Showing papers on "Ultrastructure published in 1999"

Ultrastructure of bovine embryos developed from in vitro–matured and –fertilized oocytes: Comparative morphological evaluation of embryos cultured either in serum‐free medium or in serum‐supplemented medium

Abstract: The ultrastructure of bovine embryos developed from in vitro-matured and -fertilized oocytes, cocultured with bovine cumulus/granulosa cells either in a serum-free medium (IVMD101) or in a serum-containing medium (TCM199+CS) was compared. Embryos up to the eight-cell stage had many cellular organelles and cytoplasmic components that were randomly distributed in the cytoplasm. Mitochondria were spherical or ovoid and had only a few peripheral cristae. There were no obvious differences in the ultrastructure between embryos developed in IVMD101 and TCM199+CS up to the eight-cell stage. However, conspicuous differences in the ultrastructural features between the embryos cultured in IVMD101 and TCM199+CS were observed at the morula and blastocyst stages. At the morula stage, embryos cultured in IVMD101 had cells containing elongated mitochondria, well-developed Golgi apparatus, lipid droplets, and large vesicles resembling lysosomes. The lysosome-like vesicles were partially filled with electron-dense materials and were frequently fused with lipid droplets. The blastomeres of morulae cultured in TCM199+CS contained numerous large lipid droplets and fewer lysosome-like vesicles than those cultured in IVMD101. In blastocysts cultured in IVMD101, lysosome-like vesicles were frequently observed in the trophoblast cells and lipid droplets were present in the cytoplasm of trophoblast and inner cell mass (ICM)-cells, but they were not abundant. On the other hand, the blastocysts developed in TCM199+CS contained fewer lysosome-like vesicles and large numbers of lipid droplets. This accumulation of lipid droplets was higher in the trophoblast cells than in the ICM-cells. This study showed major differences in the ultrastructural features between the morulae and blastocysts from serum-free and serum-supplemented cultures, suggesting that the ultrastructural differences may reflect physiological characteristics of embryos.

Direct probing of the surface ultrastructure and molecular interactions of dormant and germinating spores of Phanerochaete chrysosporium

Abstract: Atomic force microscopy (AFM) has been used to probe, under physiological conditions, the surface ultrastructure and molecular interactions of spores of the filamentous fungus Phanerochaete chrysosporium. High-resolution images revealed that the surface of dormant spores was uniformly covered with rodlets having a periodicity of 10 +/- 1 nm, which is in agreement with earlier freeze-etching measurements. In contrast, germinating spores had a very smooth surface partially covered with rough granular structures. Force-distance curve measurements demonstrated that the changes in spore surface ultrastructure during germination are correlated with profound modifications of molecular interactions: while dormant spores showed no adhesion with the AFM probe, germinating spores exhibited strong adhesion forces, of 9 +/- 2 nN magnitude. These forces are attributed to polysaccharide binding and suggested to be responsible for spore aggregation. This study represents the first direct characterization of the surface ultrastructure and molecular interactions of living fungal spores at the nanometer scale and offers new prospects for mapping microbial cell surface properties under native conditions.

Early events in naphthalene-induced acute Clara cell toxicity: comparison of membrane permeability and ultrastructure.

Abstract: Naphthalene causes severe dose- and site-selective injury to mouse nonciliated bronchiolar (Clara) epithelial cells. Toxicity is characterized by exfoliation of injured Clara cells into the airway lumen 24 h after exposure. The purpose of this study was to define the temporal pattern of intracellular changes immediately following naphthalene treatment, with the goal of identifying critical early events involved in cytotoxicity. Mice were injected with naphthalene or carrier and were killed 1, 2, 3, and 6 h after treatment (PT). Loss of membrane integrity was assessed by ethidium homodimer-1 permeability and confocal microscopy. Cell morphology and ultrastructure were evaluated using high-resolution light and electron microscopy. Permeable cells were found only in terminal bronchioles and increased in abundance with time PT. At 2 and 3 h PT, when most Clara cells had early signs of injury, few permeable cells were detected. Many Clara cells had apical membrane blebs that contained abundant, swollen, smooth...

Fine structure of bovine morulae and blastocysts in vivo and in vitro.

Abstract: The ultrastructure of bovine morulae and blastocysts developed from in vitro-matured and -fertilized oocytes in a serum-supplemented medium was compared with that of morulae and blastocysts collected non-surgically from superovulated cows. In the in vivo-derived morulae, two characteristic cells types could be identified by the electron-density of their cytoplasm and by their ultrastructural features. One type appeared light in color with low electron-dense cytoplasm. These cells were located in the peripheral layer of the cluster of blastomeres, possessed numerous cellular organelles such as mitochondria and Golgi apparatus and had microvilli projecting into the perivitelline space. The other cell type was distinguished by cytoplasm that stained more densely than that of the lighter-appearing cells. The darker-appearing cells generally possessed fewer organelles than the lighter cells, but many lysosome-like structures were present in the cytoplasm. The in vitro-developed morulae also contained two types of cells similar to those observed in the in vivo morulae. However, most of the in vitro-developed cells possessed numerous lipid droplets and contained fewer lysosome-like structures than the cells of the in vivo-derived morulae. The blastocysts, both in vivo and in vitro, showed a clear differentiation of trophoblast cells and inner cell mass (ICM)-cells. In the in vivo-derived blastocyst, the apical membrane of trophoblast cells was covered with large, numerous microvilli and well-developed junctional complexes were observed. Lipid droplets were present in the cytoplasm of trophoblast and ICM-cells but were not abundant. In vitro-developed blastocysts showed less well-developed junctional complexes between trophoblast cells, less well-developed apical microvilli on the trophoblast cells, and contained large numbers of lipid droplets. This accumulation of lipid droplets was higher in the trophoblast cells than in the ICM-cells. The zonae pellucidae of in vitro-developed embryos were thinner than that of the in vivo-derived embryos. This study demonstrates conspicuous differences in the ultrastructural features between the in vivo-derived and in vitro-developed embryos, suggesting that the ultrastructure may reflect the various physiological anomalies observed in previous studies.

Ultrastructural studies on the centrosome-attracting body: electron-dense matrix and its role in unequal cleavages in ascidian embryos.

Abstract: In ascidian embryos, three successive unequal cleavages occur at the posterior pole, generating a specific cleavage pattern. A recently reported novel structure designated the centrosome-attracting body (CAB) has been suggested to play essential roles in the unequal cleavages attracting centrosomes and the nucleus towards the posterior pole. To examine the morphological features of the CAB, the ultrastructure of the CAB of two ascidian species, Halocynthia roretzi and Ciona intestinalis was observed by transmission electron microscopy. Detailed observations clarified that the electron-dense matrix (EDM) was a CAB-specific component that was commonly observed in the CAB of both species but was not found in other areas of the embryo. Further observations of the CAB in various staged embryos revealed that the ultrastructure was quite stable, with no difference between points of a cell cycle or between each stage from the 8- to 64-cell stage when unequal cleavage occurred. Observations of extracted embryos implied that the EDM was the extraction-resistant component of the CAB and was tightly anchored to the plasma membrane. It has been proposed that the EDM functions as a physical attachment site at the cell cortex for microtubules emanating from centrosomes and provides a scaffold for the centrosome-attracting machinery. Interestingly, the ultrastructure of the CAB resembled germ plasm reported in other animals, raising the possibility that the CAB-containing posterior-most blastomeres are germline precursors.

Megasporogenesis in Arabidopsis thaliana L.: an ultrastructural study

Abstract: In this study, megasporogenesis of the plant model Arabidopsis thaliana was investigated by electron microscopy for the first time. The data described here could constitute a reference for future investigations of Arabidopsis mutants. During the beginning of meiosis the megaspore mother cell shows a polarity created by unequal distribution of organelles in the cytoplasm. Plastids accumulate in the chalazal region and long parallel saccules of endoplasmic reticulum, small vacuoles and some dictyosomes are found in the micropylar region. Plasmodesmata are abundant in the chalazal cell wall. The nucleus is almost centrally localized and contains a prominent excentric nucleolus and numerous typical synaptonemal complexes. After the second division of meiosis the four megaspores are separated by thin cell walls crossed by numerous plasmodesmata and do not show significant cellular organization. The young functional megaspore is characterized by a large nucleus and a large granular nucleolus. The cytoplasm is very electron dense due to the abundance of free ribosomes and contains the following randomly distributed organelles: mitochondria, a few short saccules of endoplasmic reticulum, dictyosomes and undifferentiated plastids. However, there is no apparent polarity, except for the distribution of some small vacuoles which are more abundant in the micropylar region of the cell. The degenerating megaspores are extremely electron dense and do not show any substructure.

Histochemical and ultrastructural characterization of vacuoles and spherosomes as components of the lytic system in hyphae of the fungus Botrytis cinerea.

Abstract: An integrated approach to acid phosphatase (EC 3.1.3.2) histochemistry by the azo-dye and lead-capture ('Gomori') methods in phosphate-starved hyphae of the fungus Botrytis cinerea revealed strikingly different patterns of localization of activity staining. Reaction product formed with the azo-dye method was found in numerous small organelles (<0.5 microm diameter), which also accumulated the lipophilic dye Nile Red and mislocalized the formazan indicating mitochondrial succinate dehydrogenase activity. Such small organelles were stained only weakly and sporadically with the lead-capture method; instead, lead phosphate deposits were produced mainly in large vacuoles (up to 2.5 microm diam.), similar to those accumulating the vital dye Neutral Red. Additionally, acid phosphatase activity was detected in apical secretory vesicles with the lead-capture method but not with the azo-dye method. Ultrastructural studies by transmission electron microscopy confirmed the presence of large vacuoles which showed evidence of autophagic activity, and of small moderately osmiophilic organelles. The latter are considered to be spherosomes rather than lysosomes because of their weak reaction with the lead-capture method and their high lipid content. It is suggested that their apparently strong reaction with the azo-dye method is caused partly by false localization due to the lipophilic nature of the reaction product.

The Development of Chloroplast Ultrastructure and Hill Reaction Activity During Leaf Ontogeny in Different Maize (Zea Mays L.) Genotypes

Abstract: Changes in Hill reaction activity (HRA) and ultrastructure of mesophyll cell (MC) chloroplasts were studied during the ontogeny of third leaf of maize plants using polarographic oxygen evolution measurement, transmission electron microscopy, and stereology. The chloroplast ultrastructure was compared in young (actively growing), mature, and senescing leaves of two different inbreds and their reciprocal F1 hybrids. Statistically significant differences in both HRA and MC chloroplast ultrastructure were observed between different stages of leaf ontogeny. Growth of plastoglobuli was the most striking characteristic of chloroplast maturation and senescence. The chloroplasts in mature and senescing leaves had a more developed system of thylakoids compared to the young leaves. Higher HRA was usually connected with higher thylakoid volume density of MC chloroplasts.

Ultrastructure of shizonts and merozoites of Sarcocystis falcatula in the lungs of budgerigars (Melopsittacus undulatus).

Abstract: Transmission electron microscopy was used to study the ultrastructure of schizogony of Sarcocystis falcatula in the lungs of budgerigars (Melopsittacus undulatus). Schizogony occurred exclusively by endopolygeny within endothelial cells of pulmonary capillaries, venules, and small veins. Early schizonts were elongate with a large nucleus and nucleolus, surrounded by a pellicle consisting of a plasmalemma and an inner single membrane, and contained most of the organelles and inclusion bodies found in merozoites of Sarcocystis species. As development proceeded, schizonts increased in size and conformed to the shapes of the pulmonary blood vessels. As micronemes, dense granules, the conoid, and subpellicular microtubules disappeared, there was an increase in the size and number of mitochondria, Golgi complexes, and Golgi adjuncts (apicoplasts). As the nucleus elongated, there was a progressive increase in the number of spindles located at various intervals along the nuclear envelope. Eventually, 2 merozoites formed internally immediately above each spindle. During endopolygeny, a portion of the nucleus was incorporated into each merozoite bud along with 1 or 2 Golgi adjuncts, a Golgi complex, mitochondria, endoplasmic reticulum, and ribosomes. During merozoite formation, micronemes appeared in close association with the Golgi complex and gradually increased in number. The pellicle invaginated around the merozoites so they budded at the schizont surface leaving behind a small, central residual body. Dense granules appeared after merozoites were completely formed. Schizonts were 24 x 6.8 microm and contained 24-96 merozoites. Merozoites were 5.1 x 1.8 microm and were found free in the pulmonary air passages and pulmonary capillaries and within nearly all cells of the lung except red blood cells.

Morphometric and densitometric study of the biogenesis of electron‐dense granules in Fonsecaea pedrosoi

Abstract: Fonsecaea pedrosoi is a polymorphic pathogenic fungus, etiological agent of chromoblastomycosis, that synthesizes a melanin-like pigment. Although this pigment has been described as a component of the outer layers of the cell wall, electron-dense cytoplasmic bodies have also been visualized. In this work, we have correlated the appearance of intracellular electron-dense granules with the melanization process in F. pedrosoi. For this, conidial forms were grown under conditions where melanin was not synthesized. Afterwards, cells were incubated in Hank's medium supplemented with bovine fetal serum, at 37°C, to stimulate the pigment production. The genesis of cytoplasmic bodies, with different stages of electron density, was demonstrated by transmission electron microscopy. The appearance of fungal acidic compartments, visualized by confocal laser scanning microscopy in cells stained with acridine orange, was time coincident with the formation of electron-dense granules observed by transmission electron microscopy. The quantification of granule numbers as well as morphometric and densitometric studies were performed.

Morphological and Ultrastructural Studies on in situ Spores of Oligocarpia (Gleicheniaceae) from the Lower Permian of Xinjiang, China.

Abstract: Though the fossil genus Oligocarpia is generally regarded to be of gleicheniaceous affinity, nothing is currently known about its spore ultrastructure. In this article, the micromorphology and ultrastructure of in situ spores of gleicheniaceous affinity are investigated for the first time with scanning electron microscopy and transmission electron microscopy from a compression specimen of Oligocarpia kepingensis Wang and Wu collected from the Lower Permian of Xinjiang, northwest China. Spores of O. kepingensis closely resemble the dispersed taxon Leiotriletes (Naumova) Potonie et Kremp. At the ultrastructural level, the exospore consists of three‐layered subdivisions, including a degraded and weakly preserved thin inner layer, a complex and elaborate middle layer, and homogeneous outer layer. Comparisons are made between Oligocarpia spores and those of other related fossils, as well as extant taxa based on morphological and ultrastructural evidence. These data indicate that, despite clear differences in l...

Immunocytochemical Study of the Distribution of a 16-kDa Galectin in the Chicken Retina

Abstract: PURPOSE To compare the distribution of a developmentally regulated 16-kDa galectin in the chicken retina at two different developmental stages: embryonic day 13 (ED13) and postnatal day 10 (PD10) retinas, by immunocytochemical analysis using light and transmission electron microscopy METHODS Semi-thin and thin sections from ED13 and PD10 retinas were incubated with the IgG fraction purified from a rabbit antiserum raised against the 16-kDa chicken galectin After incubation with colloidal gold particle-labeled goat anti-rabbit IgGs, tissue sections were analyzed by light and transmission electron microscopy To improve the observation by light microscopy, semi-thin immunostained sections were intensified by silver enhancement RESULTS In ED13 retinas a specific galectin labeling was detected in the region corresponding to the outer limiting membrane by light microscopy This labeling seemed to be associated with the apical villi of Miiller glial cells and their specialized junctions, as judged by transmission electron microscopy In PD10 retinas, the more relevant finding revealed by light microscopy was the detection of a widespread immunostaining at the level of all retinal layers The ultrastructural analysis indicated that the galectin labeling was detected at the cytoplasmic and nuclear compartments of Miiller cells throughout the different retinal layers Moreover, the labeling was detected in the inner limiting membrane in structures that resemble the end feet of Miiller cells The apical villi, and the specialized junctions of these glial cells, appeared more strongly stained in PD10 retinas than in ED13 retinas Finally, highly intense labeling in a group of mitochondria localized in the inner segments of cone cells was observed CONCLUSIONS The present study clearly supports the idea that the subcellular distribution of the 16-kDa galectin changes during the development of the chicken retina Morphologic changes associated with developmentally regulated expression and subcellular compartmentalization of the retinal galectin suggest that this lectin may be involved in the modulation of several processes in the visual system Its presence in the apical villi of Miiller cells may be related by modulatory functions between retina and pigment epithelium, but its presence in the cytoplasm and nucleus of these glial cells suggests a potential immunomodulatory role and its involvement in different metabolic processes between Miiller and the other retinal cells Finally, although the presence of galectins inside mitochondria has not been described before, this localization gives rise to the idea that this lectin may be involved in the modulation of mitochondrial processes

The endolymphatic sac, a potential endocrine gland?

Abstract: A previous investigation indicated that the chief cells of the endolymphatic sac produce an endogenous inhibitor of sodium re-absorption in the kidneys, which has tentatively been named ?saccin?. In this study, the ultrastructure of the endolymphatic sac and in particular the chief cells is described, demonstrating that this organ fulfils the morphological criteria of a potential endocrine gland. Accordingly, the chief cells are shown to exhibit all the organelles and characteristics of cells that simultaneously synthesize, secrete, absorb and digest proteins.

Morphologic comparisons among equine endometrium categories I, II, and III, using light and transmission electron microscopy

Abstract: Objective To evaluate whether the pathologic changes observed by light microscopy in endometrium of categories II and III were reflected by cellular changes and to describe differences in the endometrial cell ultrastructure during estrus and diestrus. Animals 18 healthy mares. Procedure Endometrial tissues biopsied during the physiologic breeding season were categorized, using light microscopy, and were studied, using transmission electron microscopy (TEM). Results Using TEM, glycogen granules were associated with giant mitochondria for all endometrial types during diestrus. Development of rough endoplasmic reticulum (RER) and Golgi apparatus suggested protein synthesis in the endometrial glands during diestrus. TEM did not reveal major ultrastructural differences, between endometrium of categories I and II. This was unlike differences identified by light microscopy. The most extensive pathologic changes were seen in category-III tissue (TEM and light microscopy). Category-III endometria had a large number of light cells with more degenerative structures and fewer organelles, and lacked cilia in the lumen of the glands. This tissue had extensive fibrotic tissue in the lamina propria and many inflammatory cells in most tissue layers. Conclusions The severe ultrastructural changes may be one of the many factors decreasing the fertility of mares with category-III, compared with category-1 and -2, endometrium.

Sperm ultrastructure of the giant clam Tridacna maxima (Tridacnidae: Bivalvia: Mollusca) from the Great Barrier Reef

Abstract: Using transmission electron microscopy, spermatozoa from a member of the Tridacnidae, or giant clams, are described for the first time and compared with spermatozoa of other bivalves, especially other heterodonts. The acrosomal vesicle of Tridacna maxima (Roding, 1798) is short (0.37 μm), blunt-conical, and exhibits a prominent basal ring. A narrow apical elaboration of the nucleus, the nuclear peg, projects deep into the basal invagination of the acrosomal vesicle. Aside from this specialization, the nucleus is a solid elongate-cylindrical structure (7.66 μm) that exhibits several small irregular lacunae. Four or occasionally three round-ovate mitochondria surround a pair of orthogonally-arranged, triplet-substructure centrioles. The proximal centriole is connected to a small indentation of the nuclear base by a thin layer of granular pericentriolar material, whereas the distal centriole is anchored to the plasma membrane by nine terminally-forked satellite fibres. The 9 + 2 pattern axoneme of the tail is continuous with the distal centriole. Comparison with other bivalves indicates a very close relationship between tridacnids and cardiids based on sperm ultrastructure. Specifically, the presence of a nuclear peg links Tridacna spp. with the cardiid genus Cerastoderma, but further information on the many unstudied genera is required to test the exact nature of this relationship. The sperm ultrastructure provides additional support for the recently proposed hypothesis that the Tridacnidae may be no more than a specialized subfamily of the Cardiidae.

Effects of chronic salt stress on the ultrastructure of Dunaliella bioculata (Chlorophyta, Volvocales): mechanisms of response and recovery

Abstract: The ultrastructural changes taking place in Dunaliella bioculata after chronic exposure to a sodium chloride-induced stress were examined. Hyperosmotic shock was induced by raising the sodium chloride concentration of the culture medium from 0·3 to 1·3 M, which affected a number of cellular organelles during the initial stages of the stress period, i.e. 24, 48 and 72 h. Changes in whole-cell volume were recorded, as well as alterations in the size of the following components: starch grains and sheath, lipid and plastoglobuli, chloroplast, pyrenoid, nucleus, mitochondria, cytoplasm, Golgi apparatus and endoplasmic reticulum. Cells were examined using transmission electron microscopy and changes to their fine structure quantified via image analysis of the electron micrographs. The image analysis program was designed to measure various geometric parameters for all the cell components within individual algal cells. Quantitative image analysis of cells subjected to a chronic salt stress revealed marked increases in the cross-sectional areas of the Golgi apparatus and the endoplasmic reticulum. The enhanced production of the Golgi apparatus within the algal cells was thought to be the direct result of a salt-stress-induced endoplasmic reticulum production within the cells. The increase in the endoplasmic reticulum was manifested as extensive networks of cortical endoplasmic reticulum. It is suggested that the endoplasmic reticulum serves both physiological and structural roles during chronic salt stress by providing the driving force behind increased synthetic/Golgi apparatus activities of the cells, and by providing a type of ‘cellular scaffolding’ to limit the degree of cell contraction in the face of long-term salt stress.

The ultrastructural effect and subcellular localization of mercuric chloride and methylmercuric chloride in insect cells (Aedes albopictusC6/36).

Abstract: Abstract. The ultrastructural effects of mercuric chloride (Hg) and methylmercuric chloride (MeHg) were studied in the Aedes albopictus C6/36 cell line. Both metal salts caused nuclear indentations, chromatin clumping and proliferation of the nucleolus. The mitochondria became pleomorphous. An increase of both free and membrane-bound ribosomes, swelling of the rough endoplasmic reticulum caused by accumulated protein and the appearance of well developed Golgi stacks all indicated the activation of protein synthesis. The activation was probably a cellular response to general stress, and the synthesized proteins may be members of the heat shock protein family. Apart from these common ultrastructural features, Hg-treated cells showed typical clusters of small electron-lucent vacuoles near the Golgi stacks. In cells exposed to MeHg, cytoplasmic tube-like structures were often observed and the disorganization of the organelles together with the appearance of blebs suggested disruption of the microtubules. Mercury accumulation was localized by an autometallographical silver staining technique both at the light and electron microscopic level; silver deposits were quantified by image analysis. For both Hg- and MeHg-treated cells, the degree of silver staining increased rapidly with increasing exposure time, but a considerable heterogeneity within the cell population was found. Lysosomes proved to be the major mercury storage sites in the Aedes cells and silver deposits could already be found after 30 min of Hg treatment. At sublethal concentrations, Hg inhibited the lysosomal marker enzyme acid phosphatase to some extent. For MeHg, no effect on this enzyme was found.

The morphology of Ichthyophonus sp. in their mugilid hosts (Pisces: Teleostei) and following cultivation in vitro. A light and electron microscopy study.

Abstract: The morphology of Ichthyophonus sp., a parasite of Mugil capito and Liza saliens, was investigated by light and transmission electron microscopy. The most frequent stage found in the fish hosts was the multinucleate spore, though germinating stages, hyphae, and endospores were also found. Different development patterns were observed in the media assayed for in vitro culture. Optimal growth and development were obtained in Eagle's minimum essential medium (MEM) supplemented with 10% fetal bovine serum at pH 7. Ultrastructural features of multinucleate spores, both in the fish host and in culture, were a fibrillar thick wall and an electron-lucent matrix, with large glycogen granules, some electron-dense bodies, large vacuoles, lipid inclusions, and endoplasmic reticulum mainly appearing among the nuclei. Mitochondria with scarce tubulovesicular cristae were observed in the different stages, mainly near the wall and the germinating sites. Condensed heterochromatin was rarely seen. A nucleus-associated organelle (NAO) was frequently observed, and dictyosome cisternae and vesicles appeared in its vicinity.

Light and electron microscopic radioautographic studies on RNA synthesis in aging mouse adrenal gland.

Abstract: Ultrastructural observation and radioautographic studies were carried out to detect aging changes of RNA synthesis in the adrenal glands of mice from fetal day 19 to postnatal 12 months by light and electron microscopic radioautography after 3H-uridine incorporation. The ultrastructural features of the cells at embryonic stages were not developed. The cell organelles appeared more developed at early postnatal stages. The organelles such as endoplasmic reticulum, ribosomes, Golgi apparatus, mitochondria with tubular or vesicular cristae and lipid droplets were more frequently observed in the cytoplasm of the cells in the 3 zones of the cortex and the medulla at later postnatal and senescent stages. The activity of RNA synthesis of adrenal glands, as expressed by grain counting per unit area as well as per cell, was the highest in the cortex and medulla at fetal day 19, and then gradually decreased with aging. The silver grains were electron microscopically localized over the nucleoli, euchromatin, endoplasmic reticulum, ribosomes and mitochondria of the cells in the 3 zones of the cortex and the medulla. The number of mitochondria per cell, the number of labeled mitochondria per cell and the mitochondrial labeling indices increased along with aging. These results demonstrated the aging changes of RNA synthesis in the adrenal glands of mice.