Regulation of regional cerebral blood flow by cholinergic fibers originating in the basal forebrain

The fMRI global signal and its association with the signal from cranial bone

The nature of the global signal, i.e. the average signal from sequential functional imaging scans of the brain or the cortex, is not well understood, but is thought to include vascular and neural components. Using resting state data, we report on the strong association between the global signal and the average signal from the part of the volume that includes the cranial bone and subdural vessels and venous collectors, separated from each other and the subdural space by multispectral segmentation procedures. While subdural vessels carried a signal with a phase delay relative to the cortex, the association with the cortical signal was strongest in the parts of the scan corresponding to the laminae of the cranial bone, reaching 80% shared variance in some individuals. These findings suggest that in resting state data vascular components may play a prominent role in the genesis of fluctuations of the global signal. Evidence from other studies on the existence of neural sources of the global signal suggests that it may reflect the action of multiple mechanisms (including cerebrovascular reactivity and autonomic control) concurrently acting to regulate global cerebral perfusion.

Region-Dependent Increase of Cerebral Blood Flow During Electrically Induced Contraction of the Hindlimbs in Rats

Elevation of cerebral blood flow (CBF) may contribute to the cerebral benefits of the regular practice of physical exercise. Surprisingly, while electrically induced contraction of a large muscular mass is a potential substitute for physical exercise to improve cognition, its effect on CBF remains to be investigated. Therefore, the present study investigated CBF in the cortical area representing the hindlimb, the hippocampus and the prefrontal cortex in the same anesthetized rats subjected to either acute (30 min) or chronic (30 min for 7 days) electrically induced bilateral hindlimb contraction. While CBF in the cortical area representing the hindlimb was assessed from both laser doppler flowmetry (LDF_CBF) and changes in p-eNOS^Ser1177 levels (p-eNOS_CBF), CBF was evaluated only from changes in p-eNOS^Ser1177 levels in the hippocampus and the prefrontal cortex. The contribution of increased cardiac output and increased neuronal activity to CBF changes were examined. Stimulation was associated with tachycardia and no change in arterial blood pressure. It increased LDF_CBF with a time- and intensity-dependent manner as well as p-eNOS_CBF in the area representing the hindlimb. By contrast, p-eNOS_CBF was unchanged in the two other regions. The augmentation of LDF_CBF was partially reduced by atenolol (a ß1 receptor antagonist) and not reproduced by the administration of dobutamine (a ß1 receptor agonist). Levels of c-fos as a marker of neuronal activation selectively increased in the area representing the hindlimb. In conclusion, electrically induced bilateral hindlimb contraction selectively increased CBF in the cortical area representing the stimulated muscles as a result of neuronal hyperactivity and increased cardiac output. The absence of CBF changes in cognition-related brain regions does not support flow-dependent neuroplasticity in the pro-cognitive effect of electrically induced contraction of a large muscular mass.

The scalability of common paradigms for assessment of cognitive function: A functional transcranial Doppler study

Cognitive paradigms induce changes in cerebral blood flow (CBF) associated with increased metabolic demand, namely neurovascular coupling (NVC). We tested the hypothesis that the effect of complexity and duration of cognitive paradigms will either enhance or inhibit the NVC response. Bilateral CBF velocity (CBFV) in the middle cerebral arteries (MCAs) via transcranial Doppler ultrasound (TCD), blood pressure (BP), electrocardiogram (ECG) and end-tidal CO₂ (EtCO₂) of 16 healthy participants (aged 21–71 years) were simultaneously recorded at rest and during randomized paradigms of different complexities (naming words beginning with P-,R-,V- words and serial subtractions of 100–2,100–7,1000–17), and durations (5s, 30s and 60s). CBFV responses were population mean normalized from a 30-s baseline period prior to task initiation. A significant increase in bilateral CBFV response was observed at the start of all paradigms and provided a similar pattern in most responses, irrespective of complexity or duration. Although significant inter-hemispherical differences were found during performance of R-word and all serial subtraction paradigms, no lateralisation was observed in more complex naming word tasks. Also, the effect of duration was manifested at late stages of 100–7, but not for other paradigms. CBFV responses could not distinguish different levels of complexity or duration with a single presentation of the cognitive paradigm. Further studies of the ordinal scalability of the NVC response are needed with more advanced modelling techniques, or different types of neural stimulation.

Origins of 1/f-like tissue oxygenation fluctuations in the murine cortex

The concentration of oxygen in the brain spontaneously fluctuates, and the distribution of power in these fluctuations has a 1/f-like spectra, where the power present at low frequencies of the power spectrum is orders of magnitude higher than at higher frequencies. Though these oscillations have been interpreted as being driven by neural activity, the origin of these 1/f-like oscillations is not well understood. Here, to gain insight of the origin of the 1/f-like oxygen fluctuations, we investigated the dynamics of tissue oxygenation and neural activity in awake behaving mice. We found that oxygen signal recorded from the cortex of mice had 1/f-like spectra. However, band-limited power in the local field potential did not show corresponding 1/f-like fluctuations. When local neural activity was suppressed, the 1/f-like fluctuations in oxygen concentration persisted. Two-photon measurements of erythrocyte spacing fluctuations and mathematical modeling show that stochastic fluctuations in erythrocyte flow could underlie 1/f-like dynamics in oxygenation. These results suggest that the discrete nature of erythrocytes and their irregular flow, rather than fluctuations in neural activity, could drive 1/f-like fluctuations in tissue oxygenation.

The Effects of Statins on Neurotransmission and Their Neuroprotective Role in Neurological and Psychiatric Disorders

Statins are among the most widely used drug classes in the world. Apart from their basic mechanism of action, which is lowering cholesterol levels, many pleiotropic effects have been described so far, such as anti-inflammatory and antiatherosclerotic effects. A growing number of scientific reports have proven that these drugs have a beneficial effect on the functioning of the nervous system. The first reports proving that lipid-lowering therapy can influence the development of neurological and psychiatric diseases appeared in the 1990s. Despite numerous studies about the mechanisms by which statins may affect the functioning of the central nervous system (CNS), there are still no clear data explaining this effect. Most studies have focused on the metabolic effects of this group of drugs, however authors have also described the pleiotropic effects of statins, pointing to their probable impact on the neurotransmitter system and neuroprotective effects. The aim of this paper was to review the literature describing the impacts of statins on dopamine, serotonin, acetylcholine, and glutamate neurotransmission, as well as their neuroprotective role. This paper focuses on the mechanisms by which statins affect neurotransmission, as well as on their impacts on neurological and psychiatric diseases such as Parkinson's disease (PD), Alzheimer's disease (AD), vascular dementia (VD), stroke, and depression. The pleiotropic effects of statin usage could potentially open floodgates for research in these treatment domains, catching the attention of researchers and clinicians across the globe.

Ultra-slow Oscillations in fMRI and Resting-State Connectivity: Neuronal and Vascular Contributions and Technical Confounds

Ultra-slow, ∼0.1-Hz variations in the oxygenation level of brain blood are widely used as an fMRI-based surrogate of "resting-state" neuronal activity. The temporal correlations among these fluctuations across the brain are interpreted as "functional connections" for maps and neurological diagnostics. Ultra-slow variations in oxygenation follow a cascade. First, they closely track changes in arteriole diameter. Second, interpretable functional connections arise when the ultra-slow changes in amplitude of γ-band neuronal oscillations, which are shared across even far-flung but synaptically connected brain regions, entrain the ∼0.1-Hz vasomotor oscillation in diameter of local arterioles. Significant confounds to estimates of functional connectivity arise from residual vasomotor activity as well as arteriole dynamics driven by self-generated movements and subcortical common modulatory inputs. Last, methodological limitations of fMRI can lead to spurious functional connections. The neuronal generator of ultra-slow variations in γ-band amplitude, including that associated with self-generated movements, remains an open issue.

Cholinergic nervous system and glaucoma: From basic science to clinical applications

The cholinergic system has a crucial role to play in visual function. Although cholinergic drugs have been a focus of attention as glaucoma medications for reducing eye pressure, little is known about the potential modality for neuronal survival and/or enhancement in visual impairments. Citicoline, a naturally occurring compound and FDA approved dietary supplement, is a nootropic agent that is recently demonstrated to be effective in ameliorating ischemic stroke, traumatic brain injury, Parkinson's disease, Alzheimer's disease, cerebrovascular diseases, memory disorders and attention-deficit/hyperactivity disorder in both humans and animal models. The mechanisms of its action appear to be multifarious including (i) preservation of cardiolipin, sphingomyelin, and arachidonic acid contents of phosphatidylcholine and phosphatidylethanolamine, (ii) restoration of phosphatidylcholine, (iii) stimulation of glutathione synthesis, (iv) lowering glutamate concentrations and preventing glutamate excitotoxicity, (v) rescuing mitochondrial function thereby preventing oxidative damage and onset of neuronal apoptosis, (vi) synthesis of myelin leading to improvement in neuronal membrane integrity, (vii) improving acetylcholine synthesis and thereby reducing the effects of mental stress and (viii) preventing endothelial dysfunction. Such effects have vouched for citicoline as a neuroprotective, neurorestorative and neuroregenerative agent. Retinal ganglion cells are neurons with long myelinated axons which provide a strong rationale for citicoline use in visual pathway disorders. Since glaucoma is a form of neurodegeneration involving retinal ganglion cells, citicoline may help ameliorate glaucomatous damages in multiple facets. Additionally, trans-synaptic degeneration has been identified in humans and experimental models of glaucoma suggesting the cholinergic system as a new brain target for glaucoma management and therapy.

Nigella sativa and thymoquinone attenuate oxidative stress and cognitive impairment following cerebral hypoperfusion in rats

Nigella sativa, a plant widely used in traditional medicine, possesses anti-inflammatory, antioxidant and neuroprotective properties. In the present study, we investigated the effect of hydroalcoholic extract of N. sativa seeds (NSE) and its active constituent, thymoquinone (TQ), on learning and memory deficits, hippocampal acetylcholine esterase (AChE) activity, and markers of redox status, mainly lipid peroxidation and superoxide dismutase (SOD) activity following cerebral hypoperfusion in rats. Cerebral hypoperfusion was induced by permanent occlusion of bilateral common carotid arteries (2VO). Male Wistar rats were administered either a vehicle (sham group: 10 ml/kg/day, ip), NSE (100, 200, and 400 mg/kg/day, ip), TQ (10, 20, and 40 mg/kg/day, ip), or donepezil (5 mg/kg/day, ip) for 10 days (three days before and seven days after ligation). Spatial learning and memory deficits were investigated using the Morris water maze (MWM) task. 2VO produced significant learning and memory deficits as evidenced by increased latency time to reach the hidden platform, increased swimming time, and decreased time spent in the target quadrant in the probe trial in the MWM task. There was also a significant increase in the lipid peroxidation level and AChE activity, and a significant decrease in SOD activity in the hippocampal portion of hypoperfused rats, as compared with the sham group. Treatment with NSE (400 mg/kg/day; p < 0.001) and TQ (40 mg/kg/day; p < 0.001), as well as donepezil significantly prevented learning and memory impairments and alleviated changes in the hippocampal lipid peroxide level and SOD and AChE activities in this model. In conclusion, our data suggest that N. sativa and thymoquinone have a beneficial role in cerebrovascular insufficiency states and dementia.

The neuritic plaque in Alzheimer's disease: perivascular degeneration of neuronal processes

Cerebrovascular pathology is common in aging and Alzheimer's disease (AD). The microvasculature is particularly vulnerable, with capillary-level microhemorrhages coinciding with amyloid beta deposits in senile plaques. In the current analysis, we assessed the relationship between cerebral microvessels and the neuritic component of the plaque in cortical and hippocampal 50- to 200-μm sections from 11 AD, 3 Down syndrome, and 7 nondemented cases in neuritic disease stages 0-VI. We report that 77%-97% of neuritic plaques are perivascular, independently of disease stage or dementia diagnosis. Within neuritic plaques, dystrophic hyperphosphorylated tau-positive neurites appear as clusters of punctate, bulbous, and thread-like structures focused around capillaries and colocalize with iron deposits characteristic of microhemorrhage. Microvessels within the neuritic plaque are narrowed by 1.0 ± 1.0 μm-4.4 ± 2.0 μm, a difference of 16%-65% compared to blood vessel segments with diameters 7.9 ± 2.0-6.4 ± 0.8 μm (p < 0.01) outside the plaque domain. The reduced capacity of microvessels within plaques, frequently below patency, likely compromises normal microlocal cerebrovascular perfusion. These data link the neuritic and amyloid beta components of the plaque directly to microvascular degeneration. Strategies focused on cerebrovascular antecedents to neuritic dystrophy in AD have immediate potential for prevention, detection, and therapeutic intervention.

How reliable is cerebral blood flow to map changes in neuronal activity?

Neuroimaging techniques, such as functional MRI, map brain activity through hemodynamic-based signals, and are invaluable diagnostic tools in several neurological disorders such as stroke and dementia. Hemodynamic signals are normally precisely related to the underlying neuronal activity through neurovascular coupling mechanisms that ensure the supply of blood, glucose and oxygen to neurons at work. The knowledge of neurovascular coupling has greatly advanced over the last 30 years, it involves multifaceted interactions between excitatory and inhibitory neurons, astrocytes, and the microvessels. While the tight relationship between blood flow and neuronal activity forms a fundamental brain function, whether neurovascular coupling mechanisms are reliable across physiological and pathological conditions has been questioned. In this review, we interrogate the relationship between blood flow and neuronal activity during activation of different brain pathways: a sensory stimulation driven by glutamate, and stimulation of neuromodulatory pathways driven by acetylcholine or noradrenaline, and we compare the underlying neurovascular coupling mechanisms. We further question if neurovascular coupling mechanisms are affected by changing brain states, as seen in behavioral conditions of sleep, wakefulness, attention and in pathological conditions. Finally, we provide a short overview of how alterations of the brain vasculature could compromise the reliability of neurovascular coupling. Overall, while neurovascular coupling requires activation of common signalling pathways, alternate unique cascades exist depending on the activated pathways. Further studies are needed to fully elucidate the alterations in neurovascular coupling across brain states and pathological conditions.

Two distinct profiles of fMRI and neurophysiological activity elicited by acetylcholine in visual cortex

fMRI changes are typically assumed to be due to changes in neural activity, although whether this remains valid under the influence of neuromodulators is relatively unknown. Here, we found evidence that intracortical acetylcholine elicits distinct profiles of fMRI and electrophysiological activity in visual cortex. Two patterns of cholinergic activity were observed, depending on the distance to the injection site, although neurovascular coupling was preserved. Our results illustrate the effects of neuromodulators on fMRI and electrophysiological responses and show that these depend on neuromodulator concentration and kinetics.

Cholinergic neuromodulation is involved in all aspects of sensory processing and is crucial for processes such as attention, learning and memory, etc. However, despite the known roles of acetylcholine (ACh), we still do not how to disentangle ACh contributions from sensory or task-evoked changes in functional magnetic resonance imaging (fMRI). Here, we investigated the effects of local injection of ACh on fMRI and neural signals in the primary visual cortex (V1) of anesthetized macaques by combining pharmaco-based MRI (phMRI) with electrophysiological recordings, using single electrodes and electrode arrays. We found that local injection of ACh elicited two distinct profiles of fMRI and neurophysiological activity, depending on the distance from the injector. Near the injection site, we observed an increase in the baseline blood oxygen-level-dependent (BOLD) and cerebral blood flow (CBF) responses, while their visual modulation decreased. In contrast, further from the injection site, we observed an increase in the visually induced BOLD and CBF modulation without changes in baseline. Neurophysiological recordings suggest that the spatial correspondence between fMRI responses and neural activity does not change in the gamma, high-gamma, and multiunit activity (MUA) bands. The results near the injection site suggest increased inhibitory drive and decreased metabolism, contrasting to the far region. These changes are thought to reflect the kinetics of ACh and its metabolism to choline.

Nucleus Basalis of Meynert Stimulation for Dementia: Theoretical and Technical Considerations

Deep brain stimulation (DBS) of nucleus basalis of Meynert (NBM) is currently being evaluated as a potential therapy to improve memory and overall cognitive function in dementia. Although, the animal literature has demonstrated robust improvement in cognitive functions, phase 1 trial results in humans have not been as clear-cut. We hypothesize that this may reflect differences in electrode location within the NBM, type and timing of stimulation, and the lack of a biomarker for determining the stimulation's effectiveness in real time. In this article, we propose a methodology to address these issues in an effort to effectively interface with this powerful cognitive nucleus for the treatment of dementia. Specifically, we propose the use of diffusion tensor imaging to identify the nucleus and its tracts, quantitative electroencephalography (QEEG) to identify the physiologic response to stimulation during programming, and investigation of stimulation parameters that incorporate the phase locking and cross frequency coupling of gamma and slower oscillations characteristic of the NBM's innate physiology. We propose that modulating the baseline gamma burst stimulation frequency, specifically with a slower rhythm such as theta or delta will pose more effective coupling between NBM and different cortical regions involved in many learning processes.

Cerebral blood flow modulations during preparatory attention and proactive inhibition

This study investigated cerebral blood flow modulations during task preparation in a precued saccade paradigm. Bilateral blood flow velocities in the middle cerebral arteries were recorded in 48 subjects using functional transcranial Doppler sonography. Video-based eye-tracking was applied for ocular recording. Antisaccade and prosaccade trials were presented in both block-wise and interleaved order. A right dominant flow response arose during task preparation. While the response was stronger during antisaccade than prosaccade trials, the degree of lateralisation did not differ between the two trial types. Direction error rates were higher and latencies were longer for antisaccades than prosaccades. There were no differences between block-wise and interleaved trials in blood flow or performance. The stronger blood flow increases during antisaccade than prosaccade preparation reflects the complexity of the upcoming task demands as well as proactive inhibition. The right hemispheric lateralisation may be attributed to preparatory attention independent of demands on inhibitory control.

[Autoregulation of cerebral blood flow in severe diffuse axonal brain injury: the role of neuroanatomical factors]

Autoregulation of cerebral blood flow (ACBF) is a system of mechanisms for maintaining stable adequate perfusion of the brain despite changes in systemic arterial pressure. In recent years, new data on the numerous metabolic and systemic mechanisms of cerebral blood flow regulation have been obtained, but the role of neurogenic regulation has not yet been fully understood and, therefore, not considered in clinical practice.

AIM

The study aim was to assess the effect of anatomical injuries to deep brain structures on the extent and duration of ACBF abnormalities in a model of severe diffuse axonal injury (DAI).

RESULTS

The study demonstrated that brain injury in the projection of a dopaminergic structure (substantia nigra) and a cholinergic structure (nucleus basalis of Meynert region) was more common in patients with impaired ACBF and was associated with a longer duration of the impairment.

CONCLUSION

The obtained data may indicate the presence of central (neurogenic) pathways of cerebral vessel tone regulation; traumatic injury of the pathways leads to a more severe and prolonged period of impaired ACBF. Probably, injury to these regulatory structures in some patients has an indirect effect on the course of intracranial hypertension. Further experimental and clinical studies in this direction are needed to elucidate all elements of neurogenic regulation of cerebral vessel tone and ACBF mechanisms.

Genetic, Transcriptome, Proteomic, and Epidemiological Evidence for Blood-Brain Barrier Disruption and Polymicrobial Brain Invasion as Determinant Factors in Alzheimer's Disease

Diverse pathogens are detected in Alzheimer's disease (AD) brains. A bioinformatics survey showed that AD genome-wide association study (GWAS) genes (localized in bone marrow, immune locations and microglia) relate to multiple host/pathogen interactomes (Candida albicans, Cryptococcus neoformans, Bornavirus, Borrelia burgdorferri, cytomegalovirus, Ebola virus, HSV-1, HERV-W, HIV-1, Epstein-Barr, hepatitis C, influenza, Chlamydia pneumoniae, Porphyrymonas gingivalis, Helicobacter pylori, Toxoplasma gondii, Trypanosoma cruzi). These interactomes also relate to the AD hippocampal transcriptome and to plaque or tangle proteins. Upregulated AD hippocampal genes match those upregulated by multiple bacteria, viruses, fungi, or protozoa in immunocompetent cells. AD genes are enriched in GWAS datasets reflecting pathogen diversity, suggesting selection for pathogen resistance, as supported by the old age of AD patients, implying resistance to earlier infections. APOE4 is concentrated in regions of high parasitic burden and protects against childhood tropical infections and hepatitis C. Immune/inflammatory gain of function applies to APOE4, CR1, and TREM2 variants. AD genes are also expressed in the blood-brain barrier (BBB), which is disrupted by AD risk factors (age, alcohol, aluminum, concussion, cerebral hypoperfusion, diabetes, homocysteine, hypercholesterolemia, hypertension, obesity, pesticides, pollution, physical inactivity, sleep disruption, smoking) and by pathogens, directly or via olfactory routes to basal-forebrain BBB control centers. The BBB benefits from statins, NSAIDs, estrogen, melatonin, memantine, and the Mediterranean diet. Polymicrobial involvement is supported by upregulation of bacterial, viral, and fungal sensors/defenders in the AD brain, blood, or cerebrospinal fluid. AD serum amyloid-β autoantibodies may attenuate its antimicrobial effects favoring microbial survival and cerebral invasion leading to activation of neurodestructive immune/inflammatory processes, which may also be augmented by age-related immunosenescence. AD may thus respond to antibiotic, antifungal, or antiviral therapy.

Neuroprotective Effects of Simvastatin and Cilostazol in L-Methionine-Induced Vascular Dementia in Rats

Vascular dementia (VaD) is a degenerative cerebrovascular disorder that leads to progressive decline in cognitive abilities and memory. Several reports demonstrated that oxidative stress and endothelial dysfunction are principal pathogenic factors in VaD. The present study was constructed to determine the possible neuroprotective effects of simvastatin in comparison with cilostazol in VaD induced by L-methionine in rats. Male Wistar rats were divided into four groups. Group I (control group), group II received L-methionine (1.7 g/kg, p.o.) for 32 days. The remaining two groups received simvastatin (50 mg/kg, p.o.) and cilostazol (100 mg/kg, p.o.), respectively, for 32 days after induction of VaD by L-methionine. Subsequently, rats were tested for cognitive performance using Morris water maze test then sacrificed for biochemical and histopathological assays. L-methionine induced VaD reflected by alterations in rats' behavior as well as the estimated neurotransmitters, acetylcholinesterase activity as well as increased brain oxidative stress and inflammation parallel to histopathological changes in brain tissue. Treatment of rats with simvastatin ameliorated L-methionine-induced behavioral, neurochemical, and histological changes in a manner comparable to cilostazol. Simvastatin may be regarded as a potential therapeutic strategy for the treatment of VaD. To the best of our knowledge, this is the first study to reveal the neuroprotective effects of simvastatin or cilostazol in L-methionine-induced VaD. Graphical Abstract ᅟ.

Vascular action as the primary mechanism of cognitive effects of cholinergic, CNS-acting drugs, a rat phMRI BOLD study

Concordant results of functional magnetic resonance imaging (fMRI) and behavioral tests prove that some non-blood-brain barrier-penetrating drugs produce robust central nervous system (CNS) effects. The anticholinergic scopolamine interferes with learning when tested in rats, which coincides with a negative blood-oxygen-level-dependent (BOLD) change in the prefrontal cortex (PFC) as demonstrated by fMRI. The peripherally acting butylscopolamine also evokes a learning deficit in a water-labyrinth test and provokes a negative BOLD signal in the PFC. Donepezil-a highly CNS-penetrating cholinesterase inhibitor-prevents the negative BOLD and cognitive deficits regardless whether the provoking agent is scopolamine or butylscopolamine. Interestingly, the non-BBB-penetrating cholinesterase inhibitor neostigmine also prevents or substantially inhibits those cognitive and fMRI changes. Intact cerebral blood flow and optimal metabolism are crucial for the normal functioning of neurons and other cells in the brain. Drugs that are not BBB penetrating yet act on the CNS highlight the importance of unimpaired circulation, and point to the cerebral vasculature as a primary target for drug action in diseases where impaired circulation and consequently suboptimal energy metabolism are followed by upstream pathologic events.

Integrative regulation of human brain blood flow

Herein, we review mechanisms regulating cerebral blood flow (CBF), with specific focus on humans. We revisit important concepts from the older literature and describe the interaction of various mechanisms of cerebrovascular control. We amalgamate this broad scope of information into a brief review, rather than detailing any one mechanism or area of research. The relationship between regulatory mechanisms is emphasized, but the following three broad categories of control are explicated: (1) the effect of blood gases and neuronal metabolism on CBF; (2) buffering of CBF with changes in blood pressure, termed cerebral autoregulation; and (3) the role of the autonomic nervous system in CBF regulation. With respect to these control mechanisms, we provide evidence against several canonized paradigms of CBF control. Specifically, we corroborate the following four key theses: (1) that cerebral autoregulation does not maintain constant perfusion through a mean arterial pressure range of 60-150 mmHg; (2) that there is important stimulatory synergism and regulatory interdependence of arterial blood gases and blood pressure on CBF regulation; (3) that cerebral autoregulation and cerebrovascular sensitivity to changes in arterial blood gases are not modulated solely at the pial arterioles; and (4) that neurogenic control of the cerebral vasculature is an important player in autoregulatory function and, crucially, acts to buffer surges in perfusion pressure. Finally, we summarize the state of our knowledge with respect to these areas, outline important gaps in the literature and suggest avenues for future research.

Rivastigmine for subcortical vascular dementia

Rivastigmine is a second-generation cholinesterase inhibitor with selectivity for the CNS, with capacity to inhibit both acetylcholinesterase and butyrylcholinesterase. Rivastigmine is currently approved for the treatment of mild-to-moderate Alzheimer's disease. In addition to its effects on cognition and activities of daily living, rivastigmine appears to be useful in preventing and controlling behavioral and neuropsychiatric manifestations in Alzheimer's disease and dementia with Lewy bodies. This drug profile could be potentially useful in patients with subcortical vascular dementia who often present these symptoms. Small open-label studies of patients with subcortical vascular dementia showed that rivastigmine improved attention, executive function, apathy and other behavioral deficits. Rivastigmine appears to be a promising agent in vascular dementia but its effects remain to be established in double-blind, placebo-controlled clinical trials.

Axo-axonal interaction in autonomic regulation of the cerebral circulation

Noradrenaline (NE) and acetylcholine (ACh) released from the sympathetic and parasympathetic neurones in cerebral blood vessels were suggested initially to be the respective vasoconstricting and dilating transmitters. Both substances, however, are extremely weak post-synaptic transmitters. Compelling evidence indicates that nitric oxide (NO) which is co-released with ACh from same parasympathetic nerves is the major transmitter for cerebral vasodilation, and its release is inhibited by ACh. NE released from the sympathetic nerve, acting on presynaptic β2-adrenoceptors located on the neighbouring parasympathetic nitrergic nerves, however, facilitates NO release with enhanced vasodilation. This axo-axonal interaction mediating NE transmission is supported by close apposition between sympathetic and parasympathetic nerve terminals, and has been shown in vivo at the base of the brain and the cortical cerebral circulation. This result reveals the physiological need for increased regional cerebral blood flow in 'fight-or-flight response' during acute stress. Furthermore, α7- and α3β2-nicotinic ACh receptors (nAChRs) on sympathetic nerve terminals mediate release of NE, leading to cerebral nitrergic vasodilation. α7-nAChR-mediated but not α3β2-nAChR-mediated cerebral nitrergic vasodilation is blocked by β-amyloid peptides (Aβs). This may provide an explanation for cerebral hypoperfusion seen in patients with Alzheimer's disease. α7- and α3β2-nAChR-mediated nitrergic vasodilation is blocked by cholinesterase inhibitors (ChEIs) which are widely used for treating Alzheimer's disease, leading to possible cerebral hypoperfusion. This may contribute to the limitation of clinical use of ChEIs. ChEI blockade of nAChR-mediated dilation like that by Aβs is prevented by statins pretreatment, suggesting that efficacy of ChEIs may be improved by concurrent use of statins.

Self-regulation of cerebral blood flow by means of transcranial Doppler sonography biofeedback

BACKGROUND

Transcranial Doppler sonography (TCD) allows the continuous non-invasive assessment of intracranial blood flow velocities with high temporal resolution. It may therefore prove suitable for biofeedback of cerebral perfusion.

PURPOSE

The study explored whether healthy individuals can successfully be trained in self-regulation of cerebral blood flow using TCD biofeedback.

METHODS

Twenty-two subjects received visual feedback of flow velocities in the middle cerebral arteries of both hemispheres. They were randomly assigned to two groups, one of which attempted to increase, the other to decrease the signal within eight training sessions. Heart rate and respiratory frequency were also monitored.

RESULTS

Both groups achieved significant changes in flow velocities in the expected directions. Modulations in heart rate and respiratory frequency during biofeedback did not account for these effects.

CONCLUSIONS

TCD biofeedback enables efficient self-regulation of cerebral blood flow. It is promising in applications such as the treatment of migraine and post-stroke rehabilitation.

Interactions between systemic hemodynamics and cerebral blood flow during attentional processing

The study explored interactions between systemic hemodynamics and cerebral blood flow during attentional processing. Using transcranial Doppler sonography, blood flow velocities in the middle cerebral arteries (MCA) of both hemispheres were recorded while 50 subjects performed a cued reaction time task. Finger arterial pressure and heart rate were also continuously monitored. Doppler sonography revealed a right dominant blood flow response. The extent of the increase measured in second two of the interstimulus interval showed a clear positive association with reaction speed. Task-related changes in blood pressure and heart rate proved predictive of changes in MCA flow velocities in limited time windows of the response. Besides an association between cerebral blood flow and attentional performance, the results suggest a marked impact of systemic hemodynamics on the blood flow response. All observed interactions are highly dynamic in time.

Current Concepts in Vascular Cognitive Impairment and Pharmacotherapeutic Implications

Objective:

To review evolution of the vascular cognitive impairment (VCI) construct, including diagnosis, pharmacotherapeutic implications, and address challenges that will shape future developments.

Data Sources:

Literature retrieval was accessed through PubMed, from 1966 to December 2008, using the terms vascular cognitive impairment, vascular dementia, post-stroke dementia, vascular cognitive disorder, mild cognitive impairment, criteria, disease progression, outcomes, treatment, prevention, biomarkers, and neuroimaging.

Study Selection and Data Extraction:

All articles in published English identified from the data sources were evaluated for inclusion. Regarding pharmacotherapy, prospective double-blind, placebo-controlled studies were included as well as extensions or relevant post hoc analyses.

Data Synthesis:

In the 1970s, “senile dementia due to hardening of the arteries” was used to describe dementia due to vascular causes. This was a narrow view of what is now known to be a common form of cognitive impairment in older people. Multiple infarct dementia (MID) was first proposed to describe dementia attributable to multiple cerebral infarcts, followed by the vascular dementia (VaD) construct, itself meant to be an improvement over MID. The VaD construct had limitations, not the least of which was that, by the time a patient was diagnosed with VaD, the opportunity for prevention was lost. Thus arose the concept of VCI, representing a group of heterogeneous disorders that share presumed vascular causes. The importance of VCI is centered on the fact that vascular risk factors are treatable, and thus should lead to a reduction in the incidence of cognitive impairment due to vascular causes. There is evidence that treatment of hypertension can lead to a reduction in the incidence of cognitive impairment and dementia, and that treatment of VaD with acetylcholinesterase inhibitors may be beneficial.

Conclusions:

Careful attention needs to be given to controlling vascular risk factors in at-risk patients. Pharmacists should play an active role in this important area of geriatric pharmacotherapy.

Cerebrospinal fluid neurochemical phenotypes in vascular dementias: original data and mini-review

BACKGROUND/AIMS

The study evaluated the patterns of cerebrospinal fluid (CSF), amyloid-beta (Abeta) peptides, total tau and phospho-tau among Alzheimer's disease (AD) and vascular dementias (VAD).

METHODS

Abeta-SDS-PAGE immunoblot and commercially available ELISAs were applied to the CSF analysis of 52 patients with probable (n = 21) and possible (n = 16) VAD, AD with cerebrovascular disease (n = 15), 30 patients with probable AD and 30 nondemented disease controls.

RESULTS

AD and AD with cerebrovascular disease displayed a similar neurochemical phenotype in contrast to nondemented disease controls and probable VAD with regard to tau, p-tau, Abeta1-40(ox) and Abeta1-42%. Possible VAD displayed AD-like changes only for Abeta1-40(ox) and Abeta1-42%.

CONCLUSION

CSF neurochemical phenotypes sufficiently discriminate probable AD and VAD from each other, but their diagnostic value is limited in case of no clear-cut clinical appearance, such as possible VAD. Conversely, CSF Abeta peptides and p-tau levels may help estimate the involvement of AD-like pathophysiological pathways in VAD subgroups.

Patterns of Cerebral Blood Flow and Systemic Hemodynamics During Arithmetic Processing

The present study explored modulations in cerebral blood flow and systemic hemodynamics during the execution of a mental calculation task in 41 healthy subjects. Time course and lateralization of blood flow velocities in the medial cerebral arteries of both hemispheres were assessed using functional transcranial Doppler sonography. Indices of systemic hemodynamics were obtained using continuous blood pressure recordings. Doppler sonography revealed a biphasic left dominant rise in cerebral blood flow velocities during task execution. Systemic blood pressure increased, whereas heart period, heart period variability, and baroreflex sensitivity declined. Blood pressure and heart period proved predictive of the magnitude of the cerebral blood flow response, particularly of its initial component. Various physiological mechanisms may be assumed to be involved in cardiovascular adjustment to cognitive demands. While specific contributions of the sympathetic and parasympathetic systems may account for the observed pattern of systemic hemodynamics, flow metabolism coupling, fast neurogenic vasodilation, and cerebral autoregulation may be involved in mediating cerebral blood flow modulations. Furthermore, during conditions of high cardiovascular reactivity, systemic hemodynamic changes exert a marked influence on cerebral blood perfusion.

Oxidative stress and erythrocyte acetylcholinesterase (AChE) in hypertensive and ischemic patients of both acute and chronic stages

Ischemic stroke is a leading cause of mortality and disability particularly in the elderly. Hypertension is the most important risk factor in strokes, representing roughly 70% of all cases. Oxidative stress is believed to be one of the mechanisms taking part in neuronal damage in stroke. It is well documented that cholinergic system plays a key role in normal brain functions and in memory disturbances of several pathological processes, such as in cerebral blood flow regulation. This study investigated the oxidative status and acetylcholinesterase (AChE) activity in whole blood in patients diagnosed with acute and chronic stages of ischemia, as well as with hypertension. Malondialdehyde (MDA) levels and protein carbonylation content showed increased levels both in the acute ischemic groups and in the hypertensive group, when compared to the control. Catalase activity and reduced glutathione (GSH) levels in the acute group were also higher than in the hypertensive, chronic ischemic and control groups (p<0.05). The activity of AChE in acute ischemic patients was significantly higher than that presented by the control, hypertensive and chronic ischemic patients (p<0.05). The hypertensive group presented AChE activity significantly lower than control and chronic groups. In spite of having a defined location the ischemic event results in a systemic disorder that induces changes, which can be detected by measuring the peripheral markers of oxidative stress and AChE activity in erythrocytes.

Rapid cerebral hemodynamic modulation during mental planning and movement execution: evidence of time-locked relationship with complex behavior

OBJECTIVE

Although there is evidence of specific associations between neuronal activity and early cerebral blood flow (CBF), little is known on a logical furtherance of this linkage, namely the association between early measures of cerebral hemodynamics and complex behavior. The present study examined the linkage between hemodynamic modulation in basal cerebral arteries and performance in a non-routine planning task by means of functional transcranial Doppler sonography (fTCD).

METHODS

The Stockings of Cambridge (SOC) was employed as planning paradigm. The middle and anterior cerebral arteries (MCA/ACA) were bilaterally insonated. Statistical methods comprised uni- and multivariate analyses of variance and multiple linear regression analyses.

RESULTS

Taking advantage of the excellent temporal resolution of fTCD, early cerebral hemodynamic modulation of the left MCA markedly predicted task accuracy. Pronounced early blood flow increase during planning and early decrease during movement execution were associated with better performance. No such blood flow modulations were observed in worse performers.

CONCLUSIONS

Early cerebral hemodynamic modulation in the left MCA proved to be a valuable neurophysiological marker that showed a great overlap with task accuracy during non-routine planning.

SIGNIFICANCE

These results support the notion that a high temporal resolution in functional monitoring is a favorable strategy to disentangle relevant neurophysiological correlates of higher cognitive functioning.

The enigma of vascular cognitive disorder and vascular dementia

The prevalence, morphology and pathogenesis of vascular dementia (VaD), recently termed vascular cognitive impairment, are a matter of discussion, and currently used clinical diagnostic criteria show moderate sensitivity (average 50%) and variable specificity (range 64-98%). In Western clinic-based series, VaD is suggested in 8-10% of cognitively impaired aged subjects. Its prevalence in autopsy series varies from 0.03 to 58%, with reasonable values of 8-15%, while in Japan it is seen in 22-35%. Neuropathologic changes associated with cognitive impairment include multifocal and/or diffuse disease and focal lesions: multi-infarct encephalopathy, white matter lesions or arteriosclerotic subcortical (leuko)encephalopathy, multilacunar state, mixed cortico-subcortical type, borderline/watershed lesions, rare granular cortical atrophy, post-ischemic encephalopathy and hippocampal sclerosis. They result from systemic, cardiac and local large or small vessel disease. Recent data indicate that cognitive decline is commonly associated with widespread small ischemic/vascular lesions (microinfarcts, lacunes) throughout the brain with predominant involvement of subcortical and functionally important brain areas. Their pathogenesis is multifactorial, and their pathophysiology affects neuronal networks involved in cognition, memory, behavior and executive functioning. Vascular lesions often coexist with Alzheimer disease (AD) and other pathologies. Minor cerebrovascular lesions, except for severe amyloid angiopathy, appear not essential for cognitive decline in full-blown AD, while both mild Alzheimer pathology and small vessel disease may interact synergistically. The lesion pattern of "pure" VaD, related to arteriosclerosis and microangiopathies, differs from that in mixed-type dementia (AD with vascular encephalopathy), more often showing large infarcts, which suggests different pathogenesis of both types of lesions. Due to the high variability of cerebrovascular pathology and its causative factors, no validated neuropathologic criteria for VaD are available, and a large variability across laboratories still exists in the procedures for morphologic examination and histology techniques.

Vascular dementia and the cholinergic pathways

Vascular cognitive impairment/vascular dementia have been the subject of a large number of studies, due to their high prevalence and broad preventive and compensatory therapeutic potential. The knowledge of the cerebral anatomy correlated to the vascular territories of irrigation enables understanding of clinical manifestations, as well as classification into the several types of syndromic presentations. The central cholinergic system exercises important neuromodulatory functions on cerebral circuits related to cognitive and behavioral integration, as well as on vasomotor control related to cerebral blood flow adjustments. The acquisition of data on the anatomy of the cholinergic pathways, including the localization of the nuclei of the basal prosencephalon and the routes of their projections, established an important milestone. The knowledge of the vascular distribution and of the trajectories of the cholinergic pathways allows identification of the strategic points where a vascular lesion can cause interruption. The ensuing denervation leads to cholinergic hypofunction in the involved territories. This information proves important to better evaluate the sites of vascular lesions, emphasizing their strategic localizations in relation to the cholinergic pathways, and offering more robust foundations for treatment aiming at enhancing cholinergic activity.

A pilot study evaluating the efficacy and safety of rivastigmine in patients with mixed dementia

BACKGROUND AND OBJECTIVE

The two most common causes of dementia in the elderly are Alzheimer's disease (AD) and vascular dementia (VaD), which can coexist as mixed dementia. The object of this study was to assess the efficacy and safety of rivastigmine in patients with mixed dementia (AD with VaD).

STUDY DESIGN

This 26-week open-label pilot study was conducted at 19 centres in the US. To reduce bias, the Alzheimer's Disease Assessment Scale-Cognitive (ADAS-Cog) raters were blinded to all efficacy measures and to patient dosage information. Patients were treated with rivastigmine and titrated to their highest tolerated dose, up to 12 mg/day (6 mg twice daily). The primary efficacy measure was cognitive function assessed by the ADAS-Cog subscale (without the concentration/distractibility item, to be consistent with cognitive outcome measures used in previous rivastigmine trials).

RESULTS

Forty-seven percent of patients treated with rivastigmine 6-12 mg/day demonstrated improvement on the ADAS-Cog at 26 weeks, with >25% of patients having a clinically significant improvement of > or =4 points. Treatment with rivastigmine (6-12 mg/day) was well tolerated by the majority of patients. The most common adverse effects occurring in >10% of patients were nausea, vomiting, dizziness and diarrhoea.

CONCLUSION

This pilot study suggests that rivastigmine treatment may have beneficial effects in the treatment of patients with mixed dementia.

Vascular determinants of cholinergic deficits in Alzheimer disease and vascular dementia

Alzheimer's disease (AD) and vascular dementia (VaD) are widely accepted as the most common forms of dementia. Cerebrovascular lesions frequently coexist with AD, creating an overlap in the clinical and pathological features of VaD and AD. This review assembles evidence for a role for cholinergic mechanisms in the pathogenesis of VaD, as has been established for AD. We first consider the anatomy and vascularization of the basal forebrain cholinergic neuronal system, emphasizing its susceptibility to the effects of arterial hypertension, sustained hypoperfusion, and ischemic cerebrovascular disease. The impact of aging and consequences of disruption of the cholinergic system in cognition and in control of cerebral blood flow are further discussed. We also summarize preclinical and clinical evidence supporting cholinergic deficits and the use of cholinesterase inhibitors in patients with VaD. We postulate that vascular pathology likely plays a common role in initiating cholinergic neuronal abnormalities in VaD and AD.

Regulation of the common carotid arterial blood flow by nicotinic receptors in the medulla of cats

BACKGROUND AND PURPOSE

Actions of glutamate and serotonin on their respective receptors in the dorsal facial area (DFA) of the medulla are known to regulate common carotid arterial (CCA) blood flow in cats. Less is known about acetylcholine action on its nicotinic receptor (nAChR) subtypes in the DFA for regulation of CCA blood flow and this aspect was investigated.

EXPERIMENTAL APPROACH

Nicotinic and muscarinic agonists and antagonists were microinjected into the DFA through a three-barrel tubing in anesthetized cats.

RESULTS

CCA blood flow was dose-dependently increased by nicotine (a non-selective nAChR agonist) and choline (a selective alpha7-nAChR agonist). These effects of nicotine were attenuated by alpha-bungarotoxin (an alpha7-nAChR antagonist), methyllycaconitine (an alpha7-nAChR antagonist), mecamylamine (a relatively selective alpha3beta4-nAChR antagonist) and dihydro-beta-erythroidine (a relatively selective alpha4beta2-nAChR antagonist). The choline-induced flow increase was attenuated by alpha-bungarotoxin and mecamylamine, but not by dihydro-beta-erythroidine. Muscarinic agonists (muscarine and methacholine) and antagonist (atropine) affected neither the basal nor the nicotine-induced increase in the CCA blood flow.

CONCLUSIONS AND IMPLICATIONS

Functional alpha7, alpha4beta2, and alpha3beta4 subunits of the nAChR appear to be present on the DFA neurons. Activations of these receptors increase the CCA blood flow. The present findings do not preclude the presence of other nAChRs subunits. Muscarinic receptors, if any, on the DFA are not involved in regulation of the CCA blood flow. Various subtypes of nAChRs in the DFA may mediate regulation of the CCA and cerebral blood flows.

Correlation between blood flow velocity in the middle cerebral artery and EEG during cognitive effort

Cognitive effort modifies blood flow velocity (BFV) in the middle cerebral artery (MCA) which can be recorded by transcranial Doppler sonography (TCD). EEG parameters can be used as indicators of cortical activation. To find temporal and spatial relation between circulatory and bioelectric phenomena, we used combined EEG and TCD measurements during cognitive experiments. Bilateral BFV in the MCAs and 16-channel scalp EEG were recorded during mental arithmetic (MA) and verbal fluency (VF) tests in 12 healthy volunteers. Temporal profile of BFV, heart rate (HR), EEG central frequency (CF), relative alpha power (ralphap), and laterality index (Li) for BFV and CF were statistically analysed. During mental effort, BFV changes showed a reproducible pattern, which was different in MA and VF tests. The Li(BFV) correlated with handedness in 9/12 subjects (75%) in the VF, and in 6/12 subjects (50%) in the MA test. Significant correlation was found between Li(BFV) and Li(CF) during VF (r(2) = 0.69). Li was more indicative for the hemispheric dominance in the VF than in the MA test. During VF test, correlation between HR and BFV was significant in 7/12 subjects. CF and ralphap provide real time assessment of the functional state of the brain tissue during cognition. The correlation between CF and BFV during mental activity suggests a short latency neurogenic and a long latency, supposedly chemical regulation of regional blood flow. Parallel analysis of EEG and flow parameters increases the confidence of determining hemispheric dominance and provides an alternative to study physiological consequences of cognitive processes.

Retinal vascular image analysis as a potential screening tool for cerebrovascular disease: a rationale based on homology between cerebral and retinal microvasculatures

The retinal and cerebral microvasculatures share many morphological and physiological properties. Assessment of the cerebral microvasculature requires highly specialized and expensive techniques. The potential for using non-invasive clinical assessment of the retinal microvasculature as a marker of the state of the cerebrovasculature offers clear advantages, owing to the ease with which the retinal vasculature can be directly visualized in vivo and photographed due to its essential two-dimensional nature. The use of retinal digital image analysis is becoming increasingly common, and offers new techniques to analyse different aspects of retinal vascular topography, including retinal vascular widths, geometrical attributes at vessel bifurcations and vessel tracking. Being predominantly automated and objective, these techniques offer an exciting opportunity to study the potential to identify retinal microvascular abnormalities as markers of cerebrovascular pathology. In this review, we describe the anatomical and physiological homology between the retinal and cerebral microvasculatures. We review the evidence that retinal microvascular changes occur in cerebrovascular disease and review current retinal image analysis tools that may allow us to use different aspects of the retinal microvasculature as potential markers for the state of the cerebral microvasculature.

Donepezil: a clinical review of current and emerging indications

This article reviews the piperidine derivative, donepezil hydrochloride (E2020, Aricept), a reversible central acetylcholinesterase inhibitor currently approved for treatment of mild-to-moderate Alzheimer's disease. Donepezil is well absorbed orally, unaffected by food or by time of administration; it reaches therapeutic levels in doses of 5-10 mg/day and peak plasma concentrations are obtained 3-4 h after oral administration. A single bedtime dose is recommended due to the long elimination half-life of the drug (70 h). Donepezil does not cause liver toxicity or significant drug interactions and is relatively well-tolerated. Initial side effects include nausea, vomiting, diarrhoea, insomnia, muscle cramps, fatigue, anorexia and syncope. Caution is advised in patients with bradycardia. Long-term use of donepezil in AD has been found to delay nursing-home placement and to result in caregiver respite. Donepezil also slows deterioration of cognition and global function in patients with moderate-to-severe AD, with improvement of abnormal behaviours. In addition to AD, donepezil demonstrates significant improvement in cognition, global function and activities of daily living in comparison with placebo-treated patients with vascular dementia and has potential therapeutic benefit for other neurological conditions.

Cholinergic dysfunction in vascular dementia

Vascular dementia (VaD) is the second most common type of dementia in the elderly after Alzheimer's disease (AD). Evidence is presented indicating the occurrence of cholinergic dysfunction in VaD, independent from AD. Controlled clinical trials of cholinesterase inhibitors (ChEIs) in VaD and in patients with AD plus cerebrovascular disease are reviewed. Compared with placebo, ChEI treatment improves cognition, behavior, and activities of daily living. Cholinergic deficits in patients with VaD may result from ischemia of basal forebrain cholinergic nuclei that are irrigated by penetrating arteries that are highly susceptible to arterial hypertension, or from ischemic lesions in basal ganglia or white matter that sever the extensive cholinergic cortical projections. Cholinergic stimulation produces increases in cortical cerebral blood flow that may be relevant to the therapeutic effect of ChEIs.

Facts, myths, and controversies in vascular dementia

Significant progress in the field of VaD resulted from publication of the NINIDS-AIREN Diagnostic Criteria for VaD (G.C. Roman, T.K. Tatemichi, T. Erkinjuntti, et al., Vascular dementia (VaD): diagnostic criteria for research studies. Report of the NINDS-AIREN International Workshop. Neurology 43 (1993) 250-260). Epidemiological studies confirmed the importance of VaD as the second most common cause of dementia in the elderly, representing 15-20% of all cases of dementia. In Europe and North America, Alzheimer's disease (AD) predominates over VaD in a 2:1 ratio; in contrast, in Japan and China VaD accounts for almost 50% of all dementias. Case-control studies have identified risk factors for VaD including ageing, hypertension, diabetes mellitus, hyperlipidemia, recurrent stroke, cardiac disease, smoking, sleep apnea, and more recently, hyperhomocysteinemia, among others. Hypertension treatment may prevent VaD and AD. This finding has enormous importance from the Public Health viewpoint to decrease the future number of patients with dementia in the elderly. Along with advances in the field of VaD came a number of controversies and damaging misconceptions and myths. Myth no. 1--Vascular dementia is a non-entity: The false idea that VaD does not exist is particularly destructive because it creates the perspective that VaD is unworthy of study or research. A condition that either does not exist or represents only a minute proportion of all cases of dementia in the elderly, lacks public health relevance and becomes a low priority for research by funding agencies and industry. In fact, vascular brain lesions are the commonest and most important component of dementia in the elderly. Myth no. 2--Vascular dementia is so difficult to diagnose that only experts can recognize and identify it accurately: VaD does exist and the diagnosis of post-stroke VaD, in particular is straightforward. Most cases fulfill NINDS-AIREN criteria for probable VaD; i.e., (1) there is acute onset of dementia demonstrated by impairment of memory and two other cognitive domains, such as orientation, praxis or executive dysfunction; (2) relevant cerebrovascular lesions are demonstrated by neuroimaging; and (3) a temporal relation between stroke and cognitive loss is evident. In the donepezil trials on VaD, post-stroke dementia represented about 75% of the >1,200 patients enrolled. Myth no. 3--Improvement in clinical trials of cholinergics in VaD is due to underlying AD, not to the vascular lesions. Experimental, clinical and pathological evidence has demonstrated cholinesterase deficits in VaD (independently of any concomitant AD pathology), including low acetylcholine in cerebrospinal fluid, and reduced choline acetyltransferase (ChAT) in the brain.

Brain hypoperfusion: a critical factor in vascular dementia

Subcortical ischemic vascular dementia is a relatively common form of dementia. Anatomical changes of ageing in the brain arteries predispose the elderly to the effects of hypotension. Depending on their circulatory pattern, particular regions of the brain are susceptible to ischemic hypoperfusive lesions. These regions include the periventricular white matter, basal ganglia, and hippocampus. Interruption of prefrontal-basal ganglia circuits important for cognition and memory may result from these lesions. Hypotension and hypoperfusion explain the high risk for the development of cognitive impairment and vascular dementia in older patients affected by orthostatic hypotension, congestive heart failure, as well as in those undergoing surgical procedures such as hip and knee replacement and coronary artery bypass graft (CABG). Recognition of the susceptibility of elderly subjects to cerebral lesions induced by hypoperfusion should result in appropriate preventive measures and better treatment.

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.

Activation of the intracerebral cholinergic nerve fibers originating in the basal forebrain increases regional cerebral blood flow in the rat's cortex and hippocampus

In the rat, activation of the intracerebral cholinergic system originating in the basal forebrain and projecting to the cortex and hippocampus releases acetylcholine in the cortex and hippocampus, which results in vasodilation and an increase in regional cerebral blood flow (rCBF) in the cortex and hippocampus. The augmentation of rCBF is independent of both systemic blood pressure and regional metabolism. The intracerebral cholinergic fibers are able to act as autonomic nerve fibers for the regulation of cortical and hippocampal blood flow.

The nucleus basalis and memory codes: auditory cortical plasticity and the induction of specific, associative behavioral memory

Receptive field (RF) plasticity develops in the primary auditory cortex (ACx) when a tone conditioned stimulus (CS) becomes associated with an appetitive or aversive unconditioned stimulus (US). This prototypical stimulus-stimulus (S-S) association is accompanied by shifts of frequency tuning of neurons toward or to the frequency of the CS such that the area of best tuning of the CS frequency is increased in the tonotopic representation of the ACx. RF plasticity has all of the major characteristics of behavioral associative memory: it is highly specific, discriminative, rapidly induced, consolidates (becomes stronger and more specific over hours to days) and can be retained indefinitely (tested to two months). Substitution of nucleus basalis (NB) stimulation for a US induces the same associative RF plasticity, and this requires the engagement of muscarinic receptors in the ACx. Pairing a tone with NB stimulation actually induces specific, associative behavioral memory, as indexed by post-training frequency generalization gradients. The degree of acquired behavioral significance of sounds appears to be encoded by the number of neurons that become retuned in the ACx to that acoustic stimulus, the greater the importance, the greater the number of re-tuned cells. This memory code has recently been supported by direct neurobehavioral tests. In toto, these findings support the view that specific, learned auditory memory content is stored in the ACx, and further that this storage of information during learning and the instantiation of the memory code involves the engagement of the nucleus basalis and its release of acetylcholine into target structures, particularly the cerebral cortex.