1,721,036 research outputs found
Wirkung von Hypericum auf die Melatonin-Tagesperiodik des dsungarischen Zwerghamsters (Phodopus sungorus)
No full textThe effects of incubation temperature on the morphology and composition of Australian Brush-turkey (Alectura lathami) chicks
No full textEnvironmental heterogeneity during embryonic development generates an important source of variation in offspring phenotypes and can influence the evolution of life histories. The effects of incubation temperature on offspring phenotypes in reptiles has been well documented but remains relatively unexplored in birds as their embryos typically develop over a narrow range of temperatures. Megapode birds (Order Galliformes; Family Megapodiidae) are unique in that their embryos tolerate and develop over a wide range of incubation temperatures, yet little is known of the effect that temperature has on hatchling morphology and composition. Australian Brush-turkey eggs collected on the day of laying were incubated in the laboratory under constant temperatures of 32, 34 and 36°C until hatching in order to determine the influence of temperature on hatchling mass, size and composition. The dry mass of the yolk-free body and residual yolk of hatchlings were temperature dependent, such that higher temperatures produced chicks of lesser yolk-free body mass and greater residual yolk mass than chicks incubated at lower temperatures. However the overall size (linear dimensions) and lipid, protein and ash content of chicks were independent of temperature
Gene expression during daily torpor: molecular mechanisms of metabolic depression
No full textDsungarische Zwerghamster (Phodopus sungorus) zeigen täglichen Torpor als Teil ihrer saisonalen Akklimatisation an die kalte Jahreszeit. Wie viele andere Kleinsäuger senken die Hamster während des Torpors ihre Stoffwechselrate zur Energieeinsparung während der täglichen Ruhephase für mehrere Stunden ab. Die verringerte Eigenwärmeproduktion führt in Abhängigkeit von der Umgebungstemperatur zu einer Erniedrigung der Körpertemperatur (Hypothermie). Verantwortlich für den Eintritt in den hypometabolen Zustand während des täglichen Torpors ist ähnlich wie beim Winterschlaf eine Stoffwechseldepression. Im Mittelpunkt der vorliegenden Arbeit standen Untersuchungen zur Genexpression beim Eintritt in den täglichen Torpor. Dabei lag das Interesse sowohl auf der Identifikation differentiell exprimierter Gene, als auch auf der Untersuchung der globalen Transkriptions- und Translationsaktivität, die einen Beitrag zur metabolischen Depression leisten könnten. Die kontinuierliche Messung der Stoffwechselrate mittels indirekter Kalorimetrie ermöglichte die Gewebeentnahme in drei metabolischen Zuständen: Normometabol (Kontrollen), torpid (bei Erreichen der minimalen Stoffwechselrate) und nach dem Erwachen aus dem Torpor (Arousal).
Die globale Transkriptionsaktivität in der Leber wurde mittels Transcriptional Run on Assays untersucht. Bei Zellkernen aus der Leber torpider Hamster konnte im Vergleich zu den normometabolen Kontrollen ein um ~40% erniedrigter Einbau radioaktiv-markierter Nukleotide in die in vitro-transkribierten mRNA-Moleküle festgestellt werden. Dies lässt auf eine Reduktion der Initiationsrate von Transkriptionsvorgängen während des Torpors schließen. Die in vitro- Transkriptionsrate der Leber-Zellkerne von Hamstern, die aus dem Torpor wieder erwacht waren (Arousal), unterschied sich nicht von den Proben der normometabolen Kontrolltiere. Zum Vergleich der Proteinsynthese in der Leber normometaboler und torpider Hamster wurden Polysomen-Profile erstellt. Im Gegensatz zu den Proben normometaboler Hamster, bei denen die Ribosomen vorwiegend in Form von Polysomen vorlagen, konnte bei den Proben torpider Hamster ein Zerfall von Polysomen beobachtet werden. Die Disaggregation von Polysomen lieferte einen Hinweis auf eine reduzierte Proteinsynthese während des Torpors. Bei Transkription und Translation handelt es sich um energieaufwendige Prozesse, die zusammen über 30% der in Form von ATP fixierten Energie beanspruchen. In der Leber, die für ~20% der Basalstoffwechselrate verantwortlich ist, konnte nachgewiesen werden, dass die Inhibition der Synthese von RNA und Protein einen wesentlichen Mechanismus der Stoffwechseldepression beim Eintritt in den täglichen Torpor darstellt.
Mittels Northernblot-Analysen wurde die mRNA-Expression von drei Isoenzymen der Pyruvat-Dehydrogenase-Kinase (PDK 1, 2 und 4) im Herzmuskel normometaboler und torpider Hamster untersucht. Die Kinasen inaktivieren durch Phosphorylierung den Pyruvat-Dehydrogenase-Komplex (PDC), was zur Umschaltung von Glucose-Verwertung auf Fettsäuren als primäres Substrat zur Energiegewinnung führt. In einer früheren Studie konnte beim Dsungarischen Zwerghamster eine positive Korrelation zwischen der Stoffwechselrate der Tiere und der Aktivität des PDC u.a. im Herzmuskel festgestellt werden, was auf eine Inaktivierung des Multienzymkomplexes während des täglichen Torpors schließen lässt. Für PDK4 konnte eine leichte Erhöhung der mRNA-Konzentration im Herzmuskel torpider Hamster im Vergleich zu normometabolen Kontrollen festgestellt werden, die jedoch nicht in einer Erhöhung des PDK4-Proteingehalts resultierte. 48-stündiger Futterentzug hingegen hatte eine drastische Erhöhung der PDK4-mRNA-Konzentration zur Folge. Die in früheren Studien an Winterschläfern beobachtete Erhöhung der PDK4-Expression im Herzmuskel könnte eine Anpassung an das chronische Fasten während des Winterschlafs darstellen. Im Gegensatz dazu kommt es während des täglichen Torpors bei Dsungarischen Zwerghamstern nicht zu langfristigem Futterentzug. Sie sind auch im Winter auf eine regelmäßige Nahrungszufuhr angewiesen. Die kurzfristige Regulation der PDKs könnte auf allosterische Effektoren zurückzuführen sein.
Als nicht-hypothesenbasierende Ansätze zur Identifikation von im Herzmuskel differentiell exprimierten Genen während des Torpors wurden zwei alternative Methoden verwendet. Bei der cDNA-RDA basierte die Differenzanalyse auf einer subtraktiven Hybridisierung und anschließender selektiver Amplifikation von cDNA-Fragmenten. Alternativ zur cDNA-RDA wurden Maus-Filterarrays zur Identifikation von Unterschieden in der Genexpression eingesetzt. Bei keinem der selektierten Kandidaten konnte die differentielle Genexpression auf Northernblots bestätigt werden. Eine metabolische Reorganisation auf der Grundlage differentieller Genexpression scheint im Herzmuskel nicht zu den zentralen Mechanismen der metabolischen Depression beim Einritt in den täglichen Torpor zu zählen.Djungarian hamsters display daily torpor spontaneously as part of their seasonal acclimation to winter conditions, providing a strategy to cope with limited food availability and cold. The torpid state during the daily period of rest is characterized by a decrease of metabolic rate resulting in a reduction of energy expenditure. Similar to hibernation, the entrance into the hypometabolic state involves an active metabolic depression that precedes the development of hypothermia.
The present thesis is focused on analyses of gene expression during the entrance into daily torpor, in order to identify differentially expressed genes as well as changes in the global transcriptional and translational activity contributing to the observed metabolic depression. Metabolic rate was measured continuously using indirect calorimetry. Tissues were sampled in defined metabolic states: during normometabolism (controls), in the torpid state (when minimal metabolic rate was first attained during entrance into torpor), and after arousal from torpor.
Transcriptional run-on assays were employed to investigate the status of transcriptional initiation as a function of the torpid state. The determination of the in vitro transcription rate in isolated nuclei reflects a snapshot of global transcriptional activity in a given physiological state. Nuclei were isolated from liver tissue of normometabolic, torpid and aroused hamsters and subjected to nuclear run-on assays at a temperature of 25°C. A ~40% decrease in transcriptional initiation was observed in liver nuclei of hamsters which had attained minimal metabolic rate during torpor as compared to nuclei from normometabolic hamsters. During arousal from torpor, the transcriptional run-on activity recovered to the normometabolic level. Polysome profile analysis of liver tissue was used to determine the proportion of actively translating polysomes. Profiles of liver samples from torpid animals show a disaggregation of polysomes compared to profiles from normometabolic hamsters, which indicates that, in addition to transcription, protein synthesis decreases during torpor. These results indicate that during torpor a specific inhibition of the energetically costly processes of RNA and protein synthesis contribute to the overall metabolic depression.
As candidates for differentially expressed genes during torpor, the mRNA expression of three isoenzymes of the pyruvate dehydrogenase kinase (PDK1, 2 and 4) were analysed in the heart of normometabolic and torpid hamsters using Northernblots. The kinases inactivate the pyruvate dehydrogenase complex (PDC) by reversible phosphorylation. PDC catalyzes the conversion of pyruvate to acetyl-CoA and is therefore a key enzyme responsible for the entry of carbon units into the tricarboxylic acid cycle. Inactivation of PDC leads to an inhibition of glucose oxidation and favours the utilization of lipids as a metabolic fuel. A previous study revealed a positive correlation between PDC activity and metabolic rate, suggesting a role of pyruvate dehydrogenase complex (PDC) inactivation in the selection of metabolic fuel during daily torpor. A weak increase in the concentration of PDK4 mRNA in the heart of torpid hamsters was observed as compared to normometabolic controls. However, this increase did not result in an altered amount of PDK4 protein in the heart of torpid hamsters. An ~10-fold increase in the mRNA encoding PDK4 occurred in the heart of hamsters after 48 h of food deprivation. The expression of PDK4 during fasting is comparable to the seasonal increase of PDK4 in the heart of hibernating ground squirrels, suggesting that this effect is due to long-term food deprivation during hibernation. Winter acclimated Djungarian hamsters display daily torpor spontaneously, without anticipatory development of starvation symptoms, even when fed ad libitum. Despite the energy savings due to daily torpor, they still rely on continuous feeding during winter. Short-term regulation of PDK activity during daily torpor could be based on allosteric effectors more than on the level of gene expression.
Two alternative methods were applied to identify differentially expressed genes in the heart during daily torpor. The cDNA-RDA is based on a subtractive hybridization and a subsequent selective amplification of cDNA-fragments representing differentially expressed transcripts. In addition, mouse Unigene filterarrays were hybridized with cDNA from normometabolic and torpid hamsters. Both experiments resulted in a set of candidate genes that appear to differ between the normometabolic and the torpid state, but none could be confirmed as differentially expressed on Northernblots. The entrance into the torpid state seems not to be the result of major changes in gene expression. Rapid and reversible mechanisms like protein phosphorylation are more likely responsible for the metabolic depression during torpor, enabling cells to resume normal function after arousal from torpor
Hormone-dependent dissociation of blood flow and secretion rate in the lingual salt glands of the estuarine crocodile, Crocodylus porosus
No full textSalt and water balance in the estuarine crocodile, Crocodylus porosus, involves the coordinated action of both renal and extra-renal tissues. The highly vascularised, lingual salt glands of C. porosus excrete a concentrated sodium chloride solution. In the present study, we examined the in vivo actions of vasoactive intestinal peptide (VIP), B-type natriuretic peptide (BNP) and angiotensin II (ANG II) on the secretion rate and blood perfusion of the lingual salt glands. These peptides were selected for their vasoactive properties in addition to their reported actions on salt gland activity in birds and turtles and rectal gland activity in elasmobranchs. The femoral artery was cannulated in seven juvenile crocodiles for delivery of peptides and measurement of mean blood pressure and heart rate. In addition, secretion rate of, and blood flow to, the salt glands were recorded simultaneously using laser Doppler flowmetry. VIP stimulated salt secretion was coupled to an increase in blood flow and vascular conductance of the lingual salt glands. BNP was a potent stimulant of salt gland secretion, resulting in a maximal secretion rate of more than 15-fold higher than baseline; however, this was not coupled to an increase in perfusion rate, which remained unchanged. ANG II failed to stimulate salt gland secretion and there was a transient decrease in salt gland blood flow and vascular conductance. It is evident from this study that blood flow to, and secretion rate from, the lingual salt glands of C. porosus are regulated independently; indeed, it is apparent that maximal secretion from the salt glands may not require maximal blood flow
The effect of organochlorines and heavy metals on sex steroid-binding proteins in vitro in the plasma of nesting green turtles, Chelonia mydas
No full textIn this study on green turtles, Chelonia mydas, from Peninsular Malaysia, the effect of selected environmental toxicants was examined in vitro. Emphasis was placed on purported hormone-mimicking chemicals such as dichlorodiphenyltrichloroethane (DDT), dichlorodiphenyldichloroethylene, dieldrin, lead, zinc and copper. Five concentrations were used: high (1 mg/L), medium (10(-1) mg/L), low (10(-2) mg/L), very low (10(-6) mg/L) and control (diluted carrier solvent but no toxicants). The results suggest that environmental pesticides and heavy metals may significantly alter the binding of steroids [i.e. testosterone (T) and oestradiol] to the plasma proteins in vitro. Competition studies showed that only Cu competed for binding sites with testosterone in the plasma collected from nesting C. mydas. Dieldrin and all heavy metals competed with oestradiol for binding sites. Furthermore, testosterone binding affinity was affected at various DDT concentrations and was hypothesised that DDT in vivo may act to inhibit steroid-protein interactions in nesting C. mydas. Although the precise molecular mechanism is yet to be described, DDT could have an effect upon the protein conformation thus affecting T binding (e.g. the T binding site on the steroid hormone binding protein molecule)
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Sex steroid binding proteins in the plasma of hatchling Chelonia mydas
No full textSex steroid binding proteins were identified in hatchling female and male Chelonia mydas by dialysis and steady-state gel electrophoresis when examined at 4 degrees C. A testosterone binding protein with high binding affinity (K (a) = 0.98 +/- 0.5 x 10(8) M(-1)) and low to moderate binding capacity (B (max) = 7.58 +/- 4.2 x 10(-5) M) was observed in male hatchlings. An oestradiol binding protein with high affinity (K (a) = 0.35 +/- 1.8 x 10(8) M(-1)) and low to moderate binding capacity (B (max) = 0.16 +/- 0.5 x 10(-4) M) was identified in female hatchlings. This study confirmed that sex steroid binding proteins (SSBPs) become inactivate in both sexes at 36 degrees C, the maximum body temperature of sea turtle hatchlings at emergence. The inactivation of SSBPs at this temperature indicates that sex steroid hormones circulate freely in the body of the green turtles and are biologically available in the blood plasma. This observation is consistent with female and male hatchling C. mydas having different physiological (hormonal) and developmental requirements around the time of emergence. Moreover, concurrently conducted competition studies showed that sex steroids including testosterone and oestradiol do compete for binding sites in both male and female C. mydas hatchling plasma. Competition also occurred between testosterone and dihydrotestosterone for binding sites in the male C. mydas plasma. However, competition studies in the plasma of female hatchling C. mydas demonstrate that oestrone does not compete with oestradiol for binding sites
Physiological mechanisms of thermoregulation in reptiles: a review
No full textThe thermal dependence of biochemical reaction rates means that many animals regulate their body temperature so that fluctuations in body temperature are small compared to environmental temperature fluctuations. Thermoregulation is a complex process that involves sensing of the environment, and subsequent processing of the environmental information. We suggest that the physiological mechanisms that facilitate thermoregulation transcend phylogenetic boundaries. Reptiles are primarily used as model organisms for ecological and evolutionary research and, unlike in mammals, the physiological basis of many aspects in thermoregulation remains obscure. Here, we review recent research on regulation of body temperature, thermoreception, body temperature set-points, and cardiovascular control of heating and cooling in reptiles. The aim of this review is to place physiological thermoregulation of reptiles in a wider phylogenetic context. Future research on reptilian thermoregulation should focus on the pathways that connect peripheral sensing to central processing which will ultimately lead to the thermoregulatory response
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
