Dynamics of Degeneration and Growth in Neurons -

Dynamics of Degeneration and Growth in Neurons (eBook)

Proceedings of the International Symposium Held in Wenner-Gren Center, Stockholm, May 1973
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2013 | 1. Auflage
616 Seiten
Elsevier Science (Verlag)
978-1-4831-4647-8 (ISBN)
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Dynamics of Degeneration and Growth in Neurons
Dynamics of Degeneration and Growth in Neurons is a collection of papers presented at the International Symposium on the Dynamics of Degeneration and Growth in Neurons, held in Stockholm, Sweden, on May 16-18, 1973. Contributors explore the dynamics of degeneration and growth of central and peripheral neurons, touching on a wide range of topics such as the neurotoxic action of 6-hydroxy-dopa on central catecholamine neurons; axonal transport of proteins in growing and regenerating neurons; and collateral reinnervation in the central nervous system. Comprised of 50 chapters, this volume begins with an overview of degeneration processes in central and peripheral neurons. Results of microfluorimetric and neurochemical studies on degenerating and regenerating adrenergic nerves are presented. The next section is devoted to axoplasmic transport as a mechanism for axonal support and growth and includes chapters dealing with the effects of degeneration and axoplasmic transport blockade on synaptic ultrastructure, function, and protein composition; the role of axoplasmic flow in trophism of skeletal muscle; and proximodistal transport of acetylcholine in peripheral cholinergic neurons. The remaining chapters discuss the nerve growth factor receptor and its specific binding in sympathetic ganglia; the noradrenergic innervation of cerebellar Purkinje cells; and the possible role of brain and peripheral monoamines in the ontogenesis of normal and drug-induced responses in the immature mammal. This book will be of interest to physiologists and neurologists.

THE LIGHT AND ELECTRON MICROSCOPICAL APPEARANCE OF ANTEROGRADE AND RETROGRADE NEURONAL DEGENERATION


GUNNAR GRANT and FRED WALBERG,     Department of Anatomy, Karolinska Institutet, Stockholm, Sweden, and Anatomical Institute, University of Oslo, Oslo, Norway

SUMMARY


A review is given of the light and electron microscopical appearance of anterograde and retrograde neuronal degeneration as this appears in neurons of the central nervous system and in ganglion cells. The three main types of anterograde degeneration are described, and details of the retrograde degeneration as this occurs in young animals are presented. The aim of the presentation is to give students interested in the tracing of neuronal connections a description of the neuronal changes that can safely be relied upon in experimental studies.

INTRODUCTION


The transection of axons in vertebrates leads to marked morphological changes, peripheral as well as central to the lesion. The changes are very characteristic and are usually more pronounced in newborn animals. In the present report a review is given of the light and electron microscopical appearance of anterograde and retrograde degenerative changes as these occur in neurons within the central nervous system and in ganglion cells that send their axons to the spinal cord and brain stem. The review will mainly be based on findings in the cat, but reference will be made to other mammals and to submammalian species. Transneuronal changes will not be included in this report. Neither will the glial reactions related to degenerative changes in the neurons be considered in detail. Students interested in the problems reviewed here will benefit from the comprehensive report by Raisman and Matthews (1972). Valuable information is also found in the monograph edited by Nauta and Ebbesson (1970).

ANTEROGRADE NEURONAL DEGENERATION


1 THE LIGHT MICROSCOPICAL APPEARANCE OF ANTEROGRADE DEGENERATION


Although the Marchi method in the hands of experienced neuroanatomists has given valuable information as to the origin and termination of degenerating fiber tracts (see especially Smith, 1951, 1956a, b; Smith et al., 1956), it is clear that this method is no longer used routinely in neurobiological laboratories. One reason for this is obviously that only degenerating myelin and not the axoplasm itself is stained when this method is used. Degenerating unmyelinated fiber tracts can therefore not be studied with the Marchi method, and myelinated fiber systems can only be followed to the region where myelin terminates. Ultrastructural studies from the last two decades have, however, shown that afferent fibers to many nuclei and regions especially within the spinal cord and brain stem are covered with myelin almost to the region where the boutons emerge. The Marchi method can therefore in such regions be used since fibers down to about 0.5 μ are impregnated. The Marchi “dust” is in these areas showing the terminal field of the afferent fibers. In spite of this fact the Marchi method has, however, not regained its earlier popularity, and it remains to be seen whether the method will be able to compete with all the currently applied silver methods.

Some of the silver impregnation methods used today visualize normal as well as degenerating neurons. Others are modifications which allow silver percipitate to occur mostly (only) on degenerating structures. The early methods, such as the Bielschowsky, the Reumont Lhermitte, and the Glees techniques, belong to the first group, the so-called “nonsuppressive” stains. Although in some laboratories valuable information has been collected with nonsuppressive stains, it was only after the introduction of the Nauta modifications (the Nauta–Gygax and Nauta–Laidlaw techniques; see Nauta, 1957) that the silver methods became popular. The Nauta–Gygax and Nauta–Laidlaw modifications are in many laboratories today standard methods.

Successfully impregnated Nauta–Gygax or Nauta–Laidlaw sections permit the student to trace in great detail degenerating fibers from a damaged area to the field of termination of the fibers. The degenerating fibers are easily seen, and stand out clearly against a yellowish or brown background, where in optimal sections the staining of normal fibers is negligible.

The light microscopical appearance of fiber degeneration in Nauta sections is very characteristic. The degenerating coarse axons appear as black fragmented fibers. The argyrophilic particles are often lying in a row so that the course of the fibers can be followed. The argyrophilic particles are irregularly outlined, beaded, and tortous.

The light microscopical picture has a somewhat different appearance in areas where the fibers terminate. The thin fragmented degenerating fibers present in a terminal region have a very beaded appearance. Furthermore, the smallest particles observed in the light microscope are irregular, oval, or round. They can lie close to perikarya or be more freely dispersed in the neuropil.

Although it is quite clear that the Nauta–Gygax and Nauta–Laidlaw modifications give a good indication of the field of termination for a fiber tract, considerable difficulties are involved when the student tries to interpret the nature of the argyrophilic particles present in the sections. The coarser particles are, of course, local deposit of silver in thick degenerating fibers, but it is virtually impossible from light microscopical sections alone to reveal whether the smallest argyrophilic particles in a section partly (or only) are degenerating terminal fibers, or also (only) degenerating boutons. We had no possibility to make statement on this important point until the electron microscope was introduced into neurobiological research. At the time when the electron microscope became available, evidence had, however, emerged which quite clearly showed that the Nauta modifications were not optimal for the demonstration of degenerating boutons (Heimer, 1967). Heimer had thus been able to convincingly demonstrate that the modified silver impregnation method introduced by Fink and himself (1967) permitted degenerating boutons to be visualized in areas where the Nauta method failed to show degeneration (see also Heimer and Wall, 1968). Electron microscopy of silver-stained Nauta and Fink-Heimer stained sections have substantiated the information obtained in the light microscope (Heimer, 1970; Heimer and Peters, 1968; Walberg, 1971, 1972).

The Fink–Heimer method should be used when information is wanted concerning the distribution of afferent fibers as well as their boutons in the area of termination for these fibers. Of great importance is, however, that the fine dust, i.e. the degenerating boutons and fine terminal axonal ramifications, only occurs at certain critical survival times. The reason for this is that the degenerating terminal structures in many places are removed by glial cells shortly after the onset of degeneration. Since, thus, the fine dust in Fink-Heimer sections obviously demonstrates degenerating boutons and fine terminal axonal ramifications, it is advantageous for the student to have a detailed knowledge of the glial activity and of the speed with which degenerating terminal structures are removed in a nucleus. This requires electron microscopy of the area. Good results may, however, also be obtained without concomitant electron microscopical investigations. A sequence of series where the interval between the survival times is very short, can give the student the necessary information.

2 THE ELECTRON MICROSCOPICAL APPEARANCE OF ANTEROGRADE DEGENERATION


The experimental electron microscopical studies made in the last decade have shown that there are three types of morphological changes that can be observed when fiber tracts are damaged in the central nervous system. They are observed in mammals as well as in submammalian species. However, the same fiber system can in different species react differently (the optic tract is a particularly good example, see below). The reason for this is at present unclear. Histochemical and biochemical studies may clarify whether there is a relation between the morphological appearance of the degeneration and the chemical reactions leading to disintegration of the neuron.

Some students have given evidence for the existence of types of degeneration diverging from those to be described here. Since these descriptions are based on observations made only in a few places, unexperienced students should not use these criteria alone for a safe identification of degenerating axons and boutons. These changes are briefly considered at the end of this chapter.

The Dark Type of Degeneration

The dark type of degeneration is conspicuous and easily diagnosed. The reaction was first described by Colonnier and Gray (1962). The most striking feature is the darkening of the degenerating boutons. This is largely due to the appearance of a finely granular background substance of the matrix in which the vesicles and mitochondria are included. The darkening is probably also caused by a shrinkage of the bouton. The degenerating bouton therefore often develops an indented outline which contrasts sharply with the normal shape....

Erscheint lt. Verlag 22.10.2013
Sprache englisch
Themenwelt Sachbuch/Ratgeber Natur / Technik Naturführer
Naturwissenschaften Physik / Astronomie
Technik
ISBN-10 1-4831-4647-2 / 1483146472
ISBN-13 978-1-4831-4647-8 / 9781483146478
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