Changes in neural circuitry associated with depression at pre-clinical, pre-motor and early motor phases of Parkinson's disease

Effects of astrocytes in the dorsal hippocampus on anxiety-like and depressive-like behaviors in hemiparkinsonian rats

Anxiety and depression are the most common neuropsychiatric manifestations of Parkinson's disease (PD) patients. Growing evidence have shown that the dorsal hippocampus (dHIPP) and astrocytes (AS) may be involved in regulating depression and anxiety, but the role and mechanism are still unclear, especially in PD-related depression and anxiety. Unilateral 6-hydroxydopamine lesions of the substantia nigra pars compacta (SNc) were used to establish the rat model of PD. Behavioral tests and measurement of monoamine levels in the depression and anxiety related brain regions were performed to investigate the effects of chemogenetic activation or inhibition of dHIPP AS on PD-related anxiety and depression. The present results showed that unilateral lesions of the SNc induced anxiety-like and depressive-like behaviors, decreased dopamine (DA) levels in some related brain regions, but did not change the density of glial fibrillary acidic protein-positive AS in the CA1, CA3 and dentate gyrus in rats. Chemogenetic inhibition of dHIPP AS significantly improved anxiety-like and depressive-like behaviors only in the lesioned rats, while chemogenetic activation of dHIPP AS had no effects on anxiety-like and depressive-like behaviors in sham-operated and the lesioned rats. Chemogenetic activation of dHIPP AS only decreased DA level in the ventral hippocampus (vHIPP) in sham-operated rats, while inhibition of dHIPP AS increased 5-hydroxytryptamine (5-HT) levels in the medial prefrontal cortex (mPFC) and vHIPP in sham-operated rats and also in the amygdala, mPFC, lateral habenula, dHIPP and vHIPP in the lesioned rats. These results indicate that chemogenetic inhibition of dHIPP AS improves the anxiety-like and depressive-like behaviors in the lesioned rats through the changes in monoamine in some brain regions.

Machine learning study on predicting depressive symptoms and genetic correlations in Parkinson's disease

Depressive symptoms are prevalent in individuals with Parkinson's disease. Previous research has demonstrated a significant association between the triglyceride glucose (TyG) index and depression. Leveraging multicenter clinical data, the present study evaluates the predictive capacity of the TyG index for depressive symptoms in PD patients, aiming to establish its potential role in identifying individuals at risk for depression. A comparative analysis of multiple machine learning models was conducted to predict depression in PD patients, ultimately selecting the most effective model. Key predictive variables, including diabetes status, sex, cholesterol levels, triglycerides, blood glucose, and sleep disturbances, were incorporated into a support vector machine (SVM)-based nomogram to assess depression risk in PD patients. Additionally, a genome-wide association study (GWAS) utilizing external databases confirmed a causal relationship between the TyG index and depression. Furthermore, this study explores the biological functions and molecular mechanisms underlying shared transcriptomic proteins between PD and depression, providing insights into potential pathophysiological links between the two conditions.

Dopamine D4 receptors in the lateral habenula regulate anxiety-related behaviors in a rat model of Parkinson's disease

Although the output of the lateral habenula (LHb) controls the activity of midbrain dopamine (DA) and 5-hydroxytryptamine (5-HT) containing systems, which are implicated in the pathophysiology of anxiety, it is not clear how activation and blockade of LHb D4 receptors affects anxiety-like behaviors, particularly in Parkinson's disease related anxiety. In this study, unilateral 6-hydroxydopamine lesions of the substantia nigra pars compacta (SNc) in rats induced anxiety-like behaviors, which attribute to hyperactivity of LHb neurons and decrease in the level of DA in the medial prefrontal cortex (mPFC), amygdala and ventral hippocampus (vHip) compared to sham-operated rats. Intra-LHb injection of D4 receptor agonist A412997 induced or increased the expression of anxiety-like behaviors, while injection of D4 receptor antagonist L741742 showed anxiolytic effects in sham-operated and the SNc-lesioned rats. However, the doses producing behavioral effects in the lesioned rats were higher than those of sham-operated rats. Intra-LHb injection of A412997 increased firing rate of LHb neurons, and decreased levels of DA and 5-HT in the mPFC, amygdala and vHip; conversely, L741742 decreased firing rate of LHb neurons, and increased levels of DA and 5-HT in two groups of rats. Compared to sham-operated rats, the duration of A412997 and L741742 action on the firing rate of neurons was markedly shortened in the lesioned rats. Collectively, these findings suggest that D4 receptors in the LHb are involved in the regulation of anxiety-like behaviors, and degeneration of the nigrostriatal pathway down-regulates function and/or expression of these receptors.

Habenula volume change in Parkinson's disease: A 7T MRI study

OBJECTIVE

Parkinson's disease (PD) is a progressive neurodegenerative disease characterized by motor and early non-motor symptoms. The habenula is implicated in the pathophysiology of depression. This study investigates habenular volume in PD patients without clinical depression to show the changes in PD unrelated to depression.

METHODS

The study used high-resolution 7 Tesla MRI data from the TRACK-PD study involving 104 PD patients and 44 healthy controls (HCs). The habenula was manually segmented, and volumes were measured, considering demographic data and depression scores via the Beck Depression Inventory (BDI).

RESULTS

No significant correlation was found between habenular volume and BDI scores in PD patients or HCs. However, the PD group exhibited a significantly larger mean and right habenular volume than HCs. Although PD patients showed higher BDI scores, indicating more subthreshold depression, these did not correlate with the habenular volume.

CONCLUSION

The results suggest that while the habenula may be involved in the symptoms of PD, its role in depression within this cohort is unclear. The changes might be related to the role of the habenula in motor symptoms. This study provides a new perspective on the role of the habenula in PD, but future research could lead to a greater understanding of the neuroanatomical features of the habenula in PD.

Impact of alogliptin on lipopolysaccharide-induced experimental Parkinson's disease: Unrevealing neurochemical and histopathological alterations in rodents

BACKGROUND

Degeneration of the nigrostriatal dopaminergic pathway has been seen as a significant cause of movement disability in Parkinson's disease (PD) patients. However, the exact reason for these degenerative changes has remained obscure. In recent years, incretins have been neuroprotective in various pathologies. In the current study, we have investigated the neuroprotective potential of alogliptin (Alo), a dipeptidyl peptidase-IV (DPP-IV) inhibitor, in a lipopolysaccharide (LPS) induced experimental model of PD.

EXPERIMENTAL APPROACH

LPS (5μg/5 μl) was infused intranigrally to induce PD in experimental rats. Post-LPS infusion, these animals were treated with Alo for 21 days in three successive dosages of 10, 20, and 40 mg/kg/day/per oral. The study is well supported with the determinations of motor functions biochemical, neurochemical, and histological analysis.

KEY RESULTS

Intranigral infusion of LPS in rats produced motor deficit. It was accompanied by oxidative stress, elevation in neuroinflammatory cytokines, altered neurochemistry, and degenerative changes in the striatal brain region. While Alo abrogated LPS-induced biochemical/neurochemical alterations, improved motor functions, and preserved neuronal morphology in LPS-infused rats.

CONCLUSION

The observed neuroprotective potential of Alo may be due to its antioxidant and anti-inflammatory actions and its ability to modulate monoaminergic signals. Nonetheless, current findings suggest that improving the availability of incretins through DPP-IV inhibition is a promising strategy for treating Parkinson's disease.

Emerging perspectives on precision therapy for Parkinson's disease: multidimensional evidence leading to a new breakthrough in personalized medicine

PD is a prevalent and progressive neurodegenerative disorder characterized by both motor and non-motor symptoms. Genes play a significant role in the onset and progression of the disease. While the complexity and pleiotropy of gene expression networks have posed challenges for gene-targeted therapies, numerous pathways of gene variant expression show promise as therapeutic targets in preclinical studies, with some already in clinical trials. With the recognition of the numerous genes and complex pathways that can influence PD, it may be possible to take a novel approach to choose a treatment for the condition. This approach would be based on the symptoms, genomics, and underlying mechanisms of the disease. We discuss the utilization of emerging genetic and pathological knowledge of PD patients to categorize the disease into subgroups. Our long-term objective is to generate new insights for the therapeutic approach to the disease, aiming to delay and treat it more effectively, and ultimately reduce the burden on individuals and society.

The habenula in Parkinson's disease: Anatomy, function, and implications for mood disorders - A narrative review

Parkinson's disease (PD), a widespread neurodegenerative disorder, often coexists with mood disorders. Degeneration of serotonergic neurons in brainstem raphe nuclei have been linked to depression and anxiety. Additionally, the locus coeruleus and its noradrenergic neurons are among the first areas to degenerate in PD and contribute to stress, emotional memory, motor, sensory, and autonomic symptoms. Another brain region of interest is habenula, which is especially related to anti-reward processing, and its function has recently been linked to PD and to mood-related symptoms. There are several neuroimaging studies that investigated role of the habenula in mood disorders. Differences in habenular size and hemispheric symmetry were found in healthy controls compared to individuals with mood disorders. The lateral habenula, as a link between the dopaminergic and serotonergic systems, is thought to contribute to depressive symptoms in PD. However, there is only one imaging study about role of habenula in mood disorders in PD, although the relationship between PD and mood disorders is known. There is little known about habenula pathology in PD but given these observations, the question arises whether habenular dysfunction could play a role in PD and the development of PD-related mood disorders. In this review, we evaluate neuroimaging techniques and studies that investigated the habenula in the context of PD and mood disorders. Future studies are important to understand habenula's role in PD patients with mood disorders. Thus, new potential diagnostic and treatment opportunities would be found for mood disorders in PD.

Investigating the Shared Genetic Etiology Between Parkinson's Disease and Depression

Background

Depression is a common symptom in Parkinson's disease (PD), resulting from underlying neuropathological processes and psychological factors. However, the extent to which shared genetic risk factors contribute to the relationship between depression and PD is poorly understood.

Objective

To examine the effects of common genetic variants influencing the etiology of PD and depression risk at the genome-wide and local genomic regional level.

Methods

We comprehensively investigated the genetic relationship between PD and depression using genome-wide association studies data. First, we estimated the genetic correlation at the genome-wide level using linkage-disequilibrium score regression, followed by local genetic correlation analysis using the GWAS-pairwise method and functional annotation to identify genes that may jointly influence the risk for both traits. Also, we performed Latent Causal Variable, Latent Heritable Confounder Mendelian Randomization, and traditional Mendelian Randomization analyses to investigate the potential causal relationship.

Results

Although the genetic correlation between PD and depression was not statistically significant at the genome-wide level, GWAS-pairwise analyses identified 16 genomic segments associated with PD and depression, implicating nine genes. Further analyses revealed distinct patterns within individual genes, suggesting an intricate pattern. These genes involve various biological processes, including neurotransmitter regulation, senescence, and nucleo-cytoplasmic transport mechanisms. We did not observe genetic evidence of causality between PD and depression.

Conclusions

Our findings did not support a genome-wide genetic correlation or a causal association between both conditions. However, we identified genomic segments but identified genomic segments linked to distinct biological pathways influencing their etiology.Further research is needed to understand their functional consequences.

How Music Moves Us: Music-induced Emotion Influences Motor Learning

Music is an important tool for the induction and regulation of emotion. Although learning a sequential motor behaviour is essential to normal motor function, to our knowledge, the role of music-induced emotion on motor learning has not been explored. Our experiment aimed to determine whether listening to different emotional music could influence motor sequence learning. We focused on two sub-components of motor sequence learning: the acquisition of the order of the elements in the sequence (the "what"), and the ability to carry out the sequence, combining the elements in a single, skilled action (the "how"). Twenty subjects performed a motor sequence-learning task with a digitizing tablet in three different experimental sessions. In each session they executed the task while listening to three different musical pieces, eliciting fearful, pleasant, and neutral mood. Eight targets were presented in a pre-set order and subjects were asked to learn the sequence while moving. Music-induced pleasure had an impact on movement kinematics with onset time and peak velocity decreasing and movement time increasing more with respect to neutral music session. Declarative learning, verbal recall of the sequence order, was improved under emotional manipulation, but only for fear-condition. Results suggest that music-induced emotion can influence both sub-components of motor learning in a different way. Music-induced pleasure may have improved motor components of sequence learning by means of increased striatal dopamine availability whereas music-induced fear may facilitate the recruitment of attentional circuits, thus acting on declarative knowledge of the sequence order.

Downregulation of PACAP and the PAC1 Receptor in the Basal Ganglia, Substantia Nigra and Centrally Projecting Edinger-Westphal Nucleus in the Rotenone model of Parkinson's Disease

Numerous in vitro and in vivo models of Parkinson's disease (PD) demonstrate that pituitary adenylate cyclase-activating polypeptide (PACAP) conveys its strong neuroprotective actions mainly via its specific PAC1 receptor (PAC1R) in models of PD. We recently described the decrease in PAC1R protein content in the basal ganglia of macaques in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD that was partially reversed by levodopa therapy. In this work, we tested whether these observations occur also in the rotenone model of PD in the rat. The rotarod test revealed motor skill deterioration upon rotenone administration, which was reversed by benserazide/levodopa (B/L) treatment. The sucrose preference test suggested increased depression level while the open field test showed increased anxiety in rats rendered parkinsonian, regardless of the received B/L therapy. Reduced dopaminergic cell count in the substantia nigra pars compacta (SNpc) diminished the dopaminergic fiber density in the caudate-putamen (CPu) and decreased the peptidergic cell count in the centrally projecting Edinger-Westphal nucleus (EWcp), supporting the efficacy of rotenone treatment. RNAscope in situ hybridization revealed decreased PACAP mRNA (Adcyap1) and PAC1R mRNA (Adcyap1r1) expression in the CPu, globus pallidus, dopaminergic SNpc and peptidergic EWcp of rotenone-treated rats, but no remarkable downregulation occurred in the insular cortex. In the entopeduncular nucleus, only the Adcyap1r1 mRNA was downregulated in parkinsonian animals. B/L therapy attenuated the downregulation of Adcyap1 in the CPu only. Our current results further support the evolutionarily conserved role of the PACAP/PAC1R system in neuroprotection and its recruitment in the development/progression of neurodegenerative states such as PD.

Neurobiology of depression in Parkinson's disease: Insights into epidemiology, molecular mechanisms and treatment strategies

Parkinson's disease (PD) is characterized mainly by motor dysfunctions due to the progressive loss of dopaminergic neurons. However, PD patients experience a multitude of debilitating non-motor symptoms, including depression, which may have deleteriously detrimental effects on life. Depression is multifactorial and exhibits a bimodal progression in PD, but its underlying molecular mechanisms are poorly understood. Studies demonstrating the pathophysiology of depression in PD and the specific treatment strategies for depression-like symptoms in PD patients are largely lacking, often underrated, under-recognized and, consequently, inadequately/under-treated. Nevertheless, reports suggest that the incidence of depression is approximately 20-30% of PD patients and may precede the onset of motor symptoms. Diagnosing depression in PD becomes difficult due to the clinical overlap in symptomatology between the two diseases, and the nigrostriatal dysfunction alone is insufficient to explain depressive symptoms in PD. Therefore, the current study provides an overview of the molecular mechanisms underlying the development of depression in PD and new insights into developing current antidepressant strategies to treat depression in PD. This review will identify and understand the molecular pathological mechanisms of depression in PD that will fundamentally help tailoring therapeutic interventions for depressive symptoms in PD.

Premotor, nonmotor and motor symptoms of Parkinson's Disease: A new clinical state of the art

Parkinson's Disease (PD) is a neurodegenerative disorder that affects dopaminergic neurons in the mesencephalic substantia nigra, causing a progressive clinical course characterized by pre-motor, non-motor and motor symptoms, which negatively impact the quality of life of patients and cause high health care costs. Therefore, the present study aims to discuss the clinical manifestations of PD and to make a correlation with the gut-brain (GB) axis, approaching epidemiology and therapeutic perspectives, to better understand its clinical progression and identify symptoms early. A literature review was performed regarding the association between clinical progression, the gut-brain axis, epidemiology, and therapeutic perspectives, in addition to detailing pre-motor, non-motor symptoms (neuropsychiatric, cognitive, autonomic, sleep disorders, sensory abnormalities) and cardinal motor symptoms. Therefore, this article addresses a topic of extreme relevance, since the previously mentioned clinical manifestations (pre-motor and non-motor) can often act as prodromal markers for the early diagnosis of PD and may precede it by up to 20 years.

Thalamic pathways mediating motor and non-motor symptoms in a Parkinson's disease model

In a recent study, Zhang, Roy, and colleagues have shown that neurons in the parafascicular (PF) thalamus project to three distinct neural structures in the basal ganglia. The neural circuits identified in the study were associated with specific motor and non-motor symptoms in a Parkinson's disease (PD) mouse model. The findings provide potential actionable therapeutic targets for this disease.

Inflammatory markers and depression in Parkinson's disease: a systematic review

BACKGROUND

Parkinson's disease (PD) patients experience non-motor symptoms (NMS), which may appear before motor manifestations. The most common NMS is depression, affecting about 30-40% of PD patients. Both PD and depression are associated with an increased inflammatory burden, with studies showing elevation of diverse inflammatory markers in patients with both conditions.

METHODS

A systematic review was conducted in PubMed and PsycINFO databases to investigate what inflammatory markers are associated with PD depression (PDD). Only studies in English that measured inflammatory markers and analyzed against depression scores in PD patients were included.

RESULTS

A total of 1132 articles were retrieved, and 14 entries were found to be eligible. Twelve were cross-sectional studies, one was a cohort, and one was a non-randomized controlled trial. IL-17A was the only marker strongly associated with PDD, while studies assessing sIL-2R and serum amyloid A found a moderate correlation. C-reactive protein, IL-10, tumor necrosis factor-α, monocyte chemoattractant protein-1, and IL-6 yielded conflicting results. Their possible roles in PDD are discussed. PDD was also related to longer disease duration and other NMS, such as anxiety, fatigue, dementia, REM sleep behavior disorder, and autonomic dysfunction.

CONCLUSION

We suggest that these markers may be used for distinguishing isolated depression from that related to neurodegeneration, especially in individuals that concurrently present with other known prodromal symptoms of PD and other α-synucleinopathies. However, future prospective studies are warranted to confirm this hypothesis.

The pathobiological basis of depression in Parkinson disease: challenges and outlooks

Depression, with an estimated prevalence of about 40% is a most common neuropsychiatric disorder in Parkinson disease (PD), with a negative impact on quality of life, cognitive impairment and functional disability, yet the underlying neurobiology is poorly understood. Depression in PD (DPD), one of its most common non-motor symptoms, can precede the onset of motor symptoms but can occur at any stage of the disease. Although its diagnosis is based on standard criteria, due to overlap with other symptoms related to PD or to side effects of treatment, depression is frequently underdiagnosed and undertreated. DPD has been related to a variety of pathogenic mechanisms associated with the underlying neurodegenerative process, in particular dysfunction of neurotransmitter systems (dopaminergic, serotonergic and noradrenergic), as well as to disturbances of cortico-limbic, striato-thalamic-prefrontal, mediotemporal-limbic networks, with disruption in the topological organization of functional mood-related, motor and other essential brain network connections due to alterations in the blood-oxygen-level-dependent (BOLD) fluctuations in multiple brain areas. Other hypothetic mechanisms involve neuroinflammation, neuroimmune dysregulation, stress hormones, neurotrophic, toxic or metabolic factors. The pathophysiology and pathogenesis of DPD are multifactorial and complex, and its interactions with genetic factors, age-related changes, cognitive disposition and other co-morbidities awaits further elucidation.

Characteristics of Cognitive Impairment and Their Relationship With Total Cerebral Small Vascular Disease Score in Parkinson's Disease

Background

This study aimed to investigate the characteristics of cognitive dysfunctions and their relationship with total cerebral small vascular disease (CSVD) in Parkinson’s disease (PD).

Methods

A total of 174 idiopathic PD patients who underwent brain magnetic resonance imaging (MRI) were recruited. Demographic information, vascular disease risk factors, motor function (MDS-UPDRS III score), and cognitive level (MoCA, MMSE) were collected for these patients. The total CSVD burden was scored based on lacunes, enlarged perivascular spaces (EPVS), high-grade white matter hyperintensities (WMH), and cerebral microbleeds (CMBs) for each subject.

Results

Cognitive scores on MoCA for language, delayed recall, and orientation were significantly reduced in PD patients with CSVD burden ≥ 1 than in those with CSVD burden = 0. Educational level, PDQ 39, and CSVD burden were significantly associated with MoCA scores in individuals with PD. For the whole group, the full model accounted for 33.6% variation in total MoCA scores. In which, CSVD burden explained 2.7% of the results, and the detection of lacunes, WMH, EPVS, and strictly lobar CMBs were significantly correlated with MoCA scores. The stability of the outcomes was confirmed by sensitivity analysis.

Conclusion

CSVD can independently contribute to cognitive decline in PD and cause damage in specific cognitive domains. Promoting neurovascular health may help preserve cognitive functions in PD.

Depression history modulates effects of subthalamic nucleus topography on neuropsychological outcomes of deep brain stimulation for Parkinson's disease

Patients with psychiatric symptoms, such as depression, anxiety, and visual hallucinations, may be at increased risk for adverse effects following deep brain stimulation of the subthalamic nucleus for Parkinson's disease, but there have been relatively few studies of associations between locations of chronic stimulation and neuropsychological outcomes. We sought to determine whether psychiatric history modulates associations between stimulation location within the subthalamic nucleus and postoperative affective and cognitive changes. We retrospectively identified 42 patients with Parkinson's disease who received bilateral subthalamic nucleus deep brain stimulation and who completed both pre- and postoperative neuropsychological testing. Active stimulation contacts were localized in MNI space using Lead-DBS software. Linear discriminant analysis identified vectors maximizing variance in postoperative neuropsychological changes, and Pearson's correlations were used to assess for linear relationships. Stimulation location was associated with postoperative change for only 3 of the 18 neuropsychological measures. Variation along the superioinferior (z) axis was most influential. Constraining the analysis to patients with a history of depression revealed 10 measures significantly associated with active contact location, primarily related to location along the anterioposterior (y) axis and with worse outcomes associated with more anterior stimulation. Analysis of patients with a history of anxiety revealed 5 measures with location-associated changes without a predominant axis. History of visual hallucinations was not associated with significant findings. Our results suggest that a history of depression may influence the relationship between active contact location and neuropsychological outcomes following subthalamic nucleus deep brain stimulation. These patients may be more sensitive to off-target (nonmotor) stimulation.

Cognitive dysfunction and neuropsychiatric aspects of Parkinson's disease

Movement abnormalities, by definition, and cognitive changes, to varying extents, affect every patient with Parkinson's disease (PD) and are attributed to the underlying neurodegenerative disease. Various psychiatric disorders occur in most patients at some point over the course of PD, including in the prodromal phase. Even though psychiatric disturbances tend to aggravate motor and cognitive deficits, they are under-recognized and under-treated, and the role of the underlying neurological disease is often minimized. To provide an integrated approach to understanding neuropsychiatric aspects of PD, this chapter reviews how cognitive changes in PD relate to the common psychiatric disturbances in PD along with the prevalence, phenomenology, pathophysiology, and treatment of each.

Neurodegeneration in the centrally-projecting Edinger-Westphal nucleus contributes to the non-motor symptoms of Parkinson's disease in the rat

BACKGROUND

The neuropathological background of major depression and anxiety as non-motor symptoms of Parkinson's disease is much less understood than classical motor symptoms. Although, neurodegeneration of the Edinger-Westphal nucleus in human Parkinson's disease is a known phenomenon, its possible significance in mood status has never been elucidated. In this work we aimed at investigating whether neuron loss and alpha-synuclein accumulation in the urocortin 1 containing (UCN1) cells of the centrally-projecting Edinger-Westphal (EWcp) nucleus is associated with anxiety and depression-like state in the rat.

METHODS

Systemic chronic rotenone administration as well as targeted leptin-saporin-induced lesions of EWcp/UCN1 neurons were conducted. Rotarod, open field and sucrose preference tests were performed to assess motor performance and mood status. Multiple immunofluorescence combined with RNAscope were used to reveal the functional-morphological changes. Two-sample Student's t test, Spearman's rank correlation analysis and Mann-Whitney U tests were used for statistics.

RESULTS

In the rotenone model, besides motor deficit, an anxious and depression-like phenotype was detected. Well-comparable neuron loss, cytoplasmic alpha-synuclein accumulation as well as astro- and microglial activation were observed both in the substantia nigra pars compacta and EWcp. Occasionally, UCN1-immunoreactive neuronal debris was observed in phagocytotic microglia. UCN1 peptide content of viable EWcp cells correlated with dopaminergic substantia nigra cell count. Importantly, other mood status-related dopaminergic (ventral tegmental area), serotonergic (dorsal and median raphe) and noradrenergic (locus ceruleus and A5 area) brainstem centers did not show remarkable morphological changes. Targeted partial selective EWcp/UCN1 neuron ablation induced similar mood status without motor symptoms.

CONCLUSIONS

Our findings collectively suggest that neurodegeneration of urocortinergic EWcp contributes to the mood-related non-motor symptoms in toxic models of Parkinson's disease in the rat.

Thalamic white matter macrostructure and subnuclei volumes in Parkinson's disease depression

Depression is a common non-motor feature of Parkinson's disease (PD) which confers significant morbidity and is challenging to treat. The thalamus is a key component in the basal ganglia-thalamocortical network critical to the pathogenesis of PD and depression but the precise thalamic subnuclei involved in PD depression have not been identified. We performed structural and diffusion-weighted imaging (DWI) on 76 participants with PD to evaluate the relationship between PD depression and grey and white matter thalamic subnuclear changes. We used a thalamic segmentation method to divide the thalamus into its 50 constituent subnuclei (25 each hemisphere). Fixel-based analysis was used to calculate mean fibre cross-section (FC) for white matter tracts connected to each subnucleus. We assessed volume and FC at baseline and 14-20 months follow-up. A generalised linear mixed model was used to evaluate the relationship between depression, subnuclei volume and mean FC for each thalamic subnucleus. We found that depression scores in PD were associated with lower right pulvinar anterior (PuA) subnucleus volume. Antidepressant use was associated with higher right PuA volume suggesting a possible protective effect of treatment. After follow-up, depression scores were associated with reduced white matter tract macrostructure across almost all tracts connected to thalamic subnuclei. In conclusion, our work implicates the right PuA as a relevant neural structure in PD depression and future work should evaluate its potential as a therapeutic target for PD depression.

Parkinson and depression: review and outlook

Depression in Parkinson's Disorder (DPD) has been estimated to appear in up to 40% of people with PD and negatively impacts quality of life, motor and cognitive deficits and functional disability. Knowledge of the pathophysiology of DPD is unclear, DPD may be related to dysfunction in subcortical nuclei and the prefrontal cortex, striatal-thalamic-prefrontal and basotemporal limbic circuits, brainstem monoamine, and indolamine (i.e. dopamine, serotonin, and norepinephrine) systems. DPD is characterized by sadness, loss of interest, increased exhaustibility, feelings of helplessness, reduced drive, dysphoria, irritability, and pessimism about future. The diagnosis is complicated by overlap with PD symptoms, Detection of depression in PD should be made by psychometric depression scales. DPD is underrecognized and undertreated in clinical practice. Treatment mainly includes antidepressive medications and behavioral interventions as psychotherapy. Dopamine agonists showed some antidepressant effects, there are no sufficient numbers of RCTs. Important randomized clinical trials (RCTs) are summarized. SSRIs and SNRIs have a satisfying efficacy in DPD. TCAs are also good for improving depression. Side effects of different antidepressants (e.g. TCAs, SSRIs, SNRIs, bupropion, MAOIs) and potential interactions should be considered. In existing guidelines so far no statements, algorithms and recommendations are given for diagnosis and treatment of DPD. Methodologically adequate designed RCTs and comparative studies (NIS) which offer evidence-based results are urgently needed having the impact of DPD in mind.

Asymmetry of the insula-sensorimotor circuit in Parkinson's disease

Patients with Parkinson's disease (PD) experience motor and non-motor symptoms, suggesting alterations of the motor and/or limbic system or more probably of their communications. We hypothesized that the communication between the insula (part of the limbic system) and sensorimotor cortex in PD is altered and hemispheric asymmetric. Furthermore, that this asymmetry relates to non-motor symptoms, and specifically, that apathy-related asymmetry is unique to PD. To test these hypotheses, we used a novel multivariate time-frequency analysis method applied to resting-state functional magnetic resonance imaging (MRI) data of 28 controls and 25 participants with PD measured in their OFF medication state. The analysis infers directionality of coupling, that is, afferent or efferent, among four anatomical regions, thus defining directed pathways of information flow, which enables the extension of symmetry measures to include directionality. A major right asymmetry reduction of the dorsal-posterior insula efferent and a slight bilateral increase of insula afferent pathways were observed in participants with PD versus controls. Between-group pathways that correlated with mild cognitive impairments combined the central-executive and default-mode networks through the right insula. Apathy-correlated pathways of the posterior insula in participants with PD versus controls exhibited reduced right efferent and increased left afferent. Because apathy scores were comparable between the groups and effects of the other motor and non-motor symptoms were statistically removed by the analysis, the differences in apathy-correlated pathways were suggested as unique to PD. These pathways could be predictors in the pre-symptomatic phase in patients with apathy.

Treatment response and age of onset as risk indicators for parkinson disease in patients with major depressive disorder: A nationwide longitudinal study

BACKGROUND

Individuals with major depressive disorder (MDD) have a higher risk of developing Parkinson disease (PD). This study investigated whether response to treatment with antidepressants for MDD can determine patients at risk of developing PD later in life.

METHODS

We enrolled 3303 patients with newly-diagnosed MDD and 13,212 controls between 2002 and 2004 using Taiwan's Nationwide Health Insurance Research Database. We stratified patients with MDD according to the number of antidepressant regimens prescribed to them and the age at MDD onset and followed all participants until the end of 2013. During follow-up, we evaluated patients for the possibility of developing PD.

RESULTS

Patients with MDD had a greater likelihood of developing PD than controls. Patients with difficult-to-treat (DTT) MDD had a higher risk of developing PD than the other MDD subgroups (hazard ratio [HR] = 3.44, 95% confidence interval [95% CI]: = 1.99-5.95). When stratified by age (<50, 50-65, >65 years), DTT patients with middle-age or late-onset MDD exhibited elevated risks of developing PD (50-65 years: HR: 7.03, 95% CI: 2.95-16.76; >65 years: HR: 2.89, 95% CI: 1.26-6.65).

DISCUSSION

Patients with MDD and an onset age of >50 years who responded poorly to antidepressant treatment have an associated higher risk of subsequently developing PD. Therefore, when treating patients with MDD, clinicians should provide intensive antidepressant treatment and evaluations for PD so that risk-prevention measures can be implemented upon MDD diagnosis.

Focus on Depression in Parkinson's Disease: A Delphi Consensus of Experts in Psychiatry, Neurology, and Geriatrics

Major and minor forms of depression are significant contributors to Parkinson's disease morbidity and caregiver burden, affecting up to 50% of these patients. Nonetheless, symptoms of depression are still underrecognized and undertreated in this context due to scarcity of evidence and, consequently, consistent clinical guideline recommendations. Here, we carried out a prospective, multicentre, 2-round modified Delphi survey with 49 questions about the aetiopathological mechanisms of depression in Parkinson's disease (10), clinical features and connections with motor and nonmotor symptoms (10), diagnostic criteria (5), and therapeutic options (24). Items were assessed by a panel of 37 experts (neurologists, psychiatrists, and a geriatrist), and consensus was achieved in 81.6% of them. Depressive symptoms, enhanced by multiple patient circumstances, were considered Parkinson's disease risk factors but not clinical indicators of motor symptom and disease progression. These patients should be systematically screened for depression while ruling out both anhedonia and apathy symptoms as they are not necessarily linked to it. Clinical scales (mainly the Geriatric Depression Scale GDS-15) can help establishing the diagnosis of depression, the symptoms of which will require treatment regardless of severity. Efficacious and well-tolerated pharmacological options for Parkinson's comorbid depression were selective serotonin reuptake inhibitors (especially sertraline), dual-action serotonin and norepinephrine reuptake inhibitors (venlafaxine, desvenlafaxine, and duloxetine), multimodal (vortioxetine, bupropion, mirtazapine, and tianeptine), and anti-Parkinsonian dopamine agonists (pramipexole, ropinirole, and rotigotine). Tricyclic antidepressants and combining type B monoamine oxidase inhibitors with serotonergic drugs have serious side effects in these patients and therefore should not be prescribed. Electroconvulsive therapy was indicated for severe and drug-refractory cases. Cognitive behavioural therapy was recommended in cases of mild depression. Results presented here are useful diagnostic and patient management guidance for other physicians and important considerations to improve future drug trial design.

Cerebral small vessel disease may worsen motor function, cognition, and mood in Parkinson's disease

INTRODUCTION

Emerging evidence has suggested that cerebral small vessel disease (CSVD) may worsen motor function and cognition in Parkinson's disease (PD). However, the effect of CSVD on anxiety and depression in patients with PD remains unknown. This study explored the multi-dimensional effects of CSVD on PD outcomes (motor, cognition, and depression/anxiety).

METHODS

This cross-sectional study included 431 patients with PD from Beijing Tiantan Hospital from May 2016 to August 2019. CSVD imaging markers were assessed and the four-point CSVD burden score was calculated. Motor function (MDS-UPDRS III score and subscores), cognition (MMSE, MoCA), anxiety (HAMA), and depression (HAMD) were assessed in these patients. The associations of CSVD with these outcomes were analyzed using the Spearman's correlation and multivariable linear regression models.

RESULTS

Motor dysfunction, cognitive impairment, depression, and anxiety were significantly worse in patients with severe CSVD than in those with mild CSVD. Multivariable linear regression showed that CSVD burden was significantly associated with motor dysfunction (MDS-UPDRS III score and rigidity and bradykinesia subscores), impaired cognition, and high levels of depression and anxiety. A marginally significant association was observed between CSVD burden and gait/postural instability in multivariable regression analysis. Among the CSVD imaging markers, white matter hyperintensity, number of lacunes, and microbleeds were positively correlated with the severity of motor, cognitive, and emotional impairments, while the perivascular space in the basal ganglia was only correlated with cognitive impairments.

CONCLUSIONS

Comorbid CSVD may affect multiple functional domains in patients with PD. Management of cerebrovascular disease may improve PD outcomes.

Hypomania, Depression, Euthymia: New Evidence in Parkinson's Disease

The field related to mood disorders in Parkinson's disease (PD) is fragmented. The aim of this cohort observational study was to evaluate whether the episodes of mood alteration could appear in different disease stages and to verify how nonmotor symptoms were led off into different stages. We enrolled 93 PD outpatients (three groups: drug naive—DN; not exhibiting motor fluctuations—n-MF; and exhibiting motor fluctuations—MF) and 50 healthy controls. Mood state was assessed through the Internal State Scale (ISS) while depressive symptoms were evaluated through the Beck Depression Inventory-II (BDI-II), nonmotor symptoms by means of the Non-Motor Symptoms Scale (NMSS), and the presence of impulse control disorders (ICDs) with the Questionnaire for Impulsive-Compulsive Disorders in Parkinson's Disease (QUIP). Clinical and pharmacological data have also been recorded. No significant differences in mood state distribution between groups were observed. Nevertheless, as regards the mood state distribution within groups, in n-MF (47.6%) and MF patients (50%), (hypo)mania presence was significantly higher than other symptoms. In DN patients, hypomania showed a prevalence of 38.1% although it was not significant. At least one ICD was reported in 29.3% of n-MF and 50% of MF patients. In the MF group, a moderate positive correlation between ISS ACTivation subscale scores and the presence of ICDs and compulsive medication use emerged. Finally, MF patients reported higher BDI-II total scores than DN. Our results show that mood alterations in PD, considering both depressive symptoms and mood elevation, are related to the advanced stages of the disease as well as the presence of ICDs, and dopaminergic therapy would not always be able to restore a normal mood condition.

Psychological Stress Phenocopies Brain Mitochondrial Dysfunction and Motor Deficits as Observed in a Parkinsonian Rat Model

Psychological distress is a public health issue as it contributes to the development of human diseases including neuropathologies. Parkinson's disease (PD), a chronic, progressive neurodegenerative disorder, is caused by multiple factors including aging, mitochondrial dysfunction, and/or stressors. In PD, a substantial loss of substantia nigra (SN) neurons leads to rigid tremors, bradykinesia, and chronic fatigue. Several studies have reported that the hypothalamic-pituitary-adrenal (HPA) axis is altered in PD patients, leading to an increase level of cortisol which contributes to neurodegeneration and oxidative stress. We hypothesized that chronic psychological distress induces PD-like symptoms and promotes neurodegeneration in wild-type (WT) rats and exacerbates PD pathology in PINK1 knockout (KO) rats, a well-validated animal model of PD. We measured the bioenergetics profile (oxidative phosphorylation and glycolysis) in the brain by employing an XF24e Seahorse Extracellular Flux Analyzer in young rats subjected to predator-induced psychological distress. In addition, we analyzed anxiety-like behavior, motor function, expression of antioxidant enzymes, mitochondrial content, and neurotrophic factors brain-derived neurotrophic factor (BDNF) in the brain. Overall, we observed that psychological distress diminished up to 50% of mitochondrial respiration and glycolysis in the prefrontal cortex (PFC) derived from both WT and PINK1-KO rats. Mechanistically, the level of antioxidant proteins, mitochondrial content, and BDNF was significantly altered. Finally, psychological distress robustly induced anxiety and Parkinsonian symptoms in WT rats and accelerated certain symptoms of PD in PINK1-KO rats. For the first time, our collective data suggest that psychological distress can phenocopy several aspects of PD neuropathology, disrupt brain energy production, as well as induce ataxia-like behavior.

Non-Motor Symptoms of the Postural Instability and Gait Difficulty Subtype in De Novo Parkinson's Disease Patients: A Cross-Sectional Study in a Single Center

BACKGROUND AND PURPOSE

Little is known about non-motor symptoms (NMSs) associated with the postural instability and gait difficulty (PIGD) phenotype, especially in de novo Parkinson's disease (PD) patients. The aims of this study were to compare NMSs between the tremor dominant (TD) and PIGD phenotypes in de novo PD patients and to determine factors that are associated with the PIGD subtype.

PATIENTS AND METHODS

In a cross-sectional study conducted at our single center, 226 de novo PD patients with a median disease duration of 2 years were recruited. Data, including comprehensive demographics, motor subtypes and NMSs were obtained. Motor subtypes were classified as PIGD and non-PIGD (TD and indeterminate) by Jankovic's method. NMSs were evaluated by the non-motor symptoms questionnaire (NMSQuest).

RESULTS

We identified 73 (32.3%), 34 (15.0%) and 119 (52.7%) patients with TD, intermediate and PIGD subtypes, respectively. Patients with the PIGD subtype had poorer ADL, motor, depression, anxiety, sleep, and non-motor scores compared with those with the TD subtype. In the NMSQuest, the prevalence of cardiovascular, sleep, mood/cognitive and miscellaneous domains was increased in patients with the PIGD subtype compared with patients with the TD subtype. Multivariable forward stepwise logistic regression revealed that the Hamilton Depression Scale (HAMD) [odds ratio (OR), 1.059; 95% confidence interval (CI), 1.016-1.104, p = 0.007] and pain (OR, 3.175; 95% CI, 1.695-5.947, p < 0.001) exhibit significant discriminative power in differentiating PIGD and non-PIGD groups.

CONCLUSION

The PIGD group had more severe cardiovascular symptoms, sleep impairments, mood disturbances and pain. We demonstrated for the first time that pain was associated with the PIGD phenotype. Prompt detection and early treatment of NMSs related to the PIGD phenotype may improve patient outcomes.

Visuospatial functioning is associated with sleep disturbance and hallucinations in nondemented patients with Parkinson's disease

Introduction: Cognitive impairment is a common symptom of Parkinson's disease (PD) associated with reduced quality of life and a more severe disease state. Previous research has shown an association between visuospatial dysfunction and worse disease course; however, it is not clear whether this is separable from executive dysfunction and/or dementia. This study sought to determine whether distinct cognitive factors could be measured in a large PD cohort, and if those factors were differentially associated with other PD-related features, specifically to provide insight into visuospatial dysfunction. Methods: Non-demented participants with PD from the Pacific Udall Center were enrolled (n = 197). Co-participants (n = 104) completed questionnaires when available. Principal components factor analysis (PCFA) was utilized to group the neuropsychological test scores into independent factors by considering those with big factor loading (≥.40). Linear and logistic regression analyses were performed to examine the relationship between the cognitive factors identified in the PCFA and other clinical features of PD. Results: Six factors were extracted from the PCFA: 1) executive/processing speed, 2) visual learning & memory/visuospatial, 3) auditory working memory, 4) contextual verbal memory, 5) semantic learning & memory, and 6) visuospatial. Motor severity (p = 0.001), mood (p < 0.001), and performance on activities of daily living scores (informant: p < 0.001, patient: p = 0.009) were primarily associated with frontal and executive factors. General sleep disturbance (p < 0.006) and hallucinations (p = 0.002) were primarily associated with visuospatial functioning and visual learning/memory. Conclusions: Motor symptoms, mood, and performance on activities of daily living were primarily associated with frontal/executive factors. Sleep disturbance and hallucinations were associated with visuospatial functioning and visual learning/memory only, over and above executive functioning and regardless of cognitive disease severity. These findings support that visuospatial function in PD may indicate a more severe disease course, and that symptom management should be guided accordingly.

Postural Dynamics Are Associated With Cognitive Decline in Parkinson's Disease

Early features of Parkinson's disease (PD) include both motor and cognitive changes, suggesting shared common pathways. A common motor dysfunction is postural instability, a known predictor of falls, which have a major impact on quality of life. Understanding mechanisms of postural dynamics in PD and specifically how they relate to cognitive changes is essential for developing effective interventions. The aims of this study were to examine the changes that occur in postural metrics over time and explore the relationship between postural and cognitive dysfunction. The study group consisted of 35 people (66 ± 8years, 12 female, UPDRS III: 22.5 ± 9.6) diagnosed with PD who were recruited as part of the Incidence of Cognitive Impairment in Cohorts with Longitudinal Evaluation—PD Gait (ICICLE-GAIT) study. Postural and cognitive assessments were performed at 18, 36, and 54 months after enrolment. Participants stood still for 120 s, eyes open and arms by their side. Postural dynamics were measured using metrics derived from a single tri-axial accelerometer (Axivity AX3, York, UK) on the lower back. Accelerometry metrics included jerk (derivative of acceleration), root mean square, frequency, and ellipsis (acceleration area). Cognition was evaluated by neuropsychological tests including the Montreal Cognitive Assessment (MoCA) and digit span. There was a significant decrease in accelerometry parameters, greater in the anteroposterior direction, and a decline in cognitive function over time. Accelerometry metrics were positively correlated with lower cognitive function and increased geriatric depression score and negatively associated with a qualitative measure of balance confidence. In conclusion, people with PD showed reduced postural dynamics that may represent a postural safety strategy. Associations with cognitive function and depression, both symptoms that may pre-empt motor symptoms, suggest shared neural pathways. Further studies, involving neuroimaging, may determine how these postural parameters relate to underlying neural and clinical correlates.

Diagnostic biomarkers for Parkinson's disease at a glance: where are we?

Parkinson's disease (PD) is a neurodegenerative disorder whose aetiology remains unclear: degeneration involves several neurotransmission systems, resulting in a heterogeneous disease characterized by motor and non-motor symptoms. PD causes progressive disability that responds only to symptomatic therapies. Future advances include neuroprotective strategies for use in at-risk populations before the clinical onset of disease, hence the continuing need to identify reliable biomarkers that can facilitate the clinical diagnosis of PD. In this evaluative review, we summarize information on potential diagnostic biomarkers for use in the clinical and preclinical stages of PD.

Early Life Stress, Depression And Parkinson's Disease: A New Approach

This review aims to shed light on the relationship that involves exposure to early life stress, depression and Parkinson's disease (PD). A systematic literature search was conducted in Pubmed, MEDLINE, EBSCOHost and Google Scholar and relevant data were submitted to a meta-analysis . Early life stress may contribute to the development of depression and patients with depression are at risk of developing PD later in life. Depression is a common non-motor symptom preceding motor symptoms in PD. Stimulation of regions contiguous to the substantia nigra as well as dopamine (DA) agonists have been shown to be able to attenuate depression. Therefore, since PD causes depletion of dopaminergic neurons in the substantia nigra, depression, rather than being just a simple mood disorder, may be part of the pathophysiological process that leads to PD. It is plausible that the mesocortical and mesolimbic dopaminergic pathways that mediate mood, emotion, and/or cognitive function may also play a key role in depression associated with PD. Here, we propose that a medication designed to address a deficiency in serotonin is more likely to influence motor symptoms of PD associated with depression. This review highlights the effects of an antidepressant, Fluvoxamine maleate, in an animal model that combines depressive-like symptoms and Parkinsonism.

Differential microstructural alterations in rat cerebral cortex in a model of chronic mild stress depression

Chronic mild stress leads to depression in many cases and is linked to several debilitating diseases including mental disorders. Recently, neuronal tracing techniques, stereology, and immunohistochemistry have revealed persistent and significant microstructural alterations in the hippocampus, hypothalamus, prefrontal cortex, and amygdala, which form an interconnected system known as the stress circuit. Most studies have focused only on this circuit, however, some studies indicate that manipulation of sensory and motor systems may impact genesis and therapy of mood disorders and therefore these areas should not be neglected in the study of brain microstructure alterations in response to stress and depression. For this reason, we explore the microstructural alterations in different cortical regions in a chronic mild stress model of depression. The study employs ex-vivo diffusion MRI (d-MRI) to assess cortical microstructure in stressed (anhedonic and resilient) and control animals. MRI is followed by immunohistochemistry to substantiate the d-MRI findings. We find significantly lower extracellular diffusivity in auditory cortex (AC) of stress groups and a significantly higher fractional anisotropy in the resilient group. Neurite density was not found to be significantly higher in any cortical ROIs in the stress group compared to control, although axonal density is higher in the stress groups. We also report significant thinning of motor cortex (MC) in both stress groups. This is in agreement with recent clinical and preclinical studies on depression and similar disorders where significant microstructural and metabolic alterations were found in AC and MC. Our findings provide further evidence that the AC and MC are sensitive towards stress exposure and may extend our understanding of the microstructural effects of stress beyond the stress circuit of the brain. Progress in this field may provide new avenues of research to help in diagnosis and treatment intervention for depression and related disorders.

Cognitive and behavioral disorders in Parkinson's disease: an update. II: behavioral disorders

Patients with Parkinson's disease (PD) can experience several behavioral symptoms, such as apathy, agitation, hypersexuality, stereotypic movements, pathological gambling, abuse of antiparkinsonian drugs, and REM sleep behavioral disorders. Psychoses and hallucinations, depression and anxiety disorders, and difficulties in recognizing and experiencing emotions also impair behavior and can cause severe psychosocial problems in patients with PD. Symptoms can be present since early stages of the disease, sometimes even before the appearance of classical motor symptoms, likely in relation to dopamine depletion in basal ganglia and/or to dysfunctions of other neurotrasmitter systems, and others can develop later, in some cases in relation to dopaminergic treatment. In this paper, we review recent literature, with particular attention to the last 5 years, on the main behavioral and emotional disturbances described in PD patients as well as the hypothesized neurofunctional substrate of such impairments. Finally, we provide some suggestions on the most suitable instruments to check and assess PD-associated behavioral defects over time.

Neuropathology of Nonmotor Symptoms of Parkinson's Disease

Parkinson's disease (PD), a multiorgan neurodegenerative disorder associated with α-synuclein deposits throughout the nervous system and many organs, is clinically characterized by motor and nonmotor features, many of the latter antedating motor dysfunctions by 20 or more years. The causes of the nonmotor manifestations such as olfactory, autonomic, sensory, neuropsychiatric, visuospatial, sleep, and other disorders are unlikely to be related to single lesions. They are mediated by the involvement of both dopaminergic and nondopaminergic systems, and diverse structures outside the nigrostriatal system that is mainly responsible for the motor features of PD. The nonmotor alterations appear in early/prodromal stages of the disease and its further progression, suggesting a topographical and chronological spread of the lesions. This lends further support for the notion that PD is a multiorgan proteinopathy, although the exact relationship between presymptomatic and later developing nonmotor features of PD and neuropathology awaits further elucidation.

Non-human primate models of PD to test novel therapies

Non-human primate (NHP) models of Parkinson disease show many similarities with the human disease. They are very useful to test novel pharmacotherapies as reviewed here. The various NHP models of this disease are described with their characteristics including the macaque, the marmoset, and the squirrel monkey models. Lesion-induced and genetic models are described. There is no drug to slow, delay, stop, or cure Parkinson disease; available treatments are symptomatic. The dopamine precursor, L-3,4-dihydroxyphenylalanine (L-Dopa) still remains the gold standard symptomatic treatment of Parkinson. However, involuntary movements termed L-Dopa-induced dyskinesias appear in most patients after chronic treatment and may become disabling. Dyskinesias are very difficult to manage and there is only amantadine approved providing only a modest benefit. In this respect, NHP models have been useful to seek new drug targets, since they reproduce motor complications observed in parkinsonian patients. Therapies to treat motor symptoms in NHP models are reviewed with a discussion of their translational value to humans. Disease-modifying treatments tested in NHP are reviewed as well as surgical treatments. Many biochemical changes in the brain of post-mortem Parkinson disease patients with dyskinesias are reviewed and compare well with those observed in NHP models. Non-motor symptoms can be categorized into psychiatric, autonomic, and sensory symptoms. These symptoms are present in most parkinsonian patients and are already installed many years before the pre-motor phase of the disease. The translational usefulness of NHP models of Parkinson is discussed for non-motor symptoms.

Translocator Protein-18 kDa (TSPO) Positron Emission Tomography (PET) Imaging and Its Clinical Impact in Neurodegenerative Diseases

In vivo exploration of activated microglia in neurodegenerative diseases is achievable by Positron Emission Tomography (PET) imaging, using dedicated radiopharmaceuticals targeting the translocator protein-18 kDa (TSPO). In this review, we emphasized the major advances made over the last 20 years, thanks to TSPO PET imaging, to define the pathophysiological implication of microglia activation and neuroinflammation in neurodegenerative diseases, including Parkinson’s disease, Huntington’s disease, dementia, amyotrophic lateral sclerosis, multiple sclerosis, and also in psychiatric disorders. The extent and upregulation of TSPO as a molecular biomarker of activated microglia in the human brain is now widely documented in these pathologies, but its significance, and especially its protective or deleterious action regarding the disease’s stage, remains under debate. Thus, we exposed new and plausible suggestions to enhance the contribution of TSPO PET imaging for biomedical research by exploring microglia’s role and interactions with other cells in brain parenchyma. Multiplex approaches, associating TSPO PET radiopharmaceuticals with other biomarkers (PET imaging of cellular metabolism, neurotransmission or abnormal protein aggregates, but also other imaging modalities, and peripheral cytokine levels measurement and/or metabolomics analysis) was considered. Finally, the actual clinical impact of TSPO PET imaging as a routine biomarker of neuroinflammation was put into perspective regarding the current development of diagnostic and therapeutic strategies for neurodegenerative diseases.