The neuropathological basis of anxiety in Parkinson’s disease

A general clinical overview of the non-motor symptoms in Parkinson's disease: Neuropsychiatric symptoms

The heterogeneity of non-motor features observed in people with Parkinson's disease (PD) is often dominated by one or more symptoms belonging to the neuropsychiatric spectrum, such as cognitive impairment, psychosis, depression, anxiety, and apathy. Due to their high prevalence in people with PD (PwP) and their occurrence in every stage of the disease, from the prodromal to the advanced stage, it is not surprising that PD can be conceptualised as a complex neuropsychiatric disorder. Despite progress in understanding the pathophysiological mechanisms underlying the neuropsychiatric signs and symptoms in PD, and better identification and diagnosis of these symptoms, effective treatments are still a major unmet need. The impact of these symptoms on the quality of life of PwP and caregivers, as well as their contribution to the overall non-motor symptom burden can be greater than that of motor symptoms and require a personalised, holistic approach. In this chapter, we provide a general clinical overview of the major neuropsychiatric symptoms of PD.

Pathways from the Superior Colliculus to the Basal Ganglia

The present work aims to review the structural organization of the mammalian superior colliculus (SC), the putative pathways connecting the SC and the basal ganglia, and their role in organizing complex behavioral output. First, we review how the complex intrinsic connections between the SC's laminae projections allow for the construction of spatially aligned, visual-multisensory maps of the surrounding environment. Moreover, we present a summary of the sensory-motor inputs of the SC, including a description of the integration of multi-sensory inputs relevant to behavioral control. We further examine the major descending outputs toward the brainstem and spinal cord. As the central piece of this review, we provide a thorough analysis covering the putative interactions between the SC and the basal ganglia. To this end, we explore the diverse thalamic routes by which information from the SC may reach the striatum, including the pathways through the lateral posterior, parafascicular, and rostral intralaminar thalamic nuclei. We also examine the interactions between the SC and subthalamic nucleus, representing an additional pathway for the tectal modulation of the basal ganglia. Moreover, we discuss how information from the SC might also be relayed to the basal ganglia through midbrain tectonigral and tectotegmental projections directed at the substantia nigra compacta and ventrotegmental area, respectively, influencing the dopaminergic outflow to the dorsal and ventral striatum. We highlight the vast interplay between the SC and the basal ganglia and raise several missing points that warrant being addressed in future studies.

Serotonin and dopamine depletion in distinct brain regions may cause anxiety in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated mice as a model of early Parkinson's disease

In this study, we aimed to evaluate the association of early anxious behavior with serotonin, dopamine, and their metabolites in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) murine model of Parkinson's disease. Forty C57BL/6 male mice were randomly divided into the control group (n = 20) and the model group (n = 20). Mice in the model group were injected intraperitoneally with MPTP. The light-dark box (LDB) and elevated plus-maze were used to monitor anxious behavior. The association of early anxious behavior with neurotransmitters in the prefrontal cortex, hippocampus, and striatum was evaluated. In our murine model, MPTP induced a decreased level of 5-hydroxytryptamine and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the prefrontal cortex, hippocampus, and striatum (all P < 0.05); however, it only induced a decreased level of dopamine and its metabolite homovanillic acid (HVA) in the striatum (both P < 0.001), with a negative correlation in the hippocampus and a positive correlation in the cortex and striatum. In the LDB, 5-hydroxytryptamine levels in the cortex and dopamine and HVA levels in the striatum were negatively correlated with anxious behavior. Moreover, in the elevate plus-maze, 5-hydroxytryptamine and 5-HIAA in the cortex and dopamine and HVA in the striatum were positively correlated with the ratio of the time spent in open arms. In the murine model of early Parkinson's disease, the balance between dopamine and 5-hydroxytryptamine systems varied among brain regions. The depletion of 5-hydroxytryptamine in the cortex and dopamine in the striatum may be associated with anxiety behaviors in MPTP-treated mice.

Predictors of anxiety in Parkinson's disease: results from a 3-year longitudinal cohort study

INTRODUCTION

Anxiety symptoms are the most common neuropsychiatric manifestation of Parkinson's disease (PD), contributing to decreased quality of life. Few longitudinal studies in PD samples have examined correlates of anxiety symptoms over time. Understanding predictor variables may help to identify novel targets for reducing anxiety in PD. The aim of this study was to identify predictors of anxiety symptoms over 3 years in a clinic-based PD cohort.

METHODS

Our cohort included patients with PD at an academic medical center in the Southeastern United States (n = 105). Visits included assessment of motor, psychiatric, and cognitive features, including neuropsychological testing. For our multivariate model, we selected 11 predictor variables with the most existing evidence or theoretical support for an association with anxiety symptoms in PD. Multivariate linear mixed model regression was performed to determine which variables were significantly associated with anxiety symptoms over time.

RESULTS

Over half of participants (57%) met the screening threshold for an anxiety disorder at some point during the study. Independent predictors of anxiety symptoms over time included symptoms of REM sleep behavior disorder (RBD) and dysautonomia.

DISCUSSION

In this PD sample, RBD and dysautonomia symptoms were significantly associated with anxiety symptoms over time. Each of these relationships has been reported in one of two prior longitudinal studies. Unlike prior studies, cognitive impairment was not a significant predictor of anxiety symptoms in our sample. Future research should confirm the direction and mechanisms underlying these relationships, including the potential for anxiety symptom reduction through treatment for RBD and dysautonomia.

Apathy and impulsiveness in Parkinson disease: Two faces of the same coin?

Apathy and impulsiveness are 2 common non-motor symptoms in Parkinson disease that could occur in different periods or simultaneously. Apathy and impulsiveness could be interpreted as opposite extremes of a spectrum of motivated behavior dependent on dopaminergic dysfunction, in which, impulsivity, is a result of a hyperdopaminergic state, whereas apathy is viewed as a hypodopaminergic. The study aimed to investigate the presence of impulsiveness and other neuropsychiatric symptoms in Parkinson disease patients with apathy symptoms. Eighty-one patients with Parkinson disease were enrolled in this retrospective study. All subjects were evaluated by the Italian version of the Dimensional Apathy Scale and the Barratt Impulsiveness Scale-version 11, to assess, respectively, apathy and impulsiveness; they were divided into 2 groups (apathy and no apathy). All patients were administered also with questionnaires assessing depressive and anxious symptoms. Statistical analyses showed relevant results. In no-apathy group, education was a significant predictor on impulsiveness (attentional and motor) and apathy (executive and emotional); depression was a significant predictor on planning impulsivity and apathy. This study aimed to consider the importance of apathy and impulsivity in Parkinson disease. Although these are considered as opposite extremes of a spectrum of motivated behavior dependent on dopaminergic dysfunction, these can also occur separately. Moreover, several variables could represent important predictors of apathy and impulsiveness, such as depression. Future investigations should deepen the role of other demographics and psychological variables.

Striatal Injury Induces Overall Brain Alteration at the Pallial, Thalamic, and Cerebellar Levels

Simple Summary

Magnetic resonance imaging showed that striatal injury leads to structural changes within several brain areas. Here, we specify these changes via gene expression of synaptic plasticity markers, neuronal markers, assessing the number of newborn cells as well as cell densities. We found that the injury resulted in long-lasting modifications involving plasticity and neural protection mechanisms in areas directly as well as indirectly connected with the damaged striatum, including the cerebellum.

Abstract

The striatal region Area X plays an important role during song learning, sequencing, and variability in songbirds. A previous study revealed that neurotoxic damage within Area X results in micro and macrostructural changes across the entire brain, including the downstream dorsal thalamus and both the upstream pallial nucleus HVC (proper name) and the deep cerebellar nuclei (DCN). Here, we specify these changes on cellular and gene expression levels. We found decreased cell density in the thalamic and cerebellar areas and HVC, but it was not related to neuronal loss. On the contrary, perineuronal nets (PNNs) in HVC increased for up to 2 months post-lesion, suggesting their protecting role. The synaptic plasticity marker Forkhead box protein P2 (FoxP2) showed a bi-phasic increase at 8 days and 3 months post-lesion, indicating a massive synaptic rebuilding. The later increase in HVC was associated with the increased number of new neurons. These data suggest that the damage in the striatal vocal nucleus induces cellular and gene expression alterations in both the efferent and afferent destinations. These changes may be long-lasting and involve plasticity and neural protection mechanisms in the areas directly connected to the injury site and also to distant areas, such as the cerebellum.

Metabolomics profiling reveals altered lipid metabolism and identifies a panel of lipid metabolites as biomarkers for Parkinson's disease related anxiety disorder

OBJECTIVES

Anxiety disorder is a common non-motor symptom in patient with Parkinson's disease (PD). We aimed to explore its pathogenesis and identify plasma biomarkers using untargeted metabolomics analysis.

METHODS

Consecutive PD patients and healthy controls were recruited. Clinical data were assessed and patients with Parkinson's disease related anxiety disorder (PDA) were recognized. Fast plasma samples were obtained and untargeted liquid chromatography-mass spectrometry-based metabolomics analysis was performed. Based on the differentially expressed metabolites from the above metabolomics analysis, correlation analyses and receiver operating characteristic curves (ROC) were further employed.

RESULTS

According to the clinical data, PDA patients had lower plasma levels of total cholesterol, triglyceride, low-density lipoprotein cholesterol, and apolipoprotein B. There were thirty-nine differentially expressed metabolites in PDA patients when compared with the other two groups from the metabolomics analysis, respectively. Fourteen lipid metabolites were simultaneously altered between these two groups, and all of them were significantly decreased. They can be further subcategorized into fatty acyls, glycerolipids, sterol lipids, sphingolipids, and prenol lipids. The plasma levels of thirteen metabolites were negatively correlated with HAMA scores except 10-oxo-nonadecanoic acid. Based on the ROC curves, the fourteen lipid metabolites can be diagnostic biomarkers for PDA patients separately and the areas under the curve of the fourteen lipid metabolites ranged from 0.681 to 0.798.

CONCLUSIONS

Significantly lower plasma lipoproteins can be found in PDA patients. A panel of fourteen lipid metabolites were also significantly decreased and can be clinical biomarkers for the diagnosis of PDA patients.