FDG-PET study of the bilateral subthalamic nucleus stimulation effects on the regional cerebral metabolism in advanced Parkinson disease

The Contribution of Type 2 Diabetes to Parkinson's Disease Aetiology

Type 2 diabetes (T2D) and Parkinson's disease (PD) are chronic disorders that have a significant health impact on a global scale. Epidemiological, preclinical, and clinical research underpins the assumption that insulin resistance and chronic inflammation contribute to the overlapping aetiologies of T2D and PD. This narrative review summarises the recent evidence on the contribution of T2D to the initiation and progression of PD brain pathology. It also briefly discusses the rationale and potential of alternative pharmacological interventions for PD treatment.

Glucose Metabolism Impairment in Parkinson's Disease

Impairments in systematic and regional glucose metabolism exist in patients with Parkinson's disease (PD) at every stage of the disease course, and such impairments are associated with the incidence, progression, and special phenotypes of PD, which affect each physiological process of glucose metabolism including glucose uptake, glycolysis, tricarboxylic acid cycle, oxidative phosphorylation, and pentose phosphate shunt pathway. These impairments may be attributed to various mechanisms, such as insulin resistance, oxidative stress, abnormal glycated modification, blood-brain-barrier dysfunction, and hyperglycemia-induced damages. These mechanisms could subsequently cause excessive methylglyoxal and reactive oxygen species production, neuroinflammation, abnormal aggregation of protein, mitochondrial dysfunction, and decreased dopamine, and finally result in energy supply insufficiency, neurotransmitter dysregulation, aggregation and phosphorylation of α-synuclein, and dopaminergic neuron loss. This review discusses the glucose metabolism impairment in PD and its pathophysiological mechanisms, and briefly summarized the currently-available therapies targeting glucose metabolism impairment in PD, including glucagon-likepeptide-1 (GLP-1) receptor agonists and dual GLP-1/gastric inhibitory peptide receptor agonists, metformin, and thiazoledinediones.

A prospective pilot study of the effects of deep brain stimulation on olfaction and constipation in Parkinson's disease

BACKGROUND

Previous studies suggest deep brain stimulation of the subthalamic nucleus (STN-DBS) may improve olfaction and constipation in PD, using subjective measures.

OBJECTIVE

To utilize objective measures to assess olfaction and constipation in PD following STN-DBS.

METHODS

In this prospective pilot study, olfaction (University of Pennsylvania Smell Identification Test [UPSIT]), bowel symptoms (ROME III questionnaires, daily bowel diaries, 100 mm visual analog scales for satisfaction with treatment and bowel habits), and motor manifestations of PD were evaluated before and after STN-DBS. Levodopa equivalent daily dose (LEDD) was calculated.

RESULTS

Ten patients (8 men, mean age 67.4 ± 6.0 years) with mean PD duration of 7.5 ± 3.7 years underwent bilateral STN-DBS, with mean follow-up of 3 months for all measures, except 7 months follow-up for bowel diaries. There was improvement in the Unified Parkinson's Disease Rating Scale motor "off" scores (33.7 ± 6.7 before and 16.1 ± 10.8 after, P = 0.001). Mean UPSIT scores (20.0 ± 6.6 versus 17.5 ± 5.7, P = 0.03) worsened from severe to total hyposmia. Seven patients had baseline constipation and completed bowel diaries. There was improvement in number of complete spontaneous bowel motions (CBSM) per week (2.2 ± 1.9 before versus 4.7 ± 2.4 after, P = 0.04), satisfaction with treatment of constipation (44 ± 27 before versus 64 ± 25 after, P = 0.02), and with bowel motions (33 ± 22 before and 48 ± 20 after, P = 0.2). However, laxative use (P = 0.15) and LEDD (P = 0.15) were unchanged.

CONCLUSION

Olfaction worsened while symptoms of constipation improved but did not resolve after STN-DBS.

Effective network of deep brain stimulation of subthalamic nucleus with bimodal positron emission tomography/functional magnetic resonance imaging in Parkinson's disease

AIMS

Deep brain stimulation of the subthalamic nucleus (STN-DBS) has become an effective treatment strategy for patients with Parkinson's disease. However, the biological mechanism underlying DBS treatment remains poorly understood.

METHOD

In this study, we investigated how STN-DBS modulated the brain network using a bimodal positron emission tomography (PET)/functional magnetic resonance imaging (fMRI) dataset. We first performed an activation likelihood estimation meta-analysis of 13 PET/SPECT studies concerning STN-DBS effects on resting-state brain activity in Parkinson's disease. Additionally, using a functional connectivity analysis in resting-state fMRI, we investigated whether these STN-DBS-affected regions were functionally connected to constitute an effective network.

RESULTS

The results revealed that STN-DBS reduced brain activity in the right thalamus, bilateral caudal supplementary area, and the left primary motor cortex, and it increased brain activity in the left thalamus during rest. Second, these STN-DBS-affected areas were functionally connected within an STN-DBS effective network.

CONCLUSION

Deep brain stimulation of the subthalamic nucleus (STN-DBS) may deactivate the motor cortex as a remote and network effect, affecting the target and the neighboring subcortical areas. These areas may constitute an effective network of STN-DBS modulation. Our results shed light on the mechanisms of STN-DBS treatment from a network perspective and highlight the potential therapeutic benefits of targeted network modulation.

PET imaging in neurology: Alzheimer's and Parkinson's diseases

PET studies play an important role in the early detection of Alzheimer's and Parkinson's diseases (AD and PD). Fluorine-18 fluorodeoxyglucose (F-FDG) PET imaging of regional cerebral glucose metabolism and PET amyloid imaging are the two major PET studies for AD. F-FDG PET is highly sensitive for the early diagnosis of AD, in predicting conversion from mild cognitive impairment to AD, and in differentiating AD from other dementias. PET amyloid imaging is positive in the majority of patients with AD. Negative amyloid PET reduces the likelihood of AD. The main limitations of PET amyloid imaging is its high positivity in the normal elderly population and in other medical conditions with amyloid pathologies. Various PET tracers are available to assess motor and cognitive dysfunctions in PD. PET tracers targeting presynaptic dopaminergic function (F-DOPA, radiolabeled PET tracers assessing the availability of dopamine transporters and vesicular monoamine transporters) and postsynaptic dopamine receptors are used to assess motor dysfunction in PD. PET tracers, particularly dopamine transporters, are highly sensitive in the early diagnosis of PD. Uptake of PET tracers in the striatum is inversely correlated with disease severity. PET is valuable in differentiating PD from other movement disorders. PET studies, particularly F-FDG PET, help to evaluate cortical metabolism in PD patients with cognitive dysfunction and dementia.

Recent progress of imaging agents for Parkinson's disease

Parkinson's disease (PD) is a common progressive, neurodegenerative brain disease that is promoted by mitochondrial dysfunction, oxidative stress, protein aggregation and proteasome dysfunction in the brain. Compared with computer tomography (CT) or magnetic resonance imaging (MRI), non-invasive nuclear radiopharmaceuticals have great significance for the early diagnosis of PD due to their high sensitivity and specificity in atypical and preclinical cases. Based on the development of coordination chemistry and chelator design, radionuclides may be delivered to lesions by attaching to PD-related transporters and receptors, such as dopamine, serotonin, and others. In this review, we comprehensively detailed the current achievements in radionuclide imaging in Parkinson's disease.

The COMT Val/Met polymorphism modulates effects of tDCS on response inhibition

BACKGROUND

Transcranial direct current stimulation (tDCS) is increasingly discussed as a new option to support the cognitive rehabilitation in neuropsychiatric disorders. However, the therapeutic impact of tDCS is limited by high inter-individual variability. Genetic factors most likely contribute to this variability by modulating the effects of tDCS.

OBJECTIVES

We aimed to investigate the influence of the COMT Val(108/158)Met polymorphism on cathodal tDCS effects on executive functioning.

METHODS

Cathodal tDCS was applied to the left dorsolateral prefrontal cortex (dlPFC) during the performance of a parametric Go/No-Go test.

RESULTS

We demonstrate an impairing effect of cathodal tDCS to the dlPFC on response inhibition. This effect was only found in individuals homozygous for the Val-allele of the COMT Val(108/158)Met polymorphism. No effects of stimulation on executive functions in Met-allele carriers were detected.

CONCLUSION

Our data indicate that i) cathodal, excitability reducing tDCS, interferes with inhibitory cognitive control, ii) the left dlPFC is critically involved in the neuronal network underlying the control of response inhibition, and iii) the COMT Val(108/158)Met polymorphism modulates the impact of cathodal tDCS on inhibitory control. Together with our previous finding that anodal tDCS selectively impairs set-shifting abilities in COMT Met/Met homozygous individuals, these results indicate that genetic factors modulate effects of tDCS on cognitive performance. Therefore, future tDCS research should account for genetic variability in the design and analysis of neurocognitive as well as therapeutic applications to reduce the variability of results and facilitate individualized neurostimulation approaches.

Submyelin potassium accumulation may functionally block subsets of local axons during deep brain stimulation: a modeling study

Deep brain stimulation has been used for over a decade to relieve the symptoms of Parkinson's disease, although its mechanism of action remains poorly understood. To better understand the direct effects of DBS on central neurons, a computational model of a myelinated axon has been constructed which includes the effects of K(+) accumulation within the peri-axonal space. Using best estimates of anatomic and electrogenic model parameters for in vivo STN axons, the model predicts a functional block along the axon due to K(+) accumulation in the submyelin space. The functional block occurs for a range of model parameters: high stimulation frequencies (>130 Hz); high extracellular K(+) concentrations (>3 x 10(-3) M); low maximum Na(+)/K(+) ATPase current densities (<0.026 A m(-2)); low diffusion coefficients for K(+) diffusion out of the submyelin space (<2.4 x 10(-9) m(2) s(-1)); small periaxonal space widths of the myelin attachment sections (<2.7 x 10(-9) m) and perinodal/internodal sections (<8.4 x 10(-9) m). These results suggest that therapeutic DBS of the STN likely results in a functional block for many STN axons, although a subset of STN axons may also be activated at the stimulating frequency.