bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrastructural observations on rabbit, hamster and mouse eggs following electrical stimulation in vitro
Authors: Gulyas Bela J.
Published: February 2005

The fine structural changes were studied in the plasma membrane, cortical granules (CGs) and meiotic spindle of rabbit, hamster and mouse eggs in response to electrical stimulation. Eggs were collected 16 to 18 hours after HCG injection, and freed from the cumulus oophorus. They were stimulated in vitro by delivering a single monophasic square wave pulse of 150 V for 1 msec. Stimulated and unstimulated eggs were fixed for fine structural observations 1, 30 and 60 minutes after stimulation. Within one minute of stimulation the microvilli of rabbit eggs were long, branching and had bulbous ends. Umbonate protrusions were also present on their surface. By 30 minutes after stimulation the rabbit eggs lacked microvilli and the perivitelline space was filled with detached vesicles. Degenerating changes were readily noticeable in the microvilli of hamster eggs by 60 minutes. Changes were not noted in the microvilli of stimulated mouse eggs. There were markedly fewer CGs in the hamster and mouse, but not rabbit, eggs by 30 minutes after stimulation, and nearly all of them disappeared in the mouse and hamster eggs by 60 minutes. The density of the CGs in the rabbit was not altered. The meiotic spindle of hamster eggs dissipated within one minute of stimulation, however, the microtubules reappeared by 60 minutes after stimulation. Rotation of the meiotic spindle occurred in the mouse and hamster eggs by 30 minutes after stimulation. In some of the mouse eggs the spindle migrated to the center and the chromosomes were in telophase.
Tight and gap junctions in a vertebrate inner ear
Authors: Nadol Joseph B. , Mulroy Michael J. , Goodenough Daniel A. , Weiss Thomas F.
Published: February 2005

The auditory organ of the alligator lizard has been investigated with the transmission electron microscope using methods which distinguish between tight and gap junctions. There is a continuous zone of tight junctions located near the endolymphatic surface of the organ forming a boundary between the endolymph in scala media and the interstitial spaces between the cells. No such tight junctions were observed between the perilymph of scala tympani and the interstitial fluid within the organ. Small gap junctions occur between hair cells and supporting cells and large gap junctions occur between adjacent supporting cells. The locations of the tight junctions suggest that the composition of the intercellular fluid in the receptor organ is probably more like perilymph than like endolymph. The presence of gap junctions between hair cells and supporting cells provides a possible morphological basis for the occurrence of intracellular responses to sound in supporting cells, and for electric coupling of receptor cells.
The histological structure of dog knee menisci with comments on its possible significance
Authors: O'Connor Brian L.
Published: February 2005

Knee‐joint menisci are poorly understood terminologically, structurally and functionally in spite of their almost universal occurrence in mammals and their considerable clinical significance in man. A study was therefore undertaken of dog knee menisci utilizing several histological techniques.

Terminologically, it is proposed that the part of the meniscus extending between the anterior and posterior horns and exclusive of them be called the meniscal “body.”

Structurally, the horns and body differ in a number of ways. The horns are oval in cross section, the body triangular. Hyalinized areas are much more frequent in the body than in the horns. The collagen of the horns is organized into discrete bundles that are separated from one another by loose connective tissue septa, while that of the body is arranged in a “herringbone” pattern; no septa are present in the body. Finally, the meniscal horns are richly supplied with blood vessels and nerves (including large myelinated fibers which apparently terminate in the horns) while the body is almost completely devoid of blood vessels and nerves.

Functionally, it is hypothesized that knee‐joint menisci may serve important sensory functions.
Development of the octopus cell area in the cat ventral cochlear nucleus
Authors: Schwartz Ann Marie , Kane Eileen S.
Published: February 2005

The octopus cell area (OCA) of the posteroventral cochlear nucleus was studied electron microscopically in kittens. The adult OCA, a region of morphologically homogenous neurons receiving heterotypic synapses from the cochlea, was used to define the mature state. The OCA reaches cytological maturity at three weeks postnatally, after progression through four stages, defined on the basis of octopus cell cytology (including relative numbers of somatic and dendritic filopodia and spines) and the frequency, ultrastructure and location of previously defined synaptic terminals. Octopus cell size was also studied in rapid Golgi impregnations. The OCA from birth through three postnatal days (stage 1) showed small neurons, few identifiable synaptic types, small, mostly unmyelinated axons, mitotic cells and undifferentiated glia. Between the fourth and seventh postnatal days (stage 2) distinct type 1 and type 2 endings appeared and dendrites thickened, expanded peripherally and developed mature spines. During stage 3 (8–19 days) loss of filopodia, increased somatic spicules, larger somas and clearer differentiation of type 1 and type 2 synapses occurred. After three postnatal weeks (stage 4) the OCA contained morphologically mature octopus cell somas, all three synaptic types ending upon somas and thick basal dendrites, and fascicles of myelinated fibers. Although cytologically mature, the OCA at this stage (about 20–35 days) is substantially smaller than the adult OCA. This smaller size will facilitate further study of OCA synaptic organization.
Disposition of 14C‐nicotine in the fertilized chick egg
Authors: Di Carlo Frederick J. , Gilani Shamshad H.
Published: February 2005

14C‐Nicotine·HCl (4.5 mg) was injected into the air space of chick eggs after one day of incubation and the distribution of radioactivity measured on days 3, 5, 7 and 12. By day 3, 98% of the dose had passed from the air space into the egg, proper. The quantity of nicotine in the yolk was highest on day 3 (74% of dose) and decreased steadily until day 12 (52%). The quantity in the albumen increased from 16% on day 3 to a maximum on day 7 and remained constant at 34% until day 12. The embryo contained 0.03% of the nicotine on day 3, and this level increased to 5% by day 12. Nicotine in the allantois increased throughout the study period (0.01% on day 3 to 3% on day 12). Although only 5% of the dose was present in the embryo, the highest concentrations of nicotine observed were in the heart, liver and carcass. The concentrations within these components of the embryo ranged from a minimum of 0.85 μg nicotine/mg dry wt in the heart to a maximum of 2.00 μg nicotine/mg dry wt in the carcass. These levels within the embryo were two to five times higher than the greatest concentrations in the yolk and albumen. The dynamics of nicotine passage from the air space into other components of the fertilized chick egg were clarified. Whereas the conventional expression of teratogenic doses of drugs in chick eggs (i.e., ppm of egg weight) assumes that the compound is distributed uniformaly, this study indicates that such expressions are inaccurate.
Ultrastructure of pericytes in mouse heart
Authors: Forbes M. S. , Rennels M. L. , Nelson E.
Published: February 2005

The pericytes of mouse myocardium are extensively branched cells that forma an incomplete layer around the endothelium of capillaries and postcapillary venules. The membranes of pericytes and endothelial cells are conected by specialized junctions. Microtubules, intermediate (10‐nm) filaments and microfilaments are oriented within circumferentially‐arranged cytoplasmic processes of pericytes so as partially to encircle the endothelial cylinder. The intracellular organization of these myocardial pericytes suggests that they are smoth muscle‐like cells which may be capable of influencing microvascular dynamics in the heart.
Movement of the hyoid in frogs during feeding
Authors: Emerson Sharon B.
Published: February 2005

Feeding, breathing, and vocalization sequences of Bufo marinus were recorded by cineradiography. Results of film analysis indicate that the hyoid moves during all three behaviors. Movement of the hyoid is critical in tongue protrusion of frogs, and a biomechanical model of this action is presented. The hyoid appears to represent a compromise morphological system for three functions, rather than an optimal system for any one. This may explain, in part, the retention of a relatively inefficient breathing mechanism in frogs.
The predominance of binucleation in isolated rat heart myocytes
Authors: Katzberg Allen A. , Farmer Barbara B. , Harris Robert A.
Published: February 2005

Myocytes of the heart of the newborn rat are mononucleated, whereas myocytes of the heart of growing, maturing rats become predominantly binucleated. This appears to be explained by mitotic division shortly after birth without cell division, i.e., karyokinesis without cytokinesis. Myocytes isolated from hearts of adult guinea pig and pigeon are also predominantly binucleated. Although only about an eighth of the cells of adult rat hearts are myocytes, most of the increase in size of the heart from birth to six months can be accounted for by change in size of these cells.
Fusion of nasal swellings in the mouse embryo: Regression of the nasal fin
Authors: Gaare John D. , Langman Jan
Published: February 2005

The nasal fin is an epithelial seam that develops by fusion between the epithelial linings of the medial and lateral nasal swellings. Shortly after its formation the nasal fin regresses and is replaced by mesenchyme, with exception of its most posterior portion which remains as the bucconasal membrane. Since the regression of the nasal fin plays an important role in the formation of the upper lip and primary palate, the breakdown of the fin was examined with the electron microscope in 12‐day‐old mouse embryos.

Shortly before the epithelial linings of the opposing nasal swellings make contact, cell degeneration characterized by condensation and fragmentation occurs in the epithelial linings of the prospective fusion areas. Apparently direct contact between the nasal swellings is not necessary to cause cell death.

After fusion has established the nasal fin, epithelial cells continue to degenerate by condensation and fragmentation. Cell degeneration, however, can not account for complete regression of the fin, since many morphologically healthy epithelial cells are always present. Since no indication was found that the surviving epithelial cells transform into mesenchymal cells, it is suggested that they are incorporated into the adjacent epithelial linings of the expanding primitive nasal and oral cavities.

The extracellular dense bodies that result from degenerating cells are engulfed by neighboring epithelial cells, in which they form phagocytic vacuoles. Some of these epithelial cells containing numerous cytoplasmic vacuoles appear to transform into large round macrophages.

When the acid phosphatase procedure was applied, many heterophagic vacuoles contained a black precipitate, indicating that, after being phagocytosed, the dense fragments are digested by lysosomal enzymes. A similar black precipitate appeared over autophagic vacuoles.
A freeze‐fracture study of the topographic relationship between inner enamel‐secretory ameloblasts in the rat incisor
Authors: Warshawsky H.
Published: February 2005

A correlated study using freeze‐fracture replicas and routine thin sectioning was done on the ameloblasts which secrete inner enamel in the rat incisor. These ameloblasts are columnar cells aligned in rows parallel to the cross‐sectional plane of the incisor. Each cell has a Tomes' process at its distal end which is contained within a cavity of interrod enamel. Tomes' processes of a particular row of cells are inclined towards the mesial side of the tooth, while those of the next row are inclined towards the lateral side, so that the processes cross each other at 90°. Freeze‐fracture replicas were used to examine the surfaces of ameloblasts between adjacent rows and the surfaces of the cells within the row. Replicas of the surfaces between rows showed that ameloblasts are curved so that their proximal and distal ends (Tomes' processes) are both directed towards the same side of the tooth. The surface of each row bears the impression left upon it by the cells in the adjacent row which have been fractured away. This cell‐impression is also curved, but in the opposite direction to the cells which it crosses. It was thus shown that not only the Tomes' processes of adjacent rows but the entire cell bodies cross one another. This crossing is slight at the proximal ends of the cells, but marked at the level of the distal junctional complex. At this level a cell from a particular row curves across several cells of the neighbouring row and forms large tight junctions with at least two cells in that row. The proximal and distal junctional complexes form zones of tight junctions around the cell. The distal complex is more extensive than the proximal and the tight junctions are better developed between adjacent rows. Gap junctions are, however, larger between cells within the rows. The study demonstrated the effectiveness of freeze‐fracture replicas in obtaining 3‐dimensional details about ameloblast shape, and this information was used to evaluate the supposed movement of ameloblasts during inner enamel formation.
Myology of the shoulder of Pontoporia blainvillei, including a review of the literature on shoulder morphology in the cetacea
Authors: Strickler Timothy L.
Published: February 2005

The purpose of this paper is to describe in detail the shoulder myology of the La Plata River Dolphin, Pontoporia blainvillei, and to review the literature on cetacean shoulder myology. Three fetal and one adult animal were used for the collection of morphological information. Pontoporia is less specialized in its shoulder anatomy that most delphinid cetaceans, and shares several characteristics with some mysticetes. The omohyoid and anterior serratus anterior muscles are found in both Pontoporia and the mysticete Balaenoptera, but are absent in most delphinids. The pectoralis abdominalis and three rhomboideus divisions are found in Pontoporia and Kogia, but in only a few delphinid species described in the literature. It is suggested that these characteristics are associated with a generalized use of the forelimb in Pontoporia.
Ultrastructural differences in efferent ducts and several regions of the epididymis of the hamster
Authors: Flickinger Charles J. , Howards Stuart S. , English H. F.
Published: February 2005

The ultrastructure of the hamster efferent ducts and epididymis was studied and the results were correlated with previously published data on the composition of luminal fluid obtained by micropuncture. Samples of the efferent ducts and parts of the epididymis designated initial segment, caput, corpus, proximal cauda, distal cauda, and “epididymal vas” were prepared. The efferent ducts contained principal cells characterized by a profusion of apical vesicles and numerous very large vacuoles that were distributed throughout the cytoplasm. Ciliated cells had few vesicles and vacuoles. Occasional cells contained many particles resembling glycogen. In the epididymis, the following trends were observed. The height of the epithelium and the size of the principal cells declined from initial segment to distal cauda. Apical vesicles and vacuoles with a light content were extremely numerous in principal cells of the initial segment and decreased progressively in the more distal regions. In the initial segment, basal and perinuclear rough endoplasmic reticulum was abundant and was distended with a material that resembled newly synthesized protein. Further distally in the epididymis cisternae of the rough endoplasmic reticulum were narrow and contained little intracisternal material. Light cells containing many vesicles, vacuoles, and lysosome‐like structures were very prominent in the caudal segments. The epithelium of the epididymal vas had features intermediate between cauda epididymidis and ductus deferens. The cytoplasmic droplet in luminal sperm began to migrate caudally between the caput and corpus epididymidis and reached the posterior extremity of the middle piece in the distal cauda. Some degenerating sperm were observed in the lumen of the distal segments of the epididymis.

The abundance of cytoplasmic vesicles and vacuoles in principal cells of the efferent ducts and initial segment of the epididymis correlated with the site of greatest fluid absorption as determined by micropuncture studies, suggesting that these structures are involved in absorption of fluid from the lumen. Between the caput and distal cauda epididymal segments, where absorption of sodium and potassium but not of fluid occurred, there were few vesicles and vacuoles in principal cells, but the “light” cells were large and numerous and contained many vacuoles. The principal cells of the initial segment were best equipped with rough endoplasmic reticulum to synthesize a protein.
Effects of estrogen on human seminiferous tubules: Light and electron microscopic analysis
Authors: Lu Cheryle C. , Steinberger Anna
Published: February 2005

Morphological features of testes from four subjects after longterm treatment with ethinyl‐estradiol (1–2 mg daily) and from five non‐treated patients with prostatic carcinoma were studied by means of light and electron microscopy. The non‐treated seminiferous tubules contained spermatogonia, spermatocytes, spermatids, spermatozoa, and Sertoli cells and showed no apparent morphologic abnormalities. On the other hand, the estrogen‐treated testicular tissue contained only Sertoli cells and very few spermatogonia within the seminiferous tubules. The nuclei of Sertoli cells occasionally contained two nucleoli. The nucleolar complex was composed of a fine granular spherical body surrounded by a large granular, reticular network. The cytoplasm of the Sertoli cell contained osmiophilic lipid‐like bodies. These lipid‐like bodies appeared more pronounced in patients treated with higher doses of estrogen, suggesting a diminution of secretion of Sertoli cell hormone. Blebbing from the outer nuclear membrane appeared to have formed numerous vesicles in the cytoplasm. These vesicles usually contained several membrane‐bound granular bodies. In the estrogen‐treated testes, there was a marked increase in thickness and infolding of the basement membrane. Two unusual patterns of the basement membrane were observed: one appeared to be a reticular anastomosis, the other, an electron‐dense trilayer. The morphological picture of seminiferous tubules from the estrogen‐treated subjects appeared to correlate well with the suppressed plasma and testicular levels of testosterone, the undetectable circulating gonadotrophins, and the elevated plasma and testicular levels of estradiol‐17β reported by Rodriguez‐Rigau et al. (1977).
Induced ovulation, development of the corpus luteum, and tubal transport in the striped skunk (Mephitis mephitis)
Authors: Wade‐Smith Julia , Richmond Milo E.
Published: February 2005

Ovulatory pattern, development of the corpus luteum (CL), and early tubal transport are described for 6 unmated and 19 mated striped skunks (Mephitis mephitis) killed after known copulation times. Ovulation is induced by copulation and occurs around 42 hours (range = 40–50 hours) after first insemination. Seventeen of 19 females killed between 36 hours and 19 days postcoitus had ovulated. Two females killed at 36 hours had not ovulated; however, their follicles showed preovulatory changes and were significantly larger (p < 0.01) than those of unmated females. Six unmated females, killed during and three weeks after the normal breeding season, had not ovulated. Ovarian events, such as preovulatory changes, ovulation, and development of the corpus luteum (CL), are described for animals killed 36 hours to 19 days post‐coitus. Maximum CL size occurred at 11 days post‐coitus and coincided with the onset of embryonic migration and enlargement. Embryonic development reflected individual variation in ovulation times. The first polar body was extruded at ovulation and the second at fertilization. Pronuclear stages were predominant at 42 to 48 hours and 3 to 8‐cell stages at 72 to 96 hours; morulae (containing up to 95 cells) entered the uterus at seven days. Blastocysts were observed first at 11 days when embryonic spacing and enlargement began. Implantation occurred by 19 days.
The role of lymphoid cells in bone resorption: Cellular immunological competence in ia rats
Authors: Schneider Gary B.
Published: February 2005

The ia (incisors absent) rat is a naturally occurring mutant that has osteopetrosis resulting from reduced bone resorption. A number of in vestigators have reported that other osteopetrotic mutant rats (op) and mice (mi and op), in addition to demonstrating the skeletal manifestations of the disease, have cellular immunological defects. In light of the fact that bone resorption has been demonstrated to be controlled by hematopoietic tissues and more specifically by mononuclear cells isolated from lymphoid organs, it seemed appropriate to investigate immunological competence in the ia rat, to determine whether or not it had this defect in common with the op rat.

Contrary to the results presented for other osteopetrotic mutants, we found that the thymuses in our ia mutants had a normal cellular composition and the T‐cell‐dependent zones in the lymph nodes were not deficient in lymphocytes. Therefore, this study was undertaken to investigate the response of ia rats to oxazolone, which produces one type of T‐cell‐dependent immune response, delayed hypersensitivity.

The results of these studies indicate that ia rats at 18 days of age have the ability to develop delayed hypersensitivity, as shown by both a blastogenic response in the lymph node draining the site of sensitization and a positive skintest. The magnitudes of these responses were similar in ia and normal littermates, both histologically and quantitatively. Therefore, the ia mutant does not appear to have a defect of the thymus‐dependent immune system, and further studies should be carried out to investigate other parameters of immunological competence in these animals.
Quantitative analyses of the fiber population in rat chorda tympani nerves and fungiform papillae
Authors: Farbman Albert I. , Hellekant Goran
Published: February 2005

The numbers of nerve fibers in 44 intact chorda tympani nerves (CT) from 34 rats were counted on electron micrographic montages of cross‐sections of the nerves. The mean number of fibers was 1,096, consisting of 641 myelinated and 455 unmyelinated fibers. There was no significant difference in the mean number of fibers between CT's from right and left sides, nor was there any significant difference in counts between CT segments taken from the middle ear and those taken from just proximal to the region where the CT joins the lingual nerve. The relative contribution of efferent and afferent fibers in the CT was assessed in 13 animals as follows. Intracranial surgery was performed to cut the root of the facial nerve just proximal to its entrance into the internal auditory meatus on the right side. After 19 to 21 days, to allow Wallerian degeneration of the efferent fibers, counts were made as above. The mean number of afferent fibers in the rat CT was 484 myelinated and 122 unmyelinated (606 total); the intact left CT's from the same animals contained a mean of 616 myelinated and 402 unmyelinated (1,018 total) fibers. The afferent limb of the CT, therefore, contains 79% of the total number of myelinated fibers and only 30% of the total number of unmyelinated fibers. Removal of the superior cervical sympathetic ganglion did not significantly affect the numbers of fibers. In order to determine whether the efferent limb of the CT contributes fibers to the fungiform papillae on the tongue, we compared the number of (CT) fibers in fungiform papillae from “de‐efferented” rat tongues with that from papillae of controls. In order to make this comparison, it was necessary to section the lingual nerve, which contributes about 75% of the total number of fibers to the fungiform papillae. This was done in both the control and de‐efferented animals. There was no significant difference in mean number of fibers in fungiform papillae innervated by a de‐efferented CT when compared with those innervated by an intact CT. There is, then, no evidence from these studies to suggest the presence of an efferent CT component within the fungiform papilla.
Immunoreactive β‐endorphin and acth in the same neurons of the hypothalamic arcuate nucleus in the rat
Authors: Sofroniew Michael V.
Published: February 2005

Immunoreactive ACTH and β‐endorphin (β‐End) were localized in the brain and pituitaries of normal and colchicine‐treated rats, using the immunoperoxidase method at the light microscopic level. On adjacent serial 5‐μm paraffin sections of anterior pituitaries, both ACTH and β‐End could be found in the same cells. On adjacent 5‐μm paraffin sections of brains of colchicine‐treated rats, both ACTH and β‐End could be found in the same perikarya of hypothalamic arcuate nucleus neurons. It appeared that all perikarya containing β‐End contained ACTH as well, suggesting that neurons producing β‐End also produce ACTH. Pathways of ACTH fibers corresponded to pathways of β‐End fibers. These findings suggest that the synthesis, and transport, of ACTH and β‐End are linked in the brain as well as in the pituitary, possibly through a common precursor.
A scanning electron microscope study of aberrations in the prism pattern of rat incisor inner enamel
Authors: Risnes Steinar
Published: February 2005

The prism pattern in the inner enamel of adult rat incisors was studied with the SEM in unfixed tissues that had been sectioned, ground, polished, and etched. Six different types of aberrations in the prism pattern were encountered: 1. Prism lamellae may be shorter than the mesio‐lateral width of enamel. 2. Prism lamellae may deviate from a transverse orientation. 3. Prism lamellae may “fuse” or “bifurcate.” 4. Prisms of two adjacent lamellae may pursue a common course. 5. Prisms may change direction. 6. Variations exist in the outline of transversely cut prism profiles. Aberrations were observed at any distance from the dentino‐enamel junction.

These observations were used as a basis for an analysis of the movement of ameloblasts during rat incisor amelogenesis. It was concluded that it is physically possible for the ameloblasts to create the observed aberrations as they move along the path of the prisms. However, the aberrations seem to make it more difficult to understand the factors controlling ameloblast movement. Occasionally crystallite bridges connecting adjacent prisms were observed. A configuration resembling a bifurcating prism is presented.
Lack of association between avian cartilages of different embryological origins when maintained in vitro
Authors: Fyfe David MacG , Hall Brian K.
Published: February 2005

The possibility that cartilages of differing embryological origins behave as separate types with respect to cell‐to‐cell associations was tested by placing the cut ends of transversely sectioned embryonic chick tibial cartilages (of mesodermal origin) in apposition to transversely sectioned Meckel's cartilages (a neural crest (ectodermal) cartilage) on the surface of a semi‐solid organ culture medium and maintaining the combinations in vitro for five to ten days. Tibia‐tibia and Meckel's cartilage‐Meckel's cartilage (homotypic) combinations, which served as controls, became united by a common extracellular matrix and by the proliferation of chondroblasts. Analysis of combinations where one partner had been prelabelled with 3H‐thymidine indicated that chondroblasts intermingled at the contact zone. In contrast, tibia‐Meckel's cartilage (heterotypic) combinations became separated by a layer of fibrous tissue. The chondroblasts at the contact zone failed to intermingle. We conclude that avian embryonic chondrocytes are not all equivalent and that part of their non‐equivalence could be related to their embryological origin either from the mesoderm or from the ectodermal neural crest.
Evidence that sclerotomal cells do not migrate medially during normal embryonic development of the rat
Authors: Gasser Raymond F.
Published: February 2005

During embryonic development the medial part of the somite disorganizes or breaks up into sclerotomal cells which, according to many published reports, migrate medially to surround the notochord. The purpose of the study was to determine whether these cells actually migrate medially toward the notochord. Distances were measured between the notochord and the adjacent neural tube and the somite or its remnant during the period of somite disorganization. Serially sectioned, normal 10.5‐ to 13.5‐day (d) rat embryos were used. Only transverse sections through the middle of the fourth cervical (C‐4) body segment were measured, corresponding to the level of somite No. 8 (10.5 d) or its dermatomyotome remnant (10.5–11.5 d) or spinal nerve C‐4 (12.5–13.5 d). Measurements were taken at six stages from photographic montages, all of which were made at precisely the same magnification. The notochord was the central axial structure from which the measurements were determined. The changes in distance show that during the period of somite breakup the neural tube grows dorsally, away from the notochord which lies adjacent to its ventral surface. Simultaneously the somite remnant moves laterally and dorsally, all the while maintaining its position relative to the overlying ectoderm and leaving behind a trail of sclerotomal cells.

Also at each stage cell counts were made on the medial sclerotomal region of the C‐4 segment. The average counts reveal that not only does the total number of cells increase substantially over the three‐day period (42–7,546), but also the total number of mitoses (3.5–200), while the mitotic index decreases (9.0–2.7). High proliferative activity is apparent in the medial sclerotomal cells throughout the 3‐day period. The evidence supports the conclusion that local proliferation of the trailing cells, which were left by the somite remnant as it moved dorsolaterally, causes the subsequent increase in density of the perichordal tissue, rather than an influx of migrating cells. Instead of sclerotomal cells migrating medially toward the notochord, the present study suggests that these cells retain their position relative to the notochord or central axis and that the medial sclerotomal region forms as a result of the growth movements of the surrounding structures.
Subdivision of mouse vibrissae on an embryological basis, with descriptions of variations in the number and arrangement of sinus hairs and cortical barrels in BALB/c (nu/+; nude, nu/nu) and hairless (hr/hr) strains
Authors: Yamakado Makoto , Yohro Takeshi
Published: February 2005

Development of vibrissae was studied in dd/y mouse embryos by scanning electron microscopy. Arrangement of vibrissae and cortical barrels were also studied by light microscopy in adult dd/y, BALB/c(nu/+), nude (BALB/c,nu/nu) and hairless (hr/hr) mice to find genetic or epigenetic variations. Rudiments of vibrissae first appear on Day 12 of pregnancy as longitudinal ridges on the developing muzzle, and each hair rudiment is represented by a dome on the ridges. The dorsal two rows (A and B; Woolsey and Van der Loos, 1970) of mystacial vibrissae are on the lateral nasal prominence, while the ventral three (C, D and E) are on the maxillary prominence. Smaller hairs of mystacial vibrissae appear at the labial part of the maxillary prominence on Day 13. The rudiments of rhinal hairs also appear at this stage on the part of the muzzle derived from the medial nasal prominence. Thus the so‐called mystacial vibrissae should be subdivided into three (or 4, including the rhinal) groups on an embryological basis. They are the lateral nasal, the maxillary and the labial.

A supernumerary sinus hair and a corresponding barrel was observed between B and C rows uni‐ or bilaterally in one third of individuals of BALB/c, nude and hairless mice. It is suggested that supernumerary hairs tend to occur between the groups of hairs as defined above. In nude and hairless mice small barrels representing labial hairs are diminished in number. The number of hair follicles, however, is normal.
The superior olivary complex in C57BL/6 mice
Authors: Ollo Christine , Schwartz Ilsa R.
Published: February 2005

The cellular and cytoarchitectural features of the lateral superior olive, the medial superior olive, the superior paraolivary nucleus and the medial, lateral and ventral nuclei of the trapezoid body are described in C57BL/6 mice using Nissl, Bodian and Golgi techniques. Principal, spindle and marginal cells are present in a well‐defined lateral superior olive. The dendrites of these cells run primarily within rostrocaudal sheets as in the cat. The principal cells of the medial nucleus of the trapezoid body are similar to the principal cells in the cat. Large multipolar cells characterize the lateral nucleus of the trapezoid body and bipolar cells with a medial‐lateral orientation are found in the medial superior olive. The largest neurons are found in the superior paraolivary nucleus and the lateral superior olive, and the medial and ventral nuclei of the trapezoid body. While brain weight and neuronal packing density change with development, the characteristic location of cell groups and the shape and Nissl‐staining pattern of neurons in the youngest brains examined were essentially unchanged in the adult mice, although dendritic maturation had occurred. The homologies of the C57BL/6 superior olivary complex nuclei with the same areas described in other mouse strains, rat and cat are discussed.

This study expands our understanding of the organization of the superior olivary complex in an inbred strain of Mus musculus and relates it to other species. The data about changes occurring during postnatal maturation may aid in the interpretation of behavioral and physiological studies of neonatal plasticity of the auditory system.
Hormonal control of apoptosis in hamster uterine luminal epithelium
Authors: Sandow Bruce A. , West Neal B. , Norman Reid L. , Brenner Robert M.
Published: February 2005

The hamster uterine luminal epithelium undergoes cyclic morphological changes, which include mitosis and hypertrophy prior to ovulation and degenerative changes after ovulation. We have previously shown that the degenerative changes are symptoms of estradiol (E2) withdrawal; they occur within 24 hours after ovariectomy, can be prevented by E2 treatment, and are associated with a decline in the content of uterine nuclear E2 receptor (West et al., 1978).

In this report, the results of an electron microscopic study of the uterine luminal epithelium in cycling and hormonally altered hamsters are described. During estrus and after ovariectomy, the death of numerous epithelial cells occurs by apoptosis. The ultrastructural alterations in such cells include condensation and margination of the chromatin, cytoplasmic condensation, amoeboid changes in cell shape with formation of pseudopodial extensions, and nuclear and cytoplasmic fragmentation. The cell fragments, or apoptotic bodies, accumulate near the basal lamina, and are then phagocytosed by macrophages, and possibly by neutrophils as well.

The ultrastructural features of cell death by apoptosis in the hamster uterus are similar to those observed by others in a variety of tissues. Because of the periodic, hormonally regulated occurrence of extensive apoptosis in the hamster uterine epithelium during the estrous cycle, this system is well‐suited for further investigations on the ultrastructural alterations that occur in cells undergoing apoptosis. In addition, apoptosis appears to be a sensitive morphological endpoint of E2 withdrawal in the hamster uterine luminal epithelium.
Epidermal growth factor‐like material in rat submandibular gland
Authors: Gresik Edward W. , Van Der Noen Hendrika , Barka Tibor
Published: February 2005

By using an antiserum specific for mouse epidermal growth factor (EGF), only the granular convoluted tubule (GCT) cells revealed immunochemical staining in rat submandibular glands. There was no regular sexual difference in the frequency or size of immunoreactive cells. Extracts of gland contained an antigen which showed a complete cross‐reactivity with mouse EGF in radioimmunoassays. The relative amounts of EGF, determined by a heterologous radioimmunoassay, were not significantly different in the glands of rats of the two sexes. Administration of testosterone caused an increase, in both sexes, in the number of GCT cells stained for EGF and in the amount of EGF in the gland. There was no significant sexual difference in these two parameters after androgen treatment.
Electron microscopic visualization of the filamentous reticulum in whole cultured presumptive chick myoblasts
Authors: Pudney Jeffrey , Singer Robert H.
Published: February 2005

This present study describes an experimental approach whereby subcellular 3‐dimensional filamentous structures present within whole cells can be examined, using a conventional transmission electron microscope. This procedure uses cells which have been cultured on carbon‐coated titanium grids, and treated with Triton X‐100 to extract the soluble cytoplasm. Subsequent fixation and critical‐point drying allows filamentous proteins to be easily visualized, due to the increase in contrast produced by removal of the ground cytoplasm. The high resolution obtainable in these preparations permitted an initial classification and description of the filamentous reticulum within cultured presumptive myoblasts. This reticulum is a continuum of filaments and cables, all elements of which appear to be interconnected. These morphological findings were then correlated with the biochemical identification of detergent‐insoluble proteins, of which only actin, myosin, and, perhaps, intermediate filament and LETS protein are the major elements.
A correlated thin‐section and freeze‐fracture analysis of guinea pig adrenocortical cells
Authors: Black Virginia H. , Robbins Edith , McNamara Nancy , Huima Tellervo
Published: February 2005

Comparison of the fine structural features of guinea pig adrenocortical cells as seen in thin sections with those revealed by freeze‐fracture confirms the structural appearance of steroid‐secreting cells as interpreted from thin sections and reveals significant new features of the membranous organelles.

Smooth‐surfaced endoplasmic reticulum appears as a network of tubules, interwoven or in parallel, and as cisternae, fenestrated and non‐fenestrated. These elements are tightly packed in the deeper cortical cells, excluding other organelles from their domain. Tubules and fenestrated cisternae possess randomly distributed intramembranous particles on their PF faces, while closely packed non‐fenestrated cisternae possess aggregates of particles interspersed with aparticulate regions on their PF faces. These differences in particle distribution suggest functional specialization among the various forms of reticulum.

Mitochondria appear as elongated structures of varying shape. Freezefracture reveals that all their cristae have circular origins from the inner membrane. Sinuous tubules, which appear as tubules in section, and straight tubules, which appear as lamellae in section, arise from single sites. Flattened sac‐like cristae may have multiple circular origins. Definite contact points seen between inner and outer membranes may facilitate passage of molecules, including steroids, into the mitochondrial compartments.

Lysosomes and peroxisomes, which are easily identified in thin sections with the aid of cytochemistry, are difficult to identify with certainty by freezefracture. Single membrane‐bound granules of slightly smaller diameter than mitochondria may represent lysosomes. Smaller granules interconnected with the tubular reticulum, as well as dilated regions of this organelle, may represent peroxisomes.

Plasma membranes show no indication of tight junctions but do have abundant gap junctions which show a zonal differentiation: small gap junctions throughout the cortex, medium‐sized regularly shaped gap junctions in zona fasciculata externa, and large irregular gap junctions in zona fasciculata interna and zona reticularis. The large junctions cover planar areas as well as surfaces of projections of one cell into another. Such junctions may allow passage of ions as well as of low‐molecular‐weight substances between the cells, facilitating or even amplifying the response to trophic hormone stimulation.
The human chondrocranium at the end of the embryonic period, proper, with particular reference to the nervous system
Authors: Müller Fabiola , O'rahilly Ronan
Published: February 2005

The chondrocranium at stage 23 (27–32 mm C.‐R., 8 postovulatory weeks) was studied in detail to fill the descriptive gap between 7 and 9 weeks. Serial sections of ten embryos, all belonging to the same developmental stage, were investigated and compared. Graphic and Perspektomat reconstructions were made from three embryos.

The chondrocranium forms a continuous mass of well‐formed cartilage, which blends with early cartilage in the nasal, orbital, and otic regions, around the future foramen rotundum, and at the site of the parietal lamina. The chondrocranium and “membrane” bones cover a relatively small portion of the brain, namely (1) the medulla and pons, (2) the caudal half of the lateral portion of the cerebellar primordium, and (3) the rostroventral part of the cerebral hemispheres. The relationships of the cranial nerves were also investigated.

The degree of cranial development is intermediate between that at stage 20 (21 mm) studied by Lewis (the only other skull so far studied adequately in a staged embryo) and that of fetuses of 40 and 43 mm investigated by Macklin. On the whole, the resemblances to the fetal skulls are greater: ossification is beginning in the tectum posterius (to form the supraoccipital), and most of the “membrane” bones (except the parietal, tympanic, lacrimal, and nasal) show osseous areas. The foramen rotundum is present. The lower angle between the chordal and prechordal parts of the basal stem ranges from 129° (which resembles that at stage 20, namely 122°) to 115° (which is the same as that at 40–43 mm). An orbito‐parietal commissure is not yet present.

The lower border of the larynx is at the level of the lower border of the fourth cervical vertebra. In the larynx, the thyroid laminae have usually not fused, the hyoid cartilage possesses greater and lesser cornua, the cricoid cartilage displays its signet‐ring form, and the arytenoids are identifiable as condensed mesenchyme with some early cartilage. The cartilage of the first pharyngeal arches is covered in its ventral three‐fourths by an osseous mandibular plate.

Morphological variations within stage 23 are minor and appeared not to be related closely to each other, so that it was not possible to arrange the embryos in a linear developmental series based on their level of cranial morphogenesis.
Cell proliferation in follicle‐associated epithelium of mouse peyer's patch
Authors: Smith M. W. , Jarvis L. G. , King I. S.
Published: February 2005

Follicle‐associated epithelium (FAE) from the mouse Peyer's patch consists of a dome part containing goblet as well as columnar epithelial cells and a crypt part, containing Paneth as well as goblet and undifferentiated epithelial cells. The proportions of columnar epithelial, goblet and Paneth cells in the FAE are similar to those found in normal crypt/villus complexes. Mitosis is confined to the crypts of the FAE. The cell‐renewal time for FAE columnar epithelial cells, estimated from experiments using tritiated thymidine, is approximately 60 hours. Large numbers of lymphoid cells are also present in the FAE, particularly in regions distal to the crypts. The similarity between follicle‐associated and villus epithelial structure is discussed, together with its possible relevance to “M” cell formation within the FAE.
Patterns of vascular sprouting in the postnatal development of the cerebral cortex of the rat
Authors: Rowan Reed A. , Maxwell David S.
Published: February 2005

Light microscopic histochemistry for alkaline phosphatase was employed in a study of the development of vascular sprouting, with respect to time and distribution, in the rat cerebral cortex. Sprouts were counted in the full thickness of the cerebral cortex at each day from birth to 21 days of age. Several distinct bursts of sprouting activity were observed at specific times and levels of cortex. From birth to 4 days of age, sprouting was intense in the superficial third of the cortex. At 7 to 8 days, a burst of sprouting was found which was greatest in the middle third. Additional bursts of sprouting appeared at 10 and 14 days.

Developing vessels with characteristics of arteries, capillaries, or sprouts were alkaline‐phosphatase positive, while veins were not. It is concluded that alkaline phosphatase is a useful marker for identification of both mature and immature vasculature, as it reveals patent and nonpatent vessels, and the sprouts which are precursors of the mature vascular bed. New vessels developing in the cortex arise mainly from blind sprouts of capillaries, evidently in response to the metabolic demands imposed by the maturational process.

At birth, the majority of intracortical vessels are capillaries. By 10 days of age, most perforating vessels from the surface have taken on arterial or venous characteristics. The findings are discussed in connection with morphological and biochemical differentiation and the pattern of vascularization in the mature cerebral cortex.
An ultrastructural study of vascular proliferation and vascular alkaline phosphatase activity in the developing cerebral cortex of the rat
Authors: Rowan Reed A. , Maxwell David S.
Published: February 2005

Alkaline phosphatase cytochemistry was employed to study the distribution of this enzyme in blood vessels during vascular differentiation and maturation during the postnatal development of the rat cerebral cortex. Enzyme reaction product was present in early vascular sprouts, and also throughout the subsequent maturation and differentiation of capillaries and arterial vessels. Cerebral capillaries appeared to be patent soon after the fusion of a sprout tip with another vessel; no evidence for delayed or synchronous opening was obtained. The distribution of alkaline phosphatase reaction product in vessel walls changed during vascular maturation. In vascular sprouts, reaction product was found mainly in the narrow lumen. As vessels became patent, reaction product appeared also on abluminal surfaces, at first chiefly in the narrow spaces between overlapping vascular cells. As vessels matured, reaction product became more generally distributed around the abluminal surface. In relatively mature capillaries and arterial vessels, it was restricted largely to endothelial cell surfaces and the spaces between smooth muscle cells. The significance of this distribution is unknown. Some possible explanations, including the possibility of artifact, are discussed. No alkaline phosphatase reaction product was found in differentiated veins.