Statistical Coding and Decoding of Heartbeat Intervals

The heart integrates neuroregulatory messages into specific bands of frequency, such that the overall amplitude spectrum of the cardiac output reflects the variations of the autonomic nervous system. This modulatory mechanism seems to be well adjusted to the unpredictability of the cardiac demand, maintaining a proper cardiac regulation. A longstanding theory holds that biological organisms facing an ever-changing environment are likely to evolve adaptive mechanisms to extract essential features in order to adjust their behavior. The key question, however, has been to understand how the neural circuitry self-organizes these feature detectors to select behaviorally relevant information. Previous studies in computational perception suggest that a neural population enhances information that is important for survival by minimizing the statistical redundancy of the stimuli. Herein we investigate whether the cardiac system makes use of a redundancy reduction strategy to regulate the cardiac rhythm. Based on a network of neural filters optimized to code heartbeat intervals, we learn a population code that maximizes the information across the neural ensemble. The emerging population code displays filter tuning proprieties whose characteristics explain diverse aspects of the autonomic cardiac regulation, such as the compromise between fast and slow cardiac responses. We show that the filters yield responses that are quantitatively similar to observed heart rate responses during direct sympathetic or parasympathetic nerve stimulation. Our findings suggest that the heart decodes autonomic stimuli according to information theory principles analogous to how perceptual cues are encoded by sensory systems

Gallery_of_mitochondria.pdf

Transmission electron micrographs of muscle mitochondria of Chymomyza costata.</p

Seasonal changes of free amino acids and thermal hysteresis in overwintering heteropteran insect, Pyrrhocoris apterus

International audienceOverwintering adults of Pyrrhocoris apterus do not tolerate freezing of their body fluids and rely on a supercooling strategy and seasonal accumulation of polyols to survive at subzero body temperatures. We sampled the adults monthly in the field during the cold season 2008-2009 and found active thermal hysteresis factors (THFs) in hemolymph of winter-sampled adults. The hysteresis between the equilibrium melting and freezing points ranged from 0.18 °C to 0.30 °C. No signs of THFs activity were found in the autumn- and spring-sampled insects. The total free amino acid pool almost doubled during winter time. The sum concentrations of 27 free amino acids ranged between 35 and 40 mM in whole body water and 40-45 mM in hemolymph during December-February. Two amino acids, Pro and α-Ala most significantly contributed to the seasonal increase, while Gln showed themost dramatic seasonal decrease. Moderate levels of amino acid accumulation in overwintering P. apterus suggest that they are by-products of protein degradation and pentose pathway activity during the state of metabolic suppression imposed by diapause and low body temperature. Potential colligative effects of accumulated amino acids, extending the supercooling capacity of overwintering P. apterus, are negligible. Non-colligative effects require further study

Insect cold tolerance and repair of chill-injury at fluctuating thermal regimes: Role of 70 kDa heat shock protein expression.

International audienceExpression of heat shock proteins has been proposed as an underlying mechanism of increased cold tolerance in insects exposed to fluctuating thermal regimes (FTRs) in comparison to constant low temperatures (CLTs). We found that the levels of Pahsp70 mRNA increase by up to 3 orders in the linden bugs, Pyrrhocoris apterus exposed to FTR -5 degrees C (22h)/25 degrees C (2h). The 2h-long warm pulses, however, were not sufficient for accumulation of PaHSP70 protein and thus no significant difference in expression of PaHSP70 protein was detected between FTR and CLT regimes. Hence, we conclude that the accumulation of PaHSP70 protein is not the mechanism underlying the increased cold tolerance in P. apterus at the particular FTR used in this study. The relevance of some other possible mechanisms is discussed

Insect cold tolerance and repair of chill-injury at fluctuating thermal regimes: Role of 70 kDa heat shock protein expression.

International audienceExpression of heat shock proteins has been proposed as an underlying mechanism of increased cold tolerance in insects exposed to fluctuating thermal regimes (FTRs) in comparison to constant low temperatures (CLTs). We found that the levels of Pahsp70 mRNA increase by up to 3 orders in the linden bugs, Pyrrhocoris apterus exposed to FTR -5 degrees C (22h)/25 degrees C (2h). The 2h-long warm pulses, however, were not sufficient for accumulation of PaHSP70 protein and thus no significant difference in expression of PaHSP70 protein was detected between FTR and CLT regimes. Hence, we conclude that the accumulation of PaHSP70 protein is not the mechanism underlying the increased cold tolerance in P. apterus at the particular FTR used in this study. The relevance of some other possible mechanisms is discussed

Insect cold-tolerance and repair of chill-injuries in adult tropical beetles exposed to fluctuating thermal regimes.

communication oral

Insect cold tolerance and repair of chill-injury at fluctuating thermal regimes: role of ion homeostasis

International audienceAdults of the bug Pyrrhocoris apterus and the beetle Alphitobius diaperinus developed chill-injury slower and survived longer when they were exposed to fluctuating thermal regimes (FTRs, where periods of low temperature were alternated with periods of higher temperature on a daily basis) rather than to constant low temperatures. The extracellular (haemolymph) concentrations of potassium ions increased with significantly higher rates in the insects exposed to constant low temperatures than in those exposed to FTRs. The concentrations of magnesium and sodium ions were maintained relatively constant or decreased slightly in both thermal regimes. The loss of body water and the increase of haemolymph osmolality contributed to, but could not fully explain, the ion concentration changes, which probably resulted also from impairing the function of an active metabolic component (ion pump) at low temperatures. This explanation was supported by observing (in P. apterus) the return toward normal [K+] during the warm “recovery” period of the FTR. Collectively, the paper stresses the importance of considering the temperature fluctuations in the experimental studies on insect cold tolerance and suggests that the positive effect of the FTR on cold tolerance may consist, at least partially, in allowing the primary ion pumping systems to re-establish the ion gradients across cell membranes and epithelia during the recovery periods at a higher temperature

Insect cold-tolerance and repair of chill-injuries in adult tropical beetles exposed to fluctuating thermal regimes.

communication oral

Cold exposure and associated metabolic changes in adult tropical beetles exposed to fluctuating thermal regimes

International audienceEnvironmental stress deleteriously affects every aspect of an ectotherm's biological function. Frequent exposure of terrestrial insects to temperature variation has thus led to the evolution of protective biochemical and physiological mechanisms. However, the physiological mechanisms underlying the positive impact of fluctuating thermal regimes (FTRs) on the fitness and survival of cold-exposed insects have not been studied. We have thus investigated the metabolic changes in adults of the beetle Alphitobius diaperinus in order to determine whether FTRs trigger the initiation of a metabolic response involving synthesis of protective compounds, such as free amino acids (FAAs) and polyols. The metabolic profile was analyzed during constant fluctuating thermal regimes (the beetles had daily pulses at higher temperatures that enabled them to recover) and compared with constant cold exposure and untreated controls. The increase of several essential amino acids (Lys, Iso, Leu, Phe and Trp) in cold-exposed beetles supports the conclusion that it results from the breakdown of proteins. Some FAAs have been shown to have cryoprotective properties in insects, but the relationship between FAAs, cold tolerance and survival has not yet been well defined. Instead of considering FAAs only as a part of the osmo- and cryoprotective arsenal, they should also be regarded as main factors involved in the multiple regulatory pathways activated during cold acclimation. Under FTRs, polyol accumulation probably contributes to the increased duration of survival in A. diaperinus

Acclimations to cold and warm conditions differently affect the energy metabolism of diapausing larvae of the european corn borer ostrinia nubilalis (Hbn.)

The European corn borer Ostrinia nubilalis is a pest species, whose fifth instar larvae gradually develop cold hardiness during diapause. The physiological changes underlying diapause progression and cold hardiness development are still insufficiently understood in insects. Here, we follow a complex of changes related to energy metabolism during cold acclimation (5°C) of diapausing larvae and compare this to warm-acclimated (22°C) and non-diapause controls. Capillary electrophoresis of nucleotides and coenzymes has shown that in gradually cold-acclimated groups concentrations of ATP/ADP and, consequently, energy charge slowly decrease during diapause, while the concentration of AMP increases, especially in the first months of diapause. Also, the activity of cytochrome c oxidase (COX), as well as the concentrations of NAD+ and GMP, decline in cold-acclimated groups, until the latter part of diapause, when they recover. Relative expression of NADH dehydrogenase (nd1), coenzyme Q-cytochrome c reductase (uqcr), COX, ATP synthase (atp), ADP/ATP translocase (ant), and prohibitin 2 (phb2) is supressed in cold-acclimated larvae during the first months of diapause and gradually increases toward the termination of diapause. Contrary to this, NADP+ and UMP levels significantly increased in the first few months of diapause, after gradual cold acclimation, which is in connection with the biosynthesis of cryoprotective molecules, as well as regeneration of small antioxidants. Our findings evidence the existence of a cold-induced energy-saving program that facilitates long-term maintenance of larval diapause, as well as gradual development of cold hardiness. In contrast, warm acclimation induced faster depletion of ATP, ADP, UMP, NAD+, and NADP+, as well as higher activity of COX and generally higher expression of all energy-related genes in comparison to cold-acclimated larvae. Moreover, such unusually high metabolic activity, driven by high temperatures, lead to premature mortality in the warm-acclimated group after 2 months of diapause. Thus, our findings strongly support the importance of low temperature exposure in early diapause for gradual cold hardiness acquisition, successful maintenance of the resting state and return to active development. Moreover, they demonstrate potentially adverse effects of global climate changes and subsequent increase in winter temperatures on cold-adapted terrestrial organisms in temperate and subpolar regions