Protein synthesis and energy metabolism in hippocampal slices during extended (24 hours) recovery following different periods of ischemia

Cerebrolysin enhances spinal cord conduction and reduces blood-spinal cord barrier breakdown, edema formation, immediate early gene expression and cord pathology after injury

Spinal cord evoked potentials (SCEP) are good indicators of spinal cord function in health and disease. Disturbances in SCEP amplitudes and latencies during spinal cord monitoring predict spinal cord pathology following trauma. Treatment with neuroprotective agents preserves SCEP and reduces cord pathology after injury. The possibility that cerebrolysin, a balanced composition of neurotrophic factors improves spinal cord conduction, attenuates blood-spinal cord barrier (BSCB) disruption, edema formation, and cord pathology was examined in spinal cord injury (SCI). SCEP is recorded from epidural space over rat spinal cord T9 and T12 segments after peripheral nerves stimulation. SCEP consists of a small positive peak (MPP), followed by a prominent negative peak (MNP) that is stable before SCI. A longitudinal incision (2mm deep and 5mm long) into the right dorsal horn (T10 and T11 segments) resulted in an immediate long-lasting depression of the rostral MNP with an increase in the latencies. Pretreatment with either cerebrolysin (CBL 5mL/kg, i.v. 30min before) alone or TiO₂ nanowired delivery of cerebrolysin (NWCBL 2.5mL/kg, i.v.) prevented the loss of MNP amplitude and even enhanced further from the pre-injury level after SCI without affecting latencies. At 5h, SCI induced edema, BSCB breakdown, and cell injuries were significantly reduced by CBL and NWCBL pretreatment. Interestingly this effect on SCEP and cord pathology was still prominent when the NWCBL was delivered 2min after SCI. Moreover, expressions of c-fos and c-jun genes that are prominent at 5h in untreated SCI are also considerably reduced by CBL and NWCBL treatment. These results are the first to show that CBL and NWCBL enhanced SCEP activity and thwarted the development of cord pathology after SCI. Furthermore, NWCBL in low doses has superior neuroprotective effects on SCEP and cord pathology, not reported earlier. The functional significance and future clinical potential of CBL and NWCBL in SCI are discussed.

Investigation of Synaptic Tagging/Capture and Cross-capture using Acute Hippocampal Slices from Rodents

Synaptic tagging and capture (STC) and cross-tagging are two important mechanisms at cellular level that explain how synapse-specificity and associativity is achieved in neurons within a specific time frame. These long-term plasticity-related processes are the leading candidate models to study the basis of memory formation and persistence at the cellular level. Both STC and cross-tagging involve two serial processes: (1) setting of the synaptic tag as triggered by a specific pattern of stimulation, and (2) synaptic capture, whereby the synaptic tag interacts with newly synthesized plasticity-related proteins (PRPs). Much of the understanding about the concepts of STC and cross-tagging arises from the studies done in CA1 region of the hippocampus and because of the technical complexity many of the laboratories are still unable to study these processes. Experimental conditions for the preparation of hippocampal slices and the recording of stable late-LTP/LTD are extremely important to study synaptic tagging/cross-tagging. This video article describes the experimental procedures to study long-term plasticity processes such as STC and cross-tagging in the CA1 pyramidal neurons using stable, long-term field-potential recordings from acute hippocampal slices of rats.

Creatine protects the immature brain from hypoxic-ischemic injury

OBJECTIVE

We tested the neuroprotective effects of creatine against hypoxic-ischemic injury in the immature brain.

METHODS

Hippocampal slices were prepared from fetal guinea pigs at 0.9 gestation and incubated in artificial cerebrospinal fluid (aCSF) equilibrated with carbogen. Slices were subjected to oxygen-glucose deprivation (OGD) for 30 or 40 minutes. Two hours after OGD, adenosine triphosphate (ATP) and protein synthesis were analyzed. Creatine (3 mM) was applied to tissue slices of the study groups 2 hours before the insult. In a second set of experiments 7-day-old Wistar rats were anesthetized, and the left carotid artery was ligated. After 1 hour of recovery the pups were subjected to a hypoxic gas mixture (8% oxygen and 92% nitrogen) for 80 minutes. Seven days later the brains of the neonates were removed and analyzed for hypoxic-ischemic injury. The rat pups of the test group were treated with creatine (3 g/kg subcutaneously) before (-64 hours, -40 hours, and -16 hours) and after (+3 hours) the hypoxic-ischemic insult, with zero time corresponding to the start of hypoxia, whereas the animals of the control group received the solvent.

RESULTS

Creatine significantly improved the recovery of protein synthesis 2 hours after OGD in hippocampal slices but had no effect on ATP levels. Whereas seven animals of the control group developed severe cystic cerebral infarction, only mild to moderate damage was observed in the rat pups of the study group. In contrast to creatine-treated pups, the volume of the ipsilateral hemisphere was considerably smaller than that of the contralateral one in control animals (104 +/- 22 versus 138 +/- 14 mL, P<.001). Except at the frontal level (A 6.0 mm), neuronal cell injury was significantly lower in the cortex of the animals that had received creatine. This was also true for the evaluated subfields in the hippocampus.

CONCLUSION

We conclude that creatine protects the immature brain from hypoxic-ischemic injury.

Profound molecular changes following hippocampal slice preparation: loss of AMPA receptor subunits and uncoupled mRNA/protein expression

The acute hippocampal slice preparation is a convenient, in vitro model widely used to study the biological basis of synaptic plasticity. Although slices may preserve their electrophysiological properties for several hours, profound molecular changes in response to the injury caused by the slicing procedure are likely to occur. To determine the magnitude and duration of these changes we examined the post-slicing expression kinetics of three classes of genes known to be implicated in long-term synaptic plasticity: glutamate AMPA receptors (GluR), transcription factors and neurotrophins. Slicing resulted in a striking loss of GluR1 and GluR3, but not of GluR2 proteins suggesting that rapid changes in the composition of major neurotransmitter receptors may occur. Slicing caused a significant induction of the transcription factors c-fos, zif268, CCAAT enhancer binding protein (C/EBP ) beta and delta mRNAs and of the neurotrophin brain-derived neurothophic factor (BDNF ) mRNA. In contrast, there was no augmentation, and sometimes a decline, in the levels of the corresponding proteins. These data reveal that significant discrepancies exist between the slice preparation and the intact hippocampus in terms of the metabolism of molecular components known to be involved in synaptic plasticity.

In vitro models of brain ischemia: the peptidergic drug cerebrolysin protects cultured chick cortical neurons from cell death

Glutamate (1 mM), iodoacetate (0.01 mM) and ionomycin (0.25 micro M) are reported to induce several characteristics of ischemia and neuronal degeneration in vitro, e.g. glutamate and ionomycin lesion result in a disturbance of Ca(2+) homeostasis, iodoacetate impairment leads to an inhibition of energy metabolism, suppression of protein synthesis and generation of oxygen free radicals. In this study these three lesion models were used to investigate the effects of the nootropic drug Cerebrolysin (Cere) on the survival of cortical neurons in culture and on the occurrence of apoptosis. The viability of the cells was evaluated with the colorimetric MTT-reduction assay. Apoptosis was detected with Bisbenzimide (Hoechst:33258), a fluorescent DNA stain. Administration of Cere resulted in dose dependent neuroprotection independent from the kind of lesion. In the glutamate model the drug almost doubled neuronal viability compared to lesioned controls. After acute glutamate exposure Cere reduced the number of apoptotic cells significantly. In spite of the protective efficacy after cytotoxic hypoxia induced by iodoacetate, the drug significantly increased the number of apoptotic neurons, indicating a shift from necrosis to apoptosis. In contrast to previous studies investigating acute ionomycin lesions, the chronic Ca(2+)-overload used here did not increase the abundance of apoptosis compared to the unlesioned control. Summarizing the findings it can be suggested that Cere is able to stabilize Ca(2+) homeostasis, to protect protein synthesis and to counteract neuronal death in different in vitro medels of ischemia.

Characterization of promoter function and cell-type-specific expression from viral vectors in the nervous system

Viral vectors have become important tools to effectively transfer genes into terminally differentiated cells, including neurons. However, the rational for selection of the promoter for use in viral vectors remains poorly understood. Comparison of promoters has been complicated by the use of different viral backgrounds, transgenes, and target tissues. Adenoviral vectors were constructed in the same vector background to directly compare three viral promoters, the human cytomegalovirus (CMV) immediate-early promoter, the Rous sarcoma virus (RSV) long terminal repeat, and the adenoviral E1A promoter, driving expression of the Escherichia coli lacZ gene or the gene for the enhanced green fluorescent protein. The temporal patterns, levels of expression, and cytotoxicity from the vectors were analyzed. In sensory neuronal cultures, the CMV promoter produced the highest levels of expression, the RSV promoter produced lower levels, and the E1A promoter produced limited expression. There was no evidence of cytotoxicity produced by the viral vectors. In vivo analyses following stereotaxic injection of the vector into the rat hippocampus demonstrated differences in the cell-type-specific expression from the CMV promoter versus the RSV promoter. In acutely prepared hippocampal brain slices, marked differences in the cell type specificity of expression from the promoters were confirmed. The CMV promoter produced expression in hilar regions and pyramidal neurons, with minimal expression in the dentate gyrus. The RSV promoter produced expression in dentate gyrus neurons. These results demonstrate that the selection of the promoter is critical for the success of the viral vector to express a transgene in specific cell types.

Lipopolysaccharides do not alter metabolic disturbances in hippocampal slices of fetal guinea pigs after oxygen-glucose deprivation

The aim of the present study was to clarify whether endotoxins [lipopolysaccharides (LPS)] have a toxic effect on fetal brain tissue after cerebral ischemia, while excluding their effect on the cardiovascular system. Experiments were therefore performed on hippocampal slices prepared from mature fetal guinea pigs. In particular, we studied the influence of LPS on nitric oxide production, energy metabolism, and protein synthesis after oxygen-glucose deprivation (OGD). Incubating hippocampal slices in LPS (4 mg/L) for as long as 12 h did not alter cGMP tissue concentrations significantly. However, 10 min after OGD of 40-min duration, cGMP tissue concentrations were substantially increased in relation to controls, and this increase was almost completely blocked by the application of 100 microM N:(omega)-nitro-L-arginine, indicating that nitric oxide synthase was activated after OGD in fetal brain tissue. Again, LPS did not have any effect on cGMP tissue concentrations after OGD. Furthermore, addition of LPS altered neither protein synthesis nor energy metabolism measured 12 h after OGD. We therefore conclude that, apart from their well-known influence on the cardiovascular system, LPS do not alter metabolic disturbances in hippocampal slices of fetal guinea pigs 12 h after OGD. A direct toxic effect of LPS on immature brain tissue within this interval does not therefore seem to be very likely. However, delayed activation of LPS-sensitive pathways that may be involved in cell death, or damage limited to a small subgroup of cells such as oligodendrocyte progenitors, cannot be fully excluded.

Effect of induced tolerance on biochemical disturbances in hippocampal slices from the gerbil during and after oxygen/glucose deprivation

To evaluate whether the state of tolerance is stable enough to be studied under in vitro conditions after induction by ischemic preconditioning in vivo, metabolic disturbances of hippocampal slices prepared from control and preconditioned gerbils were evaluated during and after oxygen/glucose deprivation (OGD). Slices were subjected to 5, 10 or 15 min OGD with or without 2h recovery. During the state of metabolic stress, changes in energy metabolism were identical in slices taken from control and preconditioned gerbils. Following OGD, however, recovery of protein synthesis was significantly improved in hippocampal slices of preconditioned animals, indicating that the effect of preconditioning on metabolic disturbances induced by transient OGD in vitro or transient ischemia in vivo is similar. It is suggested that the hippocampal slice preparation is an in vitro model suitable for the study of basic mechanisms underlying the induction of tolerance in vivo.

Alterations in tau phosphorylation in rat and human neocortical brain slices following hypoxia and glucose deprivation

Tau is a microtubule-associated protein which is regulated by phosphorylation. Highly phosphorylated tau does not bind microtubules and is the main component of the paired helical filaments seen in Alzheimer's and related neurodegenerative diseases. Recent reports suggested that patterns of tau phosphorylation changed following ischemia and/or reperfusion in vivo. We used an in vitro model employing rat and human neocortical slices to investigate changes in tau phosphorylation which accompany oxygen and glucose deprivation. Western blotting with polyclonal and phosphorylation-sensitive Tau-1 monoclonal antisera was used to monitor changes in tau which accompanied conditions of oxygen and glucose deprivation and reestablishment of these nutrients. In vitro hypoglycemia/hypoxia caused tau to undergo significant dephosphorylation in both rat and human neocortical slices after 30 and 60 min of deprivation. This dephosphorylation was confirmed using immunoprecipitation experiments after radiolabeling tau and other proteins with 32Pi. Okadaic acid, a phosphatase inhibitor, was able to prevent tau dephosphorylation in both control and ischemic slices. Lubeluzole, a benzothiazole derivative with in vivo neuroprotective activity, did not significantly alter patterns of tau phosphorylation. Restoration of oxygen and glucose following varied periods of in vitro hypoxia/hypoglycemia (15-60 min) led to an apparent recovery in phosphorylated tau. These data suggest that tau undergoes a rapid, but reversible dephosphorylation following brief periods of in vitro hypoxia/hypoglycemia in brain slices and that changes in tau phosphorylation help determine the extent of recovery following oxygen and glucose deprivation.

Cerebrolysin protects isolated cortical neurons from neurodegeneration after brief histotoxic hypoxia

A brief period of histotoxic hypoxia exhibits certain metabolic features resembling the in vivo situation of ischemia. In this study the neuroprotective effects of the peptidergic nootropic drug Cerebrolysin (Cere) against iodoacetate induced histotoxic hypoxia were investigated. For that purpose isolated cortical neurons from 9 day chicken embryos were precultured with 0 to 6.4 mg.Cere/ml medium. At the 8th day in vitro histotoxic hypoxia was induced by incubation with 0.01 or 0.1 mM iodoacetate. Cells were allowed to recover from toxic stress for 3, 6, 24 or 48 hours. Cere protected neurons dose dependently from delayed neuronal cell death due to 0.01 mM iodoacetate even after a recovery period of 48h. After induction of histotoxic hypoxia by 0.1 mM iodoacetate high concentrations of Cere again led to neuronal protection after the 3 and 6 h recovery period. Moreover the influence of Cere on the cytoskeletal protein MAP2 in neurons submitted to 0.01 mM iodoacetate was investigated. With Western blotting and immunohistochemical techniques it has been demonstrated that the drug clearly increased MAP2 abundance after histotoxic hypoxia. The present study points out that after severe damage of cortical neurons with iodoacetate Cere is able to protect neurons from delayed neuronal cell death maybe by maintaining neuronal plasticity due to avoidance of the cytoskeletal breakdown.

Ribonuclease improves the state of hippocampal sections in the post-ischemic period

Living hippocampal slices from Wistar rats were used to study the dynamics of changes in population electrical responses in field CA1 to electrical stimulation of Shaffer collaterals during the development of ischemia (imposed by exclusion of oxygen and glucose from the perfusion solution). These studies showed that during ischemia, addition of ribonuclease (a blocker of protein synthesis) to the perfusion solution resulted in a significantly smaller increase in the latent period of the response and slowed the onset of the reduction in the amplitude of the evoked potential, and promoted faster recovery of the response after the ischemia session ended. It is suggested that the reduction in protein synthesis due to ribonuclease preserved energy reserves in the nerve tissue, which in turn promoted more complete recovery of neuron function in the post-ischemic period.

Metabolic disturbances in hippocampal slices of fetal guinea pigs during and after oxygen-glucose deprivation: is nitric oxide involved?

The aim of this study was to investigate the role of nitric oxide in metabolic disturbances induced in brain tissue of fetal guinea pigs by oxygen-glucose deprivation. Experiments were performed on hippocampal slices so as to exclude the effects of nitric oxide on the cardiovascular system. Metabolic disturbances were assessed by measuring changes in energy metabolism and protein synthesis after different periods of oxygen-glucose deprivation (OGD). Ten min after OGD of 40 min duration, the concentration of cGMP in tissue slices rose from 1.35 +/- 0.38 to 18.6 +/- 1.04 pmol/mg protein (P < 0.05). This rise was almost completely inhibited by the addition of 100 microM N-nitro-L-arginine (NNLA), indicating that NO-synthase was strongly activated after OGD in fetal brain tissue. However, addition of NNLA improved neither protein synthesis nor energy metabolism measured 12 h after OGD. Thus, nitric oxide does not appear to contribute directly to processes leading to metabolic disturbances induced by transient ischemia in immature brain tissue.

Does glutamate mediate brain damage in acute encephalitis?

Cerebrospinal fluid (CSF) amino acid neurotransmitter concentrations in 23 patients with acute encephalitis were compared with those in patients with acute brain infarction, multiple sclerosis and controls. The concentration of glutamate was significantly higher in encephalitis (5.2+/-6.7 micromol/l) and stroke patients (9.6+/-14.2 micromol/l) than in MS patients (1.6+/-0.9 micromol/l) and controls (1.7+/-0.8 micromol/l; p < 0.001). The concentration of glycine was significantly higher in encephalitis (11.0+/-4.7 micromol/l) than in stroke (7.6+/-3.2 micromol/l) and MS patients (6.3+/-2.1 micromol/l) or controls (5.6+/-1.8 micromol/l; p < 0.002). Taurine levels were significantly lower in encephalitis patients than in the other groups (p = 0.04). The correlation of high glutamate levels with poor outcome was almost significant (Kendall tau 0.63, p = 0.06). Our observations suggest that exicitotoxic neurotransmission may play an important role in the series of events that lead to neuronal damage in encephalitis.

No effect of glutamate on metabolic disturbances in hippocampal slices of mature fetal guinea pigs after transient in vitro ischemia

The involvement of glutamate in the development of cerebral metabolic disturbances in mature fetuses after transient ischemia was studied using a hippocampal slice model. We investigated the effects of exogenously applied glutamate or glutamate antagonists on the recovery of energy metabolism and protein synthesis rate (PSR) in hippocampal slices of mature guinea pigs after in vitro ischemia. The slices were incubated in a thermostatically controlled flow-through chamber and gassed with carbogen (95% O2/5% CO2). In vitro ischemia was induced by transferring the slices to an aglycemic, artificial cerebrospinal fluid (aCSF) equilibrated with 95% N2/5% CO2. In a first set of experiments slices were exposed to 10 mM glutamate during a 20-40 min period of in vitro ischemia. In a second set slices were incubated in aCSF containing MK-801 (100 microM) or kynurenic acid (0.5 mM) 30 min before, during and 2 h after in vitro ischemia. After a 12 h recovery phase, the concentrations of adenylates in the slices were measured by HPLC after extraction with perchloric acid. PSR was calculated from the rate of incorporation of [14C]leucine into tissue proteins. Neither glutamate nor glutamate antagonists had any effect on the postischemic recovery of energy metabolism and PSR when applied during in vitro ischemia. It is therefore concluded that glutamate does not play a major role in the development of metabolic disturbances in hippocampal slices from mature guinea pig fetuses subjected to transient in vitro ischemia.

Ontogenetic differences in energy metabolism and inhibition of protein synthesis in hippocampal slices during in vitro ischemia and 24 h of recovery

The present study was designed to clarify whether ontogenetic differences in the vulnerability of the brain towards hypoxic-ischemic insults are only caused by the low cerebral energy demand of immature animals or whether there are additional mechanisms, such as protein synthesis (PSR), that may be involved in this phenomenon. We therefore measured tissue levels of adenylates and PSR in hippocampal slices from immature (E40) and mature (E60) guinea pigs fetuses and from adult guinea pigs during in vitro ischemia and 24 h of recovery using a recently modified method. Hippocampal slices were incubated in a temperature controlled flow-through chamber, gassed with 95% O2/5% CO2. In vitro ischemia was induced by transferring slices to a glucose-free artificial cerebrospinal fluid (aCSF) equilibrated with 95% N2/5% CO2. The duration of ischemia ranged from 10 to 40 min. Adenylates were measured by HPLC after extraction with perchloric acid. PSR was evaluated as the incorporation rate of [14C]leucine into proteins. Under control conditions, tissue levels in adenylates did not change, whereas PSR increased slightly in hippocampal slices from mature fetuses and adult animals during a 24-h control incubation period. In slices from immature fetuses ATP levels were only maintained for 2 h. During in vitro ischemia the decline in ATP, total adenylate pool, and adenylate energy charge was much slower in slices from immature fetuses than in slices from mature fetuses or adults. After in vitro ischemia, ATP and the total adenylate pool did not completely recover in mature fetuses and adults, whereas adenylate energy charge almost returned to control values independently of the developmental stage. Two hours after in vitro ischemia PSR was undisturbed in slices from immature fetuses, but severely inhibited in slices from mature fetuses and adults. With ongoing recovery, PSR in mature fetuses returned to control values, while in adults it was still inhibited even 24 h after in vitro ischemia. From these results we conclude that hippocampal slices prepared from mature guinea pig fetuses as well as from adult guinea pigs can be held metabolically stable during long-term incubation using a recently modified technique. However, in slices from immature fetuses a stable energy state could not be maintained for more than 2 h. We further conclude that postischemic disturbances in PSR closely reflect the ontogenetic changes in the vulnerability of the brain to ischemia and that low energy metabolism is certainly not the only cause of the increased vulnerability of the fetal brain to ischemia.

Comparison of biochemical disturbances in hippocampal slices of gerbil and rat during and after in vitro ischemia

To elucidate the mechanisms of ischemic cell damage, biochemical disturbances developing during and following in vitro ischemia of 5, 10 or 15 min duration were compared in hippocampal slices prepared from gerbil and rat brains. During ischemia the release of glutamate from slices into the medium was determined, and after ischaemia and 10 min of recovery slices were analyzed for ATP levels, adenylate energy charge and cGMP content. The release of glutamate into the medium during in vitro ischemia and the recovery of energy metabolism determined after 10 min of recovery was almost identical in slices prepared from gerbil and rat hippocampi. In contrast, cGMP levels measured 10 min following in vitro ischemia were significantly higher in gerbil as compared to rat slices. Since after 10 min of recovery following in vitro ischemia, cGMP levels reflect nitric oxide (NO) synthesis (inhibition by NO synthase blocker), it is concluded that increased NO synthesis may contribute to the higher sensitivity of the gerbil as compared to the rat hippocampus towards transient ischemia.