THE USE OF PHYSIOLOGICAL PARAMETERS IN MEASURING THE VEGETATIVES CONSEQUENCES OF MENTAL IMAGERY

INTRODUCTION The effects of the mental repetition of an activity entail not only the improvement of motor performances, but create vegetative consequences, which are connected to the degree of imagined effort (Decety, Jeannerod, Germain et Pastene, 1991 ). These beneficial effects of imagery have been explained by considering that the central structures of programming allow the anticipation of the metabolic requirement according to the established goals. The authors who do not agree on the explanatory theory of vegetative changes observed during the mental imagery phase, also have differing opinions concerning the existence of measurable muscular activity. Traditional instruments of measure such as heart rate and electromyography were used as well as force measurement. The force allowed us to know the, mechanical force produced, which should be zero during imagery phase not to have a conclusion in favor of a mechanical action. METHODS If we consider, with Jagasinski and Nicholls (1984,1987) that the central structure involved in the programming of a real activity, as in an imagined activity, defines the contents of this activity according to a goal, we can then assume that the mental operations occuring before the beginning of an action affect the level of effort and the energetic or metabolic resources used. We asked 24 male subjects who had obtained good results at the Sheehan imagery questionnaire to imagine a precise isometric contraction : bending the elbow. Through the use of instructions, one group of 8 subjects had to complete the task (called the goal of implication in a task), 8 other subjects had to do better than the others, surpass them (ego implication goal) while the 8 remaining subjects were given no instructions to achieve the goal. All the subjects went through two sessions including positive\negative feed-backs. In the real execution phase as well as in the imaginary phase, the measurements of heart rate and the electromyography of the biceps brachi and the force used are the primary indicators concerning the vegetative changes. RESULTS They show no trace of electromyography activity during the imagined movement if we make sure of the absence of movement during this phase by using a force transducer. Besides, there is a significant rise in the heart rate, during a real movement as well as an imagined one and this is even more evident when the subjects go from the conditions of implication in a task and implication of ego. At the same time, the subjects stated that they made less effort when they were given a positive feed-back and made higher levels of effort when they received a negative feed-back in an implication of ego situation. DISCUSSION In the mental imagery phase, all significant muscular activity is due to a mechanical action. In the absence of force production, even with the creation of an image, the muscle produces no activity. The potential of a subliminal muscular activity would be the real action in weak proportions but mechanically not significant for the chosen movement. The benefits of the mental repetition are here considered according to a symbolic perspective. and emphasize the cognitive components of the mental repetition, in other words, the individual imagined the activity to be accomplished. This is a matter of purely cognitive process. If a muscular activity is visible, the individual has gone from the stage of an intention of movement to his effective achievement, this change would come from the representation of the activity that the subject creates himself. We may conclude that measurements made with biomechanical devices can be very useful to check psychological hypotheses in sport. REFERENCES 1-BERGUS ; JONES, E.E. : Drug choice as self handicapping strategy in response to no contingent success. Journal of personnality and social psychology 76 : 14E158.1978. 2-CARVER, C.S ; SCHEIER. M F. : Attention and self regulation. A confrol theory approach lo human behavior. New York : Sp~nger- Verlag. 1981 3JAGASINSK1, C.D.; NICHOLLS. J.G. : Concepttons of a Ability and Related in Task lnvolment and Ego Involrnanl. Journal of Educational Psychology 76 : 909-919. 198

HIF-Independent Regulation of Thioredoxin Reductase 1 Contributes to the High Levels of Reactive Oxygen Species Induced by Hypoxia

Cellular adaptation to hypoxic conditions mainly involves transcriptional changes in which hypoxia inducible factors (HIFs) play a critical role. Under hypoxic conditions, HIF protein is stabilized due to inhibition of the activity of prolyl hydroxylases (EGLNs). Because the reaction carried out by these enzymes uses oxygen as a co-substrate it is generally accepted that the hypoxic inhibition of EGLNs is due to the reduction in oxygen levels. However, several studies have reported that hypoxic generation of mitochondrial reactive oxygen species (ROS) is required for HIF stabilization. Here, we show that hypoxia downregulates thioredoxin reductase 1 (TR1) mRNA and protein levels. This hypoxic TR1 regulation is HIF independent, as HIF stabilization by EGLNs inhibitors does not affect TR1 expression and HIF deficiency does not block TR1 hypoxic-regulation, and it has an effect on TR1 function, as hypoxic conditions also reduce TR1 activity. We found that, when cultured under hypoxic conditions, TR1 deficient cells showed a larger accumulation of ROS compared to control cells, whereas TR1 over-expression was able to block the hypoxic generation of ROS. Furthermore, the changes in ROS levels observed in TR1 deficient or TR1 over-expressing cells did not affect HIF stabilization or function. These results indicate that hypoxic TR1 down-regulation is important in maintaining high levels of ROS under hypoxic conditions and that HIF stabilization and activity do not require hypoxic generation of ROS

Oxygen dependence of metabolic fluxes and energy generation of Saccharomyces cerevisiae CEN.PK113-1A

<p>Abstract</p> <p>Background</p> <p>The yeast <it>Saccharomyces cerevisiae </it>is able to adjust to external oxygen availability by utilizing both respirative and fermentative metabolic modes. Adjusting the metabolic mode involves alteration of the intracellular metabolic fluxes that are determined by the cell's multilevel regulatory network. Oxygen is a major determinant of the physiology of <it>S. cerevisiae </it>but understanding of the oxygen dependence of intracellular flux distributions is still scarce.</p> <p>Results</p> <p>Metabolic flux distributions of <it>S. cerevisiae </it>CEN.PK113-1A growing in glucose-limited chemostat cultures at a dilution rate of 0.1 h^-1with 20.9%, 2.8%, 1.0%, 0.5% or 0.0% O₂in the inlet gas were quantified by ¹³C-MFA. Metabolic flux ratios from fractional [U-¹³C]glucose labelling experiments were used to solve the underdetermined MFA system of central carbon metabolism of <it>S. cerevisiae</it>.</p> <p>While ethanol production was observed already in 2.8% oxygen, only minor differences in the flux distribution were observed, compared to fully aerobic conditions. However, in 1.0% and 0.5% oxygen the respiratory rate was severely restricted, resulting in progressively reduced fluxes through the TCA cycle and the direction of major fluxes to the fermentative pathway. A redistribution of fluxes was observed in all branching points of central carbon metabolism. Yet only when oxygen provision was reduced to 0.5%, was the biomass yield exceeded by the yields of ethanol and CO₂. Respirative ATP generation provided 59% of the ATP demand in fully aerobic conditions and still a substantial 25% in 0.5% oxygenation. An extensive redistribution of fluxes was observed in anaerobic conditions compared to all the aerobic conditions. Positive correlation between the transcriptional levels of metabolic enzymes and the corresponding fluxes in the different oxygenation conditions was found only in the respirative pathway.</p> <p>Conclusion</p> <p>¹³C-constrained MFA enabled quantitative determination of intracellular fluxes in conditions of different redox challenges without including redox cofactors in metabolite mass balances. A redistribution of fluxes was observed not only for respirative, respiro-fermentative and fermentative metabolisms, but also for cells grown with 2.8%, 1.0% and 0.5% oxygen. Although the cellular metabolism was respiro-fermentative in each of these low oxygen conditions, the actual amount of oxygen available resulted in different contributions through respirative and fermentative pathways.</p

Ginkgo biloba Responds to Herbivory by Activating Early Signaling and Direct Defenses

Background: Ginkgo biloba (Ginkgoaceae) is one of the most ancient living seed plants and is regarded as a living fossil. G. biloba has a broad spectrum of resistance or tolerance to many pathogens and herbivores because of the presence of toxic leaf compounds. Little is known about early and late events occurring in G. biloba upon herbivory. The aim of this study was to assess whether herbivory by the generalist Spodoptera littoralis was able to induce early signaling and direct defense in G. biloba by evaluating early and late responses. Methodology/Principal Findings: Early and late responses in mechanically wounded leaves and in leaves damaged by S. littoralis included plasma transmembrane potential (Vm) variations, time-course changes in both cytosolic calcium concentration ([Ca 2+]cyt) and H2O2 production, the regulation of genes correlated to terpenoid and flavonoid biosynthesis, the induction of direct defense compounds, and the release of volatile organic compounds (VOCs). The results show that G. biloba responded to hebivory with a significant Vm depolarization which was associated to significant increases in both [Ca 2+] cyt and H 2O 2. Several defense genes were regulated by herbivory, including those coding for ROS scavenging enzymes and the synthesis of terpenoids and flavonoids. Metabolomic analyses revealed the herbivore-induced production of several flavonoids and VOCs. Surprisingly, no significant induction by herbivory was found for two of the most characteristic G. biloba classes of bioactive compounds; ginkgolides and bilobalides

The role of mitochondrial biogenesis and ROS in the control of energy supply in proliferating cells.

International audienceIn yeast, there is a constant growth yield during proliferation on non-fermentable substrate where the ATP generated originates from oxidative phosphorylation. This constant growth yield is due to a tight adjustment between the growth rate and the cellular mitochondrial amount. We showed that this cellular mitochondrial amount is strictly controlled by mitochondrial biogenesis. Moreover, the Ras/cAMP pathway is the cellular signaling pathway involved in the regulation of mitochondrial biogenesis, with a direct relationship between the activity of this pathway and the cellular amount of mitochondria. The cAMP protein kinase Tpk3p is the catalytic subunit specifically involved in the regulation of mitochondrial biogenesis through regulation of the mitochondrial ROS production. An overflow of mitochondrial ROS decreases mitochondrial biogenesis through a decrease in the transcriptional co-activator Hap4p, which can be assimilated to mitochondria quality control. Moreover, the glutathione redox state is shown as being an intermediate in the regulation of mitochondrial biogenesis

Mitochondrial oxidative phosphorylation is regulated by fructose-1,6-biphosphate: A possible role in crabtree effect induction ?

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