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ABSTRACT: In humans and in animal models of stroke, collateral blood flow between territories of the major pial arteries has a profound impact on cortical infarct size. However, there is a gap in our understanding of the genetic determinants of collateral formation and flow, as well as the signaling pathways and neurovascular interactions regulating this flow. Previous studies have demonstrated that collateral flow between branches of the anterior cerebral artery (ACA) and the middle cerebral artery (MCA) can protect mouse cortex from infarction after middle cerebral artery occlusion. Because the number and diameter of collaterals varies among mouse strains and after transgenic manipulations, a combination of methods is required to control for these variations. Here, we report an inexpensive approach to characterizing the cerebrovascular anatomy, and in vivo monitoring of cerebral blood flow as well. Further, we introduce a new, minimally invasive method for the occlusion of distal MCA branches. These methods will permit a new generation of studies on the mechanisms regulating collateral remodeling and cortical blood flow after stroke.
Translational Stroke Research 03/2011; 2(1):112-127.
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ABSTRACT: A BODIPY-spiropyran dyad was embedded within poly(methyl methacrylate) films spin-coated on glass slides. Visible illumination of the resulting materials excites selectively the BODIPY fragment, which then deactivates radiatively by emitting light in the form of fluorescence. Ultraviolet irradiation promotes the isomerization of the spiropyran component to the corresponding merocyanine. This photoinduced transformation activates electron and energy transfer pathways from the fluorescent to the photochromic fragment. Consistently, the BODIPY fluorescence is effectively suppressed within the photogenerated isomer. As a result, ultraviolet illumination with a laser, producing a doughnut-shaped spot on the sample, confines the fluorescent species within the doughnut hole. This behavior is an essential requisite for the implementation of super-resolution imaging schemes based on fluorescence photodeactivation. Thus, the operating principles governing the photochemical and photophysical response of this molecular switch can ultimately lead to the development of innovative probes for fluorescence nanoscopy.
Physical Chemistry Chemical Physics 10/2010; 12(37):11630-4. · 3.57 Impact Factor
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ABSTRACT: Many stroke research groups utilize the model of middle cerebral artery occlusion induced by insertion of an intraluminal thread, owing to its pragmatism and reliability of cerebral infarct generation. However, 75% of stroke cases result from a thromboembolic event and 10% from occlusive atherothrombosis in situ. Here, we characterize a mouse model of repeated thromboembolic stroke, which closely mimics the intravascular pathophysiology of arterial thrombus generation from an atherosclerotic plaque, and subsequent release of a thrombus into the cerebral circulation as an embolus. Common carotid artery thrombosis (CCAT) was induced photochemically leading to non-occlusive platelet aggregation in C57/BL6 male mice (n=35), and was followed by mechanical assistance to facilitate release of the thrombus (MRT) and thus promote embolism. Six experimental groups, differing by changes in the surgical protocol, were used for the purpose of determining which such procedure yielded the most reliable and consistent brain infarct volumes with the lowest mortality at 3 days after surgery. The group which best satisfied these conditions was a double insult group which consisted of animals that underwent CCAT for 2 min by means of argon laser irradiation (514.5 nm) at an intensity of ca. 130 W/cm(2), with concomitant injection of erythrosin B (EB) (35 mg/kg infused over those same 2 min), followed by MRT 1 min later; the entire procedure was repeated 24h later. This group showed a percent of brain lesion volume of 15+/-4% (mean+/-S.D.) with no associated 3-day mortality. Compared to a single insult group which sustained a percent brain lesion volume of 7+/-3%, there was a statistically significant (p<0.05) increase in the volume of infarction in the double-insult group.
Journal of Neuroscience Methods 06/2007; 162(1-2):244-54. · 1.98 Impact Factor
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ABSTRACT: The pathophysiology of stroke in humans is much more complex than what is typically studied in animal models. Embolic stroke models are more complex than pure ischemia models, but are more representative of human disease and may be particularly useful in the study of new therapeutic strategies. Vascular damage is a prominent feature of embolic stroke, and may be a useful therapeutic target. Serotonin antagonists, adenosine-regulating agents, free radical scavengers, matrix metalloproteinase inhibitors, and HMG-CoA reductase inhibitors are all potentially valuable agents in treating vascular damage after stroke. These agents facilitate decreased infarction volume, hemorrhage, and improved cerebral bloodflow.
Current opinion in investigational drugs (London, England: 2000) 07/2002; 3(6):896-904. · 3.31 Impact Factor
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ABSTRACT: Although vascular dysregulation has been documented in patients with extracranial vascular disease, transient ischemic attacks, and stroke, the pathomechanisms are poorly understood. To model thromboembolic stroke in rats, photochemically induced nonocclusive common carotid artery thrombosis (CCAT) was used to generate a platelet thrombus in the carotid artery of anesthetized rats. After CCAT, platelet aggregates break off the thrombus, travel to the distal cerebral vasculature, damage blood vessels, and cause small infarctions. The authors hypothesized that deficits in the endothelial nitric oxide synthase (eNOS) pathway may be responsible for vascular dysfunction after embolic stroke. To examine the functional status of the eNOS system, they measured eNOS-dependent dilation after CCAT by applying acetylcholine through a cranial window over the middle cerebral artery. The authors also measured eNOS mRNA and protein in the middle cerebral artery to determine whether functional changes were caused by alterations in expression. eNOS-dependent dilation was reduced at 6 hours, elevated at 24 hours, and returned to baseline 72 hours after CCAT. Endothelial nitric oxide synthase mRNA increased at 2 hours and was followed by a rise in protein 24 hours after CCAT. Changes in the eNOS system may account for some of the observed vascular deficits in patients with cerebrovascular disease.
Journal of Cerebral Blood Flow & Metabolism 06/2002; 22(5):612-9. · 5.01 Impact Factor
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ABSTRACT: Patients with vascular or cardiac disease may experience recurrent thrombosis and embolization to the cerebral vasculature. Transient distal platelet accumulation after common carotid artery thrombosis (CCAT) leads to hemodynamic, metabolic, and molecular events that may influence the response of the postthromboembolic brain to secondary emboli. We investigated the effect of repeated embolic episodes on histopathological outcome at various time intervals using a clinically relevant model of embolic stroke.
Six groups of rats underwent either photochemically induced CCAT followed by sham surgery or 2 episodes of CCAT separated by 10 minutes or 1, 3, 5, or 7 days. Outcome measures included routine histopathological analysis and determination of the number of infarct loci and their total volume.
Rats that underwent a second CCAT at 1, 3, or 5 days after the first insult had 20 to 30 times larger infarct volumes than rats in the single-CCAT group (P<0.05). In addition, rats in the 10-minute and 1-, 3-, and 5-day groups had 2 to 3 times as many infarcts as those in the single-CCAT group (P<0.05). Infarcts produced by double insults commonly extended through the neuraxis and were necrotic, edematous, and sometimes hemorrhagic.
A prior thromboembolic event puts the brain at risk for severe infarction after a second embolic event. These findings cannot be explained solely by a greater number of infarcts. Elucidating pathomechanisms responsible for the vulnerability of the postthromboembolic brain may provide targets for new treatment strategies to prevent the severe consequences of embolic stroke.
Stroke 04/2002; 33(4):1113-9. · 5.73 Impact Factor
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ABSTRACT: A reversible model of focal thrombotic stroke was developed in the rat and examined for histological evidence of reperfusion injury after clinically relevant times of recanalization.
The distal middle cerebral artery of 28 male Sprague-Dawley rats was occluded by 562-nm laser-driven photothrombosis for 0.5, 2, and 3 hours or permanently (each n=7) and was recanalized by 355-nm UV laser irradiation. Occlusive material was examined by transmission electron microscopy. Cortical cerebral blood flow was monitored by laser-Doppler flowmetry. Brain infarcts were examined histologically at 3 days.
After occlusion, cortical cerebral blood flow was reduced to 33+/-4% of baseline for all groups and was restored to 82+/-9%, 75+/-3%, and 93+/-7% of baseline for the 0.5-, 2-, and 3-hour groups, respectively, following recanalization after 29+/-8, 38+/-20, and 70+/-33 minutes of UV laser irradiation. The thrombotic occlusion contained compactly aggregated platelets but no fibrin, with length (1.2 to 1.8 mm) proportional to the ischemic period. During recanalization, microchannels containing erythrocytes and scattered leukocytes and bordered by intact disaggregated platelets infiltrated the thrombus. Infarct volumes (mm3) at 3 days were 12+/-3 for the permanent case and 8+/-4, 24+/-3, and 30+/-9 for the 0.5-, 2-, and 3-hour cases, respectively, thus demonstrating reperfusion injury histologically in the latter 2 groups. No hemorrhage was seen.
UV laser-facilitated dissolution of a conventionally refractory platelet thrombus provides a novel and effective method for restoring blood flow without hemorrhagic complications during thrombotic stroke. This was the first observation of histologically confirmed reperfusion injury in such a model.
Stroke 03/2002; 33(2):428-34. · 5.73 Impact Factor
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ABSTRACT: Abnormalities in cerebrovascular reactivity or hemodynamic reserve are risk factors for stroke. The authors determined whether hemodynamic reserve is reduced in an experimental model of thromboembolic stroke. Nonocclusive common carotid artery thrombosis (CCAT) was produced in rats by a rose bengal-mediated photochemical insult, and moderate hypotension (60 mm Hg/30 min) was induced 1 hour later by hemorrhage. Alterations in local cerebral blood flow (lCBF) were assessed immediately after the hypotensive period by 14C-iodoantipyrine autoradiography, and histopathologic outcome was determined 3 days after CCAT. Compared to normotensive CCAT rats (n = 5), induced hypotension after CCAT (n = 7) led to enlarged regions of severe ischemia (i.e., mean lCBF < 0.24 mL/g/min) in the ipsilateral hemisphere. For example, induced hypotension increased the volume of severely ischemic sites from 16 ± 4 mm3 (mean ± SD) to 126 ± 99 mm3 (P < 0.05). Histopathologic data also showed a larger volume of ischemic damage with secondary hypotension (n = 7) compared to normotension (22 ± 15 mm3 versus 5 ± 5 mm3, P < .05). Both hypotension-induced decreases in lCBF and ischemic pathology were commonly detected within cortical anterior and posterior borderzone areas and within the ipsilateral striatum and hippocampus. In contrast to CCAT, mechanical ligation of the common carotid artery plus hypotension (n = 8) did not produce significant histopathologic damage. Nonocclusive CCAT with secondary hypotension therefore predisposes the post-thrombotic brain to hemodynamic stress and structural damage.Keywords: Autoregulation; Cerebral blood flow; Embolic stroke; Platelets; Thrombosis
Journal of Cerebral Blood Flow & Metabolism 07/1999; 19(8):918-926. · 5.01 Impact Factor
