Age-dependent changes in ultrastructure of the defensive glands of Neocapritermes taracua workers (Isoptera,Termitidae)

Protection against predators and competitors is one of the main concerns of termite colonies, which developed a specialised defensive caste, the soldiers. However, soldiers are rare or even missing in several lineages of termites, while workers often develop new defence strategies especially in soil-feeding species. Here, we describe the morphology and ultrastructure of the autothysis-associated glands of Neocapritermes taracua workers and report their age-related changes in structure. The defensive glands of N. taracua workers consist of a pair of labial and a pair of crystal glands, whose secretions mix together through autothysis. Autothysis always occurs at the line of weakness connecting the anterior parts of the crystal-bearing pouches. The crystal glands consist of groups of bicellular secretory units (secretory and corresponding canal cells) which secrete the blue crystal material into external pouches. Their secretory activity is maximal in the middle of worker life, and is considerably lower in very young and old workers. The labial glands are composed of two types of secretory cells: the central and the parietal cells. While the central cells are developed similarly to other termites and secrete proteinaceous secretion into labial gland ducts, the parietal cells develop proteinaceous granules which may eventually bud off the cells. The secretory function of parietal cells is so far unique to N. taracua and differs from other termite species in which they are only responsible of water uptake by acini. The defensive device of N. taracua is truly exceptional as it involves a new gland and a previously undescribed function for parietal cells, being a remarkable example of evolution of morphological innovation.     

The anterior glands of adult Necator americanus (Nematoda: Strongyloidea)—I Ultrastructural studies

The ultrastructure of the amphidial, oesophageal and excretory glands of N. americanus is described. There are two amphidial glands, and each is attached to a lateral hypodermal cord. Anteriorly the glands become associated with the amphidial sense organs. The amphidial glands synthesize complex secretion granules which appear to release their contents into the sense organ. Secretions thus pass over the amphidial cilia and exit via the amphidial pore. It is suggested that the secretory activity of these glands is under direct nervous control. There are three oesophageal glands, and each synthesizes dense secretion granules. The secretions of the oesophageal glands are released into the lumen of the oesophagus and into the buccal capsule. The two excretory glands are ventral in position and connected to the tubular excretory system. These glands synthesize secretion granules of varying density. Secretions from the excretory glands may exit via the excretory pore, or pass back into the tubular excretory system, or both.     

Ultrastructure of the phallic glands of the firebrat,Thermobia domestica (packard) (Thysanura : Lepismatidae)

The exocrine glands located in the penis of Thermobia domestica (Thysanura : Lepismatidae) are composed of about 100 distinct units, each containing several cell types: one large secretory cell with an apical reservoir; 2 groups of envelope cells, an inner group of 2 superimposed cells, and an outer group of 4 cells arranged in a ring, and also 2 basal cells, called ciliary cells owing to their elongated processes, which look like the dendrite of a sensory cell. Each functional unit includes cuticular differentiations: a tubular bristle, fixed on a small tubercle; and a long “internal” ductule communicating basally with the reservoir of the glandular cell and opening distally at the tip of the bristle. A study of the modifications affecting the phallic glands during moulting, shows that the inner envelope cells deposit the cuticle that forms the ductule, the outer envelope cells elaborate the cuticule of the tubercle, while a temporary distal projection of only one of these cells ensures the formation of the bristle. In addition, a lengthening of the outer dendritic segment of the 2 ciliary cells takes place before ductule formation, but this segment partially degenerates after ecdysis. These findings are compared with data already obtained on the morphogenesis of other insect integumental glands. In T. domestica, the secretion of the phallic glands is presumed to be used, during the mating sequences, for spinning fine threads before spermatophore deposition.     

Whale tear glands in the bowhead and the beluga whales: Source and function

Orbital glands are found in many tetrapod vertebrates, and are usually separate structures, consisting of individual glands lying in the eyelids and both canthi of the orbit. In cetaceans, however, the orbital glandular units are less distinct and have been described by numerous authors as a single, periorbital mass. There are few histochemical and immunhistochemical studies to date of these structures. In this study, we examined the orbital glandular region of both the bowhead whale (Balaena mysticetus: Mysticeti) and the beluga whale (Delphinapterus leucas: Odontoceti) using histological, histochemical, and immunohistochemical techniques. Histologically, in the bowhead, three glandular areas were noted (circumorbital, including Harderian and lacrimal poles), palpebral (midway in the lower eyelid), and rim (near the edge of the eyelid). In the beluga, there was only a large, continuous mass within the eyelid itself. Histochemical investigation suggests neither sexual dimorphism nor age-related differences, but both whales had two cell types freely intermingling with each other in all glandular masses. Large cells (cell type 1) were distended by four histochemically distinct intracellular secretory granules. Smaller cells (cell type 2) were not distended (fewer granules) and had two to three histochemically distinct intracellular secretory granules. The beluga orbital glands had additional lipid granules in cell type 1. Counterintuitively, both lipocalin and transferrin were localized to cell type 2 only. This intermingling of cell types is unusual for vertebrates in whom individual orbital glands usually have one cell type with one to two different secretory granules present. The heterogeneity of the orbital fluid produced by cetacean orbital glands implies a complex function, or series of functions, for these orbital glands and their role in producing the tear fluid.     

Development of female accessory glands of Chrysomya putoria (Wiedemann) (Diptera: Calliphoridae) during oogenesis

Females of Chrysomya putoria (Diptera: Calliphoridae) have two sexual accessory glands, which are tubular and more dilated at the distal extremity. The glands open independently into the common oviduct. Two morpho-physiological regions were distinguished in the longitudinal semi-thin sections of the glands. The secretory region is constituted by three layers: a cuticular intima, lining the lumen, followed by a layer of small cells, and then a layer of very large secretory cells. The ductal region of the gland presents only two layers: the cuticular intima and a cellular layer. In both regions a basement membrane is present. Each secretory cell has in its apical region a reservoir, which enlarges throughout oogenesis; in its basal region there is a large nucleus. The ductal cells are cylindrical and smaller than the secretory cells. The glandular secretion is synthesized in the cytoplasm of the secretory cells, stored and/or modified in the reservoir, then drained to the lumen through an end apparatus seen in the apical region of the secretory cell. Histochemical tests indicate that this secretion is a glycoprotein. Measurements of the glands from females at different physiological conditions and fed on different diets correlate with the results obtained for changes in the ovary during oogenesis. Cell number averaged 561.2 ± 77.54 per gland. There was no increase in cell number during oogenesis.     

Fine structure of the silk gland in the mite Ornithocheyletia sp. (Prostigmata,Cheyletidae)

Silk spinning is widely-spread in trombidiform mites, yet scarse information is available on the morphology of their silk glands. Thus this study describes the fine structure of the prosomal silk glands in a small parasitic mite, Ornithocheyletia sp. (Cheyletidae). These are paired acinous glands incorporated into the podocephalic system, as typical of the order. Combined secretion of the coxal and silk glands is released at the tip of the gnathosoma. Data obtained show Ornithocheyletia silk gland belonging to the class 3 arthropod exocrine gland. Each gland is composed of seven pyramidal secretory cells and one ring-folded intercalary cell, rich in microtubules. The fine structure of the secretory cells points to intensive protein synthesis resulted in the presence of abundant uniform secretory granules. Fibrous content of the granules is always subdivided into several zones of two electron densities. The granules periodically discharge into the acinar cavity by means of exocytosis. The intercalary cell extends from the base of the excretory duct and contributes the wall of the acinar cavity encircling the apical margins of the secretory cells. The distal apical surface of the intercalary cell is covered with a thin cuticle resembling that of the corresponding cells in some acarine and myriapod glands. Axon endings form regular synaptic structures on the body of the intercalary cell implying nerve regulation of the gland activity.     

A pair of rosette glands in the embryo and zoeal larva of an estuarine crab Sesarma haematocheir, and classification of the tegumental glands in the embryos of other crabs

A pair of rosette glands (one of the tegumental glands in crustaceans) is present at the root of the dorsal spine of the thorax in mature embryos of the estuarine crab Sesarma haematocheir. Each rosette gland is spherical, 45-50 microm in diameter. This gland consists of three types of cells: 18-20 secretory cells, one central cell, and one canal cell. The secretory cells are further classified into two types on the basis of the morphology of secretory granules. There are 17-19 a cells, and only one b cell per rosette gland. An a cell contains spherical secretory granules of 2-3 microm in diameter. The granules are filled with highly electron-dense materials near the nucleus but have lower electron-density near the central cell. The secretory granules contained in the b cell have an irregular shape and are 1-1.5 microm in diameter. The density of the materials in the granules is uniform throughout the cytoplasm. The secretory granules contained in both the a and b cells are produced by the rough endoplasmic reticulum. Materials in the granules are exocytotically discharged into the secretory apparatus inside the secretory cell, sent to the extracellular channels in the central cell, and secreted through the canal cell. The rosette gland can be distinguished from the epidermal cells 2 weeks after egg-laying and the gland matures just before hatching. Materials produced by this gland are secreted after hatching and secretion continues through five stages of zoeal larvae. These rosette glands were never found in the megalopal larva. Rosette glands are found in the embryos of Sesarma spp. and Uca spp. In other crabs, tegumental glands are also found at the same position as in the embryo of S. haematocheir, but the fine structure of their glands is largely different from that of the rosette gland. On the basis of the morphology of secretory cells (a-g cell types), the tegumental glands of a variety of crab embryos can be classified into four types, including rosette glands (type I-IV). The function of these tegumental glands is not yet known, but different types of the gland seem to reflect the phylogeny of the crabs rather than differences of habitat.     

Zur Cytologie der Rectaldrüsen von Knorpelfischen

The stratified epithelium of the central collecting duct of the elasmobranch(Scylliorhinus canicula, Galeorhinus galeus andRaja batis) rectal gland consists of 3 to 6 layers of cells: one superficial, and several basal cell layers. In the superficial layer normally three different types of cells can be distinguished (a) goblet cells, (b) cells with apical secretory granules and (c) flask-shaped cells. The superficial layer ofScylliorhinus canicula reveals a further cell type, so-called mitochondria-rich cells. The epithelial areas built by these cells are always single-layered. The goblet-cells are very similar to goblet cells found in the intestine of vertebrates. Their dominant structures are a well developed ergastoplasm, a large Golgi-apparatus and mucous granules compactly filling the apical cell region. The cells with apical secretory granules are columnar or dumbbell shaped. They contain a rough-surfaced endoplasmic reticulum and a well developed Golgi-apparatus. The secretory granules are loosely distributed within the Golgi-field and are arranged in one or more rows just below the cell apex. The flask shaped cells are characterized by a cytoplasm rich in small vesicles. They posses few dictyosomes and several small mitochondria. There is some evidence for endocytotic activity. The mitochondria-rich cells are characterized by lateral cell interdigitations, by a basal labyrinth and by numerous mitochondria. They are similar to the excretory cells of rectal gland parenchyma. The cells of the basal epithelium layers are differenciated only to a small extent. They are joined in a loose formation with white blood cells often found in the intercellular spaces. The function of the elasmobranch rectal gland is not restricted to the excretion of concentrated salt solutions. There is also a significant secretion of mucous substances. The tubule glands are primarily excretory, the epithelium cells of the central collecting duct mainly secretory in function.     

Fine structural aspects of silk secretion in a spider (Araneus diadematus). I. Elaboration in the pyriform glands

Pyriform glands of Araneus diadematus which produce the silky material used for the attachment discs of the web, consist of two kinds of secretory cells. One, located in the distal half of the glands, elaborates finely fibrillar proteinic granules through an extensive rough endoplasmic reticulum; another, in the proximal half of the glands, secretes complex-structured granules in areas of the cell where Golgi and ergastoplasmic cisternae are equally developed. The opaque nascent granules of secretion appear in swollen Golgi saccules. These aggregate in superposed circular interconnected layers leaving an electron-lucent space between them; in the course of maturation the space is progressively filled with a fibrillar material. Histochemical tests suggest that the secretory product of the proximal half is mainly a protein rich in acidic groups and associated with a carbohydrate component. The two products, extruded by a merocrine process, form respectively the core and the envelope of the silk fibre. The dual composition of the pyriform gland silk, which did not appear from the results of chemical analyses, is compared to the association of fibroin and sericin in Lepidoptera silk and to certain double-layered Trichoptera silks.     

Regulation of secretory granule size by the precise generation and fusion of unit granules

Morphometric evidence derived from studies of mast cells, pancreatic acinar cells and other cell types supports a model in which the post-Golgi processes that generate mature secretory granules can be resolved into three steps: (1) fusion of small, Golgi-derived progranules to produce immature secretory granules which have a highly constrained volume; (2) transformation of such immature granules into mature secretory granules, a process often associated with a reduction in the maturing granule’s volume, as well as changes in the appearance of its content and (3) fusion of secretory granules of the smallest size, termed ‘unit granules’, forming granules whose volumes are multiples of the unit granule’s volume. Mutations which perturb this process can cause significant pathology. For example, Chediak–Higashi syndrome / lysosomal trafficking regulator (CHS)/(Lyst) mutations result in giant secretory granules in a number of cell types in human beings with the Chediak–Higashi syndrome and in ‘beige’ (Lyst^bg/Lyst^bg) mice. Analysis of the secretory granules of mast cells and pancreatic acinar cells in Lyst-deficient beige mice suggests that beige mouse secretory granules retain the ability to fuse randomly with other secretory granules no matter what the size of the fusion partners. By contrast, in normal mice, the pattern of granule–granule fusion occurs exclusively by the addition of unit granules, either to each other or to larger granules. The normal pattern of fusion is termed unit addition and the fusion evident in cells with CHS/Lyst mutations is called random addition. The proposed model of secretory granule formation has several implications. For example, in neurosecretory cells, the secretion of small amounts of cargo in granules constrained to a very narrow size increases the precision of the information conveyed by secretion. By contrast, in pancreatic acinar cells and mast cells, large granules composed of multiple unit granules permit the cells to store large amounts of material without requiring the amount of membrane necessary to package the same amount of cargo into small granules. In addition, the formation of mature secretory granules that are multimers of unit granules provides a mechanism for mixing in large granules the contents of unit granules which differ in their content of cargo.     

Structure of the inguinal gland in the mountain hare in various states of reproductive activity. I. The sebaceous glands

Histology and ultrastructure of sebaceous glands of the integumental inguinal gland of the hare were studied during the periods of low and high reproductive activity (in winter and in spring breeding season). It was established that the glands were functioning continually (cells in acini of all the animals used contained numerous secretory granules). The expansion of agranular endoplasmic reticulum and Golgi complex in secretory cells of sexually active animals, especially of males, shows an increased intensity of gland secretory process during the breeding season.     

Ultrastructure of the epidermal maxilla II-gland of Scutigera coleoptrata (Chilopoda, Notostigmophora) and the ground pattern of epidermal gland organs in Myriapoda

The epidermal maxilla II-gland of Scutigera coleoptrata was investigated using light and electron microscopy. The glandular epithelium surrounds a spacious integumental cavity at the base of the maxilla II. The gland is formed as a compound gland organ that is composed of thousands of epidermal gland units. Each of them consists of four different cell types: a secretory cell, an accessory or intermediary cell, and a proximal and distal canal cell. The intermediary and the two canal cells form a conducting canal. Only in the most distal part of the intermediary cell is the canal lined by a cuticle. In the area of the two canal cells, the conducting canal is completely covered by a cuticle. The canal passes through the cuticle and opens into the spacious integumental cavity, which serves as a secretion reservoir. The structural organization of the epidermal maxilla II-gland was compared to that of other compound epidermal gland organs in Chilopoda and Diplopoda. All these glandular organs in Myriapoda share the same ground pattern.     

Effects of cholinergic and adrenergic agonists on the secretion of fluid and protein by submandibular glands of the guinea-pig and the mouse

Significant differences were observed between the guinea-pig and the mouse in terms of the secretion of fluid, protein and secretory granules from submandibular glands in response to pilocarpine, phenylephrine and isoproterenol. In both the guinea-pig and the mouse, the secretory responses induced by pilocarpine, phenylephrine and isoproterenol were inhibited by pretreatment with 4-DAMP, phentolamine and propranolol, respectively. The results suggest that the submandibular glands of the guinea-pig and the mouse have M₃-cholinoreceptors, as well as α- and β-adrenoceptors, and that these receptors play different roles in the secretion of fluid, protein and secretory granules from guinea-pig and mouse submandibular glands.     

Ultrastructural investigation of a salivary gland in a centipede: structure and origin of the maxilla I-gland of Scutigera coleoptrata (Chilopoda, Notostigmophora)

The maxilla I-gland of Scutigera coleoptrata was investigated using light and electron microscopy methods. This is the first ultrastructural investigation of a salivary gland in Chilopoda. The paired gland opens via the hypopharynx into the foregut and extends up to the third trunk segment. The gland is of irregular shape and consists of numerous acini consisting of several gland units. The secretion is released into an arborescent duct system. Each acinus consists of multiple of glandular units. The units are composed of three cell types: secretory cells, a single intermediary cell, and canal cells. The pear-shaped secretory cell is invaginated distally, forming an extracellular reservoir lined with microvilli, into which the secretion is released. The intermediary cell forms a conducting canal and connects the secretory cell with the canal cell. Proximally, the intermediary cell bears microvilli, whereas the distal part is covered with a distinct cuticle. The cuticle is a continuation of the cuticle of the canal cells. This investigation shows that the structure of the glandular units of the salivary maxilla I-gland is comparable to that of the glandular units of epidermal glands. Thus, it is likely that in Chilopoda salivary glands and epidermal glands share the same ground pattern. It is likely that in compound acinar glands a multiplication of secretory and duct cells has taken place, whereas the number of intermediary cells remains constant. The increase in the number of salivary acini leads to a shifting of the secretory elements away from the epidermis, deep into the head. Comparative investigations of the different head glands provide important characters for the reconstruction of myriapod phylogeny and the relationships of Myriapoda and Hexapoda.     

Serous gland polymorphism in the skin of<Emphasis Type="Italic"> Phyllomedusa hypochondrialis azurea</Emphasis> (Anura,Hylidae): response by different gland types to norepinephrine stimulation

Stimulation by norepinephrine in physiological concentration was used on the dorsal skin of the Argentine tree-frog Phyllomedusa hypochondrialis azurea to trigger contraction of myoepithelial cells encircling the serous glands and provoke secretory release. This hylid species possesses two kinds of serous cutaneous glands, producing secretory granules or vesicles (type Ia and Ib serous units, respectively), along with serous-derived glands which synthesise lipids and store them in complex aggregates (type II units). Structural and ultrastructural observations on myoepithelia, secretory units and gland products collected in saline after discharge, revealed consistent but different responses in the three types investigated. Type Ia glands reacted intensely to treatment, with both contractile and secretory responses, type Ib glands were only mildly affected in their myoepithelia and glands of type II were not affected at all. According to data available in the literature, these findings suggest that: (a) the dense (type Ia) granules are expelled as a phasic response through bulk (holocrine) discharge, (b) the secretory (type Ib) vesicles are released as a tonic response through a merocrine mechanism and (c) lipid (type II) aggregates are exuded as a secretory component of a complex behavioural response which tends to reduce transcutaneous water loss. Furthermore, these findings indicate that the use of pharmacological modulation of myoepithelial activity allows selective collection of skin products in species characterised by serous gland polymorphism.     

Ultrastructure of endocrine cells in the stomach of two teleost fish Perca fluviatilis L. and Ameiurus nebulosus L.

Summary In the gastric mucosa of two teleost species, the perch (Perca fluviatilis) and the catfish (Ameiurus nebulosus) three endocrine cell types were found, located predominantly between the mucoid cells of the gastric mucosa. A fourth cell type is present in the gastric glands of catfish. Each cell type was defined by its characteristic secretory granules. Type-I cells were predominant in both fish. These cells contained round or oval granules with a pleomorphic core. The average diameter of granules was 400 nm for the perch and 270 nm for the catfish. Type-II cells of both species displayed small, highly osmiophilic granules about 100 nm in diameter. The secretory granules of type-III cells (260 nm in the perch and 190 nm in the catfish) were round or slightly oval in shape and were filled with a finely particulate electron-dense material. Type-IV cells of the catfish were found in the gastric glands only. Their cytoplasm was filled with homogeneous, moderately electron-dense granules averaging 340 nm in diameter. The physiological significance of these different morphological types of gastric endocrine cells requires further investigation.     

Monoclonal Antibodies to Secretory Granules in Esophageal Glands of Meloidogyne Species

Monoclonal antibodies to secretory granules in the dorsal or subventral esophageal glands were generated by injecting BALB/c mice with immunogens from preparasitic second-stage juveniles (J2) of Meloidogyne incognita. Antibodies specific for secretory granules in the J2 subventral esophageal glands or the dorsal gland were identified by indirect immunofluorescence microscopy. Only antibodies that reacted with granules in the J2 dorsal gland reacted with the esophageal gland lobe ofM. incognita adult females. The antibodies also reacted with secretory granules in both types of esophageal glands in M. javanica and M. arenaria J2 but not with granules in esophageal glands of Heterodera glycines J2.     

Histological features and histochemistry of the mucous glands in ventral skin of the frog (Rana fuscigula)

The glycoconjugate components of secretory granules were analyzed in cells of mucous glands in ventral skin from Rana fuscigula. The analysis was done with standard histochemical methods on semithin glycol methacrylate-embedded tissues. The staining patterns in semithin sections were comparable to those using paraffin-embedded tissue while the cytological detail was better preserved. The mucous glands contained at least two different types of secretory cells lining the lower two-thirds of the mature gland: a principal cell type filled with dense staining secretory granules and a solitary type containing paler staining, globular secretory granules. The principal type of cell contained variable amounts of acid glycoconjugates; predominantly carboxylated but also variably carboxylated and weakly sulfated glycoproteins. Other secretory cells contained mainly neutral glycoproteins. The results indicated that the mucus is a heterogeneous substance and that one cell type may produce different secretory products. We suggested that the variability in histochemical staining might be related to the sequence of biosynthesis of the secretory granule.     

Location and ultrastructure of sex pheromone glands in female Callosobruchus maculatus (Fabricius) (Coleoptera : Bruchidae)

The ultrastructure of the female sex pheromone glands in Callosobruchus maculatus (Coleoptera : Bruchidae) were localized using a masking technique, combined with eiectro-antennography and by a comparison of the glandular cells of sexually active (flightless) females and non-sexually active (flight-form) females. Each unicellular gland is an invagination of the integumental membrane capped by a single secretory cell. These glands are situated on the fine intersegmental membrane, which joins the pygidium to the ovipositor. The secretory cells of the glands of active females are characterized by well-developed microvilli, with many elongated mitochondria among the latter. The high metabolic activity of these cells is revealed by the presence of heterogeneous secretion vesicles, some of which contain abundant crystallized material. Deep basal invaginations indicate the uptake of substances from the haemolymph. The receptor canal is a network of fine cuticular filaments which have the same structure regardless of the female's sexual status. Cells from the glands of non-sexually active females are underdeveloped and show no invaginations of the basal membrane and very few microvilli. The localization of these glands was made possible by the use of SEM, TEM and EAG as well as by masking the suspected zones and by comparing females in different physiological states: flightless females, which were sexually active and producing pheromones; and flight-form females, non-sexually active and producing no sex pheromones. Only by adopting such a stringent method was it possible to confirm the function of the glands whose ultrastructure was studied.     

Morphology of the exocrine glands of the frog skin

Frog skin contains three distinct types of exocrine glands: granular (poison), mucous, and seromucous. The granular gland forms a syncytial secretory compartment within the acinus, which is surrounded by smooth muscle cells. The mucous and seromucous glands are easily identifiable as distinct glands. The serous and mucous secretory cells are arranged in a semilunar configuration opposite the ductal end and are filled with granules. Within the acinus, located at the ductal pole of the gland, are distinct groups of cells with few or no granules in the cytoplasm. In both the mucous and seromucous gland there is a cell type with abundant mitochondria; the one in the mucous gland is located in the region adjacent to the secretory cells. The duct of these glands is two-layered, with the individual cells appearing morphologically similar to the layers of the skin epithelium as the duct traverses the skin. The duct appears to be patent throughout its length. The morphological heterogeneity and distinct distribution of the cell types within the gland acinus may be indicative of a functional heterogeneity that allows the production of distinctly different types of secretion from the same gland type, depending on the type of stimulus.