Circadian rhythms in mice fed a single daily meal at different stages of lighting regimen

Preliminary study to investigate the distribution and effects of certain metals after inhalation of welding fumes in mice

The most important welding processes used are the gas metal arc (GMA) welding, the tungsten inert gas (TIG) welding, and the manual metal arc (MMA) welding processes. The goal of our investigation was to monitor the distribution of iron (Fe), manganese (Mn), calcium (Ca), and magnesium (Mg) in the lung, spleen, liver, and kidney of mice after inhalation exposure of different welding methods using different steel base materials. The treatment groups were the following: MMA-mild steel, MMA-molybdenum-manganese (MoMn) alloy, TIG-mild steel, and TIG-stainless steel. The samples were taken 24 and 96 h after the treatments. Most importantly, it was found that the Mn concentration in the lung' samples of the MMA-mild steel and the MMA-MoMn groups was increased extremely at both sampling times and in the spleen' samples also. In the TIG groups, the rise of the Mn concentration was only considerable in the lungs and spleens at 24 h, and emerged concentration was found in the liver in 96 h samples. Histopathology demonstrated emerged siderin content in the spleens of the treated animals and in siderin filled macrophages in the lungs mostly in all treated groups. Traces of high-level glycogen retention was found in the MMA groups at both sampling times. Similar glycogen retention in TIG-Ms and TIG stainless group's liver samples and emerged number of vacuoles, especially in the hepatocytes of the TIG-stainless steel 96 h group were also found. The mentioned results raise the consequence that there is a considerable difference in the kinetics of the Mn distribution between the MMA- and the TIG-fume-treated groups. Hence, the result suggests that manganese has a particle-size-dependent toxico-kinetics property. The anomaly of the glycogen metabolism indicates the systemic effect of the welding fumes. Also, the numerous vacuoles mentioned above show a possible liver-specific adverse effect of some components of the TIG-stainless steel welding fumes.

Temperature and circadian effects on metabolic rate of South American echimyid rodents, Trinomys setosus and Clyomys bishopi (Rodentia: Echimyidae)

Basal metabolic rate (BMR) represents the lowest level of metabolic activity capable to sustain homeostasis in an endotherm and is an important tool to compare metabolic rates of different species. Echimyidae is the most specious family within caviomorph rodents, however, little is known about the biology of its species, such as Trinomys setosus (Desmarest, 1817) and Clyomys bishopi (Ávila-Pires & Wutke, 1981), a ground and an underground dwelling echimyid, respectively. The ambient temperature and circadian effects on metabolic rate were evaluated through closed-system respirometry for these two species, as well as the circadian effects on CO2 production and respiratory exchange ratio (RER). Trinomys setosus and C. bishopi showed the lowest metabolic rates (0.56 ± 0.02 mLO2.h-1.g-1 and 0.53 ± 0.03 mLO2.h-1.g-1, respectively) at 32 °C and during the light phase. Under laboratory conditions, T. setosus showed metabolic rate variation compatible with nocturnal activity, whereas C. bishopi activity cycle remains unclear. Both species showed BMR lower than expected by allometric regressions for rodents.

Rev-erbα in the brain is essential for circadian food entrainment

Foraging is costly in terms of time and energy. An endogenous food-entrainable system allows anticipation of predictable changes of food resources in nature. Yet the molecular mechanism that controls food anticipation in mammals remains elusive. Here we report that deletion of the clock component Rev-erbα impairs food entrainment in mice. Rev-erbα global knockout (GKO) mice subjected to restricted feeding showed reduced elevations of locomotor activity and body temperature prior to mealtime, regardless of the lighting conditions. The failure to properly anticipate food arrival was accompanied by a lack of phase-adjustment to mealtime of the clock protein PERIOD2 in the cerebellum, and by diminished expression of phosphorylated ERK 1/2 (p-ERK) during mealtime in the mediobasal hypothalamus and cerebellum. Furthermore, brain-specific knockout (BKO) mice for Rev-erbα display a defective suprachiasmatic clock, as evidenced by blunted daily activity under a light-dark cycle, altered free-running rhythm in constant darkness and impaired clock gene expression. Notably, brain deletion of Rev-erbα totally prevented food-anticipatory behaviour and thermogenesis. In response to restricted feeding, brain deletion of Rev-erbα impaired changes in clock gene expression in the hippocampus and cerebellum, but not in the liver. Our findings indicate that Rev-erbα is required for neural network-based prediction of food availability.

Social interaction attenuates the extent of secondary neuronal damage following closed head injury in mice

Recovery following Traumatic Brain Injury (TBI) can vary tremendously among individuals. Lifestyle following injury, including differential social interactions, may modulate the extent of secondary injury following TBI. To examine this possibility under controlled conditions, closed head injury (CHI) was induced in C57Bl6 mice using a standardized weight drop device after which mice were either housed in isolation or with their original cagemates (“socially-housed”) for 4 weeks. CHI transiently impaired novel object recognition (NOR) in both isolated and social mice, confirming physical and functional injury. By contrast, Y maze navigation was impaired in isolated but not social mice at 1–4 weeks post CHI. CHI increased excitotoxic signaling in hippocampal slices from all mice, which was transiently exacerbated by isolation at 2 weeks post CHI. CHI slightly increased reactive oxygen species and did not alter levels of amyloid beta (Abeta), total or phospho-tau, total or phosphorylated neurofilaments. CHI increased serum corticosterone in both groups, which was exacerbated by isolation. These findings support the hypothesis that socialization may attenuate secondary damage following TBI. In addition, a dominance hierarchy was noted among socially-housed mice, in which the most submissive mouse displayed indices of stress in the above analyses that were statistically identical to those observed for isolated mice. This latter finding underscores that the nature and extent of social interaction may need to vary among individuals to provide therapeutic benefit.

Neither the SCN nor the adrenals are required for circadian time-place learning in mice

During Time-Place Learning (TPL), animals link biological significant events (e.g. encountering predators, food, mates) with the location and time of occurrence in the environment. This allows animals to anticipate which locations to visit or avoid based on previous experience and knowledge of the current time of day. The TPL task applied in this study consists of three daily sessions in a three-arm maze, with a food reward at the end of each arm. During each session, mice should avoid one specific arm to avoid a foot-shock. We previously demonstrated that, rather than using external cue-based strategies, mice use an internal clock (circadian strategy) for TPL, referred to as circadian TPL (cTPL). It is unknown in which brain region(s) or peripheral organ(s) the consulted clock underlying cTPL resides. Three candidates were examined in this study: (a) the suprachiasmatic nucleus (SCN), a light entrainable oscillator (LEO) and considered the master circadian clock in the brain, (b) the food entrainable oscillator (FEO), entrained by restricted food availability, and (c) the adrenal glands, harboring an important peripheral oscillator. cTPL performance should be affected if the underlying oscillator system is abruptly phase-shifted. Therefore, we first investigated cTPL sensitivity to abrupt light and food shifts. Next we investigated cTPL in SCN-lesioned- and adrenalectomized mice. Abrupt FEO phase-shifts (induced by advancing and delaying feeding time) affected TPL performance in specific test sessions while a LEO phase-shift (induced by a light pulse) more severely affected TPL performance in all three daily test sessions. SCN-lesioned mice showed no TPL deficiencies compared to SHAM-lesioned mice. Moreover, both SHAM- and SCN-lesioned mice showed unaffected cTPL performance when re-tested after bilateral adrenalectomy. We conclude that, although cTPL is sensitive to timing manipulations with light as well as food, neither the SCN nor the adrenals are required for cTPL in mice.

Effect of Two-step Time-restricted Feeding on the Fattening Traits in Geese

The present study was conducted to determine whether the two-step time-restricted feeding improves the fattening traits of one-step time-restricted feeding in geese. Thirty-six 8-wk-old geese were allotted into one of three groups. Group R1 (the 1-step restricted feeding group) was allowed access to feed for 2 h in the morning from 8 wk to 14 wk of age. Group R2 (the 2-step restricted feeding group) was treated as Group R1, but was additionally fed for 2 h in the afternoon from 12 wk to 14 wk of age. Group C (the control group) was fed ad libitum from 8 wk to 14 wk of age. Feed intake and body weight (BW) were recorded daily and weekly, respectively. At 14 wk of age, the blood samples were collected to determine the fasting plasma levels of glucose, triacylglycerols and uric acid before sacrifice. The results showed that daily feed intake (DFI) was lower, feed efficiency (FE) was higher in both Groups R1 and R2 than in Group C, and daily gain (DG) in Group R2 was higher than in Group R1 during the whole experimental period (p<0.05). Group R1 exhibited lower abdominal and visceral fat weights in carcass than did Group C (p<0.05), and Group R2 was in intermediate. The fasting plasma glucose levels in Group C were higher, and triacylglycerol levels in Group R1 were higher, compared with the other groups (p<0.05). It is concluded that time-restricted feeding in the fattening period not only increases FE but reduces DFI, and the additional meal during the late fattening period improves the DG without the expense of FE in geese.

The effects of feeding time and time-restricted feeding on the fattening traits of White Roman geese

This study comprises two trials that investigated the effects of feeding time and time-restricted feeding on the fattening traits and plasma metabolite levels of White Roman geese. In Trial I, 24 geese aged 8 weeks of each sex were allowed free access to a fattening diet for 1 h either in the morning (morning-feeding group) or afternoon (afternoon-feeding group). At 12 weeks of age, blood samples were collected hourly for 4 h, beginning 1 h after feeding to determine the plasma levels of glucose, triacylglycerols and uric acid. The results showed a lower (P<0.05) daily feed intake (DFI) and daily gain (DG) and higher (P<0.05) feed efficiency (FE) for the morning-feeding group compared with those of the afternoon-feeding group. In addition, the postprandial plasma levels of glucose, triacylglycerols and uric acid did not differ (P>0.05) between groups. In Trial II, 12 geese aged 8 weeks of each sex were randomly assigned to either the ad libitum feeding group (control group) or time-restricted feeding group (restricted group). The geese in the control group were fed a fattening diet ad libitum, whereas those in the restricted group were allowed access to the diet for 2 h every morning. All geese were killed at 13 weeks of age and their carcass traits were evaluated. The results showed a lower DFI and DG and higher FE for the restricted group compared with those of the control group (P<0.05). In addition, the restricted group exhibited lower visceral and abdominal fat and higher empty digestive tract and liver weights than those of the control group (P<0.05). The results showed that time-restricted feeding in the morning resulted in superior DG and FE compared with feeding in the afternoon. Moreover, time-restricted feeding implemented in the morning during the fattening period reduced DFI and increased FE in geese compared with ad libitum feeding.

Chronotolerance study of the antiepileptic drug valproic acid in mice

Background

Valproic acid (VPA) is an antiepileptic drug widely used for the treatment of absence seizures and generalized tonic-clonic seizures. The present work aims to study whether VPA-induced toxicity varies according to the dosing-time in the 24 hour-scale.

Methods

The influence of dosing-time on tolerance to VPA was investigated in 120 male Swiss mice synchronized under a light-dark cycle (12:12). The mean VPA lethal dose was first determined to be 850 ± 0.2 mg/kg, i.p.. Such a dose was administered by i.p. route to a total of 90 mice divided in six circadian stages [1, 5, 9, 13, 17 and 21 Hours After Light Onset (HALO)] (15 mice/circadian time); 30 mice were used as control (5 mice / circadian time).

Results

The surviving treated mice exhibited a significant circadian variation in rectal temperature and body weight loss (p < 0.001). The least rectal temperature change and body weight loss occurred when VPA was injected at 9 HALO. Drug dosing at 9 HALO resulted in -9 % weight loss whereas drug dosing at 17 HALO was -15 % (Ø = 20.3 HALO ± 1.1 h, p ≤ 0.0001). Lethal toxicity also varied according to circadian dosing-time (χ² = 42.1, p < 0.0001). The highest (60 %) and the lowest (6.67 %) survival rates were observed at 9 HALO and 17 HALO respectively. Cosinor analyses validated a significant circadian rhythm in survival duration with an acrophase at 8.4 HALO ± 0.75 h (p < 0.001).

Conclusions

With regards to these data the optimal tolerance to VPA occurred when the drug was administered in the second half of the light-rest span of mice which is physiologically analogous to the second half of the night for human patients.

Circadian rhythms in the hypothalamo-pituitary-adrenal (HPA) axis

The pronounced daily variation in the release of adrenal hormones has been at the heart of the deciphering and understanding of the circadian timing system. Indeed, the first demonstration of an endocrine day/night rhythm was provided by Pincus (1943), by showing a daily pattern of 17-keto-steroid excretion in the urine of 7 healthy males. Twenty years later the adrenal gland was one of the very first organs to show, in vitro, that circadian rhythmicity was maintained. In the seventies, experimental manipulation of the daily corticosterone rhythm served as evidence for the identification of respectively the light- and food-entrainable oscillator. Another 20 years later the hypothalamo-pituitary-adrenal (HPA)-axis was key in furthering our understanding of the way in which rhythmic signals generated by the central pacemaker in the hypothalamic suprachiasmatic nuclei (SCN) are forwarded to the rest of the brain and to the organism as a whole. To date, the adrenal gland is still of prime importance for understanding how the oscillations of clock genes in peripheral tissues result in functional rhythms of these tissues, whereas it has become even more evident that adrenal glucocorticoids are key in the resetting of the circadian system after a phase-shift. The HPA-axis thus still is an excellent model for studying the transmission of circadian information in the body.

Hippocampal testosterone relates to reference memory performance and synaptic plasticity in male rats

Steroids are important neuromodulators influencing cognitive performance and synaptic plasticity. While the majority of literature concerns adrenal- and gonadectomized animals, very little is known about the “natural” endogenous release of hormones during learning. Therefore, we measured blood and brain (hippocampus, prefrontal cortex) testosterone, estradiol, and corticosterone concentrations of intact male rats undergoing a spatial learning paradigm which is known to reinforce hippocampal plasticity. We found significant modulations of all investigated hormones over the training course. Corticosterone and testosterone were correlated manifold with behavior, while estradiol expressed fewer correlations. In the recall session, testosterone was tightly coupled to reference memory (RM) performance, which is crucial for reinforcement of synaptic plasticity in the dentate gyrus. Intriguingly, prefrontal cortex and hippocampal levels related differentially to RM performance. Correlations of testosterone and corticosterone switched from unspecific activity to specific cognitive functions over training. Correspondingly, exogenous application of testosterone revealed different effects on synaptic and neuronal plasticity in trained versus untrained animals. While hippocampal long-term potentiation (LTP) of the field excitatory postsynaptic potential (fEPSP) was prolonged in untrained rats, both the fEPSP- and the population spike amplitude (PSA)-LTP was impaired in trained rats. Behavioral performance was unaffected, but correlations of hippocampal field potentials with behavior were decoupled in treated rats. The data provide important evidence that besides adrenal, also gonadal steroids play a mechanistic role in linking synaptic plasticity to cognitive performance.

Circadian rhythm of stroke onset during the month of Ramadan

BACKGROUND AND PURPOSE

The onset of acute stroke exhibits a circadian pattern occurring more frequently in late morning hours. The objective of this study was to investigate the diurnal pattern of stroke during the month of Ramadan.

PATIENTS AND METHODS

We studied consecutive stroke patients 1 month before Ramadan (BR) and during Ramadan (DR) over two successive years 2007 and 2008. The age, gender, risk factor profiles were analyzed. The National Institute of Health and Stroke Scale Score (NIHSS) was used for clinical assessment at admission. The exact time of stroke onset in both groups was obtained.

RESULTS

A total of 507 patients were studied: 245 patients in the DR group and 262 patients in the BR group. The age distribution of patients was not significantly different between the two groups. There was no statistically significant difference in the sex ratio, risk factors, and NIHSS score between the two groups (P > 0.05). The higher frequency of stroke onset time in the BR group was in the time between 6:00 a.m. and noon; whereas the frequency was higher between noon and 6:00 p.m. in the DR group.

CONCLUSION

A significant shift of the circadian pattern of stroke onset time from the period between 6:00 a.m. and noon to that between noon and 6:00 pm has been found during the month of Ramadan.

Murine chronotoxicity to the antiallergic agent, cetirizine

Cetirizine is a second-generation histamine H1-receptor antagonist used in the treatment of allergic diseases. The aim of the study was to assess whether cetirizine toxicity estimated by, for example, death, body loss, and leucopenia, is circadian rhythm dependent. A total of 210 male Swiss mice, aged 9 weeks, were synchronized for 3 weeks to 12-hour light (i.e., rest span)/12-hour dark (i.e., activity span) cycles. The drug was administered per os (orally). Each lethal (DL(50) = 750 mg/kg) and sublethal (DT(50) = 55 mg/kg) dose was administered to comparable groups of animals at six different circadian time points (1, 5, 9, 13, 17, and 21 hours after light onset; HALO). The death rate was dosing time dependent (P <0.001). Drug dosing at 5 HALO resulted in maximum mortality (76.75%), whereas dosing at 17 HALO resulted in the lowest mortality rate (16.7%). Cosinor analyses validated a statistically significant circadian rhythm in death rate (P < 0.008). Changes in body weight after cetirizine administration were dosing time dependent (P < 0.01), with the dosing time of least effect (-0.7% loss) at 17 HALO and of greatest effect (-7% loss) at 5 HALO. Cosinor analyses validated a statistically significant circadian rhythm in body loss (P < 0.05). A statistically significant decrease in leukocyte number varied, according to antihistamine dosing time (P < 0.01), with the dosing time of least leucopenia (≈-17%) at 17 HALO and of greatest leucopenia (≈-28%) at 5 HALO. The results show that cetirizine dosing time at the midactivity (dark) span seems to be optimal, since it corresponds to the best tolerance.

Food for thoughts: feeding time and hormonal secretion

Many daily cycles are imposed on us by our environment, such as alternating days and nights, temperature fluctuations or rhythms in food availability. When food is accessible every day at the same time, animals will adapt their physiology and behaviour to match the daily meal. They will anticipate the access to food by waking up and being active in the hours prior to feeding, foraging for food. Adaptation of physiology to changing conditions of food availability is not only evident at the behavioural level, but also for hormonal systems. Thus, corticosteroids, melatonin, leptin/ghrelin, insulin/glucagon, orexins and thyroid hormones, which show rhythmic profiles of secretion in ad libitum feeding conditions, are sensitive to increase and/or depletion in energy supplies and will be influenced when food sources are limited or available at unusual times. The present review reports the influence of restricted feeding schedules on secretion profiles of diverse hormones compared to normal ad libitum feeding conditions in rodents. In the end, the interplay between these systems and their response to environmental challenges will allow the animal to maintain their fitness for survival.

Circadian Time‐Dependent Differences in Murine Tolerance to the Antihistaminic Agent Loratadine

Loratadine is a second-generation histamine H(1)-receptor antagonist used in the treatment of allergic diseases. The aim of the study was to assess whether lethal toxicity and motor incoordination (neurotoxicity) of loratadine is circadian rhythm-dependent. A total of 210 male Swiss mice, aged 10 wk, were synchronized for 3 wk to 12 h light (rest span)/12 h dark (activity span). The drug was administered per os. The choice of the sublethal (TD(50) = 82 mg/kg body weight) and the lethal (LD(50) = 4 g/kg body weight) dosage was based on preliminary studies. Each of these two doses was administered to comparable groups of animals at six different circadian time points (1, 5, 9, 13, 17, and 21 Hours After Light Onset [HALO]). The survival duration was dosing time-dependent (chi(2) = 16.96; p < 0.001). Drug dosing at 17 HALO resulted in best (67%) survival rate; whereas, dosing at 9 HALO resulted in poorest (21%) survival rate. Cosinor analyses (with a trial period tau = 24 h) validated a statistically significant circadian rhythm in survival rate (p < 0.04) with an acrophase (peak time Ø of best tolerance to loratadine) being at 17.5 HALO +/- 4.65 h. Troughs of motor incoordination were located at the administration times of 5 and 17 HALO (60% and 32% of animals affected, respectively), whereas peaks were located at 9 and 21 HALO (87% and 68% of animals affected, respectively). The 24 h mean of the motor incoordination was 61%, the mean proportion of animals affected by the treatment for the six different circadian times studies. The extent of this neurotoxic effect varied as a function of loratadine dosing time (p < 0.001). A statistically significant ultradian component rhythm (p < 0.01) with a trial period tau = 12 h was also validated. The obtained results show that the dosing time of loratadine at the mid-activity (dark) span seems to be optimal, since it corresponds to the longest (21 vs. 12 days) survival span and to least neurotoxicity.

Inducible clocks: living in an unpredictable world

All mammals have daily cycles of behavior (e.g., wake-sleep and feeding), and physiology (e.g., hormone secretion and body temperature). These cycles are typically entrained to the external light/dark cycle, but they can be altered dramatically under conditions of restricted food availability, changes in ambient temperature, or the presence of external stimuli such as predators. During the past 30 years, one of the best studied of these responses has been the entrainment of circadian rhythms to food availability. Experiments in rats and other rodents have provided evidence for a food-entrainable oscillator (FEO) in the mammalian circadian timing system (CTS). Until recently, however, very little was understood about the locus subserving the FEO or the functional interrelationship between the FEO and the master CTS pacemaker, the suprachiasmatic nucleus (SCN). We discuss here new data on the location of the FEO and suggest that it may involve an oscillator mechanism that is "induced" by starvation and refeeding.

Modifications of local cerebral glucose utilization during circadian food-anticipatory activity

Food-anticipatory activity that animals express before a daily timed meal is considered as the behavioral output of a feeding-entrainable oscillator whose functional neuroanatomy is still unknown. In order to identify the possible brain areas involved in that timing mechanism, we investigated local cerebral metabolic rate for glucose during food-anticipatory activity produced either by a 4-h daily access to food starting 4 h after light onset or by a hypocaloric feeding provided at the same time. Local cerebral metabolic rate for glucose measured by the labeled 2-[(14)C]-deoxyglucose technique was quantified in 40 structures. In both groups of food-restricted rats, three brain regions (the nucleus of the solitary tract, the cerebellar cortex and the medial preoptic area) showed a decrease in local cerebral metabolic rate for glucose, compared with control ad libitum animals. In addition, only one structure, the paraventricular thalamic nucleus, was affected by temporal restricted feeding, and not by hypocaloric feeding, compared with ad libitum rats. By contrast, three brain regions, i.e. the intergeniculate leaflets, the paraventricular hypothalamic and the arcuate nuclei, showed specifically metabolic decreases during anticipation of hypocaloric feeding, and not during anticipation of temporal restricted feeding, compared with the ad libitum group. Expression of food-anticipatory activity appears to be regulated by an integrated neural circuit of brainstem and hypothalamic pathways, with hypocaloric feeding involving more extensive forebrain areas than temporal restricted feeding.

Response of circulating leptin to Ramadan daytime fasting: a circadian study

Although the effects of short-term fasting on serum leptin concentrations are known, those resulting from long-lasting modifications of food intake schedule, as during the month of Ramadan, have not yet been extensively studied. Therefore, serum concentrations of leptin were measured around the clock at 4-hourly intervals before the beginning of Ramadan and on the twenty-third day of Ramadan daytime fasting in ten male subjects keeping the same usual activity pattern and general synchronisation in both situations. Time series were analysed with repeated measures ANOVA and Cosinor. No significant changes in amplitude or 24 h mean concentration were seen, but significant shifts of 5 h 30 min in peak and trough serum leptin levels were found on the twenty-third day of Ramadan.

[Circadian rhythms in the toxic effects of the histamine antagonist cetirizine in mice]

Cetirizine is a second generation histamine H(1) receptor antagonist used to provide symptomatic relief of allergic signs caused by histamine release. The aim of the study was to learn whether the survival and the motor incoordination (ataxia) side effect of cetirizine administration is dosing time-dependent.

MATERIALS AND METHODS

A total of 240 male Swiss mice, 10 weeks of age were synchronized for 3 weeks by 12 h light (rest span)/12 h dark (activity span). Different doses of cetirizine were administered orally at fixed times during the day to determine both the sublethal (TD(50)) and lethal (LD(50)) doses, which were, respectively, 55 +/- 0.35 and 750 +/- 0.40 mg/kg. In the chronotoxicologic study a single dose of cetirizine (DL(50)) was administered to comparable groups of animals at six different circadian stages [1, 5, 9, 13, 17, 21 h after light onset (HALO)].

RESULTS

The survival was statistically significant dosing time-dependent (chi(2) = 16.73; P < 0.001). Drug dosing at 17 HALO resulted in 83.3% survival rate whereas drug dosing at 5 HALO was only 23.25%. Cosinor analysis revealed a statistically significant circadian (period approximately 24 h) rhythmic component in survival. Lowest (20%) and highest (88%) ataxia occurred when cetirizine was administered, respectively, at 17 and 5 HALO. Cosinor analysis revealed a statistically significant circadian (period approximately 24 h) rhythmic component in ataxia.

CONCLUSION

Our results reveal that the best safety is shown when cetirizine is administered in the middle of the dark (activity) span of the mice, since it produces some side effects: ataxia and hyperthermia. Taking into account of the hour administration of cetirizine, improves treatment efficacy and permit the best control of allergic diseases.

Scaling the amplitudes of the circadian pattern of resting oxygen consumption, body temperature and heart rate in mammals

We questioned whether the amplitudes of the circadian pattern of body temperature (T(b)), oxygen consumption (V (O(2))) and heart rate (HR) changed systematically among species of different body weight (W). Because bodies of large mass have a greater heat capacitance than those of smaller mass, if the relative amplitude (i.e., amplitude/mean value) of metabolic rate was constant, one would expect the T(b) oscillation to decrease with the increase in the species W. We compiled data of T(b), V (O(2)) and HR from a literature survey of over 200 studies that investigated the circadian pattern of these parameters. Monotremata, Marsupials and Chiroptera, were excluded because of their characteristically low metabolic rate and T(b). The peak-trough ratios of V (O(2)) (42 species) and HR (35 species) averaged, respectively, 1.57+/-0.08, and 1.35+/-0.07, and were independent of W. The daily high values of T(b) did not change, while the daily low T(b) values slightly increased, with the species W; hence, the high-low T(b) difference (57 species) decreased with W (3.3 degrees C.W(-0.13)). However, the decrease in T(b) amplitude with W was much less than expected from physical principles, and the high-low T(b) ratio remained significantly above unity even in the largest mammals. Thus, it appears that in mammals, despite the huge differences in physical characteristics, the amplitude of the circadian pattern is a fixed (for V (O(2)) and HR), or almost fixed (for T(b)), fraction of the 24-h mean value. Presumably, the amplitudes of the oscillations are controlled parameters of physiological significance.

Effects of meal timing on tumor progression in mice

Meal timing can reset circadian clocks in peripheral tissues. We investigated the effects of such non-photic entrainment on tumor growth rate. Two experiments involved a total of 61 male B6D2F(1) mice synchronized with an alternation of 12 h of light (L) and 12 h of darkness (D) (LD12:12). Mice were randomly allocated to have access to food ad libitum, or restricted to 4 or 6 h during L or D. Rest-activity and body temperature, two circadian outputs, were monitored with an intra-peritoneal sensor. Glasgow osteosarcoma was inoculated into both flanks of each mouse ten days after meal timing onset. Before tumor inoculation, meal timing during D amplified the 24-h rhythms in rest-activity and body temperature with minimal phase alteration as compared to ad libitum feeding. Conversely, meal timing during L induced dominant 12-h or 8-h rhythmic components in activity, nearly doubled the 24-h amplitude of body temperature and shifted its acrophase (time of maximum) from approximately mid-D to approximately mid-L. Thirteen days after tumor inoculation, mean tumor weight (+/- SEM, mg) was 1503 +/- 150 in ad libitum mice, 1077 +/- 157 in mice fed during D and 577 +/- 139 in mice fed during L (ANOVA, p < 0.0001). Overall survival was prolonged in the mice fed during L (median, 17.5 days, d) as compared with those fed during D (14.5 d) or ad libitum (14 d) (Log Rank, p = 0.0035). The internal desynchronization produced by meal timing during L slowed down tumor progression, an effect possibly resulting from improved host-mediated tumor control and/or altered tumor circadian clocks.

Food-entrained circadian rhythms are sustained in arrhythmic Clk/Clk mutant mice

Daily scheduled feeding is a potent time cue that elicits anticipatory activity in rodents. This food-anticipatory activity (FAA) is controlled by a food-entrainable oscillator (FEO) that is distinct from light-entrained oscillators of the suprachiasmatic nucleus (SCN). Circadian rhythms within the SCN depend on transcription-translation feedback loops in which CLOCK protein is a key positive regulator. The Clock gene is expressed in rhythmic tissues throughout the brain and periphery, implicating its widespread involvement in the functioning of circadian oscillators. To examine whether CLOCK protein is also necessary for the FEO, the effect of daily food restriction was studied in homozygous Clock mutant (Clk/Clk) mice. The results show that Clk/Clk mutant mice exhibit FAA, even when their circadian wheel-running behavior is arrhythmic. As in wild-type controls, FAA in Clk/Clk mutants persists after temporal feeding cues are removed for several cycles, indicating that the FEO is a circadian timer. This is the first demonstration that the Clock gene is not necessary for the expression of a circadian, food-entrained behavior and suggests that the FEO is mediated by a molecular mechanism distinct from that of the SCN.

Circadian rhythm of some parameters of body composition in the elderly investigated by means of bioelectrical impedance analysis

We studied the within-day determinations of some body composition (BC) parameters in clinically healthy elderly subjects with the aim of investigating their circadian rhythms (CR), which are known to vary in a circadian manner in clinically healthy young adults. The study involved six non-smoking, clinically healthy elderly males (mean age: 75 +/- 4 years; mean weight: 71.07 +/- 10.26 kg; mean height: 170 +/- 5 cm, mean BMI: 24 +/- 1 kg/m2). The BC parameters were determined by means of bioelectrical impedance analysis (BIA) at 2-hour intervals during the day and night, with the subjects lying horizontally in bed. The time-qualified BC estimates were analysed using the Cosinor method. The analysis revealed that the healthy elderly subjects had lost the CR of a number of the BC parameters, including fat body mass, cell body mass, extracellular body mass, total body water, extracellular body water, intracellular body water, and the Na and K exchangeable pools. However, they still retained the CR of body weight and lean body mass, with the expected nocturnal phase of oscillation. The abolition of the CR of the majority of BC parameters in the elderly suggests that human senescence is characterised by consistent changes in the daily rhythmic patterns of fat, water and electrolyte metabolism.

Effects of a 1 day fast on biohumoral variables associated with human circadian rhythmicity

1. The aim of the present study was to investigate the effects of a short (1 day) fast by testing biohumoral variables associated with the human circadian rhythm. 2. Fifteen clinically healthy male volunteers (32 +/- 8 years old) participated in the study. Subjects were fed a control diet for 7 days. The last day was a control day and the following 8th day was the fasting day. Each subject was asked to collect urine seven times over a 24 h period. Chemical and hormonal variables were measured in each fractionated urine specimen. The time- qualified urinary excretion rates were biometrically analysed using conventional and chronobiological methods. 3. During fasting, significant incremental changes were detected in the urinary excretion rates of potassium, aldosterone, 17-hydroxycorticosteroids and adrenaline and significant decremental changes were detected in the excretion rates of sodium, chloride, creatinine, urea nitrogen, uric acid, 17-ketosteroids, noradrenaline and dopamine. The circadian rhythmicity of the variables was well preserved and remained almost stable throughout the fasting phase. 4. Fasting affected the mean oscillatory levels and oscillatory amplitudes of variables, suggesting that nutrients may have played roles as tonic and phasic modulators on the mechanisms that physiologically regulate ircadian rhythmicity.

Telemetry provides new insights into entrainment of activity wheel circadian rhythms and the role of body temperature in the development of ulcers in the activity-stress paradigm

Two methods of monitoring the circadian rhythm of activity in rodents: (1) an activity wheel cage, which detects the number of wheel revolutions, and (2) an internal radio transmitter, which records gross motor activity (GMA) of the animal, were compared in both normal circadian cycles and during the development of activity-stress ulcers. Rats were implanted with a biotelemetry transmitter that detected GMA and body temperature (BT) and placed in activity wheel cages. A 12 hour/12 hour light/dark cycle was maintained throughout the experiment. Subjects were subdivided into two groups: (1) unlimited access to activity wheel (AW) cages and (2) locked activity wheel (LW) cages. Following an ad-libitum habituation period, animals were allowed food access for 1 hour/day during the light. In the habituation period, the animals showed higher GMA and BT during the dark phase when housed in AW cages than in LW cages. Both GMA and number of wheel revolutions increased dramatically after the onset of food restriction for the AW animals. There was a deleterious drop in BT in AW animals as the food-restricted period continued and a significant correlation existed between severity of ulcerations and BT. The findings of this experiment demonstrate that the activity wheel imposes an alternation of the circadian cycle, which, in turn, influences rhythmicity through reentrainment. Additionally, in the activity-stress paradigm, a significant drop in BT correlates with severity of ulcerations. A disrupted circadian cycle, involving hypothermia, is proposed as the mechanism underlying the demise of animals in the activity-stress paradigm.

Temporal and spatial adaptation to food restriction in mice under naturalistic conditions

Free-living female laboratory mice, adapted to outdoor life in large pens providing a naturalistic environment, were tested for their ability to modify their foraging habits to controlled food supply. An automatic feeder box delivered a small portion of the daily quantity of seeds to each individual mouse. Eight such boxes were placed into an outdoor pen. Each day, mice had to visit all boxes to gather the daily amount of food and were rewarded only at the first visit to each box. Mice were individually recognised by an implanted microchip. Throughout a 16-day period, feeding activity concentrated in an interval time around the beginning of the daily session. During the same period, the number of different feeders visited every day by mice increased irrespective of variation in exploratory activity. The experimental set-up allowed detecting temporal and spatial adaptations to the food restriction, as well as behavioural differences due to territorial and social factors. These data permit the design of novel tests assessing behavioural changes, memory and learning in normal and genetically modified mice, both in the laboratory and in naturalistic settings.

How enteral feeding options influence corticosterone patterns in rats

Even with all the nutritional research conducted to date, it is not clear which enteral nutrition delivery and composition options are most physiologically sound. Glucocorticoid temporal patterns are reported to be shifted or disrupted with restricted feeding schedules, but because of intermittent sampling, temporal patterns have not been completely depicted. The purpose of this study was to characterize corticosterone temporal patterns while systematically varying selected enteral feeding options in a well-established nutritional animal model. A 2 x 2 x 2 x 2 randomized block experimental design was used in which enteral feeding schedules, delivery methods, kilocalorie levels (kcal), and fiber contents were systematically varied in rats (n = 80), and plasma corticosterone was measured by 125I radioimmunoassay. Blood samples were drawn hourly over 24 h. With cosinor analysis, 24-h and 12-h corticosterone rhythmic components were tested in each feeding group. Five of 16 feeding groups had a significant (p < or = 0.05) 24-h rhythmic component, and 3 more showed a trend (p > 0.05 < 0.10); 7 of these groups were on 24-h feeding schedules. When rhythmic components were detectable, groups receiving high-fiber formula displayed more uniform rhythm characteristics than did no-fiber groups. Only 1 group had a significant 12-h rhythmic component, and 1 showed a trend. Both were on 12-h, high-fiber restricted kcal feedings. In this small animal sample, no one enteral feeding option guaranteed a 24-h corticosterone pattern. The option coming closest was formula delivered on a 24-h schedule. This temporal pattern is one aspect to consider in enteral nutrition. The underlying mechanisms have yet to be elucidated.

Entrainment in calorie-restricted mice: conflicting zeitgebers and free-running conditions

Phase-shifting effects of timed calorie restriction were investigated in mice during exposure to a 12:12-h light-dark cycle. Food-anticipatory activity (FAA), the output of a food-entrainable pacemaker, was expressed before the time of feeding whether mice received daily hypocaloric food (3.3 g of chow/day) or normocaloric food (5 g of chow/day) at zeitgeber time (ZT) 2 (ZT12 = lights off). Subsequently, mice were placed in constant darkness and fed ad libitum. The onset of the nocturnal period of locomotor activity was phase advanced by 1 h in calorie-restricted mice compared with normocalorie-fed controls. The phase advance still occurred when FAA was prevented by restraining calorie-restricted mice. Giving hypocaloric food at ZT2, ZT10, ZT14, or ZT22 phase advanced the nocturnal pattern of activity by 1, 3, 1, and 1 h, respectively. After transfer to constant darkness, FAA free ran in parallel with the normal nocturnal period of locomotor activity. A light pulse during the early subjective night phase delayed both components. These results indicate that 1) timed calorie restriction under a light-dark cycle can phase advance the light-entrainable pacemaker with a phase-dependent magnitude, 2) FAA feedback is not crucial for the observed phase advance, and 3) the light-entrainable pacemaker may control the period of the food-entrainable pacemaker in mice fed ad libitum.

Food and the circadian activity of the hypothalamic-pituitary-adrenal axis

Temporal organization is an important feature of biological systems and its main function is to facilitate adaptation of the organism to the environment. The daily variation of biological variables arises from an internal time-keeping system. The major action of the environment is to synchronize the internal clock to a period of exactly 24 h. The light-dark cycle, food ingestion, barometric pressure, acoustic stimuli, scents and social cues have been mentioned as synchronizers or "zeitgebers". The circadian rhythmicity of plasma corticosteroids has been well characterized in man and in rats and evidence has been accumulated showing daily rhythmicity at every level of the hypothalamic-pituitary-adrenal (HPA) axis. Studies of restricted feeding in rats are of considerable importance because they reveal feeding as a major synchronizer of rhythms in HPA axis activity. The daily variation of the HPA axis stress response appears to be closely related to food intake as well as to basal activity. In humans, the association of feeding and HPA axis activity has been studied under physiological and pathological conditions such as anorexia nervosa, bulimia, malnutrition, obesity, diabetes mellitus and Cushing's syndrome. Complex neuroanatomical pathways and neurochemical circuitry are involved in feeding-associated HPA axis modulation. In the present review we focus on the interaction among HPA axis rhythmicity, food ingestion, and different nutritional and endocrine states.

Chronic dietary restriction influences tumor metastasis in the rat: parametric considerations

Chronic dietary restriction is a well-documented means of inhibiting tumor growth. This study examines the effects of chronic dietary restriction on tumor metastasis in the rat. We investigate the effect of 1) the degree of food restriction, 2) the effect of preexposure to food restriction, and 3) the duration of food restriction after tumor inoculation on tumor metastasis. We also compare two methods of dietary restriction: 1) the time that food is available and 2) the amount of food available. Our findings demonstrate that rats restricted to 50% of ad libitum diet for one week before inoculation with MADB106 tumor cells and for three weeks after inoculation exhibit a significant (p < 0.001) reduction in lung colonization compared with animals fed ad libitum. Animals restricted to access to food for 4 hrs/day (60% of ad libitum) for the same period of time exhibit significantly (p < 0.005) greater lung tumor colonization than animals fed ad libitum. Preadaptation to the feeding regimen for one week before tumor inoculation proved to be critical in inhibiting tumor metastasis. The tumor-inhibitory effect was not significantly influenced by the duration of restriction after inoculation or by the manner in which food restriction was implemented. Finally, we demonstrate that inhibition of tumor colonization may be mediated by enhanced natural killer cell activity in the early postinoculation period.

Phase-advanced daily rhythms of melatonin, body temperature, and locomotor activity in food-restricted rats fed during daytime

This study was performed to investigate possible effects of a timed caloric restriction on the light-dark (LD) synchronization of four biological rhythms pair-studied in the same animals. In Experiment 1, food-restricted rats kept under a photoperiod of 12 h light:12 h dark received 50% of previous ad libitum food 2 h after the onset of light. Their daily rhythm of pineal melatonin and rhythms of plasma melatonin and corticosterone were examined and compared to those of ad libitum control rats after 1 or 2 months of food restriction. A significant phase advance (about 2 h) was found for the pineal melatonin rhythm and for the daily onset of plasma melatonin. Timing of nocturnal peak of circulating corticosterone was unchanged, and a diurnal peak anticipated food presentation by about 2 h. In Experiment 2, effects of a timed caloric restriction under 12L:12D were studied on the expression of daily rhythms of body temperature and locomotor activity. To discriminate between the effects of timed meal feeding and those of the added caloric restriction, these rhythms were analyzed in food-restricted rats, as in Experiment 1, and were compared to those in sham-restricted rats, concomitantly fed twice more than food-restricted rats (i.e., a timed meal feeding without caloric restriction). Acrophase of the nocturnal peak of body temperature rhythm reached the greatest phase advance (7 h) in food-restricted rats, in which it was close to LD transition. The nocturnal component of locomotor activity rhythm also was markedly phase advanced (6 h) by caloric restriction, as indicated by wheel-running and general activity occurring form early afternoon to midnight. A smaller 4-h phase advance of the nocturnal peak of body temperature also was observed in sham-restricted rats, although the onset of locomotor activity rhythm apparently was unaffected by meal feeding and the end of activity rhythm was phase advanced by 2 h. These results indicate that timed caloric restriction is a potent phase-shifting agent that interacts with the LD cycle zeitgeber. This nonphotic stimulus phase advances melatonin, corticosterone, body temperature, and activity rhythms to different extents and thus suggests a change in the internal synchronization of the circadian system.

Multiple cytokines and acute inflammation raise mouse leptin levels: potential role in inflammatory anorexia

Several inflammatory cytokines, most notably tumor necrosis factor (TNF) and IL-1, induce anorexia and loss of lean body mass, common manifestations of acute and chronic inflammatory conditions. In C57BL/6 female mice, the administration of TNF, IL-1, and, to a lesser extent, leukemia inhibitory factor (LIF), produced a prompt and dose-dependent increase in serum leptin levels and leptin mRNA expression in fat. IL-10, IL-4, ciliary neurotrophic factor, and IL-2, cytokines not known to induce anorexia or decrease food intake, had no effect on leptin gene expression or serum leptin levels. After administration of Escherichia coli lipopolysaccharide (LPS), leptin gene expression and leptin levels were increased. These findings suggest that leptin levels may be one mechanism by which anorexia is induced during acute inflammatory conditions.

Weight loss is greater with consumption of large morning meals and fat-free mass is preserved with large evening meals in women on a controlled weight reduction regimen

The purpose of this study was to determine whether meal ingestion pattern [large morning meals (AM) vs. large evening meals (PM)] affects changes in body weight, body composition or energy utilization during weight loss. Ten women completed a metabolic ward study of 3-wk weight stabilization followed by 12 wk of weight loss with a moderately energy restricted diet [mean energy intake +/- SD = 107 +/- 6 kJ/(kg.d)] and regular exercise. The weight loss phase was divided into two 6-wk periods. During period 1, 70% of daily energy intake was taken as two meals in the AM (n = 4) or in the PM (n = 6). Subjects crossed over to the alternate meal time in period 2. Both weight loss and fat-free mass loss were greater with the AM than the PM meal pattern: 3.90 +/- 0.19 vs. 3.27 +/- 0.26 kg/6 wk, P < 0.05, and 1.28 +/- 0.14 vs. 0.25 +/- 0.16 kg/6 wk, P < 0.001, respectively. Change in fat mass and loss of body energy were affected by order of meal pattern ingestion. The PM pattern resulted in greater loss of fat mass in period 1 (P < 0.01) but not in period 2. Likewise, resting mid-afternoon fat oxidation rate was higher with the PM pattern in period 1 (P < 0.05) but not in period 2, corresponding with the fat mass changes. To conclude, ingestion of larger AM meals resulted in slightly greater weight loss, but ingestion of larger PM meals resulted in better maintenance of fat-free mass. Thus, incorporation of larger PM meals in a weight loss regimen may be important in minimizing the loss of fat-free mass.

Circadian rhythms in human body composition

The study investigates how the human body composition (BC) changes as a function of the day-night cycle. The BC was investigated using bioelectrical impedance analysis (BIA) of 10 clinically healthy subjects (CHS), monitored in supine position (readings at 2-h intervals), avoiding mealtimes, dietary abuses, and bladder and intestinal retention. Time series data were analyzed for their temporal characteristics and circadian rhythm (CR). All the variables of BC (lean body mass, fat body mass, body cell mass, total body water, intracellular and extracellular body water, sodium and potassium exchangeable pool) showed a within-day variability with nighttime crests. Such an oscillatory synchronism corroborates the hypothesis that the rest time plays a fundamental role, via its anabolic effects, in conferring the nocturnal phase to the CR of the human BC.

Daily hypocaloric feeding entrains circadian rhythms of wheel-running and body temperature in rats kept in constant darkness

Since high levels of physical activity are known to interact with the circadian system, we tested whether hyperactivity induced by hypocaloric feeding may facilitate the synchronizing effect of periodic feeding in rats in constant darkness. Wheel-running (WRR) and body temperature (BTR) rhythms were analyzed in rats fed daily 50% of ad libitum food intake. In addition to a feeding-associated component (FAC) expressed for both rhythms, WRR and BTR were phase-shifted towards the feeding time by 12.1 +/- 0.4 and 12.4 +/- 0.4 h, respectively. BTR and FAC of temperature merged into a single cosine-wave food-entrained rhythm (FER) of temperature. Similarly, WRR and FAC of activity merged into a unimodal FER of wheel-running. This indicates that daily hypocaloric feeding may synchronize circadian rhythms in rats.

Control by light of the temperature rhythm in food-restricted hamsters

To establish the relative importance of light and food in the control of core temperature (Tc) rhythm in food-restricted hamsters, mature female hamsters maintained in 14L:10D lighting were fed restricted amounts of food at the onset of light (n = 6) or at the onset of dark (n = 6) and were compared to ad lib-fed animals. After 21-25 days of this entrainment, light stimulus was shifted by 12 h, and animals were kept in shifted lighting for another 13 days. Food restriction led to a 0.6 degree decrease in the mean Tc, which was expressed entirely during the day in night-fed hamsters and was evenly divided between day and night in day-fed animals. Thus, Tc and general activity rhythms maintained the entrainment to light under both dietary conditions, with peak values for all occurring during the early night. During 13 days following the 12-h shift in lighting, Tc and activity rhythms shifted in all animals, regardless of nutritional status, from entrainment to preceding lighting, through double rhythm frequency, indicating entrainment to preceding as well as current lighting, to entrainment to current lighting. Thus, in food-restricted hamsters, light stimulus rather than predictable timing of food prevails as the entrainer of Tc and activity rhythms.

Influence of feeding schedule on chronopharmacological aspects of gentamicin in mice

The effects of the time of day of drug administration on the subchronic toxicity and pharmacokinetics of gentamicin, as well as the role of feeding schedule on circadian rhythms, were investigated in mice. ICR male mice were housed in a light-dark (LD) cycle (12:12) with food and water ad libitum (ALF) or under a time-restricted feeding (TRF) schedule (feeding time: 8 h during the light phase) for 1 day or 14 days before drug administration. The animals were given a single subcutaneous dose of gentamicin 180 mg/kg for the kinetic studies and subcutaneous doses of gentamicin 180 mg/kg/day for 14 days or 220 mg/kg/day for 18 days for the subchronic toxicity studies. A significant dosing-time dependency was shown for mortality and body weight loss, with higher values at midlight and lower ones at the middark (p < 0.05). A significant circadian rhythm was also found for gentamicin kinetics in ALF mice, with the highest clearance at middark and the lowest one at midlight (p < 0.01). The kinetic rhythm of gentamicin coincided well with the toxicity rhythm of the drug. The TRF schedule had a marked influence on the rhythms of gentamicin kinetics and toxicity, showing lowest clearance and higher toxicity at middark. The rhythm of subchronic toxicity of gentamicin seems to be due, at least in part, to the rhythm in kinetics and is strongly influenced by the feeding schedule. Thus, the timing of dosing is an important factor in the kinetics and the subchronic toxicity of gentamicin administration in mice, and the manipulation of feeding schedule can modify the rhythm of the toxicity by changing the rhythm of gentamicin kinetics.

Patterns of body temperature during feeding in rats under varying ambient temperatures

Relationships between feeding and body temperature of rats were investigated at three ambient temperatures during the whole light/dark cycle. Basal liver temperature was negatively correlated with ambient temperature. Only at 29 degrees C liver temperature indicated activation of autonomic and locomotory thermoregulatory responses due to heat stress. At 21 degrees C, liver temperature was always higher than skin temperature. Both showed a clear circadian rhythm with higher values during the dark phase. Meal-associated temperature patterns were superimposed on this circadian rhythm. Liver and skin temperatures showed a preprandial and prandial rise. Liver temperature reached an almost similar peak value just above 39 degrees C at the end of a meal, irrespective of meal size and ambient temperatures of 13 degrees C and 21 degrees C. Liver temperature reached this peak about 2 min earlier and dropped sooner than skin temperature. These results indicate a threshold liver temperature at which feeding activity stops. The present study suggests that temperatures do not exceed this value by adaptive autonomic thermoregulatory responses shifting heat flow from core to skin and by stopping all locomotory activities including feeding, thereby avoiding deterioration of vital organs and physiological processes due to hyperthermia.

Nursing chronotherapeutics: a conceptual framework

Nurses frequently make decisions about when treatments and actions are performed. The nursing concern driving this review is the timing of nursing activities to optimize desired and minimize untoward effects. A nursing conceptual framework is proposed that highlights individual and environmental factors, as they relate to rhythmic responses; as well as places within the framework for nursing actions based on customary and usual temporal patterns.

The circadian rhythm of body temperature

This paper reviews the literature on the circadian rhythm of body temperature (CRT). The review starts with a brief discussion of methodological procedures followed by the description of known patterns of oscillation in body temperature, including ultradian and infradian rhythms. Special sections are devoted to issues of species differences, development and aging, and the relationships between the CRT and the circadian rhythm of locomotor activity, between the CRT and the thermoregulatory system, and between the CRT and states of disease. A section on the nervous control of the CRT is followed by summary and conclusions.

Circadian variation in the gastric-emptying response to eating in rats previously fed once or twice daily

Four experiments dealt with circadian variation in the gastric emptying (GE) response to eating, among rats accustomed to eating once (1x) or twice daily (2x). In measuring GE response, a test meal [10 g accustomed diet per (kg body weight)3/4] was fed close to a scheduled eating time or after a delay of up to 24 h. GE response was the fraction of the ingested test meal emptied per hr, up to a known degree of emptying, e.g., 50-58% of the test meal. Animals accustomed to the prescribed eating patterns ate promptly and at similarly rapid rates at all times of day. GE response, as plotted against time of response, fit a 24-h cosine model. Acrophase (time of maximum GE response of the fitted model) was similar, being 1.5 and 2.1 h, respectively, after the starting time of the accustomed dark-span meal for 1x and 2x rats, while amplitude (1/2 the maximum-to-minimum difference) was 41 and 24% of the MESOR (rhythm-adjusted mean). Characteristics of the GE rhythm appeared to be unchanged among 1x rats, severely versus minimally restricted in food intake during a final 9 days.

Diurnal pattern of plasma cortisol in preruminant calves fasted or fed different milk proteins

The objective was to clarify the possible role of meals in the nycthemeral evolution of cortisol and the influence of intestine absorption kinetic of nutrients. Preruminant calves were fed two kinds of diets, a conventional curdled milk and a milk that did not curdle in the abomasum. These calves were also fasted for 24 h. Blood was sampled regularly during a 24-h period under three different dietary situations. Daily mean plasma cortisol was lower in calves fed uncurdled milk than in those fed curdled milk or fasted. Diurnal changes in plasma cortisol were characterized in fed animals by sharp postprandial decreases; the morning meal induced a more intense decrease than the evening one, which was followed by a regular increase of cortisol concentrations overnight. Between meals, several peak values were detected at the same times in all animals with both kinds of meals. The postprandial decreases did not occur in fasted animals, and peak values could not be linked to those occurring when animals were fed. Thus, cortisol secretion by adrenals seemed to be influenced by nutrient intestinal absorption, whereas during fasting different mechanisms were involved.