Search

Summary The authors describe the histological and ultrastructural features of a well demarcated single abscess. Histopathological features are consistent with those observed in experimental models and human materi l. In addition this study allowed the ultrastructural definition of some of the capsule components as meningothelial-like structures and myofibroblasts. Their possible role in the evolution of the lesion is discussed.

Inclusions were found in the mitral cells of olfactory bulbs of proton irradiated rats. They exhibited the fine structural features currently ascribed to lipid droplets. They were observed in the cytoplasm of perikaria and dendrites. The inclusions were tentatively interpreted as a structural manifestation of cell response to sublethal injury. This neuronal condition occurs occasionally under a variety of circumstances, but is seldom reported, and in fact, this might very well be the first electron microscopic illustration of “fatty change” in nerve cells.

De Estable-Puig, Rosita F., Juan F. Estable-Puig, M. R. ven Murthy, Simone Radouco-Thomas, Swarn Chawla, Monelly Radouco-Thomas and Corneille Radouco-Thomas: On the pathogenesis and therapy of dementia of the Alzheimer types Some neuropathological, biochemical, genetic and pharmacotherapeutic considerations. Prog. Neuro-Psychopharmacol. & Biol. Psychiat. 1986 10 (3–5): 355–390. 1. 1. The extensive literature on dementia of Alzheimer type (DAT) testifies to the enormous progress achieved in the clinical and biochemical delineation of this disease. Newly developed laboratory and imaging techniques are also being applied to the diagnosis of DAT. Nevertheless, unequivoval diagnosis still relies primarily on morphological data from biopsy or autopsy. 2. 2. An overview is presented of major morphological changes occurring at different levels of organization in the central nervous system (CNS) in DAT. 3. 3. Currently formulated etiopathogenic hypotheses of DAT are reviewed and discussed in the context of morphological alterations. 4. 4. Some of the recombinant DNA methods, that are currently available for gene analysis, are described. Some approaches for studying Alzheimer specific genes using the above methods have been suggested. 5. 5. Finally, a critical overview of the current pharmacotherapeutic armamentarium used in DAT and senile dementia is presented. The efficacy, side effects, and the main mechanisms of action of the two categories of drug therapy —supposed etiopathogenic and symptomatic— are presented.

The sequential development of the early phases of leptomeningeal cyst formation was studied in an experimental model. Light, transmission and scanning electron microscopic data were compared with those from human arachnoid cysts. Common features observed were: the participation of leptomeningeal cells in the structure of the cysts with exclusion of dural components; the absence of internal traversing trabeculae; the hyperplasia of leptomeningeal cells, particularly in the dome of the cysts. Other features of the experimental cysts were: the splitting of the pio-arachnoid membrane; the scarcity of collagen at the early stages; the presence of areas of mineralization at more advanced stages; the presence of remodeling parenchymal changes at the underlying nervous tissue.

SUMMARY Local charging effects in small biological cavities during SEM observation are apparent, even after sputter coating. Using an experimental model, the thickness of metallic coating at the bottom of cylindrical cavities has been measured and found to be less than 50% the thickness on the surface, depending on the relation of diameter to depth of the cylinder.

Localized lesions were produced in the cerebral cortices of rats by application of low temperatures to the intact skull. In animals killed 2 months after the injury, the reparative response observed involved axons and neuroglia cells. Polarizing microscopy indicated the presence of appreciable bundles of myelinatedfibers in the paralesional region. The myelinated nature of these fibers was corroborated by conventional myelin stains, phase contrast study of PPDA thick sections, and electron microscopy. Intense astrocytic gliosis was present. The nature of the glial processes in close association with the remyelinating axons and the relative participation of the different types of neuroglia in the reparative response are considered.

Effects of a single high dose of X-rays on the adult rat olfactory bulb have been studied by electron microscopy. Several features of the cell response were described (neuronal pyknosis; glial response and glycogen accumulation; edema; phagocytic activity). Approaches towards understanding the mechanisms underlying these effects and their possible functional significance are discussed. The damage of the internal granule cells gave rise to synaptic degeneration at the level of the reciprocal mitro-granular contacts in the stratum plexiforme. The importance that this work may have when applied to the study of short axon neuron connections is stressed.

La radiolesion aigue du bulbe olfactif provoque des dommages selectifs aux petits interneurons. L'examen au microscope electronique du tissu irradie a mis en evidence la presence de nombreuses terminales en degenerescence, au niveau de la couche plexiforme. Elles ont ete interpretees comme etant des dendrites appartenant aux granules radiolesees par leur position post-synaptique dans des synapses reciproques avec des dendrites mitrals. On propose d'utiliser cette methode pour l'etude des connections interneuronales courtes dans certains endroits du SNC.

Acute terminal degeneration has been studied in rat olfactory glomeruli after disconnection of the first nerve. At the 48-hour period, densification of some terminals was apparent at the electron microscopical level. This densification is due to an excessive crowding of vesicles, and to a densification of axoplasm and mitochondria. Other alterations recorded were a hyperplasia of neurofilaments isolated or associated to terminal densification, and the occurrence of diverse membranous arrays. At the 3-day period many degenerating terminals have been already engulfed by astrocytic processes. In general, the “en masse” degeneration of groups of neighboring terminals was the rule. Some images suggestive of post-synaptic dendrite involvement were also recorded.

Examination of glutaraldehyde or chrome-osmic perfused normal and X-irradiated olfactory bulb has revealed the presence of intranuclear rodlets in the irradiated granules and mitral cells and occasionally in the normal external granule cells. A close association between the filaments of the rodlets and chromosomic neighboring microfibrils was observed.

The unilateral section of the olfactory peduncle was made in adult albino rats in order to produce axonal and terminal degeneration of the whole system of centrifugal projections. This experiment was carried out with a double purpose. First, to tipify the different structural modes of axonal and terminal degeneration in a correlative light and electron microscopy study. Second, to study the distribution of these central projections to the bulb. The animals were sacrificed by fixation-perfusion 4 to 7 days post-operation and samples of olfactory bulbs were processed as routinely for electron microscopy observation. Thick sections stained with paraphenylenediamine (PPDA)(1) were utilized for phase observation.

The granular layer of the cerebellar cortex situated between the molecular and medullary layers is built up mainly of the perikarya of small interneurons, the granule cells intermingled with part of their own processes, mossy fiber terminals, fibers of passage and other less numerous intrinsic cells. Ultrastructurally they are characterized by a nucleus which occupies most of the cell body and a rim of cytoplasm. The nucleus exhibits some aggregates of chromatin and in some cells a nucleolus. In the cytoplasm very scarce organelles are observed (Fig.l). Their main synaptic connections are found, first, at the cerebellar glomerulus where granule dendrites are seen in postsynaptic position towards mossy fiber rosettes. Desmosomic attachments are observed between granule dendrites. Second, at the level of the molecular layer where parallel fiber terminals (ramifications of the peripheral axon ) are seen apposing Purkinje dendrite spines.

The main technical problems involved in the routine fine structural study of normal and pathological tissue have already been solved. In recent years, considerable attention has been focused on the diverse techniques of fixation by perfusion. Osmium tetroxide perfusion as well as aldehydic perfusion have been shown to preserve remarkably well the different elements of the nervous system. Conventional light and histochemical studies can be carried out in perfused tissue. A fairly good fixation of deeply located structures is now possible without the artifacts involved in the procedure of fixation by immersion. These studies have been extended to other tissues.Nevertheless the conventional sampling of tissue with razor blades usually lacks anatomical precision. Indeed, the study of pathological or neuroanatomical material involve very serious problems in relation to an accurate sampling of a precisely located cell group or tract or that of a minute lesion. Furthermore, the area to be studied may not necessarily be located on the surface of the organ studied and then their excision involves a considerable disruption of the surrounding tissue. The samples are in general very irregular in shape and this makes their orientation very cumbersome.