Distribution of olfactory marker protein in the rat vomeronasal organ

Olfactory marker protein (OMP) may act as a modulator within the olfactory signal-transduction cascade. It has also been shown to have some importance in development of olfactory sensory organs. Here we used high resolution immunocytochemistry to localize OMP in the rat vomeronasal organ (VNO). Immunofluorescence for OMP was abundant in cilia and in apical dendrites of sensory cells, mostly associated with intraepithelial capillaries. Perikarya were stained to a lesser extent while intense OMP immunoreactivity was seen in axons of sensory neurons. Single cells within the non-sensory portion of the VNO exhibited intense OMP immunofluorescence in apical cilia and weak cytoplasmic staining. Some of the exocrine cells in the vomeronasal glands contained OMP positive secretory granules. Electron microscopy revealed that non-sensory ciliated cells had short rod like kinocilia as well as microvilli. These cells contained secretory vesicles. Their basal portion was in close apposition to nerve endings. Our findings suggest that the sensory part of the VNO contains OMP positive sensory neurons and that the non-sensory epithelium may contain secondary sensory cells. In addition OMP may be liberated from secretory glands into vomeronasal secretions.     

Morphological characteristics of the vomeronasal organ of the newborn Asian elephant (Elephas maximus)

The 6-week-old Asian elephant (Elephas maximus) has a well-documented precocious flehmen response to pheromones, suggesting that the pheromone-detecting vomeronasal organ (VNO) is functional very early in the life of this species. To further document this, the VNOs of two newborn elephants were examined in situ and analyzed by light microscopy (LM) to ascertain their structural maturity at birth. A tubular, cartilage-encased VNO was located along the anterior base of each side of the nasal septum. Its rostral end was connected to a duct to the roof of the mouth; the caudal end was attached to a well-defined vomeronasal nerve projecting toward the brain. LM revealed distinctive differences in the mucosae bordering the horseshoe-shaped lumen: a concave, sensory mucosa, and a convex, nonsensory mucosa. Small groups of receptor neurons were observed among ciliated columnar cells in the sensory epithelium. Numerous unmyelinated nerve bundles and blood vessels filled the underlying lamina propria (LP) and a small section of the vomeronasal nerve was conspicuous at one edge. The nonsensory mucosa manifested a thinner epithelium that principally consisted of ciliated columnar cells, some of which showed a granular cytoplasm, and a conspicuous row of basal cells. The LP was replete with acinar glands and ducts that opened into the lumen. This study shows that the VNO of the newborn elephant has reached an advanced stage of structural maturity, closely resembling that of the adult. Its composition supports the view that flehmen at 6 weeks delivers pheromones to a functional VNO.     

Ultrastructural localization of alpha-galactose-containing glycoconjugates in the rat vomeronasal organ

Binding sites of Griffonia simplicifolia I-B₄ isolectin (GS-I-B₄), which recognizes terminal α-galactose residues of glycoconjugates, were examined in the juxtaluminal region of the rat vomeronasal sensory epithelium and its associated glands of the vomeronasal organ, using a lectin cytochemical technique. Lowicryl K4M-embedded ultra-thin sections, which were treated successively with biotinylated GS-I-B₄ and streptavidin-conjugated 10 nm colloidal gold particles, were observed under a transmission electron microscope. Colloidal gold particles, which reflect the presence of terminal α-galactose-containing glycoconjugates, were present in vomeronasal receptor neurons in the sensory epithelium and secretory granules of acinar cells of associated glands of the epithelium. Quantitative analysis demonstrated that the density of colloidal gold particles associated with sensory cell microvilli that projected from dendritic endings of vomeronasal neurons was considerably higher than that of microvilli that projected from neighboring sustentacular cells. The same was true for the apical cytoplasms of these cells just below the microvilli. These results suggest that of the sensory microvilli and dendritic endings contained a much larger amount of the α-galactose-containing glycoconjugates, compared with those in sustentacular microvilli. Further, biochemical analyses demonstrated several vomeronasal organ-specific glycoproteins with terminal α-galactose.     

Morphological and histological features of the vomeronasal organ in the brown bear

The vomeronasal organ (VNO) is a peripheral receptor structure that is involved in reproductive behavior and is part of the vomeronasal system. Male bears exhibit flehmen behavior that is regarded as the uptake of pheromones into the VNO to detect estrus in females. However, the morphological and histological features of the VNO in bears have not been comprehensively studied. The present study investigated the properties and degree of development of the VNO of the brown bear by histological, histochemical and ultrastructural methods. The VNO of bears was located at the same position as that of many other mammals, and it opened to the mouth like the VNO of most carnivores. The shape of the vomeronasal cartilages and the histological features of the sensory epithelium in the bear VNO were essentially similar to those of dogs. Receptor cells in the VNO of the bear possessed both cilia and microvilli like those of dogs. The dendritic knobs of receptor cells were positive for anti‐G protein alpha‐i2 subunit (G_αi2) but negative for anti‐G protein alpha‐o subunit_, indicating preferential use of the V1R‐G_αi2 pathway in the vomeronasal system of bears, as in other carnivores. The VNO of the bear possessed three types of secretory cells (secretory cells of the vomeronasal gland, multicellular intraepithelial gland cells and goblet cells), and the present findings showed that the secretory granules in these cells also had various properties. The vomeronasal lumen at the middle region of the VNO invaginated toward the ventral region, and this invagination contained tightly packed multicellular intraepithelial gland cells. To our knowledge, this invagination and intraepithelial gland masses in the VNO are unique features of brown bears. The VNO in the brown bear, especially the secretory system, is morphologically well‐developed, suggesting that this organ is significant for information transmission in this species.     

Morphology and cytology of the nasal cavity and vomeronasal organ in juvenile and adult blind mole rats (Spalax ehrenbergi)

The blind mole rat (Spalax ehrenbergi) is a fossorial solitary rodent which exhibits extensive intraspecific aggression and uses scent markings to deter contraspecific invaders. Mole rats of different ages were captured near Tel Aviv, Israel, and sacrificed by an overdose of Xylazine hydrochloride. Olfactory epithelium sites from the nasal cavity (NC) and the vomeronasal organ (VNO) were dissected and fixed for light and electron microscopy. The mole rat's olfactory epithelium of the NC consists of several cell types, of which two types are supporting cells that comprise both microvilli and cilia but differ in staining and the presence of rough endoplasmic reticulum. The third type has no cilia. Secretory goblet cells were frequent among supporting cells of adults alone. Two types of receptor cells protrude into the NC with olfactory knobs at their apical region; one type has up to 177.6 ± 9.4 cilia per knob plus microvilli, while the other type has only microvilli. The third type of sensory cell has no knob and contains microvilli only. The basal epithelium layer consists of short-bodied cells with round nuclei. The VNO of the mole rat is situated beneath the nasal septum, consisting of supporting, sensory, and basal cell types, with many cilia at the apical portion. At its anterior part, the VNO is connected to the NC by narrow canals. The abundance of cilia and microvilli in the mole rat olfactory cells provides the first anatomical evidence for their olfactory acuity. Such acuity is important in mole rats, compensating for their loss of vision and enabling them to detect and avoid rivals prior to potential aggressive encounters as well as to select food plants during foraging. Anat. Rec. 251:460–471, 1998. © 1998 Wiley-Liss, Inc.     

Localization of sex hormone binding globulin in the rat vomeronasal organ

Volatile and non-volatile derivates of gonadal steroids are known to act as pheromones in many mammalian species. Pheromones have multiple effects on the brain via the olfactory system. Their primary port of entry seems to be the vomeronasal organ (VNO) but the underlying cellular and molecular mechanisms are unclear so far. Recently we localized sex hormone binding globulin (SHBG) in both the main and the accessory olfactory system of rat with immunocytochemistry and RT-PCR. The accessory olfactory system consisting of VNO and accessory olfactory bulb showed high expression of SHBG.In the present paper we studied SHBG expression in the VNO in greater detail. In semithin sections we found SHBG immunostaining in the perinuclear cytoplasm of some of the sensory neurons, in sensory cilia and in their axons. A portion of the basal cells and some of the goblet cells in the non-sensory epithelium showed intense SHBG staining. SHBG was abundant in exocrine cells of the vomeronasal glands, perhaps compartimentalized in secretory vesicles. In situ hybridization revealed specific signals in sensory and non-sensory cells of the VNO. Our findings indicate that SHBG expressed in the VNO may be liberated into nasal secretions to bind aerosolic steroids. SHBG in sensory cells may be involved in signaling actions of pheromones.     

新生儿中耳粘膜上皮扫描电镜观察及其意义

应用扫描电镜对4例新生儿中耳粘膜上皮作全方位观察。新生儿中耳粘膜上皮表面显示纤毛细胞和无纤毛细胞。大部分无纤毛细胞顶部呈圆拱状,有丰富微绒毛;一些无纤毛细胞表面平滑,无微绒毛;少数无纤毛细胞则高隆而饱满,顶部可见多数明亮颗粒,推测此类细胞是有分泌颗粒无纤毛细胞。纤毛细胞分布密度及规律与成人相似。观察表明人中耳粘膜纤毛系统在胚胎期基本形成,但有分泌颗粒无纤毛细胞数量少,可能是杯状细胞前期或静止的杯状细胞,提示粘液分泌细胞尚未发育完善。本文指出,中耳粘膜粘液分泌细胞数量和质量的不足可能是新生儿、婴幼儿中耳纤毛粘液毯功能低下以致生物学防御系统功能较弱的重要原因。     

Ultrastructural characterization of the nasal respiratory epithelium in the rat

This ultrastructural study of the respiratory epithelium of the rat nasal mucosa revealed six morphologically distinct cell types: goblet cells, basal cells, ciliated cells, nonciliated columnar cells, cuboidal cells, and brush cells. The latter three have not been previously characterized in the rat nasal mucosa by transmission electron microscopy. Cuboidal cells observed on the conchae

1 The term “conchae” has now been accepted by NOMINA ANATOMICA VETERINARIA (1983) to replace the word “turbinate”. Therefore, dorsal nasal conchae = nasoturbinates and ventral nasal conchae = maxilloturbinates.

and lateral wall had short apical microvilli which were less dense than the microvilli of the nonciliated columnar cells. Nonciliated columnar cells also identified on the conchae and lateral wall had short microvilli and an extensive network of smooth endoplasmic reticulum in the apical region. The brush cell had distinct ultrastructural features; it was pear-shaped, with the broad base adjacent to the basement membrane and large microvilli on the surface. Microfilaments, microtubules, vesicles, and paired cisternae were found in the apical cytoplasm. Brush cells occurred singly on the conchae and lateral wall but were not identified in the respiratory epithelium of the nasal septum. These findings indicate the complexity of cell types composing the rat nasal respiratory epithelium.     

The vomeronasal organ in the frog, Rana esculenta. An electron microscopy study

The ultrastructure of the vomeronasal organ (Jacobson's VNO) of the frog, Rana esculenta, was studied under the transmission and scanning electron microscope. Four cell types were identified: ciliated, bipolar, glial-like, and basal. Ciliated cells are unique to the frog VNO and show morphological evidence of secretion; bipolar (neuronal) cells are arranged in columns and reach the free surface of the epithelium with knobs bearing microvilli. The latter are in contact with amorphous material not described previously. Glial-like cells wrap bipolar cells in the epithelium and poorly differentiated basal cells are found just over the basal lamina. The vascular pump described in mammal VNO is not present at all in the frog VNO. We conclude that in the frog the VNO is closer to the reptilian than the mammalian VNO, although the frog VNO shows some unique morphological characteristics.     

Postnatal differentiation of efferent ductule epithelium in goats: a light microscopic and ultrastructural study

Caprine efferent ductule epithelium contains ciliated and nonciliated cells. The latter cells are divided into three types: type II cells contain PAS-positive granules, type III cells contain PAS-negative vacuoles, and type I cells lack both granules and vacuoles (Goyal and Williams, Anat. Rec. 220:58-67). The objectives of this study are i) to determine when the epithelium differentiates into ciliated and nonciliated cells, ii) to determine when nonciliated cells acquire characteristics typical for type II and type III cells, and iii) to relate developmental changes in the epithelium with those in the testis. Testes and efferent ductules were examined at the light and electron microscopic levels in goats from 1-25 weeks of age. Efferent ductule epithelium contained ciliated and nonciliated cells as early as week 1. While ciliated cells were differentiated at week 1, differentiation of nonciliated cells did not occur until week > or =15. Differential features in ciliated cells included the presence of cilia at the apical border and an aggregation of mitochondria in the apical cytoplasm. Those in nonciliated cells included the presence of i) an endocytotic apparatus at week > or =15, ii) PAS-positive granules at week > or =15, and iii) PAS-negative vacuoles at week > or =25. The seminiferous tubules developed lumens at 12-15 weeks. Hence, while differentiation of ciliated cells occurred much before lumen formation in the seminiferous tubules, that of nonciliated cells coincided with, or occurred soon after, lumen formation, suggesting a role for testicular fluid contents in their differentiation. The goat efferent ductules can be characterized morphologically mature by 25 weeks.     

Transitional epithelial zone of the bovine nasal mucosa

To determine the extent and ultrastructure of epithelium lining the transitional nasal mucosa of the neonate, gnotobiotic calf tissues were prepared for scanning and transmission electron microscopy. Stratified cuboid epithelium of the rostral 40% of the nasal cavity contained few ciliated cells; the next caudal 10–15%, although ciliated, had extensive nonciliated areas. The predominant type of surface cell was nonciliated, had short microvilli, and contained a multilobate nucleus and numerous pinocytotic vesicles. In some areas the surface of these cells presented a cobblestone appearance. Basal cells contained numerous bundles of filaments, ribosomes, and basal vesicles. Caudally, nonciliated columnar cells included a cell type similar to the more rostral cuboid cell, as well as brush cells and immature secretory and ciliated cells. Goblet cells were infrequently observed. Intraepithelial nerve terminals were abundant. Other intraepithelial cells, often difficult to identify owing to varying characteristics, included lymphocytes. Based upon comparisons of this neonatal epithelium with mature epithelium, observed in earlier studies of other mammalian species, the transitional mucosa is believed normally to occupy an extensive area of the nasal cavity.     

Ultrastructure of the normal adult human female prostate gland (Skene’s gland)

The predominant cells of female prostatic glands lining their lumen were found to be tall cylindrical secretory cells with short stubby microvilli, protuberances of the apical cytoplasm, and with bleb formation. Abundant secretory vacuoles and granules, rough endoplasmic reticulum, developed Golgi complexes and numerous mitochondria are characteristic of their active secretory configuration with apocrine (apical blebs) and merocrine (secretory vacuoles and granules) type of secretion. Basal (reserve) cells were seen to be located between the secretory (luminal) cells and the basement membrane. Their ground cytoplasm is dense with rough endoplasmic reticulum and mitochondria. Their nuclei, unlike those of secretory cells, possess more peripheral condensed chromatin, denser dispersed chromatin and sporadic nucleoli. Besides the two basic types of mature prostatic cells intermediary cells were also seen, located between the basal and secretory cells or in their close vicinity. Their cytoplasm exhibits numerous profiles of rough endoplasmic reticulum and free ribosomes. Secretory vacuoles and granules were mostly practically absent (type 1 intermediary cells) so that they resembled basal (reserve) cells. In some of them, however, as in secretory cells, such secretory elements do gradually appear (type 2 intermediary cells). The finding of intermediary cells in the lining of prostatic glands supports the role of basal (reserve) cells in the renewal of cells in glands of the female prostate. The first ultrastructural analysis of the normal female prostate performed by transmission electron microscopy showed that, as in the postpubertal male, the prostatic glands in the adult female display mature secretory and basal cells. The results of the presented study further corroborate the contemporary concept of the female prostate as a functional genitourinary organ.     

Ultrastructure of the normal adult human female prostate gland (Skene's gland)

The predominant cells of female prostatic glands lining their lumen were found to be tall cylindrical secretory cells with short stubby microvilli, protuberances of the apical cytoplasm, and with bleb formation. Abundant secretory vacuoles and granules, rough endoplasmic reticulum, developed Golgi complexes and numerous mitochondria are characteristic of their active secretory configuration with apocrine (apical blebs) and merocrine (secretory vacuoles and granules) type of secretion. Basal (reserve) cells were seen to be located between the secretory (luminal) cells and the basement membrane. Their ground cytoplasm is dense with rough endoplasmic reticulum and mitochondria. Their nuclei, unlike those of secretory cells, possess more peripheral condensed chromatin, denser dispersed chromatin and sporadic nucleoli. Besides the two basic types of mature prostatic cells intermediary cells were also seen, located between the basal and secretory cells or in their close vicinity. Their cytoplasm exhibits numerous profiles of rough endoplasmic reticulum and free ribosomes. Secretory vacuoles and granules were mostly practically absent (type 1 intermediary cells) so that they resembled basal (reserve) cells. In some of them, however, as in secretory cells, such secretory elements do gradually appear (type 2 intermediary cells). The finding of intermediary cells in the lining of prostatic glands supports the role of basal (reserve) cells in the renewal of cells in glands of the female prostate. The first ultrastructural analysis of the normal female prostate performed by transmission electron microscopy showed that, as in the postpubertal male, the prostatic glands in the adult female display mature secretory and basal cells. The results of the presented study further corroborate the contemporary concept of the female prostate as a functional genitourinary organ.     

The human vomeronasal organ. III. Postnatal development from infancy to the ninth decade

The large literature on the human vomeronasal organ (VNO) offers little consensus as to its persistence in the adult. We have already documented the existence of the VNO from embryonic day 33 through the neonatal stages. This has now been extended to human adults: 27 cadaver nasal septa, aged 2–86 y, were either dissected or decalcified, serially sectioned, stained and examined. The consistent presence of the VNO is reported as a homologue, in the form of a duct-like structure on the nasal septum at all ages. Also reported are size variability, pronounced bilateral asymmetry, a nonchemosensory pseudostratified ciliated epithelium with considerable structural variation and generally without medial–lateral differentiation, nasal septal glands opening into the VNO lumen, a lack of correlation between postnatal age and VNO size, visualisation of the human VNO with certainty by histological means alone, and a minute opening as its only visible surface feature. The human VNO is a discrete structure that should not be confused with the nasopalatine fossa, the septal mucosal pits or VNO openings.     

Nonolfactory surface epithelium of the nasal cavity of the bonnet monkey: A morphologic and morphometric study of the transitional and respiratory epithelium

The purpose of the present study was to characterize ultrastructurally the nonolfactory nasal epithelium of a nonhuman primate, the bonnet monkey. Nasal cavities from eight subadult bonnet monkeys were processed for light microscopy, and scanning and transmission electron microscopy. Nonolfactory epithelium covered the majority of the nasal cavity and consisted of squamous (SE), transitional (TE), and respiratory epithelium (RE). Stratified SE covered septal and lateral walls of the nasal vestibule, while ciliated pseudostratified RE covered most of the remaining nasal cavity. Stratified, nonciliated TE was present betwen SE and RE in the anterior nasal cavity. This epithelium was distinct from the other epithelial populations in abundance and types of cells present. TE was composed of lumenal nonciliated cuboidal cells, goblet cells, small mucous granule (SMG) cells, and basal cells, while RE contained ciliated cells, goblet cells, SMG cells, basal cells, and cells with intracytoplasmic lumina lined by cilia and microvilli. TE and RE contained similar numbers of total epithelial cells and basal cells per millimeter of basal lamina. TE was composed of more SMG cells but fewer goblet cells compared to RE. We conclude that nonolfactory nasal epithelium in the bonnet monkey is complex with distinct regional epithelial populations which must be recognized before pathologic changes within this tissue can be assessed adequately.     

Fine structure of bat deep posterior lingual glands (von Ebner's)

We studied the morphology and ultrastructure of the bat (Pipistrellus k.k. and Rhinolophus f.e.) deep posterior lingual glands (Ebner's glands) during hibernation, summer and after stimulation with pilocarpine. Ebner's glands are formed by serous tubulo-alveolar adenomeres and by an excretory system organized in intercalated ducts, long excretory ducts and a main excretory duct. The latter opens in the vallum which surrounds the circumvallate papillae and in the groove of the foliate papillae. The secretory cells, which lack basal folds, show abundant and dense granules (PAS+, Alcian blue -), microvilli (scarce during hibernation), a Golgi apparatus (well developed during summer and after stimulation with pilocarpine), a large nucleus and RER cisternae stacked at the basal pole. Centrioles, lipid droplets, heterogeneous bodies (in content and density, probably lipofuscin bodies), lysosomal multivesicular bodies and large, dense granules with a microcrystalline structure were also encountered. The lateral membranes of adjacent cells are joined by desmosomes; their interdigitations are neither numerous nor prominent during summer. Microfilaments, often gathered in small bundles, lie in the lateral, peripheral cytoplasm without any relation with desmosomes. In summer and particularly after stimulation with pilocarpine, the apical pole of the secretory cells is characterized by many long microvilli, pedunculated hyaloplasmic protrusions and secretory granules. During hibernation the lumen is filled with secretory material. Myoepithelial cells are arranged among secretory cells or between them and the basal lamina. The short intercalated ducts show similarities with the analogous ducts of the parotid gland. Striated ducts are absent. Excretory ducts are endowed with: a) an inner layer of cuboidal cells characterized by poorly developed cytoplasmic organelles, rare dense granules and a few small microvilli; b) an outer layer of basal cells lying on the basal lamina. Myoepithelial cells are absent. The main excretory duct is lined by a stratified epithelium with an inner layer of conical-pyramidal cells surrounded by two-three rows of basal cells. The conical-pyramidal cells show poorly developed organelles, an apical border with small short microvilli and a prominent terminal web.     

Light and electron microscopic observation on the cervical epithelium of the rabbit. I

The light and electron microscopy of the cervical epithelium of ovulatory, estrous, and long-term ovariectomized rabbits have been studied to determine what structural changes occur under different hormonal conditions. The percentage of nonciliated secretory cells is 49.6 in ovulatory, 43.6 in estrous, and 23.7 in long-term ovariectomized rabbits, and of ciliated cells is 50.2 in ovulatory, 56.2 in estrous, and 76.3 in long-term ovariectomized animals. The values for the ovulatory and estrous rabbits are significantly different at the P <0.05 level from those of the ovariectomized animals. In all 3 groups the general ultrastructure of the normal ciliated cells is similar. Interestingly, the Golgi complex is very prominent in all. Glycogen bodies occur frequently only in ciliated cells of ovariectomized and occasionally of estrous animals. Abnormalities in cil-iation are quite common in the ovariectomized rabbits. The structure of the nonciliated secretory cells varies appreciably within and between the 3 groups. In these cells from well-developed epithelia of certain ovulatory and estrous animals, the apical cytoplasm contains secretory granules of at least three types. In addition, very irregularly shaped, dense, perinuclear granules occur, which may be another type of secretory granule or lysosomes. As compared to ciliated cells, the secretory cells have less prominent Golgi complexes, more abundant bundles of intermediate filaments, a more extensive glycocalyx on their apical surface, and more heterochromatic nuclei. In comparison to the cells of well-developed epithelia, the nonciliated cells of some other ovulatory and estrous rabbits are less well differentiated with fewer or no secretory granules and less well developed organelles. In the nonciliated cells of the long-term ovariectomized rabbits, there are no secretory or dense perinuclear granules. There is a decrease in the number of organelles that are involved in secretion, in the size of the cells, and in the amount of nuclear euchromatin.     

Identification of cytoskeletal markers for the different microvilli and cell types of the rat vomeronasal sensory epithelium

The vomeronasal organ (VNO) of the mammal nose is specialized to detect pheromones. The presumed site of the chemosensory signal transduction of pheromones is the vomeronasal brush border of the VNO sensory epithelium, which has been shown to contain two different sets of microvilli: (i) the tall microvilli of supporting cells and (ii) the short microvilli of the chemoreceptive VNO neurons that branch and intermingle with the basal portions of the longer supporting cell microvilli. A key problem when studying the subcellular distribution of possible VNO signal transduction molecules at the light microscope level is the clear discrimination of immunosignals derived from dendritic microvilli of the VNO neurons and surrounding supporting cell structures. In the present study we therefore looked for cytoskeletal marker proteins, that might help to distinguish at the light microscope level between the two sets of microvilli. By immunostaining we found that the VNO dendritic microvilli can be selectively labelled with antibodies to the calcium-sensitive actin filament-bundling protein villin, whereas supporting cell microvilli contain the actin filament cross-linking protein fimbrin, but not villin. Useful cytoplasmic marker molecules for cellular discrimination were cytokeratin 18 for supporting cells and -tubulin for dendrites of VNO neurons. A further finding was that the non-sensory epithelium of the rat VNO contains brush cells, a cell type that appears to be involved in certain aspects of chemoreception in the gut. Brush cells or other structures of the vomeronasal brush border did not contain -gustducin.     

Ultrastructure of baboon parotid gland

The parotid gland of the olive baboon, Papio anubis, was examined by electron microscopy. The acini are all serous in nature, and consist of pyramidal cells with abundant secretory granules of varying size. These granules consist of a dense matrix in which a denser spherule or lenticular body is present. Granules linked by a short isthmus are observed in the apical cytoplasm, and granules in the process of discharging their contents to the acinar lumen may be connected to the luminal plasma membrane by a neck-like protrusion. Intercalated duct cells contain granules reminiscent of those found in the rat submandibular acinar cells. The striated ducts consist of tall cells interloked in a complex fashion near their bases, with numerous vertically-oriented mitochondria lodged in their basal crenulations. Small vesicles whose contents vary in density are present in the apical cytoplasm as are large deposits of lipofuscin. The striated duct cells display a proclivity for ballooning into the duct lumen. Excretory ducts consist of simple to pseudostratified columnar epithelium, and lack basal striations or apical blebs.