Fine structural changes of myelinated nerve associated with copperhead envenomation

Summary The fine structure of right sciatic nerves of Swiss white mice was studied after being exposed to a venom solution ofAgkistrodon contortrix laticinctus (broad-banded copperhead) and to 0.9% NaCl solutions for periods of 1, 2 or 3 h. There was some Wallerian-like degeneration in all groups of nerves in the experiment. Additional neuropathological changes were noted in the nerves exposed to venom solutions.The connective tissue was affected most severely, while the basal lamina was unaffected. Schwann cells were vacuolated, and in the most extreme case, a type of myelin splitting occurred which was considered as a demyelinative effect. The results were compared to those of Martin and Rosenberg (1968) [15] on studies of the giant squid axon. References to additional fine structural studies of various other neuropathies were given.This investigation was submitted as a partial requirement for the Master of Science Degree, Department of Anatomy, Colorado State University and was supported by U.S. Public Health Service Grant # 5 RO1 GM-15591 and # 5 RO1 FD-00014 and Career Development Award # 5 KO4 GM-41786 from the National Institutes of Health (to A. T. Tu). The work was done in the Electron Microscope Training Laboratory, Colorade State University.     

Fine structural changes in the sural nerve of patients with acanthocytosis

Summary The fine structure of sural nerve biopsies is described in two brothers with normo-lipoproteinaemic acanthocytosis and an associated neurological syndrome. There was a severe reduction of myelinated fibres. The Schwann cells had an increased population of lysosomes and contained remnants of myelin. The myelin lamellae were often split at the intraperiod lines. Centrioles were found in Schwann cells, fibroblasts and endothelial cells. The significance of these findings is discussed.     

Grey matter degeneration of the C.N.S. in carcinosis

Summary Two cases of grey matter degeneration of the C. N. S. due to carcinosis are described.In the first besides elements of the cerebellum other grey complexes also were affected, in the second manifestations of deficiency-encephalopathy were found. It was emphasized that systematic diseases mostly are not so systematic as generally accepted, that many grey matter degenerations are not systematic at all, and that the carcinogenous affections do not differ essentially from the latter.C. N. S. affections in carcinosis are to be considered as unspecific, unsystematic, as only one of many etiologically different ganglion cell degenerations in which the cerebellar cortex relatively frequently partakes, as unpredictable with respect to both their occurrence at all and to the distribution and the intensity of the degeneration.

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Zusammenfassung Zwei Fälle von Degeneration der grauen Substanz des Zentralnervensystems bei Carcinose werden beschrieben. Im ersten Falle sind außer den Elementen des Kleinhirns auch andere graue Gebiete betroffen, im zweiten Fall finden sich Zeichen von Mangel-Encephalopathie. Es wird betont, daß System-Krankheiten meistens nicht so systematisch, wie allgemein angenommen, sind, daß viele Degenerationen der grauen Substanz überhaupt nicht systematisch sind und daß die carcinogenen Affektionen sich von den letzteren nicht wesentlich unterscheiden.Die Affektion des zentralen Nervensystems bei Carcinose muß man als unspezifisch und unsystematisch betrachten, als eine der ätiologisch verschiedenen Formen von Ganglienzell-Degenerationen, bei denen die Kleinhirnrinde relativ häufig beteiligt ist, sowie als nicht vorausbestimmbar sowohl hinsichtlich ihres Auftretens überhaupt als hinsichtlich der Verteilung und der Stärke der Degeneration.

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Fine structural changes in the mutant hamster with hind leg paralysis

Summary A case of non-progressive congenital myopathy is described in which there was absence of muscles and scapulo-peroneal distribution of weakness. The muscle biopsy showed preferential atrophy of Type I fibers and subsarcolemal bodies. These bodies were composed of an acidic protein with sulphahydryl groups which showed acid stable adenosine triphosphatase activity. The possibility of a maturational arrest as a cause is presented.     

Strain differences in illumination‐dependent structural changes at mouse photoreceptor ribbon synapses

Photoreceptor cells encode light signals over a wide range of intensities with graded changes in their membrane potential. At their highly specialized ribbon synapses they transmit the signals to the postsynaptic neurons by the tonic release of glutamate, which is continuously adjusted to changes in light intensity. Such a level of performance requires adaptive mechanisms, and it is suggested that illumination‐dependent changes in ribbon shape and size are one of these adaptive processes. In this study we compared structural properties of synaptic ribbons under various illumination conditions between three mouse strains: the pigmented C57BL/6 and the two albino strains Balb/c and B6(Cg)‐Tyr^c‐2J/J (coisogenic to C57BL/6). In addition, electroretinograms (ERGs) recorded in the same groups were compared. In the C57BL/6 mouse a change in illumination did not result in structural alterations of the synaptic ribbon. Similarly, in the B6(Cg)‐Tyr^c‐2J/J mouse only minor structural changes were detected. In contrast, the state of adaptation had a large influence on the ribbon structure of the Balb/c mouse. The ERG recordings showed only small functional differences between C57BL/6 and B6(Cg)‐Tyr^c‐2J/J mice, but the retinal function of Balb/c mice was strongly compromised. We conclude that illumination‐dependent changes of photoreceptor ribbon structure differ between strains and thus cannot be regarded as a general mechanism for light adaptation. J. Comp. Neurol. 521:69–78, 2013. © 2012 Wiley Periodicals, Inc.     

Fine structural analysis of the cortico-striatal pathway.

Considerable evidence has accumulated indicating that one neurotransmitter in the excitatory cortico-striatal tract is glutamate. Lesions of the tract result in reductions in the striatum of glutamate levels as well as high affinity uptake of glutamate into synaptosomes. Furthermore, such lesions eliminate the neurotoxicity of the glutamate analog kainic acid when injected into the striatum. The fine structure of the cortico-striatal pathway was studied to provide evidence regarding the morphology of glutamate nerve endings. Seven days after injection of 3H-proline (20-25 mu Ci) into the rat frontal cortex, axonally transported label appeared in the striatum with uniform distribution in a single type of nerve ending. The labeled boutons had common round vesicles and made asymmetrical contacts, mostly with dendritic spines. This morphology is typical of excitatory synapses, and similar to that previously shown for cholinergic boutons in the striatum. In four animals similarly injected with 3H-proline, kainic acid was administered directly into the striatum to induce degeneration of postsynaptic elements eight to ten hours before sacrifice. In areas affected by these injections, grains appear in patches, possibly resulting from glial swelling. Labeled boutons were seen almost four times as often in synaptic contact with degenerating dendritic elements as with normal ones. The data provide morphological evidence as to the nature of the probable glutamatergic boutons in the striatum, and show the close relationship of such boutons with the neurotoxic effects of kainic acid. This would be anticipated in view of the dependency of kainic acid neurotoxicity on the integrity of the cortico-striatal pathway.     

Time course of structural changes at identified sensory neuron synapses during long-term sensitization in Aplysia

We have used the gill- and siphon-withdrawal reflex of Aplysia californica to explore the morphological basis of the synaptic plasticity that underlies long-term sensitization. In earlier studies (Bailey and Chen, 1983, 1988a), we described 2 classes of structural changes at identified sensory neuron synapses that occur following long-term sensitization: (1) increases in the number, size, and vesicle complement of active zones and (2) an overall increase in the total number of synaptic varicosities per sensory neuron. In the present study, we have begun to examine which of these anatomical changes might be necessary for the maintenance of long-term sensitization by exploring the time course over which they occur and, in particular, their duration relative to the persistence of the memory assessed behaviorally. Toward this end we have quantitated changes in both the total number of varicosities and their active zone morphology in single HRP-labeled sensory neurons taken from long-term sensitized and control animals at different intervals (1-2 d, 1 week, and 3 weeks) following training. We have found that long-term sensitized animals examined within 48 hr after the completion of training demonstrate an increase in the total number of varicosities per sensory neuron as well as an increase in the incidence, size, and vesicle complement of their synaptic active zones compared with control animals. The increase in the number of varicosities and active zones persists unchanged for at least 1 week, and the increase in active zone number is only partially reversed at the end of 3 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)     

Phycomycosis of the C.N.S. first report of a Dutch case

A case of fibrinous meningo-encephalitis due to phycomycetes is reported. The clinical history, the morphological aspects and the typical staining properties of the fungus are discussed.     

Fine structural changes in the rat arcuate nucleus by forced running stress

The forced running stress in male rats induced some fine structural changes in the arcuate nucleus. By inducing stress for 2 days, the number of multilamellar astrocytic wrappings and endoplasmic reticular (ER) whorls increased significantly. After a stress of 12 days, half of the rats remained inactive for several weeks, and the other half regained their normal activity. In the inactive group, the ER whorls were partially degenerated at 2 weeks after the stress. These degenerative changes remained for 14 weeks after the stress with the increased lysosomes and the disorganization of r-ER. These findings may suggest that long-term stress induces degenerative changes in the arcuate nucleus neurons and that some of these changes persist with some aging-like morphological changes.     

Fine structure of synapses in the vestibular ganglion of the cat

The vestibular ganglion of cat contains two distinguishable cell types, the larger and myelinated of which are much more numerous. The smaller and unmyelinated are represented by two cell populations: the first population displays complete Schwann cell ensheathment. The sheath of the second population is usually discontinuous at more than one point. Few axosomatic synapses are present on either cell type and profiles with clear synaptic vesicles predominate on each. The populations of presynaptic profiles in general are one type: a large variety with round synaptic vesicles and an asymmetrical contact. This type contacts the cell soma or the axon hillock surface. Those containing myelinated cells are covered on one side by the myelin sheath of the cell soma. Potential origins for the presynaptic profiles and possible functional significance of the synapses is discussed.     

Fine structure of hippocampal mossy fiber synapses following rapid high-pressure freezing

Synapses of hippocampal neurons play important roles in learning and memory processes and are involved in aberrant hippocampal function in temporal lobe epilepsy. Major neuronal types in the hippocampus as well as their input and output synapses are well known, but it has remained an open question to what extent conventional electron microscopy (EM) has provided us with the real appearance of synaptic fine structure under in vivo conditions. There is reason to assume that conventional aldehyde fixation and dehydration lead to protein denaturation and tissue shrinkage, likely associated with the occurrence of artifacts. However, realistic fine-structural data of synapses are required for our understanding of the transmission process and for its simulation. Here, we used high-pressure freezing and cryosubstitution of hippocampal tissue that was not subjected to aldehyde fixation and dehydration in ethanol to monitor the fine structure of an identified synapse in the hippocampal CA3 region, that is, the synapse between granule cell axons, the mossy fibers, and the proximal dendrites of CA3 pyramidal neurons. Our results showed that high-pressure freezing nicely preserved ultrastructural detail of this particular synapse and allowed us to study rapid structural changes associated with synaptic plasticity.     

Proteolysis and proteolytic enzymes in structural plasticity of synapses

This review is focused on the role of proteolysis and proteolytic enzymes in long-term plasticity, learning, and memory. The importance of proteolysis in the activation of protein turnover, regulation of actin cytoskeleton motility, endocytosis, exocytosis, and cell adhesion processes is discussed. Experimental data on the activation of proteolytic protein cleavage during an increase in the synthesis and proteolytic cleavage of actin-bound proteins in long-term synaptic plasticity are presented. We discuss the involvement of proteasomes and lysosomes in membrane transport and long-term synaptic plasticity underlying learning and memory.