Reliability of the Circadian Rhythm of Water and Macronutrient-Rich Diets Intake in Dietary Choice

Rats with ad libitum water and the ability to self-select among three macronutrient-rich diets—carbohydrate (CHO), protein (PRO), and lipid (LIP)—show a circadian rhythmicity in their ingestion. The aim of the present study was to determine whether this circadian rhythmicity is reliable from day to day. Eight rats were offered ad libitum water and a choice of three isoenergetic diet rations providing carbohydrate, protein, and lipid. Water and food intake was recorded every 3 h for 7 days. The reliability of the circadian rhythm of water and food intake was assessed by the Intraclass Correlation Coefficient (ICC) and the test-retest reliability using the Pearson's Correlation Coefficient (r). The results showed that the circadian rhythm of water, CHO, and PRO intake are strongly reliable. However, the circadian rhythm of LIP intake is less reproducible. Among the three reliable parameters—water, CHO, and PRO, the circadian rhythm of water intake was the most reproducible over 7 days. This suggests that water intake may be used as a marker of circadian rhythmicity in ingestive behavior.     

Relative value of light and food as synchronizers of liver phosphorylase circadian rhythm.

The role played by light and feeding schedules on the circadian rhythm of glycogen content and phosphorylase activity of the liver has been studied. In one experiment, mice were subjected to a regimem of constant darkness during 21 days and compared with mice kept in 12 hrs of light alternating with 12 hrs of darkness. Both groups received food and water ad libitum. Liver glycogen content as well as phosphorylase activity showed, with slight differences, similar circadian variations. In a second experiment, mice under similar lighting conditions (LD 12:12), with water access ad libitum, were divided into two groups; one was offered food ad libitum while the other group recieved food from 0700 to 1800 only. This experiment allowed up to compare two different schedules of food intake; ad libitum, normal schedule (from 1800 to 0600) and reversed schedule (from 0700 to 1800). A complete reversal of the circadian rhythm was observed after 21 days in the group with the reverted feeding schedule. We conclude that food can function as the primary synchronizer in spite of the lighting regimen.     

Effects of Insulin Administration in Diabetic Rats on Food and Drink Rhythmic Schedules

In normal rats food and water intakes are associated in terms of time and quantity and their diurnal rhythms are synchronized. Intake behavior in streptozotocin-induced diabetic rats (ID) with marked polyphagia and polydipsia and in diabetic rats with continuous insulin administration (IT) has been studied. The daily percentages of food and water intakes during the dark phase were lower in IT than in control rats (C), being even lower in ID rats. However, all three groups showed circadian rhythmicity in food intake, although with less amplitude in the ID and IT animals compared to the C ones. A loss of the normal circadian rhythm of water intake was observed in the ID rats and although the insulin administration recovered circadian rhythmicity, it did not restore the temporal relations between food and water intakes. These results may indicate that the circadian pattern of water intake is more influenced by insulin than food intake. The daily pattern of this hormone may play an important role in the circadian modulation of the homeostatic mechanisms integrating both intake behaviors.     

Chronotoxicology of florfenicol

Sixty 3-month-old homozygote male mice were studied for circadian rhythmicity in the toxicity of florfenicol overdose. Animals were kept under a regimen of 12h light, 12h darkness (12:12 LD) with food and water available ad libitum. The LD50 (median lethal) dose was determined in a preliminary experiment and was administered to groups of 10 mice at six different clock times (hours) after light onset (HALO): 0, 4, 8, 12, 16, and 20 HALO. Cosinor analysis verified a statistically significant (P < .04) circadian rhythm in the toxic effect (mortality) of florfenicol. Mortality was greatest when the drug was injected 4h after the commencement of the activity span (16 HALO) and least when injected 4h after the start of the diurnal rest span (4 HALO). Mortality was 2.5 times greater when drug injection was given at 16 HALO than at 4 HALO.     

Effects of three-hour restricted food access during the light period on circadian rhythms of temperature, locomotor activity, and heart rate in rats

The effects of food on biological rhythms may influence the findings of chronopharmacological studies. The present study evaluated the influence of a restricted food access during the rest (light) span of nocturnally active Wistar rats on the 24 h time organization of biological functions in terms of the circadian rhythms of temperature (T), heart rate (HR), and locomotor activity (LA) in preparation for subsequent studies aimed at evaluating the influence of timed food access on the pharmacokinetics and pharmacodynamics of medications. Ten-wk-old male Wistar rats were housed under controlled 12:12 h light:dark (LD) environmental conditions. Food and water were available ad libitum, excepted during a 3 wk period of restriction. Radiotelemetry transmitters were implanted to record daily rhythms in T, HR, and LA. The study lasted 7 wk and began after a 21-d recovery span following surgery. Control baseline data were collected during the first wk (W1). The second span of 3 wk duration (W2 to W4) consisted of the restricted feeding regimen (only 3 h access to food between 11:00 and 14:00 h daily) during the L (rest span) under 12:12 h LD conditions. The third period of 3 wk duration (W5 to W7) consisted of the recovery span with ad libitium normal feeding. Weight loss in the amount of 5% of baseline was observed during W1 with stabilization of body weight thereafter during the remaining 2 wk of food restriction. The 3 h restricted food access during the L rest span induced a partial loss of circadian rhythmicity and the emergence of 12 h rhythms in T, HR, and LA. Return to ad libitum feeding conditions restored circadian rhythmicity in the manner evidenced during the baseline control span. Moreover, the MESORS and amplitudes of the T, HR, and LA 24 h patterns were significantly attenuated during food restriction (p < 0.001) and then returned to initial values during recovery. These changes may be interpreted as a masking effect, since T, HR, and LA are known to directly react to food intake. The consequences of such findings on the methods used to conduct chronokinetic studies, such as the fasting of animals the day before testing, are important since they may alter the temporal structure of the organism receiving the drug and thereby compromise findings.     

Rare sugar d-psicose protects pancreas β-islets and thus improves insulin resistance in OLETF rats

The dorsomedial hypothalamic nucleus (DMH) has been proposed as a candidate for the neural substrate of a food-entrainable oscillator. The existence of a food-entrainable oscillator in the mammalian nervous system was inferred previously from restricted feeding-induced behavioral rhythmicity in rodents with suprachiasmatic nucleus lesions. In the present study, we have characterized the circadian rhythmicity of behavior in Wfs1-deficient mice during ad libitum and restricted feeding. Based on the expression of Wfs1 protein in the DMH it was hypothesized that Wfs1-deficient mice will display reduced or otherwise altered food anticipatory activity. Wfs1 immunoreactivity in DMH was found almost exclusively in the compact part. Restricted feeding induced c-Fos immunoreactivity primarily in the ventral and lateral aspects of DMH and it was similar in both genotypes. Wfs1-deficiency resulted in significantly lower body weight and reduced wheel-running activity. Circadian rhythmicity of behavior was normal in Wfs1-deficient mice under ad libitum feeding apart from elongated free-running period in constant light. The amount of food anticipatory activity induced by restricted feeding was not significantly different between the genotypes. Present results indicate that the effects of Wfs1-deficiency on behavioral rhythmicity are subtle suggesting that Wfs1 is not a major player in the neural networks responsible for circadian rhythmicity of behavior.     

Circadian rhythms in honeybees: entrainment by feeding cycles

ABSTRACT. Colonies of the South African honeybee race Apis mellifera capensis (Escholtz) were maintained under constant conditions of illumination (200 lux), temperature (25±lC) and relative humidity (65±3%). Activity was measured at the hive entrance. After ad libitum feeding for at least 5 days, food was presented for only 2 h/day either for 1 week (series 1) or for 2 weeks (series 2). In the last part of each experiment, food was again available all the time. Colonies which showed free-running circadian activity rhythms (with periods ranging from 22.6 to 24.8 h) during ad libitum feeding were submitted to feeding cycles with inter-feeding intervals (T) of 22, 23, 24 and 25 h. In most of these experiments the rhythms were synchronized by the feeding schedule, resulting in a stable phase-angle difference between onset of activity and onset of food availability. The duration of this anticipatory activity was positively correlated with T. When ad libitum feeding was resumed, the period of the rhythm induced by the feeding schedule persisted for a few days. Thereafter, the rhythm was free-running again with a period close to that observed in the first part of the experiment. The conclusion is drawn that, under the influence of periodic feeding, the activity of honeybee colonies has the characteristics of an entrained circadian system.     

Working for food shifts nocturnal mouse activity into the day

Nocturnal rodents show diurnal food anticipatory activity when food access is restricted to a few hours in daytime. Timed food access also results in reduced food intake, but the role of food intake in circadian organization per se has not been described. By simulating natural food shortage in mice that work for food we show that reduced food intake alone shifts the activity phase from the night into the day and eventually causes nocturnal torpor (natural hypothermia). Release into continuous darkness with ad libitum food, elicits immediate reversal of activity to the previous nocturnal phase, indicating that the classical circadian pacemaker maintained its phase to the light-dark cycle. This flexibility in behavioral timing would allow mice to exploit the diurnal temporal niche while minimizing energy expenditure under poor feeding conditions in nature. This study reveals an intimate link between metabolism and mammalian circadian organization.     

Effects of feeding cycles on circadian rhythms in squirrel monkeys

Squirrel monkeys (Saimiri sciureus) were housed singly in cages equipped with a tree for climbing to measure locomotor activity, and with a movable food cup that could be arrested automatically. The animals were kept in continuous dim illumination (LL), twice interrupted by several weeks of entrainment by a light-dark (LD) 12:12 cycle. Apart from three control sections in which the food cups were unlocked continuously (ad libitum feeding), food was accessible for 3 hr per day only, with interfeeding intervals varying from 23 to 26 hr (periodic restricted feeding, or RF). During LD entrainment, the imposition of an RF schedule resulted in anticipatory behaviors, represented by increased tugs at the food cup and a pause in locomotor activity preceding the feeding time. In LL, the animals showed free-running circadian rhythms of locomotor and "feeding" activity that nearly always persisted when ad libitum feeding was replaced by RF. The period (tau) of the free-running rhythm was slightly modulated in relation to the varying interfeeding intervals (T), but entrainment was never achieved except in one test with an animal whose tau was very close to T. It is concluded that periodic availability of food represents an extremely weak zeitgeber, if any, for the circadian pacemaker of squirrel monkeys.     

Getting through to circadian oscillators: why use constant routines?

Overt 24-h rhythmicity is composed of both exogenous and endogenous components, reflecting the product of multiple (periodic) feedback loops with a core pacemaker at their center. Researchers attempting to reveal the endogenous circadian (near 24-h) component of rhythms commonly conduct their experiments under constant environmental conditions. However, even under constant environmental conditions, rhythmic changes in behavior, such as food intake or the sleep-wake cycle, can contribute to observed rhythmicity in many physiological and endocrine variables. Assessment of characteristics of the core circadian pacemaker and its direct contribution to rhythmicity in different variables, including rhythmicity in gene expression, may be more reliable when such periodic behaviors are eliminated or kept constant across all circadian phases. This is relevant for the assessment of the status of the circadian pacemaker in situations in which the sleep-wake cycle or food intake regimes are altered because of external conditions, such as in shift work or jet lag. It is also relevant for situations in which differences in overt rhythmicity could be due to changes in either sleep oscillatory processes or circadian rhythmicity, such as advanced or delayed sleep phase syndromes, in aging, or in particular clinical conditions. Researchers studying human circadian rhythms have developed constant routine protocols to assess the status of the circadian pacemaker in constant behavioral and environmental conditions, whereas this technique is often thought to be unnecessary in the study of animal rhythms. In this short review, the authors summarize constant routine methodology and what has been learned from constant routines and argue that animal and human circadian rhythm researchers should (continue to) use constant routines as a step on the road to getting through to central and peripheral circadian oscillators in the intact organism.     

Daily Changes of Plasma Corticosterone by an 8-h Daytime Feeding Occur Without Body Weight Loss or Severe Food Restriction in the Rat

Different studies have reported that daytime feeding entrains the circadian rhythm of corticosterone secretion in rats. However, it remained unclear whether calorie restriction or daytime feeding access have an effect. The aim of our study is to evaluate the effect of an 8-h daytime feeding access on the circadian rhythm of plasma corticosterone. Eleven adult male Wistar rats were assigned to two different conditions of access to food: ad lib feeding for one week and daytime feeding for the following two weeks. On the 7th, 14th and 21st day, blood samples were collected every 4 h from 08:00 to 04:00. Food intake and body weight were recorded daily. During daytime feeding, rats ingested 88% of the amount of food ingested over 24 h in the ad lib feeding period. However, body weight increased significantly from the first day to the end of experiment. Peak plasma corticosterone was 12 h shifted during daytime feeding period compared to the ad lib condition. This study showed that an 8-h daytime feeding entrained the circadian rhythm of plasma corticosterone without body weight loss or severe food restriction.     

Daily Changes of Plasma Corticosterone by an 8-h Daytime Feeding Occur Without Body Weight Loss or Severe Food Restriction in the Rat

Different studies have reported that daytime feeding entrains the circadian rhythm of corticosterone secretion in rats. However, it remained unclear whether calorie restriction or daytime feeding access have an effect. The aim of our study is to evaluate the effect of an 8-h daytime feeding access on the circadian rhythm of plasma corticosterone. Eleven adult male Wistar rats were assigned to two different conditions of access to food: ad lib feeding for one week and daytime feeding for the following two weeks. On the 7th, 14th and 21st day, blood samples were collected every 4 h from 08:00 to 04:00. Food intake and body weight were recorded daily. During daytime feeding, rats ingested 88% of the amount of food ingested over 24 h in the ad lib feeding period. However, body weight increased significantly from the first day to the end of experiment. Peak plasma corticosterone was 12 h shifted during daytime feeding period compared to the ad lib condition. This study showed that an 8-h daytime feeding entrained the circadian rhythm of plasma corticosterone without body weight loss or severe food restriction.     

Effect of food synchronization on the circadian rhythm of bone marrow and thymus lipids in rats

Young male Wistar rats reared under standard laboratory conditions with a 12:12 h light:dark regimen were fed ad libitum or were allowed access to food for only 2 h in the first half of the light or the dark part of the day. In rats fed ad libitum, marked circadian oscillation of the bone marrow triacylglycerol and phospholipid concentration and oscillation of the same fractions in the thymus were found. The restricted feeding time raised the triacylglycerol concentration in the bone marrow, but did not noticeably affect the time course of the circadian curves. The mean lipid values in the thymus of animals with a shortened feeding time did not alter, but the acrophase of the two basic fractions shifted.     

Exogenous melatonin reduces the resynchronization time after phase shifts of a nonphotic zeitgeber in the house sparrow (Passer domesticus)

Continuous melatonin administration via silastic implants accelerates the resynchronization of the circadian locomotor activity rhythm in house sparrows (Passer domesticus) after exposure to phase shifts of a weak light-dark cycle. Constant melatonin might induce this effect either by increasing the sensitivity of the visual system to a light zeitgeber or by reducing the degree of self-sustainment of the circadian pacemaker. To distinguish between these two possible mechanisms, two groups of house sparrows, one carrying melatonin implants and the other empty implants, were kept in constant dim light and subjected to advance and delay shifts of a 12-h feeding phase. The resynchronization times of their circadian feeding rhythm following the phase shifts were significantly shorter when the birds carried melatonin implants than when they carried empty implants. In a second experiment, melatonin-implanted and control birds were released into food ad libitum conditions 2 days after either a delay or an advance phase shift. The number of hours by which the activity rhythms had been shifted on the second day in food ad libitum conditions was assessed. Melatonin-implanted house sparrows had significantly larger phase shifts in their circadian feeding rhythm than control birds. This is in accordance with the first experiment since a larger phase shift at a given time reflects accelerated resynchronization. Additionally, the second experiment also excludes any possible masking effects of the nonphotic zeitgeber. In conclusion, constant melatonin accelerates resynchronization even after phase shifts of a nonphotic zeitgeber, indicating that constant high levels of melatonin can reduce the degree of self-sustainment of the circadian pacemaker independent of any effects on the photoreceptive system.     

Comparison of the circadian rhythm in cell proliferation in corneal epithelium of male rats studied under normal and hypobaric (hypoxic) conditions

Groups of 20-45-day-old rats maintained on a light (0600-1800)/dark (1800-0600) regimen with food and water available ad libitum were studied for the effect of hypoxic hypoxia on the circadian rhythm of corneal epithelial mitosis and thymidine incorporation. In experiments conducted during the months of September and November, hypoxic hypoxia was accomplished by the exposure of rats to a simulated altitude of 7500 m in one series of experiments, or to a gaseous mixture of 8% oxygen and 92% nitrogen at sea level atmospheric pressure (760 mmHg) in another series of experiments. Controls were included as well. Statistically significant (P less than 0.05) circadian rhythmicity in the corneal mitotic index was substantiated in the control animals with mesor (M) = 12.4%, amplitude (A) = 9.6% and acrophase (phi) of 0911. In the hypoxic hypoxia situation, the mesor and amplitude were depressed to 8.6 and 5.9%, respectively. In control groups, thymidine incorporation was circadian rhythmic with M = 38.5 and A = 11.3 cpm/microns DNA and acrophase of 2255. In the hypoxic hypoxia situation, the mesor was similar to the controls; whereas the amplitude was suppressed to 6.1% and acrophase was phase advanced by about 7 hr. Changes in the circadian rhythm of corneal mitosis and in thymidine incorporation under hypoxic hypoxia can be explained by programmed-in-time energy requirements during the corneal cell regeneration cycle.     

Photoperiod influences the critical caloric intake necessary to maintain reproduction among male deer mice (Peromyscus maniculatus).

The concept of critical day length is well established among rodents; reproductive function is maintained when day lengths are greater than some specific threshold. In addition to day length cues, seasonal breeding in deer mice can also be regulated by food availability. The caloric threshold necessary to support reproduction remains unspecified for seasonally breeding rodents. The present study examined the interaction between photoperiod and food availability on reproductive function in adult male deer mice (Peromyscus maniculatus). A critical caloric intake profile was constructed in long (16L:8D) and short (8L:16D) photoperiods; groups of deer mice in both photoperiods either received food ad libitum or 90, 80, or 70% of their individual ad libitum food intake for 10 wk. At autopsy, paired testes, epididymides, and seminal vesicles were removed and weighed. Body mass, total body fat, and total body water contents were also obtained. Short, as compared to long, day lengths inhibited the reproductive systems of male deer mice. However, food consumption interacted with photoperiod to affect reproductive function. Significant reductions in reproductive organ size as well as spermatogenic activity were observed among short-day mice after a 10% reduction in ad libitum food intake. Long-day animals required a 20% reduction in caloric intake to depress reproductive function. Body mass and total body water content were generally unaffected by either photoperiod or food consumption. Total body fat content was reduced in short- as compared to long-day mice. Individual reproductive responsiveness to short days increased as food availability decreased.(ABSTRACT TRUNCATED AT 250 WORDS)     

Time-restricted feeding entrains daily rhythms of energy metabolism in mice

Energy metabolism, oxygen consumption rate (VO2), and respiratory quotient (RQ) in mice were monitored continuously throughout 12:12-h light-dark cycles before, during, and after time-restricted feeding (RF). Mice fed ad libitum showed robust daily rhythms in both parameters: high during the dark phase and low during the light phase. The daily profile of energy metabolism in mice under daytime-only feeding was reversed at the beginning of the first fasting night. A few days after daytime-only feeding began, RF also reversed the circadian core body temperature rhythm. Moreover, RF for 6 consecutive days shifted the phases of circadian expression patterns of clock genes in liver significantly by 8-10 h. When mice were fed a high-fat (HF) diet ad libitum, the daily rhythm of RQ dampened day by day and disappeared on the sixth day of RF, whereas VO2 showed a robust daily rhythm. Mice fed HF only in the daytime had reversed VO2 and RQ rhythms. Similarly, mice fed HF only in the daytime significantly phase shifted the clock gene expression in liver, whereas ad libitum feeding with HF had no significant effect on the expression phases of liver clock genes. These results suggested that VO2 is a sensitive indicator of entrainment in the mouse liver. Moreover, physiologically, it can be determined without any surgery or constraint. On the basis of these results, we hypothesize that a change in the daily VO2 rhythm, independent of the energy source, might drive phase shifts of circadian oscillators in peripheral tissues, at least in the liver.     

Circadian Rhythms of Plasma Concentrations of Na+ and K+ and Their Urinary Excretion in Normal and Diabetic Rats

The effects of streptozotocin induced diabetes (50 mg/Kg) on the circadian rhythms in the excretion of sodium and potassium as well as their plasma concentration rhythms were investigated. Control (C) and diabetic (D) rats were studied during a light-dark (12h:12h) cycle and fed ad libitum. Statistically significant circadian rhythms were found for sodium and potassium excretion in C rats. The orthophases of both rhythms occurred in the dark phase, the potassium one occurring before that of sodium. In D rats there is increased excretion of both sodium and potassium with the rhythmicity maintained for sodium excretion only, which has an earlier orthophase than in the C rats. Plasma sodium and potassium concentrations showed a statistically significant circadian pattern in C rats, with orthophase in the light phase. This rhythmicity only appears in plasma potassium concentration for D rats, with orthophase at the end of the dark phase. The results in diabetic rats may suggest that the glomerular filtration rate (GFR) and/or tubular reabsorption rhythms are still contributing to the sodium excretory rhythm, and that the loss of the circadian rhythm in sodium plasma concentration has no influence on the sodium excretion rhythm. Nevertheless, the loss of the potassium excretion rhythm may suggest a disruption of the variations in the secretory process, as this excretion seems to be independent of the plasma potassium concentration rhythm, which is not lost in D rats.