bluuebunny/crossref_metadata_2025_split huggingface dataset:
Whole‐body and plasma concentrations of steroids in the turtle, Trachemys scripta, before, during, and after the temperature‐sensitive period for sex determination
Authors: White Richard B. , Thomas Peter 
Published: June 2005

AbstractTo examine endogenous steroid levels during early sexual differentiation in a reptile, we measured whole‐body and plasma steroid concentrations in a turtle (Trachemys scripta) throughout embryogenesis using radioimmunoassays. Whole embryos contained testosterone, estradiol, progesterone, and corticosterone before the temperature‐sensitive period for sex determination (TSP) (stage 14). The concentration of each of these steroids increased significantly between stage 14 and the initiation of the TSP (stage 16), but no increases were evident between stage 16 and the middle of the TSP (stage 18). No sex differences in steroid content were observed prior to the TSP (stage 14). However, presumptive male embryos (26°C incubation temperature) contained significantly more testosterone and estradiol than presumptive females (31°C incubation temperature) during the TSP (stages 16 and 18), and males contained more progesterone than females at stage 18. Plasma samples collected during the TSP (beginning at stage 17+) contained testosterone, estradiol, progesterone, androstenedione, and corticosterone. Progesterone and corticosterone were present in the highest concentrations, followed by androstenedione. Testosterone and estradiol were found in plasma at lower, similar concentrations except at stage 17+, when estradiol levels were ∼3‐fold higher than testosterone levels in both sexes. The only significant sex difference found in plasma steroid levels was for estradiol at stage 19, with males having higher levels than females. Our results demonstrate the presence of a rich steroid milieu throughout early development and support our previous findings that embryonic tissues can synthesize each of these steroids in vitro. Furthermore, a role for sex steroids in the process of sexual differentiation is strongly suggested. © 1992 Wiley‐Liss, Inc.
Inhibitory role of sex steroid in the regulation of ovarian follicle‐stimulating hormone receptors during pregnancy
Authors: Tsutsui Kazuyoshi 
Published: June 2005

AbstractThe present study was conducted to determine the role of sex steroids in the regulation of FSH receptors in pregnant rats. In the normal physiological condition, FSH bindings per unit ovarian weight (density of binding) and per 2 ovaries (total binding) increased during days 14–21 gestation. Scatchard plot analyses of the binding suggested that the increase in FSH binding was due to an increase in the number of FSH‐binding sites. The plasma FSH concentration in pregnant rats was stable during the receptor change. In contrast, the plasma estradiol‐17β concentration continuously increased from gestation day 14 to 21, and the testosterone level showed a large peak on gestation day 18. Estradiol‐17β (one silastic plate containing 13 mg crystal)‐implanted pregnant rats during 14–21 days of gestation induced significant decreases in the total FSH binding and ovarian weight on gestation day 21. Estradiol administration increased the plasma estradiol level 2.3‐fold but did not change the FSH level. Testosterone or 5 α‐dihydrotestosterone, a nonaromatizable androgen, did not influence the binding level under the same dose treatment. In contrast, continuous treatment with aminoglutethimide (2 plates containing 20 mg crystal), an inhibitor of adrenocortical steroidogenesis, for 7 days significantly increased the total FSH binding without a significant change in the ovarian weight. The plasma titers of estradiol and testosterone in pregnant rats treated with aminoglutethimide were reduced by 37% and 51%, respectively. Aminoglutethimide did not influence plasma FSH levels. These results suggest that circulating estradiol acts as a negative factor in the regulation of ovarian FSH receptors, at least during the second half of pregnancy. Other factor(s) that is (are) independent of sex steroids and FSH may contribute to FSH receptor induction. © 1992 Wiley‐Liss, Inc.
Sex differences in adrenal function in the lizard Cnemidophorus sexlineatus: II. Responses to acute stress in the laboratory
Authors: Grassman Mark , Hess David L. 
Published: June 2005

AbstractCirculating concentrations of plasma corticosterone and gonadal steroids were measured intact and gonadectomized male and female lizards (Cnemidophorus sexlineatus) following acute stress (handling) in the laboratory. There was a significant increase in plasma corticosterone after stress. Whereas intact females exhibited greater concentrations of corticosterone relative to intact males, ovariectomized females exhibited lower concentrations of corticosterone relative to castrated males. In addition to sex differences in corticosterone responses to gonadectomy, progesterone was elevated by stress in both intact and ovariectomized females but not in males. Corticosterone adjusted for castration and handling in males was negatively correlated with the plasma androgen level. The adrenal responsiveness of males to acute stress may be attenuated by androgens presumably secreted by the testis. Not only does adrenal function influence reproduction, but adrenal responses differ between males and females, and appear to be influenced by the gonadal axis. The sex differences in adrenal responses to stress likely reflect different reproductive strategies and nutritional requirements of males and females during the breeding season. © 1992 Wiley‐Liss, Inc.
The role of hypoglossal sensory feedback during feeding in the marine toad, Bufo marinus
Authors: Nishikawa Kiisa C. , Gans Carl 
Published: June 2005

AbstractBehavioral observations demonstrate that bilateral deafferentation of the hypoglossal nerves in the marine toad (Bufo marinus) prevents mouth opening during feeding. In the present study, we used high‐speed videography, electromyography (EMG), deafferentation, muscle stimulation, and extracellular recordings from the trigeminal nerve to investigate the mechanism by which sensory feedback from the tongue controls the jaw muscles of toads. Our results show that sensory feedback from the tongue enters the brain through the hypoglossal nerve during normal feeding. This feedback appears to inhibit both tonic and phasic activity of the jaw levators. Hypoglossal feedback apparently functions to coordinate tongue protraction and mouth opening during feeding. Among anurans, the primitive condition is the absence of a highly protrusible tongue and the absence of a hypoglossal sensory feedback system. The hypoglossal feedback system evolved in parallel with the acquisition of a highly protrusible tongue in toads and their relatives. © 1992 Wiley‐Liss, Inc.
The role of protein kinase C in reorganization of the cortical cytoskeleton during the transition from oocyte to fertilization‐competent egg
Authors: Capco David G. , Tutnick Joel M. , Bement William M. 
Published: June 2005

AbstractFertilization‐competent amphibian eggs (metaphase II) are programmed to undergo an actin‐myosin based contraction of the cortical cytoplasm (i.e., cortical contraction) in response to an elevation of intracellular‐free calcium which accompanies fertilization. This ability to undergo cortical contraction is acquired within a few hours after the meiotically‐arrested oocyte is triggered to resume meiosis by exposure to progesterone. This report examines the timing of changes in the contractile potential of the cortical cytoplasm as the oocyte becomes the egg, and in addition, the signal transduction events which induce these changes. We use the bisected oocyte system developed by Christensen et al. ('84; Nature 310: 150‐151) to assess the changes in cortical potential during the meiotic resumption. Immediately after progesterone treatment (less than 5% of the way through the meiotic resumption) the cortex acquires the ability to form a contractile ring, an ability which gradually disappears during the meiotic resumption. Eighty percent of the way through the meiotic resumption the cortex of the hemisphere rapidly acquires the ability to undergo cortical contraction. In contrast, when bisected in a medium containing protein kinase C (PKC) agonists, the cortex of the hemisphere undergoes cortical contraction much earlier (i.e., 50% through the meiotic resumption). In addition, treatment of oocytes with PKC agonists alone can mimic the complete spectrum of changes in cortical potential induced by progesterone, suggesting that PKC has a role in reorganization of the cortical cytoskeleton which occurs as a normal response to progesterone. In support of this, antagonists of PKC block the progesterone‐induced reorganization of the cortical cytoskeleton. © 1992 Wiley‐Liss, Inc.
Seasonal changes of the adrenocortical response to stress in birds of the Sonoran desert
Authors: Wingfield John C. , Vleck Carol M. , Moore Michael C. 
Published: June 2005

AbstractMany avian species of the North American Sonoran desert, e.g., the black‐throated sparrow, Amphispiza bilineata, cactus wren, Campylorhynchus brunneicapillus, and curve‐billed thrasher, Toxostoma curvirostre, can potentially breed from March/April to August. It is possible that, at least in summer, intense heat and aridity may have inhibitory effects on breeding by precipitating a stress response. Stress typically results in a rise in secretion of adrenocorticosteroid hormones that then inhibit reproduction by suppressing release of gonadal hormones. However, we found that plasma levels of corticosterone were not higher during summer, compared with winter, even in 1989 when summer temperatures were higher than normal. In June 1990, temperatures were also above normal and soared to the highest level recorded in Arizona (50°C). Plasma levels of corticosterone during June were high in black‐throated sparrows, but less so in two other species (Abert's towhee, Pipilo aberti, and Inca dove, Scardafella inca) found in more shady riparian and suburban habitat with constant access to water. The adrenocortical response to stress (as measured by the rate of corticosterone increase following capture) was reduced in the hottest summer months in black‐throated sparrows, cactus wrens, and curve‐billed thrashers, but less so in Abert's towhee an Inca dove. These data suggest that at least some birds breeding in the open desert with restricted access to water are able to suppress the classical adrenocortical response to stress. The response is then reactivated in winter after breeding has ceased. It is possible that this stress modulation may allow breeding to continue despite severe heat. Analysis of plasma from these species indicated that the apparent modulation of the adrenocortical response to stress was not an artifact of reduced affinity or capacity of corticosterone binding proteins. © 1992 Wiley‐Liss, Inc.
Renal clearance measurements of electrolytes in embryonic chickens
Authors: Clark N. B. , Feng J. Q. , Murphy M. J. 
Published: June 2005

AbstractPlasma ion concentrations and renal functions were examined in chick embryos after 9, 12, and 15 days of incubation. Plasma calcium and phosphate values rise steadily and significantly between days 9 and 15 of development. Values of other plasma ions (sodium, potassium, magnesium, sulfate) remain more or less the same during this developmental period. Glomerular filtration rates and urine flow rates decline steadily and significantly during this period of embryogenesis when expressed relative to body weight. Renal clearance values of calcium decrease between day 9 (16% of filtered calcium is excreted) and day 15 (4%). The latter value is the same as in birds after hatching and indicates that calcium is being conserved by the kidney of the chick during late embryogenesis. Other ions that appear to be conserved by the embryonic kidney are sodium and sulfate, whereas high percentages of filtered phosphate, potassium, and magnesium are excreted. Except for calcium, there was no significant difference between the renal handling of ions by the mesonephric kidney (functional in 9 day embryos) and the metanephric kidney (predominant in the 15 day embryos). © 1993 Wiley‐Liss, Inc.
Developmental anomalies of Xenopus embryos following microinjection of SPARC antibodies
Authors: Purcell Laura , Gruia‐Gray Jasmine , Scanga Sam , Ringuette Maurice 
Published: June 2005

AbstractThe function of SPARC (Secreted Protein, Acidic, Rich in Cysteine) in early embryonic development was assayed by microinjecting affinity‐purified antibodies directed against SPARC into the blastocoel cavity of Xenopus embryos. Microinjection of SPARC antibodies did not appear to interfere with development until late neurulation. By hatching, a broad spectrum of external developmental anomalies were observable, including bent embryonic axes, accentuated ventral masses, shortened embryonic axes, and lack of visible eye pigment. Histological sections of injected embryos demonstrated that lack of visible eye pigmentation was often associated with deformities in eye development. Bending and shortening of the embryonic axis was associated with highly disorganized myo‐tome patterns and loss of segmental boundaries. The results indicate a requirement for SPARC in the early morphological development of several tissues in Xenopus. © 1993 Wiley‐Liss, Inc.
Relationship between local cell division and cell displacement during regeneration of embryonic Xenopus eye fragments
Authors: Underwood Lauren Wunsh , Carruth Marc R. , Vandecar‐Ide Annette , Ide Charles F. 
Published: June 2005

AbstractWe examined the relationship between early healing modes and extra cell division (via tritiated thymidine incorporation) during embryonic retinal regeneration. Nasal (N) and dorsal (D) one‐third sized eye fragments were surgically created in stage 32 Xenopus laevis embryos. Embryos were injected with tritiated thymidine two days postsurgery (stage 43), and then fixed and processed for autoradiography one day postinjection (stage 46). Histological analysis revealed that all nasal one‐third sized fragments showed cell displacement in healing regions. These displaced cells were located in the ventral retinal region and showed heavy thymidine label incorporation. Alternatively, most dorsal one‐third sized fragments showed little cell displacement during healing; in addition, no extra thymidine incorporation was evident. A minority of dorsal one‐third sized fragments showed cell displacement during healing, and also showed significant local label ventrally through all regions of the eye. Therefore, in both dorsal and nasal one‐third sized retinal fragments, when cell displacements were observed during early healing, associated mitosis was apparent in ventral retinal regions. Furthermore, by 60 hours postsurgery, all eyes which showed cell displacements during healing were greater in volume than those eyes which showed little cell displacement. Increases in volume appear to be derived from a combination of both cells migrating in from underlying optic stalk tissue and from related extra cell division during healing. These data further support a model which predicts that specific healing interactions which involve cell displacement during embryonic retinal regeneration and subsequent intercalary growth underlie visuotectal pattern formation. © 1993 Wiley‐Liss, Inc.
Effects of reproductive state on molt in the Japanese quail
Authors: Hall M. R. , Laouar L. , Ivings W. 
Published: June 2005

AbstractMolt is induced in quail when they are transferred from photostimulatory long daylengths of 18L, with a fully active reproductive system, to short daylengths of 8L, when the reproductive system regresses. Gonadal steroids, but not gonadotrophins, inhibit molt in male and female Japanese quail. Molt can be induced in long‐term photostimulated (18L) quail by withdrawing gonadal steroids 1) by transferring quail to 8L, 2) by castrating males and maintaining them on a photoperiodic regime of 18L, or 3) by treating females or males with the antiestrogen, tamoxifen. In contrast, treatment of male quail with the antiandrogen, flutamide, does not induce molt even though androgen secretion is inhibited and androgen‐dependent tissues regress. Neither the exact mode of action nor the metabolite of gonadal steroids which inhibits molt is known, although estradiol is capable of inhibiting molt in females and to a lesser extent in males. Plasma levels of thyroxine are consistently elevated during molt. © 1993 Wiley‐Liss, Inc.
Embryonic mouse pre‐metatarsal development in organ culture
Authors: Klement Brenda J. , Spooner Brian S. 
Published: June 2005

AbstractEmbryonic mouse pre‐metatarsals were removed from embryos at 13 days of gestation and cultured in a defined, serum‐free medium for up to 15 days. By histological analysis, we observe that the cultured pre‐metatarsal tissue undergoes a similar developmental profile as pre‐metatarsals growing normally in vivo. The initial mesenchyme condensation regions undergo differentiation and morphogenesis to form distinct rods made up of cartilage tissue. A marker of this differentiation step is the synthesis of type II collagen. Metabolic labelling, pepsin digestion, SDS‐PAGE, and autoradiography were used to demonstrate this protein when cartilage tissue is present in the cultures. After additional culture time, terminal chondrocyte differentiation and morphogenesis take place in specific regions of the cartilage rods to form bands of hypertrophied chondrocytes. One marker of this differentiation step is the synthesis of the enzyme alkaline phosphatase. We have measured the activity of this enzyme throughout the culture period and see a substantial increase at the time of terminal chondrocyte differentiation. Another feature of hypertrophied chondrocytes is that the matrix around the cells becomes calcified. Calcified matrix in our cultured pre‐metatarsals was visualized by staining with alizarin red. By supplementing the defined culture medium with ITS, we observed that terminal chondrocyte differentiation took place in a shorter culture time. Supplementation of the medium with serum results in a similar acceleration of terminal differentiation, and, with additional culture time, an osteoid‐like matrix forms around the central region of the rods. © 1993 Wiley‐Liss, Inc.
On the existence of epithelial chloride channels in intact frogs and crayfish
Authors: Zetino Ana M. , Kirschner Leonard B. 
Published: June 2005

AbstractChloride channels in isolated amphibian skins have been shown to be open (high PCi) when the transepithelial potential (TEP) across the skin is >30 mV, inside positive, and [Cl−] in the external medium is high. In the absence of either of these signals PCl is much lower. Using Cl− efflux as a criterion, it is shown here that when the same cues are presented to intact frogs, channels open as in the in vitro preparation. The augmented efflux is partially inhibited by high I− in both preparations. However, salt‐depleted frogs do not show channel opening, differing in this regard from isolated skins.Elevating external [Cl−] resulted in an even larger efflux stimulation in crayfish than in frogs. The TEP in these animals is usually small and sometimes blood negative; it does not appear to play a role in augmenting the efflux. Gluconate and NO3− also caused Cl efflux to increase markedly. Salt‐depletion reduced the stimulation by high [Cl−] but did not abolish it as in frogs. Iodide had no effect on chloride efflux in crayfish. The results may indicate that gated channels exist in these animals, but interpretation is complicated by the possibility that the augmented efflux is due to exchange diffusion. © 1993 Wiley‐Liss, Inc.
Biochemistry, localization, and physiology of carbonic anhydrase in the gills of euryhaline crabs
Authors: Böttcher K. , Siebers D. 
Published: June 2005

AbstractCarbonic anhydrase, found at high levels in crustacean gill, is capable of catalyzing the formation of CO2 in the forward reaction or the production of HCO3− in the reverse reaction. Thus the enzyme may participate in both respiratory and ion regulatory functions. Its subcellular distribution in crab gill epithelial cells suggests that a large proportion of the enzyme is membrane‐bound, where it would be available to pharmacological treatment with membrane‐impermeable carbonic anhydrase inhibitors. These studies suggest that the enzyme plays a central role in CO2 excretion. Treatment with the permeable inhibitor acetazolamide affects osmoregulation and ion transport in addition to CO2 excretion, suggesting that the cytosolic form of carbonic anhydrase may provide HCO3 − for Cl−/HCO3 − exchange and H+ for Na+ /H+ exchange across the gill epithelium. © 1993 Wiley‐Liss, Inc.
Evidence for an alternative route of phosphoenolpyruvate metabolism in mature nucleated Rana ridibunda erythrocytes
Authors: Kaloyianni Martha , Beis Isidoros 
Published: June 2005

AbstractThe presence of phosphoenolpyruvate carboxykinase (PEPCK) activity in the direction of oxaloacetate formation in Rana ridibunda erythrocytes was detected. In addition, the levels of all the individual enzymes leading from phosphoenolpyruvate (PEP) to succinate production have been determined in Rana ridibunda hemolysates. Incubation of the intact red cells in the presence of the PEPCK activity inhibitors, quinolinic, and mercaptopicolinic acid resulted in the inhibition of the succinate levels whereas the pyruvate levels were increased. The flow of carbon through PEPCK indicates its participation to an alternative route of PEP metabolism with the advantage of two additional molecules of adenosine triphosphate (ATP) production per glucose molecule catabolized. The possible mechanisms that could control the flow of PEP either towards pyruvate or towards oxaloacetate in Rana ridibunda erythrocytes are discussed. © 1993 Wiley‐Liss, Inc.
Control of intrinsic buccal muscles by motoneurons B11, B15, and B16 in Aplysia californica
Authors: Jordan Robert , Cohen Kevin P. , Kirk Mark D. 
Published: June 2005

AbstractTo further define the control of intrinsic buccal muscles by identified motoneurons B11, B15, and B16 in Aplysia californica, we made physiological recordings from semi‐intact and isolated preparations of the buccal ganglia and buccal mass. B15 and B16 were previously known to innervate muscle 15 (also called the accessory radula closer muscle). We show here that these motoneurons also innervate other buccal muscles ipsilateral to their cell bodies; for example, B15 reliably innervates and can cause contraction in intrinsic muscle 14. Likewise, B11 appears to innervate all of the intrinsic buccal muscles, but elicits contractions only in I4. The form and time course of synaptic plasticity displayed by these motoneurons is common to all the muscles they innervate. No evidence for electrical coupling between fibers of adjacent muscles could be obtained, suggesting that all recorded innervation is direct. Like B15 and B16 (Cohen et al., '78), B11 neuromuscular synapses appear to be cholinergic, since they are reversibly antagonized by hexamethonium and d‐tubocurarine (acetylcholine [ACh] receptor antagonists). In addition, direct application of ACh elicits depolarizing responses and contractions in I4 which are also blocked by hexamethonium. Application of glutamate and GABA do not elicit depolarizations or contractions in I4 or I5. We conclude that these motoneurons control radula position through complex synaptic actions on multiple intrinsic buccal muscles, using ACh as their conventional transmitter. © 1993 Wiley‐Liss, Inc.