bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Role of Refractoriness to Long Daylength in the Annual Reproductive Cycle of the Female Bennett's Wallaby (Macropus rufogriseus rufogriseus)
Authors: Curlewis J. D. , Loudon A. S. I. 
Published: June 2005

AbstractThe beginning of the breeding season of the female Bennett's wallaby occurs when seasonal quiescence terminates 1–2 months after the summer solstice. In this study, the role of photoperiod in terminating seasonal quiescence was examined. One week before the summer solstice, five non‐lactating wallabies were transferred from natural to artificial summer solstice daylength for 5 months. The beginning of the breeding season in these animals as indicated by births, matings, and peripheral progesterone profiles was not different from that of five control animals maintained on natural photoperiod. The following year, three animals were transferred from natural to summer solstice daylength on February 25 and were held on the artificial photo‐period until September 30. Changes in plasma progesterone concentrations indicative of the beginning of the breeding season occurred on June 12–30 (range), which was significantly (P < 0.01) advanced by 29 days when compared with six control animals. These results indicate that the decrease in daylength that occurs after the summer solstice is not required to induce the termination of seasonal quiescence at the beginning of the breeding season. Further, the beginning of the breeding season can be advanced by transferring animals to long daylength early in seasonal quiescence. Photorefractoriness to long daylengths may therefore be important in the initiation of the breeding season in this species. In further experiments, groups of six animals were transferred from natural to artificial summer solstice daylength on September 26 and December 9 and pouch young were removed 7 days after the transfer. In September, reactivation of the quiescent corpus luteum followed soon after removal of pouch young (RPY) indicating that exposure to long day‐length had not induced a transition into seasonal quiescence. In December, RPY was not followed by reactivation of the quiescent corpus luteum indicating that animals were in seasonal quiescence. These results suggest that the female Bennett's wallaby may need to experience a period of shortening days after the summer solstice before exposure to long days can again initiate seasonal quiescence.
Comparison of semilunar cycles of spawning activity in Fundulus grandis and F. heteroclitus held under constant laboratory conditions
Authors: Hsiao Shyh‐Min , Meier Albert H. 
Published: June 2005

AbstractTwo closely related killifish, Fundulus grandis of the Gulf coast and F. heteroclitus of the Atlantic coast, were held under standard laboratory conditions and monitored for spawning activity. Daily egg collections for 4–5 months during summer revealed semilunar cycles of spawning activity in both F. grandis (three aquaria) and F. heteroclitus (five of six aquaria). The mean periods were near 13.7 days for F. grandis and near 14.8 days for F. heteroclitus. The shorter duration in F. grandis closely approximates the tidal cycle in the Gulf of Mexico, which is an expression of the declinational cycle of the moon (tropical month: 27.3 days). The longer duration in F. heteroclitus closely approximates the tidal cycle along the Atlantic coast, which, along with the moonlight cycle, is an expression of the synodic month (29.5 days). Unless the fish respond to subtle exogenous cues that can influence spawning under isolated laboratory conditions, these results indicate that both killifish have endogenous cycles with very precise periods. These cycles free run for several months in specific phase relationships with tidal (F. grandis) and tidal/moonlight cycles (F. heteroclitus) present in their respective natural habitats.
Effects of extracellular pH and D‐lactate efflux on regulation of intracellular pH during isotonic contractions in a molluscan muscle: A 31p‐nuclear magnetic resonance study
Authors: Wiseman Robert W. , Ellington W. Ross , Rosanske R. C. 
Published: June 2005

AbstractIsotonic contractions were electrically induced in isolated radula protractor muscles of the whelk Busycon canaliculatum, mounted and superfused under anoxic conditions in a special 5 mm phosphorus nuclear magnetic resonance (31P‐NMR) probe. 31P‐NMR spectra showed that there was a decrease in intracellular pH (pHi) from 7.29 to 7.01 during the time course of 30 min of contractile activity. Subsequent biochemical analysis of the tissue and superfusion medium showed that D‐lactate and, to a much lesser extent, alanopine and octopine were the major glycolytic end products. Approximately 75% of the total D‐lactate produced was released into the medium. When the superfusate pH was changed from 7.8 to 7.2, a much more pronounced intracellular acidification took place, as the pHi fell to 6.80. However, there was no significant effect on the extent of release of D‐lactate from the muscle. Elevation of the superfusate pH to 8.2 had no significant effect on final pHi or D‐lactate efflux. D‐lactate efflux was reduced when α‐cyanohydroxycinnamic acid or L‐lactate was added to the superfusate at pH 7.8. These treatments had no significant effect on the final pHi. Movement of proton equivalents and D‐lactate efflux are not tightly linked in this muscle system.
Regulation of ecdysteroidogenesis in prothoracic glands of the tobacco hornworm Manduca sexta
Authors: Watson R. Douglas , Thomas Mark K. , Bollenbacher Walter E. 
Published: June 2005

AbstractEcdysteroidogenesis in Manduca sexta prothoracic glands is regulated by a set of bioregulatory molecules, including prothoracicotropic hormone (PTTH) and a protein factor present in larval hemolymph, and by the competence of the glands to synthesize ecdysteroids in response to those molecules.A larval molting bioassay was used to assess the in vivo activity of Manduca PTTHs. Crude PTTH, big PTTH, and small PTTH each elicited a larval molt in head‐ligated larvae. However, big PTTH was ∽10‐fold more potent than crude PTTH, which was, in turn, several orders of magnitude more potent than small PTTH. When big and small PTTH were combined, the molting response was similar to that elicited with crude PTTH.The chemical nature of the hemolymph protein factor was also investigated. Injection of [3H]cholesterol into last‐instar larvae and fractionation of the radiolabeled hemolymph by gel filtration chromatography revealed three peaks of radioactivity. One peak eluted in fractions containing the hemolymph protein factor, a result consistent with the notion that the factor transports a sterol substrate. The possibility that the factor is a 3(2)‐ketoreductase was investigated by assessing the effect of the factor on the accumulation of RIA‐detectable ecdysteroids in prothoracic‐gland‐conditioned medium. Three of five preparations of the factor significantly enhanced the amount of RIA‐detectable ecdysteroids in conditioned medium, indicating that at least some preparations of the factor may contain ketoreductase activity.The above findings are discussed in the context of current hypotheses of how bioregulatory molecules interact with the prothoracic glands to regulate ecdysteroidogenesis in Manduca.
Ecdysteroid synthesis by crab Y‐organs
Authors: Lachaise Fabienne , Carpentier Gilles , Sommé Ghislaine , Colardeau Jacqueline , Beydon Philippe 
Published: June 2005

AbstractY‐organs of the crab Carcinus maenas synthesize two ecdysteroids—ecdysone and 25‐deoxyecdysone—which are the precursors of 20‐hydroxyecdysone and ponasterone A, respectively; 25‐deoxyecdysone was detected by using two methods: (1) radiolabeled cholesterol injection into premolt crabs, followed by in vitro incubation of their Y‐organs and high‐performance liquid chromatography (HPLC) analysis of the various ecdysteroids formed, and 2) identification of ecdysteroids secreted by incubated crab Y‐organs by means of two successive HPLC purifications, followed by radioimmunoassay (RIA) and mass spectrum analysis. The only sterols found in the Y‐organs are 7‐dehydrocholesterol and cholesterol. These are probably the ecdysone and 25‐deoxyecdysone precursors. The biological activity of 25‐deoxyecdysone, tested by its induction of the transcription of gene P1 in Drosophila fat body, was the same as that of 20‐hydroxyecdysone.
Spermiogenesis in Chaetoderma sp. (Aplacophora)
Authors: Buckland‐Nicks John , Chia Fu‐Shiang 
Published: June 2005

AbstractThe fine structure of spermiogenesis in Chaetoderma sp. has been studied with light and electron microscopy. In early spermiogenesis the Golgi body secretes a pro‐acrosomal granule posteriorly that migrates along the plasma membrane to the anterior of the spermatid. The Golgi body moves to an anterior depression in the nucleus and secretes granular vesicles that form the apical horn. A large vesicle accumulates next to the Golgi body, and an apical dense tube is produced around the apical horn that projects anterio‐laterally, over the large vesicle, and eventually contacts the pro‐acrosome. Both centrioles produce flagella, which extend anteriorly through the cytoplasm. The distal flagellum circumnavigates the nucleus and exits posteriorly. The proximal flagellum exits anteriorly alongside the apical dense tube, which further elongates. The chromatin condenses first in granules, leaving large lacunae centrally, and later into an almost homogeneous dense mass. No manchette of microtubules was observed during condensation, but individual microtubules were visible in the cytoplasm. The residual cytoplasm flows out anteriorly along the proximal flagellum and is eliminated together with the Golgi body and large vesicle. The distal flagellum breaks free from the cytoplasm and unwinds, finally exiting centrally from the mid‐piece. In the mature sperm the acrosome is at the tip of a long apical dense tube that projects anterio‐laterally from the apical horn. The nucleus terminates in the posterior end of the apical horn. The mid‐piece is composed of five mitochondria which surround the centrioles. The flagellum is harnessed to the mid‐piece by a centriolar satellite complex that is attached to the plasma membrane by the annulus. The end‐piece is filamentous and contains two central microtubules. This sperm type may be unique among Mollusca, because its structure and morphogenesis exhibit numerous differences even from its relatives, the chitons.
Distribution of integrins and their ligands in the trunk of Xenopus laevis during neural crest cell migration
Authors: Krotoski Danuta , Bronner‐Fraser Marianne 
Published: June 2005

AbstractWe have examined the distribution in Xenopus embryos of β1 subunits of integrin, as recognized by cross‐reactive antibodies against the avian integrin beta1 subunit. These antibodies recognize a doublet of bands of approximately 120 kD in Xenopus embryos. The distribution pattern of these integrin cell surface receptors was compared with that of two possible ligands, fibronectin and laminin, in the extracellular matrix during the time of neural crest cell migration. Integrin immunoreactivity in the early neurula was observed lightly outlining somite and epidermal cells and the notochord. The integrin immunostaining increased with developmental age and was observed on most cell types in the embryo but was particularly notable in the intersomitic clefts through which motoraxons grow. The immunoreactivity in this region was not, however, wholly on the axon surfaces, since intersomitic integrin remained detectable in embryos in which the neural tube had been ablated. Fibronectin and laminin were more extensively distributed than integrin at all stages examined. Immunoreactivity for both was observed around the neural tube, notochord, somites, epidermis, dorsal mesentery, and lateral plate mesoderm. The distribution of laminin and fibronectin around the somites was particularly interesting since it was non‐uniform and similar to that of integrin. Strongest staining was observed in the intersomitic clefts, and weakest staining was observed on the medial surface of the somites, which faces the neural tube and notochord. The major differences in distribution pattern between the fibronectin and laminin immunoreactivities were that only fibronectin was detected in the mesenchyme of the dorsal fin. Our results demonstrate that a molecule homologous to avian integrin is present in Xenopus embryos during neural crest cell migration and motoraxon outgrowth. Its presence in the intersomitic clefts and on the surface of many embryonic cell types together with the abundant distribution of its ligands are consistent with a potentially important developmental function in neurite outgrowth and/or muscle development.
Prolactin counteracts effects of short day lengths on pelage growth in the meadow vole, Microtus pennsylvanicus
Authors: Smale Laura , Lee Theresa M. , Nelson Randy J. , Zucker Irving 
Published: June 2005

AbstractTo test whether growth of the winter coat in short day lengths is contingent on suppression of plama prolactin (Prl) levels, female meadow voles (Microtus pennsylvanicus) were kept in short day lengths for 12 weeks and were injected daily with saline or Prl; long‐day animals were treated with either the dopamine agonist, bromocryptine (bromo), bromo plus Prl, or saline. Prl treatment prevented the growth of the winter coat normally observed after 12 weeks in short day lengths, but bromocryptine did not stimulate pelage growth in long‐day voles. Pelage growth in short day lengths appears contingent upon decreased plasma prolactin levels.
Glycine protects preimplantation mouse conceptuses from a detrimental effect on development of the inorganic ions in oviductal fluid
Authors: Van Winkle Lon J. , Haghighat Nasrin , Campione Allan L. 
Published: June 2005

AbstractTwo‐cell mouse conceptuses were cultured in media that contained various concentrations of inorganic ions and amino acids. Substrates of the amino acid transport system Gly were detrimental to development at slightly hyposmotic concentrations of other ions. In contrast, these amino acids increased the frequency at which two‐cell conceptuses developed into blastocysts at total ion concentrations of 355 to 405 mM. Data reported elsewhere is consistent with the possibility that the total ion concentration in oviductal fluid exceeds 360 mM, whereas the concentration of glycine in this fluid may be on the order of 10 mM. Therefore, a high ion concentration and glycine may counteract the potentially harmful effects of each other in situ. Like some marine organisms, preimplantation mouse conceptuses may use glycine as an intracellular osmolite because accumulation of inorganic ions could perturb the activities of some enzymes.
Preparation of nucleate and anucleate fragments of hamster and mouse eggs by centrifugation
Authors: Yanagimachi R. , Yang C. H. 
Published: June 2005

AbstractNucleate and anucleate fragments of hamster and mouse eggs can be prepared by centrifuging zona‐free eggs in a Percoll gradient. These fragments are fertilizable and can be used for various studies of nucleus–ooplasm interactions.
Immunocytochemical localization of a calcium‐binding phosphoprotein in hemocytes of heterodont bivalves
Authors: Marsh M. E. 
Published: June 2005

AbstractCalcium‐binding phosphoprotein particles are the most abundant extracellular proteins in the hemolymph of heterodont bivalves, and granular hemocytes are the most abundant cells in the same fluid. In this study, the hemocytes of Rangia cuneata were examined ultrastruc‐turally and probed with anti‐phosphoprotein IgG to demonstrate that the granulocytes are a probable source of the hemolymph phosphoprotein. The granulocyte cytoplasm is laden with large vesicles containing an amorphous homogeneous matrix and variable numbers of electron‐dense particles; the latter are ultrastructurally similar to the extracellular phosphoprotein. The vesicle particles and matrix are related forms of the hemolymph phosphoprotein as evidenced by heavy gold labeling when Lowicryl sections were sequentially treated with rabbit‐anti‐phosphoprotein IgG and colloidal gold‐anti‐rabbit IgG. The vesicles may be the loci for posttranslational phosphory‐lation and eventual secretion of the calcium‐binding phosphoprotein, or alternatively the vesicles may be digestive structures which degrade internalized phosphoprotein.
Subcellular differentiation arrested in Artemia embryos under anoxia: Evidence supporting a regulatory role for intracellular pH
Authors: Hofmann Gretchen E. , Hand Steven C. 
Published: June 2005

AbstractPrevious work has clearly documented that intracellular pH (pHi) mediates metabolic arrest during anaerobic dormancy in Artemia embryos. This study provides evidence that subcellular differentiation during preemergence development (PED) is regulated by transitions in pHi and also reports the first detailed ultrastructural description of PED in these embryos.Mitochondrial maturation, elaboration of glycogen fields, and alteration in yolk platelet structure are clearly evident during aerobic development (embryo pHi ≥ 7.9). Mitochondrial maturation involves two populations of mitochondria that are spatially segregated in embryonic cells—one in the cytoplasm and the other located inside of yolk platelets. Identification of the latter population is based in part on histochemical staining of DNA. While both mitochondrial populations mature structurally during PED, enzymatic evidence indicates that the intra‐yolk platelet population is not functional.Subcellular morphogenetic events observed during aerobic development are blocked when embryos are incubated under anoxia (pHi ⩽ 6.8) or aerobic acidosis (a quiescent state induced by artificially elevating CO2 to 60%; pHi = 6.8). Embryonic cells exposed to either of these experimental treatments for 12 h are essentially identical to cells of the undifferentiated, hour 0 embryo. Analogously, cytochrome c oxidase specific activity increases 230% over 12 h of aerobic development, but this ontogenetic increase is arrested by 12 h of anoxia or aerobic acidosis. Returning the acidified embryos to control aerobic conditions causes enzyme proliferation to resume at rates identical to aerobic, control values. A similar arrest of the proliferation of cytochrome c oxidase activity is seen under aerobic acidosis when CO2 is present at only 11%. Finally, alkalinizing the pHi of embryos under anoxia by adding ammonia to the medium results in a 37% increase in cytochrome c oxidase levels relative to those measured under anoxia. These data support pHi‐ dependent regulation of development in preemergence Artemia embryos.
Induction of locomotion in spinal tadpoles by excitatory amino acids and their agonists
Authors: Harrison Philip Hugh 
Published: June 2005

AbstractBath application of the excitatory amino acids L‐aspartate and/or L‐glutamate or their agonists N‐methyl‐D,L‐aspartate and/or kainate elicited swimming movements in spinal tadpoles. Swimming cycles induced by the amino acids were in the frequency range of natural movements, and could be evoked after sectioning all dorsal roots in the exposed spinal segments. Locomotion was only elicited by L‐aspartate or L‐glutamate at low concentrations when the bath medium was rapidly circulated over the exposed surface of the spinal cord, and was of much shorter duration than the agonist‐induced movements. These results indicate some differences between the actions of L‐aspartate and L‐glutamate and their agonists on the tadpole spinal cord.
Hemoglobin in the parthenogenetic eggs of Daphnia magna
Authors: Kobayashi Michiyori , Kato Shuichi , Ninomiya Masaki , Fujiki Masahiko , Igarashi Yoshihiko , Kajita Akihiko 
Published: June 2005

AbstractThe hemoglobin (Hb) concentration in a single parthenogenetic egg from Hb‐rich Daphnia magna was about three times that in an egg from a Hb‐poor animal. Hemoglobin‐rich animals first produced Hb‐rich eggs in air‐saturated water. The Hb concentration of the eggs gradually decreased, leading to a decrease in the Hb concentration in hemolymph in adult animals. The P50 values (equilibrium oxygen pressure at half saturation) of solutions of purified Hb were 2.9 and 7.2 torr at 20°C for Hb‐rich and Hb‐poor eggs, respectively. Hemoglobin from the eggs was separated into at least eight Hb components by isoelectric focusing. The pI values (isoelectric point) of the major Hb components of the eggs exceeded those of adult Hb. The relative amounts of Hb components with high pI values in Hb‐rich eggs were higher than those of Hb‐poor eggs. On sodium dodecyl sulfate‐polyacrylamide gel electrophoresis technique (SDS‐PAGE), the Hb from eggs was composed of 37,000 molecular weight subunits.
Homeostatic and developmental control of cell size and shape in an insect epithelium, the epidermis of Manduca sexta
Authors: Bultmann Hermann , Goodman Walter G. 
Published: June 2005

AbstractIn contrast to previously described transformations of insect epidermal cells, morphological changes in the larval epidermis of Manduca sexta involve large changes in cell volume: a threefold increase at the beginning and a twofold decrease at the end of the last feeding phase. The volume changes are determined, in part, or entirely, by changes in cell height (cell elongation and cell shortening). Initial cell elongation occurs in a region‐specific manner, whereas subsequent cell shortening affects all of the epidermis equally. As shown by ligation experiments and hormone treatments in tissue culture, larval changes in cell height, unlike cell elongation and differentiation in prepupae, are not regulated by developmental hormones (juvenile hormones, ecdysteroids). Instead, the maintenance of a normal columnar epithelium in fifth instars depends on continuous growth. Lack of food, especially protein, results in reversible cell shortening at any time during the feeding phase. Intake of water does not mitigate this cellular response; cell shortening is also insensitive to ouabain but inhibited by cold treatments. We propose that during larval growth epidermal cell height is under specific homeostatic control, independent of mechanisms regulating cell width, ploidy levels, or mitotic activity.
Heart induction in wild‐type and cardiac mutant axolotls (Ambystoma mexicanum)
Authors: Smith Steven C. , Armstrong John B. 
Published: June 2005

AbstractWe have re‐examined some of the factors affecting the induction of heart‐forming mesodern in the axolotl. The formation of functional, rhythmically contracting myocardial tissue was used as an assay. We have found that heart‐forming mesoderm is fully induced and capable of completing its developmental repertoire by the end of neurulation. As has been previously reported, pharyngeal endoderm appears to be the major inductor of heart mesoderm. Unlike previous workers, we have found that the inducing activity appears to be highly localized in the mid‐ventral pharyngeal endoderm. The endoderm retains its inductive properties, and the mesoderm retains at least some capacity to respond, long after the heart‐forming mesoderm is apparently fully induced.We have also found that RNA extracts from pharyngeal endoderm, which are capable of causing cardiac‐lethal (c/c) mutant axolotl hearts to begin beating, are not capable of inducing early wild‐type heart‐forming mesoderm. Based on these results, we speculate that induction of heart‐forming mesoderm is a two‐step process. The first signal, occurring during neurulation, directs the mesoderm to begin differentiating into cardiomyocytes, and the second, beginning in mid‐ to late neurulation and continuing until just prior to the onset of heartbeat, causes myofibrillogenesis and the initiation of rhythmic contractions. The latter signal, which is lacking in c/c mutant embryos, appears to be necessary to override an inhibition present in the embryonic milieu.