Ultrastructural immunocytochemical localization of cyclic AMP-dependent protein kinase regulatory subunits in rat parotid acinar cells

Polyclonal antibodies to types I and II regulatory (R) subunits of cyclic AMP-dependent protein kinase (cA-PK) were utilized in a post-embedding immunogold-labeling procedure to localize these proteins in rat parotid acinar cells. Both RI and RII were present in the nuclei, cytoplasm, rough endoplasmic reticulum (RER), Golgi apparatus, and secretory granules. In the nuclei, gold particles were mainly associated with the heterochromatin. In the cytoplasm, the label was principally found in areas of RER. Most gold particles were located between adjacent RER cisternae or over their membranes and attached ribosomes; occasional particles were also present over the cisternal spaces. Labeling of the Golgi apparatus was significantly greater than background, although it was slightly lower than that over the RER cisternae. In secretory granules, gold particles were present over the granule content; no preferential localization to the granule membrane was observed. Morphometric analysis revealed equivalent labeling intensities for RI and RII in the cytoplasm-RER compartment. Labeling intensities for RII in the nuclei and secretory granules were about 50% greater than in the cytoplasm-RER, and 3 to 4-fold greater than values for RI in these two compartments. Electrophoresis and autoradiography of the postnuclear parotid-tissue fraction, the contents of purified secretory granules and saliva collected from the main excretory duct, after photoaffinity labeling with [32P]-8-azido-cyclic AMP, revealed the presence of R subunits. Predominantly RII was present in the granule contents and saliva, while both RII and RI were present in the cell extracts. Additionally, R subunits were purified from saliva by affinity chromatography on agarose-hexane-cyclic AMP. These findings confirm the localization of cA-PK in parotid cell nuclei and establish the acinar secretory granules as the source of the cyclic AMP-binding proteins in saliva.     

Light and electron microscope observations on the gastric mucosa of the frog (Rana esculenta)

Summary The structure of the frog gastric and esophageal mucosa was studied in the course of a complete hibernation period and compared with that in summer frogs (see preceding article).It appeared that especially chief cells and parietal cells are liable to cytoplasmic remodelling. Thus, in chief cells the rough endoplasmic reticulum (RER) undergoes disorganization, the number of free ribosomes increases and the Golgi system becomes transformed into a compact vesicular structure. The number of pepsinogen granules in chief cells of late winter frogs is only 20% of that in frogs studied at the onset of hibernation. The loss of pepsinogen granules is at least partly due to autophagy. In addition, lysosomes are involved in focal degradation of the cytoplasm, which may ultimately result in complete degeneration of some chief cells. The presence of zymogen granules containing fibrocyte-like cells in the tunica propria proved heterophagocytosis by these cells.In parietal cells, the area occupied by smooth endoplasmic reticulum becomes reduced. The basal cytoplasm of both chief cells and parietal cells contains numerous lipid droplets, which, in contrast to those in summer frogs, are continuous with RER cisternae. The juxtaposition of lipid droplets and mitochondria seen in summer frogs is eventually lost in hibernating animals.Apart from the appearance of supra-nuclear lipid droplets, the mucous cells of the surface epithelium show no striking alterations. However, in the glandular pits both surface mucous cells and mucous neck cells contain less mucous granules than in summer frogs.The results are discussed in connection with parallel biochemical work and available literature, and in the light of our previous studies on the exocrine pancreas in hibernating frogs.     

Relationship between the golgi apparatus, gerl, and secretory granules in acinar cells of the rat exorbital lacrimal gland

The method of secretory granuleformation in the acinar cells of the rat exorbital lacrimal gland was studied by electron microscope morphological and cytochemical techniques. Immature secretory granules at the inner face of the Golgi apparatus were frequently attached to a narrow cisternal structure similar to GERL as described in neurons by Novikoff et al. (Novikoff, P. M., A. B. Novikoff, N. Quintana, and J.-J. Hauw. 1971. J. Cell Bio. 50:859-886). In the lacrimal gland. GERL was located adjacent to the inner Golgi saccule, or separated from it by a variable distance. Portions of GERL were often closely paralleled by modified cisternae of rough endoplasmic reticulum (RER), which lacked ribosomes on the surface adjacent to GERL. Diaminobenzidine reaction product of the secretory enzyme peroxidase was localized in the cisternae of the nuclear envelope, RER, peripheral Golgi vesicles, Golgi saccules, and immature and mature secretory granules. GERL was usually free of peroxidase reaction product or contained only a small amount. Thiamine pyrophosphatase reaction product was present in two to four inner Golgi saccules; occasionally, the innermost saccule was dilated and fenestrated, and contained less reaction product than the next adjacent saccule. Acid phosphatase (AcPase) reaction product was present in GERL, immature granules, and, rarely, in the innermost saccule, but not in the rest of the Golgi saccules. Thick sections of AcPase preparations viewed at 100 kV revealed that GERL consisted of cisternal, and fenestrated or tublular portions. The immature granules were attached to GERL by multiple connections to the tublular portions. These results suggest that, in the rat exorbital lacrimal gland, the Golgi saccules participate in the transport of secretory proteins, and that GERL is involved in the formation of secretory granules.     

Resident and circulating mast cells in propulsative organs of frog <Emphasis Type="Italic">Rana temporaria</Emphasis>

A histochemical and ultrastructural examination of mast cells (MCs) in “blood” and lymph hearts of the adult frog Rana temporaria showed that they are represented by two populations, i.e., resident and circulating MCs. Resident cardiac MCs have an oval or elongated shape and are located in the atrial and ventricular myocardium, as well as in connective tissue of the epicardium. Circulating MCs were identified in heart lumen lacunas and in narrow clefts produced by ventricular trabecular myocardium, as well as in blood-filled atrial and ventricular central cavities. The small round shape circulating MCs resemble lymphocytes, but their cytoplasm is filled with granules that are ultrastucturally similar to granules of cardiac resident MCs. In the lymph heart, elongated resident MCs are located in the interstitial space between the cross-striated muscle fibers and smooth muscle cells of afferent and efferent heart valves. Round circulating MCs are occasionally visible in the cavity of the lymph heart. More commonly, circulating MCs are found in the lymphatic sinus cavity located adjacent to lymph hearts. In certain parts of the lymphatic sinus walls, MCs form clusters that are in tight contact with the mesothelial cells that line the lymphatic cavity. Our histochemical investigation revealed that both resident and circulating MCs of the propulsative organs are strongly alcian blue positive, but are weakly red after safranin staining and weakly metachromatic with toluidine blue. The presence of populations of circulating MCs in adult frogs suggests that there are differences in MC biology in lower and higher vertebrates.     

Disproportional immunostaining patterns of two secretory proteins in guinea pig and rat exocrine pancreatic cells. An immunoferritin and fluorescence study

Amylase (Am) and chymotrypsinogen (Chtg) were demonstrated in rat and guinea pig exocrine pancreatic cells by immunofluorescence and immunoferritin cytochemistry on thin and ultrathin frozen sections. We describe two observations indicating that Am and Chtg may behave differently in the pre-Golgi phase of their intracellular transport. Firstly, aggregates of material within the RER cisternae of the guinea pig (so-called intracisternal granules) reacted strongly with anti-Chtg, but showed no affinity for anti-Am. Secondly, in both rat and guinea pig, the increase in labeling intensity from cytoplasm (RER) to secretory granules was larger for Chtg than for Am. We hypothesize that the two proteins do not travel in-parallel towards the Golgi complex. Compared with Chtg, Am would lag behind in the RER cisternae.     

Immunocytochemical localization of amylase and chymotrypsinogen in the exocrine pancreatic cell with special attention to the Golgi complex

Affinity-purified, monospecific rabbit antibodies against rat pancreatic alpha-amylase and bovine pancreatic alpha-chymotrypsinogen were used for immunoferritin observations of ultrathin frozen sections of mildly fixed exocrine pancreatic tissue from secretion-stimulated (pilocarpine) rats and from overnight-fasted rats and guinea pigs. The labeling patterns for both antibodies were qualitatively alike: Labeling occurred in (a) the cisternae of the rough endoplasmic reticulum (RER) including the perinuclear cisterna, in (b) the peripheral area between the RER and cis-Golgi face, and (c) all Golgi cisternae, condensing vacuoles, and secretory granules. Labeling of cytoplasmic matrix was negligible. Structures that appeared to correspond to rigid lamellae were unlabeled. Differences in labeling intensities indicated that concentration of the zymogens starts at the boundary of the RER and cis-side of the Golgi complex. These data support the view that the Golgi cisternae are involved in protein processing in both stimulated and unstimulated cells and that Golgi cisternae and condensing vacuoles constitute a functional unit.     

Comparative ultrastructure of Clara cells in neonatal and older cattle

Calf lungs were fixed with glutaraldehyde and examined by scanning (SEM) and transmission (TEM) electron microscopy to compare the ultrastructure of Clara cells in terminal bronchioles of neonatal calves and older cattle. In the neonatal calf, SEM revealed numerous smooth-surfaced Clara cells protruding above a similar number of ciliated cells, whereas in older animals the surface of Clara cells was lobulated. Thin sections examined by TEM revealed numerous cuboidal to columnar Clara cells with indented nuclei and a pale cytoplasm filled with faintly granular glycogen in the neonatal calf. Some cells were characterized by apical dense and/or pale membrane-bound granules or secretory droplets. Many cells had an apical tubular network of cisternae that were partly smooth and partly decorated with ribosomes. Ultrastructural comparison of Clara cells in a 2-day-old calf with those of 14- and 19-day-old, 4- and 5. 5-month-old, and 3.5-year-old cattle revealed a striking reduction in the amount of glycogen per cell after 14 days. The number of cells with apical granules was small at all ages, and the density of the secretory granules varied greatly in different cells. A variable amount of smooth endoplasmic reticulum (SER) was present but was less prominent than cisternae of ribosomal endoplasmic reticulum (RER). In older cattle, the limited amount of SER compared to the RER and secretory granules suggests that bovine Clara cells are more likely to be secretory than detoxifying.     

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.     

Virus-neuron interactions in the mouse brain infected with Japanese encephalitis virus

The virus-host interactions between Japanese encephalitis (JE) virus and mouse brain neurons were analyzed by electron microscopy. JE virus replicated exclusively in the rough endoplasmic reticulum (RER) of neurons. In the early phase of infection, the perikaryon of infected neurons had relatively normal-looking lamellar RER whose cisternae showed focal dilations containing progeny virions and characteristic endoplasmic reticulum (ER) vesicles. The reticular RER, consisted of rows of ribosomes surrounding irregular-shaped, membrane-unbounded cisternae and resembled that observed in JE-virus-infected PC12 cells, were also seen adjacent to the lamellar RER. The appearance of the reticular RER indicated that RER morphogenesis occurred in infected neurons in association with the viral replication. The fine network of Golgi apparatus was extensively obliterated by fragmentation and dissolution of the Golgi membranes and their replacement by the electron-lucent material. As the infection progressed, the lamellar RER was increasingly replaced by the hypertrophic RER which had diffusely dilated cisternae containing multiple progeny virions and ER vesicles. The Golgi apparatus, at this stage, was seen as coarse, localized Golgi complexes near the hypertrophic RER. In the later phase of infection, RER of infected neurons showed a degenerative change, with the cystically dilated cisternae being filled with ER vesicles and virions. Small, localized Golgi complexes frequently showed vesiculation, vacuolation, and dispersion. The present study, therefore, indicated that during the viral replication the normal lamellar RER which synthesized neuronal secretory and membrane proteins was replaced by the hypertrophic RER which synthesized the viral proteins. The hypertrophic RER eventually degenerated into cystic RER whose cisternae were filled with viral products. The constant degenerative change which occurred in the Golgi apparatus during the viral replication suggested that some of the viral proteins transported from RER to the Golgi apparatus were harmful to the Golgi apparatus and that increasing damage to the Golgi apparatus during the viral replication played the principal role in the pathogenesis of JE-virus-infected neurons in the central nervous system.     

A morphometrical study of the exocrine pancreatic cell in fasted and fed frogs

The influence of feeding on the ultrastruct of the frog exocrine pancreatic cell was studied by morphometrical procedures. Volume and surface of various cell structures were measured and expressed per unit cell volume. The average cellular size was not influenced by feeding. Though protein synthesis changes 5-to 10-fold (van Venrooij, W. J., and C. Poort. 1971. Biochim. Biophys. Acta. 247:468-470), no significant differences were observed in the amount of membrane that constitutes the rough endoplasmic reticulum (RER) and that represented the major part of total cellular membranes. The appearance of the RER changed. When fasted, most of its membrane was arranged in stacks of tightly packed, narrow cisternae. Within 4 h after feeding, these cisternae were separated and irregularly dilated, and ribosomes became ordered in typical rosettes on their surface. The total volume of the Golgi system increased twofold after feeding. The vesicular and tubular elements at the Golgi periphery did not change, but the volumes of the Golgi cisternae and the condensing vacuoles increased 2.5- and 6-fold, respectively. The increased in the amount of membrane present in these structures was only 1.6- and 3.5-fold, which reflects the more distended appearance of the cisternae and the rounded shape of the condensing vacuoles after feeding. Feeding halved the number of secretory granules per cell, and signs of exocytosis were more common than in fasted animals. These findings suggest that, in the frog pancreatic cell, fluctuations in the production of secretory proteins are not accompanied by an important breakdown and renewal of cellular membranes. This may favor a rapid and strong response of the cell to feeding.     

Fluoride causes reversible dispersal of Golgi cisternae and matrix in neuroendocrine cells

A role for heterotrimeric G proteins in the regulation of Golgi function and formation of secretory granules is generally accepted. We set out to study the effect of activation of heterotrimeric G proteins by aluminum fluoride on secretory granule formation in AtT-20 corticotropic tumor cells and in melanotrophs from the rat pituitary. In AtT-20 cells, treatment with aluminum fluoride or fluoride alone for 60 min induced complete dispersal of Golgi, ER-Golgi intermediate compartment and Golgi matrix markers, while betaCOP immunoreactiviy retained a juxtanuclear position and TGN38 was unaffected. Electron microscopy showed compression of Golgi cisternae followed by conversion of the Golgi stacks into clusters of tubular and vesicular elements. In the melanotroph of the rat pituitary a similar compression of Golgi cisternae was observed, followed by a progressive loss of cisternae from the stacks. As shown in other cells, brefeldin A induced redistribution of the Golgi matrix protein GM130 to punctate structures in the cytoplasm in AtT-20 cells, while mannosidase II immunoreactivity was completely dispersed. Fluoride induced a complete dispersal of mannosidase II and GM130 immunoreactivity. The effect of fluoride was fully reversible with reestablishment of normal mannosidase II and GM130 immunoreactivity within 2 h. After 1 h of recovery, showing varying stages of reassembly, the patterns of mannosidase II and GM130 immunoreactivity were identical in individual cells, indicating that Golgi matrix and cisternae reassemble with similar kinetics during recovery from fluoride treatment. Instead of a specific aluminum fluoride effect on secretory granule formation in the trans-Golgi network, we thus observe a unique form of Golgi dispersal induced by fluoride alone, possibly via its action as a phosphatase inhibitor.     

Ultrastructural aspects of histolytic processes in the salivary gland cells during metamorphic stages in Rhynchosciara hollaenderi (Diptera, Sciaridae).

The cytoplasm of Rhynchosciara hollaenderi late larval, prepupal and pupal salivary gland cells was studied at the ultrastructural level. In the second half of the 4th instar, evidence of an intensive secretory activity is visible in the form of numerous secretory granules in the apical area of the cells. At the same stage, the endoplasmic reticulum cisternae adjacent to Golgi groups are active in the transfer of vesicular elements. At later stages this activity rapidly diminishes. Before the appearance of the DNA puffs, i.e. at the end of the 4th instar, mitochondria begin to show a granular deposit and normal mitochondria decrease in number. These with the granular deposit form clusters and initiate formation of single autophagic vacuoles before the appearance of the DNA puffs. Later, at the time, when the 2B puff opens, the autophagic vacuoles appear in great number. Simultaneously with the formation of the autophagic vacuoles the presence of acid phosphatase in the Golgi vesicles and in autophagic vacuoles was shown. In the last stages investigated (late pupae) acid phosphatase is present free in the cytoplasm and at the same time disappearance of free ribosomes, pycnosis of polytene chromosomes and breakage of nuclear membranes occur. It is concluded that the histolysis of the salivary gland cells begins before the large DNA puffs appear, then it becomes very intensive and continues after these puffs undergo regression.     

Cytochemical studies of GERL and its role in secretory granule formation in exocrine cells

Synopsis the structure and cytochemistry of GERL was studied in several different exocrine secretory cells, including the exorbital lacrimal gland, parotid, lingual serous (von Ebner's), submandibular, and sublingual salivary glands, and exocrine pancreas of the rat; the lacrimal, parotid and pancreas of the guinea-pig; and the lacrimal gland of the monkey. GERL was morphologically and cytochemically similar in all cell types studied. It was located in the inner Golgi region and consisted of cisternal and tubular portions. Immature secretory granules were in continuity with GERL through multiple tubular connections. Modified cisternae of endoplasmic reticulum, with ribosomes only on one surface, closely paralleled parts of GERL. GERL and immature granules were intensely reactive for acid phosphatase activity, while the inner Golgi saccules were reactive for thiamine pyrophosphatase and nucleoside diphosphatase activities. In the rat exorbital lacrimal and parotid glands, reaction product for endogenous peroxidase, a secretory enzyme, was present in the endoplasmic reticulum, Golgi saccules, immature and mature secretory granules. GERL was usually free of reaction product or contained only a small amount. The widespread occurrence of GERL in secretory cells, and its intimate involvement with the formation of granules, suggest that it is an integral component of the secretory process.     

An ultrastructural and morphometric study of pre- and post-hatching satellite cells in lumbar sensory ganglia of Gallus gallus domesticus L

An electron microscopic study of satellite cells in the sensory lumbar ganglia from 12 pre- and post-hatching stages of Gallus gallus domesticus L., between the 5th and 120th d, was undertaken. A combined light and electron microscopic morphometric analysis was made in 10 and 18 d embryos and in 8, 35, 61, and 120 d post-hatching specimens. RER, SER, Golgi complex, mitochondria, free ribosomes, cell expansions, pinocytotic vesicles, subsurface cisternae and adhering, gap, and tight junctions are described from the different stages considered. Although a continuous increase in nuclear and cytoplasmic volumes is observed, there is a tendency towards a decrease in the cytoplasm/nucleus and nerve cell/satellite cell volume ratios.     

Light and electron microscopic localization of ACTH and pro-opiomelanocortin-derived peptides in human developmental and neoplastic cells

Oncofetal aspects of ACTH and pro-opiomelanocortin (POMC)-derived peptides were studied immunohistochemically at the light and electron microscopic level in human fetal pituitary glands, pituitary adenomas, and small-cell carcinoma of the lung. ACTH, beta-endorphin, and gamma-MSH were localized in the same cells of both fetal and adult pituitary, as well as in the above-mentioned neoplastic tissues. However, alpha-MSH was observed only in the early fetal pituitary, its concentration decreasing with advancing gestational age. The adult pituitary contained only a few alpha-MSH-positive cells. By immunoelectron microscopy, ACTH in the adult pituitary was localized exclusively in the secretory granules. In fetal pituitary at 9 weeks' gestation, ACTH was localized in the perinuclear spaces (PNS), cisternae of rough endoplasmic reticulum (RER), Golgi saccules, and secretory granules. The staining pattern of ACTH in these organelles varied from cell to cell. In fetal pituitaries of greater gestational ages, ACTH was localized in secretory granules. The pituitary adenomas mimicked the staining characteristics of the adult pituitary, i.e., negative or only very occasional alpha-MSH staining and localization of ACTH in the secretory granules. The ectopic ACTH-producing tumors showed a staining pattern similar to that of the early fetal pituitary, i.e., positive staining for alpha-MSH and the presence of ACTH in PNS and cisternae of RER.     

Morphofunctional study of the organization of the peripheral parenchyma of Acoela Oxyposthia praedator

The ultrastructure of undifferentiated cells in the peripheral parenchyma of Oxyposthia praedator was studied, along with the ways of their differentiation. The type I cells (3.5-4.0 microns in diameter) undergo mitotic division, while the type II cells (9 microns in diameter) produce specialized cells of the parenchyma. At the beginning of secretory cell differentiation one cistern of the rough endoplasmic reticulum (RER) is formed by the outer membrane of the nuclear envelope, the formation of other cisternae follows. The Golgi complex is formed simultaneously. The differentiated secretory cells are characterized by the abundance of RER cisternae and Golgi complexes. In the course of differentiation of other cell types RER cisternae are formed by several portions of the nuclear envelope. The Golgi complex appears in cells 12-14 microns long. The differentiation of digestive cells is characterized by autophagy. Autophagosomes are formed by RER cisternae. The consecutive stages of autophagosome formation are described. Using a cytochemical reaction revealing acid phosphatase the process of digestion of the autophagosome content was followed.     

Ultrastructure of the cell types of the anterior hypophysis in a lizard. I. Corticotrophs

Corticotrophs of the teiid lizard Cnemidophorus lemniscatus are situated in the rostral zone of the pars distalis. In normal animals, they are usually rounded cells with slightly eccentric vesicular nuclei, especially characterized by a lucent hyaloplasm and medium-sized secretory granules of uniform high density. Granules are almost spherical, with small angular deformations, and closely bounded by a fuzzy membrane. Many cells have only a few or a moderate number of granules, with large areas of cytoplasm devoid of them; in others, granules fill the supranuclear region. The cytoplasm exhibits numerous ribosomes, often in rosettes and mostly free, a series of loosely superimposed cisternae of rough endoplasmic reticulum, small dictyosomes, and elongate mitochondria of light matrix. Metyrapone administration during 2-8 days causes dramatic alterations in corticotrophs; they become hypertrophic and extensively degranulated, with a great development of the endoplasmic reticulum and Golgi apparatus, eventually showing a row of large peripheral granules of uneven structure, enclosed in ample vesicles studded with ribosomes. A lesser degree of hypertrophy and degranulation of corticotrophs appears during the first two weeks after thyroidectomy or gonadectomy, and may be partially attributed to surgical stress. Well granulated enlarged corticotrophs, with hypertrophic endoplasmic reticulum and Golgi apparatus, are probably a result of hormonal imbalance in lizards of both sexes gonadectomized for one or two months.     

Effects of hypergravity environment on the parathyroid gland of the propranolol-treated golden hamster

The fine structure of the parathyroid glands of propranolol-treated hamsters subjected to 5 x gravity environment was studied. In the parathyroid glands of the propranolol-treated hamsters exposed to hypergravity environment, the volume density occupied by the Golgi complexes and cisternae of the granular endoplasmic reticulum was increased as compared to that of propranolol-treated hamsters and was decreased as compared to that of hamsters exposed to a hypergravity environment but was almost similar to that of control hamsters. In addition, many chief cells contained rich free ribosomes, abundant mitochondria and some secretory granules located in the peripheral cytoplasm. These findings suggest that the parathyroid gland which may be suppressed by treatment of propranolol and stimulated in response to a hypergravity environment indicates the secretory activity of the control parathyroid gland.     

Fine structure of the excretory system of the deep posterior (Ebner's) salivary glands of the human tongue

Human deep posterior lingual glands (von Ebner's glands) are located beneath the circumvallate papillae. They are formed by tubuloalveolar adenomeres, intercalated ducts and excretory ducts coming together in the main excretory duct. The tubuloalveolar cells, pyramid-shaped, show large and dense secretory granules (clear cored) throughout the cytoplasm, rare basal folds and packed cisternae of rough endoplasmic reticulum (RER) at the basal pole. The columnar cells of the intercalated ducts are arranged in a monolayer. They are characterized by dense, clear-core secretory granules (mostly in the apical cytoplasm), a basal nucleus, well-developed RER and Golgi apparatus, and thin filaments distributed in supra- and perinuclear cytoplasm. Striated ducts are absent. Excretory ducts, coming together in the main duct, are lined by a bistratified epithelium. The inner layer consists of columnar cells showing bundles of tonofilaments with scarce secretory activity. The outer layer is composed of basal cells lying on the basal lamina. The main excretory duct, which opens at the bottom of the vallum, shows a stratified epithelium. The outer side is composed of 2-3 layers of malpighian cells lying on the basal lamina. The inner side consists of a single layer of cuboidal-columnar cells with dense apical granules and well-developed organelles synthesizing and condensing secretions. These cells interpolate with goblet cells, rare mitochondria-rich cells, ciliated cells and numerous small globous cells showing a clear matrix and lacking secretory granules. The cilia show a 9 + 2 microtubular structure with basal bodies provided with striated rootlets. Myoepithelial cells surround with their processes the basal portions of the secretory cells and the intercalated ducts. The conclusions concern some comparative aspects and some hypothesis on the functional role of goblet cells, ciliated cells and epithelial cells lining the different ducts, also in relation to the final secretory product.