Temporal evolution of ischemic injury evaluated with diffusion-, perfusion-, and T2-weighted MRI

OBJECTIVE: Ischemic lesions seen on diffusion-weighted imaging (DWI) are reversible if reperfusion is performed within minutes after the onset of ischemia. This study was designed to determine whether acute reversibility of DWI abnormalities is transient following brief temporary focal brain ischemia and to characterize the temporal evolution of in vivo ischemic lesions. METHODS: Eight rats were subjected to 30 minutes of temporary middle cerebral artery occlusion and underwent diffusion-, perfusion-, and T2-weighted MRI during occlusion; immediately after reperfusion; 30, 60, and 90 minutes after reperfusion; and 12, 24, 48, and 72 hours after reperfusion. Average apparent diffusion coefficient (ADCav) values and the cerebral blood flow index (CBFi) ratio were calculated in both the lateral caudoputamen and overlying cortex at each time point. The size of the in vivo ischemic abnormalities was calculated from the ADCav and the T2 maps. Postmortem triphenyltetrazolium chloride (TTC) staining was used to verify ischemic injury. RESULTS: Both the CBFi ratio and ADCav values declined significantly in the two regions during occlusion. The CBFi ratio recovered immediately after reperfusion and remained unchanged over 72 hours. However, ADCav values returned to normal at 60 to 90 minutes and secondarily decreased at 12 hours after reperfusion as compared with those in the contralateral hemisphere. The extent of the in vivo ischemic lesions maximized at 48 hours and was highly correlated with TTC-derived lesion size. CONCLUSIONS: Acute recovery of initial ADCav-defined lesions after reperfusion is transient, and secondary ADCav-defined lesions develop in a slow and delayed fashion.     

Transient and permanent resolution of ischemic lesions on diffusion-weighted imaging after brief periods of focal ischemia in rats : correlation with histopathology

BACKGROUND AND PURPOSE: The early ischemic lesions demonstrated by diffusion-weighted imaging (DWI) are potentially reversible. The purposes of this study were to determine whether resolution of initial DWI lesions is transient or permanent after different brief periods of focal brain ischemia and to evaluate histological outcomes. METHODS: Sixteen rats were subjected to 10 minutes (n=7) or 30 minutes (n=7) of temporary middle cerebral artery occlusion or sham operation (n=2). DWI, perfusion-weighted imaging (PWI), and T(2)-weighted imaging (T(2)WI) were performed during occlusion; immediately after reperfusion; and at 0.5, 1.0, 1.5, 12, 24, 48, and 72 hours after reperfusion. After the last MRI study, the brains were fixed, sectioned, stained with hematoxylin and eosin, and evaluated for neuronal necrosis. RESULTS: No MRI or histological abnormalities were observed in the sham-operated rats. In both the 10-minute and 30-minute groups, the perfusion deficits and DWI hyperintensities that occurred during occlusion disappeared shortly after reperfusion. The DWI, PWI, and T(2)WI results remained normal thereafter in the 10-minute group, whereas secondary DWI hyperintensity and T(2)WI abnormalities developed at the 12-hour observation point in the 30-minute group. Histological examinations demonstrated neuronal necrosis in both groups, but the number of necrotic neurons was significantly higher in the 30-minute group (95+/-4%) than in the 10-minute group (17+/-10%, P<0.0001). CONCLUSIONS: Transient or permanent resolution of initial DWI lesions depends on the duration of ischemia. Transient resolution of DWI lesions is associated with widespread neuronal necrosis; moreover, permanent resolution of DWI lesions does not necessarily indicate complete salvage of brain tissue from ischemic injury.     

Mice overexpressing extracellular superoxide dismutase have increased resistance to global cerebral ischemia

Transgenic mice, which exhibit a fivefold increase in brain parenchymal extracellular superoxide dismutase (EC-SOD) activity, were used to investigate the role of EC-SOD in global ischemic brain injury. Halothane-anesthetized normothermic wild-type (n = 22) and transgenic (n = 20) mice underwent 10 min of near-complete forebrain ischemia induced by bilateral carotid artery occlusion and systemic hypotension (mean arterial pressure = 30 mm Hg). After 3 days of recovery, the brains were histologically examined. Other mice underwent autoradiographic determination of regional CBF 10 min prior to, during, and 30 min after forebrain ischemia. Histologic injury in the cortex and caudoputamen was minimal in both groups. The percentage of dead hippocampal CA1 neurons was reduced in the EC-SOD transgenic group (wild type = 44 +/- 28%; EC-SOD transgenic = 23 +/- 21%, mean +/- SD, P = 0.015). CBF was similar between groups prior to ischemia. The intraischemic blood flow was severely reduced in forebrain structures and was similar between groups. Blood flow at 30 min postischemia had recovered to 50-60% of baseline values in both groups. These results indicate that EC-SOD can play an important role in defining the magnitude of selective neuronal necrosis resulting from near-complete forebrain ischemia. This implicates involvement of extracellular superoxide anions in the pathologic response to global cerebral ischemia.     

沙土鼠全脑缺血再灌注损伤的实验研究

比较暂时单次阻断和分次阻断动脉所致脑缺血损伤的严重程度.24只雄性沙土鼠经双侧颈总动脉阻断脑缺血模型,分单次阻断10min组与阻断5min,灌注10min,再阻断5min.24h后断头取脑行抗微管相关蛋白2(MAP2)免疫组化染色,计算机图像分析系统行病变范围测定.分次阻断组动物的海马下脚CA1区及额顶叶脑皮层Ⅲ～Ⅳ层缺血性损伤程度比单次长时间阻断减少了2.04%,但两者比较无明显的统计学差异(P>0.05).分次阻断间歇期行再灌注能否加重脑缺血损伤的程度主要受分次阻断的强度、阻断持续时间、再灌注时间的长短以及个体的脑血管侧支循环能力而定.     

Penumbral tissues salvaged by reperfusion following middle cerebral artery occlusion in rats.

BACKGROUND AND PURPOSE: The rat is now extensively used for studies on focal cerebral ischemia, and several novel pharmacological principles have been worked out in rat models of middle cerebral artery occlusion. The objective of the present study was to assess how ischemic tissue can be salvaged by reperfusion in a model of transient focal ischemia that gives infarction of both the caudoputamen and the neocortex. METHODS: The middle cerebral artery of anesthetized rats was occluded for 15, 30, 60, 90, 120, or 180 minutes by an intraluminal filament, and recirculation was instituted for 7 days to allow assessment of the density and localization of ischemic brain damage using histopathologic techniques. Local cerebral blood flow was measured in separate animals to verify that removal of the filament was followed by adequate recirculation. RESULTS: Following 15 minutes of middle cerebral artery occlusion seven of eight rats showed selective neuronal necrosis in the caudoputamen, while the neocortex was normal. After 30 minutes of occlusion, seven of eight animals had infarcts localized to the lateral caudoputamen, and four of eight had selective neuronal necrosis in the neocortex. Prolongation of the ischemia to 60 minutes induced cortical infarction in all eight rats. The infarct size increased progressively with increasing occlusion time, up to 120-180 minutes, when the infarcts were as extensive as those observed following 24 hours of permanent middle cerebral artery occlusion. CONCLUSIONS: The results demonstrate a time window for salvage of penumbral tissues by reperfusion that is shorter than that suggested on the basis of previous data in other species. The results probably reflect a lower collateral blood flow in the rat than in other species. This should be taken into account when the effect of pharmacological agents is studied in rats.     

Deficiency of intercellular adhesion molecule 1 fails to mitigate selective neuronal death after transient global ischemia

Recent studies have shown a crucial role of intercellular adhesion molecule 1 (ICAM-1) in expansion of infarction after focal cerebral ischemia. The purpose of the present study was to assess whether ICAM-1 is involved in selective neuronal vulnerability and reactive gliosis after transient forebrain ischemia. ICAM-1 knockout mice and wild-type mice were subjected to transient forebrain ischemia for 5, 10 or 15 min, and the hippocampus and caudoputamen were examined 7 days later with conventional histological and immunohistochemical methods. Bilateral common carotid artery occlusion with less than 10% of baseline cortical microperfusion for 10 or 15 min resulted in ischemic neuronal damage in the hippocampus and caudoputamen. The frequency and the severity of neuronal damage were similar in wild-type and knockout mice. Proliferation of reactive astrocytes in the hippocampus was also similar in both types of mice. Therefore, it is highly unlikely that ICAM-1 plays a key role in delayed neuronal death after transient global ischemia or in astroglial responses after ischemic neuronal injury.     

Changes in the somatosensory evoked potential during and immediately following temporary middle cerebral artery occlusion predict somatosensory cortex ischemic lesions in monkeys

Somatosensory evoked potentials (SEP) were recorded during and immediately following temporary middle cerebral artery (MCA) occlusion to determine whether they can be used to predict ischemic lesions to the somatosensory cortex (SI). Twenty-one cynomolgus female monkeys were subjected to four different MCA occlusion durations (15-60 min) during hypotension (45-50 mm Hg mean arterial blood pressure). The amplitude and central conduction time (CCT) of the median nerve SEP were recorded preceding, during, and following occlusion. Two groups were established based on the development of SI ischemic lesions: animals developing SI lesions formed the SI-lesion group (n = 9), and animals without ischemic lesions or with lesions outside the SI cortex formed the SI-spared group (n = 12). Changes in the SEP during and following MCA occlusion under conditions of hypotension were similar to those reported by others. The SEP disappeared in all animals within 15 min of occlusion and reappeared 5 min following reperfusion. Several differences were observed between the SI-lesion and SI-spared groups. The SI-lesion group had a more rapid decrease in SEP amplitude during the first 5 min of occlusion and had smaller SEP amplitudes and longer CCTs during reperfusion. These results suggest that changes in SEP amplitude and latency during and immediately following temporary MCA occlusion predict development of SI ischemic lesions.     

A new method for producing temporary complete cerebral ischemia in rats

A new model of temporary complete cerebral ischemia was developed and tested in 64 rats. With use of microsurgical techniques, both pterygopalatine and external carotid arteries were occluded and the basilar artery was coagulated to reduce potential collateral CBF during ischemia. After this preliminary five-vessel occlusion, temporary global ischemia was induced by occluding the common carotid arteries (CCAs) with microclips. To validate the method, CBF was measured autoradiographically in 24 anatomical regions at death after 5 min of ischemia or after 15 min of ischemia followed by 5 min of reperfusion. Mean arterial blood pressure and arterial blood gases remained stable under controlled endotracheal ventilation and anesthesia (halothane, 70% N2O, and 30% O2) throughout the CBF experiments, except for a 10-15% increase in mean arterial blood pressure for 1-5 min after bilateral CCA occlusion. After the initial five-vessel occlusion, the EEG did not change, and local CBF levels were comparable to those in anesthetized non-surgical controls. When the CCAs were occluded, the EEG flattened rapidly; after 5 min of ischemia, autoradiography showed no detectable blood flow in the forebrain and cerebellum. The local CBF levels measured after 15 min of temporary global ischemia and 5 min of reperfusion demonstrated relatively homogeneous postischemic hyperperfusion; only two of eight rats had several 1- to 3-mm areas of no-reflow. Survival studies showed increasing motor impairment after 10, 15, 30, and 60 min of temporary CCA occlusion. Ischemic neuronal damage was observed histologically in the hippocampus and basal ganglia 24 h after 10 min of temporary ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Differences in neurotransmitter synthesis and intermediary metabolism between glutamatergic and GABAergic neurons during 4 hours of middle cerebral artery occlusion in the rat: the role of astrocytes in neuronal survival.

Astrocytes are intimately involved in both glutamate and gamma-aminobutyric acid (GABA) synthesis, and ischemia-induced disruption of normal neuroastrocytic interactions may have important implications for neuronal survival. The effects of middle cerebral artery occlusion (MCAO) on neuronal and astrocytic intermediary metabolism were studied in rats 30, 60, 120, and 240 minutes after MCAO using in vivo injection of [1-13C]glucose and [1,2- 13C]acetate combined with ex vivo 13C magnetic resonance spectroscopy and high-performance liquid chromatography analysis of the ischemic core (lateral caudoputamen and lower parietal cortex) and penumbra (upper frontoparietal cortex). In the ischemic core, both neuronal and astrocytic metabolism were impaired from 30 minutes MCAO. There was a continuous loss of glutamate from glutamatergic neurons that was not replaced as neuronal glucose metabolism and use of astrocytic precursors gradually declined. In GABAergic neurons astrocytic precursors were not used in GABA synthesis at any time after MCAO, and neuronal glucose metabolism and GABA-shunt activity declined with time. No flux through the tricarboxylic acid cycle was found in GABAergic neurons at 240 minutes MCAO, indicating neuronal death. In the penumbra, the neurotransmitter pool of glutamate coming from astrocytic glutamine was preserved while neuronal metabolism progressively declined, implying that glutamine contributed significantly to glutamate excitotoxicity. In GABAergic neurons, astrocytic precursors were used to a limited extent during the initial 120 minutes, and tricarboxylic acid cycle activity was continued for 240 minutes. The present study showed the paradoxical role that astrocytes play in neuronal survival in ischemia, and changes in the use of astrocytic precursors appeared to contribute significantly to neuronal death, albeit through different mechanisms in glutamatergic and GABAergic neurons.     

Immunohistochemical investigation of ischemic and postischemic damage after bilateral carotid occlusion in gerbils

We investigated progression and recovery of neuronal damage during and after global cerebral ischemia in gerbils after bilateral occlusion of the common carotid arteries, using the immunohistochemical method (reaction for tubulin and creatine kinase BB-isoenzyme). The earliest, but reversible, ischemic lesions occurred after 3 minutes' ischemia in the subiculum-CA1 and CA2 regions of the hippocampus. The lesions became irreversible after 4 minutes' ischemia. The ischemic and postischemic lesions in the cerebral cortex, thalamus, and caudoputamen were partially or completely reversible if the ischemic period was 5 minutes, whereas delayed degeneration occurred in the pyramidal cells of the medial CA1 region after reperfusion for 48 hours (delayed neuronal death). After 10 minutes' ischemia and subsequent reperfusion, delayed neuronal death extended from the medial to the lateral CA1 region; the ischemic and postischemic lesions in the cerebral cortex, thalamus, and caudoputamen also expanded during reperfusion. Our investigation demonstrates that selective vulnerability existed in global cerebral ischemia as in incomplete or regional ischemia and suggests that neurons in many areas of the brain possessed the potential for recovery, progressive deterioration, and even delayed neuronal death depending on the severity and duration of cerebral ischemia.     

The temporal evolution of hypoglycemic brain damage

The caudate nucleus and putamen belong to the selectively vulnerable brain regions which incur neuronal damage in clinical and experimental settings of both hypoglycemia and ischemia. We have previously documented the density and distribution of the hypoglycemic damage in rat caudoputamen, but the evolution of the injury, i.e., the sequence of structural changes, has not been assessed. Therefore, in the present study we analyze the light and electron microscopic alterations in the caudoputamen of rats exposed to standardized, pure insults of severe hypoglycemia with isoelectric EEG for 10-60 min, or in rats which, following insults of 30 or 60 min, were allowed to recover for periods from 5 min to 6 months. The hypoglycemic insult produced severe nerve cell injury in the dorsolateral caudoputamen. Immediately after the insult abnormal light neurons with clearing of the peripheral cytoplasm were present. These cells disappeared early in the recovery period, as they do in the cerebral cortex. Dark neurons were also present, but unlike those in the cerebral cortex they did not appear until recovery was instituted. Their number increased for a couple of hours and they became acidophilic within 4-6 h. At this stage, electron microscopy revealed severe clumping of the nuclear chromatin and cytoplasm as well as incipient fragmentation of cell membranes, all these changes indicating an irreversible injury. Within 24 h flocculent densities appeared in the mitochondria and by day 2-3 of recovery the great majority of the medium-sized neurons had undergone karyorrhexis and cytorrhexis, their remnants being subsequently removed by macrophages. After some weeks only large and a few medium-sized neurons remained amidst reactive astrocytes and numerous macrophages. The delay in the appearance of dark, lethally injured medium-sized neurons until the recovery was instituted suggests an effect that does not become apparent until the substrate supply and energy production are restored. Furthermore, it points out again the selectivity of the hypoglycemic nerve cell injury with respect to the type (metabolic characteristics?) and topographic location of the neurons.     

Artificial neural network prediction of ischemic tissue fate in acute stroke imaging

Multimodal magnetic resonance imaging of acute stroke provides predictive value that can be used to guide stroke therapy. A flexible artificial neural network (ANN) algorithm was developed and applied to predict ischemic tissue fate on three stroke groups: 30-, 60-minute, and permanent middle cerebral artery occlusion in rats. Cerebral blood flow (CBF), apparent diffusion coefficient (ADC), and spin–spin relaxation time constant (T2) were acquired during the acute phase up to 3 hours and again at 24 hours followed by histology. Infarct was predicted on a pixel-by-pixel basis using only acute (30-minute) stroke data. In addition, neighboring pixel information and infarction incidence were also incorporated into the ANN model to improve prediction accuracy. Receiver-operating characteristic analysis was used to quantify prediction accuracy. The major findings were the following: (1) CBF alone poorly predicted the final infarct across three experimental groups; (2) ADC alone adequately predicted the infarct; (3) CBF+ADC improved the prediction accuracy; (4) inclusion of neighboring pixel information and infarction incidence further improved the prediction accuracy; and (5) prediction was more accurate for permanent occlusion, followed by 60- and 30-minute occlusion. The ANN predictive model could thus provide a flexible and objective framework for clinicians to evaluate stroke treatment options on an individual patient basis.     

Cognitive deficits after focal cerebral ischemia in mice

BACKGROUND AND PURPOSE: The interpretation of cognitive data in many experimental stroke studies is problematic because middle cerebral artery occlusion (MCAO) is associated with sensorimotor alterations that may become confounding factors in cognitive testing. The purpose of the current study was to determine if it is possible to measure MCAO-induced cognitive deficits by using short durations of ischemia that do not result in alterations in sensorimotor behavior in mice. METHODS: Male C57/Bl6 mice were subjected to 60 or 90 minutes of intraluminal MCAO or sham surgery. In the first cohort of animals (n=12/group), locomotor activity, balance, and coordination were evaluated 2 weeks after surgery. In a second cohort of animals (n=10/group), the effects of 60 minutes of MCAO on subsequent learning and memory were assessed with a step-down passive avoidance task beginning 1 week after surgery. In a third cohort of animals (n=8 to 10/group), training in a passive avoidance task was completed before 60 minutes of MCAO, then retention of the task was assessed 1 week after surgery. In all animals, infarction size was determined after 14 days of reperfusion with use of cresyl violet staining and quantitative image analysis. RESULTS: There was no significant difference in infarction volume in the cerebral cortex or caudoputamen after 60 versus 90 minutes of MCAO. However, there was a significant increase in latency to move 1 body length in the 90-minute MCAO group compared with the 60-minute MCAO and sham groups. In 2 additional cohorts of animals, 60-minute MCAO was associated with a deficit in the acquisition and retention of a passive avoidance task regardless of whether the task training occurred before or after MCAO. CONCLUSIONS: Long-term cognitive deficits can be induced in mice by using a short duration of MCAO (60 minutes) that does not result in concomitant sensorimotor deficits.     

Forebrain ischemia induced by temporary bilateral common carotid occlusion in normotensive rats

Ischemic brain lesions were induced in adult Wistar and Fischer rats by temporary occlusion of the bilateral common carotid artery. The severity of ischemic lesions depended on the duration of carotid occlusion. While 2 h occlusion resulted in 15 deaths among 40 rats and the development of ischemic lesions in 16 of 25 asymptomatic survivors, none died after 0.5 h occlusion and yet 13 of 30 apparently asymptomatic rats had ischemic lesions when examined on day 7. Histological examination combined with immunohistochemistry of autologous albumin for assessing the integrity of the blood-brain barrier (BBB) revealed two distinct lesions: (1) ischemic neural damage with extensive tissue permeation of serum albumin, (2) death of individual neurons sparing other neural elements in the absence of the BBB breakdown. Ischemic neural damage with BBB breakdown was common in animals dying within 48 h after reflow. The lesions without BBB breakdown, on the other hand, were found solely in asymptomatic animals in which groups of severely degenerated neurons were preferentially located in the CA 1 region of the hippocampus, the caudoputamen and deeper layers of the neocortex. The sequential measurements of regional cerebral blood flow (rCBF) in the bilateral hippocampus by the hydrogen clearance method disclosed a steady decrease in rCBF after the occlusion, 51% of the pre-occlusion state at 10 min, 35% at 25 min and 32% at 40 min. The simplicity of procedure could make this model suitable for the study of the pathogenesis of ischemic neuronal damage in a critically low perfusion state.     

SOD1 overexpression and female sex exhibit region-specific neuroprotection after global cerebral ischemia due to cardiac arrest.

Cardiac arrest is often associated with poor neurologic outcome since therapeutic options are limited. We tested the hypothesis that overexpression of CuZn superoxide dismutase (SOD+/-) is neuroprotective in a new murine model of cardiac arrest and cardiopulmonary resuscitation (CPR). Second, we investigated if female and male mice sustain similar injury and if sex-specific outcomes are altered by SOD overexpression. Neuronal injury was quantified 3 days after 8 mins of KCl-induced cardiac arrest by calculating the percentage of ischemic neurons for caudoputamen and hippocampal CA1 region. In rostral caudoputamen, less neuronal cell loss was found for SOD+/- mice (31%+/-22%) when compared with wild-type (WT) mice (47%+/-31%, P<0.05). Superoxide dismutase overexpression did not reduce injury in the caudal caudoputamen. No sex-linked protection was evident in either genotype in the caudoputamen. Female WT mice had less CA1 injury than male WT mice (26%+/-31% versus 54%+/-30%, P<0.05), whereas no sex difference was found in SOD+/- mice (female: 42%+/-29%; male: 37%+/-37%). Comparison of hippocampal injury between genotypes revealed no differences for either males or females. In conclusion, SOD1 overexpression and female sex were associated with significant neuroprotection in this murine cardiac arrest model. However, no additive neuroprotection was observed, and these beneficial effects were restricted to specific brain regions.     

C57BL/6 strain is most susceptible to cerebral ischemia following bilateral common carotid occlusion among seven mouse strains: selective neuronal death in the murine transient forebrain ischemia

Rats and gerbils have been used widely to investigate the molecular mechanism of selective neuronal death following transient global ischemia. Recently, the availability of transgenic mice has enabled us to examine the involvement of specific gene products in various pathophysiological conditions. However, there has been only limited information about the experimental model of cerebral ischemia in mice, particularly in regard of selective neuronal death. We examined whether bilateral carotid occlusion produced global forebrain ischemia in seven common mouse strains including C57BL/6, ICR, BALB/c, C3H, CBA, ddY and DBA/2, based on neurological signs, histological findings and cortical microcirculatory as well as India ink perfusion patterns. The C57BL/6 strain was found to be the most susceptible among seven strains. All C57BL/6 mice died within 6 h after permanent bilateral carotid occlusion. After transient bilateral carotid occlusion for 20 min, more than 90% of C57BL/6 mice showed typical neurological signs such as torsion of the neck and rolling fits, and developed selective neuronal death in the hippocampus and caudoputamen. Hypothermia prevented the neuronal death. Visualization of brain vasculature by India ink perfusion indicated that the susceptibility of the mice after bilateral carotid occlusion depended mainly on the degree of anastomosis between carotid and basilar arteries. Our results showed the feasibility of investigating selective neuronal death in transgenic mice with simple temporary occlusion of both common carotid arteries, when those from the C57BL/6 strain or inbred transgenic mice from other strains with the C57BL/6 strain in a back-cross manner are used.     

Keratinocyte growth factor prevents ischemia-induced delayed neuronal death in the hippocampal CA1 field of the gerbil brain

Fibroblast growth factors (FGFs) are polypeptides with various biological activities in vivo and in vitro, and their receptors are expressed in the widespread and specific neuronal populations of the brain. In this study, we asked whether keratinocyte growth factor (KGF), one of the FGF superfamily, would express in the brain, and have neuroprotective against ischemic brain injury. In situ hybridization analysis revealed that intense silver grains for KGF mRNA are observed in the neuronal cells of the cerebral cortex, hippocampus and amygdala in gerbil brain. Continuous cerebroventricular infusion of KGF (20 microg) for a 7 day period to gerbils starting 2 days before temporary right carotid artery occlusion (20 min) resulted in a higher survival rate than seen in vehicle-treated ischemic animals. Subsequent histological examinations showed that KGF effectively prevented delayed neuronal death of the hippocampal CA1 region. In situ detection of DNA fragmentation (TUNEL staining) revealed that ischemic animals infused with KGF contained fewer TUNEL-positive neurons in the hippocampal CA1 field than those infused with vehicle alone at the forth and seventh day after ischemia. KGF-treated brain showed over-expression of KGF mRNA in the neuronal cells of the cerebral cortex, hippocampus only in the right hemisphere, which was the side of carotid artery occlusion, 8-10 h after ischemia. These findings suggest that KGF has a protective effect against ischemic hippocampal neuronal damage in vivo, which may provide a new therapeutic strategy in the survival and reconstruction of neurons in response to cerebral injury.     

Permanent or transient chronic ischemic stroke in the non-human primate: behavioral, neuroimaging, histological, and immunohistochemical investigations

Using multimodal magnetic resonance imaging (MRI), behavioral, and immunohistochemical analyses, we examined pathological changes at the acute, sub-acute, and chronic stages, induced by permanent or temporary ischemia in the common marmoset. Animals underwent either permanent (pMCAO) or 3-h transient (tMCAO) occlusion of the middle cerebral artery (MCAO) by the intraluminal thread approach. MRI scans were performed at 1 h, 8, and 45 days after MCAO. Sensorimotor deficits were assessed weekly up to 45 days after MCAO. Immunohistological studies were performed to examine neuronal loss, astrogliosis, and neurogenesis. Remote lesions were analyzed using retrograde neuronal tracers. At day 8 (D8), the lesion defined on diffusion tensor imaging (DTI)–MRI and T2-MRI was significantly larger in pMCAO as compared with that in the tMCAO group. At D45, the former still displayed abnormal signals in T2-MRI. Post-mortem analyses revealed widespread neuronal loss and associated astrogliosis to a greater extent in the pMCAO group. Neurogenesis was increased in both groups in the vicinity of the lesion. Disconnections between the caudate and the temporal cortex, and between the parietal cortex and the thalamus, were observed. Sensorimotor impairments were more severe and long-lasting in pMCAO relative to tMCAO. The profile of brain damage and functional deficits seen in the marmoset suggests that this model could be suitable to test therapies against stroke.     

Effect of transient focal ischemia on blood-brain barrier permeability in the rat: correlation to cell injury

Prolonged ischemia is known to damage the blood-brain barrier, causing an increase in vascular permeability to proteins. We studied the time course of extravasation of endogenous albumin in rats after 1 and 2 h of middle cerebral artery (MCA) occlusion followed by 6, 12, and 24 h of recirculation. In a separate group of rats that had undergone 1 h of MCA occlusion and 6 h of recirculation, influx of [¹⁴C]aminoisobutyric acid (AIB) from blood to brain was also measured. After 1 h of occlusion followed by 6 h of recirculation, neuronal damage was evident in caudoputamen, but there were no signs of blood-brain barrier leakage to either AIB or albumin. At 12 h, the caudoputamen contained extravasated albumin, and at 24 h extravasation was extended to the somatosensory cortex. Animals subjected to 2 h of MCA occlusion showed albumin extravasation in caudoputamen already at 6 h of recirculation, and at 12 and 24 h albumin was abundant in the major part of the right hemisphere. This study suggests that damage to neurons precedes leakage of the blood-brain barrier. Even a relatively short period of ischemia such as 1 h will result in markedly increased vascular permeability. However, a longer transient ischemic insult disrupts the blood-brain barrier earlier than a shorter one. Received: 16 September 1996 / Revised, accepted: 5 February 1997     

Ischemic axonal injury and its recovery after focal cerebral ischemia

After focal cerebral infarction by occluding the middle cerebral artery (MCA) of the rat, the neuronal death occurred in the ipsilateral thalamic neurons, because axons of the thalamic neurons were injured by infarction and retrograde degeneration occurred in the thalamic neurons. However, cortical neurons adjacent to the infarction survived despite their axons injured by ischemia. We employed immunohistochemical staining for 200 kilodalton (kD) neurofilament (NF), in order to study those responses of cortical and thalamic neurons against axonal injury caused by focal cerebral infarction. In the sham operated rats the immunoreactivity to the anti-200 kD NF antibody was only detected in the axon but not in the cell bodies and dendrites. At 3 days after MCA occlusion, axonal swelling proximal to the site of ischemic injury was found in the caudoputamen and internal capsule of the ipsilateral side. At 7 days after occlusion, cell bodies and dendrites of the neurons in the ipsilateral cortex and thalamus were strongly stained with anti-NF antibodies. At 2 weeks after occlusion these responses disappeared in the cortex, but lasted in the thalamus. These phenomena are caused by stasis of the slow axonal transport, because the NF is transported by slow axonal transport. In the cortical neurons impairment of slow axonal transport recovered in the early phase after injury, but in the thalamic neurons the impairment prolonged up to 3 weeks after occlusion. The early recovery of axonal transport from ischemia seemed to be essential for survival of neurons after ischemic axonal injury.