Feeding Behavior

Alarin stimulates feeding behavior, increases body weight, and influences luteinizing hormone (LH) secretion [6].

From: Handbook of Hormones , 2016

Feeding Behavior

R.F. Chapman , in Encyclopedia of Insects (Second Edition), 2009

Publisher Summary

This chapter provides an overview of insects feeding behavior and its regulations. The most extensive studies of insect feeding behavior and its regulation have focused on two insects with completely different feeding habits: the adult black blow fly ( Phormia regina), which is a fluid feeder; and the final nymphal stage of the migratory locust (Locusta migratoria ), a grass-feeding insect. Although their feeding habits are different, there are many common features in their feeding behavior patterns and the mechanisms that control their feeding behavior. The pattern of feeding changes with the age of the insect, its previous experience, and its nutritional needs. Phytophagous insects tend to eat greater amounts in the middle of a developmental stage and more in the light than in the dark. Feeding behavior is determined to a large extent by environmental factors, although relatively few extensive studies are carried out. Temperature has a major effect on feeding behavior, as it does on other insect activities, with little feeding occurring at low or at very high temperatures.

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Molecular Mechanisms of Memory

F.D. Lorenzetti , J.H. Byrne , in Learning and Memory: A Comprehensive Reference, 2008

4.10.3.1 Behavioral Studies

Feeding behavior in Aplysia can be modified by pairing feeding with an aversive stimulus. If food is wrapped in a tough plastic net, Aplysia bite and attempt to swallow the food. However, netted food cannot be swallowed, and so it is rejected. The inability to consume the food appeared to be an aversive stimulus that modified the feeding behavior, because the trained animals no longer attempted to bite the netted food (Susswein et al., 1986).

Feeding behavior can also be operantly conditioned with an appetitive stimulus (Brembs et al., 2002). The reinforcement signal for the in vivo training protocol was a brief shock to the esophageal nerve. The esophageal nerve is believed to be part of the pathway mediating food reward because bursts of activity in this nerve occur when the animal successfully ingests food (Brembs et al., 2002). In addition, lesions to this nerve blocked in vivo appetitive classical conditioning (Lechner et al., 2000a). Also, the in vitro analog of classical conditioning discussed earlier successfully increased the number of CS-elicited motor patterns when esophageal nerve shock was used as the US (Mozzachiodi et al., 2003). In the operant conditioning paradigm, the contingent reinforcement of biting behavior by a shock to the esophageal nerve produced an increase in the frequency of biting, when measured both immediately after training and 24   h after training, as compared to animals trained with a yoke-control procedure (Brembs et al., 2002).

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Humpback Dolphins (Sousa spp.): Current Status and Conservation, Part 1

Muhammad Shoaib Kiani , Koen Van Waerebeek , in Advances in Marine Biology, 2015

6.2 Feeding

Feeding behaviour showed very little diversity (Kiani, 2014). In smaller groups, dolphins kept varying distances from each other while chasing prey in different directions. The larger groups were spread over a wide area, and were divided into several subgroups while chasing prey without any specific pattern. No information is available on prey species of S. plumbea in Pakistan. Off Natal, South Africa, all prey items were fish, 61% littoral or estuarine species and 25% demersal species primarily associated with reefs (Ross et al., 1994).

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SMELL, TASTE, AND CHEMICAL SENSING | Chemosensory Behavior

T.J. Hara , in Encyclopedia of Fish Physiology, 2011

Feeding Behavior

Gustatory, Olfactory, or Tactile – Historical Development

Feeding behavior of fish is complex and differs between species. Typically, three phases of food search can be differentiated: (1) an initial period of arousal or excitement, when the fish is alerted to the presence of the stimulus, (2) a subsequent search or exploratory phase to locate the source, and (3) a consummation phase, in which the fish seeks to ingest the potential food. In reality, however, these phases are a continuum without distinct transitions.

Various sensory systems contribute to the process of feeding. Their roles and significance vary at different phases and among fish species. Whether feeding behavior in fishes is mediated by gustatory, tactile, or olfactory stimuli has long been a subject of investigation. Bateson, as early as in 1890, listed more than 15 fish species that detect food by olfaction alone. Herrick, on the other hand, reported that barbeled fishes are able to localize food by a combination of tactile and gustatory stimulation, and emphasized that memory plays a part in gustatory and tactile discrimination, while vision and olfaction assumes greater importance during intake. Similarly, working on catfish (Amiurus nebulosus), both Parker and Olmsted claimed that responses to food substances are due to stimulation of the olfactory organ, and that blinded or barbel-less fish find food as readily as normal fish. In contrast, Bardach and others found that catfish (Plotosus sp.) can find distant chemical clues by gustation alone; olfactory deprivation does not impair their searching ability. By selective ablation of the entire sensory areas of the facial and vagal lobes, Atema further characterized distinct functional roles played by the two systems in catfish (Ictalurus sp); the former is involved in localization and pickup of food (in combination with tactile inputs), whereas the latter in the control of swallowing. Goatfish (Upeneoides bensasi), a mullet, seem to rely exclusively on barbels for feeding; they are unable to recognize a packet of meat, or to find a food hidden under mud when the barbels are removed, whereas blocking of olfaction has no effect. Barbels play a primary role in detecting food in all barbeled fishes (see also SMELL, TASTE, AND CHEMICAL SENSING | Morphology of the Gustatory (Taste) System in Fishes).

Contrary to the general belief, the gustatory system is not the sole player in feeding in fish, and at the same time, not limited to it. In fact, as described below, recent studies demonstrate that feeding behavior is initiated primarily by olfaction, and complemented by gustation. Ontogenetically, taste buds generally develop later than the olfactory system in larvae, by which time their feeding already has been established.

Searching for Feeding Stimulating Substances

Identifying the active ingredients in food has also attracted the interest of many investigators, sometimes from scientific curiosity and sometimes for its potential practical application. Some of the species studied include Japanese eel (Anguilla japonica), pigfish (Orthopristis chrysopterus), pinfish (Lagodon rhomboids), winter flounder (Pseudopleuronectes americanus), mummichog (Fundulus heteroclitus), Atlantic silverside (Menidia menidia), puffer (Fugu pardalis), and cod (Godus morhua).

All these studies, examining different aspects of feeding behavior elicited by natural food and/or food extract in diverse fish species, have shown conclusively that amino acids act either singly or in combination to play a major role in stimulating feeding behavior. Each species selectively responds to a specific mixture of compounds, but synthetic mixtures of amino acids seldom attain the effectiveness of the original extracts of natural foods. As Herrick emphasized, memory could play a part in olfactory and gustatory discrimination, while behavioral responses to chemical compounds may be learned by experience and probably are stored in temporary memory. Here, an observation on juvenile sockeye salmon ( Oncorhynchus nerka) is suggestive; they respond only to extracts of those foods constituting their current diet, but they change their extract preference concomitantly after gradual weaning to a new diet.

Feeding Behavior Is Triggered by Single Amino Acids

The mechanisms by which feeding behavior are triggered by amino acids will be examined in two fish groups: (1) fishes in which olfaction is primarily used complemented, or in combination with gustation (salmonids and goldfish, Carassius auratus), and (2) fishes in which gustation is solely involved throughout feeding behavior (catfishes).

Rainbow trout, lake char (Salvelinus namaycush), lake whitefish (Coregonus clupeaformis), and goldfish respond to 10−6  M Cys, the most potent olfactory stimulating amino acid determined electrophysiologically (see also SMELL, TASTE, AND CHEMICAL SENSING | Neurophysiology of Olfaction), by increasing locomotor activity, an initial arousal behavior, in exactly the same fashion as in response to food extracts. The enhanced locomotor activity is followed by search behavior patterns distinct for each species: (1) bottom searching in rainbow trout, (2) exploratory behavior against the tank wall in lake whitefish, (3) surfacing/jumping in lake char, and (4) gravel picking in goldfish ( Figures 1 and 2 ). Ala and Lys as well as Pro, a gustatory specific amino acid, are all effective at 10−6  M, to varying degrees, in most species ( Figure 3 ). It is important to note that the behavioral responses are stereotypic, eliciting the same behavioral patterns regardless of the type of stimuli, and concentration-dependent in all species, with thresholds 10−9–10−8  M, which approximates the physiological thresholds (see also SMELL, TASTE, AND CHEMICAL SENSING | Neurophysiology of Olfaction). Effects of Arg and Glu vary in different species suppressing locomotor activity in rainbow trout, while stimulating feeding behavior in others. For example, in rainbow trout, the elevated locomotor activity by Cys is suppressed, when a mixture of Cys and Arg is introduced ( Figure 4 ). Goldfish display typical gravel pecking searching behavior, positioning their bodies almost perpendicular to the bottom, accompanied by increased locomotor activity in response to stimulation with food extract or amino acids. Unlike in rainbow trout, Arg, Glu, and Pro are as effective as food extracts and other amino acids in inducing both locomotor and pecking activities ( Figure 3 ). These results clearly indicate that single amino acids initiate appetitive feeding behavior (arousal and searching) primarily by olfaction, and interchangeably and/or complemented by gustation in naive fishes. It is thus highly likely that, in the absence of visual cues, the olfactory system plays a major role in triggering feeding behavior in these species, and possibly others. Agmatine, decarboxylated arginine, also elicits strong feeding behavior in goldfish, most likely through olfaction, because it evokes electro-olfactogram (EOG) responses with a threshold 10−9  M in goldfish as well as in lake whitefish and walleye, but not in rainbow trout ( Figure 3 ). Agmatine is converted by bacteria from Arg to form polyamines such as putrescine, cadavarine, and spermine that stimulate the goldfish olfactory system and elicit feeding behavior. Omnivorous cyprinids and catfishes are not only predators of live invertebrates but are also scavengers of dead baits.

Figure 1. Diagram showing feeding behavior patterns elicited by food extract and chemical stimulation in fishes. On detection of stimuli, fish increase locomotor activity (appetitive behavior) followed by species-specific search behavior patterns: (a) bottom searching in rainbow trout, (b) exploratory/escape behavior against the wall in lake whitefish, (c) surfacing/jumping in lake char, and (d) gravel pecking in goldfish.

 Modified from Hara (2005).

Figure 2. Pecking behavior of goldfish; food is sorted from gravel.

Figure 3. Feeding behavior elicited by food extract (Food-Ex) and chemicals at 10−6  M in rainbow trout (A) and goldfish (B). Light bars, control; dark bars, stimulus. L-Agp, L-α-amino-guanidinopropionic acid; AA-Mix, amino acid mixture containing all tested amino acids; Finger-R, finger rinse; Q·HCl, aquinine·HCl; LGlu·Na, monosodium L-glutamate (MSG); AGB, 1-amino-4-guanidinobutane (agmatine).

 Modified from Hara (2006).

Figure 4. In rainbow trout, L-Cys stimulates locomotor activity (arousal behavior), while L-Arg suppresses it. Thus, when a mixture of both is applied, the Cys-elevated locomotor activity is suppressed.

Similarly, channel catfish elicit the entire sequence of feeding behavior in response to single amino acids. Arg, Ala, and Pro (>10−7–10−4  M) induce consummatory behavioral patterns, turning, pumping of water across the gill arches, and biting–snapping. However, feeding behavior in these fish is indistinguishable in both the intact and anosmic, indicating that the entire sequence of feeding behavior is mediated by gustation alone, although which subpopulations of the taste bud systems (oral cavity, barbels, flank, and gills) are involved in which behavioral patterns is not clear. The behavioral pattern elicited by either Ala or Arg is identical, despite the fact that considerable differences exist in the biochemical (receptor binding) and biophysical (transduction) characteristics between the two, though, electrophysiologically, both the olfactory and gustatory systems are equally sensitive to the same amino acid spectrum. Toxicants can directly or indirectly affect the fish's olfactory ability (see also TOXICOLOGY | The Effects of Toxicants on Olfaction in Fishes).

Avoiding and Spitting the Noxious/Unpalatable

Alkaloids such as quinine, strychnine, and caffeine stimulate the fish gustatory receptors at extremely low concentrations, and induce avoidance behavior and suppress locomotor activities in salmonids and goldfish. When food pellets soaked in quinine solution are sprinkled on the surface of an aquarium, both rainbow trout and goldfish pick off, apparently by vision; the former ingest them immediately, but the latter spit them out after a brief mastication. Salmonids are able to avoid the noxious at a distance, but not once they are taken into the mouth. Goldfish, by contrast, have the specialized palatal organ that enables them to sort food particles from un-palatable particulates. They suck up the mixture, if mixed with gravel, sand, or mud, and manipulate the mix in the mouth, then finally spit out. The well-developed reflex system in the vagal lobe activates the musculature of the palatal organ to effect the sorting operation (see also SMELL, TASTE, AND CHEMICAL SENSING | Neurophysiology of Gustation). The protrusion of the upper jaw and the palatal organ is basic to the substrate feeding habits of many cyprinoids ( Figure 5 ).

Figure 5. Feeding behavior of goldfish includes: (1) a suctorial intake of food particles, (2) a sorting stage where food is separated from nonfood within the oropharyngeal cavity, and (3) a final stage involving either acceptance or rejection of the particles.

 Modified from Lamb and Finger (1995).

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Neuropeptides: Food Intake

S.F. Leibowitz , K.E. Wortley , in Encyclopedia of Neuroscience, 2009

Feeding behavior and body weight are controlled by a rich network of interrelated factors. These include the orexigenic peptides in the hypothalamus and forebrain, which stimulate feeding and are regulated by neurohumoral signals and dietary nutrients such as triglycerides and glucose. They are inhibited by signals of energy abundance to prevent further consummatory behavior or are stimulated by signals of energy deficiency to promote feeding. These orexigenic systems exhibit considerable diversity and redundancy in their actions. In addition to the stimulation of food intake, these involve effects on more intricate behavioral, endocrine, and metabolic processes. These may be related to the circadian rhythm of meals, arousal of food-seeking behavior, and diet palatability, in addition to energy expenditure, nutrient metabolism, and adiposity.

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BEHAVIORAL RESPONSES TO THE ENVIRONMENT | Anthropogenic Influences on Fish Behavior

K.A. Sloman , in Encyclopedia of Fish Physiology, 2011

Taste

Feeding behavior of fish depends on taste with many fish being able to distinguish between different food sources and display food preferences. Fish may also rely on taste to alter their diet in response to environmental change; for example, there may be potential for them to select a high-sodium diet, which is known to counteract the toxicity of some trace metals. In yellow bullheads, Ictalurus natali, detergents cause disintegration of taste buds and reduce the ability of individuals to chemically detect food. In catfish, such as yellow bullheads, taste buds, known as barbels, are located on whisker-like projections from the mouth, which are used for probing the sediment and searching for food. Damage to these sensory receptors may reduce the ability of individuals to detect potential prey.

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Orexins and Control of Feeding by Learned Cues

Gorica D. Petrovich , in The Orexin/Hypocretin System, 2019

Abstract

Feeding behavior is essential for survival and is physiologically controlled through processes associated with energy and nutrient needs. In addition, environmental signals can drive appetite and eating through hedonic and cognitive processes in the absence of hunger. Cognitive cues, such as food-associated cues are powerful appetite stimulants. These cues are abundant in our environment and their stimulatory effects, together with easily accessible and affordable palatable foods, make us vulnerable to overeating. Deciphering the neural mechanisms underlying this cognitive motivation to eat is crucial for potential therapeutic interventions for those who suffer from insatiable appetites. This chapter provides an overview of the role of the neuropeptide orexin/hypocretin in the control of feeding by learned cues. The orexin system is an integral part of the feeding neural network and is critical for cue-mediated food seeking and consumption. Its dysregulation maybe be an important cause of vulnerability to enhanced cognitive motivation to eat.

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Invertebrate Learning and Memory

Riccardo Mozzachiodi , ... John H. Byrne , in Handbook of Behavioral Neuroscience, 2013

Conclusions

Feeding behavior in Aplysia has proven to be an excellent model system for comparing and contrasting the cellular and molecular mechanisms of associative learning. This chapter focused on the changes produced by appetitive operant and classical conditioning on B51 activity. However, modifications have been identified in other neurons of the feeding neural circuit following operant (B30, B63, and B65) 56,57 and classical conditioning (CBI-2 and B31/32). 39,55 Synergism among different neuronal elements modified by conditioning has emerged as a general principle for the associative storage of information in both vertebrate 7,71 and invertebrate animals. 72–74

Because of the distributed cellular substrates underlying associative learning, it is important to determine the contribution of each locus of plasticity to the expression of the learned behavioral changes. The presence of multiple sites underlying associative plasticity also raises the issue regarding to what extent the cellular mechanisms for plasticity at each site are conserved. For example, is the convergence of Ca2+ entry and activation of DA receptors observed in B51 following operant conditioning also used to bring about the contingent-dependent changes in B63? Continued analysis of the cellular and molecular mechanisms underlying appetitive classical and appetitive operant conditioning of feeding in Aplysia will provide important insights into the similarities and differences between these two main forms of associative learning.

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Invertebrate Learning and Memory

Douglas A. Baxter , ... John H. Byrne , in Handbook of Behavioral Neuroscience, 2013

Classical Conditioning of Feeding Behavior in Lymnaea

Feeding behavior of the pond snail Lymnaea stagnalis can be modified by classical conditioning (for review, see 63 ). This behavior is controlled by a central pattern generator (CPG), and the neurons and synaptic connections in the CPG are well-characterized (for review, see 64 ). Moreover, neuronal correlates of learning are known. Thus, Lymnaea is an excellent candidate for system-level analysis of learning. As a first step toward simulating learning in Lymnaea, Vavoulis et al. 46 developed a four-cell model of the feeding CPG (Figure 7.2B2). The neural network included cells N1, N2, and N3, which mediate the rhythmic neural activity underlying feeding movements, and cell SO, which is a modulatory neuron. Individual neurons in the neural network were represented by two-compartment models (Figure 7.2B1). The axonal compartment includes a fast, transient Na+ current (I NA) and a delayed-like K+ current (I K), which mediate spike activity. The somatic compartment includes currents (I ACh, I NaL, or I T), which mediate slowly developing, long-lasting changes of the membrane potential, such as plateau potentials in N1 and N2 and postinhibitory rebound in N3. The model simulates the rhythmic neural activity that mediates feeding behavior.

As a second step in modeling learning in Lymnaea, Vavoulis et al. 45 modeled the cerebral giant cells (CGCs). The CGCs are modulatory interneurons and are a locus of plasticity following appetitive classical conditioning. 65 The CGC is modeled as a single compartment, which includes (1) transient and persistent Na+ currents (I NaT and I NaP, respectively), (2) an A-type and a delayed-type K+ current (I A and I D, respectively), and (3) low- and high-voltage-activated Ca2+ currents (I LVA and I HVA, respectively). Two of the currents, I NaP and I D, are increased following conditioning. 45,65 Thus, the effects of conditioning are simulated by increasing the maximal conductances of I NaP and I D. Simulations reproduce some of the previously identified neuronal changes following conditioning, including a depolarization in CGC without a change in tonic firing in CGC. To maintain the spike waveform in CGC, however, it is necessary to hypothesize an increase in I HVA. The effects of conditioning on I HVA have yet to be examined empirically. Thus, the possible role of I HVA represents an important prediction of the model. An important next step will be to combine the CPG and CGC models and examine the extent to which the currently identified cellular correlates of conditioning can reproduce learning-induced changes in behavior.

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Mammalian Hormone-Behavior Systems

Francisco Vázquez-Cuevas , ... Mauricio Díaz-Muñoz , in Hormones, Brain and Behavior (Third Edition), 2017

1.06.5 Chronostasis: Physiological Regulation across Time

Feeding behavior starts when we feel hungry and ends when we feel satiated. If only it were as simple as that! But when do we feel hungry? The answer is quite complex, particularly in the case of humans and other domesticated animals, but when food is easily available – even in the wilderness – feeding behavior starts because it is time. Such time or, rather, times to hunt or collect and then to eat are initially selected considering the status of energy deposits and circulating levels of nutrients (homeostatic process) and adjusted on the basis of the effort involved in gathering food, the risk involved in the process, and the preferences for a particular diet (nonhomeostatic processes) ( Lenard and Berthoud, 2008; Shin et al., 2009; Berthoud et al., 2012). The latter involve cognitive processes such as motivation, learning, and memory related to previous experience (Alonso-Alonso et al., 2015). But besides cognitive processes, the animal must be able to measure the time of day. Circadian rhythms are fluctuations in physiological and behavioral parameters which are repeated almost every 24   h; these rhythms are generated by endogenous biological clocks in living organisms (Menaker et al., 1978). Circadian rhythms and their underlying clocks have evolved in relation to a cyclic environment and provide adaptive relevance by synchronizing the individual to daily environmental cycles such as light–dark, temperature, and food availability (Albrecht, 2012).

Circadian rhythms manifest themselves in physiological regulation across time or chronostasis (Aguilar-Roblero and Díaz-Muñoz, 2010; Aguilar-Roblero, 2015). Thus each physiological system adjusts itself to different but optimal values throughout the day, in a coordinated manner within the whole organism. Chronostasis operates upon ongoing homeostatic processes by updating the set point of physiological systems according to a timetable determined by the circadian clocks. In mammals the SCN is the only neural structure shown to function as a biological clock, although the molecular oscillators driving the clock are present in most (if not all) cells in the organism and are known as peripheral circadian oscillators (Albrecht, 2012; Aguilar-Roblero et al., 2015). The set point has been defined as the information used to compare the instant value of a variable by a regulatory system in order to generate an error signal to correct deviations from this value (Russek and Cabanac, 1982). The coding of this information in the system could result from the structure and dynamics of the feedback loops in the regulatory system, such as endocrine or neural networks. Alternatively, it could be represented in the concentration of chemical signals (hormones or neurotransmitters), the density of specific receptors or effectors, such as ionic channels, or even the level of gene expression related to all of the above.

The value of the set point for each physiological variable, along with its daily variations, has resulted from natural selection throughout thousands of years of evolution. However, it is possible that nowadays such set point values may be outdated, since during at least the last 1000   years we have dramatically altered the environment, and adaptation through natural selection occurs in a much larger time scale. Frequent transoceanic flights, night work, and shift work schedules are good examples of altered chronostatic regulation. These alterations are due to outdated and time-misaligned set points in relation to habits and demands of modern lifestyle and they induce physiological changes leading to obesity and metabolic diseases (Bass and Takahashi, 2010; Buxton et al., 2012).

Chronostatic regulation of feeding involves SCN neural outputs to the hypothalamic and autonomic neural networks related to feeding and metabolism, which are responsible for circadian rhythms in food intake, activity of digestive enzymes, gastrointestinal motility and absorption, and hormonal secretion of cortisol, insulin, and leptin (Kalsbeek et al., 2006; Garaulet and Madrid, 2010; Kalsbeek et al., 2011). Furthermore, restriction of food availability to 2–3   h each day entrains circadian rhythmicity of feeding behavior, endocrine secretion, and liver metabolism (Escobar et al., 1998; Díaz-Muñoz et al., 2000; Escobar et al., 2000; Aceves et al., 2003; Ángeles-Castellanos et al., 2004; Martínez-Merlos et al., 2004; Báez-Ruiz et al., 2005), even in SCN-lesion animals (Stephan, 1983, 1989; Marchant and Mistlberger, 1997). Such evidence has supported the idea of a food entrainable oscillator whose location has been so far elusive (Rosenwasser and Adler, 1986). This has lead us to propose a distributed oscillator involving neural, endocrine, and gastrointestinal elements (Aguilar-Roblero and Díaz-Muñoz, 2010) where ghrelin inputs to the DMH may play a major role as an interphase between peripheral and neural components (Mieda et al., 2004).

Recent advances in molecular genomics have shown that chronostatic regulation of feeding may occur by direct interaction among 'clock genes' and genes related to metabolism which include per 1, 2 and 3, cry 1 and 2, dec 1 and 2, rev-erb-α, rorα, bmal1 (also named arntl), and clock (Green et al., 2008). Thus, mice with a mutation in the gen clock increase their food intake during the day which decreases the amplitude of feeding circadian rhythms. They also present increases in blood levels of glucose, triacylglycerides, cholesterol, and leptin and decreases in insulin; plus, they become obese (Turek et al., 2005). On the other hand, mice with a mutation of bmal-1 show a decreased insulin sensitivity throughout the day and also become obese (Shi et al., 2013). These data clearly indicate a chronostatic regulation of metabolism which, if absent, leads to metabolic dysfunctions. Other examples of chronostatic regulation by interaction among clock and metabolic genes include (1) SIRT, a deacetylase which senses NAD+, and thus functions as a metabolic sensor; it binds to Clock/Bmal1 to promote Per2 deacetylation and degradation which, in turn, may amplify the oscillation in the transcription of other clock-controlled genes (which contain an E-BOX in their promoter region) (Nakahata et al., 2008; Grimaldi et al., 2009); (2) cyclic AMP-activated protein kinase (AMPK) also functions as a nutrient sensor due to its sensitivity to the AMP/ADP/ATP ratio; by promoting phosphorylation and dephosphorylation of different proteins including CRY, it could function as an energy-charge transducer to the circadian oscillator (Lamia et al., 2009); and (3) the PPAR-1α (and also PPAR-β/δ and PPAR-γ) a nuclear receptor functioning as a transcription factor that regulates metabolism. It has been recently shown that PPAR-1α binds PER while REV-ERBα is a target of PPAR-γ thus promoting bmal-1 expression via the PPAR gamma coactivator 1-alpha (PGC-1α) (Liu et al., 2007; Eckel-Mahan and Sassone-Corsi, 2013).

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