bluuebunny/crossref_metadata_2025 huggingface dataset:
Myogenic cell formation in regenerating rat skeletal muscle injured by mincing II. An autoradiographic study
Authors: Snow Mikel H.
Published: February 2005

Myonuclei and satellite cell nuclei were differentially labelled with 3H‐thymidine in uninjured skeletal muscle of young rats and then traced autoradiographically at intervals after mincing the radioactive hindlimb muscles to determine the source of regenerating presumptive myoblasts. Labelled nuclei were detected by light microscopic examination of 1‐m̈ thick autoradiographs and identified by electron microscopic examination of an adjacent section. Repeated injections of 3H‐thymidine during fetal and neonatal development, followed by a 4‐ to 5‐week maturation period, resulted in labelling of 20% of the myonuclei. Satellite cells were not observed to be labelled in this series. Eight to sixteen hours after mincing, 20% of the pyknotic myonuclei were labelled, whereas none of the regenerating presumptive myoblasts appeared labelled. A single injection of 3H‐thymidine administered to 18‐day‐old rats, followed by sacrifice within ten hours, resulted in labelling of 23% of the satellite cell nuclei. Myonuclei were not observed to be labelled in this series. Eight to sixteen hours after mincing, silver grains were detected over both pyknotic and regenerating cell nuclei. These experiments indicate that many satellite cells survive muscle injury and transplantation to become regenerating myogenic cells at a time when most, if not all, myonuclei are undergoing pyknosis.
Neurohistochemical evidence supporting an absence of adrenergic and cholinergic innervation in the human placenta and umbilical cord
Authors: Reilly Frank D. , Russell Paul T.
Published: February 2005

Neurohistochemical techniques were used to determine the distribution of adrenergic and cholinergic nerves in the human placenta and the umbilical cord adjacent to the chorion. These morphologic studies demonstrate the absence of neural elements in these sites. The significance of these findings to the placental innervation controversy is discussed.
The origin, migration and fine morphology of human primordial germ cells
Authors: Fujimoto Toyoaki , Miyayama Yukihiko , Fuyuta Masatoshi
Published: February 2005

Human primordial germ cells (PGCs) were observed ultrastructurally in stages from their endodermal to gonadal locations. Primitive PGCs in the hind‐gut epithelium of the 4‐week embryo, were recognized as well demarcated cells from the neighboring cells. At the time of separation, the basal lamina of the epithelium was broken, then, through the gap so opened, the PGCs started to escape into the outer mesenchyme. In embryos at five weeks, PGCs were in the migration stage, and were found in the dorsal mesentery, at the coelomic angle and in the forming germinal ridge. In embryos at six weeks or later, almost all PGCs were accumulated in the gonad. The PGC was characterized by its large size and the large and round nucleus with conspicuous nucleolus, and by the presence of abundant glycogen particles and a considerable number of lipid droplets in the cytoplasm. Alkaline phosphatase activity was demonstrated selectively on the plasma membrane of the PGC. The shape of PGC was irregular, often had pseudopodia in PGCs in the separation and migration stages, suggesting their amoeboid movement in vivo, but was generally round or elliptic in PGCs in the settlement stage. The PGC was usually surrounded by and in close association with adjacent somatic cells.
Immunological and morphological effects of vasectomy in the rabbit
Authors: Alexander Nancy J. , Tung Kenneth S. K.
Published: February 2005

Half of the rabbits developed antisperm antibodies (measured by either indirect immunofluorescence or sperm immobilization tests) after either a unilateral or bilateral vasectomy. The raised antibody levels, particularly six months or longer after vasectomy, often accompanied patchy orchitis. Seminiferous tubules from such animals exhibited sloughed, multinucleated, and immature germinal cells which were engulfed by phagocytic cells. Mononuclear infiltrates were occasionally present. The basal lamina infolded and thickened by means of supernumerary layers and appeared to be endocytosed by cells of the seminiferous tubules. Four months after vasectomy, numerous phagocytic cells were seen to migrate through the intact epithelium of zone 1 in the caput epididymidis, and were particularly prevalent in animals that exhibited testicular damage. These macrophages may serve to present sperm antigens to lymphocytes.
The carotid and orbital retia of the pronghorn, deer and elk
Authors: Carlton Candy , McKean Tom
Published: February 2005

Selective cooling of the brain during heat stress has been shown by others to be a method of temperature regulation for mammals having carotid retia. This study describes the macroscopic anatomy of the cranial circulation of elk, deer and pronghorn as it might pertain to the functioning of carotid retia and orbital retia as heat exchangers. Emphasis has been placed on describing the source of venous blood bathing these retia, for blood flow from these sources to the ophthalmic plexus and cavernous sinus will establish a temperature difference between arterial and venous blood, and influence the magnitude of this gradient. The pronghorn possesses a carotid rete with greater density and smaller calibre vessels overall and a more highly vascular orbital rete compared to the elk and the deer. These anatomical differences may indicate differences in efficiency of heat exchange in the retia. It is suggested that the orbital rete is anatomically in a position to moderate extremes of temperature by cooling arterial blood flowing to neural tissue of the eye and olfactory bulbs.
The number of nuclei in adult rat muscles with special reference to satellite cells
Authors: Schmalbruch H. , Hellhammer U.
Published: February 2005

The number and the size of different populations of nuclei were studied in skeletal muscles and in the diaphragm of male Wistar rats of 200‐250 g weight. Nuclei on cross‐sections were counted and classified by electron microscopy, their incidence was corrected for their different lengths, and the number of nuclei per mm3 of muscle was determined by light microscopy. The total number of nuclei per mm3 was 5 · 104 in the superficial part of the anterior tibial muscle, it was 10 · 104 in the soleus, and it was 15 · 104 in the diaphragm. Half of the nuclei were localized inside muscle fibres. The incidence of satellite cell nuclei on cross sections was 4% of muscle nuclei in the anterior tibial muscle, and 8% in soleus and diaphragm. The number of satellite cells per mm3 muscle were 900, 4,900, and 5,300 in these muscles.

More than half of the satellite cells were closely associated with a capillary. In the anterior tibial muscle, and in 1‐μm sections no satellite cells could be identified by light microscopy. In the soleus muscle and in the diaphragm, satellite cells were more rich in cytoplasm and many were visible in the light microscope.
Membrane alterations during cornification of mammalian squamous epithelia: A freeze‐fracture, tracer, and thin‐section study
Authors: Elias Peter M. , McNutt N. Scott , Friend Daniel S.
Published: February 2005

Tight junctions (zonulae occludentes) create a pericellular barrier to the diffusion of large molecules in non‐keratinizing mammalian epithelia. However, in cornifying epithelia such as the epidermis, the importance of tight‐junctional elements versus secreted intercellular lipid for barrier function is uncertain. In an attempt to resolve this question, we compared membrane structure in the stratum granulosum and stratum corneum of epidermis, esophagus, and vagina of newborn and adult humans and mice under both normal and various experimental conditions. We incubated pieces of epidermis in organ culture and infused tissues with lanthanum or horseradish peroxidase in vivo and in vitro. All were processed for electron microscopy of freeze‐fracture replicas or thin sections. Lanthanum seeped outward to the stratum granulosum in all tissues examined‐further apical migration was halted by lamellar‐body contents in skin. A similar pattern of intercellular lamellar lipid deposition and membrane structure occurred in all epithelia studied. Freeze‐fracture replicas of these obstructive regions revealed occasional, incomplete junctional strands (particularly in moist epithelia) and abundant lamellar material, but complete zonulae occludentes were never encountered. A possible relationship between moisture and tight junction formation was further suggested by organ culture experiments during which brief incubations stimulated an increase in the number of junctional strands and diminished numbers of lamellar bodies. We conclude that, in the epithelia studied, the deposition of secreted lamellar body contents forms the barrier to water‐soluble tracer loss: tight‐junctional elements are either absent or too fragmentary to constitute an effective barrier.
Closure of the neural tube in the cephalic region of the mouse embryo
Authors: Geelen Jan A. G. , Langman Jan
Published: February 2005

In mouse embryos varying in age from 9 to 20 somites the first closure of the neural groove was found to occur in the cervical region. The fusion process gradually proceedéd in rhombencephalic direction until it reached a level just caudal to the otic pits. Shortly afterwards the prosencephalic walls fused together independent of the rhombencephalic closure. This prosencephalic fusion process proceeded caudally in the direction of the mesencephalon until it reached the rostral portion of the rhombencephalon. In this region the two independent fusion processes met each other. In addition the prosencephalic fusion proceeded in rostral direction toward the anterior neuropore, which was the last part of the brain vesicles to close. Hence, the closure of the brain vesicles is not a zipper‐like process proceeding from the rhombencephalon to the anterior neuropore, but occurs at several places at the same time and proceeds in a rostral as well as in a caudal direction.

At the cellular level considerable differences in the fusion process were found to exist between the various brain vesicles. In the rhombencephalon the first bridge between the two opposing walls was formed by surface ectoderm and neural crest cells. In the mesencephalon single squamous ectoderm and a few neuroepithelial cells established the first contact, whereas in the prosencephalon the apical ends of several neuroepithelial cells fused together to overbridge the gap between the opposing walls. The surface ectoderm cells subsequently covered the neuroepithelial bridge. In the region of the anterior neuropore the fusion was similar to that between the prosencephalic walls, the only difference being that in the anterior neuropore area many more darkly stained particles indicating cell degeneration, were present than in the prosencephalon. It is thus concluded that considerable differences exist in the fusion of the neural walls between the various brain vesicles.
Lipids and cholesterol clefts in the lacunar cells of snake skin
Authors: Jackson Morris K. , Sharawy Mohamed
Published: February 2005

The lacunar cell layer in rat snake epidermis contains many characteristic intracellular vacuoles. The lipid nature of these large round vacuoles was demonstrated by histochemical and ultrastructural investigations. Rhomboid‐shaped clefts, similar to cholesterol ester clefts, were observed in proximity to the vacuoles.
Ultrastructural characterization of nuage in spermatocytes of the rat testis
Authors: Russell Lonnie , Frank Beryn
Published: February 2005

At least six different types of nuage, as judged by morphological appearance, were found in spermatocytes of the adult rat testis. These were characterized by form, distribution, and association with other organelles. The appearance (with time) and the dissociation of some nuage types were recorded in conjunction with other events of the spermatogenic cycle. The data indicate that all types of nuage behave in a dynamic way. Especially interesting were the findings concerning the chromatoid body. This structure was first observed in mid‐pachytene spermatocytes. By late diplotene and during the first meiotic division, it had lost its prominence such that its eventual fate could not be determined. Large dense (0.5 μm) bodies appeared de novo in the cytoplasm of newly formed secondary spermatocytes. They were seen scattered throughout the cell and in association with mitochondria. With time these bodies appeared to coalesce to form the large definitive chromatoid of a type similar to that known to be present throughout most of the remainder of spermiogenesis.
Acetylcholinesterase activity of primary sensory neurons and dorsal root fibers in the cat
Authors: McNeill M. Evelyn , Norvell John E.
Published: February 2005

Dorsal roots and spinal ganglion cells of adult cats were studied for acetylcholinesterase (AChE) content. An inverse correlation exists between cell size and AChE activity; large neurons are AChE‐negative whereas small ones are intensely AChE‐positive. A few AChE‐positive fibers were demonstrated in the dorsal roots. A possible correlation between AChE activity and substance P content of primary sensory neurons is discussed.
Distribution of surface coat material on fusing neural folds of mouse embryos during neurulation
Authors: Sadler T. W.
Published: February 2005

Fusing and non‐fusing regions of neural folds from mouse embryos were examined during neurulation for the distribution of extracellular macromolecules (surface coats) prior to and at the time of closure. Ruthenium red staining of 10th day ICR/DUB mouse embryos was used to detect the distribution of surface coat material. Light microscopic examination of fusing and non‐fusing regions in the midbrain, hindbrain, and spinal cord showed a consistent increase in ruthenium red positive material immediately prior to closure. Heavy deposits of positive staining material were present along apical neural fold borders and overlying ectoderm cells. This staining pattern was consistent in the three regions examined, but the pattern of initial contact between opposing neural folds differed. In mid‐ and hindbrain areas contact was initiated by overlying ectoderm, whereas in spinal cord regions contact was first established by neuroepithelial cells. Once contact between opposing neural folds was initiated a decrease in stainable material was observed.
Satellite cells of rat muscles as studied by freeze‐fracturing
Authors: Schmalbruch Henning
Published: February 2005

Satellite cells in rat muscles were studied by freeze‐fracturing. They were found not to be fusiform but to have several narrow projections embedded in grooves of the muscle fibre membrane. Short projections of the muscle fibre covering the outer face of the satellite cells were observed as well. In the P‐face of the cell membrane of satellite cells, membrane particles and caveolae were less frequently seen than in the P‐face of the muscle membrane. Thus the surface of the satellite cells looked more smooth than that of the muscle fibres. Junctions between muscle fibre and satellite cell were not found. The presence of cytoplasmic extensions of satellite cells may suggest that these cells are motile.
Effects of complete tail bud extirpation on early development of the posterior region of the chick embryo
Authors: Schoenwolf Gary C.
Published: February 2005

The tail bud was completely extirpated down to the yolk from 65 embryos at stages 13‐17 to determine whether the posterior part of the noto‐chord originates from the tail bud or from a more anterior region (i.e., prospective notochordal region). About 40% of the 44 surviving embryos developed near‐normal tails, con̈taining a localized defective region beginning near the base of the tail and extending a short distance posteriorly, about 15% developed truncated, cone‐shaped tails, containing a defective region beginning near the base of the tail and extending towards the tip, and about 45% developed short, ventral tail remnants, containing a localized defective region beginning near the base of the tail and extending a short distance posteriorly. The tail was absent in only one embryo. These differences were probably due primarily to variation in the amount of healing and regeneration that occurred, and were independent of the stage at which the operation took place. The tail region has a tremendous capacity for regeneration since a near‐normal tail frequently developed. The location of the beginning of the defective region near the base of the tail suggests that the tail bud primarily gives rise to tail structures. All embryos had neural tube defects, about 30% developed large, midline somites within the defective region, and about 25% developed an ourenteric outgrowth. The notochord was always normal within the defective region. These results are consistent with the view that the tail bud contributes cells to the posterior part of the neural tube, but not to the notochord.
The site of collagen resorption in the periodontal ligament of the rodent molar
Authors: Beertsen Wouter , Brekelmans Margot , Everts Vincent
Published: February 2005

In an attempt to determine the pattern of collagen phagocy‐tosis by fibroblasts in the periodontal ligament, a stereologic investigation of the mesial root of the maxillary first molar of the rat was undertaken. The distribution of fibroblasts containing intracellular collagen fibrils was studied at the electron microscope level in the periodontal ligament along resorbing and non‐resorbing surfaces of the alveolar wall. It appeared that fibroblasts with collagen‐containing vacuoles were more or less randomly distributed across the width of the periodontal ligament. No major differences were observed among the alveolar, cemental and intermediate zones of the ligament. However, local variations in the occurrence of cells containing intracellular collagen fibrils may occur. A relatively high concentration of ingested collagen fibrils was seen in fibroblasts located in the direct vicinity of osteoclasts, but not in the vicinity of osteoblasts. These observations suggest that remodelling of collagen is even‐ly distributed throughout the ligament, but may be influenced by local circumstances, such as the occurrence of bone resorption.
Attrition of the human leydig cell population with advancing age
Authors: Kaler Lawrence W. , Neaves William B.
Published: February 2005

Existing evidence suggests that the aging human male experiences a gradual decline in testosterone production, a phenomenon that should be reflected in the Leydig cell population of the testis. It has been pro‐posed that Leydig cells diminish in number with increasing age, but conflicting claims characterize reports on this topic. We have reinvestigated this possibility by histometric analysis of perfused testes from 25 men ranging from 18 to 87 years of age. Average single Leydig cell volume (2,943 ± 623 μm3, X S. D.) did not change significantly with increasing age (r = 0.24, P > 0.2), suggesting that surviving cells remain active. Total testis weight (43.5 ± 13.9 g) also did not change with age (r = 0.04, P > 0.5). However, both total Leydig cell volume and the absolute number of Leydig cells per individual decreased significantly as functions of age (r = −0.71, P < 0.002, and r = −0.61, P < 0.005, respectively). Analysis of the relationship between these two parameters indicates that the total volume of Leydig cell cytoplasm contained within the human testis is determined by the number of cells present. Our results show that a pair of young adult testes endowed with more than 700 million Leydig cells at 20 years of age may be expected to undergo an attrition rate of approximately 80 million cells per subsequent decade of life. Thus, Leydig cell attrition is an important correlate of declining androgen status in aging men.
Morphological and quantitative analysis of spermatogonia in mouse testes using whole mounted seminiferous tubules. I. The normal testes
Authors: Huckins C. , Oakberg E. F.
Published: February 2005

The spermatogonial populations in ten normal adult mice were analyzed using whole mounted seminiferous tubules. The undifferentiated A spermatogonia as well as the six generations of differentiating spermatogonia were clearly identifiable on whole mounts. Description plus quantitation of these cell types revealed that they behaved in essentially the same manner as their counterparts in the rat. Single undifferentiated A cells were classified as type A stem cell spermatogonia. They were distributed throughout the seminiferous epithelium, and by periodic mitoses, maintained their stock and furnished cells which would eventually differentiate. Although initially resembling the As spermatogonia, the progeny which were destined to differentiate were classified as type Aalv spermatogonia because they were linked by cytoplas‐mic bridges, and because they usually underwent one or more synchronous mitotic divisions to form short chains of aligned cells. Ultimately, division of Aal cells were no longer seen, and the cells appeared to gradually acquire the typical morphological characteristics of A1 spermatogonia; these continued to differentiate according to the well‐established pattern. It was concluded that the cyclic production of cohorts of A1 cells in this manner would ensure a continual supply of spermatogonia for differentiation.
Characterization of Sertoli cell‐germ cell junctional specializations in dissociated testicular cells
Authors: Romrell Lynn J. , Ross Michael H.
Published: February 2005

To further characterize Sertoli cell‐germ cell junctional specializations seminiferous tubules from sexually mature Sprague‐Dawley rats were dissociated by enzymatic and mechanical methods. Ultrastructural analysis of cell suspensions prepared by incubation in collagenase alone or by mechanical methods revealed that spermatids remained attached to Sertoli cells or Sertoli cell fragments. Such cellular associations were found only between Sertoli cell fragments and spermatids in which the developing acrosome had made contact with the plasma membrane (step 8 and subsequent steps of spermiogenesis). Furthermore, the fragments were confined to that region of the plasma membrane over the acrosome. The Sertoli cell half of this adhesive site displayed the typical elements of Sertoli cell junctions, filamentous bundles and associated cisterna of endoplasmic reticulum, in apposition to the spermatids. The spermatids demonstrated no surface specializations at the attachment sites. In contrast, in cell suspensions prepared with trypsin, spermatids were free of attachments to Sertoli cells or their fragments. These results demonstrate that: (1) the junctions act to bind cells together, (2) adhesive type contact is established between Sertoli cells and spermatids at step 8 and subsequent steps of spermiogenesis, (3) contact is restricted to the spermatid plasma membrane over the acrosome, and (4) spermatids can be freed from the junctional specializations by treatment with trypsin.
A fine structural analysis of the myelin sheath in rat spinal roots
Authors: Coggeshall Richard E.
Published: February 2005

The present study is concerned with the fine structure of the myelin sheath in rat and monkey spinal roots. Pictures are obtained that show that the intraperiod gap of the myelin sheath is continuous and opens into both the internal and external mesaxons, which in turn open into the periaxonal and endoneurial extracellular spaces. These results are compatible with the idea that the intraperiod gap is a cleft that traverses the thickness of the myelin sheath and links the periaxonal and endoneurial extracellular spaces.
Lipoprotein particles in the jejunal mucosa of postnatal developing rats
Authors: Mak Ki M. , Trier Jerry S.
Published: February 2005

The jejunal mucosa of neonatal rats contains lipid particles of the same size, electron density and intracellular and extracellular distribution as particles identified by others in adult jejunum as lipoprotein particles. As in fetal jejunum obtained during the last three days of gestation, the jejunal mucosa of unsuckled newborn rats contains exclusively lipoprotein particles the size of very low density lipoproteins (VLDL). Within one day after initiation of suckling, there is in the mucosa a spectrum of lipoprotein particles ranging widely in size from those of VLDL particles to those of chylomicrons. These particles are seen in the endoplasmic reticulum and Golgi material of absorptive cells and within interepithelial cell spaces, the extracellular spaces of the lamina propria and lymphatic lacteals. VLDL‐sized and chylomicron‐sized particles are also seen, although in decreasing number, in the jejunal mucosa of 18‐day‐old suckling rats. However, in rats of comparable age, fasted for 48 or 72 hours, only VLDL‐sized particles are seen in the jejunal mucosa. Ligation and transection of bile duct followed by fasting in rats of this age results in a marked decrease in the number of lipoprotein particles in absorptive cells. The results indicate that endogenous lipid contributes to the formation of VLDL particles whereas dietary triglycerides are needed for formation of chylomicrons.
An autoradiographic and immunocytochemical study of the neonatal rat pituitary gland
Authors: Sheridan Peter J. , Herbert Damon C.
Published: February 2005

Two‐day‐old female rats were injected with 5 nmole/kg of 6,7‐3H‐11β‐methoxy‐17‐ethylestradiol (R 2858 = moxestrol) and killed one hour later. The animals were decapitated and, the pituitary glands were removed, mounted on tissue holders and frozen in liquified propane. The tissue was then processed for autoradiography according to the thaw mount technique. At the end of the exposure time, prior to photographic development, some of the tissue was fixed in 10% formalin and then photographically developed for autoradiography. The fixed tissue was subsequently stained immunocytochemically using antibodies to luteinizing hormone or prolactin. Between 10 and 15% of the cells of the pars distalis concentrated the synthetic estrogen or its metabolite. The immunocytochemical procedure revealed that both LH‐gonadotrophs and lactotrophs concentrated the steroid. These studies along with earlier studies suggest that the neonatal rat pituitary contains only a small portion of the adult complement of estrogen receptors and that these receptors are dispersed across a number of cell types.
Surface area ratios. I. A stereological method for estimating average cell changes in membrane surface areas
Authors: Bolender Robert P.
Published: February 2005

The study (i) describes a method for estimating relative changes in membrane surface areas as they occur in stereological “average cells,” and (ii) considers the effect of the controls on these estimates. The results indicate that changes in five membrane compartments of pancreatic exocrine cells‐produced by a secretagogue (carbomylcholine chloride)‐were detected similarly when related to either an average cell surface (surface area ratio method) or to an average cell volume (method of Loud, '68). Changes, however, detected with surface densities, which relate these membrane compartments to 1 cm3 of exocrine cell cytoplasm or pancreas, were notably different from the first two estimates. This inconsistency could be explained by the fact that the surface densities were influenced not only by membrane changes within the exocrine cells, but also by changes in the number of these cells filling the cm3 of reference volume. Relating the data to an average cell reference–instead of 1 cm3–improved the accuracy of the estimates for changes in membrane surface areas by as much as several fold; the choice of controls had a similar several‐fold effect on the results.
Structure of retzius lines in partially demineralized human enamel
Authors: Weber Dennis F. , Ashrafi Shahid H.
Published: February 2005

Human third molars were partially demineralized in an acid‐alcohol solution and embedded in Epon 812. Six‐micron sections were cut from regions of the cervical enamel exhibiting prominent Retzius lines. The plastic was removed from the specimens by microincineration and were examined with the scanning electron microscope. The most prominent structural feature seen along the Retzius lines was the cervical translocation of some of the prisms. The scanning electron microscopic images also suggested that prisms were translocating in the transverse plane of the tooth. A series of pores, which appeared to be empty, were observed in association with the translocations occurring along the Retzius lines.
Intercellular junctions in the rhesus monkey pars distalis
Authors: Herbert Damon C.
Published: February 2005

Four rhesus monkey pituitary glands were examined by transmission electron microscopy. Three types of intercellular junctions, desmosomes, hemidesmosomes and zonula adherens‐type junctions, were observed between adjacent granular cells, folliculo‐stellate cells, and joining a folliculostellate cell with a granular cell. Desmosomes were most commonly observed between granular cells while the zonula adherens‐type junctions were generally found between the folliculo‐stellate cells.
Replacement of fatty marrow by active granulocytopoietic bone marrow following transplantation of mammary carcinoma into mice
Authors: Lee Minako Y. , Rosse Cornelius
Published: February 2005

The development of granulocytic hemopoiesis in the fatty marrow of metatarsal bones and caudal vertebrae of adult mice was studied in histological sections for up to six weeks following subcutaneous innoculation of granulocytosis inducing mammary carcinoma. The initial events observed were increase and engorgement of fatty marrow sinusoidal vascular beds, accompanied by numerous lymphoid mononuclear cells in the sinusoids and in the stroma. Foci of granulocytopoiesis appeared admixed with lymphoid cells in the stroma and near the endosteum. Hyperplastic granulocytopoiesis eventually predominated in the marrow of these bones as well as the femoral and sternal marrow of tumor bearing mice. The morphological findings suggested the possibility of stem cell and progenitor cell migration into fatty marrow, but activation of dormant stem cells could not be ruled out. The prevalence of granulocytopoiesis in the entire skeletal marrow in tumor bearing mice may seriously impair the production of other cellular components of the marrow including lymphocytes, reduced production of the latter would imply serious compromise for the immune system of the tumor bearing animals.
Developmental history of nervus terminalis in embryos of insectivorous bats
Authors: Brown Jerry William
Published: February 2005

Insectivorous bat embryos (TadaridaandMyotis) ranging from 6‐to 16‐mm C‐R length were examined for the presence of the nervus terminalis. These embryos have no vomeronasal nerve with which the nervus terminalis could be confused. The nerve and associated ganglion cells first appear in the 7‐mm embryo. As the embryo ages, a gradual increase in nerve size and ganglion cell numbers occurs. In the 13‐mm embryo, nerve size and ganglion cell numbers are reduced, and in older embryos both nerve and cells are absent, as in the adult. The ganglion cells arise as clusters from the nasal septal epithelium. The largest number of cell clusters occurs in the 10.5‐mm embryo. Their number then decreases and none are present in embryos of 13‐mm and longer. These cells migrate centrally along the course of the nerve which accompanies the olfactory nerve from the nasal cavity roof to a level just caudal to the olfactory bulb, where the nervus terminalis turns dorsalward along the medial telencephalic wall surface. Except in the youngest and oldest embryos the nervus terminalis, where present, divides into two or three branches to pierce the hemispheric wall, one usually entering the region of the nucleus olfactorious anterior, and the other(s), the region of the medial septal nucleus. In some cases, several ganglion cells are present along the intrahemispheric course of the nerve fibers. All ganglion cells resemble those in various sensory ganglia, and so, are probably also sensory neurons.
Ascending projections of the dorsal column in a garter snake (thamnophis siritalis): A degeneration study
Authors: Jacobs Virgil L. , Sis Raymond F.
Published: February 2005

Ascending axons in the dorsal column of garter snakes were examined following hemisection of the spinal cord at segment levels 2, 3, 4, 11, 13, and 31. After postoperative survival periods of 11 to 28 days, sections of the spinal cord and brain were processed with a silver method to demonstrate degenerated axons and preterminals.

The study demonstrated that most ascending degenerated axons are located in the outer half of the dorsal column. The somatotopic pattern of ascending fibers is evident, whereby dorsomedial fibers are primarily of caudal origin and the more dorsolateral axons are from rostral cord segments. Rostral to segment 31, all spinal segments appear to project to a strip of dorsal column adjacent to the dorsal median septum. From the septum, axons descend to terminate somatotopically on cells of the nucleus of Bischoff located caudal to the obex of the medulla.

Dorsal column degeneration ascends to the level of the dorsal column nuclei, where most fibers terminate. Degeneration from caudal cord segments terminates on caudo‐medial cells of the dorsal column nuclei, while rostral cord segments project to rostro‐lateral cells. The dorsal column nuclei consist of an expanded lateral part between tractus descendens trigemini and the vago‐solitary complex, and a contiguous, thin medial lamina of cells dorsal and medial to the vagal nuclei. The somatotopic pattern of degeneration in the dorsal column nuclei, probably of dorsal root origin, follows the mammalian organization, which suggests that the garter snake has primitive nuclei gracilis and cuneatus. Other terminal sites of degenerating fibers, although probably of spinal gray origin, are nucleus commissura infima, nucleus descendens vestibuli, and area postrema.
Evolution of the endoplasmic reticulum in the Sertoli cell cytoplasm encapsulating the heads of late spermatids in the rat
Authors: Clermont Y. , McCoshen J. , Hermo L.
Published: February 2005

Throughout stage VII and early stage VIII of the cycle of the seminiferous epithelium, the heads of the late spermatids, located in a juxtaluminal position, are embedded in apical processes of Sertoli cells. These processes contain cisternae of endoplasmic reticulum (ER) of two main types, i.e., flattened and tubular, which communicate with each other to form a continuous system. Throughout the long stage VII of the cycle, these two types of cisternae undergo marked changes. In early stage VII, the flattened cisternae, developing from the subsurface cisternae which compose the “junctional specialization,” form concentric sheets at the periphery and in the middle of each apical process. The less conspicuous tubular cisternae form a continuous network which is present in the bridge connecting the Sertoli cell body to the apical process, and extends along the dorsal and ventral aspects of the spermatid's head to end up as cup‐shaped flattened cisternae capping the bulbs of the tubulobulbar complexes described by Russell and Clermont ('76). In mid stage VII, the flattened cisternae start to regress, while the tubular cisternae become more abundant. In late stage VII, only fragments of the flattened cisternae are present, while the tubular cisternae form a profuse and elaborate network throughout the apical process. In the following stage VIII, the tubular cisternae disperse and only remnants of ER are present at the time of the release of the spermatid into the tubular lumen. These transformations of ER cisternae suggest a complex alteration in the relationship between Sertoli cells and late spermatids prior to their release as spermatozoa.
Gap junctions between cells of bone marrow: An ultrastructural study using tannic acid
Authors: Campbell Ferrell R.
Published: February 2005

In bone marrow of the mouse perfused with fixative containing tannic acid and glutaraldehyde, gap junctions were observed between certain cell types. Gap junctions were seen between adjacent reticular cells, between adjacent macrophages, and between macrophages and reticular cells. Macrophages formed gap junctions with immature neutrophils, eosinophils, monocytes, and erythroblasts. Often a single macrophage had gap junctions with neutrophilic, eosinophilic, and monocytic cells; these blood cells varied from immature to nearly mature forms. In contrast, the macrophages associated with erythroblasts had gap junctions only with erythroblasts and all the erythroblasts were in the same developmental stage. The possible role of the gap junctions in differentiation and mobilization of marrow cells is discussed.
Extracellular spaces of the rat pars intermedia as outlined by lanthanum tracer
Authors: Saland L. C.
Published: February 2005

The extracellular spaces of the rat pars intermedia were examined after perfusion with fixative containing lanthanum. The tracer reveals complex and extensive interdigitations among secretory cells. Spaces appear continuous with extracellular “channels” between the epithelial cells lining the hypophyseal cleft. Some suggestion for close contiguity between endocrine cells was present as “narrowing” or discontinuous areas within lanthanum‐filled spaces. Extracellular regions surrounding nerve fibers and terminals appear continuous with the spaces between secretory cells. Areas between cells are thought to provide access to vascular and local neurotransmitter input, as well as to provide an extensive area for extrusion of peptide hormones and endogeneous opiates.
Ultrastructural evidence for seasonal changes in pinealocytes of the 13‐lined ground squirrel, spermophilus tridecemlineatus: A qualitative and quantitative study
Authors: McNulty John A. , Dombrowski Teresa A.
Published: February 2005

The fine structure of pinealocytes in the hibernating ground squirrel, Spermophilus tridecemlineatus, was found to vary both qualitatively and quantitatively according to the season in which the animals were sacrificed. Ultrastructural features of pinealocytes from fall (prehibernation) and winter (hibernation) periods, when the animals were sexually quiescent, included: (1) arrangement of the endoplasmic reticulum into flattened stacks or concentric rings (formations which have been implicated in antigonadotropic activity of the pineal); (2) condensations of a fine granular material; and (3) dilation of the cisternae of the endoplasmic reticulum and Golgi bodies with an increased number of Golgi associated vesicles. Moreover, there was an apparent increase in the number of dense‐cored vesicles and microtubules in pinealocytes of winter animals. These findings indicate that a circannual rhythm in pinealocyte ultrastructure occurs in this species and further suggest that cellular activity is seasonal.
The effects of chronic hypoxia on the myocardial cell of normotensive and hypertensive rats
Authors: Lund Donald D. , Tomanek Robert J.
Published: February 2005

Myocardial cellular and subcellular adaptations associated with chronic hypoxia were determined in 16 week old male normotensive Wistar‐Kyoto, spontaneously hypertensive and aortic constricted rats. The animals were exposed to six weeks of hypobaric hypoxia at a simulated altitude of 6,100 (m), and their glutaraldehyde perfuse‐fixed hearts compared to normoxic controls.

Exposure to hypoxia abolished the hypertension associated with the spontaneously hypertensive and aortic constricted groups and reduced the mean heart rate in all three hypoxic groups. The magnitude of hypertrophy was significant and comparable in all three groups, based on heart weight and left ventricular fiber diameter measurements. While capillary density was significantly reduced in the spontaneously hypertensive and aortic constricted rats, exposure to hypoxia facilitated an absolute increase in the number of capillaries of the hypoxic spontaneously hypertensive and aortic constricted rats. In the hypoxic control group, the capillary density was maintained despite a 20% increase in the muscle fiber diameter, indicating a proliferation of the capillary bed in proportion to the increase in muscle mass. The myocytes in all hypoxic groups were characterized by deep invaginations of the cell membrane and an increase in the number of pinocytotic vesicles. Stereological analyses of the myocytes revealed a statistically significant decrease in the mitochondria/myofibril volume ratio in animals with pressure overload. This ratio was not significantly altered when the animals were subjected to chronic hypoxia. However, there was an increase in the number of mitochondrial profiles and a decrease in the size of individual profiles in all hypoxic groups when compared to the control group.

These findings suggest that cardiac hypertrophy associated with chronic hypobaric hypoxia, unlike hypertrophy due to pressure overload, is associated with a number of structural adaptations which may aid the heart in functioning in the hypoxic environment.
The blood supply to the splenic lymphatic nodules in the rhesus monkey
Authors: Snook Theodore
Published: February 2005

The arterioles and capillaries supplying the lymphatic nodules and marginal zone (in part) in the rhesus monkey's spleen arise from a follicular artery branch of the central artery. This follicular artery first undergoes a series of convolutions and branchings, out of which a parallel array of tightly bound arterioles and capillaries, an anteriorlar capillary bundle (ACB), leading into the central part of the nodule is formed. From the proximal end, side, and distal end of the ACB, arterioles and capillaries radiate outward through the mantle zone of the nodule to terminate in the marginal zone. Some capillaries are formed within the bundle and others not until an arteriole nearly reaches the marginal zone.

A similar ACB and capillary distribution is found in the human spleen. However, the supplying arteries, for the most part, come from recurrent penicillar arteries which pass close to the central artery before forming the bundle. This artery does not undergo the convolutions found in the rhesus monkey. In the monkey, the bundle contains a higher proportion of arteriolar vessels. It appears that in human and rhesus monkey spleens, the ACB replaces the internal capillary net of Jäger (′29).
The ultrastructure of oral (buccopharyngeal) membrane formation and rupture in the chick embryo
Authors: Waterman Robert E. , Schoenwolf Gary C.
Published: February 2005

The ultrastructure of the oral (buccopharyngeal) membrane was examined by transmission and scanning electron microscopy (SEM) from its initial formation (stage 8) to its complete disappearance (stage 20) in the chick embryo. Thinning of the oral membrane prior to rupture occurs in large measure by increased interdigitation between cells of the stomodeal ectoderm and foregut endoderm coincident with a decrease in the width of the intervening extracellular space. Large numbers of necrotic cells were not observed. Interdigitation of ectodermal and endodermal cells makes it increasingly difficult to discern two discrete epithelia, and no evidence that one germ layer disappears prior to the other was observed. Changes occurred in the fine structure of the extracellular matrix during formation and rupture of the oral membrane, and the organization of this material within the oral membrane differed from that in regions immediately lateral to it. Copious amounts of amorphous, flocculant (“lamina‐like”) material are present within the oral membrane at all stages. The basal lamina of the ectoderm exhibits small loops or folds at early stages. These decrease in number as the basal lamina becomes discontinuous prior to establishment of direct intercellular contact between cells of the ectoderm and endoderm across the intervening extracellular compartment. Initial perforations of the oral membrane are preceeded by clefts between cells on both sides of this structure, and SEM observations suggest that cells of the oral membrane continue to interdigitate, elongate, and change relative positions during the rupture process.
Immunohistochemical study of lymphocytes in rat pineal gland: Selective accumulation of T lymphocytes
Authors: Uede Toshimitsu , Ishii Yoshifumi , Matsuura Akihiro , Shimogawara Izuru , Kikuchi Kokichi
Published: February 2005

Morphologic and immunohistochemical studies were performed to examine the existence of lymphocytes in the brain of rats. Special attention was paid to the time course of the appearance of lymphocytes in and around the pineal gland. Rabbit anti‐rat T cell and anti‐rat immunoglobulin sera were used for identification of T and B cells in tissue sections. Immunoperoxidase and immunofluorescence techniques were employed to identify cells reacting with anti‐T and anti‐immunoglobulin sera.

No lymphocytes were found in the brain of rats until 20 days after birth. Small clusters of lymphocytes appeared in the pineal region by 30 days of age, after which they gradually increased in number, forming massive clusters in the pineal region by 120 days. Along with an increase in the number of lymphocytic cells, there was a gradual increase of cells reacting with anti‐T cell serum. These T cells were only a minority of pineal lymphocytes in younger animals, but 90% or more cells were stained by anti‐T cell serum at 120 days after birth. The remaining cells did not react with anti‐immunoglobulin sera either. These findings suggest that the gradual increase of T lymphocytes in the rat pineal region is a simple reflection of the normal course of maturation of T cells, and the pineal gland in the rat may have some role in immune responses within the brain.
Morphogenesis of conjunctival papillae from normal and scaleless chick embryos
Authors: Blanck Cynthia E. , McAleese Susan R. , Sawyer Roger H.
Published: February 2005

Morphogenesis of avian conjunctival papillae follows a predictable temporal and spatial pattern and is in some manner directly related to the induction of the underlying scleral ossicles. We have been able, using Scanning Electron Microscopy (SEM), to correlate all of Murray's ('43) histological stages (1–6) of papillae development, with changes in elevation and morphology of the surface of the conjunctiva. The first indication of morphogenesis is the formation of “papillae primordia”. The centers of these primordia exhibit decreased intercellular contact, and become elevated as radially symmetrical humps whose surfaces are composed of rounded cells with numerous microvillar projections. As the papillae become asymmetrical and elongate, cells near the tip of the papillae enlarge and develop microridges. During regression of the papillae, single clusters of cells appear to become lost from the surfaces of the papillae into the surrounding fluid. In contrast to normal chick embryos, those homozygous for the “scaleless” gene (Abbott and Asmundson, '57) display reduction in the number of papillae and underlying scleral ossicles (Palmoski and Goetinck, '70). SEM of the mutant conjunctival surface indicates that these papillae do not exhibit all of Murray's ('43) histological stages and are morphologically abnormal. Data from the present SEM study of the normal and scaleless conjunctiva are discussed in relation to those data of other investigators, and we suggest that Stage 4 in papillae development is critical to scleral ossicle formation.