Loss of [3H]4-DAMP binding to muscarinic receptors in the orbitofrontal cortex of Alzheimer's disease patients with psychosis.

RATIONALE: Neuropsychiatric behaviours in Alzheimer's disease (AD) patients have been associated with neocortical alterations of presynaptic cholinergic and muscarinic M2 receptor markers. In contrast, it is unclear whether non-M2 muscarinic receptors have a role to play in AD behavioural symptoms. OBJECTIVES: To correlate the alterations of neocortical postsynaptic muscarinic receptors with clinical features of AD. MATERIALS AND METHODS: [(3)H]4-DAMP were used in binding assays with lysates of Chinese hamster ovary (CHO) cells stably transfected with M1-M5 receptors. [(3)H]4-DAMP was further used to measure muscarinic receptors in the postmortem orbitofrontal cortex of aged controls and AD patients longitudinally assessed for cognitive decline and behavioural symptoms. RESULTS: [(3)H]4-DAMP binds to human postmortem brain homogenates and M1-, M3-, M4- and M5-transfected CHO lysates with subnanomolar affinity. Compared to the controls, the [(3)H]4-DAMP binding density is reduced only in AD patients with significant psychotic symptoms. The association between reduced [(3)H]4-DAMP binding and psychosis is independent of the effects of dementia severity or neurofibrillary tangle burden. CONCLUSIONS: This study suggests that the loss of non-M2 muscarinic receptors in the orbitofrontal cortex may be a neurochemical substrate of psychosis in AD and provides a rationale for further development of muscarinic receptor ligands in AD pharmacotherapy.

The relationship between homocysteine, cognition and stroke subtypes in acute stroke.

BACKGROUND: Elevations in plasma homocysteine (Hcy) have been associated with an increased risk of stroke and dementia. The mechanisms underlying these associations remain poorly understood. OBJECTIVES: This study examines the relationships between Hcy, cognition, and stroke subtype. We hypothesize that: 1) Hcy levels are inversely related to cognition, 2) Hcy levels are unrelated to stroke subtype, and 3) stroke subtype affects cognition. METHODS: We studied 169 consenting patients admitted for acute stroke during a 4 month period. Blood was drawn for Hcy levels and the Mini-Mental State Examination (MMSE) was administered within 9 days of admission. The Oxfordshire Community Stroke Project Classification was used to characterize stroke subtypes. Correlation between Hcy and MMSE scores was examined as was the relationships between Hcy and stroke subtype, and between stroke subtypes and MMSE scores. RESULTS: A significant inverse correlation between Hcy levels and MMSE scores was demonstrated (r=-0.243, p=0.001). MMSE scores also differed according to the type of stroke, with Total or Partial Anterior Circulation Infarcts (TACI/PACI) scoring lowest (F=8.77, df=2, p<0.001). Hcy levels did not differ between the various stroke subtypes (F=0.21, df=2, p=0.81). Multivariate linear regression analysis showed that age, education, and stroke subtype, but not Hcy, were independent predictors of acute MMSE scores. CONCLUSIONS: In this study sample, there was an inverse relationship between Hcy and cognition in acute stroke patients. However, Hcy was not an independent predictor for cognition in acute stroke after other factors such as stroke subtype and patient age were taken into account. These results suggest that during the acute stage of stroke, stroke subtype is a more important factor in determining cognition than Hcy levels.

Cholinergic-serotonergic imbalance contributes to cognitive and behavioral symptoms in Alzheimer's disease.

Neuropsychiatric symptoms seen in Alzheimer's disease (AD) are not simply a consequence of neurodegeneration, but probably result from differential neurotransmitter alterations, which some patients are more at risk of than others. Therefore, the hypothesis of this study is that an imbalance between the cholinergic and serotonergic systems is related to cognitive symptoms and psychological syndromes of dementia (BPSD) in patients with AD. Cholinergic and serotonergic functions were assessed in post-mortem frontal and temporal cortex from 22 AD patients who had been prospectively assessed with the Mini-Mental State examination (MMSE) for cognitive impairment and with the Present Behavioral Examination (PBE) for BPSD including aggressive behavior, overactivity, depression and psychosis. Not only cholinergic deficits, but also the cholinacetyltransferase/serotonin ratio significantly correlated with final MMSE score both in frontal and temporal cortex. In addition, decreases in cholinergic function correlated with the aggressive behavior factor, supporting a dual role for the cholinergic system in cognitive and non-cognitive disturbances associated to AD. The serotonergic system showed a significant correlation with overactivity and psychosis. The ratio of serotonin to acetylcholinesterase levels was also correlated with the psychotic factor at least in women. It is concluded that an imbalance between cholinergic-serotonergic systems may be responsible for the cognitive impairment associated to AD. Moreover, the major findings of this study are the relationships between neurochemical markers of both cholinergic and serotonergic systems and non-cognitive behavioral disturbances in patients with dementia.

Differential involvement of 5-HT(1B/1D) and 5-HT6 receptors in cognitive and non-cognitive symptoms in Alzheimer's disease.

Growing evidence suggests that a compromised serotonergic system plays an important role in the pathophysiology of Alzheimer's disease (AD). We assessed the expression of 5-HT(1B/1D) and 5-HT(6) receptors and cholinacetyltransferase (ChAT) activity in post-mortem frontal and temporal cortex from AD patients who had been prospectively assessed for cognitive function using the Mini-Mental State Examination (MMSE) and behavioral changes using the Present Behavioral Examination (PBE). 5-HT(1B/1D) and 5-HT(6) receptor densities were significantly reduced in both cortical areas. 5-HT(1B/1D) receptor density was correlated to MMSE decline in the frontal cortex, supporting its implication in memory impairment. The best predictor for lowered 5-HT(6) receptor density in the temporal cortex was the PBE measure of overactivity. The 5-HT(6)/ChAT ratio was related to aggression both in the frontal and temporal cortex. Therefore, antagonists acting at 5-HT(6) receptors could be useful in the treatment of non-cognitive symptoms associated to AD.

Transcultural expression of subcortical vascular disease.

BACKGROUND: Many transcultural issues pertaining to subcortical vascular disease remain unanswered, and there is a relative paucity of research on stroke and dementia in non-Western societies. OBJECTIVE: To describe variations in the epidemiology of stroke and dementia, the recognition of dementia as an entity across cultures, the cultural specificity of screening tools and assessment instruments, and cultural influences on the management of stroke and dementia. RESULTS: Several studies have pointed out differences in the subtypes and outcomes from stroke across different world regions. Notably, non-Western populations may have a higher rate of hemorrhage, whilst in ischemic stroke subcortical vascular disease is predominant. A low prevalence of dementia has been demonstrated in many studies of non-Western populations. Factors proposed to account for this include protective family attitudes, a lower frequency of ApoE4 and the high mortality of non-Western dementia subjects, which may mask a high age-specific incidence rate. Other medical factors such as training, diagnostic skills, the availability of investigations and healthcare provision may also play a role, as would patient specific cultural attitudes towards ageing and mental health, together with differences in language, social customs and literacy. It has been suggested that there is a major difference between Western and Asian nations in the ratio of vascular dementia to Alzheimer disease. However, few epidemiological field studies have utilized neuroimaging and the reported rates for particular diagnoses should be interpreted cautiously. A recent population study in Japan, which utilized screening by neuropsychologists and CT scanning, showed that vascular dementia accounted for nearly half the cases of dementia. Subcortical vascular disease accounts for the majority of patients with vascular dementia (VaD). CONCLUSIONS: With the rapid demographic changes taking place in non-Western countries, non-communicable diseases such as dementia and stroke will increasingly come to dominate disease burden. More studies are required to prevent and treat these diseases.

Characterization of histamine H3 receptors in Alzheimer's Disease brain and amyloid over-expressing TASTPM mice.

BACKGROUND AND PURPOSE: Histamine H3 receptor antagonists are currently being evaluated for their potential use in a number of central nervous system disorders including Alzheimer's Disease (AD). To date, little is known about the state of H3 receptors in AD. EXPERIMENTAL APPROACH: In the present study we used the radiolabelled H3 receptor antagonist [3H]GSK189254 to investigate H3 receptor binding in the amyloid over-expressing double mutant APPswe x PSI.MI46V (TASTPM) transgenic mouse model of AD and in post-mortem human AD brain samples. KEY RESULTS: No significant differences in specific H3 receptor binding were observed between wild type and TASTPM mice in the cortex, hippocampus or hypothalamus. Specific [3H]GSK189254 binding was detected in sections of human medial frontal cortex from AD brains of varying disease severity (Braak stages I-VI). With more quantitative analysis in a larger cohort, we observed that H3 receptor densities were not significantly different between AD and age-matched control brains in both frontal and temporal cortical regions. However, within the AD group, [3H]GSK189254 binding density in frontal cortex was higher in individuals with more severe dementia prior to death. CONCLUSIONS AND IMPLICATIONS: The maintenance of H3 receptor integrity observed in the various stages of AD in this study is important, given the potential use of H3 antagonists as a novel therapeutic approach for the symptomatic treatment of AD.

Genetic variation in the 5-HT2A receptor and altered neocortical [3H] ketanserin binding in Alzheimer's disease.

A common intronic single nucleotide polymorphism (T102C) in the 5-HT2A receptor gene is associated with the development of different neuropsychiatric symptoms, including hallucinations and depressive symptoms in Alzheimer's disease (AD). Differential 5-HT2A receptor binding has also been associated with the development of these symptoms in AD. However, the relationship between 5-HT2A (T102C) genotype and 5-HT2A receptor binding in AD and control human brains has not been examined. We examined the association between different 5-HT2A (T102C) genotypes and [(3)H] ketanserin binding in the temporal and frontal cortex of 20 AD and 14 control human brains. In homozygotes, but not heterozygotes, there was a significant reduction in B(max) values for [(3)H] ketanserin binding in both areas of cortex in AD compared with control subjects. This study suggests a mechanism for the generation of different neuropsychiatric symptoms in AD from a single nucleotide polymorphism with reduced receptor binding in T102C 5-HT2A receptor gene homozygotes correlating with susceptibility to depressive symptoms, whereas the relative preservation of receptor binding in heterozygotes with AD correlating with susceptibility to hallucinations.