Increase in Specific Proteins and mRNAs Following Transient Anoxia - Aglycaemia in Rat CA1 Hippocampal Slices

Oxidative-stress-induced alterations in Sp factors mediate transcriptional regulation of the NR1 subunit in hippocampus during hypoxia

Ascent to high altitude is associated with tissue hypoxia resulting from the decrease in partial pressure of atmospheric oxygen. The hippocampus, in particular, is highly vulnerable to hypoxic insult, which at least in part can be attributed to the occurrence of glutamate excitotoxicity. Although this excitotoxic damage is often related to increased NMDA receptor activation and subsequent calcium-mediated free radical generation, the mechanisms involving the transcriptional regulation of NMDA receptor subunit expression by hypoxic stress remains to be explored. Our study reveals a novel mechanism for the regulation of expression of the NR1 subunit of NMDA receptors by the Sp family of transcription factors through an oxidative-stress-mediated mechanism that also involves the molecular chaperone Hsp90. The findings not only show the occurrence of lipid peroxidation and DNA damage in hippocampal cells exposed to hypoxia but also reveal a calcium-independent mechanism of selective oxidation and degradation of Sp3 by the 20S proteasome. This along with increased DNA binding activity of Sp1 leads to NR1 upregulation in the hippocampus during hypoxic stress. The study therefore provides evidence for free radical-mediated regulation of gene expression in hypoxia and the scope of the use of antioxidants in preventing excitotoxic neuronal damage during hypoxia.

Cycloheximide Reduces the Effects of Anoxic Insult In Vivo and In Vitro

In vivo and in vitro techniques were utilized to examine the influence of a protein synthesis blocker, cycloheximide (CHX), on the damaging effects of anoxia in the rat. CHX administered 1 h before transient (30 min) forebrain ischaemia increased the survival of animals, decreased body weight loss and reduced the occurrence of delayed degeneration in the CA1 pyramidal region. The same dose of CHX injected 1 h after ischaemia induced status epilepticus, a decrease in survival rate, and did not reduce weight loss or CA1 damage in any of the surviving rats. Electrophysiological techniques were then used to determine the effects of various periods of anoxia and aglycaemia (AA) on CA1 field excitatory postsynaptic potentials (EPSPs) in hippocampal slices incubated in the presence or absence of CHX. In CHX-treated slices, recuperation of EPSP amplitude (45 +/- 16%) was significantly greater than in control slices (9 +/- 9%) following an AA episode of 3 min 45 s. No difference was seen in the percent recuperation of EPSPs in the control and CHX-treated slices after shorter or longer episodes of AA. From these studies, it appears that CHX protects against the damaging effect of ischaemia in vivo or AA in vitro.

Regulation of pp60(c-src) synthesis in rat hippocampal slices by in vitro ischemia and glucocorticoid administration

Corticosteroids, released from the adrenal gland in response to stress, bind to receptors that act as transcription factors to alter gene expression and, subsequently, protein synthesis. Using [(35)S]-methionine-cysteine incorporation to measure protein synthesis in hippocampal slices incubated under ischemic conditions, synthesis of 60 kDa and 78 kDa proteins decreases 4 hr after in vivo administration of corticosterone to rats. The former protein has been identified by immunoblotting and immunoprecipitation to be the proto-oncogene, pp60(c-src). In the absence of prior glucocorticoid administration, ischemic conditions increase the amount of immunoreactive pp60(c-src) in membranes of hippocampal slices. Chronic exposure to elevated titers of glucocorticoids has been demonstrated to result in cell loss as well as in reduced neuronal plasticity and regeneration. Given the involvement of pp60(c-src) in synaptic plasticity and cell growth, glucocorticoid-mediated reduction in its synthesis is a potential molecular marker for stress-induced alterations in brain function.

Impairment of synaptic transmission by transient hypoxia in hippocampal slices: improved recovery in glutathione peroxidase transgenic mice

There is increasing evidence that oxygen free radicals contribute to ischemic brain injury. It is unclear, however, to what extent specific antioxidant enzymes can prevent or reverse the impairment of synaptic function caused by transient hypoxia. In this study, we investigated in transgenic (Tg) mice whether a moderate increase in glutathione peroxidase-1 (GPx1) may improve the capacity of CA1 pyramidal cells to recover synaptic transmission after a short period of hypoxia in vitro. In control hippocampal slices, transient hypoxia (7-9 min) produced irreversible loss of excitatory postsynaptic potentials. Complete recovery of synaptic transmission was observed with homozygous Tg-MT-GPx-6 mice after reoxygenation, and, after repeated episodes of hypoxia, synaptic transmission was still viable in most Tg slices, in contrast to non-Tg slices. Moreover, hypoxic episodes abolished the capacity of hippocampal slices to generate long-term potentiation in area CA1 of control mice, whereas a significant extent of long-term potentiation expression was still preserved in Tg tissues. We also demonstrated that susceptibility to N-methyl-d-aspartate-mediated oxidative injury was reduced in Tg hippocampal slices. In conclusion, our results suggest that a moderate GPx increase can be sufficient to prevent irreversible functional damage produced by transient hypoxia in the hippocampus and to help maintain basic electrophysiological mechanisms involved in memory formation.

AP1 transcriptional factor activation and its relation to apoptosis of hippocampal CA1 pyramidal neurons after transient ischemia in gerbils

The cellular processes with a potential to lead to delayed death of neurons following transient (5 min) ischemia in gerbil hippocampus were evaluated. Neuronal apoptosis, visualized by the terminal transferase dUTP nick-end labelling (TUNEL) reaction, selectively appeared in the CA1 region of the pyramidal cell layer between the third and fourth days after the insult. Concomitantly, an enhanced immunoreactivity to anti-cJun/AP1 (N) antibody as a major component of activator protein 1 (AP1) transcriptional factor was observed in CA1 neurons. In contrast, in the early postischemic phase, the cJun/AP1 reaction was noticed in numerous neurons and glia-like cells of the CA2/CA3 region, hilus of the dentate gyrus, and region of mossy fiber terminals. In parallel, hippocampal protein binding to AP1, measured by the electrophoretic mobility shift assay (EMSA), showed biphasic enhancement at 3 and then 72-120 hours after ischemia. Supershifts, with antibodies against c-Fos and phospho-c-Jun constituencies of the AP1 dimer, revealed an increased amount of phosphorylated c-Jun in the late postischemic phase. Collectively, these results suggest diversity of AP1 complex function, regulated by its dimer composition as well as time and place of expression during postischemic reperfusion. The early, survival-supporting AP1 response, located mainly in ischemia-resistant areas of CA2/3, is followed by the delayed phase, characteristic of massive neuronal apoptosis in CA1 with concomitant increase of phospho-c-Jun in AP1 dimer.

Changes in the calcium dependence of glutamate transmission in the hippocampal CA1 region after brief hypoxia-hypoglycemia

Using the model of hypoxia-hypoglycemia (HH) in rat brain slices, we asked whether glutamate transmission is altered following a brief HH episode. The HH challenge was conducted by exposing slices to a glucose-free medium aerated with 95% N2-5% CO2, for approximately 4 min, and glutamate transmission in the hippocampal CA1 region was monitored at different post HH times. In slices examined </=8 h post HH, CA1 synaptic field potentials are comparable in amplitude to controls, but are less sensitive to experimental manipulations designed to attenuate intracellular Ca2+ signals, as compared with controls. Reducing calcium influx, by applying a nonspecific calcium channel blocker Co2+ or lowering external Ca2+, attenuated CA1 synaptic potentials much less in challenged slices than in controls. Buffering intracellular Ca2+ by bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid-AM (BAPTA-AM) attenuated CA1 synaptic potentials in control but not in slices post HH. Furthermore, minimally evoked excitatory postsynaptic currents displayed a lower failure rate in post-hypoxic CA1 neurons compared with controls. Based on these convergent observations, we suggest that evoked CA1 glutamate transmission is altered in the first several hours after brief hypoxia, likely resulting from alterations in intracellular Ca2+ homeostasis and/or Ca2+-dependent processes governing transmitter release.

Increased cyclin D1 in vulnerable neurons in the hippocampus after ischaemia and epilepsy: a modulator of in vivo programmed cell death?

Several observations suggest that delayed neuronal death in ischaemia, epilepsy and other brain disorders includes an apoptotic component, involving programmed cell death (PCD). PCD is hypothesized to result, in part, from aberrant control of the cell cycle. Because they are instrumental in mitosis, cyclins D are key markers to evaluate whether neurons indeed progress into the cell cycle in situations of pathology. Therefore, we investigated in rat brains, the expression of cyclins D in the delayed neuronal death that occurs following transient global ischaemia and kainate-induced seizures. Following a four-vessel occlusion insult, quantitative in situ hybridization revealed a highly significant and persistent 100% increase of cyclin D1 mRNA in the vulnerable pyramidal neurons of the CA1 hippocampal region. Ischaemia also induced a smaller and transient cyclin D1 mRNA increase in the resistant CA3 area and dentate gyrus. In contrast, the cyclin D2 and D3 mRNAs, expressed constitutively in the adult rat hippocampus, were not upregulated. Following kainate-induced seizures, cyclin D1 mRNA was induced in the vulnerable CA3 region, and to a lesser extent, in non-vulnerable regions. Cyclin D1 immunohistochemistry revealed increased protein levels in the cytoplasm and nucleus of neurons commited to die after ischaemia. Double labelling experiments indicate that cyclin D1 is also expressed in reactive astrocytes but not in microglial cells. Finally, we report that in neurons, cyclin D1 expression peaks before nuclear condensation and the appearance of DNA fragmentation. We propose that cyclin D1, when expressed at high levels in lesioned neurons, may act as a modulator of apoptosis.

Positive correlation between prolonged potentiation of binding of double-stranded oligonucleotide probe for the transcription factor AP1 and resistance to transient forebrain ischemia in gerbil hippocampus

Gel retardation electrophoresis revealed that binding of a radiolabelled double-stranded oligonucleotide probe for the nuclear transcription factor activator protein-1 was markedly potentiated in the CA1 and CA3 subfields and the dentate gyrus of the hippocampus of the gerbils with transient forebrain ischemia for 5 min, which is known to induce delayed death of pyramidal neurons exclusively in the CA1 subfield. The potentiation was transient in the vulnerable CA1 subfield, but persistent up to 18 h in the resistant CA3 subfield and dentate gyrus. However, no significant alteration was detected in endogenous levels of cyclic AMP response element binding protein phosphorylated at serine133 in these three different hippocampal structures 3 h after the reperfusion. On the other hand, hypothermia during ischemia which is known to protect the CA1 subfield against ischemic damages, led to a prolonged elevation of the activator protein-1 binding up to 9 h after the reperfusion in this vulnerable subfield at least in part through expression of c-Fos protein. Moreover, activator protein-1 binding was significantly elevated in the CA1 subfield up to 12 h after forebrain ischemia for 2 min which is shown not to induce marked damages to the vulnerable subfield. These results suggest that prolonged elevation of DNA binding activity of activator protein-1 may be responsible for molecular mechanisms underlying the unique vulnerability and/or resistance of particular subfields to a transient ischemic insult in the gerbil hippocampus.

Use of two-dimensional gel electrophoresis to characterize protein synthesis during neuronal death in cerebellar culture

Two-dimensional gel electrophoresis was performed to further investigate the biochemical changes in protein synthesis observed in two neuronal death models, induced respectively by cytosine arabinoside and glutamate. These drugs induced, respectively, apoptotic and necrotic types of cell death in cerebellar cultures, as previously reported. Most of the proteins showed decreased labeling after toxic exposure, as expected, but some polypeptides showed increased labeling or appeared to be newly synthesized. The identification of these polypeptides and their implication in neuronal death are discussed.

Cloning of multiple chicken FGF1 mRNAs and their differential expression during development of whole embryo and of the lens

Five different 5' untranslated regions (5' UTRs) of FGF1 mRNAs were cloned in chicken. The structure of these transcripts suggests that, as in mammals, distinct 5' untranslated exons are spliced to the first coding exon via alternative splicing and alternative promoter usage. In an attempt to correlate the expression of specific transcripts to distinct biological activities, the distribution of these transcripts in different tissues and during the development of both the whole embryo and the lens was studied. In tissues, we have shown a differential, but not exclusive, expression of these transcripts. In the whole embryo, the expression of one transcript correlates with later developmental processes. In the lens, only two transcripts were detected that are both differently expressed and distributed. These results suggest that the biological properties of FGF1 depend on the expression of specific FGF1 mRNAs. Because these transcripts only differ in their 5' UTRs, they could be involved in distinct translational controls.

Apoptotic features of selective neuronal death in ischemia, epilepsy and gp 120 toxicity

The occurrence of physiological cell death has been known for decades, but interest in the subject was renewed in 1972 when Kerr, Wyllie and Currie described in detail the ultrastructural changes characteristic of dying cells and coined the term apoptosis to describe the process. Cells display a wide variety of morphological changes when dying during development or following a toxic insult. A binary classification scheme suggests that physiologically appropriate death is due to apoptosis and that pathological mechanisms involve necrosis. However, recent studies indicate a potential involvement of apoptotic cell death in ischemia, status epilepticus and HIV-1 infection.

Time course of protein changes following in vitro ischemia in the rat hippocampal slice

Following 5 min in vitro ischemia, total protein synthesis is dramatically and persistently inhibited in neurons in the rat hippocampal slice. This model system was used to explore the responses of individual proteins to this irreversible insult. In vitro ischemia inhibited new protein synthesis of most proteins analyzed; however, the synthesis of a 68/70 kDa protein was substantially stimulated for the first hour after ischemia. By 3 hr postischemia, its synthesis rates were depressed to 60% of control rates. Although the total amounts of most proteins were not significantly depleted for the first few hours after ail ischemic episode, there were several notable exceptions. The levels of HSC73, a constitutively expressed member of the 70 kDa stress protein family, were reduced after in vitro ischemia. In addition, MAP-2 (microtubule-associated protein-2) and alpha-tubulin were depleted in the early hours after the insult, with MAP-2 exhibiting a detectable depletion earlier than tubulin. In contrast, the levels and distribution of a 68 kDa neurofilament protein localized to CA3 pyramidal neurons in the slice, apparently distinct from the band whose new synthesis was stimulated, were not affected by the 5 min in vitro ischemia insult. Thus, the responses of individual proteins to ischemia varied considerably, These individual responses could play an important role in the damage mechanism that is initiated in response to in vitro ischemia.

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)

Modulation of ischemic signal by antagonists of N-methyl-D-aspartate, nitric oxide synthase, and platelet-activating factor in gerbil hippocampus

Cerebral ischemia in the gerbil results in early hippocampal changes, which include transient activation and/or translocation of protein kinase C (PKC), increased enzymatic activity of ornithine decarboxylase (ODC), and elevated DNA binding ability of activator protein-1 (AP1). The time-course of all three of these postischemic responses was found to be almost parallel, peaking at 3 hr after the ischemic insult. The effectiveness of known modulators of postischemic morphological outcome (MK-801, L-NAME, and gingkolides BN 52020 and BN 52021) in counteracting the induction of PKC, ODC, and AP1 formation was tested. These drugs were administrated as followed: MK-801 (a noncompetitive inhibitor of NMDA channel), 0.8 mg/kg i.p., 30 min before ischemia, and 5 min after the insult; L-NAME (competitive inhibitor of NO synthase), 10 mg/kg i.p., 30 min before ischemia, and 5 mg/kg, 5 min after ischemia; BN52020 and BN52021 (inhibitors of platelet-activating factor: PAF receptors) were administered as a suspension in 5% ethanol in water by oral route, 10 mg/kg for 3 days before ischemia. Three of these drugs, MK-801, L-NAME, and BN52021, significantly reduced ischemia-elevated activity of PKC and ODC, whereas AP1 formation was only partially attenuated. Our observations implicate the existence of different mechanism(s) for postischemic PKC and ODC activation, which in turn is engaged in AP1 induction.

Rapid potentiation of DNA binding activities of particular transcription factors with leucine-zipper motifs in discrete brain structures of the gerbil with transient forebrain ischemia

Binding of radiolabeled double stranded oligonucleotide probes for nuclear transcription factors with leucine-zipper motifs, such as activator protein-1 (AP1), cyclic AMP response element binding protein (CREB) and Myc, was unevenly distributed in gerbil brain in a manner peculiar to each factor. Among 3 different hippocampal subfields examined, the dentate gyrus had the highest basal DNA binding activities of AP1 with progressively less potent binding in the CA3 and CA1 subfields. Similarly, the dentate gyrus was highest in the basal binding of probes for both CREB and Myc among the 3 distinct hippocampal subregions. However, transient forebrain ischemia for 5 min induced more potent enhancement of the AP1 binding in the CA1 subfield 4 h after the insult than in the CA3 subfield and dentate gyrus. In contrast, the ischemic injury similarly tripled DNA binding activities of CREB without markedly affecting those of Myc in hippocampal CA1 and CA3 subfields. Binding of the probe for AP1 was also markedly potentiated following ischemia in the thalamus, caudate putamen, frontal cortex and cerebellar cortex in a rank order of decreasing magnitude, while the ischemic insult induced slight but statistically significant potentiation of both CREB and Myc binding in the thalamus without affecting that in other discrete brain regions. These results suggest that expression of AP1 may be a determinant of unique vulnerability and/or resistance to an ischemic insult in the gerbil hippocampus.

Anoxic LTP sheds light on the multiple facets of NMDA receptors

Hippocampal neurones in the CA1 region have become a model system to study the mechanisms of long-term potentiation (LTP) and memory processes. The CA1 region is also highly vulnerable to ischaemic or anoxic episodes which induce a selective and delayed degeneration of pyramidal neurones. In CA1 neurones, anoxic episodes generate a novel form of LTP to which we refer as anoxic LTP. In common with tetanic LTP, the induction of anoxic LTP is voltage- and NMDA receptor-dependent. However, in contrast with tetanic LTP, the expression of anoxic LTP is mediated exclusively by NMDA receptors. These observations suggest that anoxic-ischaemic episodes trigger a switch in favour of NMDA receptor-operated synaptic transmission. We suggest that the multiple forms of NMDA receptor-dependent LTPs are determined by extracellular and intracellular modulatory sites of this receptor.

Increased synthesis of specific proteins during glutamate-induced neuronal death in cerebellar culture

We have previously shown that glutamate-induced neurotoxicity is mediated by a sodium-chloride component and a calcium component in our cerebellar granule cell culture. In order to further characterize these two different components, the time course of neuronal death induced by glutamate (100 microM) in basal solution and in low sodium-chloride solution was studied by morphological and biochemical criteria. As shown by phase-contrast microscopy, cerebellar granule cells exhibited clear neuronal degeneration within 4 h after exposure to this excitotoxin. These morphological changes correlated [35S]methionine incorporation into proteins which rapidly declined during the first hour of treatment. Qualitative change in [35S]methionine incorporation into proteins was further investigated by two-dimensional gel electrophoresis performed after glutamate exposure in basal solution and in low sodium-chloride solution. Most of the proteins showed a decreased labelling after glutamate exposure as expected, but some polypeptides showed an increased labelling or appeared to be newly synthesized. Furthermore, a different pattern of protein synthesis was observed when glutamate exposure was performed in basal solution or in low sodium-chloride solution. The identification of these polypeptides and their implication in the neuronal death are discussed.

Correlation between reactive sprouting and microtubule protein expression in epileptic hippocampus

Temporal lobe epilepsy in both human and rats is associated with a collateral sprouting of hippocampal mossy fibers (i.e. the axons of granule cells). This sprouting generates abnormal recurrent synaptic connections. We previously showed that in the experimental model of temporal lobe epilepsy induced by an intra-amygdaloid injection of kainate, the synaptic remodeling of mossy fibers was preceded by a transient increased expression of alpha-tubulin in granule cells. This suggests that an overproduction of tubulin polymers may be responsible, at least in part, for the elongation and side-branching of mossy fibers, which occurs 12-30 days after seizures. In the present study we show that this increased expression of alpha-tubulin is accompanied by an increased expression of the microtubule-associated proteins MAP2 and TAU. Thus, using in situ hybridization, we observe that MAP2 messenger RNA levels increased in granule cell bodies and dendrites from day 3 to two weeks after kainate treatment. This rise is associated with a concomitant transient increase of MAP2 immunoreactivity in the granule cell dendrites. TAU messenger RNA also increases in granule cell bodies, while TAU immunoreactivity increases in their axons, the mossy fibers. The time course of these changes parallels that of alpha-tubulin, and develops before and during the axonal mossy fiber sprouting. Since MAP2 and TAU are important for the initiation, elongation and stabilization of neurites, we suggest that the overexpression of these proteins via the formation of microtubules may play an important role in the sprouting of mossy fibers in epileptic rats.

Induction of c-fos mRNA expression in an in vitro hippocampal slice model of adult rats after kainate but not gamma-aminobutyric acid or bicuculline treatment

Levels of gene expression following in vitro treatment of rat hippocampal slices with kainate, gamma-aminobutyric acid (GABA), or bicuculline were measured by the reverse transcription-coupled polymerase chain reaction method. Following a short-term exposure to kainate, c-fos gene expression was induced by 12-fold in the adult, but not the newborn, hippocampus. Under the same experimental conditions, zifl268 and brain-derived neurotrophic factor (BDNF) gene expression were unchanged. Our results also demonstrate a lack of induction of c-fos, zifl268 and BDNF after short-time treatment of either adult or newborn hippocampal slices with GABA or bicuculline. The relevance of the differential induction of gene expression in the adult and newborn in an in vitro hippocampal slice model as compared to previously described in vivo models is discussed.

aFGF, bFGF and flg mRNAs show distinct patterns of induction in the hippocampus following kainate-induced seizures

We report that kainic acid-induced seizures lead to marked increases in mRNAs encoding basic and acidic fibroblast growth factors (bFGF and aFGF, respectively) and flg, one of their receptors, in the rat hippocampus. Anticonvulsant pretreatment inhibits the up-regulation of these mRNAs. The observed increase in flg mRNA levels involves the pyramidal cells of all hippocampal subfields and the granular cells of the dentate gyrus. The increased expression of aFGF and bFGF mRNAs is limited to neuron populations that are resistant to seizure-induced injury, the granular cells of dentate gyrus and pyramidal cells of CA1 region, respectively. The results suggest that the increase in the FGFs and flg may play pivotal roles in neuron survival and in long-term changes occurring in the hippocampus following seizure activity.

Acidic fibroblast growth factor is expressed abundantly by photoreceptors within the developing and mature rat retina

In order to further understand the role(s) of fibroblast growth factors (FGFs) in the development, differentiation and function of the central nervous system, we analysed the expression of the mRNA, and the presence and tissue distribution of the translated product, of one member of the FGF family, acidic FGF (aFGF), within the mammalian retina. Firstly, the relative abundance of aFGF mRNA was assayed in embryonic (between 14 and 17 days of gestation), postnatal (between 1 and 17 days after birth) and adult rat retina by quantitative reverse transcription-coupled polymerase chain reaction amplification using specific aFGF oligonucleotides. The level of expression remained uniformly low throughout the embryonic period and until postnatal day 7. Therefore the quantity of aFGF mRNA increased rapidly, reaching 80% of adult levels by eye opening (postnatal day 13). Adult levels were three-fold higher than at early developmental times. In situ hybridization of adult rat retina using specific antisense aFGF riboprobes revealed labelling in all cellular layers. Antisera raised against recombinant human aFGF revealed very little labelling of 4-day postnatal retina, but by postnatal days 8 and 17 immunoreactive aFGF was localized mainly within the photoreceptor cell bodies. Western blots of retinal extracts derived from 17-day embryonic, 4-day postnatal and adult retina probed with the same antibody revealed a single immunoreactive band of the expected molecular weight (18 kDa) in all extracts. Thus aFGF is mostly transcribed and translated within the retina subsequent to the major steps of cell birth, migration and differentiation, and seems to be abundantly expressed by maturing photoreceptor cells.

Regional variability in DNA fragmentation after global ischemia evidenced by combined histological and gel electrophoresis observations in the rat brain

We have studied whether the delayed cell death induced by transient forebrain ischemia is associated with an internucleosomal cleavage of DNA into oligonucleosome-sized fragments. The integrity of genomic DNA in various brain regions after a 20-min four-vessel ischemia was examined using gel electrophoresis. We found typical ladders of oligonucleosomal DNA fragments in the striatum and in the Ammon's horn. In the latter we also often found a random DNA degradation as a smear pattern. These findings were reinforced by a specific in situ labeling of DNA breaks in tissue sections. A dark staining of nuclei was observed in the cell bodies of neurons--in particular in the head of the caudate and in the vulnerable CA1 hippocampal area. With biochemical and histological approaches, there was no evidence of DNA degradation in regions that are resistant to the injury. We conclude that the association of multiple mechanisms of cell damage may occur after a global ischemia. The regional variability in DNA fragmentation stresses the importance of using histological approaches in parallel with gel electrophoresis.

Mossy fiber sprouting in epileptic rats is associated with a transient increased expression of alpha-tubulin

Kainate-induced seizures lead to marked increases of alpha-tubulin mRNA and protein immunoreactivity in the rat dentate gyrus. The increase in alpha-tubulin mRNA was restricted to the granule cell bodies. alpha-Tubulin immunoreactivity was enhanced in granule cell dendrites and axons (the mossy fibers), in the molecular layer. These changes peaked 6-12 days after kainate treatment and preceded the collateral sprouting of mossy fibers which occur 12 to 30 days after seizures. The present results suggest that microtubule formation contributes to the synaptic rearrangements which take place in the hippocampus after seizures.

Glutamate-induced neuronal death is not a programmed cell death in cerebellar culture

Activation of programmed cell death has recently been suggested to be involved in the delayed neuronal death of CA1 hippocampal neurons after global ischemia based on protection offered by protein synthesis inhibitors. Here, we studied the effects of transcriptional (actinomycin D) and translational (cycloheximide and anisomycin) inhibitors on glutamate-induced neuronal death in cerebellar granule cell cultures. The effects of aurintricarboxylic acid, an endonuclease inhibitor, were studied as well. No protection against glutamate toxicity could be observed with any of these inhibitors. We also analyzed the genomic DNA of glutamate-treated cells on agarose gel electrophoresis. No DNA degradation could be observed after glutamate exposure. We conclude that glutamate-induced neuronal death does not exhibit the features of apoptosis in cultured granule cells.

The NMDA receptor contributes to anoxic aglycemic induced irreversible inhibition of synaptic transmission

Percent recovery of CA1 field EPSP amplitude following various anoxic aglycemic (AA) periods was examined in rat hippocampal slices superfused with MK-801 (0.1 microM, 1 microM, 10 microM) or Mg(2+)-free artificial cerebrospinal fluid. Slices treated with 0.1 microM MK-801 showed greater percent recuperation of EPSP amplitude following 3 min 30 s of AA (36 +/- 12% vs 6 +/- 4% in controls). Higher concentrations of MK-801 resulted in a greater recovery of EPSP amplitudes in more than one time period of AA, with 10 microM MK-801 providing protection in up to 4 min 30 s AA. Percent recuperation of EPSP amplitude was smaller in Mg(2+)-free slices following 2 min (34 +/- 15% vs 81 +/- 11% in controls) and 2 min 30 (25 +/- 14% vs 77 +/- 10% in controls) of AA. These results suggest that the activation of the N-methyl-D-aspartate (NMDA) receptor channel may contribute to irreversible AA induced synaptic failure in CA1.