Ultrastructural changes in synapses of cortical neurons following combined applications of glutamate and noradrenaline

The dimensions of postsynaptic densities (PSD) of axodendritic synapses in the sensorimotor region of the rat neocortex were determined following multiple paired microiontophoretic applications of L-glutamate (Gl) and noradrenaline (NA) using electron microscopy. It was established that combined applications of Gl and NA induce a statistically significant increase in the thickness of the PSD. In this case, the intensity of the structural changes depends on the delay time (within the range of 0–5 sec) of NA action in relation to Gl. The strongest modification in PSD was observed whenever the second neurochemical signal was received at the amount of cessation of the neuronal response to the action of the first transmitter.Translated from Neirofiziologiya, Vol. 25, No. 1, pp. 5–10, January–February, 1993.     

Ultrastructural changes in isolated plastids

Summary Etioplasts were isolated from maize leaves and the changes in their ultrastructure were followed in light and in darkness for several hours. It has been shown that the regular crystalline structures of prolamellar bodies, present after the isolation in darkness, disappear after 30 to 60 minutes of illumination, and long straight tubules appear within prolamellar bodies. Their appearance is influenced by the molarity of the isolation medium used, by light intensity, duration of illumination and by the temperature at which the isolates are kept. Long tubules appear, however, also in isolated etioplasts incubated for several hours in complete darkness.In isolates illuminated for 2–3 hours long tubules disappear again, and prolamellar bodies produced eventually consist of irregularly connected short tubules. In prolamellar bodies, regions with regular and very dense arrangement of tubules sometimes develop at this stage. The thylakoids (usually perforated) are now arranged concentrically in the plastids. True grana or poly-thylakoids can never be found in isolated etioplasts, not even when the etioplasts have been illuminated for 6 hours or more (up to 24).The present investigations have indicated that in isolated etioplasts in light, tubular elements, which build up the prolamellar bodies, cannot normally be transformed into thylakoids as is the case with intact tissue.The survival of isolated etioplasts is limited at present, and for this reason changes in their fine structure could be followed successfully for as long as 6 hours (in light at 15 °C), although a certain percentage of plastids survive up to 24 hours.     

Ultrastructural changes in isolated rat hepatocytes exposed to different CCl4 concentrations

Ultrastructural data are presented on time-course changes in isolated rat hepatocyte suspensions exposed either to 1.2 or 1.8 mM CCl4 for up to 1 h. The subcellular changes at the lower concentration, but not the higher, are shown to closely parallel those reported to occur in rat hepatocytes following ingestion of CCl4.     

Simple and complex synapses shown by freeze-etching of rat cortical synaptosomes

The shape of the synaptic sites (specialized contact areas) was examined on the synaptic membrane fracture faces of freeze-etched rat cortical synaptosomes. Simple and complex synapses were differentiated on the basis of the absence or presence of unspecialized areas in the synaptic sites. The particle-free nature of these areas is discussed.     

Ultrastructural changes in the MP3 neuron of the mollusk Lymnaea stagnalis after cryopreservation of the isolated brain

Investigation of a possibility of long-term storage of frozen (-196 degrees C) viable neurons and nervous tissue is one of the central present day problems. In this study ultrastructural changes in neurons of frozen-thawed snail brain were examined as a function of time. We studied the influence of cryopreservation, cryoprotectant (Me2SO), cooling to 4-6 degrees C, and a prolonged incubation in physiological solution at 4-6 degrees C on dictyosomes of Golgi apparatus, endoplasmic reticulum (ER) cisternae and mitochondria. It has been found that responses of these intracellular structures of cryopreserved neurons to the above influences are similar: dissociation of Golgi dictyosomes, swelling of endoplasmic reticulum cisternae and mitochondrial cristae. Both freezing-thawing and cryoprotectant were seen to cause an increase in the number of lysosomes, liposomes, myelin-like structures, and to form large vacuoles. The structural changes in molluscan neurons caused by cryopreservation with Me2SO (2 M) were reversible.     

Ultrastructural changes in the mitochondria of Retzius' neuron exposed to hydrocortisone

The ultrastructure of the Retzius cell (gigantic neurone) mitochondria of the medical leech was investigated. After seven repeated injections of hydrocortisone into the coelomic cavity, the transformation of laminar cristae of mitochondria into tubule-vesiculated structures was discovered. A question of correlation between the structure and function independently of the systematical position of the organism is discussed.     

Ultrastructural changes during cholestasis induced by chlorpromazine in the isolated perfused rat liver.

Addition of cholestatic doses of chlorpromazine-HC1 to the perfusate of isolated rat livers produces widespread changes in hepatocyte membrane structure. These findings include a marked increase in intrasinusoidal cytoplasmic bullae, appearance of intracellular vacuoles within hepatocytes at both sinusoidal and biliary poles, dilation of bile canaliculi and evagination of canalicular diverticuli, and the formation of myeloid bodies within hepatocytes. These findings obtained in the bile acid depleted perfused liver may result from physiochemical interactions between chlorpromazine or its metabolites and lipid-protein components of cell membranes, consistent with chlorpromazine's properties as a cationic detergent. They occur independently of the vasoconstrictive effects of chlorpromazine and suggest that chlorpromazine may produce cholestasis by altering hepatocyte membrane function.     

The uptake of horseradish peroxidase by cortical synapses in rat brain

Summary Horseradish peroxidase (HRP) was introduced directly into the cerebral cortex of adult rats, which were allowed to survive for 60 min before perfusion fixation. After the tissue had been incubated to demonstrate HRP at the LM and EM levels, blocks of cortical tissue were taken at varying distances from the injection site. These eight blocks of tissue constituted a time sequence for HRP diffusion.Qualitative examination of the presynaptic terminals showed that the most commonly encountered profiles are the plain synaptic vesicles, many of which accumulate tracer. In some terminals labelled vesicles are lined-up in tubular fashion. Other profiles commonly labelled are coated vesicles, tubular and vacuolar cisternae, and plain and coated pinocytotic vesicles.Quantitative analyses based on the number of terminals containing labelled profiles demonstrate an early rise in the rate of labelling of both plain synaptic vesicles and coated vesicles, after which synaptic vesicle labelling rises slowly towards a plateau. By contrast, there is a late parallel increase in the rate of labelling of coated vesicles and cisternae. A more detailed analysis, based on the actual numbers of labelled and total profiles within each presynaptic terminal, highlight early and late periods of rapid labelling for plain synaptic vesicles, coated vesicles and cisternae. A further aspect of HRP incorporation studied, concerns its uptake into four delineated regions of the presynaptic terminal.Our data indicate that membrane uptake into the presynaptic terminal is accomplished mainly via coated vesicles, although plain synaptic vesicles may also be involved. Coated vesicles, in turn, appear to give rise directly to plain synaptic vesicles, with some coalescing to produce vacuolar cisternae. The latter are involved in a two-way interchange of membrane with tubular cisternae, plain synaptic vesicles and coated vesicles. An additional source of plain synaptic vesicles are the tubular cisternae. Exocytosis of plain synaptic vesicles constitutes the mechanism by which transmitter is released from the presynaptic terminal.Supported by the Nuffield Foundation. We are grateful to Mr. M. Austin for help with the photography     

Neuronal and oligodendrocytic response to cortical injury: Ultrastructural and cytochemical changes

Summary A needle wound was made in the adult rat cerebral cortex. Responses of neurons and oligodendrocytes at the site of injury were followed over a period of 450 days and correlations made between morphological and enzyme cytochemical changes to clarify some phenomena previously unresolved.Evidence from acid phosphatase activity in degenerating neurons showed no increase in the number of cytochemically stained lysosomal profiles nor changes in the subcellular localization of the acid phosphatase reaction product. Our observations indicated that the majority of dying neurons were not digested by their own acid phosphatase autodigestion but by the process of heterodigestion. The time-course study revealed that not all the traumatized neurons were eliminated but some persisted permanently in an attenuated atrophic state. The atrophic neurons were small in size with low cytoplasmic-nuclear ratios and exhibited low levels of glucose-6-phosphatase and cytochrome oxidase activities. The acid phosphatase activity was slightly increased as evidenced by cytochemically stained hypertrophic Golgi cisternae and a slight increase in the number of lysosomes. The low level of enzyme activities, concerned with carbohydrate metabolism reflected the low metabolic activity in atrophic neurons whilst an increase in Golgi-lysosomal enzyme activity suggested some anabolic process necessary for their survival.Oligodendrocytes displayed only minor changes in morphology, and their glucose-6-phosphatase and cytochrome oxidase activities were normal, suggesting that these cells have little or no involvement in the repair of a cerebral wound. The absence of significant changes in lysosomal acid phosphatase activity indicated a minimal role, if any, of oligodendrocytes in the process of phagocytosis.     

Ultrastructural changes in cells of pea root cortical explants culturedIn vitro

Summary Root cortical explants from seedlings ofPisum sativum L., cv. Little Marvel were cultured on a sterile nutrient medium in the presence of auxins or auxins and cytokinin. Explants were fixed (and subsequently processed for electron microscopic observation) at the outset and after 30, 60, and 72 hours of culture under the two hormonal conditions. In the presence of auxin alone, the cell walls of the cortical parenchyma showed distinctive structural changes involving the deposition of a new, diffusely fibrillar primary wall. A considerable increase of rough ER in the adjacent cytoplasm was associated with the new wall synthesis. These wall changes are interpreted as auxin-induced and prelude to cell enlargement and later cell separation. No dramatic changes occurred in other cytoplasmic organelles or in the nucleus. In the presence of cytokinin and auxin, the striking cytological events observed included marked nuclear changes and greater cytoplasmic density due to increased organelles associated with the onset of DNA synthesis, mitosis and cytokinesis. New cell walls formed from the developed phragmoplasts, cleaving the original parenchyma cells into smaller cellular compartments with no accompanying cell enlargement. No marked changes in the original primary cell walls were observed in cytokinin-auxin-treated explants. By 72 hours some cells already had completed two successive cell divisions. No ultrastructural evidence was obtained suggesting that these cells were committed to their known fate of differentiating into mature tracheary elements in the subsequent 2–4 days. At 72 hours each explant represented a population of actively dividing, still considerably vacuolated meristematic cells.     

Ultrastructural changes in rat epididymis after vasectomy

Summary Epididymal biopsies from rats that had undergone unilateral or bilateral vasectomies from one to eight months previously were compared with biopsies from their contralateral side or from normal controls to ascertain what ultrastructural changes had occurred. After vasectomy, spermatozoa appeared to dissolve in the lumen of the caput epididymidis and to be absorbed by the principal cells. About 5 weeks after vasectomy, numerous lamellar accumulations became apparent in the supernuclear region. Their resemblance to lysosomes or residual bodies was confirmed by an acid phosphatase reaction. After 10 weeks, similar lamellar and polymorphic accumulations on the contralateral side of animals with unilateral vasectomies indicated that resorption had also increased on the unligated side.Publication No. 627 of the Oregon Regional Primate Research Center. This study was supported by NIH Grants No. RR-00163 and HD-05969.The author wishes to thank Ms. J. Hren for her excellent technical assistance.     

Ultrastructural evidence for a sensory-motor neuron in Ctenophora

A survey of the nerve-net of four species of ctenophores, using electron microscopy, reveals two types of highly differentiated sensory neurons. These two kinds of receptors are widely distributed all over the ectodermal epithelia. These sensory neurons form synapse-like junctions with epithelial effectors, for example mucous secretory cells. The evolutionary and behavioural significance of such relationships is discussed.