Regulation of cerebral cortical blood flow by the basal forebrain cholinergic fibers and aging

Aging drives cerebrovascular network remodeling and functional changes in the mouse brain

Aging is frequently associated with compromised cerebrovasculature and pericytes. However, we do not know how normal aging differentially impacts vascular structure and function in different brain areas. Here we utilize mesoscale microscopy methods and in vivo imaging to determine detailed changes in aged murine cerebrovascular networks. Whole-brain vascular tracing shows an overall ~10% decrease in vascular length and branching density with ~7% increase in vascular radii in aged brains. Light sheet imaging with 3D immunolabeling reveals increased arteriole tortuosity of aged brains. Notably, vasculature and pericyte densities show selective and significant reductions in the deep cortical layers, hippocampal network, and basal forebrain areas. We find increased blood extravasation, implying compromised blood-brain barrier function in aged brains. Moreover, in vivo imaging in awake mice demonstrates reduced baseline and on-demand blood oxygenation despite relatively intact neurovascular coupling. Collectively, we uncover regional vulnerabilities of cerebrovascular network and physiological changes that can mediate cognitive decline in normal aging.

Influence of age on nicotinic cholinergic regulation of blood flow in rat's olfactory bulb and neocortex

The olfactory bulb receives cholinergic basal forebrain inputs as does the neocortex. With a focus on nicotinic acetylcholine receptors (nAChRs), this review article provides an overview and discussion of the following findings: (1) the nAChRs-mediated regulation of regional blood flow in the neocortex and olfactory bulb, (2) the nAChR subtypes that mediate their responses, and (3) their activity in old rats. The activation of the α4β2-like subtype of nAChRs produces vasodilation in the neocortex, and potentiates olfactory bulb vasodilation induced by olfactory stimulation. The nAChR activity producing neocortical vasodilation was similarly maintained in 2-year-old rats as in adult rats, but was clearly reduced in 3-year-old rats. In contrast, nAChR activity in the olfactory bulb was reduced already in 2-year-old rats. Thus, age-related impairment of α4β2-like nAChR function may occur earlier in the olfactory bulb than in the neocortex. Given the findings, the vasodilation induced by α4β2-like nAChR activation may be beneficial for neuroprotection in the neocortex and the olfactory bulb.

Decoupling Between Brain Activity and Cerebrospinal Fluid Movement in Neurological Disorders

Recent research has identified a link between the global mean signal of resting-state functional MRI (fMRI) and macro-scale cerebrospinal fluid movement, indicating the potential link between this resting-state dynamic and brain waste clearance. Consistent with this notion, the strength of this coupling has been associated with multiple neurodegenerative disease pathologies, especially the build-up of toxic proteins. This article aimed to review the latest advancements in this research area, emphasizing studies on spontaneous global brain activity that is tightly linked to the global mean resting-state fMRI signal, and aimed to discuss potential mechanisms through which this activity and associated physiological modulations might affect brain waste clearance. The available evidence supports the presence of a highly organized global brain activity that is linked to arousal and memory systems. This global brain dynamic, along with its associated physiological modulations, has the potential to influence brain waste clearance through multiple pathways through multiple pathways. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY: Stage 3.

Optogenetic stimulation of basal forebrain cholinergic neurons prevents neuroinflammation and neuropsychiatric manifestations in pristane induced lupus mice

BACKGROUND

Neuroinflammation has been identified as one of the primary pathogenic factors of neuropsychiatric systemic lupus erythematosus (NPSLE). However, there are no dedicated treatments available in clinics to alleviate neuroinflammation in NPSLE. It has been proposed that stimulating basal forebrain (BF) cholinergic neurons may provide potent anti-inflammatory effects in several inflammatory diseases, but its potential role in NPSLE remains unexplored. This study aims to investigate whether and how stimulating BF cholinergic neurons has a protective effect on NPSLE.

RESULTS

Optogenetic stimulation of BF cholinergic neurons significantly ameliorated olfactory dysfunction and anxiety- and depression-like phenotype in pristane induced lupus (PIL) mice. The increased expression of adhesion molecules (P-selectin and vascular cell adhesion molecule-1 (VCAM-1)), leukocyte recruitment, blood-brain barrier (BBB) leakage were significantly decreased. Notably, the brain histopathological changes, including the elevated levels of pro-inflammatory cytokines (TNF-α, IL-6 and IL-1β), IgG deposition in the choroid plexus and lateral ventricle wall and lipofuscin accumulation in the cortical and hippocampal neurons, were also significantly attenuated. Furthermore, we confirmed the colocalization between the BF cholinergic projections and the cerebral vessels, and the expression of α7-nicotinic acetylcholine receptor (α7nAChR) on the cerebral vessels.

CONCLUSION

Our data indicate that stimulation of BF cholinergic neurons could play a neuroprotective role in the brain through its cholinergic anti-inflammatory effects on cerebral vessels. Therefore, this may be a promising preventive target for NPSLE.

Aging drives cerebrovascular network remodeling and functional changes in the mouse brain

Aging is the largest risk factor for neurodegenerative disorders, and commonly associated with compromised cerebrovasculature and pericytes. However, we do not know how normal aging differentially impacts the vascular structure and function in different brain areas. Here we utilize mesoscale microscopy methods (serial two-photon tomography and light sheet microscopy) and in vivo imaging (wide field optical spectroscopy and two-photon imaging) to determine detailed changes in aged cerebrovascular networks. Whole-brain vascular tracing showed an overall ~10% decrease in vascular length and branching density, and light sheet imaging with 3D immunolabeling revealed increased arteriole tortuosity in aged brains. Vasculature and pericyte densities showed significant reductions in the deep cortical layers, hippocampal network, and basal forebrain areas. Moreover, in vivo imaging in awake mice identified delays in neurovascular coupling and disrupted blood oxygenation. Collectively, we uncover regional vulnerabilities of cerebrovascular network and physiological changes that can mediate cognitive decline in normal aging.

Hippocampal calcification and its effects on cognitive function and symptoms in dementia

BACKGROUND

Hippocampal calcification (HC), highly prevalent in older people, has not attracted attention until recently. Despite its potential effects on cognition and behaviour, and its possible impact on the diagnosis and severity of dementia, it has not been investigated. This study aimed to evaluate the prevalence of HC and its influence on cognition and behavioural symptoms in patients with dementia.

METHODS

Data from consecutive patients who visited a medical centre for dementia, for the first time between April 2016 and September 2018, were extracted and analysed. These data included the patients' demographics, the presence of HC and hippocampal thickness as measured on computed tomography, the diagnosis of dementia and its type, cognitive function measured using the Mini-Mental State Examination and the Clock Drawing Test, and the chief complaints or symptoms prompting the visit.

RESULTS

A high incidence of HC (85/267 patients) was observed. There was no significant difference in the ages of patients with and without HC. Patients with HC had higher cognitive function than those without HC at their first visit. This result was contrary to our expectations as it was not explained by the chief complaints recorded at the first visit.

CONCLUSIONS

Our study showed a high prevalence of HC in older patients with dementia. Patients with HC had better cognitive function than did those without HC during their first hospital visit. This study suggests that HC may not affect the cognitive functions related to dementia. However, further research is needed to evaluate the long-term consequences of dementia with HC.

Outcomes and Prognosis of Non-Elderly Patients with Brain Metastases-A Prospective Cohort Incorporating Individualized Assessment of Heart Rate Variability

Outcomes and prognostic factors among patients with brain metastases (BM) have been widely studied, but seldom for the non-elderly. Heart rate variability (HRV) is a physiological phenomenon and has been shown as a survival prognostic factor in cancer patients. This study aimed to evaluate the outcomes and prognosis among non-elderly BM patients with the incorporation of HRV analysis. Forty non-elderly BM patients treated using whole brain radiotherapy (WBRT) were studied from January 2010 prospectively with 5-min electrocardiography (ECG) recordings. Individualized HRV was generated by the ECG, and the time domain HRV index SDNN was chosen for survival analysis. The median overall survival (OS) for the entire group was 6.21 months. Univariate analysis revealed that a KPS < 80 (p = 0.019) and an SDNN < 10 ms (p = 0.007) demonstrated statistical significance for OS; multivariate analysis confirmed that a KPS < 80 (p = 0.004; HR = 3.060, CI = 1.437–6.517) and an SDNN < 10 ms (p = 0.010; HR = 2.664, CI = 1.262–5.624) were independent prognostic factors. Prospective studies for risk stratification among non-elderly BM patients based on our results are warranted to validate our findings.

Visual hallucinations in Alzheimer's disease do not seem to be associated with chronic hypoperfusion of to visual processing areas V2 and V3 but may be associated with reduced cholinergic input to these areas

Background

Up to 20% of patients with AD experience hallucinations. The pathological substrate is not known. Visual hallucinations (VH) are more common in dementia with Lewy bodies (DLB). In autopsy studies, up to 60% of patients with AD have concomitant Lewy body pathology. Decreased perfusion of the occipital lobe has been implicated in DLB patients with VH, and post-mortem studies point to both decreased cholinergic activity and reduced oxygenation of the occipital cortex in DLB.

Methods

We used biochemical methods to assess microvessel density (level of von Willebrand factor, a marker of endothelial cell content), ante-mortem oxygenation (vascular endothelial growth factor, a marker of tissue hypoxia; myelin-associated glycoprotein to proteolipid protein-1 ratio, a measure of tissue oxygenation relative to metabolic demand), cholinergic innervation (acetylcholinesterase and choline acetyltransferase), butyrylcholinesterase and insoluble α-synuclein content in the BA18 and BA19 occipital cortex obtained post-mortem from 23 AD patients who had experienced visual hallucinations, 19 AD patients without hallucinations, 19 DLB patients, and 36 controls. The cohorts were matched for age, gender and post-mortem interval.

Results

There was no evidence of reduced microvessel density, hypoperfusion or reduction in ChAT activity in AD with visual hallucinations. Acetylcholinesterase activity was reduced in both BA18 and BA19, in all 3 dementia groups, and the concentration was also reduced in BA19 in the DLB and AD without visual hallucinations groups. Insoluble α-synuclein was raised in the DLB group in both areas but not in AD either with or without visual hallucinations.

Conclusions

Our results suggest that visual hallucinations in AD are associated with cholinergic denervation rather than chronic hypoperfusion or α-synuclein accumulation in visual processing areas of the occipital cortex.

Electronic supplementary material

The online version of this article (10.1186/s13195-019-0519-7) contains supplementary material, which is available to authorized users.

Acetylcholine induces intracellular Ca2+ oscillations and nitric oxide release in mouse brain endothelial cells

Basal forebrain neurons increase cortical blood flow by releasing acetylcholine (Ach), which stimulates endothelial cells (ECs) to produce the vasodilating gasotransmitter, nitric oxide (NO). Surprisingly, the mechanism whereby Ach induces NO synthesis in brain microvascular ECs is unknown. An increase in intracellular Ca²⁺ concentration recruits a multitude of endothelial Ca²⁺-dependent pathways, such as Ca²⁺/calmodulin endothelial NO synthase (eNOS). The present investigation sought to investigate the role of intracellular Ca²⁺ signaling in Ach-induced NO production in bEND5 cells, an established model of mouse brain microvascular ECs, by conventional imaging of cells loaded with the Ca²⁺-sensitive dye, Fura-2/AM, and the NO-sensitive fluorophore, DAF-DM diacetate. Ach induced dose-dependent Ca²⁺ oscillations in bEND5 cells, 300 μM being the most effective dose to generate a prolonged Ca²⁺ burst. Pharmacological manipulation revealed that Ach-evoked Ca²⁺ oscillations required metabotropic muscarinic receptor (mAchR) activation and were patterned by a complex interplay between repetitive ER Ca²⁺ release via inositol-1,4,5-trisphosphate receptors (InsP₃Rs) and store-operated Ca²⁺ entry (SOCE). A comprehensive real time-polymerase chain reaction analysis demonstrated the expression of the transcripts encoding for M3-mAChRs, InsP₃R1 and InsP₃R3, Stim1-2 and Orai2. Next, we found that Ach-induced NO production was hindered by L-NAME, a selective NOS inhibitor, and BAPTA, a membrane permeable intracellular Ca²⁺ buffer. Moreover, Ach-elicited NO synthesis was blocked by the pharmacological abrogation of the accompanying Ca²⁺ spikes. Overall, these data shed novel light on the molecular mechanisms whereby neuronally-released Ach controls neurovascular coupling in blood microvessels.

Systemic administration of l-kynurenine sulfate induces cerebral hypoperfusion transients in adult C57Bl/6 mice

The kynurenine pathway is a cascade of enzymatic steps generating biologically active compounds. l-kynurenine (l-KYN) is a central metabolite of tryptophan degradation. In the mammalian brain, l-KYN is partly converted to kynurenic acid (KYNA), which exerts multiple effects on neurotransmission. Recently, l-KYN or one of its derivatives were attributed a direct role in the regulation of the systemic circulation. l-KYN dilates arterial blood vessels during sepsis in rats, while it increases cerebral blood flow (CBF) in awake rabbits. Therefore, we hypothesized that acute elevation of systemic l-KYN concentration may exert potential effects on mean arterial blood pressure (MABP) and on resting CBF in the mouse brain. C57Bl/6 male mice were anesthetized with isoflurane, and MABP was monitored in the femoral artery, while CBF was assessed through the intact parietal bone with the aid of laser speckle contrast imaging. l-KYN sulfate (l-KYNs) (300mg/kg, i.p.) or vehicle was administered intraperitoneally. Subsequently, MABP and CBF were continuously monitored for 2.5h. In the control group, MABP and CBF were stable (69±4mmHg and 100±5%, respectively) throughout the entire data acquisition period. In the l-KYNs-treated group, MABP was similar to that, of control group (73±6mmHg), while hypoperfusion transients of 22±6%, lasting 7±3min occurred in the cerebral cortex over the first 60-120min following drug administration. In conclusion, the systemic high-dose of l-KYNs treatment destabilizes resting CBF by inducing a number of transient hypoperfusion events. This observation indicates the careful consideration of the dose of l-KYN administration by interpreting the effect of kynurenergic manipulation on brain function. By planning clinical trials basing on kynurenergic manipulation possible vascular side effects should also be considered.

Effect of acupuncture-like stimulation on cortical cerebral blood flow in aged rats

This study aimed to examine the effect of acupuncture-like stimulation on cortical cerebral blood flow (CBF) in aged rats and the contribution of the intracranial cholinergic vasodilatory system on its response. In urethane-anesthetized rats of 30-37 months of age, manual acupuncture-like stimulation of a forepaw produced an increase in the CBF, independent of systemic arterial pressure. The increase in the CBF induced by forepaw stimulation was abolished by intravenous administration of cholinergic receptor antagonists. Manual acupuncture-like stimulation of a forepaw increased extracellular acetylcholine release in the cerebral cortex. These results suggest that natural somatic afferent stimulation, such as acupuncture-like stimulation, activates the intracranial - most likely, basal forebrain - cholinergic vasodilatory system in the cerebral cortex, even in extremely aged rats.

Pinocembrin improves cognition and protects the neurovascular unit in Alzheimer related deficits

Amyloid-β (Aβ) peptides accumulate in the brain and initiate a cascade of pathologic events in Alzheimer's disease. The receptor for advanced glycation end products (RAGE) has been implicated to mediate Aβ-induced perturbations in the neurovascular unit (NVU). We demonstrated that pinocembrin exhibits neuroprotection through inhibition of the Aβ and/or RAGE pathway, but the therapeutic role and mechanism involved are not ascertained. Here, we report that a 3-month treatment with pinocembrin prevents the cognition decline in APP/PS1 transgenic mice without altering Aβ burden and oxidative stress. Instead, pinocembrin is effective in conferring neurovascular protection through maintenance of neuropil ultrastructure, reduction of glial activation and levels of inflammatory mediators, preservation of microvascular function, improving the cholinergic system by conserving the ERK-CREB-BDNF pathway, and modulation of RAGE-mediated transduction. Furthermore, in an in vitro model, pinocembrin provides the NVU protection against fibrillar Aβ₁₋₄₂, accompanied by regulation of neurovascular RAGE pathways. Our findings indicate that pinocembrin improves cognition, at least in part, attributable to the NVU protection, and highlights pinocembrin as a potential therapeutic strategy for the prevention and/or treatment of Alzheimer's disease.

Cerebrovascular reactivity to carbon dioxide in Alzheimer's disease

There is growing evidence that cerebrovascular reactivity to carbon dioxide (CVRCO2) is impaired in Alzheimer's disease (AD). Preclinical and animal studies suggest chronic hypercontractility in brain vessels in AD. We review (a) preclinical studies of mechanisms for impaired CVRCO2 in AD; (b) clinical studies of cerebrovascular function in subjects with AD dementia, mild cognitive impairment (MCI), and normal cognition. Although results of clinical studies are inconclusive, an increasing number of reports reveal an impairment of vascular reactivity to carbon dioxide in subjects with AD, and possibly also in MCI. Thus, CVRCO2 may be an attractive means to detect an early vascular dysfunction in subjects at risk.

Cortical metabolic deficits in a rat model of cholinergic basal forebrain degeneration

Evidence indicates that the degeneration of basal forebrain cholinergic neurons may represent an important factor underlying the progressive cognitive decline characterizing Alzheimer's disease (AD). However, the nature of the relationship between cholinergic depletion and AD is not fully elucidated. This study aimed at clarifying some aspects of the relation existing between deficits in cerebral energy metabolism and degeneration of cholinergic system in AD, by investigating the neuronal metabolic activity of several cortical areas after depletion of basal forebrain cholinergic neurons. In cholinergically depleted rats, we evaluated the neuronal metabolic activity by assaying cytochrome oxidase (CO) activity in frontal, parietal and posterior parietal cortices at four different time-points after unilateral injection of 192 IgG-saporin in the nucleus basalis magnocellularis. Unilateral depletion of cholinergic cells in the basal forebrain induced a bilateral decrease of metabolic activity in all the analyzed areas. Frontal and parietal cortices showed decreased metabolic activity even 3 days after the lesion, when the cholinergic degeneration was still incomplete. In posterior parietal cortex metabolic activity decreased only 7 days after the lesion. The possible molecular mechanisms underlying these findings were also investigated. Real-time PCR showed an increase of CO mRNA levels at 3, 7 and 15 days after the lesion both in frontal and parietal cortices, followed by normalization at 30 days. Western Blot analysis did not show any change in CO protein levels at any time-point after the lesion. Our findings support a link between metabolic deficit and cholinergic hypofunctionality characterizing AD pathology. The present model of cholinergic hypofunctionality provides a useful means to study the complex mechanisms linking two fundamental and interrelated phenomena characterizing AD from the early stages.

Age-related changes in cerebral hemodynamics and their correlations with cardiac autonomic functions

OBJECTIVES

This study was designed to evaluate the correlations between cerebral hemodynamics and cardiac autonomic functions in aging process using transfer function techniques.

METHODS

Arterial blood pressure (ABP), middle cerebral artery flow velocity (MCAFV) detected by transcranial Doppler sonography and electrocardiogram were recorded simultaneously in 20 young (27.5 +/- 0.9 years) and 20 middle-old-aged (54.3 +/- 1.5 years) healthy volunteers. Variability of ABP, MCAFV and heart rate (HR) were diffracted into very low (VLF, 0.016-0.04 Hz), low (LF, 0.04-0.15 Hz) and high frequency (HF, 0.15-0.4 Hz) components. Cerebral vasomotor reserve was quantified by specific ABP-MCAFV transfer function measurements.

RESULTS

The young group had significantly higher LF transfer phase and HF transfer magnitudes of ABP-MCAFV transfer function; higher HF powers of HR variability; and higher baroreflex sensitivity than those of the middle-old-aged group. LF phase and HF magnitude of ABP-MCAFV transfer function were positively correlated with HF powers of HR variability.

DISCUSSION

Although aging process is not obviously associated with changes in the static values of ABP, MCAFV and HR in this study, it is accompanied by significant declines in cerebral vasomotor reserve, cardiac vagal activity and baroreflex sensitivity. Besides, age-related changes in cerebral vasomotor reserve are positively related to those in cardiac vagal activity.

Quercetin protects against the Aβ(25-35)-induced amnesic injury: involvement of inactivation of rage-mediated pathway and conservation of the NVU

Quercetin has demonstrated protective effects against Aβ-induced toxicity on both neurons and endothelial cells. However, whether or not quercetin has an effect on the neurovascular coupling is unclear. In the present study, we aim to investigate the anti-amnesic effects of quercetin and to explore the underlying mechanisms. Aβ(25-35) (10 nmol) was administrated to mice i.c.v. Quercetin was administrated orally for 8 days after injection. Learning and memory behaviors were evaluated by measuring spontaneous alternation in Morris Water Maze test and the step-through positive avoidance test. The regional cerebral blood flow was monitored before the Aβ(25-35) injection and on seven consecutive days after injection. Mice were sacrificed and cerebral cortices were isolated on the last day. The effects of quercetin on the neurovascular unit (NVU) integrity, microvascular function and cholinergic neuronal changes, and the modification of signaling pathways were tested. Our results demonstrate that quercetin treatment for Aβ(25-35)-induced amnesic mice improved the learning and memory capabilities and conferred robust neurovascular coupling protection, involving maintenance of the NVU integrity, reduction of neurovascular oxidation, modulation of microvascular function, improvement of cholinergic system, and regulation of neurovascular RAGE signaling pathway and ERK/CREB/BDNF pathway. In conclusion, in Aβ(25-35)-induced amnesic mice, optimal doses of quercetin administration were beneficial. Quercetin protected the NVU likely through reduction of oxidative damage, inactivation of RAGE-mediated pathway and preservation of cholinergic neurons, offering an alternative medication for Alzheimer's disease.

Acetylcholine and memory-enhancing activity of Ficus racemosa bark

Background:

Alzheimer's disease (AD) is a progressive neurodegenerative disorder resulting in dementia and enhancement of acetylcholine (Ach) levels in brain using acetylcholinesterase inhibitors is one of the most important approaches for the treatment of AD.

Methods:

In this study, aqueous extract of Ficus racemosa Linn. (Moraceae) bark having anti-inflammatory, antioxidant, and anticholinesterase activity was evaluated for its ability to enhance Ach levels, and to ascertain its antidementia activity in rats. This work was carried out under the assumption that the F. racemosa extract may show combination of actions which could be beneficial in the treatment of AD, such as neuroprotection, attributed to antioxidant and anti-infl ammatory property and may elevate levels of Ach like Ficus hispida extract reported earlier.

Results:

Administration of the extract at two levels viz., 250 and 500 mg/kg signifi cantly raised (P ≤ 0.05) Ach levels in hippocampi of rats compared to control. The percentage enhancement in Ach levels was found to be 22% and 38%, respectively. Further, the extract at both dosage levels elicited signifi cant reduction (P ≤ 0.05) in transfer latency on elevated plus-maze, which was used as an exteroceptive behavioral model to evaluate memory in rats.

Conclusion:

It is inferred that it would be worthwhile to explore the potential of F. racemosa in the management of Alzheimer disease.

Acute nicotine-induced tachyphylaxis is differentially manifest in the limbic system

Rapid tolerance develops to many of nicotine's behavioral and autonomic effects. A better understanding of the spatiotemporal patterns in neuronal activity as a consequence of acute nicotine tolerance (tachyphylaxis) may help explain its commonly found inverted 'U'-shaped biphasic dose-effect relationship on various behaviors. To this end, we employed high-resolution functional magnetic resonance imaging and relative cerebral blood volume (rCBV) as a marker of neuronal activity, to characterize the regional development of acute tolerance as a function of nicotine dose in naïve, anesthetized rats. A single intravenous nicotine injection at 0.1 and 0.3, but not 0.03 mg/kg, significantly increased neuronal activity in many neocortical areas. In contrast, dose-dependent increases in rCBV were most pronounced in limbic regions, such that responses seen at 0.1 mg/kg nicotine in accumbens, hippocampus, amygdala, and several other limbic areas were not seen following 0.3 mg/kg nicotine. Finally, whereas profound tolerance was observed in many cortical regions after the second of two paired nicotine injections at either 0.1 or 0.3 mg/kg, subcortical limbic structures showed only a weak trend for tolerance. Lack of rCBV changes in animals receiving nicotine methiodide, a quaternary nicotine analog that does not cross the blood-brain barrier, supports a direct neuronal effect of nicotine rather than an action on the vasculature. These data provide pharmacodynamic insight into the regional heterogeneity of nicotine tachyphylaxis development, which may be relevant to behavioral and neurobiological mechanisms associated with repeated tobacco consumption.

Targeting the neurovascular unit: development of a new model and consideration for novel strategy for Alzheimer's disease

Alzheimer's disease involves the complex and interconnected cascade of cellular and molecular events. Only a few treatments are available to slow the course of the disease at present. Recent studies suggest that neurovascular unit serves to maintain cerebral homeostasis, and pathological interactions between components of neurovascular unit lead to cerebral dysfunction. In present study, we established a functional unit trying to target major components of the neurovascular unit by the co-culture of rat cortical parenchymal culture and cerebral microvascular endothelial cells. This entity allowed the application of techniques such as immunofluorescent imaging and biological assays under defined conditions. The morphology of cell types, blood-brain barrier function and neuronal activation were investigated. The insight revealed that targeting components of the neurovascular unit, rather than just the neuron, might be a priority in Alzheimer's disease and more likely to provide cerebroprotection.

Association cortex hypoperfusion in mild dementia with Lewy bodies: a potential indicator of cholinergic dysfunction?

Dementia with Lewy bodies (DLB) is often associated with occipital hypometabolism or hypoperfusion, as well as deficits in cholinergic neurotransmission. In this study, 11 mild DLB, 16 mild AD and 16 age-matched controls underwent arterial spin-labeled perfusion MRI (ASL-pMRI) and neuropsychological testing. Patterns of cerebral blood flow (CBF) and cognitive performance were compared. In addition, combined ASL-pMRI and ChEI drug challenge (pharmacologic MRI) was tested as a probe of cholinergic function in 4 of the DLB participants. Frontal and parieto-occipital hypoperfusion was observed in both DLB and AD but was more pronounced in DLB. Following ChEI treatment, perfusion increased in temporal and parieto-occipital cortex, and cognitive performance improved on a verbal fluency task. If confirmed in a larger study, these results provide further evidence for brain cholinergic dysfunction in DLB pathophysiology, and use of pharmacologic MRI as an in vivo measure of cholinergic function.

Association between frequency domain heart rate variability and unplanned readmission to hospital in geriatric patients

Background

An accurate prediction of unplanned readmission (UR) after discharge from hospital can facilitate physician's decision making processes for providing better quality of care in geriatric patients. The objective of this study was to explore the association of cardiac autonomic functions as measured by frequency domain heart rate variability (HRV) and 14-day UR in geriatric patients.

Methods

Patients admitted to the geriatric ward of a regional hospital in Chiayi county in Taiwan were followed prospectively from July 2006 to June 2007. Those with invasive tubes and those who were heavy smokers, heavy alcohol drinkers, on medications that might influence HRV, or previously admitted to the hospital within 30 days were excluded. Cardiac autonomic functions were evaluated by frequency domain indices of HRV. Multiple logistic regression was used to assess the association between UR and HRV indices adjusted for age and length of hospitalization.

Results

A total of 78 patients met the inclusion criteria and 15 of them were readmitted within 14 days after discharge. The risk of UR was significantly higher in patients with lower levels of total power (OR = 1.39; 95% CI = 1.04-2.00), low frequency power (LF) (OR = 1.22; 95% CI = 1.03-1.49), high frequency power (HF) (OR = 1.27; 95% CI = 1.02-1.64), and lower ratios of low frequency power to high frequency power (LF/HF ratio) (OR = 1.96; 95% CI = 1.07-3.84).

Conclusion

This is the first study to evaluate the association between frequency domain heart rate variability and the risk of UR in geriatric patients. Frequency domain heart rate variability indices measured on admission were significantly associated with increased risk of UR in geriatric patients. Additional studies are required to confirm the value and feasibility of using HRV indices on admission as a non-invasive tool to assist the prediction of UR in geriatric patients.

Pharmacological MRI approaches to understanding mechanisms of drug action

Functional neuroimaging is a novel technique for the study of drug action in the brain. The emerging role of this method is intimately tied to the unique challenges to advancing drug development for neuropsychiatric disorders. This chapter first presents a brief overview of the important treatment needs that remain to be met, which serve as clinical targets for drug development. Important factors that hinder progress in drug development, which arise from clinical, scientific and economic issues, are acknowledged. This sets the stage for the unique advantages of functional neuroimaging modalities such as functional MRI (fMRI) as a biomarker and drug development tool, in both clinical and preclinical phases. The physiological basis of the fMRI signal is briefly outlined, and aspects of neural signaling related to this signal change, with emphasis on implications for pharmacology studies. The utility of fMRI for evaluating the full anatomic extent of central neurotransmitter systems in a dynamic manner is then described. This is a critical advantage, and particularly important for studies of how systems such as the monoamines modulate distributed neural networks during cognitive processes in both health and illness, and how these actions are modified with pharmacological intervention. Central catecholamine systems are seen as paradigmatic targets amenable to pharmacologic fMRI. fMRI is observed to occupy a unique position in the armamentarium of methods available to the pharmacologist and the drug development process, and poised to play an expanding role in basic and clinical neuroscience.

Association between cardiovascular autonomic functions and time to death in patients with terminal hepatocellular carcinoma

CONTEXT

A better time-to-death (TTD) prediction can facilitate decision-making processes related to plans for providing effective end-of-life care for patients in hospice wards.

OBJECTIVE

To explore the association of cardiovascular autonomic functions with TTD in patients with terminal hepatocellular carcinoma.

METHODS

A prospective study was conducted with 33 patients with hepatocellular carcinoma recruited from the hospice ward of a regional hospital in Chiayi county, Taiwan. Serum creatinine, serum glutamate oxaloacetate transaminase, serum glutamate pyruvate transaminase, blood urea nitrogen (BUN), and serum albumin were measured on the admission day. Cardiovascular autonomic functions were evaluated by frequency-domain measures of heart rate variability (HRV) on admission.

RESULTS

TTD was significantly associated with total spectrum power (TP) (r=0.55, P=0.001) and high frequency (HF power) (r=0.44, P=0.010) of HRV measurement. The accuracy of within-one-week TTD prediction was 67% for TP and HF power. The accuracy of within-two-week TTD prediction was 82% for TP and 73% for HF. In addition, TTD of the patients was also significantly associated with serum creatinine (r=-0.42, P=0.015), serum albumin (r=-0.46, P=0.007), and BUN (r=-0.44, P=0.010).

CONCLUSION

This is the first study to evaluate the association between cardiovascular autonomic functions and TTD in patients with terminal hepatocellular carcinoma. The inclusion of HRV measurement in prognostic models may improve accuracy in TTD prediction and, hence, facilitate medical decision making in hospice care.

Cerebellum cholinergic muscarinic receptor (subtype-2 and -3) and cytoarchitecture after developmental exposure to methylmercury: an immunohistochemical study in rat

The developing central nervous system (CNS) is a target of the environmental toxicant methylmercury (MeHg), and the cerebellum seems the most susceptible tissue in response to this neurotoxicant. The cholinergic system is essential for brain development, acting as a modulator of neuronal proliferation, migration and differentiation processes; its muscarinic receptors (MRs) play pivotal roles in regulating important basic physiologic functions. By immunohistochemistry, we investigated the effects of perinatal (GD7-PD21) MeHg (0.5 mg/kg bw/day in drinking water) administration on cerebellum of mature (PD36) and immature (PD21) rats, evaluating the: (i) M2- and M3-MR expression; (ii) presence of gliosis; (iii) cytoarchitecture alterations. Regarding to M2-MRs, we showed that: at PD21, MeHg-treated animals did not display any differences compared to controls, while, at PD36 there was a significant increase of M2-immunopositive Bergmann cells in the molecular layer (ML), suggesting a MeHg-related cytotoxic effect. Similarly to M2-MRs, at PD21 the M3-MRs were not affected by MeHg, while, at PD36 a lacking immunoreactivity of the granular layer (IGL) was observed after MeHg treatment. In MeHg-treated rats, at both developmental points, we showed reactive gliosis, e.g. a significant increase in Bergmann glia of the ML and astrocytes of the IGL, identified by their expression of glial fibrillar acidic protein. No MeHg-related effects on Purkinje cells were detected neither at weaning nor at puberty. These findings suggest: (i) a delayed MeHg exposure-related effect on M2- and M3-MRs, (ii) an overt MeHg-related cytotoxic effect on cerebellar oligodendroglia, e.g. reactive gliosis, (iii) a selective vulnerability of granule cells and Purkinje neurons to MeHg, with the latter that remain unharmed.

Nox2-derived reactive oxygen species mediate neurovascular dysregulation in the aging mouse brain

Aging is associated with cerebrovascular dysregulation, which may underlie the increased susceptibility to ischemic stroke and vascular cognitive impairment occurring in the elder individuals. Although it has long been known that oxidative stress is responsible for the cerebrovascular dysfunction, the enzymatic system(s) generating the reactive oxygen species (ROS) have not been identified. In this study, we investigated whether the superoxide-producing enzyme NADPH oxidase is involved in alterations of neurovascular regulation induced by aging. Cerebral blood flow (CBF) was recorded by laser-Doppler flowmetry in anesthetized C57BL/6 mice equipped with a cranial window (age=3, 12, and 24 months). In 12-month-old mice, the CBF increases evoked by whisker stimulation or by the endothelium-dependent vasodilators acetylcholine and bradykinin were attenuated by 42, 36, and 53%, respectively (P<0.05). In contrast, responses to the nitric oxide donor S-nitroso-D-penicillamine or adenosine were not attenuated (P>0.05). These cerebrovascular effects were associated with increased production of ROS in neurons and cerebral blood vessels, assessed by hydroethidine microfluorography. The cerebrovascular impairment present in 12-month-old mice was reversed by the ROS scavenger Mn (III) tetrakis (4-benzoic acid) porphyrin chloride or by the NADPH oxidase peptide inhibitor gp91ds-tat, and was not observed in mice lacking the Nox2 subunit of NADPH oxidase. These findings establish Nox2 as a critical source of the neurovascular oxidative stress mediating the deleterious cerebrovascular effects associated with increasing age.

Effects of APOE and CHRNA4 genotypes on retinal nerve fibre layer thickness at the optic disc and on risk for developing exfoliation syndrome

PURPOSE

To investigate whether CHRNA4 and APOE genotypes influence retinal nerve fibre layer (RNFL) thickness at the optic disc, intraocular pressure (IOP) and the development of exfoliation syndrome (XFS).

METHODS

A sample of 88 healthy adults (aged 50-75 years) genotyped for polymorphisms of APOE and CHRNA4 underwent an eye examination including slit-lamp examination and fundus photography, as well as measurements of visual acuity, refraction, IOP and RNFL thickness at the optic disc by optical coherence tomography. The Fisher-Boschloo unconditional full multinomial test and two sample t-tests were used in the statistical analyses.

RESULTS

There was no correlation between CHRNA4 and APOE genotypes and average RNFL thickness at the optic disc in the two eyes. Mean IOP in the eyes of APOE2 carriers was 13.18 mmHg, whereas that in the eyes of non-APOE2 carriers, at 14.82 mmHg, was significantly higher (p = 0.014). Exfoliation syndrome was found in one or both eyes in 15 persons. The presence of XFS was less likely in CC carriers of the CHRNA4 gene than in TT and TC carriers (p = 0.049).

CONCLUSIONS

We found no significant difference in RNFL thickness at the optic disc in the different genotype carriers of the APOE and CHRNA4 genes, and thereby no evidence for increased loss of ganglion cells in the retina as an effect of these genes. APOE2 carriers had significantly lower IOP than non-APOE2 carriers. However, both values are within the normal range and RNFL thickness measurements at the optic disc showed no difference between these two groups. In our study population, CC carriers of the CHRNA4 gene were less likely to develop XFS.

Symptomatic treatment of Alzheimer’s disease: identification of biomarkers to aid translation from bench to bedside

In the absence of robust pharmacodynamic markers, the potential success of novel therapeutic agents for the symptomatic relief of Alzheimer’s disease is largely unknown until the drugs enter relatively large studies, assessing clinical outcome over a 6-month period. In order to increase the efficiency of future clinical development there is, therefore, a need to identify pharmacodynamic markers of drug response, pharmacodynamic models that allow early prediction of efficacy and markers to aid the stratification of the patient population. Using literature available from cholinesterase inhibitors, memantine and Ginkgo biloba, this review focuses on the identification of potential pharmacodynamic markers/models and highlights the utility of these end points throughout the drug discovery process, from preclinical to clinical development.

Role of substantia innominata in cerebral blood flow autoregulation

Ascending projections from the substantia innominata (SI) may have an important role in the regulation of cerebral blood flow (CBF). However, several reports have suggested that unilateral lesion of the SI does not affect CBF autoregulation. On the other hand, it is also reported that several cortical and subcortical functions may be regulated not only by ipsilateral SI, but also by contralateral SI. Thus, the objective of this study is to test the hypothesis that bilateral lesions of the SI affect CBF autoregulation. Experiments were performed on anesthetized male Sprague-Dawley rats. Ibotenic acid or physiological saline was microinjected into bilateral SI. Rats were classified into four groups as follows: bilateral SI lesion rats (ibotenic acid was injected bilaterally), left or right SI lesion rats (ibotenic acid was injected into the unilateral SI and saline into the contralateral SI), and control rats (saline was injected bilaterally). Ten days after injection, CBF in the left frontal cortex was measured by laser-Doppler flowmetry during stepwise controlled hemorrhagic hypotension. In bilateral SI lesion rats, CBF was started to decrease significantly at 80 mm Hg (p<0.01). In the other three groups, CBF was well maintained until 50 mm Hg. Changes in CBF through stepwise hypotension in bilateral SI lesion rats were significantly different from the other groups (p<0.01). These results suggest that bilateral SI regulates cortical vasodilator mechanisms during hemorrhagic hypotension. Under unilateral SI lesion, some compensatory effects from the contralateral SI may maintain CBF autoregulation.

Function of the rat carotid body chemoreceptors in ageing

Some age-related deficits in the ventilatory responses have been attributed to a decline in the functionality of the carotid body (CB) arterial chemoreceptors, but a systematic study of the CB function in ageing is lacking. In rats aged 3-24 months, we have performed quantitative morphometry on specific chemoreceptor tissue, assessed the function of chemoreceptor cells by measuring the content, synthesis and release of catecholamines (a chemoreceptor cell neurotransmitter) in normoxia and hypoxia, and determined the functional activity of the intact organ by measuring chemosensory activity in the carotid sinus nerve (CSN) in normoxia, hypoxia and hypercapnic acidosis. We found that with age CBs enlarge, but at the same time there is a concomitant decrease in the percentage of chemoreceptor tissue. CB content and turnover time for their catecholamines increase with age. Hypoxic stimulation of chemoreceptor cells elicits a smaller release of catecholamines in rats after 12 months of age, but a non-specific depolarizing stimulus elicits a comparable release at all ages. In parallel, there was a marked decrease in the responsiveness to hypoxia, but not to an acidic-hypercapnic stimulus, assessed as chemosensory activity in the CSN. We conclude that in aged mammals chemoreceptor cells become hypofunctional, leading to a decreased peripheral drive of ventilation.

Effects of electrical stimulation of the nucleus basalis on two-way active avoidance acquisition, retention, and retrieval

This study assessed the role of the nucleus basalis magnocellularis (NBM) in specific memory phases of two-way active avoidance conditioning. We evaluated the effects of NBM electrical stimulation applied during different phases of the avoidance task. Rats were trained in a 30-trial acquisition session, and were tested again 24 and 48 h later. NBM stimulation was applied at different stages of memory formation of the conditioning: (1) immediately before the first training session to determine the effects on acquisition of the two-way avoidance task; (2) immediately after the first training session to evaluate effects on memory consolidation; and (3) immediately before the 24-h retention session to analyze the effects on the retrieval process. NBM stimulation before training significantly improved the acquisition of the task, without affecting subsequent retention at either 24 or 48 h. Stimulation of the NBM immediately after the first training session slightly impaired performance in the 24-h retention session. Stimulation of the NBM immediately before the 24-h retention session did not affect performance in either the 24 or 48-h retention sessions. Therefore, the NBM may play a more important role in acquisition of memory in aversively motivated conditioning tasks than in consolidation or retrieval of such memories. These results are discussed in the context of attention enhancement and cortical and amygdala activation.

The effect of cholinesterase inhibitors on the regional blood flow in patients with Alzheimer's disease and vascular dementia

The effects of therapy with cholinesterase inhibitors (ChE-I) on regional cerebral blood flow (rCBF) disturbances were investigated by means of single photon emission computed tomography (SPECT). The changes in rCBF were compared with the results of the medical examination and neuropsychological tests. The sample consisted of 41 patients with the Alzheimer's dementia (AD) and vascular dementia (VaD). The effect of ChE-I (rivastigmine) treatment was studied on 33 patients, while the nontreated control group consisted of 8 patients. In the treated patients, an increase in the rCBF was observed, while the scores of the neuropsychological tests decreased slightly. In the VaD group, the increase in rCBF was more significant in the frontal regions, whereas in the group with AD in the temporal regions, respectively. In the nontreated patients, a decrease of both rCBF and scores of neuropsychological tests were observed. The scores of the neuropsychological tests correlated with the results of rCBF. Increased levels of acetylcholine in the brain after ChE-I treatment may support the cholinergic regulation of rCBF, and in result increase it. Such effects seem to be more pronounced in the more affected brain regions.

Age-related changes in the release and uptake activity of presynaptic axon terminals of rat locus coeruleus neurons

Age-related changes in the release and uptake activity of presynaptic axon terminals of rat locus coeruleus (LC) noradrenergic neurons were studied in the frontal cortex using an extracellular single unit recording technique in vivo. Clonidine, a selective alpha(2) adrenergic agonist, and nisoxetine, a selective noradrenaline uptake inhibitor, were infused locally into the frontal cortex to examine the effects of these drugs on release and uptake activities of the axon terminals of LC neurons. Although the infusion of clonidine produced a marked suppression of release, the effect did not change with age. Infusion of nisoxetine caused an inhibition of uptake, but the effect was attenuated in aged rats. These results suggest that the release activity mediated by the presynaptic autoreceptor did not change with age, but the uptake activity mediated by the NA transporter declined with age in the axon terminals of LC neurons.