Electron microscopy of two subcellular fractions isolated from cerebral cortex homogenate

The sporulation process in Bacillus subtilis has been studied principally with KMnO(4) fixation, but also, for the purpose of comparison, with OsO(4) and mixtures of both fixatives. At a very early stage, the pre-spore is seen to consist of what seems to be the nuclear material and granular substance, surrounded by a layer of dense material destined to become the innermost layer of the spore coat. At a subsequent stage, a light interspace is observed that is destined to become the spore cortex. The mature spore shows a very complex structure. The spore coat is composed of three layers, the middle layer of which consisted of 5 to 8 lamellae of thin membranes and interspaces, both about 20 to 25 A thick. Between the inner layer of the spore coat and the spore cortex, a thin membrane with an affinity to the cortex can be observed. The spore coat is enclosed within two envelopes, one loosely surrounding the core, and the other adhering to it. The process of spore maturation has been studied in detail. Certain peculiar cellular structures have been observed that seemed to represent features of abnormal sporulation processes.     

Cellular events during partial cerebral ischemia. I. Electron microscopy of feline cerebral cortex after middle-cerebral-artery occlusion.

The feline right cerebral hemisphere was subjected to regional (incomplete) ischemia after clipping the middle cerebral artery for 5, 10, 15, 30 or 60 min, respectively. After each ischemic episode, a 10-min recirculation period was allowed, following which the brain was fixed and processed for electron microscopy. The earliest alterations, detected in the cerebral cortex after 15 min, increased in severity with longer ischemic episodes and were distributed multifocally. There was: (a) marked neuronal mitochondrial matrical swelling and progressive condensation of cytoplasm and nucleoplasm; (b) cytoplasmic swelling of astrocytes with preservation of glial mitochondrial volume; (c) capillaries, oligodendrocytes, myelin sheaths and axis cylinders did not change significantly, even after the longest interval studied: 60 min. This type of tissue reaction appears to be common for those forms of cerebral ischemia, in which circulation is either sustained partially (via collateral arteries) or restored after a period of absolute ischemia. Under these conditions, as yet undefined permeability changes in cell membranes lead to pronounced volumetric alterations of cellular compartments. Although no softening is detectable by digital examination, we suggest that such a set of structural abnormalities constitutes encephalomalacia, or the earliest stage of a lesion which is designated infarction, once it reaches irreversibility.     

Electron microscopic-cytochemical study of the effect of vinblastine on synaptosome adenylate cyclase in the rat cerebral cortex

Adenylate cyclase activity was demonstrated by means of electron microscopic cytochemistry in rat cortical synaptosomes incubated under various conditions. It was found that vinblastine caused remarkable changes in the reaction product localization: the limiting membrane reaction diminished, but the number of synaptosomes were seen to contain a course granular precipitate filling up almost the whole presynaptic cytoplasm. The regulatory role the microtubules play in the distribution of adenylate cyclase on cellular membrane is discussed.     

Spontaneous electrical activity of the rat cerebral cortex during microwave irradiation

A study was made of changes in spontaneous electrical activity of rat brain cortex induced by a single exposure to microwave radiation (electromagnetic fields of 0.1, 1.0, 10, and 35 mW/cm2). The animals were exposed in anechoic chambers to continuous waves at 2450 MHz in conditions of continuous generation. The data obtained indicate that the EEG parameters change under the effect of microwave radiation. The technique applied permits to study the occurrence and development of the CNS reactions to microwave radiation at the time of action of the factor.     

Dynamics of changes in the ultrastructure of the rat cerebral cortex in the early period of acute radiation sickness caused by neutron irradiation

A 24-hour electron microscopic examination of neuronal and capillary ultrastructure in sensorimotor complex was performed after whole-body neutron irradiation of mature rats in the dose of 10 Gy. The results suggest that postradiation neuronal changes, observed for 6 hours after irradiation, are mainly caused by direct effect of ionizing radiation. At later terms this process is influenced by blood capillary lesions. The effect of neutron irradiation at the ultrastructural level is similar to that of rarely ionizing radiation.     

Late effects of irradiation on the cerebral cortex ultrastructure of the rat]

The glial population balance is significantly disturbed by low dose X-rays even after a very short time following irradiation. The effects are able to persist for a large period of time and may possibly be involved in the onset of late radionecrosis phenomena, often noted as consequences of therapeutic irradiation in brain.     

Electron microscopic evidence for the existence of an intercellular substance in rat cerebral cortex

Summary The intercellular spaces of rat cerebral cortex are filled with a dense material, demonstrable by electron microscopy. This intercellular substance is in part preserved by chemical fixation with formaldehyde and osmium tetroxide but is solubilized and largely lost during subsequent dehydration with ethyl alcohol. Dehydration with acetone or Durcupan favors the preservation of the intercellular substance, which is preserved also by freezing and drying. Whether the intercellular substance demonstrated here is part of the outer leaflets of apposing plasma membranes (glycocalyx) or truly an intercellular substance similar to connective tissue ground substance is not known. The probability of the latter is discussed with regard to proposed physiological mechanisms.This work was supported by USPHS Research Grants NB 05175 and AM 06998.     

Electron autoradiographic study of RNA synthesis in cerebral cortex neurons in burns

RNA synthesis in neuronal nucleoli of the rat cerebral cortex was studied by electron microscopic autoradiography in rats before and 1, 12 h, 3 and 6 days after burn injury. It was ascertained that the rate of RNA synthesis begins increasing rapidly after burn injury (1 h) and reaches high level after 12 h. The decrease in the rate of RNA synthesis proceeds more slowly than the increase. This rate does not return to normal even by the close of day 6 following injury.     

Freeze-etching study of synaptosomes from rat cerebral cortex

Synaptosomes from rat cerebral cortex were studied using the freeze-etching technique. The intra-membranous structure of the pre- and postsynaptic membranes was examined. Particles with an electron-dense spot on their apex are reported from all fracture faces. Most probably these are related to transmembrane channels whose significance in the synaptic transmission is discussed.     

Electron microscopy of the medial cortex in the lizard Psammodromus algirus

The medial cortex of Psammodromus presents a three-layer organization. Most of the cell bodies are localized in a compact lamina, the cellular layer. Two plexiform layers, superficial and deep, enclose the cellular layer. The most external portion of the superficial plexiform layer is formed by a limiting glial sheet consisting of tanycytic processes that reach the surface of the cortex. Astrocytes are localized close to the glial sheet. There are two types of axon terminals within the superficial plexiform layer: type S with spheric vesicles and type F with pleomorphic vesicles. Large solitary neurons are present at middle levels of the layer. In the cellular layer there are three neuronal types: large neurons with dispersed chromatin, neurons of medium size with chromatin clumps, and electron-dense neurons. Protoplasmic astrocytes are found superficially in this layer. In the deep plexiform layer numerous neuronal cell bodies are visible, and three types can be distinguished: horizontal fusiform cells, globous neurons with indented nuclei, and electron-dense neurons. Protoplasmic astrocytes are present throughout this layer. Oligodendrocytes are more frequent in the inner third of the layer, often related to fibers of a thick fascicle running in contact with the ependyma, the alveus. The ependyma is formed by a single row of prismatic cells bordering the lateral ventricle.     

Electron microscopic cytochemical and morphometric study of the cerebral cortex synapses in postmortem autolysis

Brain tissue staining with phosphotungstic acid was performed to assay neurofilament accumulations in synapses in the molecular layer of the rat cerebral cortex at different intervals after the animals' death. It was found that autolysis began in the dense projections of presynaptic grid. Within 30 min autolysis developed in mature and very young (immature) synapses. By the 90th min autolysis in asymmetric synapses was considerably enhanced. 6 hours later autolysis involved mature and indefinite synapses.