Increased 5-HT2Areceptors in the temporal cortex of parkinsonian patients with visual hallucinations

Positive allosteric mGluR2 modulation with BINA alleviates dyskinesia and psychosis-like behaviours in the MPTP-lesioned marmoset

There is mounting evidence that positive allosteric modulation of metabotropic glutamate type 2 receptors (mGluR2) is an efficacious approach to reduce the severity of L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia, psychosis-like behaviours (PLBs), while conferring additional anti-parkinsonian benefit. However, the mGluR2 positive allosteric modulators (PAMs) tested so far, LY-487,379 and CBiPES, share a similar chemical scaffold. Here, we sought to assess whether similar benefits would be conferred by a structurally-distinct mGluR2 PAM, biphenylindanone A (BINA). Six 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmosets exhibiting dyskinesia and PLBs were administered L-DOPA with either vehicle or BINA (0.1, 1, and 10 mg/kg) in a randomised within-subject design and recorded. Behaviour was analysed by a blinded rater who scored the severity of each of parkinsonism, dyskinesia and PLBs. When added to L-DOPA, BINA 0.1 mg/kg, 1 mg/kg, and 10 mg/kg all significantly reduced the severity of global dyskinesia, by 40%, 52% and 53%, (all P < 0.001) respectively. BINA similarly attenuated the severity of global PLBs by 35%, 48%, and 50%, (all P < 0.001) respectively. Meanwhile, BINA did not alter the effect of L-DOPA on parkinsonism exhibited by the marmosets. The results of this study provide incremental evidence of positive allosteric modulation of mGluR2 as an effective therapeutic strategy for alleviating dyskinesia and PLBs, without hindering the anti-parkinsonian action of L-DOPA. Furthermore, this therapeutic benefit does not appear to be confined to a particular chemical scaffold.

CX3CR1 mediates motor dysfunction in mice through 5-HTR2a

CX3CR1 knockout could induce motor dysfunction in several neurological disease models mainly through regulating microglia's function. While CX3CR1 was expressed on neurons in a few reports, whether neuronal CX3CR1 could affect the function of neurons and mediate motor dysfunction under physiological conditions is unknown. To elucidate the roles of neuronal CX3CR1 on motor dysfunction, CX3CR1 knockout mice were created. Rotarod test and Open field test found that the CX3CR1-/- mice's motor capacity was reduced. Immunofluorescence staining detected the expression of CX3CR1 in neurons both in vivo and in vitro. Immunohistochemistry and West blot found that knockout of CX3CR1 did not affect the neurons' number in both spinal cord and brain of mice. While inhibiting the function of CX3CR1 by AZD8797 could decrease the expression of 5-Hydroxytryptamine receptor(5-HTR2a), which involved in the regulation of motor function. Further investigation revealed that CX3CR1 regulated the expression of HTR2a through the NF-κB pathway. For the first time, we reported that neuronal CXCR1 mediates motor dysfunction. Our results suggest that modulating CXCR1 activity offers a novel therapeutic strategy for motor dysfunction.

Parkinson disease psychosis: from phenomenology to neurobiological mechanisms

Parkinson disease (PD) psychosis (PDP) is a spectrum of illusions, hallucinations and delusions that are associated with PD throughout its disease course. Psychotic phenomena can manifest from the earliest stages of PD and might follow a continuum from minor hallucinations to structured hallucinations and delusions. Initially, PDP was considered to be a complication associated with dopaminergic drug use. However, subsequent research has provided evidence that PDP arises from the progression of brain alterations caused by PD itself, coupled with the use of dopaminergic drugs. The combined dysfunction of attentional control systems, sensory processing, limbic structures, the default mode network and thalamocortical connections provides a conceptual framework to explain how new incoming stimuli are incorrectly categorized, and how aberrant hierarchical predictive processing can produce false percepts that intrude into the stream of consciousness. The past decade has seen the publication of new data on the phenomenology and neurobiological basis of PDP from the initial stages of the disease, as well as the neurotransmitter systems involved in PDP initiation and progression. In this Review, we discuss the latest clinical, neuroimaging and neurochemical evidence that could aid early identification of psychotic phenomena in PD and inform the discovery of new therapeutic targets and strategies.

Effect of the mGlu4 positive allosteric modulator ADX-88178 on parkinsonism, psychosis-like behaviours and dyskinesia in the MPTP-lesioned marmoset

RATIONALE

Positive allosteric modulation of metabotropic glutamate type 4 (mGlu4) receptors is a promising strategy to alleviate parkinsonian disability and L-3,4-dihydroxyphenylalanine (L-DOPA) induced dyskinesia. ADX-88178 is a highly selective mGlu4 positive allosteric modulator (PAM) that previously enhanced the anti-parkinsonian action of L-DOPA in the 6-hydroxydopamine-lesioned rat model of Parkinson's disease (PD).

OBJECTIVES

We sought to explore the effects of ADX-88178 on psychosis-like behaviours (PLBs) in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmoset. We also aimed to determine the effect of ADX-88178 on parkinsonism and dyskinesia.

METHODS

Six MPTP-lesioned marmosets were administered L-DOPA chronically to induce stable PLBs and dyskinesias. They were then administered ADX-88178 (0.01, 0.1 and 1 mg/kg) or vehicle, in combination with L-DOPA/benserazide (15/3.75 mg/kg), both sub-cutaneously, in a randomised fashion. PLBs, parkinsonism and dyskinesia were then measured.

RESULTS

ADX-88178 mildly worsened global PLBs at the dose of 1 mg/kg (by 13%, P = 0.020). L-DOPA alone conferred 158 min of on-time, while the duration of on-time was 212 min (34% increase, P = 0.011), after adding ADX-88178 1 mg/kg to L-DOPA. Accordingly, ADX-88178 1 mg/kg reduced global parkinsonian disability, by 38% (P = 0.0096). ADX-88178 1 mg/kg diminished peak dose dyskinesia by 34% (P = 0.015). Minimal effects were provided by lower doses.

CONCLUSIONS

Whereas these results provide additional evidence of the anti-parkinsonian and anti-dyskinetic effects of mGlu4 positive allosteric modulation as an adjunct to L-DOPA, they also suggest that ADX-88178 may exacerbate dopaminergic psychosis. Further studies are needed to evaluate this possible adverse effect of mGlu4 PAMs on PD psychosis.

Modelling perception as a hierarchical competition differentiates imagined, veridical, and hallucinated percepts

Mental imagery is a process by which thoughts become experienced with sensory characteristics. Yet, it is not clear why mental images appear diminished compared to veridical images, nor how mental images are phenomenologically distinct from hallucinations, another type of non-veridical sensory experience. Current evidence suggests that imagination and veridical perception share neural resources. If so, we argue that considering how neural representations of externally generated stimuli (i.e. sensory input) and internally generated stimuli (i.e. thoughts) might interfere with one another can sufficiently differentiate between veridical, imaginary, and hallucinatory perception. We here use a simple computational model of a serially connected, hierarchical network with bidirectional information flow to emulate the primate visual system. We show that modelling even first approximations of neural competition can more coherently explain imagery phenomenology than non-competitive models. Our simulations predict that, without competing sensory input, imagined stimuli should ubiquitously dominate hierarchical representations. However, with competition, imagination should dominate high-level representations but largely fail to outcompete sensory inputs at lower processing levels. To interpret our findings, we assume that low-level stimulus information (e.g. in early visual cortices) contributes most to the sensory aspects of perceptual experience, while high-level stimulus information (e.g. towards temporal regions) contributes most to its abstract aspects. Our findings therefore suggest that ongoing bottom-up inputs during waking life may prevent imagination from overriding veridical sensory experience. In contrast, internally generated stimuli may be hallucinated when sensory input is dampened or eradicated. Our approach can explain individual differences in imagery, along with aspects of daydreaming, hallucinations, and non-visual mental imagery.

Grey matter volume loss in Parkinson's disease psychosis and its relationship with serotonergic gene expression: A meta-analysis

BACKGROUND

Neuroanatomical alterations underlying psychosis in Parkinson's Disease (PDP) remain unclear. We carried out a meta-analysis of MRI studies investigating the neural correlates of PDP and examined its relation with dopaminergic and serotonergic receptor gene expression.

METHODS

PubMed, Web of Science and Embase were searched for MRI studies (k studies = 10) of PDP compared to PD patients without psychosis (PDnP). Seed-based d Mapping with Permutation of Subject Images and multiple linear regression analyses was used to examine the relationship between pooled estimates of grey matter volume (GMV) loss in PDP and D1/D2 and 5-HT1a/5-HT2a receptor gene expression estimates from Allen Human Brain Atlas.

RESULTS

We observed lower grey matter volume in parietal-temporo-occipital regions (PDP n = 211, PDnP, n = 298). GMV loss in PDP was associated with local expression of 5-HT1a (b = 0.109, p = 0.012) and 5-HT2a receptors (b= -0.106, p = 0.002) but not dopaminergic receptors.

CONCLUSION

Widespread GMV loss in the parieto-temporo-occipital regions may underlie PDP. Association between grey matter volume and local expression of serotonergic receptor genes may suggest a role for serotonergic receptors in PDP.

The Role of α-Synuclein in the Regulation of Serotonin System: Physiological and Pathological Features

In patients affected by Parkinson's disease (PD), up to 50% of them experience cognitive changes, and psychiatric disturbances, such as anxiety and depression, often precede the onset of motor symptoms and have a negative impact on their quality of life. Pathologically, PD is characterized by the loss of dopamine (DA) neurons in the substantia nigra pars compacta (SNc) and the presence of intracellular inclusions, called Lewy bodies and Lewy neurites, composed mostly of α-synuclein (α-Syn). Much of PD research has focused on the role of α-Syn aggregates in the degeneration of SNc DA neurons due to the impact of striatal DA deficits on classical motor phenotypes. However, abundant Lewy pathology is also found in other brain regions including the midbrain raphe nuclei, which may contribute to non-motor symptoms. Indeed, dysfunction of the serotonergic (5-HT) system, which regulates mood and emotional pathways, occurs during the premotor phase of PD. However, little is known about the functional consequences of α-Syn inclusions in this neuronal population other than DA neurons. Here, we provide an overview of the current knowledge of α-Syn and its role in regulating the 5-HT function in health and disease. Understanding the relative contributions to α-Syn-linked alterations in the 5-HT system may provide a basis for identifying PD patients at risk for developing depression and could lead to a more targeted therapeutic approach.

Characterizing the relationship between L-DOPA-induced-dyskinesia and psychosis-like behaviors in a bilateral rat model of Parkinson's disease

Parkinson's disease associated psychosis (PDAP) is a prevalent non-motor symptom (NMS) that significantly erodes patients' and caregivers' quality of life yet remains vastly understudied. One potential source of PDAP in late-stage Parkinson's disease (PD) is the common dopamine (DA) replacement therapy for motor symptoms, Levodopa (L-DOPA). Given the high incidence of L-DOPA-induced dyskinesia (LID) in later phases of PD, this study sought to characterize the relationship between PDAP and LID in a bilateral medial forebrain bundle 6-hydroxydopamine hydrobromide (6-OHDA) lesion rat model. To assess PDAP in this model, prepulse inhibition (PPI), a well-validated assay of sensorimotor gating, was employed. First, we tested whether a bilateral lesion alone or after chronic L-DOPA treatment was sufficient to induce PPI dysfunction. Rats were also monitored for LID development, using the abnormal involuntary movements (AIMs) test, to examine PPI and LID associations. In experiment 2, Vilazodone (VZD), a serotonin transporter (SERT) blocker and 1A receptor (5-HT_1A) partial agonist was administered to test its potential efficacy in reducing LID and PPI dysfunction. Once testing was complete, tissue was collected for high performance liquid chromatography (HPLC) to examine the monoamine levels in motor and non-motor circuits. Results indicate that bilateral DA lesions produced motor deficits and that chronic L-DOPA induced moderate AIMs; importantly, rats that developed more severe AIMs were more likely to display sensorimotor gating dysfunction. In addition, VZD treatment dose-dependently reduced L-DOPA-induced AIMs without impairing L-DOPA efficacy, although VZD's effects on PPI were limited. Altogether, this project established the bilateral 6-OHDA lesion model accurately portrayed LID and PDAP-like behaviors, uncovered their potential relationship, and finally, demonstrated the utility of VZD for reducing LID.

Role of Pimavanserin Treatment-Continuity on Discharge From Long-term Care: Assessing the Quality of Antipsychotic Medication Review

Objective: To investigate the role of (1) antipsychotic medication review (AP-MR) documentation quality of Minimum Data Set 3.0 (MDS) surveys, and (2) treatment-continuity on discharge-to-community and clinical outcomes among long-term care (LTC) residents treated with pimavanserin. Design, Setting, and Participants: A retrospective cohort analysis of Parts A, B, and D claims from Medicare 100% sample merged with MDS data from June 2016 through December 2018 was conducted. Residents with more than 100-day LTC stay and 1 pimavanserin prescription or more with completed antipsychotic-use MDS question were selected. AP-MR documentation quality (ie, gradual dose reduction [GDR] attempts, clinical contraindication to GDR), discharge-to-community, and clinical outcomes (eg, falls, fractures) were obtained from MDS. Treatment-continuity was assessed from Part D claims. Data Analysis: Descriptive statistics (frequencies, proportions, Chi-square tests, and means) and adjusted logistic regressions (ORs with 95% CIs reported association between pimavanserin treatment-continuity and discharge-to-community. Results: Of 4,021 eligible residents, 29% (n = 1,182) attempted a GDR per AP-MR MDS documentation. Approximately 41% (n = 1,665) had documentation showing GDR was clinically contraindicated, yet 39% (n = 645) still attempted GDR. While overall discharge-to-community rates were low, it was significantly higher (P < 0.05) among LTC residents continuing (14.94%; n = 380/2,546) versus discontinuing (11.84%; n = 171/1,444) pimavanserin. OR for treatment-continuity was 1.96, 95% CI 1.50-2.55. Residents continuing pimavanserin had lower incidents of falls (2.8% vs 9.4%), hip fractures (0.29% vs 0.69%), and pelvic/femur fractures (0% vs 0.92%) versus those residents who discontinued it. Conclusions: Among LTC-stay residents, high discordance between GDR rates and AP-MR MDS documentation quality was observed. Pimvanserin treatment-continuity showed greater likelihood of discharge-to-community; continued documentation training can ensure appropriate antipsychotic use with a balanced benefit:risk profile.

Emerging role of psychosis in Parkinson's disease: From clinical relevance to molecular mechanisms

Parkinson’s disease (PD) is the second most common neurodegenerative disease. Psychosis is one of the common psychiatric presentations in the natural course of PD. PD psychosis is an important non-motor symptom, which is strongly correlated with a poor prognosis. Increasing attention is being given to PD psychosis. In this opinion review, we summarized and analyzed the identification, screening, epidemiology, mechanisms, risk factors, and therapeutic approaches of PD psychosis based on the current clinical evidence. PD psychosis tends to have a negative effect on patients' quality of life and increases the burden of family caregiving. Screening and identification in the early stage of disease is crucial for establishing tailored therapeutic strategies and predicting the long-term outcome. Development of PD psychosis is believed to involve a combination of exogenous and endogenous mechanisms including imbalance of neurotransmitters, structural and network changes, genetic profiles, cognitive impairment, and antiparkinsonian medications. The therapeutic strategy for PD psychosis includes reducing or ceasing the use of dopaminergic drug, antipsychotics, cholinesterase inhibitors, and non-pharmacological interventions. Ongoing clinical trials are expected to provide new insights for tailoring therapy for PD psychosis. Future research based on novel biomarkers and genetic factors may help inform individualized therapeutic strategies.

Changes in dynamic transitions between integrated and segregated states underlie visual hallucinations in Parkinson's disease

Hallucinations are a core feature of psychosis and common in Parkinson's. Their transient, unexpected nature suggests a change in dynamic brain states, but underlying causes are unknown. Here, we examine temporal dynamics and underlying structural connectivity in Parkinson's-hallucinations using a combination of functional and structural MRI, network control theory, neurotransmitter density and genetic analyses. We show that Parkinson's-hallucinators spent more time in a predominantly Segregated functional state with fewer between-state transitions. The transition from integrated-to-segregated state had lower energy cost in Parkinson's-hallucinators; and was therefore potentially preferable. The regional energy needed for this transition was correlated with regional neurotransmitter density and gene expression for serotoninergic, GABAergic, noradrenergic and cholinergic, but not dopaminergic, receptors. We show how the combination of neurochemistry and brain structure jointly shape functional brain dynamics leading to hallucinations and highlight potential therapeutic targets by linking these changes to neurotransmitter systems involved in early sensory and complex visual processing.

Cognition and serotonin in Parkinson's disease

Cognitive impairment affects up to 80% of patients with Parkinson's disease (PD) and is associated with poor quality of life. PD cognitive dysfunction includes poor working memory, impairments in executive function and difficulty in set-shifting. The pathophysiology underlying cognitive impairment in PD is still poorly understood, but there is evidence to support involvements of the cholinergic, dopaminergic, and noradrenergic systems. Only rivastigmine, an acetyl- and butyrylcholinesterase inhibitor, is efficacious for the treatment of PD dementia, which limits management of cognitive impairment in PD. Whereas the role of the serotonergic system in PD cognition is less understood, through its interactions with other neurotransmitters systems, namely, the cholinergic system, it may be implicated in cognitive processes. In this chapter, we provide an overview of the pharmacological, clinical and pathological evidence that implicates the serotonergic system in mediating cognition in PD.

Dementia-related psychosis and the potential role for pimavanserin

Dementia-related psychosis (DRP) is prevalent across dementias and typically manifests as delusions and/or hallucinations. The mechanisms underlying psychosis in dementia are unknown; however, neurobiological and pharmacological evidence has implicated multiple signaling pathways and brain regions. Despite differences in dementia pathology, the neurobiology underlying psychosis appears to involve dysregulation of a cortical and limbic pathway involving serotonergic, gamma-aminobutyric acid ergic, glutamatergic, and dopaminergic signaling. Thus, an imbalance in cortical and mesolimbic excitatory tone may drive symptoms of psychosis. Delusions and hallucinations may result from (1) hyperactivation of pyramidal neurons within the visual cortex, causing visual hallucinations and (2) hyperactivation of the mesolimbic pathway, causing both delusions and hallucinations. Modulation of the 5-HT2A receptor may mitigate hyperactivity at both psychosis-associated pathways. Pimavanserin, an atypical antipsychotic, is a selective serotonin inverse agonist/antagonist at 5-HT2A receptors. Pimavanserin may prove beneficial in treating the hallucinations and delusions of DRP without worsening cognitive or motor function.

Mapping brain structural differences and neuroreceptor correlates in Parkinson's disease visual hallucinations

Parkinson's psychosis (PDP) describes a spectrum of symptoms that may arise in Parkinson's disease (PD) including visual hallucinations (VH). Imaging studies investigating the neural correlates of PDP have been inconsistent in their findings, due to differences in study design and limitations of scale. Here we use empirical Bayes harmonisation to pool together structural imaging data from multiple research groups into a large-scale mega-analysis, allowing us to identify cortical regions and networks involved in VH and their relation to receptor binding. Differences of morphometrics analysed show a wider cortical involvement underlying VH than previously recognised, including primary visual cortex and surrounding regions, and the hippocampus, independent of its role in cognitive decline. Structural covariance analyses point to the involvement of the attentional control networks in PD-VH, while associations with receptor density maps suggest neurotransmitter loss may be linked to the cortical changes.

Effect of the glycine transporter 1 inhibitor ALX-5407 on dyskinesia, psychosis-like behaviours and parkinsonism in the MPTP-lesioned marmoset

Dyskinesia and psychosis are complications encountered in advanced Parkinson's disease (PD) following long-term therapy with L-3,4-dihydroxyphenylalanine (L-DOPA). Disturbances in the glutamatergic system have been associated with both dyskinesia and psychosis, making glutamatergic modulation a potential therapeutic approach for these. Treatments thus far have sought to dampen glutamatergic transmission, for example through blockade of N-methyl-D-aspartate (NMDA) receptors or modulation of metabotropic glutamate receptors 5. In contrast, activation of the glycine-binding site on NMDA receptors is required for their physiological response. Here, we investigated whether indirectly enhancing glutamatergic transmission through inhibition of glycine re-uptake would be efficacious in diminishing both dyskinesia and psychosis-like behaviours (PLBs) in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned common marmoset. Six marmosets were rendered parkinsonian by MPTP injection. Following repeated administration of L-DOPA to induce dyskinesia and PLBs, they underwent acute challenges of the glycine transporter 1 (GlyT₁) inhibitor ALX-5407 (0.01, 0.1 and 1 mg/kg) or vehicle, in combination with L-DOPA, after which the severity of dyskinesia, PLBs and parkinsonian disability was evaluated. In combination with L-DOPA, ALX-5407 0.1 and 1 mg/kg significantly reduced the severity of dyskinesia, by 51% and 41% (both P < 0.001), when compared to vehicle. ALX-5407 0.01, 0.1 and 1 mg/kg also decreased the severity of global PLBs, by 25%, 51% and 38% (all P < 0.001), when compared to vehicle. The benefits on dyskinesia and PLBs were achieved without compromising the therapeutic effect of L-DOPA on parkinsonism. Our results suggest that GlyT₁ inhibition may be a novel strategy to attenuate dyskinesia and PLBs in PD, without interfering with L-DOPA anti-parkinsonian action.

The Aversion Function of the Limbic Dopaminergic Neurons and Their Roles in Functional Neurological Disorders

The Freudian theory of conversion suggested that the major symptoms of functional neurological disorders (FNDs) are due to internal conflicts at motivation, especially at the sex drive or libido. FND patients might behave properly at rewarding situations, but they do not know how to behave at aversive situations. Sex drive is the major source of dopamine (DA) release in the limbic area; however, the neural mechanism involved in FND is not clear. Dopaminergic (DAergic) neurons have been shown to play a key role in processing motivation-related information. Recently, DAergic neurons are found to be involved in reward-related prediction error, as well as the prediction of aversive information. Therefore, it is suggested that DA might change the rewarding reactions to aversive reactions at internal conflicts of FND. So DAergic neurons in the limbic areas might induce two major motivational functions: reward and aversion at internal conflicts. This article reviewed the recent advances on studies about DAergic neurons involved in aversive stimulus processing at internal conflicts and summarizes several neural pathways, including four limbic system brain regions, which are involved in the processing of aversion. Then the article discussed the vital function of these neural circuits in addictive behavior, depression treatment, and FNDs. In all, this review provided a prospect for future research on the aversion function of limbic system DA neurons and the therapy of FNDs.

Additive effects of mGluR2 positive allosteric modulation, mGluR2 orthosteric stimulation and 5-HT2AR antagonism on dyskinesia and psychosis-like behaviours in the MPTP-lesioned marmoset

PURPOSE

Antagonising serotonin (5-HT) type 2A receptors (5-HT_2AR) is an effective strategy to alleviate both dyskinesia and psychosis in Parkinson's disease (PD). We have recently shown that activation of metabotropic glutamate 2 receptors (mGluR₂), via either orthosteric stimulation or positive allosteric modulation, enhances the anti-dyskinetic and anti-psychotic effects of 5-HT_2AR antagonism. Here, we investigated if greater therapeutic efficacy would be achieved by combining 5-HT_2AR antagonism with concurrent mGluR₂ orthosteric stimulation and mGluR₂ positive allosteric modulation.

METHODS

Five 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmosets exhibiting dyskinesia and psychosis-like behaviours (PLBs) were administered L-3,4-dihydroxyphenylalanine (L-DOPA) in combination with vehicle or the 5-HT_2AR antagonist EMD-281,014. EMD-281,014 was itself administered alone or with the mGluR₂ orthosteric agonist (OA) LY-354,740, the mGluR₂ positive allosteric modulator (PAM) LY-487,379 and combination thereof, after which the severity of dyskinesia, PLBs and parkinsonism was rated.

RESULTS

EMD-281,014 reduced dyskinesia and PLBs by up to 47% and 40%, respectively (both P < 0.001). The addition of LY-354,740, LY-487,379 and LY-354,740/LY-487,379 decreased dyskinesia by 56%, 65% and 77%, while PLBs were diminished by 55%, 63% and 71% (all P < 0.001). All treatment combinations provided anti-dyskinetic and anti-psychotic benefits significantly greater than those conferred by EMD-281,014 alone (all P < 0.05). The combination of EMD-281,014/LY-354,740/LY-487,379 resulted in anti-dyskinetic and anti-psychotic effects significantly greater than those conferred by EMD-281,014 with either LY-354,740 or LY-487,379 (both P < 0.05). No deleterious effects on L-DOPA anti-parkinsonian action were observed.

CONCLUSION

Our results suggest that combining 5-HT_2AR antagonism with mGluR₂ activation results in greater reduction of L-DOPA-induced dyskinesia and PD psychosis. They also indicate that further additive effect can be achieved when a mGluR₂ OA and a mGluR₂ PAM are combined with a 5-HT_2AR antagonist than when a mGluR₂ OA or a mGluR₂ PAM are added to a 5-HT_2AR antagonist.

Evaluating pimavanserin as a treatment for psychiatric disorders: A pharmacological property in search of an indication

Introduction: Pimavanserin is FDA-approved to treat hallucinations and delusions associated with Parkinson's disease psychosis. As a potent 5-HT_2A inverse agonist/antagonist, it could be efficacious in other psychiatric disorders. Recently, several studies have investigated this potential.Areas covered: The authors review the efficacy and adverse effects of pimavanserin for hallucinations in dementia, major depression, and schizophrenia.Expert opinion: Two controlled studies suggest pimavanserin has potential as a treatment for hallucinations in dementia. In patients with depression who did not respond to antidepressant treatment, pimavanserin augmentation was efficacious in a phase 2 study. Pimavanserin augmentation also alleviated sexual side effects of SSRI and SSNI. However, Acadia Pharmaceuticals stated in a press release that it does not plan further antidepressant trials based on its phase 3 trial, which showed a nonsignificant trend toward an antidepressant effect. Since almost all existing antipsychotics fail to substantially benefit negative symptoms, better treatments are needed. Pimavanserin augmentation of antipsychotics did benefit negative symptoms (effect size≈0.2) but failed to reduce the total PANSS score significantly in two large, well-controlled double-blind studies. Pimavanserin has a good safety profile.

Shared Genetic Background between Parkinson's Disease and Schizophrenia: A Two-Sample Mendelian Randomization Study

Background and objectives: Parkinson's disease (PD) and schizophrenia often share symptomatology. Psychotic symptoms are prevalent in patients with PD, and similar motor symptoms with extrapyramidal signs are frequently observed in antipsychotic-naïve patients with schizophrenia as well as premorbid families. However, few studies have examined the relationship between PD and schizophrenia. We performed this study to evaluate whether genetic variants which increase PD risk influence the risk of developing schizophrenia, and vice versa. Materials and Methods: Two-sample Mendelian randomization (TSMR) with summary statistics from large-scale genome-wide association studies (GWAS) was applied. Summary statistics were extracted for these instruments from GWAS of PD and schizophrenia; Results: We found an increase in the risk of schizophrenia per one-standard deviation (SD) increase in the genetically-predicted PD risk (inverse-variance weighted method, odds ratio = 1.10; 95% confidence interval, 1.05-1.15; p = 3.49 × 10^-5). The association was consistent in sensitivity analyses, including multiple TSMR methods, analysis after removing outlier variants with potential pleiotropic effects, and analysis after applying multiple GWAS subthresholds. No relationships were evident between PD and smoking or other psychiatric disorders, including attention deficit hyperactivity disorder, autism spectrum disorder, bipolar affective disorder, major depressive disorder, Alzheimer's disease, or alcohol dependence. However, we did not find a reverse relationship; genetic variants increasing schizophrenia risk did not alter the risk of PD; Conclusions: Overall, our findings suggest that increased genetic risk of PD can be associated with increased risk of schizophrenia. This association supports the intrinsic nature of the psychotic symptom in PD rather than medication or environmental effects. Future studies for possible comorbidities and shared genetic structure between the two diseases are warranted.

Vision loss and hallucinations: perspectives from neurology and ophthalmology

PURPOSE OF REVIEW

The aim of this article is to summarize the evidence for visual impairment as a risk factor for visual hallucinations in neurologic disease and recent advances in our understanding of the central visual pathways that mediate this association.

RECENT FINDINGS

Recent studies have described the prevalence Charles Bonnet syndrome and questioned its lack of association with cognitive impairment, used advanced neuroimaging to show that disinhibition of the occipital lobe is involved in the pathogenesis of visual hallucinations in Parkinson's disease, and demonstrated that visual impairment because of eye disease is a consistent risk factor for visual hallucinations across a number of different neurodegenerative disease populations.

SUMMARY

Through connections between the primary visual cortex and other brain structures, visual function is closely tied to visual hallucinations. Given that the vast majority of vision loss is caused by ophthalmic disease, much of which is preventable or treatable, the detection and treatment of vision loss in at-risk populations may reduce the burden and consequences of visual hallucinations in older adults.

An international, randomized, placebo-controlled, phase 2b clinical trial of intepirdine for dementia with Lewy bodies (HEADWAY-DLB)

INTRODUCTION

A phase 2b clinical trial, HEADWAY-DLB, was performed to assess treatment with intepirdine, a serotonin receptor antagonist, in patients with dementia with Lewy bodies (DLB).

METHODS

HEADWAY-DLB was a multinational, double-blind, randomized, placebo-controlled study. Two hundred sixty-nine DLB patients were randomized to receive placebo, 70 mg/day intepirdine, or 35 mg/day intepirdine over 24 weeks. The primary endpoint was change from baseline to week 24 on the Unified Parkinson's Disease Rating Scale-Part III (UPDRS-III).

RESULTS

Both intepirdine groups did not demonstrate significant benefits over placebo at 24 weeks on the UPDRS-III (35 mg/day: P = .1580, 70 mg/day: P = .6069). All other endpoints were not significant. Intepirdine was well tolerated, with a slightly higher incidence of gastrointestinal adverse events observed in the intepirdine groups versus placebo.

DISCUSSION

Intepirdine treatment did not lead to improvements over placebo in patients with DLB. As one of the largest DLB studies to date, HEADWAY-DLB demonstrates that international trials for DLB are feasible within a reasonable timeframe.

Serotonergic imaging in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the progressive degeneration of monoaminergic central pathways such as the serotonergic. The degeneration of serotonergic signaling in striatal and extrastriatal brain regions is an early feature of PD and is associated with several motor and non-motor complications of the disease. Molecular imaging techniques with Positron Emission Tomography (PET) have greatly contributed to the investigation of biological changes in vivo and to the understanding of the extent of serotonergic pathology in patients or individuals at risk for PD. Such discoveries provide with opportunities for the identification of new targets that can be used for the development of novel disease-modifying drugs or symptomatic treatments. Future studies of imaging serotonergic molecular targets will better clarify the importance of serotonergic pathology in PD, including progression of pathology, target-identification for pharmacotherapy, and relevance to endogenous synaptic serotonin levels. In this article, we review the current status and understanding of serotonergic imaging in PD.

Combined 5-HT2A and mGlu2 modulation for the treatment of dyskinesia and psychosis in Parkinson's disease

Antagonising the serotonin 2A (5-HT_2A) receptor is an efficacious way to alleviate dyskinesia and psychosis in Parkinson's disease (PD). However, previous research indicates that there might be a limit to the effects conferred by this approach. 5-HT_2A receptors were shown to form hetero-dimers with metabotropic glutamate 2 (mGlu₂) receptors, in which 5-HT_2A blockade and mGlu₂ activation elicit equivalent effects at the downstream signalling level. We have previously shown that mGlu₂ activation reduces both dyskinesia and psychosis-like behaviours (PLBs) induced by L-3,4-dihydroxyphenylalanine (l-DOPA), in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned primate. Here, we hypothesised that concurrent 5-HT_2A antagonism and mGlu₂ activation would provide greater anti-dyskinetic and anti-psychotic benefits than either approach alone. We conducted 3 series of experiments in the MPTP-lesioned marmoset. In the first series of experiments, the mGlu₂ positive allosteric modulator LY-487,379 and the 5-HT_2A antagonist EMD-281,014, either alone or in combination, were added to l-DOPA. In the second series of experiments, the mGlu_2/3 orthosteric agonist LY-354,740 and EMD-281,014, either alone or in combination, were added to l-DOPA. In the last series of experiments, we investigated whether mGlu₂ blockade would diminish the effects of antagonising 5-HT_2A receptors. To this end, the mGlu_2/3 orthosteric antagonist LY-341,495 and EMD-281,014, either alone or in combination, were added to l-DOPA. We found that the anti-dyskinetic effect of the combination LY-487,379/EMD-281,014 was greater than the ones conferred by LY-487,379 (by 35%, P < 0.05) and EMD-281,014 (by 38%, P < 0.01). The anti-dyskinetic and anti-psychotic effects of the combination LY-354,740/EMD-281,014 were also greater than the ones conferred by LY-354,740 (by 57% for dyskinesia and 54% for PLBs, both P < 0.001) and EMD-281,014 (by 61% for dyskinesia and 53% for PLBs, both P < 0.001). The anti-parkinsonian action of l-DOPA was maintained with all treatments. Lastly, the addition of LY-341,495 abolished the therapeutic effects of EMD-281,014 on dyskinesia and PLBs. Our results suggest that mGlu₂ activation may enhance the anti-dyskinetic and anti-psychotic effects of 5-HT_2A blockade and could provide relief to PD patients with dyskinesia and psychotic symptoms beyond what can be achieved with current therapies.

Effect of the mGlu2 positive allosteric modulator CBiPES on dyskinesia, psychosis-like behaviours and parkinsonism in the MPTP-lesioned marmoset

Advanced Parkinson's disease (PD) is often complicated by the occurrence of dyskinesia, motor fluctuations and psychosis. To this day, few treatment options are available for each of these phenomena, and they are at times not effective or elicit adverse events, leaving some patients short of therapeutic options. We have recently shown that positive allosteric modulation of metabotropic 2 (mGlu₂) receptors with the prototypical positive allosteric modulator (PAM) LY-487,379 is efficacious at alleviating both dyskinesia and psychosis-like behaviours (PLBs), while simultaneously enhancing the anti-parkinsonian action of L-3,4-dihydroxyphenylalanine (L-DOPA), in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmoset. Here, we assessed the effects of CBiPES, a mGlu₂ PAM derived from LY-487,379, but with improved pharmacokinetic properties. Six MPTP-lesioned marmosets with reproducible dyskinesia and PLBs were administered L-DOPA in combination with vehicle or CBiPES (0.1, 1 and 10 mg/kg), after which their behaviour was rated. CBiPES 10 mg/kg reduced global dyskinesia by 60% (P < 0.0001), while peak dose dyskinesia was reduced by 66% (P < 0.001), compared to L-DOPA/vehicle. CBiPES 10 mg/kg also diminished global PLBs by 56% (P < 0.0001), while peak dose PLBs were reduced by 64% (P < 0.001), compared to L-DOPA/vehicle. Lastly, CBiPES enhanced the anti-parkinsonian action of L-DOPA, by reducing global parkinsonian disability by 43% (P < 0.01), compared to L-DOPA/vehicle. Our results provide further evidence that mGlu₂ positive allosteric modulation may be an approach that could be efficacious for the treatment of dyskinesia, psychosis and motor fluctuations in PD.

QTc Interval Prolongation with Therapies Used to Treat Patients with Parkinson's Disease Psychosis: A Narrative Review

In addition to the classic motor symptoms of Parkinson's disease (PD), people with PD frequently experience nonmotor symptoms that can include autonomic dysfunction and neuropsychiatric symptoms such as PD psychosis (PDP). Common patient characteristics, including older age, use of multiple medications, and arrhythmias, are associated with increased risk of corrected QT interval (QTc) prolongation, and treatments for PDP (antipsychotics, dementia medications) may further increase this risk. This review evaluates how medications used to treat PDP affect QTc interval from literature indexed in the PubMed and Embase databases. Although not indicated for the treatment of psychosis, dementia therapies such as donepezil, rivastigmine, memantine, and galantamine are often used with or without antipsychotics and have minimal effects on QTc interval. Among the antipsychotics, data suggesting clinically meaningful QTc interval prolongation are limited. However, many antipsychotics have other safety concerns. Aripiprazole, olanzapine, and risperidone negatively affect motor function and are not recommended for PDP. Quetiapine is often sedating, can exacerbate underlying neurogenic orthostatic hypotension, and may prolong the QTc interval. Pimavanserin was approved by the US Food and Drug Administration (FDA) in 2016 and remains the only FDA-approved medication available to treat hallucinations and delusions associated with PDP. However, pimavanserin can increase QTc interval by approximately 5-8 ms. The potential for QTc prolongation should be considered in patients with symptomatic cardiac arrhythmias and those receiving QT-prolonging medications. In choosing a medication to treat PDP, expected efficacy must be balanced with potential safety concerns for individual patients.

Relevance of 5-HT2A Receptor Modulation of Pyramidal Cell Excitability for Dementia-Related Psychosis: Implications for Pharmacotherapy

Psychosis occurs across a wide variety of dementias with differing etiologies, including Alzheimer's dementia, Parkinson's dementia, Lewy body dementia, frontotemporal dementia, and vascular dementia. Pimavanserin, a selective serotonin 5-HT_2A receptor (5-HT_2AR) inverse agonist, has shown promising results in clinical trials by reducing the frequency and/or severity of hallucinations and delusions and the risk of relapse of these symptoms in patients with dementia-related psychosis. A literature review was conducted to identify mechanisms that explain the role of 5-HT_2ARs in both the etiology and treatment of dementia-related psychosis. This review revealed that most pathological changes commonly associated with neurodegenerative diseases cause one or more of the following events to occur: reduced synaptic contact of gamma aminobutyric acid (GABA)-ergic interneurons with glutamatergic pyramidal cells, reduced cortical innervation from subcortical structures, and altered 5-HT_2AR expression levels. Each of these events promotes increased pyramidal cell hyperexcitability and disruption of excitatory/inhibitory balance, facilitating emergence of psychotic behaviors. The brain regions affected by these pathological changes largely coincide with areas expressing high levels of 5-HT_2ARs. At the cellular level, 5-HT_2ARs are most highly expressed on cortical glutamatergic pyramidal cells, where they regulate pyramidal cell excitability. The common effects of different neurodegenerative diseases on pyramidal cell excitability together with the close anatomical and functional connection of 5-HT_2ARs to pyramidal cell excitability may explain why suppressing 5-HT_2AR activity could be an effective strategy to treat dementia-related psychosis.

Selective blockade of the 5-HT3 receptor acutely alleviates dyskinesia and psychosis in the parkinsonian marmoset

In Parkinson's disease (PD), management of L-3,4-dihydroxyphenylalanine (l-DOPA)-related complications, such as l-DOPA induced dyskinesia and psychosis, remains inadequate, which poses a significant burden on the quality of life of patients. We have shown, in the hemi-parkinsonian rat model of PD, that the selective serotonin type 3 (5-HT₃) receptor antagonists ondansetron and granisetron decreased the severity of established dyskinesia, and ondansetron even attenuated the development of dyskinesia. Here, we seek to confirm these favourable data on dyskinesia and to explore the effect of ondansetron on the severity of psychosis-like behaviours (PLBs) in the gold standard model of PD, the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned non-human primate. We first determined the pharmacokinetic profile of ondansetron in the marmoset. Subsequently, six MPTP-lesioned marmosets were administered l-DOPA chronically until they exhibited stable and reproducible dyskinesia and PLBs upon each administration of l-DOPA. On behavioural assessment days, ondansetron (0.01, 0.1 and 1 mg/kg) or vehicle was administered in conjunction with l-DOPA, and the severity of dyskinesia, PLBs and parkinsonism was evaluated. Ondansetron 0.1 mg/kg alleviated global dyskinesia severity by 73% (P < 0.0001) and decreased duration of on-time with disabling dyskinesia by 88% (P = 0.0491). Ondansetron 0.1 mg/kg reduced the severity of global PLBs by 80% (P < 0.0001) and suppressed on-time with disabling PLBs (P = 0.0213). Ondansetron enhanced the anti-parkinsonian action of l-DOPA, reducing global parkinsonism by 53% compared to l-DOPA (P = 0.0004). These results suggest that selective blockade of the 5-HT₃ receptor with ondansetron may be an effective approach to alleviate l-DOPA-related complications.

Visual Hallucinations and Impaired Conscious Visual Perception in Parkinson Disease

Visual hallucinations (VHs) are common in patients with Parkinson disease (PD), especially those with dementia, whereas auditory hallucinations are quite rare. Recent studies have revealed the involvement of several regions along the visual information-processing system that contribute to the pathophysiological mechanism of VHs: the eyes and retina, retinofugal projection, lateral geniculate nucleus, striate cortex, ventral pathways in the temporal cortices, and frontal and parietal cortices. In addition, the concurrent involvement of other systems in the brainstem and basal forebrain further modify VHs in PD. In this review, we discuss the pathophysiological association between the regional involvement of these areas and VHs.

Toxicokinetics and Toxicodynamics of Ayahuasca Alkaloids N,N-Dimethyltryptamine (DMT), Harmine, Harmaline and Tetrahydroharmine: Clinical and Forensic Impact

Ayahuasca is a hallucinogenic botanical beverage originally used by indigenous Amazonian tribes in religious ceremonies and therapeutic practices. While ethnobotanical surveys still indicate its spiritual and medicinal uses, consumption of ayahuasca has been progressively related with a recreational purpose, particularly in Western societies. The ayahuasca aqueous concoction is typically prepared from the leaves of the N,N-dimethyltryptamine (DMT)-containing Psychotria viridis, and the stem and bark of Banisteriopsis caapi, the plant source of harmala alkaloids. Herein, the toxicokinetics and toxicodynamics of the psychoactive DMT and harmala alkaloids harmine, harmaline and tetrahydroharmine, are comprehensively covered, particularly emphasizing the psychological, physiological, and toxic effects deriving from their concomitant intake. Potential therapeutic utility, particularly in mental and psychiatric disorders, and forensic aspects of DMT and ayahuasca are also reviewed and discussed. Following administration of ayahuasca, DMT is rapidly absorbed and distributed. Harmala alkaloids act as potent inhibitors of monoamine oxidase A (MAO-A), preventing extensive first-pass degradation of DMT into 3-indole-acetic acid (3-IAA), and enabling sufficient amounts of DMT to reach the brain. DMT has affinity for a variety of serotonergic and non-serotonergic receptors, though its psychotropic effects are mainly related with the activation of serotonin receptors type 2A (5-HT_2A). Mildly to rarely severe psychedelic adverse effects are reported for ayahuasca or its alkaloids individually, but abuse does not lead to dependence or tolerance. For a long time, the evidence has pointed to potential psychotherapeutic benefits in the treatment of depression, anxiety, and substance abuse disorders; and although misuse of ayahuasca has been diverting attention away from such clinical potential, research onto its therapeutic effects has now strongly resurged.

Cognitive impairment in Parkinson's disease: A clinical and pathophysiological overview

Cognitive dysfunction in Parkinson's disease (PD) has received increasing attention, and, together with other non-motor symptoms, exert a significant functional impact in the daily lives of patients. This article aims to compile and briefly summarize selected published data about clinical features, cognitive evaluation, biomarkers, and pathophysiology of PD-related dementia (PDD). The literature search included articles indexed in the MEDLINE/PubMed database, published in English, over the last two decades. Despite significant progress on clinical criteria and cohort studies for PD-mild cognitive impairment (PD-MCI) and PDD, there are still knowledge gaps about its exact molecular and pathological basis. Here we overview the scientific literature on the role of functional circuits, neurotransmitter systems (monoaminergic and cholinergic), basal forebrain, and brainstem nuclei dysfunction in PD-MCI. Correlations between neuroimaging and cerebrospinal fluid (CSF) biomarkers, clinical outcomes, and pathological results are described to aid in uncovering the neurodegeneration pattern in PD-MCI and PDD.

Management of psychiatric disorders in Parkinson's disease : Neurotherapeutics - Movement Disorders Therapeutics

Affective disorders (depression and anxiety), psychosis, impulse control disorders, and apathy are common and sometimes disabling psychiatric conditions in Parkinson disease (PD). Psychiatric aspects of PD are associated with numerous adverse outcomes, yet in spite of this and their high frequency, there remains incomplete understanding of epidemiology, presentation, risk factors, neural substrate, and management strategies. Psychiatric features are typically co- or multimorbid, and there is great intra- and interindividual variability in presentation [1]. The neuropathophysiological changes that occur in PD, as well as the association between PD treatment and particular psychiatric disorders, suggest a neurobiological contribution to many psychiatric symptoms. There is evidence that psychiatric disorders in PD are still under-recognized and undertreated, and although psychotropic medication use is common, randomized controlled trials demonstrating efficacy and tolerability are largely lacking. Future research on neuropsychiatric complications in PD should be oriented toward determining modifiable correlates or risk factors, and most importantly, establishing efficacious and well-tolerated treatment strategies.

Breathing new life into neurotoxic-based monkey models of Parkinson's disease to study the complex biological interplay between serotonin and dopamine

Numerous clinical studies have shown that the serotonergic system also degenerates in patients with Parkinson's disease. The causal role of this impairment in Parkinson's symptomatology and the response to treatment remains to be refined, in particular thanks to approaches allowing the two components DA and 5-HT to be isolated if possible. We have developed a macaque monkey model of Parkinson's disease exhibiting a double lesion (dopaminergic and serotonergic) thanks to the sequential use of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) and MDMA (3,4-methylenedioxy-N-methamphetamine) (or MDMA prior MPTP). We characterized this monkey model by multimodal imaging (PET, positron emission tomography with several radiotracers; DTI, diffusion tensor imaging), behavioral assessments (parkinsonism, dyskinesia, neuropsychiatric-like behavior) and post-mortem analysis (with DA and 5-HT markers). When administrated after MPTP, MDMA damaged the 5-HT presynaptic system without affecting the remaining DA neurons. The lesion of 5-HT fibers induced by MDMA altered rigidity and prevented dyskinesia and neuropsychiatric-like symptoms induced by levodopa therapy in MPTP-treated animals. Interestingly also, prior MDMA administration aggravates the parkinsonian deficits and associated DA injury. Dystonic postures, action tremor and global spontaneous activities were significantly affected. All together, these data clearly indicate that late or early lesions of the 5-HT system have a differential impact on parkinsonian symptoms in the macaque model of Parkinson's disease. Whether MDMA has an impact on neuropsychiatric-like symptoms such as apathy, anxiety, depression remains to be addressed. Despite its limitations, this toxin-based double-lesioned monkey model takes on its full meaning and provides material for the experimental study of the heterogeneity of patients.

Lewy Body Degenerations as Neuropsychiatric Disorders

Parkinson disease has historically been conceptualized as a movement disorder. In recent decades, nonmotor and neuropsychiatric symptoms have become increasingly recognized as being of paramount importance for patients with Parkinson disease. Neuropsychiatric phenomena dominate the course of the other major Lewy body disease, dementia with Lewy bodies. In this review, we survey the clinical relevance of nonmotor and neuropsychiatric symptoms to the heterogeneous presentations of Lewy body disease and their significance to ongoing research in this area. We consider how the nature of Lewy body neuropathology may help explicate the basis of nonmotor and neuropsychiatric symptoms in these two disorders.

Visual hallucinations in neurological and ophthalmological disease: pathophysiology and management

Visual hallucinations are common in older people and are especially associated with ophthalmological and neurological disorders, including dementia and Parkinson's disease. Uncertainties remain whether there is a single underlying mechanism for visual hallucinations or they have different disease-dependent causes. However, irrespective of mechanism, visual hallucinations are difficult to treat. The National Institute for Health Research (NIHR) funded a research programme to investigate visual hallucinations in the key and high burden areas of eye disease, dementia and Parkinson's disease, culminating in a workshop to develop a unified framework for their clinical management. Here we summarise the evidence base, current practice and consensus guidelines that emerged from the workshop.Irrespective of clinical condition, case ascertainment strategies are required to overcome reporting stigma. Once hallucinations are identified, physical, cognitive and ophthalmological health should be reviewed, with education and self-help techniques provided. Not all hallucinations require intervention but for those that are clinically significant, current evidence supports pharmacological modification of cholinergic, GABAergic, serotonergic or dopaminergic systems, or reduction of cortical excitability. A broad treatment perspective is needed, including carer support. Despite their frequency and clinical significance, there is a paucity of randomised, placebo-controlled clinical trial evidence where the primary outcome is an improvement in visual hallucinations. Key areas for future research include the development of valid and reliable assessment tools for use in mechanistic studies and clinical trials, transdiagnostic studies of shared and distinct mechanisms and when and how to treat visual hallucinations.

Effect of Antidepressants on Psychotic Symptoms in Parkinson Disease: A Review of Case Reports and Case Series

OBJECTIVES

The treatment of Parkinson disease (PD) psychosis remains a challenge. Only a few treatments eliciting significant relief of psychotic symptoms have passed the test of randomized controlled trials.

METHODS

Here, we conducted a review of the literature on the effect of antidepressants on PD psychosis. Because there is no randomized controlled trial that assessed the antipsychotic effects of antidepressants in PD, only case reports, case series, and open-label trials were available to review. Because of the scarce literature, statistical analysis could not be performed.

RESULTS

The following antidepressants alleviated hallucinations in PD: amoxapine, citalopram, clomipramine, escitalopram, mianserin, mirtazapine, and venlafaxine. The antidepressants were generally well tolerated, with the exception of amoxapine, which exacerbated parkinsonism.

CONCLUSIONS

Whereas the conclusions that can be drawn on the efficacy of antidepressants at reducing PD psychosis are limited because of the poor quality of the reported studies, it is encouraging to notice that there are positive anecdotal reports. Further studies are needed to confirm the potential of these drugs and also to determine if a subtype of patients or of psychotic features may be more likely to be improved by antidepressants.

The Pharmacology of Visual Hallucinations in Synucleinopathies

Visual hallucinations (VH) are commonly found in the course of synucleinopathies like Parkinson's disease and dementia with Lewy bodies. The incidence of VH in these conditions is so high that the absence of VH in the course of the disease should raise questions about the diagnosis. VH may take the form of early and simple phenomena or appear with late and complex presentations that include hallucinatory production and delusions. VH are an unmet treatment need. The review analyzes the past and recent hypotheses that are related to the underlying mechanisms of VH and then discusses their pharmacological modulation. Recent models for VH have been centered on the role played by the decoupling of the default mode network (DMN) when is released from the control of the fronto-parietal and salience networks. According to the proposed model, the process results in the perception of priors that are stored in the unconscious memory and the uncontrolled emergence of intrinsic narrative produced by the DMN. This DMN activity is triggered by the altered functioning of the thalamus and involves the dysregulated activity of the brain neurotransmitters. Historically, dopamine has been indicated as a major driver for the production of VH in synucleinopathies. In that context, nigrostriatal dysfunctions have been associated with the VH onset. The efficacy of antipsychotic compounds in VH treatment has further supported the notion of major involvement of dopamine in the production of the hallucinatory phenomena. However, more recent studies and growing evidence are also pointing toward an important role played by serotonergic and cholinergic dysfunctions. In that respect, in vivo and post-mortem studies have now proved that serotonergic impairment is often an early event in synucleinopathies. The prominent cholinergic impairment in DLB is also well established. Finally, glutamatergic and gamma aminobutyric acid (GABA)ergic modulations and changes in the overall balance between excitatory and inhibitory signaling are also contributing factors. The review provides an extensive overview of the pharmacology of VH and offers an up to date analysis of treatment options.

The Neuropsychiatry of Parkinson Disease: A Perfect Storm

Affective disorders, cognitive decline, and psychosis have long been recognized as common in Parkinson disease (PD), and other psychiatric disorders include impulse control disorders, anxiety symptoms, disorders of sleep and wakefulness, and apathy. Psychiatric aspects of PD are associated with numerous adverse outcomes, yet in spite of this and their frequent occurrence, there is incomplete understanding of epidemiology, presentation, risk factors, neural substrate, and management strategies. Psychiatric features are typically multimorbid, and there is great intra- and interindividual variability in presentation. The hallmark neuropathophysiological changes that occur in PD, plus the association between exposure to dopaminergic medications and certain psychiatric disorders, suggest a neurobiological basis for many psychiatric symptoms, although psychological factors are involved as well. There is evidence that psychiatric disorders in PD are still under-recognized and undertreated and although psychotropic medication use is common, controlled studies demonstrating efficacy and tolerability are largely lacking. Future research on neuropsychiatric complications in PD should be oriented toward determining modifiable correlates or risk factors and establishing efficacious and well-tolerated treatment strategies.

Advances in Management of Psychosis in Neurodegenerative Diseases

PURPOSE OF THE REVIEW

Psychosis is broadly defined as a disengagement from reality. It describes syndromes that impair both thought content and thought process. Psychosis negatively impacts an individual's quality of life, in addition to the families caring for them. Psychosis with different types of hallucinations and delusions occurs in the context of delirium. Neuropsychiatric symptoms (NPS) are almost universal in the course of common neurodegenerative disorders (NDD) like Alzheimer's disease (AD) or Parkinson's disease (PD). In this paper, the authors took an effort to characterize AD and PD psychosis with a special focus on the most diagnostically reliable features. Effectiveness and limitations of pharmacological interventions are discussed.

RECENT FINDINGS

Consensus diagnostic criteria have evolved for psychosis secondary to AD as well as psychosis in PD. Psychotropic medications can be effective in the treatment of NPS in NDD; however, clinicians must be mindful of the side effects. There is a consensus on benefit of initiating any acetylcholinesterase inhibitor (ACHI: donepezil, rivastigmine, and galantamine) as a first line of treatment for psychosis in AD, as it may reduce and/or avoid the need for the use antipsychotics. Pimavanserin, a selective-serotonin inverse agonist that preferentially targets 5-HT2A receptors, while avoiding activity at dopamine and other receptors commonly targeted by antipsychotics had recently been approved by FDA to treat hallucinations and delusions in PD. Quetiapine is widely prescribed for the treatment of psychosis in different NDD, but the data remains equivocal. Psychosis with different types of hallucinations and delusions may occur in the context of delirium and is almost universal as a neuropsychiatric symptom in the course of PD and AD. Currently, pimavanserin remains the only pharmacologic agent approved for treatment of psychosis in PD. In cases of other NPS in other than Parkinson's diseases, atypical antipsychotics are commonly used off-label. More research is greatly needed to advance this field and address NPS especially psychosis in geriatric population.

The neuropharmacology of sleep paralysis hallucinations: serotonin 2A activation and a novel therapeutic drug

Sleep paralysis is a state of involuntary immobility occurring at sleep onset or offset, often accompanied by uncanny "ghost-like" hallucinations and extreme fear reactions. I provide here a neuropharmacological account for these hallucinatory experiences by evoking the role of the serotonin 2A receptor (5-HT2AR). Research has shown that 5-HT2AR activation can induce visual hallucinations, "mystical" subjective states, and out-of-body experiences (OBEs), and modulate fear circuits. Hallucinatory experiences triggered by serotonin-serotonergic ("pseudo") hallucinations, induced by hallucinogenic drugs-tend to be "dream-like" with the experiencer having insight ("meta-awareness") that he is hallucinating, unlike dopaminergic ("psychotic" and "life-like") hallucinations where such insight is lost. Indeed, hallucinatory experiences during sleep paralysis have the classic features of serotonergic hallucinations, and are strikingly similar to perceptual and subjective states induced by hallucinogenic drugs (e.g., lysergic acid diethylamide [LSD] and psilocybin), i.e., they entail visual hallucinations, mystical experiences, OBEs, and extreme fear reactions. I propose a possible mechanism whereby serotonin could be functionally implicated in generating sleep paralysis hallucinations and fear reactions through 5-HT2AR activity. Moreover, I speculate on the role of 5-HT2C receptors vis-à-vis anxiety and panic during sleep paralysis, and the orbitofrontal cortex-rich with 5-HT2A receptors-in influencing visual pathways during sleep paralysis, and, in effect, hallucinations. Finally, I propose, for the first time, a drug to target sleep paralysis hallucinations and fear reactions, namely the selective 5-HT2AR inverse agonist, pimavanserin. This account implicates gene HTR2A on chromosome 13q as the underlying cause of sleep paralysis hallucinations and could be explored using positron emission tomography.

Interactions of Hallucinogens with the Glutamatergic System: Permissive Network Effects Mediated Through Cortical Layer V Pyramidal Neurons

Recordings made from layer V (L5) pyramidal cells of the prefrontal cortex (PFC) and neocortex in rodent slice preparations have shown that serotonin (5-hydroxytryptamine, 5-HT) and serotonergic hallucinogens induce an increase in the frequency of spontaneous excitatory postsynaptic currents (EPSCs) in the apical dendritic field by activating 5-HT_2A receptors. Serotonergic hallucinogens induce late EPSCs and increase recurrent network activity when subcortical or mid-cortical regions are stimulated at low frequencies (e.g., 0.1 Hz). A range of agonists or positive allosteric modulators (PAMs) for mostly G_i/o-coupled receptors, including metabotropic glutamate₂ (mGlu₂), adenosine A₁, or μ-opioid receptors, suppress these effects of 5-HT_2A receptor stimulation. Furthermore, a range of mostly G_q/11-coupled receptors (including orexin₂ [OX₂]; α₁-adrenergic, and mGlu₅ receptors) similarly induce glutamate (Glu) release onto L5 pyramidal cells. Evidence implicates a number of brain regions in mediating these effects of serotonergic hallucinogens and G_q/11-coupled receptors including the midline and intralaminar thalamic nuclei, claustrum, and neurons in deep PFC. These effects on 5-HT_2A receptors and related GPCRs appear to play a major role in the behavioral effects of serotonergic hallucinogens, such as head twitches in rodents and higher order behaviors such as rodent lever pressing on the differential-reinforcement-of-low rate 72-s (DRL 72-s) schedule. This implies that the effects of 5-HT_2A receptor activation on the activity of L5 pyramidal cells may be responsible for mediating a range of behaviors linked to limbic circuitry with connectivity between the PFC, striatum, thalamus, claustrum, striatum, amygdala, and the hippocampal formation.

Successful treatment of intractable visual hallucinations with 5-HT 2A antagonist ketanserin

Hallucinations, visual, auditory or in another sensory modality, often respond well to treatment in patients with schizophrenia. Some, however, do not and can be very chronic and debilitating. We present a patient with schizophrenia with intractable hallucinations despite state of the art care, including high-dose clozapine and transcranial magnetic stimulation. Based on the possible role of the 5-HT_2A receptor in hallucinations, we treated her with the antihypertensive drug ketanserin, a 5-HT_2A receptor antagonist.This significantly reduced her visual but not her auditory hallucinations, suggesting a possible role of the 5HT_2A receptor in the pathophysiology of specifically visual hallucinations. This is the first time ketanserin has been described to successfully reduce visual hallucinations in a patient with schizophrenia.

Beyond the dopamine hypothesis of schizophrenia to three neural networks of psychosis: dopamine, serotonin, and glutamate

Psychosis is now widely hypothesized to involve neural networks beyond the classical dopaminergic mesolimbic pathway, including serotonin and glutamate systems as well.