bluuebunny/crossref_metadata_2025 huggingface dataset:
The structure and innervation of cat knee menisci, and their relation to a “sensory hypothesis” of meniscal function
Authors: O'Connor Brian L. , McConnaughey J. Scott
Published: February 2005

Previous work on dog knee menisci demonstrated structural differences between the meniscal horns and the meniscal bodies (O'Connor, 1976). Of particular interest was the observation that the meniscal horns possessed an abundant blood and nerve supply, while the meniscal bodies did not. The presence of nerves in the meniscal horns prompted the speculation that menisci might perform a sensory function.

The present study was undertaken in order to establish whether or not similar regional differences existed in cat knee menisci, structures previously believed to lack a corpuscular mechanoreceptor system (Freeman and Wyke, 1967).

Differences between the meniscal horns and meniscal bodies similar to those reported in the dog were found to characterize cat knee menisci. In particular, the meniscal horns possessed a rich neurovascular supply, while the meniscal bodies did not. Most important, at least two morphologically different mechanoreceptors were identified in the meniscal horns, but none were identified in the meniscal bodies.
Immunocytochemical localization of renin in the submandibular gland of the mouse during postnatal development
Authors: Gresik E. W. , Michelakis A. , Barka T.
Published: February 2005

The localization of renin in the developing mouse submandibular gland was studied immunocytochemically using the unlabelled antibody‐enzyme method of Sternberger (1974). Bouin‐fixed submandibular glands of mice of both sexes were examined at 5‐day‐intervals from birth (day 0) to 50 days of age. At all stages studied, only granular convoluted tubule (GCT) cells stained immunocytochemically for renin; such cells were first seen in glands of 30‐day‐old males and of 30‐day‐old females. The size and number of renin‐containing GCT cells increased rapidly in males, attaining adult status by 50 days of age. In females, differentiation of GCT cells immunoreactive for renin was slower and less regular than in males, and at 50 days of age the GCT segment had not yet reached adult conditions with respect to the distribution of renin. Renin appears in GCT cells at later ages than other GCT cell products (e.g., EGF and amylase), suggesting the existence of independent developmental control for the expression of various biologically active substances in the GCTs.
Demonstration of neurosecretory substance in previosly scanned specimens: Adaptation of the gomori aldehyde‐fuchsin method for correlative SEM/TEM/LM histochemistry
Authors: Coates P. W. , Teh E. C.
Published: February 2005

The Gomori aldehyde‐fuchsin (AF) method for selective staining of neurosecretory substance (NSS) has been adapted to tissue previously prepared for both scanning and transmission electron microscopy (SEM/TEM). The procedure results in precise correlation of light microscopic (LM) histochemistry with SEM/TEM of the same tissue.
Shunting in intracranial microvasculature demonstrated by sem of corrosion‐casts
Authors: Anderson Bettina G. , Anderson Wesley D.
Published: February 2005

The use of methyl methacrylate corrosion‐casts has made it possible to examine the intracranial microvasculature on a three‐dimensional scale with the scanning electron microscope. By this means we have compared regions of four cerebral and cerebellar arteries among three domestic animal species. The results of this study suggest that there are from one to three different levels of interarteriolar anastomosis between branches of the same or adjacent vessels. In the horse and ox anastomoses were demonstrated (1) at the level of the precapillary arterioles, (2) along the arterioles, and (3) between small pial arteries. In the dog only the first‐named anastomoses were evident in this study. These morphological characteristics may explain, in part, the shunting mechanism by which hypoxia may be reduced among intracranial capillary networks.
The effect of lanthanum on the nexus of the anterior byssus retractor muscle of Mytilus edulis L.
Authors: Brink Peter R. , Kensler Robert W. , Dewey Maynard M.
Published: February 2005

The nexus of the anterior byssus retractor muscle (ABRM) of Mytilus has been observed with freeze‐fracture techniques. Pits appear in the EF face and particles in the PF face, designating it as an A‐type nexus. Under control conditions (lanthanum‐free) the center‐to‐center spacing of pits and particles ranged from 14.0 nm to 15.5 nm. When lanthanum chloride (5 mM) was used in incubation media before fixation and glycerination, marked changes in the nexal membrane were observed. These changes involved close packing and long‐range ordering of pits in the EF face, as shown by optical diffraction. In the presence of lanthanum the center‐to‐center spacing of the pits was 11.7 nm, while the particles remained at a spacing of 15.0 nm. From this we conclude that specific agents can alter the array of pits and particles in a nexus (gap junction).
Microfilaments, the smooth endoplasmic reticulum and synaptic ribbon fields in the pinealocytes of the baboon (Papio ursinus)
Authors: Theron J. J. , Biagio R. , Meyer A. C. , Boekkooi S.
Published: February 2005

Microfilaments (MF, 5–8 nm in diameter) are a prominent feature of the pinealocyte cytoplasm of baboons (Papio ursinus) kept under controlled lighting conditions. MF occurred as a filamentous network in these cells during the light phase of the diurnal light‐dark cycle, while a close structural association was noted between MF and the membranes of the smooth endoplasmic reticulum (SER). This association was especially evident during the dark period. Increased numbers of single synaptic ribbons (SR, vesicle‐crowned rodlets), together with large aggregations of SR, i.e., ribbon fields (RF), were seen in the pinealocyte cytoplasm of baboons killed during the dark phase. It is suggested that the vesicles of RF may arise from those of the SER and that MF may play a role in the movement of SER‐vesicles to those areas of the cytoplasm where new RF are being formed.
Retinal development in the lamprey (Petromyzon marinus L.): Premetamorphic ammocoete eye
Authors: Dickson D. Howard , Collard Tom R.
Published: February 2005

Development of the retina of the ammocoete begins early in embryogenesis, with the formation of the optic vesicle, but development of the rudimentary eye is suspended and remains arrested during larval life. Prior to the onset of metamorphosis, the retina of the ammocoete is completely undifferentiated, with the exception of a small area (Zone II) surrounding the optic nerve head, where all of the adult retinal layers are found. The photoreceptors in this area have developed to include synaptic contacts as well as inner and outer segments. The pigment epithelium in this area, too, has differentiated to include well‐formed melanin granules, myeloid bodies and endoplasmic reticulum and is closely associated with the receptor cell outer segments. With the approach of metamorphosis, differentiation of the remainder of the retina (Zone I) begins, taking place in a radial fashion from the optic nerve head. Differentiating pigment epithelial cells adjacent to the differentiated retinal zone begin to accumulate melanin granules. In the neural retina, junctional complexes are established in the form of an external limiting membrane, and connecting cilia project into the optic ventricle. Photoreceptor differentiation begins with the formation of a mitochondria‐filled ellipsoid within the inner segment.

Development and differentiation of the ammocoete retina is unique to vertebrates in that only a small area of differentiated retina is present during the larval stage. The remainder of the retina differentiates and becomes functional during metamorphosis.
The corpus luteum of the guinea pig. IV. Fine structure of macrophages during pregnancy and postpartum luteolysis, and the phagocytosis of luteal cells
Authors: Paavola Laurie G.
Published: February 2005

Little information is available on the ultrastructure of macrophages in the corpus luteum or their importance in the regression of luteal tissue. In the present study, the fine structure of activated luteal macrophages during pregnancy and the postpartum period was examined by electron microscopy of guinea pig ovaries fixed by vascular perfusion. In these corpora lutea, macrophages can readily be distinguished from luteal cells. Activated macrophages typically display three prominent inclusions in their cytoplasm: (1) heterophagic vacuoles, (2) distinctive large dense inclusions, and (3) large and small electron‐lucent vacuoles. In addition, they contain numerous smaller lysosome‐like dense bodies. Activated macrophages in corpora lutea also characteristically show many surface protrusions, such as processes, folds or pseudopodia, which often occur in close contact with nearby luteal cells. Generally, nuclei of macrophages are irregular in shape and display a dense border of heterochromatin, thus differing from those of luteal cells.

Macrophages seem to be most abundant in regressing corpora lutea, where they commonly display heterophagic vacuoles containing recognizable luteal cell fragments, evidence that these phagocytes ingest senescent luteal cells. The digestion of luteal cell components in heterophagic vacuoles presumably gives rise to the distinctive large dense inclusions typically seen in macrophages. The findings of this study indicate that macrophages play a central role in luteolysis by phagocytizing luteal cells or their remnants. They therefore appear to bring about the reduction in volume of the corpus luteum that occurs as this tissue regresses. These results taken together with those previously published (Paavola, 1978) further indicate that breakdown of the corpus luteum during postpartum luteolysis in guinea pigs involves both autophagy and heterophagy.
Functional heterogeneity in a multipinnate muscle
Authors: Herring Susan W. , Grimm Arthur F. , Grimm Betsy R.
Published: February 2005

Many mammalian muscles have a complex internal architecture. This type of structure could allow a single muscle to produce a variety of force vectors through selective regional contractions. This hypothesis was tested electromyographically in the multipinnate pig masseter by recording simultaneously from several intramuscular sites. It was found that the activity in different portions of the masseter varied systematically during the various phases of mastication. Anatomical correlates of the differential activity included fasciculus orientation and length, sarcomere length in specific jaw positions, and histochemical fiber type. The usual assumptions made about muscles for biomechanical analysis, such as uniform contraction and constant line of action, are inappropriate for complex muscles such as the pig masseter.
Development of lamellar bodies and subsurface cisterns in pyramidal cells and neuroblasts of hamster cerebral cortex
Authors: Buschmann Mb. Tank
Published: February 2005

In pyramidal cells of hamster frontal cortex lamellar bodies and subsurface cisterns sequentially occurred during development from newborn to three months of age. Neither of these two specializations of the rough endoplasmic reticulum was seen in neurons of the newborn. The first specialization that we observed was the subsurface cistern, which appeared at five days and showed a significant increase both in frequency and in length throughout development. The lamellar body was first seen at ten days of age. This specialization showed a peaking of frequency, length, and number of cisterns per body at 15 days, which subsequently decreased gradually to 3‐month‐old levels. The occurrence of lamellar body‐subsurface cistern complexes increased with age. We suggest that the lamellar body may be an ER specialization that is involved in an increased and/or stage‐specific protein synthesis in the young prior to the final maturation of the usual neuronal protein synthetic organelles, and that in the 3‐month‐old neurons, the lamellar body may be involved in modifying, storing or transporting metabolites received from the neuropil components via the subsurface cisterns. The subsurface cistern, on the other hand, by virtue of its location subjacent to the neuronal plasma membrane and of its increased frequency from birth to maturation, may be involved in the exchange of metabolites and nonsynaptic forms of communication at all ages.
The structure and distribution of the cross‐striated fibril and associated membranes in guinea pig photoreceptors
Authors: Spira Arthur W. , Milman Gordon E.
Published: February 2005

Examination of longitudinally and transversely sectioned photoreceptor cells of the guinea pig retina revealed an aggregate of thin filaments forming a single cross‐striated fibril coursing through the full length of the non‐receptor portion of the cell. The fibril begins as the ciliary rootlet from the region of the basal body of the connecting cilium. From the basal body it passes between the mitochondria of the ellipsoid and along the Golgi zone of the myoid region of the inner segment, narrowing from an irregularly shaped bundle to a ribbon‐shaped aggregate. The fibril separates into discrete strands, each curving along the nucleus, reuniting into a single bundle to pass down the cell's axon, and terminating deep within the synaptic terminal. The fibril is flanked by two separate membranous saccules, each continuous along nearly its full length. The fibril's extensive course in the guinea pig and its association with continuous membranes necessitates a reexamination of earlier proposals for the function of cross‐striated filamentous structures in photoreceptor cells.
Occurrence and distribution of muscle spindles in masticatory and suprahyoid muscles of the rat
Authors: Maier Alfred
Published: February 2005

The occurrence and distribution of muscle spindles was studied in histochemically and conventionally stained serial cross sections of 6‐week‐old and adult rat masticatory and suprahyoid muscles. Spindles were present in moderate to large numbers in jaw closers, but they were absent in jaw openers and two of four muscles of an accessory suprahyoid group. In jaw closers, 67% or more of the total spindle population was concentrated relatively distant from the temporomandibular joint, in muscle portions which contained large numbers of extrafusal fibers reacting strongly for oxidative enzymes. Because of their location, spindles in these portions should be stretched more and, subsequently, should respond with a greater afferent discharge at any given muscle length than spindles situated nearer to the joint. Spindles in jaw closers, especially the medial pterygoid and deep masseter, often occurred in clusters and complex forms near the terminal branching of intramuscular nerve trunks. No such concentrations were seen in the two muscles of the accessory suprahyoid group that had spindles. The association in jaw closers of spindles with extrafusal fibers high in oxidative enzyme activity is consistent with the view that spindles are the sensory component of a reflex system that recruits these fibers for finely‐graded contractions in response to small internal length‐changes of the muscle (Botterman et al., 1978); however, in jaw openers and two muscles of the accessory suprahyoid group, the absence of spindles, coupled with the presence of large populations of extrafusal fibers high in oxidative enzyme activity, is not easily reconciled with this concept.
Alterations within the rat thyroid gland during vitamin A deficiency
Authors: Strum Judy M.
Published: February 2005

Thyroid glands from female rats kept vitamin A deficient for one, two, and three months were examined by electron microscopy. After one month on the diet, no consistent alterations were noted. After two months, the colloid in some follicles displayed a peripheral zone of decreased density. In addition, ultimobranchial follicles within the gland had become keratinized. After two to three months on the diet, cells were seen entering the colloid. Many of these cells were identified as follicular cells since they often occurred in groups and occasionally exhibited remnants of desmosomes. Often the cells within the colloid appeared vacuolated, and by light microscopy were thought to contain lipid. However, electron microscopy revealed that these cells contained many digestive vacuoles rather than lipid droplets.

Quantitative and autoradiographic studies indicated that thyroids of vitamin A deficient rats took up less radioiodide than thyroids of control rats. The keratinization of ultimorbranchial follicles in vitamin‐A deficiency has been suggested as preliminary in the histogenesis of squamous cell carcinoma. However, an effect of vitamin A deficiency on thyroid follicular cells has not heretofore been reported. It's possible that the presence of follicular cells in the colloid reflects an accelerated turnover of these cells and could indicate an early pathological sign.
The surface structure of the completely and incompletely orthokeratinized oral epithelium in the rat: A light, scanning and transmission electron microscope study
Authors: McMillan M. D.
Published: February 2005

Mucosa from the hard and soft palates, molar gingiva, cheek and dorsal surface of the tongue of the rat was examined in the light microscope, following Mallory's triple connective tissue stain, and in the scanning and transmission electron microscopes. The epithelium covering the hard palate, gingiva, the smooth band of mucosa at the junction of the hard and soft palates, intermediate zones of the soft palate, fungiform papilla‐like structures in the central zone of the soft palate, the fungiform papillae, and the more superficial part and posterior surfaces of the filiform papillae of the tongue all exhibited complete orthokeratinization. The oral surfaces of the epithelial cells in all these areas had a honeycomb pattern of interconnecting ridges surrounding depressions. Imprints of the overlying cells that had been desquamated were apparent, and the lateral boundaries between the cells were formed by two raised ridges separated by a gap. The epithelium covering the cheek, central zone of the soft palate apart from the fungiform papilla‐like structures, lateral zones of the soft palate, gingival crevice, and the mucosa between the fungiform and filiform papillae of the tongue all exhibited incomplete orthokeratinization. The oral surfaces of the epithelial cells in all these areas were relatively smooth and did not exhibit a honeycomb pattern of interconnecting ridges. Imprints of the overlying cells that had been desquamated and the lateral boundaries between the cells were only very occasionally found. In the transmission electron microscope the outlines of the cells were compatible with the surface patterns seen in the scanning electron microscope. The possible relationships between the degree of orthokeratinization and ultrastructure of the various epithelia are discussed.
Cyclic changes in ciliation, secretion and cell height of the oviductal epithelium in women
Authors: Verhage Harold G. , Bareither Mary L. , Jaffe Randal C. , Akbar Maksood
Published: February 2005

Oviducts were obtained from women who elected to undergo sterilization either during a normal menstrual cycle, after the first trimester of pregnancy, or in the puerperium. The percent of ciliated cells, cell height and morphology of the fimbria and ampulla were determined and correlated with the stage of the reproductive cycle and plasma levels of the ovarian steroids. Mature ciliated and secretory cells were observed only at mid‐cycle. Atrophy, deciliation and loss of secretory activity coincided with elevated levels of serum progesterone. These degenerative processes continued during pregnancy. Ciliation, hypertrophy, and restoration of secretory activity occurred when serum progesterone was essentially undetectable and estradiol relatively low. During each menstrual cycle the secretory cells were observed to undergo a complete cycle of dedifferentiation‐differentiation, whereas 10‐12% of the ciliated cells lost and regenerated their cilia. Ciliogenic cells were frequently present in the epithelium obtained from women in the mid‐follicular phase. Fibrous granules, deuterosomes, procentrioles and ciliary buds were observed in the apex of these cells. Plasma levels of estradiol were higher during periods of atrophy and deciliation than they were during periods of hypertrophy and reciliation. It appears that the serum levels of estradiol were adequate to maintain a mature epithelium at all the reproductive stages included in this study. However, progesterone, when present, blocked the growth‐promoting effect of estradiol in the oviduct.
The structure of the sinus wall of the lymph node relative to its endocytic properties and transmural cell passage
Authors: Farr Andrew G. , Cho Yongock , de Bruyn Peter P. H.
Published: February 2005

The internal structure of cells lining the lymphatic sinus of the lymph node includes the presence of large bristle‐coated vesicles, transfer tubules, and vesicular organelles for the uptake and intracellular disposition of endocytosed material. The lining cells of the sinuses phagocytose particulate material from the lymph in the same manner as the sinusoidal endothelium of the bone marrow takes up particulates from the blood and, thus, are similar in this respect to the endothelial lining of the bone marrow sinusoids.

Transmission and scanning electron microscopic examination of the lymphatic sinus wall in rat lymph nodes show that the walls of the lymphatic sinuses are continuous and do not have permanent apertures allowing free communication between the extrasinusoidal and intrasinusoidal compartments in the lymph node.

Migrating lymphocytes cross the lymphatic sinus wall intracellularly, i.e., through the body of the lining cell, by making a temporary migration pore, which closes after the cell has reached the lumen of the sinus. In addition there are sporadic aggregations of macrophages in transmural positions. The direction of their movement is unknown.
Uptake of exogenous substances and marked infoldings of the fluorescent granular pericyte in cerebral fine vessels
Authors: Mato Masao , Ookawara Shigeo , Kurihara Kyoichi
Published: February 2005

Exogenous substances such as trypan blue and horseradish peroxidase administered intraventricularly are taken up by granular pericytes in cerebral fine vessels. These cells are provided with elongated and complicated infoldings. Pinocytotic vesicles occur often along the infoldings, and ends of infoldings are swollen and assume vesicular shapes. The specific morphology of the granular perithelial cells is considered to favor a removal of metabolic wates in cerebral tissue.
Characterization of intercellular junctions in the caudal portion of the developing neural tube of the chick embryo
Authors: Schoenwolf Gary C. , Kelley Robert O.
Published: February 2005

The types of intercellular junctions present within caudal levels of the chick neural tube (i.e., future lower thoracic and lumbosacral regions of the spinal cord) were determined by freeze‐fracture of stage 14 to 16 embryos. Two levels of the developing neural tube were examined: the region of the neurulation overlap zone–consisting of primary neural tube dorsally and secondary neural tube ventrally–and the portion of the primary neural tube located just cranial to the overlapping region. Gap junctions were the most numerous type of intercellular junction present within the primary neural tube. These junctions were located primarily in juxtaluminal areas, near the apices of neuroepithelial cells, and sometimes also at the bases of these same cells. In addition, focal, poorly defined tight junctions occasionally occupied juxtaluminal regions of the primary neural tube. The medullary cord (i.e., the immediate precursor of the secondary neural tube) and secondary neural tube contained gap junctions exclusively. Gap junctions were first found in these areas at the lateral borders of the medullary cord, concomitant with formation of this structure, and then at the interface between the elongated, peripheral cells of the cord and the irregularly shaped and loosely arranged central cells of this structure. Finally, gap junctions were distributed radially around secondary lumina formed by cavitation. The precise spatial and temporal correlation between the appearance of gap junctions and the specific changes occurring in cellular morphology and arrangement during secondary neurulation strongly suggest that gap junctions may have a role in coordinating cellular activities during formation of both the medullary cord and the secondary neural tube.
Revascularization of the freely grafted extensor digitorum longus muscle in the rat
Authors: Hansen‐Smith F. M. , Carlson B. M. , Irwin K. L.
Published: February 2005

The process of revascularization of free grafts of the extensor digitorum longus muscle in rats has been studied by gross, histological and electron microscopic methods. During the first day after transplantation the muscle is entirely avascular, and it consists of a thin peripheral zone of surviving muscle fibers and a large central area of ischemic muscle. The original blood vessels of the graft undergo a sequence of intrinsic and cell‐mediated destruction. Scattered sinusoidal vessels begin to grow into the graft starting on the second day, and ingrowing blood vessels progressively invade the deeper tissues of the graft. Most new vessels form in the connective tissues, but some vessels, especially larger ones, grow into persisting basal laminae from preexisting vessels and, occasionally, even into basal laminae from degenerated muscle fibers and nerves. The differentiation of new arterioles and venules in free muscle grafts is described. By the end of the first week, the entire graft is revascularized, and ultimately a fairly normal relationship between new capillaries and regenerating muscle fibers is established. In mature grafts, however, irregularities are sometimes found in the organization of smooth muscle cells associated with larger vessels.
The ultrastructure of monkey foveal photoreceptors, with special reference to the structure, shape, size, and spacing of the foveal cones
Authors: Borwein Bessie , Borwein David , Medeiros John , William McGowan J.
Published: February 2005

A systematic electron microscopic study was made of the structure of foveal cones of Macaca spp. Transverse sections of inner (IS) and outer segments (OS) were made in sequence, from the pigment epithelial zone (PEZ) to the outer limiting membrane (OLM). The smallest diameters of hundreds of cone sections were measured from electron micrographs with a Zeiss particlesize analyzer, and analyzed statistically. Some details are also included about Cebus photoreceptors.

It is claimed in the literature that foveal cones are rod‐like (cylindrical) and untapered. Our study shows the foveolar cone to be a tapered structure.

There has been some confusion between the foveola, which is rod‐free, and the fovea, which has a high concentration of cones, but is not rod‐free. Within the fovea, as the ratio of cones to rods falls from ∞ to 1, with distance from the central bouquet of cones, the cone center‐to‐center distances increase, the inner segment diameters increase, and the number of cones/sq mm decreases.

The tapered calycal processes are more massive in M. irus than M. mulatta, and the lateral fins are better developed. Lateral fins are not present in the foveola.

The cones are arranged in straight lines.
The stem‐cell zone of the small intestinal epithelium. I. Evidence from paneth cells in the adult mouse
Authors: Bjerknes Matthew , Cheng Hazel
Published: February 2005

Stem cells in the small intestinal epithelium are known to differentiate into columnar, mucous, enteroendocrine, and Paneth cells. However, the site of initiation of stem‐cell differentiation has been unknown. To approach this problem we determined the site of stem‐cell differentiation along the Paneth cell line, using light microscopic morphometry and radioautography. The smallest Paneth cells containing the smallest granules were in positions 6 and 7, while the largest ones containing the largest granules were in positions 1 and 2 at the base of the crypt. Paneth cell death was less prevalent above position 3 than it was in position 1. Since cell size, granule size, and cell death are indicators of Paneth cell age, it was deduced that there is a gradient of Paneth cell age in the crypt base, with the oldest Paneth cells at the bottom, and the youngest at the top. After single injection or continuous infusion of 3H‐thymidine, the first labeled Paneth cells to appear were the highest Paneth cells in their crypt column. Later, labeled Paneth cells became more prevalent in lower positions, and, eventually, appeared in position 1. The size of granules in labeled Paneth cells increased with time. It was concluded that Paneth cells originate in position 5 or above and then migrate downward. These results are consistent with a stem‐cell zone hypothesis, which proposes that stem cells in positions 1–4 receive no inducement to differentiate. Only those stem cells that migrate up out of the stem‐cell zone into position 5 will be induced and then begin to differentiate.
The life history of cells in renewing systems
Authors: Leblond C. P.
Published: February 2005

Cell populations may be classified into three groups: static, which do not divide in the adult (e.g., neurons), expanding, which may divide but at a decreasing rate with age (e.g., kidney cells), and renewing, which undergo active division throughout life (e.g., blood cells, intestinal and seminiferous epithelium). The first two groups consist of nonrenewing populations whose cells usually survive as long as the body itself. In contrast, the cells of renewing populations have a short life, of the order of 2 to 3 days in the intestinal epithelium of rodents and 7 to 8 weeks in their seminiferous epithelium. In the present work, the life of a nonrenewing cell—the proximal convoluted tubule cell of kidney—is compared to that of the renewing cells of small intestine and testis.

The proximal convoluted tubule cell arises during embryonic development, when it has few organelles, many free ribosomes, a pale nucleus with diffuse chromatin, and a large open‐network nucleolus. As the cell differentiates, organelles accumulate while free ribosomes decrease in number, chromatin masses appear in the nucleus, and the nucleolus becomes rather dense. With old age, some of the cells show features interpreted as senescence, particularly a small dense nucleolus.

The short‐lived columnar cells of small intestine in adult rats arise from stem cells present in the base of the crypts. These cells have features similar to those of the embryonic proximal tubule cell, particularly many free ribosomes and a large open‐network nucleolus. The stem cells give rise to cells which ascend crypts and villi. Shortly after the cells reach the villus, they acquire a full set of organelles, suggesting maturity, while free ribosomes decrease in number and the nucleolus undergoes condensation. Meanwhile radioautographic tests indicate that the production by the cells of glycoproteins identified as intestinal enzymes reaches a high level. However, when cells arrive in the villus tip region, their activity decreases, as shown by reduced enzyme production, while the nucleolus appears atrophic. The cells are then lost to the lumen.

The cells of the seminiferous epithelium also arise in the adult from stem cells with embryonic features. In the course of a complex differentiation, the nucleolus becomes atrophic and disappears. Soon thereafter the fragile spermatozoon stage is reached.

Thus, the renewing cells of the adult show in rapid succession some of the features occurring slowly during the life of nonrenewing cells: origin from embryonic‐like elements, maturation, and senescence indicated by a fragile state before life's end.
Transport across endodermal cells of the chick yolk sac during early stages of development
Authors: Mobbs Ian G. , McMillan D. B.
Published: February 2005

The endoderm of the chick yolk sac mediates the transfer of materials from the yolk mass to the embryonic circulation. There is little evidence of endocytotic activity in the area pellucida, but the endodermal cells of the area vasculosa possess many microvilli and bristle‐coated pits and vesicles, as well as a canalicular system and vacuoles in the apical cytoplasm. Three tracers, horseradish peroxidase, ferritin, and latex spheres, were injected beneath the endoderm of both cultured embryos and embryos in ovo to study the pathway of uptake of extracellular materials. All tracers were sequestered in bristle‐coated pits (200–500 nm in diameter) of the endodermal cells of the area vasculosa, but not those of the area pellucida. Both horseradish peroxidase and latex spheres (and probably ferritin) were incorporated into pleomorphic intracellular yolk drops through bristle‐coated pits and vesicles, and then into apical vacuoles, which fuse with the intracellular yolk drops. Horseradish peroxidase and ferritin were also found within apical canaliculi. The apical junctions between endodermal cells prevented the intercellular passage of the tracers. A ‘topping‐up’ hypothesis is proposed whereby endodermal cells of the area vasculosa continually sequester extracellular yolk material, which is incorporated into a digesting intracellular yolk drop while, at the same time, digested yolk products are being transported across the vascular pole of the endoderm to the extraembryonic circulation and thence to the embryo.
Stereological analysis of normal rabbit pancreatic islets
Authors: Sato Tamiko , Herman Lawrence
Published: February 2005

Stereological methods were applied to obtain morphometric data related to pancreatic islets of Langerhans in the normal rabbit. By light microscopy, it was found that 1 mm3 of pancreatic parenchyma contained 47.7 islets, constituting 2.2% of its volume. Approximately 69% of the islets had diameters less than 80 μm; 31% were greater than 80 μm. The former group of islets, however, composed only 13% of the volume of the endocrine pancreas and the latter group, 87%. Using electron microscopy, a unit volume of islet tissue was observed to consist of 86% beta cells, 7.7% alpha cells, and 2.2% delta cells. The average beta‐cell volume was 1260 μm3 and its cytoplasm consisted of 52.6% matrix, 12.7% rough endoplasmic reticulum, 10.2% secretory granules, 7.8% mitochondria, and 3.3% Golgi apparatus. A typical beta cell contained 662 mitochondria, intermediate (10‐nm) filaments whose length totalled 50 mm, and 9,200 secretory granules with a ratio of four mature granules to each immature or “pale” granule. Within alpha and beta cells, three parameters were used for the quantitation of organelles or their component parts: (1) volume; (2) surface; and (3) numerical densities. In the beta cell, the surface densities of rough endoplasmic reticulum and Golgi membranes exceeded, by two‐ or threefold, their counterparts in alpha cells. Similarly, the number of beta‐cell mitochondria exceeded by 30% that of alpha cells; but beta‐cell mitochondrial volume was twice that of the alpha cell, as were surface densities of both inner and outer mitochondrial membranes. Volume and surface densities of secretory granules within beta cells were half the values obtained for alpha cells. An alpha cell contained three times the number of granules present in a beta cell.
Innervation of the thymus gland by brain stem and spinal cord in mouse and rat
Authors: Bulloch Karen , Moore Robert Y.
Published: February 2005

Central nervous system (CNS) projections to the thymus were studied in the mouse and rat using the horseradish peroxidase (HRP)‐retrograde transport method. With discrete HRP injections localized to the thymus, labeled neurons are evident in both medulla and spinal cord. In the medulla the largest population of labeled neurons is present in the retrofacial nucleus. Within this cytoarchitectonically distinct nucleus, the majority of neurons are labeled with large HRP injections in the thymus. In addition to retrofacial nucleus, scattered labeled neurons are found throughout the rostrocaudal extent of the nucleus ambiguus and in the dorsal medullary tegmentum adjacent to the dorsal motor vagus nucleus. With HRP injections restricted to thymus parenchyma, no labeled neurons are evident in the dorsal motor vagus nucleus. Three groups of spinal cord neurons are labeled. In segments C2–C4, neurons localized to the ventral horn are labeled in two distinct columns, one located lying laterally in the ventral horn and the other located medially. Labeling of neurons in these segments is distinct from that of large motor neurons located medially in the ventral horn extending from the level of the decussation of the pyramids through the C1 segment. The location and sizes of neurons labeled in these areas following HRP injection in the thymus are identical in the mouse and rat. These observations provide evidence for previously unknown projections from spinal cord and brain stem to the thymus which may play an important role in the regulation of thymic function.
Morphological evidence of reduced bone resorption in osteopetrotic (op) mice
Authors: Marks Sandy C.
Published: February 2005

Osteopetrosis, a metabolic bone disease in which a generalized accumulation of bone mass reduces or obliterates marrow cavities, is inherited as an autosomal recessive in several mammalian species. A recently discovered mutation in mice, the osteopetrosic (op) mutation, exhibits an elevation in bone matrix synthesis and a resistance to the hypercalcemic effects of exogenous parathyroid extract when young mutants are compared with normal littermates.

This investigation examined the number, cytology, and ultrastructure of osteoclasts and the structure of bone surfaces in op mice in a morphologic assessment of bone resorption. Compared with normal littermates, op mice have a severe deficiency of osteoclasts, which also contain unusual toluidine blue‐positive and electron‐dense cytoplasmic inclusions and hypertrophy of clear zones and ruffled borders. Marrow spaces in op mice contained large numbers of megakaryocytes and large lipoid masses. Bone surfaces exhibiting evidence of resorption by scanning electron microscopy in normal littermates showed no evidence of resorption in op mice. Instead, these areas were characterized by morphologic features of bone formation.

These data offer morphologic evidence of a reduction of bone resorption in this mutation. They are interpreted to mean (1) that op mice have a severe reduction in numbers or proliferative capacity of osteoclast precursors, which may be related to the cellular inclusions in the osteoclast population, and (2) that hypertrophy of the ruffled borders and clear zones of op osteoclasts is a compensatory attempt to increase bone resorption.
Functional morphology of lingual protrusion in marine toads (Bufo marinus)
Authors: Gans Carl , Gorniak Gerard C.
Published: February 2005

Bufo marinus catches its prey by stiffening the intrinsic muscles of the tongue, rapidly flipping the tongue out of the mouth. High‐speed cinematography synchronized with computer‐analyzed electromyograms (EMGs) shows that during the flip the tongue is supported by the M. genioglossus medialis and that this muscle stiffens into a rod when stimulated. Coincident stiffening of the transversely arranged M. genioglossus basalis provides a wedge under the anterior tip of this rod. Stiffening of the M. submentalis depresses the mandibular symphysis and brings the dentary tips together. The M. submentalis also acts on the wedge of the basalis to raise and rotate the rigid rod of the medialis over the symphysial attachment. The tip of this lingual rod carries along the pad and soft tissues of the tongue. The lingual pad, positioned in the posterodorsal portion of the resting tongue, rotates during eversion so that its dorsal surface impacts onto the prey object. Retraction starts by contraction of the elongate, parallel fibers of the M. hyoglossus; this retracts the medial sulcus of the pad and holds the prey by a suction cup‐like effect. The extensibility of the buccal membranes allows the pad to be retracted first; it reaches the posterior portion of the buccal cavity before the still‐rigid, backward rotating M. genioglossus has reached the level of the symphysis.

Protraction of the hyoid facilitates the extension of the M. hyoglossus. The M. sternohyoideus only retracts the hyoid and stabilizes it when the tongue starts to pull posteriorly; it does not assist tongue protrusion. The Mm. petrohyoideus and omohyoideus show only incidental activity, and the M. depressor mandibulae participates in mouth opening but is not otherwise involved in the flip.

Previous hypotheses of the flipping mechanism are reviewed and evaluated.
Temporal patterns of neurogenesis in avian cranial sensory and autonomic ganglia
Authors: D'amico‐Martel Adele
Published: February 2005

Avian cranial sensory ganglia are embryonically derived from neural crest and epidermal placodes. Cells from these two populations interact with each other and with other components of their environment to influence the complex structural and functional organization of the ganglia. To help understand these processes, the times of terminal mitosis of cranial sensory neuroblasts were established. Birthdate patterns within each ganglion are described with particular attention given to the structural organization of the VII‐VIII ganglionic complex. Birthdate information on cranial autonomic ganglia is also included.

Chick embryos ranging in age from 1 to 8 days of incubation were treated with 3H‐thymidine and sacrificed on embryonic day 8, 10, or 18. Large, placode‐derived neurons are generated between days 2 and 5 of incubation. Embryonically smaller, neural crest‐derived cells leave the proliferative pool between days 4 and 7. Neurons of the acoustic ganglion cease their mitotic activity in an apical to basal fashion and are the only placodal neurons to form later than day 5. Of the cranial autonomic ganglia, the period of neuron production is best defined for the ciliary ganglion, where it is 2.5–5.5 days of incubation. Most later‐dividing neuroblasts in the ciliary ganglion belong to the choroid cell population.

Temporal patterns of neurogenesis are discussed in relationship to other aspects of sensory gangliogenesis including embryonic origin of neurons, condensation of ganglionic anlagen, cell degeneration, and cytological characteristics of mature ganglia.
Developmental alterations associated with spontaneous cleft lip and palate in CL/Fr mice
Authors: Millicovsky Guillermo , Ambrose L. Jeannie H. , Johnston Malcolm C.
Published: February 2005

Cleft lip with or without associated cleft palate [CL(P)], one of the most common human malformations, is believed to be caused by a combination of genetic and environmental factors. To study the morphological manifestations of genetic factors in this interaction, we compared the embryonic development of the CL/Fr mouse strain (with a mean incidence of 36% spontaneous CL(P) in our colony) with that of the C57B1/6J mouse strain (with no CL(P) in our colony). Results from our scanning electron microscopic study demonstrated that, when compared with C57B1/6J embryos, CL/Fr embryos have several developmental differences including: (1) altered facial geometry, (2) depressed ability of the surface epithelium of primary‐palate primordia to participate in the fusion process, and (3) variable hypoplasia of the lateral nasal prominences. We suggest that all of these alterations may contribute to the pathogenesis of CL(P) in the CL/Fr mouse strain.
Division of the mouse gastric mucosa into zymogenic and mucous regions on the basis of gland features
Authors: Lee E. R. , Trasler J. , Dwivedi S. , Leblond C. P.
Published: February 2005

The stomachs of adult CD1 mice were investigated by anatomical examination and light microscopy. Serial sections were prepared of entire stomachs; the various types of gastric glands were characterized; and, using every 30th or 60th serial section, maps of gland distribution were obtained through point‐plotting serial reconstruction.

Gross examination shows that the cephalic third of the stomach consists of a thin‐walled, domelike structure, the forestomach. The rest of the organ, or stomach proper, is subdivided into two parts, the thick‐walled corpus, which approximately occupies the middle third, and the less vascular pyloric antrum which forms the remaining caudal third of the organ.

Histologically, glands are absent from the forestomach mucosa but are numerous throughout the stomach proper. They are of two main types, namely, zymogenic glands, which contain, among others, zymogenic cells, and mucous glands, which lack these cells but contain mucous cells. Both gland types show a few enteroendocrine cells. Moreover, some of the mucous glands include parietal cells (mucoparietal glands), while others do not (pure mucous glands).

Mucosal maps reveal that the glands of each type are located in distinct areas of the mucosa. Thus a compact zymogenic region may be defined, occupying 56% of the glandular mucosa and containing only zymogenic glands. The mucous region, on the other hand, composed only of mucous glands, is extensive and divided into a narrow cephalic band (5.2% of the glandular mucosa) and a large caudal part (38.8%). Along the lesser curvature these parts are continuous, and together they encapsulate the zymogenic region. In proximity to the border of this region, and only there, do the mucous glands include parietal cells.

A comparison of mucosal maps and gross features indicates that the corpus includes both the zymogenic region and the cephalic band of mucous glands, whereas the antrum is composed entirely of the mucous glands of the caudal part.
The establishment of a somitomeric pattern in the mesoderm of the gastrulating mouse embryo
Authors: Tam Patrick P. L. , Meier Stephen
Published: February 2005

Mesoderm formation in the mouse embryo begins at 6.5–6.75 days p.c. (postcoitum) when a primitive streak is formed along the posterior side of the egg cylinder. Epiblast cells in a localized region separate from one another and spread laterally between the primitive endoderm and the rest of the epiblast. The newly formed mesoderm contributes to both embryonic and extraembryonic regions. When the endoderm is removed, a definitive somitomeric pattern is first observed in the lateral wings of mesoderm of the mid‐primitive‐streak‐stage embryo. The sequential appearance and the placement of somitomeres in the gastrulating mouse embryo are closely related to the general changes in physical dimensions and to the pattern of tissue growth which occur during the maturation of the egg cylinder. By the late‐primitive‐streak stage, about four somitomeres are present in the paraxial mesoderm on either side of the embryonic axis. These somitomeres will undergo morphogenesis and give rise to the cranial segments and head mesenchyme of neurulating embryos (Meier and Tam, 1982). The midline or axial mesoderm, consisting of prechordal plate and notochord, is derived from the head process mesoderm originating from the anterior end of the primitive streak. Cells of the head process are compact and adherent to the endoderm. The early presence of a somitomeric pattern which persists and is added to throughout subsequent phases of mesoderm formation suggests that spreading mesodermal cells have relatively stable neighbor relationships. This morphological evidence supports the idea that the expansion of the mesoderm during gastrulation results from tissue growth and progressive deposition of cells from the primitive streak. Cell migration may be limited principally to nonsomitomeric mesodermal cells found in the leading edge of the spreading lateral wings.