Ultrastructural Observations on the Gametocytic Stages of the Coccidium Tyzzeria chalcides Probert, Roberts & Wilson, 1988 from the Ocellated Skink Chalcides ocellatus

Gametogenesis of Tyzzeria chalcides Probert, Roberts & Wilson, 1988, from the ocellated skink, Chalcides ocellatus , occurs within the epithelium of the gali bladder. Transmission electron microscopy reveals that macrogamonts contain 2 types of wall-forming bodies. Type I bodies are large densely stained structures associated with rough endoplasmic reticulum and the Golgi apparatus. They appear to be formed within the Golgi itself. Type II bodies are less densely stained, smaller and appear to form directly from the rough endoplasmic reticulum. Canaliculi are associated with Type I wall-forming bodies and probably function to transport the wall-forming bodies to the pellicle. Micropores occur in the pellicie and large amylopectin granules, lipid globules and dense bodies are found within the cytoplasm of the macrogamont. Mature microgamonts contain in excess of 20 microgametes, each of which has 2 flagella and an associated mitochondrion. Both types of gamont are found within a parasitophorous vacuole, in the host cell, which is filled with vesicular material on which the gamonts probably feed.     

In vivo action of the anticoccidial diclazuril (Clinacox) on the developmental stages of Eimeria tenella: a histological study

Diclazuril, a new benzeneacetonitrile anticoccidial, has potent activity against various stages of Eimeria tenella. A single treatment of experimentally infected chickens during the prepatent phase (up to day 5) results in a complete interruption of the life cycle and oocyst shedding. The first- and second-generation schizonts show extensive degenerative changes that finally result in a complete loss of the parasitic stage. The degeneration is characterized by loss of internal structure, the appearance of many intracytoplasmic vacuoles, and incomplete merogony. The merozoites themselves show similar degenerative changes, including the presence of numerous small vacuoles in the cytoplasm. Diclazuril is also effective against both the micro- and macrogametocytes that have a ballooned appearance and loose their internal structure completely. In the macrogametocytes, wall-forming bodies either do not develop or disappear rapidly. Development of typical caecal lesions is prevented when treatment with diclazuril is initiated before large numbers of second-generation schizonts appear, i.e., day 3. It is concluded that diclazuril is lethal against both the asexual and the sexual stages of E. tenella. At the proposed use level of 1 ppm in the feed, the life cycle is interrupted at a very early stage and lesion development and oocyst shedding are completely prevented.     

The ultrastructure of macrogametes of Eimeria ferrisi Levine and Ivens 1965 in Mus musculus.

Macrogametes of Eimeria ferrisi occurred in epithelial cells of the cecum and colon of Mus musculus and were studied by electron microscopy. Young stages were identified as macrogamonts by the presence of wall-forming bodies. At first an outerlimiting membrane and remnants of the inner membrane complex of the former merozoite pellicle were present; the latter was later lost but in mature macrogametes 3 limiting membranes were observed. Type II wall-forming bodies appeared before type I; the former developed in expanded cisternae of the endoplasmic reticulum whereas the latter were smaller in size and appeared in the ground substance of the cytoplasm. After formation of the oocyst wall the bodies of the 2 types were no longer visible. The presenceodies of the 2 types were no longer visible. The persistence of micronemes in mature macrogametes and the presence of numerous layers of rough endoplasmic reticulum during wall formation have not been previously reported.     

Ultrastructural observations on Barroussia schneideri (apicomplexa,eucoccidiida) in the centipede Lithobius forficatus

The ultrastructure of the principal stages of Barroussia schneideri in the intestinal cells of the centipede, Lithobius forficatus, is described. The structure of the merozoites has much in common with that of other Eimeriidae: pellicle of an outer and two inner membranes, microtubules, mitochondria, micronemes, rhoptries, endoplasmic reticulum, and polysaccharide granules. The mature macrogamete has a large nucleus with a distinct nucleolus, wall-forming bodies of type 1 (WFB1), and presumably of type 2 (WFB2), and a large number of polysaccharide granules. The microgametocyte includes smaller polysaccharide granules closely associated with the cisternae of the endoplasmic reticulum. The microgametocyte surface is smooth in outline and has peripherally arranged nuclei. Microgametes have a curved nucleus, a mitochondrion, polysaccharide granules, and two flagella. One of the flagella is attached for some distance along the body.     

Fine-Structural Aspects of Microgametogenesis of Eimeria magna in Rabbits and in Kidney Cell Cultures*

SYNOPSIS. The fine-structural aspects of development of microgamonts of Eimeria magna were studied in kidney cell cultures and in experimentally infected rabbits. Spheroidal masses of gamont-like cytoplasm containing ribosomes, polyribosomes, and amylopectin granules were found within the parasitophorous vacuole; these bodies were apparently pinched off the surface of the gamont. Nucleoli were present in the early stages of nuclear division but disappeared as development proceeded. Spindles were eccentric and the nuclear membrane always remained intact in dividing nuclei. Nuclei eventually became elongate in shape, compact, and electron dense at the end oriented toward the periphery and lucent centrally. Usually, only the dense portion was incorporated into the gamete as the gamete developed by protruding from the gamont surface. Fullyformed microgametes were biflagellate and contained a nucleus, a mitochondrion, and 8-10 microtubules. Multiple-membrane complexes, which apparently originated from the nuclear envelope or endoplasmic reticulum, were found within the gamont residual body. Occasionally, 2 or 3 micro- and/or macrogamonts were seen within the same cell. In some cells one or 2 micro- or macrogamonts as well as several merozoites were present in the same parasitophorous vacuole.     

Ultrastructural differentiation of Toxoplasma gondii schizonts (types B to E) and gamonts in the intestines of cats fed bradyzoites

The ultrastructural characterisitics of four types of Toxoplasma gondii schizonts (types B, C, D and E) and their merozoites, microgamonts and macrogamonts were compared in cats killed at days 1, 2, 4 and 6 after feeding tissues cysts from the brains of mice. Schizonts, merozoites and gamonts contained most of the ultrastructural features characteristic of the phylum Apicomplexa. All four types of schizonts developed within enterocytes or intraepithelial lymphocytes. Occasionally, type B and C schizonts developed within enterocytes that were displaced beneath the epithelium into the lamina propria. Type D and E schizonts and gamonts developed exclusively in the epithelium. Tachyzoites occurred exclusively within the lamina propria. Type B schizonts formed merozoites by endodyogeny, whereas types C to E developed by endopolygeny. The parasitophorous vacuoles surrounding type B and C schizonts consisted of a single membrane, whereas those surrounding types D and E schizonts were comprised of two to four electron-dense membranes. The parasitophorous vacuole of type B schizonts had an extensive tubulovesicular membrane network (TMN); the TMN was reduced or absent in type C schizonts and completely absent in types D and E schizonts and gamonts. Type B merozoites were ultrastructurally similar to tachyzoites, except that they were slightly larger. Type C merozoites exhibited a positive periodic acid-Schiff reaction by light microscopy and ultrastructurally contained amylopectin granules. Rhoptries were labyrinthine in type B merozoites but were electron-dense in types C-E. The development of microgamonts, macrogamont and oocysts is also described.     

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.     

Fine Structure of Zygotes and Oocysts of Eimeria nieschulzi*

SYNOPSIS. Mature macrogamonts were present in the small intestine of rats 5.5 to 7.5 days postinoculation with Eimeria nieschulzi oocysts; oocysts were present at 6 to 7.5 days. Types I and II wall-forming bodies in macrogamonts began to undergo ultrastructural changes within zygotes to form the outer and inner layers of the oocyst wall. Before and during oocyst wall formation a total of 5 membranes (M1–5) were formed at or near the surface of the zygote. The outer and inner oocyst wall layers formed between M2 and M3, and M4 and M5, respectively. The mature oocyst was loosely surrounded by M1 and M2, had an electron-dense outer layer, 100–275 nm thick, and an electron-lucent inner layer, 160–180 nm thick. It also contained an electron-lucent line consisting of M3 and M4 interposed between the outer and inner layers of the oocyst wall. The micropyle, measuring 935 × 47 nm, was located in the outer layer of the oocyst wall and consisted of 10–14 alternating layers of electron-dense and lucent material. The sporont of mature oocysts was covered by M5, immediately beneath which were M6 and M7. The sporont contained a nucleus and nucleolus, lipid and amylopectin bodies, mitochondria, ribosomes, as well as smooth and rough endoplasmic reticulum. Canaliculi, Golgi complexes, and types I and II wall-forming bodies were absent.     

The sexual stages of Eimeria wyomingensis Huizinga and Winger, 1942, in experimentally infected calves

Seven of 12 calves given 10(6) Eimeria wyomingensis sporulated oocysts had sexual stages of the parasite when examined at necropsy. Clinical signs of coccidiosis were not observed in any calf. Sexual stages were located in host cells in the lamina propria of the villi in the terminal small intestine. Infected host cells underwent nuclear and cytoplasmic hypertrophy. Immature microgamonts usually had folded cytoplasm and an overall spherical to elongate shape. Mean length and width +/- SEM of immature microgamonts were 43.3 +/- 1.6 by 29.0 +/- 1.1 micron. Mature microgamonts contained hundreds of microgametes, lacked visible cytoplasmic folds, and measured 52.8 +/- 4.7 by 43.0 +/- 4.2 micron. Macrogamonts were spherical to ovoid and had a large nucleus and prominent nucleolus. Immature macrogamonts without visible wall-forming bodies measured 16.0 +/- 0.5 by 13.3 +/- 0.2 micron. Mature macrogamonts had 3-8-micron eosinophilic wall-forming bodies and measured 24.6 +/- 0.7 by 19.6 +/- 0.8 micron. Oocysts were ovoid and had a 2-3-micron-thick eosinophilic oocyst wall. A micropyle was present in appropriately sectioned oocysts. Oocysts measured 27.7 +/- 1.7 by 19.3 +/- 0.8 micron. The sexual stages of E. wyomingensis are compared to those described previously for species of Eimeria infecting the bovine small and large intestines.     

Ultrastructure of Cryptosporidium wrairi from the Guinea Pig

SYNOPSIS. The ultrastructure of the known tissue stages of Cryptosporidium wrairi Vetterling, Jervis, Merrill, and Sprinz, 1971 parasitizing the ileum of guinea pigs is described. Young trophozoites are surrounded by 4 unit membranes, the outer 2 of host origin, the inner 2 the pellicle of the parasite. Each trophozoite contains a vesicular nucleus with a large nucleolus. Its cytoplasm contains ribosomes, but eventually fills with cisternae of the rough endoplasmic reticulum. As the trophozoite matures the area of attachment of the parasite to the host cell becomes vacuolated, with vertical membranous folds. It is apparent that the parasite acquires nourishment from the host cell thru this area of attachment. As schizonts develop, (a) multiple nuclei appear, (b) the endoplasmic reticulum enlarges, (c) the attachment zone increases in area, (d) large vacuoles, which develop as endocytotic vesicles in the attachment area, are found in the cytoplasm and (e) the inner unit membrane of the parasite pellicle is resorbed around the sides of the developing schizont. Following nuclear division, merozoites develop from the schizont by budding. Merozoites have an ultrastructure similar to that described for other coccidia except that no mitochondria, micropores, or subpellicular tubules were observed. Merozoites penetrate the epithelial cell causing invagination of the microvillar membrane and lysing it. No unit membrane is formed between the parasite and the host cell. However, the cell produces one or 2 dense bands adjacent to the parasite attachment area. The macrogamete contains a nucleus, endoplasmic reticulum, attachment zone, and large vacuoles. It also contains a variety of granules, some of which are polysaccharide. The immature microgametocyte contains multiple compact nuclei. No mature microgametocytes or zygotes were found.     

The fine structure of the developing macrogamete of Eimeria maxima

The fine structure of the developing macrogamete of Eimeria maxima was studied from chicks killed at intervals from 138 to 147 h after inoculation. The macrogamete developed within a parasitophorous vacuole. Lying within the vacuole and extending for some distance around the periphery of the macrogamete were intravacuolar tubules, grouped in certain areas, and in some cases they were seen to make direct connexions with the cytoplasm of the parasite. During development, electron-pale vesicles were pinched off externally from the surface of the macrogamete. There appeared to be 2 forms of wall-forming bodies of the Type I during development, one form being less osmiophilic than the other. Other organelles present, such as wall-forming bodies of Type II, granular endoplasmic reticulum, mitochondria, canaliculi, lipid inclusions and intravacuolar folds, were similar in structure to those of other Eimeria species.     

Fine Structure of Microgametocytes and Macrogametes of Eimeria nieschulzi

SYNOPSIS. An electron microscope study of microgametocytes and macrogametes of Eimeria nieschulzi Dieben, 1924 revealed that they lie within vacuoles bounded by a host unit membrane. The vacuole surrounding the microgametocyte contains granular material. The vacuole around the macrogamete is narrower and contains vesicles and membranes. Micropores were seen on the surface of the plasma membrane of microgametocytes and macrogametes. Microtubules were seen in macrogametes. Young microgametocytes and macrogametes have a similar cytoplasmic matrix, mitochondria and nuclei. Glycogen granules apparently develop around vacuoles in both microgametocytes and macrogametes. Glycogen granules were also seen along the margins of parallel bundles of fibers in microgametocytes. As nuclei of the microgametocyte divide, they move to the periphery of the parasite. Three basal bodies, each with 9 fibers in triplet form, develop in association with each nucleus. Microgametes have 2 free flagella and a central short, attached flagellum. Basal granules lie along the outer fibers of the central flagellum. Each microgamete has an elongate mitochondrion in close contact with the nucleus. In macrogametes wall-forming bodies develop in lacunae in the cytoplasm. Smaller dark bodies with areas of low density were also seen. Wall-forming bodies and dark bodies move to the periphery of mature macrogametes.     

Fine structure of the formation and fate of the residual bodies of mouse spermatozoa with evidence for the participation of lysosomes

Routine electron microscopy in combination with subcellular localization of acid phosphatase has been employed to study the formation and fate of residual cytoplasmic bodies extruded into the tubular lumen shortly before spermiation. Prior to extrusion the spermatid cytoplasm contains lipid droplets, mitochondria, ribosomes, endoplasmic reticulum, the caudally migrated Golgi apparatus, and numerous multivesicular and multigranular bodies. These membrane-limited bodies and the Golgi zone stain heavily for acid phosphatase. Following extrusion the residual bodies undergo a series of alterations: (1) disruption of multigranular bodies with release of free granules; (2) sequestration of granules, ribosomes, and reticulum inside double-membrane-limited vacuoles derived from Golgi lamellae; (3) appearance of numerous, single-membrane-bound, cytoplasmic vacuoles; (4) fragmentation; (5) peripheral migration toward the tubular wall; and (6) phagocytosis of these migrating fragments by the Sertoli cells. The demonstration of acid phosphatase activity within free granules, the sequestering Golgi lamellae, and both classes of vacuoles suggests that initial residual body degradation occurs through lysosomal cytoplasmic autophagy.     

Fine Structure of the Esophagus of Pratylenchus penetrans

The fine structure of the esophagus of Pratylenchus penetrans is described. The gland lobe is syncytial and contains two types of nuclei: three large nuclei with little chromatin, and more numerous smaller nuclei with large amounts of chromatin. Some of the smaller nuclei are associated only with glandular tissue, whereas others are part of nerve ceils within the esophagus. Clusters of free ribosomes, rough endoplasmic reticulum, and numerous mitochondria occur in the lobe region where the secretory granules are formed. No Golgi bodies were observed. On the basis of these observations, possible differences in the mechanism of secretory granule formation between plant-parasitic nematodes are discussed. Several other minor differences between the fine structure of other plant-parasitic nematodes previously examined and that of P. penetrans are also noted.     

STUDIES ON SMALL INTESTINAL CRYPT EPITHELIUM : I. The Fine Structure of the Crypt Epithelium of the Proximal Small Intestine of Fasting Humans

Small intestinal crypt epithelium obtained from normal fasting humans by peroral biopsy of the mucosa was studied with the electron microscope. Paneth cells were identified at the base of the crypts by their elaborate highly organized endoplasmic reticulum, large secretory granules, and small lysosome-like dense bodies within the cytoplasm. Undifferentiated cells were characterized by smaller cytoplasmic membrane-bounded granules which were presumed to be secretory in nature, a less elaborate endoplasmic reticulum, many unattached ribosomes and, in some cells, the presence of glycogen. Some undifferentiated cells at the base of the crypts contained lobulated nuclei and striking paranuclear accumulations of mitochondria. Membrane-bounded cytoplasmic fragments, probably originating from undifferentiated and Paneth cells, were frequently apparent within crypt lumina. Of the goblet cells, some were seen actively secreting mucus. In these, apical mucus appeared to exude into the crypt lumen between gaps in the microvilli. The membrane formerly surrounding the apical mucus appeared to fuse with and become part of the plasma membrane of the cell, suggesting a merocrine secretory mechanism. Enterochromaffin cells were identified by their location between the basal regions of other crypt cells and by their unique intracytoplasmic granules.     

Ultrastructural studies on the sporulation of oocysts of Toxoplasma gondii. I. Development of the zygote and formation of the sporoblasts

The initial stages of sporulation in oocysts of Toxoplasma gondii were examined in samples sporulated at 27 degrees C for 0, 6, 12, 16 and 24 hours. The initial zygote was roughly spherical and was limited by a single unit membrane. A few micropores of the inactive type were present on this membrane. The cytoplasm contained a large nucleus with a nucleolus, a number of polysaccharide granules, lipid globules, mitochondria, and Golgi bodies together with a few strands of rough endoplasmic reticulum. After the initiation of sporulation little change was noted in the cytoplasm except for an increase in protein synthesis as evidenced by the augmentation of the amount of rough endoplasmic reticulum and the appearance of polyribosomes. Nuclear division occurred twice giving rise to four nuclei which were situated close to the cell periphery and well separated from each other. At this multinucleate stage a second limiting membrane was formed. The cytoplasmic mass then divided to form the two sporoblasts. This was accomplished by an invagination of the limiting membranes in combination with internally formed membranes. The two binuclear sporoblasts were roughly spherical. They were limited by two unit membranes and contained the same cytoplasmic organelles as described for the zygote.     

Ultrastructural pathology of the epidermis of molting elaterid larvae (Coleoptera) with a fungus and a bacterium in the ecdysial space

Toxins produced by the fungus Metarrhizium anisopliae and the bacterium Pseudomonas aeruginosa in the ecdysial space of a molting wireworm are absorbed through the thin new cuticle and ultrastructurally change the epidermal cells into two distinct types. One is a rounded, degenerative type characterized by a “light” cytoplasm with vesiculated rough endoplasmic reticulum, rounded mitochondria with degenerated cristae, little ground plasm, and a rounded nucleus with little nucleoplasm and large globules of condensed chromatin from which chromatin fibrils separate in loose folds or granulelike tight folds. The other type has very irregular outlines and is characterized by a “dark” cytoplasm with abundant, whorled laminae of rough endoplasmic reticulum and abundant free ribosomes in a dense ground plasm, large rounded clear vacuoles, and apparently normal mitochondria and nuclei. The fungal toxins are believed to be primarily responsible for the formation of the light cells, and the bacterial toxins, for the separation of the chromatin into fibrils in the light cells, the fusion of their nuclei into large nuclear bodies, and the changes in the cytoplasmic contents of the dark cells. The dark cells, although abnormal, appear to retain a limited secretory activity.     

Ultrastructure of macrocellular (large cell) carcinomas of the lung

The electronmicroscopic investigation of five lung tumors histodiagnosed as macrocellular carcinomas showed the ultrastructural monomorphism of large, variedly shaped neoplastic cells, lack of intercellular junctions, voluminous nuclei with many indentations of nuclear membrane, dispersed euchromatin, large and multiple nucleoli, and nuclear bodies. A reduced number of cytoplasmic organelles was characteristic for these cells, represented mainly by mitochondria, rare rough endoplasmic reticulum, free ribosomes rare Golgi vesicles and flattened tubules, and a various amount of tonofilaments. These features characterized the poorly differentiated proliferation forming these tumors. The elements of differential diagnosis from other poorly differentiated lung tumors (epidermoid and cylindrocubic) are discussed, allowing the consideration of this proliferation type with repressed differentiation and maturation as a real one in the framework of lung carcinomas.     

The neurocytes of the caudal part of the tuberomamillary nucleus in Ovis aries L. (light microscopy and electron microscopy studies)

The neurons of the pars caudalis nuclei tuberomammillaris (pc-NTM) were studed light-microscopically and electron-microscopically in sheep and rams of Merino breed. In our study we observed: In the regarded neural nucleus, there is the majority of the great neurons (up to 60 microns in diameter) rich in the NISSL's bodies. When stained with the cresyl violet, the NISSL's substance is apparently stored mainly in peripheral area of the cell body and in the distant parts of numerous protoplasmic processes, what evokes an impression of the "jagged" surface of these cells. After staining with paraldehyde fuchsin, we found purple coloured lumps of irregular shape stored outside the cell bodies, in the neuropil. The less extended cells, usually with lower content of NISSL bodies, are in pc-NTM less frequent. In the electron-microscopic study we identified 3 types of neurons: Cells rich in rough endoplasmic reticulum; "light" cells, "dark" cells. The cells of the 1st type were the most frequent ones. Cisterns of rough endoplasmic reticulum in the 1st type of cells are often dilated. The protoplasmic processes of these cells are frequently stepped over by flat tubuli of endoplasmic reticulum. The 2nd type of cells is characterized by the light cytoplasmic matrix, low quantity of endoplasmic reticulum and frequent occurrence of lipofuscin bodies. The 3rd type of cells are characterized by the high density of cytoplasmic matrix, well developed GOLGI complex, and very broad cisterns of endoplasmic reticulum, forming a labyrinth, and it is bound to a broad perinuclear space.     

Fine-structural aspects of microgametogenesis of Eimeria magna in rabbits and in kidney cell cultures.

The fine-structural aspects of development of microgamonts of Eimeria magna were studied in kidney cell cultures and in experimentally infected rabbits. Spheroidal masses of gamont-like cytoplasm containing ribosomes, polyribosomes, and amylopectin granules were found within the parasitophorus vacuole; these bodies were apparently pinched off the surface of the gamont. Nucleoli were present in the early stages of nuclear division but disappeared as development proceeded.