Animal model of TIA: an experimental study with intracarotid ADP infusion in rabbits

Animal models of transient ischemic attack: a review

Transient ischemic attack (TIA) is defined as a brief episode of neurological dysfunction caused by focal cerebral ischemia. TIA is a critical early warning signal of stroke. Patients with TIA may have long-term cognitive decline. The pathogenesis and pathological changes of TIA have not been fully elucidated. Animal models can simulate the process of human diseases and are essential tools to investigate injury mechanisms and therapeutic approaches of TIA. Most TIA animal models are based on ischemic stroke models and the definition of TIA. Each model has unique strengths and weaknesses. The establishment of a successful and reliable TIA model should follow three criteria: (1) objective evidence of cerebral arteries occlusion and reperfusion, (2) no permanent neurological deficit, and (3) no acute cerebral infarction. However, experimental animal models are impossible to be completely consistent with human TIA, because TIA itself is a heterogeneous disease. In the present review, the selection of animals, methodological development, and evaluation of cerebral blood flow of animal models of TIA are comprehensively evaluated.

Molecular magnetic resonance imaging discloses endothelial activation after transient ischaemic attack

SEE SUN ET AL DOI101093/AWW306 FOR A SCIENTIFIC COMMENTARY ON THIS ARTICLE: About 20% of patients with ischaemic stroke have a preceding transient ischaemic attack, which is clinically defined as focal neurological symptoms of ischaemic origin resolving spontaneously. Failure to diagnose transient ischaemic attack is a wasted opportunity to prevent recurrent disabling stroke. Unfortunately, diagnosis can be difficult, due to numerous mimics, and to the absence of a specific test. New diagnostic tools are thus needed, in particular for radiologically silent cases, which correspond to the recommended tissue-based definition of transient ischaemic attack. As endothelial activation is a hallmark of cerebrovascular events, we postulated that this may also be true for transient ischaemic attack, and that it would be clinically relevant to develop non-invasive in vivo imaging to detect this endothelial activation. Using transcriptional and immunohistological analyses for adhesion molecules in a mouse model, we identified brain endothelial P-selectin as a potential biomarker for transient ischaemic attack. We thus developed ultra-sensitive molecular magnetic resonance imaging using antibody-based microparticles of iron oxide targeting P-selectin. This highly sensitive imaging strategy unmasked activated endothelial cells after experimental transient ischaemic attack and allowed discriminating transient ischaemic attack from epilepsy and migraine, two important transient ischaemic attack mimics. We provide preclinical evidence that combining conventional magnetic resonance imaging with molecular magnetic resonance imaging targeting P-selectin might aid in the diagnosis of transient ischaemic attack.

Protective effects of SM-20302, an orally active GPIIb/IIIa antagonist, in an ADP/epinephrine-induced guinea pig model of transient cerebral ischemia

The potential benefits of SM-20302, (2S)-3-(3-(4-amidinobenzoylamino)propanoylamino)-2-(4-ethyl)benzensulfonylaminopropionic acid hydrochloride, a nonpeptide GPIIb/IIIa receptor antagonist, were compared with those of aspirin and ticlopidine in a transient cerebral ischemia model in guinea pigs. Transient cerebral ischemia was induced in guinea pigs by an infusion of ADP/epinephrine into the left internal carotid artery. Each compound was orally administered 1 h (SM-20302 and aspirin) or 3 h (ticlopidine) before the ADP/epinephrine infusion. The ischemic area in coronal brain slices was assessed 1 min after the cessation of ADP/epinephrine infusion by a carbon black perfusion method. In a separate experiment, neurological deficits and lactate contents of ipsilateral hemispheres were evaluated 60 min after the cessation of ADP/epinephrine infusion by neurological scores and the standard enzymatic method, respectively. SM-20302 (0.3 and 1 mg/kg p.o.) significantly reduced the ischemic area, neurological deficits and lactate contents in comparison with the vehicle control. Aspirin (100 mg/kg po) had no significant effect on either parameter. Ticlopidine (300 mg/kg p.o.) reduced the lactate content. Although a combination of aspirin (100 mg/kg p.o.) and ticlopidine (300 mg/kg po) also reduced the lactate content, no additive effect was observed. These results suggest that SM-20302 is of potential clinical benefit in the treatment of thromboembolic diseases.

A qualitative study on changes in local brain pH due to discrete cerebral microembolism

In this work autoradiography of 14C-5,5-dimethyl-2,4-oxazolidinedione (14C-DMO) was used to trace changes in local cerebral pH in embolized awake rabbits. One hour after i.v. injection of 14C-DMO small cerebral ischemic foci were produced in rabbits by injecting plastic beads into the left heart ventricle under short-acting anaesthesia, and after another hour the animals were put to death and their brains processed for autoradiography of 14C-DMO. Evidence of acidosis was in general not found in the microischemic regions, though there were a few possible exceptions. However in the hippocampus a diffuse acidosis involving a large part of the structure, could be found in 2 of the 4 experiments. This hippocampal phenomenon probably reflected the same process as has been observed using autoradiography of 2-deoxyglucose (reflecting cellular glucose uptake) on the same ischemic model increased 2-deoxyglucose phosphorylation. Because the hippocampus is involved in the memory function and the fact that small infarcts are coupled to dementia, this phenomenon should be drawn into focus for further studies.

Effects of hyperglycemia on small cerebral infarctions in awake rabbits

This study concerns the effects of hyperglycemia on small infarctions in the rabbit brain. Small ischemic foci were produced in both normoglycemic (6 mM) and hyperglycemic (25 mM) rabbits, by injecting small plastic beads into the left heart ventricle under short-acting anaesthesia. 2-deoxy-D-[14C]glucose (2-DG) autoradiography was used to trace ischemic regions in which glucose uptake was increased, either shortly after, or six hours after, the embolization (in awake rabbits). A lesion was characterized by a 2-DG activity > 120%. The obtained freeze-dried sections were inspected for infarcts (with lost tissue structure and increased transparency to light). In the short experiments (< 1 hour), lesions could be detected throughout the brains, indicating hypoxic regions with enhanced glycolysis. In some foci, mostly located in the basal ganglia (the region containing the largest lesions), a central dip could be seen in the 2-DG accumulation, suggesting a poor glucose supply to the ischemic core. The lesions in the basal ganglia of rabbits that were made hyperglycemic were smaller and did not show such dips. No infarcts could be found in the tissue sections. In the long experiments (6 hours), both infarcts and lesions could be found. The impact of hyperglycemia on the infarction process in different brain regions was evaluated by measuring the infarct volumes, and by evaluating the fraction of infarcts--number of infarcts found in freeze-dried sections/number of foci (both lesions and infarcts) found in the 2-DG autoradiograms. Hyperglycemia reduced the fraction of infarcts in the cortex, and reduced the size of infarcted areas in the brain stem. In summary, this study shows that the impact of hyperglycemia on the ischemic outcome depends on where in the brain the ischemic focus is located. This adds interesting information as to what is known about the general effects of glucose on cerebral ischemia.

Prostacyclin analogue TTC-909 reduces memory impairment in rats with cerebral embolism

The effects of the stable prostacyclin analogue TTC-909 on memory impairment in the water maze task and on neuronal damage were studied in rats with cerebral embolism induced by injecting polyvinyl acetate (PVA) into the right internal carotid artery and the ensuing embolism extending out into the right middle cerebral artery. Areas supplied by the lenticulostriate artery were most markedly damaged. In the water maze test, the PVA-embolized rats took longer to reach the platform than did the nontreated control rats. To some extent, repeated administrations of TTC-909 (200 ng/kg, IV) overcame this impairment in water maze learning in the rats. We assume that the vasodilating effects of TTC-909 maintain this blood supply to the ischemic area and that TTC-909 prevents the development of thrombosis around the PVA particles in the arterial capillaries, as a result of antiplatelet aggregative effects. These two mechanisms are likely to be involved in memory improvement. TTC-909 may prove effective for treating subjects with stroke and other cerebrovascular disorders.

Leukocyte-induced acute endothelial dysfunction in middle cerebral artery in rabbits. Response to aggregating platelets

BACKGROUND AND PURPOSE

Recent evidence suggests a possible role for leukocytes in angiospastic reactions of large cerebral arteries. This study examined the effect of activation of endogenous circulating leukocytes on endothelium-dependent relaxation in the middle cerebral artery in rabbits.

METHODS

Leukocytes were activated by rapid injection of either 40 micrograms/kg phorbol 12-myristate 13-acetate, or 0.2 mg/kg N-formyl-methionyl-leucylphenylalanine into the left carotid artery. Control rabbits received an equal volume of vehicle. Concentration-dependent isometric tension responses of the left and right middle cerebral artery to the dilators acetylcholine, ADP, sodium nitroprusside, or calcium ionophore (A23187), as well as to aggregating platelets, were compared in vitro in control animals and in animals killed 10 minutes after the injection of leukocyte activators in normal and leukocyte-depleted rabbits.

RESULTS

In the control animals there was no significant difference in the reactivity of the left and right middle cerebral arteries. The injection of the leukocyte activators led to enhanced contractile responses to aggregating platelets and a significant reduction in the endothelium-dependent relaxation in response to acetylcholine, ADP, and A23187 in the left middle cerebral artery (the injected side), whereas the effect of an endothelium-independent dilator sodium nitroprusside remained unchanged. In leukocyte-depleted rabbits the injection of either of the leukocyte activators used did not induce significant changes in the reactivity of the left middle cerebral artery.

CONCLUSIONS

Intravascular leukocyte activation appears to induce an acute disturbance of the endothelium-dependent relaxation. Under these conditions, platelet activation might result in marked angiospastic reactions of large cerebral arteries.

Endothelial dysfunction in cerebral vessels following carotid artery infusion of phorbol ester in rabbits: the role of polymorphonuclear leukocytes

The effect of 4 beta-phorbol-12 beta-myristate-13 alpha-acetate (PMA) on endothelium-dependent and endothelium-independent vasoconstriction and vasodilation was studied in isolated segments of rabbit middle cerebral artery (MCA). Concentration-dependent responses of the left and right MCA to the constrictors KCl, noradrenaline, uridine 5'-triphosphate, serotonin, and histamine, as well as to the dilators acetylcholine, bradykinin, sodium nitroprusside, and calcium ionophore (A23187), were compared in control animals and after PMA injection into the left common carotid artery. In the control animals there was no significant difference in the responses of the left and right MCA to either the constrictors or the dilators studied. After PMA injection the endothelium-dependent relaxation in response to acetylcholine, bradykinin, and A23187 was reduced in the left MCA (PMA-injected side), whereas the effect of the endothelium-independent dilator sodium nitroprusside remained unchanged. Simultaneously greater contractile responses of the left MCA to serotonin and histamine were obtained. Neither infusion of L-arginine in vivo before the PMA injection nor incubation of the isolated MCA segments with L-arginine affected this difference in MCA reactivity. Platelet depletion did not change the PMA-induced reduction in the endothelium-dependent relaxation, whereas after leukocyte depletion this reduction practically disappeared. These results suggest that the PMA-induced brain microembolia causes acute endothelial dysfunction, which is possibly mediated by intravascular activation of leukocytes and is independent of nitric oxide synthesis from L-arginine. This phenomenon might play an important role in cerebral angiospastic disorders after intravascular activation of leukocytes in cerebral ischemia and reperfusion.

Fibrin content of carotid thrombi alters the production of embolic stroke in the rat

BACKGROUND AND PURPOSE

Mechanical denudation of the endothelium of the carotid artery in animals produces a nonocclusive thrombus, but the brains of these animals have not been examined for the presence of embolic stroke.

METHODS

The endothelium of the right carotid artery of 16 Wistar rats was denuded using a balloon catheter. Phosphotungstic acid hematoxylin (PTAH) staining and scanning electron micrographs of the nonocclusive thrombi in the carotid arteries were compared with those produced by photochemical methods, and brains were examined for infarcts.

RESULTS

Although nonocclusive thrombi were present in the carotid arteries of 4 of 4 rats killed at 4 hours and in 8 of 12 killed at 24 hours, neither cerebral infarcts nor emboli were seen in the 14 brains evaluated by light microscopy. PTAH demonstrated a high fibrin content in the thrombus produced by the endothelial denudation, with almost no fibrin seen in photochemically induced thrombi. Scanning electron microscopy confirmed dense networks of fibrin in the thrombi produced by balloon denudation.

CONCLUSIONS

The composition of a nonocclusive thrombus may determine the embolic potential of this thrombus. A low fibrin content in a nonocclusive platelet thrombus may enhance the embolic potential. This suggests that platelet inhibition may also be indicated in patients with carotid artery disease who are being treated with anticoagulant.

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.

Impairment of anti-platelet-aggregating activity of endothelial cells after experimental subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Serial changes of anti-platelet-aggregating activity in the endothelial cells after experimental subarachnoid hemorrhage were studied in 30 feline two-hemorrhage models.

METHODS

One hour or 2, 4, 7, or 14 days after mimic subarachnoid hemorrhage, ADP (40 mg/kg) was infused into the basilar artery via the right vertebral artery to activate circulating platelets. Immediately after ADP infusion, the basilar artery was fixed by intra-arterial perfusion with 1.5% glutaraldehyde in 0.1 mol/L phosphate buffer and was removed. The luminal surface was examined under a scanning electron microscope.

RESULTS

One hour after subarachnoid hemorrhage, no platelets adhered or aggregated on the luminal surface. However, 4 to 7 days after subarachnoid hemorrhage, many platelets were observed adhering or aggregating on the luminal surface.

CONCLUSIONS

These findings suggest the impairment of anti-platelet-aggregating activity of endothelial cells after subarachnoid hemorrhage. This impairment may be involved in inducing cerebral ischemia during cerebral vasospasm by causing platelet adhesion and aggregation.

Effect of Y-20811, a thromboxane synthetase inhibitor, on photochemically induced cerebral embolism in rabbits

The effect of Y-20811, a selective thromboxane A2 synthetase inhibitor, was investigated on cerebral embolism using a new model of embolic cerebral infarction in rabbits. Most of cerebral infarctions were observed in the hemisphere, ipsilateral to the irradiated carotid artery. Cerebral infarction, ranging from 0.2 to 1.0 mm in size, appeared only on the surface of the cortex. The platelet emboli were identified in the carotid artery and cortex arteriole by light microscopy. In our study, 83% of the control group had cerebral infarction. Y-20811 significantly suppressed the infarction number and the incidence at doses of 1 mg/kg and 10 mg/kg (p.o.), respectively. Aspirin significantly inhibited the infarction number at a dose of 10 mg/kg, but its inhibitory effect decreased at 30 mg/kg. Ticlopidine showed no effect even at a dose of 300 mg/kg. These results indicate that Y-20811 may be useful in preventing embolic cerebral infarction and transient ischemic attacks.

Inhibition of nitric oxide synthesis increases focal ischemic infarction in rat

We investigated whether inhibition of nitric oxide (NO) biosynthesis with N-omega-nitro-L-arginine (NNA), a competitive inhibitor of NO synthase (NOS), would modify the volume of the focal ischemic infarction produced by occlusion of the middle cerebral artery (MCA) in spontaneously hypertensive rats. NNA was infused for 1 h (2.4 mg/kg/h) immediately following occlusion of the MCA. NNA increased lesion volume 24 h later by 32% over controls (150.8 +/- 16.6 to 199.2 +/- 17.4 mm3; p less than 0.001, n = 6). This effect was antagonized by co-infusion of L- but not D-arginine. The antihypertensive rilmenidine (0.75 mg/kg) reduced the lesion by 27% (p less than 0.05, n = 4). Changes in lesion size were confined to the penumbra. NNA increased arterial pressure (AP) (118 +/- 8.9 to 149 +/- 16.0 mm Hg; p less than 0.01, n = 3) but did not change regional CBF. However, elevation of AP did not change the lesion volume or distribution. We conclude that inhibition of the constitutive form of NOS in vivo increases the volume of focal ischemic infarction as a consequence of reduced NO biosynthesis. The absence of NO availability may extend lesion formation by inhibition of reactive hyperemia, platelet disaggregation, and/or release of neuroprotective neuromodulators in the penumbra, which may counteract and override any of its neurotoxic actions.

Platelet ultrastructure and secretion in acute ischemic stroke

We used transmission electron microscopy to count the organelles (dense bodies, alpha granules, and mitochondria) contained within platelets from 11 acute ischemic stroke patients and 12 healthy controls. We randomly selected for evaluation 25 platelet profiles in ultrathin sections cut from three separate blocks. Compared with those from controls, platelets from stroke patients contained significantly fewer alpha granules (p less than 0.001) and mitochondria (p less than 0.02) and showed a trend toward fewer dense bodies. Supportive of our previous studies, the amount of adenosine triphosphate secreted following stimulation by collagen also tended to be greater in platelets from stroke patients. These observations support the presence of increased platelet secretion associated with acute cerebral infarction and raise the possibility that platelet secretion may be of separate importance to the mechanical occlusion of blood vessels by platelet aggregates in the pathogenesis of cerebral infarction.

Whole blood platelet function in acute ischemic stroke. Importance of dense body secretion and effects of antithrombotic agents

We studied platelet function in whole blood, a situation that better reflects the in vivo state, from 85 patients with acute ischemic stroke and from 19 healthy controls. Patients receiving no antithrombotic drugs demonstrated increased platelet dense body secretion without an associated increase in platelet aggregation, thus raising the possibility that dense body secretion may be of separate importance in cerebral infarction. Our results also suggest that dense body secretion may occur independently of aggregation. Heparin and heparin plus warfarin were ineffective in reducing the high level of dense body secretion seen in acute cerebral infarction, whereas treatment with aspirin plus dipyridamole inhibited both dense body secretion and platelet aggregation. It seems worthwhile to investigate the usefulness of antiplatelet drugs in the treatment of acute ischemic stroke wherein clinical outcome is correlated with the extent of suppression of platelet dense body secretion.

A new model of embolic stroke produced by photochemical injury to the carotid artery in the rat

We report a new model of embolic stroke in the rat, based on endothelial disruption and platelet aggregation in the carotid artery, which leads to distal embolization and focal brain infarction. The common carotid artery was irradiated for 6.5 minutes with the focused beam of an argon laser operated at a wavelength of 514.5 nm with a peak power of 2 W and an average power of 400 mw. Ipsilateral cerebral infarcts, ranging in size from 0.1 to 1.7 mm, were produced by platelet emboli in 12 of 13 rats. A total of 44 infarcts were observed in the 12 rats: 29 in the cortex, 6 in the hippocampus, 5 in the thalamus, and 4 in the basal ganglia. Scanning electron microscopy identified platelet aggregates in the carotid artery and in a deep cortical arteriole 50 minutes after the photochemical lesion. Twenty-four hours after the experiment, scanning electron microscopy of the carotid artery revealed damaged endothelium but few remaining adherent platelets. More intense laser irradiation in 8 rats, leading to carotid occlusion, produced an infarct in only 1. This new model can be used to study the acute and chronic pathological changes in the brain associated with platelet embolism.

Experimental model for repetitive ischemic attacks in the gerbil: the cumulative effect of repeated ischemic insults

An experimental model for repeated ischemic attacks, which allows easy induction of cerebral ischemia of any desired duration and frequency, has been developed in the gerbil. With this procedure, a pronounced cumulative effect on development of edema and tissue injury was observed using 3 separate, 5-min bilateral occlusions of the common carotid arteries spaced at various time intervals. This effect was most evident when the occlusions were carried out at 1-h intervals, i.e., during the period of marked postischemic hypoperfusion. Such animals, killed after 24 h of recirculation, showed significantly more severe edema and brain tissue injury in the areas exposed to ischemia than was observed in animals killed 24 h after single 5- or 15-min occlusions. The changes of regional CBF, assayed with a [3H]nicotine method, indicated a relatively rapid onset of hypoperfusion of similar degree after each release of arterial occlusion. The hypoperfusion recovered significantly within 6 h of recirculation following either single or multiple occlusions, and no residual hypoperfusion was observed in animals which, when killed at 24 h, showed severe edema and brain tissue injury. This model should prove useful in elucidating the pathophysiological mechanisms operative in repetitive cerebral ischemia.

Experimental acute thrombotic stroke in baboons

To study the effects of antithrombotic therapy in experimental stroke, we have characterized a baboon model of acute cerebrovascular thrombosis. In this model an inflatable silastic balloon cuff has been implanted by transorbital approach around the right middle cerebral artery (MCA), proximal to the take-off of the lenticulostriate arteries (LSA). Inflation of the balloon for 3 hours in six animals produced a stereotypic sustained stroke syndrome characterized by contralateral hemiparesis. An infarction volume of 3.2 +/- 1.5 cm3 in the ipsilateral corpus striatum was documented by computerized tomographic (CT) scanning at 10 days following stroke induction and 3.9 +/- 1.9 cm3 (n = 4) at 14 days by morphometric neuropathologic determinations of brain specimens fixed in situ by pressure-perfusion with 10% buffered formalin. Immediate pressure-perfusion fixation following deflation of the balloon was performed in 16 additional animals given Evans blue dye intravenously prior to the 3 hour MCA balloon occlusion. Light microscopy and transmission electron microscopy consistently confirmed the presence of thrombotic material occluding microcirculatory branches of the right LSA in the region of Evans blue stain, but not those of the contralateral corpus striatum. When autologous 111In-platelets were infused intravenously in four animals from the above group prior to the transient 3 hour occlusion of the right MCA, gamma scintillation camera imaging of each perfused-fixed whole brain demonstrated the presence of a single residual focus of 111In-platelet activity involving only the Evans blue-stained right corpus striatum. Focal right hemispheric activity was equivalent to 0.55 +/- 0.49 ml of whole blood, and the occlusion score derived from histologic examination of the microcirculation of the Evans blue-stained corpus striatum averaged 34.8 +/- 2.8. Similar 111In-platelet imaging and histologic scoring experiments carried out in four animals pretreated with the antithrombotic combination heparin and ticlopidine showed marked reduction of both 111In-platelet activity (0.01 +/- 0.03 ml vs. 0.55 +/- 0.49 ml; p less than 0.01) and thrombotic occlusion of the microcirculation (10.8 +/- 7.4 units vs. 34.8 +/- 2.8 units; p less than 0.01) in the right corpus striatum following 3 hours of MCA occlusion. In separate control experiments 111In-labeled autologous platelets were infused after the 3 hour period of right MCA occlusion and subsequent balloon deflation in two animals; no focus of 111In-platelet activity was demonstrated in fixed whole brain.(ABSTRACT TRUNCATED AT 400 WORDS)

Cerebral embolization leads to memory impairment of several learning tasks in rats

The effects of cerebral embolization, produced by injecting microspheres into the left internal carotid artery, on passive and active avoidance tasks and water filled multiple T-maze task, were studied in male Wistar rats. The rats with cerebral embolization were markedly impaired acquisition and retention of the one-trial passive avoidance response. The impairment depended on the number of microspheres injected and continued for 2 weeks. The cerebral embolized rats were also impaired acquisition of two-way active avoidance response in a shuttle box. These impairments are not due to decrease in shock sensitivity, because there was no significant change in the flinch-jump threshold. The embolized rats also exhibited a significant disturbance in performance of water filled multiple T-maze learning. These results suggest that rats with cerebral embolization are impaired in three different types of learning tasks, and may be useful as an animal model for the vascular type of dementia.

Cerebrovascular injuries induced by activation of platelets in vivo

Intravascular platelet aggregation induced by ADP injection into the carotid artery of rabbits caused ipsilateral cerebrovascular injuries. We have observed the details of these in vivo vascular changes under the electron microscope. Intracytoplasmic vacuole (1.0-2.0 micron in diameter) formation and partial deendothelialization followed by platelet thrombus formation were characteristic changes in the middle cerebral artery. These vacuoles did not contain horseradish peroxidase (HRP) which was used as a marker of vascular permeability change. Compared with these phenomenon, increased vesicular (0.05-0.2 micron in diameter) transport was prominent, and vacuole formation was rarely seen in small vessels, namely, capillaries and arterioles in the cortex. Endothelial cell damage seemed to be more prominent in large arteries, but only the smaller vessels show marked extravasation of HRP-reaction product and perivascular edema. Blood levels of TXB2 and 6-keto PGF1 alpha were significantly increased 3 min after the ADP injection and returned to pre-injection levels at 60 min after. These results suggest that vasoactive substances resulting from platelet activation may play an important role in producing cerebrovascular injuries caused by platelet aggregation induced with ADP.

The clinical use of platelet scintigraphy with 111-In-oxine

Platelet scintigraphy was performed on 62 patients with cerebral ischaemia. Pathological scintigraphic images were obtained in 29 of the 62 patients. In 79.3% of these 29 patients the scan was abnormal in the vessel clinically affected. Platelet scintigraphy was abnormal in 21 of 34 patients with normal angiogram or only slight atherosclerosis. In patients undergoing antiplatelet therapy, platelet scintigraphy was less often positive than in untreated patients. It is suggested that platelet scintigraphy could be an appropriate technique for detecting small mural thrombi of the carotid artery, which are the source of arterio-arterial emboli, and for controlling the efficiency of antiplatelet therapy.

Intravascular aggregation after acute intracranial hypertension by epidural balloon compression in cats

The authors have studied the effect of acute intracranial hypertension produced by placement of an epidural balloon (control group) in cats, on cerebral perfusion, evoked responses, and hematological parameters. These elements were measured in similarly injured animals which underwent isovolemic hemodilution with dextran 75, after relief of intracranial hypertension. Four hours after balloon deflation, perfusion was markedly impaired in 30% of the control group, and was reduced to 11% in the dextran-infused group. The suppressed N1 amplitude of somatosensory evoked responses on the compression side, the reduced platelet aggregability, and the erythrocyte-deformability by intracranial hypertension were all significantly more restored in the dextran-infused group after decompression. The percentage of platelets with volumes between 21.75 and 48.75 cu mu (normal 9.75 to 12.75 cu mu) significantly increased after decompression. Activation of platelets during intracranial hypertension leads to an increase in platelet volume from platelet aggregation, and correlates with a decrease in platelet aggregability. It was also suggested that reduction of erythrocyte deformability was not caused by erythrocyte aggregation. The authors emphasize the role of intravascular factors such as vascular obstruction by platelet aggregates, and difficulty in passage of erythrocytes through capillaries due to reduced deformability, in the disturbance of the microcirculation following acute intracranial hypertension. The protective effect of dextran 75 by inhibition of platelets as well as hemodilution is stressed.

Effects of adenosine diphosphate administration on the vestibulo-oculomotor reflex of rabbits

Adenosine diphosphate (ADP) injection into a unilateral vertebral artery in rabbits decreased per-rotational nystagmus; the nystagmus beating toward the injected side was predominantly suppressed. This influence became obvious when the animal's blood pressure was low. Field potentials were recorded in the vestibular nuclei upon electric stimulation of the vestibular labyrinth. ADP administration into the vertebral artery also suppressed the amplitude of vestibular evoked potentials (VEPs). Effects of ADP upon the vestibulo-ocular reflex and VEP were considered to be due to regional ischemia induced by the microemboli, which consisted of platelet aggregation.

Platelet embolism in rabbit brain

Transient cerebral ischemia was induced in rabbits by selective infusion of arachidonic acid (0.35 mg/kg in 15 sec) into the internal carotid artery. Platelet emboli caused transient ischemia of the brain, reaching a maximum within a few seconds after injection. After embolism the EEG flattened, blood flow stopped in almost the entire injected hemisphere, cortical pH gradually fell from 7.31 +/- 0.09 to 7.05 +/- 0.10 and cortical K+ activity rose from 4.7 +/- 1.8 to 12.7 +/- 6.4 mmol/kg H2O. Complete ischemia lasted 3-5 min; then cerebral circulation was gradually restored without reactive hyperemia. Forty-five min after embolization, circulation had been resumed in almost the entire injected hemisphere, whereas metabolic changes were still disturbed. Eighty percent of the animals recovered complete neurological function and 20% showed permanent damage confirmed by histological examination after 1 week of recovery.

Effect of intravascular platelet aggregation on blood recirculation following prolonged ischemia of the cat brain

Reversible complete cerebro-circulatory arrest was produced in normothermic, anesthetized cats for 1 h by clamping the innominate and subclavian arteries, followed by blood recirculation of the brain for 30 min to 4 h. Blood volume of tissue samples was measured by intravenous injection of 125I-albumin and the platelet number by labelling of autologous platelets with 51Cr. The number of platelets trapped in the tissue was determined by subtracting from the total platelet count of the tissue sample those contained in the streaming blood, calculated from the blood volume by 125I-albumin. In sham-operated animals, after recirculation of autologous 51Cr labelled platelets for 60 min, no platelets were entrapped in the brain vasculature and total platelet number and fibrinogen concentration in the venous blood did not change. In animals submitted to complete cerebral ischemia for 1 h the number of trapped platelets increased significantly in the whole brain after 30 min of recirculation, i.e. the period of maximal postischemic vasodilatation and hyperemia, and highest concentrations were found in the border zone with 270 +/- 60 x 10(4) platelets/g tissue and in the brainstem with 240 +/- 70 x 10(4) platelets/g tissue. Blood platelets and fibrinogen concentration in the venous blood decreased significantly from 288 +/- 37 x 10(6)/ml and 299 +/- 50 mg% to 186 +/- 25 x 10(6)/ml platelets and 112 +/- 22 mg+ of fibrinogen, respectively. Platelets were nearly completely washed out of the brain after 4 h of recirculation. The highest increase of platelets was found in the kidney, lung and liver after 30 min of recirculation, indicating that intravascular coagulation following prolonged cerebral ischemia affects the extracerebral organs more than the brain itself.

Arterial air embolism in the cat brain

In cats air embolism of the brain was produced by injecting 0.6 ml blood foam into the innominate artery proximal to the origin of both common carotid arteries. Air embolism caused transient ischemia of the brain, reaching a maximum within 1 min after injection. Resolution of the air embolism began a few minutes later and was completed within 15 min in the center and within 30 min in the border zone of the main supplying arteries. During this phase tissue perfusion was inhomogenous with reduced flow rates in some areas and reactive hyperemia up to 300% in others. This resulted in venous hyperoxia and a decrease of arteriovenous oxygen difference to as low as 2 ml/100 ml blood. Reactive hyperemia was accompanied by brain swelling and an increase in intracranial pressure from 3.6 +/- 1.2 to 12.3 +/- 2.0 mm Hg. The reason for hyperemia was a decrease of cortical pH which fell from 7.33 +/- 0.03 to 7.03 +/- 0.05, and which caused a dilation of pial arteries up to 260%. Immediately after embolism, the EEG flattened and oxygen consumption decreased. After normalization of flow, oxygen consumption returned to normal, but EEG only partially recovered. Air embolism had little effect on the water and electrolyte content of the brain, and produced very little damage to the blood-brain barrier.

Transient ischemic attacks due to increased platelet aggregation and adhesiveness. Ultrastructural and functional correlation

The authors report 22 cases of transient ischemic attacks (TIA's) manifested by amaurosis fugax or hemiparesis or paresthesia of less than 24 hours' duration. None of the patients demonstrated 1) evidence of atherosclerotic cerebral vascular disease on angiography, 2) evidence of intracranial lesion on brain scan, 3) cardiac source of emboli, 4) arteritis or collagen disease, or 5) history of migraine. The only abnormalities found to explain the TIA's were abnormally increased platelet adhesiveness and/or aggregation. All of these patients were followed from 1 to 5 years, and had repeated coagulation studies. Treatment with antiplatelet drugs showed an excellent clinical response with associated decrease in platelet adhesiveness and aggregation. Discontinuance of the antiplatelet drug resulted in a recurrence of the TIA's which coincided with an increase in aggregation and adhesiveness. In two cases the platelet morphology was studied by transmission and scanning electron microscopy. It appears that there is a specific group of patients with TIA's in whom the sole cause of the attack is an abnormality of platelet function. For these people there is a specific therapy and a method monitoring the treatment.

Report of Joint Committee for Stroke Resources. IV. Brain edema in stroke

A classification of brain edema is provided as well as an extensive review of the animal models from which we have derived most of the basic information we have about the formation and resolution of edema. The clinical aspects of cerebral edema in stroke are discussed and also modern methods for identifying cerebral edema in the human. Attention is given to computed tomography and enhanced CT and advances in their application to this condition. Treatment of cerebral edema in the stroke patient using glycerol, dextran 40, mannitol, steroids, and other drugs is discussed and the need pointed out for controlled clinical trials of the therapeutic effectiveness of these agents.

Platelet activation in acute cerebral ischaemia. Serial measurements of platelet function in cerebrovascular disease

Circulating platelet aggregates formed in vivo were serially measured, and platelet-aggregation thresholds were determined in vitro in 82 patients with acute cerebral ischaemia. The percentage of aggregated platelets was increased in 53 patients with completed stroke (30.9% +/- 2.0) and in 29 patients with transient ischaemic attacks (34.1% +/- 2.3), all studied within 10 days of the acute event. These values were higher (P less than 0.001) than levels of aggregated platelets in 30 patients with non-vascular neurological disease (16.8% +/- 2.3). The percentage of aggregated platelets returned to normal 10 days to 6 wk after acute cerebral ischaemia. Aspirin and dipyridamole did not affect either the increase in or subsequent normalisation of circulating-platelet-aggregate levels in these patients. Platelet-aggregation sensitivity to adenosine diphosphate and adrenaline was also increased in patients with acute cerebral ischaemia, but this abnormally resolved during convalescence. Platelet activation is abnormal in acute cerebral ischaemia but usually returns to normal with or without anti-platelet therapy. This activation of platelets may contribute to the clinical manifestations of occlusive vascular disease.