Lipid droplet secretion by the rabbit harderian gland

Morphological and molecular changes in the Harderian gland of streptozotocin-induced diabetic rats

Using a rat model of type 1 diabetes (T1D) obtained by treatment with streptozotocin, an antibiotic that destroys pancreatic β-cells, we evaluated the influence of subsequent hyperglycemia on the morphology and physiology of the Harderian gland (HG). HG is located in the medial corner of the orbit of many terrestrial vertebrates and, in rodents, is characterized by the presence of porphyrins, which being involved in the phototransduction, through photo-oxidation, produce reactive oxygen species activating the autophagy pathway. The study focused on the expression of some morphological markers involved in cell junction formation (occludin, connexin-43, and α-tubulin) and mast cell number (MCN), as well as autophagic and apoptotic pathways. The expression of enzymes involved in steroidogenesis [steroidogenic acute regulatory protein (StAR), and 3β-hydroxysteroid dehydrogenase (3β-HSD)] and the level of lipid peroxidation by thiobarbituric acid reactive species assay were also evaluated. The results strongly indicate, for the first time, that T1D has a negative impact on the pathophysiology of rat HG, as evidenced by increased oxidative stress, morphological and biochemical alterations, hyperproduction and secretion of porphyrins, increased MCN, reduced protein levels of StAR and 3β-HSD, and, finally, induced autophagy and apoptosis. All the combined data support the use of the rat HG as a suitable experimental model to elucidate the molecular damage/survival pathways elicited by stress conditions.

Perilipin-2 promotes lipid droplet-plasma membrane interactions that facilitate apocrine lipid secretion in secretory epithelial cells of the mouse mammary gland

Secretory epithelial cells (sMEC) in mammary glands of lactating animals secrete lipids by a novel apocrine mechanism in which cytoplasmic lipid droplets (LD) contact and are enveloped by elements of the apical plasma membrane (APM) before being released into the lumen of the gland as membrane bound structures. The molecular properties of LD-APM contacts and the mechanisms regulating LD membrane envelopment and secretion are not fully understood. Perilipin-2 (Plin2) is a constitutive LD protein that has been proposed to tether LD to the APM through formation of a complex with the transmembrane protein, butyrophilin1a1 (BTN) and the redox enzyme, xanthine oxidoreductase (XOR). Using mice lacking Plin2 and physiological inhibition of apocrine lipid secretion, we demonstrate that LD-APM contact and envelopment are mechanistically distinct steps that they are differentially regulated by Plin2 and independent of LD secretion. We find that Plin2 is not required for formation of LD-APM contacts. However, it increases the percentage of LD that contact the APM and mediates enlargement of the LD-APM contact zone as LD undergo membrane envelopment. The effects of Plin2 LD-APM interactions are associated with increased abundances of BTN, XOR and Cidea, which are implicated as mediators of LD-APM contact formation, on membranes surrounding secreted LD, and with promotion of glycocalyx remodeling at LD-APM contact sites. We propose that Plin2 does not directly mediate contact between LD and the APM but acts by enhancing molecular interactions that stabilize LD-APM contacts and govern membrane envelopment of LD during apocrine lipid secretion. Plin2 does not appear to significantly affect the lipid content of milk in fully lactating animals, but it does increase lipid secretion at the onset of lactation in primaparous dams, which suggest a role in facilitating apocrine lipid secretion in sMEC during their initial transition to a secretory phenotype.

Preliminary study of the ameliorative effects of melatonin on cadmium-induced morphological and biochemical alterations in the rat Harderian gland

Herein is reported, for the first time in the rat Harderian gland (HG), the counteractive action of melatonin (Mlt), a well-known antioxidant radical scavenger, on the increased oxidative stress damages induced by a pro-oxidant substance, cadmium (Cd), an environmental pollutant also considered as endocrine disruptor. HG, an infraorbital gland present in almost all terrestrial vertebrates, produces a lipid secretion to lubricate the eyeball, as well as porphyrin/Mlt as light transducers. Moreover, HG is an extra-gonadal source of steroid sex hormones. Via ex vivo experiments lasting for 24 h, we verified the increased lipid peroxidation in Cd-treated glands, producing morphological alteration of the glandular epithelium, as well as an increased porphyrins accumulation. Moreover, Cd also induced a decreased protein level of the steroidogenic enzymes steroidogenic acute regulatory (StAR) and 3βHSD, and an increased mast cell number. Results obtained with Mlt cotreatment demonstrated that it decreased the levels of Cd-induced oxidative damage, with reversal of all the observed modification. Furthermore, the TUNEL assay showed that the increased number of apoptotic cells in Cd-treated HG was counteracted by the contemporaneous Mlt administration. Results confirmed that Mlt treatment restored the levels of two autophagy markers, LC3 and p62, counteracting the autophagy Cd-induced. Interestingly, the positive effects of Mlt alone were highlighted by the decreased rate of lipid peroxidation as compared with the control, confirming its antioxidant action. Combined data further confirmed the antioxidant action of Mlt in counteracting the degeneration provoked by reactive oxygen species (ROS) in the rat HG, a tissue extremely susceptible to oxidative stress condition.

International Harmonization of Nomenclature and Diagnostic Criteria (INHAND): Nonproliferative and Proliferative Lesions of the Rabbit

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions Project (www.toxpath.org/inhand.asp) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP) and North America (STP) to develop an internationally accepted nomenclature for proliferative and non-proliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying microscopic lesions observed in most tissues and organs from the laboratory rabbit used in nonclinical safety studies. Some of the lesions are illustrated by color photomicrographs. The standardized nomenclature presented in this document is also available electronically on the internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous lesions as well as lesions induced by exposure to test materials. Relevant infectious and parasitic lesions are included as well. A widely accepted and utilized international harmonization of nomenclature for lesions in laboratory animals will provide a common language among regulatory and scientific research organizations in different countries and increase and enrich international exchanges of information among toxicologists and pathologists.

A cell apoptosis probe based on fluorogen with aggregation induced emission characteristics

A fluorogen-based aggregation-induced emission zinc-dipicolylamine (AIE-ZnDPA) probe with aggregation-induced emission characteristics has been designed and synthesized to detect cell apoptosis. AIE-ZnDPA does not respond to healthy cells but selectively stains and lights up fluorescence in the membranes of early stage apoptotic cells as well as the nuclei of late stage apoptotic cells. Without zinc coordination, the precursor lipophilic AIE dipicolylamine (AIE-DPA) probe stains healthy cells and shows high affinity for lipid droplets (LDs).

Morphological aspects and expression of estrogen and progesterone receptors in the interdigital sinus in cyclic ewes

Many species that belong to Artiodactyls order show an interdigital sinus (IS), as it occurs in sheep, in all four extremities. These are considered to be scent glands responsible for sexual communication having strong attractiveness to mature males at the peak of the breeding season. The aim of this study was to evaluate, in IS in cyclic ewes, the microscopic and ultrastructure (scanning and transmission electron microscopy) anatomy, secretion composition, and mRNA and protein expression of estrogen receptors a and b and progesterone receptors. Glandular sebaceous structures occupy a superficial area of the pouch. The other glands present in the IS show a coiled tubular structure and tall and polyhedral secretory cells with irregular luminal surface resulting from the secretory process. Protein and mRNA gene transcription studies were performed to determine the presence of ER (a and b) and P4r in IS. At the follicular phase, IS cell populations analyzed using flow cytometry expressed higher levels of ERb compared with ERa (P<0.05), whereas no difference was observed between them in the luteal phase. The IS amount of secretion was the highest in the follicular phase compared with luteal phase (P<0.05) or pregnancy (P<0.001).To the best of our knowledge, for the first time, the presence of ER (a and b) within the IS was demonstrated. As estrogen action is mediated by specific receptors in target cells, the presence of these receptors in IS might be needed to trigger signaling pathways involved in conspecific chemical (sexual) communication attributed to this area.

Lipid secretory mechanisms in the mammalian harderian gland

The mammalian Harderian glands are lipid-secreting glands. In an unstimulated condition, the glandular cells frequently exocytose the lipid materials; however, no intracellular calcium ion ([Ca2+]c) changes are detectable. Cholinergic (muscarinic) secretagogues induce secretory activity and increase of [Ca2+]c. A G-protein activator, sodium fluoride, enhances the secretory activity and increase of [Ca2+]c. Removal of extracellular calcium ions inhibits the secretion enhanced by cholinergic stimulation. Under pharmacologic stimulation, glandular cells may show an apocrine-like secretory pattern. Cholinergic stimulation also induces contraction of the myoepithelial cells covering glandular end pieces; however, the reduction in volume of glandular end pieces is not prominent. Catecholamines have no effect on the release of lipid materials. These results indicate the involvement of G-proteins linking with muscarinic receptors and Ca2+ dynamics (increase of [Ca2+]c and Ca2+ influx) in lipid secretion by glandular cells and in contraction of myoepithelial cells of mammalian Harderian glands. However, the increase of [Ca2+]c in Harderian glands was less when compared with other cells--for instance, those which secrete protein.

Invasive processes in the normal Harderian gland of Syrian hamster

In this contribution we will pay special attention to several morphological findings that we can observe, under some circumstances, in the normal Harderian gland of the Syrian hamster. The accumulation of porphyrins in this gland results in mitochondrial damage and extensive cell death. Many damaged cells are secreted into the lumen of the tubule-alveoli, but most of them seem to produce an invasive process that even affects the vascular components of the gland. In this way, many blood vessels are invaded and appear partially filled with the invasive mass, which sometimes totally occludes the lumen of the vessels. We have also observed other surprising features related to a special kind of activity in certain secretory cells. Such activity results in a peculiar "segregation" of a cytoplasmic fragment, containing the nucleus. The affected cells seem to gather up their cytoplasm and nucleus towards the basal zone, while the rest of the cell, including practically the whole amount of lipid droplets, is relegated to the vicinity of the lumen. All these phenomena seem finally to result in the detachment of some clusters, composed of a limited number of cells, which display a basophilic cytoplasm practically free of lipid droplets.

Cell biology of the harderian gland

The harderian gland is an orbital gland of the majority of land vertebrates. It is the only orbital gland in anuran amphibians since the lacrimal gland develops later during phylogenesis in some reptilian species. Perhaps because it is not found in man, little interest was paid to this gland until about four decades ago. In recent years, however, the scientific community has shown new interest in analyzing the ontogenetic and morphofunctional aspects of the harderian gland, particularly in rodents, which are the preferred experimental model for physiologists and pathologists. One of the main characteristics of the gland is the extreme variety not only in its morphology, but also in its biochemical properties. This most likely reflects the versatility of functions related to different adaptations of the species considered. The complexity of the harderian gland is further shown in its control by many exogenous and endogenous factors, which vary from species to species. The information gained so far points to the following functions for the gland: (1) lubrication of the eye and nictitating membrane, (2) a site of immune response, particularly in birds, (3) a source of pheromones, (4) a source of saliva in some chelonians, (5) osmoregulation in some reptiles, (6) photoreception in rodents, (7) thermoregulation in some rodents, and (8) a source of growth factors.

Morphological investigations of the glandulae profundae plicae semilunares conjuctivae in the domestic swine (Sus scrofa domesticus) and the wild hog (Sus scrofa ferus)

Samples of glandulae profundae plicae semilunares (Harderian glands) from five domestic swine and five wild hogs were used for this research. The gland samples were fixed in Bouin solution and mounted in paraffin. The paraffin slices were stained with haematoxylin and eosin, according to the periodic-acid-Schiff (PAS) method, with alcian blue (pH 2.5), with toluidine blue (pH 4.0), and applying a combination of staining with alcian blue (pH 2.5) and the PAS method. In domestic swine and wild hogs, these glands are tubular-alveolar with wide glandular lumina. A great deal of acid mucopolysaccharides and PAS-positive substances were noted within swines' glandular cells, while, in wild hogs, PAS-positive substances were not frequent, acid mucopolysaccharides being noted in only a few glandular-acini cells. The appearance of the metachromatic phenomenon was not noted either in domestic swine or in wild hogs. In domestic swine, the level of acid mucopolysaccharides is probably due either to the housing method or to the influence of the alkaline substances that may appear on an eye's mucous conjunctive membrane during intensive breeding, such that the Harderian glands protect the mucous membrane by extracting acid mucopolysaccharides.

Protein kinase C isoenzymes in mouse harderian gland. Differential expression of the alpha- and epsilon-isoforms during pregnancy. Protein kinase C-OC

Protein kinase C (PKC) is known to be involved in the regulation of exocytosis in different cell lines and tissues. Experiments were designed to determine whether the Harderian gland of CD-1 mouse produces PKC isoenzymes and whether the expression of the isoforms changes during pregnancy. The presence of the isoenzymes was assessed by immunoblotting experiments using extract of total Harderian gland and polyclonal antisera specific for nine different PKC isoforms. Antisera giving a positive staining on Western blots were subsequently used for immunohistochemical investigation using a secondary antibody conjugated to alkaline phosphatase. Immunoblotting experiments revealed that the Harderian gland from female mouse expresses PKC isoforms-alpha, -epsilon, -zeta and -eta. These isoforms were also detected in the Harderian gland from 13-day pregnant mouse; however, striking quantitative changes were seen concerning the alpha- and epsilon-isoforms. The 80-kDa native from of PKC-alpha almost doubled in the pregnant mouse in comparison with normal female mouse whereas the amount of 50-kDa catalytic domain did not change. Protein kinase C-epsilon appeared as a 92- to 93-kDa form and a 67-kDa form. While the 92- to 93-kDa protein was expressed to a similar extent in both types of mouse, the 67-kDa form was more abundant in the Harderian gland from normal female mouse. These data were corroborated by immunohistochemical experiments and showing a diffuse and granular staining of the adenomeres. These observations demonstrate for the first time (to our knowledge) that the mouse Harderian gland produces several PKC isoenzymes that could be involved in the regulation of exocytosis and/or other functions.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of ovariectomy and ageing on the structure and ultrastructure of the female Syrian hamster Harderian gland: a stereological analysis

The effects of ovariectomy and ageing on the structure and ultrastructure of the Syrian hamster Harderian gland were investigated by techniques of quantitative stereology. Tissues were obtained from intact 6-month-old, sham-operated 6-month-old, ovariectomized 6-month-old, intact 18-month-old and ovariectomized 18-month-old female hamsters. Glands from both ovariectomized and aged hamsters showed comparable qualitative and quantitative characteristics. They showed histological alterations that included thinning of the tubule walls, lowering of luminal porphyrins, invasion of lumina by neutrophils and the occurrence of interstitial porphyrins. Glands from both ovariectomized and aged hamsters showed statistically significant differences from control animals in relation to numerical density and cellular size. Finally, quantitative studies with the electron microscope revealed significant decreases in the volume densities of the cytoplasmic organelles concerned with secretion. These results support the hypotheses that the secretory activity of the female hamster Harderian gland is influenced, directly or indirectly, by ovarian hormones, and that many of the age-related modifications of the Harderian gland reflect alterations in ovarian function.

Carbamylcholine-induced morphological changes and spatial dynamics of [Ca2+]c in Harderian glands of guinea pigs: calcium-dependent lipid secretion and contraction of myoepithelial cells

To determine whether lipid-secreting cells have cytosolic Ca2+ concentration ([Ca2+]c)-related secretory mechanisms, morphological changes and intracellular calcium dynamics of Harderian glands of guinea pigs stimulated by secretagogue were studied by electron microscopy and Fura-2/AM digital image analysis. Control glandular cells contained large lipid vacuoles that were bordered by multi-layered membranes. Rough-surfaced endoplasmic reticulum, mitochondria, and smooth-surfaced endoplasmic reticulum may be involved in lipid vacuole formation. Myoepithelial cells surrounded alveoli. After carbamylcholine (CCh, 10(-6), 10(-5), and 10(-3) M) stimulation, lipid materials within the membranous structures were frequently discharged by an exocytotic mechanism. Conspicuous deformation of glandular cells caused by vigorous contraction of myoepithelial cells was observed in isolated alveoli after 10(-6) M CCh stimulation, whereas the deformities of glandular tissues perfused via vessels were small even after 10(-3) M CCh stimulation. Connective tissue between glandular alveoli inhibited unbridled myoepithelial-cell contraction. Fura-2/AM digital imaging analysis revealed that CCh stimulation caused an increase in [Ca2+]c in isolated alveoli. The morphological reactions and changes in [Ca2+]c were prevented by atropine. When extracellular calcium ions were absent, enhanced extrusion of lipid vacuoles, myoepithelial-cell contraction, and a rise in [Ca2+]c after CCh stimulation were not observed. Nicotine and catecholamines had no effect on the secretion or on the dynamics of [Ca2+]c. It can be concluded that acetylcholine elicits exocytosis in glandular cells and contraction of the myoepithelial cells of Harderian glands, accompanied by an increase in [Ca2+]c. The dynamics of [Ca2+]c of the gland alveoli are mostly dependent on extracellular Ca2+.

An electron microscopic study of the harderian gland of the Syrian hamster with particular reference to the processes of formation and discharge of the secretory vacuoles

The lipid-secreting cells of the Harderian gland of the Syrian hamster were studied using light, transmission, and scanning electron microscopy. Three morphologically different secretory cell types are identified in the gland: type I and II cells of the male gland and, distinct from either, the female gland cell. In all secretory cell types, lipid droplets in the cytoplasm were surrounded by unit membranes. Ultrastructural evidence of the involvement of the Golgi apparatus in the formation of the secretory vacuoles was obtained. The process of secretion involved the fusion of the boundary unit membrane of the vacuole with the plasma membrane and the release of the vacuolar content alone into the lumen. No evidence of holocrine processes was observed in this study. In addition to lipids, vacuoles contained materials whose solubility properties clearly differed from those of lipids. There appear to be variations in the ultrastructural characteristics of the vacuole content of the different types of secretory cell.

Lymphoid cells in the harderian gland of the rodent Octodon degus

The Harderian gland of the degu (Octodon degus) is composed of tubulo-alveolar secretory units that share most of morphological features found in the Harderian glands of other rodents. However, a peculiar characteristic observed in the glands of female degus is the existence of lymphoid cell clusters within the connective tissue surrounding the secretory adenomeres. Lymphocytes and lymphoblasts are found associated with blood vessels and especially with nerve bundles in the medullary region of the gland. Occasionally, macrophages and plasma cells are also observed. Although the Golgi apparatus appears well developed, the ultrastructural characteristics of most of these lymphoid elements correspond to those of inactive lymphocytes. Unmyelinated fibers containing clear and dense-core vesicles are found closely related to lymphocytes. On some occasions, lymphocytes present extensive areas of apposition with structures resembling intercellular junctions. The analogy of the lymphoid clusters reported in this study with those described in the avian Harderian gland is discussed.

Postnatal development of the harderian gland in the Syrian golden hamster (Mesocricetus auratus): a light and electron microscopic study

The main objective of the present investigation was to study the morphological and chronological aspects of the development of the Harderian gland in the Syrian golden hamster. Tissues were obtained from male and female hamsters at days 1,3,5,7,10,12,15,17,20,27,37,46, and 90 after birth and processed for light and transmission electron microscopy. The present observations indicate that a well-defined temporal sequence in microscopic and ultrastructural modification is recognizable in the development of the hamster Harderian gland. Four stages of development were proposed. Between days 1-5 (first stage), the gland shows characteristics of an immature structure. The glandular cells contain many free ribosomes, few and small organelles, and large irregular-shape nuclei. Between days 7-17 (second stage), there is a marked increase of organelles involved in synthesis and secretion. The gland begins the secretion of lipids and porphyrins, but no morphological differences between male and female glands are observed. Between days 20-36 (third stage), the morphological differences between the two sexes appear and progressively develop. In 45-day-old hamsters, the Harderian gland possesses the structural characteristics of adult glands, and further developmental changes are essentially quantitative in nature (fourth stage). At all stages of development, the population of secretory cells has a uniform appearance. The morphological results are discussed as well as the possible relationship of this temporal sequence with hormonal changes.

Effect of carbamylcholine on Harderian gland morphology in rats

To determine the effect of cholinergic secretagogue on the Harderian gland of rats, several light- and electron-microscopic parameters were morphometrically assessed at different time intervals after carbamylcholine injection. In controls, two types of glandular cells (type A cells having 40-55 large vacuoles per cell profile and type B cells containing 30-38 smaller vacuoles per cell profile) and myoepithelial cells were recognized. At 5 min after injection of carbamylcholine, when rats secreted "bloody tears", many alveoli showing narrower lumina and exocytotic figures in both types of cells were observed. Some vacuoles, which were covered by thin cytoplasmic sheets, protruded into the alveolar lumina. However, there was no evidence of apocrine or holocrine secretion. At 30 min and 120 min after injection, most of the alveolar lumina were dilated, and a pronounced decrease in the number of vacuoles in the glandular cells was observed. At 300 min after injection, the secretory vacuoles in both cell types reaccumulated. Transitional forms between the two cell types were not observed. The two types of Harderian gland cells can therefore be considered independent populations rather than different secretory stages of the same cell. It appears that the secretory process of the Harderian gland of rat is affected by cholinergic stimulation of the two types of glandular cells and of myoepithelial cells.

Major ocular glands (harderian gland and lacrimal gland) of the musk shrew (Suncus murinus) with a review on the comparative anatomy and histology of the mammalian lacrimal glands

The Harderian gland of the musk shrew Suncus murinus is elongated anteroposteriorly from in front of the eye to behind the ear. The gland is divided into two portions: an anterior portion (A portion) and a posterior portion (P portion). The single secretory duct of the gland emerges from the anterior end of the P portion, receives several secretory ducts of the A portion during the course along it, runs around the ventral aspect of the eyeball, and finally opens into the anterior corner of conjunctival sacs. The two portions of the gland show a fundamentally similar histological structure, having a poorly developed intraglandular duct system and wide tubular alveoli. The quantity of lipid vacuoles and stromal connective tissue in the A portion is greater than in the P portion. The lipid vacuoles in both portions are surrounded by unit membranes, but their contents appear different. The lacrimal gland of the musk shrew is located along the ventral side of the P portion of the Harderian gland. The lacrimal duct emerges from its anterior end, runs around the ventral and anterior aspects of the ear, crosses the A portion of the Harderian gland, and finally opens at the posterior corner of conjunctival sacs. The lobules of the lacrimal gland comprise a branched duct system and terminal acini with two types of secretory cells: 1) acidic cells positive both for the periodic acid-Schiff reaction (PAS) and for Alcian blue (AB) and 2) neutral cells positive for PAS and negative for AB. Both cell types tend to make separate acini, but when present in the same acinus, the acidic cells occupy relatively peripheral positions in the acinus. Both cell types lack intercellular canaliculi. On the basis of the present study as well as previous descriptions in the literature, the author suggests that the mammalian lacrimal glands can be divided into two sets: 1) a Glandula lacrimalis superior with multiple secretory ducts associated with the upper eyelid and 2) a Glandula lacrimalis inferior with a single secretory duct opening into the lateral corner of the conjunctival sacs. These glands have a fundamentally similar histological structure; but in the rabbit, which possesses both sets of lacrimal glands, they are different. On the other hand, the secretory cells of lacrimal glands generally have no intercellular secretory canaliculi, which are characteristically present between the serous secretory cells of the salivary glands.

Ultrastructural visualization of intracellular porphyrin in the rat Harderian gland

The Harderian glands of male Albino rats 1-24 months of age were studied by electron microscopy. In most glands, a few acinar cells contained straight and curved trilaminar profiles identical in form to the material in the luminal masses of porphyrin pigment. They resembled the structures which several investigators have identified as crystals of protoporphyrin IX in porphyric human and mouse hepatocytes. Protoporphyrin IX is the predominant form synthesized by rat Harderian cells in vitro. The trilaminar profiles were within the cytoplasm but not within the lipid secretory vacuoles. A large number of the acinar cells had finely tubular endoplasmic reticulum (ER). However, cells containing the trilaminar forms consistently had dilated ER vesicles. This change may have been a prelude to cell death, for some pigment-containing cells attached to the acinar basal lamina also displayed fragmented organelles and a loss of density of the cytoplasmic matrix. In some acinar lumina there was abundant cell debris along with the trilaminar profiles. It is concluded that in the rat, some of the Harderian free porphyrins can be released through cell death.

A correlated light and electron microscopic study of the structure and secretory activity of the accessory salivary glands of the marine gastropods, Conus flavidus and C. vexillum (neogastropoda, conacea)

The structure and secretory activity of the accessory salivary gland in two species of Conus were examined using routine and histochemical techniques of light, scanning and transmission electron microscopy. The composite layers of the accessory salivary gland of Conus are a luminal epithelium, fibromuscular layer, submuscular layer, and a capsule. In C. flavidus and C. vexillum, the luminal epithelium is formed by epitheliocytes and cytoplasmic processes extending from the secretory cells, whose perikarya form the submuscular layer. The processes carry secretory cell products (chiefly Golgi-derived glycoprotein) across the fibromuscular layer and terminate between epitheliocytes (at the bases of the secretory canaliculi) or beyond the surface of the epithelial cells. Conus vexillum is distinguished from C. flavidus by its high content of lipofuscin. Epitheliocytes are the only microvillated cells in the accessory salivary gland of Conus. In C. flavidus, epitheliocytes extrude secretory granules, various types of cytoplasmic blebs and clear vesicles by apocrine "pinching off." Clear vesicles are shed from the tips of microvilli. The luminal epithelial cells of C. vexillum similarly egest clear vesicles, but normally undergo additional holocrine secretion to release lipofuscin. The secretions of epitheliocytes appear to be major products of the accessory salivary gland: consideration of secretory activities by both epitheliocytes and secretory cells will therefore be necessary when directly investigating accessory salivary gland function in Conus.

A histological study of the Harderian gland of Mongolian gerbils, Meriones meridianus

The histological structure of the gerbil Harderian gland was investigated by means of light and transmission electron microscopy. The single excretory duct of the gland is directly continuous with endpieces at the hilus and opens nasally and ventrally to the third eyelid. The excretory duct is accompanied by many acini of small serous glands around it. The gland is composed of tubuloalveoli (tubular alveoli) with wide lumina and is not divided into lobules. There is no branched duct system within the gland. The tubuloalveoli themselves convey the secretory materials to the hilus where the excretory duct begins. The alveolar epithelium is composed of only one type of glandular cell as well as myoepithelial cells. The glandular cells contain many clear secretory vacuoles containing lipids and well-developed tubular smooth endoplasmic reticulum. The secretory vacuoles are surrounded by a unit membrane and are secreted by exocytosis. The interstices of the gland contain two types of autonomic nerve varicosities and a number of melanocytes. The surface of the gland is covered with the endothelium of the orbital venous sinus.