Anticipatory changes in liver metabolism and entrainment of insulin, glucagon, and corticosterone in food-restricted rats

Circadian influences on feeding behavior

Feeding, like many other biological functions, displays a daily rhythm. This daily rhythmicity is controlled by the circadian timing system of which the central master clock is located in the hypothalamic suprachiasmatic nucleus (SCN). Other brain areas and tissues throughout the body also display rhythmic functions and contain the molecular clock mechanism known as peripheral oscillators. To generate the daily feeding rhythm, the SCN signals to different hypothalamic areas with the lateral hypothalamus, paraventricular nucleus and arcuate nucleus being the most prominent. With respect to the rewarding aspects of feeding behavior, the dopaminergic system is also under circadian influence. However the SCN projects only indirectly to the different reward regions, such as the ventral tegmental area where dopamine neurons are located. In addition, high palatable, high caloric diets have the potential to disturb the normal daily rhythms of physiology and have been shown to alter for example meal patterns. Around a meal several hormones and peptides are released that are also under circadian influence. For example, the release of postprandial insulin and glucagon-like peptide following a meal depend on the time of the day. Finally, we review the effect of deletion of different clock genes on feeding behavior. The most prominent effect on feeding behavior has been observed in Clock mutants, whereas deletion of Bmal1 and Per1/2 only disrupts the day-night rhythm, but not overall intake. Data presented here focus on the rodent literature as only limited data are available on the mechanisms underlying daily rhythms in human eating behavior.

Feeding during the resting phase causes gastrointestinal tract dysfunction and desynchronization of metabolic and neuronal rhythms in rats

BACKGROUND

Disrupted circadian rhythms may result from a misalignment between the environmental cycles (due to shift work, sleep restriction, feeding at an unusual time of day) and endogenous rhythms or by physiological aging. Among the numerous adverse effects, disrupted rhythms affect the brain-gut axis, contributing to the pathogenesis of several diseases in the gastrointestinal tract, for example, abdominal pain, constipation, gastric dyspepsia, inflammatory bowel disease, irritable bowel syndrome, and others.

METHODS

This study evaluated the rat gastric emptying, gastrointestinal motility, a clock gene, gut hormones, and the neuron activity on the nucleus of tractus solitarius (NTS), area postrema (AP), and the dorsal motor nucleus of the vagus (DMV) in rats with restricted food access to the rest phase for 4 weeks.

KEY RESULTS

Our results show that food restricted to the rest light period disturbed the expression pattern of a series of transcripts, including metabolic and circadian regulation. Also, the secretion of gastrointestinal hormones, gastric emptying, intestinal motility, and NTS, AP, and DMV activity were altered.

CONCLUSIONS & INFERENCES

These data indicate the importance of the time of the day food is ingested on the regulation of energy balance and the endocrine activity of the stomach and small intestine, emphasizing the importance of food as a powerful circadian synchronizer and an essential factor for the triggering of gastrointestinal diseases and metabolic problems. These findings offer a novel clue regarding the obesity-promoting effect attributed to feeding time and open the possibility of treating this and other intestinal disorders.

Activation of the central but not the medial and cortical amygdala during anticipation for daily nursing in the rabbit

Rabbits have remarkable nursing behavior: after parturition, does visit daily their pups for nursing only once with circadian periodicity. Before the nursing events, they present increased activity and arousal, which shift according to the timing of scheduled nursing, either during the day or night. Brain areas related to maternal behavior and neuroendocrine cells for milk secretion are also entrained. The daily return of the doe for nursing at approximately the same hour suggests a motivational drive with circadian periodicity. Previously, we reported the activation of the mesolimbic system at the time of nursing, but not 12 h before that. Aiming at a better understanding of the mechanism of this anticipatory behavior, we explored the participation of the limbic regions of the amygdala and the bed nucleus of the stria terminalis, as well as the possible activation of the hypothalamic-pituitaryadrenal axis, specifically the corticotropin-releasing factor cells in the hypothalamic paraventricular nucleus of does at different times before and after nursing. The medial and cortical amygdala, the bed nucleus of the stria terminalis, and corticotropin cells showed activation only after nursing. However, the central amygdala was also activated before nursing. We conclude that the medial and the cortical amygdala form part of the afferent olfactory pathway for entrainment, and the central amygdala participates in the anticipatory motivational circuit of the control of periodic nursing. The lack of activation of corticotropin cells before nursing is consistent with the possible harmful effects of the doe's high glucocorticoid levels on the developing pups.

Determination of diurnal rhythm of salivary corticosterone concentration in the domestic rabbit (Oryctolagus cuniculus f. domestica) using a non-invasive method

There are many advantages associated with the determination of the level of corticosterone in rabbits from saliva, since this is a non-invasive sample collection method that does not affect their welfare and provides a reliable reflection of the state of the animal at a given moment without the results being distorted as they may be, for example, when blood samples are taken. The aim of this study was to determine the diurnal rhythm in the concentration of corticosterone in the saliva of the domestic rabbit. Saliva samples were taken from six domestic rabbits five times during the daytime (at 6:00, 9:00, 12:00, 15:00 and 18:00) over the course of three consecutive days. The levels of corticosterone in the saliva of the individual rabbits displayed a diurnal rhythm during the course of the day, with a significant increase between 12:00 and 15:00 (p < 0.05). No statistically significant difference in the concentrations of corticosterone in the saliva of the individual rabbits was demonstrated. Although the basal value of corticosterone is not known in rabbits and is difficult to determine, the results of our study show the pattern of fluctuations in the concentration of corticosterone in the saliva of rabbits during the daytime.

Alternating mealtimes during pregnancy and weaning triggers behavioral changes in adult offspring

In brief

Mealtime changes in pregnant mice revealed impaired neurobehavioral development in mouse offspring. This study is the basis for investigating diseases associated with neurobehavioral development of adult offspring of pregnant shift-working women.

Abstract

Most organisms on Earth have a biological clock, and their physiological processes are regulated by a 1-day cycle. In modern society, several factors can disturb these biological clocks in humans; in particular, individuals working in shifts are exposed to stark environmental changes that interfere with their biological clock. They have a high risk of various diseases. However, there are scarce experimental approaches to address the reproductive and health consequences of shift work in the offspring of exposed individuals. In this study, considering the fact that shift workers usually have their meals during their adjusted working time, we aimed to examine the effects of a 12-h shift with usual mealtime as a plausible night work model on the neurobehavioral development of adult mouse offspring. In these offspring, early exposure to this mealtime shift differentially affected circadian rhythmic variables and total locomotor activity depending on the timing and duration of restrictive feeding. Moreover, neurobehavioral alterations such as declined short-term memory and depressive-like behavior were observed in adulthood. These results have implications for the health concerns of shift-working women and their children.

Hepatic metabolite responses to 4-day complete fasting and subsequent refeeding in rats

Background

Fasting has been widely used to improve various metabolic diseases in humans. Adaptive fasting is necessary for metabolic adaptation during prolonged fasting, which could overcome the great advantages of short-term fasting. The liver is the main organ responsible for energy metabolism and metabolic homeostasis. To date, we lack literature that describes the physiologically relevant adaptations of the liver during prolonged fasting and refeeding. For that reason, this study aims to evaluate the response of the liver of Sprague-Dawley (SD) rats to prolonged fasting and refeeding.

Methods

Sixty-six male SD rats were divided into the fasting groups, which were fasted for 0, 4, 8, 12, 24, 48, 72, or 96 h, and the refeeding groups, which were refed for 1, 3, or 6 days after 96 h of fasting. Serum glucose, TG, FFA, β-hydroxybutyrate, insulin, glucagon, leptin, adiponectin and FGF21 levels were assessed. The glucose content, PEPCK activity, TG concentration and FFA content were measured in liver tissue, and the expression of genes involved in gluconeogenesis (PEPCK and G6Pase), ketogenesis (PPARα, CPT-1a and HMGCS2) and the protein expression of nutrient-sensing signaling molecules (AMPK, mTOR and SIRT1) were determined by RT-qPCR and western blotting, respectively.

Results

Fasting significantly decreased the body weight, which was totally recovered to baseline after 3 days of refeeding. A 4-day fast triggered an energy metabolic substrate shift from glucose to ketones and caused serum hormone changes and changes in the protein expression levels of nutrient-sensing signaling molecules. Glycogenolysis served as the primary fuel source during the first 24 h of fasting, while gluconeogenesis supplied the most glucose thereafter. Serum FFA concentrations increased significantly with 48 h of fasting. Serum FFAs partly caused high serum β-hydroxybutyrate levels, which became an important energy source with the prolongation of the fasting duration. One day of refeeding quickly reversed the energy substrate switch. Nutrient-sensing signaling molecules (AMPK and SIRT1 but not mTOR signaling) were highly expressed at the beginning of fasting (in the first 4 h). Serum insulin and leptin decreased with fasting initiation, and serum glucagon increased, but adiponectin and FGF21 showed no significant changes. Herein, we depicted in detail the timing of the metabolic response and adaptation of the liver to a 4-day water-only fast and subsequent refeeding in rats, which provides helpful support for the design of safe prolonged and intermittent fasting regimens.

The role of food odor in invertebrate foraging

Foraging for food is an integral part of animal survival. In small insects and invertebrates, multisensory information and optimized locomotion strategies are used to effectively forage in patchy and complex environments. Here, the importance of olfactory cues for effective invertebrate foraging is discussed in detail. We review how odors are used by foragers to move toward a likely food source and the recent models that describe this sensory-driven behavior. We argue that smell serves a second function by priming an organism for the efficient exploitation of food. By appraising food odors, invertebrates can establish preferences and better adapt to their ecological niches, thereby promoting survival. The smell of food pre-prepares the gastrointestinal system and primes feeding motor programs for more effective ingestion as well. Optimizing resource utilization affects longevity and reproduction as a result, leading to drastic changes in survival. We propose that models of foraging behavior should include odor priming, and illustrate this with a simple toy model based on the marginal value theorem. Lastly, we discuss the novel techniques and assays in invertebrate research that could investigate the interactions between odor sensing and food intake. Overall, the sense of smell is indispensable for efficient foraging and influences not only locomotion, but also organismal physiology, which should be reflected in behavioral modeling.

Cellular activity in insular cortex across seconds to hours: Sensations and predictions of bodily states

Our wellness relies on continuous interactions between our brain and body: different organs relay their current state to the brain and are regulated, in turn, by descending visceromotor commands from our brain and by actions such as eating, drinking, thermotaxis, and predator escape. Human neuroimaging and theoretical studies suggest a key role for predictive processing by insular cortex in guiding these efforts to maintain bodily homeostasis. Here, we review recent studies recording and manipulating cellular activity in rodent insular cortex at timescales from seconds to hours. We argue that consideration of these findings in the context of predictive processing of future bodily states may reconcile several apparent discrepancies and offer a unifying, heuristic model for guiding future work.

Transcriptome analysis reveals disruption of circadian rhythms in late gestation dairy cows may increase risk for fatty liver and reduced mammary remodeling

Circadian disruption increased insulin resistance and decreased mammary development in late gestation, nonlactating (dry) cows. The objective was to measure the effect of circadian disruption on transcriptomes of the liver and mammary gland. At 35 days before expected calving (BEC), multiparous dry cows were assigned to either control (CON) or phase-shifted treatments (PS). CON was exposed to 16-h light and 8-h dark. PS was exposed to 16-h light to 8-h dark, but phase of the light-dark cycle was shifted 6 h every 3 days. On day 21 BEC, liver and mammary were biopsied. RNA was isolated (n = 6 CON, n = 6 PS per tissue), and libraries were prepared and sequenced using paired-end reads. Reads mapping to bovine genome averaged 27 ± 2 million and aligned to 14,222 protein-coding genes in liver and 15,480 in mammary analysis. In the liver, 834 genes, and in the mammary gland, 862 genes were different (nominal P < 0.05) between PS and CON. In the liver, genes upregulated in PS functioned in cholesterol biosynthesis, endoplasmic reticulum stress, wound healing, and inflammation. Genes downregulated in liver function in cholesterol efflux. In the mammary gland, genes upregulated functioned in mRNA processing and transcription and downregulated genes encoded extracellular matrix proteins and proteases, cathepsins and lysosomal proteases, lipid transporters, and regulated oxidative phosphorylation. Increased cholesterol synthesis and decreased efflux suggest that circadian disruption potentially increases the risk of fatty liver in cows. Decreased remodeling and lipid transport in mammary may decrease milk production capacity during lactation.

Oxytocinergic cells of the posterior hypothalamic paraventricular nucleus participate in the food entrained clock

The mechanisms underlying food anticipatory activity are still poorly understood. Here we explored the role of oxytocin (OT) and the protein c-Fos in the supraoptic nucleus (SON), medial (PVNm) and posterior (PVNp) regions of the paraventricular hypothalamic nucleus. Adult rats were assigned to one of four groups: scheduled restricted feeding (RF), ad libitum (AL), fasting after restricted feeding (RF-F), to explore the possible persistence of oscillations, or ad libitum fasted (AL-F). In the SON and in the PVNm, OT cells were c-Fos positive after food intake; in contrast, OT cells in the PVNp showed c-Fos activation in anticipation to food access, which persisted in RF-F subjects. We conclude that OT and non-OT cells of the SON and PVNm may play a role as recipients of the entraining signal provided by food intake, whereas those of the PVNp which contain motor preautonomic cells that project to peripheral organs, may be involved in the hormonal and metabolic anticipatory changes in preparation for food presentation and thus, may be part of a link between central and peripheral oscillators. In addition, due to their persistent activation they may participate in the neuronal network for the clock mechanism that leads to food entrainment.

Digging behavior discrimination test to probe burrowing and exploratory digging in male and female mice

Digging behavior is often used to test motor function and repetitive behaviors in mice. Different digging paradigms have been developed for behaviors related to anxiety and compulsion in mouse lines generated to recapitulate genetic mutations leading to psychiatric and neurological disorders. However, the interpretation of these tests has been confounded by the difficulty of determining the motivation behind digging in mice. Digging is a naturalistic mouse behavior that can be focused toward different goals, that is foraging for food, burrowing for shelter, burying objects, or even for recreation as has been shown for dogs, ferrets, and human children. However, the interpretation of results from current testing protocols assumes the motivation behind the behavior often concluding that increased digging is a repetitive or compulsive behavior. We asked whether providing a choice between different types of digging activities would increase sensitivity to assess digging motivation. Here, we present a test to distinguish between burrowing and exploratory digging in mice. We found that mice prefer burrowing when the option is available. When food restriction was used to promote a switch from burrowing to exploration, males readily switched from burrowing to digging outside, while females did not. In addition, when we tested a model of intellectual disability and autism spectrum disorder that had shown inconsistent results in the marble burying test, the Cc2d1a conditional knockout mouse, we found greatly reduced burrowing only in males. Our findings indicate that digging is a nuanced motivated behavior and suggest that male and female rodents may perform it differently.

Food Entrainment, Arousal, and Motivation in the Neonatal Rabbit Pup

In the newborn rabbit, the light entrainable circadian system is immature and once a day nursing provides the primary timing cue for entrainment. In advance of the mother's arrival, pups display food anticipatory activity (FAA), and metabolic and physiological parameters are synchronized to this daily event. Central structures in the brain are also entrained as indicated by expression of Fos and Per1 proteins, GFAP, a glial marker, and cytochrome oxidase activity. Under fasting conditions, several of these rhythmic parameters persist in the periphery and brain, including rhythms in the olfactory bulb (OB). Here we provide an overview of these physiological and neurobiological changes and focus on three issues, just beginning to be examined in the rabbit. First, we review evidence supporting roles for the organum vasculosum of lamina terminalis (OVLT) and median preoptic nucleus (MnPO) in homeostasis of fluid ingestion and the neural basis of arousal, the latter which also includes the role of the orexigenic system. Second, since FAA in association with the daily visit of the mother is an example of conditioned learning, we review evidence for changes in the corticolimbic system and identified nuclei in the amygdala and extended amygdala as part of the neural substrate responsible for FAA. Third, we review recent evidence supporting the role of oxytocinergic cells of the paraventricular hypothalamic nucleus (PVN) as a link to the autonomic system that underlies physiological events, which occur in preparation for the upcoming next daily meal. We conclude that the rabbit model has contributed to an overall understanding of food entrainment.

Oxytocinergic Cells of the Hypothalamic Paraventricular Nucleus Are Involved in Food Entrainment

When food is presented at a specific time of day subjects develop intense locomotor behavior before food presentation, termed food anticipatory activity (FAA). Metabolic and hormonal parameters, as well as neural structures also shift their rhythm according to mealtime. Food-entrained activity rhythms are thought to be driven by a distributed system of central and peripheral oscillators sensitive to food cues, but it is not well understood how they are organized for the expression of FAA. The hormone Oxytocin plays an important role in food intake, satiety and homeostatic glucose metabolism and although it is recognized that food is the main cue for food entrainment this hormone has not been implicated in FAA. Here we investigated the activity of oxytocinergic (OTergic) cells of the hypothalamus in relation to the timing of feeding in rabbit pups, a natural model of food entrainment. We found that OTergic cells of the supraoptic nucleus and the main body of the paraventricular nucleus (PVN) are activated after feeding which suggests that OT may be an entraining signal for food synchronization. Moreover, a detailed analysis of the PVN revealed that OTergic cells of the caudal PVN and a subpopulation in the dorsal part of the main body of this nucleus shows activation before the time of food but not 12 h later. Moreover this pattern persists in fasted subjects at the time of the previous scheduled time of nursing. The fact that those OTergic cells of the dorsal and caudal part of the PVN contain preautonomic cells that project to the adrenal, pancreas and liver perhaps may be related to the physiological changes in preparation for food ingestion, and synchronization of peripheral oscillators, which remains to be determined; perhaps they play a main role in the central oscillatory mechanism of FAA as their activity persists in fasted subjects at the time of the next feeding time.

Exercise training in ad libitum and food-restricted old rats: effects on metabolic and physiological parameters

Aging is accompanied by a decline in the healthy function of multiple organs, leading to increased incidence and mortality from diseases such as cancer and inflammatory, cardiovascular and neurodegenerative diseases. Dietary restriction is the most effective experimental intervention known to consistently slow the aging process and with positive effects on health span in different organisms, from invertebrates to mammals. Age is also associated with progressive decline in physical activity levels in a wide range of animal species: therefore, regular physical exercise could represent a safe intervention to antagonize aging. In this research we explore the effects of exercise training initiated in late middle aged rats fed with different lifelong dietary regimens: one group was fed ad libitum and the second group was subjected to every-other-day fasting. These two groups might represent examples of "normal" aging and "successful" aging. The study shows the effects of exercise and food restriction and their interaction on plasma levels of total antioxidant capacity, lactate, amino acids, and on products of protein oxidation in soleus and tibialis anterior muscles. In addition, we evaluated body composition measurement by bioelectrical impedance analysis and muscle strength by grasping test. Results show that late-onset exercise training has the potential to improve some metabolic and physiological parameters in rats with the same "chronological age" but different "biological age", without negative effects, and highlight the relevance of a personalised and selected exercise protocol, since the responsiveness to exercise may depend on the individual's "biological age".

NCB5OR Deficiency in the Cerebellum and Midbrain Leads to Dehydration and Alterations in Thirst Response, Fasted Feeding Behavior, and Voluntary Exercise in Mice

Cytosolic NADH-cytochrome-b5-oxidoreductase (NCB5OR) is ubiquitously expressed in animal tissues. We have previously reported that global ablation of NCB5OR in mice results in early-onset lean diabetes with decreased serum leptin levels and increased metabolic and feeding activities. The conditional deletion of NCB5OR in the mouse cerebellum and midbrain (conditional knock out, CKO mice) results in local iron dyshomeostasis and altered locomotor activity. It has been established that lesion to or removal of the cerebellum leads to changes in nutrient organization, visceral response, feeding behavior, and body weight. This study assessed whether loss of NCB5OR in the cerebellum and midbrain altered feeding or metabolic activity and had an effect on serum T3, cortisol, prolactin, and leptin levels. Metabolic cage data revealed that 16 week old male CKO mice had elevated respiratory quotients and decreased respiratory water expulsion, decreased voluntary exercise, and altered feeding and drinking behavior compared to wild-type littermate controls. Most notably, male CKO mice displayed higher consumption of food during refeeding after a 48-h fast. Echo MRI revealed normal body composition but decreased total water content and hydration ratios in CKO mice. Increased serum osmolality measurements confirmed the dehydration status of male CKO mice. Serum leptin levels were significantly elevated in male CKO mice while prolactin, T3, and cortisol levels remain unchanged relative to wild-type controls, consistent with elevated transcript levels for leptin receptors (short form) in the male CKO mouse cerebellum. Taken together, these findings suggest altered feeding response post starvation as a result of NCB5OR deficiency in the cerebellum.

Motivational changes that develop in a mouse model of inflammation-induced depression are independent of indoleamine 2,3 dioxygenase

Despite years of research, our understanding of the mechanisms by which inflammation induces depression is still limited. As clinical data points to a strong association between depression and motivational alterations, we sought to (1) characterize the motivational changes that are associated with inflammation in mice, and (2) determine if they depend on inflammation-induced activation of indoleamine 2,3 dioxygenase-1 (IDO1). Lipopolysaccharide (LPS)-treated or spared nerve injured (SNI) wild type (WT) and Ido1^-/- mice underwent behavioral tests of antidepressant activity (e.g., forced swim test) and motivated behavior, including assessment of (1) reward expectancy using a food-related anticipatory activity task, (2) willingness to work for reward using a progressive ratio schedule of food reinforcement, (3) effort allocation using a concurrent choice task, and (4) ability to associate environmental cues with reward using conditioned place preference. LPS- and SNI-induced deficits in behavioral tests of antidepressant activity in WT but not Ido1^-/- mice. Further, LPS decreased food related-anticipatory activity, reduced performance in the progressive ratio task, and shifted effort toward the preferred reward in the concurrent choice task. These effects were observed in both WT and Ido1^-/- mice. Finally, SNI mice developed a conditioned place preference based on relief from pain in an IDO1-independent manner. These findings demonstrate that the motivational effects of inflammation do not require IDO1. Further, they indicate that the motivational component of inflammation-induced depression is mechanistically distinct from that measured by behavioral tests of antidepressant activity.

Time-caloric restriction inhibits the neoplastic transformation of cirrhotic liver in rats treated with diethylnitrosamine

Hepatocellular cancer is the most common type of primary liver cancer. Cirrhosis is the main risk factor that generates this malady. It has been proven that caloric restriction protocols and restricted feeding schedules are protective in experimental carcinogenic models. We tested the influence of a time-caloric restriction protocol (2 h of food access during the daytime for 18 weeks) in an experimental model of cirrhosis-hepatocarcinoma produced by weekly administration of diethylnitrosamine. Our results indicate that time-caloric restriction reduced hepatomegaly and prevented the increase in blood leukocytes promoted by diethylnitrosamine. Strikingly, time-caloric restriction preserved functional and histological characteristics of the liver in fibrotic areas compared to the cirrhotic areas of the Ad Libitum-fed group. Tumoural masses in the restricted group were well differentiated; consider a neoplastic or early stage of HCC. However, time-caloric restriction enhanced collagen deposits. With regard to the cancerous process, food restriction prevented systemic inflammation and an increase in carcinoembryonic antigen, and it favoured the occurrence of diffuse multinodular tumours. Histologically, it prevented hepatocyte inflammation response, the regenerative process, and neoplastic transformation. Time-caloric restriction stimulated circadian synchronization in fibrotic and cancerous liver sections, and it increased BMAL1 clock protein levels. We conclude that time-caloric restriction prevents fibrosis from progressing into cirrhosis, thus avoiding chronic inflammation and regenerative processes. It also prevents, probably through circadian entrainment and caloric restriction, the neoplastic transformation of tumoural lesions induced by diethylnitrosamine.

Daytime restricted feeding modifies the daily regulation of fatty acid β-oxidation and the lipoprotein profile in rats

Daytime restricted feeding (2 h of food access from 12.00 to 14.00 hours for 3 weeks) is an experimental protocol that modifies the relationship between metabolic networks and the circadian molecular clock. The precise anatomical locus that controls the biochemical and physiological adaptations to optimise nutrient use is unknown. We explored the changes in liver oxidative lipid handling, such as β-oxidation and its regulation, as well as adaptations in the lipoprotein profile. It was found that daytime restricted feeding promoted an elevation of circulating ketone bodies before mealtime, an altered hepatic daily rhythmicity of 14CO2 production from radioactive palmitic acid, and an up-regulation of the fatty acid oxidation activators, the α-subunit of AMP-activated protein kinase (AMPK), the deacetylase silent mating type information regulation homolog 1, and the transcriptional factor PPARγ-1α coactivator. An increased localisation of phosphorylated α-subunit of AMPK in the periportal hepatocytes was also observed. Liver hepatic lipase C, important for lipoprotein transformation, showed a change of daily phase with a peak at the time of food access. In serum, there was an increase of LDL, which was responsible for a net elevation of circulating cholesterol. We conclude that our results indicate an enhanced fasting response in the liver during daily synchronisation to food access, which involves altered metabolic and cellular control of fatty acid oxidation as well a significant elevation of serum LDL. These adaptations could be part of the metabolic input that underlies the expression of the food-entrained oscillator.

Restricted feeding modulates the daily variations of liver glutamate dehydrogenase activity, expression, and histological location

Glutamate dehydrogenase is an important enzyme in the hepatic regulation of nitrogen and energy metabolism. It catalyzes one of the most relevant anaplerotic reactions. Although its relevance in liver homeostasis has been widely described, its daily pattern and responsiveness to restricted feeding protocols has not been studied. We explored the daily variations of liver glutamate dehydrogenase transcription, protein, activity, and histochemical and subcellular location in a protocol of daytime food synchronization in rats. Restricted feeding involved food access for 2 h each day for three weeks. Control groups included food ad libitum as well as acute fasting (21 h fasting) and refeeding (22 h fasting followed by 2 h of food access). Glutamate dehydrogenase mRNA, protein, activity, and histological location were measured every 3 h by qPCR, Western blot, spectrophotometry, and immunohistochemistry, respectively, to generate 24-h profiles. Restricted feeding promoted higher levels of mitochondrial glutamate dehydrogenase protein and activity, as well as a loss of 24-h rhythmicity, in comparison to ad libitum conditions. The rhythmicity of glutamate dehydrogenase activity detected in serum was changed. The data demonstrated that daytime restricted feeding enhanced glutamate dehydrogenase protein and activity levels in liver mitochondria, changed the rhythmicity of its mRNA and serum activity, but without effect in its expression in hepatocytes surrounding central and portal veins. These results could be related to the adaptation in nitrogen and energy metabolism that occurs in the liver during restricted feeding and the concomitant expression of the food entrainable oscillator. Impact statement For the first time, we are reporting the changes in daily rhythmicity of glutamate dehydrogenase (GDH) mRNA, protein and activity that occur in the liver during the expression of the food entrained oscillator (FEO). These results are part of the metabolic adaptations that modulate the hepatic timing system when the protocol of daytime restricted feeding is applied. As highlight, it was demonstrated higher GDH protein and activity in the mitochondrial fraction. These results contribute to a better understanding of the influence of the FEO in the energy and nitrogen handling in the liver. They could also be significant in the pathophysiology of hepatic diseases related with circadian abnormalities.

The Synergistic Role of Light-Feeding Phase Relations on Entraining Robust Circadian Rhythms in the Periphery

The feeding and fasting cycles are strong behavioral signals that entrain biological rhythms of the periphery. The feeding rhythms synchronize the activities of the metabolic organs, such as liver, synergistically with the light/dark cycle primarily entraining the suprachiasmatic nucleus. The likely phase misalignment between the feeding rhythms and the light/dark cycles appears to induce circadian disruptions leading to multiple physiological abnormalities motivating the need to investigate the mechanisms behind joint light-feeding circadian entrainment of peripheral tissues. To address this question, we propose a semimechanistic mathematical model describing the circadian dynamics of peripheral clock genes in human hepatocyte under the control of metabolic and light rhythmic signals. The model takes the synergistically acting light/dark cycles and feeding rhythms as inputs and incorporates the activity of sirtuin 1, a cellular energy sensor and a metabolic enzyme activated by nicotinamide adenine dinucleotide. The clock gene dynamics was simulated under various light-feeding phase relations and intensities, to explore the feeding entrainment mechanism as well as the convolution of light and feeding signals in the periphery. Our model predicts that the peripheral clock genes in hepatocyte can be completely entrained to the feeding rhythms, independent of the light/dark cycle. Furthermore, it predicts that light-feeding phase relationship is a critical factor in robust circadian oscillations.

Synchronization by Daytime Restricted Food Access Modulates the Presence and Subcellular Distribution of β-Catenin and Its Phosphorylated Forms in the Rat Liver

β-catenin, the principal effector of the Wnt pathway, is also one of the cadherin cell adhesion molecules; therefore, it fulfills signaling and structural roles in most of the tissues and organs. It has been reported that β-catenin in the liver regulates metabolic responses such as gluconeogenesis and histological changes in response to obesity-promoting diets. The function and cellular location of β-catenin is finely modulated by coordinated sequences of phosphorylation-dephosphorylation events. In this article, we evaluated the levels and cellular localization of liver β-catenin variants, more specifically β-catenin phosphorylated in serine 33 (this phosphorylation provides recognizing sites for β-TrCP, which results in ubiquitination and posterior proteasomal degradation of β-catenin) and β-catenin phosphorylated in serine 675 (phosphorylation that enhances signaling and transcriptional activity of β-catenin through recruitment of different transcriptional coactivators). β-catenin phosphorylated in serine 33 in the nucleus shows day-night fluctuations in their expression level in the Ad Libitum group. In addition, we used a daytime restricted feeding (DRF) protocol to show that the above effects are sensitive to food access-dependent circadian synchronization. We found through western blot and immunohistochemical analyses that DRF protocol promoted (1) higher total β-catenins levels mainly associated with the plasma membrane, (2) reduced the presence of cytoplasmic β-catenin phosphorylated in serine 33, (3) an increase in nuclear β-catenin phosphorylated in serine 675, (4) differential co-localization of total β-catenins/β-catenin phosphorylated in serine 33 and total β-catenins/β-catenin phosphorylated in serine 675 at different temporal points along day and in fasting and refeeding conditions, and (5) differential liver zonation of β-catenin variants studied along hepatic acinus. In conclusion, the present data comprehensively characterize the effect food synchronization has on the presence, subcellular distribution, and liver zonation of β-catenin variants. These results are relevant to understand the set of metabolic and structural liver adaptations that are associated with the expression of the food entrained oscillator (FEO).

Altered energy intake and the amplitude of the body temperature rhythm are associated with changes in phase, but not amplitude, of clock gene expression in the rat suprachiasmatic nucleus in vivo

Circadian rhythms in mammals are driven by a central clock in the suprachiasmatic nucleus (SCN). In vitro, temperature cycles within the physiological range can act as potent entraining cues for biological clocks. We altered the body temperature (Tc) rhythm in rats by manipulating energy intake (EI) to determine whether EI-induced changes in Tc oscillations are associated with changes in SCN clock gene rhythms in vivo. Male Wistar rats (n = 16 per diet) were maintained on either an ad libitum diet (CON), a high energy cafeteria diet (CAF), or a calorie restricted diet (CR), and Tc was recorded every 30 min for 6-7 weeks. SCN tissue was harvested from rats at zeitgeber time (ZT) 0, ZT6, ZT12, or ZT18. Expression of the clock genes Bmal1, Per2, Cry1, and Rev-erbα, the heat shock transcription factor Hsf1, and the heat shock protein Hsp90aa1, were determined using qPCR. The circadian profile of gene expression for each gene was characterized using cosinor analysis. Compared to the CON rats, the amplitude of Tc was decreased in CAF rats by 0.1 °C (p < 0.001), and increased in CR rats by 0.3 °C (p < 0.001). The amplitude of Hsp90aa1 expression was lowest in CAF rats and highest in CR rats (p = 0.045), but the amplitude of all of the clock genes and Hsf1 were unaffected by diet (p > 0.25). Compared to CON, phase advances of the Tc, Bmal1, and Per2 rhythms were observed with CR feeding (p < 0.05), but CAF feeding elicited no significant changes in phase. The present results indicate that in vivo, the SCN is largely resistant to entrainment by EI-induced changes in the Tc rhythm, although some phase entrainment may occur.

Effect of daytime-restricted feeding in the daily variations of liver metabolism and blood transport of serotonin in rat

The biogenic amine serotonin is a signaling molecule in the gastrointestinal tract, platelets, and nervous tissue. In nervous system, serotonin and its metabolites are under the control of the circadian timing system, but it is not known if daily variations of serotonin exist in the liver. To explore this possibility, we tested if the rhythmic pattern of serotonin metabolism was regulated by daytime restricted feeding (DRF) which is a protocol associated to the expression of the food entrained oscillator (FEO). The DRF involved food access for 2 h each day for 3 weeks. Control groups included food ad libitum (AL) as well as acute fasting and refeeding. Serotonin-related metabolites were measured by high pressure liquid chromatography, the anabolic and catabolic enzymes were evaluated by western blot, qPCR, and immunohistochemistry to generate 24-h profiles. The results showed in the AL group, liver serotonin, tryptophan hydroxylase-1 activity, and protein abundance as well as serotonin in plasma and serum were rhythmic and coordinated. The DRF protocol disrupted this coordinated response and damped the rhythmic profile of these parameters. We demonstrated the daily synthesis and the degradation of serotonin as well as its transport in blood. This rhythm could influence the physiological role played by serotonin in peripheral organs. DRF caused an uncoordinated response in the liver and blood serotonin rhythm. This modification could be a part of the physiology of the FEO.

Redox regulation and pro-oxidant reactions in the physiology of circadian systems

Rhythms of approximately 24 h are pervasive in most organisms and are known as circadian. There is a molecular circadian clock in each cell sustained by a feedback system of interconnected "clock" genes and transcription factors. In mammals, the timing system is formed by a central pacemaker, the suprachiasmatic nucleus, in coordination with a collection of peripheral oscillators. Recently, an extensive interconnection has been recognized between the molecular circadian clock and the set of biochemical pathways that underlie the bioenergetics of the cell. A principle regulator of metabolic networks is the flow of electrons between electron donors and acceptors. The concomitant reduction and oxidation (redox) reactions directly influence the balance between anabolic and catabolic processes. This review summarizes and discusses recent findings concerning the mutual and dynamic interactions between the molecular circadian clock, redox reactions, and redox signaling. The scope includes the regulatory role played by redox coenzymes (NAD(P)+/NAD(P)H, GSH/GSSG), reactive oxygen species (superoxide anion, hydrogen peroxide), antioxidants (melatonin), and physiological events that modulate the redox state (feeding condition, circadian rhythms) in determining the timing capacity of the molecular circadian clock. In addition, we discuss a purely metabolic circadian clock, which is based on the redox enzymes known as peroxiredoxins and is present in mammalian red blood cells and in other biological systems. Both the timing system and the metabolic network are key to a better understanding of widespread pathological conditions such as the metabolic syndrome, obesity, and diabetes.

Does Circadian Disruption Play a Role in the Metabolic-Hormonal Link to Delayed Lactogenesis II?

Breastfeeding improves maternal and child health. The American Academy of Pediatrics recommends exclusive breastfeeding for 6 months, with continued breastfeeding for at least 1 year. However, in the US, only 18.8% of infants are exclusively breastfed until 6 months of age. For mothers who initiate breastfeeding, the early post-partum period sets the stage for sustained breastfeeding. Mothers who experience breastfeeding problems in the early post-partum period are more likely to discontinue breastfeeding within 2 weeks. A major risk factor for shorter breastfeeding duration is delayed lactogenesis II (DLII; i.e., onset of milk "coming in" more than 72 h post-partum). Recent studies report a metabolic-hormonal link to DLII. This is not surprising because around the time of birth the mother's entire metabolism changes to direct nutrients to mammary glands. Circadian and metabolic systems are closely linked, and our rodent studies suggest circadian clocks coordinate hormonal and metabolic changes to support lactation. Molecular and environmental disruption of the circadian system decreases a dam's ability to initiate lactation and negatively impacts milk production. Circadian and metabolic systems evolved to be functional and adaptive when lifestyles and environmental exposures were quite different from modern times. We now have artificial lights, longer work days, and increases in shift work. Disruption in the circadian system due to shift work, jet-lag, sleep disorders, and other modern life style choices are associated with metabolic disorders, obesity, and impaired reproduction. We hypothesize that DLII is related to disruption of the mother's circadian system. Here, we review literature that supports this hypothesis, and describe interventions that may help to increase breastfeeding success.

Molecular and biochemical modifications of liver glutamine synthetase elicited by daytime restricted feeding

BACKGROUND & AIMS

The circadian clock system in the liver plays important roles in regulating metabolism and energy homeostasis. Restricted feeding schedules (RFS) become an entraining stimulus that promotes adaptations that form part of an alternative circadian clock known as the food entrained oscillator (FEO). The aim of this study was to evaluate the daily variations of glutamine synthetase (GS) in liver under a daytime RFS.

METHODS

Hepatic GS properties were analysed at 3-h intervals over a 24-h period in adult male Wistar rats maintained in a 12:12 h light–dark cycle. RFS group: food access for 2-h in light phase, during 3 weeks. AL group: feeding ad libitum. Fa group: acute fast (21 h). Fa–Re group: acute fast followed by refed 2 h.mRNA expression was measured by RT-qPCR, protein presence by Western-blot and immunohistochemistry, enzyme activity by a spectrophotometric assay, and glutamine by high pressure liquid chromatography.

RESULTS AND CONCLUSIONS

Restricted feeding schedule induced circadian rhythmicity inmRNA levels of GS and the loss of the rhythmic pattern in mitochondrial GS activity. GS activity in liver homogenates displayed a robust rhythmic pattern in AL that was not modified by RFS. The presence of GS and its zonal distribution did not show rhythmic pattern in both groups. However, acute Fa and Fa–Re diminished GS protein and activity in liver homogenates. Hepatic glutamine concentrations showed a 24-h rhythmic pattern in both groups, in an antiphasic pattern. In conclusion, daytime RFS influences the liver GS system at different levels, that could be part of rheostatic adaptations associated to the FEO, and highlight the plasticity of this system.

Local receptors as novel regulators for peripheral clock expression

Mammalian circadian control is determined by a central clock in the brain suprachiasmatic nucleus (SCN) and synchronized peripheral clocks in other tissues. Increasing evidence suggests that SCN-independent regulation of peripheral clocks also occurs. We examined how activation of excitatory receptors influences the clock protein PERIOD 2 (PER2) in a contractile organ, the urinary bladder. PERIOD2::LUCIFERASE-knock-in mice were used to report real-time PER2 circadian dynamics in the bladder tissue. Rhythmic PER2 activities occurred in the bladder wall with a cycle of ∼24 h and peak at ∼12 h. Activation of the muscarinic and purinergic receptors by agonists shifted the peak to an earlier time (7.2±2.0 and 7.2±0.9 h, respectively). PER2 expression was also sensitive to mechanical stimulation. Aging significantly dampened PER2 expression and its response to the agonists. Finally, muscarinic agonist-induced smooth muscle contraction also exhibited circadian rhythm. These data identified novel regulators, endogenous receptors, in determining local clock activity, in addition to mediating the central control. Furthermore, the local clock appears to reciprocally align receptor activity to circadian rhythm for muscle contraction. The interaction between receptors and peripheral clock represents an important mechanism for maintaining physiological functions and its dysregulation may contribute to age-related organ disorders.—Wu, C., Sui, G., Archer, S. N., Sassone-Corsi, P., Aitken, K., Bagli, D., Chen, Y. Local receptors as novel regulators for peripheral clock expression.

Daily patterns and adaptation of the ghrelin, growth hormone and insulin-like growth factor-1 system under daytime food synchronisation in rats

Daytime restricted feeding promotes the re-alignment of the food entrained oscillator (FEO). Endocrine cues which secretion is regulated by the transition of fasting and feeding cycles converge in the FEO. The present study aimed to investigate the ghrelin, growth hormone (GH) and insulin-like growth factor (IGF)-1 system because their release depends on rhythmic and nutritional factors, and the output from the system influences feeding and biochemical status. In a daily sampling approach, rats that were fed ad lib. were compared with rats on a reversed (daytime) and restricted feeding schedule by 3 weeks (dRF; food access for 2 h), also assessing the effect of acute fasting and refeeding. We undertook measurements of clock protein BMAL1 and performed somatometry of peripheral organs and determined the concentration of total, acylated and unacylated ghrelin, GH and IGF-1 in both serum and in its main synthesising organs. During dRF, BMAL1 expression was synchronised to mealtime in hypophysis and liver; rats exhibited acute hyperphagia, stomach distension with a slow emptying, a phase shift in liver mass towards the dark period and decrease in mass perigonadal white adipose tissue. Total ghrelin secretion during the 24-h period increased in the dRF group as a result of elevation of the unacylated form. By contrast, GH and IGF-1 serum concentration fell, with a modification of GH daily pattern after mealtime. In the dRF group, ghrelin content in the stomach and pituitary GH content decreased, whereas hepatic IGF-1 remained equal. The daily patterns and synthesis of these hormones had a rheostatic adaptation. The endocrine adaptive response elicited suggests that it may be associated with the regulation of metabolic, behavioural and physiological processes during the paradigm of daytime restricted feeding and associated FEO activity.

Synchronization by food access modifies the daily variations in expression and activity of liver GABA transaminase

Daytime restricted feeding (DRF) is an experimental protocol that influences the circadian timing system and underlies the expression of a biological clock known as the food entrained oscillator (FEO). Liver is the organ that reacts most rapidly to food restriction by adjusting the functional relationship between the molecular circadian clock and the metabolic networks. γ-Aminobutyric acid (GABA) is a signaling molecule in the liver, and able to modulate the cell cycle and apoptosis. This study was aimed at characterizing the expression and activity of the mostly mitochondrial enzyme GABA transaminase (GABA-T) during DRF/FEO expression. We found that DRF promotes a sustained increase of GABA-T in the liver homogenate and mitochondrial fraction throughout the entire day-night cycle. The higher amount of GABA-T promoted by DRF was not associated to changes in GABA-T mRNA or GABA-T activity. The GABA-T activity in the mitochondrial fraction even tended to decrease during the light period. We concluded that DRF influences the daily variations of GABA-T mRNA levels, stability, and catalytic activity of GABA-T. These data suggest that the liver GABAergic system responds to a metabolic challenge such as DRF and the concomitant appearance of the FEO.

Effect of restricted feeding on nocturnality and daily leptin rhythms in OVLT in aged male Wistar rats

Circadian system has direct relevance to the problems of modern lifestyle, shift workers, jet lag etc. To understand non-photic regulation of biological clock, the effects of restricted feeding (RF) on locomotor activity and daily leptin immunoreactivity (ir) rhythms in three age groups [3, 12 and 24 months (m)] of male Wistar rats maintained in light:dark (LD) 12:12 h conditions were studied. Leptin-ir was examined in the suprachiasmatic nucleus (SCN), the medial preoptic area (MPOA) and organum vasculosum of the lamina terminalis (OVLT). Reversal of feeding time due to restricted food availability during daytime resulted in switching of the animals from nocturnality to diurnality with significant increase in day time activity and decrease in night time activity. The RF resulted in % diurnality of approximately 32, 29 and 73 from % nocturnality of 82, 92 and 89 in control rats of 3, 12 and 24 m age, respectively. The increase in such switching from nocturnality to diurnality with restricted feeding was found to be robust in 24 m rats. The OVLT region showed daily leptin-ir rhythms with leptin-ir maximum at ZT-0 in all the three age groups. However leptin-ir levels were minimum at ZT-12 in 3 and 12 m though at ZT-18 in 24 m. In addition the mean leptin-ir levels decreased with increase in food intake and body weight significantly in RF aged rats. Thus we report here differential effects of food entrained regulation in switching nocturnality to diurnality and daily leptin-ir rhythms in OVLT in aged rats.

Circadian adaptations to meal timing: neuroendocrine mechanisms

Circadian rhythms of behavior and physiology are generated by central and peripheral circadian oscillators entrained by periodic environmental or physiological stimuli. A master circadian pacemaker in the hypothalamic suprachiasmatic nucleus (SCN) is directly entrained by daily light-dark (LD) cycles, and coordinates the timing of other oscillators by direct and indirect neural, hormonal and behavioral outputs. The daily rhythm of food intake provides stimuli that entrain most peripheral and central oscillators, some of which can drive a daily rhythm of food anticipatory activity if food is restricted to one daily mealtime. The location of food-entrainable oscillators (FEOs) that drive food anticipatory rhythms, and the food-related stimuli that entrain these oscillators, remain to be clarified. Here, we critically examine the role of peripheral metabolic hormones as potential internal entrainment stimuli or outputs for FEOs controlling food anticipatory rhythms in rats and mice. Hormones for which data are available include corticosterone, ghrelin, leptin, insulin, glucagon, and glucagon-like peptide 1. All of these hormones exhibit daily rhythms of synthesis and secretion that are synchronized by meal timing. There is some evidence that ghrelin and leptin modulate the expression of food anticipatory rhythms, but none of the hormones examined so far are necessary for entrainment. Ghrelin and leptin likely modulate food-entrained rhythms by actions in hypothalamic circuits utilizing melanocortin and orexin signaling, although again food-entrained behavioral rhythms can persist in lesion and gene knockout models in which these systems are disabled. Actions of these hormones on circadian oscillators in central reward circuits remain to be evaluated. Food-entrained activity rhythms are likely mediated by a distributed system of circadian oscillators sensitive to multiple feeding related inputs. Metabolic hormones appear to play a modulatory role within this system.

Diurnal and nutritional adjustments of intracellular Ca2+ release channels and Ca2+ ATPases associated with restricted feeding schedules in the rat liver

Background

Intracellular calcium is a biochemical messenger that regulates part of the metabolic adaptations in the daily fed-fast cycle. The aim of this study was to characterize the 24-h variations of the liver ryanodine and IP₃ receptors (RyR and IP₃R) as well as of the endoplasmic-reticulum and plasma-membrane Ca²⁺-ATPases (SERCA and PMCA) in daytime restricted feeding protocol.

Methods

A biochemical and immunohistochemical approach was implemented in this study: specific ligand-binding for RyR and IP₃R, enzymatic activity (SERCA and PMCA), and protein levels and zonational hepatic-distribution were determined by immunoblot and immunohistochemistry respectively under conditions of fasting, feeding, and temporal food-restriction.

Results

Binding assays and immunoblots for IP₃R1 and 2 showed a peak at the light/dark transition in the ad-libitum (AL) group, whereas in the restricted-feeding (RF) group the peak shifted towards the food-access time. In the case of RyR binding experiments, both AL and RF groups showed a modest elevation during the dark period, with the RF rats exhibiting increased binding in response to feeding. The AL group showed 24-h rhythmicity in SERCA level; in contrast, RF group showed a pronounced amplitude elevation and a peak phase-shift during the light-period in SERCA level and activity. The activity of PMCA was constant along day in both groups; PMCA1 levels showed a 24-h rhythmicity in the RF rats (with a peak in the light period), meanwhile PMCA4 protein levels showed rhythmicity in both groups. The fasted condition promoted an increase in IP₃R binding and protein level; re-feeding increased the amount of RyR; neither the activity nor expression of SERCA and PMCA protein was affected by fasting–re-feeding conditions. Histochemical experiments showed that the distribution of the Ca²⁺-handling proteins, between periportal and pericentral zones of the liver, varied with the time of day and the feeding protocol.

Conclusions

Our findings show that RF influences mainly the phase and amplitude of hepatic IP₃R and SERCA rhythms as well as discrete zonational distribution for RyR, IP₃Rs, SERCA, and PMCA within the liver acinus, suggesting that intracellular calcium dynamics could be part of the rheostatic adaptation of the liver due to diurnal meal entrainment/food entrained oscillator expression.

Effects of time of feeding on psychostimulant reward, conditioned place preference, metabolic hormone levels, and nucleus accumbens biochemical measures in food-restricted rats

RATIONALE

Chronic food restriction (FR) increases rewarding effects of abused drugs and persistence of a cocaine-conditioned place preference (CPP). When there is a single daily meal, circadian rhythms are correspondingly entrained, and pre- and postprandial periods are accompanied by different circulating levels of metabolic hormones that modulate brain dopamine function.

OBJECTIVES

The present study assessed whether rewarding effects of d-amphetamine, cocaine, and persistence of cocaine-CPP differ between FR subjects tested in the pre- and postprandial periods.

MATERIALS AND METHODS

Rats were stereotaxically implanted with intracerebral microinjection cannulae and an electrode in lateral hypothalamus. Rewarding effects of d-amphetamine and cocaine were assessed using electrical self-stimulation in rats tested 1-4 or 18-21 h after the daily meal. Nonimplanted subjects acquired a cocaine-CPP while ad libitum fed and then were switched to FR and tested for CPP at these same times.

RESULTS

Rewarding effects of intranucleus accumbens (NAc) d-amphetamine, intraventricular cocaine, and persistence of cocaine-CPP did not differ between rats tested 18-21 h food-deprived, when ghrelin and insulin levels were at peak and nadir, respectively, and those tested 1-4 h after feeding. Rats that expressed a persistent CPP had elevated levels of p-ERK1, GluA1, and p-Ser845-GluA1 in NAc core, and the latter correlated with CPP expression.

CONCLUSIONS

Psychostimulant reward and persistence of CPP in FR rats are unaffected by time of testing relative to the daily meal. Further, NAc biochemical responses previously associated with enhanced drug responsiveness in FR rats are associated with persistent CPP expression.

The output signal of Purkinje cells of the cerebellum and circadian rhythmicity

Measurement of clock gene expression has recently provided evidence that the cerebellum, like the master clock in the SCN, contains a circadian oscillator. The cerebellar oscillator is involved in anticipation of mealtime and possibly resides in Purkinje cells. However, the rhythmic gene expression is likely transduced into a circadian cerebellar output signal to exert an effective control of neuronal brain circuits that are responsible for feeding behavior. Using electrophysiological recordings from acute and organotypic cerebellar slices, we tested the hypothesis whether Purkinje cells transmit a circadian modulated signal to their targets in the brain. Extracellular recordings from brain slices revealed the typical discharge pattern previously described in vivo in single cell recordings showing basically a tonic or a trimodal-like firing pattern. However, in acute sagittal cerebellar slices the average spike rate of randomly selected Purkinje cells did not exhibit significant circadian variations, irrespective of their specific firing pattern. Also, frequency and amplitude of spontaneous inhibitory postsynaptic currents and the amplitude of GABA- and glutamate-evoked currents did not vary with circadian time. Long-term recordings using multielectrode arrays (MEA) allowed to monitor neuronal activity at multiple sites in organotypic cerebellar slices for several days to weeks. With this recording technique we observed oscillations of the firing rate of cerebellar neurons, presumably of Purkinje cells, with a period of about 24 hours which were stable for periods up to three days. The daily renewal of culture medium could induce circadian oscillations of the firing rate of Purkinje cells, a feature that is compatible with the behavior of slave oscillators. However, from the present results it appears that the circadian expression of cerebellar clock genes exerts only a weak influence on the electrical output of cerebellar neurons.

Early nocturnal meal skipping alters the peripheral clock and increases lipogenesis in mice

BACKGROUND

In humans, skipping meals, especially breakfast, has been associated with obesity and other related syndromes. Recent studies in rodents suggest that fasting and feeding times are potential factors that affect the peripheral circadian clocks and metabolism. However, the link between fasting and obesity in rodents has yet to be fully demonstrated.

METHOD

We conducted early nocturnal fasting (ENF) from zeitgeber time (ZT) 12 to 18 for 4 consecutive days in C57B6 mice. The first set of experiments was performed under ad libitum conditions, where ENF and free-feeding (FF) control groups were compared. The second set was performed under isocaloric adjustment by restricting the diet to 90% of the basal intake of ENF mice. Calorie-restricted ENF (ENF-CR) mice were then compared with isocaloric controls (IC-control). Body weight, food intake, core body temperature, activity, adiposity, and clock-related gene expression levels in the liver and adipose tissues were investigated. A stable isotopic analysis was also conducted to estimate de novo lipogenesis fluxes.

RESULTS

In the ad libitum condition, the ENF mice ate more during the day, increased their overall daily food intake and gained more weight than FF-control mice. The amplitude of the body core temperature rhythm in ENF mice was also lower than in the FF-controls. Under isocaloric conditions, ENF-CR attenuated the CR-induced body weight loss, compared with the IC-control. ENF-CR also altered the acrophase time of the expression of the clock genes, which is associated with time-shift of genes involved in lipid metabolism and increased lipogenesis, compared with the IC-control.

CONCLUSIONS

ENF in nocturnal mice disturbs the peripheral clock and increases de novo lipid synthesis and results in a predisposition to obesity.

Daytime restricted feeding modifies 24 h rhythmicity and subcellular distribution of liver glucocorticoid receptor and the urea cycle in rat liver

The timing system in mammals is formed by a set of peripheral biological clocks coordinated by a light-entrainable pacemaker located in the suprachiasmatic nucleus. Daytime restricted feeding (DRF) modifies the circadian control and uncouples the light-dependent physiological rhythmicity, food access becoming the principal external time cue. In these conditions, an alternative biological clock is expressed, the food-entrainable oscillator (FEO). Glucocorticoid hormones are an important part of the humoral mechanisms in the daily synchronisation of the metabolic response of peripheral oscillators by the timing system. A peak of circulating corticosterone has been reported before food access in DRF protocols. In the present study we explored in the liver the 24 h variations of: (1) the subcellular distribution of glucocorticoid receptor (GCR), (2) the activities of the corticosterone-forming and NADPH-generating enzymes (11β-hydroxysteroid dehydrogenase type 1 (11β-HSD-1) and hexose-6-phosphate dehydrogenase (H6PDH)), and, (3) parameters related with the urea cycle (circulating urea and activities of carbamoyl phosphate synthetase and ornithine transcarbamylase) elicited by DRF. The results showed that DRF promoted an increase of more than two times of the hepatic GCR, but exclusively in the cytosolic compartment, since the GCR in the nuclear fraction showed a reduction. No changes were observed in the activities of 11β-HSD-1 and H6PDH, but the rhythmicity of all of the urea cycle-related parameters was modified. It is concluded that liver glucocorticoid signalling and the urea cycle are responsive to feeding-restricted schedules and could be part of the FEO.

Disassociation between preprandial gut peptide release and food-anticipatory activity

Animals learn to anticipate a meal as evidenced by increases in premeal activity. This learned response appears to be independent of the nutrient status of an animal because food-anticipatory activity (FAA) can be seen after entrainment by a highly palatable food when rats remain ad libitum on chow. Mealtime feeding not only induces an increase in activity but also appears to entrain the secretion of various peptides prior to a meal including insulin, ghrelin, and glucagon-like peptide-1 (GLP-1). It is not clear whether these meal-anticipatory changes in peptides are causally associated with FAA. To assess whether FAA and preprandial peptide changes co-occur with meal entrainment using different diets, rats were conditioned to receive a 6-h chow meal, 6-h high-fat meal, or 2 h access of chocolate while ad libitum on chow in the middle of the light cycle. FAA was measured for 4 h prior to mealtime. Rats were then killed at 90, 60, and 30 min prior to mealtime and plasma was collected. Although the chocolate-entrained rats showed comparable FAA with the nonchocolate-entrained animals, they did not show anticipatory increases in the ghrelin or GLP-1. All entrainment conditions induced a decrease in insulin and an increase in glucose prior to mealtime. These data suggest that separate mechanisms may underlie the preprandial increases in ghrelin and GLP-1 and changes in FAA, insulin, and glucose.

Artificial feeding synchronizes behavioral, hormonal, metabolic and neural parameters in mother-deprived neonatal rabbit pups

Nursing in the rabbit is under circadian control, and pups have a daily anticipatory behavioral arousal synchronized to this unique event, but it is not known which signal is the main entraining cue. In the present study, we hypothesized that food is the main entraining signal. Using mother-deprived pups, we tested the effects of artificial feeding on the synchronization of locomotor behavior, plasma glucose, corticosterone, c-Fos (FOS) and PERIOD1 (PER1) rhythms in suprachiasmatic, supraoptic, paraventricular and tuberomammillary nuclei. At postnatal day 1, an intragastric tube was placed by gastrostomy. The next day and for the rest of the experiment, pups were fed with a milk formula through the cannula at either 02:00 h or 10:00 h [feeding time = zeitgeber time (ZT)0]. At postnatal days 5-7, pups exhibited behavioral arousal, with a significant increase in locomotor behavior 60 min before feeding. Glucose levels increased after feeding, peaking at ZT4-ZT12 and then declining. Corticosterone levels were highest around the time of feeding, and then decreased to trough concentrations at ZT12-ZT16, increasing again in anticipation of the next feeding bout. In the brain, the suprachiasmatic nucleus had a rhythm of FOS and PER1 that was not significantly affected by the feeding schedule. Conversely, the supraoptic, paraventricular and tuberomammillary nuclei had rhythms of both FOS and PER1 induced by the time of scheduled feeding. We conclude that the nursing rabbit pup is a natural model of food entrainment, as food, in this case milk formula, is a strong synchronizing signal for behavioral, hormonal, metabolic and neural parameters.

Circadian rhythms, the molecular clock, and skeletal muscle

Almost all organisms ranging from single cell bacteria to humans exhibit a variety of behavioral, physiological, and biochemical rhythms. In mammals, circadian rhythms control the timing of many physiological processes over a 24-h period, including sleep-wake cycles, body temperature, feeding, and hormone production. This body of research has led to defined characteristics of circadian rhythms based on period length, phase, and amplitude. Underlying circadian behaviors is a molecular clock mechanism found in most, if not all, cell types including skeletal muscle. The mammalian molecular clock is a complex of multiple oscillating networks that are regulated through transcriptional mechanisms, timed protein turnover, and input from small molecules. At this time, very little is known about circadian aspects of skeletal muscle function/metabolism but some progress has been made on understanding the molecular clock in skeletal muscle. The goal of this chapter is to provide the basic terminology and concepts of circadian rhythms with a more detailed review of the current state of knowledge of the molecular clock, with reference to what is known in skeletal muscle. Research has demonstrated that the molecular clock is active in skeletal muscles and that the muscle-specific transcription factor, MyoD, is a direct target of the molecular clock. Skeletal muscle of clock-compromised mice, Bmal1(-/-) and Clock(Δ19) mice, are weak and exhibit significant disruptions in expression of many genes required for adult muscle structure and metabolism. We suggest that the interaction between the molecular clock, MyoD, and metabolic factors, such as PGC-1, provide a potential system of feedback loops that may be critical for both maintenance and adaptation of skeletal muscle.

Chronic inhibition of endoplasmic reticulum calcium-release channels and calcium-ATPase lengthens the period of hepatic clock gene Per1

Background

The role played by calcium as a regulator of circadian rhythms is not well understood. The effect of the pharmacological inhibition of the ryanodine receptor (RyR), inositol 1,4,5-trisphosphate receptor (IP₃R), and endoplasmic-reticulum Ca²⁺-ATPase (SERCA), as well as the intracellular Ca²⁺-chelator BAPTA-AM was explored on the 24-h rhythmicity of the liver-clock protein PER1 in an experimental model of circadian synchronization by light and restricted-feeding schedules.

Methods

Liver explants from Period1-luciferase (Per1-luc) transgenic rats with either free food access or with a restricted meal schedule were treated for several days with drugs to inhibit the activity of IP₃Rs (2-APB), RyRs (ryanodine), or SERCA (thapsigargin) as well as to suppress intracellular calcium fluctuations (BAPTA-AM). The period of Per1-luc expression was measured during and after drug administration.

Results

Liver explants from rats fed ad libitum showed a lengthened period in response to all the drugs tested. The pharmacological treatments of the explants from meal-entrained rats induced the same pattern, with the exception of the ryanodine treatment which, unexpectedly, did not modify the Per1-luc period. All effects associated with drug application were reversed after washout, indicating that none of the pharmacological treatments was toxic to the liver cultures.

Conclusions

Our data suggest that Ca²⁺ mobilized from internal deposits modulates the molecular circadian clock in the liver of rats entrained by light and by restricted meal access.

Gross energy metabolism in mice under late onset, short term caloric restriction

Late onset, short-term moderate caloric restriction (CR) may have beneficial health effects. A 26% CR regime induced at 14 months of age for 70 days in male C57Bl/6 (ICRFa) mice resulted in a reduction in body mass of 17%. A decrease in daily energy expenditure was associated with decreased body mass in CR mice. There was no difference in total levels of physical activity between the CR and ad libitum (AL) groups; however, activity patterns were different. We developed a Bayesian model to dissect the impact of food anticipation activity (FAA) and feeding on physical activity. FAA was stronger in CR mice and remaining basal activity was higher in AL mice, but CR mice displayed larger diurnal variations as well as a phase shift in their diurnal activity. CR mice displayed lower body temperature, especially late during the dark phase. This was due to lower basal (activity-independent) temperature at all times of the day, coupled to a phase shift in the diurnal rhythm. The correlation between body temperature and physical activity was independent of feeding regimen and light/dark cycles. Reduction of body mass and basal temperature were major compensatory mechanisms to reduced food availability during late-onset, short-term CR.