An Electron Microscope Study of Toxoplasma

Cytoskeleton of Apicomplexan Parasites

“…It has been suggested that the conoid plays a mechanical role in invasion by parasites that must penetrate the robust barrier of the intestinal epithelium of vertebrates (26,108,121,136,138). The conoid consists of a set of counterclockwise spiraling filaments that create a pointed or coneshaped structure at the extreme apex of these parasites (26,64,136,138,153). Extrusion of the conoid can be stimulated by ionomycin-triggered calcium influx, whereas pretreatment with cytochalasin D inhibits conoid extrusion (108).…”

The Ultrastructure of Leishmania donovani

“…Sectioned material provides a much clearer picture of this structure. The study of Toxoplasma by Gustafson et al (1954) shows the nuclei in a variety of shapes, but all show a consistent dense inass within the nucleus. The present study of Leishmania donovani confirms the presence of the nuclear menlbrane; and in optimum sections, a double nuclear membrane may be seen.…”

Parasitic Diseases of Man (Recent)

“…Jacobs (104) described it as "crescentic or arc-shaped," with one end more attenuated than the other, measuring 4 to 7 (J. by 2 to 4 (J., with a vesicular nucleus, and lacking a neuromotor apparatus. Gustafson et al, ( 106), studying electron microscope sections (0.05 (J. or less), described a hollow "conoid" organelle within the cytoplasm, having its distal end asso ciated with the more pointed end of the cell membrane and its open base near the center of the cell; and associated with the "conoid" 14 to 18 solid fibrils ( "toxonemes"), attenuated distally and coarser proximally, extend ing into the cytoplasm of the cells. Toxoplasma utilizes the Krebs cycle of oxidative metabolism, with glucose as a substrate and evolution of CO2, Respiration is 85 per cent inhibited by cyanide (107).…”