Search

Using the inverted phase-contrast microscope, the living undamaged frog sciatic nerve fibers and the fibers mechanically injured to varying degrees, were studied. It was found that the swelling of myelin incisures (MI) (of Schmidt-Lanterman) occured according to the principles similar to those controlling the changes of the myelin gap (node of Ranvier) and depended on the swelling of a Schwann cell (SC) perikaryon. It was detected that this was a single process, which which could be united in a complex of nonspecific changes of a myelinated nerve fiber. It was also demonstrated that under the action of mechanical injury and hypotonic solution, swelling of MI, nodes of Ranvier and SC perikaryon occurred without modifications of outer fiber diameter, due to the pronounced local axon thinning. Electron microscopic study of the cytoskeletal axonal structures showed that there was not a simple local contraction of an axon, but a significant local increase in the density of cytoskeletal components of the axoplasm (by 200-275%). Reactive reversible remodeling of a myelinated fiber suggests a new type of interaction between the axon and SC, the mechanism of reversible translocation of liquid axoplasmic fraction to the glial cell cytoplasm.

The intraocular grafts of the septal or hippocampal embryonic tissues developing in the rat anterior eye chamber for three to four months were investigated by electron microscopy. The aim of this study was both the ultrastructural identification of the peripheral nervous fibers entering the grafts from host iris and the estimation of their capacity to establish true synaptic contacts with the central nervous system neurons of the grafts. The bundles of myelinated and unmyelinated axons, surrounded by the Schwann cell cytoplasm, were observed within the perivascular spaces of the ingrowing blood vessels. In the neuropil areas of the grafts, both types of the peripheral nervous fibers were also identified. It was demonstrated on the ultrastructural level that the unmyelinated axons lost their glial envelope of the Schwann cell and formed the typical asymmetric synapses with the dendrites and dendritic spines of the grafted neurons. The results are indicative of the high morpho-functional plasticity of both parts of the nervous system.

Although thyroid hormones are known to have a significant influence on the development of nervous system, the absence of changes in the brain of mice deficient in transthyretin--a protein providing thyroid hormone transport across the blood-brain and blood-nerve barrier--remains unexplained. Therefore, the aim of this study was to determine the effect of transthyretin on the formation of myelinated and unmyelinated nerve fibers in sciatic nerve of mice. The myelinated and unmyelinated nerve fibers were counted in sciatic nerve of 3-months-old normal and transthyretin-knockout (transthyretin(-/-)) mice 15 and 30 days after nerve crushing. No differences were detected in the number of myelinated and unmyelinated nerve fibers in intact control (wild-type) animals group vs. transthyretin(-/-) mice. By days 15 and 30 after nerve crushing the number of myelinated nerve fibers was diminished by 54.7 and 71.8%, respectively, in transthyretin(-/-) mice, as compared to that in control animals. The number of unmyelinated nerve fibers at day 15 after the injury was not different in transthyretin(-/-) and control mice, however, by day 30 the number of these fibers in control group was found to increase significantly, exceeding that one in transthyretin(-/-) mice by 27.9%. These results indicate the important contribution of transthyretin, as a thyroxin carrier protein, to the process of posttraumatic regeneration of sciatic nerve. The absence of changes in nerve fiber numbers in transthyretin-knockout mice in postembryonic period suggests the presence of transthyretin-independent mechanism of thyroxin transport into the peripheral nervous system.

Using the model of rat sciatic nerve transection and crush injury we studied influence of pyrimidine derivative xymedon on efficacy of regeneration of myelinated axons, number and phenotype of surviving sensory neurons (expressing GAP-43 and Bcl-2) and Schwann cells (S100, GAP-43, PCNA) on the 7th, 15th, 30th, 60th and 90th day after nerve injury. We found out that xymedon counteracts posttraumatic death of sensory neurons, stimulates regeneration of myelinated fibres and proliferation of Schwann cells.

Light and electron microscopy was used to study the distribution and changes of NADPH-diaphorase in the cutaneous nerve biopsy specimens in different periods of diphtheritic polyneuropathy (DP). there was a reduction in the reaction rate of the enzyme in Schwann's cells of the destructively changed nerve fibers and an increase in the remyelinated nerve fibers. The enzyme is located on the nuclear and endoplasmic reticulum membranes and ribosomes. It is suggested that there is an association of the synthesis of nitric oxide with the myelin-producing function of Schwann's cells.

Ultrastructure of certain myoneural terminals were studied on serial sections on day 3, 5 and 8 after denervation. Ultrastructure of the terminal proximal and distal regions and Schwann cell were studied by means of morphometry and reconstruction of single terminals. On day 3 after denervation Schwann cell is activated in terminal proximal regions more rapidly than in distal ones with contractility in the terminal proximal region being more significant than in distal. On day 5 after denervation changes cover both initial and terminal regions and on day 8 almost all the regions where terminal were placed earlier were occupied with Schwann cell. A suggestion is made that structural changes in the Schwann cell-terminal system are the major contributors to decrease of synaptic discharge in early stages of denervation and appearance of Schwann cell potentials in more late ones.

A decrease in the amplitude of miniature and evoked end-plate potentials (MEPPs and EPPs) as well as changes in EPP facilitation and depression during frequency stimulation were observed in psychosine-treated m. cutaneous-pectoris of the frog. Electron-microscopic investigation demonstrated severe changes in synaptic Schwann cells embracing motor terminals and disturbances in the inner mesaxon structure of the myelinated parts of motor terminals.

The nervus ischiadicus in white noninbred rats has been damaged by various means and then light- and electron-microscopically the sources of origin of macrophages, participating in removal of decay products in the distal part of the nerve have been studied. There is a close correlation between the process of Wallerian degeneration and aseptic inflammation. In the area of decay of the myelinated nervous fibers 4 types of cells have been identified and characterized. Three of them are precursors of macrophages, participating in removal of the myelin decay products: mononuclear cells of hematogenic origin, perineural cells, endoneural fibroblasts. The dynamics of these cells transformation into macrophages and into "foam cells" has been followed. The fourth type--Schwann cells; they do not directly participate in removal of the myelin decay products. They do not die, but, separating from the segments of the disintegrated myelin, dedifferentiate, proliferate and form cords, into which regenerating axons then grow in. To understand the role of various macrophages in the destructive and reparative processes, which develop in the nerves, is very important not only for searching definitive approaches in treatment of posttraumatic demyelinated processes, but for comprehending the mechanisms of certain autoimmune demyelinating diseases.

Ultrastructural changes of neurones of sympathetic vegetative nervous ganglia were studied in 15 white male rats at an age of 5-7 months. In the dynamic of postmortem changes disorders typical of hypoxic conditions of the chest predominated.

The ultrastructure of the intraadventitial and paravasal nerve trunks of the superficial adventitial plexus in major vessels of the basis cerebri in man and in dogs under normal conditions and with a subarachnoidal hemorrhagic effusion was studied at the submucroscopic level. Unlike the ultrastructure of the intra-adventitial nerve trunks the paravasal ones, lying in the cerebrospinal fluid (CSF), have an endothelial sheath that substitutes the epineurium and also has a perineurium endowed with an abundantly developed system of basal membranes containing aplanated cells and bands of collagen fibrils. With a subarachnoidal hemorrhagic effusion was in evidence the disruption of the "CSF-neural barrier". The endothelial cells break" away and fall into the CSF, the basal membrane undergoes lysis, which, apparently, contributes to the penetration of various components of the subarachuoidally effused blood deep into the nerve trunks. This results in changes occurring in the ultrastructure of axones of the pulpous and, to a lesser extent,pulpousless nerve fibers.

Neuronal organization of the vestibular ganglion of the nerve VIII in the frog (Rana temporaria) has been studied by means of light and electron microscopy. It has been stated that bipolar ganglion-forming neurons are not quite identical in their structure. They differ in size, fine organization of their cytoplasm and in the manner they construct their glial sheaths. Among ganglial neurons, two types are distinguished: myelinizated and unmyelinizated neurons. A considerable part is composed by neurons coated with myelin sheath which can be constructed according to compact or loose type of myelin. Myelinizated neurons are mostly large cells, with their cytoplasm saturated with organells. Unmyelinizated neurons are coated with a simple sheath composed of one layer of lemmocytes processes. These neurons are much smaller in size, their cytoplasm is poor in organells and contains large amount of neurophilaments.

Ultrastructural changes have been studied using 67 tumors originated from the Schwann cells. Tumors were induced by means of methylnitrosourea injection with a week intervals. Both benign (fascicular and reticular) and malignant neurinomes were obtained. Main morphological changes were found in the Schwann cells. The tumor cell ultrastructure appeared to be definetely related to the degree of the tumor maturity. The results obtained may suggest that the fine structure of neurogenic tumors is also characteristic of their normal prototype--the Schwann cells.

The spinal ganglia were transplanted into the mesocolon of adult cats for periods of from 1 day to 9 months. About 30% of differentiated sensory neurons survived during the longterm transplantation. The intensive regeneration of the sensory neurons processes was characteristic of the transplanted neurons. Total myelinization of the regenerating nerves occurred during the 3rd--5th month. Potential regeneration capacity of the differentiated neurons and possibly of their prolonged transplantation were revealed.

Electron microscopic observations have been made on transverse sections of the auditory (tympanal) nerve of the crickets at various levels from the tympanal ganglion (close to the ganglion, 150, 250, 1,000, 2,000 and 3,000 mu from the latter). In the vicinity of the ganglion, axons of the auditory receptors are separated from each other by the processes of Schwann cells. Beginning from the level of 150-250 mu, the axons are subdivided and form, with the help of collaterals, a subreceptor plexus which is similar to that found in the auditory system of the locust. Collaterals of an axon pass to the adjacent axons and deeply penetrate into the latter loosing their Schwann sheath, so that axonal membranes form a direct contact. At the site of these contacts, intracellular cleft is equal to 50-80 A. No synaptic vesicles were found in the region of the plexus. At the level of 3,000 mu, the auditory axons again attain a roundlike form and become completely isolated from each other by the processes of Schwann cells. It is suggested that in the region of the subreceptor plexus, electrotonic interaction between the receptors of the crickets takes place, as it is common in the auditory sistem of insects.