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J C Siim

Publications and source records attributed to J C Siim.

At least 37 records · Page 2Linked to original sources
PubMed1979

An ultrastructural study on the excystation of the sporozoites of Toxoplasma gondii.

The ultrastructural changes which occur during the in vitro excystation of the sporozoites of Toxoplasma gondii were examined. The excystation was carried out at 37 degrees C on suspensions of oocysts which had been ground and then treated with an excysting medium containing 0.25% trypsin and 0.75% sodium taurocholate in phosphate buffered saline, pH 7.3. It was found that sporocysts within intact oocysts were unaffected while sporocysts exposed to the medium ruptured. The sporocyst wall consisted of two layers and during excystation the four plates which form the inner layer started to curl inward. At the same time changes were seen at the specialized junctions between these plates. When the junctions finally break, the plates separate. The outer layer of the sporocyst wall is then ruptured at points directly above where the plates were joined. Each of the four portions of the sporocyst wall curled inward to form a tightly wound whorl. The sporozoites can escape through the openings created between the portions of the sporocyst wall.

Animals↗
PubMed1979

Toxoplasma Gondii: scanning electron microscope studies on the small intestine of infected and uninfected cats.

The mucosal surfaces of villi from the small intestine of cats infected with Toxoplasma gondii were studied with the scanning electron microscope and compared with those from uninfected control cats. In uninfected cats villi were predominantly leaf shaped and were lined with ridges; goblet cell openings could be seen. The enterocytes had a hexagonal surface outline and were dome-shaped. Infected cats had both normal and abnormal villi. Injured villi were shortened and attained a broad leaf shape, often with blunt edges. Enterocytes containing oocysts were enlarged, and microvilli were resolvable only on these surfaces. Ruptured cells from which parasite discharge had occurred were seen. Oocysts were observed and possessed a smooth coat.

Animals↗
PubMed1978

Observations on the ultrastructure of the sporocyst and the initiation of sporozoite formation in Toxoplasma gondii.

The ultrastructure of the immature sporocyst and the initiation of sporozoite formation in T. gondii was examined in oocysts which had been allowed to sporulate for 12 or 24 hours at 27 degrees C. The sporocyst was ellipsoidal in shape and possessed a two layered sporocyst wall. A nucleus, with associated Golgi bodies, was situated at either end of the organism. The cytoplasm of the sporocyst also contained a number of polysaccharide granules, lipid globules, mitochondria and a few strands of rough endoplasmic reticulum. Sporozoite formation was initiated by the appearance of two dense plaques at either end of the organism in the vicinity of a nucleus, adjacent to the limiting membrane of the organism.

Cell Membrane↗
PubMed1978

Light and electron microscopy on the sporulation of the oocysts of Eimeria brunetti. I. Development of the zygote and formation of the sporoblasts.

The initial stages of sporulation in oocysts of Eimeria brunetti were examined in samples sporulated at 27 degrees C for 0, 12 and 24 hours. The initial zygote was found to be roughly spherical and to contain a number of polysaccharide granules which were congregated in one region of the organism. The cytoplasm also contained some strands of rough endoplasmic reticulum together with a number of mitochondria, some Golgi bodies, and some electron translucent vacuoles. The nucleus was large, with amorphous nucleoplasm and a nucleous. The cytoplasmic mass of the zygote was limited by a single unit membrane which possessed some micropores. After initiation of the sporulation, the metabolic activity of the organism appeared to increase as evidenced by the augmentation in the cytoplasm of the amounts of rough endoplasmic reticulum, number of Golgi bodies, and the appearance of polyribosomes. However, at this stage, the presence of large spherical bodies (anlagen of the refractile bodies of the sporozoites) constituted the most obvious change in the cytoplasm of the organism. After nuclear division the daughter nuclei were situated well separated in the cytoplasm and the polysaccharide granules were evenly distributed throughout the cytoplasm of the zygote. Eventually four sporoblasts were formed by invaginations of the limiting membrane. Each sporoblast was limited by a unit membrane and contained a nucleus, and the same cytoplasmic organelles as found in the zygote. The development of the sporoblast was initially accompanied by the appearance of a second limiting membrane.

Cytoplasm↗
PubMed1978

Light and electron microscopy on the sporulation of the oocysts of Eimeria brunetti. II. Development into the sporocyst and formation of the sporozoite.

The later stages of sporulation in oocysts of Eimeria brunetti were examined in samples which had been allowed to sporulate at 27 degrees C for 24, 36 and 48 hours. It was observed that the sporoblasts became ellipsoidal and the nucleus underwent the final division. A nucleus with associated Golgi bodies was not observed at either end of the organism. The cytoplasm was limited by two unit membranes and contained rough endoplasmic reticulum, dense bodies, electron translucent vacuoles and mitochondria. The first evidence of sporozoite formation was the appearance of a dense plaque at either end of the organism. This appeared in the vicinity of the nuclei, and adjacent to the limiting membrane of the soroblast. At this stage the sporocyst wall was still unformed. Then the two sporozoites were formed from opposite ends of the organism by growth of the dense plaques and invaginations of the plasmalemma which thus formed the pellicles of the developing sporozoites. A conoid and subpellicular microtubules were observed at this stage as development continued, a number of vacuoles were found between the nucleus and the conoid. These vacuoles constituted the precursors of the rhoptries and micronemes. At the same stage a large dense body had appeared within the forming sporozoite. As the sporozoite developed, this body, anterior refractile body, is followed by the nucleus and another dense body which formed the posterior refractile body. During this period, the thin sporocyst wall was formed and Stieda and sub-Stieda bodies were now present at one end of the sporocyst. Each mature sporocyst contained two sporozoites.

Cytoplasm↗
PubMed1977

Ultrastructural studies on the endogenous development of Eimeria brunetti. II. Microgametogony and the microgamete.

The ultrastructural changes of Eimeria brunetti which occur during microgametogony in the small intestine of the domestic fowl are described. The development of the trophozoite into the microgametocyte was accompanied by cytoplasmic growth and nuclear division. The developing microgametocytes could be differentiated from developing schizonts because of ultrastructural differences in both cytoplasm and nuclei. The surface area of the microgametocyte was increased by deep invaginations of the limiting membrane. At this developmental stage, the nuclei were situated adjacent to this membrane and protrusions which developed, initiated microgamete formation. Two centrioles were positioned between each nucleus and the limiting membrane and were transformed into the basal bodies of the flagella. The flagella grew out from the basal bodies which then entered the protrusions. A mitochondrion and the dense chromatin-containing portion of the nucleus also entered each protrusion. The microgametes matured while they were attached to the residual cytoplasm of the microgametocyte; they were finally budded off into the parasitophorous vacuole. The microgamete consists of an elongated nucleus which overlaps a mitochondrion towards the arterior of the cell. At this end, a dense plaque (perforatorium) is found together with the 2 basal bodies and their attached flagella. 5 microtubules were apparent and ran longitudinally from the basal body region. In cross section they were arranged in a row of 4 with 1 diagonally opposite; only 2 of these microtubules extended to the posterior tip of the microgamete.

Animals↗
PubMed1977

Ultrastructural studies on the endogenous development of eimeria brunetti. III. Macrogametogony and the macrogamete.

The ultrastructural changes occurring during macrogametogony in Eimeria brunetti were studied in tissue from the small intestine of infected young domestic fowls. As the macrogametocyte developed, an increase in the volume of the cytoplasm and the nucleus occurred. At this early stage of development the organism was limited by a single unit membrane which possessed a number of micropores. The organism was situated in a parasitophorous vacuole which contained intra-vacuolar folds and intra-vacuolar tubules. The wall forming bodies of type II (WFB II) started to appear before the wall forming bodies of Type I (WFB I). The WFB I developed in the cytoplasmic matric whereas the WFB II were formed within the cisternae of the rough endoplasmic reticulum apparently in association with Golgi bodies. The mature WFB I were homogeneous, limited by a unit membrane, and larger than WFB II which had no limiting membrane but remained surrounded by a membrane of the rough endoplasmic reticulum. Polysaccharide granules were formed in the cytoplasm between strands of the rough endoplasmic reticulum. During maturation the WFB I & II and the polysaccharide granules increased in size and number, and as this occurred a number of electron translucent vacuoles were ejected from the surface of the macrogametocyte. The mature macrogamete possessed a large nucleus with a nucleolus, a number of multi-membranous vacuoles, mitochondria, and canaliculi. The WFB I & II were located at the cell periphery and the polysaccharide granules further towards the interior of the organism. The organism was limited by a unit membrane but during macrogametogony a homogeneous layer had developed which extensively coated the macrog...

Animals↗
PubMed1977

Observations on the ultrastructure of the late sporoblasts and the initiation of sporozoite formation in Eimeria brunetti.

The ultrastructure of the late sporoblast and the initiation of sporozite formation in E. brunetti was examined in oocysts which had been allowed to sporulate for 24 hours at 27 degrees C. The late sporoblast was ellipsoidal in shape and possessed two nuclei, and with associated Golgi bodies, situated at either end of the organism. Its cytoplasm contained numerous polysaccharide granules, electron translucentral region of the plaques. Sporozoite formation was similar to the initiation of merozoite formation in the schizont. Endodyogeny did not appear to be involved in the process of sporozoite formation.t vacuoles, dense bodies, mitochondria, and some strands of rough endoplasmic reticulum. The sporoblast, at this stage, was enclosed by two unit membranes. Sporozoite formation was initiated by the appearance of a dense plaque at either end of the organism in the vicinity of a nucleus, adjacent to the limiting membrane of the sporoblast. A conoid was present in the central region of the plaques Sporozoite formation was similar to the initiation of merozoite formation in the schizont. Endodyogeny did not appear to be involved in the process of sporozoite formation.

Animals↗
PubMed1977

Ultrastructural studies on the endogenous development of Eimeria brunetti. IV. Formation and structure of the oocyst wall.

The ultrastructural changes occurring during wall formation in the oocysts of E. brunetti were studied in tissue from the small intestine of young domestic fowls. The process of oocyst wall formation was initiated by a separation of the limiting membranes of the cytoplasmic mass of the macrogamete, to form a loose veil, consisting of 2-3 membranes, around the organism. Concomitant with the appearance of the veil, changes were observed in the Wall Forming Bodies of Type I (WFB I) and Type II (WFB II) which were present in the cytoplasm of the macrogamete. The outer layer of the oocyst wall seemed to be formed by a combination of membranes released from the surface of the organism and the contents of the WFB I. A 700 nm thick layer was thereby formed and, at this stage, the WFB I had disappeared from the cytoplasmic mass. The outer layer further condensed into a structure 250-350 nm in thickness in which 3 zones of different densities could be distinguished. The formation of the inner layer of the oocyst wall appeared to be associated with material from the WFB II and these disappeared from the cytoplasmic mass as the inner layer became evident. This inner layer was homogeneous in appearance and 80 nm thick. Comparison of the ultrastructure of the walls of oocysts obtained from chicken faeces with that of oocysts observed within the intestine showed only minor differences. The loose veil was not present in oocysts isolated from faeces and some changes were also noted in the outer zone of the outer layer of the oocyst wall. These differences could result from the mechanical and chemical treatments used for processing the faeces.

Animals↗
PubMed1977

Cytochemical electron microscopy on polysaccharide granules in the endogenous forms of Eimeria brunetti.

The endogenous stages in the life cycle of Eimeria brunetti were tested for polysaccharide material by electron microscopical cytochemistry using the periodic acid-thiocarbohydrazide-osmium tetroxide (PATO)-method. The parasites were observed within the epithelial cells of the small intestine of infected domestic fowls. Two types of granules reacted positively for polysaccharide. The first was large, approximately 500 nm by 250 nm. These granules had an appearance similar to the polysaccharide granules reported for other coccidian parasites. They were observed in mature merozoites, macrogamonts, and developing oocysts. The second type of granule was smaller (15-30 nm in diameter) and was only observed at the periphery of the residual cytoplasmic mass of mature microgamonts. It was more similar in appearance to metazoan glycogen than the former. However, since the PATO-method does not differentiate between different polysaccharides it can not be proven if these granules in fast contain glycogen. The WFBI of the macrogamete and the outer layer of the oocyst wall gave a slight positive reaction but after examination of the controls it appeared that this was not a specific reaction for polysaccharides.

Cytoplasmic Granules↗
PubMed1977

[Cytochemical study of the different stages in the life cycle of Toxoplasma gondii. IX. The polysaccharides and lipids in the parasites at developmental stages from the cat intestine].

Amylopectin was detected in all the stages examined. In the oval stages the minute granules of PAS-positive material were seen in the cytoplasm when examined on fresh-frozen sections. In merozoites, amylopectin was more conspicuous with maturation. The residual body of microgametocytes contain large amounts of amylopectin; no polysaccharide was visualized in microgamete bodies. Amylopectin was most abundant in macrogametocytes and zygotes. However, no peripheral position of PAS-positive "plastic granules" (wall-forming bodies), so characteristic of other coccidia and revealed by the electron microscopy for T. gondii macrogametocytes, was seen. Acid mucopolysaccharides in the macrogametocyte were detected in the central zone, leaving the periphery of the cell unstained. Very small, if any, amounts of lipids were detected in asexual stages of T. gondii. Unlike, large accumulation of lipid droplets were seen in growing macrogametocytes suggesting the involvement of lipids along with amylopectin in the metabolism of oocysts later discharged from the host body.

Amylopectin↗
PubMed1977

[Cytochemical study of different stages in the life cycle of Toxoplasma gondii. VII. Oxidation--reduction enzymes in the cyst forms].

Dehydrogenases of glycolysis, Kreb's cycle, and pentose-phosphate shunt were detected in cystozoites of Toxoplasma gondii strain SS-119 with various degrees of activity. A mixed oxidative metabolism may be postulated on this stage of the toxoplasma life cycle. Besides, the activity of cytochrome oxidase was detected in cystozoites; the addition of cytochrome c to the incubation medium significantly intensified the reaction intensity. Of interest seems the observation of a layer of higher enzymatic activity in the host brain tissue in the immediate neighbourhood with the cyst body. This may be regarded as the host cells' (or tissue') response to the presence of the parasite's alien body.

Dihydrolipoamide Dehydrogenase↗
PubMed1976

The effect of endo-enteric development of Toxoplasma gondii on the ultrastructure of epithelial cells of the small intestine of infected cats.

Toxoplasma gondii undergoing endo-enteric development in the small intestine of the cat affects the ultrastructure of the epithelial cells. The epithelial cells from infected cats have swollen rough endoplasmic reticulum and the mitochondria may be swollen with degenerate cristae. A statistically significant shortening of the microvilli of the epithelial cells was demonstrated. It appeared that the effect on the microvilli length was related to the parasite distribution within the small intestine. These changes occur in both cells with and without parasites present at the level of the sections studied. The abnormalities are quickly rectified after the disappearance of the endo-enteric forms of Toxoplasma.

Animals↗
PubMed1976

Ultrastructural studies on the endogenous development of Eimeria brunetti.

The schizonts of Eimeria brunetti were studied in the epithelial cells of the small intestine of infected chickens. The morphology of the host/parasite relationship was typical of that reported for other Eimeria spp. The initial dedifferentiation of the infecting organism generally occurred within the parasite cytoplasm but it was also observed that cytoplasm containing organelles could be budded off into the parasitophorous vacuole. Development into the schizont was accompanied by cytoplasmic growth and nuclear division. During nuclear division an eccentrically located nuclear spindle was present. Merozoite formation was initiated just below the limiting membrane of the schizont and was associated with the final nuclear division. The merozoites developed as protrusions from the schizont surface and merozoite organelles developed within these cytoplasmic projections. From this early stage, the developing merozoite grew and matured and the fully formed merozoites were found attached to a small residual mass of schizont cytoplasm. The 1st generation schizont is the only one which can be separately characterized. It differs from those of subsequent generations in a) possessing a refractile body, b) being larger and producing a larger number of merozoites, c) possessing invaginations of the limiting membrane, and d) the intra vacuolar folds of its parasitophorous vacuole are more extensive.

Animals↗
PubMed1975

The ultrastructural development of the macrogamete and formation of the oocyst wall of Toxoplasma gondii.

The macrogametes of Toxoplasma gondii develop within the epithelial cells of the cat ileum. As they develop the nucleus enlarges and dense patches of chromatin which were present in the nucleoplasm, disappear. Polysaccharide granules and lipid globules appear in the cytoplasm and increase in number during development. The wall-forming bodies of Type I (WFB I) appear before the wall-forming bodies of Type II (WFB II); WFB I are smaller, more osmiophilic and more numerous than the WFB II. The WFB I appear to form from vesicles produced by the smooth endoplasmic reticulum, and the WFB II form within the lacunae of the rough endoplasmic reticulum. Double membraned vacuoles appear to form from the nuclear membranes but the function of these is unknown. Throughout development the macrogamete retains a normal pellicle which possesses numerous micropores. The first evidence of oocyst wall formation is the appearance of participate matter in the parasitophorous vacuole which precipitates to form Layer 1 of the oocyst wall. Layers 2 and 3 are unit membranes which form between Layer 1 and the pellicle. During this development the organism has an organelle complement similar to that of the macrogamete. Layers 4 and 5 form between Layer 3 and the pellicle. Layer 4 is osmiophilic and its formation is accompanied by the disappearance of WFB I. Layer 5 is less osmiophilic than Layer 4 and its formation is accompanied by the disappearance of WFB II. The two innermost layers (Layers 4 & 5) in the oocyst wall of Toxoplasma are similar to those found in Isospora spp. and Eimeria spp. Toxoplasma seems to be unusual in that, firstly, it possesses an additional 3 layers and, secondly, all 5 layers are formed outside the pellicle of the original macrogamete.

Animals↗