Local exposure of the rat cortex to radiofrequency electromagnetic fields increases local cerebral blood flow along with temperature

Few studies have shown that local exposure to radiofrequency electromagnetic fields (RF) induces intensity-dependent physiological changes, especially in the brain. The aim of the present study was to detect reproducible responses to local RF exposure in the parietal cortex of anesthetized rats and to determine their dependence on RF intensity. The target cortex tissue was locally exposed to 2-GHz RF using a figure-eight loop antenna within a range of averaged specific absorption rates (10.5, 40.3, 130, and 263 W/kg averaged over 4.04 mg) in the target area. Local cerebral blood flow (CBF) and temperatures in three regions (target area, rectum, and calf hypodermis) were measured using optical fiber blood flow meters and thermometers during RF exposure. All parameters except for the calf hypodermis temperature increased significantly in exposed animals compared with sham-exposed ones during 18-min exposures. Dependence of parameter values on exposure intensity was analyzed using linear regression models. The elevation of local CBF was correlated with temperature rise in both target and rectum at the end of RF exposure. However, the local CBF elevation seemed to be elevated by the rise in target temperature, but not by that of the rectal temperature, in the early part of RF exposure or at low-intensity RF exposure. These findings suggest that local RF exposure of the rat cortex drives a regulation of CBF accompanied by a local temperature rise, and our findings may be helpful for discussing physiological changes in the local cortex region, which is locally exposed to RF.     

正常大鼠脑血流动力学的CT灌注成像研究

目的:采用多层螺旋CT灌注成像探讨正常大鼠脑血流动力学特征.方法:对15只健康Wistar大鼠进行CT灌注扫描,定量测定全脑不同区域的血流动力学参数,分析正常Wistar大鼠脑血流动力学特征.结果:正常Wistar大鼠脑部不同区域的血流动力学参数存在较大差异(P＜0.05或0.01),Wistar大鼠的CBF和CBV值以小脑最高,其次是基底节区和延髓,大脑皮质的CBF和CBV值较低:而MTT值在Wistar大鼠脑部各区域比较接近,均值比较无统计学意义(P＞0.05).结论:多层螺旋CT可用于定量评价Wistar大鼠脑组织的血液动力学特征,完全适用于小型动物模型脑部血流动力学的研究.     

Pathophysiology of the Ischemic Penumbra—Revision of a Concept

1. The original concept of the ischemic penumbra surrounding a focus of dense cerebral ischemia is based on electrophysiological observations. In the cortex of baboons following middle cerebral artery occlusion, complete failure of the cortical evoked potential was observed at a cerebral blood flow (CBF) threshold level of approx. 0.15 ml/g/min—a level at which extracellular potassium ion activity was only mildly elevated. With a greater CBF decrement to the range of 0.06–0.10 ml/g/min, massive increases in extracellular potassium occurred and were associated with complete tissue infarction. Thus, the ischemic penumbra has been conceptualized as a region in which CBF reduction has exceeded the threshold for failure of electrical function but not that for membrane failure.2. Recent studies demonstrate that the penumbra as defined classically by the flow thresholds does not survive prolonged periods of ischemia. The correlation of CBF autoradiograms with diffusion-weighted MR images and the regional distribution of cerebral metabolites reveals that the ischemic core region enlarges when adjacent, formerly penumbral, areas undergo irreversible deterioration during the initial hours of vascular occlusion. At the same time, the residual penumbra becomes restricted to the periphery of the ischemic territory, and its fate may depend critically upon early therapeutic intervention.3. In the border zone of brain infarcts, marked uncoupling of local CBF and glucose utilization is consistently observed. The correlation with electrophysiological measurements shows that metabolism-flow uncoupling is associated with sustained deflections of the direct current (DC) potential resembling transient depolarizations. Such penumbral cell depolarizations, which are associated with an increased metabolic workload, induce episodes of tissue hypoxia due to the constrained collateral flow, stimulate anaerobic glycolysis leading to lactacidosis, suppress protein synthesis, and, finally, compromise energy metabolism. The frequency of their occurrence correlates with the final volume of ischemic injury. Therefore, penumbral depolarizations are regarded as a key event in the pathogenesis of ischemic brain injury. Periinfarct DC deflections can be suppressed by NMDA and non-NMDA antagonists, resulting in a significant reduction of infarct size.4. The histopathological sequelae within the penumbra consist of various degrees of scattered neuronal injury, also termed incomplete infarction. The reduction of neuronal density at the infarct border is a flow- and time-dependent event which is accompanied by an early response of glial cells. As early as 3 hr after vascular occlusion a generalized microglial activation can be detected throughout the ipsilateral cortex. Astrocytic activation is observed in the intact parts of the ischemic hemisphere from 6 hr postocclusion onward. Thus, the penumbra is a spatially dynamic brain region of limited viability which is characterized by complex pathophysiological changes involving neuronal function as well as glial activation in response to local ischemic injury.     

Calcium Antagonist Isradipine Reduces Metabolic Alterations in Acute Cerebral Ischemia in Spontaneously Hypertensive Rats

The present study was designed to examine the effect of a calcium antagonist isradipine (PN200-110: PN) on local cerebral blood flow and brain tissue metabolism after 1-hour supratentorial ischemia induced by bilateral carotid artery ligation (BCL) in spontaneously hypertensive rats (SHR). PN, dissolved in ethanol plus polyethylene glycol 400, diluted with saline to make the final concentration of 0.25mg/ml and 2.5mg/ml, was administered subcutaneously either 30 min prior to BCL or just after the induction of incomplete cerebral ischemia (n = 7 in each group). Vehicle injection was served as a control group (n = 7). Cerebral blood flow in the parietal cortex (CBF) and the cerebellar cortex (CeBF) was measured by hydrogen clearance technique, and the supra- and infratentorial metabolites of the brain frozen in situ were determined by the enzymatic method. Blood pressure was lowered, but CBF was increased by PN administration in pre-BCL treatment study. After 1 hour of BCL, CBF decreased to around 10% or less of the resting value, being insignificant among the groups. Brain adenosine triphosphate was better preserved in PN-administered groups. The increase in lactate level tended to reduce dose dependently by PN treatment. PN also reduced the metabolic alterations in brain tissue with significance, even when administered just after the induction of forebrain ischemia. It is considered that pre- as well as post-BCL administration of PN is beneficial to attenuate the metabolic alterations in incomplete forebrain ischemia in SHR.     

CT灌注评价高碳酸血症模型下正常大鼠脑组织血流动力学变化

目的探讨CT灌注评价高碳酸血症模型下正常大鼠脑组织血流动力学变化的可行性;研究大鼠CT灌注参数变化率与α-SMA表达之间的相关性。方法 10只雄性SD大鼠,体质量250～300g,在吸入空气和吸入高浓度CO2混合气体(10%CO2和90%空气组成)后15min,分别使用GE16层Light Speed CT扫描仪对大鼠脑尾状核层面进行CT灌注扫描,原始图像经GE ADW4.2工作站Perfusion3.0脑部灌注软件处理后产生灌注曲线及伪彩图像,两次扫描前均测定大鼠的血液CO2分压、pH值等血气分析指标。检查结束后24h内,大鼠取脑固定,在尾状核中心层面切片,进行脑组织HE染色及鼠特异性SMA抗体免疫组化染色。应用SPSS11.5统计学软件进行分析:采用配对t检验,比较正常大鼠右侧尾状核在吸入空气和吸入高浓度CO2混合气体后CT灌注参数脑血容量(CBV)、脑血流量(CBF)、血管表面通透性(PS)和平均透过时间(MTT)的变化有无差异;采用Pearson相关分析分别检测大鼠右侧尾状核的SMA阳性血管染色计数与灌注参数CBV和CBF在CO2分压升高前后的变化率相关性。结果所有大鼠在吸入含10%CO2和90%空气的混合气体15min后,动脉血CO2分压均明显升高(t=9.39,P0.001),血浆pH值降低(t=13.49,P0.001)。正常SD大鼠右侧基底节区CBV、CBF、PS每100g组织分别为(10.28±4.01)mL、(304.95±88.77)mL/min、(0.26±0.37)mL/min,MTT值为(1.48±0.07)s;吸入10%CO2和90%空气的混合气体后右侧基底节区CBV、CBF值明显增加,每100g组织分别为(19.25±8.42)mL(t=4.92,P=0.001)和(507.33±167.94)mL/min(t=6.75,P0.001);吸入混合气体前后CBV、CBF增加百分比分别为(87.14±46.45)%、(65.75±22.05)%;PS及MTT变化不显著(P均0.05)。大鼠脑组织α-SMA阳性染色血管计数为(12.7±3.23)条/高倍视野。Pearson相关分析显示,正常脑组织的CBV和CBF变化率与其α-SMA阳性计数之间呈显著相关(r分别为0.652和0.890,P均0.05)。结论 CT灌注技术在改变血液CO2分压的条件下可以反映脑组织血流动力学变化;大鼠正常脑组织高碳酸血症前后CT灌注参数变化率与成熟血管数量相关。     

Effect of hypothermia on brain multi-parametric activities in normoxic and partially ischemic rats

Hypothermia, as well as anesthesia, are known to protect the brain against ischemia, hypoxia and other pathological damages. One of the mechanisms of this improvement could be by lowering brain function, and thereby lowering oxygen demand. We examined the effect of hypothermia on brain function and blood supply in awake and anesthetized rats and studied the interaction between partial ischemia and the responses to hypothermia. The brain function multiprobe (BFM) used enabled simultaneous measurements of cerebral blood flow (CBF), mitochondrial NADH redox state, extracellular K(+) concentration, DC potential and ECoG from the cerebral cortex in rats whose brain temperature was lowered by 5 degrees C. Hypothermia was induced in awake, anesthetized and brain ischemic-anesthetized rats. In anesthetized and ischemic-anesthetized rats, the time required for lowering the brain temperature by 5 degrees C was five times less than in the normal awake animals. No significant changes in CBF and NADH levels were found in response to hypothermia in the awake animals. In contrast, a significant decrease in extracellular K(+) concentration was recorded under hypothermia, probably due to the lower rate of depolarization. Hypothermia in anesthetized and in ischemic-anesthetized rats did not significantly affect the levels of mitochondrial NADH, CBF and extracellular K(+). Hypothermia under ischemia was expected to be more effective.     

Local and global cerebral blood flow and glucose utilization in the α-galactosidase A knockout mouse model of Fabry disease

Fabry disease is an X-linked lysosomal disorder characterized by deficient alpha-galactosidase A activity and intracellular accumulations of glycosphingolipids, mainly globotriaosylceramide (Gb3). Clinically, patients occasionally present CNS dysfunction. To examine the pathophysiology underlying brain dysfunction, we examined glucose utilization (CMR(glc)) and cerebral blood flow (CBF) globally and locally in 18 brain structures in the alpha-galactosidase A gene knockout mouse. Global CMR(glc) was statistically significantly reduced by 22% in Fabry mice (p < 0.01). All 18 structures showed decreases in local CMR(glc) ranging from 14% to 33%. The decreases in all structures of the diencephalon, caudate-putamen, brain stem, and cerebellar cortex were statistically significant (p < 0.05). Global cerebral blood flow (CBF) and local CBF measured in the same 18 structures were lower in Fabry mice than in control mice, but none statistically significantly. Histological examination of brain revealed no cerebral infarcts but abundant Gb3 deposits in the walls of the cerebral vessels with neuronal deposits localized to the medulla oblongata. These results indicate an impairment in cerebral energy metabolism in the Fabry mice, but one not necessarily due to circulatory insufficiency.     

Reversibility of Nimodipine Binding to Brain in Transient Cerebral Ischemia

Using autoradiography, we have measured the in vivo binding of [3H]nimodipine to brain in a rat model of reversible cerebral ischemia. Ischemia was induced by simultaneous occlusion of the middle cerebral artery (MCA) and ipsilateral common carotid artery by microaneurysm clips. Rats were studied after 15 min of ischemia (ischemic group) or after 45 min of reperfusion following 15 min of ischemia (reperfused group). Regional cerebral blood flow (CBF) was determined autoradiographically using [14C]iodoantipyrine in both ischemic (n = 6) and reperfused (n = 6) groups. During ischemia blood flow in the territory of the MCA was depressed and recovered to normal only in the distal territory of the MCA following reperfusion. [3H]Nimodipine binding in the ischemic group (n = 12) was elevated in ischemic brain regions and declined significantly (p < 0.01) in these regions in the reperfused group (n = 11). The ratio of the volume of cortex showing increased binding to the total volume of the forebrain was 0.113 +/- 0.025 (mean +/- SD) in the ischemic group and declined to 0.080 +/- 0.027 following reperfusion (p < 0.005). In general, infarct was only observed in regions showing persistent elevation of nimodipine binding following reperfusion as determined by histology performed in a separate group of rats (n = 8) after 24 h of reperfusion. We conclude that increased nimodipine binding to ischemic tissue is initially reversible with prompt reestablishment of CBF and is a sensitive indicator of early and reversible ischemia-induced cerebral dysfunction.     

C-fos expression in rat brain during heat stress

Rats, under urethane anesthesia, 0, 20, 40 or 80 min after the start of heat stress (42°C) were sacrificed for determination of c-fos expression in different brain regions. In situ hybridization and immunocytochemistry methods were used, respectively, for determination of c-fos mRNA and protein, respectively. In general, either colon temperature (T_CO), mean arterial pressure (MAP), local cerebral blood flow (CBF) or c-fos expression in different brain regions (including the preoptic area, supraoptic nuclei, paraventricular nuclei, thalamus, amygdala, nucleus tract solitarii, area postrema and ventrolateral medulla) increased at 20–40 min after the start of heat exposure. However, the heatstroke, which appears as profound decreases in both MAP and local CBF and increases in T_CO, was produced 80 min after heat stress. The c-fos expression was heavily induced in all these brain regions after the onset of heatstroke. The data suggest that c-fos expression in rat brain during heatstroke is associated with hyperthermia, arterial hypotension or cerebral ischemia.     

Cerebral Blood Flow Modulation by Basal Forebrain or Whisker Stimulation Can Occur Independently of Large Cytosolic Ca2+ Signaling in Astrocytes

We report that a brief electrical stimulation of the nucleus basalis of Meynert (NBM), the primary source of cholinergic projection to the cerebral cortex, induces a biphasic cerebral cortical blood flow (CBF) response in the somatosensory cortex of C57BL/6J mice. This CBF response, measured by laser Doppler flowmetry, was attenuated by the muscarinic type acetylcholine receptor antagonist atropine, suggesting a possible involvement of astrocytes in this type of CBF modulation. However, we find that IP3R2 knockout mice, which lack cytosolic Ca2+ surges in astrocytes, show similar CBF changes. Moreover, whisker stimulation resulted in similar degrees of CBF increase in IP3R2 knockout mice and the background strain C57BL/6J. Our results show that neural activity-driven CBF modulation could occur without large cytosolic increases of Ca2+ in astrocytes.     

Effect of fentanyl and morphine on local blood flow and tissue oxygen tension in cortical frontal-parietal area and nucleus accumbens in albino rats

The aim of this study was to examine effects of i.p. injected Fentanyl (0.005 mg/kg) and Morphine (1 mg/kg) on local cerebral blood flow (ICBF) and tissue pO2 level in frontal-parietal area of the cortex and nucleus accumbens of the rat's brain. Either fentanyl or morphine injection resulted in significant increase of local blood flow in the n.accumbens and its decrease in frontal-parietal area of cortex. Measurement of oxygen partial pressure revealed the opposite (to ICBF) changes: a decrease in n.accumbens and its increase in cortical area of the brain. Analysis of this data and electrical activity recorded from both said structures allow to conclude that they are conditioned by respective changes in functional-metabolic activity induced by intraperitoneal injection either fentanyl or morphine: its suppression in frontal-parietal area of the cortex and development of seizure-like activity in the n.accumbens.     

Neurovascular coupling in the normal brain and in hypertension, stroke, and Alzheimer disease.

The brain is critically dependent on a continuous supply of blood to function. Therefore, the cerebral vasculature is endowed with neurovascular control mechanisms that assure that the blood supply of the brain is commensurate to the energy needs of its cellular constituents. The regulation of cerebral blood flow (CBF) during brain activity involves the coordinated interaction of neurons, glia, and vascular cells. Thus, whereas neurons and glia generate the signals initiating the vasodilation, endothelial cells, pericytes, and smooth muscle cells act in concert to transduce these signals into carefully orchestrated vascular changes that lead to CBF increases focused to the activated area and temporally linked to the period of activation. Neurovascular coupling is disrupted in pathological conditions, such as hypertension, Alzheimer disease, and ischemic stroke. Consequently, CBF is no longer matched to the metabolic requirements of the tissue. This cerebrovascular dysregulation is mediated in large part by the deleterious action of reactive oxygen species on cerebral blood vessels. A major source of cerebral vascular radicals in models of hypertension and Alzheimer disease is the enzyme NADPH oxidase. These findings, collectively, highlight the importance of neurovascular coupling to the health of the normal brain and suggest a therapeutic target for improving brain function in pathologies associated with cerebrovascular dysfunction.     

Regional cerebral blood flow of the rat in acute carbon monoxide intoxication.

The effect of carbon monoxide (CO) on the regional cerebral blood flow was studied by exposing lightly anesthetized rats for 30 min to 0.5, 1.0, 1.5, and 2.0% CO gas mixtures. Cortical cerebral blood flow (CBF) increases of near 200%, 300%, and 400% control were observed at 0.5, 1.0, and 1.5% CO, respectively; whereas at 2.0% CO a reversal of the CBF increase was observed with values declining to near 300% control. The CBF response of subcortical, cerebellar, and brain stem areas was quantitatively similar to that of cortex, indicating that the CBF changes in CO intoxication are general. The decrease in CBF at 2.0% CO was related to significant decreases in arterial CO2 tension. Comparison of the CBF data to previous metabolic results in CO poisoning suggests that the CBF increases are a principal factor in the maintenance of an intact energy state in CO poisoning.     

Effect of aging on brain energy-metabolism

The aging process involves morphological and functional changes in cerebral vasculature and deterioration of mitochondrial number and function. Furthermore, slow oscillations of cerebral blood flow and oxidative metabolism occur in animals under different pathological conditions such as ischemia. The aim of this study was to evaluate the effect of aging on energy-metabolism of the rat brain during anoxia and normoxia and to further investigate the occurrence of oscillations under normoxia in the aging brain. Simultaneous hemodynamical (CBF), biochemical (NADH/NAD ratio) and electrical activity from the cerebral cortex were measured by means of a multiparametric assembly (MPA) system. Exposure of adult rats to anoxia (100% N(2)) resulted in a 36+/-2% elevation of NADH. Furthermore, exposure of the aged group to anoxia caused NADH elevation as low as 9.6+/-4% (P<0.05). The changes in the NADH levels were followed by an increase in CBF. In addition, during the normoxic periods, hemodynamic oscillations were recorded in the old animals. This study suggests that the structural and functional changes that occur in vessels in the aging brain cause disability of cerebromicrovessels to optimally deliver nutrients and oxygen to the brain, affecting the mitochondrial ability to respond to anoxia. Furthermore, this study supports the approach that the hemodynamic oscillations are related to the development of a pathological state and are not a normal cerebral function.     

Morphologic changes in the sensomotor cortex in experimental neurosis

Disturbances of higher nervous activity (experimental neurosis) are attended with morphological changes of blood circulation in the sensorimotor area of the cerebral cortex, corresponding to distonic vascular disorders, as well as with hypoxic and neuroglial changes. Observed changes in the nervous tissue also reflect adaptive and defensive mechanisms of the brain (in rabbits).     

Focal cerebral ischaemia induces corticotropin releasing factor (CRF) vascular immunoreactivity in rat occluded hemisphere

Corticotropin-releasing factor (CRF) induces the dilatation of cerebral blood vessels and increases cerebral blood flow (CBF). CRF receptor antagonists reduce ischaemic damage in the rat. In the present study, the expression of CRF around cerebral vessels has been investigated in the rat. No CRF immunoreactivity was identified around pial or intracerebral vessels in the absence of cerebral ischaemia. Four hours after middle cerebral artery occlusion (MCAo), intensely CRF-positive blood vessels were evident on the ischaemic cortical surface and in the peri-infarct and infarct zone. Increased CRF immunoreactivity was also detected in swollen axons in subcortical white matter, caudate nucleus and lateral olfactory tract of the ipsilateral hemisphere, consistent with the failure of axonal transport. These data provide morphologic support for a role of CRF in the pathophysiology of cerebral ischaemia.     

Acute Restraint-Mediated Increases in Glutamate Levels in the Rat Brain: An In Vivo <Superscript>1</Superscript>H-MRS Study at 4.7 T

It is well known that a variety of stressors induces a significant alteration in various putative neurotransmitters in the mammalian CNS. However, relatively little attention has been paid on the alteration of central glutamate neurotransmission, which is a major excitatory neurotransmitter in the brain. The present study aimed to determine whether acute restraint stress induces the changes in neurotransmitter level, especially glutamate, in rat brain and to examine whether 1-h recovery time after the termination of stress can revert to its pre-stress state. In vivo ¹H-NMR spectra were acquired from the cerebral cortex and hippocampus (control: N = 10, stress: N = 10, stress + 1 h rest: N = 10) immediately or after 1 h rest from restraint stress. All in vivo proton spectra were automatically analyzed using LCModel. We found that acute restraint stress induced significant increase in glutamate concentrations in the cerebral cortex and the hippocampus of rat. However, the level could not revert to its pre-stress state by the end of 1-h recovery period in cerebral cortex of rats. In addition, glutamine/glutamate ratio, which may function as an index of the glutamatergic neurotransmission, was significantly lower in the cerebral cortex of both stress and 1 h stress + 1 h recovery groups, as compared to control. Our finding may provide important evidence for altered glutamatergic activity after the stress and suggest a potential biochemical marker for eventual diagnosis and/or therapy monitoring in mood disorder.     

Alterations in cation levels and Na-K ATPase activity in rat cerebral cortex during the development of cobalt-induced epilepsy

Abstract— This study was carried out to ascertain what biochemical changes might be present in cobalt-induced epilepsy in the rat. Sodium, potassium, calcium, magnesium, Na-K ATPase activity, water content, protein content and the ability of the tissue to utilize oxygen were measured in (1) the area of the cerebral cortex in which the cobalt was implanted; (2) in an area adjacent to but not including the area of the lesion; and (3) in the homotopic area of the contralateral cerebral cortex. The greatest changes were observed in the area of the lesion itself, with marked increases in calcium, magnesium and sodium contents and decreases in potassium content, Na-K ATPase activity, protein content and the ability of the tissue to utilize oxygen. The only significant findings in the area adjacent to the lesion and in the contralateral cortex were a modest elevation of sodium and a modest decrease in potassium at different time periods after implantation of the cobalt. We feel that the changes observed at the site of cobalt implantation may reflect tissue destruction which is unrelated to the epileptic process.