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° 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.
observations on microgametogenesis and the structure of the microgamete of lsosporu ,felis. Acta path. microbiol. scand. Sect. B, 88: 151-159, 1980.The endogenous forms of lsospora felis were observed within the epithelial cells of the small intestine of the cat. They 'were situated within a parasitophorous vacuole which was limited by a multimembranous wall. The ultrastructural features of microgametogenesis were studied at 8 days posiinfection. The initial phase of microgamont development consisted of cytoplasmic growth accompanied by a number of nuclear divisions. The gamont was enclosed by a pellicle and its surface area was greatly increased by deep invaginations. In the later stages of development the numerous nuclei were situated close to the pellicle. Each nucleus has peripherally condensed chromatin. Formation of the microgametes occurred as protrusions from the microgamont surface. Two basal bodies. the dense portion of a nucleus and a mitochondrion entered each protrusion. The microgametes matured while still attached to the gamont from which they finally budded off into the parasitophorous vacuole leaving a large residual cytoplasmic mass. The mature microgamete was found to consist of an elongate nucleus which overlaps with a mitochondrion towards the anterior end of the organism. The anterior portion contains a dense perforatorium and two basal bodies with attached flagella. In addition a number of microtubules (5-9) were found to run longitudinally from the basal body region.
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