Hungry Animals Research Articles

17β-estradiol promotes acute refeeding in hungry mice via membrane-initiated ERα signaling

ObjectiveEstrogen protects animals from obesity through estrogen receptor α (ERα), partially by inhibiting overeating in animals fed ad libitum. However, the effects of estrogen on feeding behavior in hungry animals remain unclear. In this study, we examined the roles of 17β-estradiol (E2) and ERα in the regulation of feeding in hungry female animals and explored the underlying mechanisms. MethodsWild-type female mice with surgical depletion of endogenous estrogens were used to examine the effects of E2 supplementation on acute refeeding behavior after starvation. ERα-C451A mutant mice deficient in membrane-bound ERα activity and ERα-AF20 mutant mice lacking ERα transcriptional activity were used to further examine mechanisms underlying acute feeding triggered by either fasting or central glucopenia (induced by intracerebroventricular injections of 2-deoxy-D-glucose). We also used electrophysiology to explore the impact of these ERα mutations on the neural activities of ERα neurons in the hypothalamus. ResultsIn the wild-type female mice, ovariectomy reduced fasting-induced refeeding, which was restored by E2 supplementation. The ERα-C451A mutation, but not the ERα-AF20 mutation, attenuated acute feeding induced by either fasting or central glucopenia. The ERα-C451A mutation consistently impaired the neural responses of hypothalamic ERα neurons to hypoglycemia. ConclusionIn addition to previous evidence that estrogen reduces deviations in energy balance by inhibiting eating at a satiated state, our findings demonstrate the unexpected role of E2 that promotes eating in hungry mice, also contributing to the stability of energy homeostasis. This latter effect specifically requires membrane-bound ERα activity.

Role of orexin peptide system in emotional overeating induced by brain reward stimulation in fed rats

Introduction: The purpose of this work was to prove that the reaction of food self-deprivation in “fed up” rats is a suitable model for studying the emotional overeating in the experiment.
 Methods: The self-deprivation reaction, i.e. self-isolation of an animal from food during electrical self-stimulation of the brain, was studied in animals with food deprivation. To reproduce the self-stimulation of the lateral hypothalamus, the male Wistar rats were trained to press a pedal in a Skinner box. After training, the rats received food deprivation, then a feeder was placed in the Skinner box, and a conditioned food reflex was developed in rats within 5 days.
 Results and discussion: The food self-deprivation reaction was observed in the ”satiated” rats with a current intensity of 10% and above the threshold for self-stimulation. Hungry animals pressed the pedal for hypothalamic self-stimula­tion and took no notice of the feeding trough. Sulpiride, a dopamine D2 antagonist (5 and 20 mg/kg i.p.), administered to the “satiated” rats decreased both the eating behavior and self-stimulation in food self-deprivation testing. SB-408124, an orexin A receptor antagonist (0.5 mg/ml, 20 μl intranasally) reduced only the number of pellets eaten, but not the number of pedal presses.
 Conclusion: The orexin A receptors are preferably involved in emotional eating compared with orexin B (OX2R TCS-OX2-29) and D2 dopamine receptors. Because emotional eating is significantly related to clinical eating disorders, like bulimia and binge eating disorder, it seems promising to use drugs of the orexin system to treat and prevent the issue.

Spring poisoning hazards

Poisoning in the spring may occur in livestock from exposure to glyphosate which is used prior to sowing of plant crops or from ingestion of poisonous plants. Glyphosate is of low toxicity but many products contain a carrier which is irritant to tissues. Plant poisoning may occur because other forage is unavailable and hungry animals will eat unpalatable toxic plants if other food sources are scare. Some plants such as bluebell (Hyacinoides species) and ransom (wild garlic, Allium urinsum) grow in profusion in the spring. Bluebells cause gastrointestinal and cardiac effects and Allium species cause anaemia. Some plants are more toxic in the spring as concentrations of toxic compounds are high compared with other times of the year. This is the case with hemlock (Conium maculatum) and water hemlock (Cicuta virosa). Both these plants cause neurological effects and water hemlock, in particular, causes very rapid onset of clinical signs. Spring flowering plants such as Rhododendron and Pieris species are commonly associated with poisoning, particularly in ruminants. Both these species contain grayanotoxins which cause gastrointestinal and cardiac effects. Access to areas where poisonous plants are known to grow should be restricted and good quality forage provided. Treatment options for management of poisoning in livestock are limited and, in some cases, the only sign of exposure is sudden death.

Non-spatial information on the presence of food elevates search intensity in ant workers, leading to faster maze solving in a process parallel to spatial learning.

Experience can lead to faster exploitation of food patches through spatial learning or other parallel processes. Past studies have indicated that hungry animals either search more intensively for food or learn better how to detect it. However, fewer studies have examined the contribution of non-spatial information on the presence of food nearby to maze solving, as a parallel process to spatial learning. We exposed Cataglyphis niger ant workers to a food reward and then let them search for food in a maze. The information that food existed nearby, even without spatial information, led to faster maze solving compared to a control group that was not exposed to the food prior to the experiment. Faster solving is probably achieved by a higher number of workers entering the maze, following the information that food is present nearby. In a second experiment, we allowed the ants to make successive searches in the maze, followed by removing them after they had returned to the nest and interacted with their naïve nestmates. This procedure led to a maze-solving time in-between that displayed when removing the workers immediately after they had reached the food and preventing their return to the colony, and that of no removal. The workers that interacted upon returning to the nest might have transferred to naïve workers information, unrelated to spatial learning, that food existed nearby, and driven them to commence searching. Spatial learning, or an increase in the correct movements leading to the food reward relative to those leading to dead-ends, was only evident when the same workers were allowed to search again in the same maze. However, both non-spatial information on the presence of food that elevated search intensity and spatial learning led to faster maze solving.

A Neural Circuit Arbitrates between Persistence and Withdrawal in Hungry Drosophila

SummaryIn pursuit of food, hungry animals mobilize significant energy resources and overcome exhaustion and fear. How need and motivation control the decision to continue or change behavior is not understood. Using a single fly treadmill, we show that hungry flies persistently track a food odor and increase their effort over repeated trials in the absence of reward suggesting that need dominates negative experience. We further show that odor tracking is regulated by two mushroom body output neurons (MBONs) connecting the MB to the lateral horn. These MBONs, together with dopaminergic neurons and Dop1R2 signaling, control behavioral persistence. Conversely, an octopaminergic neuron, VPM4, which directly innervates one of the MBONs, acts as a brake on odor tracking by connecting feeding and olfaction. Together, our data suggest a function for the MB in internal state-dependent expression of behavior that can be suppressed by external inputs conveying a competing behavioral drive.

Deconstrucción de la montaña como paisaje sublime en las estrategias artísticas contemporáneas.

Esta aportación teórico-práctica nos propone un desestabilizador viaje al mito de la montaña sublime, donde los ojos contemplativos del sujeto romántico, en su obsesiva búsqueda de belleza, quedan relegados a un segundo plano. Nos presenta el paisaje desde una mirada híbrida, ya que muestra a través de la visualización de un video, textos e imágenes dos visiones paralelas: aquella visión subjetiva de la naturaleza interiorizada por el ser humano, junto a la visión deshumanizada de un hipotético animal hambriento –cabra, vaca, lobo– otrora depredador asiduo de aquel lugar. La aportación reflexiona sobre el paisaje desde una concepción del mismo como espacio transcultural, fruto de la fusión de las distintas nociones de paisaje que el ser humano proyecta sobre la naturaleza desde el mundo urbano, rural, científico, vital o fenomenológico.

Neural Basis of Ventromedial Hypothalamic Oxytocin-Driven Decrease in Appetite

ObjectivesOxytocin (OT) administration in the ventromedial hypothalamic nucleus (VMH) reduces chow intake. The nature of VMH OT’s anorexigenic action remains unclear. Here we provide insight into neural mechanisms underlying VMH OT-driven anorexia by (a) identifying feeding-related brain sites activated by VMH OT injection; (b) measuring VMH OT receptor (OTr) mRNA changes in response to hunger and palatability; and (c) examining how VMH OT affects episodic sweet solution intake in sated and hungry rats. MethodWe established effective doses of VMH OT in deprivation-induced and scheduled feeding and determined whether an OT antagonist blocks the effect. Then, OT (or antagonist) was injected in the VMH of sated rats given episodically sucrose and saccharin solutions. OT was also injected in hungry animals offered simultaneously chow and sugar water. Brain activation after VMH OT was determined by Fos immunoreactivity (IR). OTr expression was established with rtPCR after chow deprivation or saccharin exposure. ResultsVMH OT decreased intake of chow and the effect was reversed by the antagonist, though the antagonist alone was not orexigenic. OT did not affect intakes of energy-dilute saccharin and sucrose solutions in sated or hungry rats. Fos IR was elevated in the VMH and energy balance-related paraventricular and arcuate nuclei, but not reward areas. VMH OTr expression was higher in hungry rats than in sated controls; saccharin intake had no effect. ConclusionOT acting in the VMH decreases intake driven by energy not by palatability, and it stimulates activity of hypothalamic sites controlling energy balance.

The Hungry Worm Feeds the Bird

Earthworms (Lumbricidae) are important prey for many birds. Based on their own feeding ecology, earthworms can be separated into two ecotypes: the detritivores that feed on organic material and the geophages that feed on soil particles and organic matter. Detritivores collect their food on the surface during the night when they are exposed to nocturnal predators. Hungry animals tend to show more risk-prone behaviour and may therefore be more vulnerable to bird predation, so we expect well-fed detritivorous earthworms to visit the surface less frequently. In this study, we tested this hypothesis in dairy farmland in the province of Fryslân, The Netherlands. Two uniform grasslands were split, with each half receiving either an early (1 February 2014) or a late (14 March 2014) farmyard manure application. Every two weeks, nocturnal surface activity of earthworms was measured by counting surfacing earthworms from a slowly pushed cart. Furthermore, soil samples were taken for total abundances and to measure individual body conditions of earthworms. As predicted, the density of surfacing earthworms was on average 2.5 times higher in the fields before farmyard manure was applied. Immature detritivores had significantly lower body masses in fields not yet manured, suggesting that these growing earthworms were hungry. Differences in surfacing behaviour and body mass disappeared after all fields had been given farmyard manure. We conclude that hunger forces detritivorous earthworms to the surface. After manure application, they appear satisfied and avoid the risk of depredation by birds by staying away from the soil surface. To promote earthworm availability for meadow birds, spreading farmyard manure on the surface should occur as late in spring as possible. In this way, hungry earthworms are forced to the surface and are available as meadow bird prey for longer periods.

Lateral line makes Pachón cavefish sleepless

As life choices go, it might seem extreme, but for blind Mexican cavefish, the choice to forgo sight was probably a no-brainer: eye running-costs are high in the dark, oxygen-poor cave waters where the fish make their homes. In addition, many truly sightless cavefish also make do with very little sleep, requiring as little as 5–20% of the sleep required by their surface-dwelling cousins. But Alex Keene, from Florida Atlantic University, USA, highlights that ‘little was known about the neural mechanisms underlying this dramatic behavioural shift’. Intrigued by the phenomenon, Keene and graduate student James Jaggard began investigating the neural mechanisms that have led cavefish populations to reduce their dependence on sleep.Explaining that sleep is defined as occurring when animals are slow to respond to physical stimuli, Jaggard focused on the Pachón cavefish population – which have dramatically reduced their eyes – filming the fish for 24 h to determine how long they sleep. Categorizing fish as asleep when they ceased moving for 60 s or more, Jaggard noticed that the cave fish took fewer sleep bouts, only achieving a total of ∼1 h of sleep a day, compared with the ∼7 h taken in more frequent bouts by the sighted relatives above ground. But what mechanism has caused the cavefish to cut their sleep so dramatically?As sensory systems – such as vision, hearing and smell – are known to play a significant role in regulating sleep, Jaggard and Keene decided to inactivate the fish's lateral line – which senses water flow and the presence of prey – to find out whether that system affected the fish's sleep pattern. Bathing the fish in the antibiotic gentamicin, which damages vibration-sensitive hair cells in the hearing systems of mammals, Keene recorded the fish's sleep patterns and was impressed to see that the cavefish now slept as much as their surface cousins. This suggests that enhanced sensory input underlies the evolutionarily derived sleep loss in Pachón cavefish, and the team adds, ‘these findings reveal a wake-promoting role for the lateral line’. However, when Jaggard tested the impact of gentamicin on other sleepless cavefish populations (Molino, Tinaja, Los Sabinos and Chica cavefish), none of them gained more sleep time, suggesting that each of the subterranean populations has independently evolved distinct mechanisms for regulating sleep.Another question that intrigued Jaggard and Keene was why cavefish miss out on sleep. As sleep loss could extend the time available for foraging in their barren cave homes, the duo starved Pachón fish and discovered that the hungry animals increased the amount of sleep to ∼6 h day−1. So, the fish may be able to modulate the amount of sleep that they take depending on food availability to maximise foraging opportunities when food is available.Finally, Jaggard tested which flow sensitive receptors on the surface of the Pachon fish are responsible for keeping the fish awake longer, by selectively coating the flow sensors on different portions of the body with adhesive. Recording how much the fish slept, Jaggard could see that the flow sensors on the fish's head and trunk were essential for regulating sleep, as the treated fish slept more. And when he compared the amount of time that the fish indulged in sleep between individuals – which can vary significantly – it was clear that the fish that slept the least had the greatest numbers of flow sensors.Summing up, Keene says, ‘The evolution of enhanced sensory capabilities contributes to sleep loss in cavefish’, and he is eager to selectively disable the lateral line sensors in order to learn more about their contribution to sleep regulation in these extraordinary fish.

Hunger-Driven Motivational State Competition

Behavioral choice is ubiquitous in the animal kingdom and is central to goal-oriented behavior. Hypothalamic Agouti-related peptide (AgRP) neurons are critical regulators of appetite. Hungry animals, bombarded by multiple sensory stimuli, are known to modify their behavior during times of caloric need, rapidly adapting to a consistently changing environment. Utilizing ARCAgRP neurons as an entry point, we analyzed the hierarchical position of hunger related to rival drive states. Employing a battery ofbehavioral assays, we found that hunger significantly increases its capacity to suppress competing motivational systems, such as thirst, anxiety-related behavior, innate fear, and social interactions, often only when food is accessible. Furthermore, real-time monitoring of ARCAgRP activity revealed time-locked responses to conspecific investigation in addition to food presentation, further establishing that, even at the level of ARCAgRP neurons, choices are remarkablyflexible computations, integrating internal state, external factors, and anticipated yield. VIDEO ABSTRACT.

Reflection of the State of Hunger in Impulse Activity of Nose Wing Muscles and Upper Esophageal Sphincter during Search behavior in Rabbits.

Reflection of the state of hunger in impulse activity of nose wing muscles and upper esophageal sphincter muscles was studied in chronic experiments on rabbits subjected to 24-h food deprivation in the absence of locomotion and during search behavior. In the absence of apparent behavioral activity, including sniffing, alai nasi muscles of hungry rabbits constantly generated bursts of action potentials synchronous with breathing, while upper esophageal sphincter muscles exhibited regular aperiodic low-amplitude impulse activity of tonic type. Latent form of food motivation was reflected in the structure of temporal organization of impulse activity of alai nasi muscles in the form of bimodal distribution of interpulse intervals and in temporal structure of impulse activity of upper esophageal sphincter muscles in the form of monomodal distribution. The latent form of food motivation was manifested in the structure of temporal organization of periods of the action potentials burst-like rhythm, generated by alai nasi muscles, in the form of monomodal distribution, characterized by a high degree of dispersion of respiratory cycle periods. In the absence of physical activity hungry animals sporadically exhibited sniffing activity, manifested in the change from the burst-like impulse activity of alai nasi muscles to the single-burst activity type with bimodal distribution of interpulse intervals and monomodal distribution of the burst-like action potentials rhythm periods, the maximum of which was shifted towards lower values, which was the cause of increased respiratory rate. At the same time, the monomodal temporal structure of impulse activity of the upper esophageal sphincter muscles was not changed. With increasing food motivation in the process of search behavior temporal structure of periods of the burst-like action potentials rhythm, generated by alai nasi muscles, became similar to that observed during sniffing, not accompanied by animal's locomotion, which is typical for the increased respiratory rhythm frequency. Increased hunger motivation was reflected in the temporal structure of impulse activity of upper esophageal sphincter muscles in the form of a shift to lower values of the maximum of monomodal distribution of interpulse intervals on the histogram, resulting in higher impulse activity frequency. The simultaneous increase in the frequency of action potentials bursts generation by alai nasi muscles and regular impulse activity of upper esophageal sphincter muscles is a reliable criterion for enhanced food motivation during search behavior in rabbits.

Tradeoffs between predation risk and fruit resources shape habitat use of landbirds during autumn migration

ABSTRACT While foraging, animals often trade off between food and safety, reducing feeding in response to increased predation risk. This response, however, may not be a viable option for animals that are energetically compromised. Many single-species studies have shown that hungry animals select habitats within which foraging opportunities are greater even if predation pressures are higher, but it is unclear whether these patterns can be extrapolated to entire communities. Here, we examined the stopover habitat use of 28 frugivorous landbird species along the coast of Maine, USA, during an energetically demanding period of the annual cycle, fall migration. Across 6 stopover sites, we determined whether or not a tradeoff existed between using safe habitat patches (patches with high woody plant stem density) and patches with high food resources (patches with high fruit abundance). Controlling for raptor abundance at a site, landbird migrants were captured at higher rates in sites where no tradeoff existed, ...

Food odors trigger an endocrine response that affects food ingestion and metabolism.

Food odors stimulate appetite and innate food-seeking behavior in hungry animals. The smell of food also induces salivation and release of gastric acid and insulin. Conversely, sustained odor exposure may induce satiation. We demonstrate novel effects of food odors on food ingestion, metabolism and endocrine signaling in Drosophila melanogaster. Acute exposure to attractive vinegar odor triggers a rapid and transient increase in circulating glucose, and a rapid upregulation of genes encoding the glucagon-like hormone adipokinetic hormone (AKH), four insulin-like peptides (DILPs) and some target genes in peripheral tissues. Sustained exposure to food odors, however, decreases food intake. Hunger-induced strengthening of synaptic signaling from olfactory sensory neurons (OSNs) to brain neurons increases food-seeking behavior, and conversely fed flies display reduced food odor sensitivity and feeding. We show that increasing the strength of OSN signaling chronically by genetic manipulation of local peptide neuromodulation reduces feeding, elevates carbohydrates and diminishes lipids. Furthermore, constitutively strengthened odor sensitivity altered gene transcripts for AKH, DILPs and some of their targets. Thus, we show that food odor can induce a transient anticipatory endocrine response, and that boosted sensitivity to this odor affects food intake, as well as metabolism and hormonal signaling.

The activity of isolated neurons and the modulatory state of an isolated nervous system represent a recent behavioural state.

Behavioural/motivational state is known to influence nearly all aspects of physiology and behaviour. The cellular basis of behavioural state control is only partially understood. Our investigation, performed on the pond snail Lymnaea stagnalis whose nervous system is useful for work on completely isolated neurons, provided several results related to this problem. First, we demonstrated that the behavioural state can produce long-term changes in individual neurons that persist even after neuron isolation from the nervous system. Specifically, we found that pedal serotonergic neurons that control locomotion show higher activity and lower membrane potential after being isolated from the nervous systems of hungry animals. Second, we showed that the modulatory state (the chemical neuroactive microenvironment of the central ganglia) changes in accordance with the nutritional state of an animal and produces predicted changes in single isolated locomotor neurons. Third, we report that observed hunger-induced effects can be explained by the increased synthesis of serotonin in pedal serotonergic neurons, which has an impact on the electrical activity of isolated serotonergic neurons and the intensity of extrasynaptic serotonin release from the pedal ganglia.

Interconnection between parameters of motor activity and blood glucose concentration in newborn rats at starvation and under glucose load conditions

The study is carried out the 1st-, 3rd-, 5th-, 7th, and 10th-day old free moving or loosely fixed rat pups (P1-10). In satiated and submitted to the 24-h starvation rat pups, parameters of spontaneous periodical motor activity (SPMA) and the blood glucose content were studied. The total glucose level in hungry rat pups was, on average, 1.5-2.5 times lower than in satiated animals. Administration of glucose to hungry rat pups increased 6-11 times its concentration in blood as compared with the animals not obtaining glucose. The glucose administration to the satiated rat pups led to a rise of its level in blood from 2 to 5 times as compared with intact animals, which was 2-3 times less than in the case of hungry animals. Analysis of pattern of motor activity recorded under conditions of the glucose deficit caused by the 24-h starvation of rat pups did not reveal significant changes of ratio of rhythmical components. Introduction of glucose to hungry and to the lesser degree to satiated rat pups led to potentiation of the minute rhythm of activity in all age groups. An exception was the first day after birth when the glucose administration to satiated rat pups promoted an enhancement of the decasecond rhythm and a decrease of the total level of motor activity. Comparison of ontogenetic dynamics of the SPMA parameters and the glucose content in blood of hungry rat pups revealed the clearly expressed regularity absent in the satiated animals: the glucose level in blood was higher during activity than in the state of rest. The performed study has shown that intensity, duration, and, to a degree, pattern of SPMA in the newborn rat pups depend on the level of satiety, and can be significantly changed in the artificially produced hypo- or hyperglycemia. The existing ontogenetic fluctuations in the character of reaction at performance of the glucose tolerance test can be connected both with morphofunctional maturation of the motor system and with immaturity of various chains of carbohydrate metabolism.

Nutritional State Modulates the Neural Processing of Visual Motion

Food deprivation alters the processing of sensory information, increasing neural activity in the olfactory and gustatory systems in animals across phyla. Neural signaling is metabolically costly, and a hungry animal has limited energy reserves, so we hypothesized that neural activity in other systems may be downregulated by food deprivation. We investigated this hypothesis in the motion vision pathway of the blowfly. Like other animals, flies augment their motion vision when moving: they increase the resting activity and gain of visual interneurons supporting the control of locomotion and gaze. In the present study, walking-induced changes in visual processing depended on the nutritional state-they decreased with food deprivation and recovered after subsequent feeding. We found that changes in the motion vision pathway depended on walking speed in a manner dependent on the nutritional state. Walking also reduced response latencies in visual interneurons, an effect not altered by food deprivation. Finally, the optomotor reflex that compensates for visual wide-field motion was reduced in food-deprived flies. Thus, walking augmented motion vision, but the effect was decreased when energy reserves were low. Our results suggest that energy limitations may drive the rebalancing of neural activity with changes in the nutritional state.

Electromyographic analysis of goal-directed grasping behavior in the American lobster.

Animals spontaneously initiate goal-directed behavior including foraging action based on their appetitive motivation. The American lobster Homarus americanus exhibits grasping behavior with its crusher claw as feeding behavior that can be initiated after appropriate operant conditioning. In order to quantitatively characterize the goal-directed grasping behavior with a time resolution fine enough for neurophysiological analysis of its initiation and control mechanisms, we made simultaneous electromyographic (EMG) recording from grasping- and reaching-related muscles of the crusher claw while animals initiated grasping behavior. We developed an in vivo extracellular recording chamber that allowed the animal under a semi-restrained condition to perform operant reward learning of claw grasping. Three muscles in the crusher claw (propodite-dactyl closer/opener and coxal protractor) were found to be closely associated with spontaneous grasping behavior. In spontaneous grasping, the activation of those muscles consistently preceded the grasping onset time and exhibited different activity patterns from the grasp induced by a mechanical stimulus. Furthermore, we found that the timing of coxal protractor activation was closer to the grasp onset and its activity was briefer for goal-directed grasping behavior in trained and hungry animals than for non-goal-directed spontaneous grasping behavior in naive or satiated animals. It is suggested that the goal-directed grasping behavior of lobster is characterized, at least partly, by experience-dependent briefer activity of specific muscles involved in reaching action.

The amphetamine sensitization model of schizophrenia symptoms and its effect on schedule-induced polydipsia in the rat

Amphetamine enhances dopamine (DA) transmission and induces psychotic states or exacerbates psychosis in at-risk individuals. Amphetamine sensitization of the DA system has been proposed as a rodent model of schizophrenia-like symptoms. In humans, excessive nonphysiologic drinking or primary polydipsia is significantly associated with a diagnosis of schizophrenia. In rodents, nonphysiologic drinking can be induced by intermittent presentation of food in the presence of a drinking spout to a hungry animal; this phenomenon is termed, "schedule-induced polydipsia" (SIP). This study aims to determine the effects of amphetamine sensitization on SIP. We injected rats with amphetamine (1.5mg/kg) daily for 5days. Following 4weeks of withdrawal, animals were food restricted and exposed to the SIP protocol (noncontingent fixed-time 1-min food schedule) for daily 2-h sessions for 24days. Results showed that previously amphetamine-injected animals drank more in the SIP protocol and drank more than controls when the intermittent food presentation schedule was removed. These findings suggest that hyperdopaminergia associated with schizophrenia may contribute to the development of polydipsia in this population. Whether animals that develop SIP have DA dysfunction or aberrant activity of other circuits that modulate DA activity has yet to be clearly defined.

Effects of Electric Stimulation of the Hunger Center in the Lateral Hypothalamus on Slow Electric Activity and Spike Activity of Fundal and Antral Stomach Muscles in Rabbits under Conditions of Hunger and Satiation

In chronic experiments on rabbits, the effect of electric stimulation of the hunger center in the lateral hypothalamus on myoelectric activity of the fundal and antral parts of the stomach was studied under conditions of hunger and satiation in the absence of food. Stimulation of the lateral hypothalamus in rabbits subjected to 24-h food deprivation and in previously fed rabbits produced incessant seeking behavior, which was followed by reorganization of the structure of temporal organization of slow wave electric activity of muscles of the stomach body and antrum specific for hungry and satiated animals. Increased hunger motivation during electric stimulation of the lateral hypothalamus manifested in the structure of temporal organization of slow wave electric activity of the stomach body and antrum muscles in rabbits subjected to 24-h food deprivation in the replacement of bimodal distribution of slow wave periods to a trimodal type typical of 2-day deprivation, while transition from satiation to hunger caused by electric stimulation of the lateral hypothalamus was associated with a shift from monomodal distributions of slow wave periods to a bimodal type typical of 24-h deprivation. Reorganization of the structure of temporal organization of slow wave electric activity of the stomach body and antrum muscles during electric stimulation of the lateral hypothalamus was determined by descending inhibitory influences of food motivational excitation on activity of the myogenic pacemaker of the lesser curvature of the stomach.

The drive to strive: goal generation based on current needs

Hungry animals are influenced by a multitude of different factors when foraging for sustenance. Much of the work on animal foraging has focused on factors relating to the amount of time and energy animals expend searching for and harvesting foods. Models that emphasize such factors have been invaluable in determining when it is beneficial for an animal to search for pastures new. When foraging, however, animals also have to determine how to direct their search. For what food should they forage? There is no point searching for more of a particular food when you are sated from eating it. Here we review work in macaques and humans that has sought to reveal the neural circuits critical for determining the subjective value of different foods and associated objects in our environment and tracking this value over time. There is mounting evidence that a network composed of the orbitofrontal cortex (OFC), amygdala, and medial thalamus is critical for linking objects in the environment with food value and adjusting those valuations in real time based on current biological needs. Studies using temporary inactivation methods have revealed that the amygdala and OFC play distinct yet complementary roles in this valuation process. Such a network for determining the subjective value of different foods and, by extension, associated objects, must interact with systems that determine where and for how long to forage. Only by efficiently incorporating these two factors into their decisions will animals be able to achieve maximal fitness.