bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes in the fine structure of the parietal yolk sac of the rat placenta with increasing gestational age
Authors: Jollie William P.
Published: February 2005

The fine structure of the portion of the parietal yolk sac which extends across the fetal surface of the rat placenta (which is the only portion of the parietal yolk sac which persists after the sixteenth day of pregnancy) was examined sequentially on the even numbered days during the second half of gestation. The placental parietal yolk sac was seen to consist of two cellular layers, trophoblast and endodermal epithelium, which were separated by a thick, amorphous membrane (of Reichert). The trophoblast attenuated with increasing gestational age and, on day 18, became perforated by fenestrations which were closed by diaphragmata. By day 22, the attenuated trophoblast was patently perforate, and maternal blood was exposed to Reichert's membrane. Since throughout gestation, the cells of the parietal endoderm formed a discontinuous layer, at all stages Reichert's membrane was exposed to the vitelline cavity. When ferritin and thorotrast were injected i.v., both separately and together, the former passed readily from maternal blood through Reichert's membrane and was phagocytosed by cells of the parietal endoderm. Thorotrast, however, did not cross Reichert's membrane. Since the rodent yolk‐sac complex is known to serve as a placental route, selective permeability of Reichert's membrane may help regulate maternofetal exchange.
Histochemical and autoradiographic studies of the formation of the metrial gland in the pregnant rat
Authors: Larkin Lynn H. , Schultz Richard L.
Published: February 2005

It is shown in this study that cells of the mesometrial triangle proliferate at a high rate in the early formative period of the metrial gland. This, plus observations of sequential apperance of specific cell types during growth of this tissue, indicate that the metrial cells are formed in situ.

Support for the hypothesis of in situ formation of metrial gland tissue also was obtained by observation of apparent differentiation of metrial cells from a precursor cell type. The precursor cells appear to arise from fibroblast‐like cells located in the mesometrial triangle throughout the formative period of the metrial gland. Quantitative autoradiographic studies indicate that the precursor cells accumulate glycogen, undergo division, and subsequently produce diastase‐resistant, PAS‐positive granules that are characteristic of metrial cells. These cells, which contain specific granules and glycogen, are an individual cell type and are referred to as mononucleate metrial cells. The experiments suggest that the mononucleate metrial cells undergo karyokinesis without cytokinesis resulting in typical binucleate metrial cells. Binucleate metrial cells synthesize DNA and appear to become polyploid rather than forming multinucleated cells or binucleate daughter cells. Some nuclei apparently attain a high ploidy, but the majority of binucleates are not highly polyploid.
A new cytoplasmic organelle, related to both lipid and glycogen storage materials in the yolk sac of the bat, Tadarida brasiliensis cynocephala
Authors: Stephens R. J. , Easterbrook N.
Published: February 2005

The gestation period of Tadarida is approximately four months long extending from late February to June. During the first half of gestation the yolk sac undergoes a complete collapse bringing two layers of endodermal cells into contact with one another and obliterating the cavity of the yolk sac. Both the endodermal and the mesodermal cells hypertrophy and develop into a glandular‐looking organ during the latter half of gestation. Approximately a month before parturition the endodermal cells become progressively laden with lipid and glycogen. Immediately before birth, however, both of these storage materials are depleted. This depletion is preceded by the formation of an extensive array of hexagonal membranous channels within the cytoplasm. Some of the membranes of this organelle are closely applied to lipid droplets and glycogen granules can be observed in linear patterns within the hexagonal channels. Tissues taken at term showed the membranes of the hexagonal channels continuous with a paracrystalline membranous structure. The close morphological association of the membranous organelle to both the lipid and glycogen storage materials indicates that it is involved in their metabolism in the yolk sac of the bat.
Eighteen hundred years of controversy: The paranasal sinuses,
Authors: Blanton Patricia L. , Biggs Norman L.
Published: February 2005

The reason for the presence of the paranasal sinuses has been a controversial subject since the time of Galen, 130–201 A.D. In a review of the literature, the diversity of the numerous functions ascribed to these air‐filled cavities was found to be astounding. Many functions were ascribed only on the basis of opinion rather than scientific investigation and recent studies have illustrated the fallacy of these opinions. To date, not one proposed function has been universally accepted to be the essential reason for their existence.

This review of the literature deals mainly with those theories of anatomical and physiological significance of the paranasal sinuses having received the most consideration and many of which are currently considered tenable. These are, as follows: (1) impart resonance to the voice; (2) humidify and warm inspired air; (3) increase the area of the olfactory membrane; (4) absorb shock applied to the head for protection of sensory organs; (5) secrete mucus for keeping the nasal chambers moist; (6) thermally insulate the nervous centers; (7) aid facial growth and architecture; (8) exist as evolutionary remains and/or unwanted air spaces; and (9) lighten the bones of the skull for maintenance of proper balance of the head.
Sympathetic nerve pathways to the human heart, and their variations
Authors: Ellison Jeffrey P. , Williams Terence H.
Published: February 2005

Stimulated by the needs of surgery, common variations in the sympathetic pathways to the heart have acquired a practical significance. The cervical and upper thoracic sympathetic trunk was dissected on 24 sides in human fetuses at term, and the cardiac rami together with their communications studied and illustrated. To enable us to classify the cervical rami according to their sites of origin, the cervical sympathetic trunk was subdivided midway between ganglia into portions called ganglionic divisions; these divisions keeping the names applied to the ganglia in the Nomina Anatomica.

Intermediate ganglia were found on the visceral outflow of the sympathetic trunk and are referred to as “distal intermediate ganglia” to distinguish them from the intermediate ganglia that have been described proximal to the sympathetic trunk.

Thoracic cardiac rami were almost invariably present, the third and fourth thoracic ganglia most frequently providing substantial contributions. Some thoracic cardiac rami were traced as far as the left anterior descending coronary plexus.

The question of bilateral symmetry was also examined. Whilst a variety of features are commonly present on both sides, the first dissection in a cervicothoracic sympathectomy is no reliable guide to the detailed anatomy of the second side. The sympathetic pathways to the heart are extremely variable in their topography, and the diversity of arrangements encountered accounts for the morphological contradictions in the literature. So numerous are the possible variations that the outcome of a sympathectomy is unpredictable. Where denervation is incomplete, collateral sprouting and regeneration of nerves could even lead to hyperstimulation via the sympathetic pathways.
Effects of cold on the skeletal growth of albino rats
Authors: Lee Marjorie M. C. , Chu P. C. , Chan H. C.
Published: February 2005

Two groups of male albino rats of 26 days old, were kept at 5°C and 28°C respectively. Their growth was studied by weekly gross measurements and biweekly radiographic investigations for 16 weeks. Compared with the controls at 28°C, the rats kept at 5°C showed the following effects of cold in their growth: (1) Smaller measurements at all ages; (2) Slower growth rates in the first two to four weeks; (3) Relatively shorter tail and shorter feet but body weight was the same as the controls of the same body lengths irrespective of age; (4) Shorter but relatively thicker bones; (5) A disto‐proximal stunting gradient was observed in the tail and limb bones, showing more severe effect in the distal segments and decreasing effect in the proximal segments; (6) Retardation of skeletal maturational status in the naked appendages (tail and foot); (7) Decreased number (1.4) of ossified caudal vertebrae.

The above phenomena were discussed as results of possible reduction of blood flow to the skeletal tissue on cold exposure.
The prenatal development of the human humerus
Authors: Gray D. J. , Gardner Ernest
Published: February 2005

Forty pairs of humeri, from a series of embryos and fetuses ranging from 26 to 342 mm in crown‐rump length, were measured, radiographed, and sectioned for microscopic study.

A primary bony collar was present before the end of the embryonic period, and in a 27 mm embryo it extended for nearly one‐third of the length of the humerus. Erosion of the collar occurred at the end of the embryonic period. By about 37 mm, endochondral ossification began, and cartilage canals were invading the proximal epiphysis.

As endochondral ossification proceeded proximally and distally and growth zones became established, periosteal bone formation also proceeded longitudinally and, until about 18 weeks, extended about one millimeter beyond the zone of cartilage destruction in the growth zones. Subsequently the extents of periosteal and endochondral ossification were the same and at term occupied 79% of the length of the humerus.

Trabeculation of the bony collar began in the embryonic period. Fusion of endochondral trabeculae with the inner aspect of the periosteal shell began by 61 mm. A central marrow cavity free of trabeculae was consistently present after 86 mm. Evidence of reconstruction appeared in the proximal end by 73 mm and in the distal end by 113 mm, and was always present after 97 and 125 mm respectively.
Unique aspects of reproduction in the female pronghorn (Antilocapra americana Ord)
Authors: O'gara Bart W.
Published: February 2005

Investigation of the reproductive tracts of 78 pregnant pronghorns (Antilocapra americana Ord) revealed that even though twin births were the rule, three‐seven ova were commonly ovulated, fertilized, and developed into expanded blastocysts. Some mortality occurred in the thread‐stage because of knotting and tangling of the blastocysts. When more than one embryo per uterine horn survived the thread‐stage, the one distal to the corpus uteri was displaced or its membranes were pierced by the necrotic tip of the proximal embryo. Thus, excess blastocysts and embryos were eliminated during the thread‐stage or at the time of implantation.

The pronghorn uterus was bicornuate with an average of 92 caruncles which increased approximately 250 times in volume during gestation. The placenta was of the epitheliochorial type. Transuterine migration of ova occurred. When the embryos were 50–75 mm in length, their membranes met in the corpus uteri. The cervix had 4 or 5 muscular valves with papillae projecting caudally. During late gestation a cervical plug formed in the posterior valve.
Morphogenetic studies of the rabbit. XXXVIII. Epigenetic probing of the genome
Authors: Sawin P. B. , Muehlke Marjorie
Published: February 2005

This study is concerned with the use of the initial gradient of fusion of the neural arch lamellae of the vertebrae on days 31–34 postconception as epigenetic reference points for analysis of the growth retardation and malformation induced systemically by one specific gene, Da (chondrodystrophy), and the modification of such effect induced by the genomes of two different strains (DA and IIIDa). Although during this period the fusion process is confined to vertebrae 29–36, aproximately 10 to 14 days later it is extended throughout the vertebral column.

Intra‐ and inter‐strain comparisons measured by incidence, range, and peak of neural arch fusion (NAF) confirm the same general nature of the growth effects resulting from the gene (Da) and genomes (DA, IIIDa) and from their interaction, i.e., Da and DA acting additively in retarding the growth (in this case fusion) process, whereas IIImo, IIIDa, and IIIep are in opposition. The study (1) increases knowledge of the generality or systemic nature of the Da retardation effect; (2) demonstrates a stronger effect of the polygenic genome in suppressing the effects of the major gene than previously found in the lumbar gradient; (3) reveals the usefulness of epigenetic reference points in defining the limits of endogenous (and possibly of exogenous) influences upon growth and developmental processes in time and locale; and (4) reveals the existence of at least one new genetic element within IIImo which has also been transferred to the IIIDa genome by the breeding procedure described.
The relation between human fetal mouth opening reflexes and closure of the palate
Authors: Humphrey Tryphena
Published: February 2005

The status of the palatal shelves of shelves of human fetuses (before, during and after palatal shelf elevation) was correlated with mouth opening reflexes recorded cinematographically by Doctor Davenport Hooker for many of the same fetuses. Some deductions and conclusions follow.

Mouth opening reflexes begin before palatal shelf elevation and are a significant factor in tongue withdrawal from between the vertical shelves through traction resulting from mandibular depression. (2) The upward pull on the palatal shelves created by differences in pressure between the closed nasal area and the oral region when the tongue is withdrawn (epithelial plugs fill external nares completely) is an active force for palatal shelf elevation. (3) Palatal shelf movements are variable in character and closure sometimes results in the shelf borders enfolding each other. (4) On mouth closure, pressure on the shelves by the tongue and the amniotic fluid entering the mouth helps maintain shelf position before fusion. (5) Human palatal shelf elevation without shelf contact in the midline is not necessarily part of normal closure, but, especially if the shelves are far apart, a stage in cleft palate formation. (6) Increased mandibular growth follows rather than precedes tongue withdrawal. Other factors influencing closure are discussed.
Morphological and biochemical observations on the catecholamine‐storing vesicles of rat adrenomedullary cells during insulin‐induced hypoglycemia
Authors: D'anzi Francis A.
Published: February 2005

The purpose of this study is to demonstrate a structure – function relationship between the release of catecholamines and the depletion of catecholamine‐storing vesicles from cells of the adrenal medulla. The approach taken here is a comparative study of storage vesicle morphology and population, as determined electron microscopically, and of catecholamine concentration, as determined fluorometrically, in adrenomedullary cells at various times during the extrusion phase of the secretory process.

To achieve an increased rate of catecholamine release from the gland, animals were made hypoglycemic by the administration of insulin. At one‐hour intervals following this injection and just prior to sacrifice, the severity of the imposed hypoglycemic state was determined from analysis of the blood serum glucose level. The fine structure alterations in adrenomedullary cells of one gland were then compared with the change in catecholamine content of the contralateral gland.

The decline in blood serum glucose following insulin administration resulted in a decrease in both the adrenaline‐stroing vesicle population and adrenaline content of the gland.
Uptake and storage of thorotrast by the rodent yolk sac placenta: An electron microscopic study
Authors: Carpenter S. J. , Ferm V. H.
Published: February 2005

Electron microscopy was used to investigate the uptake and storage of electrondense particulate matter by the rodent yolk sac placenta. Pregnant hamsters were given single intra‐uterine injections of Thorotrast on day 13, 14 or 15 of gestation and killed at intervals between 15 minutes and 48 hours thereafter. Electron microscopic examination of yolk sacs removed from the injected animals revealed the rapid and progressive uptake of the tracer particles by the visceral epithelial cells of these fetal membranes. Pinocytic vacuoles (phagosomes) containing Thorotrast were visible in the apical cytoplasm of epithelial cells as early as 15 minutes after injection and became increasingly abundant in these cells at later post‐injection intervals up to 18 hours. Epithelial cells which became fully engorged with Thorotrast vacuoles exhibited various pathologic changes, possibly caused by the interference of the metabolically inert metal particles with intracellular digestive mechanisms (the lysosome system). There was no evidence, however, of transport of Thorotrast particles through or between the yolk sac epithelial cells. The connective tissue spaces and blood vessels of the yolk sac, as well as underlying fetal compartments, were free of the tracer particles at all observed intervals after injection.
Rib development in chick embryos analyzed by means of tantalum foil blocks
Authors: Sweeney Robert M. , Watterson Ray L.
Published: February 2005

Rib development in chick embryos, with special emphasis on the origin of ribforming cells, has been analyzed by inserting tantalum foil blocks parallel to certain somites of the prospective rib‐forming level. Intact edges of bent pieces of foil the width of 4–6 somites were inserted through the somatopleure at stage 14–16 either (1) immediately lateral to the nephrotome, (2) between proximal and distal portions of the lateral plate or (3) within the distal lateral plate. Edges of similar pieces of foil containing a triangular notch the width of 2 somites were likewise inserted through the somatopleure of stage 14–16 embryos (4) immediately lateral to the nephrotome or (5) between proximal and distal portions of the lateral plate.

On the basis of the modified rib pattersn studied in toto after 11 days of incubation it was concluded that the (1) original somatic mesoderm does not participate in formation of vertebral rib components, (2) original somatic mesoderm plays some role in formation of sternal rib components (ribs 3–7) but probably does not contribute chondroblasts for this purpose, and (3) distalmost somatic mesoderm is not involved in rib formation. Consistent types of modified wings are described and also modifications of the body wall, breast and ventral feather tracts of the right side.
Ultrastructure of the metrial gland cell in the pregnant rat
Authors: Larkin Lynn H. , Flickinger Charles J.
Published: February 2005

The metrial gland cells of the pregnant rat were studied with the electron microscope from day 12 through day 15 of pregnancy. Prominent features of their fine structure included abundant granular endoplasmic reticulum, a large Golgi complex, and numerous dense granules. These granules were bounded by a single membrane and contained a dense material, smooth vesicles, and membranous whorls. It is suggested that the dense material is aggregated in the mature granules by the coalescence of smaller progranules that are derived from the Golgi apparatus. The nature and fate of these granules is discussed in relation to the possible secretion of relaxin by metrial cells.
Influence of unilateral ovariectomy on follicular development in cycling rats
Authors: Peppler Richard D. , Greenwald Gilbert S.
Published: February 2005

Ovarian follicular development was analyzed in intact and unilaterally ovariectomized cyclic rats. Holtzman rats, followed for three successive cycles, were classified as 4‐ or 5‐day animals, with estrus designated as day 1. Intact 4‐ and 5‐day animals were killed on each day of the estrous cycle and one ovary from each animal was saved for histology and examined for normal follicles larger than 352 μ. Cycling rats were unilaterally ovariectomized on day 1 and killed on each of the remaining days of the immediate estrous cycle and day 1 of the next cycle. The follicular population (normal follicles larger than 352 μ) was studied in the remaining ovary.

During the estrous cycle of intact rats, there was a gradual increase in the number of follicles with a diameter of 518 to 571 μ and greater; however, the total number of follicles ranging in size from 352 to 571 μ and larger remained relatively constant. At day 5, in the 5‐day cycling rat, the ovaries were depleted of follicles measuring from 395 to 570 μ.

Following unilateral ovariectomy on day 1, there was a temporary decrease in the number of follicles larger than 448 μ. This agreed with the finding that animals semi‐spayed on day 1 and injected with 20 I.U. human chorionic gonadotropin on day 2 (PM) did not ovulate, whereas intact animals ovulated an average of seven eggs after the same treatment. The remaining ovary of animals unilaterally ovariectomized on day 1 showed a significant increase by the next estrus in the number of follicles larger than 448 μ.

The method of compensatory ovulation in the rat involved doubling the number of large follicles which ultimately matured during the estrous cycle. This resulted from increased proliferation of smaller follicles in the course of the cycle rather than from decreased follicular atresia.
Electron microscopic observations on the morphogenesis of the albino rat lung, with special reference to pulmonary epithelial cells
Authors: O'Hare Karen Hitchcock , Sheridan Michael N.
Published: February 2005

Electron microscopic observations of developing albino rat lung provide further evidence for the endodermal origin of the type I and II pulmonary epithelial cells, and for the mesodermal origin of the interstitial pulmonary cells.

Cytoplasmic glycogen increased in the fetal endodermal cells from day 16 to the twentieth day of gestation. Further development revealed a decrease of this substance in the differentiating pulmonary epithelial cells, and a concurrent increase in the mesodermal interstitial pulmonary cells, these being cells formerly characterized by their high lipid content. A continuous basement membrane delineated the mesodermal and endodermal components of the developing rat lung from day 16 to the third postnatal day. Tight junctions between adjacent endodermal epithelial cells were present throughout this same gestational period. Lamellar bodies, which are characteristic of the type II pulmonary epithelial cell, may be found simultaneously with large quantities of cytoplasmic glycogen. This feature is considered characteristic of fetal endodermal components.

A definite continuum of ultrastructural changes may be traced from the endodermal, columnar epithelial cells to the definitive type I and II pulmonary epithelial cells. Comparable observations for the mesodermal components reveal a progression leading to mature interstitial pulmonary cells.
Ultrastructural aspects of calf submandibular glands
Authors: Shackleford John M. , Wilborn Walter H.
Published: February 2005

Submandibular gland biopsies from four calves were examined by electron microscopy. Most of the parenchyma consists of mucous acini capped by seromucous demilunes. Secretory product of the demilunes reaches the acinar lumen via intercellular canaliculi located between adjacent demilunar cells or by narrow apical extensions of demilunar cells bordering the lumen in common with acinar cells. Intercellular canaliculi are absent between mucous acinar cells, but intercellular space is present at junctions of demilunar cells, acinar cells, and intercalated duct cells. Intercalated ducts are short and connect mucous acini with striated ducts. Striated ducts show more basal infoldings and mitochondria than those of bovine parotid glands. Nuclear bodies are present in most epithelial cell types of the gland but are larger and more easily recognized in nuclei of striated duct cells. Attempts are made to correlate the structure of bovine submandibular glands with its secretion of small amounts of hypotonic saliva relative to the larger volume of isotonic saliva secreted by parotid glands of the same animal.
A comparison of shortening and Z line degradation in post‐mortem bovine, porcine, and rabbit muscle
Authors: Henderson D. W. , Goll Darrel E. , Stromer M. H.
Published: February 2005

Ultrastructural changes in bovine, porcine, and rabbit muscle have been studied during the first 24 hours post‐mortem. Samples were taken for phase and electron microscopy immediately after death, after 4, 8, and 24 hours of post‐mortem storage at 2° and 37°C, and after 24 hours post‐mortem at 16° and 25°C. The results show that two kinds of structural changes occur in muscle during the first 24 hours post‐mortem: (a) a variable amount of shortening, this shortening occurring via a sliding of filaments in all species and at all post‐mortem storage temperatures examined, and (b) degradation of the Z line, and at higher storage temperatures, of the M line also. Shortening of unrestrained muscle occurs soonest post‐mortem at 37°C in all three species and is completed within four hours post‐mortem in porcine and rabbit muscle and within eight hours post‐mortem in bovine muscle. Post‐mortem short‐ening of unrestrained rabbit and porcine muscle is greatest at 37°C (sarcomere lengths of 1.5 μ); shortening of rabbit muscle is minimal at 2°C (sarcomere lenght of 1.7 μ), but shortening of porcine muscle is minimal at 25°C (sarcomere length of 1.8 μ) and is slightly greater at 2°C (sarcomere length of 1.6 μ) than at 16°C. Post‐mortem shortening of bovine muscle is greatest at 2°C (sarcomere length of 1.3 μ), is minimal at 16–25°C (sarcomere length of 1.8 μ), and increases between 25–37°C (sarcomere length of 1.5 μ at 37°C). Sarcomere length measurements show that some variation occurs in the extent of post‐mortem shortening within the same muscle.

Z line degradation occurs sooner post‐mortem and to a greater extent at storage temperatures of 25°C or above than at temperatures of 16°C or below. Also, bovine muscle Z lines are clearly more resistant to post‐mortem degradation than porcine or rabbit muscle Z lines. Loss of fibrillar structure in porcine or rabbit muscle Z lines occurs during the first four hours post‐mortem at 37°C, but eight hours of post‐mortem storage at 37°C are required to cause loss of fibrillar structure of bovine muscle Z lines. After 24 hours at 25 or 37°C, Z lines of rabbit and porcine muscle are usually completely absent; M lines are also frequently absent in this muscle.
Fine structure of the hamster sperm head
Authors: Yanagimachi R. , Noda Y. D.
Published: February 2005

The fine structure of the principal components of the sperm head of the golden hamster (Mesocricetus auratus) is described. The acrosome investing the anterior half of the sperm nucleus comprises two regions, the anteriorly located, enlarged region (acrosome cap) and the posteriorly located, thin region (acrosome collar). The acrosome contains substances which are different in electron density. The less electron‐dense material is present in the anterior part of the acrosome cap. The electron‐dense material is located along the outer acrosome membrane of the posterior part of the acrosome cap and also in the acrosome collar. A cytoplasmic element distributed over the surface of the sperm nucleus is abundant in the regions called perforatorium, subacrosomal ring, and post‐nuclear cap. The perforatorium and subacrosmal ring consist of the densely packed cytoplasmic element invested by the inner acrosome membrane. The post‐nuclear cap is a layer of densely packed cytoplasmic element tightly adhering to the overlying plasma membrane. At the time of sperm death in the epididymis, uterus, and physiological salt solution (Tyrode's) the acrosome cap and plasma membrane tend to undergo drastic degenerative changes. On the other hand, the nucleus, acrosome collar, perforatorium, and post‐nuclear cap remain morphologically unchanged in many spermatozoa during the initial stage of sperm degeneration. Comparisons are made of the structures of the acrosome, perforatorium, and post‐nuclear cap of the hamster spermatozoa with those of other mammalian species.
Morphologic alterations in somatotrophs of the rat adenohypophysis following administration of hypothalamic extracts
Authors: Coates P. W. , Ashby E. A. , Krulich L. , Dhariwal A. P. S. , McCann S. M.
Published: February 2005

Hypothalamic extracts injected intravenously into rats produced morphologic alterations in somatotrophs of the pars distalis as observed with light and electron microscopy. Histological changes were correlated with pituitary growth hormone content as determined by bioassay by the tibia test in the same tissue samples. Statistical analysis of data derived from fine structure (number of secretory granules/somatotroph profile) was useful as an index of granule storage and release. Increased numbers of secretory granules, hypertrophy of the Golgi complex, and increased granule extrusion which were observed within five minutes after injection of hypothalamic extract supported the concept that growth hormone‐relasing factor in the hypothalamic extract was effective not only in releasing growth hormone but also in stimulating its biosynthesis. Significant increases in both growth hormone content and granule counts agreed with this concept. Extremes of granulation and variable organelle morphology were apparent 15 minutes after injection with hypothalamic extract, although overall granule counts and bioassable growth hormone were within normal limits. By 30 minutes somatotrophs depleted of granules were common, suggesting granule release of major proportion which was consistent with significant decreases in number of granules and growth hormone content. Granules remaining in somatotrophs were aligned peripherally. Vesicular Golgi complexes were prominent. Increased numbers of presumed lysosomes may be related to membrane and/or secretory product accumulation which may result from granule synthesis and release. Somatotrophs from control rats appeared normal.
Prenatal growth in the albino rat: Effects of number, intrauterine position and resorptions
Authors: Barr Mason , Jensh Ronald P. , Brent Robert L.
Published: February 2005

Data from 103 litters of albino rats were analyzed for the effects of the number of fetuses in the litter and in each uterine horn, resorptions, and intra‐uterine position on variations in fetal weight. The right uterine horn tended to contain more fetuses than the left. There appeared to be systemic control over both the number of fetuses in the litter and their distribution between the horns. The number of fetuses per litter and the number per horn had separate and different effects on fetal weight. The number of fetuses in the horn was a more important determinant of fetal weight than was the number in the litter. Fetal weight was higher and the effect of the number of fetuses in the horn was stronger in horns with early resorptions than in horns without resorptions. Resorptions had no effect on the weight of adjacent fetuses or on fetal weight variation in the horn which suggests that resorptions influence fetal growth systemically rather than locally. Fetal mortality was highest in the lower one‐third of the uterine horn and lowest in the upper one‐third. Fetal weight variation increased as the number of fetuses per horn increased and as mean fetal weight decreased. Intrauterine position was a significant determinant of fetal weight. The heaviest fetuses occupied the middle of the uterine horn while the lightest fetuses were at either end. The importance of these findings in prenatal growth and teratologic studies is discussed.
The early pattern of cardiac innervation in the fetal guinea pig
Authors: Hoar Richard M. , Hall James L.
Published: February 2005

Embryonic hearts were obtained from 78 guinea pig embryos at 20–40 days of gestation. They were frozen quickly, freeze‐dried and prepared by the Falck catecholamine fluorescent method for demonstration of adrenergic fibers. Other hearts were fixed in 10% formalin and examined after silver impregnation with the Holmes technique. The results of the two methods were correlated to visualize the total neural pattern as well as the specific adrenergic elements of the developing hearts.

The present study indicates that vagal fibers, accompanied by the primordia of the cardiac ganglia, reach the atrial wall on the twenty‐fifth day of gestation in the guinea pig. They penetrate the wall and are distributed by individual branches throughout the atrial wall from days 26 to 29 inclusive. From day 30 to parturition, the basic pattern of atrial distribution is elaborated by the lengthening, thickening, and branching of individual fibers. Sympathetic fibers pass to the atrial wall from the twenty‐fifth to twenty‐ninth day, those coursing with the vagus nerve arriving on the twenty‐fifth day, while the remaining fibers arrive on the twenty‐sixth to the twenty‐ninth days.

A ventricular ground plexus of sympathetic fibers is present just deep to the epicardium on the twenty‐sixth day, and from this point until 30 days of gestation the ground plexus penetrates the ventricular myocardial wall. The sympathetic fibers at first course along the edge of a muscle bundle, but not between muscle fibers. The nerves become thicker at 29 days but do not exceed 2 μ. They branch slightly at 27 days, and at 30 days they are well branched and appear to overlie the surface of the muscle bundles simulating a perimysial plexus. At 40 days a very dense perimysial plexus is visible which contains some fluorescent nerves.

Complete autonomic innervation is established by the thirtieth day of gestation.
The satellite cell bud and myoblast in denervated mammalian muscle fibers
Authors: Hess A. , Rosner S.
Published: February 2005

Satellite cells, rarely seen on normal muscle fibers, are located between the sarcolemma and the basement membrane of a muscle fiber. Limb muscles and the extraocular muscles of adult guinea pigs were denervated and studied from two to seven days after operation. Satellite cells are now frequently seen. A nucleus surrounded by a small amount of cytoplasm separates from a denervated muscle fiber and forms a satellite cell. A series of clefts and membranes forms in the periphery of the muscle fiber to make separation channels and pinch off the muscle cell nucleus and its cytoplasm from the parent fiber. This cell, now called a satellite cell bud, can be seen in the process of splitting off from the parent muscle fiber, with portions of the same cell separated from and still part of the muscle fiber. The sacs of endoplasmic reticulum in the satellite cell bud dilate markedly. Centrioles and a cilium form in the satellite cell bud. The bud elongates, and concentrations of ribosomes and polyribosomes appear in its cytoplasm. Small points of contact, with membrane thickenings, between bud and parent fiber allow the elongating bud to be kept longitudinally oriented under the basement membrane of its parent fiber. Muscle filaments form in the elongating bud, which is now a myoblast. Hence, satellite cells arise from portions of denervated muscle fibers themselves, elongate, and become myoblasts.
The fate of isologous, homologous and heterologous ferritin molecules in the rat
Authors: Han S. S. , Han I. H. , Johnson A. G.
Published: February 2005

The fate of heterologous, isologous and homologous ferritin‐I125 injected into rat footpads was compared by determination of radioactivity in sera and organs, and by radioautography and electron microscopy. The clearance of heterologous ferritin‐I125 from circulation was significantly faster than that of isologous or homologous ferritin‐I125. This was supported by measurement of radioactivity in various organs, and by radioautography and electron microscopy of popliteal lymph nodes which reveled structural details of macrophages undergoing antigen uptake.

These observations permit the following conclusions. (1) In most reticuloendothelial cells there is some nonspecific pinocytosis of antigen which is not related to immunogenicity. (2) The induction of massive immunologically specific pinocytosis by macrophages may be due to specific antigen recognition by receptors located at the cell surface. (3) Heterologous ferritin ingested by macrophages are mostly found in vacuoles or scattered in the ground cytoplasm. However, some appear in the nucleoplasm, usually in association with loose strands of chromatin materials. (4) Ferritin molecules are conspicuously absent from mitochondria, the rough‐surfaced endoplasmic reticulum and Golgi apparatus. (5) The fiber‐associated reticular cells of the primary nodule and germinal centers may correspond to “dendritic reticular cells” or “dendritic macrophages,” capable of long‐term retention of antigens.
Protein absorption and transport by the guinea pig visceral yolk sac placenta
Authors: King Barry F. , Enders Allen C.
Published: February 2005

The cytological basis for protein transport across the guinea pig visceral yolk sac at 36–44 days of gestation was studied by means of electron microscopy following injection of horseradish peroxidase and ferritin. These results were compared with those obtained after administration of colloidal thorium dioxide. Distribution of the tracer molecules was studied at 2, 10, 20, 40, and 160 minutes after injection into the uterine lumen. All three tracer molecules were rapidly absorbed by endoderm cells. Although most of the protein appeared to be retained in droplets in endoderm cells, some protein was transmitted. Peroxidase was found to be rapidly transmitted across the yolk sac, ferritin somewhat more slowly, and colloidal thorium was not transmitted at all. Protein which had exited from the endoderm cells followed any of three pathways: (1) it crossed the visceral basement membrane and entered the vitelline capillaries; (2) it crossed the mesodermal compartment, crossed the mesothelial cells and entered the exocoelomic cavity; or (3) some of the protein was sequestered by macrophages in the splanchnic mesoderm. The pathways observed are consistent with those suggested by previous authors for the passage of maternal antibodies and serum proteins to the guinea pig fetus.
Morphology and cytochemistry of the Golgi apparatus of rat salivary gland acinar cells
Authors: Hand Arthur R.
Published: February 2005

The ultrastructure and cytochemistry of the Golgi apparatus was studied in acinar cells of the parotid and von Ebner's glands of the rat. The Golgi apparatus was composed of four to six stacked cisternae, numerous small vesicles, and condensing vacuoles. The latter appeared to form as dilatations of the innermost Golgi cisterna, and their irregular membrane suggested fusion with or fission of small vesicles. Nucleoside diphosphatase and thiamine pyrophosphatase activities were localized to the inner Golgi cisternae. Acid phosphatase activity was localized to condensing vacuoles, coated vesicles, and an irregular, narrow cisterna found in the internal region of the Golgi apparatus and termed the internal Golgi lamella. The morphology and relationships of the Golgi apparatus indicate that it plays an important role in secretory granule formation. The presence of nucleoside diphosphatase activity may reflect the role of the Golgi apparatus in the addition of carbohydrates to the secretory proteins. It is suggested that the internal Golgi lamella develops from the inner Golgi cisterna after secretory granule formation is completed. Acid phosphatase activity in condensing vacuoles may be a mechanism for lysosomal regulation of the secretory process.
Regeneration of rat submandibular gland following partial extirpation. A light and electron microscopic study
Authors: Hanks C. T. , Chaudhry A. P.
Published: February 2005

A wedge of parenchymal tissue was excised from the left submandibular gland of six week old male Sprague‐Dawley rats. The animals were randomly grouped by body weight and killed at intervals of one day to five weeks following the operation. Tissue from and adjacent to the site of injury was removed and prepared for routine light and electron microscopy. Light microscopic findings consisted of degeneration and necrosis of the parenchymal tissue during the first 24 hours, followed by hyperemia and endothelial as well as epithelial proliferation from one to three days. Extensive epithelial proliferation occurred during the next two weeks, followed by regeneration of new lobules, beginning at the periphery of the injured lobes.

Ultrastructurally, the new parenchymal tissue appeared to have regenerated from residual duct cells. Dedifferentiated epithelial cells gave rise to two different cell lines: one line which transformed into terminal tubules and acinar cells, and another which became striated ducts. These differentiating cells were organizing into lobules as early as three weeks after the operation. Because of their proximity to cells of regenerating striated ducts as well as intercalated ducts and acini, the myoepithelial cells appeared to be of epithelial origin.
Action of metabolic hormones on the fine structure of rat liver cells. I. Effects of fasting on the ultrastructure of hepatocytes
Authors: Cardell Robert R.
Published: February 2005

This report provides information on the ultrastructure of liver parenchymal cells from rats fasted 2, 15–21, and 21–40 hours. Fasting rats from 2 through 40 hours provokes alterations in the quantity and patterns of glycogen, amounts and forms of the rough endoplasmic reticulum, and the quantity of smooth endoplasmic reticulum in hepatocytes. After two hours of fasting glycogen occurs as clumps of α particles in restricted areas of the cytosome, the smooth endoplasmic reticulum is relatively sparse, and the rough endoplasmic reticulum is displayed as parallel cisternae comprising the characteristic basophilic bodies of the hepatocyte. Fasting the rat for 15 hours and longer decreases the amount of hepatic glycogen which appears predominantly as β particles in restricted regions of the liver cell. The prolonged fast provokes a dramatic proliferation of smooth endoplasmic reticulum in the liver parenchymal cell. The tubules of this organelle are continuous with the cisternae of rough endoplasmic reticulum and extend deep into the glycogen areas of the hepatocyte. Arguments are presented to support the concept that the smooth endoplasmic reticulum develops from rough endoplasmic reticulum and that its membranes provide a site for the location of enzymes involved in glycogen metabolism.
Renewal of the epithelium in the descending colon of the mouse. I. Presence of three cell populations: Vacuolated‐columnar, mucous and argentaffin
Authors: Chang W. W. L. , Leblond C. P.
Published: February 2005

The epithelium of the descending colon was examined in the mouse using one‐micron thick Epon embedded sections of formaldehyde‐fixed tissues stained with the periodic acid‐Schiff and iron‐hematoxylin techniques, and radioautographed at various time intervals after a single injection of tritium labeled thymidine.

Four cell types may be described: vacuolated cells located in the lower twothirds of the crypts, columnar cells in the upper third and on the surface, mucous cells and argentaffin (granule‐containing) cells distributed throughout crypt and surface.

One hour after injection of 3H‐thymidine, only some vacuolated and mucous cells are labeled; cells of both types may show mitotic figures, but only in the lower two‐thirds of the crypts.

By 36 hours, label appears in cells of the upper third of the crypts; some of these cells are intermediate between vacuolated and columnar, while others are full‐fledged columnar cells. Labeled mucous cells also appear at this level. Occasionally, a labeled argentaffin cell may be found at that time toward the base of the crypts.

By three days, labeled columnar and mucous cells are found on the surface. Extrusion of such labeled cells is usually seen toward the fourth day.

It is concluded that the epithelium of the descending colon of the mouse includes three cell lines. In the first one, vacuolated cells divide to produce more vacuolated cells, but as they migrate upwards, they lose their vacuoles while ceasing to divide and become typical columnar cells. Together they make up the vacuolated‐columnar cell line. The mucous cells arise from mitosis of cells with a small amount of mucus. As daughter cells migrate upwards, their theca swells, presumably because production of mucus exceeds release, whereas, on the surface, the theca becomes narrow as release predominates. In the third cell line, the argentaffin cells do not divide and appear to originate from poorly differentiated vacuolated cells at the base of the crypts. The latter cells may also give rise to the young mucous cells capable of division. The three cell lines would thus have a common stem cell.
Renewal of the epithelium in the descending colon of the mouse. III. Diurnal variation in the proliferative activity of epithelial cells
Authors: Chang W. W. L.
Published: February 2005

The rate of proliferation of epithelial cells in the descending colon was investigated in four groups of adult mice sacrificed one hour after injection of 3H‐thymidine respectively at 04:00, 10:00, 16:00 and 22:00 h of the day. Semithin (1 μ) Epon embedded sections of the colon were radioautographed after staining with periodic acid‐Schiff and iron‐hematoxylin.

Measurement of the number of mitoses as well as the labeling indices show a diurnal variation in the rate of proliferation of both vacuolated and mucous cells. The peak of mitotic activity in both cell types seems to be around 12:00–13:00 h and the nadir around 20:00–22:00 h.

In the vacuolated‐columnar cell line, the rate of proliferation of the poorly differentiated cells at the base of the crypt is not much influenced by diurnal variation, while that of the more differentiated cells located higher up is. Mucous cells, which are believed to originate in the poorly differentiated vacuolated cells in the lower portion of the crypt, are also strongly affected. Therefore, the more differentiated cells are, the more susceptible they are to diurnal variation in mitotic activity.

The number of epithelial cells lining the crypt varies throughout the day in a similar manner as the rate of cell proliferation. A slight daily variation is also noted in the number of cells in the surface epithelium. These variations are accounted for by a delayed effect of the population pressure resulting from the mitotic peak. The numbers of vacuolated‐columnar and mucous cells vary like those of the whole epithelial population, while argentaffin cells fluctuate more widely. In any case, the three main cell lines of the descending colon of the mouse are influenced to some extent by diurnal variations.
A morphological study of the development of the human liver. I. Development of the hepatic diverticulum
Authors: Severn Charles B.
Published: February 2005

The development of the hepatic diverticulum was examined in 38 human embryos representing somite stages 1, 5, 8 and 10 through 29, inclusive. Interpretations were based on light microscopic study of serial sections of these embryos.

The liver primordium was first identified in a five‐somite embryo as a flat plate of endodermal cells continuous with, but lying ventral to, the endoderm of the foregut at the anterior intestinal portal. It is positioned caudal and ventral to the developing heart. This plate of endoderm subsequently undergoes a progressive folding due to differential growth of adjacent structures. During the folding process there is a close spatial relationship between the cells of the endodermal plate and the caudal and ventral endothelial lining of the atrium and the sinus venosus. The result of this folding is the establishment of a “T‐shaped” diverticulum which projects ventrally and cephalically from the gut tract. The hepatic diverticulum is established by the 20 somite‐stage embryo. This mode of development of the hepatic diverticulum is compared to the classical interpretation and to the development of other visceral organs.