bluuebunny/crossref_metadata_2025_split huggingface dataset:
Seasonal testosterone levels in leydig and sertoli cells of the snapping turtle (Chelydra serpentina) in natural populations
Authors: Mesner Peter W. , Mahmoud I. Y. , Cyrus Rodney V. 
Published: June 2005

AbstractLeydig cells were enzymatically separated from the seminiferous tubules and were then purified by isoosmotic Percoll gradient centrifugation so that steroidogenic activity in the two sites could be measured separately. After purification, the cells in fractions 29–31 were identified as Leydig cells since these tested positively for 3β hydroxysteroid dehydrogenase activity (3β HSD), had steroidogenic ultrastructural features (smooth endoplasmic reticulum), and were capable of synthesizing testosterone (T) in vitro. The rest of the fractions tested negatively for the 3β HSD activity and were incapable of synthesizing detectable amounts of T. Sertoli cells from seminiferous tubules also showed the above steroidogenic properties. The T concentration of intratubular origin (Sertoli cells) was low prior to spermatogenesis but began to rise at the onset of the spermatogenic phase (late May to early June). The level of Sertoli T increased steadily during the summer. In late August to early September intratubular T reached a peak that coincided with spermiation and maximal testicular development. Leydig cells (interstitial origin) were more active prior to spermatogenesis, producing large amounts of T at a time of minimal testicular mass. The sharply rising T concentrations peaked in May or early June (mating period). After the onset of spermatogenesis, T of interstitial origin began to drop until early August to early September when, like T of intratubular origin, it peaked in synchrony with spermiation and maximal testes development. During September the testes regressed rapidly and T from both sources declined significantly. Throughout the cycle the Leydig cells appeared to be the major site of testosterone synthesis. © 1993 Wiley‐Liss, Inc.
Unreduced diploid eggs produced by interspecific hybrids between Oryzias latipes and O. curvinotus
Authors: Sakaizumi Mitsuru , Shimizu Yasushi , Matsuzaki Takashi , Hamaguchi Satoshi 
Published: June 2005

AbstractMale hybrids produced from reciprocal crosses between Oryzias latipes and O. curvinotus are sterile, whereas females do lay eggs. Fertilized by the sperm of one of the parental species, such eggs develop into triploid males and females. We examined allozyme patterns of triploids that developed from the eggs fertilized by sperms of non‐parental strains of O. latipes or a closely related species, O. luzonensis. Expression of three allelic products in triploid offsprings indicated unreduced diploidy of the eggs produced by the hybrid females.In order to test the clonality of the diploid eggs produced by the hybrid females, we examined the progeny of hybrid females for their immunological clonality and DNA content. Progeny of a hybrid female crossed with a male of an inbred strain of O. latipes was demonstrated to belong to a single immunological clone. Differences in frequency of hypotriploidy and mosaicism were observed between strains of O. latipes that produced hybrid females.Because O. latipes is a fish that is used widely as a model organism in experimental biology, the hybrid females that produce unreduced diploid eggs provide a unique model with which to examine the underlying causes of polyploidy and clonal reproduction in vertebrates. © 1993 Wiley‐Liss, Inc.
A structural and functional polymorphism in the hemoglobin O2 transport system of the blood clam Noetia ponderosa
Authors: Mangum Charlotte P. , Cockey Elizabeth M. 
Published: June 2005

AbstractA sample of arcid blood clams (Noetia ponderosa) from the Atlantic coast of Virginia had red blood cells containing a hemoglobin composed of only one electrophoretically separable component. Both the red blood cells and hemoglobin extracts had a moderately high oxygen affinity. A sample from the Gulf of Mexico had red blood cells containing hemoglobins composed of two components. According to previous reports, this population contains a homodimer of one chain and a heterodimer of that chain plus another. Both the red blood cells and the hemoglobin extracts had a much lower oxygen affinity. Thus, in this species, the O2 carrier is qualitatively (and, according to the previous report, quantitatively) polymorphic, and the polymorphism is reflected in respiratory properties as well as quaternary structure. The origin of the different hemoglobin phenotypes, however, is not yet clear. © 1993 Wiley‐Liss, Inc.
Evolution of oviductal gestation in amphibians
Authors: Wake Marvalee H. 
Published: June 2005

AbstractOviductal retention of developing embryos, with provision for maternal nutrition after yolk is exhausted (viviparity) and maintenance through metamorphosis, has evolved independently in each of the three living orders of amphibians, the Anura (frogs and toads), the Urodela (salamanders and newts), and the Gymnophiona (caecilians). In anurans and urodeles obligate viviparity is very rare (less than 1% of species); a few additional species retain the developing young, but nutrition is yolk‐dependent (ovoviviparity) and, at least in salamanders, the young may be born before metamorphosis is complete. However, in caecilians probably the majority of the approximately 170 species are viviparous, and none are ovoviviparous. All of the amphibians that retain their young oviductally practice internal fertilization; the mechanism is cloacal apposition in frogs, spermatophore reception in salamanders, and intromission in caecilians. Internal fertilization is a necessary but not sufficient exaptation (sensu Gould and Vrba: Paleobiology 8:4–15, '82) for viviparity. The salamanders and all but one of the frogs that are oviductal developers live at high altitudes and are subject to rigorous climatic variables; hence, it has been suggested that cold might be a “selection pressure” for the evolution of egg retention. However, one frog and all the live‐bearing caecilians are tropical low to middle elevation inhabitants, so factors other than cold are implicated in the evolution of live‐bearing. Viviparity might facilitate life in a rigorous environment, but likely is not “caused” by such an existence. © 1993 Wiley‐Liss, Inc.
Monotreme development with particular reference to the extraembryonic membranes
Authors: Hughes R. L. 
Published: June 2005

AbstractThis paper considers many of the salient features of monotreme development, particularly morphogenesis of the extraembryonic membranes.The uterine endometrium of both monotremes and marsupials exhibits a progesterone driven luteal phase where accelerated utilization of endometrial nutrients is evidenced by a rapid post‐primitive streak expansion in the dimensions of the extraembryonic membranes. Monotremes share with marsupials, birds, and reptiles an unspecialized vertebrate mode of genesis of the embryonic disc on the peripheral surface of the yolk‐sac.The fused vascularized respiratory chorioallantois is estimated to have a functional life of not more than the terminal 4 to 5 days of the monotreme incubation period. This time interval is of a slightly greater order of magnitude than that found in marsupials with a fused chorioallantois, so far described, but in the context of the proportional elapse of post‐primitive streak organogenesis would fall within the marsupial grade.The dominant extraembryonic membrane for nutritive and respiratory function in both monotremes and marsupials is the yolk‐sac.This contribution shows that monotremes and marsupials share a much larger suite of developmental anatomical features than previously reported. The evolutionary biologist is confronted with the challenge of how to assign an appropriate weighting to these features as marsupials are considered by many researchers to be allied phylogenetically more closely with eutherian mammals than with monotremes. © 1993 Wiley‐Liss, Inc.
Development and structure of the placenta and fetal membranes of nonhuman primates
Authors: King Barry F. 
Published: June 2005

AbstractThis survey examines placental and fetal membrane structure, function, and development in nonhuman primates. It will focus on these aspects of fetal membranes in species exemplifying the two main types of primate placentation. The chorioallantoic placentas of most strepsirhine primates (e.g., lorises and lemurs), are diffuse, villous and epitheliochorial in structure. Villi are stout, usually unbranched and interdigitate with indentations in the uterine lining. Early in gestation trophoblast cells are columnar but with advancing gestational age considerable thinning of the interhemal membrane occurs. The villous tips have indented regions that appear to be involved in absorption of histotroph. Accessory placental structures known as areolae or chorionic vesicles occur in many strepsirhines. These are cup‐shaped specializations that develop opposite the mouths of uterine glands and appear active in absorption of glandular secretions. In addition, most strepsirhines are characterized by a large yolk sac early in gestation, a transient choriovitelline placenta, and most have a large allantoic sac. In strepsirhines, amniogenesis occurs by folding. In contrast, the chorioallantoic placentas of most haplorhines are discoidal, villous, and hemochorial. The species emphasized in the review are macaque monkeys. The placental villi are covered by a layer of syncytiotrophoblast; the latter is active in maternal‐fetal transport and hormone synthesis. In some haplorhines, extravillous trophoblast invades deeply into the endometrium and also into spiral arteries supplying the placenta. Other fetal membranes include 1) nonvillous chorion (chorion laeve); there is evidence supporting both an absorptive and synthetic role for trophoblast of the chorion laeve; 2) yolk sac, which is unusual in that a secondary yolk sac is formed. The yolk sac has both synthetic and absorptive functions in early gestation; and 3) amnion; amniogenesis in haplorhines occurs by cavitation. © 1993 Wiley‐Liss, Inc.
Embryonic diapause in vertebrates
Authors: Mead Rodney A. 
Published: June 2005

AbstractEmbryonic diapause occurs in many species of vertebrates, but the physiological mechanisms which control this fascinating process are exceedingly different in the diverse groups which employ this reproductive strategy. In nonmammalian species and some bats, reduction in rate of embryonic development is temperature dependent, but this is not the case in most mammals. Development becomes arrested at the blastocyst stage of embryogenesis in mammals which exhibit delayed implantation, whereas postimplantation development is continuous but retarded in species exhibiting delayed development. The hormonal control of diapause is remarkably different in the various species. Pituitary secretion of prolactin prevents implantation in the tammar wallaby but hastens renewed development and implantation in the mink and spotted skunk. Ovariectomy results in the eventual death of blastocysts in mustelids but induces renewed development and implantation in the armadillo. Luteal function, as evidenced by elevated progesterone secretion, is essentially constant in the roe deer and armadillo, whereas the luteal cells fail to complete their differentiation and secrete low levels of progesterone in carnivores. Progesterone will induce implantation in the tammar wallaby, but estrogen is required to induce renewed development and implantation in rodents. Neither progesterone and/or estrogens appear to be capable of stimulating implantation in carnivores. The uterus plays an important role in maintaining the embryos in a viable state throughout the period of diapause. In many species the uterus undergoes histological changes and secretes increased amounts of protein, yet we still do not understand the role, if any, these proteins play in initiating renewed embryonic development. Thus the phenomenon of embryonic diapause still holds many mysteries for scientists to solve. © 1993 Wiley‐Liss, Inc.
Developmental changes in the acetylcholine influence on heart muscle of Rana catesbeiana: in situ and in vitro effects
Authors: Pelster Bernd , Burggren Warren W. , Petrou Steven , Wahlqvist Inger 
Published: June 2005

AbstractThe influence of acetylcholine (ACh) on cardiac performance of larval (Taylor Kollros [TK] stages II‐XVIII) and postmetamorphic (3–609 g) Rana catesbeiana was analyzed in situ (circulatory system intact) and in vitro (isolated heart or ventricular strip preparations).Topical application of ACh to the heart in situ resulted in a dose‐dependent decrease in heart rate and in a slight decrease in systolic ventricular pressure in all developmental stages. Injection of acetylcholine in to the ventricle lumen in situ caused a dose‐dependent transient decrease in systolic ventricular pressure, with little heart rate effect. Intraventricular ACh injection also changed the hemodynamic coupling between ventricle and conus arteriosus, generating a biphasic pressure profile in the conus due to sequential contractions of the ventricle and of the conus. In situ the sensitivity of the ventricle to ACh decreased during larval development, with the lowest sensitivity in small postmetamorphic adults.ACh applied in vitro to cardiac muscle strips or small hearts produced a negative inotropic effect. The ACh dose necessary to induce a 50% reduction in muscle strip contraction force in vitro decreased substantially during larval development, indicating an increase in ACh sensitivity with development.The effects of ACh both in vitro and in situ were diminished or eliminated by topical application or injection of atropine, suggesting the presence of muscarinic cholinergic receptors. After preincubation with the acetylcholinesterase blocker eserine, injection of ACh in to the conus arteriosus decreased systolic ventricular pressure with a delay of 4–10 seconds, probably representing the minimum blood circulation time.The observed inotropic and chronotropic responses result from the action of ACh on cardiac muscle, primarily affecting systolic ventricular pressure, and on the cardiac pacemaker, mainly influencing heart rate. These responses occur as early as TK, stage II, indicating a well‐developed set of mechanisms to regulate cardiovascular performance early in development. © 1993 Wiley‐Liss, Inc.
In vitro motilities of the unconventional myosins, brush border myosin‐I, and chick brain myosin‐V exhibit assay‐dependent differences in velocity
Authors: Wolenski Joseph S. , Cheney Richard E. , Forscher Paul , Mooseker Mark S. 
Published: June 2005

AbstractTwo types of in vitro motility assays are currently used for examining the mechanochemical properties of purified myosins. The Nitella bead movement assay (Sheetz and Spudich: Nature 303:31–35, 1983) allows determination of both velocity and directionality of movement, but is of limited utility because of the fragile nature of the dissected Nitella internodal cells. On the other hand, the sliding actin filament assay (Kron and Spudich: Proc. Natl. Acad. Sci. U.S.A. 83:6272–6276, 1986) is technically much simpler to perform than the Nitella assay, and is suitable for the study of numerous physiological parameters. As it is currently used, however, the sliding actin filament assay does not indicate the directionality of motor movement. Previous studies have demonstrated that the velocities of filament‐forming conventional myosins‐II from either muscle or nonmuscle cells are comparable in both motility assays (Umemoto and Sellers: J. Biol. Chem. 265:14864–14869, 1990). However, similar studies using unconventional myosins are lacking. In the present report we have compared the rates of two structurally distinct unconventional myosins: brush border (BB) myosin‐I and chick brain (CB) myosin‐V (p190‐calmodulin), using the sliding actin filament and Nitella‐based in vitro motility assays. These two unconventional myosins differ from conventional myosins in that they appear unable to associate in to bipolar filaments, and have extended rod‐like neck domains which bind multiple calmodulin light chains in a Ca2+‐sensitive manner. Unlike conventional myosins, both of these unconventional myosins exhibit motility rates using the Nitella assay (BB myosin‐I:∼10 nm/s; CB myosin‐V:∼30 nm/s) that are 5‐to 10‐fold slower than that determined for these myosins using the sliding filament assay (BB myosin‐I: 40–67 nm/s; CB myosin‐V: 260–340 nm/s). © 1993 Wiley‐Liss, Inc.
Threshold photoperiods for the induction of short day traits in collared lemmings (Dicrostonyx groenlandicus)
Authors: Nagy Tim R. , Gower Barbara A. , Stetson Milton H. 
Published: June 2005

AbstractWhen exposed to short photoperiod collared lemmings undergo a number of physiological and morphological changes including an increase in body weight, a change in body composition, development and enlargement of the bifid “digging” claw, and a molt to a white winter pelage. We investigated the threshold photoperiods for the induction of these traits in male and female lemmings born and raised under a 22L:2D photoperiod and transferred at weaning (19 days of age) to various other photoperiods. Male lemmings showed the characteristic increase in body weight when exposed to 16 hr of light or less per day whereas females required a photoperiod of 14 hr of light or less per day to elict an increase in body weight. The thresold photoperiods for the increase in bifid claw size were 16 and 18 hr of light per day in male and female lemmings, respectively. The molt to the white winter pelage began under a longer photoperiod in females (16L:8D) than in males (14L:10D). Testes and seminal vesicles were significantly inhibited by photoperiods of 22L:2D and 20L:4D. Likewise, uterine weights were inhibited by maintenance on a photoperiod of 22L:2D. Taken together, these data show that the threshold photoperiods for the induction of the short day traits in collared lemmings are both trait‐ and sex‐dependent. These observations also suggest that under some conditions, exposure to long photoperiods can inhibit sexual maturation. © 1993 Wiley‐Liss, Inc. © 1993 Wiley‐Liss, Inc.
Interactions between the pharyngeal jaw apparatus, feeding behaviour, and ontogeny in the cichlid fish, Haplochromis piceatus: A study of morphological constraints in evolutionary ecology
Authors: Galis Frietson 
Published: June 2005

AbstractI found evidence of a morphological constraint on the food choice of young stages of a cichlid fish. The constraint is not a developmental one because it is not imposed by developmental changes. I found no evidence of developmental constraints. In gradual transitions developmental constraints may be rare, in contrast to their regular occurrence in sudden transitions. I suggest that flexible muscle activation and reserve capacity (structural capacity in excess of functional demand) provide organisms with mechanisms that buffer against the effects of form changes and as such facilitate ontogenetic and evolutionary changes.A mathematical model for piercing prey in the pharyngeal jaws is applied to a juvenile cichlid fish. The maximum possible biting forces and the best biting directions were calculated. Piercing forces were measured that were generated when natural prey were pierced. The results were compared with the feeding behaviour in the laboratory and in the field and with results from an adult. The model predicts great flexibility of the pharyngeal jaw apparatus. Furthermore, the model predicts that a shift in biting point, prey size, or predator size leads to changes in muscle recruitment. The m.transversus ventralis is predicted to play an important role in pharyngeal biting.The model explains why large fish can easily pierce Chaoborus larvae and pupae, whereas a fish of 2.5 cm is just able to pierce larvae (symmorphosis) and is unable to pierce pupae. The inability of small fish to pierce pupae is due to a morphological constraint. This constraint is imposed by the size of the cross‐sectional areas of the muscles that generate the biting force. © 1993 Wiley‐Liss, Inc.
Mechanisms of osmoregulation in the green alga Dunaliella salina
Authors: Thompson Guy A. 
Published: June 2005

AbstractThe halotolerant alga, D. salina, offsets the high (up to 5 M) external NaCl concentration in its environment by maintaining a nearly equivalent level of intracellular glycerol. Cells experiencing sudden hypoosmotic shock respond initially by volume expansion and then convert glycerol to osmotically inactive starch. Within 2 min following dilution of cells from 1.7 M NaCl to 0.85 M NaCl, their volume and surface area increase by 50%. Concurrently, the plasma membrane phosphatidylinositol 4,5‐bisphosphate (PIP2) level falls by 30% due to hydrolysis by a GTP‐binding, protein‐activated phospholipase C that produces inositol trisphosphate and diacylglycerol (DAG). Following the short‐lived rise of PIP2‐derived DAG, a second and larger peak of DAG is produced by the hydrolysis of phosphatidylcholine and through de novo synthesis. Since protein kinase C is not detectably stimulated, DAG may act through the alternative pathway of increasing actin nucleation sites, thereby facilitating expansion of the cell's cytoskeleton. D. salina contains a family of at least 4 low molecular weight (28–30 kDa) GTP‐binding proteins. The major one of these (28 kDa) is immunologically cross‐reactive with antibodies to the yeast ypt1 protein that is involved in intracellular vesicle trafficking. The D. salina 28 kDa protein may play a similar role in facilitating the plasma membrane expansion triggered by hypoosmotic shock. During this expansion, which features a massive fusion of cytoplasmic vesicles with the plasma membrane, there is significant translocation of the 28 kDa GTP‐binding protein from the ER‐enriched microsomal fraction to the plasma membrane, chloroplast, and cytosol. Factors regulating these translocations are under study. © 1994 Wiley‐Liss, Inc.
Dealing with salt stress in animal cells: The role and regulation of glycine betaine concentrations
Authors: Dragolovich Julia 
Published: June 2005

AbstractGlycine betaine is the end product of a two step oxidation of choline. Although glycine betaine is a common osmolyte in the cells of many species, the mechanism(s) regulating its synthesis in response to hyperosmotic stress has not been thoroughly studied in animals. We localized glycine betaine production in the mitochondrial matrix of cardiac cells from the horseshoe crab (Limulus polyphemus). Isolated Limulus mitochondria take up choline and convert it to glycine betaine. The uptake rate is stimulated by exposure to hyperosmotic medium and mediated in part by a Na+‐dependent, high affinity transporter. The increased choline concentrations in hyperosmotically stressed mitochondria result in increased glycine betaine concentrations. Thus, choline transport by Limulus mitochondria is the rate‐limiting step in glycine betaine synthesis. Oysters (Crassostrea virginica) appear to have a different regulatory strategy. Oysters from the Atlantic Ocean accumulate more glycine betaine than oysters from the Chesapeake Bay when hyperosmotically stressed. Gill mitochondria isolated from both oyster populations take up choline at similar rates. However, the Atlantic Coast oyster mitochondria synthesize 3–4 times as much glycine betaine as their Bay counterparts. Thus, in oysters, the regulatory step may be at the level of the synthetic enzymes. © 1994 Wiley‐Liss, Inc.