Acquired Hemicerebral Atrophy Secondary to Chronic Internal Carotid Steno-Occlusive Disease: A Case Series.

Cerebral atrophy is a common finding in elderly patients; however, cerebrovascular disease causing progressive focal cerebral atrophy and dysfunction is unusual. In this report, we present 3 cases of hemicerebral atrophy due to ipsilateral internal carotid artery (ICA) stenosis or occlusion mimicking neurodegenerative conditions. Patient 1 had a frontal dysexecutive syndrome potentially consistent with a diagnosis of behavioral variant frontotemporal dementia; however, neuroimaging revealed a chronically occluded left ICA and a pattern of atrophy restricted to the left middle cerebral artery territory, suggestive of a vascular etiology. Patient 2 presented with progressively worsening seizures and right-sided weakness consistent with left hemispheric dysfunction, with radiographic evidence of left hemicerebral atrophy. Angiography revealed a chronic dissection of the left ICA leading to left cerebral hypoperfusion. Patient 3 had asymmetric parkinsonism, alien limb, and cognitive impairment consistent with a diagnosis of corticobasal syndrome. His imaging, however, revealed atrophy and encephalomalacia within the anterior circulation watershed territories with chronic, severe stenosis of the left ICA suggestive of a chronic hypoperfused state. In this case series, we report 3 examples of hemicerebral atrophy secondary to chronic ipsilateral ICA vascular disease with diverse progressive clinical symptoms mimicking primary neurodegenerative conditions. This case series highlights the importance of considering chronic hypoperfusion and large-vessel severe stenosis or occlusion in patients with cognitive impairment and evidence of asymmetric brain atrophy. In addition to symptomatic treatment, the management of vascular risk factors including treatment with antiplatelet agents, statins, and revascularization procedures can be considered.

Dynamic autoregulation of cerebral blood flow measured non-invasively with fast diffuse correlation spectroscopy.

Cerebral autoregulation (CA) maintains cerebral blood flow (CBF) in the presence of systemic blood pressure changes. Brain injury can cause loss of CA and resulting dysregulation of CBF, and the degree of CA impairment is a functional indicator of cerebral tissue health. Here, we demonstrate a new approach to noninvasively estimate cerebral autoregulation in healthy adult volunteers. The approach employs pulsatile CBF measurements obtained using high-speed diffuse correlation spectroscopy (DCS). Rapid thigh-cuff deflation initiates a chain of responses that permits estimation of rates of dynamic autoregulation in the cerebral microvasculature. The regulation rate estimated with DCS in the microvasculature (median: 0.26 s-1, inter quartile range: 0.19 s-1) agrees well (R = 0.81, slope = 0.9) with regulation rates measured by transcranial Doppler ultrasound (TCD) in the proximal vasculature (median: 0.28 s-1, inter quartile range: 0.10 s-1). We also obtained an index of systemic autoregulation in concurrently measured scalp microvasculature. Systemic autoregulation begins later than cerebral autoregulation and exhibited a different rate (0.55 s-1, inter quartile range: 0.72 s-1). Our work demonstrates the potential of diffuse correlation spectroscopy for bedside monitoring of cerebral autoregulation in the microvasculature of patients with brain injury.

Noninvasive optical monitoring of critical closing pressure and arteriole compliance in human subjects.

The critical closing pressure ( CrCP) of the cerebral circulation depends on both tissue intracranial pressure and vasomotor tone. CrCP defines the arterial blood pressure ( ABP) at which cerebral blood flow approaches zero, and their difference ( ABP - CrCP) is an accurate estimate of cerebral perfusion pressure. Here we demonstrate a novel non-invasive technique for continuous monitoring of CrCP at the bedside. The methodology combines optical diffuse correlation spectroscopy (DCS) measurements of pulsatile cerebral blood flow in arterioles with concurrent ABP data during the cardiac cycle. Together, the two waveforms permit calculation of CrCP via the two-compartment Windkessel model for flow in the cerebral arterioles. Measurements of CrCP by optics (DCS) and transcranial Doppler ultrasound (TCD) were carried out in 18 healthy adults; they demonstrated good agreement (R = 0.66, slope = 1.14 ± 0.23) with means of 11.1 ± 5.0 and 13.0 ± 7.5 mmHg, respectively. Additionally, a potentially useful and rarely measured arteriole compliance parameter was derived from the phase difference between ABP and DCS arteriole blood flow waveforms. The measurements provide evidence that DCS signals originate predominantly from arteriole blood flow and are well suited for long-term continuous monitoring of CrCP and assessment of arteriole compliance in the clinic.

Non-Invasive Respiratory Impedance Enhances Cerebral Perfusion in Healthy Adults.

Optimization of cerebral blood flow (CBF) is the cornerstone of clinical management in a number of neurologic diseases, most notably ischemic stroke. Intrathoracic pressure influences cardiac output and has the potential to impact CBF. Here, we aim to quantify cerebral hemodynamic changes in response to increased respiratory impedance (RI) using a non-invasive respiratory device. We measured cerebral perfusion under varying levels of RI (6 cm H2O, 9 cm H2O, and 12 cm H2O) in 20 healthy volunteers. Simultaneous measurements of microvascular CBF and middle cerebral artery mean flow velocity (MFV), respectively, were performed with optical diffuse correlation spectroscopy and transcranial Doppler ultrasound. At a high level of RI, MFV increased by 6.4% compared to baseline (p = 0.004), but changes in cortical CBF were non-significant. In a multivariable linear regression model accounting for end-tidal CO2, RI was associated with increases in both MFV (coefficient: 0.49, p < 0.001) and cortical CBF (coefficient: 0.13, p < 0.001), although the magnitude of the effect was small. Manipulating intrathoracic pressure via non-invasive RI was well tolerated and produced a small but measurable increase in cerebral perfusion in healthy individuals. Future studies in acute ischemic stroke patients with impaired cerebral autoregulation are warranted in order to assess whether RI is feasible as a novel non-invasive therapy for stroke.

Fast blood flow monitoring in deep tissues with real-time software correlators.

We introduce, validate and demonstrate a new software correlator for high-speed measurement of blood flow in deep tissues based on diffuse correlation spectroscopy (DCS). The software correlator scheme employs standard PC-based data acquisition boards to measure temporal intensity autocorrelation functions continuously at 50 - 100 Hz, the fastest blood flow measurements reported with DCS to date. The data streams, obtained in vivo for typical source-detector separations of 2.5 cm, easily resolve pulsatile heart-beat fluctuations in blood flow which were previously considered to be noise. We employ the device to separate tissue blood flow from tissue absorption/scattering dynamics and thereby show that the origin of the pulsatile DCS signal is primarily flow, and we monitor cerebral autoregulation dynamics in healthy volunteers more accurately than with traditional instrumentation as a result of increased data acquisition rates. Finally, we characterize measurement signal-to-noise ratio and identify count rate and averaging parameters needed for optimal performance.

Altered myogenic vasoconstriction and regulation of whole kidney blood flow in the ASIC2 knockout mouse.

Previous studies from our laboratory have suggested that degenerin proteins contribute to myogenic constriction, a mechanism of blood flow regulation and protection against pressure-dependent organ injury, in renal vessels. The goal of the present study was to determine the importance of one family member, acid-sensing ion channel 2 (ASIC2), in myogenic constriction of renal interlobar arteries, myogenic regulation of whole kidney blood flow, renal injury, and blood pressure using ASIC2(+/+), ASIC2(+/-), and ASIC2(-/-) mice. Myogenic constriction in renal interlobar arteries was impaired in ASIC2(+/-) and ASIC2(-/-) mice, whereas constriction to KCl/phenylephrine was unchanged. Correction of whole kidney renal vascular resistance (RVR) during the first 5 s after a 10- to 20-mmHg step increase in perfusion pressure, a timeframe associated with myogenic-mediated correction of RVR, was slowed (4.2 ± 0.9, 0.3 ± 0.7, and 2.4 ± 0.3 resistance units/s in ASIC2(+/+), ASIC2(+/-), and ASIC2(-/-) mice). Although modest reductions in function were observed in ASIC2(-/-) mice, greater reductions were observed in ASIC2(+/-) mice, which may be explained by protein-protein interactions of ASIC2 with other degenerins. Isolated glomeruli from ASIC2(+/-) and ASIC2(-/-) mice had modest alterations in the expression of inflammation and injury markers (transforming growth factor-ß, mouse anti-target of antiproliferative antibody-1, and nephrin), whereas ASIC2(+/-) mice had an increase in the remodeling marker collagen type III. Consistent with a more severe loss of function, mean arterial pressure was increased in ASIC2(+/-) mice (131 ± 3 mmHg) but not in ASIC2(-/-) mice (122 ± 3 vs. 117 ± 2 mmHg in ASIC2(+/+) mice). These results suggest that ASIC2 contributes to transduction of the renal myogenic response and are consistent with the protective role of myogenic constriction against renal injury and hypertension.

Impaired myogenic constriction of the renal afferent arteriole in a mouse model of reduced ßENaC expression.

Previous studies demonstrate a role for ß epithelial Na(+) channel (ßENaC) protein as a mediator of myogenic constriction in renal interlobar arteries. However, the importance of ßENaC as a mediator of myogenic constriction in renal afferent arterioles, the primary site of development of renal vascular resistance, has not been determined. We colocalized ßENaC with smooth muscle α-actin in vascular smooth muscle cells in renal arterioles using immunofluorescence. To determine the importance of ßENaC in myogenic constriction in renal afferent arterioles, we used a mouse model of reduced ßENaC (ßENaC m/m) and examined pressure-induced constrictor responses in the isolated afferent arteriole-attached glomerulus preparation. We found that, in response to a step increase in perfusion pressure from 60 to 120 mmHg, the myogenic tone increased from 4.5 ± 3.7 to 27.3 ± 5.2% in +/+ mice. In contrast, myogenic tone failed to increase with the pressure step in m/m mice (3.9 ± 0.8 to 6.9 ± 1.4%). To determine the importance of ßENaC in myogenic renal blood flow (RBF) regulation, we examined the rate of change in renal vascular resistance following a step increase in perfusion pressure in volume-expanded animals. We found that, following a step increase in pressure, the rate of myogenic correction of RBF is inhibited by 75% in ßENaC m/m mice. These findings demonstrate that myogenic constriction in afferent arterioles is dependent on normal expression of ßENaC.

The effects of PRX-07034, a novel 5-HT6 antagonist, on cognitive flexibility and working memory in rats.

RATIONALE: Accumulating evidence indicates that schizophrenia and autism spectrum disorder patients are marked by cognitive deficits in working memory and strategy switching. There is accumulating evidence that 5-hydroxytryptamine (5-HT)(6) receptors may serve as a useful target to improve cognitive functioning. OBJECTIVES: In the present experiments, the novel 5-HT(6) antagonist, PRX-07034, was examined for its selectivity of the 5-HT(6) receptor, as well as its effect on delayed spontaneous alternation and strategy switching. METHODS: The binding affinity of PRX-07034 to the 5-HT(6) receptor, other 5-HT receptors, as well as other G-protein coupled receptors, ion channels, and transporters was evaluated. Cyclic AMP production was measured from transfected HEK-293 cells. In separate behavioral experiments, rats received different doses of PRX-07034 (0.1, 1, or 3 mg/kg, i.p.) 30 min prior to delayed spontaneous alternation testing or prior to the acquisition and switch phases in a place-response switch test. RESULTS: The results indicated that PRX-07034 is both a potent (Ki = 4-8 nM) and highly selective 5-HT(6) receptor antagonist (≥100-fold selectivity for the 5-HT(6) receptor compared to 68 other GPCRs, ion channels, and transporters, except D(3) (Ki = 71 nM) and 5-HT(1B) (Ki = 260 nM) receptors. For cyclic AMP quantification, PRX-07034 demonstrated antagonist activity (IC(50) = 19 nM) without an effect on basal levels and did not show any agonist activity up to 10 µM. PRX-07034 at 1 and 3 mg/kg (but not 0.1 mg/kg) significantly enhanced delayed spontaneous alternation. The drug at 1 and 3 mg/kg also enhanced switching between a place and response strategy, but did not affect initial learning of either a place or response discrimination. CONCLUSIONS: These findings demonstrate that PRX-07034 is a selective 5-HT(6) receptor antagonist that may represent a novel treatment for enhancing working memory and cognitive flexibility.

PRX-00023, a selective serotonin 1A receptor agonist, reduces ultrasonic vocalizations in infant rats bred for high infantile anxiety.

To address the development of early anxiety disorders across the lifespan, the High USV line of rats was bred based on rates of infant ultrasonic vocalization in the 40-50 kHz range of predominant frequencies (USV) to maternal separation at postnatal day (P) 10. In this study, rates of USV in High line infants (pups: Postnatal Day 11+/-1) were compared to those of randomly-bred controls in response to EPIX compound PRX-00023, a unique serotonin (5-HT) agonist, acting exclusively at the 5-HT1A receptor, or buspirone, a nonspecific 5HT1A agonist. After testing, pups were examined for sedation and other drug-related effects. The results indicated that all doses of buspirone reduced USV rates in isolation, consistent with other reports. PRX-00023 significantly reduced USV rates at the lowest doses (0.01-0.05 mg/kg). None of the PRX-00023 doses produced sedation, whereas all but the lowest dose of buspirone (0.1 mg/kg) produced sedation effects. The results suggest that this compound alleviates infantile anxiety-like behavior with great specificity in rats bred for high anxiety/depressive phenotypes by selectively targeting 5-HT1A receptors, possibly by both pre- and post-synaptic mechanisms.

Pressure-induced constriction is inhibited in a mouse model of reduced betaENaC.

Recent studies suggest certain epithelial Na(+) channel (ENaC) proteins may be components of mechanosensitive ion channel complexes in vascular smooth muscle cells that contribute to pressure-induced constriction in middle cerebral arteries (MCA). However, the role of a specific ENaC protein, betaENaC, in pressure-induced constriction of MCAs has not been determined. The goal of this study was to determine whether pressure-induced constriction in the MCA is altered in a mouse model with reduced levels of betaENaC. Using quantitative immunofluorescence, we found whole cell betaENaC labeling in cerebral vascular smooth muscle cells (VSMCs) was suppressed 46% in betaENaC homozygous mutant (m/m) mice compared with wild-type littermates (+/+). MCAs from betaENaC +/+ and m/m mice were isolated and placed in a vessel chamber for myographic analysis. Arteries from betaENaC+/+ mice constricted to stepwise increases in perfusion pressure and developed maximal tone of 10 +/- 2% at 90 mmHg (n = 5). In contrast, MCAs from betaENaC m/m mice developed significantly less tone (4 +/- 1% at 90 mmHg, n = 5). Vasoconstrictor responses to KCl (4-80 mM) were identical between genotypes and responses to phenylephrine (10(-7)-10(-4) M) were marginally altered, suggesting that reduced levels of VSMC betaENaC specifically inhibit pressure-induced constriction. Our findings indicate betaENaC is required for normal pressure-induced constriction in the MCA and provide further support for the hypothesis that betaENaC proteins are components of a mechanosensor in VSMCs.

Impaired pressure-induced constriction in mouse middle cerebral arteries of ASIC2 knockout mice.

Recent studies from our laboratory demonstrated the importance of mechanosensitive epithelial Na(+) channel (ENaC) proteins in pressure-induced constriction in renal and cerebral arteries. ENaC proteins are closely related to acid-sensing ion channel 2 (ASIC2), a protein known to be required for normal mechanotransduction in certain sensory neurons. However, the role of the ASIC2 protein in pressure-induced constriction has never been addressed. The goal of the current study was to investigate the role of ASIC2 proteins in pressure-induced, or myogenic, constriction in the mouse middle cerebral arteries (MCAs) from ASIC2 wild-type (+/+), heterozygous (+/-), and null (-/-) mice. Constrictor responses to KCl (20-80 mM) and phenylephrine (10(-7)-10(-4) M) were not different among groups. However, vasoconstrictor responses to increases in intraluminal pressure (15-90 mmHg) were impaired in MCAs from ASIC2(-/-) and (+/-) mice. At 60 and 90 mmHg, MCAs from ASIC2(+/+) mice generated 13.7 +/- 2.1% and 15.8 +/- 2.0% tone and ASIC2(-/-) mice generated 7.4 +/- 2.8% and 12.5 +/- 2.4% tone, respectively. Surprisingly, MCAs from ASIC2(+/-) mice generated 1.2 +/- 2.2% and 3.9 +/- 1.8% tone at 60 and 90 mmHg. The reason underlying the total loss of myogenic tone in the ASIC2(+/-) is not clear, although the loss of mechanosensitive beta- and gamma-ENaC proteins may be a contributing factor. These results demonstrate that normal ASIC2 expression is required for normal pressure-induced constriction in the MCA. Furthermore, ASIC2 may be involved in establishing the basal level of myogenic tone.

20-Hydroxyeicosatetraenoic acid (20-HETE) stimulates migration of vascular smooth muscle cells.

AIM: We tested the hypothesis that 20-HETE production contributes to platelet derived growth factor (PDGF)-BB stimulated migration of VSMC in a cell culture model. METHODS: Studies were performed with A10 cells which are a rat vascular smooth muscle derived cell line. Migration was determined using a Boyden chamber chemotactic assay. RESULTS: Pre-treatment of cells with two doses of 20-HETE (100 and 500 nM) significantly increased PDGF-BB stimulated VSMC migration by 34-58% of control; whereas, prior incubation of cells with inhibitors of 20-HETE production, 17-ODYA (1-25 M) or HET0016 (100 nM), significantly decreased PDGF-BB stimulated migration by 40-90%. 20-HETE mediated increase in PDGF-BB migration was completely prevented by the 20-HETE antagonist, WIT-002. In order to determine what second messenger pathways are involved in the 20-HETE mediated stimulation of VSM migration, experiments were performed with specific inhibitors of tyrosine kinase (tyrphostin 25, 10 microM), mitogen-activated extracellular signal-regulated kinase (MEK, PD98059, 20 microM and U0126, 10 microM), protein kinase C (Myr-PKC, 50 microM), and phosphoinositide 3-kinases (PI3Ks) (wortmannin, 50 nM). Blockade of MEK and PI3K all abolished the increase in 20-HETE mediated migration. CONCLUSION: 20-HETE stimulates PDGF-mediated VSM migration acting through pathways that involve MEK and PI3K.

ENaC proteins contribute to VSMC migration.

Vascular smooth muscle cell (VSMC) migration plays a key role in tissue repair after arterial wall injury. VSMC migration requires integration of chemical and mechanical signaling mechanisms. Recently, we showed that epithelial Na(+) channel (ENaC) proteins are expressed in VSMCs and that ENaC inhibition abolishes pressure-induced constriction in isolated artery segments. However, whether ENaC proteins play a role in VSMC migration is unknown. The goal of this study was to determine whether ENaC molecules are required for VSMC migration. Using RT-PCR, immunoblotting, and immunolabeling, we detected expression of alpha-, beta-, and gammaENaC transcripts and proteins in cultured VSMCs (SV40-LT and A10 cells). Of the three proteins, betaENaC was the most readily detected in both cell lines by immunolocalization and Western blotting. Inhibition of ENaC activity with 1 microM benzamil blunted VSMC migration associated with wound healing (40.3% at 8 h and 26.2% at 24 h) and in response to the chemotactic stimulant platelet-derived growth factor-BB (38.1%). Furthermore, silencing ENaC gene expression with small interfering RNA blunted VSMC migration. These data indicate that expression of ENaC proteins is required for normal VSMC migration and suggest a potential new role for ENaC proteins in vascular tissue repair.