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J A Zivin

Publications and source records attributed to J A Zivin.

At least 19 recordsLinked to original sources
PubMed1999

Changes in expression of the DNA repair protein complex DNA-dependent protein kinase after ischemia and reperfusion.

Reperfusion of ischemic tissue causes an immediate increase in DNA damage, including base lesions and strand breaks. Damage is reversible in surviving regions indicating that repair mechanisms are operable. DNA strand breaks are repaired by nonhomologous end joining in mammalian cells. This process requires DNA-dependent protein kinase (DNA-PK), composed of heterodimeric Ku antigen and a 460,000 Da catalytic subunit (DNA-PKcs). In this study, a rabbit spinal cord model of reversible ischemia was used to demonstrate the effect of acute CNS injury on the activity and expression of DNA-dependent protein kinase. The DNA-binding activity of Ku antigen, analyzed by an electrophoretic mobility shift assay, increased during reperfusion after a short ischemic insult (15 min of occlusion), from which the animals recover neurological function. After severe ischemic injury (60 min of occlusion) and reperfusion that results in permanent paraplegia, Ku DNA binding was reduced. Protein levels of the DNA-PK components-Ku70, Ku80, and DNA-PKcs-were monitored by immunoblotting. After 60 min of occlusion, the amount of DNA-PKcs and the enzyme poly(ADP-ribose) polymerase (PARP) decreased with the same time course during reperfusion. Concurrently 150 and 120 kDa fragments were immunostained by an anti-DNA-PKcs monoclonal antibody. This antibody was shown to cross-react with alpha-fodrin breakdown products. The 120 kDa fodrin peptide is associated with caspase-3 activation during apoptosis. Both DNA-PKcs and PARP are also substrates for caspase-3-like activities. The results are consistent with a model in which after a short ischemic insult, DNA repair proteins such as DNA-PK are activated. After severe ischemic injury, DNA damage overwhelms repair capabilities, and cell death programs are initiated.

Animals↗
PubMed1999

Modification of postsynaptic densities after transient cerebral ischemia: a quantitative and three-dimensional ultrastructural study.

Abnormal synaptic transmission has been hypothesized to be a cause of neuronal death resulting from transient ischemia, although the mechanisms are not fully understood. Here, we present evidence that synapses are markedly modified in the hippocampus after transient cerebral ischemia. Using both conventional and high-voltage electron microscopy, we performed two- and three-dimensional analyses of synapses selectively stained with ethanolic phosphotungstic acid in the hippocampus of rats subjected to 15 min of ischemia followed by various periods of reperfusion. Postsynaptic densities (PSDs) from both area CA1 and the dentate gyrus were thicker and fluffier in postischemic hippocampus than in controls. Three-dimensional reconstructions of selectively stained PSDs created using electron tomography indicated that postsynaptic densities became more irregular and loosely configured in postischemic brains compared with those in controls. A quantitative study based on thin sections of the time course of PSD modification indicated that the increase in thickness was both greater and more long-lived in area CA1 than in dentate gyrus. Whereas the magnitude of morphological change in dentate gyrus peaked at 4 hr of reperfusion (140% of control values) and declined thereafter, changes in area CA1 persisted and increased at 24 hr of reperfusion (191% of control values). We hypothesize that the degenerative ultrastructural alteration of PSDs may produce a toxic signal such as a greater calcium influx, which is integrated from the thousands of excitatory synapses onto dendrites, and is propagated to the neuronal somata where it causes or contributes to neuronal damage during the postischemic phase.

Animals↗
PubMed1999

Persistent phosphorylation of cyclic AMP responsive element-binding protein and activating transcription factor-2 transcription factors following transient cerebral ischemia in rat brain.

The transcription factors cyclic AMP responsive element-binding protein (CREB) and activating transcription factor-2 were studied in rat brains subjected to 15 min ischemia followed by varied periods of reperfusion using western blot and immunocytochemical analyses. The total amounts of both CREB and activating transcription factor-2 were not altered in the hippocampus after ischemia. In contrast, levels of the phosphorylated forms of both transcription factors decreased during ischemia but rebounded following reperfusion. The phospho-forms of CREB and activating transcription factor-2 showed regional and temporal differences in their expression. Phospho-CREB was increased relative to control levels at 30 min, and continued to increase for at least three days postischemia, mainly in dentate granule cells. The level of phospho-activating transcription factor-2 appeared to be higher in CAI pyramidal cells than in dentate granule cells after ischemia. The present findings suggest that the signaling pathways for phosphorylation of CREB may be neuroprotective for dentate cells, which are relatively resistant to ischemic insults. The increased phospho-activating transcription factor-2 may reflect increased stresses in these neurons. The more modest activation of CREB pathways in CA1 neurons may not be enough to overcome the increased stresses in these neurons, contributing to delayed neuronal death.

Activating Transcription Factor 2↗
PubMed1999

Thrombolysis with tissue plasminogen activator alters adhesion molecule expression in the ischemic rat brain.

BACKGROUND AND PURPOSE: We tested the hypothesis that treatment of embolic stroke with recombinant human tissue plasminogen activator (rhtPA) alters cerebral expression of adhesion molecules. METHODS: Male Wistar rats were subjected to middle cerebral artery occlusion by a single fibrin-rich clot. P-selectin, E-selectin, and intercellular adhesion molecule-1 (ICAM-1) immunoreactivity was measured at 6 or 24 hours after embolic stroke in control rats and in rats treated with rhtPA at 1 or 4 hours after stroke. To examine the therapeutic efficacy of combined rhtPA and anti-ICAM-1 antibody treatment at 4 hours after embolization, ischemic lesion volumes were measured in rats treated with rhtPA alone, rats treated with rhtPA and anti-ICAM-1 antibody, and nontreated rats. RESULTS: Administration of rhtPA at 1 hour after embolization resulted in a significant reduction of adhesion molecule vascular immunoreactivity after embolization in the ipsilateral hemisphere compared with corresponding control rats. However, when rhtPA was administered to rats at 4 hours after embolization, significant increases of adhesion molecule immunoreactivity in the ipsilateral hemisphere were detected. A significant increase of ICAM-1 immunoreactivity was also detected in the contralateral hemisphere at 24 hours after ischemia. A significant reduction in lesion volume was found in rats treated with the combination of rhtPA and anti-ICAM-1 antibody compared with rats treated only with rhtPA. CONCLUSIONS: The present study suggests that the time of initiation of thrombolytic therapy alters vascular immunoreactivity of inflammatory adhesion molecules in the ischemic brain and that therapeutic benefit can be obtained by combining rhtPA and anti-ICAM-1 antibody treatment 4 hours after stroke.

Animals↗
PubMed1998

Activation of nuclear factor-kappaB in the rabbit spinal cord following ischemia and reperfusion.

The transcription factor NF-kappaB is a ubiquitously expressed inducible regulator of a broad range of genes. Recent studies have shown that activation of NF-kappaB predominantly is associated with protecting cells from apoptosis, but in some cell models, it is associated with promoting cell death. We used a rabbit spinal cord model of reversible ischemia to determine whether NF-kappaB was activated by ischemic and reperfusion injury. DNA binding activity of NF-kappaB was analyzed by an electrophoretic mobility shift assay in animals subjected to varying durations of ischemia and reperfusion. A low level of constitutive NF-kappaB DNA binding was detected in normal lumbar spinal cord extracts. Animals subjected to a short ischemic insult of 15 min, from which they usually recover neurologic function, had a significant increase in the amount of active NF-kappaB in nuclear extracts after 18 h reperfusion. There was no change in nuclear NF-kappaB DNA binding in animals occluded for 60 min that are permanently paraplegic and exhibit extensive neuropathological damage. The amount of deoxycholate-releasable NF-kappaB sequestered in the cytosol, however, decreased after 18 h reperfusion in rabbits occluded for 60 min. This correlated with a decrease in the amount of RelA(p65) NF-kappaB subunit. The results suggest that activation of NF-kappaB after a limited ischemic injury may participate in a neuroprotective response and not in cell death.

Animals↗
PubMed1998

Assembly of proteins to postsynaptic densities after transient cerebral ischemia.

Transient ischemia leads to changes in synaptic efficacy and results in selective neuronal damage during the postischemic phase, although the mechanisms are not fully understood. The protein composition and ultrastructure of postsynaptic densities (PSDs) were studied by using a rat transient ischemic model. We found that a brief ischemic episode induced a marked accumulation in PSDs of the protein assembly ATPases, N-ethylmaleimide-sensitive fusion protein, and heat-shock cognate protein-70 as well as the BDNF receptor (trkB) and protein kinases, as determined by protein microsequencing. The changes in PSD composition were accompanied by a 2.5-fold increase in the yield of PSD protein relative to controls. Biochemical modification of PSDs correlated well with an increase in PSD thickness observed in vivo by electron microscopy. We conclude that a brief ischemic episode modifies the molecular composition and ultrastructure of synapses by assembly of proteins to the postsynaptic density, which may underlie observed changes in synaptic function and selective neuronal damage.

Adenosine Triphosphatases↗
PubMed1998

Acute hypertension promotes hemorrhagic transformation in a rabbit embolic stroke model: effect of labetalol.

We examined the relationship between acute hypertension following cerebral embolization and subsequent hemorrhagic transformation (HT) in a rabbit embolic stroke model. We have shown previously that the likelihood and severity of hemorrhage were significantly correlated with the magnitude of an acute hypertensive response to embolization. It was not clear, however, whether hypertension actually caused hemorrhage or was merely a marker of more severe stroke. In the current studies, we attempted to clarify the relationship between acute hypertension and HT by either pharmacologically inducing or attenuating the brief hypertensive response to embolization in rabbits. Under halothane anesthesia, two catheters were implanted in the right carotid arteries of male New Zealand white rabbits, one oriented toward the heart and one toward the brain. The animals were allowed to awaken and were embolized using blood clot emboli injected into the middle cerebral artery. Blood pressure was monitored via the second carotid catheter. In the first experiment, hypertension was induced with angiotensin II, administered at the time of embolization or 1 h later. In the second experiment, we attempted to attenuate the hypertensive response using intravenous labetalol. The animals were sacrificed 18 h after embolization and the brains evaluated for hemorrhage. In the first experiment, administration of angiotensin II immediately after embolization did not increase the hypertensive response to embolization further than that spontaneously occurring, and no angiotensin II-related HT was observed. In contrast, an additional angiotensin-II-induced hypertensive episode 1 h after embolization significantly increased the number of 5-mm serial brain sections displaying HT, from 3.0 +/- .3 (mean +/- SE) in Controls to 5.4 +/- .8 in treated animals. In the second experiment, administration of labetalol (15 mg/kg) significantly reduced the number of brain sections with visible HT, from 3.2 +/- .5 in controls to 1.6 +/- .4 in treated animals. Acute hypertension during the first hour after cerebral embolization promotes HT in this rabbit embolic stroke model. Labetalol prevents blood pressure elevation and reduces the extent of HT in the same model.

Acute Disease↗
PubMed1998

Factors determining the therapeutic window for stroke.

The duration of the window to treat acute cerebral ischemia has become an important question since the first effective drug for stroke victims has become available. Statistical analysis of relevant animal studies suggests that irreversible focal injury begins within a few minutes and is complete within about 6 hours. There will be substantial difficulties in attempting to obtain accurate estimates of the duration of ischemia that causes permanent damage in patients unless technical obstacles are overcome. Empirical estimates of the therapeutic window for stroke can be obtained from properly designed clinical trials, but optimal care will continue to necessitate urgent treatment.

Animals↗
PubMed1997

Reversible ischemia increases levels of Alzheimer amyloid protein precursor without increasing levels of mRNA in the rabbit spinal cord.

In a rabbit spinal cord ischemia model (RSCIM), the time courses of neuropathological damage of the spinal cord and neurological impairment of the motor functions are well established, demonstrating that the extent of neuropathological damage and the severity of neurological impairment are closely correlated. We used the RSCIM to elucidate the effects of reversible (15 min) and irreversible (60 min) ischemia on the endogenous levels of amyloid protein precursors (APPs) at both the mRNA and protein levels in the caudolumbar/sacral region of the spinal cord. We speculate that endogenous APPs are induced by ischemia as either trophic factors or stress-induced proteins in the RSCIM. A 15-min occlusion transiently increased the APP protein levels in neurons, which returned to the original levels by the end of 60 min occlusion. The increase in APP protein levels during 15-min ischemic insult does not appear to involve regulation at the mRNA level. The increased level of APPs, particularly of the soluble form, could support the possibility that APPs play a neuroprotective role in the RSCIM as stress-induced proteins. In contrast, failure to maintain the increased APP protein levels or to increase the mRNA, as seen in the 60-min ischemia samples, may be one of the causal factors that induce necrosis and neuronal cell death leading to irreversible neurological impairment.

Amyloid beta-Protein Precursor↗
PubMed1997

Effect of ischemic cerebral volume changes on behavior.

Ischemia causes long-term effects on brain volume and neurologic function but the relationship between the two is poorly characterized. We studied the relationships between brain volume and three measures of rodent behavior after cerebral ischemia was induced by injecting several thousand microspheres into the internal carotid arteries of rats. Forty eight hours later, each subject was rated using a global neurologic rating scale. Several weeks later, the subjects were tested for open field activity and visual spatial learning. Post-mortem we measured the volume of the cerebral hemispheres and estimated the volume densities of cortex, white matter, hippocampus, basal ganglia, thalamus, ventricle, and visible infarction. Ischemia caused significant impairment, as measured by the global rating scale; the probability of an abnormal rating was correlated with the number of microspheres trapped in the brains. Visual spatial learning was significantly impaired by ischemia, but this deficit was independent of the count of microspheres, whether the subject was abnormal at 48 h, and whether the left or right hemisphere was embolized. Cerebral hemisphere volume was reduced from 430 mm3 to 376 mm3 (P < 0.05). The cortex was reduced from 22 to 19% of cerebrum (P < 0.05) and the white matter compartment was reduced to similar degree. The lesion volume was 6% of cerebrum, comparable to that seen with other ischemia methods. The global outcome rating was significantly related to total cerebral volume, but not to volume changes in any single compartment. On the other hand, visual spatial learning was significantly influenced by volume changes in the cortex and white matter, but not by the topography of the visible infarctions. Open field activity was not altered by infarction. Our data suggests that the total volume of brain tissue lost to infarction may partially determine global neurological rating independently of the topography of the volume loss. Integrative functions such as learning may depend more on the integrity of specific compartments and less on the total volume of intact brain. The volume of visible cystic infarction was not related to long term behavioral outcome. These results should be confirmed using another method of inducing ischemia.

Animals↗
PubMed1997

Neuroprotective therapies in stroke.

Neuroprotective drugs are known to reduce neurological damage in animal models of stroke, but none are generally accepted for the treatment of patients with acute stroke. Thrombolytic therapy with alteplase (recombinant tissue-type plasminogen activator; rt-PA) has been shown to improve outcomes in patients with stroke, but it must be given quite rapidly after stroke onset. The efficacy of alteplase therapy has proven that acute treatment is possible, and methods used in those trials will be applicable to neuroprotective development. A variety of neuroprotective drugs have already been tested and more trials are likely. Glutamate antagonists have been most extensively evaluated, but they are relatively disappointing since they have phencyclidine-like adverse events that limit the tolerable doses. Several other classes of neuroprotectives are in development, although their mechanisms of action are not well established. Combinations of neuroprotectives and thrombolytics are likely to be tested in clinical trials in the near future.

Animals↗
PubMed1996

Acute hypertension, but not thrombolysis, increases the incidence and severity of hemorrhagic transformation following experimental stroke in rabbits.

Hemorrhagic transformation (HT) is a poorly understood yet frequent complication of stroke. A transient increase in blood pressure (BP) occurs immediately after experimental embolization in rabbits and we evaluated the relationship between this acute hypertensive response and subsequent hemorrhagic transformation, as well as the attenuation of this hypertensive response with an anesthetic dose of halothane. We also examined embolism-induced HT during infusion of the thrombolytic agents tissue plasminogen activator and streptokinase. A blood clot embolus was injected into the internal carotid artery and flushed into the middle cerebral artery. In the first experiment, BP was monitored in anesthetized or unanesthetized rabbits for 20 min prior to and up to 1 h after embolization. In the second experiment, animals were embolized half-way through an infusion of tPA (3.0 mg/kg; 20% administered as an iv bolus, with the remainder infused over 30 min) or streptokinase (30,000 U/kg iv infused over 30 min). In unanesthetized animals, the HT score (number of brain sections displaying visible HT) was significantly correlated with the peak mean arterial pressure recorded at embolization (r = 0.60, n = 24, P < 0.01). No relationship was observed between BP and HT score in animals anesthetized with halothane. Although HT incidence and extent were significantly related to elevated BP in the unanesthetized animals, halothane administration actually increased HT incidence. Embolization during thrombolytic infusion did not increase the occurrence or severity of HT. These data suggest that acute hypertension, but not ongoing thrombolysis, is a significant risk factor for HT following cerebral embolization.

Acute Disease↗
PubMed1996

The AMPA antagonist LY293558 improves functional neurological outcome following reversible spinal cord ischemia in rabbits.

Glutamate (Glu) neurotoxicity is an important element of a number of neurological disorders including central nervous system (CNS) ischemia. We evaluated the effects of the novel AMPA Glu antagonist LY293558 on functional neurological outcome in two rabbit stroke models. In the reversible spinal cord ischemia model, ischemia of the caudal lumbar spinal cord was produced by temporary occlusion of the abdominal aorta. LY293558 was administered 5 min after recirculation as a 16 mg/kg i.v. bolus followed by 2.2 mg/kg infused over 1 h. Control animals received saline. LY293558 significantly increased the duration of ischemia required to produce paraplegia, from 30.5 +/- 15.8 min (mean +/- SD) controls to 50.1 +/- 11.5 in treated animals (p < 0.01). In an irreversible model of cerebral ischemia, 50 microns plastic microspheres were injected into the carotid artery and lodged in the cerebral microvasculature. LY293558 did not significantly reduce neurological damage in this model. These data suggest that LY293558 may have therapeutic benefit following some types of ischemic injury.

Animals↗