Reexpression of developmentally regulated MAP2c mRNA after ischemia: colocalization with hsp72 mRNA in vulnerable neurons

MAP2 IHC detection: a marker of antigenicity in CNS tissues

Immunohistochemistry (IHC) is used to detect antibody-specific antigens in tissues; the results depend on the ability of the primary antibodies to bind to their antigens. Therefore, results depend on the quality of preservation of the specimen. Many investigators have overcome the deleterious effects of over-fixation on the binding of primary antibodies to specimen antigens using IHC, but if the specimen is under-fixed or fixation is delayed, false negative results could be obtained despite certified laboratory practices. Microtubule-associated protein 2 (MAP2) is an abundant microtubule-associate protein that participates in the outgrowth of neuronal processes and synaptic plasticity; it is localized primarily in cell bodies and dendrites of neurons. MAP2 immunolabeling has been reported to be absent in areas of the entorhinal cortex and hippocampus of Alzheimer's disease brains that were co-localized with the dense-core type of amyloid plaques. It was hypothesized that the lack of MAP2 immunolabeling in these structures was due to the degradation of the MAP2 antigen by the neuronal proteases that were released as the neurons lysed leading to the formation of these plaques. Because MAP2 is sensitive to proteolysis, we hypothesized that changes in MAP2 immunolabeling may be correlated with the degree of fixation of central nervous system (CNS) tissues. We detected normal MAP2 immunolabeling in fixed rat brain tissues, but MAP2 immunolabeling was decreased or lost in unfixed and delayed-fixed rat brain tissues. By contrast, two ubiquitous CNS-specific markers, myelin basic protein and glial fibrillary acidic protein, were unaffected by the degree of fixation in the same tissues. Our observations suggest that preservation of various CNS-specific antigens differs with the degree of fixation and that the lack of MAP2 immunolabeling in the rat brain may indicate inadequate tissue fixation. We recommend applying MAP2 IHC for all CNS tissues as a pre-screen to assess the quality of the tissue preservation and to avoid potentially false negative IHC results.

Early cellular events in the penumbra of human spontaneous intracerebral hemorrhage

Spontaneous intracerebral hemorrhage causes high morbidity and mortality rates, and yet its treatment remains controversial, partly because of a poor understanding of the pathogenesis and timescale of injury in the surrounding brain. This study was undertaken to clarify the cellular reactions around human spontaneous intracerebral hematomas and relate these to hematoma duration and volume, in order to provide further data that might aid the development of therapeutic strategies. Brain tissue from the margin of the hematoma in 33 fatal cases of spontaneous intracerebral hemorrhage and corresponding tissue from 13 normal controls was studied using immunohistochemistry for heat-shock proteins, metallothionein, and various neuronal, glial, macrophage, and endothelial markers. Hematoma volumes were calculated from computed tomographic (CT) scans and autopsy measurements, whereas hematoma age was estimated from clinical records. The results showed that cellular events are time dependent, but not related to hematoma volume, and are identifiable in neurons, glia, and endothelium as early as 5 hours after hemorrhage. Peripheral macrophage infiltration begins at 5 days. The results suggest that the therapeutic window in humans for reperfusion of the ischemic penumbra of a hematoma is less than 5 hours, although progression of the infarcted core to the penumbral periphery within 1 to 3 days suggests a wider cytoprotective window. Edema, caused by blood-brain barrier breakdown, was also identified at 5 hours, and prompt treatment of this may reduce the space-occupying effects of the hematoma and, possibly, the morbidity and mortality.

Betamethasone-related acute alterations of microtubule-associated proteins in the fetal sheep brain are reversible and independent of age during the last one-third of gestation

OBJECTIVE

The purpose of this study was to examine whether glucocorticoid effects on neuronal cytoskeleton, which we have shown previously at 0.87 gestation when the hypothalamo-pituitary-adrenal axis matures, are age-dependent and reversible.

STUDY DESIGN

Fetal sheep received 3.3 microg kg(-1) h(-1) betamethasone (n = 10) or saline solution (n = 9) intravenously over 48 hours at 0.75 gestation (ie, before the hypothalamo-pituitary-adrenal axis matures and when betamethasone is administered clinically).

RESULTS

Betamethasone diminished microtubule-associated protein (MAP) 1B and 2 immunoreactivity in the frontal neocortex and caudate putamen (P < .05) and MAP2 in the hippocampus (P < .05), which is similar to the effects that are seen at 0.87 gestation. In agreement, the number of glucocorticoid receptors did not differ at both ages. Loss of MAP1B and MAP2 immunoreactivity was not accompanied by neuronal death and was reversible within 24 hours.

CONCLUSION

Alteration of neuronal cytoskeletal proteins caused by antenatal betamethasone exposure is transient and independent of age during late gestation.

Induced hippocampal neuron protection in an optimized gerbil ischemia model: insult thresholds for tolerance induction and altered gene expression defined by ischemic depolarization

Preconditioning of hippocampal CA1 neurons was evaluated in a gerbil model of transient global ischemia using extracellular recording of DC potential shifts characteristic of ischemic depolarization to precisely define the duration of both priming and test insults. Brief ischemia resulting in depolarizations of 2.5 to 3.5 minutes consistently induced maximal tolerance (95% protection) against subsequent challenges 2 days later with an approximate doubling of the insult duration required for complete CA1 neuron loss from 6 to 12 minutes depolarization when evaluated 1 week after the test insult. Significant protection persisted at 2 months survival, although the apparent injury threshold regressed to approximately 8 minutes, indicating delayed progression of injury after longer test insults. In situ hybridization was used to evaluate depolarization thresholds for induction of mRNAs encoding the 70 kDa heat shock/stress protein, hsp72, as well as several immediate-early genes (c-fos, c-jun, junB, and junD). Immediate-early genes were prominently expressed after short insults inducing tolerance, whereas appreciable hsp72 induction only occurred after insults approaching the threshold for neuron injury. These results establish an ischemic preconditioning model with the predictability needed for mechanistic studies and demonstrate that prior transcriptional activation of the postischemic heat shock response is not required for expression of delayed tolerance.

Effect of antenatal betamethasone treatment on microtubule-associated proteins MAP1B and MAP2 in fetal sheep

Betamethasone has been used extensively to accelerate fetal lung maturation, yet little is known of its effects on neuronal morphogenesis in the developing fetus. Microtubule-associated proteins (MAPs) are a diverse family of cytoskeletal proteins that are important for brain development and the maintenance of neuroarchitecture. Vehicle (n = 7) or betamethasone (10 ug h-1, n = 7) was infused I.V. to fetal sheep over 48 h beginning at 0.87 of gestation (128 days of gestation), producing fetal plasma betamethasone concentrations resembling those to which the human fetus is exposed during antenatal glucocorticoid therapy. Paraffin sections of the left hemisphere were stained with monoclonal antibodies against MAP1B and the MAP2 isoforms MAP2a,b,c and MAP2a,b. The level of the juvenile isoform MAP2c was determined by comparison of the two MAP2 immunostainings. We were able to detect MAP1B and MAP2 immunoreactivity (IR) in the fetal sheep brain. MAP2c was the major MAP2, constituting 90.2 % of the total MAPBetamethasone exposure diminished MAP1B IR in the frontal cortex and caudate putamen (P < 0.05) but not in the hippocampus. A decrease of MAP2 IR was found in the frontal cortex, hippocampus and caudate putamen (P < 0.05). Loss of MAP2 IR was mainly due to the loss of MAP2c IR. Haematoxylin-eosin staining did not demonstrate irreversible neuronal damage. Regional cerebral blood flow determined using coloured microspheres was significantly decreased by 28 % in the frontal cortex and by 36 % in the caudate putamen but not in the hippocampus 24 h after the onset of betamethasone exposure (P < 0.05). The loss of MAP1B and MAP2a,b,c IR showed a significant correlation to the cerebral blood flow decrease only in the frontal cortex (P < 0.05). These data suggest that mechanisms other than metabolic insufficiency caused by the decreased cerebral blood flow may contribute to the loss of MAPs. The results suggest that clinical doses of betamethasone may have acute effects on cytoskeletal proteins in the fetal brain.

Upregulation of MAP1B and MAP2 in the rat brain after middle cerebral artery occlusion: effect of age

Although stroke in humans usually afflicts the elderly, most experimental studies on the nature of cerebral ischemia have used young animals. This is especially important when studying restorative processes that are age dependent. To explore the potential of older animals to initiate regenerative processes after cerebral ischemia, the authors studied the expression of the juvenile-specific cytoskeletal protein, microtubule-associated protein (MAP) 1B, and the adult-specific protein, MAP2, in male Sprague-Dawley rats at 3 months and 20 months of age. The levels of MAP1B and MAP2 transcripts and the corresponding proteins declined with increasing age in the hippocampus. In the cortex, the levels of the transcripts did not change significantly with age, but the morphologic features of immunostained fibers were clearly affected by age; that is, cortical MAP1B fibers became thicker, and MAP2 fibers, more diffuse, in aged rats. Focal cerebral ischemia, produced by reversible occlusion of the right middle cerebral artery, resulted in a large decrease in the expression of both MAP1B and MAP2 in the infarct core at the messenger ribonucleic acid and protein levels. However, at 1 week after the stroke, there was vigorous expression of MAP1B and its messenger ribonucleic acid, as well as MAP2 protein, in the border zone adjacent to the infarct of 3-month-old and 20 month-old male Sprague-Dawley rats. The upregulation of these key cytologic elements generally was diminished in aged rats compared with young animals, although the morphologic features of fibers in the infarct border zone were similar in both age groups. These results suggest that the regenerative potential of the aged rat brain appears to be competent, although attenuated, at least with respect to MAP1B and MAP2 expression up to 20 months of age.

Cell cycle-related gene expression in the adult rat brain: selective induction of cyclin G1 and p21WAF1/CIP1 in neurons following focal cerebral ischemia

The present studies were initiated to investigate whether p53 transactivated target genes are induced in a rat model of focal cerebral ischemia. Therefore, we applied in situ hybridization, immunocytochemistry and western blotting to study the temporal and spatial expression of p53 and its transcriptional targets Bax, p21 and cyclin G1 following permanent middle cerebral artery occlusion in the rat. Cyclin G1 immunoreactivity was constitutively expressed in the nuclei of cells in the choroid plexus and ependymal cell layer and in the cytoplasm of cell bodies and dendrites of pyramidal neurons of the cerebral cortex. Cyclin G1 messenger RNA and protein levels transiently increased to 150% of contralateral levels in neurons of the ipsilateral frontal and parietal cortex and striatum 3 h following middle cerebral artery occlusion. A low level of constitutively expressed p21 messenger RNA and protein was found in nuclei of cells in the choroid plexus, oligodendrocytes and neurons. p21 messenger RNA and protein levels gradually increased to 250% and 140% of contralateral levels in areas bordering the infarct core up to 6 h following middle cerebral artery occlusion. In contrast, p53 and Bax messenger RNA and protein levels, and protein levels of p27, cyclin-dependent kinase 5, p35 and cyclin E decreased in the infarct core and border areas with time after middle cerebral artery occlusion. The selective up-regulation of cyclin G1 and p21 in neurons in the border zone of a focal ischemic infarct indicates their involvement in an adaptive response to ischemic injury. The possible participation of cyclin G1 and p21 in a signal transduction pathway associated with ischemia-induced cellular stress is discussed.

Reduction of infarct volume by halothane: effect on cerebral blood flow or perifocal spreading depression-like depolarizations

Halothane is a strong inhibitor of potassium evoked spreading depression (SD) in cats. In the current study, we investigate halothane effects on induction of perifocal SD-like depolarizations, CBF, and infarct evolution in focal ischemia. Calomel and platinum electrodes measured cortical direct current potential and CBF in ectosylvian, suprasylvian, and marginal gyri. Left middle cerebral artery occlusion (MCAO) induced permanent focal ischemia for 16 hours in artificially ventilated cats (30% oxygen, 70% nitrous oxide) under halothane (0.75%, n = 8) or alpha-chloralose anesthesia (60 mg/kg intravenously, n = 7). Under alpha-chloralose, MCAO induced severe ischemia in ectosylvian and suprasylvian gyri(mean CBF < 10 mL/100 g/min), and direct current potentials turned immediately into terminal depolarization. In marginal gyri, CBF reduction was mild (more than 20 mL/100 g/min), and in six of seven animals, frequent SD-like depolarizations turned into terminal depolarization at a later stage of the experiments. Under halothane, MCAO induced severe ischemia (less than 10 mL/100 g/min) and immediate terminal depolarization only in ectosylvian gyrus. In suprasylvian gyrus, residual CBF remained significantly higher (more than 10 mL/100 g/min) than under alpha-chloralose, whereas in marginal gyri, CBF did not differ between groups. Compared with chloralose, the number of transient depolarizations was significantly reduced in marginal gyrus, and in suprasylvian gyrus transient but significantly longer depolarizations than in marginal gyrus were recorded. Except for one animal, transient depolarizations did not turn into terminal depolarization under halothane, and infarct volume reduction was particularly seen in suprasylvian gyrus. We conclude that halothane, the most commonly used anesthetic in studies of experimental brain ischemia, has protective properties, which may depend on both cerebrovascular and electrophysiologic influences.

Co-expression of MAP-2 and GFAP in cells developing from rat EGF responsive precursor cells

In this study we have performed a detailed analysis of EGF-responsive precursors as they develop into neurons and astrocytes using antibodies to nestin, microtubule-associated protein 2 (MAP-2c and MAP-2ab) and glial fibriallary acidic protein (GFAP). Surprisingly, at early time points, most GFAP-positive cells also stained for MAP-2c, and we postulate that this may be a normal stage of astroglial development. At 7 days most of the cells had developed into astrocytes and MAP-2ab-positive cells only represented 5% of the total neuronal population. This study shows that (i) MAP-2c is a marker for early precursors, (ii) the majority of cells developing from. EGF-responsive precursors develop into glia and (iii) only a small population of cells arising from expanded populations of EGF-responsive precursors develop into neurons expressing MAP-2ab. Thus, certain critical signals important for full neuronal differentiation may be missing from this system.

Microtubular proteolysis in focal cerebral ischemia

Calpain, a neutral protease activated by calcium, may promote microtubular proteolysis in ischemic brain. We tested this hypothesis in an animal model of focal cerebral ischemia without reperfusion. The earliest sign of tissue injury was observed after no more than 15 min of ischemia, with coiling of apical dendrites immunolabeled to show microtubule-associated protein 2 (MAP2). After 6 h of ischemia, MAP2 immunoreactivity was markedly diminished in the infarct zone. Quantitative Western analysis demonstrated that MAP2 was almost unmeasurable after 24 h of ischemia. An increase in calpain activity, shown by an antibody recognizing calpain-cleaved spectrin fragments, paralleled the loss of MAP2 immunostaining. Double-labeled immunofluorescent studies showed that intraneuronal calpain activity preceded evidence of MAP2 proteolysis. Perikaryal immunolabeling of tau protein became increasingly prominent between 1 and 6 h in neurons located within the transition zone between ischemic and unaffected tissue. Western blot experiments confirmed that dephosphorylation of tau protein occurred during 24 h of ischemia, but was not associated with significant loss of tau antigen. We conclude that focal cerebral ischemia is associated with early microtubular proteolysis caused by calpain.

Molecular correlates of delayed neuronal death following transient forebrain ischemia in the rat

Following transient forebrain ischemia selective and delayed neuronal degeneration occurs in the CA1 sector of the hippocampus. It is presently unclear whether this cell death is related to programmed cell death (PCD), which occurs in neurons during development of the CNS. Recently, the expression of various genes, such as c-fos, c-jun mkp-1, cyclin D1, and hsp70 was found to be associated with PCD in model systems. We and others have described that these genes are also upregulated in the hippocampus following ischemia. Most notably, c-fos, c-jun, and hsp70 are expressed specifically in CA1 neurons at survival times shortly preceding cell degeneration in rat models of global ischemia. In addition, the gene products could be detected by immunohistochemical methods, despite a general impairment of protein synthesis. These finding are especially relevant, since recent report suggests a functional role for Fos family proteins and c-jun in PCD in neurons of the superior cervical ganglion. These results could be indicative for the occurrence of a PCD-related program in CA1 neurons ad corroborate several other lines of evidences, such as occurrence of DNA fragmentation. Clearly, further studies are necessary to elucidate the functional role of the gene inductions following ischemia in vivo.

Selective neuronal vulnerability in the hippocampus--a role for gene expression?

Proposed mechanisms of neurodegeneration focus generally on the triggering of toxic biochemical pathways by an increased intracellular concentration of Ca2+. Recent evidence also suggests that Ca2+ causes transcriptional activation of so-called 'cell-death genes'. Efforts to elucidate the basis of selective vulnerability have relied on animal models of delayed neuronal death in the hippocampus. Biochemical and morphological data indicate that delayed neuronal death is a form of programmed cell death, or apoptosis. Observations that specific genes are activated transcriptionally for prolonged times in neuronal populations that are undergoing delayed death suggest that active gene expression is part of the neuronal-death cascade. Although a direct causal role remains to be proven, evidence implicates certain genes in neuronal-death pathways.

Immunocytochemical and in situ hybridization approaches to the optimization of brain slice preparations

Methods are described for determining the expression of specific mRNAs and proteins in brain slices, in order to elucidate changes in gene expression during preparation of vibratome slices from hippocampus of adult rats. In situ hybridization with 35S-labeled oligonucleotides was used to evaluate the level and distribution of c-fos and hsp72 mRNAs in 15-microns frozen sections prepared from these slices. Commercially available antibodies were used to examine the distribution of induced Fos and Jun proto-oncogenes as well as expression of the neuronal cytoskeletal protein, microtubule-associated protein 2 (MAP2), in 50-microns vibratome sections from immersion-fixed slices. These studies confirm the induction of c-fos and hsp72 mRNAs during routine incubation, as previously observed in hippocampal slices obtained with a tissue chopper and incubated under somewhat different conditions, indicating that such responses are likely to be common features of many slice preparations. Accumulation of Fos and Jun immunoreactivities in neurons and glia was generally consistent with the distribution of c-fos mRNA induction observed in slices, and the neuronal component of this response was comparable to the expression of these proteins observed after transient ischemia in vivo. MAP2 immunoreactivity detected in the dendritic processes of neurons tended to show an increase in staining intensity during slice incubation, although loss of dendritic staining in specific regions was occasionally observed in association with the absence of Fos and Jun expression and histological evidence of neuron damage. These results support the use of MAP2 immunoreactivity as a sensitive indicator of neuronal integrity in slices.(ABSTRACT TRUNCATED AT 250 WORDS)