Nucleus basalis neuronal loss, neuritic plaques and choline acetyltransferase activity in advanced Alzheimer's disease

Deep Brain Stimulation of Nucleus Basalis of Meynert improves learning in rat model of dementia

Background

Deep brain stimulation (DBS) of the nucleus basalis of Meynert (NBM) has been preliminarily investigated as a potential treatment for dementia. The degeneration of NBM cholinergic neurons is a pathological feature of many forms of dementia. Although stimulation of the NBM has been demonstrated to improve learning, the ideal parameters for NBM stimulation have not been elucidated. This study assesses the differential effects of varying stimulation patterns and duration on learning in a dementia rat model.

Methods

192-IgG-saporin (or vehicle) was injected into the NBM to produce dementia in rats. Next, all rats underwent unilateral implantation of a DBS electrode in the NBM. The experimental groups consisted of i-normal, ii-untreated demented, and iii-demented rats receiving NBM DBS. The stimulation paradigms included testing different modes (tonic and burst) and durations (1-hr, 5-hrs, and 24-hrs/day) over 10 daily sessions. Memory was assessed pre- and post-stimulation using two established learning paradigms: novel object recognition (NOR) and auditory operant chamber learning.

Results

Both normal and stimulated rats demonstrated improved performance in NOR and auditory learning as compared to the unstimulated demented group. The burst stimulation groups performed better than the tonic stimulated group. Increasing the daily stimulation duration to 24-hr did not further improve cognitive performance in an auditory recognition task and degraded the results on a NOR task as compared with 5-hr.

Conclusion

The present findings suggest that naturalistic NBM burst DBS may offer a potential effective therapy for treating dementia and suggests potential strategies for the reevaluation of current human NBM stimulation paradigms.

Early loss of locus coeruleus innervation promotes cognitive and neuropathological changes before amyloid plaque deposition in a transgenic rat model of Alzheimer's disease

AIMS

The locus coeruleus (LC) is the main source of noradrenaline (NA) in the mammalian brain and has been found to degenerate during the initial stages of Alzheimer's disease (AD). Recent studies indicate that at late stages of the amyloid pathology, LC-pathological alterations accelerate AD-like pathology progression by interfering with the neuromodulatory and anti-inflammatory properties of NA. However, the impact of LC degeneration at the earliest stages of amyloidosis on the AD-like pathology is not well understood.

METHODS

The LC was lesioned in wild-type (wt) and McGill-R-Thy1-APP transgenic rats (APP tg) by administering N-(2-chloroethyl)-N-ethyl-bromo-benzylamine (DSP4) before amyloid plaque deposition. Cognitive deficits and AD-like neuropathological changes were measured after the LC lesion.

RESULTS

Four months post-treatment, rats displayed a decrease in brain noradrenergic innervation. The LC lesion in APP tg-treated rats enhanced cognitive deficits and decreased hippocampal cholinergic innervation and neurotrophin expression. In addition, the APP tg-treated rats displayed an increased microglial and astroglial cell number in close vicinity to hippocampal amyloid-beta burdened neurons. The recruited microglia showed cellular alterations indicative of an intermediate activation state.

CONCLUSIONS

Our results indicate that early LC demise aggravates the early neuroinflammatory process, cognitive impairments, cholinergic deficits and neurotrophin deregulation at the earliest stages of the human-like brain amyloidosis.

TDP-43 promotes tau accumulation and selective neurotoxicity in bigenic Caenorhabditis elegans

Although amyloid β (Aβ) and tau aggregates define the neuropathology of Alzheimer's disease (AD), TDP-43 has recently emerged as a co-morbid pathology in more than half of patients with AD. Individuals with concomitant Aβ, tau and TDP-43 pathology experience accelerated cognitive decline and worsened brain atrophy, but the molecular mechanisms of TDP-43 neurotoxicity in AD are unknown. Synergistic interactions among Aβ, tau and TDP-43 may be responsible for worsened disease outcomes. To study the biology underlying this process, we have developed new models of protein co-morbidity using the simple animal Caenorhabditis elegans. We demonstrate that TDP-43 specifically enhances tau but not Aβ neurotoxicity, resulting in neuronal dysfunction, pathological tau accumulation and selective neurodegeneration. Furthermore, we find that synergism between tau and TDP-43 is rescued by loss-of-function of the robust tau modifier sut-2. Our results implicate enhanced tau neurotoxicity as the primary driver underlying worsened clinical and neuropathological phenotypes in AD with TDP-43 pathology, and identify cell-type specific sensitivities to co-morbid tau and TDP-43. Determining the relationship between co-morbid TDP-43 and tau is crucial to understand, and ultimately treat, mixed pathology AD.

OUP accepted manuscript

Cognitive deficits in Alzheimer’s disease, specifically amnestic (memory dominant) deficits, are associated with cholinergic degeneration in the basal forebrain. The cholinergic nucleus within the basal forebrain, the nucleus basalis of Meynert, exhibits local atrophy and reduced cortical tract integrity on MRI, and reveals amyloid-β and phosphorylated-tau pathology at autopsy. To understand the pathophysiology of nucleus basalis of Meynert atrophy and its neocortical projections in Alzheimer’s disease, we used a combined post-mortem in situ MRI and histopathology approach. A total of 19 Alzheimer’s disease (10 amnestic and nine non-amnestic) and nine non-neurological control donors underwent 3 T T₁-weighted MRI for anatomical delineation and volume assessment of the nucleus basalis of Meynert, and diffusion-weighted imaging for microstructural assessment of the nucleus and its projections. At subsequent brain autopsy, tissue dissection and immunohistochemistry were performed for amyloid-β, phosphorylated-tau and choline acetyltransferase. Compared to controls, we observed an MRI-derived volume reduction and altered microstructural integrity of the nucleus basalis of Meynert in Alzheimer’s disease donors. Furthermore, decreased cholinergic cell density was associated with reduced integrity of the nucleus and its tracts to the temporal lobe, specifically to the temporal pole of the superior temporal gyrus, and the parahippocampal gyrus. Exploratory post hoc subgroup analyses indicated that cholinergic cell density could be associated with cortical tract alterations in amnestic Alzheimer’s disease donors only. Our study illustrates that in Alzheimer’s disease, cholinergic degeneration in the nucleus basalis of Meynert may contribute to damaged cortical projections, specifically to the temporal lobe, leading to cognitive deterioration.

N-Methyl-D-aspartate (NMDA) and cannabinoid CB2 receptors form functional complexes in cells of the central nervous system: insights into the therapeutic potential of neuronal and microglial NMDA receptors

BACKGROUND

The cannabinoid CB2 receptor (CB2R), which is a target to afford neuroprotection, and N-methyl-D-aspartate (NMDA) ionotropic glutamate receptors, which are key in mediating excitatory neurotransmission, are expressed in both neurons and glia. As NMDA receptors are the target of current medication in Alzheimer's disease patients and with the aim of finding neuromodulators of their actions that could provide benefits in dementia, we hypothesized that cannabinoids could modulate NMDA function.

METHODS

Immunocytochemistry was used to analyze the colocalization between CB2 and NMDA receptors; bioluminescence resonance energy transfer was used to detect CB2-NMDA receptor complexes. Calcium and cAMP determination, mitogen-activated protein kinase (MAPK) pathway activation, and label-free assays were performed to characterize signaling in homologous and heterologous systems. Proximity ligation assays were used to quantify CB2-NMDA heteromer expression in mouse primary cultures and in the brain of APPSw/Ind transgenic mice, an Alzheimer's disease model expressing the Indiana and Swedish mutated version of the human amyloid precursor protein (APP).

RESULTS

In a heterologous system, we identified CB2-NMDA complexes with a particular heteromer print consisting of impairment by cannabinoids of NMDA receptor function. The print was detected in activated primary microglia treated with lipopolysaccharide and interferon-γ. CB2R activation blunted NMDA receptor-mediated signaling in primary hippocampal neurons from APPSw/Ind mice. Furthermore, imaging studies showed that in brain slices and in primary cells (microglia or neurons) from APPSw/Ind mice, there was a marked overexpression of macromolecular CB2-NMDA receptor complexes thus becoming a tool to modulate excessive glutamate input by cannabinoids.

CONCLUSIONS

The results indicate a negative cross-talk in CB2-NMDA complexes signaling. The expression of the CB2-NMDA receptor heteromers increases in both microglia and neurons from the APPSw/Ind transgenic mice, compared with levels in samples from age-matched control mice.

Basal forebrain cholinergic system in the dementias: Vulnerability, resilience, and resistance

The basal forebrain cholinergic neurons (BFCN) provide the primary source of cholinergic innervation of the human cerebral cortex. They are involved in the cognitive processes of learning, memory, and attention. These neurons are differentially vulnerable in various neuropathologic entities that cause dementia. This review summarizes the relevance to BFCN of neuropathologic markers associated with dementias, including the plaques and tangles of Alzheimer's disease (AD), the Lewy bodies of diffuse Lewy body disease, the tauopathy of frontotemporal lobar degeneration (FTLD-TAU) and the TDP-43 proteinopathy of FTLD-TDP. Each of these proteinopathies has a different relationship to BFCN and their corticofugal axons. Available evidence points to early and substantial degeneration of the BFCN in AD and diffuse Lewy body disease. In AD, the major neurodegenerative correlate is accumulation of phosphotau in neurofibrillary tangles. However, these neurons are less vulnerable to the tauopathy of FTLD. An intriguing finding is that the intracellular tau of AD causes destruction of the BFCN, whereas that of FTLD does not. This observation has profound implications for exploring the impact of different species of tauopathy on neuronal survival. The proteinopathy of FTLD-TDP shows virtually no abnormal inclusions within the BFCN. Thus, the BFCN are highly vulnerable to the neurodegenerative effects of tauopathy in AD, resilient to the neurodegenerative effect of tauopathy in FTLD and apparently resistant to the emergence of proteinopathy in FTLD-TDP and perhaps also in Pick's disease. Investigations are beginning to shed light on the potential mechanisms of this differential vulnerability and their implications for therapeutic intervention.

Blood Biomarkers for Alzheimer's Disease in Down Syndrome

Epidemiological evidence suggests that by the age of 40 years, all individuals with Down syndrome (DS) have Alzheimer's disease (AD) neuropathology. Clinical diagnosis of dementia by cognitive assessment is complex in these patients due to the pre-existing and varying intellectual disability, which may mask subtle declines in cognitive functioning. Cerebrospinal fluid (CSF) and positron emission tomography (PET) biomarkers, although accurate, are expensive, invasive, and particularly challenging in such a vulnerable population. The advances in ultra-sensitive detection methods have highlighted blood biomarkers as a valuable and realistic tool for AD diagnosis. Studies with DS patients have proven the potential blood-based biomarkers for sporadic AD (amyloid-β, tau, phosphorylated tau, and neurofilament light chain) to be useful in this population. In addition, biomarkers related to other pathologies that could aggravate dementia progression-such as inflammatory dysregulation, energetic imbalance, or oxidative stress-have been explored. This review serves to provide a brief overview of the main findings from the limited neuroimaging and CSF studies, outline the current state of blood biomarkers to diagnose AD in patients with DS, discuss possible past limitations of the research, and suggest considerations for developing and validating blood-based biomarkers in the future.

Involvement of Cholinergic, Adrenergic, and Glutamatergic Network Modulation with Cognitive Dysfunction in Alzheimer's Disease

Alzheimer's disease (AD), the most common cause of dementia, is a progressive neurodegenerative disease. The number of AD cases has been rapidly growing worldwide. Several the related etiological hypotheses include atypical amyloid β (Aβ) deposition, neurofibrillary tangles of tau proteins inside neurons, disturbed neurotransmission, inflammation, and oxidative stress. During AD progression, aberrations in neurotransmission cause cognitive decline-the main symptom of AD. Here, we review the aberrant neurotransmission systems, including cholinergic, adrenergic, and glutamatergic network, and the interactions among these systems as they pertain to AD. We also discuss the key role of N-methyl-d-aspartate receptor (NMDAR) dysfunction in AD-associated cognitive impairment. Furthermore, we summarize the results of recent studies indicating that increasing glutamatergic neurotransmission through the alteration of NMDARs shows potential for treating cognitive decline in mild cognitive impairment or early stage AD. Future studies on the long-term efficiency of NMDA-enhancing strategies in the treatment of AD are warranted.

The diagonal band of Broca in health and disease

The diagonal band of Broca (DBB) contains the second largest cholinergic cell group in the human brain, known as the nucleus of the vertical limb of the DBB (nvlDBB). It has major projections to the hippocampus, but it is often underinvestigated, partly due to its ill-defined anatomical boundaries and hence the difficulty of reliable sampling. In this chapter, we have reviewed the historical literature to reestablish the anatomy of the nvlDBB, distinguishing it from neighboring basal forebrain cholinergic nuclei. Although varying degrees of neuronal loss in the nvlDBB have been reported in a range of neurological disorders, and in the aged brain, the significant nvlDBB cholinergic neuronal loss reported in Lewy body dementias is of particular interest. Retrograde tracer study in rodents has demonstrated reciprocal connections between the DBB and the hippocampal CA2 subfield, an area particularly susceptible to Lewy pathologies. Previous functional studies have demonstrated that the nvlDBB is particularly involved in memory retrieval, a cognitive domain severely affected in Lewy body disorders. Based on these observations, we propose an anatomical and functional connection between the cholinergic component of the nvlDBB (Ch2) and the hippocampal CA2.

Treatment of Alzheimer's diseases using donepezil nanoemulsion: an intranasal approach

Alzheimer disease (AD) is very common among the older people. There are few medications available as oral and suspension dosage forms for the management of AD. Due to the rising cases of AD and the associated risks of the existing line of treatment, oil in water (o/w) nanoemulsion (NE) loaded with donepezil was prepared to explore intranasal route of administration. The NE was prepared using labrasol (10%), cetyl pyridinium chloride (1% in 80% water), and glycerol (10%), with a drug concentration of 1 mg/ml. The developed NE was characterized for particle size, polydispersity index (PDI), and zeta potential. In vitro release studies were conducted to observe the release of drug. Further in vivo studies of developed NE were done on Sprague Dawley rats using technetium pertechnetate (^99mTc) labeled formulations to investigate the nose to brain drug delivery pathway. The nanoemulsion showed particle size of 65.36 nm with a PDI of 0.084 and zeta potential of -10.7 mV. In vitro release studies showed maximum release of 99.22% in 4 h in phosphate-buffered saline, 98% in 2 h in artificial cerebrospinal fluid, and 96% in 2 h in simulated nasal fluid. The cytotoxicity and antioxidant activity of the NE showed dose-dependent cytotoxicity and % radical scavenging activity (%RSA). The images of giemsa staining also confirmed that the developed formulation has no impact on the morphology of cells. Scintigrams showed maximum uptake of NE in the brain. The findings suggested that the developed NE loaded with donepezil hydrochloride could serve as a new approach for the treatment of Alzheimer via nose to brain drug delivery. Graphical abstract.

Polygenic Risk Score for Alzheimer's Disease Is Associated With Ch4 Volume in Normal Subjects

Alzheimer's disease (AD) is a common neurodegenerative disease. APOE is the strong genetic risk factor of AD. The existing genome-wide association studies have identified many single nucleotide polymorphisms (SNPs) with minor effects on AD risk and the polygenic risk score (PRS) is presented to combine the effect of these SNPs. On the other hand, the volumes of various brain regions in AD patients have significant changes compared to that in normal individuals. Ch4 brain region containing at least 90% cholinergic neurons is the most extensive and conspicuous in the basal forebrain. Here, we investigated the relationship between the combined effect of AD-associated SNPs and Ch4 volume using the PRS approach. Our results showed that Ch4 volume in AD patients is significantly different from that in normal control subjects (p-value < 2.2 × 10-16). AD PRS, is not associated with the Ch4 volume in AD patients, excluding the APOE region (p-value = 0.264) and including the APOE region (p-value = 0.213). However, AD best-fit PRS, excluding the APOE region, is associated with Ch4 volume in normal control subjects (p-value = 0.015). AD PRS based on 8070 SNPs could explain 3.35% variance of Ch4 volume. In addition, the p-value of AD PRS model in normal control subjects, including the APOE region, is 0.006. AD PRS based on 8079 SNPs could explain 4.23% variance of Ch4 volume. In conclusion, PRS based on AD-associated SNPs is significantly related to Ch4 volume in normal subjects but not in patients.

HDAC2 dysregulation in the nucleus basalis of Meynert during the progression of Alzheimer's disease

AIMS

Alzheimer's disease (AD) is characterized by degeneration of cholinergic basal forebrain (CBF) neurons in the nucleus basalis of Meynert (nbM), which provides the major cholinergic input to the cortical mantle and is related to cognitive decline in patients with AD. Cortical histone deacetylase (HDAC) dysregulation has been associated with neuronal degeneration during AD progression. However, whether HDAC alterations play a role in CBF degeneration during AD onset is unknown. We investigated global HDAC protein levels and nuclear HDAC2 immunoreactivity in tissue containing the nbM, changes and their association with neurofibrillary tangles (NFTs) during the progression of AD.

METHODS

We used semi-quantitative western blotting and immunohistochemistry to evaluate HDAC and sirtuin (SIRT) levels in individuals that died with a premortem clinical diagnosis of no cognitive impairment (NCI), mild cognitive impairment (MCI), mild/moderate AD (mAD) or severe AD (sAD). Quantitative immunohistochemistry was used to identify HDAC2 protein levels in individual cholinergic nbM nuclei and their colocalization with the early phosphorylated tau marker AT8, the late-stage apoptotic tau marker TauC3 and Thioflavin-S, a marker of β-pleated sheet structures in NFTs.

RESULTS

In AD patients, HDAC2 protein levels were dysregulated in the basal forebrain region containing cholinergic neurons of the nbM. HDAC2 nuclear immunoreactivity was reduced in individual cholinergic nbM neurons across disease stages. HDAC2 nuclear reactivity correlated with multiple cognitive domains and with NFT formation.

CONCLUSIONS

These findings suggest that HDAC2 dysregulation contributes to cholinergic nbM neuronal dysfunction, NFT pathology, and cognitive decline during clinical progression of AD.

Precision and False Perceptual Inference

Accurate perceptual inference fundamentally depends upon accurate beliefs about the reliability of sensory data. In this paper, we describe a Bayes optimal and biologically plausible scheme that refines these beliefs through a gradient descent on variational free energy. To illustrate this, we simulate belief updating during visual foraging and show that changes in estimated sensory precision (i.e., confidence in visual data) are highly sensitive to prior beliefs about the contents of a visual scene. In brief, confident prior beliefs induce an increase in estimated precision when consistent with sensory evidence, but a decrease when they conflict. Prior beliefs held with low confidence are rapidly updated to posterior beliefs, determined by sensory data. These induce much smaller changes in beliefs about sensory precision. We argue that pathologies of scene construction may be due to abnormal priors, and show that these can induce a reduction in estimated sensory precision. Having previously associated this precision with cholinergic signaling, we note that several neurodegenerative conditions are associated with visual disturbances and cholinergic deficits; notably, the synucleinopathies. On relating the message passing in our model to the functional anatomy of the ventral visual stream, we find that simulated neuronal loss in temporal lobe regions induces confident, inaccurate, empirical prior beliefs at lower levels in the visual hierarchy. This provides a plausible, if speculative, computational mechanism for the loss of cholinergic signaling and the visual disturbances associated with temporal lobe Lewy body pathology. This may be seen as an illustration of the sorts of hypotheses that may be expressed within this computational framework.

Review: Revisiting the human cholinergic nucleus of the diagonal band of Broca

Although the nucleus of the vertical limb of the diagonal band of Broca (nvlDBB) is the second largest cholinergic nucleus in the basal forebrain, after the nucleus basalis of Meynert, it has not generally been a focus for studies of neurodegenerative disorders. However, the nvlDBB has an important projection to the hippocampus and discrete lesions of the rostral basal forebrain have been shown to disrupt retrieval memory function, a major deficit seen in patients with Lewy body disorders. One reason for its neglect is that the anatomical boundaries of the nvlDBB are ill defined and this area of the brain is not part of routine diagnostic sampling protocols. We have reviewed the history and anatomy of the nvlDBB and now propose guidelines for distinguishing nvlDBB from other neighbouring cholinergic cell groups for standardizing future clinicopathological work. Thorough review of the literature regarding neurodegenerative conditions reveals inconsistent results in terms of cholinergic neuronal loss within the nvlDBB. This is likely to be due to the use of variable neuronal inclusion criteria and omission of cholinergic immunohistochemical markers. Extrapolating from those studies showing a significant nvlDBB neuronal loss in Lewy body dementia, we propose an anatomical and functional connection between the cholinergic component of the nvlDBB (Ch2) and the CA2 subfield in the hippocampus which may be especially vulnerable in Lewy body disorders.

Differential deregulation of NGF and BDNF neurotrophins in a transgenic rat model of Alzheimer's disease

Evidence from human neuropathological studies indicates that the levels of the neurotrophins nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are compromised in Alzheimer's disease. However, the causes and temporal (pathology-dependent) evolution of these alterations are not completely understood. To elucidate these issues, we investigated the McGill-R-Thy1-APP transgenic rat, which exhibits progressive intracellular and extracellular amyloid-beta (Aβ) pathology and ensuing cognitive deficits. Neurochemical analyses revealed a differential dysregulation of NGF and BDNF transcripts and protein expression. While BDNF mRNA levels were significantly reduced at very early stages of amyloid pathology, before plaques appeared, there were no changes in NGF mRNA expression even at advanced stages. Paradoxically, the protein levels of the NGF precursor were increased. These changes in neurotrophin expression are identical to those seen during the progression of Alzheimer's disease. At advanced pathological stages, deficits in the protease cascade controlling the maturation and degradation of NGF were evident in McGill transgenic rats, in line with the paradoxical upregulation of proNGF, as seen in Alzheimer's disease, in the absence of changes in NGF mRNA. The compromise in NGF metabolism and BDNF levels was accompanied by downregulation of cortical cholinergic synapses; strengthening the evidence that neurotrophin dysregulation affects cholinergic synapses and synaptic plasticity. Our findings suggest a differential temporal deregulation of NGF and BDNF neurotrophins, whereby deficits in BDNF mRNA appear at early stages of intraneuronal Aβ pathology, before alterations in NGF metabolism and cholinergic synapse loss manifest.

Anticholinergic Drug Use and Risk to Cognitive Performance in Older Adults with Questionable Cognitive Impairment: A Cross-Sectional Analysis

BACKGROUND

Age-associated decline in central cholinergic activity makes older adults susceptible to the harmful effects of anticholinergic (AC) medications; however, there is an inadequate understanding of the association and possible effects of AC drugs on cognition. This cross-sectional study examines the associations of AC medications on cognition among older adults with questionable cognitive impairment (QCI).

METHODS

For this cross-sectional study, we used a multicenter database of community-dwelling older adults (N = 7351) aged 60+ years with QCI, from September 2005 to March 2014, as the baseline data. The Anticholinergic Drug Scale was used to categorize AC drug load into no, low, or moderate/high groups. Individuals with a Clinical Dementia Rating-Sum of Boxes score between 0.5 and 2.5 were identified as having QCI, while cognitive performance was evaluated using the Neuropsychological Test Battery. The mean z-scores of neuropsychological tests were grouped into a global cognition score.

RESULTS

Participants who took AC medications were older, largely female, and had a higher prevalence of incontinence than those without AC exposure. Global cognition was significantly greater in the moderate/high-AC group than the no-AC group (-0.23 ± 0.53 vs. -0.32 ± 0.53). Multivariable linear regression showed that the global cognition score among the low- and moderate/high-AC groups, compared with the no-AC group, was 0.064 higher (p = 0.006 and p = 0.12, respectively).

CONCLUSIONS

This cross-sectional study indicates that older adults with QCI who were exposed to AC medications might have higher global cognitive scores than those without AC exposure. The observed associations indicate that older adults might experience some beneficial cognitive effects from AC drugs, possibly due to the therapeutic effects of these medications in controlling comorbidities, thus outweighing their adverse effects on cognition.

Nanotubes impregnated human olfactory bulb neural stem cells promote neuronal differentiation in Trimethyltin-induced neurodegeneration rat model

Neural stem cells (NSCs) are multipotent self-renewing cells that could be used in cellular-based therapy for a wide variety of neurodegenerative diseases including Alzheimer's diseases (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS). Being multipotent in nature, they are practically capable of giving rise to major cell types of the nervous tissue including neurons, astrocytes, and oligodendrocytes. This is in marked contrast to neural progenitor cells which are committed to a specific lineage fate. In previous studies, we have demonstrated the ability of NSCs isolated from human olfactory bulb (OB) to survive, proliferate, differentiate, and restore cognitive and motor deficits associated with AD, and PD rat models, respectively. The use of carbon nanotubes (CNTs) to enhance the survivability and differentiation potential of NSCs following their in vivo engraftment have been recently suggested. Here, in order to assess the ability of CNTs to enhance the therapeutic potential of human OBNSCs for restoring cognitive deficits and neurodegenerative lesions, we co-engrafted CNTs and human OBNSCs in TMT-neurodegeneration rat model. The present study revealed that engrafted human OBNSCS-CNTs restored cognitive deficits, and neurodegenerative changes associated with TMT-induced rat neurodegeneration model. Moreover, the CNTs seemed to provide a support for engrafted OBNSCs, with increasing their tendency to differentiate into neurons rather than into glia cells. The present study indicate the marked ability of CNTs to enhance the therapeutic potential of human OBNSCs which qualify this novel therapeutic paradigm as a promising candidate for cell-based therapy of different neurodegenerative diseases.

Cholinergic neurodegeneration in an Alzheimer mouse model overexpressing amyloid-precursor protein with the Swedish-Dutch-Iowa mutations

Alzheimer's disease (AD) is a chronic neurodegenerative disorder that is mainly characterized by beta-amyloid (Aβ) plaque deposition, Tau pathology and dysfunction of the cholinergic system causing memory impairment. The aim of the present study was to examine (1) anxiety and cognition, (2) Aβ plaque deposition and (3) degeneration of cholinergic neurons in the nucleus basalis of Meynert (nbM) and cortical cholinergic innervation in an Alzheimer mouse model (APP_SweDI; overexpressing amyloid precursor protein (APP) with the Swedish K670N/M671L, Dutch E693Q, and Iowa D694N mutations). Our results show that 12-month-old APP_SweDI mice were more anxious and had more memory impairment. A large number of Aβ plaques were already visible at the age of 6 months and increased with age. A significant decrease in cholinergic neurons was seen in the transgenic mouse model in comparison to the wild-type mice, identified by immunohistochemistry against choline acetyltransferase (ChAT) and p75 neurotrophin receptor as well as by in situ hybridization. Moreover, a significant decrease in cortical cholinergic fiber density was found in the transgenic mice as compared to the wild-type. In the cerebral cortex of APP_SweDI mice, swollen cholinergic varicosities were seen in the vicinity of Aβ plaques. In conclusion, the present study shows that in an AD mouse model (APP_SweDI mice) a high Aβ plaque load in the cortex causes damage to cholinergic axons in the cortex, followed by subsequent retrograde-induced cell death of cholinergic neurons and some forms of compensatory processes. This degeneration was accompanied by enhanced anxiety and impaired cognition.

An inflammatory and trophic disconnect biomarker profile revealed in Down syndrome plasma: Relation to cognitive decline and longitudinal evaluation

INTRODUCTION

Given that Alzheimer's pathology develops silently over decades in Down syndrome (DS), prognostic biomarkers of dementia are a major need.

METHODS

We investigated the plasma levels of Aβ, proNGF, tPA, neuroserpin, metallo-proteases and inflammatory molecules in 31 individuals with DS (with and without dementia) and in 31 healthy controls. We examined associations between biomarkers and cognitive decline.

RESULTS

Aβ40 and Aβ42 were elevated in DS plasma compared to controls, even in DS individuals without dementia. Plasma Aβ correlated with the rate of cognitive decline across 2 years. ProNGF, MMP-1, MMP-3, MMP-9 activity, TNF-α, IL-6, and IL-10 were higher in DS plasma, even at AD-asymptomatic stages. Declining plasma Aβ42 and increasing proNGF levels correlated with cognitive decline. A combined measure of Aβ and inflammatory molecules was a strong predictor of prospective cognitive deterioration.

CONCLUSIONS

Our findings support the combination of plasma and cognitive assessments for the identification of DS individuals at risk of dementia.

MicroRNA-132 and early growth response-1 in nucleus basalis of Meynert during the course of Alzheimer's disease

The cholinergic nucleus basalis of Meynert, which is important for memory functions, shows neuronal activation ('up-phase') during the early stages of Alzheimer's disease and neurodegeneration ('down-phase') in later stages of Alzheimer's disease. MicroRNA-132 (miR-132) and the transcription factor early growth response-1 (EGR1) were proposed as possible candidate molecules regulating such an up-down activity pattern of the nucleus basalis of Meynert during the course of Alzheimer's disease, as they both show this up-down pattern of expression in the prefrontal cortex during the course of Alzheimer's disease. Not only do these two molecules stimulate synaptic activity and plasticity, they are also involved in Alzheimer's disease pathology and might, in addition, affect cholinergic function. In the nucleus basalis of Meynert, we investigated the expression of miR-132 and EGR1 along the entire course of Alzheimer's disease. Forty-nine post-mortem nucleus basalis of Meynert samples were studied, ranging from non-demented controls (Braak stage = 0) to late Alzheimer's disease patients (Braak stage = VI), and from clinical Reisberg scale 1 to 7. Each Braak stage contained seven samples, that were all well matched for confounding factors, i.e. age (range 58-91), sex, post-mortem delay, cerebrospinal fluid pH (as a measure for agonal state), APOE genotype, clock time of death, tissue fixation time, and tissue storage time. The alterations of these two molecules were studied over the course of Alzheimer's disease in relation to the expression of 4G8-stained amyloid-β, hyperphosphorylated tau stained by antibody AT8, neuronal fibrillary tangles and neuropil threads stained by silver, and in relation to alterations in choline acetyltransferase. We found that the expression of miR-132 and EGR1 in the nucleus basalis of Meynert was quite stable during the early stages of Alzheimer's disease and decreased significantly only during late Alzheimer's disease stages. In addition, miR-132 and EGR1 showed a significant positive correlation with choline acetyltransferase expression (r = 0.49, P < 0.001 and r = 0.61, P < 0.001), while choline acetyltransferase expression showed a significantly negative correlation with hyperphosphorylated tau (r = -0.33, P = 0.021) but no correlation with 4G8-stained amyloid-β. From the functional changes of miR-132 and EGR1 along the course of Alzheimer's disease we conclude: (i) that these two molecules may play a role in keeping the cholinergic function intact in early Alzheimer's disease stages; and (ii) that these molecules may contribute to the late neurodegeneration of this cholinergic nucleus.

Effects of rs3846662 Variants on HMGCR mRNA and Protein Levels and on Markers of Alzheimer's Disease Pathology

3-Hydroxy-3-methyglutaryl coenzyme A reductase (HMGCR) is a cholesterol-regulating gene with statin relevance. rs3846662 being involved in regulation of HMGCR alternative splicing, we explored its impact on HMGCR messenger RNA (mRNA) and protein levels in the brain and the associations between those levels and levels of Alzheimer's disease pathological markers. We used brain samples derived from a cohort of 33 non-demented controls and 90 Alzheimer's disease autopsied-confirmed cases. HMGCR mRNA levels were determined in the frontal cortex (n = 114) and cerebellum (n = 110) using Taqman-qPCR, and HMGCR protein levels were determined in the frontal cortex (n = 117) using a commercial enzyme immunoassay. While densities of neurofibrillary tangles and senile plaques were determined in the frontal cortex (n = 74), total tau, phosphorylated Tau, and beta-amyloid 1-42 levels were determined in the frontal cortex (n = 94) and cerebellum (n = 91) using commercial enzyme immunoassays. Despite an increase in full-length HMGCR mRNA ratio in the frontal cortex of women carrying the AA genotype, there were no associations between rs3846662 and HMGCR mRNA or protein levels. An increased Δ13 HMGCR mRNA ratio was associated with increased levels of HMGCR proteins and neurofibrillary tangles in the frontal cortex but with reduced beta-amyloid 1-42 levels in the cerebellum, suggesting a brain cell type- or a disease progression-dependent association.

Nucleus basalis of Meynert revisited: anatomy, history and differential involvement in Alzheimer's and Parkinson's disease

It has been well established that neuronal loss within the cholinergic nucleus basalis of Meynert (nbM) correlates with cognitive decline in dementing disorders such as Alzheimer's disease (AD). Friedrich Lewy first observed his eponymous inclusion bodies in the nbM of postmortem brain tissue from patients with Parkinson's disease (PD) and cell loss in this area can be at least as extensive as that seen in AD. There has been confusion with regard to the terminology and exact localisation of the nbM within the human basal forebrain for decades due to the diffuse and broad structure of this "nucleus". Also, while topographical projections from the nbM have been mapped out in subhuman primates, no direct clinicopathological correlations between subregional nbM and cortical pathology and specific cognitive profile decline have been performed in human tissue. Here, we review the evolution of the term nbM and the importance of standardised nbM sampling for neuropathological studies. Extensive review of the literature suggests that there is a caudorostral pattern of neuronal loss within the nbM in AD brains. However, the findings in PD are less clear due to the limited number of studies performed. Given the differing neuropsychiatric and cognitive deficits in Lewy body-associated dementias (PD dementia and dementia with Lewy bodies) as compared to AD, we hypothesise that a different pattern of neuronal loss will be found in the nbM of Lewy body disease brains. Understanding the functional significance of the subregions of the nbM could prove important in elucidating the pathogenesis of dementia in PD.

Feasibility of β-sheet breaker peptide-H102 treatment for Alzheimer's disease based on β-amyloid hypothesis

β-amyloid hypothesis is the predominant hypothesis in the study of pathogenesis of Alzheimer's disease. This hypothesis claims that aggregation and neurotoxic effects of amyloid β (Aβ) is the common pathway in a variety of etiological factors for Alzheimer's disease. Aβ peptide derives from amyloid precursor protein (APP). β-sheet breaker peptides can directly prevent and reverse protein misfolding and aggregation in conformational disorders. Based on the stereochemical structure of Aβ1-42 and aggregation character, we had designed a series of β-sheet breaker peptides in our previous work and screened out a 10-residue peptide β-sheet breaker peptide, H102. We evaluated the effects of H102 on expression of P-tau, several associated proteins, inflammatory factors and apoptosis factors, and examined the cognitive ability of APP transgenic mice by behavioral test. This study aims to validate the β-amyloid hypothesis and provide an experimental evidence for the feasibility of H102 treatment for Alzheimer's disease.

Nerve growth factor metabolic dysfunction in Alzheimer's disease and Down syndrome

Alzheimer's disease (AD) is a devastating neurodegenerative condition and the most common type of amnestic dementia in the elderly. Individuals with Down syndrome (DS) are at increased risk of developing AD in adulthood as a result of chromosome 21 trisomy and triplication of the amyloid precursor protein (APP) gene. In both conditions, the central nervous system (CNS) basal forebrain cholinergic system progressively degenerates, and such changes contribute to the manifestation of cognitive decline and dementia. Given the strong dependency of these neurons on nerve growth factor (NGF), it was hypothesized that their atrophy was caused by NGF deficits. However, in AD, the synthesis of NGF is not affected at the transcript level and there is a marked increase in its precursor, proNGF. This apparent paradox remained elusive for many years. In this review, we discuss the recent evidence supporting a CNS deficit in the extracellular metabolism of NGF, both in AD and in DS brains. We describe the nature of this trophic disconnection and its implication for the atrophy of basal forebrain cholinergic neurons. We further discuss the potential of NGF pathway markers as diagnostic indicators of a CNS trophic disconnection.

Reactivation of atrophic neurons in Alzheimer's disease

Decreased metabolic rate may precede cognitive impairment in Alzheimer's disease (AD) and is thus an early occurring hallmark. Several observations in post-mortem brain indicate that activated neurons are better able to withstand aging and AD, a phenomenon paraphrased by us as 'use it or lose it'. Moreover, a number of pharmacological and nonpharmacological studies support the concept that activation of the brain has beneficial effects and may to a certain degree restore several aspects of cognition and other central functions. For instance, the circadian system may be restimulated in Alzheimer patients by exposing them to more light or transcutaneous nerve stimulation. A procedure has been developed to culture human post-mortem brain tissue that allows testing of the efficacy of putative stimulatory compounds such as neurotrophins.

Potential therapeutic uses of mecamylamine and its stereoisomers

Mecamylamine (3-methylaminoisocamphane hydrochloride) is a nicotinic parasympathetic ganglionic blocker, originally utilized as a therapeutic agent to treat hypertension. Mecamylamine administration produces several deleterious side effects at therapeutically relevant doses. As such, mecamylamine's use as an antihypertensive agent was phased out, except in severe hypertension. Mecamylamine easily traverses the blood-brain barrier to reach the central nervous system (CNS), where it acts as a nicotinic acetylcholine receptor (nAChR) antagonist, inhibiting all known nAChR subtypes. Since nAChRs play a major role in numerous physiological and pathological processes, it is not surprising that mecamylamine has been evaluated for its potential therapeutic effects in a wide variety of CNS disorders, including addiction. Importantly, mecamylamine produces its therapeutic effects on the CNS at doses 3-fold lower than those used to treat hypertension, which diminishes the probability of peripheral side effects. This review focuses on the pharmacological properties of mecamylamine, the differential effects of its stereoisomers, S(+)- and R(-)-mecamylamine, and the potential for effectiveness in treating CNS disorders, including nicotine and alcohol addiction, mood disorders, cognitive impairment and attention deficit hyperactivity disorder.

Lipidomics of Alzheimer's disease: current status

Alzheimer's disease (AD) is a cognitive disorder with a number of complex neuropathologies, including, but not limited to, neurofibrillary tangles, neuritic plaques, neuronal shrinkage, hypomyelination, neuroinflammation and cholinergic dysfunction. The role of underlying pathological processes in the evolution of the cholinergic deficit responsible for cognitive decline has not been elucidated. Furthermore, generation of testable hypotheses for defining points of pharmacological intervention in AD are complicated by the large scale occurrence of older individuals dying with no cognitive impairment despite having a high burden of AD pathology (plaques and tangles). To further complicate these research challenges, there is no animal model that reproduces the combined hallmark neuropathologies of AD. These research limitations have stimulated the application of 'omics' technologies in AD research with the goals of defining biologic markers of disease and disease progression and uncovering potential points of pharmacological intervention for the design of AD therapeutics. In the case of sporadic AD, the dominant form of dementia, genomics has revealed that the ε4 allele of apolipoprotein E, a lipid transport/chaperone protein, is a susceptibility factor. This seminal observation points to the importance of lipid dynamics as an area of investigation in AD. In this regard, lipidomics studies have demonstrated that there are major deficits in brain structural glycerophospholipids and sphingolipids, as well as alterations in metabolites of these complex structural lipids, which act as signaling molecules. Peroxisomal dysfunction appears to be a key component of the changes in glycerophospholipid deficits. In this review, lipid alterations and their potential roles in the pathophysiology of AD are discussed.

Oral bioavailability of the ether lipid plasmalogen precursor, PPI-1011, in the rabbit: a new therapeutic strategy for Alzheimer's disease

Introduction

Docosahexaenoic acid (DHA) and DHA-containing ethanolamine plasmalogens (PlsEtn) are decreased in the brain, liver and the circulation in Alzheimer's disease. Decreased supply of plasmalogen precursors to the brain by the liver, as a result of peroxisomal deficits is a process that probably starts early in the AD disease process. To overcome this metabolic compromise, we have designed an orally bioavailable DHA-containing ether lipid precursor of plasmalogens. PPI-1011 is an alkyl-diacyl plasmalogen precursor with palmitic acid at sn-1, DHA at sn-2 and lipoic acid at sn-3. This study outlines the oral pharmacokinetics of this precursor and its conversion to PlsEtn and phosphatidylethanolamines (PtdEtn).

Methods

Rabbits were dosed orally with PPI-1011 in hard gelatin capsules for time-course and dose response studies. Incorporation into PlsEtn and PtdEtn was monitored by LC-MS/MS. Metabolism of released lipoic acid was monitored by GC-MS. To monitor the metabolic fate of different components of PPI-1011, we labeled the sn-1 palmitic acid, sn-2 DHA and glycerol backbone with¹³C and monitored their metabolic fates by LC-MS/MS.

Results

PPI-1011 was not detected in plasma suggesting rapid release of sn-3 lipoic acid via gut lipases. This conclusion was supported by peak levels of lipoic acid metabolites in the plasma 3 hours after dosing. While PPI-1011 did not gain access to the plasma, it increased circulating levels of DHA-containing PlsEtn and PtdEtn. Labeling experiments demonstrated that the PtdEtn increases resulted from increased availability of DHA released via remodeling at sn-2 of phospholipids derived from PPI-1011. This release of DHA peaked at 6 hrs while increases in phospholipids peaked at 12 hr. Increases in circulating PlsEtn were more complex. Labeling experiments demonstrated that increases in the target PlsEtn, 16:0/22:6, consisted of 2 pools. In one pool, the intact precursor received a sn-3 phosphoethanolamine group and desaturation at sn-1 to generate the target plasmalogen. The second pool, like the PtdEtn, resulted from increased availability of DHA released during remodeling of sn-2. In the case of sn-1 18:0 and 18:1 plasmalogens with [¹³C₃]DHA at sn-2, labeling was the result of increased availability of [¹³C₃]DHA from lipid remodeling. Isotope and repeated dosing (2 weeks) experiments also demonstrated that plasmalogens and/or plasmalogen precursors derived from PPI-1011 are able to cross both the blood-retinal and blood-brain barriers.

Conclusions

Our data demonstrate that PPI-1011, an ether lipid precursor of plasmalogens is orally bioavailable in the rabbit, augmenting the circulating levels of unesterified DHA and DHA-containing PlsEtn and PtdEtn. Other ethanolamine plasmalogens were generated from the precursor via lipid remodeling (de-acylation/re-acylation reactions at sn-2) and phosphatidylethanolamines were generated via de-alkylation/re-acylation reactions at sn-1. Repeated oral dosing for 2 weeks with PPI-1011 resulted in dose-dependent increases in circulating DHA and DHA-containing plasmalogens. These products and/or precursors were also able to cross the blood-retinal and blood-brain barriers.

Cholinergic system function and cognition in mild cognitive impairment

Evidence for cholinergic dysfunction in very early stages of neurodegeneration like mild cognitive impairment (MCI) is inconclusive. Previous positron emission tomography (PET) studies based on small samples investigated if it is related to memory impairment. We examined whether cortical acetylcholine esterase (AChE) activity is reduced at this stage and correlated with cognitive function. N-[(11)C]-methyl-4-piperidyl acetate ([11C]MP4A), a positron emission tomography tracer for measuring cerebral AChE activity in vivo, was applied in 21 controls and 17 MCI patients. Parametric images of AChE activity were analyzed using standard atlas regions. Principal components analysis (PCA) of regional values of AChE activity and correlation analysis with neuropsychological test results was performed. Cortical AChE activity showed a significant decline in MCI patients compared with controls which was most pronounced in temporal regions. They formed the main part of a principal component that was related significantly to verbal and nonverbal memory, language comprehension and executive function. Cholinergic dysfunction is an early hallmark even before onset of dementia at the clinical stage of MCI. Its impact especially on temporal neocortex is associated with impaired neuropsychological function.

Compensatory responses to age-related decline in odor quality acuity: cholinergic neuromodulation and olfactory enrichment

The perceptual differentiation of odors can be measured behaviorally using generalization gradients. The steepness of these gradients defines a form of olfactory acuity for odor quality that depends on neural circuitry within the olfactory bulb and is regulated by cholinergic activity therein as well as by associative learning. Using this system as a reduced model for age-related cognitive decline, we show that aged mice, while maintaining almost the same baseline behavioral performance as younger mice, are insensitive to the effects of acutely elevated acetylcholine, which sharpens generalization gradients in young adult mice. Moreover, older mice exhibit evidence of chronically elevated acetylcholine levels in the olfactory bulb, suggesting that their insensitivity to further elevated levels of acetylcholine may arise because the maximum capacity of the system to respond to acetylcholine has already been reached. We propose a model in which an underlying, age-related, progressive deficit is mitigated by a compensatory cholinergic feedback loop that acts to retard the behavioral effects of what would otherwise be a substantial age-related decline in olfactory plasticity. We also treated mice with 10-day regimens of olfactory environmental enrichment and/or repeated systemic injections of the acetylcholinesterase inhibitor physostigmine. Each treatment alone sharpened odor quality acuity, but administering both treatments together had no greater effect than either alone. Age was not a significant main effect in this study, suggesting that some capacity for acetylcholine-dependent plasticity is still present in aged mice despite their sharply reduced ability to respond to acute increases in acetylcholine levels. These results suggest a dynamical framework for understanding age-related decline in neural circuit processing in which the direct effects of aging can be mitigated, at least temporarily, by systemic compensatory responses. In particular, a decline in cholinergic efficacy can precede any breakdown in cholinergic production, which may help explain the limited effectiveness of cholinergic replacement therapies in combating cognitive decline.

A new 18F-labeled fluoroacetylmorpholino derivative of vesamicol for neuroimaging of the vesicular acetylcholine transporter

With the aim of producing selective radiotracers for in vivo imaging of the vesicular acetylcholine transporter (VAChT) using positron mission tomography (PET), here, we report synthesis and analysis of a new class of conformationally constrained vesamicol analogues with moderate lipophilicity. The sequential ring opening on trans-1,4-cyclohexadiene dioxide enabled an approach to synthesize 6-arylpiperidino-octahydrobenzo[1,4]oxazine-7-ols [morpholino vesamicols]. The radiosynthesis of the [18F]fluoroacetyl-substituted derivative ([18F]FAMV) was achieved starting from a corresponding bromo precursor [2-Bromo-1-[7-hydroxy-6-(4-phenyl-piperidin-1-yl)-octahydro-benzo[1,4]oxazin-4-yl]-ethanone] and using a modified commercial computer-controlled module system with a radiochemical yield of 27+/-4%, a high radiochemical purity (99%) and a specific activity of 35 GBq/micromol. In competitive binding assays using a PC12 cell line overexpressing VAChT and [3H]-(-) vesamicol, 2-fluoro-1-[7-hydroxy-6-(4-phenyl-piperidin-1-yl)-octahydro-benzo[1,4]oxazin-4-yl]-ethanone (FAMV) demonstrated a high selectivity for binding to VAChT (K(i): 39.9+/-5.9 nM) when compared to its binding to sigma 1/2 receptors (Ki>1500 nM). The compound showed a moderate lipophilicity (logD (pH 7)=1.9) and a plasma protein binding of 49%. The brain uptake of [18F]FAMV was about 0.1% injected dose per gram at 5 min after injection and decreased continuously with time. Notably, an increasing accumulation of radioactivity in the lateral brain ventricles was observed. After 1 h, the accumulation of [18F]FAMV, expressed as ratio to the cerebellum, was 4.5 for the striatum, 2.0 for the cortical and 1.5 for the hippocampal regions, measured on brain slices using ex vivo autoradiography. At the present time, 75% of [18F]FAMV in the plasma was shown to be metabolized to various hydrophilic compounds, as detected by high-performance liquid chromatography. The degradation of [18F]FAMV was also detected in brain extracts as early as 15 min post injection (p.i.) and increased to 50% at 1 h postinjection. In conclusion, although the chemical properties of [18F]FAMV and the selectivity of binding to VAChT appear to be promising indicators of a useful PET tracer for imaging VAChT, a low brain extraction, in combination with only moderate specific accumulation in cholinergic brain regions and an insufficient in vivo stability prevents the application of this compound for neuroimaging in humans.

Peripheral ethanolamine plasmalogen deficiency: a logical causative factor in Alzheimer's disease and dementia

Although dementia of the Alzheimer's type (DAT) is the most common form of dementia, the severity of dementia is only weakly correlated with DAT pathology. In contrast, postmortem measurements of cholinergic function and membrane ethanolamine plasmalogen (PlsEtn) content in the cortex and hippocampus correlate with the severity of dementia in DAT. Currently, the largest risk factor for DAT is age. Because the synthesis of PlsEtn occurs via a single nonredundant peroxisomal pathway that has been shown to decrease with age and PlsEtn is decreased in the DAT brain, we investigated potential relationships between serum PlsEtn levels, dementia severity, and DAT pathology. In total, serum PlsEtn levels were measured in five independent population collections comprising >400 clinically demented and >350 nondemented subjects. Circulating PlsEtn levels were observed to be significantly decreased in serum from clinically and pathologically diagnosed DAT subjects at all stages of dementia, and the severity of this decrease correlated with the severity of dementia. Furthermore, a linear regression model predicted that serum PlsEtn levels decrease years before clinical symptoms. The putative roles that PlsEtn biochemistry play in the etiology of cholinergic degeneration, amyloid accumulation, and dementia are discussed.

A polymorphism in lipoprotein lipase affects the severity of Alzheimer's disease pathophysiology

Emerging evidences indicate a role for lipoprotein lipase (LPL) in degenerative states. Genetic variations in the LPL gene were previously associated to lipid imbalance and coronary artery disease (CAD) risk and severity, a condition that shares pathological features with common Alzheimer's disease (AD). To evaluate whether these genetic variations associate with the risk and pathophysiology of common AD, autopsy-confirmed patients (242 controls, 153 AD) were genotyped for a PvuII single nucleotide polymorphism (SNP; rs285; referred to as the P+ allele) of LPL. Brain LPL mRNA levels, cholesterol levels, amyloid concentration, senile plaques and neurofibrillary tangles density counts were measured and contrasted with specific LPL genotypes. When adjusted for age and sex, homozygosity for the P+ allele resulted in an odds ratio of 2.3 for the risk of developing AD. More importantly, we report that the presence of the P+ allele of LPL significantly affects its mRNA expression level (n = 51; P = 0.026), brain tissue cholesterol levels (n = 55; P = 0.0013), neurofibrillary tangles (n = 52; P = 0.025) and senile plaque (n = 52; P = 0.022) densities. These results indicate that a common polymorphism in the lipoprotein lipase gene modulates the risk level for sporadic AD in the eastern Canadian population but more importantly, indirectly modulates the pathophysiology of the brain in autopsy-confirmed cases.

Altered synaptic function in Alzheimer's disease

Alzheimer's disease is the leading cause of dementia in the elderly, presenting itself clinically by progressive loss of memory and learning. Since synaptic density correlates more closely with cognitive impairment than any other pathological lesion observable in the disease pathology, an increased understanding of the mechanisms behind synaptic disconnection is of vital importance. Our lab investigated the neurotransmitter-specific status of distinct cortical presynaptic bouton populations in various transgenic mouse models of the Alzheimer's-like amyloid pathology in order to assess their involvement throughout the progression of the pathology. These studies have revealed that the amyloid pathology appears to progress in a neurotransmitter-specific manner where the cholinergic terminals appear most vulnerable, followed by the glutamatergic terminals and finally by the somewhat more resilient GABAergic terminals. This review will discuss additional studies which also provide evidence of a neurotransmitter-specific pathology as well as comment on the potential explanations for the observed vulnerabilities, touching upon metabolic demand, trophic support and receptor mediated activation.

Increased Metabolic Activity in Nucleus Basalis of Meynert Neurons in Elderly Individuals With Mild Cognitive Impairment as Indicated by the Size of the Golgi Apparatus

In this study, we examined the metabolic activity of nucleus basalis of Meynert (NBM) neurons in individuals clinically diagnosed with no cognitive impairment (NCI, n = 8), mild cognitive impairment (MCI, n = 9), and subjects with moderate Alzheimer disease (AD, n = 7). We used Golgi apparatus (GA) size as a measure of neuronal metabolic activity. Subjects with MCI showed increased NBM metabolic activity; they had significantly more neurons with larger GA size as compared with NCI and AD subjects. In contrast, more NBM neurons with extremely small GA sizes, indicating reduced metabolic activity, were seen in AD. When these cases were classified according to their AD pathology (Braak I-II, III-IV, or V-VI), Braak III-IV subjects showed significantly increased GA sizes, comparable with the increase in clinically diagnosed MCI, whereas in Braak V-VI, GA sizes were dramatically reduced. Of all MCI and NCI subjects with similar Braak III-IV pathology, the MCI subjects again had significantly larger GA sizes. The larger NBM neuronal GA size seen in MCI suggests increased metabolic activity, associated with both the clinical progression from NCI to MCI, and with the early stages of AD pathology.

The amyloid pathology progresses in a neurotransmitter-specific manner

Past studies using transgenic models of early-staged amyloid pathology, have suggested that the amyloid pathology progresses in a neurotransmitter-specific manner where cholinergic terminals appear most vulnerable, followed by glutamatergic terminals and finally by somewhat more resistant GABAergic terminals. To determine whether this neurotransmitter-specific progression persists at later pathological stages, presynaptic bouton densities, and the areas of occupation and localization of plaque adjacent dystrophic neurites were quantified in 18-month-old APP(K670N, M671L)+PS1(M146L) doubly transgenic mice. Quantification revealed that transgenic animals had significantly lower cholinergic, glutamatergic and GABAergic presynaptic bouton densities. Cholinergic and glutamatergic dystrophic neurites appear to be heavily influenced by fibrillar Abeta as both types displayed a decreasing area of occupation with respect to increasing plaque size. Furthermore, cholinergic dystrophic neurites reside in closer proximity to plaques than glutamatergic dystrophic neurites, while GABAergic dystrophic neurites were minimal regardless of plaque size. To investigate whether similarities exist in the human AD pathology, a monoclonal antibody (McKA1) against the human vesicular glutamate transporter 1 (VGluT1) was developed. Subsequent staining in AD brain tissue revealed the novel presence of glutamatergic dystrophic neurites, to our knowledge the first evidence of a structural glutamatergic deficit in the AD pathology.

Sleep and circadian abnormalities in a transgenic mouse model of Alzheimer's disease: a role for cholinergic transmission

The Tg2576 mouse model of Alzheimer's disease (AD) exhibits age-dependent amyloid beta (Abeta) deposition in the brain. We studied electroencephalographically defined sleep and the circadian regulation of waking activities in Tg2576 mice to determine whether these animals exhibit sleep abnormalities akin to those in AD. In Tg2576 mice at all ages studied, the circadian period of wheel running rhythms in constant darkness was significantly longer than that of wild type mice. In addition, the increase in electroencephalographic delta (1-4 Hz) power that occurs during non-rapid eye movement sleep after sleep deprivation was blunted in Tg2576 mice relative to controls at all ages studied. Electroencephalographic power during non-rapid eye movement sleep was shifted to higher frequencies in plaque-bearing mice relative to controls. The wake-promoting efficacy of the acetylcholinesterase inhibitor donepezil was lower in plaque-bearing Tg2576 mice than in controls. Sleep abnormalities in Tg2576 mice may be due in part to a cholinergic deficit in these mice. At 22 months of age, two additional deficits emerged in female Tg2576 mice: time of day-dependent modulation of sleep was blunted relative to controls and rapid eye movement sleep as a percentage of time was lower in Tg2576 than in wild type controls. The rapid eye movement sleep deficit in 22 month-old female Tg2576 mice was abolished by brief passive immunization with an N-terminal antibody to Abeta. The Tg2576 model provides a uniquely powerful tool for studies on the pathophysiology of and treatments for sleep deficits and associated cholinergic abnormalities in AD.

Brain cholinesterases: I. The clinico-histopathological and biochemical basis of Alzheimer's disease

Substantial evidence is presented demonstrating that it is the cholinesterases (ChEs) that constitute the organizer, the connector and the safeguard for multiple neurochemical functions and mature anatomical architecture of the brain. In Alzheimer's disease (AD), the histopathological characteristics are initially and primarily associated with the degeneration of the acetylcholinesterase (AChE) system in various brain regions. Multiple classic and/or putative neurotransmitters and neuromodulators, virtually all the peptide hormones of the endocrine and neuroendocrine systems in the brain, their specific synthesizing and hydrolyzing marker enzymes and associated uptake processes (transporters), and receptors, do not actually participate in the formation of senile plaques and neurofibrillary tangles in the brains of patients suffering from AD. The massive perturbation in different neurochemicals seen in AD is essentially caused by the ChEs-associated pathology. The graded patterns of brain ChEs expression affect the preferential vulnerability and severity of the AD clinico-pathologic presentation. It seems that the common law in nature may also dominate the destiny of brain ChEs system, i.e., the weaker the cells express AChE, the more susceptible the cells are to AD degeneration, and vice versa.

Do disorders of movement cause movement disorders and dementia?

Neurons require long-distance microtubule-based transport systems to ferry vital cellular cargoes and signals between cell bodies and axonal or dendritic terminals. Considerable progress has been made on developing a molecular understanding of these processes and how they are integrated into normal neuronal functions. Recent work also suggests that these transport systems may fail early in the pathogenesis of a number of neurodegenerative diseases.

Therapeutic strategies for Alzheimer disease: focus on neuronal reactivation of metabolically impaired neurons

Based on several lines of evidence, it has been hypothesized that decreased neuronal metabolic rate may precede cognitive impairment, contributing to neuronal atrophy as well as reduced neuronal function in Alzheimer disease (AD). Additionally, studies have shown that stimulation of neurons through different mechanisms may protect those cells from the deleterious effects of aging and AD, a phenomenon we paraphrased as "use it or lose it." Therefore, it is attractive to direct the development of therapeutic strategies toward stimulation of metabolic rate/neuronal activity to improve cognition and other symptoms in AD. A number of pharmacological and nonpharmacological approaches discussed here support the concept that stimulation of the brain has beneficial effects and may, to a certain degree, restore several aspects of cognition and other central functions. For instance, the circadian system, which controls the sleep/wake cycle, may be stimulated in AD patients by exposing them to more light or transcutaneous nerve stimulation. We will also discuss a procedure that has been developed to culture human postmortem brain tissue, which allows testing of the efficacy of putative stimulatory compounds.

Cholinergic neuropathology in a mouse model of Alzheimer's disease

Transgenic mice overexpressing mutant human amyloid precursor protein (PDAPP mice) develop several Alzheimer's disease (AD)-like lesions including an age-related accumulation of amyloid-beta (Abeta)-containing neuritic plaques. Although aged, heterozygous PDAPP mice also exhibit synaptic and glial cell changes characteristic of AD pathology, no evidence of widespread neuronal loss has been observed. The present study sought to determine whether homozygous PDAPP mice, which express very high levels of Abeta peptide, exhibit AD-like cholinergic degenerative changes, and whether the changes parallel the deposition of Abeta plaques. Mice were examined at 2 and 4 months and at 1 and 2 years of age. There was an age-related increase in the density of Abeta plaques in the cortex and hippocampus of the PDAPP animals; at 4 months of age there were very few plaques, and at 2 years there was a very high density of plaques. There was an age-related reduction in the density of cholinergic nerve terminals in the cerebral cortex; at 2 months there was a normal density of nerve terminals, but as early as age 4 months there was an approximately 50% reduction. However, at age 2 years there was no difference in the number or size of basal forebrain cholinergic somata compared with 2-month-old PDAPP mice. These data indicated that the homozygous PDAPP mouse exhibits cholinergic nerve terminal degenerative pathology and that the cortical neurodegenerative changes occur before the deposition of Abeta-containing neuritic plaques.

Brain aging and Alzheimer's disease; use it or lose it

(1) Alzheimer's disease is a multifactorial disease in which age and APOE-epsilon 4 are important risk factors. (2) The neuropathological hallmarks of AD, i.e. amorphous plaques, neuritic plaques (NPs), pretangles, neurofibrillary tangles (NFT) and cell death are not part of a single pathogenetic cascade but may occur independently. (3) In brain areas where classical AD changes, i.e. NPs and NFTs, are present, such as the CA1 area of the hippocampus, the nucleus basalis of Meynert and the tuberomamillary nucleus, a decreased metabolic rate is found. The decreased metabolic rate appears not to be induced by the presence of pretangles, NFT or NPs. (4) Decreased metabolic rate may precede cognitive impairment and is thus an early occurring hallmark of AD, which, in principle, may be reversible. The observation that the administration of glucose or insulin enhances memory in AD patients also supports the view that AD has a metabolic basis. (5) Moreover, several observations in postmortem brain indicate that activated neurons are better able to withstand aging and AD, a phenomenon paraphrased by us as 'use it or lose it'. (6) It is, therefore, attractive to direct the development of therapeutic strategies towards restimulation of neuronal metabolic rate in order to improve cognition and other symptoms in AD. A number of pharmacological and non-pharmacological studies support the concept that activation of the brain has beneficial effects and may, to a certain degree, restore several aspects of cognition and other central functions. For instance, the circadian system may be restimulated in AD patients by exposing them to more light or transcutaneous nerve stimulation. A procedure has been developed to culture human postmortem brain tissue that allows testing of the efficacy of putative stimulatory compounds such as neurotrophins.

Alzheimer's disease and the basal forebrain cholinergic system: relations to beta-amyloid peptides, cognition, and treatment strategies

Alzheimer's disease (AD) is the most common form of degenerative dementia and is characterized by progressive impairment in cognitive function during mid- to late-adult life. Brains from AD patients show several distinct neuropathological features, including extracellular beta-amyloid-containing plaques, intracellular neurofibrillary tangles composed of abnormally phosphorylated tau, and degeneration of cholinergic neurons of the basal forebrain. In this review, we will present evidence implicating involvement of the basal forebrain cholinergic system in AD pathogenesis and its accompanying cognitive deficits. We will initially discuss recent results indicating a link between cholinergic mechanisms and the pathogenic events that characterize AD, notably amyloid-beta peptides. Following this, animal models of dementia will be discussed in light of the relationship between basal forebrain cholinergic hypofunction and cognitive impairments in AD. Finally, past, present, and future treatment strategies aimed at alleviating the cognitive symptomatology of AD by improving basal forebrain cholinergic function will be addressed.