8. Age-related decrease activity of neurovacular coupling: a TCD study
M. Zaletel, B. Zvan and J. Pretnar Oblak
Neurology, University Medical Centre Ljubljana, Ljubljana, Slovenia
Background: A noninvasive assessment of neurovascular coupling, during normal ageing, would be of great importance. For this purpose, we simultaneously recorded visual evoked potentials (VEP) and visually evoked cerebral blood flow velocity responses (VEFR).
Methods: The records were made from a group of healthy younger subjects (37.5±9.4 years) as well as healthy older ones (69.5±5.9 years). The stimulus was a black-and-white checkerboard with visual contrasts of 1%, 10% and 100%. The VEFR were measured in the posterior cerebral artery using transcranial Doppler (TCD), and the VEP were recoded from occipital leads.
Results: To test the relationship between the VEFR, the VEP and the visual contrast, a linear regression analysis was performed which showed a significant positive association between the VEP in the VEFR (r = 0.66, P<0.01) of the younger and older subjects (r = 0.74, P<0.01). The regression coefficient of the younger subjects was significantly higher (b = 0.54) than that of the older ones (b = 0.40) (P<0.01).
Discussion: We found a linear relationship between VEP and VEFR in younger as well as in older subjects. Our major finding was that the regression coefficient was significantly lower in older subjects as compared to younger ones. This finding suggested a diminished function of neurovascular coupling in older subjects. Although the studies have explored the relationship between evoked potentials and vascular responses detected by fMRI and near infrared spectroscopy (NIRS), none of them has studied the effect of ageing on this relationship. An indirect study with TCD using control system analysis has suggested that neurovascular coupling mechanism is unaffected by moderate ageing as estimated by Doppler parameters. In our study as well as in the other TCD studies that have also reported diminished responses in older subjects, however, the age of the subjects was importantly greater.
Conclusions: We concluded that a simultaneous recording of VEFR and VEP at graded visual contrasts indicates diminished neurovascular coupling in older subjects.
231. Effect of different anesthetics on neurovascular coupling
H. Radhakrishnan, K. Thakur, W. Wu, S. Ruvinskaya, J. Marota, D. Boas and M.A. Franceschini
Radiology/Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts, USA
Objective: In response to somatosensory stimulation, thalamic afferent activity in layer IV generates the first somatosensory evoked potential (SEP) component P1. This is followed by secondary activity in superficial layers (N1), and later by cortico-cortical interactions (P2 and N2).
The hemodynamic response following stimulation historically has been attributed to the initial neuronal activity in layer IV (P1). In (Franceschini 2008) we found N1 and P2 are better predictors of hemodynamic response than P1. Using alpha-chloralose as the anesthetic and parametric stimuli, we could not detect differences between N1 and P2. Here, modulating the electrical and hemodynamic responses with different anesthetics we could uncouple N1 and P2 and determine which SEP components more strongly correlate with the hemodynamic response.
Methods: We divided 40 male Harlan Sprague-Dawley rats into 6 groups, with different maintaining anesthetics: alpha-chloralose, isoflurane, pentobarbital, ketamine-xylazine, fentanyl-droperidol, and propofol. Simultaneous EEG (4 scalp electrodes) and Diffuse Optical Imaging (DOI) measurements (32 channel CW system) were obtained during event-related electrical forepaw stimulation. Electrical stimuli comprised 0.2 ms pulses with current <0.2 mA (motor threshold), delivered at 3 Hz. In each rat we performed 10 twelve-minute runs, presenting stimuli with durations of 1, 3, 5, 7, 9, 11, and 13 s with average ISI of 12 s. Following the stimulation runs, we measured baseline blood flow (BF) and vascular reactivity to a hypercapnia challenge using Diffuse Correlation Spectroscopy (DCS) to evaluate differences between anesthetics.
The DOI and EEG data were analyzed as described in (Franceschini 2008). BF velocity was obtained as described in (Cheung 2001).
Results: SEP and hemodynamic responses were linear with stimulus duration, in agreement with (Ances 2000; Franceschini 2008; Martindale 2005; Ureshi 2004). For the GABAergic anesthetics used (alpha-chloralose, isoflurane, pentobarbital and propofol) we found the P2 SEP component could predict the hemodynamic responses statistically significantly better than P1 or N1. Rats anesthetized with Ketamine-Xylazine and Fentanyl showed pronounced N2 SEP responses; if this component was included as a linear regressor for all anesthetics, the P2-N2 hemodynamic prediction had a significantly larger R2 and F-score than any other combination of SEP components.
Conclusion: Using these six anesthetics we could uncouple the N1 and P2 contributions to the hemodynamic response and determined that P2 and N2 cortico-cortical interactions drive hemodynamic responses, with the N2 negative SEP component driving vasoconstriction to counteract the vasodilatory role of P2. The different anesthetics exhibited significant differences in baseline BF, but BF always increased with hypercapnia. Including baseline BF as a regressor did not improve hemodynamic predictions, indicating that baseline BF minimally affects neurovascular coupling. Finally, neurovascular coupling appears unaltered by the type of anesthesia.
239. Blood-brain barrier abnormalities in patients with vascular cognitive impairment quantified by dynamic contrast-enhanced MRI
G. Rosenberg, S. Taheri, R. Sood, C. Gasparovic, J. Prestopnik, E. Edmonds, C. Ford and J. Adair
Neurology, University of New Mexico Health Sciences Center, Albuquerque, New Mexico, USA
Background and aims: The incidence of vascular cognitive impairment (VCI) is increasing worldwide due to the aging of the populations. Progress in diagnosis and treatment of VCI has been impeded because of the heterogeneity of the illness and the overlap particularly in the early stages with other causes of impaired cognition. Several biomarkers have been used to identify pathological abnormalities in patient with VCI: proton magnetic resonance spectroscopy (1H-MRS) showed reduced levels of N-acetylaspartate (NAA) in the white matter, suggesting ischemic changes, and elevated levels of albumin are found in the cerebrospinal fluid (CSF), suggesting BBB disruption.
Purpose: White matter damage is a prominent feature in small vessel form of VCI. Disruption of the blood-brain barrier (BBB) is proposed as a cause of the white matter damage. We used quantitative contrast-enhanced MRI to determine the role of the blood-brain barrier (BBB) in the white matter injury. We hypothesized that BBB abnormalities would be associated with reduced NAA and increased CSF albumin index.
Methods: To test the hypothesis we used dynamic contrast-enhanced MRI (DCEMRI) with Gadolinium-DTPA (Gd-DTPA) to quantify BBB permeability, 1H-MRS to measure NAA, and lumbar puncture to obtain CSF to calculate the albumin index. Forty patients suspected to have VCI were recruited into the study along with 20 age-matched controls. A consensus diagnosis was made based on clinical findings, neuropsychological test results, and MRI.
Results: We recruited 40 patients with leukoaraiosis and symptoms suggstive of VCI. After evaluation 27 were diagnosed as VCI-no dementia (VCI-ND) (one had VCI-dementia), and 10 had leukoaraiosis with minimal findings (LEUK). Three patients could not be classified. From the controls, we established normal values for BBB permeabilty in white matter as 3 × 10−4 ml/gm/min. We found increased BBB permeability over controls in 26 of the VCI patients (P<0.05). Total permeability and intensity in localized regions of increased permeability were calculated and used for cluster analysis (R statistical package), which separated the VCI patients into three groups: low, mid, and high permeability. Those in the lower group were mainly LEUK, while the higher two groups were VCI-ND patients. Those in the mid and highest permeability groups had significantly lower NAA than the lowest BBB group (P<0.05). Albumin index was highest in the high permeability group (P<0.05). Patients (n = 15) classified clinically as small vessel disease were more likely to be in the mid and high permeability groups.
Conclusions: Our results provide quantitative evidence using DCEMRI of an abnormality in BBB permeability in patients with VCI. Our results suggest that BBB permeability is an additional biomarker, complementing reduced white matter NAA and elevated CSF albumin index. One explanation for the increased permeability is that on-going inflammation causes secondary myelin damage. Another is that secondary damage occurs during tissue repair or angiogenesis. Long-term followup will identify a sub group of patients with progressive disease and abnormalities of the BBB suggestive of inflammation. Determination of the natural history of BBB abnormalities is now feasible and could aid clinical trials.
273. Relationship between cerebral oxygen exchange (COE) and cerebral blood volume (CBV) in chopsticks operation
N. Oka1, K. Yoshino1, S. Ishizaki2 and T. Kato3
1Graduate School of Media and Governance; 2Department of Media and Governance, Keio University, Kanagawa; 3Department of Brain Environmental Research, KATOBRAIN Co., Ltd., Tokyo, Japan
Background and aims: In rehabilitation medical treatment, evaluation by the brain activity has been widely accepted. Our previous research using near-infrared light imaging confirmed tendencies that an increase/decrease in COE (cerebral oxygen exchange) is related to a degree of task difficulty and performance improvement in sensory-motor cortical areas (BA6,4,3,1,2). In the prior research, it is known that the hand movements stimulate the sensory-motor cortical areas in the same side. Therefore, the relationship between COE and CBV (cerebral blood volume) in sensory-motor cortical areas by the same side movements was examined in this research.
Methods: Subjects were five normal adults (three males and two females) who use chopsticks by their right hands. The performance was evaluated by the number of small cube moved using chopsticks to a plate (10 cm away) in one trial (15 s). Tasks were right hand condition and left condition. One condition was composed of 20 trials. The measurement regions was determined to sensory motor cortical areas based on 10 to 20 international EEG methods. The analysis were performed in significant regions where COE changes (O-D values) were found between the tasks (t-test: P<0.05). The relationships between COE and CBV were examined by the average using all trials.
Purpose: The purpose of this study was to examine the relationships between COE (oxyhemoglobin minus deoxyhemoglobin: O–D) and CBV (oxyhemoglobin plus deoxyhemoglobin: O–D) in the sensory motor areas on the same side as the hand.
Results: In right hand condition, COE did not increase (0<O–D) but CBV increased (0<O+D) in the right sensory-motor cortical areas. On the other hand, in left hand condition, COE increased (O-D <0) and CBV decreased (O+D <0) (Figure).
Change of sensory-motor area in right hemisphere.
Conclusions: In this study, it was showed that CBV did not increase even if COE increased. This results suggested it is necessary to reconsider direct coupling regarding CBV increase as cortical activation.
321. Human brain functional analysis through proper orthogonal decomposition during single word trial
K. Oyama1, T. Sugiura1 and T. Kato2
1Department of Mechanical Engineering, Keio University, Yokohama; 2KATOBRAIN Co., Ltd., Tokyo, Japan
Objectives: The aim of this study is to make an indicator which reflects oxygen consumption in a capillary synchronized with neural activity and make a comparison of temporal changes of the index with those of hematocrit through analyses of hemoglobin changes measured on human scalp with near infrared light with application of a multivariate statistical technique.
Methods: We regarded time courses of oxygenated hemoglobin and deoxygenated hemoglobin obtained through single trial of a language task as time series data of coupled oscillators in mechanical systems. We divided the time courses into stimulus period and rest period and then applied proper orthogonal decomposition (POD), which can extract principal components from time series data, to each time period. Based on the assumption that increase in deoxygenated hemoglobin during stimulus reflects oxygen consumption in a capillary and increase in oxygenated hemoglobin after stimulus reflects oxygen supply, we obtained characteristic patterns of oxygen consumption and oxygen supply from stimulus time period and rest time period, respectively. Then we computed temporal changes in magnitude of two kinds of patterns based on the similarity to the representative patterns.
Results: Temporal changes of the index of cerebral oxygen exchange expressed by a ratio of the magnitude of oxygen consumption to that of oxygen supply are shown in Figure. The index reaches its maximum a few seconds after stimulus onset, showing deoxygenation in a capillary in early phase of neural activity and preceding increase in hematocrit, and gradually decreases the following seconds.
Index of cerebral oxygen exchange.
Conclusions: We obtained an index of cerebral oxygen exchange synchronized with neural activity through application of POD to the time courses of oxygenated hemoglobin and deoxygenated hemoglobin. A comparison of changes of the index with those of hematocrit revealed a temporal difference between the two.
624. Characteristics of adult patients with moyamoya disease in china and significant increase of cerebral blood flow post encephalo-duro-arterio-synangiosis (EDAS)
L. Duan, Z. Li, W. Yang, P. Xian, W. Shi, J. Feng, R. Zong, F. Zhao and Z. Zhang
Department of Neurosurgery, Affiliated 307 Hospital, Academy of Military Medical Sciences, Beijing, China
Objective: To describe the clinical features and the efficacy of encephalo-duro-arterio-synangiosis (EDAS) in adult patients with Moyamoya disease (MMD) in China.
Methods: Data from 312 patients aged ⩾18 with DSA/MRA confirmed MMD in our hospital between December 2002 and September 2008 were retrospectively reviewed. All patients underwent EDAS and were followed up for at least 3 Month (median 26-month). 83 cases were accepted DSA examination and 171 cases were repeated PET after operation 3–6 months.
Results: Majority of our adult patients presented with cerebral ischemia (173 case with infarction 55.4%, 76 case with TIA 24.4%) with the rest of 63 patients with cerebral hemorrhage (20.2%). After EDAS, neurological signs and symptoms were significantly improved in 219 out of 249 with ischemia. There was no rebleeding case in the haemorrhage group. PET examinations showed that post-operative cerebral blood flow was increased clearly on 138 of the 171 patients (80.7%). Post-operative DSA examinations revealed a revascularization on 66 of the 83 hemispheres (79.5%). Logistic regression analyze show the females and younger have better revascularization.
Conclusions: Largest case collection in our hospital so far demonstrated that adult patients in China with moyamoya disease present with different clinical features compared with other countries. There are significant higher incidence of cerebral infarction (55.4% versus 14.9% in Japan). EDAS is also an effective surgical treatment in adult MMD patients in terms of clinical improvement and radiological evidence by DSA for revascularization and PET for increased brain blood flow.
632. Ca2+ changes in astrocytes and neurons of mice primary somatosensory cortex in relation to activity-dependent rises in cerebral blood flow
B.L. Lind and M. Lauritzen
Department of Neuroscience and Pharmacology, University of Copenhagen, Copenhagen N, Denmark
Activity-dependent rises in cerebral blood flow are robust markers of neuronal activity in functional imaging studies, but it is still incompletely understood how the vascular signals are produced. Specifically, it is unknown to what extent vascular mediators from astrocytes or neurons contribute to the local vasodilatation, but it is believed that local cerebrovasodilatation is closely linked to Ca2+ rises in neurons and or astrocytes. The aim in this study was to investigate Ca2+ dynamics in mouse sensory cortex in relation to local evoked vasodilatation.
Mouse sensory barrel cortex was activated by stimulation of the contralateral infraorbital nerve (IO). The 8 weeks old male mice were anaesthetized with ketamine and xylazine while prepared surgically, and α-chloralose during the experiment. End-inspiratory CO2 and blood pressure were monitored continuously. CBF responses were monitored through a cranial window using Laser-Doppler flowmetry (n = 4), and Ca2+ imaging was carried out in vivo using a 2- photon microscope (n = 8) (Leica SP-5). The Laser-Doppler probe was placed just above the craniotomy, and microelectrodes were inserted into layers 2/3 in the right whisker cortex. In 2-photon experiments we used 2 types of fluorescent dyes: Rhod2, which was surface loaded and entered astrocytes, and Oregon Green Bapta which was bulk-loaded using extracellular microinjections in the cerebral cortex. The cranial windows were covered with agar and a cover-glass was positioned before imaging. IO stimulation was done at stimulation intensity of 1.5 mA, in trains of 5–45 s at 1 Hz.
Stimulation produced clear local CBF responses concomitantly with a local field potential (LFP). IO stimulation also increased intracellular Ca2+ levels in both neurons and astrocytes. The Ca2+ response consisted of a low-frequency positive oscillation that lasted for as long as the stimulation, and of shorter peaks of 0.1 to 0.2 s following every stimulation, superimposed on the low-frequency signal. Astrocytes and neurons appeared to respond within the same narrow time frame. Ca2+ responses comprised of a rapid increase followed by a slower downslope, and based on the current data it was not possible to define a difference in Ca2+ dynamics of cell bodies of astrocytes and neurons. In conclusion, activity-dependent rises in CBF were accompanied by rises in both astrocytic and neuronal Ca2+ during activation of rat cerebral cortex in response to somatosensory stimulation. This may point to both astrocytic and neuronal sources of local cerebrovasodilators in response to activation.
772. Neuronal PGE2 is involved in cerebral blood flow response to somatosensory stimulation in chloralose anesthetized rats
A. Kocharyan1, B. Stefanovic2,3 and A.C. Silva1
1Cerebral Microcirculation Unit, Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA; 2Imaging Research, Sunnybrook Health Sciences Centre; 3Medical Biophysics, University of Toronto, Toronto, ON, Canada
Objectives: Cyclooxygenase (COX-1 and COX-2) products are important factors in the fine physiological processes of neurovascular coupling (Wang H. et al, 2005; Stefanovic B. et al, 2006). However, the specific roles of each COX isoform in eliciting the local vascular response to neural activity remains poorly understood and conflicting data exist (Niwa K et al, 2000; Takano et al, 2006).
In the present study we investigated the influence of the selective COX-1 and COX-2 inhibitors and prostaglandin E2 (PGE2) EP1 subtype receptor antagonist on the cerebral blood flow (CBF) response and the microcirculatory volume in the superficial cortical layers in a rodent model of somatosensory stimulation.
Methods: Laser-Doppler flow and somatosensory-evoked potentials (SEPs) elicited in response to electrical stimulation of the contralateral forepaw (2 mA, 333 μs, 3 Hz) were recorded in alpha-chloralose-anesthetized rats (n = 5 to 8 per group) with implanted cranial windows during local superfusion (5 μL/mins) of SC-560 (5 × 10−4M), NS-398 (6 × 10−4M), SC-19220 (10−4M) or respective vehicle. Arterial blood pressure, respiration patterns, oxygen saturation, arterial blood gases, arterial pH and rectal temperature were maintained during the experiments.
To estimate vessel volume we used two-photon imaging of intravenously administered rhodamine-labeled dextran (70,000 MW) with 805 nm excitation through a cranial window. High-resolution images at 5 μm axial steps before and during forepaw stimulation from 3 different levels (pial vessels, layer I and layer II-III) were 3D reconstructed (Metamorph) and the areas covered by the microvasculature were compared in different conditions.
For immunohistochemistry 30 μm thick cryosections were incubated first in either anti-COX-1 or anti-COX-2 antibodies (Cayman), stained with DAB or fluorescent secondary antibodies then in anti-c-Fos (Calbiochem) or anti-rat brain pyramidal cells or anti-s100β (SWANT) or Iba1 (Wako) antibodies and stained with DAB-Ni or respective fluorescent secondary antibodies.
Results: We found that cortical superfusion with the specific COX-2 inhibitor NS-398 and EP1 antagonist SC-19220 caused a significant attenuation of the CBF response to somatosensory stimulation to 61.5 and 74.2%, respectively, (P<0.05) of the response obtained during superfusion with vehicle. In contrast, the preferential COX-1 inhibitor SC-560 did not change the CBF response (P>0.05). Furthermore, local superfusion of the responsive area with PGE2 (10−5M), one of the vasoactive products of cyclooxygenase, resulted in recovery of the NS-398 attenuated CBF response back to 84.6% (P<0.05) of the original response. Double-immunohistochemistry shows that numerous cortical COX-2-positive cells are expressing c-Fos after somatosensory stimulation. All the investigated COX-2 cells also are positive for pyramidal cell marker. In contrast, COX-1 cells are co-localized with microglial cell marker Iba1 and do not co-localize with the astrocytic marker s100β.
We also found an increase in the rhodamine covered area in 3D reconstructed two-photon images by 7.4, 52.2 and 24.6% respectively in the level of pial vessels, layer I and layer II–III in response to forepaw stimulation. Superfusion with NS-398 significantly attenuated this vasodilatation response of pial vessels and in layer II–III.
Conclusion: Products of cyclooxygenase are modulators of the neurovascular coupling and production of the neuron-originated prostaglandins such as PGE2 is necessary for the normal cerebrovascular reactivity to forepaw stimulation.
906. BKCa and Kir channel phosphorylation contributes to the impairment of neurovascular coupling in diabetes mellitus
H.-L. Xu, F. Vetri, L.-Z. Mao and D.A. Pelligrino
Neuroanesthesia Research Laboratory, Department of Anesthesiology, University of Illinois-Chicago, Chicago, Illinois, USA
Introduction: Protein kinase (PKC) activation has been linked to diabetes mellitus-associated cerebral vasodilatory dysfunctions. However, its effect on cerebral neurovascular coupling in diabetes is virtually unexplored. The in vivo properties of large conductance Ca2+-operated K+ (BKCa) and inward rectifier K+ (Kir) channels that participate in the process of neurovascular coupling have been reported to be impaired in the diabetic cerebrovasculature.1 Since those channels have been reported to play a role in neurovascular coupling,2 the possibility exists of an aberrant neurovascular coupling in diabetes. In this study, we tested the hypothesis that diabetes mellitus leads to the impairment of neurovascular coupling, due to PKC activation.
Methods: The in vivo reactivity of pial arterioles was evaluated in age-matched rats (streptozotocin-induced diabetics [8 weeks] and non-diabetic controls) using a closed cranial window and intravital microscopy. Neurovascular coupling was assessed via the measurement of diameter changes in pial arterioles, localized to the hindlimb region of the somatosensory cortex, during sciatic nerve stimulation (SNS).
Results: Compared to non-diabetic controls, diabetic rats showed a significant attenuation in the pial arteriolar relaxation response to SNS, which was consistently accompanied by a substantially decreased responses to suffusion of the BKCa channel opener, NS1619, and the Kir agonist, KCl. Topical applications of the PKC inhibitor, Calphostin C, which did not alter pial arteriolar reactivity in non-diabetic rats, largely restored these diabetes-impaired pial arteriolar responses, suggesting the involvement of PKC activation in BKCa and Kir channel dysfunction and the disruption of neurovascular coupling during diabetes. These findings were further supported by the inhibitory effect of the acute PKC activation on all the aforementioned pial arteriolar responses in non-diabetic rats. That is, pial arteriolar responses to SNS, NS1619 and KCl were revealed to be markedly decreased by topical application of PKC agonist phorbol 12,13-dibutyrate (PdBu). The fact that PdBu suffusion did not affect the pial arteriolar responses to adenosine, SNAP, and hypercapnia ruled out the possibility of non-specific effects of PdBu application.
Conclusions: Collectively, these results suggest that PKC-mediated phosphorylation may be linked to diminished BKCa and Kir channel function. One manifestation of this may be an impairment of neurovascular coupling during diabetes mellitus.
This work was supported by Juvenile Diabetes Research Foundation (JDRF 3-2008-462) to F. Vetri, NIH grant (HL 088259) to Dale A. Pelligrino, and American Heart Association grant (AHA 0635337N) to H.L. Xu.
929. Diversity of neural-hemodynamic relationships depending on patterns of cortical processing during bilateral somatosensory activation in rats
M. Nemoto, Y. Hoshi and Y. Iguchi
Integrated Neuroscience, Tokyo Institute of Psychiatry, Tokyo, Japan
Objectives: Neural-hemodynamic relationships may vary depending on patterns of cortical processing. The purpose of this study is to investigate how cortical hemodynamics represents neural activity in functional paradigms that drive different patterns of cortical processing, and which facets of neural activity are reflected in hemodynamic changes.
Methods: Ten adult male Sprague-Dawley rats were studied. We introduced functional paradigms consisting of unilateral and bilateral electrical stimulation to rat hindpaws under alpha-chloralose anesthesia, and simultaneously measured broad-band extracellular field potentials and optical intrinsic signals at 586 nm wavelengths, which are associated with changes in CBV, in the somatosensory cortices. We analyzed the field potential signals through frequency-band filtering (local field potential, LFP<100 Hz; multi-unit activity, MUA>300 Hz, using finite impulse response filters) to estimate synaptic and population spiking activities, and examined LFP-MUA-hemodynamic relationships. In the bilateral stimulation paradigms, we modulated neural interactions by varying time-lag between contra- and ipsilateral stimuli. Furthermore, to assess dependence of their relationships on the temporal structure within the LFPs, we extracted low-frequency (<25 Hz) and high-frequency (>30 Hz) components from the LFPs. We evaluated differences between the low- and high-frequency components of LFPs in correlations with MUA and hemodynamic responses.
Results: While applying unilateral stimulation, we observed both neural and optical signals in the bilateral somatosensory cortices. Ipsilateral optical responses indicating CBV-increase had peak magnitudes of ∼30% and mediocaudal shifts relative to contralateral responses. Correlation analyses revealed different scale factors between the contra- and ipsilateral responses in LFP-MUA and LFP-CBV relationships. While applying bilateral stimulation with varying time-lags, hemodynamic responses were strongly suppressed at 40 and 60 ms time-lags. This hemodynamic suppression quantitatively reflected suppressed LFP responses to contralateral testing stimulation rather than linear summation, with slowly-fluctuating LFP responses to ipsilateral conditioning stimulation. Consequently, CBV-related responses more linearly correlated with MUA than with LFPs in overall responses to bilateral stimulation. However, when extracting high-frequency components (>30 Hz) from LFPs, we found a similar scale factor between the contra- and ipsilateral responses in the LFP-MUA and LFP-CBV relationships, resulting in a significant linear relationship among high-frequency LFPs, MUA and cortical hemodynamics even in overall responses to bilateral stimulation.
Conclusions: There existed diversity of LFP-MUA-hemodynamic relationships depending on patterns of cortical processing during bilateral somatosensory activation. Cortical hemodynamics was not equally susceptible to overall LFP signals but particularly to a certain components of LFP signals. Furthermore, application of broad-band gamma LFPs may restore linear relationships between LFPs and cortical hemodynamics in such complex functional paradigms that drive different cortical processing.
952. Decreased number and function of endothelial progenitor cells in Alzheimer's disease
K. Chu, S.-T. Lee, K.-H. Jung, J. Sunwoo, J.-J. Bahn, S. Lee, M. Kim and J.-K. Roh
Department of Neurology, Seoul National University Hospital, Seoul, South Korea
Objects: Neurovascular senescence contributes to the progression of Alzheimer's disease (AD). Because circulating endothelial progenitor cells (EPCs) provide a cellular reservoir for the endothelial replacement, we investigated whether AD patients have dysfunctional EPCs to study the involvement of EPCs in AD pathogenesis.
Methods: We enrolled consecutive newly-diagnosed AD (n = 55), non-AD neurodegenerative diseases (n = 37), and non-demented risk factor control subjects (RF control, n = 55 and 37) after matching for age, sex, and Framingham risk score. EPC colony forming units (CFU-EPC) were cultured in peripheral blood samples and used for various ex vivo assays.
Results: CFU-EPC was significantly lower in the AD patients than in ithe RF controls. In the AD patients, a lower CFU-EPC was independently associated with either a lower mini mental state examination or a higher clinical dementia rating scale score, indicating a greater reduction in CFU-EPC in advanced AD. Patients with non-AD neurodegenerative diseases showed similar CFU-EPC levels compared to their RF controls. EPCs from AD patients showed reduced chemotaxis, increased senescence, reduced paracrine angiogenic activity, and altered gene expression pattern compared to EPCs from RF controls. Ex vivo addition of Aβ1–42 to the EPC culture reduced EPC counts and endothelial nitric oxide synthase/Akt phosphorylations.
Conclusion: Our results showed that AD patients have dysfunctional, suggesting that an abnormal capacity to regenerate endothelium is associated with AD.
975. Nicotine exposure inhibits 17β-estradiol-mediated protection of the hippocampal CA1 region against cerebral ischemia in female rats
A. Raval, A. Bhatt, I. Saul and M. Perez-Pinzon
Department of Neurology, University of Miami, Miami, Florida, USA
Objective: Women are naturally protected against cerebral ischemia owing to the effects of circulating estrogens.1,2 Nicotine addiction in women modulates estrogen metabolism, reduces circulating estrogen levels and increases the risk/damage of ischemic stroke. The exact mechanism by which nicotine abrogates the protective effects of endogenous estrogen leading to increased incidence of ischemia in females is not known. Here, using a rat model of global cerebral ischemia, our goals are:
to determine whether chronic nicotine treatment abrogates beneficial effects of estrogen on hippocampal neurons subjected to ischemia, and
to determine whether nicotine exposure antagonizes estrogen signaling by reducing the number of estrogen receptor(s).
Methods: Normally cycling or 7 days post-ovariectomized rats were injected with nicotine/saline daily (1 mg/kg BW in saline; i.p.) for 15 days. To investigate the efficacy of estrogen in nicotine-exposed rats, ovariectomized and nicotine-treated rats were injected with a bolus of 17β-estradiol (5 μg/Kg in oil; i.p.). Following last treatment rats were divided in to two groups. Rats of the first group were exposed to cerebral ischemia produced by 10 min of bilateral carotid occlusion and systemic hypotension (50 mm Hg). Seven days after ischemia rat brains were fixed for histopathological assessment. Hippocampal sections at the level of 3.8 mm posterior to bregma were examined for normal neurons. For Western blot analysis, hippocampi were collected from second group of treated rats. The Western blots were quantified by densitometric analysis. Results are expressed as mean±SEM. Statistical significance was determined with an ANOVA test followed by a Bonferroni's post-hoc test.
Results: The number of normal neurons per slice in the CA1 hippocampal region in naïve rats was 1268±31 (n = 5) and the ischemic insult to saline-treated females rats decreased the normal neuronal count to 29% (496±57; n = 4; P<0.001). Nicotine exposure followed by ischemic insult to normal cycling rats decreased the number of live neurons to only 13% (177±21; n = 6; P<0.05 as against ischemia). The ischemic insult to ovariectomized rats resulted in 18% of normal neurons in the CA1 region (250±58; n = 6; P<0.001 as compared to naïve). A bolus of 17β-estradiol to ovariectomized rats significantly protected CA1 region against ischemia (47% of naïve; 601±89; n = 5). In contrast, 17β-estradiol treatment to nicotine-exposed ovariectomized rats could not confer a similar degree of protection (27% of naïve; 373±52; n = 6). In parallel, nicotine exposure reduced hippocampal ERβ protein levels by 47% and 40% in normally cycling or ovariectomized plus 17β-estradiol treated rats, respectively,as compared to the non-treated control groups (P<0.05). In contrast to ERβ, the ERα protein level remained unchanged following nicotine exposure.
Conclusion: Chronic nicotine exposure reduced protein levels of estrogen receptor-β in the hippocampus and abrogated estrogen-conferred protection against cerebral ischemia in the female rat.
Grant support: AHA-SDG-National Center #0730089N and James and Esther King Biomedical Research Program, Florida Department of Health 07KN-10.
1027. Exhausted cerebral autoregulation is spatially associated with cortical atrophy
J. Fierstra1, J. Poublanc1, H. Wang1, J. Han2, J. Fisher2, A. Crawley1 and D. Mikulis1
1Medical Imaging; 2Anesthesia, University Health Network, University of Toronto, Toronto, ON, Canada
Objectives: The physiological impact of severely impaired cerebral autoregulatory vascular reactivity on gray matter integrity is unknown. We hypothesized that cortical gray matter supplied by a defective vascular system with exhausted dilatory autoregulation reserve will show evidence of cortical atrophy.
Methods: 250 BOLD-MRI cerebrovascular reactivity (CVR) studies were reviewed to identify subjects with severe unilateral impairment in CVR (impaired blood flow response to a vasoactive stimulus such as a change in PetCO2.), vasodilatory reserve (negative CVR) but with normal appearing gray matter on FLAIR. Patients with lacunar infarcts in the white matter were excluded. 17 patients were identified each having a high grade stenosis or occlusion of the ICA or MCA on one side regardless of etiology, secondary to Moyamoya, atherosclerosis, or unknown. CVR studies were performed by applying precision control of imposing acute transient vasodilatory stimulus end-tidal pCO2 CO2 between baseline (40 mm Hg) and to 50 mm Hg, (Respiract, TRI, Toronto, Canada) during BOLD MRI acquisition on a GE T HDX MRI system.1 A D T1-weighted volume (voxel 0.78 × 0.78 × 2.2 mm) was acquired and analyzed for cortical thickness using freesurfer (http://surfer.nmr.mgh.harvard.edu/). CVR and cortical thickness maps were overlapped to determine a ROI encompassing the region of negative impaired CVR. This ROI was mirrored to the normal hemisphere providing a normal versus abnormal hemisphere ROI comparison in each subject. Mean cortical thickness between right and left hemisphere ROIs for each subject was measured and a paired t-test was applied.
Results: The ROI with negative impaired CVR showed thinner cortex (2.23 mm ± 0.077) than the corresponding contra lateral side (2.42 mm±0.052) (P = 0.0005) in 16 of the 17 cases. Mean cortical thickness was 2.23 mm±0.077 on the abnormal side, and 2.42 mm±0.052 on the normal side (P = 0.0005). The figure shows the relationship between the spatial extent of abnormal impaired CVR (blue) and the spatial extent of cortical thinning (light blue) in one subject, (decreased extent of light blue in right hemisphere = thinner cortex and increased extent of blue in right hemisphere = negative CVR).
Conclusions: The data indicates that a spatial correspondence exists between exhaustion of autoregulatory capacitiy, vasodilatory capacity and cortical thinning. The findings imply that relate the inability to augment flow in response to metabolic stimuli, (as is also normally seen with neuronal activation), may be deleterious to the health of the preservation of gray matter.
1050. Effects of Ginkgo biloba on CBF assessed by quantitative MR perfusion
D. Lin, M. Dizon, D. Yousem and P. Barker
Radiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
Objectives: Ginkgo biloba, a frequently used dietary supplement for dementia, peripheral vascular and cerebrovascular insufficiency, is thought to mediate an increased blood flow. The purpose of this study was to determine the effects on regional cerebral blood flow (CBF), using dynamic susceptibility contrast perfusion MRI, in elderly healthy humans before and after 4 weeks of oral intake of Ginkgo supplements.
Methods: 11 healthy men (mean age 61±10 years) participated in this study. Each subject underwent MRI studies at baseline and at 4 weeks after taking 60 mg Ginkgo biloba capsules twice daily. In one of the 11 subjects, six MRI studies were conducted on different days at baseline prior to Ginkgo administration to evaluate the reproducibility of perfusion measurements. Whole brain perfusion MRI was performed at 1.5T using a gradient echo EPI sequence (TR/TE 2000/60 ms, 30 dynamics) during bolus injection of 0.1 mmol/kg GdDTPA at 5 cc/sec. CBF maps were generated using an arterial input function and singular value decomposition. Regions of interest were drawn from each cerebral hemisphere at the level of the centrum semiovale, as well as the right and left frontal-parietal gray matter and white matter. CBF computed from each region was normalized to that in the cerebellar hemispheres. The effects of Ginkgo were analyzed by comparison of the normalized CBF before and after treatment using a paired t-test.
Results: Perfusion MRI provides reproducible measurements of CBF within the same individual, with a normalized CBF in the right cerebral hemisphere of 1.35±0.14 (10.37% s.d.) and in the left cerebral hemisphere of 1.42±0.14 (9.85% s.d.) For assessment of the effects of Ginkgo on CBF before and after treatment, 9 out of 11 studies were analyzable and shown in Figure. There was no significant difference between the normalized CBF measurements (n = 9) before and after treatment in the right hemisphere (P = 0.66), left hemisphere (P = 0.9), right white matter (P = 0.54), left white matter (P = 0.14), right gray matter (P = 0.57) and left gray matter (P = 0.73).
Conclusions: Quantitative determination of CBF can be made by MR perfusion techniques with a good reproducibility within the same individual, therefore may provide a useful means to assess physiological changes in normal subjects and individuals with dementia. Based on this method, no significant difference could be detected in CBF after Ginkgo administration in normal elderly individuals using the study design described here.
KatoT. Principle and technique of NIRS-Imaging for human brain FORCE: Fast-oxygen response in capillary event. International Congress Series2004;1270:85–90.
7.
FeenyBFKappagantuR. On the Physical Interpretation of Proper Orthogonal Modes in Vibrations. Journal of Sound and Vibration1998;211(4):607–16.
8.
Microcirculation2004;11:605–13.
9.
Nature Neurosci2006;9:1397–403.
10.
LogothetisNK. Nature2001;412:150–57.
11.
KayserC. Cereb Cortex2004;14:881–91.
12.
NiessingJ. Science2005;309:948–51.
13.
MukamelR. Science2005;309:951–54.
14.
NirY. Curr Biol2007;17:1275–85.
15.
PrivmanE. J Neurosci2007;27:6234–42.
16.
McCulloughLD and HurnPD. Trends Endocrinol Metab2003;14:228.
17.
BramlettH. Pathophysiology2005;12:17.
18.
Vesely. MRM2001;45:1011–13.
19.
AhlemeyerBKrieglsteinJ. Neuroprotective effects of ginkgo biloba extract. Cell Mol Life Sci2003;60:1779–92.
20.
SantosRFGaldurozJCBarbieriACastiglioniMLYtayaLYBuenoOF. Cognitive performance, spect, and blood viscosity in elderly non-demented people using ginkgo biloba. Pharmacopsychiatry2003;36:127–33.
