Changes In Local Cerebral Blood Flow Research Articles

Astrocytic GPCR-Induced Ca2+ Signaling Is Not Causally Related to Local Cerebral Blood Flow Changes.

Activation of Gq-type G protein-coupled receptors (GPCRs) gives rise to large cytosolic Ca2+ elevations in astrocytes. Previous in vitro and in vivo studies have indicated that astrocytic Ca2+ elevations are closely associated with diameter changes in the nearby blood vessels, which astrocytes enwrap with their endfeet. However, the causal relationship between astrocytic Ca2+ elevations and blood vessel diameter changes has been questioned, as mice with diminished astrocytic Ca2+ signaling show normal sensory hyperemia. We addressed this controversy by imaging cortical vasculature while optogenetically elevating astrocyte Ca2+ in a novel transgenic mouse line, expressing Opto-Gq-type GPCR Optoα1AR (Astro-Optoα1AR) in astrocytes. Blue light illumination on the surface of the somatosensory cortex induced Ca2+ elevations in cortical astrocytes and their endfeet in mice under anesthesia. Blood vessel diameter did not change significantly with Optoα1AR-induced Ca2+ elevations in astrocytes, while it was increased by forelimb stimulation. Next, we labeled blood plasma with red fluorescence using AAV8-P3-Alb-mScarlet in Astro-Optoα1AR mice. We were able to identify arterioles that display diameter changes in superficial areas of the somatosensory cortex through the thinned skull. Photo-stimulation of astrocytes in the cortical area did not result in noticeable changes in the arteriole diameters compared with their background strain C57BL/6. Together, compelling evidence for astrocytic Gq pathway-induced vasodiameter changes was not observed. Our results support the notion that short-term (<10 s) hyperemia is not mediated by GPCR-induced astrocytic Ca2+ signaling.

Transient Hypoperfusion to Ischemic/Anoxic Spreading Depolarization is Related to Autoregulatory Failure in the Rat Cerebral Cortex

BackgroundIn ischemic stroke, cerebral autoregulation and neurovascular coupling may become impaired. The cerebral blood flow (CBF) response to spreading depolarization (SD) is governed by neurovascular coupling. SDs recur in the ischemic penumbra and reduce neuronal viability by the insufficiency of the CBF response. Autoregulatory failure and SD may coexist in acute brain injury. Here, we set out to explore the interplay between the impairment of cerebrovascular autoregulation, SD occurrence, and the evolution of the SD-coupled CBF response.MethodsIncomplete global forebrain ischemia was created by bilateral common carotid artery occlusion in isoflurane-anesthetized rats, which induced ischemic SD (iSD). A subsequent SD was initiated 20–40 min later by transient anoxia SD (aSD), achieved by the withdrawal of oxygen from the anesthetic gas mixture for 4–5 min. SD occurrence was confirmed by the recording of direct current potential together with extracellular K+ concentration by intracortical microelectrodes. Changes in local CBF were acquired with laser Doppler flowmetry. Mean arterial blood pressure (MABP) was continuously measured via a catheter inserted into the left femoral artery. CBF and MABP were used to calculate an index of cerebrovascular autoregulation (rCBFx). In a representative imaging experiment, variation in transmembrane potential was visualized with a voltage-sensitive dye in the exposed parietal cortex, and CBF maps were generated with laser speckle contrast analysis.ResultsIschemia induction and anoxia onset gave rise to iSD and aSD, respectively, albeit aSD occurred at a longer latency, and was superimposed on a gradual elevation of K+ concentration. iSD and aSD were accompanied by a transient drop of CBF (down to 11.9 ± 2.9 and 7.4 ± 3.6%, iSD and aSD), but distinctive features set the hypoperfusion transients apart. During iSD, rCBFx indicated intact autoregulation (rCBFx < 0.3). In contrast, aSD was superimposed on autoregulatory failure (rCBFx > 0.3) because CBF followed the decreasing MABP. CBF dropped 15–20 s after iSD, but the onset of hypoperfusion preceded aSD by almost 3 min. Taken together, the CBF response to iSD displayed typical features of spreading ischemia, whereas the transient CBF reduction with aSD appeared to be a passive decrease of CBF following the anoxia-related hypotension, leading to aSD.ConclusionsWe propose that the dysfunction of cerebrovascular autoregulation that occurs simultaneously with hypotension transients poses a substantial risk of SD occurrence and is not a consequence of SD. Under such circumstances, the evolving SD is not accompanied by any recognizable CBF response, which indicates a severely damaged neurovascular coupling.

Endothelial signaling at the core of neurovascular coupling: The emerging role of endothelial inward-rectifier K+ (Kir2.1) channels and N-methyl-d-aspartate receptors in the regulation of cerebral blood flow.

Neurovascular coupling (NVC) represents the mechanisms whereby an increase in neuronal activity (NA) may lead to local vasodilation and increase in regional cerebral blood flow (CBF). It has long been thought that neurons and astrocytes generate the vasoactive mediators regulating local changes in CBF, whereas cerebrovascular endothelial cells are not able to directly sense NA. Unexpectedly, recent evidence demonstrated that brain microvascular endothelial cells may sense NA through inward-rectifier K+ (Kir2.1) channels and may detect synaptic activity via N-methyl-d-aspartate (NMDA) receptors (NMDARs). In the present perspective, therefore, we discuss the hypothesis that endothelial Kir2.1 channels and NMDARs play a key role in NVC and in CBF regulation, which is crucial to unravel the cellular and molecular underpinnings of blood oxygen level-dependent signals.

The effect of hyperglycemia on neurovascular coupling and cerebrovascular patterning in zebrafish

Neurovascular coupling (through which local cerebral blood flow changes in response to neural activation are mediated) is impaired in many diseases including diabetes. Current preclinical rodent models of neurovascular coupling rely on invasive surgery and instrumentation, but transgenic zebrafish coupled with advances in imaging techniques allow non-invasive quantification of cerebrovascular anatomy, neural activation, and cerebral vessel haemodynamics. We therefore established a novel non-invasive, non-anaesthetised zebrafish larval model of neurovascular coupling, in which visual stimulus evokes neuronal activation in the optic tectum that is associated with a specific increase in red blood cell speed in tectal blood vessels. We applied this model to the examination of the effect of glucose exposure on cerebrovascular patterning and neurovascular coupling. We found that chronic exposure of zebrafish to glucose impaired tectal blood vessel patterning and neurovascular coupling. The nitric oxide donor sodium nitroprusside rescued all these adverse effects of glucose exposure on cerebrovascular patterning and function. Our results establish the first non-mammalian model of neurovascular coupling, offering the potential to perform more rapid genetic modifications and high-throughput screening than is currently possible using rodents. Furthermore, using this zebrafish model, we reveal a potential strategy to ameliorate the effects of hyperglycemia on cerebrovascular function.

Astrocytic calcium release mediates peri-infarct depolarizations in a rodent stroke model.

Stroke is one of the most common diseases and a leading cause of death and disability. Cessation of cerebral blood flow (CBF) leads to cell death in the infarct core, but tissue surrounding the core has the potential to recover if local reductions in CBF are restored. In these areas, detrimental peri-infarct depolarizations (PIDs) contribute to secondary infarct growth and negatively affect stroke outcome. However, the cellular pathways underlying PIDs have remained unclear. Here, we have used in vivo multiphoton microscopy, laser speckle imaging of CBF, and electrophysiological recordings in a mouse model of focal ischemia to demonstrate that PIDs are associated with a strong increase of intracellular calcium in astrocytes and neurons. We found that astroglial calcium elevations during PIDs are mediated by inositol triphosphate receptor type 2-dependent (IP3R2-dependent) release from internal stores. Importantly, Ip3r2-deficient mice displayed a reduction of PID frequency and overall PID burden and showed increased neuronal survival after stroke. These effects were not related to local CBF changes in response to PIDs. However, we showed that the release and extracellular accumulation of glutamate during PIDs is strongly curtailed in Ip3r2-deficient mice, resulting in ameliorated calcium overload in neurons and astrocytes. Together, these data implicate astroglial calcium pathways as potential targets for stroke therapy.

Improved partial volume correction method for detecting brain activation in disease using Arterial Spin Labeling (ASL) fMRI.

The insight provided by fMRI, particularly BOLD fMRI, has been critical to the understanding of human brain function. Unfortunately, the application of fMRI techniques in clinical research has been held back by several factors. In order for the clinical field to successfully apply fMRI, two main challenges posed by aging and diseased brains need to be overcome: (1) difficulties in signal measurement and interpretation, and (2) partial voluming effects (PVE). Recent work has addressed the first challenge by developing fMRI methods that, in contrast to BOLD, provide a direct measurement of a physiological correlate of function. One such method is Arterial Spin Labeling (ASL) fMRI, which provides images of cerebral blood flow (CBF) in physiologically meaningful units. Although the problems caused by PVE can be mitigated to some degree through the acquisition of high spatial resolution fMRI data, both hardware and experimental design considerations limit this solution. Our team has developed a PVE correction (PVEc) algorithm that produces CBF images that are theoretically independent of tissue content and the associated PVE. The main drawback of the current PVEc method is that it introduces an inherent smoothing of the functional data. This smoothing effect can reduce the sensitivity of the method, complicating the detection of local changes in CBF, such as those due to stroke or activation. Here, we present results from an improved PVEc algorithm (ssPVEc), which uses high-resolution structural space information to correct for the tissue-driven heterogeneity in the ASL signal. We tested the ssPVEc method on ASL images obtained on patients with asymptomatic carotid occlusive disease during rest and motor activation. Our results showed that the sensitivity of the ssPVEc method (defined as the average T-value in the activated region) was at least 1.5 times greater than that of the original, functional space, fsPVEc, for all patients.

Cortical reorganization after experimental traumatic brain injury: a functional autoradiography study.

Cortical sensorimotor (SM) maps are a useful readout for providing a global view of the underlying status of evoked brain function, as well as a gross overview of ongoing mechanisms of plasticity. Recent evidence in the rat controlled cortical impact (CCI) injury model shows that the ipsilesional (injured) hemisphere is temporarily permissive for axon sprouting. This would predict that size and spatial alterations in cortical maps may occur much earlier than previously tested and that they might be useful as potential markers of the postinjury plasticity period as well as indicators of outcome. We investigated the evolution of changes in brain activation evoked by affected hindlimb electrical stimulation at 4, 7, and 30 days following CCI or sham injury over the hindlimb cortical region of adult rats. [(14)C]-iodoantipyrine autoradiography was used to quantitatively examine the local cerebral blood flow changes in response to hindlimb stimulation as a marker for neuronal activity. The results show that although ipsilesional hindlimb SM activity was persistently depressed from 4 days, additional novel regions of ipsilesional activity appeared concurrently within SM barrel and S2 regions as well as posterior auditory cortex. Simultaneously with this was the appearance of evoked activity within the intact, contralesional cortex that was maximal at 4 and 7 days, compared to stimulated sham-injured rats, where activation was solely unilateral. By 30 days, however, contralesional activation had greatly subsided and existing ipsilesional activity was enhanced within the same novel cortical regions that were identified acutely. These data indicate that significant reorganization of the cortical SM maps occurs after injury that evolves with a particular postinjury time course. We discuss these data in terms of the known mechanisms of plasticity that are likely to underlie these map changes, with particular reference to the differences and similarities that exist between rodent models of stroke and traumatic brain injury.

Cerebral Vascular Blood Flow Changes During ‘Brain Freeze’

‘Brain freeze’ commonly occurs when ice cold food or liquid is rapidly consumed. It's mechanism remains unclear, however rapid cooling of the brain through the upper palate may cause local cerebral blood flow changes. The purpose of this study was to examine whether ‘brain freeze’ induces the hypothesized cerebrovascular changes.Using transcranial Doppler, we evaluated cerebral blood flow velocity (CBFV) in the middle (MCA) and anterior (ACA) cerebral arteries in 13 healthy adults while consuming ice and ambient water. Subjects drank ice water through a straw against the palate until pain developed. CBFV, heart rate, and blood pressure were analyzed, before pain, during pain and after pain.Consumption of ice water produced a tendency towards increased cerebral flow velocity in the ACA (P=0.078) but not the MCA (P=0.24). Ice water also resulted in greater cerebrovascular resistance during the experimentally induced “brain freeze” when compared to following ambient water consumption.Our results support a vascular mechanism for brain freeze. Ice water consumption resulted in a significantly greater cerebrovascular resistance as compared to that during ambient water consumption. However, the fact that cerebral flow increased during pain along with increases in blood pressure may suggest autoregulation was not as effective. Supported by NASA and NIH.

Role of the Peripheral Sympathetic Innervations in Controlling Cerebral Blood Flow after the Transection of Bilateral Superior Cervical Sympathetic Ganglia Two Weeks Later

Background: Cerebral blood vessels are mainly supplied by sympathetic nerves arising from the superior cervical ganglia and cerebral blood volume may be influenced by bilateral superior cervical ganglionectomy (SCG). Various stages of cerebral blood volume changes depended on the time following bilateral excision of SCG. In this study, we emphasize the subacute effect (two weeks) on the local cerebral blood flow (LCBF). Material and Methods: Sprague-Dawley rats weighing 250 ~ 400 gm (n = 20) were selected into two groups. Under the ambient temperature 20oC, the first group animals (n = 10) received sham operation and the other group animals (n = 10) underwent bilateral SCG. The LCBF and O2 delivery of 14 brain struc-tures were measured for each animal by the use of 14C-iodoantipyrine technique two weeks after the opera-tion. Results: The average of LCBF was decreased from 150 ml/100 gm/min to 129 ml/100 gm/min after bi-lateral SCG. Only the LCBF at basal ganglia was increased from 108 ml/min/100 g in the sham-operated group to 118 ml/min/100g in the SCG group. A mean of 14% reduction of LCBF was estimated. In 14 brain structures, the delivery amount of O2 was all decreased, except in basal ganglia. However, these changes of LCBF and the delivery amount of O2 at these 14 brain structures did not reach the significant differences. Conclusions: The present results show that chronic effect (two weeks) of bilateral SCG on LCBF was not only in a decrease of the LCBF, but also a decrease of local cerebral O2 delivery. However, the changes didn’t show the significant differences.

Persistent cerebrovascular effects of MDMA and acute responses to the drug

Acutely, 3,4,-methylenedioxymethamphetamine (MDMA) induces cerebrovascular dysfunction [Quate et al., (2004)Psychopharmacol., 173, 287-295]. In the longer term the same single dose results in depletion of 5-hydroxytrptamine (5-HT) nerve terminals. In this study we examined the cerebrovascular consequences of this persistent neurodegeneration, and the acute effects of subsequent MDMA exposure, upon the relationship that normally exists between local cerebral blood flow (LCBF) and local cerebral glucose utilization (LCMRglu). Dark agouti (DA) rats were pre-treated with 15 mg/kg i.p. MDMA or saline. Three weeks later, rats from each pre-treatment group were treated with an acute dose of MDMA (15 mg/kg i.p.) or saline. Quantitative autoradiographic imaging was used to measure LCBF or LCMRglu with [(14)C]-iodoantipyrine and [(14)C]-2-deoxyglucose, respectively. Serotonergic terminal depletion was assessed using radioligand binding with [(3)H]-paroxetine and immunohistochemistry. Three weeks after MDMA pre-treatment there were significant reductions in densities of 5-HT transporter (SERT)-positive fibres (-46%) and [(3)H]-paroxetine binding (-47%). In animals pre-treated with MDMA there were widespread significant decreases in LCMRglu, but no change in LCBF indicating a persistent loss of cerebrovascular constrictor tone. In both pre-treatment groups, acute MDMA produced significant increases in LCMRglu, while LCBF was significantly decreased. In 50% of MDMA-pre-treated rats, random areas of focal hyperaemia indicated a loss of autoregulatory capacity in response to MDMA-induced hypertension. These results suggest that cerebrovascular regulatory dysfunction resulting from acute exposure to MDMA is not diminished by previous exposure, despite a significant depletion in 5-HT terminals. However, there may be a sub-population, or individual circumstances, in which this dysfunction develops into a condition that might predispose to stroke.

Optimal window for ictal blood flow mapping: Insight from the study of discrete temporo-limbic seizures in rats

Rationale Measurement of local cerebral blood flow (LCBF) is routinely used to locate the areas involved in the generation and spread of seizures in epileptic patients. Since the spatial distribution and extent of ictal LCBF depends on the epileptogenic network, but also on the timing of injection of tracer, we used a rat model of amygdala kindled seizures to follow time-dependent changes in the distribution of seizure-induced LCBF changes. Methods Rats were implanted with a left amygdala electrode and were stimulated until reaching stage 1. LCBF was measured by the quantitative [ 14C]iodoantipyrine autoradiographic technique. The tracer was injected either at 15 s before seizure induction (early ictal) or simultaneously with the amygdala stimulation (ictal) in rats undergoing a stage 0 or 1 seizure. Results During stage 0 seizures, LCBF rates increased significantly ipsilaterally in medial and central amygdala and substantia nigra. During stage 1 seizures, LCBF increased unilaterally in amygdala, piriform cortex, substantia nigra, ventral tegmental area and cerebellum and bilaterally in several limbic and subcortical structures, excepted in hippocampus and pallidum. When pooling stages 0 and 1 but considering only tracer injection time, discrete LCBF changes occurred ipsilaterally in amygdala and substantia nigra at early ictal time. At true ictal time, significant changes occurred in several subcortical structures bilaterally while limbic structures displayed more localized and lateralized changes. Conclusion LCBF mapping appears unable to identify in rats the ictal onset zone of clinically significant amygdala-triggered seizures (stage 1), while the study of sub-clinical seizures (stage 0) allowed to correctly locate the amygdala onset of the seizures within the limbic network. Compared to human SPECT studies, this work confirms that some ictal hyperperfused areas belong to the spreading network rather than to the epileptogenic zone. The spatial recruitment of remote subcortical structures could be further investigated to strengthen the rationale of therapeutic stimulation of basal ganglia in drug-resistant epilepsies.

Time Course and Mapping of Cerebral Perfusion during Amygdala Secondarily Generalized Seizures

Measurement of local cerebral blood flow (LCBF) is routinely used to locate the areas involved in generation and spread of seizures in epilepsy patients. Because the spatial distribution and extent of ictal CBF depends on the epileptogenic network, but also on the timing of injection of tracer, we used a rat model of amygdala-kindled seizures to follow the time-dependent changes in the distribution of LCBF changes. Rats were implanted in the left amygdala and were fully kindled. LCBF was measured by the quantitative [(14)C]iodoantipyrine autoradiographic technique bilaterally in 35 regions. The tracer was injected at 30 s before seizure induction (early ictal), simultaneous with the application of stimulation (ictal), at 60 s after stimulation (late ictal), at the end of the electrical afterdischarge (early postictal), and at 6 min after the stimulation (late postictal). Rates of LCBF increased over control levels during the early ictal phase ipsilaterally in medial amygdala, frontal cortex, and ventromedian thalamus and bilaterally in the whole hippocampus, thalamic nuclei, and basal ganglia. During the ictal phase, all regions underwent hyperperfusion (81-416% increases). By 60 s after stimulation, rates of LCBF returned to control levels in most brain areas, despite ongoing seizure activity. At later times, localized foci of hypoperfusion were observed in hippocampus bilaterally, with a slight predominance in CA1 on the side of origin of the seizures. This study shows a rapid spread of activation from the stimulated amygdala bilaterally to numerous limbic, cortical, and subcortical structures. The largest hyperperfusion was recorded during the ictal period with tracer injections simultaneous with the stimulation. The unilateral site of origin of seizures led to minor asymmetrical and lateralized findings, merely at early ictal and late postictal times, whereas intermediate tracer injections induced bilateral changes. Only late postictal measurements allowed the identification of significant changes in focal structures: the hippocampus is known to play a critical role in the spread of limbic seizures.

Changes in cerebral blood flow modalities during hemorrhage in rats

The optimal life sign monitor in the practice of emergency medicine would be a technique to detect the earliest pathological change. Since the brain is the most sensitive organ in response to hypoxia/ischemia, cardio-pulmonary resuscitation should be brain-oriented (Peter Safar, 1998). Nevertheless, monitoring of cerebral blood flow (CBF) is not performed in the practice of emergency medicine in either civilian or military environments. CBF reactivity monitoring is an appropriate primary parameter to evaluate cerebral resuscitation due to a systemic or regional cerebral injury leading to possible irreversible brain injury. Unlike CBF monitoring this technique of CBF reactivity is being proposed as a non-invasive, mobile, and non-operator dependant means of evaluating an unconscious patient. The ideal life sign monitor would be one that reflects CBF non-invasively, continuously and globally. Because the most common cause of death following serious military and civilian injuries is hemorrhage, the goal of this study was to describe CBF changes during hemorrhage and to compare various CBF modalities in order to identify the optimal CBF vital sign monitor. A computer controlled rat hemorrhage model was introduced for resuscitation purposes. In anesthetized rats blood was removed at a rate required to achieve a mean arterial blood pressure (MABP) of 40 mmHg over 15 min. Shed blood was measured and used as an indicator of compensation/decompensation phase. Continuous recording was taken during 30 minutes of compensatory phase with intracranial rheoencephalogram – (iREG; n = 14), laser Doppler flowmetry (LDF; n = 3), and carotid flow by ultrasound (n = 11). Data were stored and processed off-line. During the initial phase of hemorrhage, when MABP was close to 40 mmHg, intracranial REG amplitude transiently increased (81 %), while LDF (78 %) and carotid flow (52 %) decreased and changed with systemic arterial pressure. Intracranial REG amplitude change suggests classical CBF autoregulation, indicating its close relationship to arteriolar changes 1. The studies indicated that 1) iREG may reflect cerebrovascular responses more accurately than changes in local CBF measured by LDF and carotid flow; CBF autoregulation was present at the beginning of SAP 40 mmHg. The physiological background or resolution of this virtual conflict is: Flow through large arteries may be constant despite changes of regional flow in tissue 2 REG may indicate promise as a continuous, non-invasive life sign monitoring tool with potential advantages over EKG, ultrasound, and other measurement techniques normally applied in clinical practice. Additional quantitative studies are in progress; the following studies are needed: 1) to test CBF autoregulation during the entire period of hemorrhage (with CO2 inhalation); 2) to estimate REG during graded increases in intracranial pressure; 3) to estimate REG during graded decreases in SAP; and 4) to test various data processing methods of the REG signal.

Changes in the intracranial rheoencephalogram at lower limit of cerebral blood flow autoregulation

Cerebral blood flow (CBF) reactivity monitoring is an appropriate primary parameter to evaluate cerebral resuscitation due to a systemic or regional cerebral injury leading to possible irreversible brain injury. Use of the electrical impedance method to estimate CBF is rare, as the method's anatomical background is not well understood. Use of intracranial rheoencephalography (iREG) during hemorrhage and comparison of iREG to other CBF measurements have not been previously reported. Our hypothesis was that iREG would reflect early cerebrovascular alteration (CBF autoregulation). Studies comparing iREG, laser Doppler flowmetry and ultrasound were undertaken on anesthetized rats to define CBF changes during hemorrhage. Blood was removed at a rate required to achieve a mean arterial blood pressure (MABP) of 40 mm Hg over 15 min. Estimation of CBF was taken with intracranial, bipolar REG (REG I; n = 14), laser Doppler flowmetry (LDF; n = 3) and carotid flow by ultrasound (n = 11). Data were processed off-line. During the initial phase of hemorrhage, when MABP was close to 40 mm Hg, intracranial REG amplitude transiently increased (80.94%); LDF (77.92%) and carotid flow (52.04%) decreased and changed with systemic arterial pressure. Intracranial REG amplitude change suggests classical CBF autoregulation, demonstrating its close relationship to arteriolar changes. The studies indicate that iREG might reflect cerebrovascular responses more accurately than changes in local CBF measured by LDF and carotid flow. REG may indicate promise as a continuous, non-invasive life-sign monitoring tool with potential advantages over ultrasound, the CBF measurement technique normally applied in clinical practice. REG has particular advantages in non-hospital settings such as military and emergency medicine.

Nonlinear correlation between field potential and local cerebral blood flow in rat somatosensory cortex evoked by changing the stimulus current

The relationship between local cerebral blood flow (LCBF) and field potential (FP) evoked by hindpaw stimulation in rat somatosensory cortex has been investigated while changing stimulus current. The change in LCBF was measured using laser-Doppler flowmetry and the field potential was acquired using a tungsten electrode inserted into the cortex of alpha-chloralose-anesthetized rats. The cortex was activated by electrical stimulation of the hind paw with 5 Hz pulses (0.1 ms) applied at currents of 1.0, 1.5, 2.0 and 2.5 mA for 5 s. It was found that the summed FP is nonlinear with respect to stimulus current, whereas the integrated LCBF response is linear across the range of currents used in the experiment. This means that the relationship between the summed FP and integrated LCBF is nonlinear as a function of stimulus current.

Mechanisms of pain-induced local cerebral blood flow changes in the rat sensory cortex and thalamus

It is a well-known phenomenon that cerebral blood flow is coupled to neural activation induced by non-noxious somatosensory stimulation. However, basic questions related to pain-induced cerebral blood flow changes remain unanswered. In the present study, the sciatic nerve of anesthetized rats was subjected to electric stimulation with noxious and non-noxious parameters. Changes in local cerebral blood flow and neuronal activity were determined simultaneously in the sensory cortex and in the thalamus by laser-Doppler flowmetry and c- fos immunohistochemistry, respectively. The role of different vasoregulatory mechanisms and the pain-induced increase in mean arterial blood pressure (MABP) were examined with specific blocking agents and by means of rapid intra-arterial transfusion. Noxious stimulation resulted in significant enhancement of neuronal activity both in the thalamus and in the somatosensory cortex indicated by marked c- fos expression in these areas. Cortical and thalamic blood flow (cBF and tBF) increased by 47±4 and 44±3% during the stimulation while the MABP elevated by 35±2%. Similar changes in MABP induced by intra-arterial transfusion had no effect on tBF, while cBF increased only by 18±5%. Blockade of ATP sensitive potassium channels (K + ATP) and sympathetic β-receptors significantly attenuated the pain-induced blood flow increases in both investigated areas, while inhibition of nitric oxide synthase was effective only in the thalamus. The blockade of the sympathetic α-receptors, opiate receptors, and the cyclooxygenase enzyme had no effect on the pain-induced cerebral blood flow elevations. These findings demonstrate that during noxious stimulation, cerebral blood flow is adjusted to the increased neural activity by the interaction of vasoconstrictor autoregulatory and specific vasodilator mechanisms, involving the activation of sympathetic β-receptors, K + ATP-channels and the release of nitric oxide.

A Scanning Technique to Measure Regional Cerebral Blood Flow and Oxyhemoglobin Level

OBJECTIVE The application of a laser scanning technique to measure regional cerebral blood flow (CBF) and tissue hemoglobin oxygenation (HbO2) using the rat closed cranial window preparation is described. METHODS Twenty-nine male Wistar rats were used to consecutively measure local CBF by laser Doppler flowmetry and tissue HbO2 by a microspectrophotometric method at multiple corresponding cortical locations. The scanning technique used a computer-controlled micromanipulator. Data from three experimental models are presented: the whisker stimulation model, the ischemia-reperfusion model, and the sinus-vein thrombosis model. Sequential changes in local CBF and HbO2 data before, during, and after stimulation, ischemia, and sinus thrombosis were examined. Data from predefined locations within the same region were correlated with the topographical location and then arranged in a three-dimensional image. RESULTS In the whisker stimulation model, we found a disproportionate increase in CBF (32 ± 12%) as compared with that of HbO2 (9 ± 4%) during stimulation. In the ischemia-reperfusion model, the three-dimensional image showed heterogeneous low CBF (depending on the area) and homogeneous HbO2 at a reduced level during ischemia and postischemic hyperperfusion. However, the range of oxygenation was normal after reperfusion. In the sinus-vein thrombosis model, drainage of the unsaturated blood via the collateral pathways was noted. CONCLUSION The laser scanning technique is useful for visualizing sequential changes in hemodynamic-metabolic interactions of cortical brain tissue. This technique can reveal phenomena not detected by traditional monitoring procedures.

A scanning technique to measure regional cerebral blood flow and oxyhemoglobin level.

The application of a laser scanning technique to measure regional cerebral blood flow (CBF) and tissue hemoglobin oxygenation (HbO2) using the rat closed cranial window preparation is described. Twenty-nine male Wistar rats were used to consecutively measure local CBF by laser Doppler flowmetry and tissue HbO2 by a microspectrophotometric method at multiple corresponding cortical locations. The scanning technique used a computer-controlled micromanipulator. Data from three experimental models are presented: the whisker stimulation model, the ischemia-reperfusion model, and the sinus-vein thrombosis model. Sequential changes in local CBF and HbO2 data before, during, and after stimulation, ischemia, and sinus thrombosis were examined. Data from predefined locations within the same region were correlated with the topographical location and then arranged in a three-dimensional image. In the whisker stimulation model, we found a disproportionate increase in CBF (32 +/- 12%) as compared with that of HbO2 (9 +/- 4%) during stimulation. In the ischemia-reperfusion model, the three-dimensional image showed heterogeneous low CBF (depending on the area) and homogeneous HbO2 at a reduced level during ischemia and postischemic hyperperfusion. However, the range of oxygenation was normal after reperfusion. In the sinus-vein thrombosis model, drainage of the unsaturated blood via the collateral pathways was noted. The laser scanning technique is useful for visualizing sequential changes in hemodynamic-metabolic interactions of cortical brain tissue. This technique can reveal phenomena not detected by traditional monitoring procedures.

Regional alterations in an excitatory amino-acid transporter, blood flow, and glucose metabolism after middle cerebral artery occlusion in the rat

A rise in the extracellular concentration of excitatory amino acids (EAA) plays a pivotal role in ischemic brain injury. EAA concentrations are regulated by uptake mechanisms through high-affinity EAA transporters. Since EAA uptake is energy-dependent, it is a matter of interest to explore the relationship between the EAA transporter and derangement of flow-metabolism during ischemia. We examined the regional changes in EAA transporters after permanent occlusion of the middle cerebral artery in rats by in vitro autoradiography using [3H]-D-aspartate as a ligand, and correlated these changes to the local cerebral blood flow (LCBF) and local cerebral glucose metabolism (LCMRglc) determined by in vivo double-labeled autoradiography. The values of specific binding of [3H]-D-aspartate decreased maximally by 20% in the ischemic core. The magnitude of the reduction in specific binding correlated well with the changes in LCBF and LCMRglc. In half of the regions with LCMRglc between 80 and 120% of the intact side, the values of the specific binding were relatively preserved, while in the remainder of the regions in the ischemic hemisphere, with LCMRglc ranging from 40 to 160% of the intact side, there was a reduction in specific binding. These results suggest that energy failure and the related perturbation caused by ischemia can decrease EAA uptake capacity, leading to further deterioration.

The effects of chronic nitric oxide synthase suppression on glioma pathophysiology

Nitric oxide synthase (NOS) is strongly expressed in glioma and has an important role in tumour blood flow (TBF) regulation. Whether manipulation of NOS function within a tumour can have any therapeutic effect is unknown. This study therefore evaluated the pathophysiological effects of chronic systemic NOS inhibition on experimental rodent glioma blood flow, growth and necrosis.To determine the duration and pathophysiological effects of systemic NOS inhibition, Ng-nitroL-arginine methyl ester (L-NAME) was given to rats bearing C6 glioma acutely (single dose i.v., 30 mg kg) or for either 4 or 7 days (i.p. 75 mg kg day) prior to study.TBF and local cerebral blood flow (LCBF) were measured using C14-iodoantipyrine quantitative autoradiography. Tumour volume, tumoural necrosis and tumoural NOS were measured using conventional neuropathology and immunocytochemistry.Acute and 4-day L-NAME administration produced significant TBF reductions (‘;48 and ‘;39%, respectively) with less marked changes in LCBF (‘;35 and ‘;15%, respectively). Seven-day L-NAME administration reduced tumour volume ( p =0.12), increased tumoural necrosis ( p <0.05), but immunohistochemistry showed no difference in tumoural NOS expression. These results confirm that NOS has a significant role in the pathophysiology of experimental glioma, and that in this glioma model the effects of chronic systemic NOS inhibition are, for the period under study, predominately anti-tumoural. Whether chronic NOS inhibition is useful as an adjunct in glioma therapy or provides the opportunity for novel therapeutic approaches requires further study.