bluuebunny/crossref_metadata_2025 huggingface dataset:
The morphology and kinetics of spermatogonial degeneration in normal adult rats: An analysis using a simplified classification of the germinal epithelium
Authors: Huckins C.
Published: February 2005

The phenomena of spermatogonial degeneration have been studied in normal adult rat testes using a simplified classification of the germinal epi‐thelium based upon the six types of differentiating spermatogonia. The following features distinguished this from schemes based on acrosome development. Rather than 14 stages of unequal duration, there are only six stages, five of which are of the same length. The classification starts at the beginning of spermatogenesis with A1 spermatogonia rather than at the onset of spermiogenesis. The classification is derived from actual biological events in spermatogenesis, namely generation times of spermatogonia, rather than upon arbitrary events in acrosome development. Most importantly, this new classification can be used with most types of preparations and in most experimental conditions.

Examination of tubular whole mounts reveals that degeneration preferentially occurs in types A2 and A3 and to a lesser extent A4 spermatogonia, and is rarely seen in generations of A1 In or B cells. Deterioration is first manifested in clusters of cells joined by the intercellular bridges as they complete DNA synthesis and enter the G2 phase of cell cycle. It is characterized by a denser staining of the nuclear membrane, coalescence of chromatin into several pyknotic bodies, and eventual extrusion of the nuclear mass, leaving a cytoplasmic ghost. The sequential steps in degeneration may often be traced from one end of a synctial chain to the other, suggesting that the process may start with just one cell and then spread via intercellular bridges to involve all spermatogonia within the clone. Quantitatively, degeneration is a relatively constant feature of spermatogonial development. Only 25% of the theoretically possible number of pre‐leptotene spermatocytes are produced from the original population of A1 spermatogonia; most of this loss is incurred during the maturation of A2 and A3 generations. While the reason for spermatogonial degeneration in the normal germinal epithe‐lium remain obscure, it is proposed that the numerical ratio of A spermatogonia to Sertoli cells may be a significant limiting factor.
Observations on the development of the human atrioventricular node and bundle
Authors: Truex Raymond C. , Marino Thomas A. , Marino Deborah R.
Published: February 2005

This light microscopic study of the cardiac junctional tissues was based on 27 human embryos, fetuses and postnatal hearts. Evidence was presented that superficial and deep portions of the postnatal AV node were derived from two cellular primordia in the posterior wall of the common atrium at the 6‐mm stage. The small right primordia was associated with the right venous valve and gave rise to the loosely organized superficial AV node that extended posteriorly to the coronary sinus ostium. A larger left primordia formed the more compact deep subdivision of the AV node located against the anulus fibrosus. In most postnatal hearts the two subdivisions are partially or completely fused to form the adult AV node. Failure of the nodal primordia to fuse during cardiogenesis may result in two separate nodal cell aggregates above the anulus. The present observations provide a rational explanation for the two AV nodal masses described in the literature and an additional specimen that is illustrated in this communication.

An AV bundle was first identified in a 13‐mm embryo and appeared to be derived from large clear cells of the posterior AV canal. At 25 mm the bundle formed a broad band across the top of the IV septum and continued into both ventricles. At this stage multiple cell strands penetrated the endocardial cushion to connect the AV bundle to the two nodal primordia. Failure of normal fusion between the AV node primordia and AV bundle can result in a variety of junctional anomalies including congenital heart block.
Immuno‐histochemical localization of cyclic nucleotides in the periodontium: Mechanically‐stressed cells in vivo
Authors: Davidovitch Zeev , Montgomery Paul C. , Yost Robert W. , Shanfeld Joseph L.
Published: February 2005

Cyclic AMP and cyclic GMP, considered to be cell proliferation regulators, have been reported to fluctuate in proliferating fibroblasts in vitro. The objectives of this experiment were to study the localization, distribution and staining patterns of these cyclic nucleotides in mechanically‐stressed, proliferating periodontal fibroblasts in vivo. Cat canines were tipped by force applications for 0 to 48 hours and serial sagittal sections of fresh frozen, unfixed, undecalcified jaws were processed immuno‐histochemically for the localization of cAMP and cGMP. Periodontal tension sites were studied microscopically. Fibroblastic staining for cAMP, which was localized mainly in the cell periphery, did not change appreciably as a result of tension. However, staining intensity increased one hour after the application of force, decreased after 6 hours and increased again at 24 hours. Staining for cGMP, initially covering the entire cell area, was concentrated over nuclei three hours after onset of tension, and diffused over cell periphery and cytoplasm thereafter. Intensity of staining for cGMP was maximal at 3 hours and low at 12 and 48 hours. These results demonstrate that stress‐induced fibroblastic responses in vivo involve alterations in staining intensity for both cyclic nucleotides which may correspond with fluctuations of these regulators, reported to occur in vitro in various stages of the mitotic cycle. Moreover, this technique enables the identification of the involved cells in a stimulated, non‐synchronized cell population.
Immuno‐histochemical localization of cyclic nucleotides in mineralized tissues: Mechanically‐stressed osteoblasts in vivo
Authors: Davidovitch Zeev , Montgomery Paul C. , Yost Robert W. , Shanfeld Joseph L.
Published: February 2005

Previous experiments indicate that bone cells respond to external stimuli with fluctuations of cyclic nucleotide levels. The objective of this experiment was to study the response of alveolar bone to the application of tensile forces through an examination of the osteoblastic staining pattern for cAMP and cGMP. Cat canines were tipped by 80‐g force for 0 to 48 hours. Fresh frozen, unfixed, undecalcified jaws were sectioned sagittally and stained immuno‐histochemically for cAMP and cGMP. In tension sites, osteoblastic staining intensity for cAMP decreased gradually from one to three hours, and then increased by 24 hours. Intense staining for cGMP, visible in osteoblasts of all treated cats, peaked after three hours of treatment and then again at 24 hours. Generally, groups of cGMP‐stained osteoblasts were found adjacent to unstained osteoblasts. The observed fluctuations in the osteoblasts staining pattern for cAMP and cGMP indicates involvement of these substances in the early response of osteoblasts to mechanical stimuli in vivo.
Ultrastructure of the parotid gland of the nine‐banded armadillo
Authors: Ruby John R.
Published: February 2005

The parotid gland of the nine‐banded armadillo (Dasypus novemcinctus) was examined by electron microscopy. In general, the ultrastructural morphology of this gland appears similar to that described in other species. The most unusual feature of the gland is that the secretory granules of the acinar cells contain a wide variety of substructures. These substructures range from a single dense core within a homogeneous matrix to a more complex cordlike network extending throughout the granule. It is suggested that this diversity of substructures is indicative of a maturation process of the secretory granules. The intercalated ducts are secretory. The myoepithelial cells are numerous, extend throughout the gland, and are associated with the striated ducts.
The influence of thyroid and testicular hormones on globule leucocytes in the rat duodenal crypt epithelium
Authors: Carriere R. , Buschke M.
Published: February 2005

The globule leucocyte is a cell with a wide distribution in the digestive, respiratory, biliary, urinary and genital tract epithelia of homeotherms. It occurs in the crypts of the rat small intestine and within the epithelium on the villous bases but not on the remainder of the villi. A characteristic feature of this cell is the presence of acidophilic cytoplasmic granules, 0.5 to a few m̈m in diameter. The nucleus resembles that of intraepithelial intestinal lymphocytes. In this investigation, a quantitative study was made of the effect of thyroidectomy and/or castration on the number of globule leucocytes in the duodenal crypts of immature and adult rats. In sham‐operated rats, globule leucocytes were rare, occurring with a frequency of 1 or 2 per 1,000 epithelial cells. After thyroidectomy, they increased to 14‐20 per 1,000 epithelial cells. Castration did not influence the number of globule leucocytes but resulted in an increase in the number, size and acidophilia of their cytoplasmic granules. In immature rats, but not in adults, castration combined with thyroidectomy enhanced the effect of thyroidectomy, increasing globule leucocyte number to 32 per 1,000 epithelial cells.

Treatment of thyroidectomized‐castrates with thyroxine, initiated 38 days after operation, reduced the crypt globule leucocyte population to normal, whereas treatment with testosterone did not. Growth hormone failed to influence the elevated number of globule leucocytes in thyroidectomized rats, suggesting that this action of thyroxine was not mediated via an influence on growth hormone release.

Because of their similar nuclear morphology, intraepithelial crypt lymphocytes were also counted and there was no obvious relationship in the fluctuations of these two cell populations.

It is suggested that the greater number of crypt globule leucocytes in thyroid deficiency may reflect changes in the intestinal secretory immunoglobulin system and this is being investigated, beginning with a study of the distribution of IgE.
Investigations on the turnover of adrenocortical mitochondria. XII. Studies on the mechanism of the acth‐induced elongation of the half‐life of rat zona fasciculata mitochondria
Authors: Nussdorfer Gastone G. , Neri Giuliano , Mazzocchi Giuseppina
Published: February 2005

The half‐life of rat adrenocortical mitochondria was determined by high resolution autoradiography and liquid scintillation spectroscopy as previously described (Mazzocchi et al., '76). The results obtained by the two approaches were in good agreement. In the normal rats the half‐life of adrenocortical mitochondria averaged 11 days. ACTH significantly increased mitochondrial half‐life to about 16 days, and chloramphenicol significantly decreased this parameter in both untreated and ACTH‐administered rats to about seven days. It is suggested that the ACTH‐induced maintenance and slowing down of the degradation rate of adrenocortical mitochondria requires continuous mitochondrial DNA‐dependent protein synthesis.
Supraependymal neurons overlying the periventricular region of the third ventricle of the guinea pig: A correlative scanning—transmission electron microscopic study
Authors: Mitchell J. A. , Card J. P.
Published: February 2005

The frequency of occurrence, distribution and morphology of supraependymal neurons associated with the third ventricular wall of the guinea pig were investigated by correlative scanning and transmission electron microscopy. Each of the specimens was located on the ciliated ventricular wall between the inferior border of the thalamus and the non‐ciliated ependyma associated with the median eminence. Prominent clusters of neuronal perikaria in association with massive process bundles were observed in 7 of the 31 specimens examined. In those specimens lacking prominent neuronal networks a more diffuse array of independent nerve fibers was sometimes seen on the ependymal surface. Neuronal perikaria exhibited numerous surface protrusions and were covered by a rich meshwork of crisscrossing, varicosed fibers. Many of these cells were associated with multiple processes of varying diameters and lengths which either coursed independently over the ventricular surface or formed fasciculated bundles. As process bundles traversed the ependymal surface, individual processes branched off and either terminated within the ventricular lumen or penetrated the subjacent ependymal lining. Fibers also made contact with adjacent supraependymal neuronal elements. Correlative transmission electron microscopic observations indicate that both the perikaria and processes of such supraependymal networks possess ultrastructural features characteristic of neurons. The morphological characteristics of the intraventricular neuronal networks suggest that they may be engaged in functional interactions with the cerebrospinal fluid, with adjacent supraependymal neuronal elements and with the subjacent neuropil.
Identification of neuro‐epithelial bodies in rabbit fetal lungs by scanning electron microscopy: A correlative light, transmission and scanning electron microscopic study
Authors: Cutz E. , Chan W. , Sonstegard K. S.
Published: February 2005

In the present study, neuro‐epithelial bodies (NEB) were identified by scanning electron microscopy (SEM) within the bronchial epithelium of near‐term rabbit fetuses. The surface features and topography of NEB were correlated by light and transmission electron microscopy.

In SEM, the surfaces of NEB were easily visualized in smaller peripheral airways because of paucity of ciliated cells in these regions. The NEB formed crater‐like pits, which were lined with microvilli and had smooth‐surfaced non‐ciliated cells around the rim. Stereo‐pair photographs revealed that the latter cells protruded above adjacent bronchiolar mucosa. The SEM also revealed that NEB were preferentially located near or at bronchiolar bifurcations.

This is the first report of the three‐dimensional structure of pulmonary NEB. Their direct contact with the airway lumen, as well as their strategic location in bronchiolar mucosa, support the suggestion that they are intrapulmonary receptors and help to regulate air‐flow in peripheral airways.
An electron microscope study of crystal calcium carbonate formation in the mouse otolith
Authors: Nakahara Hiroshi , Bevelander Gerrit
Published: February 2005

The ultrathin sections of the developing otolith of mouse fetuses 15.5 days to 20 days after birth were observed with the aid of the electron microscope.

The first step of otolith formation is an aggregation of organic clusters observed in the sacculus of the 15.5‐day fetus. These organic structures are modified and assume a hexagonal shape in the 17.5‐day fetus. The unmineralized stages of the otolith referred to as the preotolith, serve as the template for future development.

One day after birth, at either end of the preotolith, minute tube‐like structures develop in which needle‐shaped crystallites are initiated. Crystallites continue to develop throughout the hexagonal template which give rise to a structure containing many regularly arranged needle‐shaped crystallites. Based on the present observations, the mouse otolith is considered a multi‐iso‐oriented crystal.
Endoplasmic reticulum‐Golgi apparatus relationships in the rat spermatid
Authors: Hermo L. , Clermont Y. , Rambourg A.
Published: February 2005

The appearance of the spermatid Golgi apparatus was studied, both in thin sections of rat testes fixed in glutaraldehyde and treated with either tannic acid or ferrocyanide‐reduced osmium, and in relatively thick sections (0.25‐0.5 μm) of glutaraldehyde fixed tissue impregnated with uranyl acetate followed by lead and copper citrate. With any one of these three procedures, the Golgi apparatus of young spermatids examined at the Golgi and cap phases appeared as a compact hemispherical mass whose base was located next to the developing acrosomic system. The cortical region of the hemisphere was composed mainly of several stacks of saccules. The central core or medullary region contained numerous vesicular and tubular membranous profiles. Numerous cisternae of the endoplasmic reticulum (ER) were closely applied to the surface of the Golgi apparatus. In thin sections, the ER cisternae were separated from the stacks of saccules by small spherical or elongated membranous profiles. In thick sections, most of these elements formed a network of tubules, some of which being continuous with ER cisternae. Cisternae of the endoplasmic reticulum near the cis‐face of the Golgi stacks also branched and traversed the cortical region of the Golgi apparatus through gaps seen between the stacks of saccules to reach the central core region. Some of these were closely applied to the trans elements of Golgi stacks although never in continuity with them. Finally, ER cisternae were found located within the stacks themselves between Golgi saccules; here the membranes of the closely apposed cisternae of the endoplasmic reticulum and Golgi saccules remained separated by a space of about 12 nm. Thus, in the spermatid, the endoplasmic reticulum was closely related with all components of the Golgi apparatus.
Localization of a highly specific neuronal protein, serotonin binding protein, in thyroid parafollicular cells
Authors: Bernd Paulette , Gershon Michael D. , Nunez Eladio A. , Tamir Hadassah
Published: February 2005

A highly specific serotonin binding protein (SBP) has been found in serotonergic neurons in both brain and gut. This protein has an extremely high affinity for serotonin and may be a storage protein. Serotonin is found in many endocrine cells, including parafollicular cells of the sheep thyroid, as well as in neurons. SBP is also present in sheep thyroid. The present study was done to localize the protein in the gland. Thyroid glands were divided into five segments. Concentrations of serotonin and SBP, as well as parafollicular cell volume were measured in each. Serotonin was assayed by enzymatic conversion to melatonin using tritiated S‐adenosylmethionine. SBP was assayed by molecular sieve chromatography on sephadex G‐50. The relative volume of parafollicular cells was obtained by stereological analysis of electron micrographs. Experiments were also done to demonstrate these cells by histofluorescence and radioautography following incubation with tritiated 5‐hydroxytryptophan. Good correlations were found between serotonin and SBP concentrations, and parafollicular cell volume. These peaked in the rostro‐central portion of the gland and were minimal at the poles. We conclude that thyroid SBP is probably localized in parafollicular cells.
The differential absorptive activity of epithelial cells of the rat epididymus before and after castration
Authors: Moore H. D. M. , Bedford J. M.
Published: February 2005

Horseradish peroxidase introduced into the lumen of the rat epididymis was taken up by the columnar cells of the epithelium by five minutes and more so after longer periods. The apical cells and particularly the clear cells in the caput and cauda epididymidis, respectively, showed significantly greater endocytotic activity than the principal cell in both locations. Within 14 days after castration, however, such differences in absorptive activity among the various cell types were essentially obscured because of increased endocytosis by the androgen‐deficient principal cells. The results are discussed briefly in terms of the function of different epithelial cell types and secretory/absorptive activity in the epididymis.
The guidance of optic axons in the developing and adult mouse retina
Authors: Goldberg Stephen , Frank Beryn
Published: February 2005

Previous studies in chick embryos (Goldberg, '77) indicated that unidirectional guidance of retinal axons toward the optic nerve is restricted to the vitread portion of the ganglion cell fiber layer (GCFL) of the retina; random fiber growth was noted after deflection of the optic axons sclerad to the GCFL.

The present study on mice confirms these observations. Silver‐stained flat mounts of retinal colobomas were examined. Many optic axons in colobomas do not exit normally from the eye, but travel randomly when deflected sclerad to the GCFL. Newborn mouse axons grew around retinal lesions in a highly directed manner. Such axons were always situated in the vitread portion of the GCFL.

The unidirectional guidance found in newborn mice was absent in adults. Deflected adult axons traveled randomly regardless of their level within the GCFL. We propose that defective guidance largely accounts for failure of axonal regeneration in the adult mouse retina. The inability of the adult axons to fasciculate (adhere to one another and form fiber bundles) suggests that impaired cellular adhesivity may be part of the mechanism of regenerative failure.
Formation of concentric saccules in murine parietal cells after injection of diazo‐oxo‐norleucine
Authors: Michaels John E.
Published: February 2005

After treatment with various chemical and physical agents, flattened or ring‐like saccules may occur in the cytoplasm of parietal cells of the gastric glands of several species of mammals. In the current investigation, similar structures appeared after treatment with high dosages of diazo‐oxo‐nor‐leucine (DON), a glutamine antagonist. A tentative sequence for their formation is suggested. Saccules formed of unit membrane became abundant in some parietal cells of the treated mice. Single saccules often had narrow lumens and peripheral distensions. The saccules, either singular or several stacked together, became progressively more curved, enclosing a region of cytoplasm that often contained glycogen‐like particles and occasionally vesicles or other organelles. Many of the concentric saccules were close to an intracellular canaliculus. Membrane bound cytoplasm containing glycogen‐like particles occasionally occurred in the canaliculi, suggesting that exocytosis had occurred. Cytochemistry revealed that glycoproteins were associated with the concentric saccules, probably located on the luminal surface. The glycogen‐like particles in all locations stained in a manner characteristic of glycogen. It is suggested that the concentric saccules may form from, vesicles of the tubulovesicular system.
Cell death during detachment of the lens rudiment from ectoderm in the chick embryo
Authors: Garcia‐Porrero J. A. , Colladoand J. A. , Ojeda J. L.
Published: February 2005

The distribution and cytological characters of physiological cell death associated with formation of the lens vesicle in the chick embryo was studied by means of vital staining, light and electron microscopy.

We have established a constant pattern of cell death which differs in some aspects from that reported for mammals and amphibians. The necrotic process is observed initially in the dorsal part of the lens cup (stage 15). The necrotic area progressively surrounds the lens pore as invagination proceeds (stage 16) and at stage 17 is located in the zone of fusion of the invaginated lens. After detachment of the lens (stages 18, 19 and 20) dead cells appear in the ectoderm, in the superficial epithelium of the lens vesicle and in the space between both structures.

Ultrastructurally we observe isolated dead cells in different stages of degeneration and in phagocytosed cells. Phagocytosis is carried out by the neighboring healthy epithelial cells. Phagocytic activity was detected concomitant with the beginning of the necrotic process. Cell fragments were occasionally detected within the lens cavity.
The cellular pattern of corpus luteal growth during pregnancy in the rat
Authors: Meyer Geoffrey T. , Bruce Neville W.
Published: February 2005

The cellular pattern of corpus luteal (CL) growth was studied in rats at Days 6, 10, 12, 14, 16, 17 and 22 of pregnancy: term is Day 23. Measurements were taken of the percentage of the CL occupied by luteal cells, connective tissue and vascular space, luteal cell and nuclear volumes, and the number of luteal and endothelial cells in each of three CL in both ovaries of five rats at each stage of pregnancy. Total CL volume increased from 1.08‐3.23 μl over Days 10‐17. This was mainly due to an increase in luteal cell volume from 3.72 pl to 9.30 pl. Neither the number of luteal cells per CL (range 212,000‐287,000) nor the percentage of the CL occupied by luteal cells (range 85‐90%) had much influence on growth. Nuclear volume increased roughly in proportion to cytoplasmic volume but near term it decreased despite little change in cytoplasmic volume. The number of endothelial cells per CL increased steadily from 398,000 at Day 6 to 1,545,000 at Day 22. There was a strong negative correlation (r = −0.78) between the number of luteal cells per CL and mean luteal cell volume that was evident at all stages of pregnancy. There was a positive, but weaker correlation (r = 0.35) between number of luteal cells and CL volume. Thus, CL volume seems to be partly determined by the number of luteal cells at Day 6 but this effect is moderated by local control of luteal cell volume.
Distribution of glycogen in prefusion human palatal epithelium
Authors: Meller Samuel M. , Barton Lorraine H.
Published: February 2005

Various stages of embryonic human secondary palatal development were examined for the presence of epithelial glycogen. Utilizing periodic acid‐Schiff's reagent staining of thich plastic sections and osmium ferrocyanide enhancement of thin sections, dramatic changes in epithelial glycogen distribution were noted during palatogenesis. Prior to fusion, the epithelium destined to adhere in the midline exhibited a marked diminution of glycogen in the superficial cell layer. This cell layer was composed of slender dense cells and cuboidal cells undergoing lysis. Adjacent nonfusing epithelium was markedly different and contained large glycogen reserves in its superficial cell layer. Glycogen may play a role either as precursor for specific adhesive macromolecules or as a physical agent capable under the influence of appropriate enzymes of causing cell lysis.
Scanning electron microscopy of frozen sections: A method for studying selected planes in small specimens
Authors: Carri Nestor , Suburo Angela
Published: February 2005

A procedure for studying small biological specimens with the SEM, using frozen sections of fixed material is described. Controlled fixation schedules and convenient handling of sections insure optimal preservation of cell shape and size. The greatest advantage of the method presented is to allow scanning through any desired plane of the specimen, even in those planes parallel to an epithelial face. SEM of frozen sections is thus helpful for the study of cell distribution and organization within a tissue.
Degeneration of mouse oocytes in response to polycyclic aromatic hydrocarbons
Authors: Gulyas Bela J. , Mattison Donald R.
Published: February 2005

Destruction of mouse oocytes in primordial and small primary follicles in response to treatment with 3‐methylcholanthrene (MC) was studied at the ultrastructural level. Four‐week old C57Bl/6N (B6) strain mice received a single injection of 80 mg/Kg MC in corn oil intraperitoneally. Controls received only corn oil. Ovaries from animals were prepared for light and electron microscopic examination at specified intervals after treatment. The number of primordial follicles remained constant in control animals. In contrast, their number decreased significantly (P < 0.01) by three days, and they were depleted by seven days after MC treatment. Subtle degenerative modifications were noted in the ooplasm of primordial follicles two days after treatment. These changes consisted of vesiculation of mitochondrial cristae, increased electron density of the mitochondrial matrix, myelin structures in lipid droplets and in mitochondria. More advanced stages of degeneration of primordial follicles were characterized by further vesiculation or disappearance of mitochondrial cristae, chromatin clumping, and increased density of the ooplasm. Small primary follicles had undergone similar initial degeneration as primordial follicles. In more advanced stages of degeneration nuclear and cytoplasmic contents condensed, endoplasmic reticulum, Golgi complex and mitochondria swelled, small vesicles and multivesicular bodies appeared. In the most advanced stages of degeneration of small primary follicles it appeared that small portions of the oocyte were engulfed by the surrounding follicular cells. It is concluded that exposure of B6 mice to a single dose of MC results in atresia of oocytes in primordial and small primary follicles. Ultrastructurally, these degenerating oocytes of treated mice looked much like the spontaneously atretic oocytes in untreated animals.
Scanning electron microscopy of bronchiolar neuroepithelial bodies in neonatal mouse lungs
Authors: Hung Kuen‐Shan , Chapman Albert L. , Mestemacher Michelle A.
Published: February 2005

Scanning electron microscopy of the bronchiolar neuroepithelial bodies (NEB's) in the neonatal mouse lungs was undertaken and correlated with the accompanying transmission electron microscopy. The NEB's appeared as isolated organoids along the entire length of the bronchioles, and often were located at the branching points. The boundary of the NEB's was outlined by the ciliated and Clara cells. Both granulated cells and modified Clara cells participated in the formation of the NEB. The modified Clara cells covered most of the surface of the NEB leaving only small oval areas for the exposed surfaces of the specialized cells which contained numerous cytoplasmic granules. Short and regular microvilli projected from the exposed surfaces of the granulated cells, while only sparse microvilli of irregular length were seen on the surfaces of the modified Clara cells.

This scanning electron microscopy of the NEB's further established these organoids as separate morphological entities. In addition, the findings that the NEB's could be easily identified with the scanning electron microscope and subsequently dissected out for further studies would help future investigations of their functions which are not clearly known.
Intraepidermal cell surface fine structure: Preservation and examination at high resolution
Authors: Lempert Todd E. , Elias Peter M.
Published: February 2005

Morphological and functional studies on cell surfaces have been limited largely to cultured cells because of injury wrought to cells of solid tissues by commonly employed mechanical, enzymatic, or chelator dispersal methods. By using the staphylococcal epidermolytic toxin we avoided this problem; the toxin cleaves the intercellular spaces of human and mouse squamous epithelia without ultrastructural evidence of cytotoxicity. We studied the cell surface topography of neonatal mouse epidermis obtained two hours after injection of highly purified epidermolytic toxin. Immediately after sacrifice intraepithelial surfaces were exposed while the animals were immersed in fixative. Specimens were either freeze‐fractured or embedded for transmission electron microscopy, or were critical‐point‐dried prior to platinum/carbon replication for transmission and scanning electron microscopy. Replicas could be prepared for transmission electron microscopy only if they were first stabilized with parloidion and then cleaned with both bleach and 40% chromate. By using these four complementary morphological methods (freeze‐fracture, scanning electron microscopy, transmission electron microscopy of surface replicas, and standard thin sections), we could positively identify external membrane structures. The convoluted surface was studded by tenuous microvilli, scattered 15‐20 nm particles, and hemispherical desmosomal mounds. Desmosomal plaques displayed randomly arrayed 15‐20 nm globular particles comparable in distribution and density to particles observed in freeze‐fractured desmosomes, and suggesting that desmosomal integral membrane particles span the external leaflet of the plasma membrane.
Hormones and the lung. I. Thyroid hormones and glucocorticoids in lung development
Authors: Hitchcock Karen R.
Published: February 2005

It has been proposed that thyroid hormones may have a role in the regulation of lung development and the maturation of the surfactant system. The purpose of this study was to examine the effects of exogenous thyroxine (T4) on rat lung development and to investigate possible interactions of this hormone with the glucocorticoids, other hormones implicated in the regulation of lung development.

A number of different experimental protocols were utilized: T4 was administered to day 17 and 18 rat fetuses from untreated animals as well as from animals which had been adrenalectomized or treated with the 11‐β‐hydroxylase inhibitor, Metopirone; replacement hydrocortisone was administered to some groups. Sham‐operated and untreated animals were included as controls. Animals were sacrificed from days 19‐22 (term, day 22‐23) of gestation and the fetal lungs were examined. Accelerated lung development was observed in all experimental groups receiving T4. Alveolar epithelial cells were more differentiated in comparison to controls. Glycogen deposits were diminished, cell flattening was more advanced, mitochondria, Golgi complexes and rough endoplasmic reticulum were more prominent, and lamellar bodies, storage sites for pulmonary surfactant, were greatly increased in number. Secretion of lamellar bodies into the alveolar space was also stimulated. The results also indicated that T4 and glucocorticoids act together in the acceleration of lung development. Under conditions of decreased glucocorticoids (Metopirone treatment and adrenalectomy), stimulatory effects of T4 were still evident but less pronounced; hydrocortisone replacement increased the observed stimulation. Maximal acceleration of lung development was observed subsequent to T4 and uncontrolled surgical stress. These results demonstrate that T4 can accelerate rat lung development and that this acceleration is maximal in the presence of glucocorticoids.
Survey of the morphology of the dog kidney
Authors: Bulger Ruth Ellen , Cronin Robert E. , Dobyan Dennis C.
Published: February 2005

Dogs are frequent subjects in experimental studies of renal physiology and pathology in spite of the paucity of information on their normal renal morphology. In this study, gross morphology, light microscopy, and scanning and transmission electron microscopy were used to describe dog renal anatomy. The dog has a multilobed kidney with the medulla fused into an elongate crest and a renal pelvis of elaborate shape. The outer zone of the medulla lacks a definitive outer stripe. The proximal tubule consists of four distinct anatomical segments. Dark cells are abundant in the collecting duct of the inner medulla. The majority of the nephron segments demonstrate remarkable similarities to those of the human kidney and less to those of the kidney of the laboratory rat.
Ependymal changes in experimental hydrocephalus
Authors: Page Robert B. , Rosenstein Jeffrey M. , Dovey Barbara J. , Leure‐Dupree Alphonse E.
Published: February 2005

A morphologic investigation of ependyma over gray matter (caudate nucleus) and over periventricular white matter (tapetum) of the rabbit lateral ventricle was performed four months after the induction of experimental hydrocephalus. Ependymal cells over the caudate nucleus are not modified by hydrocephalus. They remain cuboidal and heavily ciliated. Numerous microvilli cover the cell surface. The extracellular space of the neuropil is not expanded. Ependymal cells over the periventricular white matter are markedly modified. The characteristic response of these ependymal cells is to enlarge and to form lacunae in their apical cytoplasm. Their apical, horizontal cytoplasmic processes elongate as adjacent ependymal cells separate. The ex‐tracellular space of the neuropil is expanded.

It is proposed that the changes seen in ependymal cells over periventricular white matter are a response to enlargement of the ventricular surface permitted by the orientation of neuronal and glial fibers parallel to the ventricular surface. With expansion of the ventricular surface, overlapping apical processes become elongated and modified, containing a terminal web. With further enlargement, sliding of an overlapping apical process of one cell uncovers the apical process of its neighboring cell. By this mechanism, the ventricular surface area of any ependymal cell whose surface has been partially covered by its neighbor is increased. With further progression, this compensation fails and the neuropil is exposed to the ventricular cavity.

Over caudate nucleus, expansion of ventricular surface is hindered by the disposition of fascie adherentes along intercellular clefts oriented perpendicular to the ventricular surface. Lateral sliding of horizontal apical processes does not occur as such processes are not found in ependyma over the caudate nucleus.

The differential response of the ventricular surface in these two areas characteristically seen in hydrocephalus is; determined by regional differences in the morphology of their ependymal cells and underlying neuropil.
The innervation of the mouse adrenal cortex
Authors: Migally Nabil
Published: February 2005

The fine structure of the mouse adrenal cortex was examined with the electron microscope for the presence of neural elements. Several axon terminals containing mostly clear vesicles (60 nm) were noted in the vicinity (250 nm) of the capsular fibroblasts. In the subcapsular region, myelinated as well as unmyelinated fibers were commonly found. Preterminal and terminal axons were also found in close relationship to the parenchymal cells in the zona glomerulosa. Nerve bundles were the most common neural elements in the zona fasciculata. In the zona reticularis axon terminals containing both clear (60 nm) and dense core (120 nm) vesicles were seen in close proximity (30 nm) to parenchymal cells. Although this study did not delineate the type of fibers involved, the axon terminals resemble those of autonomic nerves.

This study demonstrates innervation of the mouse adrenal cortex, thus corroborating similar reports by others in different species.
Fine structural differentiation of germ layers in the mouse at the time of mesoderm formation
Authors: Batten Bruce E. , Haar Jack L.
Published: February 2005

The morphology of early postimplantation mouse egg cylinders was studied using light and electron microscopy. Implantation sites at seven, seven and one‐half and eight days of gestation were dissected from the myometrium and whole implants, including both decidua and egg cylinders were processed for electron microscopy. Pre‐primitive streak egg cylinders were composed of two germ layers, a tall columnar ectoderm and an outer visceral endodermal layer. Ectodermal cells demonstrated large oval nuclei and an organelle sparse cytoplasm except for many free polyribosomes. The visceral endodermal layer was composed of two cell populations. One visceral endodermal cell type observed was tall columnar in shape and appeared absorptive as demonstrated by many microvilli, pinocytotic profiles and lysosomal granules. This population was confined to extraembryonic regions of the egg cylinder. The second visceral endodermal cell type, squamous in shape, evidenced only a few microvilli, pinocytotic profiles and lysosomal granules. This population was confined to the embryonic region of the egg cylinder. Concurrent with the formation of the primitive streak an increased number of cellular junctions and nuclear pores became evident in the ectoderm. Mesodermal cells were large and stellate‐shaped exhibiting many filapodia which made contact with adjacent mesodermal elements. Later the cephalic region of the primitive streak proliferated resulting in the migration of wedge‐shaped mass of cells, the head process. At the most ventral extremity of the post‐primitive streak egg cylinder the cells of the head process became intimately associated with the ectoderm by areas of focal contact and gap junctions.
Morphology of the perforating cartilage canals in the proximal tibial growth plate of the chick
Authors: Hunt Curtiss D. , Ollerich Dwayne A. , Nielsen Forrest H.
Published: February 2005

Perforating canals arise exclusively from junctional canals just above the reserve zone and they do not branch after entering the proliferative zone. They are uniformly spaced and arranged in parallel array. The cartilage canals terminate near the beginning of the zone of hypertrophic cartilage cells. Vascular components within the perforating canals consist of a central arteriole surrounded by enlarged, interconnected capillaries which are individually in contact with the adjacent cartilage matrix. TEM shows that the capillary endothelium is extremely attenuated, possesses numerous fenestrations and lacks a continuous basement membrane. The central arteriole is enlarged through the midpart of the canal and then narrows to communicate with the capillaries near the bottom of the canal. The large capillaries ascend from their point of origin and recombine near the top of the growth plate to exit as a single venule. The vascular arrangement therefore describes a system in which the outgoing blood runs in close proximity, but counter to, the incoming blood. This vascular arrangement within the perforating cartilage canal would most likely allow the zone of maturing cartilage cells to receive the highest concentration of nutrients.
Fine structural studies of the rat vas deferens
Authors: Kennedy Samuel W. , Heidger Paul M.
Published: February 2005

A fine structural study of the normal rat vas deferens was undertaken utilizing perfusion fixation. Morphological features not previously appreciated were revealed using this technique of fixation, and included the following.

The rat vas deferens exhibited a gross morphological and microscopic differentiation along its length: A proximal segment was characterized by a thin muscular wall, an epithelium of low height (comparable to that of the cauda epididymidis) and a distended lumen typically filled with an accumulation of sperm; a distal segment exhibited a thick muscular wall, a convoluted mucosa, and a pseudostratified columnar epithelium with long stereocilia extending into the lumen. The transition from the morphology typical of the proximal segment to that of the distal segment was gradual and progressive, marked by an increase in the mass of the muscular wall and in the height and ultrastructural complexity of the epithelium. Clear or “foamy” cells, characteristic of the cauda epididymidis, were observed in the initial centimeter of the vas deferens. Also, a cell type designated as “mitochondrion‐rich” was observed in the distal vas segment. The structure of the small mitochondria in such cells, however, did not conform to the description of mitochondria in similar cells found in the human (Hoffer, '76). Intraepithelial macrophages containing residual accumulations which often resembled spermatozoan remnants in advanced stages of dissolution were present in all segments of the rat vas deferens, confirming in this species a spermiophagic role for such cells.
Transventricular blood vessels in the third ventricle of the armadillo brain
Authors: Ives Phillip Jay , McArthur Newell H.
Published: February 2005

Transventricular filaments were observed with scanning electron microscopy on the dorsolateral wall of the infundibular recess of the third ventricle of the armadillo brain. Two to seven transventricular filaments per animal were present in 6 of 18 animals. There were two types of transventricular filaments, ciliated and bare. Using transmission electron microscopy, we determined that these filaments consisted of a single, central capillary surrounded by ciliated ependymal cells and a small accumulation of axons in five animals. In one animal, a bare filament had a central capillary surrounded by a large accumulation of axons with no surrounding ependyma. The consistent location and structure of these filaments indicate a possible function for a small vascular network, as well as a possible commissural network connecting right and left hypothalami in the region of infundibular nuclei.
Morphology of osteoclasts in resorbing fetal rat bone explants: Effects of PTH and AIF in vitro
Authors: Wezeman Frederick H. , Kuettner Klaus E. , Horton John E.
Published: February 2005

Osteoclastic bone resorption was studied using 45Ca‐labeled fetal rat bones cultured in the presence of parathyroid hormone (PTH) and an anti‐invasion factor (AIF) derived from bovine hyaline cartilage which is enriched in a collagenase inhibitor. The specific morphological expressions of osteoclasts cultured in PTH and AIF were observed in both light and electron microscopy and analyzed cytometrically. Stimulation of bone resorption with PTH revealed significant increases in the numbers and activity of osteoclasts, whereas bones cultured in the presence of AIF showed significant decreases in numbers of osteoclasts and altered cell features including the loss of osteoclast contact with bone surfaces. These structural modifications were evaluated with 45Ca release data derived from matched‐pair explants of fetal rat bones, revealing the existence of a relationship between resorptive states of the cultured bones and morphological expressions of osteoclastic activity.
The choroid plexus of the mature and aging rat: The choroidal epithelium
Authors: Peters Alan , Swan Roy C.
Published: February 2005

The choroid plexus of mature and old rats has been examined by both scanning and transmission electron microscopy. It has been shown that the macrophages lying upon the ventricular surface of the choroid plexus have a close association with burr‐like protrusions that extend from the apical surfaces of the choroidal epithelial cells. These protrusions have a dark cytoplasm filled with vesicles and tubules, and projecting from them are thin, shrunken microvilli. It is suggested that these protrusions are phagocytosed by the macrophages and that they are the source of some of the inclusions which become increasingly common within the cytoplasm of macrophages in older rats. The lateral surfaces of the choroidal epithelial cells have also been examined in the scanning electron microscope after exposure of the surfaces by dissection. In such preparations it is apparent that the elaborate interdigitations between adjacent cells are effected by irregular and vertically arranged folds confined to the basal portions of the lateral cell surfaces. Lastly, it has been shown that at the junction between the choroid plexus and the ependyma in the lateral ventricle, there are two modes of transition between the choroidal and ependymal epithelia. In one, typical choroidal and ependymal epithelial cells lie next to each other to produce a distinct and continuous boundary. In the other mode the boundary is also continuous, but there are modified ependymal cells present. These modified cells have short, relatively sparsely distributed microvilli and not more than one or two cilia.