Striatal glutamatergic hyperactivity in Parkinson's disease

Molecular-Informed Network Analysis Unveils Fatigue-Related Functional Connectivity in Parkinson's Disease

BACKGROUND

Fatigue in Parkinson's disease (PD) is a prevalent and debilitating non-motor symptom. Despite its significant impact on quality of life, the underlying neurochemical and network-based mechanisms remain poorly understood.

OBJECTIVES

This observational study applied a multimodal imaging approach to explore potential links between the functional connectivity of neurotransmitter-specific circuits and fatigue in a sample of patients with PD.

METHODS

We acquired resting-state functional magnetic resonance imaging data in 35 patients with PD including 18 with clinically significant fatigue and 17 without. We applied the receptor-enriched analysis of functional connectivity by targets (REACT) pipeline to derive patients' specific molecularly enriched networks informed by the spatial distribution of the dopamine, noradrenaline, serotonin transporters, and metabotropic glutamate 5 receptors as assessed using molecular imaging data in independent samples of healthy controls. We then conducted whole-brain analyses inspecting both categorical differences between groups of patients with and without clinically significant fatigue, and associations exploring the full within-sample variation in symptom ratings.

RESULTS

We found a significant decrease in noradrenaline-enriched and glutamate-enriched functional connectivity in key regions, belonging to the sensorimotor, salience, and default mode network, with increasing fatigue severity. Notably, noradrenaline-enriched functional connectivity reductions were widespread, while glutamate-enriched functional connectivity reductions were more restricted to the supplementary motor area. No significant relationships between fatigue and dopamine or serotonin-enriched functional connectivity were found.

CONCLUSIONS

These findings offer supportive evidence for the putative involvement of the noradrenaline and glutamate systems in the genesis of fatigue in PD, opening new directions for treatment development exploring these neurochemical systems. © 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Atypical plume-like events contribute to glutamate accumulation in metabolic stress conditions

Neural glutamate homeostasis is important for health and disease. Ischemic conditions, like stroke, cause imbalances in glutamate release and uptake due to energy depletion and depolarization. We here used the glutamate sensor SF-iGluSnFR(A184V) to probe how chemical ischemia affects the extracellular glutamate dynamics in slice cultures from mouse cortex. SF-iGluSnFR imaging showed spontaneous glutamate release indicating synchronous network activity, similar to calcium imaging with GCaMP6f. Glutamate imaging further revealed local, atypically large, and long-lasting plume-like release events. Plumes occurred with low frequency, independent of network activity, and persisted in tetrodotoxin (TTX). Blocking glutamate uptake with TFB-TBOA favored plumes, whereas blocking ionotropic glutamate receptors (iGluRs) suppressed plumes. During chemical ischemia plumes became more pronounced, overly abundant and contributed to large-scale glutamate accumulation. Similar plumes were previously observed in cortical spreading depression and migraine models, and they may thus be a more general consequence of glutamate uptake dysfunctions in neurological and neurodegenerative diseases.

Tissue zinc restoration alleviates the levodopa-induced dyskinesia via impeding ERK phosphorylation

PURPOSE

Levodopa administration has been the standard therapy for Parkinson's disease (PD) and prolonged treatment is associated with levodopa-induced dyskinesia (LID). This study aimed to identify the effects of zinc (Zn) supplements on LID and to explore the underlying mechanisms.

METHODS

Male C57BL/6J mice were injected with 6-OHDA at medial forebrain bundle, followed by daily levodopa injection to induce LID. The mice were supplemented with Zn of 0, 0.3, 1.2, or 2.4 mg/kg for 4 weeks.

RESULTS

In the LID mice, Zn supplements restored tissue Zn levels and alleviated global, forelimb, and orolingual abnormal involuntary movements (AIMs). Signaling pathway assessments showed that Zn supplements significantly reduced expressions of phosphorylated glutamate receptor 1 (p-GluR1) and phosphorylation levels of extracellular-signal-regulated kinase (p-ERK/ERK). Correlations between the AIMs score, p-ERK, and tissue Zn levels were established. In addition, Zn supplements reduced numbers of glial fibrillary acidic protein (GFAP) positive cells and compensatory tyrosine hydroxylase (TH) positive cells. These alleviating effects of Zn supplements were strictly regulated in a dose dependent manner.

CONCLUSION

Appropriate doses of Zn supplements alleviated AIMs in the LID mouse model, potentially via impeding ERK phosphorylation, inhibiting astrocyte activation, and attenuating striatal compensation of TH positive cells.

Glutamatergic dysfunction in neurodegenerative diseases focusing on Parkinson's disease: Role of glutamate modulators

Parkinson's disease (PD) is a prevalent neurodegenerative disorder resulting from the degeneration of dopamenergic neurons in the substantia nigra pars compacta (SNpc). Research has predominantly centered on understanding the dysfunction of dopaminergic neurotransmission in PD. Recently, more studies discussed the potential role of other neurotransmitters in PD neuropathology. One of the most important non-dopaminergic neurotransmitters involved in the pathogenesis of PD is glutamate, which is widely involved in glutamatergic neurotransmission in different brain regions, including SNpc. The development and progression of PD neuropathology and levodopa-induced dyskinesias (LID) are associated with glutamate neurotoxicity. Therefore, this review seeks to explore the possible involvement of glutamatergic signaling in PD development and assess the therapeutic potential of glutamate receptor antagonists in treating the disorder.

The alteration of glutamate involved in the brain of Parkinson's disease patients using glutamate chemical exchange saturation transfer (GluCEST)

Increased levels of glutamate, a novel regulator of neuroinflammation, is involved in the pathogenesis of Parkinson's disease (PD). Although glutamate chemical exchange saturation transfer (GluCEST) is widely used in central nervous system (CNS) disorders, it has been less commonly used in clinical practice for PD. Here, to explore the clinical significance of variations in glutamate levels in the striatum and thalamus in PD, we included forty-nine PD patients and forty-four healthy controls (HCs). Glutamate levels were analyzed by performing magnetization transfer ratio asymmetry (MTRasym) using GluCEST data. Four regions of interest (ROIs) were manually outlined on GluCEST images, and MTRasym values were calculated for each. FreeSurfer was used to calculate the volumes. We found that MTRasym values in the striatum and thalamus were elevated in PD. Variations in MTRasym values were correlated with motor scores. It has been found that the volume of the left pallidal nucleus were reduced in PD. The glutamate levels in the striatum and thalamus were significantly different from those in HCs and associated with disease progression. Collectively, glutamate metabolic abnormalities may be present in PD pathophysiology and associated with disease progression. GluCEST imaging may have potential to become an imaging technology for measuring glutamate alterations in the striatum and thalamus in PD.

Altered Brain Iron Depositions of Spinocerebellar Ataxia Type 3: From Pre-Symptomatic to Symptomatic Stage

BACKGROUND

Spinocerebellar ataxia type 3 (SCA3) is a rare hereditary neurodegeneration disease. The iron distribution of SCA3 is poorly understood, yet quantitative susceptibility mapping (QSM) has rarely been used in SCA3.

METHODS

We prospectively investigated QSM of SCA3 (19 pre-symptomatic and 41 symptomatic) and 37 healthy controls (HCs) recruited from 2018.05 to 2021.01. Group susceptibility was cross-sectionally compared, and the associations between altered brain iron deposition and clinical symptoms, neurofilament light chain (Nfl), and fractional anisotropy of the bilateral corticospinal tracts and cerebellar peduncles were explored. 12 SCA3 participants were followed for at least a year.

RESULTS

Compared to HCs, bilateral SN were observed with significantly increased susceptibility in pre-symptomatic SCA3. Most of the supratentorial nuclei and the right dental nucleus had increased susceptibility in symptomatic than in pre-symptomatic stage and were partially correlated with symptomatic severity, disease duration, and damaged cerebellar peduncles (p < 0.05) but not Nfl (p > 0.05). The left substantia nigra (SN) demonstrated the highest diagnostic efficacy in identifying pre- (AUC = 0.904) and symptomatic SCA3 (AUC = 0.938). The longitudinal study also confirmed the significant change in the left SN (p < 0.01).

CONCLUSIONS

Our in vivo QSM evidence demonstrates disease-specific patterns for brain iron depositions in SCA3. Brain iron deposition abnormality is an early event of the SCA3's occurrence and development. The left SN might be a critical site for the disease's start and development.

SLC1A4 and Serine Homeostasis: Implications for Neurodevelopmental and Neurodegenerative Disorders

The solute carrier family 1 member 4 (SLC1A4) gene encodes a neutral amino acid transporter, also referred to as alanine-serine-cysteine transporter 1, ASCT1, that helps maintain amino acid balance in the brain and periphery. In the brain, SLC1A4 plays an important role in transporting levo (L) and dopa (D) isomers of serine. L-serine is required for many cellular processes, including protein and sphingolipid synthesis, while D-serine is a co-agonist required for normal neurotransmission through N-methyl-D-aspartate receptors. Through its roles transporting L-serine across the blood-brain barrier and regulating synaptic D-serine levels, SLC1A4 helps establish and maintain brain health across the lifespan. This review examines the role of SLC1A4 in neurodevelopment and neurodegeneration and assesses the therapeutic potential of serine supplementation to treat neurodevelopmental symptoms associated with mutations in SLC1A4, as well as schizophrenia, depression, traumatic brain injury, and Alzheimer's and Parkinson's diseases.

Emerging biophysical techniques for probing synaptic transmission in neurodegenerative disorders

Plethora of research has shed light on the critical role of synaptic dysfunction in various neurodegenerative disorders (NDDs), including Alzheimer's disease (AD), Parkinson's disease (PD), Amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD). Synapses, the fundamental units for neural communication in the brain, are highly vulnerable to pathological conditions and are central to the progression of neurological diseases. The presynaptic terminal, a key component of synapses responsible for neurotransmitter release and synaptic communication, undergoes structural and functional alterations in these disorders. Understanding synaptic transmission abnormalities is crucial for unravelling the pathophysiological mechanisms underlying neurodegeneration. In the quest to probe synaptic transmission in NDDs, emerging biophysical techniques play a pivotal role. These advanced methods offer insights into the structural and functional changes occurring at nerve terminals in conditions like AD, PD, HD & ALS. By investigating synaptic plasticity and alterations in neurotransmitter release dynamics, researchers can uncover valuable information about disease progression and potential therapeutic targets. The review articles highlighted provide a comprehensive overview of how synaptic vulnerability and pathology are shared mechanisms across a spectrum of neurological disorders. In major neurodegenerative diseases, synaptic dysfunction is a common thread linking these conditions. The intricate molecular machinery involved in neurotransmitter release, synaptic vesicle dynamics, and presynaptic protein regulation are key areas of focus for understanding synaptic alterations in neurodegenerative diseases.

Multiomics approach identifies dysregulated lipidomic and proteomic networks in Parkinson's disease patients mutated in TMEM175

Parkinson's disease (PD) represents one of the most frequent neurodegenerative disorders for which clinically useful biomarkers remain to be identified and validated. Here, we adopted an untargeted omics approach to disclose lipidomic, metabolomic and proteomic alterations in plasma and in dermal fibroblasts of PD patients carrying mutations in TMEM175 gene. We revealed a wide dysregulation of lysosome, autophagy, and mitochondrial pathways in these patients, supporting a role of this channel in regulating these cellular processes. The most significant altered lipid classes were Fatty acyls, Glycerophospholipids and Phosphosphingolipids. The plasma level of Phosphatidylcholines (PC) and Phosphatidylinositol (PI) 34:1 significantly correlated with an earlier age at onset of the disease in TMEM175 patients (p = 0.008; p = 0.006). In plasma we also observed altered amino acids metabolic pathways in PD patients. We highlighted that increased level of L-glutamate strongly correlated (p < 0.001) with the severity of motor and non-motor symptoms in PD_TMEM175 patients. In dermal fibroblasts, we disclosed alterations of proteins involved in lipids biosynthesis (PAG15, PP4P1, GALC, FYV1, PIGO, PGPS1, PLPP1), in the insulin pathway (IGF2R), in mitochondrial metabolism (ACD10, ACD11, ACADS) and autophagy (RAB7L). Interestingly, we quantified 43 lysosomal or lysosomal-related proteins, which were differentially modulated between TMEM175 patients and controls. Integrative correlation analysis of proteome and lipidome of PD_TMEM175 cellular models identified a strong positive correlation of 13 proteins involved in biosynthetic processes with PC and Ceramides. Altogether, these data provide novel insights into the molecular and metabolic alterations underlying TMEM175 mutations and may be relevant for PD prediction, diagnosis and treatment.

Acute transcutaneous auricular vagus nerve stimulation modulates presynaptic SV2A density in healthy rat brain: An in vivo microPET study

Vagus nerve stimulation (VNS) is the subject of exploration as an adjunct treatment for neurological disorders such as epilepsy, chronic migraine, pain, and depression. A non-invasive form of VNS is transcutaneous auricular VNS (taVNS). Combining animal models and positron emission tomography (PET) may lead to a better understanding of the elusive mechanisms of taVNS. We evaluated the acute effect of electrical stimulation of the left vagus nerve via the ear on brain synaptic vesicle glycoprotein 2A (SV2A) as a measure of presynaptic density and glucose metabolism in naïve rats. Female Sprague-Dawley rats were imaged with [11C]UCB-J (n = 11) or [18F]fluorodeoxyglucose ([18F]FDG) PET (n = 13) on two separate days, (1) at baseline, and (2) after acute unilateral left taVNS or sham stimulation (30 min). We calculated the regional volume of distribution (VT) for [11C]UCB-J and standard uptake values (SUV) for [18F]FDG. We observed regional reductions of [11C]UCB-J binding in response to taVNS ranging from 36% to 59%. The changes in taVNS compared to baseline were significantly larger than those induced by sham stimulation. The differences were observed bilaterally in the frontal cortex, striatum, and midbrain. The [18F]FDG PET uptake remained unchanged following acute taVNS or sham stimulation compared to baseline values. This proof-of-concept study shows for the first time that acute taVNS for 30 min can modulate in vivo synaptic SV2A density in cortical and subcortical regions of healthy rats. Preclinical disease models and PET ligands of different targets can be a powerful combination to assess the therapeutic potential of taVNS.

The impact of Parkinson's disease on striatal network connectivity and corticostriatal drive: An in silico study

Striatum, the input stage of the basal ganglia, is important for sensory-motor integration, initiation and selection of behavior, as well as reward learning. Striatum receives glutamatergic inputs from mainly cortex and thalamus. In rodents, the striatal projection neurons (SPNs), giving rise to the direct and the indirect pathway (dSPNs and iSPNs, respectively), account for 95% of the neurons, and the remaining 5% are GABAergic and cholinergic interneurons. Interneuron axon terminals as well as local dSPN and iSPN axon collaterals form an intricate striatal network. Following chronic dopamine depletion as in Parkinson's disease (PD), both morphological and electrophysiological striatal neuronal features have been shown to be altered in rodent models. Our goal with this in silico study is twofold: (a) to predict and quantify how the intrastriatal network connectivity structure becomes altered as a consequence of the morphological changes reported at the single-neuron level and (b) to investigate how the effective glutamatergic drive to the SPNs would need to be altered to account for the activity level seen in SPNs during PD. In summary, we predict that the richness of the connectivity motifs in the striatal network is significantly decreased during PD while, at the same time, a substantial enhancement of the effective glutamatergic drive to striatum is present.

Corticostriatal glutamate-mediated dynamic therapeutic efficacy of electroacupuncture in a parkinsonian rat model

BACKGROUND

Motor impairments are the defining cardinal features of Parkinson's disease (PD), resulting from malfunction of the cortico-basal ganglia circuit. Clinical data have demonstrated that electroacupuncture (EA) stimulation may benefit motor symptoms in PD without adverse effects. However, the specific effects of EA on PD and the underlying mechanisms remain largely unclear.

METHODS

This study investigated the effects of EA stimulation during and after 100 Hz application in a rat model of PD created by unilateral injection of 6-hydroxydopamine (6-OHDA). To establish optimal treatment parameters of EA, motor behaviours were dynamically assessed using open field and rotarod tests. Additionally, we evaluated corticostriatal spine plasticity using immunoelectron microscopy and measured the levels of dopaminergic and glutamatergic neurotransmitters through microdialysis, in vivo electrochemistry and high-performance liquid chromatography. Neural activity dynamics were recorded by measuring local field potentials in both the motor cortex and the striatum. Furthermore, chemogenetic techniques were employed to manipulate corticostriatal glutamatergic neurons and clarify the mechanisms that contribute to the therapeutic benefits of EA in the PD rat model.

RESULTS

Chronic EA stimulation resulted in a gradual and long-lasting alleviation of motor symptoms, independent of nigrostriatal dopamine (DA) restoration. Notably, EA stimulation modulated corticostriatal spine plasticity and reduced excessive glutamate transmission in PD model rats. Moreover, EA effectively inhibited aberrant corticostriatal synchronised high-beta (25-40 Hz) oscillations, which serves as a pathological biomarker of PD. Conversely, chronic chemogenetic activation of corticostriatal glutamatergic neurons hindered these positive outcomes of EA treatment in PD model rats.

CONCLUSIONS

This study sheds light on the temporal dynamics and optimal parameters of EA treatment in PD. It emphasises the significance of inhibiting corticostriatal glutamate transmission in EA's therapeutic benefits for PD. Targeting glutamatergic neurons with EA holds promise as a non-dopaminergic intervention for managing motor symptoms and abnormal neural activity with PD.

KEY POINTS

EA commonly protects dopaminergic neuronsby reducing neuroinflammation, oxidative stress, and apoptosis. New findings reveal that EA alleviates motor symptoms in a parkinsonian rat model without restoring striatal dopamine levels. EA effectively suppresses excessiveglutamate transmission and high-beta synchronization, contributing to motorsymptom relief. Activation of corticostriatalglutamatergic projections may hinder the efficacy of EA.

Synaptic and membrane properties of cholinergic interneurons in the striatum of aristaless-related homeobox gene mutant mice

A whole-cell patch-clamp study was carried out to investigate membrane and synaptic properties of cholinergic interneurons in the striatum of aristaless-related homeobox gene (ARX) mutant mice. Brain slices were prepared from mice knocked in two types of ARX, P355L (PL) and 333ins (GCG)7 (GCG). The input resistance of cholinergic interneurons in PL or GCG mice was significantly smaller than that in wild type (WT), whereas resting membrane potential, threshold of action potentials, spontaneous firing rate, sag ratio or afterhyperpolarization of the mutant mice were not significantly different from those of WT mice. In GCG mice, NMDA/AMPA ratio of excitatory postsynaptic currents (EPSCs) evoked in cholinergic interneurons was significantly smaller than that in WT and PL mice, whereas the ratio between PL and WT mice was not significantly different. Although inhibitory effects induced by dopamine D2-like receptor activation on the inhibitory postsynaptic currents (IPSCs) were not significantly different between WT and PL or GCG mice, increase in the paired pulse ratio of IPSCs by dopamine D2-like receptor activation was abolished in PL and GCG mice. The present results have found abnormalities of neuronal activities as well as its modulation in the basal ganglia in ARX mutant mice, clarifying basic mechanisms underlying related disorders.

Effect of 5-alpha reductase inhibitors in animal models of Parkinson's disease

Parkinson's disease (PD) is characterized by motor symptoms due to loss of brain dopamine and non-motor symptoms, including gastrointestinal disorders. Although there is no cure for PD, symptomatic treatments are available. L-Dopa is the gold standard PD therapy, but most patients develop dyskinesias (LID), which are challenging to manage. Amantadine is recognized as the most effective drug for LID, but its adverse effects limit the use in patients. Here we review how 5α-reductase inhibitors (5ARIs), drugs used to treat benign prostatic hyperplasia and alopecia, exhibit beneficial effects in PD animal models. 5ARIs show neuroprotective properties in brain and gut dopaminergic systems, and reduce dyskinesias in rodent model of PD. Additionally, the 5ARI finasteride dampened dopaminergic-induced drug gambling in PD patients. Neuroprotection and antidyskinetic activities of 5ARIs in animal models of PD suggest their potential repurposing in men with PD to address gut dysfunction, protect brain DA and inhibit dyskinesias.

Unveiling the muscle-brain axis: A bidirectional mendelian randomization study investigating the causal relationship between sarcopenia-related traits and brain aging

BACKGROUND

Observational studies suggest an association between sarcopenia-related traits and brain aging, but whether this association reflects a causal relationship remains unclear. This study aims to employ Mendelian randomization (MR) methods to investigate the causal impact of sarcopenia-related traits on brain aging.

METHODS

This study presents a comprehensive analysis of genome-wide association study (GWAS) summary data associated with sarcopenia-related traits. The data were derived from a large-scale cohort, encompassing measures such as grip strength, lean body mass, and walking pace. Measurements of brain aging were obtained from neuroimaging genetics, utilizing meta-analysis (ENIGMA) to combine magnetic resonance imaging (MRI) data from 33,992 participants. The primary methodology employed in this analysis was the inverse-variance-weighted method (IVW). Additionally, sensitivity analyses were conducted, to assess heterogeneity and pleiotropy.

RESULT

Appendicular lean mass(ALM) is negatively correlated with Pallidum aging; Whole body fat-free mass shows a negative correlation with Amygdala aging; Leg fat-free mass (left) and Leg fat-free mass (right) are negatively correlated with Pallidum aging; Usual walking pace is positively correlated with Nucleus Accumbens aging. Cerebellum WM aging is negatively correlated with Leg fat-free mass (left) and Leg fat-free mass (right); Hippocampus aging is negatively correlated with Hand grip strength (left) and Hand grip strength (right). Ventricles aging is positively correlated with Usual walking pace; Nucleus Accumbens aging is positively correlated with Leg fat-free mass (left) and Leg fat-free mass (right); Putamen aging is positively correlated with ALM.

CONCLUSION

Our study confirms that reduced muscle mass speeds up brain aging. Walking too fast raises the risk of brain aging, while maintaining or increasing appendicular lean mass, overall muscle mass, and muscle mass in both legs lowers the risk of brain aging.

NMDA receptor remodeling and nNOS activation in mice after unilateral striatal injury with 6-OHDA

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by selective dopaminergic loss. Non dopaminergic neurotransmitters such as glutamate are also involved in PD progression. NMDA receptor/postsynaptic density protein 95 (PSD-95)/neuronal nitric oxide synthase (nNOS) activation is involved in neuronal excitability in PD. Here, we are focusing on the evaluating these post-synaptic protein levels in the 6-OHDA model of PD. Adult male C57BL/6 mice subjected to unilateral striatal injury with 6-OHDA were assessed at 1-, 2-, or 4-weeks post-lesion. Animals were subjected to an apomorphine-induced rotation test followed by the analysis of protein content, synaptic structure, and NOx production. All biochemical analysis was performed comparing the control versus lesioned sides of the same animal. 6-OHDA mice exhibited contralateral rotation activity, difficulties in coordinating movements, and changes in Iba-1 and glial fibrillary acidic protein (GFAP) expression during the whole period. At one week of survival, the mice showed a shift in NMDA composition, favoring the GluN2A subunit and increased PSD95 and nNOS expression and NOx formation. After two-weeks, a decrease in the total number of synapses was observed in the lesioned side. However, the number of excitatory synapses was increased with a higher content of GluN1 subunit and PSD95. After four weeks, NMDA receptor subunits restored to control levels. Interestingly, NOx formation in the serum increased. This study reveals, for the first time, the temporal course of behavioral deficits and glutamatergic synaptic plasticity through NMDAr subunit shift. Together, these data demonstrate that dopamine depletion leads to a fine adaptive response over time, which can be used for further studies of therapeutic management adjustments with the progression of PD.

Adenosine A2A Receptor Blockade Provides More Effective Benefits at the Onset Rather than after Overt Neurodegeneration in a Rat Model of Parkinson's Disease

Adenosine A2A receptor (A2AR) antagonists are the leading nondopaminergic therapy to manage Parkinson's disease (PD) since they afford both motor benefits and neuroprotection. PD begins with a synaptic dysfunction and damage in the striatum evolving to an overt neuronal damage of dopaminergic neurons in the substantia nigra. We tested if A2AR antagonists are equally effective in controlling these two degenerative processes. We used a slow intracerebroventricular infusion of the toxin MPP+ in male rats for 15 days, which caused an initial loss of synaptic markers in the striatum within 10 days, followed by a neuronal loss in the substantia nigra within 30 days. Interestingly, the initial loss of striatal nerve terminals involved a loss of both dopaminergic and glutamatergic synaptic markers, while GABAergic markers were preserved. The daily administration of the A2AR antagonist SCH58261 (0.1 mg/kg, i.p.) in the first 10 days after MPP+ infusion markedly attenuated both the initial loss of striatal synaptic markers and the subsequent loss of nigra dopaminergic neurons. Strikingly, the administration of SCH58261 (0.1 mg/kg, i.p. for 10 days) starting 20 days after MPP+ infusion was less efficacious to attenuate the loss of nigra dopaminergic neurons. This prominent A2AR-mediated control of synaptotoxicity was directly confirmed by showing that the MPTP-induced dysfunction (MTT assay) and damage (lactate dehydrogenase release assay) of striatal synaptosomes were prevented by 50 nM SCH58261. This suggests that A2AR antagonists may be more effective to counteract the onset rather than the evolution of PD pathology.

L-Carnitine in the Treatment of Psychiatric and Neurological Manifestations: A Systematic Review

OBJECTIVE

L-carnitine (LC), a vital nutritional supplement, plays a crucial role in myocardial health and exhibits significant cardioprotective effects. LC, being the principal constituent of clinical-grade supplements, finds extensive application in the recovery and treatment of diverse cardiovascular and cerebrovascular disorders. However, controversies persist regarding the utilization of LC in nervous system diseases, with varying effects observed across numerous mental and neurological disorders. This article primarily aims to gather and analyze database information to comprehensively summarize the therapeutic potential of LC in patients suffering from nervous system diseases while providing valuable references for further research.

METHODS

A comprehensive search was conducted in PubMed, Web Of Science, Embase, Ovid Medline, Cochrane Library and Clinicaltrials.gov databases. The literature pertaining to the impact of LC supplementation on neurological or psychiatric disorders in patients was reviewed up until November 2023. No language or temporal restrictions were imposed on the search.

RESULTS

A total of 1479 articles were retrieved, and after the removal of duplicates through both automated and manual exclusion processes, 962 articles remained. Subsequently, a meticulous re-screening led to the identification of 60 relevant articles. Among these, there were 12 publications focusing on hepatic encephalopathy (HE), while neurodegenerative diseases (NDs) and peripheral nervous system diseases (PNSDs) were represented by 9 and 6 articles, respectively. Additionally, stroke was addressed in five publications, whereas Raynaud's syndrome (RS) and cognitive disorder (CD) each had three dedicated studies. Furthermore, migraine, depression, and amyotrophic lateral sclerosis (ALS) each accounted for two publications. Lastly, one article was found for other symptoms under investigation.

CONCLUSION

In summary, LC has demonstrated favorable therapeutic effects in the management of HE, Alzheimer's disease (AD), carpal tunnel syndrome (CTS), CD, migraine, neurofibromatosis (NF), PNSDs, RS, and stroke. However, its efficacy appears to be relatively limited in conditions such as ALS, ataxia, attention deficit hyperactivity disorder (ADHD), depression, chronic fatigue syndrome (CFS), Down syndrome (DS), and sciatica.

Suppression of presynaptic corticostriatal glutamate activity attenuates L-dopa-induced dyskinesia in 6-OHDA-lesioned Parkinson's disease mice

A common adverse effect of Parkinson's disease (PD) treatment is L-dopa-induced dyskinesia (LID). This condition results from both dopamine (DA)-dependent and DA-independent mechanisms, as glutamate inputs from corticostriatal projection neurons impact DA-responsive medium spiny neurons in the striatum to cause the dyskinetic behaviors. In this study, we explored whether suppression of presynaptic corticostriatal glutamate inputs might affect the behavioral and biochemical outcomes associated with LID. We first established an animal model in which 6-hydroxydopamine (6-OHDA)-lesioned mice were treated daily with L-dopa (10 mg/kg, i.p.) for 2 weeks; these mice developed stereotypical abnormal involuntary movements (AIMs). When the mice were pretreated with the NMDA antagonist, amantadine, we observed suppression of AIMs and reductions of phosphorylated ERK1/2 and NR2B in the striatum. We then took an optogenetic approach to manipulate glutamatergic activity. Slc17a6 (vGluT2)-Cre mice were injected with pAAV5-Ef1a-DIO-eNpHR3.0-mCherry and received optic fiber implants in either the M1 motor cortex or dorsolateral striatum. Optogenetic inactivation at either optic fiber implant location could successfully reduce the intensity of AIMs after 6-OHDA lesioning and L-dopa treatment. Both optical manipulation strategies also suppressed phospho-ERK1/2 and phospho-NR2B signals in the striatum. Finally, we performed intrastriatal injections of LDN 212320 in the dyskenesic mice to enhance expression of glutamate uptake transporter GLT-1. Sixteen hours after the LDN 212320 treatment, L-dopa-induced AIMs were reduced along with the levels of striatal phospho-ERK1/2 and phospho-NR2B. Together, our results affirm a critical role of corticostriatal glutamate neurons in LID and strongly suggest that diminishing synaptic glutamate, either by suppression of neuronal activity or by upregulation of GLT-1, could be an effective approach for managing LID.

Antagonism of metabotropic glutamate receptor type 5 prevents levodopa-induced dyskinesia development in a male rat model of Parkinson's disease: Electrophysiological evidence

Levodopa-induced dyskinesia (LID) is a common complication in patients with advanced Parkinson's disease (PD) undergoing treatment with levodopa. Glutamate receptor antagonists can suppress LID; however, the underlying mechanisms remain unclear. Here, we aimed to evaluate the effect of 3-((2-methyl-1,3-thiazol-4-yl)ethynyl)pyridine (MTEP), a metabotropic glutamate receptor 5 (mGluR5) antagonist, on dyskinesia. We recorded the neuronal activity of the entopeduncular nucleus and examined responses to cortical electric stimulation in the control group (n = 6) and three groups of rats (male PD model). Saline was intraperitoneally administered to dopamine lesioned (DL) rats (n = 6), levodopa/benserazide (L/B) was administered to LID rats (n = 8), and L/B combined with MTEP was administered to MTEP rats (n = 6) twice daily for 14 days. We administered L/B to LID and MTEP rats 48 h after the final administration of MTEP to examine the chronic effect of MTEP. The control and DL groups did not have LID. The MTEP group had less LID than the LID group (p < .01) on day 1 and day 18. The control group had a typical triphasic pattern consisting of early excitation (early-Ex), inhibition, and late excitation (late-Ex). However, the inhibition phase disappeared, was partially observed, and was fully suppressed in the DL, LID, and MTEP groups, respectively. The cortico-striato-entopeduncular pathway is important in the pathophysiology of LID. mGluR5 antagonism suppresses LID progression by preventing physiological changes in the cortico-striato-entopeduncular pathway. Future studies are required to validate these results.

Blood D-serine levels correlate with aging and dopaminergic treatment in Parkinson's disease

We recently described increased D- and L-serine concentrations in the striatum of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys, the post-mortem caudate-putamen of human Parkinson's disease (PD) brains and the cerebrospinal fluid (CSF) of de novo living PD patients. However, data regarding blood D- and L-serine levels in PD are scarce. Here, we investigated whether the serum profile of D- and L-serine, as well as the other glutamate N-methyl-D-aspartate ionotropic receptor (NMDAR)-related amino acids, (i) differs between PD patients and healthy controls (HC) and (ii) correlates with clinical-demographic features and levodopa equivalent daily dose (LEDD) in PD. Eighty-three consecutive PD patients and forty-one HC were enrolled. PD cohort underwent an extensive clinical characterization. Serum levels of D- and L-serine, L-glutamate, L-glutamine, L-aspartate, L-asparagine and glycine were determined using High Performance Liquid Chromatography. In age- and sex-adjusted analyses, no differences emerged in the serum levels of D-serine, L-serine and other NMDAR-related amino acids between PD and HC. However, we found that D-serine and D-/Total serine ratio positively correlated with age in PD but not in HC, and also with PD age at onset. Moreover, we found that higher LEDD correlated with lower levels of D-serine and the other excitatory amino acids. Following these results, the addition of LEDD as covariate in the analyses disclosed a selective significant increase of D-serine in PD compared to HC (Δ ≈ 38%). Overall, these findings suggest that serum D-serine and D-/Total serine may represent a valuable biochemical signature of PD.

Microbiota-gut-brain axis and its therapeutic applications in neurodegenerative diseases

The human gastrointestinal tract is populated with a diverse microbial community. The vast genetic and metabolic potential of the gut microbiome underpins its ubiquity in nearly every aspect of human biology, including health maintenance, development, aging, and disease. The advent of new sequencing technologies and culture-independent methods has allowed researchers to move beyond correlative studies toward mechanistic explorations to shed light on microbiome-host interactions. Evidence has unveiled the bidirectional communication between the gut microbiome and the central nervous system, referred to as the "microbiota-gut-brain axis". The microbiota-gut-brain axis represents an important regulator of glial functions, making it an actionable target to ameliorate the development and progression of neurodegenerative diseases. In this review, we discuss the mechanisms of the microbiota-gut-brain axis in neurodegenerative diseases. As the gut microbiome provides essential cues to microglia, astrocytes, and oligodendrocytes, we examine the communications between gut microbiota and these glial cells during healthy states and neurodegenerative diseases. Subsequently, we discuss the mechanisms of the microbiota-gut-brain axis in neurodegenerative diseases using a metabolite-centric approach, while also examining the role of gut microbiota-related neurotransmitters and gut hormones. Next, we examine the potential of targeting the intestinal barrier, blood-brain barrier, meninges, and peripheral immune system to counteract glial dysfunction in neurodegeneration. Finally, we conclude by assessing the pre-clinical and clinical evidence of probiotics, prebiotics, and fecal microbiota transplantation in neurodegenerative diseases. A thorough comprehension of the microbiota-gut-brain axis will foster the development of effective therapeutic interventions for the management of neurodegenerative diseases.

Neuroactive steroids and Parkinson's disease: Review of human and animal studies

The greater prevalence and incidence of Parkinson's disease (PD) in men suggest a beneficial effect of sex hormones. Neuroactive steroids have neuroprotective activities thus offering interesting option for disease-modifying therapy for PD. Neuroactive steroids are also neuromodulators of neurotransmitter systems and may thus help to control PD symptoms and side effect of dopamine medication. Here, we review the effect on sex hormones (estrogen, androgen, progesterone and its metabolites) as well as androstenediol, pregnenolone and dehydroepiandrosterone) in human studies and in animal models of PD. The effect of neuroactive steroids is reviewed by considering sex and hormonal status to help identify specifically for women and men with PD what might be a preventive approach or a symptomatic treatment. PD is a complex disease and the pathogenesis likely involves multiple cellular processes. Thus it might be useful to target different cellular mechanisms that contribute to neuronal loss and neuroactive steroids provide therapeutics options as they have multiple mechanisms of action.

Astrocyte Responses Influence Local Effects of Whole-Brain Magnetic Stimulation in Parkinsonian Rats

BACKGROUND

Excessive glutamatergic transmission in the striatum is implicated in Parkinson's disease (PD) progression. Astrocytes maintain glutamate homeostasis, protecting from excitotoxicity through the glutamate-aspartate transporter (GLAST), whose alterations have been reported in PD. Noninvasive brain stimulation using intermittent theta-burst stimulation (iTBS) acts on striatal neurons and glia, inducing neuromodulatory effects and functional recovery in experimental parkinsonism.

OBJECTIVE

Because PD is associated with altered astrocyte function, we hypothesized that acute iTBS, known to rescue striatal glutamatergic transmission, exerts regional- and cell-specific effects through modulation of glial functions.

METHODS

6-Hydroxydopamine-lesioned rats were exposed to acute iTBS, and the areas predicted to be more responsive by a biophysical, hyper-realistic computational model that faithfully reconstructs the experimental setting were analyzed. The effects of iTBS on glial cells and motor behavior were evaluated by molecular and morphological analyses, and CatWalk and Stepping test, respectively.

RESULTS

As predicted by the model, the hippocampus, cerebellum, and striatum displayed a marked c-FOS activation after iTBS, with the striatum showing specific morphological and molecular changes in the astrocytes, decreased phospho-CREB levels, and recovery of GLAST. Striatal-dependent motor performances were also significantly improved.

CONCLUSION

These data uncover an unknown iTBS effect on astrocytes, advancing the understanding of the complex mechanisms involved in TMS-mediated functional recovery. Data on numerical dosimetry, obtained with a degree of anatomical details never before considered and validated by the biological findings, provide a framework to predict the electric-field induced in different specific brain areas and associate it with functional and molecular changes. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Activation of mGlu2/3 receptors in the striatum alleviates L-DOPA-induced dyskinesia and inhibits abnormal postsynaptic molecular expression

Group II metabotropic glutamate receptors (mGlu2/3 receptors) have been regarded as promising candidates for the treatment of L-DOPA-induced dyskinesia (LID); however, confirmation is still lacking. As the hub of the basal ganglia circuit, the striatum plays a critical role in action control. Supersensitive responsiveness of glutamatergic corticostriatal input may be the key mechanism for the development of LID. In this study, we first examined the potency of LY354740 (12 mg/kg, i.p.) in modulating glutamate and dopamine release in lesioned striatum of stable LID rats. Then, we injected LY354740 (20nmoL or 40nmoL in 4 μL of sterile 0.9 % saline) directly into the lesioned striatum to verify its ability to reduce or attenuate L-DOPA-induced abnormal involuntary movements. In experiment conducted in established LID rats, after continuous injection for 4 days, we found that LY354740 significantly reduced the expression of dyskinesia. In another experiment conducted in parkinsonism rat models, we found that LY354740 attenuated the development of LID with an inverted-U dose-response curve. The role of LY354740 in modulating striatal expressions of LID-related molecular changes was also assessed after these behavioral experiments. We found that LY354740 significantly inhibited abnormal expressions of p-Fyn/p-NMDA/p-ERK1/2/p-HistoneH3/ΔFosB, which is in line with its ability to alleviate abnormal involuntary movements in both LID expression and induction phase. Our study indicates that activation of striatal mGlu2/3 receptors can attenuate the development of dyskinesia in parkinsonism rats and provide some functional improvements in LID rats by inhibiting LID-related molecular changes.

Depolarization shift in the resting membrane potential of inferior colliculus neurons explains their hyperactivity induced by an acoustic trauma

Introduction

Neuronal hyperactivity has been associated with many brain diseases. In the auditory system, hyperactivity has been linked to hyperacusis and tinnitus. Previous research demonstrated the development of hyperactivity in inferior colliculus (IC) neurons after sound overexposure, but the underlying mechanism of this hyperactivity remains unclear. The main goal of this study was to determine the mechanism of this hyperactivity.

Methods

Experiments were performed on CBA/CaJ mice in a restrained, unanesthetized condition using intracellular recordings with sharp microelectrodes. Recordings were obtained from control (unexposed) and unilaterally sound overexposed groups of mice.

Results

Our data suggest that sound exposure-induced hyperactivity was due to a depolarizing shift of the resting membrane potential (RMP) in the hyperactive neurons. The half width of action potentials in these neurons was also decreased after sound exposure. Surprisingly, we also found an RMP gradient in which neurons have more hyperpolarized RMPs with increasing depth in the IC. This gradient was altered in the overexposed animals.

Distribution of [11C]-JNJ-42491293 in the marmoset brain: a positron emission tomography study

JNJ-42491293 is a metabotropic glutamate 2 (mGlu2) positive allosteric modulator (PAM) that was radiolabelled with [11C]- to serve as a positron emission tomography (PET) ligand. Indeed, in vitro, the molecule displays high selectivity at mGlu2 receptors. However, PET experiments performed in rats, macaques and humans, have suggested that [11C]-JNJ-42491293 could interact with an unidentified, non-mGlu2 receptor binding site. The brain distribution of [11C]-JNJ-42491293 has not been determined in the brain of the common marmoset, a small non-human primate increasingly used in neuroscience research. Here, we investigated the distribution of [11C]-JNJ-42491293 in the marmoset brain. Three marmosets underwent brain magnetic resonance imaging (MRI) and 90-min dynamic PET scans with [11C]-JNJ-42491293 in combination with vehicle or the mGlu2 PAM AZD8529 (0.1, 1 and 10 mg/kg). In the scans in which [11C]-JNJ-42491293 was co-administered with vehicle, the brain areas with the highest standardised uptake values (SUVs) were the midbrain, cerebellum and thalamus, while the lowest SUVs were found in the pons. The addition of AZD8529 (0.1, 1 and 10 mg/kg) to [11C]-JNJ-42491293 did not modify the SUVs obtained with [11C]-JNJ-42491293 alone, and ex vivo blocking autoradiography with PAM AZD8529 (10, 100, 300 µM) on marmoset brain sections showed increased signals in the blocking conditions compared to vehicle, suggesting that no competition occurred between the 2 ligands. The results we obtained here do not suggest that [11C]-JNJ-42491293 interacts selectively, or even at all, with mGlu2 receptors in the marmoset, in agreement with findings previously reported in macaque and human.

Perturbation of serine enantiomers homeostasis in the striatum of MPTP-lesioned monkeys and mice reflects the extent of dopaminergic midbrain degeneration

Loss of dopaminergic midbrain neurons perturbs l-serine and d-serine homeostasis in the post-mortem caudate putamen (CPu) of Parkinson's disease (PD) patients. However, it is unclear whether the severity of dopaminergic nigrostriatal degeneration plays a role in deregulating serine enantiomers' metabolism. Here, through high-performance liquid chromatography (HPLC), we measured the levels of these amino acids in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys and MPTP-plus-probenecid (MPTPp)-treated mice to determine whether and how dopaminergic midbrain degeneration affects the levels of serine enantiomers in various basal ganglia subregions. In addition, in the same brain regions, we measured the levels of key neuroactive amino acids modulating glutamatergic neurotransmission, including l-glutamate, glycine, l-aspartate, d-aspartate, and their precursors l-glutamine, l-asparagine. In monkeys, MPTP treatment produced severe denervation of nigrostriatal dopaminergic fibers (⁓75%) and increased the levels of serine enantiomers in the rostral putamen (rPut), but not in the subthalamic nucleus, and the lateral and medial portion of the globus pallidus. Moreover, this neurotoxin significantly reduced the protein expression of the astrocytic serine transporter ASCT1 and the glycolytic enzyme GAPDH in the rPut of monkeys. Conversely, concentrations of d-serine and l-serine, as well as ASCT1 and GAPDH expression were unaffected in the striatum of MPTPp-treated mice, which showed only mild dopaminergic degeneration (⁓30%). These findings unveil a link between the severity of dopaminergic nigrostriatal degeneration and striatal serine enantiomers concentration, ASCT1 and GAPDH expression. We hypothesize that the up-regulation of d-serine and l-serine levels occurs as a secondary response within a homeostatic loop to support the metabolic and neurotransmission demands imposed by the degeneration of dopaminergic neurons.

Homeostasis of serine enantiomers is disrupted in the post-mortem caudate putamen and cerebrospinal fluid of living Parkinson's disease patients

L-serine generated in astrocytes plays a pivotal role in modulating essential neurometabolic processes, while its enantiomer, D-serine, specifically regulates NMDA receptor (NMDAR) signalling. Despite their physiological relevance in modulating cerebral activity, serine enantiomers metabolism in Parkinson's disease (PD) remains elusive. Using High-Performance Liquid Chromatography (HPLC), we measured D- and L-serine levels along with other amino acids known to modulate NMDAR function, such as L-glutamate, L-aspartate, D-aspartate, and glycine, in the post-mortem caudate putamen (CPu) and superior frontal gyrus (SFG) of PD patients. Moreover, we examined these amino acids in the cerebrospinal fluid (CSF) of de novo living PD, Alzheimer's disease (AD), and amyotrophic lateral sclerosis (ALS) patients versus subjects with other neurological disorders (OND), used as control. We found higher D-serine and L-serine levels in the CPu of PD patients but not in the SFG, a cerebral region that, in contrast to the CPu, is not innervated by nigral dopaminergic terminals. We also highlighted a significant elevation of both serine enantiomers in the CSF samples from PD but not in those of AD and ALS patients, compared with control subjects. By contrast, none or only minor changes were found in the amount of other neuroactive amino acids mentioned above. Our findings identify D-serine and L-serine level upregulation as a biochemical signature associated with nigrostriatal dopaminergic degeneration in PD.

Foliglurax, a positive allosteric modulator of the metabotrophic glutamate receptor 4, protects dopaminergic neurons in MPTP-lesioned male mice

Overactivity of the corticostriatal glutamatergic pathway is documented in Parkinson's disease (PD) and stimulation of presynaptic metabotropic glutamate (mGlu) receptors 4 on these striatal afferents inhibits glutamate release normalizing neuronal activity in the basal ganglia. Moreover, mGlu4 receptors are also expressed in glial cells and are able to modulate glial function making this receptor a potential target for neuroprotection. Hence, we investigated whether foliglurax, a positive allosteric modulator of mGlu4 receptors with high brain exposure after oral administration, has neuroprotective effects in MPTP mice to model early PD. Male mice were treated daily from day 1 to 10 with 1, 3 or 10 mg/kg of foliglurax and administered MPTP on the 5th day then euthanized on the 11th day. Dopamine neuron integrity was assessed with measures of striatal dopamine and its metabolites levels, striatal and nigral dopamine transporter (DAT) binding and inflammation with markers of striatal astrocytes (GFAP) and microglia (Iba1). MPTP lesion produced a decrease in dopamine, its metabolites and striatal DAT specific binding that was prevented by treatment with 3 mg/kg of foliglurax, whereas 1 and 10 mg/kg had no beneficial effect. MPTP mice had increased levels of GFAP; foliglurax treatment (3 mg/kg) prevented this increase. Iba1 levels were unchanged in MPTP mice compared to control mice. There was a negative correlation between dopamine content and GFAP levels. Our results show that positive allosteric modulation of mGlu4 receptors with foliglurax provided neuroprotective effects in the MPTP mouse model of PD.

Astrocytic modulation of neuronal signalling

Neuronal signalling is a key element in neuronal communication and is essential for the proper functioning of the CNS. Astrocytes, the most prominent glia in the brain play a key role in modulating neuronal signalling at the molecular, synaptic, cellular, and network levels. Over the past few decades, our knowledge about astrocytes and their functioning has evolved from considering them as merely a brain glue that provides structural support to neurons, to key communication elements. Astrocytes can regulate the activity of neurons by controlling the concentrations of ions and neurotransmitters in the extracellular milieu, as well as releasing chemicals and gliotransmitters that modulate neuronal activity. The aim of this review is to summarise the main processes through which astrocytes are modulating brain function. We will systematically distinguish between direct and indirect pathways in which astrocytes affect neuronal signalling at all levels. Lastly, we will summarize pathological conditions that arise once these signalling pathways are impaired focusing on neurodegeneration.

Intermittent Theta Burst Stimulation Improves Motor and Behavioral Dysfunction through Modulation of NMDA Receptor Subunit Composition in Experimental Model of Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder characterized by the progressive degeneration of the dopaminergic system, leading to a variety of motor and nonmotor symptoms. The currently available symptomatic therapy loses efficacy over time, indicating the need for new therapeutic approaches. Repetitive transcranial magnetic stimulation (rTMS) has emerged as one of the potential candidates for PD therapy. Intermittent theta burst stimulation (iTBS), an excitatory protocol of rTMS, has been shown to be beneficial in several animal models of neurodegeneration, including PD. The aim of this study was to investigate the effects of prolonged iTBS on motor performance and behavior and the possible association with changes in the NMDAR subunit composition in the 6-hydroxydopamine (6-OHDA)-induced experimental model of PD. Two-month-old male Wistar rats were divided into four groups: controls, 6-OHDA rats, 6-OHDA + iTBS protocol (two times/day/three weeks) and the sham group. The therapeutic effect of iTBS was evaluated by examining motor coordination, balance, spontaneous forelimb use, exploratory behavior, anxiety-like, depressive/anhedonic-like behavior and short-term memory, histopathological changes and changes at the molecular level. We demonstrated the positive effects of iTBS at both motor and behavioral levels. In addition, the beneficial effects were reflected in reduced degeneration of dopaminergic neurons and a subsequent increase in the level of DA in the caudoputamen. Finally, iTBS altered protein expression and NMDAR subunit composition, suggesting a sustained effect. Applied early in the disease course, the iTBS protocol may be a promising candidate for early-stage PD therapy, affecting motor and nonmotor deficits.

Fatigue in fluctuating Parkinson's disease patients: possible impact of safinamide

Fatigue is a common non-motor symptom in Parkinson's disease (PD). Among other pathophysiological mechanisms, neuroinflammation, a pathological PD hallmark associated with changes in glutamatergic transmission in basal ganglia, has been proposed as a crucial factor closely related to fatigue. To test the hypothesis that safinamide could represent an effective treatment of fatigue in PD patients, given its dual mechanism of action (it selectively and reversibly inhibits MAOB and modulates glutamate release), we administered the validated versions of fatigue severity scale (FSS) and Parkinson fatigue scale-16 (PFS-16) to 39 fluctuating PD patients with fatigue before and after a 24-week treatment period with safinamide as add-on therapy. An assessment of secondary variables such as depression, quality of life (QoL), and motor and non-motor symptoms (NMS) was conducted. After 24 weeks of treatment with safinamide, both FSS (p < 0.001) and PF-S16 (p = 0.02) scores were significantly lower than at baseline. Moreover, 46.2% and 41% of patients scored below the cut-off for the presence of fatigue according to FSS and PFS-16, respectively (responders). At follow-up, a significant difference emerged between responders and non-responders in mood, QoL, and NMS. Fatigue improved in fluctuating PD, and more than 40% of patients were "fatigue-free" after a 6 month treatment with safinamide. Patients without fatigue at follow-up displayed significantly better scores in QoL domains, such as mobility or activities of daily living, although disease severity remained stable, supporting the hypothesis that fatigue could considerably affect QoL. Drugs that interact with multiple neurotransmission systems, such as safinamide, could be useful in reducing this symptom.

Impact of Sex on Neuroimmune contributions to Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease. Inflammation has been observed in both the idiopathic and familial forms of PD. Importantly, PD is reported more often in men than in women, men having at least 1.5- fold higher risk to develop PD than women. This review summarizes the impact of biological sex and sex hormones on the neuroimmune contributions to PD and its investigation in animal models of PD. Innate and peripheral immune systems participate in the brain neuroinflammation of PD patients and is reproduced in neurotoxin, genetic and alpha-synuclein based models of PD. Microglia and astrocytes are the main cells of the innate immune system in the central nervous system and are the first to react to restore homeostasis in the brain. Analysis of serum immunoprofiles in female and male control and PD patients show that a great proportion of these markers differ between male and female. The relationship between CSF inflammatory markers and PD clinical characteristics or PD biomarkers shows sex differences. Conversely, in animal models of PD, sex differences in inflammation are well documented and the beneficial effects of endogenous and exogenous estrogenic modulation in inflammation have been reported. Targeting neuroinflammation in PD is an emerging therapeutic option but gonadal drugs have not yet been investigated in this respect, thus offering new opportunities for sex specific treatments.

Chronic Gq activation of ventral hippocampal neurons and astrocytes differentially affects memory and behavior

Network dysfunction is implicated in numerous diseases and psychiatric disorders, and the hippocampus serves as a common origin for these abnormalities. To test the hypothesis that chronic modulation of neurons and astrocytes induces impairments in cognition, we activated the hM3D(Gq) pathway in CaMKII+ neurons or GFAP+ astrocytes within the ventral hippocampus across 3, 6, and 9 months. CaMKII-hM3Dq activation impaired fear extinction at 3 months and acquisition at 9 months. Both CaMKII-hM3Dq manipulation and aging had differential effects on anxiety and social interaction. GFAP-hM3Dq activation impacted fear memory at 6 and 9 months. GFAP-hM3Dq activation impacted anxiety in the open field only at the earliest time point. CaMKII-hM3Dq activation modified the number of microglia, while GFAP-hM3Dq activation impacted microglial morphological characteristics, but neither affected these measures in astrocytes. Overall, our study elucidates how distinct cell types can modify behavior through network dysfunction, while adding a more direct role for glia in modulating behavior.

Glutamatergic neurotransmission: A potential pharmacotherapeutic target for the treatment of cognitive disorders

In the mammalian brain, glutamate is regarded to be the primary excitatory neurotransmitter due to its widespread distribution and wide range of metabolic functions. Glutamate plays key roles in regulating neurogenesis, synaptogenesis, neurite outgrowth, and neuron survival in the brain. Ionotropic and metabotropic glutamate receptors, neurotransmitters, neurotensin, neurosteroids, and others co-ordinately formulate a complex glutamatergic network in the brain that maintains optimal excitatory neurotransmission. Cognitive activities are potentially synchronized by the glutamatergic activities in the brain via restoring synaptic plasticity. Dysfunctional glutamate receptors and other glutamatergic components are responsible for the aberrant glutamatergic activity in the brain that cause cognitive impairments, loss of synaptic plasticity, and neuronal damage. Thus, controlling the brain's glutamatergic transmission and modifying glutamate receptor function could be a potential therapeutic strategy for cognitive disorders. Certain drugs that regulate glutamate receptor activities have shown therapeutic promise in improving cognitive functions in preclinical and clinical studies. However, several issues regarding precise functional information of glutamatergic activity are yet to be comprehensively understood. The present article discusses the scope of developing glutamatergic systems as prospective pharmacotherapeutic targets to treat cognitive disorders. Special attention has been given to recent developments, challenges, and future prospects.

Heteromerization of Dopamine D2 and Oxytocin Receptor in Adult Striatal Astrocytes

The ability of oxytocin (OT) to interact with the dopaminergic system through facilitatory D2-OT receptor (OTR) receptor-receptor interaction in the limbic system is increasingly considered to play roles in social or emotional behavior, and suggested to serve as a potential therapeutic target. Although roles of astrocytes in the modulatory effects of OT and dopamine in the central nervous system are well recognized, the possibility of D2-OTR receptor-receptor interaction in astrocytes has been neglected. In purified astrocyte processes from adult rat striatum, we assessed OTR and dopamine D2 receptor expression by confocal analysis. The effects of activation of these receptors were evaluated in the processes through a neurochemical study of glutamate release evoked by 4-aminopyridine; D2-OTR heteromerization was assessed by co-immunoprecipitation and proximity ligation assay (PLA). The structure of the possible D2-OTR heterodimer was estimated by a bioinformatic approach. We found that both D2 and OTR were expressed on the same astrocyte processes and controlled the release of glutamate, showing a facilitatory receptor-receptor interaction in the D2-OTR heteromers. Biochemical and biophysical evidence confirmed D2-OTR heterodimers on striatal astrocytes. The residues in the transmembrane domains four and five of both receptors are predicted to be mainly involved in the heteromerization. In conclusion, roles for astrocytic D2-OTR in the control of glutamatergic synapse functioning through modulation of astrocytic glutamate release should be taken into consideration when considering interactions between oxytocinergic and dopaminergic systems in striatum.

Zinc Deficiency Exacerbates Behavioral Impediments and Dopaminergic Neuron Degeneration in a Mouse Model of Parkinson Disease

BACKGROUND

Circulating zinc (Zn) concentrations are lower than normal in patients with Parkinson disease (PD). It is unknown whether Zn deficiency increases the susceptibility to PD.

OBJECTIVES

The study aimed to investigate the effect of dietary Zn deficiency on behaviors and dopaminergic neurons in a mouse model of PD and to explore potential mechanisms.

METHODS

Male C57BL/6J mice aged 8-10 wk were fed Zn adequate (ZnA; 30 μg/g) or Zn deficient (ZnD; <5 μg/g) diet throughout the experiments. Six weeks later 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) was injected to generate the PD model. Controls were injected with saline. Thus, 4 groups (Saline-ZnA, Saline-ZnD, MPTP-ZnA, and MPTP-ZnD) were formed. The experiment lasted 13 wk. Open field test, rotarod test, immunohistochemistry, and RNA sequencing were performed. Data were analyzed with t-test, 2-factor ANOVA, or Kruskal-Wallis test.

RESULTS

Both MPTP and ZnD diet treatments led to a significant reduction in blood Zn concentrations (P_MPTP = 0.012, P_Zn = 0.014), reduced total distance traveled (P_MPTP < 0.001, P_Zn = 0.031), and affected the degeneration of dopaminergic neurons in the substantia nigra (P_MPTP < 0.001, P_Zn = 0.020). In the MPTP-treated mice, the ZnD diet significantly reduced total distance traveled by 22.4% (P = 0.026), decreased latency to fall by 49.9% (P = 0.026), and reduced dopaminergic neurons by 59.3% (P = 0.002) compared with the ZnA diet. RNA sequencing analysis revealed a total of 301 differentially expressed genes (156 upregulated; 145 downregulated) in the substantia nigra of ZnD mice compared with ZnA mice. The genes were involved in a number of processes, including protein degradation, mitochondria integrity, and α-synuclein aggregation.

CONCLUSIONS

Zn deficiency aggravates movement disorders in PD mice. Our results support previous clinical observations and suggest that appropriate Zn supplementation may be beneficial for PD.

Glutamate modulation for the treatment of levodopa induced dyskinesia: a brief review of the drugs tested in the clinic

Levodopa is the standard treatment for Parkinson's disease, but its use is marred by the emergence of dyskinesia, for which treatment options remain limited. Here, we review the glutamatergic modulators that were assessed for their antidyskinetic potential in clinical trials, including N-methyl-D-aspartate (NMDA) antagonists, agonists at the glycine-binding site on NMDA receptors, metabotropic glutamate (mGlu) 4 agonists, mGlu₅ antagonists, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) antagonists and glutamate release inhibitors. Several agents that were investigated are not selective for their targets, raising uncertainty about the extent to which glutamatergic modulation contributed to their effects. Except for amantadine, the use of glutamatergic modulators for the treatment of dyskinesia in Parkinson's disease remains largely investigational, with promising results obtained with mGlu₅ negative allosteric modulation.