A possible mechanism for the aglycemia-induced depression of glutamatergic excitation in the striatum

We have studied the possible mechanisms underlying the decrease of excitatory transmission induced by glucose deprivation by using electrophysiological recordings in corticostriatal slices. Extracellular field potentials were recorded in the striatum after cortical stimulation; these potentials were progressively reduced by glucose deprivation. The reduction started 5 minutes after the onset of aglycemia. The field potential was fully suppressed after 40 minutes of glucose deprivation. After the washout of the aglycemic solution only a partial recovery was observed. Aglycemia also induced a delayed inward current during single-microelectrode voltage-clamp recordings from spiny neurons. This inward current was coupled with an increased membrane conductance. The A1 adenosine receptor antagonists, 8-cyclopentyl-1,3-dimethylxanthine (CPT, 1 micromol/L) and 1,3-dipropyl-8-cyclopentylxanthine (CPX, 300 nmol/L), significantly reduced the aglycemia-induced decrease of field potential amplitude. Moreover, in the presence of CPT and CPX, a full recovery of the field potential amplitude after the interruption of the aglycemic solution was observed. Conversely, these antagonists affected neither the inward current nor the underlying conductance increase produced by glucose deprivation. The ATP-sensitive potassium channel blockers glibenclamide (10 micromol/L) and glipizide (100 nmol/L) had no effect on the aglycemia-induced decrease of the field potential amplitude. We suggest that endogenous adenosine, but not ATP-dependent potassium channels, plays a significant role in the aglycemia-induced depression of excitatory transmission at corticostriatal synapses probably through a presynaptic mechanism. Moreover, adenosine is not involved in the postsynaptic changes induced by glucose deprivation in spiny striatal neurons.     

Vitamin E prevents apoptosis in cortical neurons during hypoxia and oxygen reperfusion

Cerebral ischemia followed by oxygen reperfusion induces apoptosis in hippocampal neurons in stroke-prone spontaneously hypertensive rats (SHRSP) but not in Wistar Kyoto rats (WKY). The overproduction of oxygen-free radicals that occurs in the tissues of SHRSP is implicated in reoxygenation injury after hypoxia. Antioxidants inhibit reoxygenation injury in hippocampal slices, and temporal cortices in Alzheimer's disease increase sensitivity to oxygen-free radicals. Because this sensitivity may contribute to the development of the disease, we have studied hypoxia and oxygen reperfusion using cortical neurons isolated from WKY and SHRSP (at 15 days of gestation). We have tried to determine whether cortical neurons are damaged under these conditions, and whether neurons from SHRSP are more vulnerable than those from WKY. We have tried also to verify whether neuronal damage is minimized by vitamin E using the following techniques: (a) Trypan blue staining, (b) in situ staining of apoptosis, (c) ultrastructural examination, and (d) measurement of lactic dehydrogenase (LDH) activity in the bathing medium. Furthermore, we have examined the mechanisms involved in the development of neuronal damage and have studied ways of minimizing it. We demonstrated that 36 hours of hypoxia significantly increased the rate of cell death in SHRSP (p < 0.01), although 12 to 24 hours of hypoxia did not increase cell death in either WKY or SHRSP. In addition, 6 to 36 hours of hypoxia and 1.5 to 5 hours of oxygen reperfusion heavily damaged cells of both WKY and SHRSP, and most became apoptotic or necrotic. In contrast, cells incubated with 50 to 300 microg/ml of vitamin E remained intact, although 10 to 20 microg/ml of vitamin E did not totally preserve the cells. Moreover, vitamin E protected the neurons from high concentrations of sodium nitroprusside (nitric oxide donor) in a dose-dependent manner. Vitamin E, when added to the cells, increased in concentration in a time-dependent manner over a 24-hour period and in a dose-dependent manner below 200 microg/ml, and it was detected mostly in the mitochondria. We also demonstrated that serial treatments with allopurinol (a xanthine oxidase inhibitor) or superoxide dismutase preserved neurons during hypoxia and oxygen reperfusion. These data indicate that SHRSP neurons are weaker than WKY neurons in long-term hypoxia; oxygen radical generation occurs in the early minutes after reperfusion, and then the oxygen-free radicals cause heavy damage to the cells; and antioxidants including vitamin E react with the radicals, thereby preventing apoptosis and necrosis. Therefore, antioxidants appear to be the most important agents in lowering oxygen-free radical damage in cortical neurons.     

Retina subjected to components of ischemia in vitro. Selective vulnerability and minimum lethal exposure of neurons and glia to oxygen and/or glucose deprivation and to loss of exchange with incubating medium

Rabbit retinas were incubated at 37 C in media lacking oxygen, glucose, or both, or sealed in a small compartment without medium to convert them to a "closed system." They were then returned to control medium before being fixed for microscopy. Other retinas were incubated only in control medium and then fixed. Conversion of the retina to a closed system caused irreversible damage to all cell types within 40 minutes. Combined deprivation of oxygen and glucose also irreversibly damaged the neuronal cells within 40 minutes, but Mueller cells,the principal glial cells of the retina, were not irreversibly altered by 90 minutes of the deprivation. Deprivation of oxygen alone caused irreversible damage to receptor cells in 80 minutes, but the cells of the inner nuclear layer, ganglion cells, and Mueller cells retained normal structure for at least 180 minutes. Deprivation of glucose alone damaged receptor cells in 160 minutes and the other neuronal cells in 180 minutes, but did not irreversibly damage Mueller cells by 200 minutes.     

beta-Hydroxybutyrate fuels synaptic function during development. Histological and physiological evidence in rat hippocampal slices

To determine whether ketone bodies sustain neuronal function as energy substrates, we examined the effects of beta-hydroxybutyrate (betaHB) on synaptic transmission and morphological integrity during glucose deprivation in rat hippocampal slices. After the depression of excitatory postsynaptic potentials (EPSPs) by 60 min of glucose deprivation, administration of 0.5-10 mM D-betaHB restored EPSPs in slices from postnatal day (PND) 15 rats but not in slices from PND 30 or 120 rats. At PND 15, adding D-betaHB to the media allowed robust long-term potentiation of EPSPs triggered by high frequency stimulation, and prevented the EPSP-spike facilitation that suggests hyperexcitability of neurons. Even after PND 15,D-betaHB blocked morphological changes produced by either glucose deprivation or glycolytic inhibition. These results indicate that D-betaHB is not only able to substitute for glucose as an energy substrate but is also able to preserve neuronal integrity and stability, particularly during early development.     

Ceramide is involved in triggering of cardiomyocyte apoptosis induced by ischemia and reperfusion

Involvement of ceramide signaling in the initiation of apoptosis induction in myocardial cells by in vitro and in vivo ischemia and reperfusion was analyzed. Synthetic cell permeable C2-ceramide induced apoptotic death of rat neonatal cardiomyocytes in vitro. In vitro ischemia (oxygen/serum/glucose deprivation) led to a progressive accumulation of ceramide in cardiomyocytes. After 16 hours of simulated in vitro reperfusion (readdition of oxygen, serum and glucose), the level of ceramide in surviving cells was found to have returned to baseline, whereas, levels in nonadherent dead cells remained high. In the rat heart left coronary artery occlusion model, ischemia with the subsequent reperfusion, but not ischemia alone, induced apoptosis in myocardial cells as demonstrated by DNA electrophoresis and measurement of soluble chromatin degradation products. The content of ceramide in ischemic area was elevated to 155% baseline levels at 30 minutes, and to 330% after 210 minutes of ischemia. Ischemia (30 minutes) followed by reperfusion (180 minutes) increased the ceramide level to 250% in the ischemic area. The combination of results obtained in both in vitro and animal models demonstrate for the first time that ceramide signaling can be involved in ischemia/reperfusion death of myocardial cells.     

Selective impairment of response to acetylcholine after ischemia/reperfusion in mice

BACKGROUND AND PURPOSE: We previously reported that the endothelium-dependent dilation of pial arterioles by either topical acetylcholine (ACh) or bradykinin (BK) was markedly inhibited after 10 minutes of near total ischemia after bilateral carotid occlusion. The present study tests the responses after 10 minutes of reperfusion and investigates the effect of either oxygen or oxygen radical scavengers on the results. METHODS: Mice were subjected to bilateral carotid ligation or sham ligation. Pial arteriolar diameters were monitored by an image-splitting technique at a craniotomy site. In separate studies, the responses to topically suffused ACh, BK, or sodium nitroprusside (SNP) were tested before ischemia. After 10 minutes of ischemia and 10 minutes of reperfusion, the response was assessed again. Sham-operated mice were observed in each study. Cerebral blood flow was continuously monitored with a laser-Doppler technique. Additional separate studies were conducted as follows: presence of superoxide dismutase plus catalase during ischemia and reperfusion, or increase in the inspired oxygen (arterial oxygen) and oxygen in suffusate. RESULTS: The response to ACh was significantly impaired after 10 minutes of reperfusion. The responses to BK and SNP were unaffected. Radical scavengers failed to influence the impaired response to ACh. Elevations of arterial and suffusate oxygen levels to over 300 mm Hg failed to prevent the impairment. CONCLUSIONS: After 10 minutes of reperfusion, a selective impairment of the response to ACh remains. The response to another endothelium-dependent dilator, BK, recovered, and the response to endothelium-independent SNP was unaffected. Because neither radical scavengers nor oxygen altered the outcome with respect to ACh, I suggest that neither radical generation nor hypoxia accounts for the selective impairment of dilation by ACh. Rather, I hypothesize that reduced shear during ischemia diminishes the ability of the endothelium to synthesize and/or release the endothelium-derived relaxing factor for ACh. I hypothesize further that this impaired release or synthesis persists throughout the 10-minute period of reperfusion.     

Endogenous monocarboxylates sustain hippocampal synaptic function and morphological integrity during energy deprivation

The ability to fuel neurons via glycogenolysis is believed to be an important function of glia. Indeed, the slow, rather than immediate, depression of synaptic transmission in hippocampal slices during exogenous glucose deprivation suggests that intrinsic energy reservoirs help to sustain neurotransmission. It is believed that glia fuel neighboring neurons via diffusible monocarboxylates such as pyruvate and lactate, although a role for glucose has been proposed also. Using alpha-cyano-4-hydroxycinnamate (4-CIN) to inhibit monocarboxylate transport and cytochalasin B (CCB) to inhibit glucose transport, we examined the role of glucose and monocarboxylates in supporting the functional and morphological integrity of hippocampal neurons during glucose deprivation. Although 200 microM 4-CIN failed to depress EPSPs supported by 10 mM glucose, pretreatment with 4-CIN accelerated the depression of EPSPs during glucose deprivation. 4-CIN also accelerated the decline in glucose-supported EPSPs after administration of 50 microM CCB, whereas CCB failed to alter the slow decay of pyruvate-supported EPSPs during pyruvate deprivation. 4-CIN did not alter the morphology of pyramidal neurons in the presence of 10 mM glucose but produced significant damage during glucose deprivation or CCB administration. These results suggest that endogenous monocarboxylates rather than glucose maintain neuronal integrity during energy deprivation. Furthermore, EPSPs supported by 2-3.3 mM glucose were sensitive to 4-CIN, suggesting that endogenous monocarboxylates are involved in maintaining neuronal function even under conditions of mild glucose deprivation.     

p53-independent down-regulation of cyclin D1 and p21Waf1 in the process of immortalization of human esophageal epithelial cells

The temporal correlation between adenosine outflow and changes in field excitatory post synaptic potentials (fEPSP) occurring during ischemia-like conditions was investigated in rat hippocampal slices. Five-minute long ischemia-like conditions resulted in a 100% depression of fEPSP amplitude, followed by a complete recovery after 6-7 min of reperfusion. By reducing the duration of the ischemic insult to 2 min, fEPSP was depressed by 50%. During both 5 and 2 min of ischemia-like conditions, a significant increase in adenosine outflow was detected. During reperfusion, when fEPSP amplitude recovered completely, the adenosine level in the extracellular fluid returned to basal values. The strict relationship between the increase in adenosine outflow and fEPSP inhibition supports the hypothesis that adenosine is largely responsible for the synaptic transmission depression during cerebral ischemia.     

Dual Isoflurane-induced Preconditioning Improves Neuroprotection in Rat Brain In Vitro and the Role of Extracellular Signal-regulated Protein Kinase

Objective To test the ability of isoflurane-induced preconditioning against oxygen and glucose deprivation (OGD) injury in vitro.Methods Rat hippocampal slices were exposed to 1 volume percentage (vol%),2vol% or 3vol% isoflurane respectively for 20 minutes under normoxic conditions (95% O2/5% CO2) once or twice (12 slices in each group) before OGD,with 15-minute washout after each exposure.During OGD experiments,hippocampus slices were bathed with artificial cerebrospinal fluid (ACSF) lacking glucose and perfused with 95% N2 and 5% CO2 for 14 minutes,followed by a 30-minute reperfusion in normal ACSF.The CA1 population spike (PS) was measured and used to quantify the degree of neuronal function recovery after OGD.To assess the role of mitogen-activated protein kinases (MAPKs) in isoflurane preconditioning,U0126,an inhibitor of extracellular signal-regulated protein kinase (ERK1/2),and SB203580,an inhibitor of p38 MAPK,were used before two periods of 3vol% isoflurane exposure.Results The degree of neuronal function recovery of hippocampal slices exposed to lvol%,2vol%,or 3vol% isoflurane once was 41.88%±9.23%,55.05%± 11.02%,or 63.18%±10.82% respectively.Moreover,neuronal function recovery of hippocampal slices exposed to lvol%,2vol%,or 3vol% isoflurane twice was 53.7S%±12.04%,63.50%±11.06%,or 76.25%±12.25%,respectively.Isoflurane preconditioning increased the neuronal function recovery in a dose-dependent manner.U0126 blocked the preconditioning induced by dual exposure to 3vol% isoflurane (6.13%±1.56%,P<0.01) and ERK1 /2 activities.Conclusions Isoflurane is capable of inducing preconditioning in hippocampal slices in vitro in a dose-dependent manner,and dual exposure to isoflurane with a lower concentration is more effective in triggering preconditioning than a single exposure.Isoflurane-induced neuroprotection might be involved with ERK1/2 activities.     

Mechanism of NADH transfer between alcohol dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase

To investigate the correlation between neural activity and intracellular Ca2+ ([Ca2+]i) mobilization in immature and adult brain during ischemia (hypoxia and glucose deprivation) and deprivation of glucose, hippocampal slices were prepared from 7-, 10-day-old and adult rats. Population spikes (PS) and antidromic responses (AR) were recorded in the pyramidal cell layer of the CA1 area as an index of neural function. [Ca2+]i mobilization of the stratum radiatum in the CA1 area was measured using the fluorescent dye fura-2 AM. The rise in [Ca2+]i occurred earlier in the adult animal and the decay times for the orthodromic PS and antidromic responses were shorter in the adult during ischemia. The field potentials and antidromic responses decreased substantially prior to the elevation of [Ca2+]i in both developing and adult brains. Furthermore, ATP levels decreased substantially before the elevation of [Ca2+]i during ischemia. These results suggest that neural activity and intracellular Ca2+ homeostasis in the immature rats brain are more resistant to energy failure than adult rats and that neuronal activity in the developing and adult brain is impaired initially by energy depletion during ischemia. In the immature animal, during glucose deprivation, the antidromic responses were slowly decayed or even failed to extinguish and [Ca2+]i levels were maintained for a longer period or even failed to rise in spite of the rapid loss of PS. Furthermore, ATP levels were well preserved at the time of PS loss. These results agree well with our previous reports showing that glucose plays an important role in the preservation of synaptic transmission in addition to its major function as an energy substrate.     

Ascorbyl free radical as a real-time marker of free radical generation in briefly ischemic and reperfused hearts. An electron paramagnetic resonance study

The role of free radicals in myocardial reperfusion injury remains controversial. We have developed a new method using ascorbyl free radical (AFR) as a real-time, quantitative marker of free radical generation during myocardial reperfusion. A total of 35 dogs were studied. Twelve open-chest dogs underwent either 5 minutes (n = 5) or 20 minutes (n = 7) of coronary artery occlusion and 30 minutes of reperfusion. Seven additional animals undergoing 20 minutes of coronary occlusion also received the antioxidant enzymes superoxide dismutase and catalase, beginning 10 minutes before occlusion through the end of reperfusion. Exogenous ascorbate was infused intravenously, and the concentration of AFR in the great cardiac vein was continuously measured by electron paramagnetic resonance spectroscopy. Preocclusion AFR concentration was similar in the three groups. Upon reperfusion, AFR rose significantly in each animal group (P < .05). However, the AFR rise in the 20-minute-occlusion group, 38 +/- 17%, was significantly greater than in the 5-minute-occlusion group, 27 +/- 14% (P < .002). In addition, in the animals that received superoxide dismutase and catalase, the rise in the AFR was markedly attenuated, 13 +/- 6% (P < .002). Two dogs that received ascorbate but did not undergo coronary artery occlusion/reperfusion sequences showed no change in coronary venous AFR signal, indicating the stability of the signal over time. Five dogs received ascorbate while undergoing interventions to alter coronary venous flow: intravenous saline, dobutamine, dipyridamole, and nitroglycerin. Coronary venous AFR changes were minimal despite large coronary flow alterations, indicating that the AFR signal is independent of changes in coronary venous flow.(ABSTRACT TRUNCATED AT 250 WORDS)     

The neurotoxicity of sulfur-containing amino acids in energy-deprived rat hippocampal slices

The rat hippocampal slice preparation and its electrophysiology were used to assess the toxicity of two sulfur-containing amino acids, L-cysteate (CA) and L-cysteine (CYS). Both compounds were innocuous under normal conditions but became toxic in energy-deprived (lack of oxygen or glucose) slices. CA and CYS toxicity was apparent as both reduced the number of slices that normally recover their neuronal function (evoked CA1 population spike) after a standardized period of hypoxia or glucose deprivation (GD). The competitive N-methyl-D-aspartate (NMDA) antagonist DL-2-amino-5-phosphonovalerate blocked the toxicity of both CA and CYS in hypoxic slices, but it was effective only against CYS toxicity in glucose-deprived slices. The glycine antagonist 7-chlorokynurenate blocked CA and CYS toxicity in hypoxic slices but was unable to block their toxicity in glucose-deprived tissue. Perfusing slices with medium containing a high magnesium concentration blocked the toxicity of CA in both hypoxic and glucose-deprived slices, a treatment that was ineffective against CYS toxicity under either condition. Calcium depletion from the perfusion medium completely blocked the damaging effect of both amino acids in hypoxic slices, but it only partially blocked the toxicity of CA and did not block that of CYS in glucose-deprived slices. These results suggest that CA and CYS activate different NMDA receptor subsets and other glutamate receptor subtypes. Moreover, the results indicate a possible difference between the mechanism that lead to hypoxic neuronal damage and the one that lead to hypoglycemic neuronal damage.     

Variation in mRNA expression of alpha-adrenergic, neurokinin and muscarinic receptors amongst four arteries of the rat

The effects of Mg2+ concentration (Mg2+o, 0, 1.2, 2.4, and 4.8 mM) on the incidence of reperfusion arrhythmias and on the cellular electrical activity were studied in spontaneously beating rat hearts. The surface electrogram and the membrane potential were recorded in control conditions, during 10 min of regional ischemia (ligature of the left anterior descending coronary artery), and on reflow. Changes in Mg2+o did not alter action potential morphology but the depolarization induced by ischemia decreased with increasing Mg2+o. In hearts perfused with Mg2+ free solution or 1.2 mM subthreshold delayed afterdepolarizations (DADs) were often detected during ischemia. Moreover, DADs could be identified as initial events in the production of extrabeats or tachycardia appearing on reperfusion under these conditions. Chaotic electrical activity during fibrillation precluded the observation of DADs. The overall incidence (100%) and severity of ventricular tachyarrhythmias (80% tachycardia and fibrillation) was similar in both groups. At high Mg2+o, subthreshold DADs were occasionally observed during ischemia and often on reperfusion where they did not lead to the development of overt arrhythmias. Consequently, the incidence, severity, and duration of arrhythmic episodes on reflow was markedly reduced. Raising Mg2+ only on reperfusion did not prevent the development of arrhythmias, whose morphology in the intracellular recordings was similar to that found in hearts perfused without Mg2+ or with 1.2 mM. The recovery of sinus rhythm after 10 min of reperfusion was linearly related to Mg2+o. Our data strengthen the view that reperfusion arrhythmias belong to the Ca2+ mediated non reentrant type and suggest that Mg2+ counteracts these arrhythmias by depressing cytosolic Ca2+ oscillations. Besides, it appears that raising Mg2+o reduces ischemic K+o accumulation. The resulting changes in resting potential could contribute to lower DADs amplitude and thus decrease the arrhythmogenic potential of the Ca2+i oscillations induced by reperfusion.     

Proarrhythmic actions of flecainide in an isolated tissue model of ischemia and reperfusion

Flecainide may increase the incidence of cardiac arrhythmias in acute ischemia. The objective of this study was to determine the cellular actions underlying this effect in an isolated tissue model of acute ischemia and reperfusion. Transmembrane electrical activity was recorded with conventional microelectrode techniques from epi- and endocardial surfaces of right ventricular free walls from guinea pig hearts. Endocardium was stimulated. Tissues were equilibrated in Tyrode's solution for 60 min, then exposed to simulated ischemia (hypoxia, acidosis, lactate, hyperkalemia, no glucose) for 15 min and reperfused with normal Tyrode's solution for 30 min. In the absence of flecainide, sustained and nonsustained ventricular tachycardia occurred in 78% of hearts during ischemic conditions and 78% in early reperfusion (n = 14). Premature beats occurred in 14% of hearts in early reperfusion. Ventricular tachycardia was associated with abbreviation of endocardial effective refractory period and action potential duration, plus prolongation of transmural conduction time. Flecainide abolished premature beats at a concentration of 1 mumol/l or higher. However, an increase in the incidence of ventricular tachycardia occurred in both ischemia and reperfusion at all concentrations of flecainide (0.03-10.0 mumol/l). Proarrhythmic effects of flecainide were associated with selective prolongation of transmural conduction time in ischemia and early reperfusion. In epicardial slices flecainide lengthened conduction time transverse, but not parallel to fiber orientation. Our results suggest that proarrhythmic effects of flecainide in acute ischemia and reperfusion are mediated by potentiation of the arrhythmogenic effects of ischemia on anisotropic properties of the myocardium.     

Direct administration and utilization of [1-13C]glucose by fetal brain and liver tissues under normal and ischemic conditions: 1H, 31P, and 13C NMR studies

The acute and delayed effects of anoxia on synaptic transmission and long-term potentiation (LTP) were examined in the CA1 region of rat hippocampal slices. Oxygen deprivation for 20 minutes completely but reversibly depressed excitatory postsynaptic potentials mediated by both N-methyl-D-aspartate receptors (NMDAR) and non-NMDAR. Although LTP was reliably produced by a single tetanus delivered 30 minutes after reoxygenation, LTP could not be induced when a tetanus was delivered 70 to 100 minutes after reoxygenation. A tetanus delivered 100 minutes after reoxygenation produced lasting synaptic enhancement when 100 mumol/L D,L-amino-phosphonovaleric acid (APV), a competitive NMDAR antagonist, was administered during the period of oxygen deprivation. The delayed effects of oxygen deprivation were not blocked when APV was administered after oxygen deprivation. Similarly, the delayed effects on LTP induction were overcome by inhibitors of nitric oxide synthase when the nitric oxide synthase inhibitors were administered during anoxia, but not when administered after oxygen deprivation. These results suggest that untimely activation of NMDAR and nitric oxide release during anoxia produce delayed inhibition of LTP induction and may be involved in the memory defects that occur subsequent to cerebral hypoxia.     

Prior repeated exposure to a 5-HT3 receptor agonist does not alter the ethanol-induced conditioned taste aversion in rats

The cardiovascular adaptations of seals that contribute to their ability to tolerate long periods of diving asphyxial hypoxia result in episodic regional ischemia during diving and abrupt reperfusion upon termination of the dive. These conditions might be expected to result in production of oxygen-derived free radicals and other forms of highly reactive oxygen species. Seal organs vary during dives with respect to the degree and persistence of ischemia. Myocardial perfusion is reduced and intermittent; kidney circulation is vigorously vasoconstricted. Heart and kidney tissues from ringed seals (Phoca hispida) and domestic pigs (Sus scrofa) were compared in reactions to experimental ischemia. Resulting production of hypoxanthine, indicative of ATP degradation, was higher in pig than in seal tissues. Activity of superoxide dismutase (SOD), an oxygen radical scavenger, was higher in seal heart. We suggest that these results indicate enhanced protective cellular mechanisms in seals against the potential hazard of highly reactive oxygen forms. SOD activity was unexpectedly higher in pig kidney.     

Transient neurophysiological changes in CA3 neurons and dentate granule cells after severe forebrain ischemia in vivo

Transient neurophysiological changes in CA3 neurons and dentate granule cells after severe forebrain ischemia in vivo. J. Neurophysiol. 80: 2860-2869, 1998. The spontaneous activities, evoked synaptic responses, and membrane properties of CA3 pyramidal neurons and dentate granule cells in rat hippocampus were compared before ischemia and 相似文献   

The role of xanthine dehydrogenase (xanthine oxidase) in ischemia-reperfusion injury in rat kidney

Xanthine dehydrogenase (XDH) and xanthine oxidase (XO) are enzymes involved in the metabolism of purines in various organisms. XO produces superoxide radicals, suggesting that is responsible for tissue ischemia-reperfusion injury. To test this notion further studies were performed on rat kidneys and the time course of changes in purine nucleotides, oxypurines and XDH and XO activity was determined. At 24 hours after reperfusion subsequent to 30-minute ischemia, serum creatinine increased to 0.83 +/- 0.74 mg/dl from 0.28 +/- 0.06 mg/dl (the level prior to ischemia, the control). Renal ATP and ADP contents were reduced after ischemia lasting for 30 minutes and restored 10 minutes after reperfusion following 30 minutes of ischemia. The renal AMP content increased after 30 minutes of ischemia and recovered within 10 minutes after reperfusion. The total adenine nucleotide (TAN) content was reduced gradually during ischemia-reperfusion in the rat kidney. Although the energy charge was reduced following 30 minutes of ischemia, it was restored to the control level 10 minutes following reperfusion. Hypoxanthine (HX) and xanthine (X), which had accumulated at 30 minutes after ischemia, were reduced to the control levels 10 minutes after reperfusion. There were no significant changes in the pre-ischemia values of total XDH and XO activities or XDH/XO ratio during the period nor at various time intervals (up to 24 hours) during reperfusion. It was shown that HX and X accumulate without significant conversion of XDH to XO during ischemia. Therefore the putative role of XO in ischemia-reperfusion injury seems to more complex than initially predicted.     

Restriction fragment length polymorphism analysis of highly virulent strains of infectious bursal disease viruses from Holland, Turkey, and Taiwan

Ascorbyl free radical (AFR), can be considered as an atoxic and endogenous indicator of oxidative stress. The purpose of our experiments was to investigate the influence of the severity and length of ischemia on the extent of AFR release during myocardial ischemia and reperfusion. For that purpose, isolated perfused rat hearts were submitted to a global ischemia, either total (residual flow 0%) or low flow (residual flow 5%), of 20 or 60 min length. Coronary effluents were collected at different times of experimentation and analyzed with Electron Spin Resonance (ESR) spectroscopy. AFR ESR doublet (g = 2.0054, aH = 0.188 MT) was not detected in coronary effluents collected during control perfusion periods. Nevertheless, during low-flow ischemia, a weak AFR release was noted. Moreover, a sudden and massive AFR liberation was observed at the time of reperfusion: this AFR release was weaker after low-flow ischemia than after total ischemia and was enhanced when the duration of ischemia increased from 20 min to 60 min. The large liberation of AFR noticed during global total ischemia was associated with a greater depression in myocardial contractile function and a lower recovery in coronary flow. In conclusion, our study demonstrates that AFR production at the time of reperfusion depends on the duration and strength of the ischemia, and is related to free radical injury. According to previously described ascorbate/AFR properties, we can conclude that AFR liberation in coronary effluents could represent a marker of oxidative stress during ischemia and/or reperfusion of hearts. This AFR release could be considered a sign of the severity of the ischemic episode, and could be related to the functional impairment during reperfusion.     

Oxygen/glucose deprivation in hippocampal slices: altered intraneuronal elemental composition predicts structural and functional damage

Effects of oxygen/glucose deprivation (OGD) on subcellular elemental composition and water content were determined in nerve cell bodies from CA1 areas of rat hippocampal slices. Electron probe x-ray microanalysis was used to measure percentage water and concentrations of Na, P, K, Cl, Mg, and Ca in cytoplasm, nucleus, and mitochondria of cells exposed to normal and oxygen/glucose deficient medium. As an early (2 min) consequence of OGD, evoked synaptic potentials were lost, and K, Cl, P, and Mg concentrations decreased significantly in all morphological compartments. As exposure to in vitro OGD continued, a negative DC shift in interstitial voltage occurred ( approximately 5 min), whereas general elemental disruption worsened in cytoplasm and nucleus (5-42 min). Similar elemental changes were noted in mitochondria, except that Ca levels increased during the first 5 min of OGD and then decreased over the remaining experimental period (12-42 min). Compartmental water content decreased early (2 min), returned to control after 12 min of OGD, and then exceeded control levels at 42 min. After OGD (12 min), perfusion of hippocampal slices with control oxygenated solutions (reoxygenation) for 30 min did not restore synaptic function or improve disrupted elemental composition. Notably, reoxygenated CA1 cell compartments exhibited significantly elevated Ca levels relative to those associated with 42 min of OGD. When slices were incubated at 31 degreesC (hypothermia) during OGD/reoxygenation, neuronal dysfunction and elemental deregulation were minimal. Results show that in vitro OGD causes loss of transmembrane Na, K, and Ca gradients in CA1 neurons of hippocampal slices and that hypothermia can obtund this damaging process and preserve neuronal function.