ISSN:0741-0581    

DOI:10.1002/jemt.1060150402

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractIn order to analyze connections between neurons in the vetebrate central nervous system, methods have been developed to label a given population of axons of known origin so that they can be differentiated from other, non‐labeled structures. Three such methods are reviewed here: experimentally induced orthograde (Wallerian) degeneration, axon transport of radioactive proteins demonstrated by autoradiography, and axon transport of macromolecules that can be reacted histochemically to yield a visible reaction product. Each of the methods has particular strengths and weaknesses. Degeneration methods may differentiate between different functional classes of axons which have different fiber diameters. However, degeneration distorts the morphology of axon terminals, making them more difficult to interpret, and degenerating terminals may be removed rapidly by phagocytosis. Autoradiography of radioactive terminals preserves normal fine structure, but the necessary exposure times extend the method by weeks or months, and care must be exercised to distinguish labeled axons from other structures exhibiting background or transneuronal radioactivity. Histochemical methods, such as those used to demonstrate horseradish peroxidase conjugated to wheat germ lectin (WGA‐HRP), are sensitive and rapid, but the injection site must be carefully characterized, and the presence of transneuronal label may make interpretation of the results difficult.Experimental methods of axonal labeling have been invaluable in studying neuronal networks. Each of the methods described here may be of particular value, given the nature of the system to be analy

ISSN:0741-0581    

DOI:10.1002/jemt.1060150403

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractFor more than a century the Golgi method has been providing structural information about the organization of neuronal networks. Recent developments allow the extension of the method to the electron microscopic analysis of the afferent and efferent synaptic connections of identified, Golgi‐impregnated neurones. The introduction of degeneration, autoradiographic, enzyme histochemical, and immunocytochemical methods for the characterization of Golgi‐impregnated neurones and their pre‐and postsynaptic partners makes it possible to establish the origin and also the chemical composition of pre‐and postsynaptic elements. Furthermore, for a direct correlation of structure and function the synaptic interconnections between physiologically characterized, intracellularly HRP‐filled neurones and Golgi‐impregnated cells can be studied. It is thought that most of the neuronal communication takes place at the synaptic junction. In the enterprise of unravelling the circuits underlying the synaptic interactions, the Golgi technique continues to be a powerful tool

ISSN:0741-0581    

DOI:10.1002/jemt.1060150404

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractPhaseolus vulgarisleucoagglutinin (PHA‐L) is a plant lectin that is anterogradely transported by neurons in the central nervous system. PHA‐L is selectively taken up by cells at iontophoretic injection sites and, when immunohistochemically demonstrated, labels individual neurons completely, including their dendrites, axons, and terminal boutons. PHA‐L is generally not taken up by fibers passing through the injection site and, because it produces a Golgi‐like staining of even very fine axons over long distances, it is sometimes possible to light microscopically reconstruct individual neurons and their entire axon terminal arbors. When prepared for electron microscopy, the PHA‐L‐labeled terminals are densely and completely stained, allowing their synaptic relationships to be defined. These properties make PHA‐L advantageous for studying the patterns of projection and the modes of termination of select groups of neurons in their target nuclei.We used PHA‐L to study the extraretinal innervation of the cat's dorsal lateral geniculate nucleus, a thalamic visual center. Although much is known about the retinal contribution to geniculate synaptic circuitry, relatively little is known about other sources of innervation, even though these provide the majority of synaptic terminals in the nucleus (Guillery:Z. Zellforsch., 96:1–38, 39–48, 1969; Wilson et al.:Proc. R. Soc. Lond. [Biol.], 221:441–436, 1984). We used both light and electron microscopy to describe synaptic circuitry from three extraretinal sources of projections to the lateral geniculate nucleus: the visual cortex, the perigeniculate nucleus, and the parabrachial region of the brainstem. Cortical terminals labeled with PHA‐L were small and formed asymmetrical synaptic contacts onto small‐caliber dendrites of geniculate neurons. Peri‐geniculate terminals formed symmetrical synaptic contacts primarily onto small‐caliber dendrites, but some synapses were also formed onto the proximal, retinorecipient portions of geniculate dendrites. Parabrachial terminals synaptically contacted the retinorecipient portions of dendritic appendages and shafts, small‐caliber dendrites, and the specialized dendritic (F2) terminals of geniculate interneurons. The symmetry of the parabrachial synaptic contacts was variable and was related to the postsynaptic target. Contacts onto dendritic appendages were asymmetrical while those onto dendritic shafts and F2 terminals were symmetrical. Our data suggest that in unlabeled material these brainstem terminals would be difficult to distinguish from cortical or perigeniculate profiles. The positioning of the parabrachial input onto the retinorecipient portions of geniculate dendrites indicates that this projection is well situated to control primary retinal transmission through the nucleus, while the location of most cortical and perigeniculate innervations implicates them in secondary feedback interactions or other

ISSN:0741-0581    

DOI:10.1002/jemt.1060150405

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractDuring the past two decades new techniques have been developed to directly test the dogma that neuronal structure is correlated with neuronal function. In the earliest experiments, Procion yellow was injected into neurons after they had been characterized physiologically; these neurons were then viewed through the light microscope. Recent advances in the method generally employ horseradish peroxidase as the dye which is injected since it diffuses quite readily throughout the injected neuron and produces a stable reaction product for both light and electron microscopic studies. This review explores the utility of examining synaptic circuitry after physiologically recording from axons or neurons and then injecting horseradish peroxidase into them. As a model system, we studied the cat lateral geniculate nucleus and investigated, at the electron microscopic level, the synaptic contribution to this nucleus from retinogeniculate axons, from interneurons, and from the axon collaterals of neurons that project to visual cortex.

ISSN:0741-0581    

DOI:10.1002/jemt.1060150406

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractSingle crystal MgO specimens having low load Vickers indentations were thinned in an ion milling machine employing a single ion gun, and their characteristics were investigated with optical microscopy and high voltage electron microscopy (HVEM). It was found that the state of cleanliness of the specimen chamber of the ion milling machine had a very marked influence on the quality of the thinned specimens. If the specimen chamber was not well cleaned before ion milling a fresh specimen, the latter tended to show amorphisation due to the deposition on the specimen of the debris left in the chamber from the previously ion‐milled specimens. Such observations were made from MgO specimens ion milled in several different types of commercial ion milling machine employing a single gun. It is proposed that to obtain good‐quality ion milled TEM specimens, it is important to clean the specimen chamber thoroughly prior to mill

ISSN:0741-0581    

DOI:10.1002/jemt.1060150407

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractTo study cellular shapes, growth patterns, and fine structure during early stages of CNS development in rat embryos, preparative procedures were evaluated and modified to meet two criteria: (1) Coronal semithin sections should reveal undeformed telencephalic hemispheres that were symmetrically expanded on both sides of midline structures and were surrounded by contiguous mesenchyme. (2) In electron micrographs, cells should have intact, undistorted surface membranes, evenly distributed nucleoplasm and well preserved cytoplasmic organelles. To meet these criteria, 378 fetuses with a gestational age of 11–20 days (E11–E20) were used to test and modify procedures for anesthesia, embryo removal and handling, dissection, fixation, dehydration, and embedding of the embryonic CNS. Most specimens were in an early stage of development (E11–E13), which, in case of the neopallial wall, is the preneural period. The tests produced methods that met the above criteria and identified the most common artifacts and their causes. Deformities of the cerebral hemispheres and separations between the brain and its coverings were usually caused by trauma during embryo removal and during handling before fixation. Changes in cellular volumes, especially swelling during fixation and dehydration, were the most important causes of histological artifacts. The procedures and methods that consistently produced the best light and electron microscopic preservation of the E11–E13 rat CNS are described. Fixation was best when the brains were treated with glutaraldehyde and s‐collidine buffer, followed by osmium tetroxide in s‐collidine buffer. A surprisingly beneficial effect of sodium chloride in the dehydrating alcoho

ISSN:0741-0581    

DOI:10.1002/jemt.1060150408

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractA new image detection system has been developed to display transmission electron microscope (TEM) images on a CRT without a video camera system. Deflection coils placed in both the upper space of an objective lens and in the lower space of the first intermediate lens scan a small electron probe simultaneously. The electrical signal acquired through an improved scintillator and a photomultiplier is synchronized with the scanning signal and displayed in a similar fashion to a conventional scanning TEM (STEM) instrument. A preliminary system using a 100 kV conventional TEM (CTEM) equipped with a hairpin‐type electron gun, produced an image with a spatial resolution of 1 n

ISSN:0741-0581    

DOI:10.1002/jemt.1060150409

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractA reliable two‐stage carbon replica technique has been developed to extract precipitates from zirconium alloys. Using this technique, all precipitating phases can be extracted from Zircaloy‐2, Zr‐Cr‐Fe, and Zr‐Nb‐Fe alloys. Precipitate identification using EDS X‐ray analysis and convergent beam electron diffraction was greatly facilitated in comparison to thin foils. In addition, the sensitivity for the detection of trace elements in particles was increased using extraction replicas. The chemical compositions of the precipitates as determined from both replica and thin foils were in excell

ISSN:0741-0581    

DOI:10.1002/jemt.1060150410

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractOwing to the particular environment of the JEM4000EX HREM at the University of Pennsylvania, it became necessary to control the magnetic environment around the microscope. The unstable magnetic environment included two components, a slowly wandering vertical DC magnetic field and an AC magnetic field. The effects of these fields on the microscope performance were to introduce an uncertainty in the objective lens defocus value over a series of images and to reduce the attainable resolution of the microscope, respectively. A solution is presented in which these fields are stably reduced well within the limits of sensitivity of the JEOL, Ltd. JEM4000EX for high‐resolution imaging. This solution is based on a feedback loop using a pseudo‐Helmholtz coil to generate a well‐defined vertical magnetic

ISSN:0741-0581    

DOI:10.1002/jemt.1060150411

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY