Alligator tears: a reevaluation of the lacrimal apparatus of the crocodilians

The Harderian gland is a poorly understood anterior ocular gland that occurs in most terrestrial vertebrates. Numerous extraorbital functions have been ascribed to the Harderian gland, principally based on its association with the nasolacrimal duct. Few studies have centered on archosaurs and the majority of those available focused solely on the Harderian gland of birds. Little is known about the lacrimal apparatus of the crocodilians. We examined the lacrimal apparatus of several specimens of Alligator mississippiensis anatomically, histologically, and histochemically and studied the embryogenesis of this system. The nasolacrimal duct possesses a distal secretory area, which is more convoluted than that of typical mammals or lepidosaurs. The alligator Harderian gland possesses a unique combination of characteristics found in lepidosaurs, birds, and mammals. Like that of both mammals and lepidosaurs, it is a large, tuboloacinar gland that appears to secrete both mucoprotein and lipids. However, the presence of blood vessels and immune cells is reminiscent of that of the avian Harderian gland. The immunogenesis of the alligator Harderian gland appears to be tied to the development of the vascular system. The presence of a distinct palpebral gland in the anterior aspect of the ventral eyelid is a feature unique to alligators. Based on position, this gland does not appear to be homologous to the anterior lacrimal gland of lepidosaurs. Lymphatic aggregations were also found in the palpebral gland. The presence of interstitial immune cells in the orbital glands of alligators suggests that the alligator lacrimal apparatus, like that of birds, may play a role in the head-associated lymphatic tissue system.     

Microscopic anatomy of the orbital Harderian gland in the common tree shrew (Tupaia glis)

The orbital Harderian gland of the common tree shrew (Tupaia glis) was investigated at the macroscopic and microscopic levels. In the glands of both sexes only one acinar cell type was found. The cell is characterized by the presence of numerous lipid vacuoles of variable size and by a small number of PAS-positive, electron-dense granules distributed throughout the cytoplasm, which are predominant at the basal portion of each acinar cell. The duct system is well developed within the gland. The content of lipid vacuoles within the acinar cells is secreted from the apical portions by exocytosis, indicating the exocrine function of the organ. Apart from the lipid vacuoles, both acinar and ductal luminal contents of the Harderian gland also contain accretion of electron-dense materials. The vascularization within the Harderian gland is unique in that two capillary types (small fenestrated and irregular sinusoidal capillaries) could be demonstrated. The presence of fenestrated capillaries together with other morphological features (such as accumulation of the small electron-dense granules at the basal pole and the presence of basolateral microvilli) near the basal portion of the acinar cells suggest that the Harderian gland in T. glis might also be involved in an endocrine function.     

Immunocytochemical localization of seminal proteins in salivary and lacrimal glands of the rat

Antibodies against 10 different secretory proteins from the accessory sex glands of the male rat were used for immunohistochemical studies of salivary and lacrimal glands from intact and castrated rats, at the light- and electron-microscopic levels. In the parotid gland, secretory acinar cells showed immunoreactivity with antibodies against prostatic binding protein, cystatin-related peptide and acid phosphatase (isoenzyme pI 8.0; 5.6) typical of ventral prostate, and seminal vesicle secretion VI. Western blotting analysis indicated that immunoreactivity against prostatic binding protein was attributable to a subunit, presumably C3. Acid phosphatase pI 5.6 showed a molecular weight of 66 kDa, which is at variance with the prostatic form. Immunoreactivity for secretory transglutaminase, derived from the coagulating gland, was restricted to myoepithelial and stromal cells. In castrated animals, the immunoreactivity of acinar cells was reduced to the background level, whereas stromal transglutaminase immunoreactivity was unaltered. The distribution pattern of immunoreactivity for the proteins mentioned was almost identical in the lacrimal gland. Significant differences were however observed in the immunoreactivity of the inframandibular gland, where serous glandular cells were non-immunoreactive for seminal proteins, with the exception of acid phosphatase isoenzyme pI 8.0. Granules present in the convoluted granular ducts were immunoreactive particularly for acid phosphatase (isoenzyme pI 5.6)but much less for cystatin-related peptide; immunoreactivity was reduced after castration. The straight portion of the inframandibular duct system was immunoreactive for transglutaminase, but no influence of castration was visible. The distribution of immunoreactivity for seminal proteins present in the salivary and lacrimal glands and the pronounced androgen-dependence of their expression point to functional relationships of the respective proteins at both glandular sites.     

Aquaporin-5 (AQP5), a water channel protein, in the rat salivary and lacrimal glands: immunolocalization and effect of secretory stimulation

Aquaporin-5 (AQP5) is a water channel protein and is considered to play an important role in water movement across the plasma membrane. We raised anti-AQP5 antibody and examined the localization of AQP5 protein in rat salivary and lacrimal glands by immunofluorescence microscopy. AQP5 was found in secretory acinar cells of submandibular, parotid, and sublingual glands, where it was restricted to apical membranes including intercellular secretory canaliculi. In the submandibular gland, abundant AQP5 was also found additionally at the apical membrane of intercalated duct cells. Upon stimulation by isoproterenol, apical staining for AQP5 in parotid acinar cells tended to appear as clusters of dots. These results suggest that AQP5 is one of the candidate molecules responsible for the water movement in the salivary glands.     

Secretory and basal cells of the epithelium of the tubular glands in the male Mullerian gland of the caecilian Uraeotyphlus narayani (Amphibia: Gymnophiona)

Caecilians are exceptional among the vertebrates in that males retain the Mullerian duct as a functional glandular structure. The Mullerian gland on each side is formed from a large number of tubular glands connecting to a central duct, which either connects to the urogenital duct or opens directly into the cloaca. The Mullerian gland is believed to secrete a substance to be added to the sperm during ejaculation. Thus, the Mullerian gland could function as a male accessory reproductive gland. Recently, we described the male Mullerian gland of Uraeotyphlus narayani using light and transmission electron microscopy (TEM) and histochemistry. The present TEM study reports that the secretory cells of both the tubular and basal portions of the tubular glands of the male Mullerian gland of this caecilian produce secretion granules in the same manner as do other glandular epithelial cells. The secretion granules are released in the form of structured granules into the lumen of the tubular glands, and such granules are traceable to the lumen of the central duct of the Mullerian gland. This is comparable to the situation prevailing in the epididymal epithelium of several reptiles. In the secretory cells of the basal portion of the tubular glands, mitochondria are intimately associated with fabrication of the secretion granules. The structural and functional organization of the epithelium of the basal portion of the tubular glands is complicated by the presence of basal cells. This study suggests the origin of the basal cells from peritubular tissue leukocytes. The study also indicates a role for the basal cells in acquiring secretion granules from the neighboring secretory cells and processing them into lipofuscin material in the context of regression of the Mullerian gland during the period of reproductive quiescence. In these respects the basal cells match those in the epithelial lining of the epididymis of amniotes.     

Morphology of the Harderian gland of some Australian geckos

This study of the morphology, histology, histochemistry, and ultrastructure of the Harderian gland in Geckos (Squamata, Gekkota) revealed previously unreported variation. The gecko Harderian gland is unlike that of other squamates in that each cell of the secretory epithelium has both lipid and protein secretory granules. Lipid secretion has not been reported previously for the squamate Harderian gland. The structure of the protein granules resembles that described for a scincomorph lizard (Podarcis, Lacertidae). Differences between representatives of the subfamilies Gekkoninae and Diplodactylinae suggest possible phylogenetic constraints in the structure or function of Harderian glands within gekkotan lineages. The structural relationship between the Harderian gland and the lacrimal duct supports previous suggestions of a possible functional link between the Harderian gland and the vomeronasal organ. J Morphol 231:253–259, 1997. © 1997 Wiley-Liss, Inc.     

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.     

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.     

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.     

Anatomy of the major lacrimal gland of rhesus monkeys (Macaca mulatta)

The major lacrimal gland of rhesus monkeys is impalpable within the fatty connective tissue of the upper lateral quadrant of the orbit. Acini of the lacrimal glands are composed of both sparsely and heavily granulated cells that histochemically resemble serous acinar cells of the submandibular salivary gland. The cytoplasmic granules are strongly periodic acid-Schiff (PAS)-positive, and some are also stained by alcian blue for acidic mucosubstances. The lacrimal gland has a simple duct system of intralobular ducts and interlobular excretory ducts. Lymphocytes and plasma cells are common in the periductal stroma. Major lacrimal glands of rhesus monkeys are suitable for comparative and correlative studies of lacrimal and salivary diseases and radiation responses.     

Morphology of defense glands of the opilionids (daddy longlegs) Leiobunum vittatum and L. flavum (Arachnida: Opiliones: Palpatores: Phalangiidae)

Opilionid defense glands consist of 0.5 × 0.9-mm sacs attached to the underside of low tubercles located on the dorsal side of the cephalothorax, posterior to the first pair of legs. Each gland opens via an elongated slit, located in the posterior floor of a crater that is situated at the summit of the tubercle. The center of the sac, called the reservoir, is lined by a cuticle consisting of epicuticle and endocuticle which is continuous through the slit with the exoskeleton. The layers of cuticle vary in thickness with different locations in the gland. A hemocoelomic (basement) membrane, 0.5–1, μ thick, forms the boundary between glandular cells and hemocoel. The gland has a nonsecretory portion consisting only of cuticle-supporting cells and a secretory portion consisting of secretory and cuticle-supporting cells. The cuticle lining the reservoir in the secretory area is broached by many cuticle-lined ductules, each of which drains an isolated intercellular space called the intercalated cistern. This in turn drains microvilli-lined canaliculi located between and extending into secretory cells. The cisterns are devoid of microvilli. Secretory cell cytoplasm contains a Golgi apparatus, many free ribosomes, rough endoplasmic reticulum (RER), two types of granules (speckled and dense), and mitochondria. Speckled granules are partially filled with fairly large particles and are found in association with the Golgi apparatus. They also surround canaliculi into which they empty. Dense granules are packed with very small particles, have a gray homogeneous appearance, and are scattered throughout the cytoplasm. Mitochondria containing matrix granules tend to scatter throughout the cytoplasm but are concentrated around canaliculi.     

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.     

The post-embryonic changes in Melipona quadrifasciata anthidioides Lep. (Hym. Apoidea). II. Development of the salivary glands system

The paper deals with the development of the salivary gland system in Melipona quadrifasciata anthidioides, which begins in the prepupal stage. The silk glands degenerate by autolysis at the end of the larval stage. Degeneration is characterized by cytoplasmic vacuolization and pycnosis of the nuclei of the secretory cells. The glandular secretory portion of degenerated silk glands separates from the excretory ducts. The salivary glands develop from the duct of the larval silk glands. The thoracic salivary glands develop from the ducts of the secretory tubules and the head salivary glands from the terminal excretory duct. The mandibular glands appear in the prepupa as invaginations of mandibular segments, and their differentiation to attain the adult configuration occurs during pupation. The hypopharyngeal glands have their origin from evaginations of the ventral anterior portion of the pharynx. A long tubule first appears with walls formed by more than one cellular layer. Then some cells separate from the lumen of the duct, staying attached to it by a cuticular channel in part intracellular. The initial duct constitutes the axial duct, in which the channel of the secretory cells opens. During the development of salivary and mandibular glands, they recapitulate primitive stages of the phylogeny of the bees. During the development of salivary glands system, mitosis accounts for only part of the growth. Most of the growth occurs by increase in size of cells rather than by cell division. In brown-eyed and pigmented pupae six days before emergence, the salivary gland system is completely developed, although not yet functioning.     

The Harderian gland of the Dhub lizard Uromastyx microlepis of the Kuwaiti desert: an ultrastructural approach

Harderian glands exist in the orbits of most terrestrial vertebrates. The basic function of the gland is the lubrication of the eye. The present study was carried out to shed some light on the ultrastructure of the still enigmatic Harderian gland of the lizard Uromastyx microlepis, a common species in Kuwait and other Gulf areas. The Harderian gland of Uromastyx microlepis is well developed, relatively large in size and lingual in shape. The epithelial cells of the anterior part of the gland are characterized by the presence of membrane bound granules of almost homogeneous consistency. These secretory granules are gathered in compartments and separated by membranes and stacks of granular endoplasmic reticulum (GER). Most of the lumina were empty. Moderate amounts of GER, free ribosomes and pleiomorphic mitochondria were observed in the perinuclear area of the epithelial cells. The medial and caudal parts of the gland were rich in special secretory granules, GER, free ribosomes and pleiomorphic mitochondria. The anterior part of the gland could represent the future lacrimal gland of mammals. A network of myoepithelial cells was recognized around the gland tubules. While no melanocytes or lymphocytes were observed in the scarce interstitial tissue, macrophages, that might have an immune function in the gland, were observed.     

Histology,histochemistry, and ultrastructure of the harderian gland of the snake Coluber viridiflavus

Analyses of the histology, histochemistry, and ultrastructre of the Harderian gland of Coluber viridiflavus prove the gland to be compound acinar and to produce a seromucous secretion. Acinar cells (type I) contain secretory granules that are composite, consisting ultrastructurally of three distinct parts that are sharply separated. They are similar to the “special secretory granules” described in the cells of the Harderian gland of the lizard Podarcis s. sicula. Some acini of the most anterior and posterior parts of the gland are mucous. Acinar cells (type II) of this type contain secretory granules that are Alcian blue/PAS positve. At the ultrastructural level, they appear homogeneous and of low density, characteristic of mucous secretions. These mucus-secreting anterior and posterior parts of the Harderian gland may by considered as regions of intial differentiation of the anterior and posterior lacrimal galnds.     

Microstructure of the eye tunics,eyelids and ocular glands of the Sulawesi bear cuscus (Ailurops ursinus Temminck, 1824) (Phalangeridae: Marsupialia) based on anatomical,histological and histochemical studies

This study described the anatomy, histology and the histochemical analysis of the eye tunics, the upper and lower eyelid, the third eyelid, the lacrimal gland and the superficial gland of the third eyelid in adult Sulawesi bear cuscus. The eyeball and the eyelids with the orbital glands were harvested immediately post-mortem. The eyeball in the Sulawesi bear cuscus had a sphere-like shape. The pupil was round, and the lens was a circular biconvex body. There was neither tapetum lucidum nor Harderian gland. Similarly, there were no eyelashes in the lower eyelid. The lymphoid follicles and the high endothelial venules (HEV) were found in the lymphoid region only in the third eyelid and in the connective tissue of the superficial gland of the third eyelid. The third eyelid in the bear cuscus resembled the letter “T.” The lacrimal gland and superficial gland of the third eyelid were multilobar tubuloacinar glands. The histological analysis and histochemical studies showed that the lacrimal gland in the Sulawesi bear cuscus produced a mucoserous secretion with predominantly serous cells. In contrast, the superficial gland of the third eyelid produced a serous secretion with a single acinus mucous in character.     

The harderian gland of the frog, Rana esculenta, during the annual cycle: histology, histochemistry and ultrastructure

The Harderian gland in Rana esculenta has been studied during the annual cycle at the histological, histochemical and ultrastructural levels. The Harderian gland has an acinar structure and is the only orbital gland in anuran amphibia. It develops at the medial corner of the orbit from the conjunctival epithelium at the premetamorphic stage. In the adult the glandular secretion reaches a maximum during the months of July and August, drops in September and resumes slowly from October onwards. The secretion is seromucoid and the secretory granules are released into the acinar lumen, mainly by exocytosis. Porphyrins were not detected. No sexual dimorphism was observed in the glandular cells. The resumption of secretory activity in October and the enhancement of secretion in May are marked by the appearance of "blue nuclei" (Mallory stain) in a relatively high percentage of glandular cells. This unusual blue colour, using the Mallory stain (by which nuclei stain red), disappears after digestion of paraffin sections with RNAase, but not with DNAase and trypsin. The blue staining may, therefore, indicate an increased amount of nuclear RNA. The Harderian gland in the frog most probably serves to lubricate and moisten the eye in the absence of the lacrimal gland. However, the gland may also represent an immunoactive organ owing to the presence of numerous mast cells and plasma cells in the interacinar spaces.     

Localization of gamma-glutamyl transpeptidase in human sweat glands: an immunohistochemical study using a monoclonal antibody

We studied the distribution of gamma-glutamyl transpeptidase (gamma-GT) by use of a monoclonal antibody (MAb) against human kidney gamma-GT in human sweat glands. In the eccrine sweat gland, the enzyme was localized along the luminal membrane and small apocrine extrusions of the superficial cells of the secretory portion. The intercellular canaliculi between basal cells were occasionally immunoreactive. In the secretory portion of the apocrine gland, luminal membrane and apocrine extrusions of various sizes and stages at the apices of the secretory cells exhibited positive reactions. Immunoreaction was also seen in the Golgi area of the cuboidal secretory cells. No positive reaction was observed in the myoepithelial cells of either gland or in the excretory duct cells.     

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.     

Androgen receptor in rat Harderian and submandibular glands

Summary Androgens regulate the development and sexual dimorphism of rodent Harderian and submandibular glands. This effect is believed to be mediated by the androgen receptor. Immunohistochemistry and immunoblotting were carried out to study the receptor in normal, castrated and dihydrotestosterone-supplemented rat Harderian and submandibular glands. Immunohistochemically, the most intense nuclear staining was observed in the acinar cells of the submandibular glands, followed by intercalated duct cells. The granular convoluted tubules showed weak immunostaining and the striated ducts were negative. In the Harderian gland, nuclear staining was seen in both type I and II secretory cells. Castration and treatment had no effect on the expression of the androgen receptor protein in either gland. A 110 K androgen receptor signal was detected by immunoblotting in the Harderian gland but not in the submandibular gland. An experiment was designed to explore the possible effect of proteinases on the receptor protein in the homogenate of submandibular gland. Our results demonstrate the cell-specific location of the receptor in Harderian and submandibular glands, and show that the expression of the receptor protein is androgen-independent.