Cytochemical and Electron Microscope Studies on the Pharynx and Intestinal Epithelium of Nippostrongylus brasiliensis

Abstract

Pharynx and intestinal epithelium were studied with various cytochemical methods and the electron microscope. The pharynx possesses the characteristic triradiate lumen and is lined internally with cuticle. Its wall is muscular and myofilaments of two types, about 7 m,a and 15 my/ in diameter, can be seen in cross section. Besides the myofilaments, large branching mitochondria are present with many cristae. A pharyngeal gland is also present appearing in cross section as a single dense triangular cell, along the ventral margin. Cells of the intestinal epithelium are so large that a typical cross section of the intestine passes through only two or three cells. These show some of the properties of intestinal mucosa, such as a microvillar border, terminal web, and terminal bars at the cell margin. The nucleus is usually situated toward the base of the cell where most of the mitochondria also occur. The mitochondria contain cristae with characteristic triangular or forked apices. The cell also contains endoplasmic reticulum, Golgi apparatus, secretory granules, free ribosomal particles, and glycogen. The presence of a large quantity of ribosomes and also secretory granules in the cytoplasm suggests that the cell is involved in the synthesis and secretion of digestive enzymes. Several additional kinds of inclusion bodies are also present, suggestive of intracellular bacteria and lysosome-like bodies. The pharynx or esophagus of nematodes is a cylindrical tube with an internal cuticular lining (Hyman, 1951) and has a lumen which is characteristically triradiate. The pharyngeal wall contains radial muscle fibers and the pharyngeal gland as well as other cell components. Immediately posterior to the muscular pharynx is the relatively simple, tubular, thinwalled intestine. Studies on the intestinal epithelium of nematodes have shown it to be composed of a single layer of columnar epithelial cells whose most striking feature is the presence of a bacillary layer (brush border) on the internal surface. This bacillary layer has been regarded as immobilized (Hyman, 1951). In other electron microscopic studies were also described in the bacillary layer of Ancylostoma duodenale (by Browne and Chowdhury, 1959) and in Trichinella spiralis (by Beckett and Received for publication 25 May 1966. * These investigations were supported in part by Grant AI-00884 of the U. S. Public Health Service, NIAID, and in part by Grant HD-1242 of the National Institute of Child Health and Human Development, and U. S. Public Health Service General Research Support Grant FR-5367. The author was supported by the Mr. and Mrs. Frank G. Logan Fellowship Fund of the University of Chicago. t Present address: Division of Microbiology, Medical Research Center, Brookhaven National Laboratory, Upton, Long Island, New York 11973. Boothroyd, 1960). It is doubtful, however, that these projections should be considered as cilia in the usual sense. Several investigators have demonstrated the presence of microvilli in the intestinal epithelium of Ascaris (Bretschneider, 1954; Joyon and Collin, 1962; Kessel et al., 1961; Sheffield, 1964; Tokin, 1959). Microvilli have also been reported in other nematodes such as Capillaria hepatica (by Wright, 1963) and Rhabditis strongyloides (by Peebles, 1957). The intestinal epithelium of the nematode presumably has a dual role acting in secretion as well as food absorption. In keeping with its secretory role, several zymogen-like granules are usually present (Chitwood and Chitwood, 1950). The intestinal epithelium also acts as a storage place for glycogen, and is thus involved in the carbohydrate metabolism of the organism (von Brand, 1960). MATERIALS AND METHODS Nippostrongylus brasiliensis was maintained in laboratory rats. Adult worms were obtained from the intestine of the rats after 10 days of infection. For light microscopy the worms were fixed in hot formalin-acetic-alcohol and Zenker's fluid, subsequently dehydrated and embedded in paraffin. The sections were stained with hematoxylin-eosin and Mallory's triple stain (Humason, 1962) for general histology and in Prussian blue (Lillie, 1954) to detect the presence of iron. A slide of opossum prostate tissue known to contain iron was stained as control. One-,A sections of Epon-embedded material were stained in azure B to study the presence