1,721,142 research outputs found
Effects of recombinant tissue plasminogen activator after intraluminal thread occlusion in mice - Role of hemodynamic alterations
No full textBackground and Purpose-It has been suggested that recombinant tissue plasminogen activator (rtPA) may cause an aggravation of injury after transient focal ischemia via excitotoxic side effects. Such rtPA toxicity would be of major clinical significance since rtPA is increasingly used in stroke treatment. This study was conducted to evaluate the effects of dose, application time, and hemodynamic changes after intravenous rtPA treatment in focal ischemia. Methods-Mice were subjected to a 90-minute episode of middle cerebral artery thread occlusion, and rtPA effects were assessed by laser-Doppler flowmetry, [C-14]iodoantipyrine autoradiography, and triphenyltetrazolium chloride staining. Results and Conclusions-We provide evidence that rtPA provokes complex hemodynamic alterations in the ischemic brain tissue, which include an initial hyperperfusion and a more delayed hypoperfusion response. Changes are most pronounced in the periphery of the ischemic infarct, where regional blood flow drops below critical thresholds of tissue viability. Our observations suggest that changes of perfusion may at least partly explain the rtPA-induced increase of infarct size, which has previously been reported and which we also confirmed in the present experiments. Notably, both the secondary hypoperfusion and increase of infarct volume were abolished when rtPA-treated animals received additional heparin infusions. This finding suggests that a secondary hypercoagulability may compromise brain perfusion after rtPA delivery. Accordingly, early treatment with heparin might help to prevent the rtPA-induced changes
Tissue Plasminogen Activator-Induced Ischemic Injury Is Reversed by NMDA Antagonist MK-801 in vivo
No full textIn vitro studies suggested that tissue plasminogen activator (t-PA) may aggravate ischemic injury by enhancing N-methyl-D-aspartate (NMDA) receptor signalling. It remained unclear whether NMDA signalling is also relevant for t-PA toxicity in vivo. We herein examined effects of intravenous t-PA (10 mg/kg), administered alone or in combination with the NMDA antagonist MK-801 (0.2 mg/kg), following 90 min of middle cerebral artery occlusion in mice. In our study, MK-801 alone, administered intra-peritoneally, neither affected infarct volume nor brain swelling at 24 h after reperfusion. t-PA significantly increased infarct size, in accordance with previous findings. t-PA-induced ischemic injury was completely abolished and brain swelling markedly reduced when t-PA-treated animals received additional MK-801 injections. To elucidate how t-PA influences brain damage, we examined actions of t-PA on the expression of NO synthases by immunohistochemistry, showing that t-PA does not influence neuronal NO synthase, but increases inducible NO synthase in ischemic areas. The effect of t-PA on inducible NO synthase levels was completely reversed after cotreatment with MK-801. Our study provides in vivo evidence in a model of focal cerebral ischemia that t-PA-induced brain injury involves an NMDA receptor-dependent mechanism. Copyright (C) 2005 S. Karger AG, Base
Effects of pinealectomy and melatonin on the retrograde degeneration of retinal ganglion cells in a novel model of intraorbital optic nerve transection in mice
No full textThe effects of pinealectomy and of intraperitoneally administered melatonin on the retrograde degeneration of retinal ganglion cells (RGCs) were examined in a novel model of optic nerve (ON) transection in C57BL/6J mice. RGCs were prelabeled with the fluorescent tracer 1,1'-dioctadecyl-3,3,3',3'-tetramethyl indocarbocyanine perchlorate (Di-I), and the ON was cut inside the orbital cavity 7 days later. The degree of RGC injury was assessed by counting viable Di-I labeled RGCs in various locations of the retina. In unlesioned control eyes, a mean ganglion cell density of 1891 +/- 30/mm(2) (mean +/- S.E.M.) was determined. The cell density markedly declined at 14 days after axotomy (295 +/- 9 cells/mm(2); 15.6% of contralateral). Sham-pinealectomy did not influence the density of RGCs at 14 days after ON transection (382 +/- 37 cells/mm(2)). In pinealectomized animals, on the other hand, the RGC number was significantly reduced as compared with untreated and sham-pinealectomized animals (91 +/- 33 RGCs/mm(2)). The effect of pinealectomy was reversed after i.p. administration of melatonin (4 mg/kg bw bolus followed by continuous infusion of 8 mg/kg bw/day) (286 +/- 27 cells/mm(2)) In nonpinealectomized. animals., on the contrary, i.p. melatonin did not influence the RGC density (344 +/- 20 cells/mm(2)). The present results suggest that endogenous melatonin prevents the delayed degeneration of adult central nervous system (CNS) neurons in vivo, and that exogenous substitution of melatonin may be useful to protect injured neurons against cell death under conditions of melatonin deficiency, e.g. in the aged brain, when melatonin synthesis and secretion have decreased
The role of small extracellular vesicles in cerebral and myocardial ischemia-Molecular signals, treatment targets, and future clinical translation
No full textThe heart and the brain mutually interact with each other, forming a functional axis that is disturbed under conditions of ischemia. Stem cell-derived extracellular vesicles (EVs) show great potential for the treatment of ischemic stroke and myocardial infarction. Due to heart-brain interactions, therapeutic actions of EVs in the brain and the heart cannot be regarded in an isolated way. Effects in each of the two organs reciprocally influence the outcome of the other. Stem cell-derived EVs modulate a large number of signaling pathways in both tissues. Upon ischemia, EVs prevent delayed injury, promote angiogenesis, enhance parenchymal remodeling, and enable functional tissue recovery. The therapeutic effects greatly depend on EV cargos, among which are noncoding RNAs like microRNAs (miRNAs) and proteins, which modulate cell signaling in a differential way that not always corresponds to each other in the two tissues. Interestingly, the same miRNA or protein localized in EVs can modulate different signaling pathways in the ischemic heart and brain, which may have diverse consequences for disease outcomes. Paying careful attention to unveiling these underlying mechanisms may provide new insights into tissue remodeling processes and identify targets for ischemic stroke and myocardial infarction therapies. Some of these mechanisms are discussed in this concise review, and consequences for the clinical translation of EVs are presented
Extracellular Vesicles as Diagnostic Tool in Transient Ischemic Attack and Ischemic Stroke
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Opportunities and Limitations of Vascular Risk Factor Models in Studying Plasticity-Promoting and Restorative Ischemic Stroke Therapies
No full textMajor efforts are currently made promoting neuronal plasticity and brain remodeling in the postacute stroke phase. Experimental studies evaluating new stroke therapies are mostly performed in rodents, which compared to humans exhibit a short lifespan. These studies widely employ young, otherwise healthy, rodents that lack the vascular risk factors and comorbidities of stroke patients. These risk factors compromise postischemic neurological recovery and brain plasticity and in several contexts reduce the brain responsiveness to recovery-inducing plasticity-promoting treatments. By examining risk factor models, which have hitherto been used for studying experimentally induced ischemic stroke, this review outlines the possibilities and limitations of risk factor models in the evaluation of plasticity-promoting and restorative stroke treatments
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Animal models of ischemic stroke and their impact on drug discovery
No full textIntroduction: Representing the leading cause of long-term disability, ischemic stroke urgently needs further research and drug development. This review summarizes current animal models of ischemic stroke that can be used for drug discovery.
Areas covered: Several reproducible models of permanent and transient focal cerebral ischemia have been established in a variety of animal species including rats and mice, in which a brain-supplying artery, often the middle cerebral artery, is occluded by mechanical devices including sutures, clips and hooks, pharmacological agents or delivery of blot clots. The authors review existing literature about these models, outlining their utility for evaluating acute and post-acute stroke treatments. Since stroke is an age-related disease that strongly affects humans with vascular risk factors and co-morbidities, the authors give focus to strategies replicating risk factors in ischemic stroke models. Furthermore, the authors present models of spontaneous stroke.
Expert opinion: It is important that animal models mimic clinical conditions in a reliable and clinically relevant way, so here, they should replicate the pathophysiology of human stroke, stroke-associated risk factors and doses, times and modes of drug treatment. We propose that risk factor models should more widely be used in early drug discovery, if possible already during the identification of treatment targets.No Full Tex
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