Food anticipatory activity behavior of mice across a wide range of circadian and non-circadian intervals

AgRP neurons encode circadian feeding time

Food intake follows a predictable daily pattern and synchronizes metabolic rhythms. Neurons expressing agouti-related protein (AgRP) read out physiological energetic state and elicit feeding, but the regulation of these neurons across daily timescales is poorly understood. Using a combination of neuron dynamics measurements and timed optogenetic activation in mice, we show that daily AgRP-neuron activity was not fully consistent with existing models of homeostatic regulation. Instead of operating as a 'deprivation counter', AgRP-neuron activity primarily followed the circadian rest-activity cycle through a process that required an intact suprachiasmatic nucleus and synchronization by light. Imposing novel feeding patterns through time-restricted food access or periodic AgRP-neuron stimulation was sufficient to resynchronize the daily AgRP-neuron activity rhythm and drive anticipatory-like behavior through a process that required DMHPDYN neurons. These results indicate that AgRP neurons integrate time-of-day information of past feeding experience with current metabolic needs to predict circadian feeding time.

Rest phase snacking increases energy resorption and weight gain in male mice

OBJECTIVE

Snacking, i.e., the intake of small amounts of palatable food items, is a common behavior in modern societies, promoting overeating and obesity. Shifting food intake into the daily rest phase disrupts circadian rhythms and is also known to stimulate weight gain. We therefore hypothesized that chronic snacking in the inactive phase may promote body weight gain and that this effect is based on disruption of circadian clocks.

METHODS

Male mice were fed a daily chocolate snack either during their rest or their active phase and body weight development and metabolic parameters were investigated. Snacking experiments were repeated in constant darkness and in clock-deficient mutant mice to examine the role of external and internal time cues in mediating the metabolic effects of snacking.

RESULTS

Chronic snacking in the rest phase increased body weight gain and disrupted metabolic circadian rhythms in energy expenditure, body temperature, and locomotor activity. Additionally, these rest phase snacking mice assimilated more energy during the inactive phase. Body weight remained increased in rest phase snacking wildtype mice in constant darkness as well as in clock-deficient mutant mice under a regular light-dark cycle compared to mice snacking in the active phase. Weight gain effects were abolished in clock-deficient mice in constant darkness.

CONCLUSIONS

Our data suggest that mistimed snacking increases energy resorption and promotes body weight gain. This effect requires a functional circadian clock at least under constant darkness conditions.

Pathway-specific GABAergic inhibition contributes to the gain of resilience against anorexia-like behavior of adolescent female mice

Anorexia nervosa is one of the most debilitating mental illnesses that emerges during adolescence, especially among females. Anorexia nervosa is characterized by severe voluntary food restriction and compulsive exercising, which combine to cause extreme body weight loss. We use activity-based anorexia (ABA), an animal model, to investigate the neurobiological bases of vulnerability to anorexia nervosa. This is a Mini-Review, focused on new ideas that have emerged based on recent findings from the Aoki Lab. Our findings point to the cellular and molecular underpinnings of three ABA phenomena: (1) age-dependence of ABA vulnerability; (2) individual differences in the persistence of ABA vulnerability during adolescence; (3) GABAergic synaptic plasticity in the hippocampus and the prefrontal cortex that contributes to the suppression of the maladaptive anorexia-like behaviors. We also include new data on the contribution to ABA vulnerability by cell type-specific knockdown of a GABA receptor subunit, α4, in dorsal hippocampus. Although the GABA system recurs as a key player in the gain of ABA resilience, the data predict why targeting the GABA system, singularly, may have only limited efficacy in treating anorexia nervosa. This is because boosting the GABAergic system may suppress the maladaptive behavior of over-exercising but could also suppress food consumption. We hypothesize that a sub-anesthetic dose of ketamine may be the magic bullet, since a single injection of this drug to mid-adolescent female mice undergoing ABA induction enhances food consumption and reduces wheel running, thereby reducing body weight loss through plasticity at excitatory synaptic inputs to both excitatory and inhibitory neurons. The same treatment is not as efficacious during late adolescence but multiple dosing of ketamine can suppress ABA vulnerability partially. This caveat underscores the importance of conducting behavioral, synaptic and molecular analyses across multiple time points spanning the developmental stage of adolescence and into adulthood. Since this is a Mini-Review, we recommend additional literature for readers seeking more comprehensive reviews on these subjects.

Studying food entrainment: Models, methods, and musings

The ability to tell time relative to predictable feeding opportunities has a long history of research, going back more than 100 years with behavioral observations of honeybees and rats. Animals that have access to food at a particular time of day exhibit “food anticipatory activity” (FAA), which is a preprandial increase in activity and arousal thought to be driven by food entrained circadian oscillator(s). However, the mechanisms behind adaptation of behavior to timed feeding continue to elude our grasp. Methods used to study circadian entrainment by food vary depending on the model system and the laboratory conducting the experiments. Most studies have relied on rodent model systems due to neuroanatomical tools and genetic tractability, but even among studies of laboratory mice, methods vary considerably. A lack of consistency within the field in experimental design, reporting, and definition of food entrainment, or even FAA, makes it difficult to compare results across studies or even within the same mutant mouse strain, hindering interpretation of replication studies. Here we examine the conditions used to study food as a time cue and make recommendations for study design and reporting.

Multiple entrained oscillator model of food anticipatory circadian rhythms

For many animal species, knowing when to look for food may be as important as knowing where to look. Rats and other species use a feeding-responsive circadian timing mechanism to anticipate, behaviorally and physiologically, a predictable daily feeding opportunity. How this mechanism for anticipating a daily meal accommodates more than one predictable mealtime is unclear. Rats were trained to press a lever for food, and then limited to one or more daily meals at fixed or systematically varying times of day. The rats were able to anticipate up to 4 of 4 daily meals at fixed times of day and two ‘daily’ meals recurring at 24 h and 26 h intervals. When deprived of food, in constant dark, lever pressing recurred for multiple cycles at expected mealtimes, consistent with the periodicity of the prior feeding schedule. Anticipation did not require the suprachiasmatic nucleus circadian pacemaker. The anticipation rhythms could be simulated using a Kuramoto model in which clusters of coupled oscillators entrain to specific mealtimes based on initial phase and intrinsic circadian periodicity. A flexibly coupled system of food-entrainable circadian oscillators endows rats with adaptive plasticity in daily programming of foraging activity.

Creating Detailed Metadata for an R Shiny Analysis of Rodent Behavior Sequence Data Detected Along One Light-Dark Cycle

Automated mouse phenotyping through the high-throughput analysis of home cage behavior has brought hope of a more effective and efficient method for testing rodent models of diseases. Advanced video analysis software is able to derive behavioral sequence data sets from multiple-day recordings. However, no dedicated mechanisms exist for sharing or analyzing these types of data. In this article, we present a free, open-source software actionable through a web browser (an R Shiny application), which performs an analysis of home cage behavioral sequence data, which is designed to spot differences in circadian activity while preventing p-hacking. The software aligns time-series data to the light/dark cycle, and then uses different time windows to produce up to 162 behavior variables per animal. A principal component analysis strategy detected differences between groups. The behavior activity is represented graphically for further explorative analysis. A machine-learning approach was implemented, but it proved ineffective at separating the experimental groups. The software requires spreadsheets that provide information about the experiment (i.e., metadata), thus promoting a data management strategy that leads to FAIR data production. This encourages the publication of some metadata even when the data are kept private. We tested our software by comparing the behavior of female mice in videos recorded twice at 3 and 7 months in a home cage monitoring system. This study demonstrated that combining data management with data analysis leads to a more efficient and effective research process.

Safety assessment of HEA-enriched Cordyceps cicadae mycelia on the central nervous system (CNS), cardiovascular system, and respiratory system in ICR male mice

Cordyceps cicadae, an entomopathogenic fungus, is a source of traditional Chinese medicine in China. Due to the low yield of wild C. cicadae, artificial cultivation approaches will be needed to meet the increasing market demand. Using bioreactor culture can increase mass production and the abundance of the active component, N6-(2-hydroxyethyl)-adenosine (HEA). Here, we describe a safety assessment for a novel mycelium preparation method. Many studies have confirmed the safety of C. cicadae mycelia. However, the acute safety pharmacology of the C. cicadae enriched with the high HEA (3.90 mg/g) compound has not been evaluated. This study evaluated the central nervous system (CNS), cardiovascular system, and respiratory system in ICR male mice via oral gavage administration. For each requested item, two batches of eight mice tested on a vehicle (0.5% carboxymethyl cellulose, CMC) and C. cicadae mycelia (1,000 mg/kg) were performed. The heart rate at 60 min for the vehicle and C. cicadae mycelium treatment was 700.3 ± 55.4 and 603.0 ± 42.3 bpm, respectively (p = .4279). For echocardiographic analysis, the LV mass of the vehicle and drug treatment was 86.7 ± 6.4 and 80.2 ± 7.7, respectively (p = .0933). In the respiratory test, the tidal volume of the vehicle and drug treatments was 0.11 ± 0.01 and 0.14 ± 0.01 at 60 min, respectively (p = .4262). These results demonstrate that the oral administration of HEA-enriched C. cicadae mycelia is safe for the CNS, cardiovascular, and respiratory systems.

Physical activity patterns of free living dogs diagnosed with osteoarthritis

Osteoarthritis (OA) affects about 90% of dogs > 5 yr of age in the United States, resulting in reduced range of motion, difficulty climbing and jumping, reduced physical activity, and lower quality of life. Our objective was to use activity monitors to measure physical activity and identify how activity counts correlate with age, body weight (BW), body condition score (BCS), serum inflammatory markers, veterinarian pain assessment, and owner perception of pain in free-living dogs with OA. The University of Illinois Institutional Animal Care and Use Committee approved the study and owner consent was received prior to experimentation. Fifty-six client-owned dogs (mean age = 7.8 yr; mean BCS = 6.1) with clinical signs and veterinary diagnosis of OA wore HeyRex activity collars continuously over a 49-d period. Blood samples were collected on day 0 and 49, and dog owners completed canine brief pain inventory (CBPI) and Liverpool osteoarthritis in dogs (LOAD) surveys on day 0, 21, 35, and 49. All data were analyzed using SAS 9.3 using repeated measures and R Studio 1.0.136 was used to generate Pearson correlation coefficients between data outcomes. Average activity throughout the study demonstrated greater activity levels on weekends. It also showed that 24-h activity spiked twice daily, once in the morning and another in the afternoon. Serum C-reactive protein concentration was lower (P < 0.01) at day 49 compared to day 0. Survey data indicated lower (P < 0.05) overall pain intensity and severity score on day 21, 35 and 49 compared to day 0. BW was correlated with average activity counts (P = 0.02; r = -0.12) and run activity (P = 0.10; r = -0.24). Weekend average activity counts were correlated with owner pain intensity scores (P = 0.0813; r = -0.2311), but weekday average activity count was not. Age was not correlated with total activity count, sleep activity, or run activity, but it was correlated with scratch (P = 0.03; r = -0.10), alert (P = 0.03; r = -0.13), and walk (P = 0.09; r = -0.23) activities. Total activity counts and activity type (sleep, scratch, alert, walk, and run) were not correlated with pain scored by veterinarians, pain intensity or severity scored by owners, or baseline BCS. Even though the lack of controls and/or information on the individual living conditions of dogs resulted in a high level of variability in this study, our data suggest that the use of activity monitors have the potential to aid in the management of OA and other conditions affecting activity (e.g., allergy; anxiety).

Progressive increase in the complexity and translatability of rodent testing to assess space-radiation induced cognitive impairment

Ground-based rodent models have established that space radiation doses (approximately those that astronauts will be exposed to on a mission to Mars) significantly impair performance in a wide range of cognitive tasks. Over the last 40 years there has been a progressive increase in both the complexity and the translatability (to humans) of the cognitive tasks investigated. This review outlines technical and conceptual advances in space radiation rodent testing approaches, along with the advances in analytical approaches, that will make data from ground based studies more amenable to probabilistic risk analysis. While great progress has been made in determining the impact of space radiation on many advanced cognitive processes, challenges remain that need to be addressed prior to commencing deep space missions. A summary of on-going attempts to address existing knowledge gaps and the critical role that rodent studies will have in establishing the impact of space radiation on even more complex (human) cognitive tasks are presented and discussed.

Automated monitoring of mouse feeding and body weight for continuous health assessment

Routine health assessment of laboratory rodents can be improved using automated home cage monitoring. Continuous, non-stressful, objective assessment of rodents unaware that they are being watched, including during their active dark period, reveals behavioural and physiological changes otherwise invisible to human caretakers. We developed an automated feeder that tracks feed intake, body weight, and physical appearance of individual radio frequency identification-tagged mice in social home cages. Here, we experimentally induce illness via lipopolysaccharide challenge and show that this automated tracking apparatus reveals sickness behaviour (reduced food intake) as early as 2-4 hours after lipopolysaccharide injection, whereas human observers conducting routine health checks fail to detect a significant difference between sick mice and saline-injected controls. Continuous automated monitoring additionally reveals pronounced circadian rhythms in both feed intake and body weight. Automated home cage monitoring is a non-invasive, reliable mode of health surveillance allowing caretakers to more efficiently detect and respond to early signs of illness in laboratory rodent populations.

Flexible clock systems: adjusting the temporal programme

Under natural conditions, many aspects of the abiotic and biotic environment vary with time of day, season or even era, while these conditions are typically kept constant in laboratory settings. The timing information contained within the environment serves as critical timing cues for the internal biological timing system, but how this system drives daily rhythms in behaviour and physiology may also depend on the internal state of the animal. The disparity between timing of these cues in natural and laboratory conditions can result in substantial differences in the scheduling of behaviour and physiology under these conditions. In nature, temporal coordination of biological processes is critical to maximize fitness because they optimize the balance between reproduction, foraging and predation risk. Here we focus on the role of peripheral circadian clocks, and the rhythms that they drive, in enabling adaptive phenotypes. We discuss how reproduction, endocrine activity and metabolism interact with peripheral clocks, and outline the complex phenotypes arising from changes in this system. We conclude that peripheral timing is critical to adaptive plasticity of circadian organization in the field, and that we must abandon standard laboratory conditions to understand the mechanisms that underlie this plasticity which maximizes fitness under natural conditions.This article is part of the themed issue 'Wild clocks: integrating chronobiology and ecology to understand timekeeping in free-living animals'.

α4-GABAA receptors of hippocampal pyramidal neurons are associated with resilience against activity-based anorexia for adolescent female mice but not for males

Activity-based anorexia (ABA) is an animal model of anorexia nervosa, a mental illness with highest mortality and with onset that is most frequently during adolescence. We questioned whether vulnerability of adolescent mice to ABA differs between sexes and whether individual differences in resilience are causally linked to α4βδ-GABAAR expression. C57BL6/J WT and α4-KO adolescent male and female mice underwent ABA induction by combining wheel access with food restriction. ABA vulnerability was measured as the extent of food restriction-evoked hyperactivity on a running wheel and body weight losses. α4βδ-GABAAR levels at plasma membranes of pyramidal cells in dorsal hippocampus were assessed by electron microscopic immunocytochemistry. Temporal patterns and extent of weight loss during ABA induction were similar between sexes. Both sexes also exhibited individual differences in ABA vulnerability. Correlation analyses revealed that, for both sexes, body weight changes precede and thus are likely to drive suppression of wheel running. However, the suppression was during the food-anticipatory hours for males, while for females, suppression was delayed by a day and during food-access hours. Correspondingly, only females adaptively increased food intake. ABA induced up-regulation of α4βδ-GABAARs at plasma membranes of dorsal hippocampal pyramidal cells of females, and especially those females exhibiting resilience. Conversely, α4-KO females exhibited greater food restriction-evoked hyperactivity than WT females. In contrast, ABA males did not up-regulate α4βδ-GABAARs, did not exhibit genotype differences in vulnerability, and exhibited no correlation between plasmalemmal α4βδ-GABAARs and ABA resilience. Thus, food restriction-evoked hyperactivity is driven by anxiety but can be suppressed through upregulation of hippocampal α4βδ-GABAARs for females but not for males. This knowledge of sex-related differences in the underlying mechanisms of resilience to ABA indicates that drugs targeting α4βδ-GABAARs may be helpful for treating stress-induced anxiety and anorexia nervosa of females but not males.

Sex differences in circadian food anticipatory activity are not altered by individual manipulations of sex hormones or sex chromosome copy number in mice

Recent studies in mice have demonstrated a sexual dimorphism in circadian entrainment to scheduled feeding. On a time restricted diet, males tend to develop food anticipatory activity (FAA) sooner than females and with a higher amplitude of activity. The underlying cause of this sex difference remains unknown. One study suggests that sex hormones, both androgens and estrogens, modulate food anticipatory activity in mice. Here we present results suggesting that the sex difference in FAA is unrelated to gonadal sex hormones. While a sex difference between males and females in FAA on a timed, calorie restricted diet was observed there were no differences between intact and gonadectomized mice in the onset or magnitude of FAA. To test other sources of the sex difference in circadian entrainment to scheduled feeding, we used sex chromosome copy number mutants, but there was no difference in FAA when comparing XX, XY-, XY-;Sry Tg, and XX;Sry Tg mice, demonstrating that gene dosage of sex chromosomes does not mediate the sex difference in FAA. Next, we masculinized female mice by treating them with 17-beta estradiol during the neonatal period; yet again, we saw no difference in FAA between control and masculinized females. Finally, we observed that there was no longer a sex difference in FAA for older mice, suggesting that the sex difference in FAA is age-dependent. Thus, our study demonstrates that singular manipulations of gonadal hormones, sex chromosomes, or developmental patterning are not able to explain the difference in FAA between young male and female mice.

The effects of graded levels of calorie restriction: V. Impact of short term calorie and protein restriction on physical activity in the C57BL/6 mouse

Calorie restriction (CR) delays the onset of age-related disease and extends lifespan in a number of species. When faced with reduced energy supply animals need to lower energy demands, which may be achieved in part by reducing physical activity (PA). We monitored changes in PA using implanted transmitters in male C57BL/6 mice in response to graded levels of CR (10 to 40%) or matched levels of graded protein restriction (PR) for 3 months. Mice were fed at lights out and ad libitum controls were limited to dark-phase feeding (12AL) or 24hr/day. Total daily PA declined in a non-linear manner over the first 30 days of CR or PR, remaining stable thereafter. Total daily PA was not related to the level of CR or PR. Total daily PA over the last 20 days of restriction was related to circulating leptin, insulin, tumor necrosis factor-α (TNF-α) and insulin-like growth factor (IGF)-1 levels, measured after 3 months. Mice under restriction showed a high level of activity in the 2hrs before feeding (food anticipatory activity: FAA). FAA followed a complex pattern, peaking around day 20, falling on ∼day 37 then increasing again. FAA was also positively related to the level of restriction and inversely to leptin, insulin, TNF-α and IGF-1. Non-FAA, in contrast, declined over the period of restriction, generally more so in mice under greater restriction, thereby offsetting to some extent the increase in FAA. Mice under PR displayed no changes in PA over time or in comparison to 12AL, and showed no increase in FAA.

MicroRNAs modulate core-clock gene expression in pancreatic islets during early postnatal life in rats

AIMS/HYPOTHESIS

Evidence continues to emerge detailing a fine-tuning of the regulation of metabolic processes and energy homeostasis by cell-autonomous circadian clocks. Pancreatic beta cell functional maturation occurs after birth and implies transcriptional changes triggered by a shift in the nutritional supply that occurs at weaning, enabling the adaptation of insulin secretion. So far, the developmental timing and exact mechanisms involved in the initiation of the circadian clock in the growing pancreatic islets have never been addressed.

METHODS

Circadian gene expression was measured by quantitative RT-PCR in islets of rats at different postnatal ages up to 3 months, and by in vitro bioluminescence recording in newborn (10-day-old) and adult (3-month-old) islets. The effect of the microRNAs miR-17-5p and miR-29b-3p on the expression of target circadian genes was assessed in newborn rat islets transfected with microRNA antisense or mimic oligonucleotides, and luciferase reporter assays were performed on the rat insulin-secreting cell line INS832/13 to determine a direct effect. The global regulatory network between microRNAs and circadian genes was computationally predicted.

RESULTS

We found up to a sixfold-change in the 24 h transcriptional oscillations and overall expression of Clock, Npas2, Bmal1, Bmal2, Rev-erbα, Per1, Per2, Per3 and Cry2 between newborn and adult rat islets. Synchronisation of the clock machinery in cultured islet cells revealed a delayed cell-autonomous rhythmicity of about 1.5 h in newborn compared with adult rats. Computational predictions unveiled the existence of a complex regulatory network linking over 40 microRNAs displaying modifications in their expression profiles during postnatal beta cell maturation and key core-clock genes. In agreement with these computational predictions, we demonstrated that miR-17-5p and miR-29b-3p directly regulated circadian gene expression in the maturing islet cells of 10-day-old rats.

CONCLUSIONS/INTERPRETATION

These data show that the circadian clock is not fully operational in newborn islets and that microRNAs potently contribute to its regulation during postnatal beta cell maturation. Defects in this process may have long-term consequences on circadian physiology and pancreatic islet function, favouring the manifestation of metabolic diseases such as diabetes.

Neural correlates of food anticipatory activity in mice subjected to once- or twice-daily feeding periods

In rodents, restricted food access to a limited period each day at a predictable time results in the appearance of food anticipatory activity (FAA). Two shorter periods of food access each day can result in two FAA bouts. In this study, we examine FAA under 12:12 and 18:6 photoperiods in mice (Mus musculus) with one or two food access periods per day and measure the activation of the suprachiasmatic, dorsomedial and arcuate nuclei by assaying Fos protein expression, while making use of tissue-type plasminogen activator knockout mice to assess the role of neural plasticity in adaptation to restricted feeding cycles. Long days were utilised to allow for temporal separation of two restricted feeding periods during the light phase. Mice fed twice per day generally divided FAA into two distinct bouts, with mice lacking tissue-type plasminogen activator showing reduced FAA. Increases in Fos expression in response to one restricted feeding period per day were seen in the dorsomedial and arcuate nuclei in both 12:12 and 18:6 conditions, with an increase seen in the SCN in only the 12:12 condition. These increases were eliminated or reduced in the two feeding time conditions (done in 18:6 only). Both activity patterns and Fos expression differed for single restricted feeding times between 18:6 and 12:12 photoperiods. Fos activation was lower during RF in 18:6 than 12:12 across all three brain regions, a pattern not reflective of changes in FAA. These data suggest that involvement of these regions in FAA may be influenced by photoperiodic context.

Circadian clocks govern calorie restriction-mediated life span extension through BMAL1- and IGF-1-dependent mechanisms

Calorie restriction (CR) increases longevity in many species by unknown mechanisms. The circadian clock was proposed as a potential mediator of CR. Deficiency of the core component of the circadian clock-transcriptional factor BMAL1 (brain and muscle ARNT [aryl hydrocarbon receptor nuclear translocator]-like protein 1)-results in accelerated aging. Here we investigated the role of BMAL1 in mechanisms of CR. The 30% CR diet increased the life span of wild-type (WT) mice by 20% compared to mice on anad libitum(AL) diet but failed to increase life span ofBmal1(-/-)mice. BMAL1 deficiency impaired CR-mediated changes in the plasma levels of IGF-1 and insulin. We detected a statistically significantly reduction of IGF-1 in CRvs.AL by 50 to 70% in WT mice at several daily time points tested, while inBmal1(-/-)the reduction was not significant. Insulin levels in WT were reduced by 5 to 9%, whileBmal1(-/-)induced it by 10 to 35% at all time points tested. CR up-regulated the daily average expression ofBmal1(by 150%) and its downstream target genesPeriods(by 470% forPer1and by 130% forPer2). We propose that BMAL1 is an important mediator of CR, and activation of BMAL1 might link CR mechanisms with biologic clocks.-Patel, S. A., Chaudhari, A., Gupta, R., Velingkaar, N., Kondratov, R. V. Circadian clocks govern calorie restriction-mediated life span extension through BMAL1- and IGF-1-dependent mechanisms.

Entrainment of mouse peripheral circadian clocks to <24 h feeding/fasting cycles under 24 h light/dark conditions

The circadian clock system in peripheral tissues can endogenously oscillate and is entrained by the light-dark and fasting-feeding cycles in mammals. Although the system's range of entrainment to light-dark cycles with a non-24 h (<24 h) interval has been studied, the range of entrainment to fasting-feeding cycles with shorter periods (<24 h) has not been investigated in peripheral molecular clocks. In the present study, we measured this range by monitoring the mouse peripheral PER2::LUCIFERASE rhythm in vivo at different periods under each feeding cycle (Tau (T) = 15-24 h) under normal light-dark conditions. Peripheral clocks could be entrained to the feeding cycle with T = 22-24 h, but not to that with T = 15-21 h. Under the feeding cycle with T = 15-18 h, the peripheral clocks oscillated at near the 24-h period, suggesting that they were entrained to the light-dark cycle. Thus, for the first time, we demonstrated the range of entrainment to the non-24 h feeding cycle, and that the circadian range (T = 22-24 h) of feeding stimulus is necessary for peripheral molecular clock entrainment under light-dark cycles.

Behavioural changes are a major contributing factor in the reduction of sarcopenia in caloric-restricted ageing mice

BACKGROUND

In rodent models, caloric restriction (CR) with maintenance of adequate micronutrient supply has been reported to increase lifespan and to reduce age-induced muscle loss (sarcopenia) during ageing. In the present study, we further investigated effects of CR on the onset and severity of sarcopenia in ageing male C57BL/6 J mice. The aim of this study was to investigate whether CR induces changes in behaviour of the animals that could contribute to the pronounced health-promoting effects of CR in rodents. In addition, we aimed to investigate in more detail the effects of CR on the onset and severity of sarcopenia.

METHODS

The mice received either an ad libitum diet (control) or a diet matching 70 E% of the control diet (C). Daily activity, body composition (dual energy X-ray absorptiometry), grip strength, insulin sensitivity, and general agility and balance were determined at different ages. Mice were killed at 4, 12, 24, and 28 months. Skeletal muscles of the hind limb were dissected, and the muscle extensor digitorum longus muscle was used for force-frequency measurements. The musculus tibialis was used for real-time quantitative PCR analysis.

RESULTS

From the age of 12 months, CR animals were nearly half the weight of the control animals, which was mainly related to a lower fat mass. In the control group, the hind limb muscles showed a decline in mass at 24 or 28 months of age, which was not present in the CR group. Moreover, insulin sensitivity (oral glucose tolerance test) was higher in this group and the in vivo and ex vivo grip strength did not differ between the two groups. In the hours before food was provided, CR animals were far more active than control animals, while total daily activity was not increased. Moreover, agility test indicated that CR animals were better climbers and showed more climbing behaviours.

CONCLUSIONS

Our study confirms earlier findings that in CR animals less sarcopenia is present. The mice on the CR diet, however, showed specific behavioural changes characterized by higher bursts of activity within a short time frame before consumption of a 70 E% daily meal. We hypothesize that the positive effects of CR on muscle maintenance in rodents are not merely a direct consequence of a lower energy intake but also related to a more active behaviour in a specific time frame. The burst of activity just before immediate start of eating, might lead to a highly effective use of the restricted protein sources available.

Effects of photoperiod on food intake, activity and metabolic rate in adult neutered male cats

With the continued rise in feline obesity, novel weight management strategies are needed. To date, strategies aimed at altering physical activity, an important factor in weight maintenance, have been lacking. Photoperiod is known to cause physiological changes in seasonal mammals, including changes in body weight (BW) and reproductive status. Thus, our objective was to determine the effect of increased photoperiod (longer days) on voluntary physical activity levels, resting metabolic rate (RMR), food intake required to maintain BW, and fasting serum leptin and ghrelin concentrations in adult cats. Eleven healthy, adult, neutered, male domestic shorthair cats were used in a randomized crossover design study. During two 12-week periods, cats were exposed to either a short-day (SD) photoperiod of 8 h light: 16 h dark or a long-day (LD) photoperiod of 16 h light: 8 h dark. Cats were fed a commercial diet to maintain baseline BW. In addition to daily food intake and twice-weekly BW, RMR (via indirect calorimetry), body composition [via dual-energy X-ray absorptiometry (DEXA)] and physical activity (via Actical activity monitors) were measured at week 0 and 12 of each period. Fasting serum leptin and ghrelin concentrations were measured at week 0, 6 and 12 of each period. Average hourly physical activity was greater (p = 0.008) in LD vs. SD cats (3770 vs. 3129 activity counts/h), which was primarily due to increased (p < 0.001) dark period activity (1188 vs. 710 activity counts/h). This corresponded to higher (p < 0.0001) daily metabolizable energy intake (mean over 12-week period: 196 vs. 187 kcal/day), and increased (p = 0.048) RMR in LD cats (9.02 vs. 8.37 kcal/h). Body composition, serum leptin and serum ghrelin were not altered by photoperiod. More research is needed to determine potential mechanisms by which these physiological changes occurred and how they may apply to weight management strategies.

Circadian mechanisms of food anticipatory rhythms in rats fed once or twice daily: clock gene and endocrine correlates

Circadian clocks in many brain regions and peripheral tissues are entrained by the daily rhythm of food intake. Clocks in one or more of these locations generate a daily rhythm of locomotor activity that anticipates a regular mealtime. Rats and mice can also anticipate two daily meals. Whether this involves 1 or 2 circadian clocks is unknown. To gain insight into how the circadian system adjusts to 2 daily mealtimes, male rats in a 12∶12 light-dark cycle were fed a 2 h meal either 4 h after lights-on or 4 h after lights-off, or a 1 h meal at both times. After 30 days, brain, blood, adrenal and stomach tissue were collected at 6 time points. Multiple clock genes from adrenals and stomachs were assayed by RT-PCR. Blood was assayed for corticosterone and ghrelin. Bmal1 expression was quantified in 14 brain regions by in situ hybridization. Clock gene rhythms in adrenal and stomach from day-fed rats oscillated in antiphase with the rhythms in night-fed rats, and at an intermediate phase in rats fed twice daily. Corticosterone and ghrelin in 1-meal rats peaked at or prior to the expected mealtime. In 2-meal rats, corticosterone peaked only prior the nighttime meal, while ghrelin peaked prior to the daytime meal and then remained elevated. The olfactory bulb, nucleus accumbens, dorsal striatum, cerebellum and arcuate nucleus exhibited significant daily rhythms of Bmal1 in the night-fed groups that were approximately in antiphase in the day-fed groups, and at intermediate levels (arrhythmic) in rats anticipating 2 daily meals. The dissociations between anticipatory activity and the peripheral clocks and hormones in rats anticipating 2 daily meals argue against a role for these signals in the timing of behavioral rhythms. The absence of rhythmicity at the tissue level in brain regions from rats anticipating 2 daily meals support behavioral evidence that circadian clock cells in these tissues may reorganize into two populations coupled to different meals.

Dopamine receptor 1 neurons in the dorsal striatum regulate food anticipatory circadian activity rhythms in mice

Daily rhythms of food anticipatory activity (FAA) are regulated independently of the suprachiasmatic nucleus, which mediates entrainment of rhythms to light, but the neural circuits that establish FAA remain elusive. In this study, we show that mice lacking the dopamine D1 receptor (D1R KO mice) manifest greatly reduced FAA, whereas mice lacking the dopamine D2 receptor have normal FAA. To determine where dopamine exerts its effect, we limited expression of dopamine signaling to the dorsal striatum of dopamine-deficient mice; these mice developed FAA. Within the dorsal striatum, the daily rhythm of clock gene period2 expression was markedly suppressed in D1R KO mice. Pharmacological activation of D1R at the same time daily was sufficient to establish anticipatory activity in wild-type mice. These results demonstrate that dopamine signaling to D1R-expressing neurons in the dorsal striatum plays an important role in manifestation of FAA, possibly by synchronizing circadian oscillators that modulate motivational processes and behavioral output.

Pregnancy-induced changes in ultradian rhythms persist in circadian arrhythmic Siberian hamsters

The impact of pregnancy and lactation on ultradian rhythms (URs) and circadian rhythms (CRs) of locomotor activity was assessed in circadian rhythmic and arrhythmic Siberian hamsters maintained in a long-day photoperiod (16h light/day). Progressive decrements in CR robustness and amplitude over the course of gestation were accompanied by enhanced URs. Dark-phase UR period and amplitude increased during early gestation and complexity and robustness increased during late gestation. The persistence of pregnancy-associated enhancements of URs in circadian arrhythmic (ARR) hamsters suggests that reproductive modulation of the UR waveform is not dependent on coherent circadian organization. The increased incidence of dark-phase URs appeared more rapidly in ARR dams than entrained (ENTR) dams. Throughout gestation, the percentage of dams with dark-phase URs was significantly greater in the ARR group. Gestational increases in UR complexity and robustness emerged earlier and were greater in ARR than ENTR dams. The attenuation of CRs during lactation is correlated with increased expression of URs. Relaxation of circadian control of the dam's behavior may increase fitness by permitting more efficient interactions with circadian arrhythmic pups.

Large, binge-type meals of high fat diet change feeding behaviour and entrain food anticipatory activity in mice

Male C57BL/6 mice fed ad libitum on control diet but allowed access to a palatable high fat diet (HFD) for 2 h a day during the mid-dark phase rapidly adapt their feeding behaviour and can consume nearly 80% of their daily caloric intake during this 2 h-scheduled feed. We assessed food intake microstructure and meal pattern, and locomotor activity and rearing as markers of food anticipatory activity (FAA). Schedule fed mice reduced their caloric intake from control diet during the first hours of the dark phase but not during the 3-h period immediately preceding the scheduled feed. Large meal/binge-like eating behaviour during the 2-h scheduled feed was characterised by increases in both meal number and meal size. Rearing was increased during the 2-h period running up to scheduled feeding while locomotor activity started to increase 1 h before, indicating that schedule-fed mice display FAA. Meal number and physical activity changes were sustained when HFD was withheld during the anticipated scheduled feeding period, and mice immediately binged when HFD was represented after a week of this "withdrawal" period. These findings provide important context to our previous studies suggesting that energy balance systems in the hypothalamus are not responsible for driving these large, binge-type meals. Evidence of FAA in HFD dark phase schedule-fed mice implicates anticipatory processes in binge eating that do not involve immediately preceding hypophagia or regulatory homeostatic signalling.

Behavioral and neural correlates of acute and scheduled hunger in C57BL/6 mice

In rodents, daily feeding schedules induce food anticipatory activity (FAA) rhythms with formal properties suggesting mediation by food-entrained circadian oscillators (FEOs). The search for the neuronal substrate of FEOs responsible for FAA is an active area of research, but studies spanning several decades have yet to identify unequivocally a brain region required for FAA. Variability of results across studies leads to questions about underlying biology versus methodology. Here we describe in C57BL/6 male mice the effects of varying the ‘dose’ of caloric restriction (0%, 60%, 80%, 110%) on the expression of FAA as measured by a video-based analysis system, and on the induction of c-Fos in brain regions that have been implicated in FAA. We determined that more severe caloric restriction (60%) leads to a faster onset of FAA with increased magnitude. Using the 60% caloric restriction, we found little evidence for unique signatures of neuronal activation in the brains of mice anticipating a daily mealtime compared to mice that were fasted acutely or fed ad-libitum–even in regions such as the dorsomedial and ventrolateral hypothalamus, nucleus accumbens, and cerebellum that have previously been implicated in FAA. These results underscore the importance of feeding schedule parameters in determining quantitative features of FAA in mice, and demonstrate dissociations between behavioral FAA and neural activity in brain areas thought to harbor FEOs or participate in their entrainment or output.

Cognitive assessment of mice strains heterozygous for cell-adhesion genes reveals strain-specific alterations in timing

We used a fully automated system for the behavioural measurement of physiologically meaningful properties of basic mechanisms of cognition to test two strains of heterozygous mutant mice, Bfc (batface) and L1, and their wild-type littermate controls. Both of the target genes are involved in the establishment and maintenance of synapses. We find that the Bfc heterozygotes show reduced precision in their representation of interval duration, whereas the L1 heterozygotes show increased precision. These effects are functionally specific, because many other measures made on the same mice are unaffected, namely: the accuracy of matching temporal investment ratios to income ratios in a matching protocol, the rate of instrumental and classical conditioning, the latency to initiate a cued instrumental response, the trials on task and the impulsivity in a switch paradigm, the accuracy with which mice adjust timed switches to changes in the temporal constraints, the days to acquisition, and mean onset time and onset variability in the circadian anticipation of food availability.

Intermittent feeding schedules--behavioural consequences and potential clinical significance

Food availability and associated sensory cues such as olfaction are known to trigger a range of hormonal and behavioural responses. When food availability is predictable these physiological and behavioural responses can become entrained to set times and occur in anticipation of food rather than being dependent on the food-related cues. Here we summarise the range of physiological and behavioural responses to food when the time of its availability is unpredictable, and consider the potential to manipulate feeding patterns for benefit in metabolic and mental health.

Automated, quantitative cognitive/behavioral screening of mice: for genetics, pharmacology, animal cognition and undergraduate instruction

We describe a high-throughput, high-volume, fully automated, live-in 24/7 behavioral testing system for assessing the effects of genetic and pharmacological manipulations on basic mechanisms of cognition and learning in mice. A standard polypropylene mouse housing tub is connected through an acrylic tube to a standard commercial mouse test box. The test box has 3 hoppers, 2 of which are connected to pellet feeders. All are internally illuminable with an LED and monitored for head entries by infrared (IR) beams. Mice live in the environment, which eliminates handling during screening. They obtain their food during two or more daily feeding periods by performing in operant (instrumental) and Pavlovian (classical) protocols, for which we have written protocol-control software and quasi-real-time data analysis and graphing software. The data analysis and graphing routines are written in a MATLAB-based language created to simplify greatly the analysis of large time-stamped behavioral and physiological event records and to preserve a full data trail from raw data through all intermediate analyses to the published graphs and statistics within a single data structure. The data-analysis code harvests the data several times a day and subjects it to statistical and graphical analyses, which are automatically stored in the "cloud" and on in-lab computers. Thus, the progress of individual mice is visualized and quantified daily. The data-analysis code talks to the protocol-control code, permitting the automated advance from protocol to protocol of individual subjects. The behavioral protocols implemented are matching, autoshaping, timed hopper-switching, risk assessment in timed hopper-switching, impulsivity measurement, and the circadian anticipation of food availability. Open-source protocol-control and data-analysis code makes the addition of new protocols simple. Eight test environments fit in a 48 in x 24 in x 78 in cabinet; two such cabinets (16 environments) may be controlled by one computer.

Circadian regulation of food-anticipatory activity in molecular clock-deficient mice

In the mammalian brain, the suprachiasmatic nucleus (SCN) of the anterior hypothalamus is considered to be the principal circadian pacemaker, keeping the rhythm of most physiological and behavioral processes on the basis of light/dark cycles. Because restriction of food availability to a certain time of day elicits anticipatory behavior even after ablation of the SCN, such behavior has been assumed to be under the control of another circadian oscillator. According to recent studies, however, mutant mice lacking circadian clock function exhibit normal food-anticipatory activity (FAA), a daily increase in locomotor activity preceding periodic feeding, suggesting that FAA is independent of the known circadian oscillator. To investigate the molecular basis of FAA, we examined oscillatory properties in mice lacking molecular clock components. Mice with SCN lesions or with mutant circadian periods were exposed to restricted feeding schedules at periods within and outside circadian range. Periodic feeding led to the entrainment of FAA rhythms only within a limited circadian range. Cry1(-/-) mice, which are known to be a "short-period mutant," entrained to a shorter period of feeding cycles than did Cry2(-/-) mice. This result indicated that the intrinsic periods of FAA rhythms are also affected by Cry deficiency. Bmal1(-/-) mice, deficient in another essential element of the molecular clock machinery, exhibited a pre-feeding increase of activity far from circadian range, indicating a deficit in circadian oscillation. We propose that mice possess a food-entrainable pacemaker outside the SCN in which canonical clock genes such as Cry1, Cry2 and Bmal1 play essential roles in regulating FAA in a circadian oscillatory manner.

Meal frequency patterns determine the phase of mouse peripheral circadian clocks

Peripheral circadian clocks in mammals are strongly entrained by light-dark and eating cycles. Their physiological functions are maintained by the synchronization of the phase of organs via clock gene expression patterns. However, little is known about the adaptation of peripheral clocks to the timing of multiple daily meals. Here, we investigated the effect of irregular eating patterns, in terms of timing and volume, on their peripheral clocks in vivo. We found that the phase of the peripheral clocks was altered by the amount of food and the interval between feeding time points but was unaffected by the frequency of feeding, as long as the interval remained fixed. Moreover, our results suggest that a late dinner should be separated into 2 half-dinners in order to alleviate the effect of irregular phases of peripheral clocks.

Daily scheduled high fat meals moderately entrain behavioral anticipatory activity, body temperature, and hypothalamic c-Fos activation

When fed in restricted amounts, rodents show robust activity in the hours preceding expected meal delivery. This process, termed food anticipatory activity (FAA), is independent of the light-entrained clock, the suprachiasmatic nucleus, yet beyond this basic observation there is little agreement on the neuronal underpinnings of FAA. One complication in studying FAA using a calorie restriction model is that much of the brain is activated in response to this strong hunger signal. Thus, daily timed access to palatable meals in the presence of continuous access to standard chow has been employed as a model to study FAA in rats. In order to exploit the extensive genetic resources available in the murine system we extended this model to mice, which will anticipate rodent high fat diet but not chocolate or other sweet daily meals (Hsu, Patton, Mistlberger, and Steele; 2010, PLoS ONE e12903). In this study we test additional fatty meals, including peanut butter and cheese, both of which induced modest FAA. Measurement of core body temperature revealed a moderate preprandial increase in temperature in mice fed high fat diet but entrainment due to handling complicated interpretation of these results. Finally, we examined activation patterns of neurons by immunostaining for the immediate early gene c-Fos and observed a modest amount of entrainment of gene expression in the hypothalamus of mice fed a daily fatty palatable meal.