Microsphere embolism-induced cortical cholinergic deafferentation and impairments in attentional performance

Reduced substantia innominata volume mediates contributions of microvascular and macrovascular disease to cognitive deficits in Alzheimer's disease

The relationships between cholinergic system damage and cerebrovascular disease are not entirely understood. Here, we investigate associations between atrophy of the substantia innominata (SI; the origin of cortical cholinergic projections) and measures of large and small vessel disease; specifically, elongation of the juxtaposed internal carotid artery termination and Cholinergic Pathways Hyperintensity scores (CHIPS). The study (n = 105) consisted of patients with Alzheimer's disease (AD) and/or subcortical ischemic vasculopathy, and elderly controls. AD and subcortical ischemic vasculopathy groups showed greater impingement of the carotid termination on the SI and smaller SI volumes. Both carotid termination elongation and CHIPS were associated independently with smaller SI volumes in those with and without AD. Atrophy of the SI mediated effects of carotid termination elongation on language and memory functions and the effect of CHIPS on attention/working memory. In conclusion, SI atrophy was related to cerebrovascular disease of the large and small vessels and to cognitive deficits in people with and without AD.

Whole-Brain Monosynaptic Afferent Inputs to Basal Forebrain Cholinergic System

The basal forebrain cholinergic system (BFCS) robustly modulates many important behaviors, such as arousal, attention, learning and memory, through heavy projections to cortex and hippocampus. However, the presynaptic partners governing BFCS activity still remain poorly understood. Here, we utilized a recently developed rabies virus-based cell-type-specific retrograde tracing system to map the whole-brain afferent inputs of the BFCS. We found that the BFCS receives inputs from multiple cortical areas, such as orbital frontal cortex, motor cortex, and insular cortex, and that the BFCS also receives dense inputs from several subcortical nuclei related to motivation and stress, including lateral septum, central amygdala, paraventricular nucleus of hypothalamus, dorsal raphe, and parabrachial nucleus. Interestingly, we found that the BFCS receives inputs from the olfactory areas and the entorhinal–hippocampal system. These results greatly expand our knowledge about the connectivity of the mouse BFCS and provided important preliminary indications for future exploration of circuit function.

Cognitive Function After Carotid Artery Revascularization

Clinical investigations designed to contrast the efficacy of carotid endarterectomy (CEA) versus best medical therapy and CEA versus carotid artery stenting (CAS) in patients with carotid artery stenosis have been based on the traditional endpoints of stroke, myocardial infarction, and death. Cognitive function is being increasingly recognized as an important outcome measure that affects patient well-being and functional status. However, it has not been evaluated systematically in the context of carotid revascularization. A decline in cognitive function could occur from microembolic ischemia during surgical dissection (CEA) or intravascular instrumentation (CAS). It could also occur from hypoperfusion during clamping (CEA) or balloon dilation (CAS). Conversely, restoring perfusion could improve cognitive dysfunction that might have occurred from a state of chronic hypoperfusion. It is still unclear whether these complex interactions ultimately result in a net improvement or a deterioration of cognitive function. Furthermore, it is not known whether the 2 methods of carotid revascularization have a differential effect on cognitive outcomes. It is becoming increasingly clear, though, that there is a positive relationship between improvement in cognition and improvement in functional outcome of patients. Vascular surgeons will be well served to remain informed and even actively engaged in the development of this field if they wish to continue providing the high-quality, well-informed care they have traditionally offered to patients with carotid stenosis.

Heartsick: psychiatric and inflammatory implications of cerebromicrovascular disease

BACKGROUND

Cerebromicrovascular disease (CMVD) strikes 87% of the population older than 65 years and is linked to an increased risk of ischemic stroke, depression, cognitive impairment, and Alzheimer's disease. Despite the wealth of knowledge on the consequences to the body stemming from poor vascular health, little focus has been placed on the consequences to the brain.

DESIGN

In this review, we present the preclinical and clinical evidence that supports the role of CMVD in behavioral dysfunction, argues for a clinical need for better recognition of the vascular depression phenotype, and calls for a more integrative translational approach to CMVD.

RESULTS AND CONCLUSIONS

Although the concept of cerebrovascular-induced behavioral change has existed for over 100 years, the difficulty of diagnosis, the slow progression of CMVD, and the lack of causative data have led to an underestimation of the patient population and poor treatment strategies. Preclinical studies have focused on the use of microsphere embolic models and vascular inflammation models to assess the mechanisms of, and treatment options for, CMVD. Though preclinical models provide support for correlative data collected in the clinic, translational reciprocity has not been established. The lack of clinical appreciation for the role of cerebrovascular health in brain function may result in missed diagnoses and inadequate treatment of underlying cardiovascular disease. Enhanced recognition of symptoms and disease presentation will allow for earlier prevention, detection, and identification of novel targets for drug development and other intervention strategies.

Microembolism induces anhedonia but no detectable changes in white matter integrity in aged rats

Microvascular disease leads to alterations of cerebral vasculature including the formation of microembolic (ME) strokes. Though ME are associated with changes in mood and the severity and progression of cognitive decline, the effect of ME strokes on cerebral microstructure and its relationship to behavioral endpoints is unknown. Here, we used adult and aged male rats to test the hypotheses that ME lesions result in subtle changes to white and gray matter integrity as detected by high-throughput diffusion tensor imaging (DTI) and that these structural disruptions correspond to behavioral deficits. Two weeks post-surgery, aged animals showed depressive-like behaviors in the sucrose consumption test in the absence of altered cerebral diffusivity as assessed by ex-vivo DTI. Furthermore, DTI indices did not correlate with the degree of behavioral disruption in aged animals or in a subset of animals with observed tissue cavitation and subtle DTI alterations. Together, data suggest that behavioral deficits are not the result of damage to brain regions or white matter tracts, rather the activity of other systems may underlie functional disruption and recovery.

Microembolism infarcts lead to delayed changes in affective-like behaviors followed by spatial memory impairment

Microvascular disease is defined by microvascular events including arterial wall thickening, microvascular lesions, and microembolic stroke. Characteristics of microvascular disease are observed in the vast majority of patients presenting with late-life depression, and changes in affective behavior may precede microvascular-associated changes in cognitive decline. The current study used a microsphere injection model to test the hypothesis that microembolism infarcts induce depressive-like behaviors in rodents. Further, the study sought to determine whether microembolism-induced changes in affective-like behavior preceded deficits in spatial memory. Microbeads were injected into the internal carotid artery to generate microembolic lesions and behavior was assessed at either a short recovery (SR) time point (4-6 days post-surgery) or long recovery (LR) time point (14-17 days post-surgery). A separate cohort of rats was used to assess spatial memory in the Barnes Maze at the LR time point and beyond (35 days post-surgery). Microembolism infarcts led to an increase in anxiety- and depressive-like behaviors at the LR, but not the SR, time point as evidenced by reduced time in the center of the open field, reduced consumption of a sucrose solution, increased latency to approach a novel female at 14 days and impaired spatial memory at 33 days. A thorough analysis of histological markers and lesion volume revealed that gross histological damage was not predictive of behavioral outcomes, suggesting that alterations in neuronal function may underlie behavioral deficits. Collectively, these data demonstrate that microembolism infarcts are sufficient to induce changes in affective-like behavior and these changes precede alterations in spatial memory.

Cognitive changes after surgery vs stenting for carotid artery stenosis

OBJECTIVES

Cognitive function has not been evaluated systematically in the context of carotid endarterectomy (CEA) versus carotid artery stenting (CAS). Cognitive decline can occur from microembolization or hypoperfusion during CEA or CAS. Carotid revascularization may, however, also improve cognitive dysfunction resulting from chronic hypoperfusion. We compared cognitive outcomes in consecutive asymptomatic patients undergoing CAS or CEA.

METHODS

This is a prospective nonrandomized single-center study of patients with asymptomatic carotid stenosis ≥ 70% undergoing CAS or CEA using standard techniques. Neurologic symptoms were evaluated by history, physical examination, and the National Institutes of Health Stroke Scale. A 50-minute cognitive battery was performed 1 to 3 days before and 4 to 6 months after CEA/CAS. The tests (Trail Making Tests A/B, Processing Speed Index (PSI) of the Wechsler Adult Intelligence Scale - Third Edition (WAIS-III), Boston Naming Test, Working Memory Index (WMI) of the Wechsler Memory Scale - Third Edition (WMS-III), Controlled Oral Word Association, and Hopkins Verbal Learning Test) for six cognitive domains (motor speed/coordination and executive function, psychomotor speed, language (naming), working memory/concentration, verbal fluency, and learning/memory) were conducted by a neuropsychologist. The primary analysis of impact of treatment modality was a normalized cognitive change score.

RESULTS

Forty-six patients underwent prepost testing (CEA = 25, CAS = 21). Women comprised 36% of the cohort, mean preprocedural stenosis was 84%, and 54% were right-sided lesions. All patients were successfully revascularized without periprocedural complications. The scores for each test improved after CEA except WMI, which decreased in 20 of 25 patients. Improvement occurred in all tests after CAS except PSI, which decreased in 18 of 21 patients. In addition to comparing the changes in individual test scores, overall cognitive change was measured by calculating the change in composite cognitive score (CCS) postprocedure versus baseline. To compute the CCS, the raw scores from each test were transformed into z scores and then averaged to calculate each patient's composite score. The composite score at baseline was then compared with that from the postprocedure testing. The CCS improved after both CEA and CAS, and the changes were not significantly different between the groups (.51 vs .47; P = NS).

CONCLUSIONS

Carotid revascularization results in an overall improvement in cognitive function. There are no differences in the composite scores of five major cognitive domains between CEA and CAS. When individual tests are compared, CEA results in a reduction in memory, while CAS patients show reduced psychomotor speed. Larger studies will help confirm these findings.

Neurovascular function in Alzheimer's disease patients and experimental models

The ability of the brain to locally augment glucose delivery and blood flow during neuronal activation, termed neurometabolic and neurovascular coupling, respectively, is compromised in Alzheimer's disease (AD). Since perfusion deficits may hasten clinical deterioration and have been correlated with negative treatment outcome, strategies to improve the cerebral circulation should form an integral element of AD therapeutic efforts. These efforts have yielded several experimental models, some of which constitute AD models proper, others which specifically recapture the AD cerebrovascular pathology, characterized by anatomical alterations in brain vessel structure, as well as molecular changes within vascular smooth muscle cells and endothelial cells forming the blood-brain barrier. The following paper will present the elements of AD neurovascular dysfunction and review the in vitro and in vivo model systems that have served to deepen our understanding of it. It will also critically evaluate selected groups of compounds, the FDA-approved cholinesterase inhibitors and thiazolidinediones, for their ability to correct neurovascular dysfunction in AD patients and models. These and several others are emerging as compounds with pleiotropic actions that may positively impact dysfunctional cerebrovascular, glial, and neuronal networks in AD.

Intact memory in TGF-β1 transgenic mice featuring chronic cerebrovascular deficit: recovery with pioglitazone

The roles of chronic brain hypoperfusion and transforming growth factor-beta 1 (TGF-β1) in Alzheimer's disease (AD) are unresolved. We investigated the interplay between TGF-β1, cerebrovascular function, and cognition using transgenic TGF mice featuring astrocytic TGF-β1 overexpression. We further assessed the impact of short, late therapy in elderly animals with the antioxidant N-acetyl-L-cysteine (NAC) or the peroxisome proliferator-activated receptor-γ agonist pioglitazone. The latter was also administered to pups as a prophylactic 1-year treatment. Elderly TGF mice featured cerebrovascular dysfunction that was not remedied with NAC. In contrast, pioglitazone prevented or reversed this deficit, and rescued the impaired neurovascular coupling response to whisker stimulation, although it failed to normalize the vascular structure. In aged TGF mice, neuronal and cognitive indices--the stimulus-evoked neurometabolic response, cortical cholinergic innervation, and spatial memory in the Morris water maze--were intact. Our findings show that impaired brain hemodynamics and cerebrovascular function are not accompanied by memory impairment in this model. Conceivably in AD, they constitute aggravating factors against a background of aging and underlying pathology. Our data further highlight the ability of pioglitazone to protect the cerebrovasculature marked by TGF-β1 increase, aging, fibrosis, and antioxidant resistance, thus of high relevance for AD patients.

Role of cerebral microemboli in the causation of Alzheimer’s disease and vascular dementia

Vascular risk factors are involved in the causation of both vascular dementia (VaD) and Alzheimer’s disease (AD), which together account for up to 80% of all dementias. Asymptomatic spontaneous cerebral emboli (SCE) have been shown to predict future risk of cerebrovascular accidents and silent strokes on MRI. Over a period of years, SCE could potentially cause progressive brain damage and dementia. Our research has shown that SCE occur more frequently in both AD and VaD compared with controls without dementia. SCE are associated with depressive symptoms and predict a more rapid progression of dementia. SCE may be a common mechanism of vascular brain damage that explains the AD, VaD and mixtures of the two. SCE may be a potentially treatable target to slow progression and possibly prevent these dementias.

Nerve Growth Factor Differentially Affects Spatial and Recognition Memory in Aged Rats

In rats, object discrimination depends on the integrity of the cholinergic system, thus it could be expected that nerve growth factor (NGF) can improve the behavior in aged subjects. The interactive effect of age and cholinergic improvement was assessed behaviorally in young and aged rats. Animals were injected by infusion of NGF into the lateral ventricles and they were tested in two behavioral tasks: an object-location and an object-recognition task. Spatial and recognition memory were assessed in an open field containing five different objects. Rats were submitted to six consecutive sessions. Both age-groups showed comparable habituation of exploratory response in Session 1-4. Discrimination index (DI) was calculated to assess responses to spatial change in Session 5 and object change in Session 6. Control young and aged rats were able to discriminate between familiar and novel object, however DI was lower in aged rats. Treatment with NGF induced decline of object discrimination in both age-groups. Different results were obtained in spatial displacement test. NGF was able to improve spatial memory in aged rats, but had no effect in young controls. These data confer on NGF potential role in improving spatial but not episodic memory in aged rats.