Hemodynamic consequences of common carotid artery thrombosis and thrombogenically activated blood in rats

Inflammasome-Regulated Pyroptotic Cell Death in Disruption of the Gut-Brain Axis After Stroke

Approximately 50% of stroke survivors experience gastrointestinal complications. The innate immune response plays a role in changes to the gut-brain axis after stroke. The purpose of this study is to examine the importance of inflammasome-mediated pyroptosis in disruption of the gut-brain axis after experimental stroke. B6129 mice were subjected to a closed-head photothrombotic stroke. We examined the time course of inflammasome protein expression in brain and intestinal lysate using western blot analysis at 1-, 3-, and 7-days post-injury for caspase-1, interleukin-1β, nod-like receptor protein 3 (NLRP3), and apoptosis speck-like protein containing a caspase-recruiting domain (ASC) and gasdermin-D (GSDMD) cleavage. In a separate group of mice, we processed brain tissue 24 and 72 h after thrombotic stroke for immunohistochemical analysis of neuronal and endothelial cell pyroptosis. We examined intestinal tissue for morphological changes and pyroptosis of macrophages. We performed behavioral tests and assessed gut permeability changes to confirm functional changes after stroke. Our data show that thrombotic stroke induces inflammasome activation in the brain and intestinal tissue up to 7-day post-injury as well as pyroptosis of neurons, cerebral endothelial cells, and intestinal macrophages. We found that thrombotic stroke leads to neurocognitive and motor function deficits as well as increased gut permeability. Finally, the adoptive transfer of serum-derived EVs from stroke mice into naive induced inflammasome activation in intestinal tissues. Taken together, these results provide novel information regarding possible mechanisms underlying gut complications after stroke and the identification of new therapeutic targets for reducing the widespread consequences of ischemic brain injury.

Inhibition of the inflammasome complex reduces the inflammatory response after thromboembolic stroke in mice

Inflammation is a major contributor to the pathogenesis of cerebral ischemia and stroke. In the peripheral immune response, caspase-1 activation involves the formation of a macromolecular complex termed the inflammasome. We determined whether nucleotide-binding, leucine-rich repeat, pyrin domain containing 1 (NLRP1), molecular platform consisting of capase-1, apoptosis-associated speck-like protein containing a caspase-activating recruitment domain (ASC), and NLRP1, is expressed in the normal and postischemic brain. Mice underwent thromboembolic stroke to investigate the formation of the inflammasome and subsequent activation of downstream inflammatory responses. Western blot analysis showed expression and activation of interleukin (IL) IL-1beta and IL-18 at 24 h after stroke. Size-exclusion chromatography and coimmunoprecipitation analysis showed protein association between NLRP1, ASC, caspase-1, and the X-linked inhibitor of apoptosis protein (XIAP). After ischemia, immunohistochemical analysis revealed inflammasome proteins in neurons, astrocytes, and microglia/macrophages. The potential of the inflammasome as an antiinflammatory target was showed by interference of inflammasome activation resulting in reduced cytokine levels in mice treated after ischemia with a neutralizing antibody against NLRP1. These findings show that the inflammasome complex forms after focal brain ischemia and may be a novel therapeutic target for reducing the detrimental consequences of postischemic inflammation.

The Effect of Hypothermia and Hyperthermia on Acute Brain Injury

The brain is extraordinarily susceptible to changes in temperature. Hyperthermia has been shown to exacerbate the biochemical cascade of secondary brain injury. Inversely, hypothermia limits the damaging effects of secondary brain injury. There has been a great deal of investigation regarding the detrimental effects of hyperthermia and the neuroprotection of hypothermia in animal studies. Within the last decade, clinical trials have begun to establish how the brain reacts to both temperature extremes. In the future, studies of hypothermia will continue in the quest of the optimal timing and degree of hypothermia. Hyperthermia will be examined in depth for its detrimental effects on an injured brain. Interventions for the prevention and treatment of hyperthermia will be explored. Nurses will implement cooling strategies to induce hypothermia, applying interventions to prevent complications, and they will also diagnose hyperthermia, deciding when and if to intervene pharmacologically and therapeutically. These advanced nursing actions will be guided by knowledge and understanding of available evidence. This article presents the pathophysiology of secondary brain injury and how it is affected by both hypothermia and hyperthermia. A review of the research leading up to clinical trials is explored, as well as a discussion of the future of temperature modulation for the brain injury patient. This information will help healthcare providers understand the effect that both hypothermia and hyperthermia have on the acutely injured brain.

Endothelial nitric oxide synthase pathophysiology after nonocclusive common carotid artery thrombosis in rats

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.

Temporal profile of enhanced vulnerability of the postthrombotic brain to secondary embolic events

BACKGROUND AND PURPOSE

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Delayed hypovolemic hypotension exacerbates the hemodynamic and histopathologic consequences of thromboembolic stroke in rats

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 (ICBF) 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 ICBF < 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 ICBF 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.

Thromboembolic events predispose the brain to widespread cerebral infarction after delayed transient global ischemia in rats

BACKGROUND AND PURPOSE

Transient distal platelet accumulation after common carotid artery thrombosis (CCAT) leads to hemodynamic, metabolic, and molecular events that may influence the response of the postthrombotic brain to secondary insults. We investigated how a thromboembolic insult would affect histopathological outcome when combined with an ischemic insult induced 24 hours later.

METHODS

Three groups of rats underwent either (1) CCAT+10 minutes of normothermic 2-vessel occlusion (n=6), (2) CCAT+sham ischemia procedures (n=6), or (3) sham CCAT procedures+10 minutes of 2-vessel occlusion (n=6). At 7 days, rats were perfused for quantitative histopathological and immunocytochemical analysis.

RESULTS

Rats undergoing combined insults (group 1) had significantly larger areas of ischemic injury (P<0.05) within the cerebral cortex, striatum, and thalamus compared with the other, single-injury groups. Increased ischemic damage included selective neuronal necrosis, infarction, and focal hemorrhage. By means of glial fibrillary acidic protein immunocytochemistry and lectin histochemistry, reactive astrocytes and microglia were found to be associated with widespread tissue necrosis. In contrast, infrequent infarction or CA1 hippocampal neuronal necrosis was observed in groups 2 and 3, respectively.

CONCLUSIONS

A prior thromboembolic event is a risk factor for widespread cerebral infarction and hemorrhage when combined with a delayed ischemic insult. The understanding of what factors enhance the susceptibility of the postthrombotic brain to secondary insults may aid in the development of neuroprotective strategies to be applied after transient ischemic attacks to prevent the initiation of stroke.

The effect of nitric oxide synthase inhibition on acute platelet accumulation and hemodynamic depression in a rat model of thromboembolic stroke

The relative importance of hemodynamic factors in the pathogenesis of thrombotic or embolic stroke is unclear. Of particular therapeutic interest are those substances that facilitate vasodilation and the clearance of platelet aggregates in the compromised microvasculature. A likely contributor to these functions is nitric oxide because it is known to inhibit platelet aggregability and promote vascular relaxation. To investigate the involvement of nitric oxide in the hemodynamic changes after experimental ischemia, photochemically induced nonocclusive common carotid artery thrombosis (CCAT) was studied. CCAT is a rat model of unilateral carotid artery stenosis and platelet embolization to the brain. This study characterized the acute hemodynamic consequences of CCAT and the resultant pattern of platelet deposits with and without nitric oxide synthase inhibition by nitro-L-arginine methyl ester (L-NAME). In addition, the subacute local cerebral blood flow changes were studied at 24 hours. Right CCAT was produced in 30 male Wistar rats injected with (111)In-labeled platelets. Between 5 and 15 minutes after thrombosis, rats were treated with either 15 mg/kg of L-NAME (intravenously) or saline vehicle. Hemodynamic changes were studied 30 to 45 minutes after thrombosis using [14C]iodoantipyrine autoradiography. Eight coronal levels were analyzed, and cortical and subcortical regions of interest were defined. Significant increases were observed in total platelets in the ipsilateral hemisphere after L-NAME treatment, and in the distribution of platelets in the anterior frontal and occipital cortices with nitric oxide synthase inhibition, encompassing the anterior and posterior border zone areas of the ipsilateral cortex. Otherwise, foci of labeled platelets were detected throughout the ipsilateral and contralateral hemispheres. Mean local cerebral blood flow images (n = 5) revealed a moderate bilateral global reduction in flow acutely, which normalized in the untreated thrombosed group by 24 hours. In contrast, the L-NAME-treated groups (sham and experimental) had lasting, widespread reductions in flow of approximately 25%. Pairwise comparisons between groups showed that CCAT/L-NAME was significantly different from shams in the corpus callosum and different from L-NAME shams in the internal capsule (P < 0.05) These hemodynamic and platelet accumulation changes may partially account for the aggravation of cognitive and sensorimotor deficits previously reported in this model of thromboembolic stroke.

The role of nitric oxide in the pathophysiology of thromboembolic stroke in the rat

Although nitric oxide (NO) has been shown to play an important role in the pathophysiology of cerebral ischemia, its contribution to the pathogenesis of experimentally induced thromboembolic stroke is unknown. In this study, we pharmacologically manipulated NO levels in the acute post-thrombotic stage and determined the effects on behavior and histopathology. The following drugs were used: nitro-L-arginine-methyl ester (L-NAME), a non-specific endothelial and neuronal nitric oxide synthase (eNOS and nNOS) inhibitor, 3-bromo-7-nitroindazole (7-NI), a specific inhibitor for nNOS, the NO precursor, exogenous L-arginine and the NO-donor, 3-morpholino-sydnonimine (SIN-1). Male Wistar rats (n = 76) were randomly assigned to receive vehicle or drug immediately after common carotid artery thrombosis (CCAT). Regional measurements of cortical NOS activity using the [3H]L-arginine to [3H]L-citrulline conversion assay were decreased 1 h after treatment with L-NAME and 7-NI by 50 and 65%, respectively; hippocampal NOS activity was reduced with L-NAME by 35% and with 7-NI by 65%. L-NAME significantly worsened forelimb placing as compared to other groups. 7-NI accelerated sensorimotor recovery. Water maze retention deficits were noted 48 h after CCAT and these were exacerbated by L-NAME treatment. Histopathological protection was conferred in the hippocampus by 7-NI and SIN-1; conversely, L-NAME increased neuronal injury in the contralateral cortex. L-arginine had no effect on these outcomes. In conclusion, both structural and functional consequences of CCAT can be aggravated by limiting endothelial NO production in the acutely post-thrombotic brain. In contrast, inhibition of nNOS and infusion of an NO donor has a beneficial effect on pathology.

L-arginine does not improve cortical perfusion or histopathological outcome in spontaneously hypertensive rats subjected to distal middle cerebral artery photothrombotic occlusion

The potential of nitric oxide (NO) to influence positively or negatively the outcome of mechanically induced focal cerebral ischemia is still controversial. Recent evidence suggests that NO of vascular origin, whether synthesized from exogenously administered L-arginine (L-Arg) or from NO donor compounds, is beneficial but that of neuronal origin is not. However, the therapeutic potential of NO to ameliorate stroke induced by arterial thrombosis has not been reported. We assessed the therapeutic effect of L-Arg administration in spontaneously hypertensive rats (SHR) subjected to permanent photothrombotic occlusion of the distal middle cerebral artery (dMCA). The ipsilateral carotid artery was left unligated to enhance L-Arg delivery into the putative penumbral region. Local CBF (LCBF) was assessed at 30 min by the [14C]iodoantipyrine technique (n = 9), while histological infarct volumes and index of peripheral ischemic cell change were determined at 3 days (n = 7). Rats (n = 9) given 300 mg/kg L-Arg at 18 and 3 h before photothrombotic dMCA occlusion and at 5 min afterward displayed no significant differences in LCBF compared with animals (n = 8) injected with water (the carrier vehicle) and similarly irradiated. Infarct volumes were also similar, being 37.0 +/- 9.7 mm3 (SD) in the vehicle-treated and 49.1 +/- 17.2 mm3 (SD) in the L-Arg-treated groups (both n = 7), as were assessments of ischemic neuronal density in the penumbra. In contrast, L-Arg administered intravenously in a dose of 300 mg/kg to nonischemic SHR (n = 5) increased cortical CBF by approximately 75% during a 70-min observation period. We conclude that thrombotic processes superimposed upon cerebral ischemia may facilitate tissue reactions that offset the potentially beneficial effect of L-Arg, and this caveat must be considered when proposing L-Arg for clinical treatment of focal thrombotic stroke.

Widespread hemodynamic depression and focal platelet accumulation after fluid percussion brain injury: a double-label autoradiographic study in rats

Cerebrovascular damage leading to subsequent reductions in local cerebral blood flow (lCBF) may represent an important secondary injury mechanism following traumatic brain injury (TBI). We determined whether patterns of 111-indium-labeled platelet accumulation were spatially related to alterations in lCBF determined autoradiographically 30 min after TBI. Sprague-Dawley rats (n = 8), anesthetized with halothane and maintained on a 70:30 (vol/vol) mixture of nitrous oxide/oxygen and 0.5% halothane, underwent parasagittal fluid percussion brain injury (1.7-2.2 atm). 111-Indium-tropolone-labeled platelets were injected 30 min prior to TBI while [14C]-iodoantipyrine was infused 30 min after trauma. Sham-operated animals (n = 7) underwent similar surgical procedures but were not injured. In autoradiographic images of the indium-labeled platelets, focal sites of platelet accumulation within the traumatized hemisphere were restricted to the pial surface (five of eight rats), the external capsule underlying the lateral parietal cortex (five of eight rats), and within cerebrospinal fluid (CSF) compartments (six of eight rats). In contrast, mild-to-moderate reductions in lCBF, not restricted to sites of platelet accumulation, were seen throughout the traumatized hemisphere. Flow reductions were most severe in coronal sections underlying the impact site. For example, within the lateral parietal cortex and hippocampus, lCBF was significantly reduced [p <0.01; analysis of variance (ANOVA)] from 1.71 +/- 0.34 (mean +/- SD) and 0.78 +/- 0.12 ml/g/min, respectively, versus 0.72 +/- 0.17 and 0.41 +/- 0.06 ml/g/min within the traumatized hemisphere. Significant flow reductions were also seen in remote cortical and subcortical areas, including the right frontal cortex and striatum. These results indicate that focal platelet accumulation and widespread hemodynamic depression are both early consequences of TBI. Therapeutic strategies directed at these early microvascular consequences of TBI may be neuroprotective by attenuating secondary ischemic processes.

Treatment of experimental brain injury with moderate hypothermia and 21-aminosteroids

Studies of experimental traumatic brain injury have found that histologic injury is significantly reduced and behavioral outcome improved in animals treated with moderate hypothermia (32-33 degrees C) or a 21-aminosteroid. Because these treatments are thought to work through different neurochemical mechanisms, their combined use might be expected to be more efficacious than either treatment alone. To test this hypothesis, we studied each treatment separately and in combination in a rodent model of controlled cortical contusion. Treatment with moderate hypothermia (32 degrees C for 4 h), a 21-aminosteroid (U-74389G, Upjohn, 10 mg/kg intravenously, repeated 3 h after the first dose), or both, was initiated 10, 25, or 40 min after injury. The brains were perfused 24 h after injury, and sagittal sections were stained for the 68-kDa "core" neurofilament subunit, a marker of axonal injury. The total number of positively stained axons in the ipsilateral internal capsule were counted under light microscopy. Compared with the control group (injury but no treatment), treatment with each therapy alone or combined, initiated 10 min after injury, caused significant reductions in the number of stained axons (21-aminosteroid alone-35% reduction; hypothermia alone-55% reduction; combination-48% reduction). The number of positively stained axons was significantly reduced in the aminosteroid and combination therapy groups at all three postinjury times (p = 0.01) and in the hypothermia groups treated at 10 or 25 min (p = 0.01) but not at 40 min after injury. We concluded that combination therapy with hypothermia and 21-aminosteroids was no more efficacious than either therapy alone, and that 21-aminosteroid therapy was more efficacious than hypothermia when treatment was initiated 40 min after injury.

Simplified model of krypton laser-induced thrombotic distal middle cerebral artery occlusion in spontaneously hypertensive rats

BACKGROUND AND PURPOSE

The effects of thrombotic occlusion of the middle cerebral artery on compromised ischemic tissue may be different from and more severe than those of cerebral ischemia induced by mechanical occlusion of the artery. Photothrombosis, which is based on photochemical damage to the endothelium and subsequent platelet aggregation, is an efficient method to induce thrombosis in vivo. This study aimed to improve and simplify this unique method for an ischemia model of middle cerebral artery occlusion in rats.

METHODS

Male spontaneously hypertensive rats (5 to 6 months old, 300 to 450 g) were anesthetized with halothane, endotracheally intubated, and mechanically ventilated. A krypton laser operating at 568 nm was used to irradiate the exposed distal middle cerebral artery with an intact dura above the rhinal fissure. The photosensitizing dye rose bengal (20 mg/kg body wt) was administered intravenously over 90 seconds starting simultaneously with 4 minutes of laser irradiation at a power of 20 mW to cause thrombotic occlusion of this artery.

RESULTS

The irradiated middle cerebral artery was completely occluded by intraluminal thrombi within 3 minutes after simultaneous laser irradiation and rose bengal infusion. Thrombosed materials were not stained by phosphotungstic acid-hematoxylin stain (ie, aggregated platelets lacked apparent fibrin). The mean volume of 3-day-old infarction, indicated by the lack of staining with 2,3,5-triphenyltetrazolium chloride, was 84.8 +/- 17.4 mm3 (mean +/- SD, n = 6).

CONCLUSIONS

We demonstrated a reproducible and minimally traumatic model of brain infarction induced by the thrombotic distal middle cerebral artery occlusion in rats.

Characterization of an anterior circulation rat subarachnoid hemorrhage model

BACKGROUND AND PURPOSE

Our aim was to demonstrate the feasibility of an angiographically controlled rat model for the study of macrocirculatory and microcirculatory changes of the anterior intracranial circulation after subarachnoid hemorrhage.

METHODS

Subarachnoid hemorrhage was induced by transorbital injection of 0.3 mL of nonheparinized autologous arterial blood into the chiasmatic cistern. Changes in regional cerebral blood flow were continuously recorded with the use of laser-Doppler flowmetry over the parietal cortex. Angiographic verification of middle cerebral artery diameter was performed by carotid catheterization at baseline and 2 days after injection of blood or artificial cerebrospinal fluid. We monitored intracranial and systemic blood pressure during and after injections.

RESULTS

Injection of artificial cerebrospinal fluid in the control group did not change the diameter of the middle cerebral artery. Injection of blood caused a significant arterial narrowing of 17.5%, from 0.37 +/- 0.04 mm to 0.31 +/- 0.04 mm after 2 days (P = .0001). In the control group regional cerebral blood flow decreased to 75.9 +/- 16.8% of preinjection control but quickly recovered to 99.7 +/- 19.4%. Intracranial pressure increased for 5 minutes after the injection to a maximum of 27.3 +/- 8.9 mm Hg, accompanied by a 10% decrease in mean arterial pressure. A fall in cerebral blood flow to 53.1 +/- 26.3% in blood-injected animals that recovered to only 80.7 +/- 16.9% of baseline values during the observation period of 30 minutes was noted. A peak intracranial pressure of 45.7 +/- 11.5 mm Hg occurred 2 minutes after injection with a decrease in mean arterial pressure of 13%, resulting in a markedly lower cerebral perfusion pressure than in the control group.

CONCLUSIONS

An angiographically controlled model of subarachnoid hemorrhage primarily involving the anterior circulation is feasible in the rat. The resulting narrowing of the middle cerebral artery reflects moderate vasospasm and will allow further microcirculatory studies with cranial windows.

Nonocclusive common carotid artery thrombosis in the rat results in reversible sensorimotor and cognitive behavioral deficits

BACKGROUND AND PURPOSE

Microemboli released during transient ischemic attack, stroke, and cardiac surgery are thought to cause a variety of functional deficits in humans. The purpose of this study was to characterize the type and extent of neurobehavioral deficits present after photochemically induced common carotid artery thrombosis (CCAT), a thromboembolic model of stroke in the rat that results in a platelet emboli shower.

METHODS

Thirty-two male Wistar rats were assigned to four groups. Groups 1 (n = 8) and 3 (n = 8) were long-term (6-week survival) and short-term (2-week survival) experimental groups subjected to right CCAT with the use of the photochemical technique. Groups 2 (n = 8) and 4 (n = 8) served as sham-operated controls for each experimental group. A battery of behavioral tests was applied daily beginning 24 hours after thrombosis; this consisted of elicited forelimb placing, postural reflex, beam balance, beam walking, and open field activity. Cognitive testing with a water maze task was performed on post-CCAT days 30 to 33 for groups 1 and 2 and on post-CCAT day 2 for groups 3 and 4. Ten-micrometer coronal brain sections were stained with hematoxylin and eosin, and infarct location and frequency were determined.

RESULTS

Significant sensorimotor deficits were observed, which recovered within 2 weeks after CCAT. The data that follow are derived by combining the two experimental groups and comparing these with the two sham groups. The following tests showed significant effects after CCAT: contralateral elicited forelimb placing, ipsilateral elicited forelimb placing, beam balance, and beam walking score. Cognitive dysfunction was seen acutely (group 3 animals) at 2 days after CCAT; Morris water maze length and latency to target were significantly greater in the experimental group. No deficits were seen in postural reflex, open field activity, or delayed cognitive testing. Histopathological assessment revealed small infarcts in 11 of 16 thrombosed rats. However, a strong relationship between neurobehavioral deficits and infarct location was not consistently demonstrated.

CONCLUSIONS

CCAT produces consistent sensorimotor and cognitive behavioral deficits that recover within 2 weeks of injury. Behavioral outcome was not necessarily associated with overt histopathological damage, suggesting that reversible injury mechanisms, both vascular and neuronal, may be partly responsible for the temporary loss of function. These data strengthen the role of CCAT as a clinically relevant model of thromboembolic stroke.

Complementary use of T2-weighted and postcontrast T1- and T2*-weighted imaging to distinguish sites of reversible and irreversible brain damage in focal ischemic lesions in the rat brain

The evolution of a photochemically induced cortical infarct was monitored using T2-, postcontrast (GdDOTA) T1-, and postcontrast (DyDTPA-BMA) T2*-weighted NMR imaging techniques. Data acquired with these different NMR imaging types were compared, both qualitatively and quantitatively. The T2*-weighted NMR images after spordiamide injection (DyDTPA-BMA) were perfusion-weighted images that allowed the differentiation between several infarct-related areas in terms of different degrees of perfusion deficiency. No quantitative information on cerebral blood flow (CBF) was obtained. A clear distinction was made between areas with a complete lack of CBF located in the core of the lesion and temporary CBF insufficiencies in the rim surrounding this core. Concomitant observations on T2-weighted and postcontrast T1-weighted images revealed the same temporary rim characterized by an increased water content, and an intact blood-brain barrier (BBB), as well as by reduced perfusion. This rim appeared within the first hours after infarct induction, reached a maximum 24 h later, and lasted between 3-5 days, when its size gradually decreased until complete disappearance. These observations suggest the existence of an area at risk. Only on postcontrast T1-weighted images, the core of the lesion remained visible during the whole experimental period (10 days) and reflected in all likelihood the irreversibly damaged ischemic central core. The combined application of different NMR imaging techniques when studying focal cerebral infarctions in the rat brain allowed us to distinguish, in terms of NMR characteristics, zones of reversible from irreversible brain damage and to estimate the severity of the damage. This might offer an appropriate experimental setup for the screening of cerebroprotective compounds.

Acadesine reduces indium-labeled platelet deposition after photothrombosis of the common carotid artery in rats

BACKGROUND AND PURPOSE

The adenosine-regulating agent acadesine has been shown to reduce the incidence of myocardial infarction and stroke after cardiopulmonary bypass surgery. The present study examined the effect of acadesine on the accumulation of indium-labeled platelet emboli and infarct size after photothrombosis of the common carotid artery.

METHODS

Rats were anesthetized with halothane and preloaded with 111In-tropolone-labeled platelets (50 to 80 microCi) 30 minutes before nonocclusive common carotid artery thrombosis induced by a rose bengal-mediated photochemical insult. Intravenous infusion of acadesine (0.5, 1, or 2 mg/kg per minute) or vehicle was begun 30 minutes before right common carotid artery thrombosis and continued for an additional 15 minutes. Rats were then killed and brains processed for the autoradiographic quantitation of labeled platelet aggregates. In a separate group of rats, infarct areas and volumes were determined in treated (acadesine 1 mg/kg per minute) (n = 9) and nontreated (n = 9) rats 7 days after thrombosis.

RESULTS

Although the ratio of right-to-left common carotid artery radioactivity was not affected by treatment, acadesine at 1 and 2 mg/kg per minute significantly decreased (P < .01) platelet deposition within the right cerebral cortex, hippocampus, and striatum. For example, within the frontoparietal cortex, numbers of platelet aggregates were 11.8 +/- 1.8 (mean +/- SEM), 6.1 +/- 1.4, 2.3 +/- 0.6, and 3.2 +/- 0.8 in rats infused with vehicle, 0.5, 1, and 2 mg/kg per minute acadesine, respectively. In addition, infarct volume was reduced by 48% in acadesine-treated (1 mg/kg per minute) rats, with a significant reduction in infarct area at the coronal level 3.7 mm anterior to bregma (P < .01).

CONCLUSIONS

These results support a prophylactic role for acadesine in reducing the accumulation of platelet emboli during vascular thrombosis and subsequent brain infarction. Acadesine treatment in patients at risk for embolic stroke could potentially lead to cerebral protection.

Glutamate antagonist MK-801 attenuates incomplete but not complete infarction in thrombotic distal middle cerebral artery occlusion in Wistar rats

The purpose of this study was to investigate the effects of a non-competitive N-methyl-D-aspartate antagonist, MK-801, on incomplete infarction (selective neuronal necrosis), a zone of which had been found previously in a thrombotic distal middle cerebral artery (MCA) occlusion model in Wistar rats. Male Wistar rats were treated with 1 mg/kg of MK-801 or saline 30 min before MCA occlusion. Laser irradiation with intravenous administration of Rose Bengal dye was used to cause thrombotic distal MCA occlusion. The ipsilateral common carotid artery was occluded permanently and the contralateral carotid artery for 60 min. Head temperature was controlled at 36 degrees C. Cerebral blood flow (CBF) was determined with laser-Doppler flowmetry. Three days after the ischemic insult, brains were perfusion-fixed and volumes of cortical (complete and incomplete) infarction were determined. There were no significant differences in physiological variables or CBF between the two groups. Volumes of complete infarction were equivalent between the two groups (94.9 +/- 15.6 mm3 and 91.6 +/- 14.0 mm3 in the control and MK-801 treated groups, respectively). In MK-801 treated group, the volume of incomplete infarction was reduced by 44% (6.4 +/- 1.7 mm3 vs. 3.6 +/- 2.1 mm3 in control and MK-801 treated groups, respectively, P < 0.05). Although the zone responsive to MK-801 was small in this thrombotic MCA occlusion model, our present study revealed that MK-801 has a beneficial effect on the tissue zone containing selective neuronal alterations (incomplete infarction). Our results support the concept that this drug is effective in the area of less severe ischemia.

Delayed induction of mild hypothermia to reduce infarct volume after temporary middle cerebral artery occlusion in rats

Deep to moderate hypothermia (24 degrees to 30 degrees C) during focal cerebral ischemia reduces infarct volume but must be initiated before the onset of ischemia to be effective and has deleterious pulmonary, myocardial and neurological effects. It is not known whether mild hypothermia (32 degrees to 33 degrees C) protects against ischemic neuronal damage, whether hypothermia induced after the onset of ischemia has protective effects, or whether these effects are associated with alterations in cortical blood flow. In this study, mild whole-body hypothermia was induced in rats just before or 10, 30, or 60 minutes after the onset of 2 hours of temporary middle cerebral artery occlusion; rewarming began immediately after reversal of occlusion and normothermia was maintained throughout 22 hours of reperfusion. Infarct volume, measured 24 hours after the end of reperfusion, was significantly smaller in rats made hypothermic within 30 minutes after the onset of ischemia than in normothermic controls; hypothermia induced at 60 minutes of ischemia did not reduce infarct volume. Cortical blood flow, measured by laser Doppler ultrasound flowmetry, was not significantly different between groups during ischemia; however, postischemic cortical blood flow correlated positively with total infarct volume. These results indicate that mild hypothermia initiated during temporary focal ischemia in rats can reduce infarct volume without attenuating the reduction in cortical blood flow.

Correlations between morphological changes in platelet aggregates and underlying endothelial damage in cerebral microcirculation of mice

BACKGROUND AND PURPOSE

The aim of this study was to test the hypothesis that, once formed, platelet aggregates may injure underlying cerebrovascular endothelium. Such injury could make the same site selectively attractive to the next wave of passing emboli or activated platelets. This vicious circle could account for repetitive, stereotypic symptoms in transient ischemic attacks.

METHODS

In pial arterioles, minor endothelial injury was produced by a laser/dye technique. After various periods of platelet aggregation at the damaged site, the vessels were fixed in situ for electron microscopic study. The degree of platelet activation (rounded and/or degranulated forms) was evaluated by counting these forms in the electron photomicrographs. These counts were related to the degree of endothelial damage ascertained in the micrographs. Other statistical relations were also examined.

RESULTS

Endothelial damage progressed in parallel with the duration of platelet aggregation and the degree of platelet degranulation at the site. Correlations were number of activated platelets versus degree of damage, r = .43, P < .03; duration of aggregation versus damage, r = .52, P < .01; and number of degranulated platelets versus the degree of endothelial damage, r = .83, P < .001. If an aggregate embolized, endothelial damage did not appear to progress. No correlation existed between the duration of exposure to the laser and the degree of injury.

CONCLUSIONS

The parallel between changes in platelets and endothelial damage could represent either an effect of endothelium on platelets or an effect of platelets on endothelium. Although the former alternative cannot be totally ruled out, the observations seem to fit best the hypothesis that progressive endothelial damage can result from increasing activation and degranulation of overlying platelets.

The ultrastructure of photochemically induced thrombi with embolization in a rat model

BACKGROUND AND PURPOSE

Photochemical techniques, currently used in stroke and cancer research, produce endothelial damage and thrombosis. To further characterize these thrombi and to determine whether they embolize, we studied the ultrastructure of photochemically damaged carotid arteries and small vessels distal to the irradiated carotid.

METHODS

The right carotid artery of 9 Wistar rats was irradiated with a laser (632 nm, 200 mW/cm2, 15 minutes) after the injection of the photosensitizing dye Photofrin II, 12.5 mg/kg. There were 6 additional control rats: laser only, 2 rats; dye only, 2; carrier only (5% dextrose), 1; and normal, 1. The carotid artery and cerebral arterioles were studied using scanning and transmission electron microscopy.

RESULTS

Endothelial damage was present in all irradiated carotid arteries, and consisted of exposure of the subendothelium and the formation of a nonocclusive thrombus. Although most cerebral arterioles were normal, 32 of these vessels contained peripheral blood elements, with platelet or red blood cell aggregates present in 15. The endothelium adjacent to the aggregates was intact. A few scattered endothelial cells had been lost in the carotid artery of control animals (compatible with normal cell turnover), with a few platelets adhering to the exposed subendothelium.

CONCLUSIONS

Aggregates of blood cells and platelets in cerebral vessels in the absence of endothelial denudation verifies embolism as the mechanism for cerebral vascular occlusion in this experimental model. The possibility of embolization distal to the site of photochemical irradiation has implications for potential applications of photochemistry for cancer treatment and the ablation of vascular malformations and/or aneurysms.

Transient platelet accumulation in the rat brain after common carotid artery thrombosis. An 111In-labeled platelet study

BACKGROUND AND PURPOSE

Thromboembolic events are a major cause of ischemic stroke. To obtain evidence for platelet embolization after cerebrovascular injury, the accumulation of indium-labeled platelets was documented after photothrombosis of the rat common carotid artery.

METHODS

Heterologous blood was collected from donor rats, and the isolated platelets were labeled with 111In-tropolone. Labeled platelets were then infused into Wistar rats 30 minutes before right carotid artery thrombosis. Nonocclusive common carotid artery thrombosis was induced by a laser-driven rose bengal-mediated photochemical insult to the vascular endothelium, and the rats were killed 15 minutes or 3 hours later. Carotid arteries and brains were immediately removed and dissected for regional radioactivity assessment or sectioned for the autoradiographic visualization of platelet emboli.

RESULTS

At 15 minutes after thrombosis, the ratio of right-to-left common carotid artery radioactivity was significantly elevated compared with control (33 +/- 12 [mean +/- SEM] versus 0.97 +/- 0.2). Within individual brain regions, including the frontal and frontoparietal cortices and hippocampus, significant elevations in right-to-left radioactivity ratios were also documented. Autoradiographic images revealed multiple foci of 111In-labeled platelets throughout the thrombosed hemisphere. At the level of the frontal cortex, bilateral platelet accumulation was seen. Regional counts demonstrated significantly increased platelet density within selective cortical and subcortical regions. In contrast to the 15-minute findings, right-to-left ratios of carotid arteries or brain regional radioactivities were not significantly elevated at 3 hours after injury. In addition, the areal densities of autoradiographically visualized platelets in the 3-hour group were not different from control except in the right frontal cortex.

CONCLUSIONS

These data demonstrate (1) the acute accumulation of labeled platelets in downstream vessels after nonocclusive common carotid artery thrombosis, (2) that platelet accumulation is widespread and also involves contralateral areas, and (3) that platelet accumulation within the thrombosed carotid artery and brain is largely transient.

Intraischemic but not postischemic brain hypothermia protects chronically following global forebrain ischemia in rats

We investigated whether postischemic brain hypothermia (30 degrees C) would permanently protect the hippocampus following global forebrain ischemia. Global ischemia was produced in anesthetized rats by bilateral carotid artery occlusion plus hypotension (50 mm Hg). In the postischemic hypothermic group, brain temperature was maintained at 37 degrees C during the 10-min ischemic insult but reduced to 30 degrees C starting 3 min into the recirculation period and maintained at 30 degrees C for 3 h. In normothermic animals, intra- and postischemic brain temperature was maintained at 37 degrees C. After recovery for 3 days, 7 days, or 2 months, the extent of CA1 hippocampal histologic injury was quantitated. At 3 days after ischemia, postischemic hypothermia significantly protected the hippocampal CA1 sector compared with normothermic animals. For example, within the medial, middle, and lateral CA1 subsectors, the numbers of normal neurons were increased 20-, 13-, and 9-fold by postischemic hypothermia (p < 0.01). At 7 days after the ischemic insult, however, the degree of postischemic hypothermic protection was significantly reduced. In this case, the numbers of normal neurons were increased an average of only threefold compared with normothermia. Ultrastructural analysis of 7-day postischemic hypothermic rats demonstrated CA1 pyramidal neurons showing variable degrees of injury surrounded by reactive astrocytes and microglial cells. At 2 months after the ischemic insult, no trend for protection was demonstrated. In contrast to postischemic hypothermia, significant protection was seen at 2 months following intraischemic hypothermia. These data indicate that intraischemic, but not postischemic, brain hypothermia provides chronic protection to the hippocampus after transient brain ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Failure of MK-801 to reduce infarct volume in thrombotic middle cerebral artery occlusion in rats

BACKGROUND AND PURPOSE

We examined the effects of the noncompetitive N-methyl-D-aspartate receptor antagonist MK-801 using a newly developed stroke model of thrombotic distal middle cerebral artery occlusion under conditions of carefully controlled head temperature.

METHODS

Male Sprague-Dawley rats were treated with 1 mg/kg of MK-801 or saline before the induction of ischemia. An argon laser-activated dye laser (562 nm) was used to cause thrombotic distal middle cerebral artery occlusion. In experiments 1 and 2, the single laser beam (20 mW) was separated into three beams. Each beam was positioned onto the distal middle cerebral artery at three sites along the vessel. The photosensitizing dye rose bengal (20 mg/kg) was administered intravenously over 2 minutes; the three points were then irradiated for 3 minutes. In experiment 3, higher power of the laser (three separate irradiations using a single beam of 20 mW) was used. The ipsilateral common carotid artery was occluded permanently, and the contralateral carotid artery was occluded for 60 minutes. Head temperature was controlled at 36 degrees C in experiment 1 and not controlled in experiments 2 and 3. Three days after the ischemic insult, brains were perfusion-fixed and infarct volumes were determined.

RESULTS

Head temperature was mildly hypothermic (34-35 degrees C before ischemia, with a further decrease of 1-2 degrees C during the initial 60 minutes of ischemia) in experiment 2. However, no differences were observed in head temperature between the MK-801-treated and control groups. Cortical infarct volume in experiment 1 was 89 +/- 29 mm3 (mean +/- SD) in the treated group, which was not different from the control value of 84 +/- 40 mm3. Infarct volumes were smaller (58 +/- 35 mm3 and 54 +/- 14 mm3) in the control groups of experiments 2 and 3, respectively. However, MK-801 also failed to reduce infarct volumes in experiments 2 and 3.

CONCLUSIONS

MK-801 is not effective in this stroke model of focal thrombotic infarction under conditions of either controlled (normothermic) or uncontrolled (mildly hypothermic) head temperature.

Comparative histopathologic consequences of photothrombotic occlusion of the distal middle cerebral artery in Sprague-Dawley and Wistar rats

BACKGROUND AND PURPOSE

We have developed a minimally invasive model of photothrombotic occlusion of the distal middle cerebral artery in rats and have evaluated the patterns and features of the resulting histopathologic injury in two normotensive strains.

METHODS

Food-deprived male Sprague-Dawley (n = 14) and Wistar (n = 10) rats anesthetized with halothane/nitrous oxide underwent a small craniotomy to expose the right distal middle cerebral artery just above the rhinal fissure. The animals were injected intravenously with the photosensitizing dye rose bengal, and the distal middle cerebral artery was irradiated with light from an argon laser-activated dye laser at three separate points to induce thrombotic occlusion. The ipsilateral common carotid artery was then permanently occluded, and the contralateral common carotid artery was occluded for 60 minutes. Three days later, the brains were perfusion-fixed and prepared for histopathologic examination, and infarct volume was determined by quantitative planimetry.

RESULTS

In Sprague-Dawley rats, a large consistent temporoparietal cortical infarct was observed; mean +/- SD infarct volume was 130.5 +/- 40.0 mm3 (coefficient of variation, 30.7%) and a relatively small adjacent zone of selective neuronal necrosis ("incomplete infarction"), amounting to only 9.1% of the total injury volume, was also seen. By contrast, Wistar rats had smaller and more variable cortical infarcts (volume, 48.4 +/- 26.9 mm3; coefficient of variation, 55.6%) but displayed a much more substantial zone of incomplete cortical infarction (volume, 20.8 +/- 10.1 mm3; 30.1% of the total injury volume). In neither strain was infarct size related to alterations of blood pressure. In both strains, infarcts were limited to the cortex, typically involving the parietal cortex, somatosensory cortex, and forelimb region. Three rats exhibited infarcts in the contralateral hemisphere.

CONCLUSIONS

This model has the advantages of necessitating only minimal surgery, allowing the dura to remain intact, and avoiding mechanical trauma to the brain surface. In Sprague-Dawley rats, the resulting large cortical infarct exhibited relatively small interanimal variation, making the model suitable, for example, for replicate studies of pharmacotherapy. In Wistar rats, the large zone of incomplete infarction, a unique feature heretofore undescribed in rodent models of permanent focal ischemia, lends the model to the study of the pathomechanisms underlying graded cortical ischemic injury.

Serotonin release into plasma during common carotid artery thrombosis in rats

BACKGROUND AND PURPOSE

We have tested the hypothesis that platelet-derived serotonin is released into the bloodstream during cerebrovascular thrombosis.

METHODS

Nonocclusive common carotid artery thrombosis was produced photochemically in 22 anesthetized adult male Wistar rats using the photosensitizing dye rose bengal and irradiation with an argon-pumped dye laser. Plasma serotonin levels were recorded before, during, and after photothrombosis by intra-arterial in vivo microdialysis with the probe placed distal to the site of thrombosis.

RESULTS

During and immediately after the common carotid artery thrombosis, serotonin levels increased significantly to a peak value of 781 nmol/l (p less than 0.001 by analysis of variance), representing a 15-fold increase compared with baseline levels. The increased serotonin levels gradually decreased but remained significantly elevated for 90 minutes. Ultrastructural analysis of the carotid thrombi identified a dense mass of aggregated platelets at various stages of degranulation.

CONCLUSIONS

These results are the first to demonstrate directly that serotonin accumulation occurs in plasma during and after the acute phase of common carotid artery thrombosis. Increased plasma serotonin levels may play a major role in the cerebral blood flow and blood-brain barrier abnormalities previously documented in this model of large-vessel thrombotic stroke.