Involvement of prelimbic 5-HT7 receptors in the regulation of anxiety-like behaviors in hemiparkinsonian rats

Recent advances in anxiety disorders: Focus on animal models and pathological mechanisms

Anxiety disorders have become one of the most severe psychiatric disorders, and the incidence is increasing every year. They impose an extraordinary personal and socioeconomic burden. Anxiety disorders are influenced by multiple complex and interacting genetic, psychological, social, and environmental factors, which contribute to disruption or imbalance in homeostasis and eventually cause pathologic anxiety. The selection of a suitable animal model is important for the exploration of disease etiology and pathophysiology, and the development of new drugs. Therefore, a more comprehensive understanding of the advantages and limitations of existing animal models of anxiety disorders is helpful to further study the underlying pathological mechanisms of the disease. This review summarizes animal models and the pathogenesis of anxiety disorders, and discusses the current research status to provide insights for further study of anxiety disorders.

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

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

Anxiety in synucleinopathies: neuronal circuitry, underlying pathomechanisms and current therapeutic strategies

Synucleinopathies are neurodegenerative disorders characterized by alpha-synuclein (αSyn) accumulation in neurons or glial cells, including Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). αSyn-related pathology plays a critical role in the pathogenesis of synucleinopathies leading to the progressive loss of neuronal populations in specific brain regions and the development of motor and non-motor symptoms. Anxiety is among the most frequent non-motor symptoms in patients with PD, but it remains underrecognized and undertreated, which significantly reduces the quality of life for patients. Anxiety is defined as a neuropsychiatric complication with characteristics such as nervousness, loss of concentration, and sweating due to the anticipation of impending danger. In patients with PD, neuropathology in the amygdala, a central region in the anxiety and fear circuitry, may contribute to the high prevalence of anxiety. Studies in animal models reported αSyn pathology in the amygdala together with alteration of anxiety or fear learning response. Therefore, understanding the progression, extent, and specifics of pathology in the anxiety and fear circuitry in synucleinopathies will suggest novel approaches to the diagnosis and treatment of neuropsychiatric symptoms. Here, we provide an overview of studies that address neuropsychiatric symptoms in synucleinopathies. We offer insights into anxiety and fear circuitry in animal models and the current implications for therapeutic intervention. In summary, it is apparent that anxiety is not a bystander symptom in these disorders but reflects early pathogenic mechanisms in the cortico-limbic system which may even contribute as a driver to disease progression.

Restoration and targeting of aberrant neurotransmitters in Parkinson's disease therapeutics

Neurotransmitters are considered as a fundamental regulator in the process of neuronal growth, differentiation and survival. Parkinson's Disease (PD) occurs due to extensive damage of dopamine-producing neurons; this causes dopamine deficits in the midbrain, followed by the alternation of various other neurotransmitters (glutamate, GABA, serotonin, etc.). It has been observed that fluctuation of neurotransmission in the basal ganglia exhibits a great impact on the pathophysiology of PD. Dopamine replacement therapy, such as the use of L-DOPA, can increase the dopamine level, but it majorly ameliorates the motor symptoms and is also associated with long-term complications (for e.g., LID). While the non-dopaminergic system can efficiently target non-motor symptoms, for instance, the noradrenergic system regulates the synthesis of BDNF via the MAPK pathway, which is important in learning and memory. Herein, we briefly discuss the role of different neurotransmitters, implementation of neurotransmitter receptors in PD. We also illustrate the recent advances of neurotransmitter-based drugs, which are currently under in vivo and clinical studies. Reinstating normal neurotransmitter levels has been believed to be advantageous in the treatment of PD. Thus, there is an increasing demand for drugs that can specifically target the neurotransmission system and reinstate the normal levels of neurotransmitters, which might prevent or delay neurodegeneration in PD.

Lesions of the lateral habenula produce anxiolytic effects in a rat model of Parkinson's disease

Objective: This study was designed to investigate the effects of lateral habenula (LHb) lesion on anxiety-like behaviors in parkinsonian rats.Methods: Anxiety-like behaviors were assessed by the open field and elevated plus maze (EPM) tests in control, medial forebrain bundle (MFB)-lesioned, MFB- and LHb-lesioned and MFB-lesioned and LHb sham-lesioned rats, respectively. The levels of extracellular dopamine (DA), serotonin (5-HT) and noradrenaline (NA) in the basolateral amygdala (BLA) were measured by in vivo microdialysis and neurochemistry.Results: Compared to control rats, MFB lesions in rats decreased the percentage of time spent in the central area in the open field test and the percentages of open arm time and open arm entries in the EPM test, indicating the induction of anxiety-like behaviors, and this lesion also decreased the level of extracellular DA in the BLA. Further, rats in the MFB + LHb lesion group showed increased percentage of time spent in the central area and the percentages of open arm time and open arm entries compared to rats in the MFB lesion group, suggesting anxiolytic effects after lesioning the LHb. Neurochemical results found that lesions of the LHb increased the levels of extracellular DA and 5-HT in the BLA in the MFB and LHb lesion groups, whereas NA level was not altered.Discussion: These findings suggest that depletion of DA plays an important role in anxiety-like behaviors, and lesions of the LHb produce anxiolytic responses in MFB-lesioned rats, which are related to increased levels of extracellular DA and 5-HT in the BLA.

5-HT7 receptors in Alzheimer's disease

Even though the involvement of serotonin (5-hydroxytryptamine; 5-HT) and its receptors in Alzheimer's disease (AD) is widely accepted, data on the expression and the role of 5-HT₇ receptors in AD is relatively limited. Therefore, the objective of the present work was to study the expression of serotonergic 5-HT₇ receptors in postmortem samples of AD brains and correlate it with neurotransmitter levels, cognition and behavior. The study population consisted of clinically well-characterized and neuropathologically confirmed AD patients (n = 42) and age-matched control subjects (n = 18). Reverse-transcription quantitative polymerase chain reaction (RT-qPCR) and high-performance liquid chromatography were performed on Brodmann area (BA) 7, BA10, BA22, BA24, hippocampus, amygdala, thalamus and cerebellum to measure mRNA levels of 5-HT₇ receptors (HTR7), as well as the concentrations of various monoamine neurotransmitters and their metabolites. Decreased levels of HTR7 mRNA were observed in BA10. A significant association was observed between HTR7 levels in BA10 and BEHAVE-AD cluster B (hallucinations) (rs(28) = 0.444, P < 0.05). In addition, a negative correlation was observed between HTR7 levels in BA10 and both MHPG concentrations in this brain region (rs(45) = -0.311; P < 0.05), and DOPAC levels in the amygdala (rs(42) = -0.311; P < 0.05). Quite surprisingly, no association was found between HTR7 levels and cognitive status. Altogether, this study supports the notion of the involvement of 5-HT₇ receptors in psychotic symptoms in AD, suggesting the interest of testing antagonist acting at this receptor to specifically treat psychotic symptoms in this illness.

Optimal Treatment of Depression and Anxiety in Parkinson's Disease

Depression and anxiety are highly prevalent and have major adverse effects on function and quality of life in Parkinson's disease (PD). Optimal management requires that motor symptoms and psychiatric symptoms be simultaneously addressed. While there is fairly robust evidence for the treatment of motor symptoms, there are no completed randomized controlled trials to guide pharmacological treatment of anxiety in PD and no nonpharmacologic interventions have proven efficacious. Several high-quality trials for depression in PD suggest a number of antidepressants and cognitive behavioral therapy may help, but there is no data on rates of recurrence, comparative efficacy, or augmentation strategies. In order to address the gaps in knowledge, the authors provide a summary of the current evidence for treating depression and anxiety in PD and offer an algorithm that extends beyond the current literature based on clinical experience working in a multidisciplinary specialty center.

Alpha-naphthylisothiocyanate-induced cholestatic mice display anxiety-like behavior closely related with enhanced serotoninergic signaling transduction in central nervous system

Cholestasis is a pathophysiological process caused by the damage of hepatocytes or obstruction of bile flow, which often leads to emotional disorder in central nervous system. Alpha-naphthylisothiocyanate (ANIT) is the most widely used chemical to induce cholestatic models; however, the neurobehavior of ANIT-induced cholestatic model has not been investigated. The present study was designed to evaluate the anxiety-like behavior of cholestatic mice induced by a single (i.p.) injection of ANIT and its potential mechanism. For validating the model, the alanine aminotransferase, glutamic oxaloacetic transaminase, alkaline phosphatase, and total bile acid in the serum of mice were detected, and the pathological sections of hepatic lobes were also observed. After that, a series of behavioral tests were used to detect the anxiety-like behavioral changes of the ANIT-induced cholestatic mice, and then the level of 5-hydroxytryptamine and 5-hydroxyindole acetic acid in serum and prefrontal cortex were detected. Our data showed that ANIT-induced cholestatic mice exhibited increased anxiety-like behaviors in the open-field test and elevated plus maze test. Moreover, the concentration of 5-hydroxyindole acetic acid significantly decreased in the serum and the prefrontal cortex of ANIT-induced cholestatic mice compared with the control group. In addition, the expression of 5-hydroxytryptamine 1A, 5-hydroxytryptamine 2C, 5-hydroxytryptamine 3A, and 5-hydroxytryptamine 7 receptors increased in the prefrontal cortex of the model mice compared to their controls. Our results suggest that ANIT-induced cholestatic mice can display anxiety-like behavior closely related with enhanced serotoninergic signaling transduction in central nervous system.

Anxiety in Parkinson's Disease: Correlation with Depression and Quality of Life

Introduction  Anxiety is common in patients with Parkinson's disease (PD). Its prevalence ranges from 20 to 40% but despite that, the high prevalence anxiety in PD is often undiagnosed and untreated. This research was aimed to study the pattern of anxiety with regard to its prevalence and risk factors and to establish the association of anxiety with depression and quality of life (QOL) in patients with PD. Methods  A total of 105 patients with PD were prospectively observed. Demographic and clinical variables were recorded and patients were assessed for anxiety (the Parkinson anxiety scale [PAS]), depression (geriatric depression scale [GDS]), and QOL (Parkinson's Disease Questionnaire-39 [PDQ-39]). Multiple forward logistic regression analysis was done for parameters showing association with anxiety. Pearson's correlation was used to calculate the strength of association of depression and QOL with anxiety. Results  Anxiety was present in 56 PD patients (53.3%). Episodic anxiety was noted in 50%, avoidance behavior in 35%, and persistent anxiety in 15% of these patients. There was significant association of anxiety with duration of disease ( p = 0.001), severity ( p < 0.005), levodopa equivalent dose (LED; p = 0.001), and tremor phenotype of PD ( p = 0.004). Anxiety coexisted with depression in 50 patients (79.4%), which was statistically significant in our cohort ( p = 0.001). There was significant linear relationship between the PAS and PDQ-39. Conclusion  Anxiety exerts a negative impact on the QOL as revealed by proportionately worsening PDQ-39 and PAS scores. Screening for anxiety will allow efficient delivery of support and treatment to patients with PD and their families.

Leite L, da S. Tavares-Henriques M, Lopes LAF, Oliveira LGR, Silva-Filho SE, da Silveira APS, Cuman RKN, de S. Silva-Comar FM, Comar JF, do A. Brasileiro L, dos Santos JN, de Freitas WR, Leão KV, da Silva JG, Klein RC, Klein MHF, da S. Ramos BH, Fernandes CKC, de L. Ribas DG, Oesterreich SA. Modulation of the Serotonergic Receptosome in the Treatment of Anxiety and Depression: A Narrative Review of the Experimental Evidence

Serotonin (5-HT) receptors are found throughout central and peripheral nervous systems, mainly in brain regions involved in the neurobiology of anxiety and depression. 5-HT receptors are currently promising targets for discovering new drugs for treating disorders ranging from migraine to neuropsychiatric upsets, such as anxiety and depression. It is well described in the current literature that the brain expresses seven types of 5-HT receptors comprising eighteen distinct subtypes. In this article, we comprehensively reviewed 5-HT1-7 receptors. Of the eighteen 5-HT receptors known today, thirteen are G protein-coupled receptors (GPCRs) and represent targets for approximately 40% of drugs used in humans. Signaling pathways related to these receptors play a crucial role in neurodevelopment and can be modulated to develop effective therapies to treat anxiety and depression. This review presents the experimental evidence of the modulation of the “serotonergic receptosome” in the treatment of anxiety and depression, as well as demonstrating state-of-the-art research related to phytochemicals and these disorders. In addition, detailed aspects of the pharmacological mechanism of action of all currently known 5-HT receptor families were reviewed. From this review, it will be possible to direct the rational design of drugs towards new therapies that involve signaling via 5-HT receptors.

Neuropsychiatric Disorders in Parkinson's Disease: What Do We Know About the Role of Dopaminergic and Non-dopaminergic Systems?

Besides the hallmark motor symptoms (rest tremor, hypokinesia, rigidity, and postural instability), patients with Parkinson’s disease (PD) have non-motor symptoms, namely neuropsychiatric disorders. They are frequent and may influence the other symptoms of the disease. They have also a negative impact on the quality of life of patients and their caregivers. In this article, we will describe the clinical manifestations of the main PD-related behavioral disorders (depression, anxiety disorders, apathy, psychosis, and impulse control disorders). We will also provide an overview of the clinical and preclinical literature regarding the underlying mechanisms with a focus on the role of the dopaminergic and non-dopaminergic systems.

Report from a multidisciplinary meeting on anxiety as a non-motor manifestation of Parkinson's disease

Anxiety is a severe problem for at least one-third of people living with Parkinson's disease (PD). Anxiety appears to have a greater adverse impact on quality of life than motor impairment. Despite its high prevalence and impact on daily life, anxiety is often undiagnosed and untreated. To better address anxiety in PD, future research must improve knowledge about the mechanism of anxiety in PD and address the lack of empirical evidence from clinical trials. In response to these challenges, the Parkinson's Foundation sponsored an expert meeting on anxiety on June 13th and 14th 2018. This paper summarizes the findings from that meeting informed by a review of the existing literature and discussions among patients, caregivers, and an international, clinician-scientist, expert panel working group. The goal is to provide recommendations to improve our understanding and treatment of anxiety in PD.

Activation and blockade of α2-adrenoceptors in the prelimbic cortex regulate anxiety-like behaviors in hemiparkinsonian rats

At present, whether α₂-adrenoceptors in the prelimbic cortex (PrL) are involved in Parkinson's disease-related anxiety is unclear. We examined the effects of PrL α₂-adrenoceptors on anxiety-like behaviors in rats with unilateral 6-hydroxydopamine lesions of the medial forebrain bundle. Compared to the sham operation, the lesion induced anxiety-like responses as measured by the open field test and elevated plus-maze test. Intra-PrL injection of the α₂-adrenoceptor agonist clonidine (1.25, 2.5 or 5 μg/rat) produced anxiolytic effects in sham-operated and lesioned rats. Furthermore, intra-PrL injection of the α₂-adrenoceptor antagonist idazoxan (1, 2 or 4 μg/rat) induced anxiogenic effects in two groups of rats. The effective doses produced by clonidine and idazoxan in lesioned rats were higher than those in sham-operated rats. Neurochemical results showed that intra-PrL injection of clonidine (5 μg/rat) or idazoxan (4 μg/rat) decreased or increased dopamine (DA) and noradrenaline (NA) and serotonin (5-HT) levels in the medial prefrontal cortex (mPFC) and amygdala in sham-operated and lesioned rats, respectively. These results suggest that α₂-adrenoceptors in the PrL are involved in the regulation of anxiety-like behaviors, which is attributable to changes in DA, NA and 5-HT levels in the mPFC and amygdala after activation and blockade of α₂-adrenoceptors.

Medial prefrontal cortex in neurological diseases

The medial prefrontal cortex (mPFC) is a crucial cortical region that integrates information from numerous cortical and subcortical areas and converges updated information to output structures. It plays essential roles in the cognitive process, regulation of emotion, motivation, and sociability. Dysfunction of the mPFC has been found in various neurological and psychiatric disorders, such as depression, anxiety disorders, schizophrenia, autism spectrum disorders, Alzheimer's disease, Parkinson's disease, and addiction. In the present review, we summarize the preclinical and clinical studies to illustrate the role of the mPFC in these neurological diseases.