Sleep changes in fasting rats

The Effects of Different Modalities of an Acute Energy Deficit on Sleep and Next Morning Appetitive and Compensatory Behavior in Healthy Young Adults: The EDIES Protocol

Sleep is bi-directionally linked to energy balance. This crossover study design will evaluate the acute effect of a moderate energy deficit (500 kcal) induced by diet, exercise, or mixed (-250 kcal by diet and 250 kcal by exercise) on sleep and the next morning's appetitive responses. The study sample comprises 24 healthy young adults. The experimental measurements will be conducted in a naturalistic, momentary manner and partly assessed by the participants. The participants will undergo a run-in period in order to stabilize their sleep schedules and provide them with training on the study protocol and measurements. Indirect calorimetry will be used to determine their resting metabolic rate and peak oxygen consumption (VO₂ peak). Then, they will take part in a control session (CTL), followed by three energy deficit sessions in random order: a diet-induced energy deficit session (DED), an exercise-induced energy deficit session (EED), and a mixed energy deficit session (MED). All experimental sessions will be separated by a one-week washout. The participants' sleep will be monitored by ambulatory polysomnography, and the next morning's appetitive response will be evaluated via ad libitum food intake, appetite sensations, and food reward, measured by a food liking and wanting computerized test.

The Role of Leptin in Rodent and Human Sleep: A Transdiagnostic Approach with a Particular Focus on Anorexia Nervosa

This narrative review addressed to both clinicians and researchers aims to assess the role of hypoleptinemia in disordered sleep with a particular focus on patients with anorexia nervosa (AN). After introducing circadian rhythms and the regulation of circulating leptin, we summarize the literature on disordered sleep in patients with AN and in fasting subjects in general. We highlight novel single-case reports of substantially improved sleep within days after initiation of off-label metreleptin treatment. These beneficial effects are set in relationship to current knowledge of disordered sleep in animal models of an impaired leptin signaling. Specifically, both absolute and relative hypoleptinemia play a major role in animal models for insomnia, obstructive sleep apnea and obesity hypoventilation syndrome. We pinpoint future research required to complement our understanding of the role of leptin in sleep in patients with acute AN. Moreover, within the section clinical applications we speculate that human recombinant leptin may be useful for the treatment of treatment-resistant sleep-wake disorders, which are associated with (relative) hypoleptinemia. Overall, we stress the role of the hormone leptin in sleep.

Understanding the Role of Orexin Neuropeptides in Drug Addiction: Preclinical Studies and Translational Value

Orexins (also known as hypocretins) are neuropeptides that participate in the regulation of energy metabolism, homeostasis, sleep, feeding, stress responses, arousal, and reward. Particularly relevant to the scope of the present review is the involvement of the orexin system in brain mechanisms that regulate motivation, especially highly motivated behavior, arousal, and stress, making it an ideal target for studying addiction and discovering treatments. Drug abuse and misuse are thought to induce maladaptive changes in the orexin system, and these changes might promote and maintain uncontrolled drug intake and contribute to relapse. Dysfunctional changes in this neuropeptidergic system that are caused by drug use might also be responsible for alterations of feeding behavior and the sleep-wake cycle that are commonly disrupted in subjects with substance use disorder. Drug addiction has often been associated with an increase in activity of the orexin system, suggesting that orexin receptor antagonists may be a promising pharmacological treatment for substance use disorder. Substantial evidence has shown that single orexin receptor antagonists that are specific to either orexin receptor 1 or 2 can be beneficial against drug intake and relapse. Interest in the efficacy of dual orexin receptor antagonists, which were primarily developed to treat insomnia, has grown in the field of drug addiction. Treatments that target the orexin system may be a promising strategy to reduce drug intake, mitigate relapse vulnerability, and restore “normal” physiological functions, including feeding and sleep. The present review discusses preclinical and clinical evidence of the involvement of orexins in drug addiction and possible beneficial pharmacotherapeutic effects of orexin receptor antagonists to treat substance use disorder.

KLF4 Exerts Sedative Effects in Pentobarbital-Treated Mice

KLF4 is a zinc-finger transcription factor that plays an essential role in many biological processes, including neuroinflammation, neuron regeneration, cell proliferation, and apoptosis. Through effects on these processes, KLF4 has likely roles in Alzheimer's disease, Parkinson's disease, and traumatic brain injury. However, little is known about the role of KLF4 in more immediate behavioral processes that similarly depend upon broad changes in brain excitability, such as the sleep process. Here, behavioral approaches, western blot, and immunohistochemical experiments were used to explore the role of KLF4 on sedation and the potential mechanisms of those effects. The results showed that overexpression of KLF4 prolonged loss of righting reflex (LORR) duration in pentobarbital-treated mice and increased c-Fos expression in the lateral hypothalamus (LH) and the ventrolateral preoptic nucleus (VLPO), while it decreased c-Fos expression in the tuberomammillary nucleus (TMN). Moreover, overexpression of KLF4 reduced the expression of p53 in the hypothalamus and increased the expression of STAT3 in the hypothalamus. Therefore, these results suggest that KLF4 exerts sedative effects through the regulation of p53 and STAT3 expression, and it indicates a role of KLF4 ligands in the treatment of sleep disorders.

Sleep homeostasis during daytime food entrainment in mice

Twenty-four hour rhythms of physiology and behavior are driven by the environment and an internal endogenous timing system. Daily restricted feeding (RF) in nocturnal rodents during their inactive phase initiates food anticipatory activity (FAA) and a reorganization of the typical 24-hour sleep-wake structure. Here, we investigate the effects of daytime feeding, where food access was restricted to 4 hours during the light period ZT4-8 (Zeitgeber time; ZT0 is lights on), on sleep-wake architecture and sleep homeostasis in mice. Following 10 days of RF, mice were returned to ad libitum feeding. To mimic the spontaneous wakefulness associated with FAA and daytime feeding, mice were then sleep deprived between ZT3-6. Although the amount of wake increased during FAA and subsequent feeding, total wake time over 24 hours remained stable as the loss of sleep in the light phase was compensated for by an increase in sleep in the dark phase. Interestingly, sleep that followed spontaneous wake episodes during the dark period and the extended period of wake associated with FAA, exhibited lower levels of slow-wave activity (SWA) when compared to baseline or after sleep deprivation, despite a similar duration of waking. This suggests an evolutionary mechanism of reducing sleep drive during negative energy balance to enable greater arousal for food-seeking behaviors. However, the total amount of sleep and SWA accumulated during the 24 hours was similar between baseline and RF. In summary, our study suggests that despite substantial changes in the daily distribution and quality of wake induced by RF, sleep homeostasis is maintained.

Towards an integrated approach to understand Mexican cavefish evolution

The Mexican tetra, Astyanax mexicanus, comes in two forms: a classical river-dwelling fish and a blind and depigmented cave-dwelling fish. The two morphotypes are used as models for evolutionary biology, to decipher mechanisms of morphological and behavioural evolution in response to environmental change. Over the past 40 years, insights have been obtained from genetics, developmental biology, physiology and metabolism, neuroscience, genomics, population biology and ecology. Here, we promote the idea that A. mexicanus, as a model, has reached a stage where an integrated approach or a multi-disciplinary method of analysis, whereby a phenomenon is examined from several angles, is a powerful tool that can be applied to understand general evolutionary processes. Mexican cavefish have undergone considerable selective pressure and extreme morphological evolution, an obvious advantage to contribute to our understanding of evolution through comparative analyses and to pinpoint the specific traits that may have helped their ancestors to colonize caves.

Hypothalamic Neurons that Regulate Feeding Can Influence Sleep/Wake States Based on Homeostatic Need

Eating and sleeping represent two mutually exclusive behaviors that satisfy distinct homeostatic needs. Because an animal cannot eat and sleep at the same time, brain systems that regulate energy homeostasis are likely to influence sleep/wake behavior. Indeed, previous studies indicate that animals adjust sleep cycles around periods of food need and availability. Furthermore, hormones that affect energy homeostasis also affect sleep/wake states: the orexigenic hormone ghrelin promotes wakefulness, and the anorexigenic hormones leptin and insulin increase the duration of slow-wave sleep. However, whether neural populations that regulate feeding can influence sleep/wake states is unknown. The hypothalamic arcuate nucleus contains two neuronal populations that exert opposing effects on energy homeostasis: agouti-related protein (AgRP)-expressing neurons detect caloric need and orchestrate food-seeking behavior, whereas activity in pro-opiomelanocortin (POMC)-expressing neurons induces satiety. We tested the hypotheses that AgRP neurons affect sleep homeostasis by promoting states of wakefulness, whereas POMC neurons promote states of sleep. Indeed, optogenetic or chemogenetic stimulation of AgRP neurons in mice promoted wakefulness while decreasing the quantity and integrity of sleep. Inhibition of AgRP neurons rescued sleep integrity in food-deprived mice, highlighting the physiological importance of AgRP neuron activity for the suppression of sleep by hunger. Conversely, stimulation of POMC neurons promoted sleep states and decreased sleep fragmentation in food-deprived mice. Interestingly, we also found that sleep deprivation attenuated the effects of AgRP neuron activity on food intake and wakefulness. These results indicate that homeostatic feeding neurons can hierarchically affect behavioral outcomes, depending on homeostatic need.

Sleep-Wake Cycling and Energy Conservation: Role of Hypocretin and the Lateral Hypothalamus in Dynamic State-Dependent Resource Optimization

The hypocretin (Hcrt) system has been implicated in a wide range of physiological functions from sleep-wake regulation to cardiovascular, behavioral, metabolic, and thermoregulagtory control. These wide-ranging physiological effects have challenged the identification of a parsimonious function for Hcrt. A compelling hypothesis suggests that Hcrt plays a role in the integration of sleep-wake neurophysiology with energy metabolism. For example, Hcrt neurons promote waking and feeding, but are also sensors of energy balance. Loss of Hcrt function leads to an increase in REM sleep propensity, but a potential role for Hcrt linking energy balance with REM sleep expression has not been addressed. Here we examine a potential role for Hcrt and the lateral hypothalamus (LH) in state-dependent resource allocation as a means of optimizing resource utilization and, as a result, energy conservation. We review the energy allocation hypothesis of sleep and how state-dependent metabolic partitioning may contribute toward energy conservation, but with additional examination of how the loss of thermoregulatory function during REM sleep may impact resource optimization. Optimization of energy expenditures at the whole organism level necessitates a top-down network responsible for coordinating metabolic operations in a state-dependent manner across organ systems. In this context, we then specifically examine the potential role of the LH in regulating this output control, including the contribution from both Hcrt and melanin concentrating hormone (MCH) neurons among a diverse LH cell population. We propose that this hypothalamic integration system is responsible for global shifts in state-dependent resource allocations, ultimately promoting resource optimization and an energy conservation function of sleep-wake cycling.

Neuronal Mechanisms for Sleep/Wake Regulation and Modulatory Drive

Humans have been fascinated by sleep for millennia. After almost a century of scientific interrogation, significant progress has been made in understanding the neuronal regulation and functions of sleep. The application of new methods in neuroscience that enable the analysis of genetically defined neuronal circuits with unprecedented specificity and precision has been paramount in this endeavor. In this review, we first discuss electrophysiological and behavioral features of sleep/wake states and the principal neuronal populations involved in their regulation. Next, we describe the main modulatory drives of sleep and wakefulness, including homeostatic, circadian, and motivational processes. Finally, we describe a revised integrative model for sleep/wake regulation.

Orexin/Hypocretin System: Role in Food and Drug Overconsumption

The neuropeptide orexin/hypocretin (OX), while largely transcribed within the hypothalamus, is released throughout the brain to affect complex behaviors. Primarily through the hypothalamus itself, OX homeostatically regulates adaptive behaviors needed for survival, including food intake, sleep-wake regulation, mating, and maternal behavior. However, through extrahypothalamic limbic brain regions, OX promotes seeking and intake of rewarding substances of abuse, like palatable food, alcohol, nicotine, and cocaine. This neuropeptide, in turn, is stimulated by the intake of or early life exposure to these substances, forming a nonhomeostatic, positive feedback loop. The specific OX receptor involved in these behaviors, whether adaptive behavior or substance seeking and intake, is dependent on the particular brain region that contributes to them. Thus, we propose that, while the primary function of OX is to maintain arousal for the performance of adaptive behaviors, this neuropeptide system is readily co-opted by rewarding substances that involve positive feedback, ultimately promoting their abuse.

To sleep or not to sleep: neuronal and ecological insights

Daily, animals need to decide when to stop engaging in cognitive processes and behavioral responses to the environment, and go to sleep. The main processes regulating the daily organization of sleep and wakefulness are circadian rhythms and homeostatic sleep pressure. In addition, motivational processes such as food seeking and predator evasion can modulate sleep/wake behaviors. Here, we discuss the principal processes regulating the propensity to stay awake or go to sleep-focusing on neuronal and behavioral aspects. We first introduce the neuronal populations involved in sleep/wake regulation. Next, we describe the circadian and homeostatic drives for sleep. Then, we highlight studies demonstrating various effects of motivational processes on sleep/wake behaviors, and discuss possible neuronal mechanisms underlying their control.

Neuronal substrates for initiation, maintenance, and structural organization of sleep/wake states

Animals continuously alternate between sleep and wake states throughout their life. The daily organization of sleep and wakefulness is orchestrated by circadian, homeostatic, and motivational processes. Over the last decades, much progress has been made toward determining the neuronal populations involved in sleep/wake regulation. Here, we will discuss how the application of advanced in vivo tools for cell type–specific manipulations now permits the functional interrogation of different features of sleep/wake state regulation: initiation, maintenance, and structural organization. We will specifically focus on recent studies examining the roles of wake-promoting neuronal populations.

The ETS-5 transcription factor regulates activity states in Caenorhabditis elegans by controlling satiety

Animal behavior is shaped through interplay among genes, the environment, and previous experience. As in mammals, satiety signals induce quiescence in Caenorhabditis elegans Here we report that the C. elegans transcription factor ETS-5, an ortholog of mammalian FEV/Pet1, controls satiety-induced quiescence. Nutritional status has a major influence on C. elegans behavior. When foraging, food availability controls behavioral state switching between active (roaming) and sedentary (dwelling) states; however, when provided with high-quality food, C. elegans become sated and enter quiescence. We show that ETS-5 acts to promote roaming and inhibit quiescence by setting the internal "satiety quotient" through fat regulation. Acting from the ASG and BAG sensory neurons, we show that ETS-5 functions in a complex network with serotonergic and neuropeptide signaling pathways to control food-regulated behavioral state switching. Taken together, our results identify a neuronal mechanism for controlling intestinal fat stores and organismal behavioral states in C. elegans, and establish a paradigm for the elucidation of obesity-relevant mechanisms.

Glucose Induces Slow-Wave Sleep by Exciting the Sleep-Promoting Neurons in the Ventrolateral Preoptic Nucleus: A New Link between Sleep and Metabolism

Sleep-active neurons located in the ventrolateral preoptic nucleus (VLPO) play a crucial role in the induction and maintenance of slow-wave sleep (SWS). However, the cellular and molecular mechanisms responsible for their activation at sleep onset remain poorly understood. Here, we test the hypothesis that a rise in extracellular glucose concentration in the VLPO can promote sleep by increasing the activity of sleep-promoting VLPO neurons. We find that infusion of a glucose concentration into the VLPO of mice promotes SWS and increases the density of c-Fos-labeled neurons selectively in the VLPO. Moreover, we show in patch-clamp recordings from brain slices that VLPO neurons exhibiting properties of sleep-promoting neurons are selectively excited by glucose within physiological range. This glucose-induced excitation implies the catabolism of glucose, leading to a closure of ATP-sensitive potassium (KATP) channels. The extracellular glucose concentration monitors the gating of KATP channels of sleep-promoting neurons, highlighting that these neurons can adapt their excitability according to the extracellular energy status. Together, these results provide evidence that glucose may participate in the mechanisms of SWS promotion and/or consolidation.

SIGNIFICANCE STATEMENT

Although the brain circuitry underlying vigilance states is well described, the molecular mechanisms responsible for sleep onset remain largely unknown. Combining in vitro and in vivo experiments, we demonstrate that glucose likely contributes to sleep onset facilitation by increasing the excitability of sleep-promoting neurons in the ventrolateral preoptic nucleus (VLPO). We find here that these neurons integrate energetic signals such as ambient glucose directly to regulate vigilance states accordingly. Glucose-induced excitation of sleep-promoting VLPO neurons should therefore be involved in the drowsiness that one feels after a high-sugar meal. This novel mechanism regulating the activity of VLPO neurons reinforces the fundamental and intimate link between sleep and metabolism.

Distinct genetic architecture underlies the emergence of sleep loss and prey-seeking behavior in the Mexican cavefish

BACKGROUND

Sleep is characterized by extended periods of quiescence and reduced responsiveness to sensory stimuli. Animals ranging from insects to mammals adapt to environments with limited food by suppressing sleep and enhancing their response to food cues, yet little is known about the genetic and evolutionary relationship between these processes. The blind Mexican cavefish, Astyanax mexicanus is a powerful model for elucidating the genetic mechanisms underlying behavioral evolution. A. mexicanus comprises an extant ancestral-type surface dwelling morph and at least five independently evolved cave populations. Evolutionary convergence on sleep loss and vibration attraction behavior, which is involved in prey seeking, have been documented in cavefish raising the possibility that enhanced sensory responsiveness underlies changes in sleep.

RESULTS

We established a system to study sleep and vibration attraction behavior in adult A. mexicanus and used high coverage quantitative trait loci (QTL) mapping to investigate the functional and evolutionary relationship between these traits. Analysis of surface-cave F2 hybrid fish and an outbred cave population indicates that independent genetic factors underlie changes in sleep/locomotor activity and vibration attraction behavior. High-coverage QTL mapping with genotyping-by-sequencing technology identify two novel QTL intervals that associate with locomotor activity and include the narcolepsy-associated tp53 regulating kinase. These QTLs represent the first genomic localization of locomotor activity in cavefish and are distinct from two QTLs previously identified as associating with vibration attraction behavior.

CONCLUSIONS

Taken together, these results localize genomic regions underlying sleep/locomotor and sensory changes in cavefish populations and provide evidence that sleep loss evolved independently from enhanced sensory responsiveness.

Transcranial slow oscillation stimulation during NREM sleep enhances acquisition of the radial maze task and modulates cortical network activity in rats

Slow wave sleep, hallmarked by the occurrence of slow oscillations (SO), plays an important role for the consolidation of hippocampus-dependent memories. Transcranial stimulation by weak electric currents oscillating at the endogenous SO frequency (SO-tDCS) during post-learning sleep was previously shown by us to boost SO activity and improve the consolidation of hippocampus-dependent memory in human subjects. Here, we aimed at replicating and extending these results to a rodent model. Rats were trained for 12 days at the beginning of their inactive phase in the reference memory version of the radial arm maze. In a between subjects design, animals received SO-tDCS over prefrontal cortex (PFC) or sham stimulation within a time frame of 1 h during subsequent non-rapid eye movement (NREM) sleep. Applied over multiple daily sessions SO-tDCS impacted cortical network activity as measured by EEG and behavior: at the EEG level, SO-tDCS enhanced post-stimulation upper delta (2–4 Hz) activity whereby the first stimulations of each day were preferentially affected. Furthermore, commencing on day 8, SO-tDCS acutely decreased theta activity indicating long-term effects on cortical networks. Behaviorally, working memory for baited maze arms was enhanced up to day 4, indicating enhanced consolidation of task-inherent rules, while reference memory errors did not differ between groups. Taken together, we could show here for the first time an effect of SO-tDCS during NREM sleep on cognitive functions and on cortical activity in a rodent model.

Histamine from brain resident MAST cells promotes wakefulness and modulates behavioral states

Mast cell activation and degranulation can result in the release of various chemical mediators, such as histamine and cytokines, which significantly affect sleep. Mast cells also exist in the central nervous system (CNS). Since up to 50% of histamine contents in the brain are from brain mast cells, mediators from brain mast cells may significantly influence sleep and other behaviors. In this study, we examined potential involvement of brain mast cells in sleep/wake regulations, focusing especially on the histaminergic system, using mast cell deficient (W/W^v) mice. No significant difference was found in the basal amount of sleep/wake between W/W^v mice and their wild-type littermates (WT), although W/W^v mice showed increased EEG delta power and attenuated rebound response after sleep deprivation. Intracerebroventricular injection of compound 48/80, a histamine releaser from mast cells, significantly increased histamine levels in the ventricular region and enhanced wakefulness in WT mice, while it had no effect in W/W^v mice. Injection of H1 antagonists (triprolidine and mepyramine) significantly increased the amounts of slow-wave sleep in WT mice, but not in W/W^v mice. Most strikingly, the food-seeking behavior observed in WT mice during food deprivation was completely abolished in W/W^v mice. W/W^v mice also exhibited higher anxiety and depression levels compared to WT mice. Our findings suggest that histamine released from brain mast cells is wake-promoting, and emphasizes the physiological and pharmacological importance of brain mast cells in the regulation of sleep and fundamental neurobehavior.

Activation of organum vasculosum of lamina terminalis, median preoptic nucleus, and medial preoptic area in anticipation of nursing in rabbit pups

Rhythmic feeding in rabbit pups is a natural model to study food entrainment because, similar to rodents under a schedule of food restriction, these animals show food-anticipatory activity (FAA) prior to daily nursing. In rodents, several brain systems, including the orexinergic system, shift their activity to the restricted feeding schedule, and remain active when subjects are hungry. As the lamina terminalis and regions of the preoptic area participate in the control of behavioral arousal, it was hypothesized that these brain regions are also activated during FAA. Thus, the effects of daily milk ingestion on FOS protein expression in the organum vasculosum of lamina terminalis (OVLT), median preoptic nucleus (MnPO), and medial preoptic area (MPOA) were examined using immunohistochemistry before and after scheduled time of nursing in nursed and fasted subjects. Additionally, FOS expression was explored in orexin (ORX) cells in the lateral hypothalamic area and in the supraoptic nucleus (SON) because of their involvement in arousal and fluid ingestion, respectively. Pups were entrained by daily nursing, as indicated by a significant increase in locomotor behavior before scheduled time of nursing in both nursed and fasted subjects. FOS was significantly higher in the OVLT, MnPO, and MPOA at the time of nursing, and decreased 8 h later in nursed pups. In fasted subjects, this effect persisted in the OVLT, whereas in the MnPO and MPOA, values did not drop at 8 h later, but remained at the same level or higher than those at the time of scheduled nursing. In addition, FOS was significantly higher in ORX cells during FAA in nursed pups in comparison with 8 h later, but in fasted subjects it remained high during most fasting time points. Additionally, OVLT, SON, and ORX cells were activated 1.5 h after nursing. We conclude that the OVLT, MnPO, and MPOA, but not SON, may participate in FAA, as they show activation before suckling of periodic milk ingestion, and that sustained activation of the OVLT, MnPO, and MPOA by fasting may contribute to the high arousal state associated with food deprivation. In agreement with this, ORX cells also remain active after expected nursing, which is consistent with reports in other species.

Sleep structure and feeding pattern changes induced by the liver's thermal status in the rat

Given the liver's importance in controlling metabolic homeostasis in mammals, we sought to establish (i) whether the thermal status of this organ was involved in the link between sleep, thermoregulation and food intake and (ii) how the hypothalamic structures affect the functional interactions between processes involved in regulation of the body's energy balance. In 10 freely moving rats, the liver was heated artificially to and maintained at set-point temperatures of 39.5, 40.0 and 40.5 °C for 4 h. Each animal's feeding activity, cortical temperature and brown adipose tissue (T(BAT) ) temperature were measured continuously. Sleep organization and wakefulness were scored from electroencephalograms. Each animal served as its own control. Heating the liver induced a decrease in food intake and T(BAT) , corresponding to the development of a hypometabolic hypothermic status. The total amounts of wakefulness and rapid eye movement sleep fell, whereas the total amount of slow wave sleep increased accordingly. Our findings show that the liver is involved significantly in the body's thermodynamic equilibrium. The organ's thermal status can induce well-coordinated behavioural and autonomic adaptive responses involved in the control of food intake and in the maintenance of body homeothermia. Our study provides indirect evidence of the existence of hepatic thermosensors afferent to feeding and sleeping hypothalamic integrating centres that can be stimulated by physiological increases in liver temperature.

Orexin/hypocretin plays a role in the response to physiological disequilibrium

In the decade since the discovery that pathology of the orexin/hypocretin system is causative for the sleep disorder narcolepsy, considerable progress has been made in understanding the functional role of the neuropeptide. Two, apparently separate functions of orexin have emerged as a consensus from studies to date. The first is the effect on vigilance state boundaries, as exemplified by narcolepsy. Thus the absence of orexin severely limits the ability to maintain prolonged periods of wakefulness or sleep and also allows the unregulated appearance of cataplexy as sudden muscle weakness during wakefulness. The second function is that orexin acts as a signaling molecule in transferring information about physiological disequilibrium to the central nervous system. Orexin activates the central arousal and motor systems during such disequilibrium and so may facilitate the necessary response and adaptation to restore equilibrium. A feasible relationship between these two functions is therefore that the maintenance of prolonged and active wakefulness is an integral part of this adaptive process. Furthermore, the limit placed on the onset of sleep by orexin suggests that these adaptive processes then continue during sleep to become integrated into the development of a coping strategy for the longer term.

Restricted feeding-induced sleep, activity, and body temperature changes in normal and preproghrelin-deficient mice

Behavioral and physiological rhythms can be entrained by daily restricted feeding (RF), indicating the existence of a food-entrainable oscillator (FEO). One manifestation of the presence of FEO is anticipatory activity to regularly scheduled feeding. In the present study, we tested if intact ghrelin signaling is required for FEO function by studying food anticipatory activity (FAA) in preproghrelin knockout (KO) and wild-type (WT) mice. Sleep-wake activity, locomotor activity, body temperature, food intake, and body weight were measured for 12 days in mice on a RF paradigm with food available only for 4 h daily during the light phase. On RF days 1-3, increases in arousal occurred. This response was significantly attenuated in preproghrelin KO mice. There were progressive changes in sleep architecture and body temperature during the subsequent nine RF days. Sleep increased at night and decreased during the light periods while the total daily amount of sleep remained at baseline levels in both KO and WT mice. Body temperature fell during the dark but was elevated during and after feeding in the light. In the premeal hours, anticipatory increases in body temperature, locomotor activity, and wakefulness were present from RF day 6 in both groups. Results indicate that the preproghrelin gene is not required for the manifestation of FAA but suggest a role for ghrelinergic mechanisms in food deprivation-induced arousal in mice.

Recurrent restriction of sleep and inadequate recuperation induce both adaptive changes and pathological outcomes

Chronic restriction of a basic biological need induces adaptations to help meet requisites for survival. The adaptations to chronic restriction of sleep are unknown. A single episode of 10 days of partial sleep loss in rats previously was shown to be tolerated and to result in increased food intake and loss of body weight as principal signs. The purpose of the present experiment was to investigate the extent to which adaptation to chronic sleep restriction would ameliorate short-term effects and result in a changed internal phenotype. Rats were studied during 10 wk of multiple periods of restricted and unrestricted sleep to allow adaptive changes to develop. Control rats received the same ambulatory requirements only consolidated into periods that lessened interruptions of their sleep. The results indicate a latent period of relatively stable food and water intake without weight gain, followed by a dynamic phase marked by enormous increases in food and water intake and progressive loss of body weight, without malabsorption of calories. Severe consequences ensued, marked especially by changes to the connective tissues, and became fatal for two individuals. The most striking changes to internal organs in sleep-restricted rats included lengthening of the small intestine, decreased size of adipocytes, and increased incidence of multilocular adipocytes. Major organs accounted for an increased proportion of total body mass. These changes to internal tissues appear adaptive in response to high energy production, decomposition of lipids, and increased need to absorb nutrients, but ultimately insufficient to compensate for inadequate sleep.

Abnormal response of melanin-concentrating hormone deficient mice to fasting: hyperactivity and rapid eye movement sleep suppression

Melanin-concentrating hormone (MCH) is a hypothalamic neuropeptide that has been implicated in energy homeostasis. Pharmacological studies with MCH and its receptor antagonists have suggested additional behavioral roles for the neuropeptide in the control of mood and vigilance states. These suggestions have been supported by a report of modified sleep in the MCH-1 receptor knockout mouse. Here we found that MCH knockout (MCH(-)(/)(-)) mice slept less during both the light and dark phases under baseline conditions. In response to fasting, MCH(-)(/)(-) mice exhibited marked hyperactivity, accelerated weight loss and an exaggerated decrease in rapid eye movement (REM) sleep. Following a 6-h period of sleep deprivation, however, the sleep rebound in MCH(-)(/)(-) mice was normal. Thus MCH(-)(/)(-) mice adapt poorly to fasting, and their loss of bodyweight under this condition is associated with behavioral hyperactivity and abnormal expression of REM sleep. These results support a role for MCH in vigilance state regulation in response to changes in energy homeostasis and may relate to a recent report of initial clinical trials with a novel MCH-1 receptor antagonist. When combined with caloric restriction, the treatment of healthy, obese subjects with this compound resulted in some subjects experiencing vivid dreams and sleep disturbances.

The hypothalamic peptidergic system, hypocretin/orexin and vigilance control

Using forward and reverse genetics, the genes (hypocretin/orexin ligand and its receptor) involved in the pathogenesis of the sleep disorder, narcolepsy, in animals, have been identified. Mutations in hypocretin related-genes are extremely rare in humans, but hypocretin-ligand deficiency is found in most narcolepsy-cataplexy cases. Hypocretin deficiency in humans can be clinically detected by CSF hypocretin-1 measures, and undetectably low CSF hypocretin-1 is now included in the revised international diagnostic criteria of narcolepsy. Since hypocretin-ligand deficiency is the major pathophysiology in human narcolepsy, hypocretin replacements (using hypocretin agonists or gene therapy) are promising future therapeutic options. New insights into the roles of hypocretin system on sleep physiology have also rapidly increased. Hypocretins are involved in various fundamental hypothalamic functions such as feeding, energy homeostasis and neuroendocrine regulation. Hypocretin neurons project to most ascending arousal systems (including monoaminergic and cholinergic systems), and generally exhibit excitatory inputs. Together with the recent finding of the sleep promoting system in the hypothalamus (especially in the GABA/galanin ventrolateral preoptic area which exhibits inhibitory inputs to these ascending systems), the hypothalamus is now recognized as the most important brain site for the sleep switch, and other peptidergic systems may also participate in this regulation. Meanwhile, narcolepsy now appears to be a more complex condition than previously thought. The pathophysiology of the disease is involved in the abnormalities of sleep and various hypothalamic functions due to hypocretin deficiency, such as the changes in energy homeostasis, stress reactions and rewarding. Narcolepsy is therefore, an important model to study the link between sleep regulation and other fundamental hypothalamic functions.

Physiological changes in glucose differentially modulate the excitability of hypothalamic melanin-concentrating hormone and orexin neurons in situ

The physiological signaling mechanisms that link normal variations in body energy status to the activity of arousal- and metabolism-regulating brain centers are not well understood. The melanin-concentrating hormone (MCH) and orexin/hypocretin types of neurons of the lateral hypothalamus (LH) exert opposing effects on arousal and metabolism. We examined whether shifts in brain extracellular glucose that correspond to physiological changes in blood glucose can alter the electrical output of neurochemically and biophysically defined LH cells in mouse brain slices. Here, we show that physiologically relevant concentrations of glucose dose-dependently enhance the electrical excitability of MCH neurons by inducing depolarization and increasing membrane resistance. We also demonstrate that the same physiological shifts in glucose have the opposite effects on the electrical activity of orexin neurons. We propose that these direct actions of glucose on the arousal- and metabolism-regulating LH neurons play a key role in the translation of normal variations in body energy resources into appropriate changes in arousal and metabolism.

Roles of orexin/hypocretin in regulation of sleep/wakefulness and energy homeostasis

The finding of orexin (hypocretin) deficiency in patients with narcolepsy suggests that this hypothalamic neuropeptide plays a crucial role in regulating and maintaining sleep/wakefulness states and energy homeostasis. Orexin might be especially important for stabilization of behavioral states, because the major symptom in narcolepsy is instability of each behavioral state, which results in sleep/wakefulness fragmentation. The efferent and afferent systems of orexin neurons suggest interactions between these cells and arousal/sleep-wakefulness centers in the brainstem as well as important feeding centers in the hypothalamus. Electrophysiological studies have shown that orexin neurons are regulated by monoamines and acetylcholine as well as metabolic cues, including leptin, glucose, and ghrelin. Thus, orexin neurons have the requisite functional interactions with hypothalamic feeding pathways and monoaminergic/cholinergic centers, and provide a critical link between peripheral energy balance and the central mechanisms that coordinate sleep/wakefulness and motivated behavior such as food seeking.

Restriction-refeeding of calories and protein induces changes to slow wave and paradoxical sleep that parallel changes in body lipid and protein levels in rats

Recent data have suggested that the activity of various brain nuclei is modulated during sleep. In this context, we developed the idea that sleep may participate in adapting brain responsiveness to feeding, so as to tune the control of peripheral energy metabolism. In order to characterize the nature of a possible link between sleep and peripheral energy metabolism, we have investigated the relationship between sleep parameters [wakefulness (W), slow wave sleep (SWS), paradoxical sleep (PS)] and the intensity of peripheral lipid and protein deposition processes. To achieve this, by manipulating the amount and quality of food available to rats, we induced states of energy or protein depletion/repletion which would specifically affect lean or fat body mass, which was quantified by an analysis of body composition. In parallel, using a permanently implanted cortical electrode, we measured electroencephalogram signals (EEG) to quantify the time spent in W, SWS and PS. Analysis of EEG changes in relation to the changes induced in body composition, showed that (1) the amount of sleep (PS and SWS) followed the evolution of energy supply levels, and (2) the time spent in PS relative to SWS varied to a considerable degree (14-23.5%) and followed the same trend as the ratio of lean body mass to fat mass. These results suggest the possible existence of quantitative and qualitative interactions between sleep quality and the anabolic and catabolic processes of peripheral fat and protein deposition.

Influence of long-term food restriction on sleep pattern in male rats

The present purpose was to determine the effects of different schedules of long-term food restriction (FR) applied to rats from weaning to the 8th week. Rats were distributed into FR and ad libitum groups at weaning and fed at 7 am, at 7 pm, and finally, restricted rats fed ad libitum. The restricted rats started with 6 g/day and the food was increased by 1 g per week until reaching 15 g/day by adulthood. The rats were implanted with electrodes to record electrocorticogram/eletromyogram signals. Their wake-sleep cycles were monitored over 3 consecutive days (72 h of recording). The FR group fed at 7 am showed an increase in awake time, and decrease in slow wave sleep (SWS) and paradoxical sleep (PS) during the three light periods compared with the control recordings whereas in the dark periods, these sleep parameters were the opposite. The restricted group fed in the evening showed no statistical significances at diurnal periods; however, a significant decrease was observed in the dark recordings for awake time, but the SWS and PS were increased in relation to controls. The analysis of the 24-h period demonstrated that both FR groups presented increase in SWS time. After being FR, the rats were fed ad libitum and their sleep was monitored for 3 additional days. During the first dark recording, the decrease in awake time and increase in SWS were still present; however, as ad libitum food continued, these sleep parameters returned to control values, reestablishing the normal sleep pattern. These results suggest that dietary restriction, regardless to the feeding schedule, caused increase in total sleep time, during the active period.

Thermal and nutritional modulation of sleep in infant rats

Infant rats cycle rapidly between periods of high muscle tone (indicative of wakefulness) and periods of atonia (indicative of sleep). Here, the influence of air temperature on sleep in 8-day-old rats was examined by testing pups at thermoneutrality (35 degrees C) and during moderate (28 degrees C) and extreme (20 degrees C) cold challenge; also, pups were tested 1, 4, and 8 hr after infusion of milk to assess the effects of food deprivation on sleep. Whereas moderate cooling slightly reduced sleep durations and altered the temporal patterning of myoclonic twitching, extreme cooling substantially decreased sleep durations and inhibited twitching. In contrast, food deprivation had little effect. Therefore, thermoregulatory mechanisms engaged during moderate cooling sustain sleep, whereas extreme cooling overwhelms these mechanisms, thereby promoting arousal.

Reverse pharmacology of orexin: from an orphan GPCR to integrative physiology

Orexins, which were initially identified as endogenous peptide ligands for two orphan G-protein coupled receptors (GPCRs), have been shown to have an important role in the regulation of energy homeostasis. Furthermore, the discovery of orexin deficiency in narcolepsy patients indicated that orexins are highly important factors for the sleep/wakefulness regulation. The efferent and afferent systems of orexin-producing neurons suggest interactions between these cells and arousal centers in the brainstem as well as important feeding centers in the hypothalamus. Electrophysiological studies have shown that orexin neurons are regulated by humoral factors, including leptin, glucose, and ghrelin as well as monoamines and acetylcholin. Thus, orexin neurons have functional interactions with hypothalamic feeding pathways and monoaminergic/cholinergic centers to provide a link between peripheral energy balance and the CNS mechanisms that coordinate sleep/wakefulness states and motivated behavior such as food seeking.

Reduced food anticipatory activity in genetically orexin (hypocretin) neuron-ablated mice

Daily restricted feeding (RF) produces an anticipatory locomotor activity rhythm and entrains the peripheral molecular oscillator independently of the central pacemaker located in the suprachiasmatic nucleus (SCN). As orexins (hypocretins) are neuropeptides that coordinate sleep/wake patterns and motivated behaviours, such as food seeking, we studied the involvement of orexin in the food anticipatory activity (FAA) induced by RF. Daily RF shifted the mRNA rhythm of a clock-controlled gene mDbp in the cerebral cortex and caudate putamen but not in the SCN. Under these experimental conditions, prepro-orexin mRNA and orexin A immunoreactivity in the lateral hypothalamic area (LHA) did not show daily variation. Fasting increased the number of orexin A-ir cells, while RF did not. However, RF shifted the peak of Fos expression of the orexin neurons from night to day. Genetic ablation of orexin neurons in orexin/ataxin-3 transgenic mice severely reduced the formation of FAA under RF conditions. The expression of mNpas2 mRNA, a transcription factor thought to be involved in regulation of the food entrainable oscillator as well as mPer1 and mBmal1 mRNA, was reduced in the forebrain of orexin/ataxin-3 mice. Based on these results, we suggest that activity of the orexin neuron in the LHA contributes to the promotion and maintenance of FAA.

A tryptophan-rich protein diet efficiently restores sleep after food deprivation in the rat

Sleep depends on the quantity and quality of the diet. Several studies have shown that food deprivation results in a reduction in sleep duration. It has also been demonstrated that in the newborn, the supply of certain essential amino acids improves sleep through their action on the synthesis of specific neurotransmitters. The aim of the present study was to test if the quantity and/or quality of dietary protein could improve the recovery of sleep during re-feeding after caloric deprivation. Sleep parameters were compared in rats fed ad libitum, food restricted during 4 days, or reefed isocalorically after food restriction with three dietary regimens varying in terms of the amount (14% versus 30%) or quality (milk protein or alpha-lactalbumin) of protein. The results showed that sleep recovery, in particular slow-wave sleep, was improved in rats re-fed with alpha-lactalbumin. This result confirms the close relationship between feeding and sleep and suggest that alpha-lactabumin could be used to improve sleep in adult submitted to nutritional disturbances such as food restriction, shift work, Ramadan.

The hypocretin/orexin system in health and disease

Using positional cloning in a canine model of narcolepsy and mouse gene knockouts, genes involved in the pathogenesis of narcolepsy in animals have been identified. Hypocretin/orexin ligand and hypocretin/orexin receptor genes are key to the pathogenesis of narcolepsy in animals. Mutations in hypocretin-related genes are rare in humans, but hypocretin-ligand deficiency is found in many cases. Hypocretins/orexins are novel hypothalamic neuropeptides involved in various hypothalamic mechanisms, such as energy homeostasis and neuroendocrine function. Hypocretin-deficient human narcolepsy appears to be a more complex condition than a simple sleep disorder, and it may serve as an important disease model for studying hypothalamic function in health and disease.

Effects of systematic variation in presatiation and fasting on the behavioural satiety sequence in male rats

Preclinical research on the neurobiology of appetite regulation is increasingly employing detailed behavioural assessment in addition to measures of food intake. One of the most widely used approaches examines treatment effects on the behavioural satiety sequence (BSS), a concept describing the predictable pattern of behavioural change (feeding-->grooming-->resting) associated with the process of satiation in rats, mice and other mammals. Surprisingly, however, comparatively little published detail is available concerning the impact of more natural appetite modulators on the BSS. In two separate experiments, a continuous monitoring technique was used to calibrate the effects of prefeeding (3, 6 and 9 min) and prior fasting (3, 6 and 12 h) on the microstructure of rat behaviour during a 1 h test with palatable mash. Prefeeding significantly increased eating latencies and reduced both food intake and total duration (but not frequency) of feeding behaviour. The reduction in time spent eating was most evident during the first 15 min of the test when feeding is normally at peak levels. Although behavioural structure was fully preserved in all test conditions, the two larger preloads resulted in shifts to the left (i.e., an acceleration) in the BSS. In contrast, fasting for 6 and 12 h (but not 3 h) increased food intake and duration (but not frequency) of feeding behaviour in the early part of the test. All fasting conditions (including 3 h) produced considerable shifts to the right (i.e., a delay) in the BSS, confirming the greater sensitivity of this measure relative to food intake per se. The potential utility of these reference profiles is discussed in relation to drug-induced changes in food intake and the BSS.

Hypothalamic orexin neurons regulate arousal according to energy balance in mice

Mammals respond to reduced food availability by becoming more wakeful and active, yet the central pathways regulating arousal and instinctual motor programs (such as food seeking) according to homeostatic need are not well understood. We demonstrate that hypothalamic orexin neurons monitor indicators of energy balance and mediate adaptive augmentation of arousal in response to fasting. Activity of isolated orexin neurons is inhibited by glucose and leptin and stimulated by ghrelin. Orexin expression of normal and ob/ob mice correlates negatively with changes in blood glucose, leptin, and food intake. Transgenic mice, in which orexin neurons are ablated, fail to respond to fasting with increased wakefulness and activity. These findings indicate that orexin neurons provide a crucial link between energy balance and arousal.

Masculine sexual activity affects slow wave sleep in Golden hamsters

The sleep pattern is modified by events occurring during wakefulness. In rats, it has been shown that male sexual behavior has a direct influence on sleeping patterns, increasing slow wave sleep (SWS) duration. On the other hand, the sexual behavior pattern of the male Golden hamster differs from the copulatory pattern of male rats. Male hamsters copulate faster and they do not display the motor inhibition observed in rats after each ejaculation. Moreover, close to exhaustion, hamsters display a behavioral pattern known as Long Intromission, which has been linked to an sexual inhibitory process. The present study was performed to determine the effects of male sexual activity on the sleep pattern in hamsters. Subjects were allowed to copulate for 30 and 60 min. In addition, the effect of locomotor activity was also assessed. The results show that male sexual behavior induced a significant increase of SWS II, with a reduction of wakefulness. No effect was observed on REM sleep. Locomotor activity produced only a slight effect on sleep. The results are discussed in terms of the similarities between the effects observed after sexual behavior on sleep in rats and hamsters, despite the substantial differences in the behavioral pattern.

Differential distribution and regulation of OX1 and OX2 orexin/hypocretin receptor messenger RNA in the brain upon fasting

To further understand the functions of the orexin/hypocretin system, we examined the expression and regulation of the orexin/hypocretin receptor (OX1R and OX2R) mRNA in the brain by using quantitative in situ hybridization. Expression of OX1R and OX2R mRNA exhibited distinct distribution patterns. Within the hypothalamus, expression for the OX1R mRNA was largely restricted in the ventromedial (VMH) and dorsomedial hypothalamic nuclei, while high levels of OX2R mRNA were contained in the paraventricular nucleus, VMH, and arcuate nucleus as well as in mammilary nuclei. In the amygdala, OX1R mRNA was expressed throughout the amygdaloid complex with robust labeling in the medial nucleus, while OX2R mRNA was only present in the posterior cortical nucleus of amygdala. High levels of OX2R mRNA were also observed in the ventral tegmental area. Moreover, both OX1R and OX2R mRNA were observed in the hippocampus, some thalamic nuclei, and subthalamic nuclei. Furthermore, we analyzed the effect of fasting on levels of OX1R and OX2R mRNA in the hypothalamic and amygdaloid subregions. After 20 h of fasting, levels of OX1R mRNA were significantly increased in the VMH and the medial division of amygdala. An initial decrease (14 h) and a subsequent increase (20 h) in OX1R mRNA levels after fasting were observed in the dorsomedial hypothalamic nucleus and lateral division of amygdala. Levels of OX2R mRNA were augmented in the arcuate nucleus, but remained unchanged in the dorsomedial hypothalamic nucleus, paraventricular hypothalamic nucleus, and amygdala following fasting. The time-dependent and region-specific regulatory patterns of OX1R and OX2R suggest that they may participate in distinct neural circuits under the condition of food deprivation.

Endogenous and exogenous factors on sleep-wake cycle regulation

A number of theories have proposed the involvement of different brain structures and neurotransmitters in order to explain the regulation of the sleep wake cycle. However, there is no clear consensus as to the mechanisms through which the brain structures and their various neurotransmitters interact to produce theses phases. Perhaps the problem is related to the fact sleep is a very fragile state, easily modified or influenced by a variety of substances or experimental manipulations. In this paper, we describe the evidence of two different groups of factors that induce important changes on the sleep wake cycle. The endogenous factors: neurotransmitters; hormone; peptides; and some substances of lipidic nature and exogenous factors: stress, food intake, learning, sleep deprivation, sensorial stimulation, exercise and temperature on the regulation the sleep-wake cycle. Likewise, we propose a hypothesis which attempts to reconcile the fact that endogenous and exogenous factors have similar effects.

Ventromedial hypothalamic lesions prevent the fasting-induced changes in day-night pattern of locomotor activity

The time-course of day-night organization of running wheel activity during prolonged fasting was studied in rats, with or without electrolytic lesions in the ventromedial hypothalamus (VMH). For each individual, dates were referenced to the metabolic transition from lipid to protein utilization in late fasting; this was estimated by daily weighing. In fasted sham-operated controls, daytime activity increased progressively over the fast. This fasting-induced rise in diurnal activity was not due to daily handling, since it was observed also in non-handled (fasted) controls. The pattern of the increase in sham-operated rats differed between 2-hour periods (8-10 h to 18-20 h). The distribution of nocturnal activity was also modified during food deprivation: nocturnal activity in late fasting increased in the 20-22 h period and concomitantly decreased in the two 4-6 h and 6-8 h periods. By contrast, VMH lesions markedly limited and delayed the rise in diurnal running activity, irrespective of the 2-hour period. They prevented any significant change in nocturnal activity pattern over the fast. In fasted sham-operated rats, the data may be interpreted as a phase-advance of the nocturnal pattern of locomotor activity, concomitant with the increase of activity during daytime. These changes were suppressed by the VMH lesions. This suggests that the fasting-induced changes in the day-night pattern of locomotor activity are centrally mediated by a neuronal circuit involving the ventromedial hypothalamus.

Functional consequences of sustained sleep deprivation in the rat

Sleep deprivation disrupts vital biological processes that are necessary for cognitive ability and physical health, but the physiological changes that underlie these outward effects are largely unknown. The purpose of the present studies in the laboratory rat is to prolong sleep deprivation to delineate the pathophysiology and to determine its mediation. In the rat, the course of prolonged sleep deprivation has a syndromic nature and eventuates in a life-threatening state. An early and central symptom of sleep deprivation is a progressive increase in peripheral energy expenditure to nearly double normal levels. An attempt to alleviate this negative energy balance by feeding rats a balanced diet that is high in its efficiency of utilization prolongs survival and attenuates or delays development of malnutrition-like symptoms, indicating that several symptoms can be manipulated to some extent by energy and nutrient consumption. Most changes in neuroendocrine parameters appear to be responses to metabolic demands, such as increased plasma catecholamines indicating sympathetic activation. Plasma total thyroid hormones, however, decline to severely low levels; a metabolic complication that is associated with other sleep deprivation-induced symptoms, such as a decline in body temperature to hypothermic levels despite increased energy expenditure. Metabolic mapping of the brain revealed a dissociation between the energy metabolism of the brain and that of the body. Sleep deprivation's effects on cerebral structures are heterogeneous and unidirectional toward decreased functional activity. The hypometabolic brain structures are concentrated in the hypothalamus, thalamus and limbic systems, whereas few regions in the rest of the brain and none in the medulla, are affected. Correspondence can be found between some of the affected cerebral structures and several of the peripheral symptoms, such as hyperphagia and possible heat retention problems. The factor predisposing to mortality is a decreased resistance to infection. Lethal opportunistic organisms are permitted to infect the bloodstream, which presumably results in a cascade of toxic-like reactions. Host defense is thus the first system to fail. There is neither fever nor marked tissue inflammatory reactions typical of infectious disease states, suggesting that sleep deprivation is immunosuppressive. Each of the four abnormalities identified--(1) a deep negative energy balance and associated malnutrition; (2) heterogeneous decreases in cerebral function; (3) low thyroid hormone concentrations; and (4) decrease resistance to infection--can be viewed as having an early origin during the sleep deprivation process to signify the foremost pathogenic situation to which the other abnormalities might be secondarily related.(ABSTRACT TRUNCATED AT 400 WORDS)

Stress ulcers in rats: the role of food intake, body weight, and time of day

Rats were housed in activity wheels (n = 32) or in hanging cages (n = 32) for 2 weeks. Food intake of rats in hanging cages was curtailed to match body weight to that of the activity group. All rats then received 6 g of food at one of four different times of day (n = 8, each mealtime) for 4 consecutive days and were sacrificed 24 h after the last meal. Twenty-three rats in the activity group and 13 rats in the hanging cage group had ulcers in the glandular portion of the stomach. Ulcers were significantly larger and more numerous in the activity group, and activity levels were highly correlated with area of ulceration. In both groups, terminal body weight was also significantly correlated with area of ulceration. No statistically reliable mealtime effects were observed because of large within-group variability. Because many rats in hanging cages developed ulcers in the absence of wheel running, the results suggest that restricted food supply and loss of body weight are initiating factors in ulcer formation, while excessive wheel running contributes to the severity of ulcerations in the glandular stomach.

Sleep changes in fasting rats after chronic glycerol feeding

Species which do not enter torpor during fasting and which were efficiently able to spare their body proteins during the first two phases of fasting (which are commonly comprised of 3 successive phases) also increase their daily amount of slow-wave sleep (SWS) during the first two phases. Since in fasting animals the ability to spare proteins was reported to be improved when they were previously fed with a diet enriched with glycerol, it was supposed that, after such a diet, food-deprived rats would increase their daily quota of SWS. In addition, the tolerance to food deprivation, defined as the time elapsed to reach the end of phase II, should also be improved since this tolerance is known to be critically modulated by protein utilization. The daily proportions of wakefulness (W), SWS and paradoxical sleep (PS) were thus studied in Wistar rats after 16 weeks of feeding (i.e., when they were 27 weeks old) with an enriched glycerol diet. These daily W and sleep state proportions were then evaluated until the middle of fasting phase II (MII), i.e., when protein catabolism in the rat appears to be at its lowest level. The rats were able to tolerate more than 5 weeks of food deprivation, which represented an increase of 123% of the fasting tolerance previously reported in rats of the same age but which were fed normally before fasting onset. At MII the daily proportion of SWS was significantly (vs. fed state, p less than 0.01) increased (due to an increase in the daily mean episode duration), at the expense of W (due to a lowering in the daily occurrence of W episodes).(ABSTRACT TRUNCATED AT 250 WORDS)

Fasting-induced rise in locomotor activity in rats coincides with increased protein utilization

The aim of this study was to investigate the possible relation between the modifications in locomotor activity (on running wheel) which occur during prolonged fasting and changes in the utilization of energy reserves. In 18-week-old rats, we found that the rate of body mass loss reflects the changes in nitrogen excretion that occur over three phases of fasting: (I) initially decreasing, (II) maintained at a low level and (III) increasing. Locomotor activity started to increase during phase II without a change in its nycthemeral pattern. By contrast, the 10-fold higher daily locomotor activity that occurred in phase III was marked by a higher proportion of diurnal activity. Using 9-, 18-, and 33-week-old rats, in order to obtain a different timing in the metabolic changes during fasting, we could confirm the coincidence between the later rise in locomotor activity and the occurrence of phase III. Refeeding of rats of either age in phase III rapidly suppressed fasting-induced changes in locomotor activity. These data accord with the idea that behavioral changes reflecting the search for food are triggered by a later and reversible change in the utilization of body protein vs. lipid stores during prolonged fasting.