Serial expression of hypoxia inducible factor-1α and neuronal apoptosis in hippocampus of rats with chronic ischemic brain

Selective vulnerability of hippocampal CA1 and CA3 pyramidal cells: What are possible pathomechanisms and should more attention be paid to the CA3 region in future studies?

Transient ischemia and reperfusion selectively damage neurons in brain, with hippocampal pyramidal cells being particularly vulnerable. Even within hippocampus, heterogeneous susceptibility is evident, with higher vulnerability of CA1 versus CA3 neurons described for several decades. Therefore, numerous studies have focused exclusively on CA1. Pediatric cardiac surgery is increasingly focusing on studies of hippocampal structures, and a negative impact of cardiopulmonary bypass on the hippocampus cannot be denied. Recent studies show a shift in selective vulnerability from neurons of CA1 to CA3. This review shows that cell damage is increased in CA3, sometimes stronger than in CA1, depending on several factors (method, species, age, observation period). Despite a highly variable pattern, several markers illustrate greater damage to CA3 neurons than previously assumed. Nevertheless, the underlying cellular mechanisms have not been fully deciphered to date. The complexity is reflected in possible pathomechanisms discussed here, with numerous factors (NMDA, kainate and AMPA receptors, intrinsic oxidative stress potential and various radicals, AKT isoforms, differences in vascular architecture, ratio of pro- and anti-apoptotic Bcl-2 factors, vulnerability of interneurons, mitochondrial dysregulation) contributing to either enhanced CA1 or CA3 vulnerability. Furthermore, differences in expressed genome, proteome, metabolome, and transcriptome in CA1 and CA3 appear to influence differential behavior after damaging stimuli, thus metabolomics-, transcriptomics-, and proteomics-based analyses represent a viable option to identify pathways of selective vulnerability in hippocampal neurons. These results emphasize that future studies should focus on the CA3 field in addition to CA1, especially with regard to improving therapeutic strategies after ischemic/hypoxic brain injury.

The Brain at High Altitude: From Molecular Signaling to Cognitive Performance

The brain requires over one-fifth of the total body oxygen demand for normal functioning. At high altitude (HA), the lower atmospheric oxygen pressure inevitably challenges the brain, affecting voluntary spatial attention, cognitive processing, and attention speed after short-term, long-term, or lifespan exposure. Molecular responses to HA are controlled mainly by hypoxia-inducible factors. This review aims to summarize the cellular, metabolic, and functional alterations in the brain at HA with a focus on the role of hypoxia-inducible factors in controlling the hypoxic ventilatory response, neuronal survival, metabolism, neurogenesis, synaptogenesis, and plasticity.

Time course of cell death due to acoustic overstimulation in the mouse medial geniculate body and primary auditory cortex

It has previously been shown that acoustic overstimulation induces cell death and extensive cell loss in key structures of the central auditory pathway. A correlation between noise-induced apoptosis and cell loss was hypothesized for the cochlear nucleus and colliculus inferior. To determine the role of cell death in noise-induced cell loss in thalamic and cortical structures, the present mouse study (NMRI strain) describes the time course following noise exposure of cell death mechanisms for the ventral medial geniculate body (vMGB), medial MGB (mMGB), and dorsal MGB (dMGB) and the six histological layers of the primary auditory cortex (AI 1-6). Therefore, a terminal deoxynucleotidyl transferase dioxyuridine triphosphate nick-end labeling assay (TUNEL) was performed in these structures 24 h, 7 days, and 14 days after noise exposure (3 h, 115 dB sound pressure level, 5-20 kHz), as well as in unexposed controls. In the dMGB, TUNEL was statistically significant elevated 24 h postexposure. AI-1 showed a decrease in TUNEL after 14 days. There was no statistically significant difference between groups for the other brain areas investigated. dMGB's widespread connection within the central auditory pathway and its nontonotopical organization might explain its prominent increase in TUNEL compared to the other MGB subdivisions and the AI. It is assumed that the onset and peak of noise-induced cell death is delayed in higher areas of the central auditory pathway and takes place between 24 h and 7 days postexposure in thalamic and cortical structures.

A new rodent model of cerebral hyperperfusion

BACKGROUND

Most studies of hyperperfusion and hyperperfusion syndrome after carotid endarterectomy or carotid stenting are based on clinical observation or meta-analyses in patients, whereas there is little corresponding fundamental research since proper animal model that can reproduce phenotype stably is not available. Therefore, we developed a rat model in which the pathophysiologic process of hyperperfusion can be mimicked.

METHODS

Global ischemia was induced by occluding bilateral common carotid arteries (BCAO) for 2 weeks. After that, the ligature was loosened to allow reperfusion. Phenylephrine was administered at concentrations of 10, 20, 30, 40, 50, 80, and 120 μg/mL for rapidly elevating blood pressure. Relative cerebral blood flow in relation to mean arterial pressure (MAP) was measured with Laser Doppler techniques. Sham animals underwent the same surgical operation but without artery-occlusion and received the same concentrations of phenylephrine.

RESULTS

Mild hypertension rapidly increased cerebral blood flow. Phenylephrine at different concentrations produced different effects on blood pressure. Hyperperfusion can be induced by phenylephrine at around 30 μg/mL, whereas phenylephrine at 80 μg/ml or higher induced arrhythmia and further cardiac dysfunction thus failed to induce hyperperfusion.

CONCLUSIONS

Our data suggest that 30-50 μg/mL phenylephrine mildly elevated MAP and cerebral blood flow to the level exceeding 100% of baseline. This hyperperfusion model possesses several advantages including high phenotype reproducibility, low experimental failure rate and low animal mortality rate. It can be applied to study carotid stenosis or ischemia/reperfusion injury in rats.

Immunoreactivity of neurogenic factor in the guinea pig brain after prenatal hypoxia

Chronic prenatal hypoxia is considered to cause perinatal brain injury. It can result in neurological disorders such as cerebral palsy or learning disabilities. These neurological problems are related to chronic placental insufficiency (CPI), which leads to chronic hypoxemia and hypoglycemia. The effects of hypoxia on neurogenesis during development have been a matter of controversy. We therefore investigated the effect of chronic prenatal hypoxia in the brain of the fetal guinea pig using the guinea pig CPI model. Chronic placental insufficiency was induced by unilateral uterine artery ligation at 30-32 days of gestation (dg: with term defined as ∼67dg). At 50 and 60dg, fetuses were sacrificed and assigned to either the growth-restricted (GR) or control (no ligation) group. Immunohistochemistry was performed with HIF-1α, PCNA, NeuN and BDNF antibodies in the cerebral cortex and dentate gyrus. The number of NeuN-IR and BDNF-IR cells was lesser in GR fetuses than in controls in the cerebral cortex and dentate gyrus at 60dg (p<0.05). The growth of the developing brain is dependent upon the availability of growth factors such as BDNF. The reduction in the number of neuronal cells observed in our GR group was associated with the observed reduction in BDNF protein found at 60dg. There was no significant difference between control and GR fetuses in the densities of PCNA-IR cells in the subventricular zone and subgranular zone at 50 and 60dg. These findings suggest that the survival of neurons in the cerebral cortex is decreased by chronic prenatal hypoxia at 60dg.

Protective effects of pulsatile flow during cardiopulmonary bypass

BACKGROUND

Children with congenital heart disease are often operated at a very young age. Cardiopulmonary bypass (CPB) has become indispensable for these sometimes very complex operations, but one cannot neglect a possible negative impact of CPB on organ function. Traditionally, CPB was developed with non-pulsatile flow but there are clinical observations that pulsatile flow might be superior with improved patient outcomes. Therefore, we attempted to elucidate whether CPB with pulsatile flow preserves organ integrity compared with nonpulsatile flow.

METHODS

We studied 27 piglets of 4 weeks age and divided them into 3 experimental groups: control group (no CPB); non-pulsatile and pulsatile-CBP with 90-minutes CPB and 120-minutes recovery and reperfusion. Thereafter, histology of kidney, liver, and hippocampus was performed. Moreover, we measured adenosine triphosphate (ATP) content in these organs.

RESULTS

Histologic evaluation revealed that laminar flow produced significant cellular edema in the kidney and hippocampus. Additionally, markers for hypoxia, apoptosis, and nitrosative stress were elevated but predominately in the hippocampus and proximal tubules of the kidney. Most of these alterations were reduced to or near control levels with pulsatile CPB. Moreover, ATP content of all 3 organs examined was higher and kidney and liver enzymes were lower in the pulsatile group compared with the non-pulsatile CPB. With regard to histologic changes, the liver seemed to be a less sensitive organ.

CONCLUSIONS

In our study during pulsatile CPB, organ damage was significantly attenuated as compared with non-pulsatile CPB. Therefore, in pediatric patients pulsatile CPB may improve clinical outcomes.

Combustion smoke-induced inflammation in the cerebellum and hippocampus of adult rats

AIMS

The effect of combustion smoke inhalation on the respiratory system is widely reported but its effects on the central nervous system remain unclear. Here, we aimed to determine the effects of smoke inhalation on the cerebellum and hippocampus which are areas vulnerable to hypoxia injury.

METHODS

Adult male Sprague-Dawley rats were subjected to combustion smoke inhalation and sacrificed at 0.5, 3, 24 and 72 h after exposure. The cerebellum and hippocampus were subjected to Western analysis for VEGF, iNOS, eNOS, nNOS and AQP4 expression; ELISA analysis for cytokine and chemokine levels; and immunohistochemistry for GFAP/AQP4, RECA-1/RITC and TUNEL. Aminoguanidine (AG) was administered to determine the effects of iNOS after smoke inhalation.

RESULTS

Both the cerebellum and hippocampus showed a significant increase in VEGF, iNOS, eNOS, nNOS and AQP4 expression with corresponding increases in inflammatory cytokines and chemokines and increased AQP4 expression and RITC permeability after smoke exposure. AG was able to decrease the expression of iNOS, followed by VEGF, eNOS, nNOS, RITC and AQP4 after smoke exposure. There was also a significant increase in TUNEL+ cells in the cerebellum and hippocampus which were not significantly reduced by AG. Beam walk test revealed immediate deficits after smoke inhalation which was attenuated with AG.

CONCLUSION

The findings suggest that iNOS plays a major role in the central nervous system inflammatory pathophysiology after smoke inhalation exposure with concomitant increase in proinflammatory molecules, vascular permeability and oedema, for which the cerebellum appears to be more vulnerable to smoke exposure than the hippocampus.

Learning and survival memory undergoing a permanent bilateral carotid ligation in rats

PURPOSE

To evaluate the effect of cerebral hypoxia-ischemia on memory and learning survival of rats submitted to permanent bilateral carotid ligation (PBCL).

METHODS

Twenty-four survivors of PBCL were evaluated after 30 days with regard to memory and learning using a water survival maze. Twenty-three healthy rats were used as control group. The results were expressed by their means and standard error of the mean (SEM). p<0.05 was used for rejecting the null hypothesis. The study was approved by the Ethics Committee for animal investigation.

RESULTS

The mortality rate for the surgery was 44.4%. The latency time to find the survival platform was higher in rats that underwent PBCL (Normal: 10.24 ± 1.85s -

STUDY

25.30 ± 4.69s - Mann - Whitney p=0.0388). Additionally, the type of swimming and the spatial stability of the studied rats on the survival platform were compromised in these animals.

CONCLUSION

The permanent bilateral carotid ligation induces change in the learning and survival memory.

Hypoxia markers are expressed in interneurons exposed to recurrent seizures

An early but transient decrease in oxygen availability occurs during experimentally induced seizures. Using pimonidazole, which probes hypoxic insults, we found that by increasing the duration of pilocarpine-induced status epilepticus (SE) from 30 to 120 min, counts of pimonidazole-immunoreactive neurons also increased (P < 0.01, 120 vs 60 and 30 min). All the animals exposed to SE were immunopositive to pimonidazole, but a different scenario emerged during epileptogenesis when a decrease in pimonidazole-immunostained cells occurred from 7 to 14 days, so that only 1 out of 4 rats presented with pimonidazole-immunopositive cells. Pimonidazole-immunoreactive cells robustly reappeared at 21 days post-SE induction when all animals (7 out of 7) had developed spontaneous recurrent seizures. Specific neuronal markers revealed that immunopositivity to pimonidazole was present in cells identified by neuropeptide Y (NPY) or somatostatin antibodies. At variance, neurons immunopositive to parvalbumin or cholecystokinin were not immunopositive to pimonidazole. Pimonidazole-immunopositive neurons expressed remarkable immunoreactivity to hypoxia-inducible factor 1α (HIF-1α). Interestingly, surgical samples obtained from pharmacoresistant patients showed neurons co-labeled by HIF-1α and NPY antibodies. These interneurons, along with parvalbumin-positive interneurons that were negative to HIF-1α, showed immunopositivity to markers of cell damage, such as high-mobility group box 1 in the cytoplasm and cleaved caspase-3 in the nucleus. These findings suggest that interneurons are continuously endangered in rodent and human epileptogenic tissue. The presence of hypoxia and cell damage markers in NPY interneurons of rats and patients presenting with recurrent seizures indicates a mechanism of selective vulnerability in a specific neuronal subpopulation.