A predictive model of the dynamics of body weight and food intake in rats submitted to caloric restrictions.

International audienceDynamics of body weight and food intake can be studied by temporally perturbing food availability. This perturbation can be obtained by modifying the amount of available food over time while keeping the overall food quantity constant. To describe food intake dynamics, we developed a mathematical model that describes body weight, fat mass, fat-free mass, energy expenditure and food intake dynamics in rats. In addition, the model considers regulation of food intake by leptin, ghrelin and glucose. We tested our model on rats experiencing temporally variable food availability. Our model is able to predict body weight and food intake variations by taking into account energy expenditure dynamics based on a memory of the previous food intake. This model allowed us to estimate this memory lag to approximately 8 days. It also explains how important variations in food availability during periods longer than these 8 days can induce body weight gains

Impact of receptor clustering on ligand binding

<p>Abstract</p> <p>Background</p> <p>Cellular response to changes in the concentration of different chemical species in the extracellular medium is induced by ligand binding to dedicated transmembrane receptors. Receptor density, distribution, and clustering may be key spatial features that influence effective and proper physical and biochemical cellular responses to many regulatory signals. Classical equations describing this kind of binding kinetics assume the distributions of interacting species to be homogeneous, neglecting by doing so the impact of clustering. As there is experimental evidence that receptors tend to group in clusters inside membrane domains, we investigated the effects of receptor clustering on cellular receptor ligand binding.</p> <p>Results</p> <p>We implemented a model of receptor binding using a Monte-Carlo algorithm to simulate ligand diffusion and binding. In some simple cases, analytic solutions for binding equilibrium of ligand on clusters of receptors are provided, and supported by simulation results. Our simulations show that the so-called "apparent" affinity of the ligand for the receptor decreases with clustering although the microscopic affinity remains constant.</p> <p>Conclusions</p> <p>Changing membrane receptors clustering could be a simple mechanism that allows cells to change and adapt its affinity/sensitivity toward a given stimulus.</p

Receptor clustering affects signal transduction at the membrane level in the reaction-limited regime.

International audienceMany types of membrane receptors are found to be organized as clusters on the cell surface. We investigate the potential effect of such receptor clustering on the intracellular signal transduction stage. We consider a canonical pathway with a membrane receptor (R) activating a membrane-bound intracellular relay protein (G). We use Monte Carlo simulations to recreate biochemical reactions using different receptor spatial distributions and explore the dynamics of the signal transduction. Results show that activation of G by R is severely impaired by R clustering, leading to an apparent blunted biological effect compared to control. Paradoxically, this clustering decreases the half maximal effective dose (ED50) of the transduction stage, increasing the apparent affinity. We study an example of inter-receptor interaction in order to account for possible compensatory effects of clustering and observe the parameter range in which such interactions slightly counterbalance the loss of activation of G. The membrane receptors' spatial distribution affects the internal stages of signal amplification, suggesting a functional role for membrane domains and receptor clustering independently of proximity-induced receptor-receptor interactions

A mathematical model of leptin resistance

International audienceObesity is often associated with leptin resistance, which leads to a physiological system with high leptin concentration but unable to respond to leptin signals and to regulate food intake. We propose a mathematical model of the leptin-leptin receptors system, based on the assumption that leptin is a regulator of its own receptor activity, and investigate its qualitative behavior. Based on current knowledge and previous models developed for body weight dynamics in rodents, the model includes the dynamics of leptin, leptin receptors and the regulation of food intake and body weight. It displays two stable equilibria, one representing a healthy state and the other one an obese and leptin resistant state. We show that a constant leptin injection can lead to leptin resistance and that a temporal variation in some parameter values influencing food intake can induce a change of equilibrium and a pathway to leptin resistance and obesity

Dynamics of communal vocalizations in a social songbird, the zebra finch (Taeniopygia guttata)

International audienceColonies or communities of animals such as fishes, frogs, seabirds, or marine mammals can be noisy. Although vocal communication between clearly identified sender(s) and receiver(s) has been well studied, the properties of the noisy sound that results from the acoustic network of a colony of gregarious animals have received less attention. The resulting sound could nonetheless convey some information about the emitting group. Using custom-written software for automatic detection of vocalizations occurring over many hours of recordings, this study reports acoustic features of communal vocal activities in a gregarious species, the zebra finch (Taeniopygia guttata). By biasing the sex ratio and using two different housing conditions (individual versus communal housing), six groups of zebra finches were generated, with six different social structures that varied both in terms of sex-composition and proportion of paired individuals. The results showed that the rate of emission and the acoustic dynamic both depended on the social structure. In particular, the vocal activity of a group of zebra finches depended mainly on the number of unpaired birds, i.e., individuals not part of a stably bonded pair

Water restriction influences intra-pair vocal behavior and the acoustic structure of vocalisations in the opportunistically breeding zebra finch (Taeniopygia guttata)

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Songbird mates change their call structure and intra-pair communication at the nest in response to environmental noise

International audienceThe coordination of behaviours between mates is a central aspect of the biology of the monogamous pair bonding in birds. This coordination may rely on intrapair acoustic communication, which is surprisingly poorly understood. Here we examined the impact of an increased level of background noise on intrapair acoustic communication at the nest in the zebra finch, Taeniopygia guttata. We monitored how partners adapted their acoustic interactions in response to a playback of wind noise inside the nestbox during incubation. Both zebra finch parents incubate and use coordinated call duets when they meet at the nest. The incubating parent can vocalize to its partner either outside the nestbox (sentinel duets) or inside the nestbox (relief and visit duets), depending on the context of the meeting. Pairs use these duets to communicate on predation threats (sentinel duets), incubation duties (relief) and other nesting activities (visit duets). Each of these duets probably represents a critical component of pair coordination. In response to the noise playback, partners called less and more rapidly during visit and relief duets. Female and male calls were more regularly and precisely alternated during relief duets. Mates increased the number of visit duets and their spatial proximity during sentinel duets. Furthermore, both females and males produced louder, higher-frequency and less broadband calls. Taken together our results show that birds use several strategies to adjust to noise during incubation, underlining the importance of effective intrapair communication for breeding pairs

Predicted body weight for a 16 week experiment with different combinations of food availability patterns.

<p>In blue H1 followed by H0 (line) or H1 (squares), in green H4 followed by H0 (line) or H4 (squares) and in red twice H0. In cases with H0 in the last 8 weeks (lines), the body weight tends to the same value, whatever the past variations.</p

Simulated evolution of body weight (red line) compared to experimental data (mean standard deviation in black).

<p>In each group, the food input matches the experimental patterns and the first 5 days of the simulation were conducted with <i>Ad libitum</i> diet to be closer to the experiment. Parameter values were estimated with data from groups AL and H1 and predictions were made with these parameter values on groups H0 and H4. Top left: AL; top right: H0; bottom left: H1; bottom right: H4.</p