脑温变化对大鼠局灶脑缺血再灌注组织兴奋性氨基酸的影响

目的　研究轻度高温、亚低温对局灶脑缺血组织兴奋性氨基酸 (EAA)的影响。方法　建立大鼠大脑中动脉缺血再灌注线栓模型 ,诱导目标脑温 ,用HPLC荧光法检测脑组织谷氨酸 (Glu)、天冬氨酸 (Asp)、甘氨酸 (Gly)含量。结果　轻度高温组Glu、Asp、Gly明显增高 ;亚低温组则明显降低。结论　轻度高温促进EAA增高 ,在持续增加Glu“兴奋毒性”方面起重要作用 ;亚低温抑制EAA增高 ,在降低Glu“兴奋毒性”方面起重要作用。     

脑泰方对缺血再灌注损伤沙鼠大脑皮层氨基酸类神经递质含量的影响

目的 :探讨脑泰方对缺血再灌注损伤沙鼠大脑皮层氨基酸类神经递质含量的影响。方法 :采用沙土鼠双侧颈总动脉阻断模型。利用高效液相色谱 -荧光法检测大脑皮层氨基酸含量。结果 :脑泰方可显著降低沙鼠脑缺血再灌注损伤时大脑皮层兴奋性氨基酸类神经递质(EAAs)Glu、Asp含量 (P <0 .0 1) ,并显著升高抑制性氨基酸类神经递质 (IAAs)GABA、Gly、Tau含量 (P <0 .0 1) ,提高GABA/Glu比值。结论 :调节脑组织兴奋性和抑制性氨基酸类神经递质含量的平衡可能是脑泰方抗脑缺血再灌注损伤的机制之一。     

脑缺血再灌注细胞外液兴奋性氨基酸与一氧化氮的变化及丹参的影响

目的　观察脑缺血再灌注细胞外液兴奋性氨基酸 (EAAs)与一氧化氮 (NO)的变化及丹参的影响。方法　采用沙土鼠全脑缺血再灌注模型 ,应用微透析技术及高压液相色谱测量方法 ,观察纹状体区细胞外液中EAAs及NO代谢产物变化。结果　在对照组 ,脑缺血 30min后 ,细胞外液中EAAs水平明显增加 ,随着再灌注时间延长EAAs水平逐渐接近正常 ,同时细胞外液中NO代谢产物也明显升高。L 精氨酸 (L Arg)组 ,EAAs及NO代谢产物水平均高于对照组 (P <0 .0 1) ;丹参组 ,EAAs及NO代谢产物水平均低于对照组 (P <0 .0 1) ,在丹参加L Arg组 ,EAAs及NO代谢产物水平与对照组差异无显著性意义。结论　脑缺血后 ,纹状体区细胞外液EAAs及NO代谢产物水平均明显增加 ,丹参不仅可降低EAAs及NO代谢产物水平 ,而且可逆转L Arg的损害作用     

Regulatory role of excitatory amino acids in reproduction

Glutamate, the major excitatory amino acid (EAA) transmitter in the central nervous system, has been implicated as a critical mediator in brain function. Glutamate and its receptors are found in all key hypothalamic areas critically involved in reproduction. Administration of glutamate and its agonists can bring about LH release in animals with a steroid background. Antagonists of the ionotropic glutamate receptors inhibited LH release and abolished the steroid-induced and the preovulatory LH surge. Both NMDA and non-NMDA receptor antagonists can also inhibit pulsatile LH release in castrated animals. The preoptic area has been implicated as a primary site of action of NMDA, while non-NMDA agonists have been suggested to act primarily at the arcuate/median eminence level. While EAAs may act directly on GnRH neurons to enhance GnRH release, the majority of evidence suggests that an indirect mechanism, involving EAA activation of nitric oxide and/or catecholamines, plays a major role in the GnRH-releasing effects of EAAs. Furthermore, there is also some evidence that the tonic inhibitory effect of opioids on GnRH may also involve, at least in part, a suppression of glutamate. Finally, EAA stimulation of GnRH/LH release is markedly attenuated in middle-aged rats, suggesting that a defect in glutamate neurotransmission may underlie the attenuated LH surge observed in aging.     

Excitatory amino acid neurotransmission evidence for a role in neuroendocrine regulation.

There is compelling evidence that endogenous excitatory amino acid neurotransmission is an important component of the neuroendocrine transmission line that regulates anterior pituitary-hormone release and, thus, reproduction. Excitatory amino acids (EAAs), such as glutamate and aspartate, are found in large quantities in neuroendocrine tissues such as the hypothalamus, and neurons from a variety of hypothalamic nuclei respond with marked excitation to EAA application. Exogenous EAA administration rapidly increases the release of GnRH, LH, and prolactin secretion in vivo and in vitro. Antagonist studies demonstrate that EAA-receptor activation is involved in a number of reproductive-endocrine events, such as the induction of puberty, seasonal breeding, steroid-induced LH secretion, and the preovulatory surge of LH and prolactin in the female. EAA regulation of these neuroendocrine events appears to be achieved through modulation and regulation of hypothalamic GnRH secretion.     

新生大鼠缺血缺氧后胶质性谷氨酸转运体的表达及GM1的干预研究

目的探讨新生大鼠缺血缺氧性脑损伤后胶质性谷氨酸转运体的表达及神经节苷脂（GM1）的干预作用。方法通过建立新生大鼠缺血缺氧性脑损伤动物模型，应用免疫组化方法，观察缺血缺氧后不同时期大脑皮质胶质性谷氨酸转运体EAATI、EAAT2的动态表达度GM1对其表达的影响。结果缺血缺氧后6hEAAT1的表达开始上升、第2d达高峰，第3d恢复到假手术组水平；EAAT2的表达在缺血缺氧后12h开始上升，第3d达高峰，第5d恢复到假手术组水平；GM1干预组脑组织损伤明显减轻，EAAT1和EAAT2的表达较单纯缺血缺氧组显著增加（P〈0．01），持续时间延长。结论缺血缺氧诱导胶质性谷氨酸转运体的表达，GM1提高胶质性谷氨酸转运体的表达可能是GM1脑保护作用的重要机制之一。     

脑梗塞后出血与梗塞面积及预后的关系

为探讨脑梗塞后出血与梗塞面积及患者预后的关系，对49例血性脑梗塞（HI）患者进行了CT动态观察（其中大面积脑梗塞出血27例），并与22例大面积非出血性脑梗塞（NHI）患者作对照，两组患者均在病初及病程第四周各进行临床神经功能缺损程度评分一次，以第二次的评分减少值作为判断脑功能恢复的指标。结果表明，脑梗塞面积越大，出血的可能性越大；HI患者的预后明显差于NHI患者。说明预防脑梗塞后出血对改善患者预后具有重要意义。     

Electrical Impedance Properties of Normal and Chronically Infarcted Left Ventricular Myocardium

Background: Previous reports have disclosed that a significant difference exists between the electrical impedance properties of healthy and chronically infarcted ventricular myocardium.Purpose: To assess the potential utility of electrical impedance as the basis for mapping in chronically infarcted left ventricular myocardium. Specifically: (1) to delineate electrical impedance properties of healthy and chronically infarcted ventricular myocardium, with special emphasis on the infarction border zone; (2) to correlate impedance properties with tissue histology; (3) to correlate impedance properties with electrogram amplitude and duration; (4) To demonstrate that endocardial impedance can be measured effectively in vivo using an electrode mounted on a catheter inserted percutaneously.Methods: An ovine model of chronic left ventricular infarction was utilized. Sites of healthy myocardium, densely infarcted myocardium and the infarction border zone were investigated. Bulk impedance was measured in vitro using capacitor cell, four-electrode and unipolar techniques. Epicardial and endocardial impedances were measured in vivo using four-electrode and unipolar techniques. Impedance was measured at multiple frequencies. Electrographic amplitude, duration and amplitude/duration ratio were measured using bipolar electrograms during sinus rhythm. Quantitation of tissue content of myocytes, collagen, elastin and neurovascular elements was performed.Results: Densely infarcted myocardial impedance was significantly lower than healthy myocardium. Impedance gradually decreased in the border zone transitioning between healthy myocardium and dense infarction. Decreasing impedance correlated with a decrease in tissue myocyte content. The magnitude of the difference in impedance between densely infarcted and healthy myocardium increased as the measurement frequency decreased. Healthy myocardium exhibited a marked frequency dependence in its impedance properties; this phenomenon was not observed in densely infarcted myocardium. There was a direct association between impedance and both electrogram amplitude and amplitude/duration ratio. There was an inverse association between impedance and electrogram duration. Endocardial impedance, measured in vivo using a electrode catheter inserted percutaneously, was demonstrated to distinguish between healthy and infarcted myocardium.Conclusions: The electrical impedance properties of healthy and infarcted left ventricular myocardium differ markedly. The properties of the infarction border zone are intermediate between healthy and infarcted myocardium. Impedance may be a useful assay of cardiac tissue content and adaptable for cardiac mapping in vivo.Condensed Abstract. To delineate the electrical impedance properties of healthy and chronically infarcted left ventricular myocardium emphasizing the infarction border zone, impedance was measured in chronically infarcted ovine hearts. Densely infarcted myocardial impedance was significantly lower than healthy myocardium. Impedance gradually decreased in the infarction border zone in transition between healthy myocardium and dense infarction. This correlated with a decreasing myocyte content. The magnitude of the difference in impedance between densely infarcted and healthy myocardium increased as measurement frequency decreased. There was a direct association between impedance and electrogram characteristics. Endocardial impedance, measured in vivo using an electrode catheter inserted percutaneously, distinguished between healthy and infarcted myocardium     

Attenuation of focal cerebral ischemic injury in transgenic mice overexpressing CuZn superoxide dismutase.

Oxygen-derived free radicals have been implicated in the pathogenesis of vasogenic edema and infarction caused by ischemia and reperfusion injury. In earlier studies, exogenously supplied liposome-entrapped CuZn superoxide dismutase (CuZn-SOD) ameliorated ischemic brain edema and infarction in rats following focal cerebral ischemia. To ascertain directly the role of SOD in the protection against superoxide radical-induced injury, we measured infarct size and water content 24 hr following focal cerebral ischemia in nontransgenic mice and in transgenic mice bearing the human SOD1 gene. These transgenic mice have 3.1-fold higher cellular CuZn-SOD activity in the brain than do their nontransgenic littermates. We also measured antioxidant levels (reduced glutathione and reduced ascorbate) of contralateral cortex, infarct cortex, surrounding cortex, and striatum. Infarct size and brain edema were significantly decreased in transgenic mice compared with nontransgenic mice. Reduced glutathione and reduced ascorbate levels decreased in the ischemic hemisphere, but levels in surrounding cortex and striatum were significantly higher in transgenic mice than in nontransgenic mice. These results indicate that increased endogenous SOD activity in brain reduces the level of ischemic damage and support the concept that superoxide radicals play an important role in the pathogenesis of infarction and edema following focal cerebral ischemia.     

Aromatic and branched-chain amino acids in autopsied brain tissue from cirrhotic patients with hepatic encephalopathy

Concentrations of the branched-chain amino acids (BCAAs) valine, leucine, and isoleucine and the aromatic amino acids (AAAs) phenylalanine and tyrosine were measured in three areas of dissected brain tissue obtained at autopsy from nine cirrhotic patients who died in hepatic encephalopathy. The controls were an equal number of subjects free from neurological, psychiatric or hepatic diseases, matched for age and time interval from death to freezing of autopsied brain samples. Amino acids were measured using high-performance liquid chromatography with fluorimetric detection. In brain tissue of cirrhotic patients, no changes in BCAA concentrations were observed compared with controls. On the other hand, phenylalanine levels were found to be increased 141% in prefrontal cortex, 86% in frontal cortex and 26% in caudate nucleus, and tyrosine content was increased by 71% in prefrontal cortex and 28% in frontal cortex with no significant increase in caudate nucleus. Alterations in the concentration of AAAs may lead to disturbances of monoamine neurotransmitters in brain. Such changes could play a role in the pathogenesis of hepatic encephalopathy resulting from chronic liver disease in man.     

Right Ventricular Infarction: The Role of Echocardiography

Echocardiographic evaluation of patients with right ventricular (RV) ischemia and infarction has a clear clinical relevance, because the presence of RV infarction is associated with a highly increased early in-hospital mortality, which can be dramatically reduced by successful early reperfusion. However, infarcted RV did recover its function regardless of the infarcted artery patency. This observation suggests that RV myocardium almost always remains viable. This article illustrates the clinical value of echocardiography, including the transthoracic and transesophageal approaches, Doppler, and three-dimensional ultrasound, for the assessment of RV dimensions, shape, and global and regional function, and the estimation of right atrial involvement that in cases of ischemia may further modulate RV performance. In addition, the use of stress echocardiography to detect RV ischemia and evaluate the viability of infarcted RV myocardium is discussed.     

Reperfusion Injury: Basic Concepts and Protection Strategies

Prolonged ischemia such as that following myocardial infarction or occurring during long-term coronary bypass procedures causes serious damage to the myocardium. Early reperfusion is an absolute prerequisite for the survival of ischemic tissue. However, reperfusion has been referred to as the double edged sword because reperfusing ischemic myocardium carries with it a component of injury known as reperfusion injury. Reperfusion injury includes a number of events, such as reperfusion arrhythmias, myocardial infarction, stunning, vascular damage, and endothelial dysfunction. The underlying mechanism of reperfusion injury is not entirely known, but the existing evidence suggests that oxygen free radicals generated during the first few minutes of reflow lead to damage of cellular membranes, intracellular calcium overload, and uncoupling of excitation-contraction coupling. Although controversial, free radical scavengers, in general, are highly effective in the attenuation of reperfusion injury in animal models. Newer endogenous protection strategies, which include ischemic and heat shock preconditioning, are known to reduce reperfusion injury following ischemia.     

丹皮酚对缺糖缺氧再灌注损伤大鼠海马神经元EAA、NMDA受体表达的影响及机制探讨

目的观察丹皮酚对缺糖缺氧（OGD）再灌注损伤大鼠海马神经元兴奋性氨基酸（EAA）、N．甲基．D．天门冬氨酸（NMDA）受体表达的影响,探讨该药的神经保护作用机制。方法原代培养新生大鼠海马神经元8～12d后随机分为4组,其中对照组正常换液培养;模型组、丹皮酚组、地佐环平（MK-801）组均制备OGD再灌注损伤模型,在此基础上丹皮酚组于每个再灌注时间点前分别加入丹皮酚,MK-801组则加入MK-801溶液;倒置相差显微镜下观察神经元一般形态学变化,用MTr法测定神经元存活率,分别采用放射配基结合实验及RT-PCR法测定NMDA受体结合力、NR1亚基mRNA表达,以氨基酸分析仪检测EAA含量。结果模型组神经元肿胀或变形,突起缩短并逐渐消失,胞质内颗粒变性明显、甚至完全崩解;丹皮酚组及MK-801组神经元形态改变均较模型组减轻,胞体完整,突起较清楚,基本保持完整。与对照组比较,模型组神经元存活率明显降低,NMDA受体结合力、NR1亚基mRNA表达及E从含量明显升高,而丹皮酚组及MK_801组上述指标均较模型组明显改善（P均〈0．05）。结论丹皮酚对离体培养的大鼠海马神经元OGD再灌注损伤具有保护作用,其作用机制可能与抑制EAA及NMDA受体表达有关。     

Impaired perfusion after myocardial infarction is due to reperfusion-induced deltaPKC-mediated myocardial damage

OBJECTIVE: To improve myocardial flow during reperfusion after acute myocardial infarction and to elucidate the molecular and cellular basis that impedes it. According to the AHA/ACC recommendation, an ideal reperfusion treatment in patients with acute myocardial infarction (AMI) should not only focus on restoring flow in the occluded artery, but should aim to reduce microvascular damage to improve blood flow in the infarcted myocardium. METHODS: Transgenic mouse hearts expressing the deltaPKC (protein kinase C) inhibitor, deltaV1-1, in their myocytes only were treated with or without the deltaPKC inhibitor after ischemia in an ex vivo AMI model. deltaV1-1 or vehicle was also delivered at reperfusion in an in vivo porcine model of AMI. Microvascular dysfunction was assessed by physiological and histological measurements. RESULTS: deltaPKC inhibition in the endothelial cells improved myocardial perfusion in the transgenic mice. In the porcine in vivo AMI model, coronary flow reserve (CFR), which is impaired for 6 days following infarction, was improved immediately following a one-minute treatment at the end of the ischemic period with the deltaPKC-selective inhibitor, deltaV1-1 ( approximately 250 ng/kg), and was completely corrected by 24 h. Myocardial contrast echocardiography, electron microscopy studies, and TUNEL staining demonstrated deltaPKC-mediated microvascular damage. epsilonPKC-induced preconditioning, which also reduces infarct size by >60%, did not improve microvascular function. CONCLUSIONS: These data suggest that deltaPKC activation in the microvasculature impairs blood flow in the infarcted tissue after restoring flow in the occluded artery and that AMI patients with no-reflow may therefore benefit from treatment with a deltaPKC inhibitor given in conjunction with removal of the coronary occlusion.     

Melatonin protects from the long-term consequences of a neonatal hypoxic-ischemic brain injury in rats

Abstract:  Among the main factors responsible for perinatal brain injury, inflammation, hypoxia-ischemia and formation of free radicals (FR) appear to play key roles. Melatonin, an endogenously produced indoleamine formed in higher amounts in adults than in neonates, is a potent FR scavenger as well as an indirect antioxidant. Herein, we examined whether melatonin provides significant protection against brain damage and its long-term consequences in a neonatal model of hypoxia-ischemia (HI). Seven day-old rats were subjected to permanent legation of the right common carotid artery followed to 2.5 hrs hypoxia 3 hrs later (HI). The neuroprotective effect of melatonin was evaluated 7 days after HI, or when rats reached adulthood, using behavioral and histological analyses. A beneficial effect was observed with 5 mg/kg melatonin administered before HI. The same dose repeated three times reduced further injury. A significant protective effect was found when 15 mg/kg melatonin was given 30 min before HI or when the same dose was given after HI and administration repeated after 24 and 48 hrs. The latter schedule of administration was used to assess the long-term protective effects. Melatonin did not affect growth rate and behavior at adulthood, but significantly improved the behavioral asymmetry and learning deficits induced by HI. Consistently, brain injury was significantly attenuated in the melatonin-treated ischemic group. The present study demonstrates that melatonin administration before or after HI in immature rats has an excellent and long-lasting benefit on ischemic outcomes suggesting that the drug could represent a potentially safe approach to perinatal brain damage in humans.     

Myocardial enzyme depletion in infarcted human hearts: infarct size and equivalent tissue mass

Myocardial activities of several enzymes were measured in infarcted and non-infarcted areas of heart sections obtained from eight patients who died after acute myocardial infarction. Similar data were obtained from four patients with cardiovascular disorders who died from causes other than myocardial infarction and from six patients without previously known heart disease. It was found that both non-infarcted and infarcted tissue samples contained considerably altered enzyme activities. This finding explains the low correlations between enzymatic and histological estimates of infarct size previously reported. However, when the residual myocardial activities of different enzymes were compared with each other, a close correlation was found between creatine kinase, alpha-hydroxybutyrate dehydrogenase, and aspartate aminotransferase. It appears that the pathological changes in the myocardial activities of these enzymes may be explained by the phenomenon of diluted myocardium. This indicates that myocardial injury, as estimated from plasma enzyme activities, may still be expressed meaningfully in gram equivalents of healthy myocardium.     

Is inflammation good for the ischemic heart - perspectives beyond the ordinary

Summary In recent years, early reperfusion of the myocardial infarct has become the mainstay of optimal therapeutic management sinct it limits ventricular injury and infarct expansion and improves patient survival [14]. It has become clear that reperfusion promotes effective tissue repair and decreases ventricular remodeling even under circumstances where reperfusion is effected at too late a time to limit myocardial necrosis [4]. One of the striking differences between reperfused and non-reperfused myocardial infarctions is that the early intense inflammatory reaction which ensues immediately upon reperfusion has been demonstrated to potentially extend myocardial injury [9]. Substantial evidence suggests that this inflammatory reaction is important in tissue repair, leading to an obvious paradox with regard to the role of the inflammatory reaction. This communication takes the position that inflammatory injury occurring upon reperfusion of the infarcted myocardium results from the overwhelming of tissue defenses against inflammation resulting from the sudden entry of large amounts of neutrophils to an area of infarction where chemotactic factors have built up to high concentration. However, we hypothesize that inflammation fundamentally evolved as a protective mechanism to promote tissue healing and protect jeopardized myocardium. In this presentation, we will discuss our approach and data designed to evaluate potential protective roles of the inflammatory reaction after reperfusion.     

Dietary branched chain amino acids ameliorate injury-induced cognitive impairment

Neurological dysfunction caused by traumatic brain injury results in profound changes in net synaptic efficacy, leading to impaired cognition. Because excitability is directly controlled by the balance of excitatory and inhibitory activity, underlying mechanisms causing these changes were investigated using lateral fluid percussion brain injury in mice. Although injury-induced shifts in net synaptic efficacy were not accompanied by changes in hippocampal glutamate and GABA levels, significant reductions were seen in the concentration of branched chain amino acids (BCAAs), which are key precursors to de novo glutamate synthesis. Dietary consumption of BCAAs restored hippocampal BCAA concentrations to normal, reversed injury-induced shifts in net synaptic efficacy, and led to reinstatement of cognitive performance after concussive brain injury. All brain-injured mice that consumed BCAAs demonstrated cognitive improvement with a simultaneous restoration in net synaptic efficacy. Posttraumatic changes in the expression of cytosolic branched chain aminotransferase, branched chain ketoacid dehydrogenase, glutamate dehydrogenase, and glutamic acid decarboxylase support a perturbation of BCAA and neurotransmitter metabolism. Ex vivo application of BCAAs to hippocampal slices from injured animals restored posttraumatic regional shifts in net synaptic efficacy as measured by field excitatory postsynaptic potentials. These results suggest that dietary BCAA intervention could promote cognitive improvement by restoring hippocampal function after a traumatic brain injury.     

Calpain system and its involvement in myocardial ischemia and reperfusion injury

Calpains are ubiquitous non-lysosomal Ca2+-dependent cysteine proteases also present in myocardial cytosol and mitochondria.Numerous experimental studies reveal an essential role of the calpain system in myocardial injury during ischemia,reperfusion and postischemic structural remodelling.The increasing Ca2+-content and Ca2+-overload in myocardial cytosol and mitochondria during ischemia and reperfusion causes an activation of calpains.Upon activation they are able to injure the contractile apparatus and impair the energy production by cleaving structural and functional proteins of myocytes and mitochondria.Besides their causal involvement in acute myocardial dysfunction they are also involved in structural remodelling after myocardial infarction by the generation and release of proapoptotic factors from mitochondria.Calpain inhibition can prevent or attenuate myocardial injury during ischemia,reperfusion,and in later stages of myocardial infarction.     

Postischemic tissue injury by iron-mediated free radical lipid peroxidation

Cell damage initiated during ischemia matures during reperfusion. Mechanisms involved during reperfusion include the effects of arachidonic acid and its oxidative products prostaglandins and leukotrienes, reperfusion tissue calcium overloading, and damage to membranes by lipid peroxidation. Lipid peroxidation occurs by oxygen radical mechanisms that require a metal with more than one ionic state (transitional metal) for catalysis. We have shown that cellular iron is delocalized from the large molecules where it is normally stored to smaller chemical species during postischemic reperfusion. Postischemic lipid peroxidation is inhibited by the iron chelator deferoxamine. Intervention in the reperfusion injury of membranes by chelation of transitional metals is a new and promising therapeutic possibility for protection of the heart and brain.