in Parkinson's disease (PD) patients. Emerging evidence suggests a possible role of CaMKIIa and its interacting partners in the development of LID. In this study, we found that CaMKIIa was found to form complexes with GluN2B after chronic administration of L-dopa in adult rat striatal neurons. Intrastriatal injection of KN-93 significantly reduced the level of GluN2B in CaMKIIa precipitates with a dose dependent response, as well as reduced the Global ALO AIM score without ablation of the therapeutic response to L-dopa. In parallel, intrastriatal injection of MK-801 significantly alleviated the level of CaMKIIa in GluN2B precipitates compared to LID group (p < 0.01), and this is accompanied by realizing improvement of the Global ALO AIM score also without affect the efficacy of L-dopa. In summary, the present study indicated that CaMKIIa-GluN2B interaction had an important role in the development of LID. Disrupt of this link by intrastriatal infusion of KN-93 or MK-801 ameliorated dyskinesia in 6-OHDA-lesioned PD rats.

Differentiation in Theta and Beta Electrocortical Activity between Visual and Physical Perturbations to Walking and Standing Balance

Human balance is a complex process in healthy adults, requiring precisely timed coordination among sensory information, cognitive processing, and motor control. It has been difficult to quantify brain dynamics during human balance control due to limitations in brain-imaging modalities. The goal of this study was to determine whether by using high-density electroencephalography (EEG) and independent component analysis, we can identify common cortical responses to visual and physical balance perturbations during walking and standing. We studied the responses of 30 healthy young adults to sensorimotor perturbations that challenged their balance. Subjects performed four 10 min trials of beam walking and tandem stance while either being mediolaterally pulled at the waist or viewing brief 20° field-of-view rotations in virtual reality. We recorded high-density EEG, motion capture, lower leg electromyography (EMG), and neck EMG. We hypothesized that both physical pull and visual rotation perturbations would elicit time-frequency fluctuations in theta (4-8 Hz) and beta (13-30 Hz) bands, with increased occipito-parietal activity during visual rotations compared with pull perturbations. Our results confirmed this hypothesis. For both perturbations, we found early theta synchronization and late alpha-beta (8-30 Hz) desynchronization following perturbation onset. This pattern was strongest in occipito-parietal areas during visual perturbations and strongest in sensorimotor areas during pull perturbations. These results suggest a similar time-frequency electrocortical pattern when humans respond to sensorimotor conflict, but with substantive differences in the brain areas involved for visual versus physical perturbations. Our findings may have important implications for assessing and training balance in individuals with and without motor disabilities.

Acetylcholine Neurotransmitter Receptor Densities in the Striatum of Hemiparkinsonian Rats Following Botulinum Neurotoxin-A Injection

Cholinergic neurotransmission has a pivotal function in the caudate-putamen, and is highly associated with the pathophysiology of Parkinson's disease. Here, we investigated long-term changes in the densities of the muscarinic receptor subtypes M₁, M₂, M₃ (mAchRs) and the nicotinic receptor subtype α₄β₂ (nAchRs) in the striatum of the 6-OHDA-induced hemiparkinsonian (hemi-PD) rat model using quantitative in vitro receptor autoradiography. Hemi-PD rats exhibited an ipsilateral decrease in striatal mAchR densities between 6 and 16%. Moreover, a massive and constant decrease in striatal nAchR density by 57% was found. A second goal of the study was to disclose receptor-related mechanisms for the positive motor effect of intrastriatally injected Botulinum neurotoxin-A (BoNT-A) in hemi-PD rats in the apomorphine rotation test. Therefore, the effect of intrastriatally injected BoNT-A in control and hemi-PD rats on mAchR and nAchR densities was analyzed and compared to control animals or vehicle-injected hemi-PD rats. BoNT-A administration slightly reduced interhemispheric differences of mAchR and nAchR densities in hemi-PD rats. Importantly, the BoNT-A effect on striatal nAchRs significantly correlated with behavioral testing after apomorphine application. This study gives novel insights of 6-OHDA-induced effects on striatal mAchR and nAchR densities, and partly explains the therapeutic effect of BoNT-A in hemi-PD rats on a cellular level.

Dose-dependent effects of adenosine antagonists on tacrine-induced tremulous jaw movements

The present study examines the effect of three adenosine receptor antagonists on tremulous jaw movements (TJMs), an animal model of tremor. Forty-five rats were pre-treated with one adenosine antagonist: caffeine (0.0, 5.0, or 10.0 mg/kg; non-selective adenosine receptor antagonist), 8-cyclopentyltheophylline (CPT; 0.0, 5.0, or 10.0 mg/kg; selective adenosine A₁ receptor antagonist), or SCH 58261 (0.0 or 8.0 mg/kg; selective adenosine A_2A receptor antagonist) followed by TJM induction with tacrine (0.0, 0.75, or 2.5 mg/kg; acetylcholinesterase inhibitor). CPT and SCH 58261 both significantly reduced TJMs while caffeine did not. Unexpectedly, both SCH 58261 and CPT reduced TJMs even in the absence of tacrine. Also, CPT showed a robust reduction of TJMs, achieved at both (5.0 mg/kg) and (10.0 mg/kg) doses and regardless of tacrine dose. In conclusion, this study shows adenosine receptor antagonism to generally suppress low-dose tacrine-induced TJMs. In concert with two prior studies, these results are suggestive of behavioral evidence for a biphasic effect of adenosine A_2A receptor antagonists (caffeine and SCH 58261) that is modulated by tacrine, and a model of this effect is proposed.

Haloperidol ameliorates androgen-induced behavioral deficits in developing male rats

The purpose of present study was to infer the potential effects of testosterone increase in some male-based childhood-onset neuropsychiatric disorders, such as Tourette syndrome. Thus, the influence of early postnatal androgen exposure upon the neurobehaviors and its possible neural basis were investigated in the study. Male pup rats received consecutive 14-day testosterone propionate (TP) subcutaneous injection from postnatal day (PND) 7. The TP treatment produced the hyperactive motor behavior and grooming behavior as well as the increased levels of dopamine, tyrosine hydroxylase and dopamine transporter in the mesodopaminergic system and the elevated levels of serotonin in the nucleus accumbens, without affecting the levels of glutamate, γ-aminobutyric acid, norepinephrine and histamine in the caudate putamen and nucleus accumbens of PND21 and PND49 rats. Dopamine D2 receptor antagonist haloperidol was administered to the early postnatal TP-exposed PND21 and PND49 male rats 30 min prior to open field test. Haloperidol significantly ameliorated the motor behavioral and grooming behavioral defects induced by early postnatal TP exposure. The results demonstrated that early postnatal androgen exposure significantly disturbed the brain activity of developing male rats via enhancing the mesodopaminergic activity. It was suggested that abnormal increments of testosterone levels during the early postnatal development might be a potential risk factor for the incidence of some male-based childhood-onset neuropsychiatric disorders by affecting the mesodopaminergic system.