MPTP-Induced Impairment of Cardiovascular Function

Phosphorylated α-synuclein deposited in Schwann cells interacting with TLR2 mediates cell damage and induces Parkinson's disease autonomic dysfunction

Despite the significant frequency of autonomic dysfunction (AutD) in Parkinson's disease (PD) patients, its pathogenesis and diagnosis are challenging. Here, we aimed to further explore the mechanism of phosphorylated α-synuclein (p-α-syn) deposited in vagus nerve Schwann cells (SCs) causing SCs damage and PD AutD. 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, 20 mg/kg) was administrated to C57BL/6 mice twice a week for 35 days. Following the final injection, locomotor functions, gastrointestinal symptoms, urine functions, and cardiovascular system functions were evaluated. Meanwhile, we examined p-α-syn deposited in vagus nerve SCs, Toll-like receptor 2 (TLR2) activation, and SCs loss using immunofluorescence, western blot, and Luxol fast blue staining. In vitro, the rat SCs line RSC96 cells were exposed to α-synuclein preformed fibril (α-syn PFF), and cell viability was detected by CCK8. Co-IP was used to identify the interaction between p-α-syn and TLR2. Furthermore, the role of TLR2 in p-α-syn-mediated SCs damage was confirmed by the administration of CU-CPT22, a specific blocker of TLR2. In vivo, apart from dyskinesia, MPTP mice exhibited constipation, urinary dysfunction, and cardiovascular failure, which were associated with the deposition of p-α-syn in vagus nerve SCs, TLR2 activation, and vagus nerve demyelination. In vitro, stimulation of α-syn PFF induced a time-dependent loss of viability, and p-α-syn deposited in RSC96 cells induced a cellular inflammatory response by interacting with TLR2, resulting in cell dysfunction and apoptosis. However, both SCs inflammatory response and cell viability were alleviated after inhibition of TLR2. Furthermore, 1 h fecal pellets and water content, the frequency of 1 h urine, blood pressure, heart rate, and heart rate variability of mice in the MPTP + CU-CPT22 group were also improved. Our results support the perspective that p-α-syn interacts with TLR2 induced SCs damage and is involved in PD AutD, which sheds fresh light on the mechanism of PD AutD and indicates a promising treatment for PD AutD targeting SCs p-α-syn/ TLR2 signaling pathway.

Investigating affective neuropsychiatric symptoms in rodent models of Parkinson's disease

Affective neuropsychiatric disorders such as depression, anxiety and apathy are among the most frequent non-motor symptoms observed in people with Parkinson's disease (PD). These conditions often emerge during the prodromal phase of the disease and are generally considered to result from neurodegenerative processes in meso-corticolimbic structures, occurring in parallel to the loss of nigrostriatal dopaminergic neurons. Depression, anxiety, and apathy are often treated with conventional medications, including selective serotonin reuptake inhibitors, tricyclic antidepressants, and dopaminergic agonists. The ability of these pharmacological interventions to consistently counteract such neuropsychiatric symptoms in PD is still relatively limited and the development of reliable experimental models represents an important tool to identify more effective treatments. This chapter provides information on rodent models of PD utilized to study these affective neuropsychiatric symptoms. Neurotoxin-based and genetic models are discussed, together with the main behavioral tests utilized to identify depression- and anxiety-like behaviors, anhedonia, and apathy. The ability of various therapeutic approaches to counteract the symptoms observed in the various models is also reviewed.

Trigeminal electrical stimulation with ULFTENS of the dorsal anterior mucosal surface of the tongue: Effects on Heart Rate Variability (HRV)

BACKGROUND

Trigeminal electrical stimulation of the dorsal anterior mucosal surface of the tongue has demonstrated its efficacy in a variety of neurological disorders in which anatomical or functional alterations are present. The pathogenesis of such disorders is often linked to altered arousal circuits, and the benefits of tongue stimulation are attributed to the rebalancing of this system. Dental ULFTENS shows efficacy in acting on the muscular, autonomic system and control of the descending pathways that modulate pain. It is administered at the skin level in the area anterior to the tragus and not on the mucosal surface of the tongue. The use of this stimulation technique at the tongue level could have new applications and clinical results if it were able to reduce the activity of arousal circuits.

MATERIAL AND METHOD

A new intraoral device allowed electrical stimulation of the dorsal anterior mucosa of the tongue in 32 healthy young women. The effects on HRV were monitored by photoplethysmographic wave (PPG) and compared with a control group. The HRV parameters studied were RMSSD, HF, LF, LF/HF, REC, DET.

RESULTS

The group of stimulated subjects showed a significant change in some of the HRV parameters that was maintained even in the epoch after the end of electrical stimulation. This effect can be considered as a vagal activation and a change of HRV trend. The control group of unstimulated subjects showed an opposite trend. There were no undesirable or annoying effects of stimulation.

CONCLUSION

Stimulation of the dorsal anterior (trigeminal) mucosal surface of the tongue with ULFTENS applied with an intraoral device was shown to be able to increase HRV.

Microglia-derived PDGFB promotes neuronal potassium currents to suppress basal sympathetic tonicity and limit hypertension

Although many studies have addressed the regulatory circuits affecting neuronal activities, local non-synaptic mechanisms that determine neuronal excitability remain unclear. Here, we found that microglia prevented overactivation of pre-sympathetic neurons in the hypothalamic paraventricular nucleus (PVN) at steady state. Microglia constitutively released platelet-derived growth factor (PDGF) B, which signaled via PDGFRα on neuronal cells and promoted their expression of Kv4.3, a key subunit that conducts potassium currents. Ablation of microglia, conditional deletion of microglial PDGFB, or suppression of neuronal PDGFRα expression in the PVN elevated the excitability of pre-sympathetic neurons and sympathetic outflow, resulting in a profound autonomic dysfunction. Disruption of the PDGFB^MG-Kv4.3^Neuron pathway predisposed mice to develop hypertension, whereas central supplementation of exogenous PDGFB suppressed pressor response when mice were under hypertensive insult. Our results point to a non-immune action of resident microglia in maintaining the balance of sympathetic outflow, which is important in preventing cardiovascular diseases.

Nitric Oxide Involvement in Cardiovascular Dysfunctions of Parkinson Disease

Parkinson’s disease (PD) is characterized by the loss of dopaminergic neurons in the substantia nigra, causing motor changes. In addition to motor symptoms, non-motor dysfunctions such as psychological, sensory and autonomic disorders are recorded. Manifestations related to the autonomic nervous system include the cardiovascular system, as postural hypotension, postprandial hypotension, and low blood pressure. One of the mediators involved is the nitric oxide (NO). In addition to the known roles such as vasodilator, neuromodulator, NO acts as an important mediator of the immune response, increasing the inflammatory response provoked by PD in central nervous system. The use of non-specific NOS inhibitors attenuated the neurodegenerative response in animal models of PD. However, the mechanisms by which NO contributes to neurodegeneration are still not well understood. The literature suggest that the contribution of NO occurs through its interaction with superoxides, products of oxidative stress, and blocking of the mitochondrial respiratory chain, resulting in neuronal death. Most studies involving Parkinsonism models have evaluated brain NO concentrations, with little data available on its peripheral action. Considering that studies that evaluated the involvement of NO in the neurodegeneration in PD, through NOS inhibitors administration, showed neuroprotection in rats, it has prompted new studies to assess the participation of NOS isoforms in cardiovascular changes induced by parkinsonism, and thus to envision new targets for the treatment of cardiovascular disorders in PD. The aim of this study was to conduct a literature review to assess available information on the involvement of nitric oxide (NO) in cardiovascular aspects of PD.

Cardiac Changes in Parkinson's Disease: Lessons from Clinical and Experimental Evidence

Dysautonomia is a common non-motor symptom in Parkinson's disease (PD). Most dysautonomic symptoms appear due to alterations in the peripheral nerves of the autonomic nervous system, including both the sympathetic and parasympathetic nervous systems. The degeneration of sympathetic nerve fibers and neurons leads to cardiovascular dysfunction, which is highly prevalent in PD patients. Cardiac alterations such as orthostatic hypotension, heart rate variability, modifications in cardiogram parameters and baroreflex dysfunction can appear in both the early and late stages of PD, worsening as the disease progresses. In PD patients it is generally found that parasympathetic activity is decreased, while sympathetic activity is increased. This situation gives rise to an imbalance of both tonicities which might, in turn, promote a higher risk of cardiac damage through tachycardia and vasoconstriction. Cardiovascular abnormalities can also appear as a side effect of PD treatment: L-DOPA can decrease blood pressure and aggravate orthostatic hypotension as a result of a negative inotropic effect on the heart. This unwanted side effect limits the therapeutic use of L-DOPA in geriatric patients with PD and can contribute to the number of hospital admissions. Therefore, it is essential to define the cardiac features related to PD for the monitorization of the heart condition in parkinsonian individuals. This information can allow the application of intervention strategies to improve the course of the disease and the proposition of new alternatives for its treatment to eliminate or reverse the motor and non-motor symptoms, especially in geriatric patients.

Animal models of Parkinson's disease: a guide to selecting the optimal model for your research

Parkinson's disease (PD) is a complex, multisystem disorder characterised by α-synuclein (SNCA) pathology, degeneration of nigrostriatal dopaminergic neurons, multifactorial pathogenetic mechanisms and expression of a plethora of motor and non-motor symptoms. Animal models of PD have already been instructive in helping us unravel some of these aspects. However, much remains to be discovered, requiring continued interrogation by the research community. In contrast with the situation for many neurological disorders, PD benefits from of a wide range of available animal models (pharmacological, toxin, genetic and α-synuclein) but this makes selection of the optimal one for a given study difficult. This is especially so when a study demands a model that displays a specific combination of features. While many excellent reviews of animal models already exist, this review takes a different approach with the intention of more readily informing this decision-making process. We have considered each feature of PD in turn - aetiology, pathology, pathogenesis, motor dysfunctions and non-motor symptoms (NMS) - highlighting those animal models that replicate each. By compiling easily accessible tables and a summary figure, we aim to provide the reader with a simple, go-to resource for selecting the optimal animal model of PD to suit their research needs.

Cardiac tyrosine hydroxylase activation and MB-COMT in dyskinetic monkeys

The impact of age-associated disorders is increasing as the life expectancy of the population increments. Cardiovascular diseases and neurodegenerative disorders, such as Parkinson’s disease, have the highest social and economic burden and increasing evidence show interrelations between them. Particularly, dysfunction of the cardiovascular nervous system is part of the dysautonomic symptoms of Parkinson’s disease, although more studies are needed to elucidate the role of cardiac function on it. We analyzed the dopaminergic system in the nigrostriatal pathway of Parkinsonian and dyskinetic monkeys and the expression of some key proteins in the metabolism and synthesis of catecholamines in the heart: total and phosphorylated (phospho) tyrosine hydroxylase (TH), and membrane (MB) and soluble (S) isoforms of catechol-O-methyl transferase (COMT). The dopaminergic system was significantly depleted in all MPTP-intoxicated monkeys. MPTP- and MPTP + L-DOPA-treated animals also showed a decrease in total TH expression in both right (RV) and left ventricle (LV). We found a significant increase of phospho-TH in both groups (MPTP and MPTP + L-DOPA) in the LV, while this increase was only observed in MPTP-treated monkeys in the RV. MB-COMT analysis showed a very significant increase of this isoform in the LV of MPTP- and MPTP + L-DOPA-treated animals, with no significant differences in S-COMT levels. These data suggest that MB-COMT is the main isoform implicated in the cardiac noradrenergic changes observed after MPTP treatment, suggesting an increase in noradrenaline (NA) metabolism. Moreover, the increase of TH activity indicates that cardiac noradrenergic neurons still respond despite MPTP treatment.

Bone Mineral Density and Related Scores in Parkinson's Disease: A Systematic Review and Meta-Analysis

BACKGROUND

Parkinson's disease (PD) is the second most common degenerative neurologic disorder in older adults, and increasing attention has been paid to bone health in PD. Although several studies have shown that patients with PD have a lower bone mineral density (BMD) than do non-PD controls, there have been no systematic reviews in recent years.

METHODS

PubMed, Medline, and Web of Science were used to search relevant studies up to May 2020. BMD, BMD T score, and BMD Z score of patients with and without PD were statistically analyzed. Meta-analysis was conducted using Review Manager version 5.3.

RESULTS

This meta-analysis included 17 studies comprising 10,289 individuals. In the meta-analysis, adults with PD had lower total body, total hip, total radius, lumbar spine, total femur, femur neck, right-hand, and left-hand BMD than did non-PD controls. The T score of total body BMD, total hip BMD, total radius BMD, lumbar spine BMD, L1-L4 spine BMD, total femur BMD, and femur neck BMD in adults with PD were lower than those in non-PD controls. Futhermore, the Z score of total body BMD, total hip BMD, total radius BMD, lumbar spine BMD, L1-L4 spine BMD, and femur neck BMD was lower in adults with PD than in non-PD controls.

CONCLUSIONS

Patients with PD had a lower BMD, BMD T score, and BMD Z score compared with non-PD controls. Therefore, clinicians should routinely monitor BMD of patients with PD to prevent falling and fragility fractures in older adults and optimize BMD before surgical treatment of severe spinal deformity caused by PD.

Cold Exposure After Exercise Impedes the Neuroprotective Effects of Exercise on Thermoregulation and UCP4 Expression in an MPTP-Induced Parkinsonian Mouse Model

Moderate exercise and mild hypothermia have protective effects against brain injury and neurodegeneration. Running in a cold environment alters exercise-induced hyperthermia and outcomes; however, evaluations of post-exercise cold exposure related to exercise benefits for the brain are relatively rare. We investigated the effects of 4°C cold exposure after exercise on exercise-induced thermal responses and neuroprotection in an MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine)-induced Parkinsonian mouse model. Male C57BL/6J mice were pretreated with MPTP for five consecutive days and follow-up treadmill exercise for 4 weeks. After 1-h running at a 22°C temperature, the mice were exposed to a 4°C environment for 2 h. An MPTP injection induced a transient drop in body and brain temperatures, while mild brain hypothermia was found to last for 4 weeks after MPTP treatment. Preventing brain hypothermia by exercise or 4°C exposure was associated with an improvement in MPTP-induced striatal uncoupling protein 4 (UCP4) downregulation and nigrostriatal dopaminergic neurodegeneration. However, 4°C exposure after exercise abrogated the exercise-induced beneficial effects and thermal responses in MPTP-treated mice, including a low amplitude of exercise-induced brain hyperthermia and body temperature while at rest after exercise. Our findings elucidate that post-exercise thermoregulation and UCP4 expression are important in the neuroprotective effects of exercise against MPTP toxicity.