The midgut ultrastucture of the third-instar of Dermatobia hominis (L., Jr.) was investigated using transmission electron microscopy (TEM). The tubular midgut bears a monolayer of epithelial cells with the plasma membrane showing multiple folding where it adjoins the basement membrane. Septate junctions bound the epithelial cells on each side. These cells have electrolucent cytoplasm containing mitochondria, vacuoles, rough and smooth endoplasmic reticula, lamellar bodies, and a prominent nucleus with dispersed chromatin. The peritrophic matrix is close to elongate microvilli, which are sometimes forked. Regenerative cells, in an undifferentiated state when closest to the basement membrane, are scattered throughout the epithelial cells. A thick basement membrane, surrounded by thick connective tissue including muscle, tracheal tubes, and extracellular matrix is linked to epithelial cells by hemidesmosome-like structures. Entero-endocrine, goblet or cuprophilic cells were not observed.
Transmission electron microscopy (TEM) was used to study two types of endocrine cells front the midgut of adult female Luttzomyia longipalpis (Lutz & Neiva). Endocrine cells rarely have been observed in Nematocera, even using TEM, and were present in small numbers dispersed among the monolayer of midgut digestive epithelial cells. Triangular shaped "closed" cells were observed along the basement membrane, bounded on each side by digestive cells; these cells closed distally before reaching the epithelial lumen. These endocrine cells appeared to deliver active granules that were secreted through a cellular membrane into the hemolymph. A second cell type occupied a similar position to the closed cells, but opened into the midgut lumen via microvilli, where the secretory products may be delivered. Each cell type possessed both electron-lucent and electron-dense vesicles with secretory granules which may indicate different stages in maturation and activity. These granular secretory products are probably peptidergic substances, with secretion mediated by diet via basal and baso-lateral receptors that were bound to membranes or microvilli.
The binding of lectins to the midgut of the female sand fly Lutzomyia longipalpis (Lutz & Neiva) was investigated using lectin-gold conjugates. Midguts from laboratory-reared flies provided fructose solution and/or blood fed on hamster were dissected at 6, 24, and 48 h and at 5 and 7 d after feeding. Before examination by transmission electron microscopy, each midgut was sectioned, incubated with lectins from four sources (Canavalia ensiformis [ConA], Helix pomata agglutinin [HPA], peanut agglutinin [PNA], and wheat germ agglutinin [WGA] ), then conjugated with colloidal gold. Only HPA, which is specific for N-acetyl-galactosamine (GalNAc), bound to the midgut. Binding sites were cytoplasmic secretory granules and microvilli throughout the length of the midgut epithelium. Binding occurred in sand flies fed fructose as well as in flies receiving a blood meal. The presence of GalNAc on the midgut microvilli of sand flies before, during, and after blood feeding indicates this amino-sugar is not altered by digestion. As a structural component, GalNAc may represent a terminal on a receptor molecule. The failure of the sand fly peritrophic matrix to bind WGA by N-acetylglucosamine may be caused by the complex composition of the membrane, which renders N-glycan inaccessible to the lectin-gold conjugate.
Salivary glands of Dermatobia hominis (L., Jr.) (Diptera: Oestridae) larvae were studied under light and electron microscopy. The salivary glands of second (L2) and third instars (L3) are similar and consist of pairs of translucent tubules. The individual efferent ducts unite to form a single deferent duct, which inserts dorsally into the cephalopharingeal skeleton. Each gland has a monolayer of epithelial cells surrounded by basement membrane and connective tissue. The cellular plasma membrane is enfolded at its base, forming a labyrinthine area. The cell surface is linked to the basement membrane (BM) by hemidesmosomes and to adjacent cells by septet junctions and desmosomes. Irregular channels with several vesicles occur between the cytoplasm and BM. Golgi complex, rough and smooth endoplasmic reticulum, ribosome, lysosomes, multivesicular bodies, and myelin figures are usually present in the cells. The nucleus is large, with diffuse chromatin. The connective tissue circling the BM contains collagen fibrils, muscle fibers and tracheal tubes. Lined cuticle encloses the efferent and deferent ductal cells, which have few, widely dispersed mitochondria, free ribosomes, microtubules, and a large nucleus with diffuse chromatin.
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