Infranuclear Cytoplasm Research Articles

Further contribution on glycogen in fetal intestinal epithelium

In the first half of pregnancy the well-known occurrence of glycogen incorporation in the supra- and infranuclear cytoplasm of the villous enterocytes was verified. This enormous glycan store is evidently of very little functional importance. It seems to be an expression of a disordered glycogenolysis. These masses of glycogen are incorporated into impressive glycogenosomes, which are the predominante cytoplasmic inclusions for a short period of time. According to the present results it is not certain whether lysosomal glycogenolysis happens. There is no morphological or functional evidence for a utilization og glycogen.

Principal cells of the vas deferens are involved in water transport and steroid synthesis in the adult rat.

Principal cells show marked structural differences in the proximal, middle, and distal regions of the vas deferens, reflective of diverse functional activities. In the present study, we performed electron microscopy to examine the structural features of principal cells using glutaraldehyde-fixed, Epon-embedded material, while functional parameters were examined using light microscopic immunocytochemistry on Bouin-fixed, paraffin-embedded material. In the proximal region, the cuboidal principal cells resembled those of the cauda epididymidis, but few clear cells and occasional narrow cells were present. In the middle region, principal cells often contained blebs of their apical cytoplasm containing vesicular and tubular profiles. These blebs extended far from the cell surface and appeared to be liberated into the lumen, suggesting an apocrine type of secretion. In the distal region, dilated intercellular spaces containing numerous membranous profiles of different shapes and sizes were noted between adjacent principal cells and overlying basal cells. The use of an anti-aquaporin-1 antibody revealed an intense reaction over the endothelial cells of numerous vascular channels in the lamina propria. Taken together, these observations suggested water transport from the lumen of the vas deferens via the dilated spaces to underlying vascular channels, the function of which may be to concentrate sperm. The infranuclear cytoplasm of principal cells of this region showed whorls of smooth endoplasmic reticulum (sER). Large intracytoplasmic cavities were found within the sER aggregates, and these contained membranous profiles that appeared to peel off from the surrounding sER elements. Various images of such cavities closely juxtaposed to the lateral plasma membrane suggested that the membranous profiles of the intercellular spaces were derived from them. Use of anti-3beta-hydroxysteroid dehydrogenase antibody revealed an intense reaction over principal cells of the vas deferens, as well as over the blebs in the lumen of the vas deferens, which is indicative of the steroid synthesis performed by these cells. The release of sER membranous profiles into the dilated spaces and the presence of blebs in the lumen may represent a means of transporting steroids that are destined for different sites out of the principal cells. Steroids in the blebs would be ultimately destined for utilization by luminal sperm, while those steroids in the dilated spaces are designed for utilization by muscle layers of the lamina propria. In summary, principal cells of the vas deferens appear to be involved in synthesis and secretion of steroids and in eliminating water from the lumen of the vas deferens.

Olfactory mucosa of the South American armadillo Chaetophractus villosus: an ultrastructural study.

The sense of olfaction in armadillos plays an important role, suggested by the great development of the nasal structures, olfactory bulbs, and related brain regions. The mammalian olfactory mucosa is a privileged site of neuronal death and regeneration during the whole life span. A detailed knowledge of its ultrastructure is convenient for gaining insight into the factors controlling those phenomena. We performed this work in species not previously studied in order to provide a firm basis for further research on those factors. No information is available on the histology and ultrastructure of the olfactory mucosa in the order Xenarthra to which armadillos belong. Samples from the endoturbinals of the armadillo Chaetophractus villosus were prepared for light and electron microscopic examination by the usual conventional means. The olfactory epithelium of Chaetophractus villosus shows the classical three types of cells: supporting cells, olfactory receptor neurons, and basal cells. The olfactory neurons and the basal cells were similar to that described in other species. Two different types of supporting cells are described. An outstanding characteristic of the supporting cells is the normal presence of abundant phagosomes, apical secretory granules, apocrine-like protrusions, and highly developed smooth endoplasmic reticulum. Apoptotic bodies are frequently found in the infranuclear cytoplasm of supporting cells. The ductular epithelium of Bowman's glands reveals secretory activity. The lamina propria shows mixed Bowman's glands. Great development of smooth endoplasmic reticulum is observed in the mucous acinar cells. Evidence for merocrine and apocrine mechanisms in the Bowman's glands is presented. The presence of apoptotic bodies and phagosomes in supporting cells suggests a participation in the cellular events induced by cell death and proliferation of the olfactory epithelium. The variety of characteristics exhibited by the supporting cells of the olfactory mucosa may contribute to a deeper understanding of their scarcely known functions.

Fine structure of cholesterolosis in the human gallbladder and the mechanism of lipid accumulation.

Gallbladders with cholesterolosis removed surgically for cholelithiasis were studied by light and electron microscopy as well as by cytochemical methods to demonstrate the presence of free cholesterol in the epithelial cells. Lipid droplets were found not only in the submucosa, but also in the infranuclear cytoplasm of epithelial cells. These contained well developed mitochondria and an agranular endoplasmic reticulum. Macrophages were often present between the epithelial cells and the submucosa, and protruded numerous processes, which also contained well developed cell organelles, abundant lysosomes and lipid droplets. With the excessive lipid deposition, macrophages were filled with lipid droplets and became foam cells. In the epithelial cells, many reaction precipitates occurred after digitonin treatment and some of them were observed in the endoplasmic reticulum. It is suggested, therefore, that free cholesterol is absorbed by epithelial cells and thereafter becomes esterified in the endoplasmic reticulum and thus appears as lipid droplets. Lipid droplets synthesized in the epithelial cells may then be released into the intercellular space, and phagocytosed there by macrophages. It is thus suggested that macrophages filled with lipid droplets may become too large and rigid to pass through the endothelium of lymph vessels, and those large "foam cells" may cause the destruction of lymph vessels. Those sequential events should eventually advance the accumulation of foam cells in the submucosa.

Fine structure of cholesterolosis in the human gallbladder and the mechanism of lipid accumulation

Gallbladders with cholesterolosis removed surgically for cholelithiasis were studied by light and electron microscopy as well as by cytochemical methods to demonstrate the presence of free cholesterol in the epithelial cells. Lipid droplets were found not only in the submucosa, but also in the infranuclear cytoplasm of epithelial cells. These contained well developed mitochondria and an agranular endoplasmic reticulum. Macrophages were often present between the epithelial cells and the submucosa, and protruded numerous processes, which also contained well developed cell organelles, abundant lysosomes and lipid droplets. With the excessive lipid deposition, macrophages were filled with lipid droplets and became foam cells. In the epithelial cells, many reaction precipitates occurred after digitonin treatment and some of them were observed in the endoplasmic reticulum. It is suggested, therefore, that free cholesterol is absorbed by epithelial cells and thereafter becomes esterified in the endoplasmic reticulum and thus appears as lipid droplets. Lipid droplets synthesized in the epithelial cells may then be released into the intercellular space, and phagocytosed there by macrophages. It is thus suggested that macrophages filled with lipid droplets may become too large and rigid to pass through the endothelium of lymph vessels, and those large “foam cells” may cause the destruction of lymph vessels. Those sequential events should eventually advance the accumulation of foam cells in the submucosa. Microsc. Res. Tech., 39:14–21, 1997. © 1997 Wiley-Liss, Inc.

Lectin histochemistry and carcinoembryonic antigen in spontaneous colonic cancers of cotton-top tamarins (Saguinus oedipus).

The glycoconjugate-binding properties and the expression of carcinoembryonic antigen in colonic cancers of cotton-top tamarins at the German Primate Center are described. Deviating from findings in non-tumorous colonic epithelia of cotton-top tamarins was the presence of UEA-, SBA-, or DBA-binding sites in the infranuclear cytoplasm of colonic epithelial cells, staining of entire cells, and the occurrence of subepithelial extracellular glycoconjugates in and adjacent to colonic cancers. Carcinoembryonic antigen, which normally was limited to the fuzzy coat of the colonic epithelium, was demonstrated in the cytoplasm of the cancer cells.

Ultrastructure of the main excretory duct epithelium of the female mouse submandibular gland with special reference to sexual dimorphism

The fine structure of the main excretory duct epithelium (MEDE) of female mouse submandibular gland was investigated by scanning and transmission electron microscopy and the results compared with the previously established structure of male mouse MEDE. A comparative analysis of the subepithelial capillaries of both sexes was also performed. In this pseudostratified epithelium, principal cell-types were observed: types-I, -II, -III and basal cells. This differed significantly from male MEDE, where type-II and -III are absent and type-I cells are the most numerous. The latter cell-type had abundant mitochondria, a few lipid-containing granules, lysosomes in the infra-nuclear cytoplasm and well-developed basal infoldings. These cells were also characterized by abundant glycogen granules throughout the cytoplasm, many profiles of strands of smooth endoplasmic reticulum in the apical region, and lysosomes in the infranuclear region. Type-II cells were the second most numerous. Their most characteristic features were the presence of tubular vesicles which appeared to be invaginated from the plasma membrane, RER, SER, free ribosomes, a few peroxisomes with nucleoids, and primary lysosomes in extremely light cytoplasm. They had many mitochondria throughout the cytoplasm, except in the apical region, a few lipid-containing granules and no basal infoldings. Type-III cells were very few and were characterized by well developed basal infoldings, abundant free ribosomes, RER, SER, vesicles containing moderately dense material, and many lipid-containing granules. They also had many mitochondria throughout the cytoplasm, except apically. Basal cells had a large nucleus and the cytoplasm had few organelles.(ABSTRACT TRUNCATED AT 250 WORDS)

Electron microscopic observation of the transitional portion in the human eccrine sweat gland.

The transitional portion in human eccrine sweat glands was observed by transmission electron microscope (TEM). The transitional portion, consisting of columnar epithelial cells (columnar cells) and basal cells, formed a very short segment about 25 to 50 microns in length. The portion was abruptly connected to the secretory segment, and shifted to the excretory duct without marked ultrastructural changes. The columnar cells were morphologically characterized by small apical vesicles as reported in previous reports. Considering the frequency of the mitosis of the columnar cells, the transitional portion seemed to be one of the areas of cell proliferation in the gland. Basal cells were sparse in the region connecting the secretory segment, but dense near the duct. Basal cells in the secretory segment side of the transitional portion, containing thin microfilament-bundles in the infranuclear cytoplasm, were considered to be immature myoepithelial cells. On its ductal side, however, the basal cells showed morphological profiles similar to ductal peripheral cells. These findings suggest that the differentiation of myoepithelial cells occurs in the transitional portion of eccrine sweat glands.

Regional differences in the morphology of the goat epididymis: A light microscopic and ultrastructural study

The goat epididymis, based on morphological differences, was divided into five regions; regions I and II, and the proximal part of region III constituted the head; the distal part of region III and region IV, the body; and region V, the tail. The epithelium of all regions contained principal and basal epithelial cells and intraepithelial lymphocytes and macrophages. In addition, regions II to IV also contained a few apical cells. Clear cells were absent. The epithelium varied in height from the tallest in region I (88 +/- 33 microns) to the shortest in region V (38 +/- 5 microns). Conversely, the luminal diameter, thickness of smooth muscle wall, and luminal sperm concentration were highest in region V. The irregular epithelial height of regions I and IV accounted for a stellate lumen in contrast to the oval lumen of the other regions. Whereas the lumen of region I contained only a few sperm, those of regions II, III, and IV were filled with sperm. Principal cells were the only cell type that showed striking cytological differences between regions. While they contained absorptive features (canaliculi, pinocytotic and coated vesicles, and subapical vacuoles) in all regions, the principal cells of region II were filled with large, heterogeneous vacuoles (up to 5 microns in diameter), suggesting that they may be preferentially involved in transporting and digesting particulate material. Besides absorptive features, principal cells of all regions contained morphological correlates of protein synthesis such as highly developed Golgi complexes in the supranuclear area and numerous cisternae of RER near the Golgi body and in the infranuclear cytoplasm. The cisternae of RER were more developed in region IV, and in some instances, they were distended with flocculent material resembling newly synthesized protein. Unlike the protein synthesizing organelles, principal cells of all regions lacked morphological correlates of steroid hormone synthesis. These results are compared with previously published data on the regional differences in the epididymis of other species, especially with those of the rat and the bull, in an effort to understand the significance of the epididymis in sperm maturation.

Histologic changes in the mouse epididymis fixed in the abdominal cavity.

Histologic changes in the mouse epididymides were examined by light and electron microscopy 1, 3, 6 and 10 weeks after surgical fixation of the testes and epididymides to the internal abdominal wall at 2 months of age. In the epididymides subjected to the cryptorchid surgery, the principal cells in the segment next to the initial segment became taller, the nuclei were translocated to a higher position, and the widened infranuclear cytoplasm turned pale. The supranuclear cytoplasm showed a decrease in PAS stainability. Electron microscopy revealed that the infranuclear cytoplasm, which is occupied by small vesicular endoplasmic reticulum in the normal cells, was filled with distended rough endoplasmic reticulum. These changes first appeared one week after operation, further developing with time. Similar changes were observed when the epididymis was in the abdominal position with the testis in the scrotal position, or with the efferent duct ligated to block the testicular fluid flow into the epididymis. It is suggested that the epididymal changes recorded in this paper are induced by the elevation of temperature caused by the translocation from the scrotum to the abdomen.

Localization of Chromogranin A-Immunoreactivity in Bovine Gastrointestinal Endocrine Cells with Special Reference to Grimelius Silver Stain.

Immunohistochemical studies of the gastrointestinal tract were carried out to characterize the cells exhibiting immunoreactivity for chromogranin A (CGA), a glycosylated protein primarily found in secretory granules of the adrenal medulla. Double immunostaining for gastrointestinal hormones and CGA revealed that in the bovine gastrointestinal tract CGA immunoreactivity occurs in mucosal epithelial cells containing gastrin, glucagon, substance P or motilin, but not in those containing somatostatin. Combined staining with anti-CGA serum and Grimelius' silver demonstrated frequent association of the two stains in a variety of endocrine cells. However, intracellular distribution of the two stains was different: CGA-immunoreactivity was detected in both supra- and infranuclear cytoplasm, whereas Grimelius' silver was mostly localized in the infranuclear region. These results suggest that CGA is the target of Grimelius' silver, as postulated recently (Rindi et al., 1986), but that some subcellular structure-related modification of molecules such as sialation is necessary for the positive Grimelius reaction.

Immature rat epididymal epithelial cells grown in static primary monolayer culture on permeable supports

N-acetylglucosaminidase (NAG), acid phosphatase (ACP) and alkaline phosphatase (AKP) were localised histochemically in fixed cells from the 37-day-old rat epididymis grown in static monolayer culture for 2-8 days. ACP and NAG were cytosolic enzymes found in perinuclear positions, whereas staining of AKP ws consistent with a membranous position. These enzymes were also examined in frozen tissue sections of the epididymis, from rats of the equivalent age, where NAG had intense activity in both supra- and infra-nuclear cytoplasm and ACP was more active apically. For the first time AKP was localised along basolateral membranes of the epithelium and in the lumen of the mid-caput region. The monolayer in culture was of principal cells only and they maintained their polarity and ultrastructural characteristics, but the height of the cells was reduced compared to that obtained in situ.

Heterotopic synaptic bodies in the auditory hair cells of adult lizards.

The auditory hair cells of adults of eight species of lizards (three gekkonids: Coleonyx variegatus, Gekko gecko, and Cosymbotus platyurus; two teiids: Ameiva ameiva and Cnemidophorus tigris; one anguid: Celestus costatus; one lacertid: Podarcis (Lacerta) sicula; and one iguanid: Crotaphytus wislizeni) were studied by transmission electron microscopy. Heterotopic synaptic bodies were found in some of the auditory hair cells of all of the above species, occurring frequently in the gekkonids but infrequently in other species. The groups of heterotopic synaptic bodies occurred mainly in the infranuclear cytoplasm between the hair cell nucleus and the hair cell plasma membrane. The groups of synaptic bodies that were close to the hair cell nucleus were usually associated with specialized arrays of rough and smooth endoplasmic reticulum. The numbers of heterotopic synaptic bodies were greatest in the gekkonid species and were especially large in Coleonyx variegatus, where an average of 36.8 synaptic bodies occur in one group. The functional significance of the presence of heterotopic synaptic bodies in the auditory hair cells of adults animals is not known.

Annulate lamellae of the pancreatic exocrine cells in starved rats.

The ultrastructure of annulate lamellae in the pancreatic exocrine cells of rats starved for 3-42 days was studied. Annulate lamellae were rarely encountered in the pancreatic exocrine cells of control rats, but their incidence and size of stack was increased in those of starved rats depending on the duration of starvation, despite marked ultrastructural changes in these cells. Annulate lamellae were located in the para- or infranuclear cytoplasm of the cells and most of them were continuous with the relative normal rough endoplasmic reticulum. A close apposition in parallel was often found between the annulate lamellae and the outer nuclear envelope and occasionally pores in line with those of the nuclear membrane were observed in the lamellae of rough endoplasmic reticulum in 35- and 42-day-starved rats. An unequivocal continuity between the annulate lamellae and the nucleus and/or rough endoplasmic reticulum in pancreatic exocrine cells might be related to their origin and function.

The trophotaenial placenta of a viviparous goodeid fish. III: Protein uptake by trophotaeniae, the embryonic component.

Protein uptake and degradation by trophotaenial cells of the viviparous goodeid fish Ameca splendens were studied colorimetrically and ultrastructurally using horseradish peroxidase (HRP) as a tracer and acid (ACPase) and alkaline (ALPase) phosphatase cytochemistry. Trophotaeniae are ribbon-like external projections of the embryonic gut that are equivalent to greatly hypertrophied intestinal villi. During gestation within the ovarian lumen, trophotaeniae are directly apposed to the internal ovarian epithelium (IOE) where they establish a placental association between the developing embryo and maternal organism. Trophotaenial absorptive cells possess an ALPase reactive brush border, an endocytotic apparatus, and ACPase reactive standing lysosomes. Ultrastructural studies of protein uptake indicate that cells of the trophotaenial epithelium take up HRP by micropinocytosis and degrade it within lysosomes. Initially (from 1.5-10 min), HRP is taken up in vitro at 22 degrees C at the apical cell surface and passes via endocytotic vesicles into an apical canalicular system. From 1.5 to 10 min exposure, HRP passes passes from the apical canalicular system to a series of small collecting vesicles. After 10 min, HRP is detected within large ACPase reactive supranuclear lysosomes. Three hours after an initial 1 h exposure to HRP, most peroxidase activity within supranuclear lysosomes is no longer detected. Presence of Golgi complexes, residual bodies, and secretory granules in the infranuclear cytoplasm suggest that products of protein uptake and hydrolysis are discharged across basal and lateral cell surfaces and into the trophotaenial circulation. Trophotaeniae of embryos incubated in vitro in HRP-saline take up HRP at an initial rate of 13.5 ng HRP/mg trophotaenial protein/min. The system becomes saturated after 3 h. Trophotaeniae incubated at 4 degrees C show little or no uptake. In trophotaeniae continuously pulsed with HRP for 1 h, then incubated in HRP-free saline, levels of absorbed peroxidase declined at a rate of 0.5 ng/mg trophotaenial protein/min. HRP does not appear to enter the embryo via extra-trophotaenial routes. These findings are consistent with the putative role of trophotaeniae as the embryonic component of the functional placenta of goodeid fishes. Trophotaenial uptake of maternal nutrients accounts for a massive (15,000%) increase in embryonic dry weight during gestation.

Three-dimensional reconstruction of a small-granule paracrine cell cluster in an adult hamster bronchus.

Amine precursor uptake and decarboxylation (APUD) small-granule cells were stained by periodic acid-Schiff (PAS)-lead hematoxylin in 0.5-micron etched Epon sections of adult hamster lung fixed for transmission electron microscopy. The leading edge of a small-granule cell cluster was identified in a segmental bronchus as a single PAS-positive cell. From 256 serial thin sections through its entirety, a three-dimensional wooden reconstruction of the cluster and morphometric estimates of the apical and basal surfaces, cell volume, and intracytoplasmic distribution of mitochondria and small granules was made. Of moderate size, the body consisted of 16 small-granule cells, 11 forming its ovoid core with five outlying cells diverging at the margin; these were pyramidal, possessing wide bases and thin apical processes. At the bronchial surface, processes from the 11-cell core emerged together, whereas the divergent cells emerged in groups of two and three. Ten Clara-like cells and one ciliated cell encircled the core. Altogether they formed a pseudostratified epithelium in contrast to the surrounding simple columnar epithelium. Deeper in the cluster, numerous cytoplasmic extensions interdigitated with those from adjacent cells, and toward the base the Clara-like and APUD cells were increasingly interposed. In marked contrast to the apical cytoplasm, the infranuclear cytoplasm of the latter was densely packed with ca. 1,000 A electron-dense granules; and the basal, presumptively secretory face of each cell was five to six times greater than the area exposed to the bronchial lumen. Judged by granule size and ultrastructure, only one APUD cell type was recognized in the reconstructed cluster. Beneath it many fibrocytic processes were separated from the APUD cells by only the thickness of the basal lamina. Two fascicles of smooth muscle approached the cluster within 0.4-0.8 micron. Unmyelinated nerve fibers came as close but contacted only the muscle. Capillaries, in contrast, came no closer than 15 micron from the base of the body. Evidently, 1) fibrocytes and smooth muscle are more likely targets for secretions from such a paracrine body than cells reached through the blood-stream, and 2) not all small-granule cell clusters are innervated.

Morphology of the bovine epididymis.

The epididymis of the bull was divided into six regions, and morphological differences between regions were studied. The epithelium of all regions contained four cell types: principal and basal epithelial cells, and intraepithelial lymphocytes and macrophages. The epithelium of regions II-V also contained a few apical cells. Principal cells of all regions possessed an endocytotic apparatus including stereocilia underlain by canaliculi, coated vesicles, and subapical vacuoles (up to 1 micron in diameter); however, large vacuoles with a flocculent content and multivesicular bodies (up to 5 microns in diameter) were most numerous in regions II, III, and IV. The unique features of principal cells of region I were the presence of well-developed Golgi bodies, few lipid droplets, and whorls of smooth endoplasmic reticulum in the supranuclear cytoplasm. Numerous mitochondria, distended cisternae of rough endoplasmic reticulum, and dense granules characterized the infranuclear cytoplasm of the principal cells of regions II-VI; however, these features were more developed in region V. Apical cells were characterized by the apical location of the nucleus, many mitochondria in the apical cytoplasm, and few microvilli at the luminal border. Basal cells with few cytoplasmic lipid droplets were present throughout the length of the epididymis but appeared more numerous in region V. Intraepithelial lymphocytes were present at all levels of the epithelium but were never seen in the lumen. Intraepithelial macrophages containing heterogeneous granules, eccentric nuclei, and pseudopods were invariably seen near the basal area of the epithelium in all regions. These observations are discussed in an effort to define the role of each cell type in the epididymal epithelium.

Ultrastructural localization of acid phosphatase activity in the jejunal absorptive cells of fasted rats

Ultrastructural localization of acid phosphatase activity was investigated in the jejunal absorptive cells of 21 d fasted rats (about 500 g). The enzyme activity was localized on the membrane of microvilli, the lateral cell membrane, the Golgi complex, the lysosomes and the GERL of Novikoff (a part of the smooth surfaced endoplasmic reticulum located in close proximity to the Golgi saccules) of jejunal absorptive cells. Moreover, the lysosomes of various sizes and shapes with acid phosphatase activity was characteristically encountered in the infranuclear cytoplasm. The lysosomes appeared to be autolysosomes .

Glycogen accumulations in differentiating mesonephric ducts and tubuli in male human embryos.

Human mesonephric duct epithelial cells contained empty appearing regions in the infranuclear cytoplasm when prepared for transmission electron microscopy using glutaraldehyde and osmium fixation. The same regions stained positively with PAS in Epon sections for light microscopy suggesting that glycogen was present. Incubation with saliva abolished the reaction. For electron microscopy the glycogen stained very intensely if a mixture of osmium tetroxide and potassium ferrocyanide was used instead of osmium alone. Glycogen accumulations were present between the ages of 5 to 10 weeks and absent at the age of 15 weeks. Reports by others indicate that glycogen may be present in different reactive forms in relation to its staining behaviour after various fixatives. The present results, and similar studies in other tissues, indicate that osmium tetroxide-potassium ferrocyanide fixative should be used routinely for preservation of embryos and fetuses and where indicated, for ultrastructural identification of glycogen and cytoplasmic filaments in clinical specimens.

Ultrastructure of the mouse epididymal duct with special reference to the regional differences of the principal cells.

It is generally known that spermatozoa aquire the capacity for fertilization during passage through the proximal region of the epididymal duct and are then stored in the distal region of the duct (BEDFORD, 1975; HAMILTON, 1975). The mouse epididymal duct has been divided into five segments (I-V) by light microscopy; Segments I, II and III constitute the head of the epididymis, Segment IV the body, and Segment V the tail; Segments I, II and III seem to belong to the proximal region, and Segments IV and V to the distal region (TAKANO, 1980). In this electron microscope study, we have examined the regional differences of the principal cells of the epididymal duct to understand the functional significance of each segment.The principal cells decrease in height distalwards from Segments I to V. The nucleus is situated basally in the cells, with a well developed Golgi apparatus located above it. The endoplasmic reticulum in Segments I, II and III is generally vesicular, and is distributed throughout the cytoplasm. The ribosomes attached to the endoplasmic reticulum increase in number from Segments I to III. In Segments IV and V, flattened rough endoplasmic reticulum is seen in the basal cytoplasm of the cells. The multivesicular bodies are usually located in the supranuclear cytoplasm. They are large in Segment II and frequent in Segments II and IV. The dense bodies are specific in appearance for the cells in each segment. They are seen in the supranuclear cytoplasm in Segment I and in the infranuclear cytoplasm in Segments III, IV and V. Few dense bodies are found in Segment II. The apical cytoplasm contains coated and non-coated vesicles. These vesicles consist of large and small types in Segments I, II and III. They are of the small type in Segments IV and V. The luminal surface membrane has coated or non-coated invaginations between stereocilia.The findings suggest that the principal cells have secretory and absorptive functions specific for each segment. Discussion shall be made on the possibility that the secretion of the specific epididymal substances may provide the fertilizing ability to spermatozoa and the absorption pertains to the testicular fluid, epididymal secretions and substances bound to spermatozoa.