Morphological changes and stress responses in neurons in cerebral cortex infiltrated by diffuse astrocytoma

Image Analysis Reveals Microstructural and Volumetric Differences in Glioblastoma Patients with and without Preoperative Seizures

Purpose: Seizures related to tumor growth are common in glioma patients, especially in low-grade glioma patients this is often the first tumor manifestation. We hypothesize that there are associations between preoperative seizures and morphologic features (e.g., tumor size, location) and histogram features in patients with glioblastoma (GB). Methods: Retrospectively, 160 consecutive patients with initial diagnosis and surgery of GB (WHO IV) and preoperative MRI were analyzed. Preoperative MRI sequences were co-registered (T2-FLAIR, T1-contrast, DTI) and tumors were segmented by a neuroradiologist using the software ITK-snap blinded to the clinical data. Tumor volume (FLAIR, T1-contrast) and histogram analyses of ADC- and FA-maps were recorded in the contrast enhancing tumor part (CET) and the non-enhancing peritumoral edema (FLAIR). Location was determined after co-registration of the data with an atlas. Permutation-based multiple-testing adjusted t statistics were calculated to compare imaging variables between patients with and without seizures. Results: Patients with seizures showed significantly smaller tumors (CET, adj. p = 0.029) than patients without preoperative seizures. Less seizures were observed in patients with tumor location in the right cingulate gyrus (adj. p = 0.048) and in the right caudate nucleus (adj. p = 0.009). Significant differences of histogram analyses of FA in the contrast enhancing tumor part were observed between patients with and without seizures considering also tumor location and size. Conclusion: Preoperative seizures in GB patients are associated with lower preoperative tumor volume. The different histogram analyses suggest that there might be microstructural differences in the contrast enhancing tumor part of patients with seizures measured by fractional anisotropy. Higher variance of GB presenting without seizures might indicate a more aggressive growth of these tumors.

Aluminum-Induced Synaptic Plasticity Impairment via PI3K-Akt-mTOR Signaling Pathway

Aluminum (Al) is an environmental neurotoxin with extensive exposure by humans, but the molecular mechanism of its toxicity is still unclear. Several studies have indicated that exposure to aluminum can impair learning and memory function. The purpose of this study was to investigate the mechanism of LTP injury and the effect of aluminum exposure on related signal pathways. The results showed that the axonal dendrites of neurons in the hippocampal CA1 area of rats exposed to maltol aluminum showed neuritic beading and the dendritic spines were reduced. This resulted in dose-dependent LTP inhibition and led to impaired learning and memory function in rats. The PI3K-Akt-mTOR pathway may play a crucial role in this process.

Biodistribution and clearance of magnetoelectric nanoparticles for nanomedical applications using energy dispersive spectroscopy

AIM

The biodistribution and clearance of magnetoelectric nanoparticles (MENs) in a mouse model was studied through electron energy dispersive spectroscopy.

MATERIALS & METHODS

This approach allows for detection of nanoparticles (NPs) in tissues with the spatial resolution of scanning electron microscopy, does not require any tissue-sensitive staining and is not limited to MENs.

RESULTS

The size-dependent biodistribution of intravenously administrated MENs was measured in vital organs such as the kidneys, liver, spleen, lungs and brain at four different postinjection times including 1 day, 1 week, 4 and 8 weeks, respectively.

CONCLUSION

The smallest NPs, 10-nm MENs, were cleared relatively rapidly and uniformly across the organs, while the clearance of the larger NPs, 100- and 600-nm MENs, was highly nonlinear with time and nonuniform across the organs.

Neuroprotective Effects Against POCD by Photobiomodulation: Evidence from Assembly/Disassembly of the Cytoskeleton

Postoperative cognitive dysfunction (POCD) is a decline in memory following anaesthesia and surgery in elderly patients. While often reversible, it consumes medical resources, compromises patient well-being, and possibly accelerates progression into Alzheimer's disease. Anesthetics have been implicated in POCD, as has neuroinflammation, as indicated by cytokine inflammatory markers. Photobiomodulation (PBM) is an effective treatment for a number of conditions, including inflammation. PBM also has a direct effect on microtubule disassembly in neurons with the formation of small, reversible varicosities, which cause neural blockade and alleviation of pain symptoms. This mimics endogenously formed varicosities that are neuroprotective against damage, toxins, and the formation of larger, destructive varicosities and focal swellings. It is proposed that PBM may be effective as a preconditioning treatment against POCD; similar to the PBM treatment, protective and abscopal effects that have been demonstrated in experimental models of macular degeneration, neurological, and cardiac conditions.

Ki-67 is a valuable prognostic factor in gliomas: evidence from a systematic review and meta-analysis

Ki-67 has been widely used as an indicator of cell proliferation in gliomas. However, the role of Ki-67 as a prognostic marker is still undefined. Thus, we conducted a meta-analysis of the published literatures in order to clarify the impact of Ki-67 on survival in glioma cases. Eligible studies were identified in PubMed, EMBASE, ISI Web of Science, Cochrane Central Register of Controlled Trials, Science Direct and Wiley Online Library with the last search updated on August 31, 2014. The clinical characteristics, overall survival (OS) and progression- free survival (PFS) together with Ki-67 expression at different time points were extracted. A total of 51 studies, covering 4,307 patients, were included in the current meta-analysis. The results showed that overexpression of Ki-67 can predict poor OS (HR=1.66, 95%CI: 1.53-1.80; Z=11.87; p=0.000) and poor PFS (HR=1.67, 95%CI: 1.47-1.91; Z=7.67; p=0.000) in gliomas. Moreover, subgroup analyses also indicated that high level of Ki-67 expression was related to poor OS and PFS in glioma patients regardless of region, pathology type, cut-off value and statistical method. In conclusion, the current meta-analysis revealed that Ki-67 expression might be a predicative factor for poor prognosis of glioma patients, emphasizing its importance as a predictor.

Gap junctions and hemichannels composed of connexins: potential therapeutic targets for neurodegenerative diseases

Microglia are macrophage-like resident immune cells that contribute to the maintenance of homeostasis in the central nervous system (CNS). Abnormal activation of microglia can cause damage in the CNS, and accumulation of activated microglia is a characteristic pathological observation in neurologic conditions such as trauma, stroke, inflammation, epilepsy, and neurodegenerative diseases. Activated microglia secrete high levels of glutamate, which damages CNS cells and has been implicated as a major cause of neurodegeneration in these conditions. Glutamate-receptor blockers and microglia inhibitors (e.g., minocycline) have been examined as therapeutic candidates for several neurodegenerative diseases; however, these compounds exerted little therapeutic benefit because they either perturbed physiological glutamate signals or suppressed the actions of protective microglia. The ideal therapeutic approach would hamper the deleterious roles of activated microglia without diminishing their protective effects. We recently found that abnormally activated microglia secrete glutamate via gap-junction hemichannels on the cell surface. Moreover, administration of gap-junction inhibitors significantly suppressed excessive microglial glutamate release and improved disease symptoms in animal models of neurologic conditions such as stroke, multiple sclerosis, amyotrophic lateral sclerosis, and Alzheimer's disease. Recent evidence also suggests that neuronal and glial communication via gap junctions amplifies neuroinflammation and neurodegeneration. Elucidation of the precise pathologic roles of gap junctions and hemichannels may lead to a novel therapeutic strategies that can slow and halt the progression of neurodegenerative diseases.

The biphasic role of microglia in Alzheimer's disease

Neuroinflammation is involved in the pathogenesis of Alzheimer's disease (AD). Microglia, macrophage-like resident immune cells in the brain, play critical roles in the inflammatory aspects of AD. Microglia may be activated by oligomeric and fibrillar species of amyloid β (Aβ) that are constituents of senile plaques and by molecules derived from degenerated neurons, such as purines and chemokines, which enhance their migration and phagocytosis. The main neurotoxic molecules produced by activated microglia may be reactive oxygen species, glutamate, and inflammatory cytokines such as tumor-necrosis-factor-α and interleukin- (IL-) 1β These molecules differentially induce neurotoxicity. Aβ itself directly damages neurons. In terms of neuroprotective properties, microglia treated with fractalkine or IL-34 attenuate Aβ neurotoxicity by Aβ clearance and the production of antioxidants. Therefore, regulation of the microglial role in neuroprotection may be a useful therapeutic strategy for AD.

Epilepsy in patients with a brain tumour: focal epilepsy requires focused treatment

Brain tumours frequently cause epileptic seizures. Medical antiepileptic treatment is often met with limited success. Pharmacoresistance, drug interactions and adverse events are common problems during treatment with antiepileptic drugs. The unpredictability of epileptic seizures and the treatment-related problems deeply affect the quality of life of patients with a brain tumour. In this review, we focus on both clinical and basic aspects of possible mechanisms in epileptogenesis in patients with a brain tumour. We provide an overview of the factors that are involved in epileptogenesis, starting focally at the tumour and the peritumoral tissue and eventually extending to alterations in functional connectivity throughout the brain. We correlate this knowledge to the known mechanisms of antiepileptic drugs. We conclude that the underlying mechanisms of epileptogenesis in patients with a brain tumour are poorly understood. The currently available antiepileptic drugs have little to no influence on the known epileptogenic mechanisms that could contribute to the poor efficacy. Better understanding of focal changes that are involved in epileptogenesis may provide new tools for optimal treatment of both the seizures and the underlying tumour. In our opinion, therapy for every patient with a brain tumour suffering from epilepsy should first and foremost aim at eliminating the tumour as well as the epileptic focus through resection combined with postoperative treatment, and only if this strategy does not result in adequate seizure control should medical antiepileptic treatment be intensified. If this strategy, however, results in sustained seizure freedom, tapering of antiepileptic drugs should be considered in the long term.

Functional organization of dendritic Ca2+ signals in midbrain dopamine neurons

Dendritic Ca2+ plays an important role not only in synaptic integration and synaptic plasticity, but also in dendritic excitability in midbrain dopamine neurons. However, the functional organization of dendritic Ca2+ signals in the dopamine neurons remains largely unknown. We therefore investigated dendritic Ca2+ signals by measuring glutamate-induced Ca2+ increases along the dendrites of acutely isolated midbrain dopamine neurons. Maximal doses of glutamate induced a [Ca2+]c rise with similar amplitudes in proximal and distal dendritic regions of a dopamine neuron. Glutamate receptors contributed incrementally to the [Ca2+]c rise according to their distance from the soma, with a reciprocal decrement in the contribution of voltage-operated Ca2+ channels (VOCCs). The contribution of AMPA and NMDA receptors increased with dendritic length, but that of metabotropic glutamate receptors decreased. At low doses of glutamate at which spontaneous firing was sustained, the [Ca2+]c rise was higher in the distal than the proximal regions of a dendrite, possibly due to the increased spontaneous firing rate. These results indicate that functional organization of Ca2+ signals in the dendrites of dopamine neurons requires different combination of VOCCs and glutamate receptors according to dendritic length, and that regional Ca2+ rises in dendrites respond differently to applied glutamate concentration.

Rapid dendritic and axonal responses to neuronal insults

Glutamate is the major excitatory neurotransmitter in the mammalian central nervous system playing critical roles in basal synaptic transmission and mechanisms of learning and memory. Under normal conditions, glutamate is sequestered within synaptic vesicles (approximately 100 mM) with extracellular glutamate concentrations being limited (<1 microM), via retrieval by plasma-membrane transporters on neuronal and glial cells. In the case of central nervous system trauma, stroke, epilepsy, and in certain neurodegenerative diseases, increased concentrations of extracellular glutamate (by vesicular release, cell lysis and/or decreased glutamate transporter uptake/reversal) stimulate the overactivation of local ionotropic glutamate receptors that trigger neuronal cell death (excitotoxicity). Other natural agonists, such as domoic acid, alcohol and auto-antibodies, have also been reported to induce excitotoxicity.

DIFFUSION TENSOR TRACTOGRAPHY

OBJECTIVE

Benign extracerebral lesions such as meningiomas may cause hemiparesis by compression and deviation without infiltrating the white matter. We used magnetic resonance diffusion tensor imaging and diffusion tensor tractography to investigate the effects of benign extracerebral lesions on the corticospinal tract (CST).

METHODS

Thirteen patients with extracerebral lesions (11 benign meningiomas and 2 benign cysts) underwent magnetic resonance diffusion tensor imaging and diffusion tensor tractography of the CST using fiber assignment by continuous tractography. The CST was reconstructed and assessed by comparing the ipsilateral and unaffected contralateral fibers. The tumor volume, relative fractional anisotropy, fiber deviation, relative fiber number, and relative fiber per voxel were compared between patients without and with temporary presurgical hemiparesis.

RESULTS

Seven patients without hemiparesis and five patients with temporary hemiparesis were analyzed; one patient had permanent weakness and was excluded from analysis. There was no significant difference in the tumor volume, relative fractional anisotropy, presence of cerebral edema, or CST deviation between groups. In patients with temporary hemiparesis, the median relative fiber number (mean, 0.35 ± 0.32) and relative fiber per voxel (mean, 0.49 ± 0.14) were significantly reduced compared with patients without hemiparesis (0.92 ± 0.55, P = 0.04; and 0.96 ± 0.28, P &lt; 0.01, respectively).

CONCLUSION

In patients with benign extracerebral lesions, reduction in fiber number and fiber per voxel, but not fiber deviation, correlated with temporary hemiparesis. Clinical recovery was possible even if the CST fibers detected by diffusion tensor tractography were reduced by benign extracerebral lesions.

Sensorimotor deficits associated with brain tumor progression and tumor-induced brain plasticity mechanisms

The objective of this study was to investigate functional deficits and reactive peri-tumoral brain plasticity events in glioma-bearing rats. 9L gliosarcoma cells were implanted into the forelimb region of the sensorimotor cortex in Fischer rats. Control animals underwent the same operation without tumor implantation. Sensitive tests for detecting sensorimotor dysfunction, including forelimb-use asymmetry, somatosensory asymmetry, and vibrissae-evoked forelimb placing tests, were conducted. We found that tumor-bearing animals exhibited significant composite behavioral deficits on day 14 post-tumor injection compared to surgical controls. With the assistance of magnetic resonance imaging, we demonstrated a significant correlation between tumor volume and magnitude of somatosensory asymmetry, indicating that the somatosensory asymmetry test can provide an effective and efficient means to measure and predict tumor progression. Histopathological assessments were performed after the rats were sacrificed 14 days following tumor implantation. Immunostaining revealed that densities of microtubule-associated protein 2, glial fibrillary acid protein, von Willebrand factor, and synaptophysin were all significantly upregulated in the peri-tumoral area, compared to the corresponding region in surgical controls, suggesting synaptic plasticity, astrocyte activation and angiogenesis in response to tumor insult. Understanding the behavioral and bystander cellular events associated with tumor progression may lead to improved evaluation and development of new brain tumor treatments that promote, or at least do not interfere with, functional adaptation.

Roles of volume-sensitive chloride channel in excitotoxic neuronal injury

Excitotoxicity is associated with stroke, brain trauma, and a number of neurodegenerative disorders. In the brain, during excitotoxic insults, neurons undergo rapid swelling in both the soma and dendrites. Focal swellings along the dendrites called varicosities are considered to be a hallmark of acute excitotoxic neuronal injury. However, it is not clear what pathway is involved in the neuronal anion flux that leads to the formation and resolution of excitotoxic varicosities. Here, we assessed the roles of the volume-sensitive outwardly rectifying (VSOR) Cl- channel in excitotoxic responses in mouse cortical neurons. Whole-cell patch-clamp recordings revealed that the VSOR Cl- channel in cultured neurons was activated by NMDA exposure. Moreover, robust expression of this channel on varicosities was confirmed by on-cell and nystatin-perforated vesicle patch techniques. VSOR channel blockers, but not blockers of GABA(A) receptors and Cl- transporters, abolished not only varicosity resolution after sublethal excitotoxic stimulation but also necrotic death after sustained varicosity formation induced by prolonged NMDA exposure in cortical neurons. The present slice-patch experiments demonstrated, for the first time, expression of the VSOR Cl- channels in somatosensory pyramidal neurons. NMDA-induced necrotic neuronal death in slice preparations was largely suppressed by a blocker of the VSOR Cl- channel but not of the GABA(A) receptor. These results indicate that VSOR Cl- channels exert dual, reciprocal actions on neuronal excitotoxicity by serving as major anionic pathways both for varicosity recovery after washout of an excitotoxic stimulant and for persistent varicosity formation under prolonged excitotoxic insults leading to necrosis in cortical neurons.

Therapeutic aspects of chaperones/heat-shock proteins in neuro-oncology

Tumors of the CNS frequently have devastating consequences in terms of cognitive and motor function, personality and mortality. Despite decades of work, current therapies have done little to alter the course of these deadly diseases. The discovery that chaperones/heat-shock proteins play an important role in tumor biology and immunology have sparked much interest in utilizing these proteins as targets of therapeutics, or as therapeutics themselves, in the treatments of a variety of cancers. Neuro-oncology has only recently taken notice of these entities, and the purpose of this review is to provide a background, an update and a view to the future for the roles of chaperones/heat-shock proteins in the treatment of brain tumors.

Neuritic beading induced by activated microglia is an early feature of neuronal dysfunction toward neuronal death by inhibition of mitochondrial respiration and axonal transport

Recent studies suggest that excitotoxicity may contribute to neuronal damage in neurodegenerative diseases including Alzheimer disease, Parkinson disease, amyotrophic lateral sclerosis, and multiple sclerosis. Activated microglia have been observed around degenerative neurons in these diseases, and they are thought to act as effector cells in the degeneration of neural cells in the central nervous system. Neuritic beading, focal bead-like swellings in the dendrites and axons, is a neuropathological sign in epilepsy, trauma, ischemia, aging, and neurodegenerative diseases. Previous reports showed that neuritic beading is induced by various stimuli including glutamate or nitric oxide and is a neuronal response to harmful stimuli. However, the precise physiologic significance of neuritic beading is unclear. We provide evidence that neuritic beading induced by activated microglia is a feature of neuronal cell dysfunction toward neuronal death, and the neurotoxicity of activated microglia is mediated through N-methyl-d-aspartate (NMDA) receptor signaling. Neuritic beading occurred concordant with a rapid drop in intracellular ATP levels and preceded neuronal death. The actual neurite beads consisted of collapsed cytoskeletal proteins and motor proteins arising from impaired neuronal transport secondary to cellular energy loss. The drop in intracellular ATP levels was because of the inhibition of mitochondrial respiratory chain complex IV activity downstream of NMDA receptor signaling. Blockage of NMDA receptors nearly completely abrogated mitochondrial dysfunction and neurotoxicity. Thus, neuritic beading induced by activated microglia occurs through NMDA receptor signaling and represents neuronal cell dysfunction preceding neuronal death. Blockage of NMDA receptors may be an effective therapeutic approach for neurodegenerative diseases.