The synapsin I brain distribution in ischemia

Acetylation, methylation, and ubiquitination of proteins in experimental ischemic stroke in mice: a bioinformatics analysis

The experimental results available in the ProteomeXchange database (accession code PXD016538) (Simats et al. (2020) Molecular and Cellular Proteomics, 19(12), 1921-1936) obtained using a comprehensive multi-omics approach were analyzed in mouse blood to identify potential biomarkers of ischemic stroke. Acetylation, methylation, and ubiquitination were considered as post-translational modifications. The analysis of the significance of changes in the level of protein modification was evaluated for ischemic tissue in comparison with tissue undamaged by stroke and control taken from mice after sham operation. At the level of statistically significant differences according to the Mann-Whitney test (p < 0.05), 2 proteins were found (Q02248 and Q8BL66); for additional 7 proteins, the differences were at the level of a statistical trend (p < 0.1). For 7 of 9 selected proteins there are reports in the literature, for their association with cerebral ischemia.

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.

Ganoderma lucidum aqueous extract prevents hypobaric hypoxia induced memory deficit by modulating neurotransmission, neuroplasticity and maintaining redox homeostasis

Oxidative stress due to hypobaric hypoxia at extreme altitudes causes severe neuronal damage and irreversible cognitive loss. Owing to contraindications of current drug therapies, the aim of the study was to investigate memory enhancing potential of aqueous extract of Ganoderma lucidum (GLAQ) and underlying neuroprotective mechanism using rat hypobaric hypoxia test model. Rats exposed to hypobaric hypoxia showed deranged spatial memory in morris water maze test with hippocampal damage and vasogenic cerebral edema. All these changes were prevented with GLAQ treatment. Blood and biochemical analysis revealed activation of hypoxic ventilatory response, red blood cells induction, reversal of electrolyte and redox imbalance, and restoration of cellular bioenergetic losses in GLAQ treated animals. Notably, GLAQ treatment ameliorated levels of neurotransmitters (catecholamines, serotonin, glutamate), prevented glucocorticoid and α-synuclein surge, improved neuroplasticity by upregulating CREB/p-CREB/BDNF expression via ERK1/ERK2 induction. Further, restoration of nuclear factor erythroid 2-related factor with stabilization of hypoxia inducible factors and inflammatory markers were evidenced in GLAQ treated rats which was additionally established in gene reporter array using an alternative HT22 cell test model. Conclusively, our studies provide novel insights into systemic to molecular level protective mechanism by GLAQ in combating hypobaric hypoxia induced oxidative stress and memory impairment.

hESC-derived Olig2+ progenitors generate a subtype of astroglia with protective effects against ischaemic brain injury

Human pluripotent stem cells (hPSCs) have been differentiated to astroglia, but the utilization of hPSC-derived astroglia as cell therapy for neurological diseases has not been well studied. Astroglia are heterogeneous, and not all astroglia are equivalent in promoting neural repair. A prerequisite for cell therapy is to derive defined cell populations with superior therapeutic effects. Here we use an Olig2-GFP human embryonic stem cell (hESC) reporter to demonstrate that hESC-derived Olig2(+) progenitors generate a subtype of previously uncharacterized astroglia (Olig2PC-Astros). These Olig2PC-Astros differ substantially from astroglia differentiated from Olig2-negative hESC-derived neural progenitor cells (NPC-Astros), particularly in their neuroprotective properties. When grafted into brains subjected to global ischaemia, Olig2PC-Astros exhibit superior neuroprotective effects and improved behavioural outcome compared to NPC-Astros. Thus, this new paradigm of human astroglial differentiation is useful for studying the heterogeneity of human astroglia, and the unique Olig2PC-Astros may constitute a new cell therapy for treating cerebral ischaemia and other neurological diseases.

Iron mediates endothelial cell damage and blood-brain barrier opening in the hippocampus after transient forebrain ischemia in rats

Blood cells are transported into the brain and are thought to participate in neurodegenerative processes following hypoxic ischemic injury. We examined the possibility that transient forebrain ischemia (TFI) causes the blood-brain barrier (BBB) to become permeable to blood cells, possibly via dysfunction and degeneration of endothelial cells in rats. Extravasation of Evans blue and immunoglobulin G (IgG) was observed in the hippocampal CA1-2 areas within 8 h after TFI, and peaked at 48 h. This extravasation was accompanied by loss of tight junction proteins, occludin, and zonula occludens-1, and degeneration of endothelial cells in the CA1-2 areas. Iron overload and mitochondrial free radical production were evident in the microvessel endothelium of the hippocampus before endothelial cell damage occurred. Administration of deferoxamine (DFO), an iron chelator, or Neu2000, an antioxidant, blocked free radical production and endothelial cell degeneration. Our findings suggest that iron overload and iron-mediated free radical production cause loss of tight junction proteins and degeneration of endothelial cells, opening of the BBB after TFI.

Isolation and characterization of LCHN: a novel factor induced by transient global ischemia in the adult rat hippocampus

Using mRNA differential display to identify cerebral ischemia-responsive mRNAs, we isolated and cloned a cDNA derived from a novel gene, that has been designated LCHN. Antisense mRNA in situ hybridization and immunoblotting confirmed LCHN expression to be induced in the rat hippocampus following transient forebrain ischemia. The deduced amino acid sequence of the novel LCHN cDNA contains an open reading frame of 455 amino acids, encoding a protein with a predicted molecular mass of approximately 51 kDa. Although LCHN is highly conserved between rat, mouse, and human, the deduced amino acid sequence of LCHN does not possess significant homology to other known genes. LCHN immunoreactivity is detected within the somatodendritic compartment of neurons, is also present on dendritic growth cones, but is not detected on astrocytes. The induction of LCHN in the hippocampus following ischemic injury may have functional consequences, as the ectopic over-expression of LCHN generated neurons with longer and more branched axons and dendrites. Taken together, these data suggest that LCHN could play a role in neuritogenesis, as well as in neuronal recovery and/or restructuring in the hippocampus following transient cerebral ischemia.

Effect of hypothermia on postmortem alterations in MAP2 immunostaining in the human hippocampus

Ischemic neuronal injury induce degradation of microtubule-associated protein 2 (MAP2). In addition to ischemia, postmortem brains show alterations in MAP2 immunoreactivity in the hippocampus, suggesting that the factors inducing cytoskeletal disruption in postmortem brain are similar to those in ischemic brains. Hypothermia reduces the severity of ischemic injury including disruption of MAP2 in the hippocampus. However, whether hypothermia reduces postmortem changes of MAP2 was not clear. In this study, we evaluated the effect of hypothermia on postmortem degradation of MAP2 in the human hippocampus at various postmortem intervals using immunohistochemistry. In postmortem brains without hypothermia (the normothermic group), the locus of MAP2 immunoreactivity moved from the dendrites to the cell bodies prior to becoming undetectable with increasing postmortem interval, particularly in the CA1-subiculum region. On the other hand, the change in MAP2 immunoreactivity was remarkably attenuated in brains of death from cold (the hypothermic group). The present study demonstrated that MAP2 disruption is remarkable in the CA1-subiculum region of autopsied brains and that hypothermia reduces the postmortem change of MAP2, as observed in ischemic brain. Therefore, immunostaining of MAP2 in the hippocampus could be used to diagnose hypothermia.

Effect of hypothermia on postmortem alterations in MAP2 immunostaining in the human hippocampus

Ischemic neuronal injury induce degradation of microtubule-associated protein 2 (MAP2). In addition to ischemia, postmortem brains show alterations in MAP2 immunoreactivity in the hippocampus, suggesting that the factors inducing cytoskeletal disruption in postmortem brain are similar to those in ischemic brains. Hypothermia reduces the severity of ischemic injury including disruption of MAP2 in the hippocampus. However, whether hypothermia reduces postmortem changes of MAP2 was not clear. In this study, we evaluated the effect of hypothermia on postmortem degradation of MAP2 in the human hippocampus at various postmortem intervals using immunohistochemistry. In postmortem brains without hypothermia (the normothermic group), the locus of MAP2 immunoreactivity moved from the dendrites to the cell bodies prior to becoming undetectable with increasing postmortem interval, particularly in the CA1-subiculum region. On the other hand, the change in MAP2 immunoreactivity was remarkably attenuated in brains of death from cold (the hypothermic group). The present study demonstrated that MAP2 disruption is remarkable in the CA1-subiculum region of autopsied brains and that hypothermia reduces the postmortem change of MAP2, as observed in ischemic brain. Therefore, immunostaining of MAP2 in the hippocampus could be used to diagnose hypothermia.

Glucose/oxygen deprivation induces the alteration of synapsin I and phosphosynapsin

Synapsin I is believed to be involved in regulating neurotransmitter release and in synapse formation. Its interactions with the actin filaments and synaptic vesicles are regulated by phosphorylation. Because exocytosis and synapsin I phosphorylation are a Ca(2+)-dependent process, it is possible that an ischemic insult modifies the presynaptic proteins. However, the neuronal damage and the changes in synapsin I as well as its phosphorylation level as a result of glucose/oxygen deprivation (GOD) and reperfusion in organotypic hippocampal slice cultures have not been established. In this study, the level of synapsin I and phosphosynapsin was measured in organotypic hippocampal slice cultures in order to determine the role of synapsin I in the presynaptic nerve terminals during GOD/reperfusion. Propidium iodide fluorescence was observed in the CA1 area after GOD for 30 min, which could be detected in the whole pyramidal cell layer during reperfusion for 24 h. The immunofluorescence of the neuron specific nuclear protein, NeuN, showed a negative correlation with the PI fluorescence. During GOD/reperfusion, the immunofluorescence of synapsin I increased in the stratum radiatum and the stratum oriens of the CA1 area and the stratum lucidum and the stratum oriens of the CA3 area. The phosphosynapsin level evidently increased in the stratum lucidum of the CA3 area after GOD for 30 min, which was reduced to the control level after reperfusion. These results suggested that the neuronal damage and degenerations were observed as a result of GOD/reperfusion and the increase in synapsin I and its phosphorylation might play a role in modulating the release of neurotransmitters via exocytosis and in the formation of new synapses after brain ischemia.

Calpain induces proteolysis of neuronal cytoskeleton in ischemic gerbil forebrain

We investigated the relationship between the activity of calcium-dependent protease (calpain) and the ischemic neuronal damage. We also investigated the mechanism of ischemic resistance in astrocytes. In gerbil, a 10-min forebrain ischemia was induced by occlusion of both common carotid arteries. The calpain-induced proteolysis of cytoskeleton (fodrin) was examined by immunohistochemistry. Immunolocalization of micro and m-calpain was also examined. Intact fodrin was observed both in neurons and astrocytes, but proteolyzed fodrin was not observed in normal brain. Fifteen minutes after ischemia, proteolysis of fodrin took place in putamen, parietal cortex and hippocampal CA1. The proteolysis extended to thalamus 4 h after ischemia after which the immunoreactivity faded down in all areas except hippocampus. On day 7, the proteolysis was still observed only in hippocampus. Neurons with the proteolysis of soma resulted in neuronal death. Throughout the experiment, the proteolysis was not observed in astrocytes. micro -Calpain was observed only in neurons but m-calpain was observed both in neurons and astrocytes. The ischemia induced only micro -calpain activation, which resulted in fodrin proteolysis of neurons with differential spatial distribution and temporal course. The proteolysis was developed rapidly and was completed within 24 h in all vulnerable regions except hippocampal CA1. The proteolysis preceded the neuronal death. The mechanism of the proteolysis seemed to be involved by Ca(2+) influx via glutamate receptor and rapid neuronal death seemed reasonable. The reason why neuronal death in CA1 evolved slowly was not clarified. In astrocytes, fodrin was not proteolyzed by m-calpain. The low Ca(2+)-sensitivity of m-calpain may be the reason of ischemic resistance in astrocytes.

Dendritic and synaptic pathology in experimental autoimmune encephalomyelitis

Evidence has shown that excitotoxicity may contribute to the loss of central nervous system axons and oligodendrocytes in multiple sclerosis and experimental autoimmune encephalomyelitis (EAE). Because dendrites and synapses are vulnerable to excitotoxicity, we examined these structures in acute and chronic models of EAE. Immunostaining for microtubule-associated protein-2 showed that extensive dendritic beading occurred in the white matter of the lumbosacral spinal cord (LSSC) during acute EAE episodes and EAE relapses. Retrograde labeling confirmed that most motoneuron dendrites were beaded in the white matter of the LSSC in acute EAE. In contrast, only mild swelling was observed in the gray matter of the LSSC. Dendritic beading showed marked recovery during EAE remission and after EAE recovery. In addition, synaptophysin, synapsin I, and PSD-95 immunoreactivities were significantly reduced in both the gray and white matter of the LSSC during acute EAE episodes and EAE relapses, but showed partial recovery during EAE remission and after EAE recovery. Pathologically, both dendritic beading and the reduction in synaptic protein immunoreactivity were well correlated with inflammatory cell infiltration in the LSSC at different EAE stages. We propose that dendritic and synaptic damage in the spinal cord may contribute to the neurological deficits in EAE.

Toluene inhalation induces glial cell line-derived neurotrophic factor, transforming growth factor and tumor necrosis factor in rat cerebellum

Rats were exposed to toluene (1500 ppm for 4 h per day) for 7 days. After toluene inhalation, only granule cells in the dentate gyrus of the hippocampus were slightly shrunken. In the cerebellum, several Purkinje cells were shrunken and lost, and the white matter was thinner than in controls. Microtubule-associated protein 2 (MAP2)-immunopositive filaments of neuronal processes were slightly disarrayed in the radial layer of the hippocampus, and were fragmented in the molecular layer of the cerebellum. It was considered that toluene induced neuronal changes both in the cerebellum and the hippocampus. To elucidate the effect of neurotrophic factors on those neuronal changes, glial cell line-derived neurotrophic factor (GDNF), transforming growth factor (TGF) and tumor necrosis factor (TNF) in rat brain were examined immunohistochemically. In control rats, TNF-alpha was not stained in either the hippocampus or the cerebellum, while TGF-beta1 was scarcely expressed in the cerebellum. GDNF was minimally expressed in the Purkinje cells in the cerebellum. After toluene-treatment, TGF-beta1 was over-expressed in the endothelium of the capillary vessel walls in both regions. In the cerebellum, TNF-alpha was induced only in the granule cells, while GDNF expression was enhanced in the Purkinje cells. These data suggest that toluene induces astrocyte activation through TGF-beta1 upregulation, which then induces GDNF in the Purkinje cells and TNF-alpha in the granule cells of the cerebellum. The differences in the expression of the neurotrophic factors may account for neurobehavioral changes after toluene exposure.

Changes in presynaptic proteins, SNAP-25 and synaptophysin, in the hippocampal CA1 area in ischemic gerbils

A general consensus exists that the presynaptic terminals in the hippocampal CA1 area are resistant to ischemic stress in spite of the loss of their target cells (CA1 pyramidal neurons). We have verified this by immunostaining and Western immunoblotting using the antibodies for presynaptic proteins, synaptosomal-associated protein of 25 kDa (SNAP-25) and synaptophysin in gerbils after bilateral carotid artery ligature. In the immunohistochemical analysis, decreases in SNAP-25 and synaptophysin immunoreactivities in the strata radiatum and oriens, especially around the apical dendrite of CA1 neurons, and disappearance of SNAP-25 immunoreactivity in the alveus were observed on day 2 after ischemia. On days 7 and 14, SNAP-25-positive granular materials were expressed in the CA1 area, and intense synaptophysin immunoreactivity around surviving CA1 neurons was observed. Western immunoblot analysis revealed significant decreases of SNAP-25 and synaptophysin (about 60% of control levels) on day 2, and then increase of their proteins (130--140% of control levels) on day 14. These results indicate that presynaptic degeneration occurs in the hippocampal CA1 area after ischemia, and it precedes the delayed neuronal death of CA1 neurons. The presynaptic terminal damage may be responsible for some pathological changes in ischemic brains.

Protective and regenerative response endogenously induced in the ischemic brain

Neuronal cells are highly vulnerable to ischemic insult. Because adult neurons are highly differentiated and cannot self-propagate, loss of neurons often results in functional deficits in mammalian brains. However, it has recently been shown that neurons and neuronal circuits exhibit protective and regenerative responses in a rodent model of experimental ischemia. At first, neurons respond by producing several protective proteins such as heat shock proteins (HSPs) after sublethal ischemia and then acquire tolerance against a subsequent ischemic insult (ischemic tolerance). Once neurons suffer irreversible injury, two repair processes, neurogenesis and synaptogenesis, are endogenously induced. Neuronal stem and (or) progenitor cells can proliferate in two brain areas in adult animals: the subventricular zone and the subgranular zone in the dentate gyrus. After ischemic insult, these stem (progenitor) cells proliferate and differentiate into neurons in the dentate gyrus of the hippocampus. Reactive synaptogenesis has been also observed in the injured brain following a period of long-term infarction, but it is unclear if it can compensate for disconnected circuits. Understanding the molecular mechanism underlying these protective and regenerative responses will be important in developing a new strategy for aimed at the augmentation of resistance against ischemic insult and the replacement of injured neurons and neuronal circuits.Key words: ischemic tolerance, neurogenesis, synaptogenesis.

Transient increase in rab 3A and synaptobrevin immunoreactivity after mild hypoxia in neonatal rats

1. In the present work we describe the short term effects of mild neonatal hypoxia on the synapse as assessed by the immunoreactivity (IR) of two synaptic proteins: rab 3A and synaptobrevin (VAMP). 2. Using the sensitive methodology of immunoblotting, we measured rab 3A and VAMP-IR in homogenates from the cerebral cortex, hippocampus, and corpus striatum of control (breathing room air) and hypoxiated (breathing 95.5% N2-6.5% O2 for 70 min) 4-day-old rats at 1, 2, and 6 h after the end of the hypoxia. Immunostaining with examination by light microscopy was performed using the synaptic protein-specific antibodies on fixed brain sections from animals belonging to the same litter and submitted to hypoxia. 3. A transient increase of VAMP-IR was observed in the hippocampus and corpus striatum, and for rab 3A in the striatum, 1 h after initiating reoxygenation. At the following time points the values returned to control levels. This effect was less clearly observed in the immunostained sections. 4. Mild hypoxia has an effect on sensitive brain regions, eliciting an increase in the IR of at least two proteins involved in the synaptic vesicle cycle. The transient nature of this effect possibly indicates the activation of endogenous neuroprotective mechanisms.

Changes in mint1, a novel synaptic protein, after transient global ischemia in mouse hippocampus

Mints (munc18-interacting proteins) are novel multimodular adapter proteins in membrane transport and organization. Mint1, a neuronal isoform, is involved in synaptic vesicle exocytosis. Its potential effects on development of ischemic damage to neurons have not yet been evaluated. The authors examined changes in mint1 and other synaptic proteins by immunohistochemistry after transient global ischemia in mouse hippocampus. In sham-ischemic mice, immunoreactivity for mint1 was rich in fibers projecting from the entorhinal cortex to the hippocampus and in the mossy fibers linking the granule cells of the dentate gyrus to CA3 pyramidal neurons. Munc18-1, a binding partner of mint1, was distributed uniformly throughout the hippocampus, and synaptophysin 2, a synaptic vesicle protein, was localized mainly in mossy fibers. After transient global ischemia, mint1 immunoreactivity in mossy fibers was dramatically decreased at 1 day of reperfusion but actually showed enhancement at 3 days. However, munc18-1 and synaptophysin 2 were substantially expressed in the same region throughout the reperfusion period. These findings suggest that mint1 participates in neuronal transmission along the excitatory pathway linking the entorhinal cortex to CA3 in the hippocampus. Because mint1 was transiently decreased in the mossy fiber projection after ischemia, functional impairment of neuronal transmission in the projection from the dentate gyrus to CA3 pyramidal neurons might be involved in delayed neuronal death.

Potential role of calcineurin for brain ischemia and traumatic injury

Calcineurin belongs to the family of Ca2+/calmodulin-dependent protein phosphatase, protein phosphatase 2B. Calcineurin is the only protein phosphatase which is regulated by a second messenger, Ca2+. Furthermore, calcineurin is highly localized in the central nervous system, especially in those neurons vulnerable to ischemic and traumatic insults. For these reasons, calcineurin is considered to play important roles in neuron-specific functions. Recently, on the basis of the finding that FK506 and cyclosporin A serve as calcineurin-specific inhibitors, this enzyme has become the subject of much study. It is clear that calcineurin is involved in many neuronal (or non-neuronal) functions such as neurotransmitter release, regulation of receptor functions, signal transduction systems, neurite outgrowth, gene expression and neuronal cell death. In this review, we describe the calcineurin functions, functions of the substrates, and the pathogenesis of traumatic and ischemic insults, and we discuss the potential role of calcineurin. There are many similarities in traumatic and ischemic pathogenesis of the brain in which the release of excessive glutamate is followed by an intracellular Ca2+ increase. However, the intracellular cascade which leads to neuronal cell death after the release of excess Ca2+ is unclear. Although calcineurin is thought to be a key toxic enzyme on the basis of studies using immunosuppressants (FK506 or cyclosporin A), many of the functions of the substrates for calcineurin protect against neuronal cell death. We concluded that calcineurin is a bi-directional enzyme for neuronal cell death, having protective and toxic actions, and the balance of the bi-directional effects may be important in ischemic and traumatic pathogenesis.

Transient increase of synapsin-I immunoreactivity in the mossy fiber layer of the hippocampus after transient forebrain ischemia in the mongolian gerbil

Synapsin-I is a vesicular phosphoprotein, which regulates neurotransmitter release, neurite development, and maturation of synaptic contacts during normal development and following various brain lesions in adulthood. In the present study, we have examined by immunohistochemistry possible modifications in the expression of synapsin-I in the hippocampus of Mongolian gerbils after transient forebrain ischemia. The animals were subjected to 5 min of transient forebrain ischemia through bilateral common carotid occlusion, and were examined at different time-points post-ischemia. Transient forebrain ischemia produces cell death of the majority of CA1 pyramidal neurons of the hippocampus and polymorphic hilar neurons of the dentate gyrus. This is followed by reactive changes, including synaptic reorganization and modifications in the expression of synaptic proteins, which provide the molecular bases of synaptic plasticity. Transient decrease of synapsin-I immunoreactivity was observed in the inner zone of the molecular layer of the dentate gyrus, thus suggesting denervation and posterior reinervation in this area. In addition, a strong increase in synapsin-I immunoreactivity was observed in the hilus of the dentate gyrus and in the mossy fiber layer of the hippocampus at 2, 4 and 7 days after ischemia. Parallel increases in synaptophysin immunoreactivity were not observed, thus suggesting a selective induction of synapsin-I after ischemia. The present results indicate that synapsin-I participates in the reactive response of granule cells to transient forebrain ischemia in the hippocampus of the gerbil, and suggest a role for this protein in the plastic adaptations of the hippocampus following injury.

Quantitative analysis of synaptophysin immunoreactivity in human neocortex after cardiac arrest: confocal laser scanning microscopy study

Transient global ischaemia caused by cardiac arrest results in lesions that involve all brain structures. The aim of this study was to investigate the condition of synapses in patients surviving, but remaining in a persistent vegetative state, following resuscitation after cardiac arrest. We performed a quantitative analysis of the distribution and density of elements containing a synaptic vesicle protein--synaptophysin (p38)--in human neocortex in cases which survived for 1 week, 2 months, and 1 year after the cardiac arrest. Neurologically healthy cases that died following an accident served as control. Dual-channel confocal laser scanning microscopy (CLSM) was used to image p38-immunoreactivity (IR) and lipofuscin autofluorescence. In control cases no statistically significant differences were found for p38-IR between layers II-III and V-VII. However, the temporal cortex had a higher density of p38-immunoreactive structures than the motor cortex. In postischaemic cases a reduction in the density of p38-IR elements was apparent, mainly in the frontal and motor cortices and less pronounced in the temporal cortex. The least decrease compared with controls was observed in the visual cortex. In the 1 week survival case, a maximal decrease in p38-IR (35% below control) was found. In this case, the number of p38-IR elements per visual field was decreased, and big aggregates of p38-IR structures were observed. In general, the amounts of p38-IR structures were higher in all of the control cases compared with the postischaemic cases.

Measurement of regional N-acetylaspartate after transient global ischemia in gerbils with and without ischemic tolerance: an index of neuronal survival

We investigated the correlation between N-acetylaspartate (NAA) level and neuronal density in the hippocampal CA1 region of the brain after occlusion of both common carotid arteries for 5 minutes and reperfusion for 3 hours to 4 weeks in gerbils with and without ischemic preconditioning (tolerance). Animals were divided into four groups--the sham operated group, the nonpreconditioning (non-p) group, the single-preconditioning (single-p) group with 2-minute ischemia once 2 days before 5-minute ischemia, and the double-preconditioning (double-p) group with 2-minute ischemia twice 2 days before 5-minute ischemia (n = 6 for each group). The CA1 region was dissected out from freeze-dried sections for high-performance liquid chromatographic assay of NAA, and adjacent sections were stained with cresyl violet for measurement of the neuronal density. Both NAA (pmol/microg dry weight) and the neuronal density (cells/mm) decreased in the non-p group after 3 days (NAA = 24.0 +/- 3.0; neuronal density = 65 +/- 38 cells/mm) and 7 days (NAA = 17.9 +/- 2.5; neuronal density = 20 +/- 15 cells/mm) and in the single-p group after 7 days (26.4 +/- 3.0, 106 +/- 30) compared with the control group (NAA = 32.9 +/- 3.0; neuronal density = 203 +/- 9 cells/mm). There was no decrease in the double-p group. The NAA level and the neuronal density showed a good linear correlation. The regional NAA level may be used as an index of neuronal viability.

Determination of synapsin I and synaptophysin in body fluids by two-site enzyme-linked immunosorbent assays

Two-site enzyme-linked immunosorbent assays (ELISA) have been established for the specific and sensitive determination of two membrane proteins of the small synaptic vesicles (SSV), namely: peripheral synapsin I and integral synaptophysin. The ELISA used highly specific capture monoclonal antibodies (mAB) and polyclonal antibodies (pAB) as detectors. For synapsin I, the mAB were newly generated, whereas for synaptophysin, the commercially available mAB SY38 was applied. In order to calibrate the ELISA and to raise pAB, both proteins were purified in the mg-range. Synapsin I was purified by conventional means from human and porcine brain and synaptophysin was purified by immunoaffinity chromatography from porcine brain. Using the ELISA, neither synapsin I nor synaptophysin could be determined in serum or cerebrospinal fluid (CSF) from healthy donors or patients suffering various neurological disorders or pheochromocytomas. For this reason, the degradation of both proteins in serum and CSF was investigated. With the exception of synaptophysin measured in serum, both proteins exhibited fast rates of degradation. Despite the negative results in human body fluids, the two ELISA are appropriate for the quantification of these membrane proteins in neuronal or neuroendocrine cell extracts or preparations of SSV.

Delayed neuronal death after global incomplete ischemia in dogs is accompanied by changes in phospholipase C protein expression

Activation of phospholipase C (PLC) increases intracellular Ca2+ and may play a role in delayed neuronal death after ischemia. Because changes in intracellular Ca2+ are believed to participate in ischemic neuronal injury, we tested the hypothesis that PLC beta protein levels are temporally altered in brain regions that undergo neurodegeneration after global incomplete ischemia. Dogs (n = 12) were subjected to 20 minutes of global incomplete ischemia followed by recovery of either 1 (n = 5) or 7 days (n = 7). Six sham-operated animals were used as nonischemic controls. In hematoxylin and eosin-stained brain sections, neuronal density at 1 day after ischemia was unchanged relative to nonischemic controls in hippocampus CA1, caudate, and cerebellar cortex (anterior lobule). However, at 7 days after ischemia, neuronal densities were decreased to 56 +/- 15% (mean +/- SD) and 75 +/- 17% of control in CA1 and caudate, respectively. At 1 and 7 days after ischemia, the percentage of neurons showing ischemic injury increased from 13 +/- 10 to 40 +/- 35% in CA1, 24 +/- 25 to 59 +/- 16% in cerebellum, and 4 +/- 2 to 18 +/- 12% in caudate. Densitometric analysis of immunocytochemically stained brain sections from controls (n = 3). 1 day after ischemia (n = 3), and 7 days after ischemia (n = 5) revealed that PLC beta immunoreactivity was increased in cerebellum at 1 day (0.274 +/- 0.013 v 0.295 +/- 0.005 optical density units [OD] in control and 1 day, respectively) and 7 days (0.108 +/- 0.009 v 0.116 +/- 0.005 O.D. in control and 7 days, respectively). PLC beta immunoreactivity was unchanged after ischemia in caudate and hippocampus. Western blot analysis of PLC beta immunoreactivity in the cerebellar cortex and hippocampus in the control (n = 3), 1 day (n = 2), and 7 days after ischemia (n = 2) groups showed that PLC beta levels were increased after ischemia in cerebellum 266% and 227% above control at 1 and 7 days, respectively. However, in hippocampus, PLC expression after ischemia was unchanged at 97% and 84% of control at 1 and 7 days, respectively. These results show that delayed neuronal degeneration after global incomplete ischemia is accompanied by regional abnormalities in PLC levels. Elevated PLC levels early may represent an aberrant signal transduction mechanism resulting in delayed cell damage, whereas decreased PLC levels later after ischemia may reflect ongoing neurodegeneration.

Subtle neuronal death in striatum after short forebrain ischemia in rats detected by in situ end-labeling for DNA damage

BACKGROUND AND PURPOSE

Neuronal cell death after global brain ischemia occurs predominantly by necrosis, whereas only a minor fraction of cell death may occur through apoptosis. Brief or moderate insults are thought to facilitate apoptosis, which is associated with DNA fragmentation. After 10 minutes of four-vessel occlusion in rats, conventional neuropathological analysis shows neuronal cell death in hippocampal CA1 but not in the striatum. Thus, we compared hippocampus and striatum for occurrence of cells with DNA fragmentation.

METHODS

A brief insult of 10 minutes of forebrain ischemia was induced in rats using four-vessel occlusion, and groups of brains were studied at 1, 3, 6, and 12 hours and at 1, 3, and 7 days after ischemia. In situ end-labeling (ISEL) was used to detect neurons undergoing DNA fragmentation. The hippocampal CA1 area was compared with the striatum. Conventional staining and immunohistochemical markers served to exclude ischemic neuronal cell death in the striatum.

RESULTS

Hippocampal CA1 neurons were ISEL-positive by 3 days after ischemia. In contrast, positive cells became evident in the striatum between 3 hours to 3 days after ischemia. The ISEL-positive cells were scattered throughout the striatum with a preference for the dorsomedial areas and accounted for about 0.2% of the neurons per striatal area at 1 day. Conventional staining and immunohistochemical markers failed to reveal areas of overt cell damage in the striatum.

CONCLUSIONS

The scattered cell damage in the striatum after brief forebrain ischemia suggests the occurrence of an apoptotic process. The striatum therefore may be prone to subtle cell death due to metabolic insults.

Ischemia and lesion induced imbalances in cortical function

Cortical structures are often critically affected by ischemic and traumatic lesions which may cause transient or permanent functional disturbances. These disorders consist of changes in the membrane properties of single cells and alterations in synaptic network interactions within and between cortical areas including large-scale reorganizations in the representation of the peripheral input. Prominent functional modifications consisting of massive membrane depolarizations, suppression of intracortical inhibitory synaptic mechanisms and enhancement of excitatory synaptic transmission can be observed within a few minutes following the onset of cortical hypoxia or ischemia and probably represent the trigger signals for the induction of neuronal hyperexcitability, irreversible cellular dysfunction and cell death. Pharmacological manipulation of these early events may therefore be the most effective approach to control ischemia and lesion induced disturbances and to attenuate long-term neurological deficits. The complexity of secondary structural and functional alterations in cortical and subcortical structures demands an early and powerful intervention before neuronal damage expands to intact regions. The unsatisfactory clinical experience with calcium and N-methyl-D-aspartate antagonists suggests that this result might be achieved with compounds that show a broad spectrum of actions at different ligand-activated receptors, voltage-dependent channels and that also act at the vascular system. Whether the same therapy strategies developed for the treatment of ischemic injury in the adult brain may be applied for the immature cortex is questionable, since young cortical networks with a high degree of synaptic plasticity reveal a different response pattern to hypoxic and ischemic insults. Age-dependent molecular biological, morphological and physiological parameters contribute to an enhanced susceptibility of the immature brain to these noxae during early ontogenesis and have to be investigated in more detail for the development of adequate clinical therapy.

Increased F1/GAP-43 mRNA accumulation in gerbil hippocampus after brain ischemia

To assess whether ischemia could induce GAP-43 mRNA expression, we performed in situ hybridization in gerbil brains that had been subjected to 5 min of global ischemia. In control dentate granule cells, little hybridization was detected in contrast to the intense signal generated by pyramidal neurons of the adult hippocampal formation. After ischemia, we detected a robust GAP-43 signal over hippocampal granule cells at 3 h of reperfusion, persisting through 7 days, and disappearing by 14 days. This demonstrated GAP-43 gene induction after ischemia, and suggests that GAP-43 may be involved in reactive events, including fiber sprouting and synaptic reorganization, that follow ischemia.

A synaptic vesicle-associated protein (SVP-38) as an early indicator of delayed neuronal death

Sixteen gerbils were subjected to 5 min of forebrain ischemia. Their brains were processed for immunohistochemical staining using monoclonal antibodies against a synaptic vesicle-associated protein 38 (SVP-38) and microtubule-associated protein 2 (MAP2) after recirculation times of 10 min, and 1, 4, and 7 days. After 10 min recirculation, SVP-38 immunoreactive dots were observed only in the CA1 region of the hippocampus. After 1 day recirculation, SVP-38 immunostaining was diffuse and weak throughout the hippocampus, despite preservation of MAP2 immunoreactivity. After 4 and 7 days recirculation, SVP-38 immunoreactivity had been restored in the whole hippocampus, despite the complete loss of MAP2 immunoreactivity due to delayed neuronal death. Our results demonstrate an immediate and significant change in the immunoreactivity of a synaptic vesicle-associated protein at the beginning of the process of delayed neuronal death. Thus, changes in the immunoreactivity of synaptic vesicle-associated proteins such as SVP-38 appear to be one of the earliest indicators of the onset of neuronal death.

Synaptic pathology of spinal anterior horn cells in amyotrophic lateral sclerosis: an immunohistochemical study

We have applied immunohistochemical techniques to study synaptic alterations of the spinal anterior horn in amyotrophic lateral sclerosis (ALS), and other disorders involving upper or lower motor neurons. A monoclonal antibody to synaptophysin was used. Spinal cord tissues from normal individuals served as controls. As compared to these, a decrease in synaptophysin immunoreactivity was evident in the neuropil in the spinal anterior horn of ALS patients. However, synaptophysin expression in the perikarya and dendrites of remaining normal-appearing neurons in these patients was not decreased and occasionally it was even higher than in control neurons. Similar results were obtained with specimens from patients with lower motor neuron disease. Synaptophysin immunoreactivity in the neuropil and perikarya of the cases with focal spinal cord lesions with bilateral descending tract degeneration was similar to normal controls. Our data suggest that the alterations in synaptophysin expression occurring in ALS are mainly associated with the loss of lower motor neurons, and that the occasional increased perikaryal expression may be due to the neuronal atrophy, compensatory accumulation or abnormal synaptic vesicle degradation.

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.

Vascular dementia in Spatz-Lindenberg's disease (SLD): cortical synaptophysin immunoreactivity as compared with dementia of Alzheimer type and non-demented controls

The generalized form of von Winiwarter-Buerger's disease (WBD) occasionally involves the brain. However, pure cerebral forms of the disease were also described by Spatz and Lindenberg ("Spatz-Lindenberg's disease", SLD). Both, the type I, which involves the large basal arteries, and the type II, which results in a sickle-shaped granular atrophy of the cerebral cortex, are often accompanied by ("vascular") dementia, which Lindenberg and Spatz mainly attributed to the bilateral involvement of the second frontal gyrus by granular atrophy. Recently, synaptic deprivation of the cortical gray matter has been shown to occur in the dementia of Alzheimer type (DAT) and other neurodegenerative disorders. In DAT, the synaptic loss highly correlated with the degree of the mental impairment. We wanted to examine whether similar changes also occurred in dementia of vascular origin, for which SLD, although infrequent, is a typical example. In fact, we found that in three cases of typical SLD type II the synaptophysin immunoreactivity of the cortical neuropil in areas without overt infarcts or scar formation was as much reduced as in Alzheimer's disease. Although it must be taken into account that in the present cases the synapse loss might, at least in part, be due to secondary (Wallerian) degeneration as a result of the neuronal loss in the "watershed" regions of the arterial blood supply, it cannot be excluded that a decline of cortical synaptic contacts in areas without necroses or scars may occur as a primary event, contributing to the pathogenesis of the dementia. Final conclusions can only be expected from investigations into further cases of cerebro-vascular disorders with and without dementia.

The role of synaptic proteins in the pathogenesis of disorders of the central nervous system

Complex sets of nervous system functions are dependent on proper working of the synaptic apparatus, and these functions are regulated by diverse synaptic proteins that are distributed in various subcellular compartments of the synapse. The most extensively studied synaptic proteins are synaptophysin, the synapsins, growth associated protein 43 (GAP-43), SV-2, and p65. Moreover, synaptic terminals contain a great number of other proteins involved in calcium transport, neurotransmission, signaling, growth and plasticity. Probes against various synaptic proteins have recently been used to study synaptic alterations in human disease, as well as in experimental models of neurological disorders. Such probes are useful markers of synaptic function and synaptic population density in the nervous system. For the present, we will review the role of synaptic proteins in the following conditions: Alzheimer's disease (AD) and other disorders including ischemia, disorders where synapse-associated proteins are abnormally accumulated in the nerve terminals, synaptic proteins altered after denervation, and synaptic proteins as markers in neoplastic disorders. The study of the molecular alterations of the synapses and of plasticity might yield important clues as to the mechanisms of neurodegeneration in AD, and of the patterns of presynaptic and dendritic damage under diverse pathological conditions.