Microscopic Study of Mechanoreceptors and Chemoreceptors of Anterior and Posterior Ends of Toxocara Canis Using Scanning Electron Microscopy and Light Microscope

The present study investigated the fine structure of amphids and phasmids, cuticle, muscles, and digestive tracts of Toxocara canis using optical and electron microscopy, hematoxylin-eosin (H&E) staining, and other specific stains. A number of 38 adult T.canis worms were obtained from the animal shelter of Urmia, and their small intestines were fixated in acidified formal alcohol and 10% formalin solutions. The anterior and posterior parts of male and female T.canis worms were prepared and cut at a thickness of 4-5 μm according to the conventional method in the histological laboratory. The samples were then stained using H&E and specific periodic acid-Schiff, Masson's trichrome, and Orcein staining. The structure of amphid (anterior), phasmid (posterior), cuticle, muscles, and digestive tracts of male and female worms were studied under light microscopy. Basal, intermediate, cortex, and cuticle surface coating of the parasite were visible. Alae were also observed as the thickenings in the cuticle. The muscle layer structure consists of non-branched cylindrical cells. The intestinal tract is composed of cuticular cogs, the esophagus is of filamentous-muscular structure, and the intestine is made of columnar epithelial tissue with microvilli and glycocalyx. The amphid structure consisted of cuticular protrusions with penetrations of the cephalic framework into their inner layers. Phasmid structure also includes protrusions in the cuticle and invagination of sensory neurons. It was concluded that for the most part, the histological structure of the cuticle can be studied by optical microscopy. The muscle structure in this parasite was very similar to the skeletal muscle in mammals. Furthermore, the epithelial structure of the intestine in this parasite was largely similar to the intestinal epithelium in mammals. Finally, regarding the amphid and phasmid structures, it was observed that they were protrusions covered by cuticles where neural, filamentous, and muscular structures were the core of these protrusions.