bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydration‐induced modulation of feeding responsiveness in terrestrial slugs
Authors: Prior David J. 
Published: June 2005

AbstractIn various species of animals the level of body hydration is known to affect feeding responsiveness. In order to understand the mechanisms that underlie this form of behavioral modulation, hydration‐induced changes in feeding have been examined in the terrestrial slugs Limax pseudoflavus and Lehmannia valentiana. Air‐dehydration of slugs to 70–60% of initial body weight (%IBW) abolishes feeding. Feeding responsiveness is rapidly restored in these slugs after they are allowed to rehydrate in contact with a moist surface. Injections of hyperosmotic mannitol or sucrose solution also result in abolition of feeding, thus suggesting that hemolymph osmotic pressure is involved in modulation of the feeding response. Correspondingly, if mannitol‐injected or air‐dehydrated slugs are injected with 0.1 × saline, feeding is restored in a manner similar to that observed following contact‐rehydration. Feeding was restored, however, only in those slugs whose hemolymph was diluted to at least 180–190 mOsm/kg H2O, which is the hemolymph osmolality of slugs at 75–70% IBW. The present results are consistent with the hypothesis that hydration modulation of feeding in slugs is mediated by hemolymph osmotic pressure.
Thermal acclimatization of hepatic polysubstrate monooxygenase and UDP‐ glucuronosyltransferase of mature rainbow trout (Salmo gairdneri)
Authors: Koivusaari Ulla 
Published: June 2005

AbstractThe thermal acclimatization of hepatic cytochrome P‐450‐dependent polysubstrate monooxygenase (PSMO) and UDP‐glucuronosyltransferase of mature rainbow trout (Salmo gairdneri) was studied.The results indicate that the PSMO system, 7‐ethoxycoumarin and benzo(a)pyrene as substrates, shows almost ideal acclimatization pattern in autumn during water cooling. The enzyme activities were identical if measurements were carried out at acclimatization (=environmental) temperatures which were 20°C in August and 5°C in November. If a constant incubation temperature (18°C) was used, the PSMO activities were significantly higher in cold (5°C)‐acclimatized fish. The acclimatization process could be seen both in specific and total activities. The content of cytochrome P‐450 remains at constant level from August to November.In early summer during water warming the PSMO activities increased considerably in both sexes in all incubation conditions.The specific and total UDP‐glucuronosyltransferase activities were significantly higher in warm‐acclimatized fish both in the autumn and in the spring if the activities were measured at environmental temperature. No differences could be detected if the measurements were carried out at constant experimental temperature (18°C).
Unusual glucose phosphate isomerase isozyme patterns in lymphocytes from two C57BL/6J ↔ A/J allophenic mice
Authors: Balinsky Doris , Spannaus Donna J. , Yang Han‐Yi , Briggs Carol J. , Meyer Terry E. , Warner Carol M. 
Published: June 2005

AbstractAnalysis of C57BL/6J ↔ A/J allophenic mice for their lymphocyte composition, using H‐2 antigens as external markers, and glucose phosphate isomerase (GPI) isozymes as internal markers, has led to the discovery of two unusual mice. Both mice showed heterodimers of GPI isozymes upon electrophoresis of the lymphocyte lysate. Specific anti‐H‐2 antisera confirmed that the cells of the mice were of C57BL/6J and A/J origin, as expected, but that the “A/J” cells seemed to behave as F1 hybrids containing the Gpi‐1a and Gpi‐1b alleles. Possible origins of the Gpi‐1b allele in the “A/J” cells are discussed.
Experimental evidence for the accumulation of egg pigment in the brain cavities of Xenopus tadpoles
Authors: Kordylewski Leszek 
Published: June 2005

AbstractThe origin and fate of darkly pigmented clusters of cells that float freely in the brain cavities of the tadpoles of Xenopus laevis have been experimentally investigated. The results point to the conclusion that the clusters are the sites of egg pigment accumulation, which remain within the brain cavities or at its walls until metamorphosis.
Electron microscopic observations on sperm entry into eggs of the rose bitterling, Rhodeus ocellatus
Authors: Ohta Tadayuki , Iwamatsu Takashi 
Published: June 2005

AbstractMorphological studies on gametes and sperm entry into the egg of Rhodeus ocellatus were conducted using transmission and scanning electron microscopy. The spermatozoon has a round head, a mitochondrion, and a flagellum but no acrosomal structure. The egg is enclosed in a chorion that has a micropyle at the animal pole. After a spermatozoon attaches to the well‐developed microvilli of the egg surface facing the micropyle, it is covered by the microvilli and incorporated into the egg cytoplasm with membrane fusion occurring between gametes. The egg cytoplasm just beneath the micropyle swelled a little while incorporating the spermatozoon and promptly plugged the micropyle. The nuclear envelope of the spermatozoon disappeared first at the apical region of the head and then progressed posteriorly through a process of vesiculation. The nucleus of the sperm head at once initiated decondensation upon incorporation through the effects of the egg cytoplasm. The mechanism of block to polyspermy in Rhodeus eggs is discussed.
Progesterone induces incubatory changes in the brooding pouch of the frog Gastrotheca riobambae (Fowler)
Authors: Del Pino Eugenia M. 
Published: June 2005

AbstractProgesterone induces closure, vascularization, and the formation of embryonic chambers around inert beads in the brooding pouch of the frog Gastrotheca riobambae (Fowler). These changes of the pouch resemble those occurring during normal reproduction. In contrast to progesterone, human chorionic gonadotropin induces pouch closure only in females with large ovaries. The results suggest that pituitary gonadotropin indirectly induces the incubatory changes of the pouch by stimulating the secretion of a progesterone‐like hormone from the ovary.
Myosin expression in the developing ascidian embryo
Authors: Meedel Thomas H. 
Published: June 2005

AbstractMyosin accumulation was examined in developing ascidian embryos by measuring its ATPase activity and by resolving myosin heavy chains on polyacrylamide gels. Both procedures used a myosin‐enriched fraction that was prepared by exploiting the unusual solubility properties of this protein. Myosin ATPase was first observed at neurulation and increased 25‐ to 50‐fold by the time of larval hatching, a sequence similar to that found previously for muscle acetylcholinesterase. This similarity to acetylcholinesterase, and the finding of at least two‐thirds of the ATPase activity in the larval tail, imply that most of the myosin studied was muscle myosin. The pattern of expression based on ATPase assays was confirmed in part by gel analysis, but since this technique was less sensitive the appearance of myosin heavy chain was not demonstrated unambiguously until later in development. As found earlier with acetylcholinesterase, actinomycin D treatment only interfered with accumulation of myosin ATPase during early stages of increasing enzymatic activity. Despite certain similarities noted in their ontogeny, differences in the initial increase in the activity of these enzymes and the time of their first response to actinomycin D suggest that the events concerned with the expression of acetylcholinesterase occur 1 hour before those of myosin ATPase. The appearance of these two proteins, representing different enzymes of the muscle cell, is probably controlled independently.
Spermatogenesis in the mexican axolotl, Ambystoma mexicanum
Authors: Miltner Mary Jane , Armstrong John B. 
Published: June 2005

AbstractTritiated‐thymidine autoradiography was used to follow the progress of cells through spermatogenesis in the axolotl, Ambystoma mexicanum. Results indicate that, at 18°C, the most rapidly maturing germ cells spend 5 days in leptotene, 5 days in zygotene, 22 days in pachytene, 1 day in diplotene, 6 days completing meiosis I, 10 days as secondary spermatocytes, and about 12 days in spermiogenesis. In these laboratory bred and raised urodeles, mature sperm spend an additional 60 days in the testes before the first label appears in spermatophores. The data suggest that, at least for some animals, there is minimal storage of mature sperm in the vas deferens. Cyst counts on longitudinal sections through the testes revealed large differences in the proportion of cells at different stages in animals examined during the same season. The results show that spermatogenesis passes through the testes of each animal in a wave that, however, is not coordinated with that of other animals in the colony. The overall timing of spermatogenesis is consistent with the results of mutagenesis studies with the alkylating agent, EMS. EMS reacts preferentially with late spermatids and a dominant lethal effect is seen about 60 days after the mutagen treatment, corresponding to the time interval between late spermatids and mature sperm ready to be laid in spermatophores.
Hydrostatic pressure inhibition of hormone‐induced resumption of meiotic maturation in isolated oocytes
Authors: Cloud J. G. 
Published: June 2005

AbstractPrior to ovulation, fully grown oocytes of both the amphibian (Rana pipiens) and the starfish (Piaster ochraceus), like those of many other organisms, are arrested in late prophase I of meiosis. Reinitiation of meiotic maturation in oocytes from either of these organisms is hormonally induced. Although the meiosis‐inducing substance (MIS) for each organism is chemically dissimilar (a steroid in the frog and a purine in the starfish) induction of oocyte maturation in both biological systems appears to be initiated by the interaction of the MIS with the plasma membrane of the oocyte. The objective of this investigation was to determine if elevated hydrostatic pressure affected hormonal induction of oocyte maturation and to compare the effect of pressure on oocytes stimulated with different meiosis‐inducing substances. In isolated oocytes from either the frog or the starfish, increasing ambient pressure reduced the percentage of oocytes which matured, and a stepwise increase in pressure resulted in a corresponding shift in the dose response curves of hormone‐induced, oocyte maturation to the right. In experiments using only starfish oocytes, this inhibitory effect of pressure was found to be reversible and limited to the initial period of the maturation event. Taken together, these data suggest that elevated ambient pressure inhibits an early cellular event in the hormonal induction of meiotic maturation which is common to both amphibian and starfish oocytes.
The extent of intracellular acidification during anoxia in the catch muscles of two bivalve molluscs
Authors: Ellington W. Ross 
Published: June 2005

AbstractIntracellular pH (pHi) changes during anoxia in in vitro preparations of the posterior adductor muscle of the blue mussel Mytilus edulis and the byssus retractor muscle of the ribbed mussel Geukensia demissa were observed using phosphorus nuclear magnetic resonance spectrometry. During 12 h of experimental anoxia, the pHi in M. edulis muscles fell from 6.96 to 6.70. Over the same time period, the pHi in G. demissa muscle fell from 6.95 to 6.56. The relatively small degree of intracellular acidification probably reflects low rates of anaerobic energy metabolism in these muscles. However, the degree of pHi change may be sufficient to have important regulatory effects on energy metabolism in catch muscle.
Protrusive activity, mode and rate of locomotion, and pattern of adhesion of Fundulus deep cells during gastrulation
Authors: Trinkaus J. P. , Erickson C. A. 
Published: June 2005

AbstractThe mechanism of locomotion of deep cells of Fundulus heteroclitus was studied in vivo during gastrulation with the aid of time‐lapse cinemicrography (Nomarski differential interference contrast optics), scanning electron microscopy of cells known to be moving at the time of fixation, and cell culture. These are our findings: (1) Deep cells usually move rapidly, at about 10–15 μm/min, regardless of whether they move by blebbing or spreading. Evidence suggests that this high speed is associated with weak adhesion of the trailing edge: it remains rounded, without large retraction fibers, and it advances continuously with advance of the leading edge, not sporadically, as it would if it adhered strongly. (2) In contrast, when stationary cells in close contact separate, they remain connected at first by large retraction fibers, suggesting strong punctate adhesions. (3) Fundulus deep cells appear to move in two ways: a) protrusion of blebs, followed by much cytoplasmic flow; b) spreading of lamellipodia, preceded by filopodia and frequent cell shortening. Locomotion by shortening of a long lobopodium is really a form of spreading movement, since the tip of a lobopodium always spreads. (4) Filopodia were not found except at the leading edge of a spreading lamellipodium and often spread themselves; perhaps filopodia and lamellipodia are interconvertible. (5) A lamellipodial margin may form undulations in vivo that move backward like ruffles in vitro. (6) At all times, whether stationary or moving, the surface of any given deep cell is smooth, raising unanswered questions concerning the source of surface for their rapid protrusive activity.
Prostaglandins and preovulatory follicular maturation in mice
Authors: Downs Stephen M. , Longo Frank J. 
Published: June 2005

AbstractExperiments have been carried out in an effort to reverse the indomethacin‐induced inhibition of preovulatory follicular development in immature superovulated mice utilizing prostaglandins E2 and F2α. All mice were primed with 5 IU pregnant mare's serum gonadotropin followed 40 h later by 80 IU luteinizing hormone (LH). Animals were sacrificed 10½ or 11½–12 h post‐LH, at which time ovaries were fixed and prepared for microscopic observation. Control mice receiving both indomethacin and prostaglandin (PG) vehicles averaged 92% germinal vesicle breakdown, and 82% of maturing oocytes were surrounded by an expanded cumulus oophorus. Ovarian weight increased by 29% and the apical walls of preovulatory follicles demonstrated appreciable thinning following LH administration. In mice receiving indomethacin plus PG vehicle, follicular maturation was suppressed in a dose dependent manner; in mice receiving 10 mg/kg, less than 50% of the oocytes resumed meiosis and, of these, only 9% were accompanied by cumulus expansion. Ovarian weight gain was also inhibited, and the apical follicle wall exhibited few signs of preovulatory thinning. PGE2 and PGF2α both reversed the inhibition of cumulus and oocyte maturation induced by indomethacin, though PGE2 was more effective. Only PGF2α promoted apical follicullar thinning, and neither PG had a significant effect on ovarian weight. We conclude that, in mice, PGs may play an integral role during preovulatory maturation of the oocyte and cumulus, as well as thinning of the apical wall.
Transport of spermatozoa in the sheep oviduct: Preovulatory sequestering of cells in the caudal isthmus
Authors: Hunter R. H. F. , Nichol R. 
Published: June 2005

AbstractProgression of ram spermatozoa within the sheep oviduct has been studied in relation to the time of ovulation. Ewes were mated at the onset of estrus and, at increasing intervals thereafter, the oviduct isthmus was transected 1.5–2.0 cm proximal to the utero‐tubal junction. The incidence of fertilization and number of accessory spermatozoa were examined in eggs recovered 1 to 3 days after surgery.Ovulation occurred 24–26 hours after the onset of estrus. None of 52 eggs recovered from 48 oviducts transected up to 21 hours after mating was fertilized, nor were spermatozoa associated with the zona pellucida. Two of 33 eggs (6.1%) from 29 oviducts transected between 22 and 24 hours after mating were fertilized, while 3 of 14 eggs (21.4%) and 13 of 16 eggs (81.3%) were fertilized with transection at 25 and 26 hours, respectively. The mean numbers of accessory spermatozoa on eggs in the latter two groups were 0.7 (range 0–2) and 7.9 (range 0–26). Results from transection at 27–30 hours after mating indicated a progressive release and adovarian movement of spermatozoa.Viable spermatozoa are apparently sequestered in the caudal isthmus for as long as 17–18 hours, until shortly before ovulation, when a local transfer of ovarian follicular hormones is thought to facilitate their redistribution. The adrenergic stimulation of powerful adovarian waves of contraction in the isthmus at this time may also act to provoke the capacitation and hyperactivation of ram spermatozoa.
Intersegmental coordination in the crayfish swimmeret system reconsidered
Authors: Macmillan D. L. , Altman J. S. , Kien J. 
Published: June 2005

AbstractStein ('71, '74) demonstrated that lesions in areas 78 and 81 of the nerve cord of the crayfish Procambarus affected intersegmental coordination. In these areas he found neurons which appeared to be local interneurons and whose discharge was correlated with motor discharge in the swimmeret roots. He suggested that these neurons might be responsible for intersegmental coordination and termed them coordinating fibres. We reexamined the same areas of the ventral nerve cord in the crayfish Cherax by recording extracellularly from small bundles of axons during rhythmic activity in the swimmeret motor nerves. All the units we located that exhibited correlated discharge appeared to be plurisegmental. Physiological examination revealed that such units may be sensory, motor, or interneurons. We confirmed this finding morphologically by staining some of the units intracellularly with cobalt. Deafferentation experiments and the effects of stimulating units showing correlated discharge suggest that all three types of neurons may be involved in intersegmental coordination. We conclude that the that the present coordinating fibre model should be abandoned.
Preimplantation development of the primate embryo after in vitro fertilization
Authors: Dukelow W. Richard , Chan P. J. , Hutz R. J. , Demayo F. J. , Dooley V. D. , Rawlins R. G. , Ridha M. T. 
Published: June 2005

AbstractThe developing use of in vitro fertilization (IVF) as a human clinical procedure has prompted the exploitation of nonhuman primates to assess the chromosomal and biochemical normality of embryos produced by IVF. Of 1995 oocytes recovered from squirrel monkeys, 628 (31.5%) matured and 339 (54.0%) fertilized. Fertility can be significantly enhanced by the addition of 1 or 10 μM dbcAMP to the culture medium. Chromosome analysis of oocytes and embryos used in these studies revealed an incidence of abnormality between 7 and 25%, comparable with that found for both in vivo and in vitro fertilized embryos from other laboratory species. There is no evidence that the IVF technique increases chromosomal abnormality. There was a decrease in protein synthesis of oocytes at maturation and during the early embryonic development stages, but an increase in the rate of RNA synthesis as development progressed. There was steroid uptake in early preimplantation embryos. The temporal relationships of early embryonic developmental events in the squirrel monkey have been determined.
Developmental aspects of X chromosome inactivation in eutherian and metatherian mammals
Authors: VandeBerg John L. 
Published: June 2005

AbstractThe single active X principle has served for two decades as a focal point for research on the cyclic activation and inactivation of gene loci. Differences in X chromosome inactivation patterns of eutherian and marsupial mammals provide probes for investigating the mechanisms of the X inactivation process.In eutherian mammals, the X chromosome is inactivated early in meiotic prophase in males and remains inactive throughout the rest of spermatogenesis. During meiosis in females, the inactive X chromosome is activated so that both X chromosomes are active in oocytes. During the early cleavage divisions of female embryos, the paternally derived X is activated. It and the maternally derived X remain active until differentiation begins in early embryogenesis. At that time, the paternally derived X is inactivated in cells that give rise to extraembryonic membranes, whereas a random process determines which X chromosome is inactivated in cells that give rise to the embryo itself.Although less is known about developmental aspects of X inactivation in female marsupials, it is clear that the paternal X is preferentially inactive in postembryonic somatic cells. Furthermore, the paternal X is partially active at some loci in some cell types, indicating that it is not regulated as a single unit. The successful adaptation of a small (80–150 g), fecund marsupial to simple laboratory conditions now enables extensive experimentation on the large number of marsupials at various developmental stages. This capability, coupled with the application of newly developed cellular and molecular techniques to questions about X chromosome inactivation, shows great promise for advancing our understanding of the mechanisms that control the cyclic behavior of X chromosome activity.
DNA modification, differentiation, and transformation
Authors: Jones Peter A. , Taylor Shirley M. , Wilson Vincent 
Published: June 2005

AbstractSubstantial evidence has accumulated over the last 5 years that the methylation of cytosine residues in vertebrate DNA is implicated in the control of gene expression. We have used analogs of cytidine, modified in the 5 position, as specific inhibitors of DNA methylation to probe the relationship between this process and cellular differentiation. 5‐Azacytidine effected marked changes in the differentiated state of cultured cells and induced the formation of biochemically differentiated state of cultured cells and induced the formation of biochemically differentiated muscle, fat, and chondrocytes from mouse fibroblast cell lines. Since the analog is a powerful inhibitor of DNA methylation, we suggest that this inhibition is causally related to the mechanism of phenotypic conversion. DNA extracted from cells treated with 5‐azacytidine was hemimethylated and was used as an efficient acceptor of methyl groups in an in vitro reaction in the presence of eukaryotic methylases. In vitro methylation was inhibited if the subtrate DNA was preincubated with a diverse range of chemical carcinogens including benzo(a)pyrene diolepoxide. Thus, chemical carcinogens may induce changes in gene expression by alteration of cellular methylation patterns.Recent experiments have also demonstrated that freshly explanted diploid fibroblasts from mice, hamsters, and humans lose substantial quantities of 5‐methylcytosine during cell division and aging in culture. Taken together, these experiments suggest that the genomic distribution of 5‐methylcytosine might have importance in normal differentiation and also in the aberrant gene expression found in cancer and senescence in culture.