Quantitative analysis of glucose after transient ischemia in the gerbil hippocampus by light and electron microscope radioautography

Radioautographology general and special

A new concept, termed "radioautographology" is advocated and its contents are reviewed. This term is the coinage synthesized from "radioautography" and "(o)logy", expressing a new science derived from radioautography. The concept of radioautographology (RAGology) is a science to localize the radioactive substances in the biological structure of the objects and to analyze and to study the significance of these substances in the biological structure. On the other hand, the old term radioautography (RAG) or autoradiography (ARG) is the technique to demonstrate the pattern of localization of various radiolabeled compounds in biological specimens. The specimens used in biology and medicine are cells and tissues. They are fixed, sectioned and made contact with the radioautographic emulsions, exposed and developed to produce metallic silver grains. Such specimens are designated as radioautographs (or autoradiographs) and the patterns of pictures made of silver grains are named radioautograms. Those people who produced radioautographs were formerly named radioautographers (or autoradiographers) who were only technicians, while those who study RAGology are not technicians but scientists and should be called as radioautographologists. The science of radioautographology was developed in the 20th century and can be divided into two parts, general radioautographology and special radioautographology, as most natural sciences usually can. The general radioautographology is the technology of RAG which consists of 3 fields of sciences, physics concerning radioactivity, histochemistry treating the cells and tissues and photochemistry dealing with the photographic emulsions. The special radioautographology, on the other hand, consists of applications of general radioautographology to various biological and medical sciences. The applications can be classified into several scientific fields, i.e., cellular molecular biology, anatomy, histology, embryology, pathology and pharmacology. Studies carried out in our laboratory were summarized and reviewed. The results obtained from the technology includes 4-dimensional structures of the organs taking the time dimension into account by labeling cells and localizing the sites of incorporation, synthesis, discharge of the labeled compounds in connection with the time lapse and aging of animals. All the results obtained from such applications should be systematized as a new filed of science in the future in the 21st century.

Special cytochemistry in cell biology

Cytochemistry is a science of localizing chemical components of cells and organelles on histological sections by using various techniques. We first aimed at studying cytochemistry by developing new techniques using various principles such as enzyme cytochemistry, microincineration, microspectrophotometry, radioautography, cryo-techniques, X-ray microanalysis and immunocytochemistry. We first concentrated on developing methodologies in the 1960s to 1970s. We then applied these special techniques to various kinds of cells in men and animals. Earlier, I proposed to classify these methods into three categories, i.e., chemical, physical, and biological techniques. The methodology has been well developed to form a new science which should be designated as "general cytochemistry" similarly to the general histology. On the other hand, these techniques should be applied to various cells in various organ systems, such as the skeletal, muscular, digestive, respiratory, urinary, reproductive, endocrine, circulatory, nervous and sensory systems similarly to the special histology or the histology of organs. I summarize the results of cytochemical studies on cells of various organs carried out in our laboratory during these 44 years since 1955. The results obtained from cytochemical studies applied to various cells in respective organ systems should be designated as "special cytochemistry."

Stress protein inductions after brain ischemia

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

Radioautographology: the proposal of a new concept

A new concept termed "radioautographology" is advocated. This term was synthesized from "radioautography" and "ology", expressing a new science derived from radioautography. The concept of radioautographology (RAGology) is that of a science whose objective is to localize radioactive substances in the biological structure of objects and to analyze and study the significance of these substances in the biological structure. On the other hand, the old term radioautography (RAG) is the technique used to demonstrate the pattern of localization of various radiolabeled compounds in specimens. The specimens used in biology and medicine are cells and tissues. They are fixed, sectioned and placed in contact with the radioautographic emulsions, which are exposed and developed to produce metallic silver grains. Such specimens are designated as radioautographs and the patterns of pictures made of silver grains are named radioautograms. The technicians who produce radioautographs are named radioautographers, while those who study RAGology are scientists and should be called radioautographologists. The science of RAGology can be divided into two parts, general RAGology and special RAGology, as most natural sciences usually can. General RAGology is the technology of RAG which consists of three fields of science, i.e., physics concerning radioactivity, histochemistry for the treatment of cells and tissues, and photochemistry dealing with the photographic emulsions. Special RAGology, on the other hand, consists of applications of general RAGology. The applications can be classified into several scientific fields, i.e., cellular and molecular biology, anatomy, histology, embryology, pathology and pharmacology. Studies carried out in our laboratory are summarized and reviewed. All the results obtained from such applications should be systematized as a new field of science in the future.

Calcium, energy metabolism and the development of selective neuronal loss following short-term cerebral ischemia

Short-term cerebral ischemia results in the delayed loss of specific neuronal subpopulations. This review discusses changes in energy metabolism and Ca2+ distribution during ischemia and recirculation and considers the possible contribution of these changes to the development of selective neuronal loss. Severe ischemia results in a rapid decline of ATP content and a subsequent large movement of Ca2+ from the extracellular to the intracellular space. Similar changes are seen in tissue subregions containing neurons destined to die and those areas largely resistant to short-term ischemia, although differences have been observed in Ca2+ uptake between individual neurons. The large accumulation of intracellular Ca2+ is widely considered as a critical initiating event in the development of of neuronal loss but, as yet, definitive evidence has not been obtained. the increased intracellular Ca2+ content activates a number of additional processes including lipolysis of phospholipids and degradation or inactivation of some specific proteins, all of which could contribute to altered function on restoration of blood flow to the brain. Reperfusion results in a rapid recovery of ATP production. Cytoplasmic Ca2+ concentration is also restored during early recirculation as a result of both removal to the extracellular space and uptake into mitochondria. Within a few hours of recirculation, subtle increases in intracellular Ca2+ and a reduced capacity for mitochondrial respiration have been detected in some ischemia-susceptible regions. Both of these changes could potentially contribute to the development of neuronal loss. More pronounced alterations in Ca2+ homeostasis, resulting in a second period of increased mitochondrial Ca2+, develop with further recirculation in ischemia-susceptible regions. The available evidence suggests that these increases in Ca2+, although developing late, are likely to precede the irreversible loss of neuronal function and may be a necessary contributor to the final stages of this process.

Ischemic delayed neuronal death. A mitochondrial hypothesis

BACKGROUND

A brief period of global brain ischemia causes cell death in hippocampal CA1 pyramidal neurons days after reperfusion in rodents and humans. Other neurons are much less vulnerable. This phenomenon is commonly referred to as delayed neuronal death, but the cause has not been fully understood although many mechanisms have been proposed.

SUMMARY OF REVIEW

Hippocampal CA1 neuronal death usually occurs 3 to 4 days after an initial ischemic insult. Such a delay is essential for the mechanism of this type of cell death. Previous hypotheses have not well explained the reason for the delay and the exact mechanism of the cell death, but a disturbance of mitochondrial gene expression could be a possibility. Reductions of mitochondrial RNA level and the activity of a mitochondrial protein, encoded partly by mitochondrial DNA, occurred exclusively in CA1 neurons at the early stage of reperfusion and were aggravated over time. In contrast, the activity of a nuclear DNA-encoded mitochondrial enzyme and the level of mitochondrial DNA remained intact in CA1 cells until death. Immunohistochemical staining for cytoplasmic dynein and kinesin, which are involved in the shuttle movement of mitochondria between cell body and the periphery, also showed early and progressive decreases after ischemia, and the decreases were found exclusively in the vulnerable CA1 subfield.

CONCLUSIONS

A disturbance of mitochondrial DNA expression may be caused by dysfunction of the mitochondrial shuttle system and could cause progressive failure of energy production of CA1 neurons that eventually results in cell death. Thus, the mitochondrial hypothesis could provide a new and exciting potential for elucidating the mechanism of the delayed neuronal death of hippocampal CA1 neurons.

Time course of hippocampal glucose utilization and persistence of parvalbumin immunoreactive neurons after ibotenic acid-induced lesions of the rat dentate area

The effects of ibotenic acid induced lesions of the dentate gyrus on hippocampal glucose utilization and parvalbumin-positive neurons were evaluated in male Wistar rats. Ibotenic acid was injected in the right dorsal dentate gyrus. Quantification of glucose utilization was performed 3 days, 3 weeks, or 3 months after the lesion using the 14C-2-deoxyglucose method. Nissl-stained sections and sections stained for acetylcholinesterase were used as references for anatomical delineation of the hippocampal cytoarchitecture. Additional sections were stained for parvalbumin. The results revealed widespread reductions of glucose utilization in all layers and sectors of the hippocampus in the ipsilateral lesioned hemisphere and also in the nonlesioned contralateral hemisphere. The reductions occurred as early as 3 days after the lesion and persisted up to 3 months. In neither hippocampal structure did glucose utilization return to control levels. Immunohistochemical visualization of parvalbumin-containing neurons revealed that these putatively inhibitory neurons persisted in the otherwise granule-cell-depleted area. The data show that interruption of the excitatory trisynaptic pathway from the entorhinal cortex to the CA1 at the level of the dentate gyrus affects hippocampal glucose utilization irreversibly and uniformly. Since some inhibitory neurons seem to survive the ibotenic acid lesion, we suggest that the reductions of hippocampal glucose utilization reflect an imbalance in favor of inhibitory neurons in the ipsilateral hippocampus after the lesion, which manifests also in the contralateral hemisphere via the commissural pathways.

Evolving concepts about the role of acidosis in ischemic neuropathology

Cerebral ischemia is one of the most common neurological insults. Many pathological events are undoubtedly triggered by ischemia, but only recently has it become accepted that ischemic cell injury arises from a complex interaction between multiple biochemical cascades. Tissue acidosis is a well established feature of ischemic brain tissue, but its role in ischemic neuropathology is still not fully understood. Within the last few years, new evidence has challenged the historically negative view of acidosis and suggests that it may play more of a beneficial role than previously thought. This review reintroduces the concept of acidosis to ischemic brain injury and presents some new perspectives on its neuroprotective potential.

Changes of mitochondrial DNA and heat shock protein gene expressions in gerbil hippocampus after transient forebrain ischemia

Hippocampal CA1 neurons are the most vulnerable to transient cerebral ischemia. However, the mechanism has not been fully understood. The level of mRNA for cytochrome C oxidase (COX) subunit I (COX-I), which is encoded by mitochondrial (mt) DNA, progressively decreased in the hippocampal CA1 neurons of gerbils from 3 h of reperfusion after 3.5 min of transient forebrain ischemia and completely disappeared at 7 days. The activity of COX protein also showed an early decrease in CA1 cells and was followed by reduction of the level of COX-I DNA after 2 days. However, succinic dehydrogenase, an mt enzyme encoded by nuclear DNA, maintained normal activity until 1 day in the CA1 cells and significantly decreased at 7 days. The mRNA for mt heat shock protein (HSP) 60 began to increase at 3 h in the CA1 cells and was sustained until 1 day. The mRNAs for 72-kDa heat shock protein and 73-kDa heat shock cognate protein, which are located mainly in the cytoplasm, were induced together in the CA1 cells with a peak at 1-2 days. These results suggest that a disturbance of mt DNA expression occurred in the CA1 neurons at the early stage of reperfusion and was aggravated over the course of time. The disturbance could cause progressive failure of energy production of the cells that eventually results in neuronal cell death.

Disturbance of a mitochondrial DNA expression in gerbil hippocampus after transient forebrain ischemia

Hippocampal CA1 neurons are the most vulnerable to transient cerebral ischemia. However, the mechanism has not been fully understood. The level of mRNA for cytochrome c oxidase subunit I (COX-I), which is encoded by mitochondrial DNA (mtDNA), progressively decreased in the hippocampal CA1 neurons of gerbils from 1 to 3 h of the reperfusion after 3.5 min of transient forebrain ischemia, and completely disappeared at 7 days. The activity of cytochrome c oxidase (COX) protein also showed the early decrease in the CA1 cells, and was followed by the reduction of the level of COX-I DNA after 2 days. However, the activity of succinic dehydrogenase (SDH), a mitochondrial enzyme that is encoded by nuclear DNA, maintained normal activity until 1 day in the CA1 cells, and significantly decreased at 7 days. These results suggest that disturbance of mitochondrial DNA expression occurred in the CA1 neurons at the early stage of reperfusion, and was aggravated in the course of time. The disturbance could cause progressive failure of energy production of the cells that eventually results in the neuronal cell death.

Early disturbance of a mitochondrial DNA expression in gerbil hippocampus after transient forebrain ischemia

The level of mRNA for cytochrome c oxidase subunit I (COX-I), which is encoded by mitochondrial DNA (mtDNA), progressively decreased in the hippocampal CA1 neurons of gerbils from 1-3 h of the reperfusion after 3.5 min of transient forebrain ischemia, and completely disappeared at 7 days. The activity of cytochrome c oxidase (COX) protein also showed the early decrease in the CA1 cells, and was followed by the reduction of the level of COX-I DNA after 2 days. However, the activity of succinic dehydrogenase (SDH), a mitochondrial enzyme that is encoded by nuclear DNA, maintained normal activity until 1 day in the CA1 cells, and significantly decreased at 7 days. These results suggest that the early onset and the progressive disturbance of a mitochondrial DNA expression found selectively in the CA1 neurons could cause progressive failure of energy production of the cells that eventually results in the neuronal cell death.

Energy metabolism and selective neuronal vulnerability following global cerebral ischemia

A short period of global ischemia results in the death of selected subpopulations of neurons. Some advances have been made in understanding events which might contribute to the selectivity of this damage but the cellular changes which culminate in neuronal death remain poorly defined. This overview examines the metabolic state of tissue in the post-ischemic period and the relationship of changes to the development of damage in areas containing ischemia-susceptible neurons. During early recirculation there is substantial recovery of ATP, phosphocreatine and related metabolites in all brain regions. However, this recovery does not signal restitution of normal energy metabolism as reductions of the oxidative metabolism of glucose are seen in many areas and may persist for several days. Furthermore, decreases in pyruvate-supported respiration develop in mitochondria from at least one ischemia-susceptible region at times coincident with the earliest histological evidence of ischemia-induced degeneration. These mitochondrial changes could simply be an early marker of irreversible damage but the available evidence is equally consistent with these contributing to the degenerative process and offering a potential site for therapeutic intervention.

Postischemic neuronal damage causes astroglial activation and increase in local cerebral glucose utilization of rat hippocampus

The purpose of the present study was to determine the consequences of postischemic neuronal damage on CMRglc. Forebrain ischemia of 10 min duration was induced in male Wistar rats. The extent of neuronal damage and the numbers of immunocytochemically detected astrocytes in the hippocampal CA1 subfield as well as CMRglc were determined 2, 5, 7, and 14 days after ischemia. CBF was additionally measured 7 days postischemia. CMRglc was decreased in cortical and thalamic structures up to 5 days postischemia, and was normalized again on day 7 after ischemia. In the hippocampal areas, CMRglc was decreased only on day 2 after ischemia, was normalized after 5 days, and increased in the stratum oriens and pyramidale of the CA1 subfield from postischemic day 7 onward. Neuronal damage was clearly demonstrable 5 days after ischemia and further increased up to day 7. The number of GFAP-reactive astrocytes increased markedly at day 7 postischemia. It is assumed that the activation of astrocytes is induced by neuronal damage, and that the astroglial metabolism is responsible for the increase in CMRglc of the CA1 subfield 7 days after ischemia. The decrease in CBF of the CA1 subfield 7 days after ischemia could be caused by a reduced density of perfused capillaries.

Glucose utilization in rat hippocampus after long-term recovery from ischemia

The influence on hippocampal glucose utilization of a transient 10-min forebrain ischemia was quantified in male Wistar rats after 2 and 3 weeks as well as after 3 months by application of the [14C]2-deoxyglucose technique. Ischemia was induced by occlusion of the carotid arteries and simultaneous lowering of the blood pressure to 40 mm Hg. For identification of the hippocampal architecture, sections were stained for perikarya (cresyl violet) and for acetylcholinesterase. The hippocampal regions clearly showed different responses to the ischemic insult. The necrotic pyramidal cells being almost completely removed, significant increases in glucose utilization occurred in most layers of the CA1 sector at 2 and 3 weeks post ischemia, while widespread reductions prevailed in all other sectors and the dentate gyrus. At 3 months after the ischemic insult, glucose utilization was reduced in all hippocampal structures including the CA1 region. The increases in glucose utilization in the CA1 sector are suggested to indicate long-lasting presynaptic hyperexcitation, while the widespread reductions in glucose utilization demonstrate that neuronal activity is also altered in hippocampal areas that do not show major histological damage.

Postischemic glucose utilization in rat hippocampal layers

The influence on hippocampal glucose utilization was determined in male Wistar rats 7 days after a 10-min forebrain ischemia. Ischemia was induced by clamping of the carotid arteries and lowering blood pressure to 40 mm Hg. Despite severe neuronal damage as assessed by histological techniques, local cerebral glucose utilization (LCGU) was significantly increased in the pyramidal and radiatum layer of the CA1 sector, while in layers of the CA2, CA3 and CA4 sector and dentate gyrus. LCGU was reduced compared to non-ischemic controls. The increases in LCGU are suggested to reflect long-lasting hyperexcitation in the selectively vulnerable CA1 sector, implicating a correlation between cellular hypermetabolism and neuronal damage.

Maintenance of local cerebral blood flow after acute neuronal death: possible role of non-neuronal cells

In brain, a major factor regulating local perfusion is local neuronal activity. However, we have recently discovered that, in rat, five days after selective neuronal destruction in the parietal cortex by local microinjections of the excitotoxin ibotenic acid, local cerebral blood flow, within the lesion, remains in the normal range. We studied whether proliferating non-neuronal cells and/or local changes in microvascular density participate to maintain local cerebral blood flow. Rats were anesthetized (halothane 1-3%), ibotenic acid (10 micrograms in 1 microliter) was locally microinjected in a restricted region of the parietal cortex, and animals were allowed to recover. Three, five, seven, 11, 30 days later local cerebral blood flow was measured autoradiographically under chloralose anesthesia (40 mg/kg, s.c.) by the [14C]iodoantipyrine technique. Cellular density or microvascular area were determined on sections stained with Thionine or processed for the endothelial marker alkaline phosphatase, respectively. Local neurons were destroyed by 24 h after microinjections of ibotenic acid. However, from three to 11 days after lesion local cerebral blood flow was unchanged (P greater than 0.05; n = 5), thereafter declining so that by 30 days blood flow was 48 +/- 6% of control (P less than 0.05; n = 5). Cellular density increased within the lesion by 17.5-fold at seven to 11 days (P less than 0.01) and declined to a 11.7-fold elevation above control at day 30 (P less than 0.01). New cells consisted of macrophages, endothelium and glial fibrillary acidic protein-positive astrocytes. The microvascular area increased 4.2-fold from three to 11 days (P less than 0.01). The patency of the presumably newly formed vessels was determined by the presence of intravascular red blood cells, which were revealed histochemically. The area occupied by red blood cells within cerebral microvessels, in contrast to microvascular area, did not increase until seven days after lesion, reaching a 3.2-fold increase at 11 days. Thus within the lesion, local cerebral blood flow remains constant during the phase in which cellular and microvascular density increases. The presumably newly formed vessels cannot contribute to maintain local cerebral blood flow since during this phase they are not patent; rather patency develops coincident with the decline in local cerebral blood flow. We conclude that non-neuronal cells, most likely activated macrophages, may be an important factor regulating local cerebral perfusion, after acute neuronal death.

Glucose utilization of ischemic hippocampal slices

Hippocampal brain slices that were 1000 mu thick were prepared from Sprague-Dawley rats and studied using in vitro glucose utilization under well-oxygenated conditions or after a 15 min anoxic insult produced with a nitrogen atmosphere. Autoradiography reveals that glucose utilization is increased in CA1 and CA3 stratum radiatum of 1000 mu slices, even with full oxygenation, compared to the same regions in 540 mu slices. Following anoxia, there is an initial addition increase in stratum oriens of CA1 and CA3 glucose utilization that is followed by a decline in glucose utilization in all slice regions within an hour of the insult. Because increased glucose utilization is apparent at the slice surfaces as well as at the interior, it is suggested that thick brain slices are a model of brain ischemia, not just hypoxia.

Ultrastructural metabolic activity following quick-freezing and freeze-substitution in tetrahydrofuran in the superior cervical ganglion

A method of quick-freezing and freeze-substitution has been developed for localizing diffusible substances such as 2-deoxyglucose-6-phosphate (2-DG-6-P) ultrastructurally in neural tissue. Quick-freezing under pressure provides well preserved tissue down to 30-35 microns from the surface. This allows blocks of neural tissue to be quick-frozen and analysed for diffusible substances in areas removed from the freezing face. Freeze-substitution in tetrahydrofuran following quick-freezing was found to dissolve and remove 2-deoxyglucose (2-DG) but not 2-DG-6-P. Consequently, this technique extends the ability to analyse localization of glucose utilization to postsynaptic as well as presynaptic sites. We have applied the technique to isolated superior cervical ganglion while provoking selective increases in energy metabolism. Exposure to an elevated extracellular potassium (12 mM) concentration produced a pattern of metabolic activity with enhanced neuropil labelling (neuronal and glial processes). With antidromic stimulation of the external carotid nerves, deoxyglucose uptake in neuronal and glial soma in the caudal portion of the ganglion was enhanced more than neuropil labelling. This caudal region corresponds to the region of origin of the cell bodies of the external carotid nerve. Results from this technique suggest that the contribution of glia to overall rate of energy metabolism may be significant and that this is a promising method for correlating the relationship between functional activity and cellular electrical activity.

Effect of dihydroergotoxine mesylate (Hydergine) on delayed neuronal death in the gerbil hippocampus

The CA 1 neurons in the gerbil hippocampus exhibiting necrosis with delayed onset following 5 min ischemia were reduced markedly by the systemic administration of dihydroergotoxine mesylate (Hydergine; HYG). Immediately after 5 min of forebrain ischemia, the animals were injected intraperitoneally with HYG. Seven days after ischemia, perfusion-fixed brains were processed by conventional histology. The number of neurons per millimeter in the CA 1 pyramidal cell layer were calculated and they were labelled neuronal density. In the control group, the neuronal density was 66.03 +/- 7.37 (mean +/- SEM), in the vehicle group, it was 11.25 +/- 4.93. The neuronal density in the HYG group was 69.19 +/- 6.49. The difference in the neuronal density between the HYG group and the control group was not statistically significant. These data indicate that HYG protects on the CA 1 neurons, and this suggest that the suppression of adrenoceptors by this drugs may be the main mechanism of action. This morphologic outcome may explain the functional amelioration of mental impairment by HYG.

Prevention of delayed neuronal death in gerbil hippocampus by ion channel blockers

We used a gerbil model of cerebral ischemia to study the effects of ion channel blockers on neuronal death resulting from enhanced glutamate release and calcium ion influx. The common carotid arteries of gerbils were occluded for 5 minutes and injected intraperitoneally immediately after ischemia with an alkylene iminopropylene derivative (glutamate blocker) or a piperazinyl ethanol derivative (calcium blocker) given at high or low doses. Two vehicle groups received saline or 0.2% methyl cellulose solution. Seven days later, the gerbils were perfusion-fixed and their brains were processed for histologic study. The number of neurons per millimeter (neuronal density) of the CA1 region was calculated, and the neuronal density in each group was statistically compared using the Mann-Whitney U test. Compared with a control group not subjected to carotid ligation, neurons of the two vehicle groups and the low-dose calcium blocker group were almost nonexistent in the CA1 region. Neuronal densities of the glutamate blocker group and the high-dose calcium blocker group were similar and were found to be within normal limits by statistical analysis. Our study shows that detrimental membrane phenomena and the incidence of delayed neuronal death may be counteracted by the systemic administration of these ion channel blockers after ischemic insult.

The mechanism of ischemia-induced brain cell injury. The membrane theory

Temporal ischemia of the brain injures only the selectively vulnerable brain cells. The dying process evolves along with glutamate-mediated intracellular signal-transduction system, together with a loss of Ca2+ homeostasis. Such post-ischemic changes eventually disrupt functional and structural integrity of the cell membrane and kill the neuron. Molecular basis in pharmacoprotective agents is discussed.