Monoaminergic activities in Lewy body dementia: relation to hallucinosis and extrapyramidal features

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.

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.

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.

Visual hallucinations, thalamocortical physiology and Lewy body disease: A review

One of the core diagnostic criteria for Dementia with Lewy Bodies (DLB) is the presence of visual hallucinations. The presence of hallucinations, along with fluctuations in the level of arousal and sleep disturbance, point to potential pathological mechanisms at the level of the thalamus. However, the potential role of thalamic dysfunction in DLB, particularly as it relates to the presence of formed visual hallucinations is not known. Here, we review the literature on the pathophysiology of DLB with respect to modern theories of thalamocortical function and attempt to derive an understanding of how such hallucinations arise. Based on the available literature, we propose that combined thalamic-thalamic reticular nucleus and thalamocortical pathology may explain the phenomenology of visual hallucinations in DLB. In particular, diminished α7 cholinergic activity in the thalamic reticular nucleus may critically disinhibit thalamocortical activity. Further, concentrated pathological changes within the posterior regions of the thalamus may explain the predilection for the hallucinations to be visual in nature.

Reduction of RPT6/S8 (a Proteasome Component) and Proteasome Activity in the Cortex is Associated with Cognitive Impairment in Lewy Body Dementia

Lewy body dementia is the second most common neurodegenerative dementia and is pathologically characterized by α-synuclein positive cytoplasmic inclusions, with varying amounts of amyloid-β (Aβ) and hyperphosphorylated tau (tau) aggregates in addition to synaptic loss. A dysfunctional ubiquitin proteasome system (UPS), the major proteolytic pathway responsible for the clearance of short lived proteins, may be a mediating factor of disease progression and of the development of α-synuclein aggregates. In the present study, protein expression of a key component of the UPS, the RPT6 subunit of the 19S regulatory complex was determined. Furthermore, the main proteolytic-like (chymotrypsin- and PGPH-) activities have also been analyzed. The middle frontal (Brodmann, BA9), inferior parietal (BA40), and anterior cingulate (BA24) gyrus' cortex were selected as regions of interest from Parkinson's disease dementia (PDD, n = 31), dementia with Lewy bodies (DLB, n = 44), Alzheimer's disease (AD, n = 16), and control (n = 24) brains. Clinical and pathological data available included the MMSE score. DLB, PDD, and AD were characterized by significant reductions of RPT6 (one-way ANOVA, p < 0.001; Bonferroni post hoc test) in prefrontal cortex and parietal cortex compared with controls. Strong associations were observed between RPT6 levels in prefrontal, parietal cortex, and anterior cingulate gyrus and cognitive impairment (p = 0.001, p = 0.001, and p = 0.008, respectively). These findings highlight the involvement of the UPS in Lewy body dementia and indicate that targeting the UPS may have the potential to slow down or reduce the progression of cognitive impairment in DLB and PDD.

The neurobiological basis of cognitive impairment in Parkinson's disease

The recent formalization of clinical criteria for Parkinson's disease with dementia (PDD) codifies many studies on this topic, including those assessing biological correlates. These studies show that the emergence of PDD occurs on the background of severe dopamine deficits with, the main pathological drivers of cognitive decline being a synergistic effect between alpha-synuclein and Alzheimer's disease pathology. The presence of these pathologies correlates with a marked loss of limbic and cortically projecting dopamine, noradrenaline, serotonin, and acetylcholine neurons, although the exact timing of these relationships remains to be determined. Genetic factors, such as triplications in the α-synuclein gene, lead to a clear increased risk of PDD, whereas others, such as parkin mutations, are associated with a reduced risk of PDD. The very recent formalization of clinical criteria for PD with mild cognitive impairment (PD-MCI) allows only speculation on its biological and genetic bases. Critical assessment of animal models shows that chronic low-dose MPTP treatment in primates recapitulates PD-MCI over time, enhancing the current biological concept of PD-MCI as having enhanced dopamine deficiency in frontostriatal pathways as well as involvement of other neurotransmitter systems. Data from other animal models support multiple transmitter involvement in cognitive impairment in PD. Whereas dopamine dysfunction has been highlighted because of its obvious role in PD, the role of the other neurotransmitter systems, neurodegenerative pathologies, and genetic factors in PD-MCI remains to be fully elucidated.

Dementia with Lewy bodies is associated with higher scores on the Geriatric Depression Scale than is Alzheimer's disease

BACKGROUND

Several reports suggest a higher morbidity of depression in patients with dementia with Lewy bodies (DLB) than in patients with Alzheimer's disease (AD). However, these results have not been duplicated consistently. The psychiatric symptoms of dementia, including depression, are important for its diagnosis and management. Thus, the aim of the present study was to clarify the characteristics of the depressive symptoms in DLB compared with AD using the Geriatric Depression Scale (GDS).

METHODS

We examined the GDS score for 86 patients with probable DLB (based on the Consensus Criteria for the clinical diagnosis of DLB) and 86 patients with probable AD (based on criteria of the National Institute for Neurological and Communicative Disorders and Stroke-Alzheimer's Disease and Related Disorders Association), who were matched according to age, sex, education, and Mini-Mental State Examination (MMSE) scores. We also examined correlations between GDS scores and age, sex, or MMSE scores in both groups. Correlations between GDS scores and metaiodobenzylguanidine (MIBG) scintigraphy were examined in patients with DLB. To characterize the GDS in DLB, its profile was examined using factor structures.

RESULTS

Scores for DLB patients were twice as high on the GDS as those for AD patients. There was no correlation between GDS score and age, sex, or MMSE scores in either group. Furthermore, there was no correlation between the results of MIBG scintigraphy and GDS scores in the DLB group. Using factor structures, the depression symptom profile of these diseases suggested that depression-specific symptoms, such as mood, worry, or future outlook, were more frequent in the DLB group than non-specific symptoms, such as lack of energy, decreased concentration, or apathy.

CONCLUSIONS

The data suggest that depressive symptoms are highly specific symptoms of DLB, independent of other features of this disorder. The GDS could be used as a subsidiary tool in differentiating DLB from AD and is more useful than clinical observations of depression.

Amitriptyline and lorazepam improved catatonia and occipital hypoperfusion in a patient with DLB

A 76-year-old woman presented with catatonia, refusal to eat due to delusion, and visual hallucination. Single photon emission computed tomography showed remarkable occipital hypoperfusion and frontal hyperperfusion. (123)I metaiodobenzyl guanidine myocardial scintigraphy revealed decreased uptake. She was diagnosed as probable dementia with Lewy bodies (DLB). Intravenous or oral L-dopa had no effect on catatonia. Amitriptyline and lorazepam improved catatonia and visual hallucination. Cerebral blood flow of the frontal and occipital lobes seemed to be normalized. Occipital hypoperfusion is one of the features of DLB. Although the mechanism of perfusion abnormality in DLB remains to be clarified, our case suggested that it might be reversible.

New approaches to understanding hallucinations in Parkinson's disease: phenomenology and possible origins

The authors review current literature on hallucinations in Parkinson's disease (PD). Recent neuropathological studies showed that hallucinations occur in synucleinopathies and are a significant predictor of Lewy Body depositions. Therefore, hallucinations are a hallmark of PD and of dementia with Lewy Bodies. Visual hallucinations are mostly complex and kinematic; preserved or disturbed insight on the nature of hallucinations is a major prognostic factor, although eventually all hallucinators will present with reduced insight. Current theories on the origin of hallucinations point to visual dysfunction, dream overflow and cognitive impairment, yet objection can be raised on each one of the putative models of hallucinations. Understanding of the origin of hallucinations is required in order to develop treatments: all treatment evaluations were focused in general on psychosis, and only clozapine obtained positive evidence-based ratings on efficacy. However, it is likely that cholinesterase inhibitors, antipsychotics and anti-5-hydroxytryptamine(3) agents and drugs acting on sleep regulation will have different and perhaps opposite effects on different types of hallucinations, whether they are accompanied by disturbed insight, sleep disorders or other psychotic features. Further studies will try to separate phenomenology and responses to treatment and will investigate the relevance of concomitant sleep disorders and abnormality of frontoparietal networks involved in the attention process.

Non-dopaminergic treatment of cognitive impairment and dementia in Parkinson's disease: A review

OBJECTIVE

To review the clinical management of cognitive impairment and dementia related to Parkinson's disease (PD), with emphasis on pharmacologic intervention strategies such as cholinesterase inhibitors.

DATA SOURCES

A MEDLINE, EMBASE, PsychINFO, and Cochrane Collaboration search of English language literature from 1970 to 2004 was performed to identify reviews, studies, case reports, and letters pertaining to the treatment of cognitive impairment in PD. The bibliographies of selected articles were reviewed for additional references.

STUDY SELECTION

Human studies or case reports in adults with PD describing the use of drug and other therapies for the treatment of cognitive impairment in PD.

DATA EXTRACTION

Studies were reviewed for study design, number of subjects, outcome measures, dosage, side-effects, particularly, worsening of PD motor symptoms.

CONCLUSION

The strongest evidence for the pharmacological treatment of cognitive impairment and dementia in PD supports the use of cholinesterase inhibitors. Evidence for the efficacy and safety of other agents in PD dementia is either insufficient or inconclusive, but offers intriguing clues for potential future treatments. No reports from the Cochrane Collaboration were found.

Effect of oral administration of zanapezil (TAK-147) for 21 days on acetylcholine and monoamines levels in the ventral hippocampus of freely moving rats

Zanapezil (TAK-147 (3-[1benzylpiperdin-4-yl]-1-(2,3,4,5-tetrahydro-1 H-1-benzazepin-8-yl) propan-1-one fumarate)) is a selective acetylcholine (ACh) esterase inhibitor under investigation as a drug for Alzheimer's disease (AD) treatment. In this study, the effects of TAK-147 at 2 mg kg(-1) p.o. for 21 days, compared to donepezil (E2020), on the levels of ACh, catecolamines and indoleamines were investigated in the ventral hippocampus (VH) of freely moving rats by microdialysis-high-performance liquid chromatography. The results revealed that the VH contains 92.05+/-21.97 fmol 20 microl(-1) ACh and the following monoamines levels (pg 30 microl(-1)), norepinephrine (NE) 1.92+/-0.39, epinephrine (Epi) 1.91+/-0.183, 3-methoxy-4-hydroxyphenylglycol (MHPG) 11.53+/-3.22, normetanephrine 3.26+/-0.61, dopamine (DA) 0.77+/-0.23, 3,4-dihydroxyphenylacetic acid (DOPAC) 3.37+/-1.01, homovanillic acid (4-hydroxy-3-methoxyphenylacetic acid; HVA) 4.04+/-0.93, 3-methoxytyramine 0.64+/-0.13, serotonin (5-HT) 0.73+/-0.16 and 5-hydroxyindoleacetic acid (5-HIAA) 313.15+/-18.42. On the 21st day and prior to the last dose, TAK-147 increased ACh, Epi, DA and 5-HT, whereas E2020 increased MHPG, Epi and DA. Following the last dose, TAK-147 increased NE, whereas E2020 increased NE, ACh and 5-HT in addition to their effects prior to the last dose. TAK-147 decreased HVA : DA ratio, but only marginally decreased DOPAC : DA and 5-HIAA : 5-HT ratios. On the other hand, E2020 decreased ratios of HVA : DA, DOPAC : DA (prior to the last dose), and 5-HIAA : 5-HT (90-180 min after the last dose). Both drugs decreased MHPG : NE only at 180 min after the last dose. The results also showed that TAK-147 increased Epi : NE ratio prior to and for 120 min following the last dose, whereas E2020 increased the ratio only before the last dose. The present results show that TAK-147 at a subthreshold dose could differentially increase ACh and 5-HT, compared to MHPG increased by E2020. The last dose of each drug could extend their effects to other monoamines. The increase of the monoamines levels, in addition to that on the ACh, and decrease of their oxidation could be of value in the treatment of the AD, other dementic diseases and the cohort neurological disorders depending on the type of the monoamine underlying the disorder.

Treatment of dementia with Lewy bodies and Parkinson's disease dementia

Cognitive decline and dementia affect approximately 30% to 40% of patients with idiopathic Parkinson's disease during the course of their illness. PD-dementia (PDD) and dementia with Lewy bodies (DLB) are second to Alzheimer's disease in causing degenerative dementia in the elderly. The nosological distinction of the conditions has remained controversial because of broad clinical and pathological overlap. Treatment issues in both clinical settings are virtually identical. Treatment of Parkinsonism is often complicated by drug-induced psychosis and reduced levodopa responsiveness. Cognition, alertness, attention, as well as apathy or aggressive behavior have been shown to respond to treatment with cholinesterase inhibitors in randomized controlled trials both in DLB and PDD. Such treatment may also improve hallucinosis, but many patients will require add-on treatment with atypical neuroleptics to control drug-induced psychotic reactions. Clozapine and quetiapine are the drugs most commonly used and, contrary to classic neuroleptics, risperidone or olanzapine do not seem to cause severe side effects according to published data.

Abnormal metabotropic glutamate receptor expression and signaling in the cerebral cortex in diffuse Lewy body disease is associated with irregular alpha-synuclein/phospholipase C (PLCbeta1) interactions

Diffuse Lewy body disease (DLBD) is a degenerative disease of the nervous system, involving the brain stem, diencephalic nuclei and cerebral cortex, associated with abnormal a-synuclein aggregation and widespread formation of Lewy bodies and Lewy neurites. DLBD presents as pure forms (DLBDp) or in association with Alzheimer disease (AD) in the common forms (DLBDc). Several neurotransmitter abnormalities have been reported including those of the nigrostriatal and mesocorticolimbic dopaminergic system, and central noradrenergic, serotoninergic and cholinergic pathways. The present work examines metabotropic glutamate receptor (mGluR) expression and signaling in the frontal cortex of DLBDp and DLBDc cases in comparison with age-matched controls. Abnormal L-[3H]glutamate specific binding to group I and II mGluRs, and abnormal mGluR1 levels have been found in DLBD. This is associated with reduced expression levels of phospholipase C beta1 (PLCbeta1), the effector of group I mGluRs following protein G activation upon glutamate binding. Additional modification in the solubility of PLCbeta1 and reduced PLCbeta1 activity in pure and common DLBD further demonstrates for the first time abnormal mGluR signaling in the cerebral cortex in DLBD. In order to look for a possible link between abnormal mGluR signaling and a-synuclein accumulation in DLBD, immunoprecipitation studies have shown alpha-synuclein/PLCbeta1 binding in controls and decreased alpha-synuclein/PLCbeta1 binding in DLBD. This is accompanied by a shift in the distribution of a-synuclein, but not of PLCbeta1, in DLBD when compared with controls. Together, these results support the concept that abnormal a-synuclein in DLBD produces functional effects on cortical glutamatergic synapses, which are associated with reduced alpha-synuclein/PLCbeta1 interactions, and, therefore, that mGluRs are putative pharmacological targets in DLBD. Finally, these results emphasize the emergence of a functional neuropathology that has to be explored for a better understanding of the effects of abnormal protein interactions in degenerative diseases of the nervous system.

Progress in clinical neurosciences: Parkinson's disease with dementia and dementia with Lewy bodies

Dementia occurs in up to 30% of people with Parkinson's disease and is a major cause of disability. Pathologically, Parkinson's dementia, where dementia follows the onset of parkinsonism by at least one year, overlaps with dementia with Lewy bodies. We review the functional impact, definitions, neuropsychology, epidemiology and pathophysiology of Parkinson's dementia, dementia with Lewy bodies and their overlap. Associated psychiatric and imaging findings are also considered. Lastly, current and emerging approaches to assessment and treatment in patients with these Lewy body associated dementias are presented.

Modulation of striatal serotonin and opioid receptor mRNA expression following systemic N-methyl-norsalsolinol administration

The dihydroxylated tetrahydroisoquinoline derivative, 2(N)-methyl-norsalsolinol (NMNorsal), was identified in L-DOPA-treated patients with Parkinson's disease and proposed to be responsible for behavioral changes. In the present study, we investigated the effect of NMNorsal on serotonin and opioid receptors gene expression in caudate nucleus of Wistar rats. Using RT-PCR, serotonin 5-HT2A, micro- and delta-opioid receptor mRNA levels were determined after NMNorsal administration (40 mg/kg, i.p.). There was a marked increase of 5-HT2A and delta-opioid receptor mRNA levels with a maximum after 48 h. In contrast, micro-opioid receptor mRNA levels were significantly decreased to 10% after 24 h and 21% after 48 h, respectively. Our present results demonstrate for the first time that the atypical heterocylic L-DOPA/dopamine metabolite NMNorsal is able to modify long-term regulation of serotonin and opioid receptor expression in striatum. Since the occurrence of hallucinosis or psychosis following L-DOPA treatment is related to the serotonergic system, these results probably reflect a link between NMNorsal and L-DOPA side effects in Parkinson's disease. However, further experiments are needed.

Patterns of cerebral atrophy in dementia with Lewy bodies using voxel-based morphometry

Previous cross-sectional MRI studies based on region-of-interest analyses have shown that increased cerebral atrophy is a feature of both Dementia with Lewy bodies (DLB) and Alzheimer's disease (AD). Relative preservation of the hippocampus and temporal lobe structures in DLB compared to AD has been reported in region-of-interest-based studies. Recently, image processing techniques such as voxel-based morphometry (VBM) have been developed to provide an unbiased, visually informative, and comprehensive means of studying patterns of cerebral atrophy. We report the first study to use the voxel-based approach to assess patterns of cerebral atrophy in DLB compared to control subjects and AD. Regional gray matter volume loss was observed bilaterally in the temporal and frontal lobes and insular cortex of patients with DLB compared to control subjects. Comparison of dementia groups showed preservation of the medial temporal lobe, hippocampus, and amygdala in DLB relative to AD. Significant gray matter loss was also observed in the thalamus of AD patients compared to DLB.

Acetylcholine in cortical inference

Acetylcholine (ACh) plays an important role in a wide variety of cognitive tasks, such as perception, selective attention, associative learning, and memory. Extensive experimental and theoretical work in tasks involving learning and memory has suggested that ACh reports on unfamiliarity and controls plasticity and effective network connectivity. Based on these computational and implementational insights, we develop a theory of cholinergic modulation in perceptual inference. We propose that ACh levels reflect the uncertainty associated with top-down information, and have the effect of modulating the interaction between top-down and bottom-up processing in determining the appropriate neural representations for inputs. We illustrate our proposal by means of an hierarchical hidden Markov model, showing that cholinergic modulation of contextual information leads to appropriate perceptual inference.

A positive association between 5HT re-uptake binding sites and depression in dementia with Lewy bodies

BACKGROUND

Depression is a common and distressing problem in the context of dementia, and is significantly more common in Dementia with Lewy bodies (DLB) than in Alzheimer's disease. The neurochemical basis for depression in DLB has not been investigated.

AIM

To investigate the association between depression and 5HT transporter re-uptake binding in DLB patients.

METHOD

A representative cohort of dementia patients received annual assessments, which included a standardised evaluation of depression until death. At post-mortem, (3H) cyanoimipramine autoradiography was used to quantify 5HT transporter re-uptake sites in the hippocampus and adjacent temporal cortex (Brodmann Area-BA 36, and 20); and parietal neocortex (BA 7a).

RESULTS

Twenty-one cases were evaluated neurochemically, of whom seven had experienced a major depressive disorder. Major depression was associated with a significant preservation of 5HT transporter re-uptake sites in the parietal neocortex compared with non-affected cases (BA 7a area 1 t = 3.3, P = 0.004; BA 7a area 3 t = 3.8, P = 0.001).

CONCLUSION

This preliminary report is important in challenging some of the assumptions about cortical monoamine functioning in depressed dementia.

Brain aging research at the close of the 20th century: from bench to bedside

Remarkable and continued growth in the field of brain aging research has been fueled by a confluence of factors. Developments in molecular biology, imaging, and genetics coupled with the imperative caused by the aging of the population has created fertile ground for improved understanding of the interaction between brain function and behavior. Aging changes in neurochemical systems may account for the spectrum of cognitive and behavioral states of successfully aged pen sons, but may also contribute to enhanced vulnerability to depressive or dementing illness. In particular, the refinement of in vivo imaging approaches to investigating the structure and function of the aging brain has provided the opportunity to strengthen our knowledge of the biological substrate of the aging brain and neuropsychiatrie disorders, and translate these into therapeutics.

Antipsychotic drug use in neurodegenerative disease in the elderly: problems and potential from a pharmacological perspective

The past decade has seen the introduction of several new antipsychotics for the treatment of schizophrenia. These drugs demonstrate substantially lower levels of extrapyramidal side effects (EPS) than the classical antipsychotics, as well as having (often poorly supported) claims of increased efficacy at ameliorating certain schizophrenic syndromes. Increasingly, these 'atypical' drugs are being used in the treatment of psychotic or related behavioural disturbances in patients with neurodegenerative disease. Thus, some newer antipsychotics are particularly valuable in ameliorating the L-dopa-induced psychosis in Parkinson's disease, while behavioural problems in dementing disorders, such as those occurring in Alzheimer's disease, are also frequently treated by antipsychotic drugs. The relationship between drug pharmacology and neurotransmitter pathology is essential to understanding the relative efficacy of individual antipsychotic drugs in treating the psychotic and behavioural disturbances of neurodegenerative disorders.

Neuropsychiatric aspects of Alzheimer's disease

The increase in research studies focusing on neuropsychiatric symptoms over the last decade has greatly increased our knowledge base, particularly with regard to the frequency of these symptoms and their impact on both patients and carers. We still have a poor understanding of the natural course of these symptoms and their biologic correlates, however, and more specific treatment studies are needed to inform clinical management.

Neuropsychiatric aspects of dementia with Lewy bodies

Neuropsychiatric symptoms are prominent clinical features of dementia with Lewy bodies (DLB). Visual hallucinations have been reported to be particularly common. Auditory hallucinations, delusions, and depression also may be characteristic to DLB. Misidentification delusions may be more common than with other types of delusional syndromes. Supersensitivity to neuroleptic drugs is common, making treatment of these symptoms difficult, and newer, atypical compounds have been recommended. However, supersensitive reactions to these medicines have been reported. Patients with DLB, especially those with visual hallucinations, are reported to have a marked cholinergic deficit, and cholinergic drugs may be beneficial in reducing the neuropsychiatric symptoms.

Striatal dopaminergic markers in dementia with Lewy bodies, Alzheimer's and Parkinson's diseases: rostrocaudal distribution

Dementia with Lewy bodies (DLB) is a neuropsychiatric disease associated with extrapyramidal features which differ from those of Parkinson's disease, including reduced effectiveness of L-dopa and severe sensitivity reactions to neuroleptic drugs. Distinguishing Alzheimer's disease from DLB is clinically relevant in terms of prognosis and appropriate treatment. Dopaminergic activities have been investigated at coronal levels along the rostrocaudal striatal axis from a post-mortem series of 25 DLB, 14 Parkinson's disease and 17 Alzheimer's disease patients and 20 elderly controls. [(3)H]Mazindol binding to the dopamine uptake site was significantly reduced in the caudal putamen in DLB compared with controls (57%), but not as extensively as in Parkinson's disease (75%), and was unchanged in Alzheimer's disease. Among three dopamine receptors measured (D1, D2 and D3), the most striking changes were apparent in relation to D2. In DLB, [(3)H]raclopride binding to D2 receptors was significantly reduced in the caudal putamen (17%) compared with controls, and was significantly lower than in Parkinson's disease at all levels. D2 binding was significantly elevated at all coronal levels in Parkinson's disease compared with controls, most extensively in the rostral putamen (71%). There was no change from the normal pattern of D2 binding in Alzheimer's disease. The only significant alteration in D1 binding ([(3)H]SCH23390) in the groups examined was an elevation (30%) in the caudal striatum in Parkinson's disease. There were no differences in D3 binding, measured using [(3)H]7-OH-DPAT, in DLB compared with controls. A slight, significant decrease in D3 binding in the caudal striatum of Parkinson's disease (13%) patients and an increase in Alzheimer's disease (20%) in the dorsal striatum at the level of the nucleus accumbens were found. The concentration and distribution of dopamine were disrupted in both DLB and Parkinson's disease, although in the caudate nucleus the loss of dopamine in DLB was uniform whereas in Parkinson's disease the loss was greater caudally. In the caudal putamen, dopamine was reduced by 72% in DLB and by 90% in Parkinson's disease. The homovanillic acid : dopamine ratio, a metabolic index, indicated compensatory increased turnover in Parkinson's disease, which was absent in DLB despite the loss of substantia nigra neurons (49%), dopamine and uptake sites. These differences between DLB, Parkinson's disease and Alzheimer's disease may explain some characteristics of the extrapyramidal features of DLB and its limited response to L-dopa and severe neuroleptic sensitivity. The distinct changes in the rostrocaudal pattern of expression of dopaminergic parameters are relevant to the interpretation of the in vivo imaging and diagnosis of DLB.

Acetylcholine in mind: a neurotransmitter correlate of consciousness?

The cholinergic system is one of the most important modulatory neurotransmitter systems in the brain and controls activities that depend on selective attention, which are an essential component of conscious awareness. Psychopharmacological and pathological evidence supports the concept of a 'cholinergic component' of conscious awareness. Drugs that antagonize muscarinic receptors induce hallucinations and reduce the level of consciousness, while the nicotinic receptor is implicated as being involved in the mechanism of action of general (inhalational) anaesthetics. In degenerative diseases of the brain, alterations in consciousness are associated with regional deficits in the cholinergic system. In Alzheimer's disease (AD), there is a loss of explicit (more than implicit) memory and hypoactivity of cholinergic projections to the hippocampus and cortex, while the visual hallucinations experienced by subjects with Dementia with Lewy bodies (DLB) are associated with reductions in neocortical ACh-related activity. In Parkinson's disease, the additional loss of pedunculopontine cholinergic neurones, which control REM (rapid eye movement) sleep or dreaming, is likely to contribute to REM abnormalities, which also occur in DLB. Widespread basal-forebrain and rostral brainstem cholinergic pathways, which include converging projections to the thalamus, appear to be located strategically for generating and integrating conscious awareness. Alleviation of a range of cognitive and non-cognitive symptoms by drugs that modulate the cholinergic system, which are being developed for the treatment of AD and related disorders, could be caused by changes in consciousness.

Nigrostriatal dopaminergic activities in dementia with Lewy bodies in relation to neuroleptic sensitivity: comparisons with Parkinson's disease

BACKGROUND

In dementia with Lewy bodies (DLB) mild extrapyramidal symptoms are associated with moderate reductions in substantia nigra neuron density and concentration of striatal dopamine. Many DLB patients treated with typical neuroleptics suffer severe adverse reactions, which result in decreased survival.

METHODS

In a series of DLB cases, with and without neuroleptic sensitivity, substantia nigra neuron densities, striatal dopamine and homovanillic acid concentrations, and autoradiographic [3H]mazindol and [3H]raclopride binding (to the dopamine transporter and D2 receptor, respectively) were analyzed and compared to control and idiopathic Parkinson's disease cases.

RESULTS

D2 receptors were up-regulated in neuroleptictolerant DLB and Parkinson's disease compared to DLB without neuroleptic exposure and controls. D2 receptors were not up-regulated in DLB cases with severe neuroleptic reactions. Dopamine uptake sites were reduced concomitantly with substantia nigra neuron density in Parkinson's disease compared to controls, but there was no significant correlation between substantia nigra neuron density and [3H]mazindol binding in DLB groups. There was no significant difference in substantia nigra neuron density, [3H]mazindol binding, and dopamine or homovanillic acid concentration between neuroleptic-tolerant and -sensitive groups.

CONCLUSIONS

Failure to up-regulate D2 receptors in response to neuroleptic blockade or reduced dopaminergic innervation may be the critical factor responsible for neuroleptic sensitivity.

Salsolinol, catecholamine metabolites, and visual hallucinations in L-dopa treated patients with Parkinson's disease

We could quantify the tetrahydroisoquinoline derivative salsolinol in urine of patients with Parkinson's disease and normal control subjects by means of high performance liquid chromatography and electrochemical detection. Urine levels of salsolinol were positively related to the homovanillic acid/3-O-methyl-dopa ratio in the cerebrospinal fluid that reflects dopamine metabolism. In the patient group with visual hallucinations, mean salsolinol level was significantly increased to almost the 3-fold of those found in patients without hallucinations. Since the daily L-dopa doses of both patient groups were nearly identical this result is not due to different L-dopa medications. Additionally, either high values of the main serotonin metabolite, 5-hydroxyindole acetic acid (HIAA) or the L-dopa/3-O-methyl-dopa ratio were found in cerebrospinal fluid of patients with hallucinations. The enhanced salsolinol levels in patients with visual hallucinations seem to be due to an overloaded dopaminergic pathway with an imbalance between dopaminergic and serotonergic systems. Thus, salsolinol appears as a predictor for hallucinosis in Parkinson's disease.

Dementia with Lewy bodies. A distinct non-Alzheimer dementia syndrome?

Lewy body formation is central to the pathological phenotype of a spectrum of disorders. The most familiar of these is the extrapyramidal syndrome of idiopathic Lewy-body Parkinson's disease (PD). Studies of dementia in the elderly suggest that another manifestation of Lewy body pathology is equally or more common than Parkinson's disease. This syndrome of Dementia with Lewy bodies (DLB) has been given a number of diagnostic labels and is characterised by dementia, relatively mild parkinsonism, visual hallucinations, and fluctuations in conscious level. Although many of these features can arise in Parkinson's disease, the patients with DLB tend to have early neuropsychiatric features which predominate the clinical picture, and the diagnosis of the syndrome in practice is more concerned with the differential diagnosis of Alzheimer's disease (AD). Distinction from AD has clinical importance because of potentially differing therapeutic implications. Diagnostic guidelines for the clinical diagnosis and pathological evaluation of DLB are reviewed. Research into the disorder has centered around characterising the clinical, neuropsychological, pathological, neurochemical and genetic relationships with Alzheimer's disease on the one hand, and Parkinson's disease on the other. Many cases of DLB have prominent pathological features of AD and there are some shared genetic risk factors. Differences from the pathology of PD are predominantly quantitative rather than qualitative and evidence is discussed which suggests that DLB represents a clinicopathological syndrome within the spectrum of Lewy body disorders. The possibility that the syndrome represents a chance association of PD and AD is not supported by published studies.

The basis for behavioural disturbances in dementia

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Joseph Hyrtl (1811-94)

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Visual hallucinosis: the major clinical determinant of distorted chromatic contour perception in Parkinson's disease

Recently distorted chromatic contour perception has been demonstrated in Parkinson's disease (PD). The aim of our study is to determine the clinical factors which influence chromatic contour perception in PD. Chromatic and achromatic contour perception, colour discrimination and clinical data were evaluated in 73 patients with PD. We used a computer-aided method to determine the chromatic fusion time (CFT) which indicates the acuity of monochromatic contour perception. Chromatic CFT was generally shortened in patients as compared to controls (p < 0.01), whereas achromatic CFT was not significantly different. Variance analysis revealed the ability of colour discrimination and the risk of visual hallucinations as statistically significant (p < 0.05) variables influencing contour perception of certain stimuli. In contrast, disease stage, disease duration and disease severity have no relevant effect on chromatic contour perception in Parkinson's disease. On the basis of those properties one may suggest that distorted chromatic contour perception is due to an impairment at a central stage of visual processing in PD and an imbalance of the serotonergic system. Whether CFT is a reliable method to predict the individual risk of hallucinosis in PD has to be evaluated.

The role of serotonergic-cholinergic interactions in the mediation of cognitive behaviour

Cholinergic systems have been linked to cognitive processes such as attention, learning and mnemonic function. However, other neurotransmitter systems, such as the serotonergic one, which may have only minor effects on cognitive function on their own, interact with cholinergic function and their combined effects may have marked behavioural actions. Some studies have dealt with serotonergic-cholinergic interactions, but it is unclear whether both systems affect cognition directly or whether interactions at a behavioural level result from additional alterations in non-cognitive factors. This distinction is difficult, since it is possible that the diverse cholinergic and serotonergic systems serve different roles in the mediation of cognitive processes, both at the neuroanatomical and neurochemical level. Nevertheless, it is possible that cholinergic systems primarily alter accuracy in cognitive tasks, whereas serotonergic neurotransmission modulates behaviour by altering bias (motivation, motor processes). Whether serotonin alters accuracy or bias, however, may also depend on the cognitive process under investigation: it is suggested that attention, stimulus processing and/or arousal can be influenced by both cholinergic and serotonergic systems independently from each other. Cholinergic and serotonergic projections to cortex and thalamus may be of importance in the mediation of these cognitive processes. Serotonergic-cholinergic interactions could also be of importance in the mediation of learning processes and trial-by-trial working memory. The data available do not allow an unambiguous conclusion about the role of these interactive processes in the mediation of long-term reference memory. These processes may rely on serotonergic-cholinergic interactions at the hippocampal level. It is concluded that serotonergic-cholinergic interactions play an important role in the mediation of behavioural, including cognitive, performance, but that further studies are necessary in order to elucidate the exact nature of these interactions.