Cerebral ischemia in the gerbil: transmission electron microscopic and immunoelectron microscopic investigation

Different changes in pre- and postsynaptic components in the hippocampal CA1 subfield after transient global cerebral ischemia

To date, ischemia-induced damage to dendritic spines has attracted considerable attention, while the possible effects of ischemia on presynaptic components has received relatively less attention. To further examine ischemia-induced changes in pre- and postsynaptic specializations in the hippocampal CA1 subfield, we modeled global cerebral ischemia with two-stage 4-vessel-occlusion in rats, and found that three postsynaptic markers, microtubule-associated protein 2 (MAP2), postsynaptic density protein 95 (PSD95), and filamentous F-actin (F-actin), were all substantially decreased in the CA1 subfield after ischemia/reperfusion (I/R). Although no significant change was detected in synapsin I, a presynaptic marker, in the CA1 subfield at the protein level, confocal microscopy revealed that the number and size of synapsin I puncta were significantly changed in the CA1 stratum radiatum after I/R. The size of synapsin I puncta became slightly, but significantly reduced on Day 1.5 after I/R. From Days 2 to 7 after I/R, the number of synapsin I puncta became moderately decreased, while the size of synapsin I puncta was significantly increased. Interestingly, some enlarged puncta of synapsin I were observed in close proximity to the dendritic shafts of CA1 pyramidal cells. Due to the more substantial decrease in the number of F-actin puncta, the ratio of synapsin I/F-actin puncta was significantly increased after I/R. The decrease in synapsin I puncta size in the early stage of I/R may be the result of excessive neurotransmitter release due to I/R-induced hyperexcitability in CA3 pyramidal cells, while the increase in synapsin I puncta in the later stage of I/R may reflect a disability of synaptic vesicle release due to the loss of postsynaptic contacts.

The temporal and spatial changes of actin cytoskeleton in the hippocampal CA1 neurons following transient global ischemia

Transient global ischemia usually results in delayed neuronal death in selective brain regions, prior to which a rapid loss of dendritic spines has been widely reported in these regions. Dendritic spines are characterized by a highly branched meshwork of actin cytoskeleton (F-actin), which is extremely vulnerable to the ATP-depleted conditions such as hypoxia/ischemia. However, the ischemia-induced changes of F-actin are still not clarified in the vulnerable brain areas. This study was designed to examine the temporal and spatial alterations of F-actin in the CA1 subfield of rat hippocampus following reperfusion after global cerebral ischemia. Phalloidin staining and confocal microscopic examination showed that F-actin disappeared from the dentritic spines in the CA1 stratum radiatum, but aggregated into thread- or fiber-like structures on days 1.5-2 after ischemia. This was followed by a nearly complete loss of F-actin in the CA1 subfield on days 3-7 after ischemia. Colocalization analysis demonstrated that the F-actin threads or fibers were located mainly within the dentritic trunks. As revealed by Nissl and Fluoro-Jade B staining, the decrease of F-actin proceeded concurrently with the evolution of ischemic damage. Consistently, western blots detected a significant decrease of F-/G-actin ratio in the dissected CA1 subfield after ischemia. To our knowledge, this is the first report on the change of F-actin in the ischemic brain. Although the underlying mechanisms remain to be elucidated, our findings may provide an important structural clue for the neuronal dysfunction induced by ischemia.

The effects of epothilone D on microtubule degradation and delayed neuronal death in the hippocampus following transient global ischemia

Disruption of microtubule cytoskeleton plays an important role during the evolution of brain damage after transient cerebral ischemia. However, it is still unclear whether microtubule-stabilizing drugs such as epothilone D (EpoD) have a neuroprotective action against the ischemia-induced brain injury. This study examined the effects of pre- and postischemic treatment with different doses of EpoD on the microtubule damage and the delayed neuronal death in the hippocampal CA1 subfield on day 2 following reperfusion after 13-min global cerebral ischemia. Our results showed that systemic treatment with 0.5 mg/kg EpoD only slightly alleviated the microtubule disruption and the CA1 neuronal death, while treatment with 3.0 mg/kg EpoD was not only ineffective against the CA1 neuronal death, but also produced additional damage in the dentate gyrus in some ischemic rats. Since the pyramidal cells in the CA1 subfield and the granule neurons in the dentate gyrus are known to be equipped with dynamically different microtubule systems, this finding indicates that the effects of microtubule-disrupting drugs may be unpredictably complicated in the central nervous system.

Global cerebral ischemia due to circulatory arrest: insights into cellular pathophysiology and diagnostic modalities

Circulatory arrest (CA) remains a major unresolved public health problem in the United States; the annual incidence of which is ~0.50 to 0.55 per 1000 population. Despite seminal advances in therapeutic approaches over the past several decades, brain injury continues to be the leading cause of morbidity and mortality after CA. In brief, CA typically results in global cerebral ischemia leading to delayed neuronal death in the hippocampal pyramidal cells as well as in the cortical layers. The dynamic changes occurring in neurons after CA are still unclear, and predicting these neurological changes in the brain still remains a difficult issue. It is hypothesized that the "no-flow" period produces a cytotoxic cascade of membrane depolarization, Ca²⁺ ion influx, glutamate release, acidosis, and resultant activation of lipases, nucleases, and proteases. Furthermore, during reperfusion injury, neuronal death occurs due to the generation of free radicals by interfering with the mitochondrial respiratory chain. The efficacy of many pharmacological agents for CA patients has often been disappointing, reflecting our incomplete understanding of this enigmatic disease. The primary obstacles to the development of a neuroprotective therapy in CA include uncertainties with regard to the precise cause(s) of neuronal dysfunction and what to target. In this review, we summarize our knowledge of the pathophysiology as well as specific cellular changes in brain after CA and revisit the most important neurofunctional, neuroimaging techniques, and serum biomarkers as potent predictors of neurologic outcome in CA patients.

Chloride Cotransporters as a Molecular Mechanism underlying Spreading Depolarization-Induced Dendritic Beading

Spreading depolarizations (SDs) are waves of sustained neuronal and glial depolarization that propagate massive disruptions of ion gradients through the brain. SD is associated with migraine aura and recently recognized as a novel mechanism of injury in stroke and brain trauma patients. SD leads to neuronal swelling as assessed in real time with two-photon laser scanning microscopy (2PLSM). Pyramidal neurons do not express aquaporins and thus display low inherent water permeability, yet SD rapidly induces focal swelling (beading) along the dendritic shaft by unidentified molecular mechanisms. To address this issue, we induced SD in murine hippocampal slices by focal KCl microinjection and visualized the ensuing beading of dendrites expressing EGFP by 2PLSM. We confirmed that dendritic beading failed to arise during large (100 mOsm) hyposmotic challenges, underscoring that neuronal swelling does not occur as a simple osmotic event. SD-induced dendritic beading was not prevented by pharmacological interference with the cytoskeleton, supporting the notion that dendritic beading may result entirely from excessive water influx. Dendritic beading was strictly dependent on the presence of Cl(-), and, accordingly, combined blockade of Cl(-)-coupled transporters led to a significant reduction in dendritic beading without interfering with SD. Furthermore, our in vivo data showed a strong inhibition of dendritic beading during pharmacological blockage of these cotransporters. We propose that SD-induced dendritic beading takes place as a consequence of the altered driving forces and thus activity for these cotransporters, which by transport of water during their translocation mechanism may generate dendritic beading independently of osmotic forces.

SIGNIFICANCE STATEMENT

Spreading depolarization occurs during pathological conditions such as stroke, brain injury, and migraine and is characterized as a wave of massive ion translocation between intracellular and extracellular space in association with recurrent transient focal swelling (beading) of dendrites. Numerous ion channels have been demonstrated to be involved in generation and propagation of spreading depolarization, but the molecular machinery responsible for the dendritic beading has remained elusive. Using real-time in vitro and in vivo two-photon laser scanning microscopy, we have identified the transport mechanisms involved in the detrimental focal swelling of dendrites. These findings have clear clinical significance because they may point to a new class of pharmacological targets for prevention of neuronal swelling that consequently will serve as neuroprotective agents.

The role of PSD-95 and cypin in morphological changes in dendrites following sublethal NMDA exposure

Focal swelling or varicosity formation in dendrites and loss of dendritic spines are the earliest indications of glutamate-induced excitotoxicity. Although it is known that microtubule dynamics play a role in varicosity formation, very little is known about the proteins that directly impact microtubules during focal swelling and dendritic spine loss. Our laboratory has recently reported that the postsynaptic protein PSD-95 and its cytosolic interactor (cypin) regulate the patterning of dendrites in hippocampal neurons. Cypin promotes microtubule assembly, and PSD-95 disrupts microtubule organization. Thus, we hypothesized that cypin and PSD-95 may play a role in altering dendrite morphology and spine number in response to sublethal NMDA-induced excitotoxicity. Using an in vitro model of glutamate-induced toxicity in rat hippocampal cultures, we found that cypin overexpression or PSD-95 knockdown increases the percentage of neurons with varicosities and the number of varicosities along dendrites, decreases the size of varicosities after sublethal NMDA exposure, and protects neurons from NMDA-induced death. In contrast, cypin knockdown or PSD-95 overexpression results in opposite effects. We further show that cypin regulates the density of spines/filopodia: cypin overexpression decreases the number of protrusions per micrometer of dendrite while cypin knockdown results in an opposite effect. Cypin overexpression and PSD-95 knockdown attenuate NMDA-promoted decreases in protrusion density. Thus, we have identified a novel pathway by which the microtubule cytoskeleton is regulated during sublethal changes to dendrites.

Stem cells: implications in experimental ischaemic stroke therapy

Ischaemic stroke is a syndrome characterized by rapid onset of neurological injury due to interruption of blood flow to the brain. Widespread neuronal damage throughout the CNS has been shown to cause marked and multifarious functional impairments in the ischaemic brain. Recent advances as enumerated above have propelled acute ischaemic stroke management into a therapeutic era. However, once the damage from a stroke event has maximized, little can be done to recover premorbid function. Experimental animal data suggests that stem cell therapy may be an effective alternate to the conventional disease management strategies of ischaemic stroke. Therefore, the present review focuses on detailing the scope of stem cell therapy in the treatment of ischaemic stroke.

Low perfusion pressure during CPB may induce cerebral metabolic and ultrastructural changes

BACKGROUND

Recently we reported on cerebral metabolic changes suggesting ischemia in piglets during nitroprusside-induced low-pressure CPB. We here investigated whether a mean arterial pressure (MAP) of 40-45 mmHg could provoke similar changes by a NO-independent intervention.

METHODS

Piglets underwent 60 minutes normothermic followed by 90 minutes hypothermic CPB. The LP-group (n=8) had MAP of 40-45 mmHg by phentolamine while the HP-group (n=8) had MAP of 60-80 mmHg by norepinephrine. Cerebral glucose, lactate, pyruvate and glycerol were determined. In the last two animals of each group, cerebral tissue was examined by electron microscopy.

RESULTS

Cerebral lactate was higher in the LP-group than the HP-group during normothermic CPB. Compared with baseline, cerebral glucose of the LP-group decreased whereas lactate/pyruvate-ratio, lactate and glycerol-concentrations increased during normothermic CPB. In the HP-group these parameters remained unchanged. Electron microscopy showed 31.2% and 8.3% altered mitochondria in the cortical micrographs taken from the LP- and the HP-group, respectively (p<0.001).

CONCLUSION

MAP below 45 mmHg during CPB was associated with cerebral biochemical and morphological changes consistent with anaerobic metabolism and subcellular injury.

Microtubule-associated protein 2 (MAP2)--a promising approach to diagnosis of forensic types of hypoxia-ischemia

The loss of neuronal immunoreactivity of the cytoskeletal microtubule-associated protein 2 (MAP2) is known to be a marker of--at least--transient functional failure of neurons following ischemia. Because there are no specific neuropathological findings in forensic types of acute hypoxia-ischemia, detection of this relevant cause of death is often complicated and a reliable ischemic biomarker would be of great importance. We therefore investigated the neuronal immunoreactivity of MAP2 in human cases of forensic significance. A control group (n=27) was compared to a group of cases of hypoxia-ischemia (n=45), comprising death due to hanging (n=19), drowning (n=14) and carbon monoxide (CO) poisoning (n=12). Using immunohistochemical staining, the percentage of MAP2-positive neurons in the hippocampus (areas CA1-CA4) and frontal cortex (layers II-VI) was evaluated and compared. The hypoxia-ischemia group showed decreased MAP2 immunostaining in the hippocampal areas CA2-CA4 (P<0.05) and in cortical layers II-VI (P<0.001) compared to controls. Most vulnerable regions seem to be the hippocampal CA4 area and cortical layers III-V. Within the hypoxia-ischemia group, death due to CO poisoning was characterized by the lowest MAP2 immunoreactivity. The hypoxic-ischemic groups differ from controls by a distinct decrease of MAP2 immunostaining. Thus, the loss of MAP2 immunoreactivity may support the diagnosis of neuronal injury in forensic types of hypoxia-ischemia, although investigations on postmortem tissue must be interpreted cautiously.

Timing of neuronal and glial ultrastructure disruption during brain slice preparation and recovery in vitro

Hippocampal slices often have more synapses than perfusion-fixed hippocampus, but the cause of this synaptogenesis is unclear. Ultrastructural evidence for synaptogenic triggers during slice preparation was investigated in 21-day-old rats. Slices chopped under warm or chilled conditions and fixed after 0, 5, 25, 60, or 180 minutes of incubation in an interface chamber were compared with hippocampi fixed by perfusion or by immersion of the whole hippocampus. There was no significant synaptogenesis in these slices compared with perfusion-fixed hippocampus, but there were other structural changes during slice preparation and recovery in vitro. Whole hippocampus and slices prepared under warm conditions exhibited an increase in axonal coated vesicles, suggesting widespread neurotransmitter release. Glycogen granules were depleted from astrocytes and neurons in 0-min slices, began to reappear by 1 hour, and had fully recovered by 3 hours. Dendritic microtubules were initially disassembled in slices, but reassembled into normal axial arrays after 5 minutes. Microtubules were short at 5 minutes (12.3 +/- 1.1 microm) but had recovered normal lengths by 3 hours (84.6 +/- 20.0 microm) compared with perfusion-fixed hippocampus (91 +/- 22 microm). Microtubules appeared transiently in 15 +/- 3% and 9 +/- 4% of dendritic spines 5 and 25 minutes after incubation, respectively. Spine microtubules were absent from perfusion-fixed hippocampus and 3-hour slices. Ice-cold dissection and vibratomy in media that blocked activity initially produced less glycogen loss, coated vesicles, and microtubule disassembly. Submersing these slices in normal oxygenated media at 34 degrees C led to glycogen depletion, as well as increased coated vesicles and microtubule disassembly within 1 minute.

Microtubule-associated protein 2 (MAP2) associates with the NMDA receptor and is spatially redistributed within rat hippocampal neurons after oxygen-glucose deprivation

MAP2 (microtubule-associated protein 2) is a cytoskeletal phosphoprotein that regulates the dynamic assembly characteristics of microtubules and appears to provide scaffolding for organelle distribution into the dendrites and for the localization of signal transduction apparatus in dendrites, particularly near spines. MAP2 is degraded after ischemia and other metabolic insults, but the time course and initial triggers of that breakdown are not fully understood. This study determined that MAP2 resides in a complex with the NMDA receptor, suggesting that spatially localized changes may be important in the mechanism of MAP2 redistribution and breakdown after oxygen-glucose deprivation (OGD). Using OGD in the adult rat hippocampal slice as a model system, this study demonstrated that MAP2 breakdown occurs very early after OGD, with the first statistical decrease in MAP2 levels within the first 30 min after the insult. There is a dramatic redistribution of MAP2 to the somata of pyramidal neurons, particularly neurons at the CA1-subiculum border. Free radicals and nitric oxide are not involved in the damage to MAP2. NMDA-receptor activation plays a prominent role in the MAP2 breakdown. In direct response to NMDA receptor activation, calcium influx, likely through the receptor ion channel complex, as well as release of calcium from the mitochondria through activation of the 2Na(+)-Ca(2+) exchanger of mitochondria, triggers MAP2 degradation. The proteolysis of MAP2 is limited by endogenous calpain activity, likely via the spatial access of calpain to MAP2.

Dentate gyrus: alterations that occur with hippocampal injury

Injury to the brain usually manifests not in a diffuse uniform manner but rather with selective sites of damage indicative of differential vulnerability. This question of neuronal susceptibility has been one of major interest both in disease processes as well as damage induced by environmental factors. For experimental examination, brain structures with obvious neuronal subpopulations and organization such as the cerebellum and the hippocampus have offered the most promise. In the hippocampus distinct neuronal populations exist that demonstrate differential vulnerability to various forms of insult including ischemia, excitotoxicity, and environmental factors. The more recent data regarding the presence of neuronal progenitor cells in the subgranular zone of the dentate offers the opportunity to expand such experimental examination to the process of injury-induced neurogenesis. Thus, more recent studies have expanded the examination of the hippocampus to include models of damage to the dentate neurons in addition to the highly vulnerable pyramidal neurons. A number of these models are presented for both human disease and experimental animal conditions. Examination of the responses between these distinct cell populations offers the potential for understanding factors that are critical in neuronal death and survival.

Optical scatter imaging detects mitochondrial swelling in living tissue slices

Mitochondrial swelling is observed in neuronal injury and is a key event in many pathways to cell death. Currently, there is no technique for directly measuring mitochondrial size changes within living tissue slices with a field of view of several millimeters. In this paper, we test our hypothesis that Mie light-scatter theory can be used to study mitochondrial swelling in living tissue sections. Using a unique dual-angle scatter ratio (DASR) optical imaging system previously demonstrated to be sensitive to latex particle size changes and N-methyl-D-aspartate (NMDA) treatment of hippocampal slices, we studied mitochondrial swelling induced by 500 microM NMDA treatment of hippocampal slices. We observed a strong (R(2) = 0.73) and significant (P < 0.000005) correlation between the electron microscopy-determined diameters of swollen, intact mitochondria and the DASR imaging. We examined the robustness of the technique by evaluating the correlation between the dual-angle scatter ratio and the diameter of the dendrites, observed to swell, in NMDA-treated slices and found no correlation (R(2) = 0.06). The advantage of DASR imaging over electron microscopy or other methods of studying mitochondrial swelling is the sensitivity of DASR imaging to mitochondrial swelling over a large field of view (>9 mm(2)) in an intact tissue slice. This novel technique may allow for the study of regional changes in mitochondrial swelling and recovery as sequential events within a single specimen. This technique will eventually be useful in studying the efficacy of stroke and other disease therapies targeting mitochondrial swelling.

Changes in the apparent diffusion coefficient of water and T2 relaxation time in gerbil hippocampus after mild ischemia

Selective neuronal death of the hippocampal CA1 area after mild ischemia is known as delayed neuronal death (DND). Progression of DND was evaluated using 7T MRI in gerbils. In the CA1, the T2 relaxation time started to increase on day 3 and was significantly higher on day 4 than that of the control gerbils. However, the apparent diffusion coefficient of water (ADC) was significantly lower on day 1 than in the control and continued to decline up to day 4. Changes in T2 coincided with loss of MAP2 immunoreactivity, while the ADC decrease preceded these changes. After 1 month, the ADC had returned to within the normal range, while T2 had decreased to below the control level. These results suggest that MRI is useful for monitoring DND.

Ischemic cell death in brain neurons

This review is directed at understanding how neuronal death occurs in two distinct insults, global ischemia and focal ischemia. These are the two principal rodent models for human disease. Cell death occurs by a necrotic pathway characterized by either ischemic/homogenizing cell change or edematous cell change. Death also occurs via an apoptotic-like pathway that is characterized, minimally, by DNA laddering and a dependence on caspase activity and, optimally, by those properties, additional characteristic protein and phospholipid changes, and morphological attributes of apoptosis. Death may also occur by autophagocytosis. The cell death process has four major stages. The first, the induction stage, includes several changes initiated by ischemia and reperfusion that are very likely to play major roles in cell death. These include inhibition (and subsequent reactivation) of electron transport, decreased ATP, decreased pH, increased cell Ca(2+), release of glutamate, increased arachidonic acid, and also gene activation leading to cytokine synthesis, synthesis of enzymes involved in free radical production, and accumulation of leukocytes. These changes lead to the activation of five damaging events, termed perpetrators. These are the damaging actions of free radicals and their product peroxynitrite, the actions of the Ca(2+)-dependent protease calpain, the activity of phospholipases, the activity of poly-ADPribose polymerase (PARP), and the activation of the apoptotic pathway. The second stage of cell death involves the long-term changes in macromolecules or key metabolites that are caused by the perpetrators. The third stage of cell death involves long-term damaging effects of these macromolecular and metabolite changes, and of some of the induction processes, on critical cell functions and structures that lead to the defined end stages of cell damage. These targeted functions and structures include the plasmalemma, the mitochondria, the cytoskeleton, protein synthesis, and kinase activities. The fourth stage is the progression to the morphological and biochemical end stages of cell death. Of these four stages, the last two are the least well understood. Quite little is known of how the perpetrators affect the structures and functions and whether and how each of these changes contribute to cell death. According to this description, the key step in ischemic cell death is adequate activation of the perpetrators, and thus a major unifying thread of the review is a consideration of how the changes occurring during and after ischemia, including gene activation and synthesis of new proteins, conspire to produce damaging levels of free radicals and peroxynitrite, to activate calpain and other Ca(2+)-driven processes that are damaging, and to initiate the apoptotic process. Although it is not fully established for all cases, the major driving force for the necrotic cell death process, and very possibly the other processes, appears to be the generation of free radicals and peroxynitrite. Effects of a large number of damaging changes can be explained on the basis of their ability to generate free radicals in early or late stages of damage. Several important issues are defined for future study. These include determining the triggers for apoptosis and autophagocytosis and establishing greater confidence in most of the cellular changes that are hypothesized to be involved in cell death. A very important outstanding issue is identifying the critical functional and structural changes caused by the perpetrators of cell death. These changes are responsible for cell death, and their identity and mechanisms of action are almost completely unknown.

Membrane dysfunction induced by in vitro ischemia in rat hippocampal CA1 pyramidal neurons

Intracellular and single-electrode voltage-clamp recordings were made to investigate the process of membrane dysfunction induced by superfusion with oxygen and glucose-deprived (ischemia-simulating) medium in hippocampal CA1 pyramidal neurons of rat tissue slices. To assess correlation between potential change and membrane dysfunction, the recorded neurons were stained intracellularly with biocytin. A rapid depolarization was produced approximately 6 min after starting superfusion with ischemia-simulating medium. When oxygen and glucose were reintroduced to the bathing medium immediately after generating the rapid depolarization, the membrane did not repolarize but depolarized further, the potential reaching 0 mV approximately 5 min after the reintroduction. In single-electrode voltage-clamp recording, a corresponding rapid inward current was observed when the membrane potential was held at -70 mV. After the reintroduction of oxygen and glucose, the current induced by ischemia-simulating medium partially returned to preexposure levels. These results suggest that the membrane depolarization is involved with the membrane dysfunction. The morphological aspects of biocytin-stained neurons during ischemic exposure were not significantly different from control neurons before the rapid depolarization. On the other hand, small blebs were observed on the surface of the neuron within 0.5 min of generating the rapid depolarization, and blebs increased in size after 1 min. After 3 min, neurons became larger and swollen. The long and transverse axes and area of the cross-sectional cell body were increased significantly 1 and 3 min after the rapid depolarization. When Ca2+-free (0 mM) with Co2+ (2.5 mM)-containing medium including oxygen and glucose was applied within 1 min after the rapid depolarization, the membrane potential was restored completely to the preexposure level in the majority of neurons. In these neurons, the long axis was lengthened without any blebs being apparent on the membrane surface. These results suggest that the membrane dysfunction induced by in vitro ischemia may be due to a Ca2+-dependent process that commences approximately 1.5 min after and is completed 3 min after the onset of the rapid depolarization. Because small blebs occurred immediately after the rapid depolarization and large blebs appeared 1.5-3 min after, it is likely that the transformation from small to large blebs may result in the observed irreversible membrane dysfunction.

Changes in the diffusion of water and intracellular metabolites after excitotoxic injury and global ischemia in neonatal rat brain

The reduction of the apparent diffusion coefficient (ADC) of brain tissue water in acute cerebral ischemia, as measured by diffusion-weighted magnetic resonance imaging, is generally associated with the development of cytotoxic edema. However, the underlying mechanism is still unknown. Our aim was to elucidate diffusion changes in the intracellular environment in cytotoxic edematous tissue. The ADC of intracellular metabolites was measured by use of diffusion-weighted 1H-magnetic resonance spectroscopy after (1) unilateral N-methyl-D-aspartate (NMDA) injection and (2) cardiac arrest-induced global ischemia in neonatal rat brain. The distinct water ADC drop early after global ischemia was accompanied by a significant reduction of the ADC of all measured metabolites (P < 0.01, n = 8). In the first hours after excitotoxic injury, the ADC of water and the metabolites taurine and N-acetylaspartate dropped significantly (P < 0.05, n = 8). At 24 and 72 hours after NMDA injection brain metabolite levels were diminished and metabolite ADC approached contralateral values. Administration of the NMDA-antagonist MK-801 1.5 hours after NMDA injection completely normalized the water ADC but not the metabolite ADC after 1 to 2 hours (n = 8). No damage was detected 72 hours later and, water and metabolite ADC had normal values (n = 8). The contribution of brain temperature changes (calculated from the chemical shift between the water and N-acetylaspartate signals) and tissue deoxygenation to ischemia-induced intracellular ADC changes was minor. These data lend support to previous suggestions that the ischemia-induced brain water ADC drop may partly be caused by reduced diffusional displacement of intracellular water, possibly involving early alterations in intracellular tortuosity, cytoplasmic streaming, or intracellular molecular interactions.

Glutamate receptor antagonists inhibit calpain-mediated cytoskeletal proteolysis in focal cerebral ischemia

Excitatory amino acids may promote microtubular proteolysis observed in ischemic neuronal degeneration by calcium-mediated activation of calpain, a neutral protease. We tested this hypothesis in an animal model of focal cerebral ischemia without reperfusion. Spontaneously hypertensive rats were treated with 2, 3-dihydroxy-6-nitro-7-sulfamoyl-benzo-(F)quinoxaline (NBQX), a competitive antagonist of the neuronal receptor for alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), or cis-4-[phosphono-methyl]-2-piperidine carboxylic acid (CGS 19755), a competitive antagonist of the N-methyl-d-aspartate (NMDA) receptor. After treatment, all animals were subjected to permanent occlusion of the middle cerebral artery for 6 or 24 h. Infarct volumes measured in animals pretreated with CGS 19755 after 24 h of ischemia were significantly smaller than those quantified in ischemic controls. Rats pretreated with NBQX showed partial amelioration of cytoskeletal injury with preserved immunolabeling of microtubule-associated protein 2 (MAP 2) at 6 and 24 h and reduced accumulation of calpain-cleaved spectrin byproducts only at 6 h. Prevention of cytoskeletal damage was more effective after pretreatment with CGS 19755, as shown by retention of MAP 2 immunolabeling and significant restriction of calpain activity at both 6 and 24 h. Preserved immunolabeling of tau protein was observed at 6 and 24 h only in animals pretreated with CGS 19755. Western analysis performed on ischemic cortex taken from controls or rats pretreated with either NBQX or CGS 19755 suggested that loss of tau protein immunoreactivity was caused by dephosphorylation, rather than proteolysis. These results demonstrate a crucial link between excitotoxic neurotransmission, microtubular proteolysis, and neuronal degeneration in focal cerebral ischemia.

Disruption of MAP-2 immunostaining in rat hippocampus after traumatic brain injury

The effects of diffuse brain injury on dendritic morphology in rat hippocampus and cortex were examined in this study using the recently described impact acceleration model of traumatic brain injury (Marmarou et al., 1994). Dendritic structure was visualized using immunostaining of microtubule associated protein-2 (MAP-2). Brains were studied 24, 48, and 72 h after brain injury. Results from immunohistochemistry and light microscopy indicated a time-dependent disruption of dendritic cytoarchitecture in the CA1 subregion and in the hilus of the hippocampus but not in the dentate gyrus or CA3 subregion. Similar disruption was observed in the cortical mantle overlying the hippocampus. Although disruption of dendritic structure was observed at 24 h, the most severe damage was at 48 h after injury with evidence of at least partial recovery of MAP-2 immunostaining by 72 h. In the most severe damage, dendrites appeared to be fragmented, scattered, and unaligned, consisting of irregularly spaced and darkly stained swollen segments. A mixed pattern of immunostaining was observed in somata of hilar cells, with some appearing normal while others stained only faintly, appearing to have lost their typical polygonal shape. Semiquantitative rankings confirmed these qualitative findings. Immediate post-injury behavioral evaluations of injury severity were compared to the degree of disruption of MAP-2 immunostaining. The results of this study indicate that diffuse brain injury is associated not only with axonal damage but also with injury to dendrites.

Role of apoptotic proteins in ischemic hippocampal damage

In this review, we have presented evidence that apoptotic proteins may be involved in ischemic cell death. We tried to keep in mind that focal and global ischemia almost certainly produces different forms of cell death. For example, necrotic cell death is clearly part of a focal cerebral infarct, although it is not seen in brief global insults. We also tried to make the point that not all apoptosis is the same and that various forms of non-necrotic cell death, including ischemic cell death after global ischemia, may share some of the same molecular mechanisms as classic forms of apoptosis. Finally, we wish to leave the reader with the clear impression that all the evidence is not in hand. More work needs to be done in animals to define the role of apoptotic proteins. For example, glial cells probably are important in necrosis and may play a role in ischemic cell death after transient global ischemia. Yet it is likely that glial cells die from injury in a different manner than neurons. A better understanding of these processes should lead to new therapeutic approaches that may make possible the salvaging of neurons well after an ischemic insult.

Rapid alteration of tau in oligodendrocytes after focal ischemic injury in the rat: involvement of free radicals

Glial inclusions containing the microtubule-associated protein tau are present in a variety of chronic neurodegenerative conditions. We now report a rapid and time-dependent increase of tau immunoreactivity within oligodendrocytes after focal cerebral ischemia in the rat. The number of tau positive oligodendrocytes in the ipsilateral subcortical white matter increased six- to eightfold by 40 minutes after permanent middle cerebral artery occlusion (MCAO). Tau was detected using antibodies that label both the N- and C-terminal of the protein, suggesting accumulation of full-length protein within these cells. Pretreatment with the spin trap agent alpha-phenyl-tert-butyl-nitrone (PBN)(100mg/kg) reduced the number of tau-positive oligodendrocytes by 55% in the subcortical white matter of the ischemic hemisphere compared with untreated animals at 40 minutes after MCAO. In contrast, pretreatment with glutamate receptor antagonists MK-801 (0.5 mg/kg) or 2,3-dihydroxy-6-nitro-7-sulpfamoyl-benzo(f)quinoxaline (NBQX) (2 x 30 mg/kg), failed to reduce the number of tau-positive oligodendrocytes after 40 minutes of ischemia. The results indicate that oligodendrocytes respond rapidly to an ischemic challenge and that free radical-mediated mechanisms are involved in the cascade leading to increased tau immunoreactivity.

The effect of postmortem delay on the distribution of microtubule-associated proteins tau, MAP2, and MAP5 in the rat

Breakdown or disruption of the cytoskeleton has been implicated in the neurodegenerative processes of a variety of diseases, including Alzheimer disease (AD) and stroke. Studies of such diseases in the human involve the use of postmortem brain tissue. Postmortem delay may vary considerably from a few hours to a few days, and within this period, a degree of cytoskeletal breakdown may occur. It is therefore crucial to examine alterations occurring in the cytoskeleton as a result of postmortem delay and subtract these from those caused by the disease. In this study, the distribution of tau, MAP2, and MAP5 immunohistochemistry was examined following postmortem intervals of 0-72 h in the rat cerebral cortex, corpus callosum, caudate nucleus, and hippocampus. Each microtubule-associated protein (MAP) underwent unique changes that were dependent both on postmortem interval and the brain region examined. Following long postmortem delays, some of the changes in these proteins were similar to those seen in rodent models of cerebral ischemia. These results demonstrate that MAPs are not stable during postmortem delay in the rat. Therefore, caution must be exercised when interpreting changes in MAPs in human postmortem tissue, especially in cases where ischemic injury may be involved. Examination of control tissue carefully matched for postmortem delay is therefore essential to allow meaningful interpretation of cytoskeletal abnormalities in human neurodegenerative disease.

Purkinje cell vulnerability to mild traumatic brain injury

In this study we examined the cerebellar response to mild traumatic brain injury by assessing microglial activation and Purkinje cell loss. Activated microglia were identified using the antibodies OX-42 and ED-1 as well as isolectin B4. The anti-Purkinje cell antibody PEP-19 was used to evaluate Purkinje cell loss after injury. The mechanism of cell injury was examined using a monoclonal antibody to the inducible 72-kDa heat shock protein. A monoclonal antibody to the N-terminal sequence of Fos was used as a marker for neuronal activation. There was progressive activation of microglia in the cerebellar vermis within a few days after forebrain injury. In coronal sections the processes of activated microglia were oriented in "stripes" perpendicular to the cortical surface. In sagittal sections the activated microglia were in irregularly shaped clusters or in a fan-like distribution that radiated from the Purkinje cell layer toward the cortical surface. There was a significant loss of Purkinje cells 7 days postinjury as compared to the control group. There was no evidence of induction of heat shock protein in the cerebellum. In addition, there was no evidence of induction of c-Fos protein in either the cerebellar cortex or inferior olivary nuclei within the first 3 h after injury. These studies demonstrate that a fluid percussive impact to the forebrain results in cerebellar damage. The close anatomical association between activated microglia and Purkinje cells suggests that Purkinje cell injury is the cause of the microglial activation. The mechanism of Purkinje cell death, however, remains unclear.

Survival of parvalbumin-immunoreactive neurons in the gerbil hippocampus following transient forebrain ischemia does not depend on HSP-70 protein induction

HSP-70 was induced in the gerbil following 20 min of forebrain ischemia. The induction, as revealed with immunohistochemistry, is stronger and longer-lasting in CA3 and dentate gyrus than in CA1. Most neurons in this region, except GABAergic interneurons containing the calcium-binding protein parvalbumin, eventually cease to live as a result of delayed cell death. Double-labeling of inducible HSP-70 and parvalbumin has shown that no co-localization occurs in the hippocampus and neocortex of the gerbil in this model of transient forebrain ischemia. These results show that different thresholds of sensitivity and vulnerability exist for different subpopulations of neurons in the ischemic hippocampus, and suggest that HSP-70 protein induction is probably not essential for the survival of particular neuronal subpopulations subjected to transient ischemia.

Global brain ischemia and reperfusion: Golgi apparatus ultrastructure in neurons selectively vulnerable to death

The neocortex and the hippocampus were examined for lipid peroxidation products and ultrastructural alterations by fluorescence and electron microscopy, respectively, in rats subjected to 10 min of cardiac arrest or 10 min cardiac arrest and either 90 or 360 min reperfusion. Lipid peroxidation products were observed after 90 min reperfusion in the perikarya and proximal dendrites of neocortical pyramidal neurons and in the hippocampal hilar cells and CA1, region; the fluorescence was most intense at the base of the apical dendrite, the region of the Golgi apparatus. After 90 min of reperfusion, the CA1, showed considerable stretches of rough endoplasmic reticulum devoid of ribosomes and the Golgi cisternae were shorter and widely dilated. The neocortex showed similar endoplasmic reticulum changes, but no significant alterations to the Golgi were noted. In addition there were areas where strings of ribosomes appear to be detaching from the endoplasmic reticulum. After 360 min reperfusion in both the neocortex and the hippocampus, the damage appeared more severe. The Golgi was fragmented into vacuoles, membranous whorls had appeared, and dense aggregates of smooth vesicles were seen coalescing with each other and the vacuoles. These observations suggest that early Golgi involvement is a more important marker of lethal injury than ribosome release from the endoplasmic reticulum. The areas of disturbed Golgi ultrastructure correspond to those areas that show evidence of lipid peroxidation and imply that lipid peroxidation may be causally related to the disturbance in Golgi ultrastructure.

Tau protein is altered by focal cerebral ischaemia in the rat: an immunohistochemical and immunoblotting study

Breakdown of the cytoskeleton may be involved in the evolution of ischaemic brain damage and alterations in microtubule-associated proteins may play an important role in this process. In the present study, tau, a microtubule-associated protein predominantly located in axons, was examined after 2 or 6 h of focal cerebral ischaemia in the rat. Immunohistochemistry revealed increased Tau1 staining in the neuropil, some perikarya and in glial cells throughout the dorsolateral caudate nucleus and ventrolateral neocortex in the ipsilateral hemisphere at both 2 and 6 h after occlusion of the middle cerebral artery. Contrastingly, immunostaining of another tau antibody, TP70, was unchanged in the neuropil, but was increased specifically in glial cells in these regions. Immunoblotting revealed the presence of additional tau bands in tissue extracts of the caudate nucleus and ventrolateral neocortex ipsilateral to the occluded middle cerebral artery as detected by both tau antibodies after either 2 or 6 h. The results suggest that tau is dephosphorylated and/or degraded in axons and some neuronal perikarya in response to focal cerebral ischaemia. In contrast to the response in neurons, increased immunoreactivity of both tau antibodies in glial cells indicates a differential response of neuronal and glial tau to focal cerebral ischaemia.

Golgi electron microscopic study of the cerebral cortex after transient cerebral ischemia and reperfusion in the gerbil

Fine structures of defined neurons and their dendritic processes were studied in the cerebral cortex of gerbil brains by using Golgi electron microscopy during progressive cerebral ischemia for 10 and 20 min and after reperfusion for up to 72 h following transient ischemia for 20 min. The periphery of ascending dendrites of the vulnerable neurons in layers III and Vb became distended immediately after ischemia with swollen mitochondria and disintegrated microtubules, but the proximal portion of the same dendrites remained unchanged. After reperfusion for 6 h, distension of the dendroplasm of the impregnated dendrites in layer I receded, but the proximal portion of the same dendrites showed indentation caused by swollen astrocytic processes and derangement of microtubules inside. Polyribosomes in most neuronal perikarya were disaggregated, but severe neuronal damage was rarely found among those neuronal cell bodies impregnated by the Golgi method. Recovery with reaggregation of polyribosomes and realignment of microtubules was more clearly observed after reperfusion for 24 h and thereafter in impregnated neurons. These results indicated that impregnation during progressive ischemia occurred in many neurons with progressive structural damage but that impregnation during reperfusion occurred in a limited number of neurons with limited damage, allowing us to observe the recovery process, and that neuronal derangement in the dendrosomatic direction initially occurred both in the irreversibly damaged neurons and in the reversibly damaged ones. It is possible that disintegration of microtubules and the resulting disruption of dendritic transport may contribute to subsequent development of delayed neuronal death, if the recovery process does not take place promptly. Golgi electron microscopy is useful for ultrastructural investigation of defined neurons and their dendrites together and may be applicable for investigation of selected neuropathologic conditions.

Alterations in tau immunostaining in the rat hippocampus following transient cerebral ischemia

Previous studies in gerbils have shown that cytoskeletal disruption and a loss of the dendritic microtubule-associated protein, MAP2, may occur after short periods of transient global ischemia. tau, a predominantly axonal microtubule-associated protein, has not been examined following ischemia. We compared neuronal damage with alterations in MAP2, tau, and 72-kD heat shock protein (HSP72) immunostaining at various reperfusion times following 20 min of ischemia in the rat four-vessel occlusion model. tau accumulated in neuronal cell bodies throughout the hippocampal formation 30 min to 2 h after the ischemic insult. Perikaryal tau immunostaining was transient in most regions, but persisted in polymorphic hilar neurons. This was accompanied by a loss of immunostaining in the target of many hilar neurons, the inner molecular layer of the dentate gyrus. The same neuronal populations that exhibited increased tau immunostaining of perikarya later displayed an induction of HSP72 immunoreactivity. In contrast, loss of MAP2 immunostaining was not consistently observed before neuronal death and did not correspond to HSP72 induction. The altered tau immunostaining is not the direct result of excitotoxic insult, as intrahippocampal injection of kainic acid did not cause the somal accumulation of tau, but did cause disruption of MAP2 immunostaining. Taken together, the results suggest that the somal accumulation of tau is an early, sensitive, and selective marker of ischemic insult.

Dose-related effects of cycloheximide on delayed neuronal death in the gerbil hippocampus after bilateral transitory forebrain ischemia

Degeneration of dendrites followed by punctate chromatin condensation in the CA1 area of the hippocampus is a characteristic of delayed neuronal death following bilateral forebrain ischemia. The effects of the protein synthesis inhibitor cycloheximide on delayed neuronal death following 20 min of bilateral forebrain ischemia were examined in the gerbil hippocampus at the 4th day of reperfusion. Low doses of cycloheximide beginning 10 min after ischemia (1.0 microgram/g body weight in saline followed by 1.0 microgram/g every 24 h) reduced the number of dying cells in the CA1 area, whereas high doses (2.0 micrograms/g, followed by 1.0 microgram/g every 12 h) increased the number of dying cells. No effects were seen when a single dose of cycloheximide was injected 1 h before ischemia. These results indicate that the effects of cycloheximide are dose-dependent, low doses reduce, high doses increase cell death. These findings also indirectly suggest that protein synthesis may play a role in the extent of delayed neuronal death. Some involved proteins could be heat shock proteins, which are induced after ischemia and had been correlated with increased resistance to injury. However, changes of heat shock immunoreactivity in the postischemic hippocampus were not seen in the present study following cycloheximide injection.

Fructose-1,6-bisphosphate fails to ameliorate delayed neuronal death in the CA1 area after transient forebrain ischaemia in gerbils

Fructose-1,6-bisphosphate has been shown to reduce ischaemic-induced brain damage in rabbits and gerbils. In view of these findings, we investigated the effects of fructose-1,6-bisphosphate on delayed neuronal death, following bilateral forebrain ischaemia, in the gerbil hippocampus at the fourth day of reperfusion. We subjected gerbils to bilateral forebrain ischaemia for 20 min. Fructose-1,6-bisphosphate was administered: intraperitoneally at a dose of 1 g/kg in saline in hr before the occlusion or at a dose of 1 g/kg 1 hr before the occlusion and every 24 hr for 3 days; or intraventricularly at a dose of 0.1 g/kg just after the carotid occlusion. No significant differences in the number of dying cells in the CA1 area were found between each group of treated animals when compared with controls. This study suggests that fructose-1,6-bisphosphate, administered according to these three different schedules, fails to ameliorate delayed neuronal death after 20 min of bilateral forebrain ischaemia in the CA1 area of the gerbil hippocampus.

Differential vulnerability in the hindbrain neurons and local cerebral blood flow during bilateral vertebral occlusion in gerbils

Differential vulnerability in the hindbrain neurons was examined immunohistochemically during hindbrain ischemia in the gerbil. Hindbrain ischemia was produced by extracranial occlusion of the bilateral vertebral arteries just before their entry into the transverse foramen of the cervical vertebra. Local cerebral blood flow was measured by quantitative autoradiographic technique after 5 min of ischemia and was reduced to less than 5 ml/100 g per min in the cerebellum, the pons, and the medulla, indicating that severe and reproducible hindbrain ischemia was induced immediately after occlusion. For immunohistochemical investigation, four gerbils each were used for each ischemic period of 5, 10, 15, and 30 min. Immunohistochemical lesions, detected by the reaction for microtubule-associated protein 2, were visible in the lateral vestibular nucleus and the cerebellar interpositus nucleus even after 5 min of ischemia. These results suggested that these areas were more vulnerable than others, although blood flow was markedly reduced in various regions of the hindbrain. In contrast, areas related to respiratory or cardiovascular control were rather resistant to ischemia. The present study suggests that selective vulnerability during hindbrain ischemia depends mainly on different metabolic characteristics inherent to various neurons in the hindbrain.

Acute anoxia-induced alterations in MAP2 immunoreactivity and neuronal morphology in rat hippocampus

Cerebral ischemia induces major neuronal morphological alterations. It is not clear, however, whether this is directly caused by O2 deprivation. To determine the effect of hypoxia on cytoskeletal structures and neuronal morphology, we performed experiments and examined anoxia-induced changes in microtubule-associated protein 2 (MAP2) and cell morphology in hippocampal slices in vitro. Anoxia (measured PO2 = 0 Torr) induced a marked loss in dendritic MAP2 immunoreactivity and cell swelling of hippocampal neurons by 2 h after O2 reinstitution. These changes were severe in CA1 and CA3 neurons and comparatively mild in dentate gyrus neurons. Quantitative analysis showed that 10 min of anoxia induced a 30% loss of MAP2-positive dendrites but this increased to 70% after 30 min of anoxia. A concurrent major increase in somata area of about 100% and 200% was observed in CA1 and CA3 neurons respectively. Somata area in the lower dentate gyrus, however, increased either insignificantly or by only 30% for the respective periods of anoxia. These results suggest that deprivation of O2 can by itself induce a major loss in dendritic MAP2 immunoreactivity and changes in cell morphology in hippocampal neurons. These alterations occur rapidly after hypoxia, and the severity of these changes is directly related to the duration of anoxia and brain region in the hippocampus.

Paraneoplastic cerebellar degeneration with a circulating antibody against neurons and non-neuronal cells

We describe a woman with paraneoplastic cerebellar degeneration associated with para-ovarian adenocarcinoma, who had a circulating antibody with a corresponding antigen not only in cerebellar Purkinje cells but also in neurons located in the molecular layer of the human and rat cerebellum. The antigen was also present in neurons in the cerebral cortex, brain stem, anterior horn cells, dorsal root ganglia, intestinal autonomic neurons, retinal ganglion cells, Schwann cells of the peripheral nerve and epithelial cells of the renal glomerulus in rats. Immunoelectron microscopy revealed immunoprecipitates in the smooth and rough endoplasmic reticulum and polyribosomes in human and rat cerebellar Purkinje cells and other neuronal cell bodies as well as Schwann cells of the peripheral nerve. Even though patients with this disorder manifest primarily with cerebellar and some extracerebellar signs, the antigen also exists in many neurons other than cerebellar Purkinje cells and even in non-neuronal cells. The clinicopathologic significance of the observed immunologic reaction in diverse neurons remains to be determined.

Parvalbumin immunoreactivity in the hippocampus of the gerbil after transient forebrain ischaemia: a qualitative and quantitative sequential study

Parvalbumin immunoreactivity is examined in the hippocampus of the Mongolian gerbil (Meriones unguiculatus) in controls and in animals subjected to 20 min of forebrain ischaemia produced by bilateral clipping of the carotids. In comparison with other species, the hippocampus of the gerbil is characterized by strong immunoreactivity of the (presumably excitatory) perforant pathway, and weak immunoreactivity (low numbers of neurons and scarce dendritic arbors) in nonpyramidal nerve cells (inhibitory neurons) of the CA1 area. These properties may play some role in the development and maintenance of seizures in this susceptible species. Parvalbumin immunoreactivity is rapidly and ephemerally increased in the hippocampus 15 min after reperfusion. Later on, there is a transitory decrease of parvalbumin immunoreactivity which is followed by an increase 6 h later in the stratum granulare hilus and CA3 area, and not until the first and second days in the CA1 area. This increase significantly surpasses the number of immunoreactive neurons in control animals in CA1 and CA3 from 48 h after reperfusion onwards. The effect is similar using different anaesthetics and does not occur in sham-operated animals. In contrast with these findings, the number of parvalbumin-immunoreactive neurons in the somatosensory cortex is not affected in our model of forebrain ischaemia. On the other hand, GABA-immunoreactive neurons in CA1 are preserved during the first week after reperfusion, although an increase in the number of these cells occurs at the end of this period. Delayed neuronal death occurs in the CA1 area 48 h after ischaemia, and marked reduction in the number of CA1 neurons is found by the end of the first week. Eighty per cent of the remaining cells in CA1 at day 7, and 83% at day 15, are parvalbumin-immunoreactive nonpyramidal neurons in contrast to 3% parvalbumin-immunoreactive cells in control animals. These findings indicate that GABAergic neurons in CA1 are preserved after forebrain ischaemia, and that parvalbumin in CA1 neurons is associated with survival.

Identity of the dorsal hippocampal region most vulnerable to cerebral ischemia

Our previous investigations demonstrated that neurons in the area between the subiculum and the medial CA1 region and another area between the lateral CA1 and the CA3 region of the hippocampus are very vulnerable to cerebral ischemia in gerbils, where irreversible damages have been observed occur as early as 4-5 min after unilateral or bilateral common carotid artery occlusion. The present study was aimed to characterize these areas anatomically by using the immunohistochemical and zinc histochemical as well as Golgi silver impregnation methods. Our results indicated that these two areas which are topographically apart on the coronal section actually had a common origin in the rostral part of the hippocampus and that they were separated by insertion of the Ca1 neurons between them in the more caudal part of the hippocampus. The distribution pattern of mossy fibers indicated that these areas belonged to the CA2 region. The double immunohistochemical and zinc histochemical procedure confirmed that these areas developed ischemic lesions promptly even without reperfusion but that the CA1 region did not develop similar lesions until after reperfusion for 12-24 h if the ischemic period was brief. While the reason for the observed susceptibility of the CA2 region is not certain at the present time, it is important to distinguish the ischemic lesions in the CA2 region from those in the CA1 and CA3 regions.

Electron microscopic investigation of the cerebral cortex after cerebral ischemia and reperfusion in the gerbil

Prompt dendritic damage has been observed in the hippocampus of the gerbil brain after transient cerebral ischemia. In the present study, we studied the frontoparietal cortex of the gerbil brain electron microscopically after brief bilateral carotid occlusion to assess the vulnerability of dendritic processes. After ischemia for 5 min, there was swelling of the periphery of dendrites accompanied by swelling of mitochondria, cytoplasmic vacuolation and disintegration of microtubules in layer I, which spread to layer III after ischemia for 20 min. After reperfusion for 3-24 h following ischemia for 20 min, swelling in the periphery of dendrites and of mitochondria inside receded but vacuole formation and disintegration of microtubules propagated proximally. In neuronal perikarya, polyribosomal disaggregation was observed after ischemia for 20 min and persisted thereafter, while fragmentation of rough endoplasmic reticulum (ER) and microvacuolation occurred after reperfusion for 3 h. Electron-dense clumping of neuronal perikarya was observed after reperfusion for 6 h particularly in layers III and Vb, which increased in number for up to 72 h. The observed progressive damage in dendrites may be common to neurons vulnerable to cerebral ischemia and may significantly contribute to development of delayed neuronal death.

The microglial reaction in the rat hippocampus following global ischemia: immuno-electron microscopy

Transient arrest of the cerebral circulation leads to neuronal cell death in selectively vulnerable regions of the central nervous system. It has recently been shown at the light microscopical level that neuronal necrosis is accompanied by a rapid microglial reaction in ischemia (Gehrmann et al. (1992) J. Cereb. Blood Flow Metab. 12:257-269). In the present study we have examined the postischemic microglial reaction in the dorsal rat hippocampus at the ultrastructural level using immuno-electron microscopy. Global ischemia was produced by 30 min of four-vessel occlusion and the microglial reaction then studied after 8, 24 and 72 h. In sham-operated controls microglial cells were not phagocytic; they were randomly distributed throughout the neuropil and occasionally made contacts with other structures such as dendrites in CA1. Ultrastructural signs of activation were observed from 1 day postlesion onward. Reactive microglial cells were consistently seen to phagocytose degenerating neurons particularly in the CA1 stratum pyramidale and in the CA4 sector. They were sometimes interposed between two morphologically distinct types of CA1 neurons, i.e., "dark" (degenerating) and "pale" (surviving) types of neurons. Phagocytic microglial cells also became positive for major histocompatibility complex (MHC) class II antigens at these locations from 1 day after ischemia onward. Furthermore, activated microglial cells were frequent along degenerating dendrites in the stratum radiatum of CA1. After survival times of up to 72 h microglial cells, but not astrocytes, were occasionally observed to undergo mitosis. In addition to their random distribution across the neuropil, microglial cells were frequently observed in a perivascular position under normal conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunocytochemical study of an early microglial activation in ischemia

Transient arrest of the cerebral blood circulation results in neuronal cell death in selectively vulnerable regions of the rat brain. To elucidate further the involvement of glial cells in this pathology, we have studied the temporal and spatial distribution pattern of activated microglial cells in several regions of the ischemic rat brain. Transient global ischemia was produced in rats by 30 min of a four-vessel occlusion. Survival times were 1, 3, and 7 days after the ischemic injury. The microglial reaction was studied immunocytochemically using several monoclonal antibodies, e.g., against CR3 complement receptor and major histocompatibility complex (MHC) antigens. Two recently produced monoclonal antibodies against rat microglial cells, designated MUC 101 and 102, were also used to identify microglial cells. Following ischemia, the microglial reaction was correlated with the development of neuronal damage. The earliest presence of activated microglial cells was observed in the dorsolateral striatum, the CA1 area, and the dentate hilus of the dorsal hippocampus. However, the microglial reaction was not confined to areas showing selective neuronal damage, but also occurred in regions that are rather resistant to ischemia, such as the CA3 area. Particularly in the frontoparietal cortex, the appearance of MHC class II-positive microglial cells provided an early indication of the subsequent distribution pattern of neuronal damage. The microglial reaction would thus seem to be an early, sensitive, and reliable marker for the occurrence of neuronal damage in ischemia.

Intracerebral distribution of albumin after transient cerebral ischemia: light and electron microscopic immunocytochemical investigation

The blood-brain barrier breaks down following cerebral ischemia, but the exact sequence of events for extravasation of serum proteins and their parenchymal distribution remain uncertain. We studied the distribution of serum albumin in the hippocampus of the gerbil brain using light and electron microscopic immunocytochemical techniques. With light microscopy, there was no reaction for albumin for the first 12 h after unilateral common carotid artery occlusion for 10 min and reperfusion. At 12 h, the reaction was weak and limited to the neuropil in the subiculum-CA1 region (between the subiculum and the medial CA1 region). After 24 h, the reaction became intense in the neuropil and neuronal perikarya in the subiculum-CA1 and medial CA1 regions. The electron microscopic immunocytochemical study of the subiculum-CA1 and medial CA1 regions revealed electron-dense immunoprecipitates in the extracellular space and the peripheral part of the apical dendrites as early as 30 min after reperfusion and in the astrocytic cytoplasm after reperfusion for 1 h. However, immunoprecipitates were not found in the neuronal perikarya until after reperfusion for 24 h. The present study demonstrated prompt appearance of albumin in the extracellular space of the brain parenchyma after re-establishment of cerebral circulation and prompt accumulation in the peripheral part of the dendrites with spreading to neuronal perikarya, likely in the process of degeneration and death.

The microglial reaction in the rat dorsal hippocampus following transient forebrain ischemia

We have examined the distribution and time course of the microglial reaction in the rat dorsal hippocampus after 25-min transient forebrain ischemia (four-vessel occlusion model). Microglial cells were visualized in brain sections using lectin staining with the Griffonia simplicifolia B4-isolectin following intervals of reperfusion ranging from 20 min to 4 weeks. Increased staining of microglial cells was detected in the dentate hilus and area CA1 as early as 20 min after reperfusion. These same regions demonstrated more intense microglial staining after 24 h. The strongest microglial reaction was observed 4-6 days after reperfusion when reactive microglia were abundant throughout all laminae of CA1 and the dentate hilus. Following longer reperfusion intervals, the microglial reaction became less intense; however, it remained above normal levels until the end of the fourth week. At all time points examined, microglial reactivity in the CA3 pyramidal and dentate granule cell layers was considerably lower than that observed in CA1 and dentate hilus. Our results are consistent with the known serial pathological changes associated with cerebral ischemia, but, in addition, show that the examination of the microglial reaction provides an extremely sensitive indicator of subtle and morphologically nonapparent neuronal damage during the early stages of injury.

An immunohistochemical study of MAP2 and clathrin in gerbil hippocampus after cerebral ischemia

Changes in MAP2 and clathrin immunoreactivity were studied in gerbil hippocampus after transient cerebral ischemia. MAP2 immunoreactivity decreased significantly by 1 h in the subiculum-CA1 and CA2 areas which correspond to reactive change, while no decrease was observed in CA1 until day 4. Before the initiation of delayed neuronal death, MAP2 immunoreactivity was not changed in CA1. On the other hand clathrin immunoreactivity increased in the pyramidal cell layer of CA1 by 3 h after ischemia and remained high for 2 days. Clathrin immunoreactivity in the pyramidal cell layer of CA1 diminished after delayed neuronal death. The transient change of clathrin was noted especially in CA1 in the period prior to delayed neuronal death. These results imply an abnormal change in clathrin turnover after ischemia, which may participate in the pathogenesis of delayed neuronal death.

Immunohistochemical distribution of calcium-activated neutral proteinases and endogenous CANP inhibitor in the rabbit hippocampus

Intracellular accumulation of Ca2+ after brain ischemia is regarded as one of the principal causes of neuronal death, but details of the intracellular events occurring after Ca2+ accumulation have not yet been described. We propose that a calcium-activated neutral proteinase which can degrade neuronal cytoskeletal proteins might link Ca2+ accumulation and irreversible injury of the neuronal intracellular structure. First, therefore, we examined the distribution of calcium-activated neutral proteinase in normal brains. Immunohistochemical distribution of calcium-activated neutral proteinases (CANP) with high and low sensitivity to Ca2+ (muCANP and mCANP) and of endogenous CANP inhibitor was investigated in the dorsal hippocampus of the rabbit. muCANP-immunoreactivity was detected in almost all of the pyramidal cells and granule cells and in some other neurons. A full-length staining from perikarya to dendrites was shown in muCANP-positive neurons. mCANP-immunoreactivity was found mainly in four kinds of hippocampal interneurons: 1) basket cells in the stratum oriens of Ammon's horn, 2) pyramidal basket cells at the boundary of pyramidal cell layer and stratum oriens, 3) polymorphic cells in the hilar region of dentate gyrus, and 4) pyramidal or fusiform basket cells at the inner boundary of the granule cell layer and the hilar region. The distribution of these four kinds of neurons was similar to that of parvalbumin-containing GABAergic neurons. CANP inhibitor immunoreactivity was confined to pyramidal cells in the CA3-CA3c region and some hilar neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential vulnerability of microtubule components in cerebral ischemia

Differential vulnerability of the major components of microtubules was examined in ischemic gerbil brains by a light microscopic, immunohistochemical method using monoclonal antibodies for microtubule-associated protein (MAP) 1A and MAP2, polyclonal antibody for MAP1 and 2 as well as monoclonal antibody for alpha-tubulin. Progressive cerebral ischemia during unilateral carotid occlusion for 5, 15 and 120 min and reperfusion for 3, 12 and 48 h following bilateral carotid occlusion for 10 min were studied. Ischemic lesions in the subiculum-CA1 region were visualized by all antibodies after ischemia for 5 min but the antibody for alpha-tubulin was less sensitive. The antibody for alpha-tubulin was also less sensitive than antibodies for MAPs for detection of early postischemic lesions. Differential sensitivity was also observed in the cerebral cortex and other brain regions. Microtubules in myelinated axons were more stable than those in dendrites. The observed loss of immunohistochemical reactivities for MAPs and alpha-tubulin may have been caused by activation of calcium-dependent proteolytic enzymes such as calpains. The discrepancy between MAPs and alpha-tubulin could be due to differences in affinities or topographic distributions of these proteins within microtubules.

Ultrastructural investigation of the CA1 region of the hippocampus after transient cerebral ischemia in gerbils

Ultrastructural damage leading to delayed neuronal death was investigated in the mid-CA1 region of the hippocampus from the stratum (str.) moleculare to oriens after transient bilateral forebrain ischemia in Mongolian gerbils. After ischemia for 5 min without recirculation, mild swelling of the peripheral part of the apical and basal dendrites was already apparent in the str. moleculare and str. oriens. Mitochondria in the dendrites were also swollen in the same area. During recirculation for 12 h to 3 days, swelling of the dendritic cytoplasm persisted with formation of microvacuoles, but swelling of mitochondria receded. Microvacuolation and loss of microtubules were also observed in the proximal part of the dendrites during this period, and swelling and disruption of internal cristae were observed in mitochondria after recirculation for 3 days. The dendrites became severely degenerated after recirculation for 4 days. In the pyramidal cell bodies, no abnormality was observed at the end of ischemia for 5 min, but disaggregation of polyribosomes and swelling of the endoplasmic reticulum were observed 12 h after recirculation. Proliferation of the endoplasmic reticulum in parallel arrays occurred after recirculation for 1 day and persisted. Severe degeneration of the pyramidal cell bodies was obvious after recirculation for 4 days. The findings observed in the present investigation suggested that the neuronal structure most vulnerable to ischemia was the peripheral part of the dendrites and postischemic neuronal damage occurred early in this part of the dendrites.

Disruption of microtubules as an early sign of irreversible ischemic injury. Immunohistochemical study of in situ canine hearts

Structural disruption of the cytoskeleton may be involved in irreversible ischemic injury. In the present study, ischemic changes in microtubules during various periods of myocardial ischemia were studied with an immunohistochemical technique in open-chest dogs. In intact myocardium, microtubules were stained as a filamentous network throughout cytoplasm and a circular network around the nucleus, which disappeared with colchicine treatment. In brief ischemia of less than 15 minutes, microtubule patterns were unaltered. After 20 minutes, however, characteristic microtubule stains were partly lost in patchy lesions. As an increase in ischemic period, lesions of loss of microtubule stains were increased in number and size. After 120 minutes of reperfusion following 60 minutes of ischemia, the lesions with intact actin filaments but with disrupted microtubules were replaced by the severely injured cells in which the regular myofibrillar registrations were distinctly disrupted. After 24 hours of reperfusion following 40 minutes of occlusion of the left circumflex artery, the percent area of disrupted microtubules at 40 minutes of ischemia was replaced by that of irreversibly injured lesions in the posterior papillary muscle. These results indicate that disruption of microtubules during ischemia heralds irreversible ischemic injury. However, in in vitro study, the myocardium incubated in hypoxic solution for 60-120 minutes demonstrated earlier disruption of the microtubules than the vinculin. Electron microscopic study also showed minimal irreversible changes in the lesions with disrupted microtubules. Thus, taken together, we conclude that microtubules that support the structural integration of myofibrils and other organelles are disrupted in severe myocardial ischemia before the irreversible injury, promoting the irreversible change after reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro ischemia and protein synthesis in the rat hippocampal slice: the role of calcium and NMDA receptor activation

The rat hippocampal slice was developed as a model for investigating the effects of ischemia on protein synthesis in different cell types, as synthesis is an early functional indicator of cell damage. Five min of in vitro ischemia inhibited protein synthesis in CA1 pyramidal and subicular neurons 3 h later, despite recovery of the energy charge. Morphology of these neurons was also affected. In contrast, glia and capillary endothelial cells showed increased synthesis at this time point, and no apparent structural changes. Exposure of slices to buffer lacking calcium and containing the non-competitive NMDA receptor blocker ketamine, during the 5 min ischemia, prevented both the inhibition of protein synthesis and the morphologic changes in the neurons. However, if buffer only lacked calcium, or only contained ketamine, both forms of ischemic damage occurred. Thus, the neuronal protein synthesis inhibition and the impaired morphology appear to be mediated by either extracellular calcium or NMDA receptor activation. In contrast to the neurons, the ischemia-induced stimulation of protein synthesis in glia and capillary endothelial cells was not affected by the above treatments, indicating that neither NMDA receptor activation nor extracellular calcium is necessary for this effect.

Effects of ischemia on cholinergic neurotransmission and electrolyte content in newborn pig lumbar spinal cord

The biochemical changes of the elements of cholinergic neurotransmission (choline acetyltransferase, ChAT; acetylcholinesterase, AChE; butyrylcholinesterase, BuChE; and muscarinic cholinergic receptors, mAChR) as well as the electrolyte content were studied in ischemic lumbar spinal cord segments of newborn pigs. Ischemia was elicited by ligating the aorta for 30 min. Although no significant changes were observed in the sodium, potassium and calcium content of ischemic spinal cords, the calcium content was slightly elevated, to 119.3% of the control value. Whereas significant depletions were observed in both AChE and ChAT activities (to 69.1 and 87.7% of the control value, respectively), there was no significant change in BuChE activity as compared to the control value. The mAChR were also decreased, from 33.25 +/- 2.2 to 27.18 +/- 1.9 fmol/mg protein, while the Kd value was not significantly altered. It is concluded that even a relatively brief interruption of the oxygen supply can cause severe damage in the lumbar spinal cord of the newborn pig, affecting the cholinergic neurotransmission elements. This animal model might be suitable for studying the effects of hypoxia in newborns and children during chest operations involving the descending aorta.