Ischemic delayed neuronal death. A mitochondrial hypothesis

Optical methods for probing mitochondrial function in brain slices

Brain slice preparations have become useful tools for studying multiple facets of normal brain function and for investigations of brain pathophysiology. Recently, a variety of neurological disorders have been linked to dysfunction of brain mitochondria. In this report we discuss optical methods for probing mitochondrial function in brain slices. Absorption spectrophotometric and spectrofluorometric techniques are described for measuring changes in the redox activity of mitochondrial cytochromes and the primary respiratory chain substrate nicotinamide adenine dinucleotide (NADH), respectively. A spectrofluorometric method is described also for measuring changes in mitochondrial membrane potential using the potential-sensitive fluorescent indicator JC-1. These methods used together have proven to be useful for studying dysfunction of mitochondria following in vitro ischemia in hippocampal slices, and might also be valuable for investigations of mitochondrial involvement in other neurological disorders.

BCL-2 transduction, using a herpes simplex virus amplicon, protects hippocampal neurons from transient global ischemia

Transient global ischemia results in selective neuronal damage of hippocampal CA1 neurons. Five minutes of bilateral common carotid artery occlusion, in the Mongolian gerbil, effectively restricts forebrain blood flow, resulting in a delayed neuronal death of CA1 pyramidal cells. While there is a delay of approximately 72 h in the appearance of cell death, markers related to the mechanism of ischemic death become apparent well before neurons die. Ischemia-induced increases in the cell-death-promoting protein, bax, may disrupt the bcl-2/bax ratio necessary for normal neuronal functioning and thus promote transient ischemic death. In order to locally maintain this critical bcl-2/bax ratio and thus protect CA1 neurons from delayed neuronal death, a herpes simplex viral (HSV) vector was used to selectively introduce human bcl-2, under the control of the herpes IE 4/5 promoter, into the CA1 region of the gerbil hippocampus. Twenty-four hours prior to ischemia surgery, 1 microl of HSVbcl-2 was infused unilaterally into the CA1 region at a rate of 2 nl/min. Seventy-two hours after ischemia the animals were sacrificed and processed using Nissl, silver degeneration, and immunohistochemical (anti-human bcl-2) staining. Immunohistochemistry demonstrated both glial and neuronal bcl-2 expression around the HSVbcl-2 infusion site. The evaluation following silver degeneration staining indicated a further degeneration of CA1 neurons in the immediate area of the viral vector infusion. This damage seems to be the result of cellular debris associated with the processing of the viral amplicons. Silver degeneration staining is not present in the areas that demonstrate bcl-2 staining. These neurons appear to have been rescued from ischemic damage. This result was confirmed using the Nissl staining. Therefore, by altering the local ratio of bcl-2/bax using the HSVbcl-2 vector one may protect CA1 pyramidal cell from the delayed neuronal death of transient global ischemia.

Selective impairment of fast anterograde axonal transport in the peripheral nerves of asymptomatic transgenic mice with a G93A mutant SOD1 gene

Transgenic mice that express a mutant Cu/Zn superoxide dismutase (SOD1) gene have been provided a valuable model for human amyotrophic lateral sclerosis (ALS). We studied a possible impairment of fast axonal transport in transgenic mice carrying a Gly93-->Ala (G93A) mutant SOD1 gene found in human familial ALS (FALS). Left sciatic nerve was ligated for 6 h in transgenic (Tg) and age-matched wild-type (WT) mice. Immunohistochemical analyses were performed for accumulations of kinesin and cytoplasmic dynein on both sides of the ligation site. Clinical function and histology in the spinal cords, sciatic nerves and gastrocnemius muscles were also assessed. The mice were examined at an early asymptomatic stage (aged 19 weeks) and a late stage (30 weeks) just before the development of the symptoms. WT mice showed an apparent increase in immunoreactivities for kinesin and cytoplasmic dynein at proximal and distal of the ligation, respectively. In contrast, the young Tg mice showed a selective decrease of kinesin accumulation in the proximal of the ligation. The mice were asymptomatic with a mild histological change only in muscles. The old Tg mice showed a marked reduction of the immunoreactivity for kinesin and cytoplasmic dynein on both sides of the ligation. They had a significant loss of spinal motor neurons, relatively small myelinated fiber densities of sciatic nerves, and severe muscular changes. These results provide direct evidence that the SOD1 mutation leads to impaired fast axonal transport, particularly in the anterograde direction at an early, asymptomatic stage preceding loss of spinal motor neurons and peripheral axons. This impairment may contribute to subsequent selective motor neuron death in the present model implicated for human FALS.

Stress protein inductions after brain ischemia

1. Hippocampal CA1 neurons are the most vulnerable to transient cerebral ischemia. However, the mechanism has not been fully understood. 2. The mRNAs for 72-kd (HSP72) and 73-kd (HSC73) heat shock proteins (HSPs), which are located mainly in the cytoplasm, were greatly induced together in CA1 cells, with a peak at 1-2 days in gerbils. However, immunoreactive HSP72 protein was only minimally expressed in CA1 neurons. 3. The mRNA for mitochondrial HSP60 began to increase at 3 hr in CA1 cells and was sustained until 1 day. 4. The level of mRNA for cytochrome c oxidase subunit I (COX-I) progressively decreased in CA1 neurons after a transient ischemia and completely disappeared at 7 days. The activity of cytochrome c oxidase (COX) protein also showed an early decrease in CA1 cells and was followed by a reduction in the level of COX-I DNA after 2 days. 5. These results suggest that HSP gene inductions were inhibited at the translational level but that mitochondrial DNA expression was disturbed at the transcriptional level. A disturbance of mitochondrial DNA expression could cause progressive failure of energy production of CA1 cells that eventually results in neuronal cell death.

Early postischemic dantrolene-induced amelioration of poly(ADP-ribose) polymerase-related bioenergetic failure in neonatal rat brain slices

In the infant brain, ischemia-induced ionic and enzyme mechanisms may independently lead to cell death by energy depletion: resequestration of calcium mobilized from intracellular stores consumes ATP, and activated poly(ADP-ribose) polymerase (PARP) uses oxidized nicotinamide adenine dinucleotide to form polyADP-ribosyl nuclear proteins associated with DNA damage. Using 31P nuclear magnetic resonance spectroscopy, we have monitored intracellular pH and cellular energy metabolites in ex vivo neonatal rat cerebral cortex before, during, and after substrate and oxygen deprivation. In an insult that exhibited secondary energy failure and apoptosis we identified a relative 25% augmentation of high-energy phosphates at the end of recovery when the ryanodine-receptor antagonist, dantrolene, was introduced in the early (0- to 40-minute) but not late (40- to 120-minute) stage of recovery (P < 0.05). In contrast to the absence of a late dantrolene-sensitive effect, inhibition of PARP with 3-methoxybenzamide was as effective (P < 0.05) as early dantrolene, even when introduced after a 40-minute delay. The dantrolene and 3-methoxybenzamide effects on high-energy phosphates were not additive, rather the early dantrolene-sensitive effect nullified the potential 3-methoxybenzamide effect. Therefore, in this vascular-independent neonatal preparation, postischemic mobilization of calcium from intracellular stores is associated with PARP-related energy depletion. Inhibition of either of these processes confers improved postischemic bioenergetic recovery in the developing brain.

Cytosolic redistribution of cytochrome c after transient focal cerebral ischemia in rats

Recent in vitro cell-free studies have shown that cytochrome c release from mitochondria is a critical step in the apoptotic process. The present study examined the expression of cytochrome c protein after transient focal cerebral ischemia in rats, in which apoptosis was assumed to contribute to the expansion of the ischemic lesion. In situ labeling of DNA breaks in frozen sections after 90 minutes of middle cerebral artery (MCA) occlusion showed a significant number of striatal and cortical neurons, which were maximized at 24 hours after ischemia, exhibiting chromatin condensation, nuclear segmentation, and apoptotic bodies. Cytosolic localization of cytochrome c was detected immunohistochemically in the ischemic area as early as 4 hours after 90 minutes of MCA occlusion. Western blot analysis of the cytosolic fraction revealed a strong single 15-kDa band, characteristic of cytochrome c, only in the samples from the ischemic hemisphere. Western blot analysis of the mitochondrial fraction showed a significant amount of mitochondrial cytochrome c in nonischemic brain, which was decreased in ischemic brain 24 hours after ischemia. These results provide the first evidence that cytochrome c is being released from mitochondria to the cytosol after transient focal ischemia. Although further evaluation is necessary to elucidate its correlation with DNA fragmentation, our results suggest the possibility that cytochrome c release may play a role in DNA-damaged neuronal cell death after transient focal cerebral ischemia in rats.

Overexpression of SOD1 in transgenic rats protects vulnerable neurons against ischemic damage after global cerebral ischemia and reperfusion

Transient global cerebral ischemia resulting from cardiac arrest is known to cause selective death in vulnerable neurons, including hippocampal CA1 pyramidal neurons. It is postulated that oxygen radicals, superoxide in particular, are involved in cell death processes. To test this hypothesis, we first used in situ imaging of superoxide radical distribution by hydroethidine oxidation in vulnerable neurons. We then generated SOD1 transgenic (Tg) rats with a five-fold increase in copper zinc superoxide dismutase activity. The Tg rats and their non-Tg wild-type littermates were subjected to 10 min of global ischemia followed by 1 and 3 d of reperfusion. Neuronal damage, as assessed by cresyl violet staining and DNA fragmentation analysis, was significantly reduced in the hippocampal CA1 region, cortex, striatum, and thalamus in SOD1 Tg rats at 3 d, as compared with the non-Tg littermates. There were no changes in the hippocampal CA3 subregion and dentate gyrus, resistant areas in both SOD1 Tg and non-Tg rats. Quantitative analysis of the damaged CA1 subregion showed marked neuroprotection against transient global cerebral ischemia in SOD1 Tg rats. These results suggest that superoxide radicals play a role in the delayed ischemic death of hippocampal CA1 neurons. Our data also indicate that SOD1 Tg rats are useful tools for studying the role of oxygen radicals in the pathogenesis of neuronal death after transient global cerebral ischemia.

Synaptic activity-dependent modulation of mitochondrial gene expression in the rat hippocampus

In order to identify genes that may underlie the maintenance of long-term potentiation (LTP) at perforant path synapses, complementary DNA libraries were synthesised from dentate gyrus total RNA extracts prepared 48 h after the induction of LTP and from control dentate gyrus extracts. Through differential screening of the LTP library we have identified the mitochondrial 12S rRNA (mt12SrRNA) as a transcript that was elevated at this late time. Northern blot analyses showed that the elevation in mt12SrRNA expression began around 8 h and persisted for at least 2 weeks post-tetanus. We then examined the expression patterns of other mitochondrially-encoded genes and demonstrated a similar elevation in their expression. mt12SrRNA levels were also elevated in other hippocampal regions, including areas CA3 and CA1 and were elevated following low-frequency stimulation or in the presence of an N-methyl-D-aspartate receptor antagonist where induction of LTP was precluded. Taken together, these observations suggest that a long-lasting up-regulation of energy production may be triggered by synaptic activity and this activity need not be of sufficient strength to induce LTP, but may be related to the induction of a metaplastic state.

DNA fragmentation and HSP72 gene expression by adenovirus-mediated gene transfer in postischemic gerbil hippocampus and ventricle

A replication defective adenoviral vector containing the E. coli lacZ gene (AdCMVnLacZ) was directly injected into right hippocampus and lateral ventricle immediately after 5 min of transient global ischemia in gerbils. The relations between the lacZ gene expression and DNA fragmentation or heat shock protein 72 (HSP72) immunoreactivity were examined up to 21 days post ischemia. The lacZ gene was transiently expressed at 1 day in the hippocampus except around the CA1 region, while a large number of the periventricular cells strongly expressed the lacZ gene from 8 h to 7 days. In CA1 layer, terminal deoxynucleotidyl dUTP nick end labeling (TUNEL) positive cells, which were present only adjacent to the needle track at 8 h to 1 day, became more extensive in the whole CA1 layer at 3 to 7 days. TUNEL-positive cells were also detected around the DG at 1 day, around the needle track at 8 h to 3 days, and in the choroid plexus cells at 7 days. HSP72 staining was detected in the subiculum at 1 to 3 days, the dentate granule cells at 8 h to 1 day, and in the CA3 or CA4 pyramidal cells at 1 to 3 days. Some lacZ expressing cells were double-positive with HSP72 in DG, while the majority of those were distinguished from the TUNEL-positive cells. Pyramidal neurons were almost completely lost in the CA1 sector at 7 days after the ischemia. The present study demonstrates the successful LacZ gene transfer into the hippocampus and ventricle of postischemic gerbil brain except in the vulnerable CA1 layer by adenoviral vector injection. However, adenovirus-mediated gene transfer may induce indirect apoptotic cell death in the DG and ventricle, in addition to direct traumatic injury around the needle track.

An incomplete cerebral ischemia produced a delayed dysfunction in the rat hippocampal system

We investigated whether functional changes occur with incomplete cerebral ischemia which do not lead to neural cell death. If functional changes are recognized, it is necessary to clarify whether they occur immediately after ischemia or after a lag of a few days similar to the pathological changes. Long-term potentiation (LTP) in both the Schaffer collateral-CA1 and the perforant path-dentate gyrus synapses in halothane-anesthetized rats were examined 1 day and 4 days after 10 min clamping of the bilateral common carotid arteries. LTP was substantially attenuated after clamping of the bilateral common carotid arteries. In Schaffer-CA1 synapses, the inhibition of LTP was significant on both the 1 day and 4 days after-clamping group. In perforant path-dentate gyrus synapses, LTP was significantly inhibited on only the 4 days after-clamping group. These results suggest that functional damages may occur with incomplete ischemia without any histological damages. In the 1 day after-clamping group, LTP was reduced, but the changes in LTP differed from the inhibition of the 4 days after-clamping group. Therefore, a so-called delayed dysfunction might exist in the hippocampal neurons, despite absence of pathological changes.

Energy thresholds in brain mitochondria. Potential involvement in neurodegeneration

Decreases in mitochondrial respiratory chain complex activities have been implicated in neurodegenerative disorders such as Parkinson's disease, Huntington's disease, and Alzheimer's disease. However, the extent to which these decreases cause a disturbance in oxidative phosphorylation and energy homeostasis in the brain is not known. We therefore examined the relative contribution of individual mitochondrial respiratory chain complexes to the control of NAD-linked substrate oxidative phosphorylation in synaptic mitochondria. Titration of complex I, III, and IV activities with specific inhibitors generated threshold curves that showed the extent to which a complex activity could be inhibited before causing impairment of mitochondrial energy metabolism. Complex I, III, and IV activities were decreased by approximately 25, 80, and 70%, respectively, before major changes in rates of oxygen consumption and ATP synthesis were observed. These results suggest that, in mitochondria of synaptic origin, complex I activity has a major control of oxidative phosphorylation, such that when a threshold of 25% inhibition is exceeded, energy metabolism is severely impaired, resulting in a reduced synthesis of ATP. Additionally, depletion of glutathione, which has been reported to be a primary event in idiopathic Parkinson's disease, eliminated the complex I threshold in PC12 cells, suggesting that antioxidant status is important in maintaining energy thresholds in mitochondria. The implications of these findings are discussed with respect to neurodegenerative disorders and energy metabolism in the synapse.

Induction of protein inhibitor of neuronal nitric oxide synthase/cytoplasmic dynein light chain following cerebral ischemia

Administration of inhibitors of neuronal nitric oxide synthase or deletion of the encoding gene in rodents provided evidence that neuronal nitric oxide synthase activity may contribute to neuronal cell death following global and focal cerebral ischemia. In the present study, we investigated by in situ hybridization the expression of an endogenous inhibitor of neuronal nitric oxide synthase activity, designated protein inhibitor of neuronal nitric oxide synthase and homologous to cytoplasmic dynein light chain, in the post-ischemic rat brain. Following global ischemia induced by cardiac arrest, messenger RNA expression of protein inhibitor of neuronal nitric oxide synthase was rapidly induced in pyramidal neurons of the hippocampal CA3 region and granule cell of the dentate gyrus which are resistant to ischemic damage. In vulnerable CA1 pyramidal neurons however, protein inhibitor of neuronal nitric oxide synthase expression remained at basal level after global ischemia and was associated with an increase in nicotinamide adenine dinucleotide phosphate-diaphorase activity and subsequent DNA fragmentation indicating ischemia-mediated neuronal cell death. Following focal cerebral ischemia induced by permanent occlusion of the middle cerebral artery, transcripts of protein inhibitor of neuronal nitric oxide synthase progressively accumulated in cortical neurons bordering the infarct area. After transient middle cerebral artery occlusion however, messenger RNA levels of protein inhibitor of neuronal nitric oxide synthase increased in the reperfused neocortex. Our findings indicate that cerebral ischemia leads to an increase in neuronal expression of protein inhibitor of neuronal nitric oxide synthase in brain regions where sustained or "uncoupled" nitric oxide synthase activity may be detrimental to neurons. Lack of post-ischemic induction of protein inhibitor of neuronal nitric oxide synthase in CA1 pyramidal neurons may result in high nitric oxide synthase activity after global ischemia and could contribute to delayed neuronal cell death.

Culture medium components modulate retina cell damage induced by glutamate, kainate or "chemical ischemia"

The aim of this study was to determine whether culture-conditioned medium (CCM) can prevent neuronal damage caused by excitotoxicity or by "chemical ischemia" in cultured chick retina cells. Excitotoxic conditions were obtained by incubating retina cells with glutamate or kainate and "chemical ischemia" was induced by metabolic inhibition. In this case, cultures were briefly exposed to sodium cyanide, to block oxidative phosphorylation and iodoacetic acid, to block glycolysis. The assessment of neuronal injury was made spectrophotometrically by quantification of cellularly reduced MTT. Stimulation of retina cells with glutamate or kainate in serum deprived culture medium (BME-FCS), lead to a decrease in the MTT metabolism that was dependent on the time of exposure to the toxic agents. CCM prevented cell damage, either when present during the stimulation period or during the recovery period. This protection was more prominent in the case of kainate-induced neuronal death. "Chemical ischemia" also lead to a decrease of the MTT metabolism in a time-dependent manner and CCM protected retina cells from "ischemia"-induced lesions when present during the stimulation period and during the recovery period. The protective effect of CCM was partially decreased by the tyrosine kinase inhibitor, genistein, when the cells were stimulated with kainate, but not with glutamate, or when the cells were subjected to "chemical ischemia". CCM protected retina cells against both the acute and the delayed toxicity induced by either glutamate or kainate, or by "chemical ischemia", when present during both the insult and the recovery period. The presence of survival factors in the media may effectively inhibit the cell death signals generated by glutamate receptor activation or by "chemical ischemia".

Calcium influx from the extracellular space promotes NADH hyperoxidation and electrical dysfunction after anoxia in hippocampal slices

A characteristic event during reperfusion after cerebral ischemia in vivo, and reoxygenation after anoxia in vitro, is hyperoxidation of the electron carriers of the mitochondrial respiratory chain. Current studies have tested the hypothesis that there is a relation among calcium molecules derived from extracellular sources, mitochondrial hyperoxidation, and electrical recovery after anoxia in hippocampal slices. Rat hippocampal slices were superfused with artificial cerebrospinal fluids (ACSF) containing calcium chloride (CaCl2) in concentrations of: 0.5, 1, 2, and 4 mmol/L. Slices were made anoxic and then allowed to recover for 60 minutes. Reduction-oxidation shifts of NADH were measured by rapid-scanning spectrofluorometry. Synaptic activity was indicated by population spike amplitudes in the CA1 pyramidal cell subfield of the hippocampus in response to stimulation of the Schaffer collaterals. Low calcium ACSF concentrations ameliorated NADH hyperoxidation and improved synaptic transmission recovery after anoxia. High calcium ACSF concentrations had opposite effects. These data suggest a link between mitochondrial hyperoxidation and electrical recovery after postanoxia reoxygenation and support the hypothesis that cytosolic calcium overload promotes mitochondrial hyperoxidation and limits electrical recovery.

Ultrastructure of astrocytes associated with selective neuronal death of cerebral cortex after repeated ischemia

Astrocytic swelling after ischemic insult has been considered a sign of parturbed cell viability. Investigations using cultured astrocytes and C6 glioma cells have revealed that viable astrocytes swell, spatially buffering various metabolites which are increased by the metabolic turmoil following ischemic insults. In the present study, we have studied the temporal profile of ultrastructural changes of astrocytes in the cerebral cortex associated with progressive selective neuronal, death where infarction is not induced. We occluded the left carotid artery of the Mongolian gerbil twice for 10 minutes at a 5 hr interval. In this model, following reperfusion, selective neuronal death progresses in the coronal section cut at the infundibular level. The whole brains of the sham operated control and postischemic animals were fixed by transcardiac perfusion of glutaraldehyde fixatives, at 15 min, 5 and 12 hr after the 2nd 10 min ischemia. Ultrathin sections including the 3rd and 5th cortical layers were prepared from the cut surface at the level of infundibulum. Mild swelling of astrocytic processes and perivascular end-feet was observed in the 15 min group. Glycogen granules were not prominent. In the 5 hr group, we found a few necrotic neurons disseminated in the cortex. All astrocytic cell processes were swollen with increased number of glycogen granules, especially marked in the perivascular end-feet. In the 12 hr group, necrotic neurons increased in number, astrocytic swelling was more extensive, and glycogen granules were evident in astrocytes. No cellular destruction was observed. We conclude: 1. Swelling progresses in astrocytes which however still remain viable and this process is associated with selective progression of neuronal death. 2. Glycogen granules increase in the swollen yet viable astrocytic cell processes.

Expression of the glial cell line-derived neurotrophic factor gene in rat brain after transient MCA occlusion

Change of the glial cell line-derived neurotrophic factor (GDNF) gene expression in rat brain was examined after transient middle cerebral artery (MCA) occlusion of adult rats. Northern blot analysis showed that the mRNA began to be induced in the occluded MCA from 1 h of reperfusion with a peak at 3 h, and almost diminished by 1 day of reperfusion. Immunohistochemical analysis with brain sections showed an expression of GDNF-like immunoreactivity in neurons of the cerebral cortex and caudate after 90 min of ischemia in a similar way to the mRNA, but the staining was more disseminated and stronger in the cerebral cortex than the caudate. No glial cell was stained in the brain sections. The present results indicate that the GDNF gene was expressed in an early stage of reperfusion in neuronal cells of the MCA territory, but that the staining property was different between in the cerebral cortex and caudate.

Axonal structure and function after axolemmal leakage in the squid giant axon

Membrane leakage is a common consequence of traumatic nerve injury. In order to measure the early secondary effects of different levels of membrane leakage on axonal structure and function we studied the squid giant axon after electroporation at field strengths of 0.5, 1.0, 1.6, or 3.3 kV/cm. Immediately after mild electroporation at 0.5 kV/cm, 40% of the axons had no action potentials, but by 1 h all of the mildly electroporated axons had recovered their action potentials. Many large organelles (mitochondria) were swollen, however, and their transport was reduced by 62% 1 h after this mild electroporation. One hour after moderate electroporation at 1.0 kV/cm, most of the axons had no action potentials, most large organelles were swollen, and their transport was reduced by 98%, whereas small organelle transport was reduced by 75%. Finally at severe electroporation levels of 1.65-3.0 kV/cm all conduction and transport was lost and the gel-like axoplasmic structure was clumped or liquefied. The structural damage and transport block seen after severe and moderate poration were early secondary injuries that could be prevented by placing the porated axons in an intracellular-type medium (low in Ca2+, Na+, and Cl-) immediately after poration. In moderately, but not severely, porated axons this protection of organelle transport and structure persisted, and action potential conduction returned when the axons were returned to the previously injurious extracellular-type medium. This suggests that the primary damage, the axolemmal leak, was repaired while the moderately porated axons were in the protective intracellular-type medium.

Activation of CPP-32 protease in hippocampal neurons following ischemia and epilepsy

Recent in vitro studies indicate an involvement of members of the interleukin-1beta converting enzyme (ICE) family of proteases in programmed neuronal cell death. Cell death of hippocampal neurons in animal models of cerebral ischemia and epilepsy shows morphological features of apoptosis and can be prevented by administration of protein synthesis inhibitors suggesting that de novo synthesis of components of the cell death program is necessary for neuronal apoptosis. In the present study we demonstrate by in situ hybridization analysis that expression of CPP-32, an ICE-related protease, is significantly upregulated in CA1 hippocampal neurons following global ischemia induced by cardiac arrest and in hippocampal neurons of the CA3/CA4 region after kainate-mediated epilepsy, respectively. Moreover, an increase in CPP-32-like proteolytic activity was detected in hippocampal extracts 24 h after ischemia using the fluorogenic CPP-32 substrate Ac-DEVD-AMC. Activation of CPP-32 clearly preceded cell death of hippocampal neurons as assessed by in situ end-labelling of nuclear DNA fragments. These results indicate that CPP-32 protease may be activated at both the transcriptional and post-translational level during neuronal apoptosis and that activation correlates with the selective vulnerability of hippocampal pyramidal neurons to ischemic and epileptic insults.

'Chemical ischemia' in cultured retina cells: the role of excitatory amino acid receptors and of energy levels on cell death

In this study, we determined whether the retina cell death observed in response to an ischemic-like insult is related to an overactivation of the ionotropic glutamate receptors and/or to a collapse of the energy levels. Cultured chick retina cells were submitted to 'chemical ischemia' by metabolic inhibition with sodium cyanide and iodoacetic acid, which block oxidative phosphorylation and glycolysis, respectively. The assessment of neuronal injury was made spectrophotometrically by quantification of cellularly reduced MTT, which gives information about mitochondrial function, or by staining with fluorescein diacetate (FDA), which correlates with changes in the plasma membrane permeability. 'Chemical ischemia' induced both an acute and a delayed time-dependent degeneration of chick retina cells. We observed that 2 min after the ischemic insult, the levels of ATP were reduced to a minimum. On the other hand, the metabolic inhibition induced the release of aspartate, glutamate and gamma-aminobutyric acid, and the activation of AMPA/kainate receptors during the period of metabolic arrest was partially responsible for the loss of mitochondrial function. However, the NMDA and non-NMDA receptor antagonists (MK-801 and CNQX) did not prevent the plasma membrane damage caused by sodium cyanide and iodoacetic acid. The results show that the collapse of the energy levels, rather than the increase in excitatory amino acids, appears to underlie the observed cell injury, suggesting an important relationship between ischemia-induced depletion of high-energy metabolites and retina cell degeneration.

In vivo adenovirus-mediated gene transfer and the expression in ischemic and reperfused rat brain

In an attempt to study whether ischemic brain could express a foreign gene in vivo, a replication-defective adenoviral vector containing the Escherichia coli lacZ gene was directly injected into the ischemic or reperfused cerebral cortex of rat, and temporal and spatial profiles of the exogenous gene expression were compared with that of the control brain. Right middle cerebral artery (MCA) of rat was continuously occluded by an insertion of nylon thread for 2 days, or only transiently occluded for 90 min and then the blood flow was restored for 21 days. The adenoviral vector was administered just after the MCA occlusion or reperfusion in the case of continuous ischemia and reperfusion, respectively. Adenoviral vector was transferred into the continuous ischemic brain, and the lacZ gene was expressed until 2 days of the occlusion in the cerebral cortex of the occluded MCA territory with the number of expressing cells smaller and the staining just weaker than that of the control brain. In contrast, expression of the lacZ gene was not or only minimally observed in the reperfused brain until 2 days. However, the expression dramatically exploded at 7 days of reperfusion at a level similar to that of the control, and the expression diminished by 21 days. A few neurons in the ipsilateral thalamus, hypothalamus, and basal ganglia, and in the contralateral cerebral cortex expressed the lacZ gene at 7 days after reperfusion, a phenomenon similar to the case of the control. The majority of brain cells that expressed the lacZ gene were neurons, and a part (5-10%) were astroglial cells. Traumatic injury and immunological response in the brain were minimal both in the cases of control and ischemia/reperfusion. The present study shows an effective gene transfer and the expression in neural cells of ischemic and reperfused brains in vivo, and suggests a great potential of the gene therapy for ischemic stroke patients in the future.

Inhibition of nonselective cation channels reduces focal ischemic injury of rat brain

The effect of the novel inhibitor of receptor-activated and calcium store-operated nonselective cation channels, (RS)-(3,4-dihydro-6,7-dimethoxyisoquinoline-1-gamma 1)-2-phenyl-N, N-di-[2(2,3,4-trimethoxyphenyl) ethyl]acetamide (LOE 908 MS), on focal cerebral ischemia was studied in halothane-anesthetized rats submitted to permanent suture occlusion of the right middle cerebral artery (MCA). The treated group (n = 7) received subcutaneous injections of 30 mg/kg LOE 908 MS (in 1 ml saline) 10 min after vascular occlusion and again after 3 h. The untreated group (n = 11) was injected subcutaneously with 1 ml saline at the same times. Evolution of infarct was monitored by electrophysiological recording of EEG and cortical steady potential and by diffusion-weighted magnetic resonance imaging during the initial 6 h of vascular occlusion. The hemodynamic, biochemical, and morphological changes were studied after 6 h by combining autoradiographic measurement of blood flow with histological stainings and pictorial measurements of ATP, glucose, and tissue pH. In the untreated animals, the ischemic lesion volume [defined as the region in which the apparent diffusion coefficient (ADC) of water declined to below 80% of control] steadily increased by approximately 50% during the initial 6 h of vascular occlusion relative to the first set of data 10 min postocclusion. In the treated animals, in contrast, the ADC lesion volume declined by approximately 20% during the same interval. Treatment also led to a significant reduction in the number of periinfarct depolarizations. After 6 h of vascular occlusion, blood flow was significantly higher in the treated animals, and the volume of ATP-depleted and morphologically injured tissue representing the infarct core was 60-70% smaller. The volume of severely acidic tissue, in contrast, did not differ, indicating that LOE 908 MS does not reduce the size of ischemic penumbra. These findings demonstrate that postocclusion treatment of permanent focal ischemia with LOE 908 MS delays the expansion of the infarct core into the penumbra for a duration of at least 6 h and therefore substantially prolongs the window of opportunity for the reversal of the ischemic impact in the peripheral parts of the evolving infarct.

MPP+ induced apoptotic cell death in SH-SY5Y neuroblastoma cells: an electron microscope study

PD is a common, late-onset neurodegenerative disorder that results in part from the gradual loss of dopaminergic neurons in the substantia nigra pars compacta. The neurotoxin MPTP can induce PD-like clinical symptomatology and neuropathological destruction and, thus, has been used as a PD model. The human neuroblastoma cell line SH-SY5Y possesses many of the qualities of human neurons and, as such, has served as a model for them. Apoptosis is the mode of cell death induced in SH-SY5Y cells by MPTP, and this was confirmed with nick end labeling and bisbenzimide staining. Transmission electron microscopic analysis of the ultrastructural changes occurring in neurotoxin exposed SH-SY5Ys revealed many morphological characteristics consistent with apoptosis. These changes included plasmalemmal blebbing, altered cytosolic density, nuclear condensation and fragmentation, pronounced vacuole formation, ribosomal dispersion, and the disappearance of the golgi complex, microtubules, and smooth endoplasmic reticulum. Limited amounts of rough endoplasmic reticulum and mitochondria exhibited normal morphology throughout the apoptotic changes but then were disrupted during secondary necrotic changes. The in vitro induction of apoptosis by a parkinsonism neurotoxin might be reflective of the mechanisms of in vivo nigral degeneration occurring during PD.

Dissociative expression of adenoviral-mediated E. coli LacZ gene between ischemic and reperfused rat brains

A replication-defective adenoviral vector containing the E. coli lacZ gene was directly injected into the ischemic or reperfused cerebral cortex of rats. An administration of adenoviral vector showed a slight to moderate expression of the lacZ gene in the cerebral cortex of the middle cerebral artery (MCA) region until 2 days after the MCA occlusion. In contrast, expression of the lacZ gene was not observed, or only minimally so, in the reperfused brain until 2 days after a 90 min of transient MCA occlusion. However, the lacZ expression dramatically increased at 7 days after the reperfusion, then diminished by 21 days. The majority of brain cells that expressed the lacZ gene were neurons and a fraction (5-10%) were astroglial cells. The present study showed that an exogenous gene was transferred and expressed in neural cells of ischemic and reperfused brains in vivo, but the temporal profile of the expression is dissociative.