Influence of thyroid hormones on neuronal death and differentiation in larval Rana pipiens.

The sphingid moth, Manduca sexta, typically passes through five larval instars, a pupal, and an adult stage. The larval labial glands secrete silk in the first instar and a viscous lubricant in the fifth. During metamorphosis the glands develop into salivary organs which produce an invertase-rich secretion. In normal development, the uniform population of cells in the duct of the larval gland transforms into the four sequentially arranged regions of secretory and conductive cells of the adult gland. In order to determine when competence to form the adult gland is established, fragments of labial gland ducts from first through fifth instar larvae were implanted into pupae. These gland fragments underwent metamorphosis with their hosts, passing through the same developmental phases. Glands from as early as the first instar were competent to form histologically and functionally normal adult regions. In later instars, transplants of measured fragments demonstrated that larval cells were programmed in situ to develop into the four adult cell types.     

Silk formation mechanisms in the larval salivary glands of<Emphasis Type="Italic">Apis mellifera</Emphasis> (Hymenoptera: Apidae)

The mechanism of silk formation inApis mellifera salivary glands, during the 5th instar, was studied. Larval salivary glands were dissected and prepared for light and polarized light microscopy, as well as for scanning and transmission electron microscopy. The results showed that silk formation starts at the middle of the 5th instar and finishes at the end of the same instar. This process begins in the distal secretory portion of the gland, going towards the proximal secretory portion; and from the periphery to the center of the gland lumen. The silk proteins are released from the secretory cells as a homogeneous substance that polymerizes in the lumen to form compact birefringent tactoids. Secondly, the water absorption from the lumen secretion, carried out by secretory and duct cells, promotes aggregation of the tactoids that form a spiral-shape filament with a zigzag pattern. This pattern is also the results of the silk compression in the gland lumen and represents a high concentration of macromolecularly well-oriented silk proteins.     

Morphological, micromorphological and histochemical studies on the parotid salivary glands of the one-humped camel (Camelus dromedarius).

The morphology, blood and nerve supply of the parotid salivary glands of the one-humped camel were studied in detail. The intraglandular portion of the duct system was also examined. The histological and histochemical studies showed that the parotid salivary glands of the camel are of the tubuloacinar type and are serumocoid in nature. The secretory acini and tubules show themselves in 3 different forms according to the different phases of their secretory cycle. The duct system of the gland contains goblet cells between its lining epithelium. The intercalated ducts show ampullation followed by narrowing that help in mixing the secretion. Intraepithelial glands are found in the terminal part of the parotid duct.     

An ultrastructural analysis of the salivary system of the terrestrial mollusc, Limax maximus.

The bilateral salivary glands, ducts, and nerves of the giant garden slug Limax maximus control the secretion of saliva and its transport to the buccal mass. Each salivary nerve, which originates at the buccal ganglion, contains over 3000 axon profiles. The axons innervate the musculature of the duct and branch within the gland. The salivary duct is composed of several muscular layers surrounding an epithelial layer which lines the duct lumen. The morphology of the duct epithelium indicates that it may function in ion or water balance. The salivary gland contains four major types of secretory cells. The secretory products are released from vacuoles in the gland cells, and are presumably transported by cilia in the collecting ducts of the gland into the larger muscular ducts.     

麦蛾柔茧蜂幼虫唾液腺的显微与超微形态观察

本文采用解剖学观察、显微摄影、透射电镜等方法对麦蛾柔茧蜂Habrobracon hebetor幼虫唾液腺的显微形态、超微结构以及发育特性进行了观察和分析。麦蛾柔茧蜂幼虫唾液腺为一对无色透明至乳白色的管状腺体,自口腔沿中肠两侧向后延伸,单侧腺体在中部先分支、后合并成一不规则环状,端部呈单盲管状。唾液腺管道长度随幼虫龄期增加而呈线性增长。对唾液腺切片进行超微结构观察,发现腺管由两类差异明显的单层细胞组成,I型细胞微绒毛层较厚,胞内除有丰富的内质网和线粒体之外,还含有大量囊泡,并观察到囊泡运输分泌颗粒的现象;II型细胞微绒毛短,胞内的内质网和线粒体数量丰富。本文研究为深入探究寄生蜂幼虫的消化生理以及寄生蜂-寄主互作机制奠定了基础。     

Fine structure of the parotid and mandibular glands of the cotton rat (Sigmodon hispidus).

The parotid and mandibular glands of the cotton rat were examined by light and transmission electron microscopy. Parotid gland: Acinar cells were serous in nature, and contained electron-dense granules. Intercalated duct cells contained electron-dense granules. Striated duct cells had small granules of moderate and high electron densities. Mandibular gland: Acinar cells were seromucous in nature, and contained granules of low and moderate electron densities. Intercalated duct cells contained granules of moderate and high electron densities. Striated ducts were comprised of two portions - a secretory portion and a striated portion without granules. The secretory portion had many electron-dense granules. A sexual dimorphism was obserbed in these granules, which were smaller and fewer in females than in males.     

Macromolecular array patterns of silk gland secretion in social Hymenoptera larvae

The cocoon, produced by most holometabolous insects, is built with silk that is usually produced by the larval salivary gland. Although this silk has been widely studied in the Lepidoptera, its composition and macromolecular arrangement remains unknown in the Hymenoptera. The macromolecular array patterns of the silk in the larval salivary gland of some meliponids, wasps, and ants were analyzed with polarized-light microscopy, and they were compared with those of Bombyx mori (Lepidoptera). There is a birefringent secretion in the glandular lumen of all larvae, due to filamentous structural proteins that display anisotropy. The silk in the distal, middle and proximal regions of the secretory portion of Formicidae and Vespidae glands presented a lattice optical pattern. We found a different pattern in the middle secretory portion of the Meliponini, with a zigzag rather than a lattice pattern. This indicates that the biopolymer fibers begin their macromolecular reorganization at this glandular region, different from the Formicidae and the Vespidae, in which the zigzag optical pattern was only found at the lateral duct. Probably, the mechanism of silk production in the Hymenoptera is a characteristic inherited from a common ancestor of Vespoidea and Sphecoidea; the alterations in the pattern observed in the Meliponini could be a derived characteristic in the Hymenoptera. We found no similarity in the macromolecular reorganization patterns of the silk between the Hymenoptera species and the silkworm.     

Morphology,histochemistry and physiology of the major salivary glands in the echidna Tachyglossus aculeatus (Monotremata)

The three major salivary glands of the monotreme echidna are described. The parotid is a typical serous gland with tubulo-acinar secretory endpieces and a well-developed system of striated ducts. The mandibular gland, although light microscopically resembling a mucous gland, secretes very little glycoprotein. Its cells are packed instead with serous granules, resembling in fine structure the “bull's eye” granules in the mandibular gland of the European hedgehog Erinaceus europaeus. The sublingual glands secrete an extremely viscous mucous saliva. Expulsion of this saliva through the narrow ducts is probably aided by contraction of the extensive myoepithelial sheaths surrounding the secretory tubules. Application of the glyoxylic acid induced fluorescence method failed to demonstrate adrenergic innervation in any of the glands.     

Peculiar salivary glands in a silk‐producing mite Bakericheyla chanayi (Cheyletidae)

This is the first ultrastructural investigation of salivary glands in the family Cheyletidae. In both sexes of Bakericheyla chanayi, paired acinous salivary glands and tubular coxal glands were shown to be united into the common podocephalic system. The secretory portion of the salivary gland includes medial and lateral lobes composed of the five and two cells, respectively, with clearly distinct ultrastructure. The cytoplasm of the cells is occupied by the secretory granules containing fine fibrous material. The fine structure of both cell types suggest a proteinaceous nature of their secretions. A single central process extending from the apical face of each secretory cell passes through the common acinar cavity to enter the conducting duct. A pair of intercalary cells at the base of the conducting duct links it with the secretory portion of the gland. Extending towards the acinar cavity, protrusions of intercalary cells alternate the apical regions of the secretory cells and form with them highly‐specialized contacts characterized by the apical network of microtubules and microfilaments. Two possible ways of secretion are suggested: 1) exocytosis into the acinar cavity and 2) direct passage via the central processes. The detection of axon profiles in the gland body suggests a neural control for the glandular cell function. In tritonymphs, neither secretion nor large lateral lobe cells were observed up to the pharate stage when the lateral lobe undergoes rapid differentiation. The arrangement of the acinous gland is compared to that of other arthropods. Its composition appears to be close to the class three of insect glands. The involvement of the lateral lobe cells in silk production is discussed. J. Morphol. 276:772–786, 2015. © 2015 Wiley Periodicals, Inc.     

Cellular metamorphosis. II. The larval labial gland duct and its prospective adult fates in the tobacco hornworm.

The larval labial gland of the sphingid moth, Manduca sexta, produces a viscous secretion, presumably a lubricant, facilitating the burrowing which precedes pupation. During metamorphosis, the gland transforms into a salivary organ, producing an invertase-rich digestive secretion. The single-cell type found in the duct of the larval gland transforms into the four structurally and functionally distinct cell types found in the four sequentially arranged secretory and conductive regions of the adult salivary gland. Surgical experiments were performed to study the prospective fates of different parts of the larval gland. The glands were bisected and one or both fragments were left in situ to undergo metamorphosis. In addition, fragments of the larval gland were implanted in pupal hosts and went through metamorphosis free of their prior attachments. The four linearly arrayed adult regions originate from correspondingly positioned areas in the larval duct.     

Anatomy and ultrastructure of the salivary (prosomal) glands in unfed water mite larvae Piona carnea (C.L. Koch, 1836) (Acariformes: Pionidae)

Anatomy and ultrastructure of prosomal salivary glands in the unfed water mite larvae Piona carnea (C.L. Koch, 1836) were examined using serial semi-thin sections and transmission electron microscopy. Three pairs of alveolar salivary glands shown are termed lateral, ventro-lateral and medial in accordance with their spatial position. These glands belong to the podocephalic system and are situated on the common salivary duct from back to forth in the above mentioned sequence. The arrangement of the medial glands is unusual because they are situated one after another on the medial (axial) body line, therefore they are termed anterior and posterior medial glands. The secretory duct of the anterior medial gland mostly turns right, and the duct of the posterior gland turns left. The salivary glands are located in the body cavity partly inside the gnathosoma and in the idiosoma in front of the brain (synganglion). Each gland is represented by a single acinus (alveolus) and is composed of several cone shaped secretory cells arranged around the large central (intra-acinar) cavity with the secretory duct base. The cells of all glands are filled with secretory vesicles of different electron density. The remaining cell volume is occupied by elements of rough endoplasmic reticulum, and the membrane enveloping vesicles may have ribosomes on its external surface. Large nuclei provided with large nucleoli occupy the basal cell zones. The pronounced development of the prosomal salivary glands indicates their important role in extra-oral digestion of water mite larvae.     

Fine structure of the mandibular gland of the Djungarian hamster (Phodopus sungarus)

The mandibular gland of the Djungarian hamster was examined by light microscopy, and transmission and scanning electron microscopies. Its acinar cells reacted with periodic acid-Schiff (PAS) and were weakly stained with alcian blue (AB). There were intercellular canaliculi between the acinar cells. These cells therefore appeared to be seromucous. The acinar epithelium was composed of light cells containing various spherical secretory granules. The granular cells of the mandibular gland possessed many acidophilic granules exhibiting a positive reaction to PAS stain. They were frequently observed at the junction of the acini and intercalated ducts in all mandibular glands examined. All of these cells were light and contained secretory granules of varying size and density. The intercalated ducts consisted exclusively of light cells possessing a few round granules of high density in the apical region. The striated ducts were comprised of two portions--a secretory portion and a typical striated portion without secretory granules. The secretory portion consisted of light, dark and specifically light epithelial cells containing acidophilic granules, which exhibited a strongly positive PAS reaction. The epithelium of typically striated portions was composed of light and dark cells containing fine vacuoles in the apical region. The mandibular gland of the Djungarian hamster revealed no histological differences between sexes.     

Ultrastructure of human labial salivary glands. 3. Myoepithelium and ducts

Myoepithelial cells were present between the basal lamina and the acinar secretory cells of human labial salivary glands. In form and disposition, they resembled myoepithelial cells in the major salivary glands. Many of these cells possessed single cilia on their upper surfaces. Such cilia occasionally extended into invaginations of the overlying secretory cell. The intercalated ducts were variable in occurrence. Their epithelium ranged from columnar to squamous, and showed few signs of secretory activity. Few intralobular ducts possessed basal striations. While mitochondria were abundant in non-striated cells, they were randomly disposed in both basal and apical cytoplasm, and the basal plasmalemma showed only occasional infoldings. The paucity of true striated ducts in labial salivary glands may be responsible for the high concentration of sodium and chloride in unstimulated labial gland salivary secretions.     

Immunohistochemical localization of Na+,K+-ATPase in rodent and human salivary and lacrimal glands

The enzyme Na+,K+-ATPase was localized immunohistochemically in major salivary glands of mouse, rat, and human and in exorbital lacrimal glands of the rodents. Immunoreactive Na+,K+-ATPase was abundant in the basolateral membranes of all epithelial cells lining striated and intra- and interlobular ducts of all glands. Reactivity of intercalated ducts varied among gland type and species. Cells lining granular ducts in rodent submandibular gland showed a heterogeneous staining pattern in rat but stained homogeneously in mouse. Secretory cells varied greatly in their content of immunoreactive Na+,K+-ATPase. As with all duct cells, staining was present only at the basolateral surface and was never observed at the luminal surface of reactive secretory cells. Mucous cells failed to show any reactivity in any gland examined. Serous cells showed a gradient of immunostaining intensity ranging from strongly positive in demilunes of human sublingual gland to negative in rat submandibular gland and lacrimal glands of rats and mice. The presence of basolaterally localized Na+,K+-ATPase in most serous cells but not in mucous cells suggests that the enzyme contributes to the ion and water content of copious, low-protein serous secretions. The intense immunostaining of cells in most if not all segments of the duct system supports the idea that the ducts are involved with modification of the primary saliva, and extends this concept to include all segments of the duct system.     

The duct system of the avian salt gland as a transporting epithelium: structure and morphometry in the duck Anas platyrhynchos

Summary The duct system of the nasal salt gland of the duck comprises central canals, secondary ducts and main ducts. The secondary and main ducts consist of a layer of columnar cells overlying a layer of small cuboidal cells. The columnar cells have complex intercellular spaces showing evidence of Na⁺ K⁺ -ATPase at the apical regions. Approximately 70% of surface area of the duct system is external to the gland. During adaptation to salt water the duct system increases in size as does the gland. Although the components of the gland of adapted ducks, including the duct system within the gland, increase in size compared with normal ducks, the percentage volume densities of the components remain similar in both categories of ducks, i.e. the duct system increases in size in proportion to the glandular tissue. The volume of the duct system external to the gland is six to seven times larger than the volume within the gland. Thus, if ductal modification of secreted fluid occurs, it will be most likely to take place in the ducts external to the gland.Total surface areas of the duct system were measured from serial sections of glands and ducts from one normal and one adapted duck. These were used to calculate possible flux rates of water and sodium across the duct epithelium, assuming the occurrence of either water reabsorption or sodium secretion. Although these flux rates are high it is shown that they are similar to calculated flux rates across the luminal surface of the secretory tubules.     

Fine structure of the mandibular gland in volcano rabbit

The mandibular glands of 6 male and 6 female volcano rabbits were examined by means of light and transmission electron microscopy. The acinar cells of the glands were seromucous in nature, and contained faintly basophilic granules. The cells were classified into the light cells containing granules of low or moderate densities and the clear cells having polygonal granules of low density. The preacinar cells were occasionally observed at the site between acinus and intercalated duct. These cells had many weakly basophilic granules which contained fine granular materials of moderate density. The intercalated ducts were composed of light cells containing cored granules. The striated duct cells consisted of light cells and dark cells. Both of them contained a few vacuoles and vesicles, but no secretory granules. No sex-and age-related differences were observed in the mandibular gland of the volcano rabbit. The mandibular gland of the volcano rabbit was similar to the rabbit mandibular gland rather than the pika mandibular gland morphologically.