Preischemic hyperglycemia and postischemic alteration of rat brain pyruvate dehydrogenase activity

Transient cerebral ischemia in normoglycemic animals is followed by a decrease in glucose utilization, reflecting a postischemic cerebral metabolic depression and a reduction in the activity of the pyruvate dehydrogenase complex (PDHC). Preischemic hyperglycemia, which aggravates ischemic brain damage and invariably causes seizure, is known to further reduce cerebral metabolic rate. To investigate whether these effects are accompanied by changes in PDHC activity, the postischemic cerebral cortical activity of this enzyme was investigated in rats with preischemic hyperglycemia (plasma glucose 20-25 mM). The results were compared with those obtained in normoglycemic animals (plasma glucose 5-10 mM). The activated portion of PDHC and total PDHC activity were measured in neocortical samples as the rate of decarboxylation of [14C]pyruvate in crude brain mitochondrial homogenates after 5 min, 15 min, 1 h, 6 h, and 18 h of recirculation following 15 min of incomplete cerebral ischemia. In normoglycemic animals the fraction of activated PDHC, which rises abruptly during ischemia, was reduced to 19-25% during recirculation compared with 30% in sham-operated controls. In hyperglycemic rats the fraction of activated PDHC was higher during the first 15 min of recirculation. However, after 1 and 6 h of recirculation, the fraction was reduced to values similar to those measured in normoglycemic animals. Fifteen of 26 rats experienced early (1-4 h post ischemia) seizures in the recovery period. The PDHC activity appeared unchanged prior to these early postischemic seizures. We conclude that the accentuated depression of postischemic metabolic rate observed in hyperglycemic animals is not coupled to a corresponding postischemic depression of PDHC.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of ulinastatin on postischemic brain edema in cats]

The effect of ulinastatin on postischemic brain edema was investigated in adult mongrel cats. Focal brain ischemia was produced by occlusion of the left middle cerebral artery (MCA) through the transorbital approach. Following two hours of occlusion, the brain was reperfused for two hours. In all seven animals of the ulinastatin-treated group, ulinastatin was administered intravenously at a dose of 50000 U/kg before and after occlusion. In the control group, six animals were given only vehicle. Measurements of regional cerebral blood flow (rCBF) were performed before MCA occlusion by the hydrogen clearance method, and then repeated every 30 minutes during and after occlusion. Following two-hour reperfusion, the animals were sacrificed by intravenous KCl injection. Specific gravity of the cortex, where rCBF was measured, was determined by microgravimetric method. In the analysis of specific gravity of the cortex, in which mean rCBF during ischemia was above 15ml/100g/min, no significant difference was found between the ulinastatin-treated and control groups. In the specimen with mean rCBF below 15ml/100g/min during ischemia, cortical specific gravity was reduced remarkably in the control group, while not decreased in the ulinastatin-treated group. The difference was statistically significant between two groups (p less than 0.001). These findings suggest antiedema effect of ulinastatin.     

Effect of aminophylline on postischemic edema and brain damage in cats

We attempted to ameliorate postischemic edema and brain tissue injury in cats by administering aminophylline to reduce the reactive hyperemia that supposedly aggravates both these sequelae. Forty-one cats were subjected to 1 hour of middle cerebral artery occlusion and were killed after 3 hours, 3 days, or 14 days of recirculation; one half of the cats received 0.916 ml/kg of a 25 mg/ml solution of aminophylline by infusion at a constant rate via the femoral vein starting 10 minutes before release of the occlusion and continuing for 5 minutes after initiation of recirculation; the other half received saline. Regional cerebral blood flow was monitored by the hydrogen clearance method and water content was evaluated by specific gravity measurements after 3 hours of recirculation; the status of the blood-brain barrier was assessed with Evans blue tracer. Morphologic observations were carried out in cats killed after 3 or 14 days of recirculation. Aminophylline-treated cats killed after 3 hours of recirculation showed significantly reduced hyperemia and edema and no leakage of Evans blue, which was present in all untreated cats killed after 3 hours or 3 days of recirculation. Morphologic observations revealed conspicuously more severe ischemic brain tissue damage in the untreated than in the aminophylline-treated cats after 3 and 14 days of recirculation. Our studies indicate the beneficial effect of administration of aminophylline in the amelioration of postischemic edema and brain tissue injury, which is presumably achieved by reduction of reactive hyperemia.     

The effects of hyperglycemia on ischemic brain edema

The effects of hyperglycemia on ischemic brain edema in rats were studied by measuring the local changes in water content of brain and cerebrovascular permeability using a transient middle cerebral artery (MCA) occlusion model. Rats, fasted except for water for 12-16 hours, were used. They were anesthetized with halothane and the stem of the left MCA was occluded for 2 hours by a microclip. Reperfusion was performed by removal of the clip. The rats were allowed to awake from anesthesia after removal of the clip. Hyperglycemia was induced by intraperitoneal injection of 50% glucose and same volume of physiological saline was injected intraperitoneally 20 minutes before MCA occlusion in control rats. Cerebrovascular permeability was measured by quantitative autoradiography using 14C-alpha-amino-isobutyric acid (14C-AIB) 2 hours after reperfusion. The specific gravity of cerebral tissue, determined by the gradient column with bromobenzene and kerosene, was used to study local changes in brain water content 2 hours after MCA occlusion and 2 hours after reperfusion. In hyperglycemic rats, plasma glucose content-ration rose to over 500 mg/dl at the peak and then declined. A hyperglycemic state around 300 mg/dl was maintained during the experiments. Elevation of hematocrit and plasma osmolarity were observed in hyperglycemic rats. At 2 hours after MCA occlusion, specific gravity of the brain was decreased in the left MCA territory, especially in the frontal cortex, in both groups. The decrease in the frontal cortex in hyperglycemic rats was statistically significant compared with that in the control rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

脑出血急性期患者高血糖对脑水肿及预后的影响

目的 探讨脑出血患者急性期血糖水平对脑水肿及预后的影响.方法 脑出血患者95例,在急性期检测其空腹血糖水平,根据血糖水平分为高血糖组(38例)和正常血糖组(57例),通过头颅CT观察两组脑水肿的变化.在发病3个月后随访,采用改良Rankin量表(mRS)对两组患者进行神经功能评分,以评价其预后.结果 高血糖组患者急性期血肿周围脑水肿体积[(17.55±2.48)ml]显著高于正常血糖组[(11.50±3.76)ml](P＜0.05);发病3个月后高血糖组mRS评分(3.50 ±0.71)显著高于正常血糖组(2.80±0.63)(P＜0.05).结论 脑出血患者急性期高血糖可加重脑水肿并影响其预后,应及时进行干预.     

Exo-focal postischemic neuronal death in the rat brain

We describe delayed neuronal damage in ipsilateral areas remote from the ischemic area of rat brain after transient focal ischemia induced by embolization of the right middle cerebral artery (MCA). After 15, 30, 60 and 90 min of MCA occlusion, recirculation was achieved by removal of the embolus. Chronological changes in the distribution of the neuronal damage were determined by using the 45Ca autoradiographic technique and the histological method, and the mechanism involved was investigated by measuring local cerebral glucose metabolism. Depending on the duration of ischemia, 45Ca accumulation extended to the lateral segment of the caudate putamen and to the cerebral cortex, both supplied by the occluded MCA. Moreover, 3 days after ischemic insult, 45Ca had accumulated in the ipsilateral substantia nigra and ventral posterior nucleus of the thalamus. Histological examination revealed that the neurons in both areas suffered damage and were selectively reduced in number. Cerebral glucose utilization decreased in the thalamus, but increased approximately 30% (P less than 0.01) in the substantia nigra compared with the value in the corresponding contralateral area. Both areas lie outside the ischemic area, but have transsynaptic connections with the ischemic focus. Based on the present study, we suggest that the mechanisms of delayed neuronal death in these two remote areas may not be identical, but that this phenomenon may be caused by a transsynaptic process associated with the ischemic focus.     

The influence of preischemic hyperglycemia on acute changes in the apparent diffusion coefficient of brain water following global ischemia in rats

We report the effect of increased plasma glucose levels on changes in the apparent diffusion coefficient of brain water (ADCw) during the first few minutes of global ischemia in rats. Brain ADCw values were acquired every 15 s using a diffusion-weighted line-scan MR pulse sequence. Preischemic hyperglycemia was achieved by infusion of 50% dextrose (i.v.) prior to KCl-induced cardiac arrest global ischemia. Analysis based on single voxels (3.4 μl) in brain demonstrated significant differences in the time course of ADCw decline between normoglycemic (n=8) and hyperglycemic (n=6) groups. Mean data from the hyperglycemic group indicated a biphasic decline of ADCw that was characterized by an initial rapid drop followed by a plateau of approximately 1 min before gradually declining and leveling off to its minimum value. In the normoglycemic group, ADCw declined to the same value as in the hyperglycemic group, but without a notable plateau. In the cerebral cortex, the times to maximal and half maximal ADCw drop following global ischemia in the hyperglycemic group were 3.96 and 2.26 min respectively. Corresponding time intervals for the normoglycemic group were 1.86 and 1.14 min, respectively. The time course for changes in ADCw demonstrated here is significantly different than that for anoxic depolarization reported under similar experimental conditions and suggests that events other than the complete loss of membrane ionic homeostasis and subsequent cell swelling may be involved in the initial decline of ADCw in global cerebral ischemia.     

Erythropoietin protects from post-traumatic edema in the rat brain.

Erythropoietin (Epo) is gaining interest in various neurological insults as a possible neuroprotective agent. We determined the effects of recombinant human Epo (rhEpo, 5000 IU per kg bw) on brain edema induced in rats by traumatic brain injury (TBI; impact-acceleration model; rhEpo administration 30 mins after injury). Magnetic resonance imaging (MRI) and a gravimetric technique were applied. In the MRI experiments, the apparent diffusion coefficient (ADC) and the tissue T(1) relaxation time were measured hourly in the neocortex and caudoputamen, during a 6 h time span after TBI. In the gravimetric experiments, brain water content (BWC) was determined in these two regions, 6 h after TBI. Apparent diffusion coefficient measurements showed that rhEpo decreased brain edema early and durably. Gravimetric measurements showed that rhEpo decreased BWC at H(6) in the neocortex as well as in the caudoputamen. No significant differences in ADC, in T(1), or in BWC were found between rhEpo treated-TBI rats and sham-operated rats. Our findings show that post-traumatic administration of rhEpo can significantly reduce the development of brain edema in a model of diffuse TBI. Further studies should be conducted to identify the biochemical mechanisms involved in these immediate effects and to assess the use of rhEpo as a possible therapy for post-traumatic brain edema.     

Influence of various agents on the development of brain edema in the rat following microembolism. Protective effect of gamma-butyrolactone

Brain edema was induced in rats by injecting 50 mu microspheres, labelled with 85Sr, into the internal carotid artery. The use of radioactive microspheres as embolic agents enabled the number of microspheres to be determined in each cerebral hemisphere. Edema was assessed 12 or 24 h after embolization by measuring brain water content and, in some experiments, sodium and potassium. Pretreatments with dexamethasone, parachlorophenylalanine (an inhibitor of 5-hydroxytryptamine synthesis), mepyramine and metiamide (H1 and H2 histamine receptor antagonists) or aminophylline did not influence significantly the development of brain edema evaluated 24 h after embolization. Aminophylline treatment (100 mg/kg) markedly increased mortality following embolization. Gamma-butyrolactone (300 mg/kg, every 2 h) inhibited significantly the development of brain edema evaluated 12 hours after embolization. Increases in water and sodium in the embolized cerebral hemisphere were reduced by about 50%. This protective effect may be related to the known depressant action on brain metabolism.     

高血糖大鼠脑出血后脑水肿及COX-2的变化

目的 观察高血糖对脑出血后脑水肿及COX-2表达的影响,探讨胰岛素是否具有神经保护作用.方法 采用STZ法诱导高血糖模型,立体定向技术制作大鼠脑出血模型,干湿重法测量脑组织含水量和免疫组化法测定脑组织COX-2的表达.结果 与正常血糖组模型大鼠比较,高血糖组大鼠脑组织含水量明显增加(P<0.05),血肿周围COX-2阳性细胞表达明显增高(P<0.05);而胰岛素干预使上述各项指标降低至正常血糖组水平.结论 COX-2参与了大鼠血肿周围脑组织损伤的病理生理过程,高血糖可加重脑组织损伤,胰岛素则对神经有保护作用.     

Amelioration by cyclosporin A of brain damage following 5 or 10 min of ischemia in rats subjected to preischemic hyperglycemia

It has recently been shown that the immunosuppressant cyclosporin A (CsA) dramatically ameliorates the selective neuronal necrosis which results from 10 min of forebrain ischemia in rats. Since CsA is a virtually specific blocker of the mitochondrial permeability transition (MPT) pore which is assembled under adverse conditions, such as mitochondrial calcium accumulation and oxidative stress, the results suggest that the delayed neuronal death is due to an MPT. In the present study we explored whether CsA can also ameliorate the aggravated brain damage which is observed in hyperglycemic subjects, and which encompasses rapidly evolving neuronal lesions, edema, and postischemic seizures. Anaesthetised rats with a plasma glucose concentration of ≈13 mM were subjected to 10 min of forebrain ischemia, and allowed a recovery period of 7 days. In these animals, CsA prevented seizure from occurring and virtually eliminated neuronal necrosis. In order to allow even higher plasma glucose values (≈20 mM) to be studied, with long-term recovery, the duration of ischemia had to be reduced to 5 min. Again, CsA suppressed seizure activity and reduced neuronal damage. However, the effects were not as marked or consistent as in the 10 min group, suggesting that excessive tissue acidosis recruits mechanisms of damage which are not sensitive to CsA.     

Influence of lactate accumulation on calcium content of ischemic and postischemic brain

In this study, the cerebral hemisphere content of calcium as well as selected parameters of oxidative metabolism and electrophysiological function were assessed in normoglycemic and hyperglycemic rats that were exposed to ischemia produced by electrocautery of the vertebral arteries and reversible occlusion of the carotid arteries. In hyperglycemic animals, 0.5 h of ischemia was associated with large accumulations of lactate (27 mmol/kg), whereas normoglycemic animals showed lesser lactate accumulation (17 mmol/kg). At this sampling time (0.5 h of ischemia), both groups of ischemic animals showed tissue calcium contents that were unchanged from preischemic control levels. In normoglycemic animals, release of the carotid clamps and recirculation for 1.5-24 h was associated with normalization of lactate, ATP and phosphocreatine, clinical behavior, and EEG. During this 24 h of recirculation, cerebral calcium levels showed no changes. Hyperglycemic ischemic animals recirculated for 1.5-24 h showed a persistent lactic acidosis, depressed ATP and phosphocreatine, gross EEG abnormalities, seizures, and a high mortality rate. Again, during this 24 h period, cerebral calcium content showed no changes from preischemic control or from the matched saline-treated group. These data suggest that significant accumulation of calcium in brain tissue is not an early event in ischemic-hyperglycemic brain damage, and thus does not provide support for a role of calcium in the production of this form of ischemic damage.     

The two patterns of reactive astrocytosis in postischemic rat brain

The distribution and time course of postischemic astrocyte hypertrophy and hyperplasia and the relationship to neuronal viability or necrosis was studied in rats subjected to 30 min of carotid and vertebral artery occlusion followed by reperfusion from 3 h to 5 weeks. Intermediate filaments (IFs) were evaluated by electron microscopy, IF proteins by immunohistochemistry, and astrocyte division by [3H]thymidine uptake. Glial fibrillary acidic protein (GFAP) increased in damaged and nondamaged brain regions by 2 days and was associated with cell enlargement, increases in IF, and transformation of GFAP-negative into GFAP-positive glia. Cell hypertrophy and increased GFAP persisted only in regions of neuronal necrosis whereas the number and size of GFAP-positive astrocytes returned to control levels in nondamaged regions by 2 weeks. Astrocyte hyperplasia was not seen until 3 days and was confined to damaged brain regions. Vimentin-positive astrocytes were numerous by 2 days in damaged brain and remained only in those regions at 5 weeks. The data demonstrate that reactive astrocytosis develops in undamaged brain, but is reversible with prolonged survival, whereas reactive astrocytosis that accompanies structural brain damage persists for prolonged periods and is associated with hyperplasia, as well as hypertrophy. In addition, the results show that astrocyte expression of vimentin is more specific than GFAP in identifying regions of permanent ischemic injury during the early postischemic period.     

Early proliferative changes in astrocytes in postischemic noninfarcted rat brain

Transient cerebral ischemia in rats was produced by permanent occlusion of the vertebral arteries and 30-minute occlusion of the common carotid arteries. This model produces ischemic necrosis of neurons in the corpus striatum, cerebral cortex, and hippocampus; infarcts, with necrosis of neuropil, astrocytes, and blood vessels, are rare. Changes in striatal astrocytes at 40 minutes and 3 hours of reperfusion were evaluated by electron microscopy, and quantitative estimates of increases in cytoplasmic and mitochondrial area were performed. In areas of corpus striatum with moderate ischemic cell change, the percentage of astrocytic nuclei increased from 10.79% in controls to 17.76% at 40 minutes after ischemia (p < 0.01) and 19.86% at 3 hours (p < 0.01). Astrocytic cytoplasm was expanded and contained increased numbers of mitochondria, many of which were pleomorphic and had dilated intracristal spaces and condensed matrix. Rough endoplasmic reticulum was increased. Total mitochondrial area and number of mitochondrial profiles rose significantly in the astrocytic perikarya and foot processes at 3 hours postischemia. The greater number of astrocytes, the increases in mitochondria and rough endoplasmic reticulum and the configurational changes in the mitochondria suggest increased metabolic activity of astrocytes in postischemic, noninfarcted brain.     

The effect of postischemic blood glucose levels on ischemic brain damage in the rat

The effect of insulin-induced hypoglycemia following 10.5 minutes of forebrain ischemia was studied in the rat. All groups received preischemic glucose loading (2 gm/kg) to promote brain infarction. Following completion of ischemia, rats received either 2 to 3 IU/kg (low-dose group) or 8 to 20 IU/kg (high-dose group) insulin. During the survival period, blood glucose concentrations were maintained in the ranges of 1.2 to 2.9 mM and 2.9 to 4.9 mM, respectively, for the low-dose and high-dose insulin groups. Control rats were given 2 gm/kg glucose immediately following ischemia. During the recovery period, until perfusion at 7 days, they were given glucose, 2 gm/kg, twice daily by intraperitoneal injection, and their drinking water was supplemented with 25% glucose. Mortality (p less than 0.05) and postischemic seizure incidence (p less than 0.01) were significantly reduced in the low-dose insulin group compared to the control group. Mortality was increased in the high-dose insulin group compared to the control group and was associated with an increased incidence of postischemic seizures. Neuropathological examination revealed no cortical infarction in the low-dose or high-dose insulin-treated rats compared to a 60% incidence of cortical infarction in the control group. In addition, the high-dose insulin-treated group showed a significant reduction in striatal and hippocampal CA1 selective neuronal necrosis compared to control rats with comparable survivals (p less than 0.05). The findings suggest that postischemic blood glucose concentrations play an important role in modulating both ischemic infarction and selective neuronal necrosis.     

Strong attenuation of ischemic and postischemic brain edema in rats by a novel free radical scavenger

Regional changes in the amount of free fatty acids, polyphosphoinositides, and water content in the cerebral cortex were examined using a middle cerebral artery occlusion model of rats. The amount of various free fatty acids increased as polyphosphoinositides decreased during 3 and 6 hours of ischemia in the occluded middle cerebral artery territory. After 3 hours of reperfusion following 3 hours of ischemia, free fatty acids partially recovered while polyphosphoinositides did not. Water content increased significantly after 3 and 6 hours of ischemia, and a further increase was found after 3 hours of reperfusion following 3 hours of ischemia. The change of polyenoic fatty acids in this occluded middle cerebral artery territory was much smaller than that in the case of decapitation ischemia, although the amounts of polyphosphoinositides and monoenoic and saturated fatty acids showed almost identical changes in both cases, probably because polyenoic fatty acids may be washed out and/or peroxidatively consumed in the middle cerebral artery occlusion model due to its residual blood flow. Changes in the area surrounding the occluded middle cerebral artery territory were similar to the above results, although less dramatic. However, there was no change in free fatty acids, polyphosphoinositides, and water content in the contralateral cortex. A novel free radical scavenger (MCI-186), which prevents both nonenzymatic peroxidation and lipoxygenase activity in vitro, markedly attenuated the ischemic and postischemic brain swelling. These results suggest that free radical mechanisms may be involved in ischemic and postischemic brain edema.     

Neuronal plasticity and dendritic spines: effect of environmental enrichment on intact and postischemic rat brain.

The authors compared the influence of environmental enrichment on intact and lesioned brain, and tested the hypothesis that postischemic exposure to an enriched environment can alter dendritic spine density in pyramidal neurons contralateral to a cortical infarct. The middle cerebral artery was occluded distal to the striatal branches in spontaneously hypertensive rats postoperatively housed either in a standard or in an enriched environment. Intact rats were housed in the same environment. Three weeks later the brains were perfused in situ. The dendritic and spine morphology was studied with three-dimensional confocal laser scanning microscopy after microinjection of Lucifer yellow in pyramidal neurons in layers II/III and V/VI in the somatosensory cortex. In intact rats, the number of dendritic spines was significantly higher in the enriched group than in the standard group in all layers ( P < 0.05). Contralateral to the infarct, pyramidal neurons in layers II/III, which have extensive intracortical connections that may play a role in cortical plasticity, had significantly more spines in the enriched group than in the standard group ( P < 0.05). No difference was observed in layers V/VI. They conclude that housing rats in an enriched environment significantly increases spine density in superficial cortical layers in intact and lesioned brain, but in deeper layers of intact brain.     

Effects of cerebroprotective agents on cerebral blood flow and on postischemic energy metabolism in the rat brain

Male Wistar rats were subjected to forebrain ischemia of 10 min duration by clamping both common carotid arteries and simultaneously lowering systemic blood pressure to 40 mm Hg by exsanguination. Recovery was achieved by removing the arterial clamps and reinfusing the blood. Cortical levels of high-energy phosphates and glycolytic substrates were determined enzymatically. Naftidrofuryl (10 or 20 mg/kg i.p.) or ketamine (5 mg/kg i.v.) were applied 30 min prior to the induction of ischemia. S(-)-Emopamil (4 mg/kg) or nimodipine (50 micrograms/kg) were administered by intravenous infusion over 30 min. Nimodipine and emopamil increased the blood glucose level and lowered preischemic blood pressure. Under control conditions, a tendency toward a higher cortical glucose level was observed in treated brains. Brain energy stores were exhausted after ischemia in control and treated animals to the same degree. Lactate levels, however, were higher in emopamil-treated animals. This effect was attributed to the elevated preischemic glucose levels. During the early recovery period, the restoration of high-energy phosphates was accelerated by both calcium entry blockers. Nimodipine and emopamil increased the levels of glucose and glucose-6-phosphate in the early postischemic period. Naftidrofuryl (10 mg/kg) increased the level of creatine-phosphate and ATP after 2 min of recovery. Naftidrofuryl (20 mg/kg) exerted no effect on cerebral energy metabolism, but considerably reduced postischemic blood pressure (possibly thereby masking its ameliorative action). Ketamine accelerated the postischemic restoration of high-energy phosphates. In the conscious rat, local cerebral blood flow (LCBF) was determined with the 14C-iodoantipyrine technique following emopamil (20 mg/kg s.c.) or naftidrofuryl (10 mg/kg i.v.) application.(ABSTRACT TRUNCATED AT 250 WORDS)