The temporal organization of ingestive behaviour and its interaction with regulation of energy balance

Body weight of man and animals is under homeostatic control mediated by the adjustment of food intake It is discussed in this review that besides signals reporting energy deficits, optimized programs of body clocks take part in feeding behaviour as well Circadian light- and food-entrainable clocks determine anticipatory adaptive behavioural and physiological mechanisms, promoting or inhibiting food intake In fact these clocks form the constraints within which the homeostatic regulation of feeding behaviour is operating Therefore, a strong interaction between circadian and homeostatic regulation must occur. In this homeostatic control, a wide variety of regulatory negative feedback mechanisms, or satiety signals, play a dominant role. In this respect several gut hormones and body temperature function as 'short-term' satiety factors and determine meal sizes and intermeal intervals Leptin, secreted by fat cells in proportion to the size of adipose tissue mass, is probably an important determinant of the 'long-term' regulation of feeding behaviour by setting the motivational background level for feeding behaviour. Thus, initiation or termination of meals at any particular point in time, depends on the resultant of all satiety signals and on constraints imposed by circadian light- and food-entrainable oscillators. (C) 2002 Elsevier Science Ltd. All rights reserved

Ablation of capsaicin-sensitive afferent nerves affects insulin response during an intravenous glucose tolerance test

We investigated the role of sensory nerves in glucose tolerance in conscious Wistar rats neonatally treated with neurotoxin capsaicin or vehicle. Intravenous glucose tolerance tests (IVGTT, 150, 300 and 450 mg in 30 min) were performed to measure glucose tolerance, and glucose, insulin and glucagon levels were measured. Higher glucose concentration resulted in a greater insulin response in both capsaicin- and vehicle-treated rats. However, glucose-stimulated insulin secretion was attenuated in capsaicin-treated animals, even though glucose levels did not differ. Glucagon levels did not differ between both groups. These results show that capsaicin-sensitive nerves are involved in glucose-stimulated insulin secretion, but are not directly involved in the regulation of blood glucose levels. Moreover, they suggest that capsaicin-sensitive nerves could be involved in the regulation of insulin sensitivity. We hypothesize that sensory afferents could play a role in the aetiology of pathologies where glucohomeostatic mechanisms are disturbed, as is in type 2 diabetes mellitus. (c) 2005 Elsevier Inc. All rights reserved

The timing of meals

In most individuals, food intake occurs as discrete bouts or meals, and little attention has been paid to the factors that normally determine when meals will occur when food is freely available. On the basis of experiments using rats, the authors suggest that when there are no constraints on obtaining food and few competing activities, 3 levels of interacting controls normally dictate when meals will start. The first is the genetically determined circadian activity pattern on which nocturnal animals tend to initiate most meals in the dark. The second is the regularly occurring changing of the light cycle: These changes provide temporal anchors. The third relates to the size of the preceding meal, such that larger meals cause a longer delay until the onset of the next meal. Superimposed on these 3 are factors related to learning, convenience, and opportunity

Overfeeding, Autonomic Regulation and Metabolic Consequences

The autonomic nervous system plays an important role in the regulation of body processes in health and disease. Overfeeding and obesity (a disproportional increase of the fat mass of the body) are often accompanied by alterations in both sympathetic and parasympathetic autonomic functions. The overfeeding-induced changes in autonomic outflow occur with typical symptoms such as adiposity and hyperinsulinemia. There might be a causal relationship between autonomic disturbances and the consequences of overfeeding and obesity. Therefore studies were designed to investigate autonomic functioning in experimentally and genetically hyperphagic rats. Special emphasis was given to the processes that are involved in the regulation of peripheral energy substrate homeostasis. The data revealed that overfeeding is accompanied by increased parasympathetic outflow. Typical indices of vagal activity (such as the cephalic insulin release during food ingestion) were increased in all our rat models for hyperphagia. Overfeeding was also accompanied by increased sympathetic tone, reflected by enhanced baseline plasma norepinephrine (NE) levels in both VMH-lesioned animals and rats rendered obese by hyperalimentation. Plasma levels of NE during exercise were, however, reduced in these two groups of animals. This diminished increase in the exercise-induced NE outflow could be normalized by prior food deprivation. It was concluded from these experiments that overfeeding is associated with increased parasympathetic and sympathetic tone. In models for hyperphagia that display a continuously elevated nutrient intake such as the VMH-lesioned and the overfed rat, this increased sympathetic tone was accompanied by a diminished NE response to exercise. This attenuated outflow of NE was directly related to the size of the fat reserves, indicating that the feedback mechanism from the periphery to the central nervous system is altered in the overfed state.

Debris Disks: Probing Planet Formation

Debris disks are the dust disks found around ~20% of nearby main sequence stars in far-IR surveys. They can be considered as descendants of protoplanetary disks or components of planetary systems, providing valuable information on circumstellar disk evolution and the outcome of planet formation. The debris disk population can be explained by the steady collisional erosion of planetesimal belts; population models constrain where (10-100au) and in what quantity (>1Mearth) planetesimals (>10km in size) typically form in protoplanetary disks. Gas is now seen long into the debris disk phase. Some of this is secondary implying planetesimals have a Solar System comet-like composition, but some systems may retain primordial gas. Ongoing planet formation processes are invoked for some debris disks, such as the continued growth of dwarf planets in an unstirred disk, or the growth of terrestrial planets through giant impacts. Planets imprint structure on debris disks in many ways; images of gaps, clumps, warps, eccentricities and other disk asymmetries, are readily explained by planets at >>5au. Hot dust in the region planets are commonly found (<5au) is seen for a growing number of stars. This dust usually originates in an outer belt (e.g., from exocomets), although an asteroid belt or recent collision is sometimes inferred.Comment: Invited review, accepted for publication in the 'Handbook of Exoplanets', eds. H.J. Deeg and J.A. Belmonte, Springer (2018

Changes in habitat associations during range expansion: disentangling the effects of climate and residence time

The distributions of many species are not at equilibrium with their environment. This includes spreading non-native species and species undergoing range shifts in response to climate change. The habitat associations of these species may change during range expansion as less favourable climatic conditions at expanding range margins may constrain species to use only the most favourable habitats, violating the species distribution model assumption of stationarity. Alternatively, changes in habitat associations could result from density-dependent habitat selection; at range margins, population densities are initially low so species can exhibit density-independent selection of the most favourable habitats, while in the range core, where population densities are higher, species spread into less favourable habitat. We investigate if the habitat preferences of the non-native common waxbill Estrilda astrild changed as they spread in three directions (north, east and south-east) in the Iberian Peninsula. There are different degrees of climatic suitability and colonization speed across range expansion axes, allowing us to separate the effects of climate from residence time. In contrast to previous studies we find a stronger effect of residence time than climate in influencing the prevalence of common waxbills. As well as a strong additive effect of residence time, there were some changes in habitat associations, which were consistent with density-dependent habitat selection. The combination of broader habitat associations and higher prevalence in areas that have been colonised for longer means that species distribution models constructed early in the invasion process are likely to underestimate species’ potential distribution