scholarly journals Astrocyte membrane structure: changes after circulatory arrest.

1981 ◽  
Vol 88 (3) ◽  
pp. 660-663 ◽  
Author(s):  
D M Landis ◽  
T S Reese
Keyword(s):  
Membrane Structure ◽  
Circulatory Arrest ◽  
Freeze Fracture ◽  
Rapid Freezing ◽  
Normal Numbers ◽  
Membrane Specialization ◽  
Structure Changes ◽  
Glial Membrane ◽  
The Brain

Membranes of the astrocytic processes investing small blood vessels and the surface of the brain contain numerous arrays of orthogonally packed particles as revealed by the freeze-fracture technique. The structure of these particle arrays, which we have termed "assemblies," is the same whether tissue is prepared for freeze-fracture by conventional fixation or by quick excision and rapid freezing. However, assemblies are progressively replaced by amorphous clumps and then disappear as the interval between decapitation and rapid freezing increases. Nearly normal numbers of assemblies may be maintained in cerebellar slices in vitro, but there too they disappear at low PO2 or in the presence of dinitrophenol. No other neuronal or glial membrane specialization exhibits a comparable lability.

Membrane structure in mammalian astrocytes: a review of freeze-fracture studies on adult, developing, reactive and cultured astrocytes

1981 ◽  
Vol 95 (1) ◽  
pp. 35-48
Author(s):  
D. M. Landis ◽  
T. S. Reese
Keyword(s):  
Cerebrospinal Fluid ◽  
Membrane Structure ◽  
Plasma Membranes ◽  
Freeze Fracture ◽  
Brain Parenchyma ◽  
Specific Pattern ◽  
Cultured Astrocytes ◽  
Fluid Compartments ◽  
Polygonal Particle ◽  
The Brain

The application of freeze-fracture techniques to studies of brain structure has led to the recognition of two unsuspected specializations of membrane structure, each distributed in a specific pattern across the surface of astrocytes. ‘Assemblies’ (aggregates of uniform, small particles packed in orthogonal array into rectangular or square aggregates) are found to characterize astrocytic plasma membranes apposed to blood vessels or to the cerebrospinal fluid at the surface of the brain. These particle aggregates are much less densely packed in astrocytic processes in brain parenchyma. Assemblies are not fixation artifacts, have been shown to extend to the true outer surface of the membrane, are remarkably labile in the setting of anoxia, and are at least in part protein. The function of assemblies is unknown, but their positioning suggests that they may have a role in the transport of some material into or out of the blood and cerebrospinal fluid compartments. A second specialization of intramembrane particle distribution, the polygonal particle junction, links astrocytic processes at the surface of the brain, and also links proximal, large caliber astrocytic processes in brain parenchyma. The function of this membrane specialization also is unknown, but it may subserve a mechanical role.

Ultrastructural Investigations of the Contractile Filaments of Amoebae

1974 ◽  
Vol 32 ◽  
pp. 188-189
Author(s):  
P.L. Moore
Keyword(s):  
Cytoplasmic Streaming ◽  
Three Dimensional ◽  
Freeze Fracture ◽  
Amoeboid Movement ◽  
Different Types ◽  
Chemical Conditions ◽  
Complete Interpretation

Previous freeze fracture results on the intact giant, amoeba Chaos carolinensis indicated the presence of a fibrillar arrangement of filaments within the cytoplasm. A complete interpretation of the three dimensional ultrastructure of these structures, and their possible role in amoeboid movement was not possible, since comparable results could not be obtained with conventional fixation of intact amoebae. Progress in interpreting the freeze fracture images of amoebae required a more thorough understanding of the different types of filaments present in amoebae, and of the ways in which they could be organized while remaining functional.The recent development of a calcium sensitive, demembranated, amoeboid model of Chaos carolinensis has made it possible to achieve a better understanding of such functional arrangements of amoeboid filaments. In these models the motility of demembranated cytoplasm can be controlled in vitro, and the chemical conditions necessary for contractility, and cytoplasmic streaming can be investigated. It is clear from these studies that “fibrils” exist in amoeboid models, and that they are capable of contracting along their length under conditions similar to those which cause contraction in vertebrate muscles.

Ultrastructure of melanocyte-keratinocyte interactions and pigment transfer in vitro

1978 ◽  
Vol 36 (2) ◽  
pp. 650-651
Author(s):  
Raul I. Garcia ◽  
Evelyn A. Flynn ◽  
George Szabo
Keyword(s):  
Direct Injection ◽  
Skin Pigmentation ◽  
Freeze Fracture ◽  
Pigment Granule ◽  
Time Lapse ◽  
Ultrastructural Level ◽  
Lanthanum Tracer ◽  
A Cell

Skin pigmentation in mammals involves the interaction of epidermal melanocytes and keratinocytes in the structural and functional unit known as the Epidermal Melanin Unit. Melanocytes(M) synthesize melanin within specialized membrane-bound organelles, the melanosome or pigment granule. These are subsequently transferred by way of M dendrites to keratinocytes(K) by a mechanism still to be clearly defined. Three different, though not necessarily mutually exclusive, mechanisms of melanosome transfer have been proposed: cytophagocytosis by K of M dendrite tips containing melanosomes, direct injection of melanosomes into the K cytoplasm through a cell-to-cell pore or communicating channel formed by localized fusion of M and K cell membranes, release of melanosomes into the extracellular space(ECS) by exocytosis followed by K uptake using conventional phagocytosis. Variability in methods of transfer has been noted both in vivo and in vitro and there is evidence in support of each transfer mechanism. We Have previously studied M-K interactions in vitro using time-lapse cinemicrography and in vivo at the ultrastructural level using lanthanum tracer and freeze-fracture.

Warm and freeze-fracture of cotton seed radicles

1987 ◽  
Vol 45 ◽  
pp. 984-985
Author(s):  
E. L. Vigil ◽  
E. F. Erbe
Keyword(s):  
Thin Film ◽  
Water Vapor ◽  
Fracture Surface ◽  
Membrane Structure ◽  
Room Temperature ◽  
Freeze Fracture ◽  
Longitudinal Axis ◽  
Fracture Plane ◽  
Cotton Seeds ◽  
Condensed Water

In cotton seeds the radicle has 12% moisture content which makes it possible to prepare freeze-fracture replicas without fixation or cryoprotection. For this study we have examined replicas of unfixed radicle tissue fractured at room temperature to obtain data on organelle and membrane structure.Excised radicles from seeds of cotton (Gossyplum hirsutum L. M-8) were fractured at room temperature along the longitudinal axis. The fracture was initiated by spliting the basal end of the excised radicle with a razor. This procedure produced a fracture through the tissue along an unknown fracture plane. The warm fractured radicle halves were placed on a thin film of 100% glycerol on a flat brass cap with fracture surface up. The cap was rapidly plunged into liquid nitrogen and transferred to a freeze- etch unit. The sample was etched for 3 min at -95°C to remove any condensed water vapor and then cooled to -150°C for platinum/carbon evaporation.

Effect of pH and inhibitors on beta-amyloid fibril assembly

1996 ◽  
Vol 54 ◽  
pp. 752-753
Author(s):  
Beverly E. Maleeff ◽  
Timothy K. Hart ◽  
Stephen J. Wood ◽  
Ronald Wetzel
Keyword(s):  
Amyloid Fibril ◽  
Peptide Fragment ◽  
Hydrophobic Peptides ◽  
Amyloid Fibril Formation ◽  
Effects Of Ph ◽  
Severity Of The Disease ◽  
Kinetics Of ◽  
The Brain

Alzheimer's disease is characterized post-mortem in part by abnormal extracellular neuritic plaques found in brain tissue. There appears to be a correlation between the severity of Alzheimer's dementia in vivo and the number of plaques found in particular areas of the brain. These plaques are known to be the deposition sites of fibrils of the protein β-amyloid. It is thought that if the assembly of these plaques could be inhibited, the severity of the disease would be decreased. The peptide fragment Aβ, a precursor of the p-amyloid protein, has a 40 amino acid sequence, and has been shown to be toxic to neuronal cells in culture after an aging process of several days. This toxicity corresponds to the kinetics of in vitro amyloid fibril formation. In this study, we report the biochemical and ultrastructural effects of pH and the inhibitory agent hexadecyl-N-methylpiperidinium (HMP) bromide, one of a class of ionic micellar detergents known to be capable of solubilizing hydrophobic peptides, on the in vitro assembly of the peptide fragment Aβ.

Novel Phospholipid-Based Labrasol Nanomicelles Loaded Flavonoids for Oral Delivery with Enhanced Penetration and Anti-Brain Tumor Efficiency

2020 ◽  
Vol 17 (3) ◽  
pp. 229-245
Author(s):  
Gang Wang ◽  
Junjie Wang ◽  
Rui Guan
Keyword(s):  
Drug Delivery ◽  
Brain Tumor ◽  
Oral Delivery ◽  
Safe Delivery ◽  
Drug Delivery Vehicles ◽  
Therapeutic Benefits ◽  
Delivery Vehicles ◽  
The Brain

Background: Owing to the rich anticancer properties of flavonoids, there is a need for their incorporation into drug delivery vehicles like nanomicelles for safe delivery of the drug into the brain tumor microenvironment. Objective: This study, therefore, aimed to prepare the phospholipid-based Labrasol/Pluronic F68 modified nano micelles loaded with flavonoids (Nano-flavonoids) for the delivery of the drug to the target brain tumor. Methods: Myricetin, quercetin and fisetin were selected as the initial drugs to evaluate the biodistribution and acute toxicity of the drug delivery vehicles in rats with implanted C6 glioma tumors after oral administration, while the uptake, retention, release in human intestinal Caco-2 cells and the effect on the brain endothelial barrier were investigated in Human Brain Microvascular Endothelial Cells (HBMECs). Results: The results demonstrated that nano-flavonoids loaded with myricetin showed more evenly distributed targeting tissues and enhanced anti-tumor efficiency in vivo without significant cytotoxicity to Caco-2 cells and alteration in the Trans Epithelial Electric Resistance (TEER). There was no pathological evidence of renal, hepatic or other organs dysfunction after the administration of nanoflavonoids, which showed no significant influence on cytotoxicity to Caco-2 cells. Conclusion: In conclusion, Labrasol/F68-NMs loaded with MYR and quercetin could enhance antiglioma effect in vitro and in vivo, which may be better tools for medical therapy, while the pharmacokinetics and pharmacodynamics of nano-flavonoids may ensure optimal therapeutic benefits.

Electromagnetic field in Alzheimer’s disease: a literature review of recent preclinical and clinical studies

2020 ◽  
Vol 17 ◽  
Author(s):  
Reem Habib Mohamad Ali Ahmad ◽  
Marc Fakhoury ◽  
Nada Lawand
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Neurodegenerative Disorder ◽  
In Vivo Studies ◽  
Key Factors ◽  
Potential Benefits ◽  
Preclinical And Clinical Studies ◽  
The Brain

: Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by the progressive loss of neurons leading to cognitive and memory decay. The main signs of AD include the irregular extracellular accumulation of amyloidbeta (Aβ) protein in the brain and the hyper-phosphorylation of tau protein inside neurons. Changes in Aβ expression or aggregation are considered key factors in the pathophysiology of sporadic and early-onset AD and correlate with the cognitive decline seen in patients with AD. Despite decades of research, current approaches in the treatment of AD are only symptomatic in nature and are not effective in slowing or reversing the course of the disease. Encouragingly, recent evidence revealed that exposure to electromagnetic fields (EMF) can delay the development of AD and improve memory. This review paper discusses findings from in vitro and in vivo studies that investigate the link between EMF and AD at the cellular and behavioural level, and highlights the potential benefits of EMF as an innovative approach for the treatment of AD.

Serotonin elicits long-lasting enhancement of rhythmic respiratory activity in turtle brain stems in vitro

2001 ◽  
Vol 91 (6) ◽  
pp. 2703-2712 ◽  
Author(s):  
Stephen M. Johnson ◽  
Julia E. R. Wilkerson ◽  
Daniel R. Henderson ◽  
Michael R. Wenninger ◽  
Gordon S. Mitchell
Keyword(s):  
Brain Stem ◽  
Respiratory Activity ◽  
Dependent Manner ◽  
Frequency Increase ◽  
Burst Frequency ◽  
Bath Application ◽  
Burst Amplitude ◽  
Dose Dependent ◽  
The Brain

Brain stem preparations from adult turtles were used to determine how bath-applied serotonin (5-HT) alters respiration-related hypoglossal activity in a mature vertebrate. 5-HT (5–20 μM) reversibly decreased integrated burst amplitude by ∼45% ( P < 0.05); burst frequency decreased in a dose-dependent manner with 20 μM abolishing bursts in 9 of 13 preparations ( P < 0.05). These 5-HT-dependent effects were mimicked by application of a 5-HT1A agonist, but not a 5-HT1B agonist, and were abolished by the broad-spectrum 5-HT antagonist, methiothepin. During 5-HT (20 μM) washout, frequency rebounded to levels above the original baseline for 40 min ( P < 0.05) and remained above baseline for 2 h. A 5-HT3 antagonist (tropesitron) blocked the post-5-HT rebound and persistent frequency increase. A 5-HT3 agonist (phenylbiguanide) increased frequency during and after bath application ( P < 0.05). When phenylbiguanide was applied to the brain stem of brain stem/spinal cord preparations, there was a persistent frequency increase ( P < 0.05), but neither spinal-expiratory nor -inspiratory burst amplitude were altered. The 5-HT3receptor-dependent persistent frequency increase represents a unique model of plasticity in vertebrate rhythm generation.

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