The alterations of N-Methyl-D-aspartate receptor expressions and oxidative DNA damage in the CA1 area at the early time after ischemia-reperfusion insult

Expression and changes of Ca2+-ATPase in neurons and astrocytes in the gerbil hippocampus after transient forebrain ischemia

Ca2+-ATPase is one of the most powerful modulators of intracellular calcium levels. In this study, we focused on chronological changes in the immunoreactivity and protein levels of Ca2+-ATPase in the hippocampus after 5 min of transient forebrain ischemia. Ca2+-ATPase immunoreactivity was significantly altered in the hippocampal CA1 region and in the dentate gyrus, but not in the CA2/3 region after ischemic insult. In the sham-operated group, Ca2+-ATPase immunoreactivity was detected in the hippocampus. Ca2+-ATPase immunoreactivity in the CA1 region and in the dentate gyrus, and its protein levels peaked 3 h after ischemic insult. At this time, CA1 pyramidal cells and dentate polymorphic cells showed strong Ca2+-ATPase immunoreactivity. Thereafter, Ca2+-ATPase immunoreactivity reduced in the CA1 region and in the dentate gyrus. One day after ischemic insult, Ca2+-ATPase immunoreactivity was observed in some CA1 non-pyramidal cells, and 4 days after ischemic insult, Ca2+-ATPase immunoreactivity was detected in astrocytes throughout the CA1 region, but Ca2+-ATPase immunoreactivity in the dentate gyrus had nearly disappeared. Our results suggest that Ca2+-ATPase changes may be associated with a response to ischemic damage in hippocampal CA1 pyramidal cells, and that increased Ca2+-ATPase immunoreactivity in the reactive astrocytes may be associated with the maintenance of intracellular calcium levels.

Experimental subarachnoid hemorrhage induces changes in the levels of hippocampal NMDA receptor subunit mRNA

NMDA receptors may play a crucial role in nerve cell death following subarachnoid hemorrhage (SAH). Changes in NMDA receptor-mediated transmission appear before neuronal death in rodent models of transient ischemia, and NMDA receptor function is known to be dependent on subunit composition. Here, we have investigated whether mRNA expression of the NMDA receptor subunits is altered in the hippocampal formation 3-5 h following experimental SAH, and correlated these early alterations to subsequent delayed cell death. SAH was induced by intraluminal perforation of the internal carotid artery intracranially, and cerebral blood flow (CBF) was bilaterally monitored by laser-Doppler flowmetry. Early changes in NMDA receptor subunit mRNA and early nerve cell death were analyzed at 3-5 h after SAH, and delayed nerve cell death was analyzed at 2-7 days after SAH. Duration of ipsilateral CBF reduction below 30% of baseline (CBF30) was predictive of ipsilateral delayed nerve cell death in the CA1 2-7 days after SAH. At CBF30 > 9 min, we found downregulation of mRNA for NR2A, NR2B, and NR3B at 3-5 h after SAH, whereas the levels of NR1 mRNA were unaffected. The downregulation of NR2A and NR2B mRNA may result in a reduced NMDA receptor function. Such reduction may be sufficient to provide neuroprotection in the dentate gyrus, where no cell death appears, but insufficient to rescue neurons in the hippocampus proper following SAH.

Ischemia-induced changes of platelet endothelial cell adhesion molecule-1 in the hippocampal CA1 region in gerbils

We observed chronological changes of platelet endothelial cell adhesion molecule-1 (PECAM-1), final mediator of neutrophil transendothelial migration, immunoreactivity, and protein level in the gerbil hippocampus proper after 5 min of transient ischemia. One day after ischemic insult, PECAM-1 immunoreactivity and protein level increased slightly in the hippocampus proper. Thereafter, PECAM-1 immunoreactivity and protein level increased significantly in the hippocampus proper by 4 days after ischemic insult. Especially, PECAM-1 in the hippocampal CA1 region was higher than that in the CA2/3 region. Five days after ischemic insult, PECAM-1 immunoreactivity decreased compared to the 4 days post-ischemic group. However, the RNA levels of PECAM-1 in the hippocampus proper were significantly decreased in the 4 days post-ischemic groups compared to that in the sham-operated group. This result suggests that the increase of PECAM-1 and decrease of PECAM-1 RNA in the CA1 region 4 days after ischemia may be associated with transmigration of neurotrophil.

Changes of pyridoxal kinase expression and activity in the gerbil hippocampus following transient forebrain ischemia

In the previous study, we observed chronological alterations of glutamic acid decarboxylase (GAD), which is the enzyme converting glutamate into GABA. GAD isoforms (GAD65 and GAD67) differ substantially in their interactions with cofactor pyridoxal 5'-phosphate, which is catalyzed by pyridoxal kinase (PLK). In the present study, we examined the chronological changes of PLK expression and activity in the hippocampus after 5 min transient forebrain ischemia in gerbils. PLK immunoreactivity in the sham-operated group was detected weakly in the hippocampus. Ischemia-related change of PLK immunoreactivity in the hippocampus was significant in the hippocampal cornu ammonis (CA1)region, not in the hippocampal CA2/3 region and dentate gyrus. PLK immunoreactivity was observed in non-pyramidal GABAergic neurons at 30 min to 3 h after ischemic insult. At 12 h after ischemic insult, PLK immunoreactivity was shown in many CA1 pyramidal cells as well as some non-pyramidal cells. At this time point, PLK immunoreactivity and protein content was highest after ischemia. Thereafter, PLK immunoreactivity and protein content is decreased time-dependently by 4 days after ischemic insult. Four days after ischemia, some astrocytes expressed PLK in the CA1 region. The specific PLK activity was not altered following ischemic insult up to 2 days after ischemic insult. Thereafter, the specific PLK activity decreased time-dependently. However, total activity of PLK was significantly increased 12-24 h after ischemic insult, and thereafter total activity of PLK decreased. Therefore, we suggest that the over-expression of PLK in the CA1 pyramidal cells at 12 h after ischemia may induce increase of GAD in the CA1 pyramidal cells, which plays an important role in delayed neuronal death via the increase of GABA or enhancement of GABA shunt pathway.

Expression and changes of galanin in neurons and microglia in the hippocampus after transient forebrain ischemia in gerbils

In the present study, we investigated chronological changes of galanin (GAL), well known as the potassium channel opener, immunoreactivity and GAL protein level in the hippocampus of the gerbil at the various times after 5 min transient forebrain ischemia. In the sham-operated group, weak GAL immunoreactivity was found in non-pyramidal cells. At 12 h after ischemia-reperfusion, the number of GAL-immunoreactive neurons and GAL immunoreactivity were significantly increased in the hippocampus compared to 3 h after ischemic insult, especially in the hippocampal CA1 region. Thereafter the number of GAL-immunoreactive neurons and GAL immunoreactivity decrease time-dependently in the hippocampus. Four days after transient ischemia, GAL immunoreactivity was low as compared with the sham-operated group. At this time point after ischemic insult, GAL immunoreactivity was shown in microglia in the CA1 region because delayed neuronal death happened in the CA1 pyramidal cells. The result of Western blot showed the pattern of GAL expression similar to that of immunohistochemical data. These results suggest that the early increase of GAL in the CA1 pyramidal cells may be associated with the reduction of the excitotoxic damage, that long-lasting enhanced expression of endogenous GAL at 12 h-2 days after ischemia may be associated with efflux of potassium ion into the extracellular space, and that GAL expression in microglia 4 days after ischemia may be associated with reduction of ischemic damage.

Ischemia-Related Changes in Galanin Expression in the Dentate Hilar Region after Transient Forebrain Ischemia in Gerbils

Although galanin (GAL) protects hippocampal neurons from ischemic damage, no study has examined ischemia-related changes in endogenous GAL in the hippocampal dentate gyrus. We investigated the chronological changes of GAL, well-known as the potassium channel opener, expression in the dentate gyrus at various times after 5 min of transient forebrain ischemia in gerbils. A few GAL-immunoreactive (IR) neurons were found in the polymorphic layer of the sham-operated group. Three hours after ischemia-reperfusion, the pattern of GAL immunoreactivity was similar to that of the sham-operated group and the number of GAL-IR neurons and immunoreactivity were highest 12 h after ischemic insult. At this time, GAL-IR neurons in the polymorphic layer showed strong GAL immunoreactivity. Thereafter, GAL-IR neurons and immunoreactivity significantly decreased in the dentate hilar region. Four days after ischemic insult, GAL-IR neurons were not detectable. In addition, the results of a Western blot study showed a pattern of GAL expression similar to the immunohistochemical changes. GAL protein content also was highest 12 h after ischemia. In conclusion, the increased expression of endogenous GAL in the dentate gyrus after ischemia is related to response to the ischemic damage.

In vivo protein transduction: biologically active intact pep-1-superoxide dismutase fusion protein efficiently protects against ischemic insult

Reactive oxygen species (ROS) are implicated in reperfusion injury after transient focal cerebral ischemia. The antioxidant enzyme Cu,Zn-superoxide dismutase (SOD) is one of the major means by which cells counteract the deleterious effects of ROS after ischemia. Recently, we reported that denatured Tat-SOD fusion protein is transduced into cells and skin tissue. Moreover, PEP-1 peptide, which has 21 amino acid residues, is a known carrier peptide that delivers full-length native proteins in vitro and in vivo. In the present study, we investigated the protective effects of PEP-1-SOD fusion protein after ischemic insult. A human SOD gene was fused with PEP-1 peptide in a bacterial expression vector to produce a genetic in-frame PEP-1-SOD fusion protein. The expressed and purified fusion proteins were efficiently transduced both in vitro and in vivo with a native protein structure. Immunohistochemical analysis revealed that PEP-1-SOD injected intraperitoneally (i.p.) into mice can have access into brain neurons. When i.p.-injected into gerbils, PEP-1-SOD fusion proteins prevented neuronal cell death in the hippocampus caused by transient forebrain ischemia. These results suggest that the biologically active intact forms of PEP-1-SOD provide a more efficient strategy for therapeutic delivery in various human diseases related to this antioxidant enzyme or to ROS, including stroke.

Neuroprotective effects of grape seed extract on neuronal injury by inhibiting DNA damage in the gerbil hippocampus after transient forebrain ischemia

Grape seed extract (GSE) possess cardioprotective abilities by functioning as in vivo antioxidants and by virtue of their ability to directly scavenge ROS including hydroxyl and peroxyl radicals. In the present study, we investigated the neuroprotective effects of grape seed extract (GSE) in the gerbil hippocampus after 5 min transient forebrain ischemia. Neuronal cell density in GSE-treated ischemic animals was significantly increased as compared with vehicle-treated ischemic animals 4 days after ischemic insult. In the GSE-treated groups, about 60% of pyramidal cells of the sham-operated group were stained with cresyl violet 4 days after ischemic insult. In this study, we found that GSE had neuroprotective effects on neuronal injury by inhibiting DNA damage in the CA1 region after ischemia. In vehicle-treated groups, 8-hydroxy-2'-deoxyguanosine (8-OHdG) immunoreactivity was significantly changed time-dependently, whereas the immunoreactivity in the GSE-treated group was similar to the sham-operated group. In addition, we confirmed that astrocytes and microglia did not show significant activation in the CA1 region 4 days after ischemia-reperfusion, because many CA1 pyramidal cells were not damaged. Therefore, these results suggest that GSE can protect ischemic neuronal damage by inhibiting DNA damage after transient forebrain ischemia.

Very delayed neuronal loss occurs in the glomerular layer of the main olfactory bulb following transient ischemia in gerbils

Olfactory dysfunction could happen following various insults such as ischemic-hypoxic state. Neurons of the main olfactory bulb (MOB) are resistant to ischemic damage. In the present study, we investigated the ischemia-related changes of neurons and glial cells in the glomerular layer (GL) of the gerbil MOB after transient ischemia. The number of NeuN-immunoreactive neurons became to decrease from 10 days after ischemic insult. Fifteen days after ischemic insult, astrocytes and microglia were increased in number. By 60 days after ischemia, NeuN-immunoreactive neurons were significantly decreased by 42% per glomerulus. At this time period, astrocytes and microglia were pronouncedly increased. This result indicates that neuronal loss must be much delayed in the GL following transient ischemia.

Chronological alterations of neurofilament 150 immunoreactivity in the gerbil hippocampus and dentate gyrus after transient forebrain ischemia

In this study, we observed the chronological alterations of neurofilament 150 (NF-150) immunoreactivity in the gerbil hippocampus and dentate gyrus after 5 min transient forebrain ischemia. NF-150 immunoreactivity in the sham-operated group was mainly detected in mossy fibers and in the hilar region of the dentate gyrus. NF-150 immunoreactivity and protein contents of NF-150 and RT 97 (polyphosphorylation epitopes of neurofilament) were significantly decreased at 15 min after ischemic insult. Between 30 min and 12 h after ischemic insult, NF-150 immunoreactivity and protein content were significantly increased as compared with the sham-operated group. Thereafter, NF-150 immunoreactivity and protein content started to decrease. At 12 h after ischemic insult, unlike dentate gyrus, NF-150 immunoreactivity increased in pyramidal cells of the CA1 region. Thereafter, NF-150 immunoreactivity in the CA1 region started to decrease, and 4 days after ischemic insult, NF-150 immunoreactivity nearly was similar to that of the sham-operated group. These biphasic patterns of NF-150 immunoreactivity in the hippocampus and dentate gyrus are reverse correlated with that of the intracellular calcium influx. For calcium detection in the CA1 region, we also conducted alizarin red staining. Alizarin red positive neurons were detected in some neurons at 15-30 min after ischemic insult. At 12 h after ischemia, alizarin red positive neurons were decreased. Thereafter, alizarin red positive neurons started to decrease, but alizarin positive neurons were significantly increased in dying neurons 4 days after ischemia. These results suggest that ischemia-related changes of NF-150 expression may be caused by the calcium following transient forebrain ischemia.

Ischemia-related change of ceruloplasmin immunoreactivity in neurons and astrocytes in the gerbil hippocampus and dentate gyrus

In the present study, we investigated the temporal and spatial alterations of ceruloplasmin immunoreactivity in the gerbil hippocampus and dentate gyrus after 5 min transient forebrain ischemia. In sham-operated animals, ceruloplasmin immunoreactivity in the hippocampal CA2/3 areas was higher than that of other areas. Ceruloplasmin immunoreactivity and its protein content significantly increased and were highest in the CA1 area 1 day after ischemia-reperfusion. At this time point, the immunoreactivity was shown in pyramidal cells of the CA1 area. Four days after ischemia-reperfusion, ceruloplasmin immunoreactivity was shown in astrocytes in the hippocamapal CA1 area. These results suggest that reactive oxygen species (ROS) do not immediately damage neuronal cytosol, unlike DNA. An interval of time is required for the full expression of the cytoplasmic protein injury by ROS. This delayed neuronal injury 1 day after ischemic insult might provide a window of opportunity for therapeutic interventions using antioxidants.

Ischemia-related changes of adrenocorticotropic hormone immunoreactivity and its protective effect in the gerbil hippocampus after transient forebrain ischemia

In the present study, the temporal and spatial alterations of adrenocorticotropic hormone (ACTH) immunoreactivity in the gerbil hippocampus after 5 min transient forebrain ischemia were investigated as followed up 7 days after ischemic insult, and the effects of ACTH after ischemic insult were also investigated 4 days after ischemic insult. The ectopic expression of ACTH (1-24 fragments) immunoreactive neurons in the cornus ammonis 1 (CA1) region of hippocampus and hilar region of the dentate gyrus 1 day after the ischemic insult was observed. Judging from the double immunofluorescence study, these neurons contain GABA. Four days after ischemic insult, the ACTH immunoreactivity was localized in CA1 pyramidal cells and glia near the stratum pyramidale, which normally do not express ACTH. In addition, in the saline-treated groups, the percentage of the detected Cresyl Violet positive neurons was 11.2% compared with the sham-operated group 4 and 7 days after ischemic insult. In these groups, the OX-42 immunoreactive microglia were detected in the strata pyramidale, oriens and radiatum. However, in the Org2766 (analog of ACTH)-treated group, 57.8% neurons compared with the sham-operated group were stained with Cresyl Violet 4 and 7 days after ischemic insult. In these groups, the OX-42 immunoreactive microglia were significantly reduced in the stratum pyramidale. These results suggest that transient forebrain ischemia may provoke selective ectopic and enhanced expression of ACTH in the hippocampus, and further suggest that ACTH plays an important role in reducing the ischemic damage.

Changes of glial Na+–K+ ATPase (α1 subunit) immunoreactivity in the gerbil hippocampus after transient forebrain ischemia

In the present study to evaluate the effects of ischemia on sodium-potassium adenosine triphosphatase (Na(+)-K+ ATPase) alpha1 subunit (alpha6F) expression in the glia, the immunodensities of both Na(+)-K+ ATPase and the glial fibrillary acidic protein in the hippocampus were measured and analyzed. In the sham hippocampus, alpha6F immunoreactivity was mainly observed in the both the molecular layer and the polymorphic layer of dentate gyrus. At 30 min after ischemic insult, the alpha6F immunoreactivity was markedly decreased in the molecular layer of the dentate gyrus, in contrast to the appearance of this immunoreactivity in the hilar neurons. Up to 12 h after ischemic insult, the alpha6F immunoreactivity was re-enhanced in the molecular layer of dentate gyrus. In addition, the alpha6F immunoreactivity appeared slightly in the glial components in the hippocampal region. Four days after ischemia-reperfusion, the intensity of alpha6F immunoreactivity in the glial cells was highest. At this time point, strong alpha6F immunoreactivity was colocalized with GFAP immunoreactivity in the strata radiatum of the CA1 and the molecular layer of the dentate gyrus. These results suggest that the enhancement of alpha6F immunoreactivity may be a compensatory response to regulate the ion homeostasis in the brain. In addition, the maintenance of Na(+)-K+ ATPase activity in the astrocytes may explain the resistant characteristics of these cells to ischemic insults.

Elevation of Na+-K+ ATPase immunoreactivity in GABAergic neurons in gerbil CA1 region following transient forebrain ischemia

In a previous study, we suggested that GABAergic neurons might be resistant to ischemic insult, because of the maintenance of the GABA shunt, which is one of the ATP synthetic pathways in neurons. In the present study, we identified Na(+)-K(+) ATPase immunoreactivity in the gerbil hippocampus in order to determine whether changes in Na(+)-K(+) ATPase immunoreactivity correlate with GABA shunt following ischemic insult. At 12 h after ischemia-reperfusion, Na(+)-K(+) ATPase immunoreactivity accumulated in some neurons in the CA1 region. However, the protein content of Na(+)-K(+) ATPase was not altered. Interestingly, the density of Na(+)-K(+) ATPase immunoreactivity in neurons and the protein content in the CA1 region was intensified in the 24 h post-ischemic group. As a result of double immunofluorescence study, Na(+)-K(+) ATPase immunoreactive neurons were identified with GABAergic neurons. Therefore, our findings suggest that the increase of Na(+)-K(+) ATPase in GABAergic neurons may be able to explain the resistance of these cells to ischemic insult, and support our previous hypothesis that GABA may play an important role as a metabolite in the survival of GABAergic neurons after ischemic insult.

Temporal alterations in voltage gated Ca2+ channel immunoreactivities in the gerbil hippocampus following ischemic insults

In the present study, temporal changes of voltage-gated Ca(2+) channel (VGCC) immunoreactivities were evaluated in the gerbil hippocampus following ischemia. P/Q-type VGCC immunoreactivity was elevated in the hippocampus in the 3 h post-ischemic group. In the 30 min post-ischemic group, N-type VGCC immunoreactivity began to increase only in the CA1 region. L-type (alpha1C) VGCC immunoreactivity was significantly increased in the 12 h post-ischemic group. L-type (alpha1D) VGCC immunoreactivity began to increase in the CA1 region in the 30 min post-ischemic group and peaked in the 12 h post-ischemic group. These findings suggest that the altered VGCC immunoreactivities following ischemia may play an important role in the ischemic neuronal injury.

The alteration of corticotropin-releasing factor (CRF) receptor immunoreactivity in the gerbil hippocampus and neocortex following ischemic insults

Recently, we suggested that the ectopic expression of corticotropin-releasing factor (CRF) is associated with processes linked to neuronal injury and/or degeneration in response to an ischemic insult. However, little experimental data currently links the CRF receptor directly to neuronal death induced by ischemia. Therefore, in the present study, we investigated the temporal and spatial changes in CRF receptor immunoreactivity in the hippocampus and the neocortex after transient ischemia. CRF receptor immunoreactivity in the hippocampus was reduced up to 24h after ischemia insult, as compared to the sham. Interestingly, CRF receptor immunoreactivity disappeared in the CA1 region of the hippocampus at 4 days in the post-ischemic group. The other regions of hippocampus maintained their immunoreactivities at this time point. On the other hand, in the neocortex, 3h after transient ischemia, the CRF receptor immunoreactivity was elevated in regions vulnerable to ischemia. At 12h post-ischemia, its immunoreactivity had decreased versus the sham operated animals. These results suggest that the selectively ectopic expression of CRF following ischemia, which we reported previously, may regulate inflammatory responses. In addition, these findings also suggest that the mechanisms of neuronal death as mediated by CRF receptor differ in the hippocampus and the neocortex.

Changes in superoxide dismutase and catalase activities of rat brain regions during early global transient ischemia/reperfusion

It has been widely recognized that the hippocampus and striatum are clearly more susceptible to oxidative stress than the remaining brain regions. However, the mechanism involved is not known. The activities of the antioxidant enzymes CuZn-superoxide dismutase (SOD), Mn-SOD and catalase were measured in the hippocampus and striatum and the results were compared to cortex and cerebellum (less susceptible to oxidative stress) after 3 h of a global transient ischemia/reperfusion. CuZn-SOD activities were reduced in all brain regions, but mainly in the hippocampus and striatum. Mn-SOD activity was lowered in the striatum, whereas catalase activity was reduced in the hippocampus and striatum. Our findings indicate that in the earlier phase of ischemia/reperfusion the decay in activities of catalase and SOD may be related with the high susceptibility of the hippocampus and striatum to oxidative damage.

Changes in Na(+)-K(+)-Cl(-) cotransporter immunoreactivity in the gerbil hippocampus following transient ischemia

We examined alterations in Na(+)-K(+)-Cl(-) cotransporter 1 (NKCC1) immunoreactivity following ischemia. Twelve hours after ischemia, NKCC1 immunoreactivity in the CA1 region and in the hilar region was significantly diminished. Twenty-four hours after ischemia, NKCC1 immunoreactivity was intensified in these hippocampal regions as well as CA2-3. Two days after ischemia, NKCC1 immunoreactivity in the CA1 and the hilar neurons had disappeared, although in the CA2-3 and the granule cell layer NKCC1 immunoreactivities had recovered to the sham level. This finding suggests that NKCC1 may play an important role in the ischemic neuronal injury induced by excitotoxicity as well as neuronal edema.