Plasma cortisol response to feeding in African green vervets

The timing of a single daily meal of monkey chow in African green vervets exerts a synchronizing influence on plasma cortisol concentrations with an initial increase after feeding followed by a decrease to minimal levels five hours after feeding.     

Early dinner or “dinner like a pauper”: Evidence,the habitual time of the largest meal of the day – dinner – is predisposing to severe COVID-19 outcome – death

ABSTRACT

COVID-19 and metabolic syndrome are devastating pandemics. Effective control of metabolic parameters and their dysfunction may help prevent or minimize the acute and devastating effects of SARS-CoV-2 by reducing the local inflammatory response and blocking the entry of the virus into cells. With such consideration in mind, we gathered data from dietary surveys conducted in nine European countries to explore the relationship between actual clock hour of the large dinner meal and also interval in minutes between it and sunset in the respective countries and death rate above the median rate of per one million people as an index of mortality due to COVID-19 infection. Clock time of the dinner meal varied between 16:00 and 21:00 h across the European counties sampled, and the correlation between dinner mealtime and death rate was strongly correlated, R = 0.7991 (two-tailed p = 0.0098), with R ² explaining 63% of the variation within the data. This strong linear positive correlation indicates that the later the clock time of the dinner meal, the higher is the death rate (and vice versa). The relationship between meal timing in reference to sunset, utilized as a gross surrogate marker of the activity/rest synchronizer of circadian rhythms, and death rate was negative and even slightly stronger, R = ?0.8025 (two-tailed p = 0.0092), with R ² explaining 64% of the variation within the data. This strong linear negative correlation indicates that the shorter the interval between the dinner meal and sunset, i.e., the closer the time of the largest meal of the day to bedtime, the greater is the death rate (and vice versa). Our preliminary approach to nighttime eating, in terms of the day’s largest caloric intake, as a risk factor for the predisposing conditions of obesity, metabolic syndrome, type 2 diabetes, and other commonly associated comorbidities of being overweight, and death from COVID-19 infection reveals strong correlation with the time of the dinner meal, both in terms of its actual clock and circadian time.     

Eating meals before wheel-running exercise attenuate high fat diet-driven obesity in mice under two meals per day schedule

Mice that exercise after meals gain less body weight and visceral fat compared to those that exercised before meals under a one meal/exercise time per day schedule. Humans generally eat two or three meals per day, and rarely have only one meal. To extend our previous observations, we examined here whether a “two meals, two exercise sessions per day” schedule was optimal in terms of maintaining a healthy body weight. In this experiment, “morning” refers to the beginning of the active phase (the “morning” for nocturnal animals). We found that 2-h feeding before 2-h exercise in the morning and evening (F-Ex/F-Ex) resulted in greater attenuation of high fat diet (HFD)-induced weight gain compared to other combinations of feeding and exercise under two daily meals and two daily exercise periods. There were no significant differences in total food intake and total wheel counts, but feeding before exercise in the morning groups (F-Ex/F-Ex and F-Ex/Ex-F) increased the morning wheel counts. These results suggest that habitual exercise after feeding in the morning and evening is more effective for preventing HFD-induced weight gain. We also determined whether there were any correlations between food intake, wheel rotation, visceral fat volume and skeletal muscle volumes. We found positive associations between gastrocnemius muscle volumes and morning wheel counts, as well as negative associations between morning food intake volumes/body weight and morning wheel counts. These results suggest that morning exercise-induced increase of muscle volume may refer to anti-obesity. Evening exercise is negatively associated with fat volume increases, suggesting that this practice may counteract fat deposition. Our multifactorial analysis revealed that morning food intake helps to increase exercise, and that evening exercise reduced fat volumes. Thus, exercise in the morning or evening is important for preventing the onset of obesity.     

Evening physical activity alters wrist temperature circadian rhythmicity

The adequate time to perform physical activity (PA) to maintain optimal circadian system health has not been defined. We studied the influence of morning and evening PA on circadian rhythmicity in 16 women with wrist temperature (WT). Participants performed controlled PA (45?min continuous-running) during 7 days in the morning (MPA) and evening (EPA) and results were compared with a no-exercise-week (C). EPA was characterized by a lower amplitude (evening: 0.028?±?0.01?°C versus control: 0.038?±?0.016?°C; p?<?0.05) less pronounced second-harmonic (power) (evening: 0.41?±?0.47 versus morning: 1.04?±?0.59); and achrophase delay (evening: 06:35?±?02:14?h versus morning: 04:51?±?01:11?h; p?<?0.05) as compared to MPA and C. Performing PA in the late evening might not be as beneficial as in the morning.     

Combined organizational and activational effects of short and long photoperiods on spatial and temporal memory in rats

The present study examined the effects of photoperiod on spatial and temporal memory in adult Sprague-Dawley rats that were conceived and reared in different day lengths, i.e., short day (SD-8:16 light/dark) and long day (LD-16:8 light/dark). Both male and female LD rats demonstrated increased spatial memory capacity as evidenced by a lower number of choices to criterion in a 12-arm radial maze task relative to the performance of SD rats. SD rats also demonstrated a distortion in the content of temporal memory as evidenced by a proportional rightward shift in the 20 and 60 s temporal criteria trained using the peak-interval procedure that is consistent with reduced cholinergic function. The conclusion is that both spatial and temporal memory are sensitive to photoperiod variation in laboratory rats in a manner similar to that previously observed for reproductive behaviour.     

Circadian and light-induced conductance changes in putative pacemaker cells of Bulla gouldiana

The ocular circadian rhythm of compound action potential frequency in Bulla gouldiana is driven by rhythmic changes in the membrane potential of putative circadian pacemaker cells. Changes in the membrane potential of these neurons is required for light-induced phase shifts of the rhythm. We have tested the proposition that these changes in membrane potential reflect underlying changes in ionic conductances. We have found that: 1. Membrane conductance in the dark is highest during the subjective night when the cells are hyperpolarized, decreases as the cells depolarize spontaneously near projected dawn and is lowest during the subjective day. The changes in membrane potential and conductance follow a similar time course. 2. Long pulses of light delivered to eyes during their subjective night produce a characteristic response: There is initially a large, phasic depolarization accompanied by a burst of CAPs; this is followed by a repolarizing phase during which CAP activity is reduced to zero; and finally a tonic depolarization develops that is accompanied by a resumption of CAP activity at a steady rate. 3. During the subjective night, the tonic depolarization is accompanied by a decrease in conductance compared to the previous dark value. However, light pulses of similar duration delivered to eyes during their subjective day causes tonic depolarizations and increased CAP activity, but no measurable change in conductance. 4. Membrane responses to light are sensitive to agents that reduce Ca2+ flux. Light pulses during the subjective night produce a phasic depolarization, but the repolarization phase is eliminated in low Ca2+/EGTA seawater and is reduced in 5 mM Ni2+.(ABSTRACT TRUNCATED AT 250 WORDS)     

The full moon as a synchronizer of circa-monthly biological rhythms: Chronobiologic perspectives based on multidisciplinary naturalistic research

Biological rhythmicity is presumed to be an advantageous genetic adaptation of fitness and survival value resulting from evolution of life forms in an environment that varies predictably-in-time during the 24 h, month, and year. The 24 h light/dark cycle is the prime synchronizer of circadian periodicities, and its modulation over the course of the year, in terms of daytime photoperiod length, is a prime synchronizer of circannual periodicities. Circadian and circannual rhythms have been the major research focus of most scientists. Circa-monthly rhythms triggered or synchronized by the 29.5 day lunar cycle of nighttime light intensity, or specifically the light of the full moon, although explored in waterborne and certain other species, have received far less study, perhaps because of associations with ancient mythology and/or an attitude naturalistic studies are of lesser merit than ones that entail molecular mechanisms. In this editorial, we cite our recent discovery through multidisciplinary naturalistic investigation of a highly integrated circadian, circa-monthly, and circannual time structure, synchronized by the natural ambient nyctohemeral, lunar, and annual light cycles, of the Peruvian apple cactus (C. peruvianus) flowering and reproductive processes that occur in close temporal coordination with like rhythms of the honey bee as its pollinator. This finding led us to explore the preservation of this integrated biological time structure, synchronized and/or triggered by environmental light cues and cycles, in the reproduction of other species, including Homo sapiens, and how the artificial light environment of today in which humans reside may be negatively affecting human reproduction efficiency.     

Combination of meal and exercise timing with a high-fat diet influences energy expenditure and obesity in mice

In mice, obesity has been observed not only in those freely fed a high-fat diet (HFD) but also in those fed while physically inactive. In contrast, a HFD during physically active periods protects against obesity and the impairments in the circadian rhythm induced by free feeding of a HFD. Although exercise is known to be effective for obesity prevention and management, the optimal timing of exercise has not yet been determined. In the present experiments, we aimed to determine the best combination of daily timing of HFD consumption and exercise for the prevention of HFD-induced weight gain in mice. In this experiment, “morning” refers to the beginning of the active phase (the “morning” for nocturnal animals). Increases in body weight related to free feeding of a HFD was significantly reduced with 4?h of exercise during the late (evening) or middle (noon) active period compared to 4?h of exercise during the early (morning) active period or free access to exercise, which resulted in hours of exercise similar to that of morning exercise. These results suggested that eating in the morning or at noon followed by exercise in the evening could prevent weight gain more effectively than exercise in the morning followed by eating at noon or in the evening. The group fed a HFD for 4?h in the morning had lower body weight than the group fed a HFD for 4?h in the evening without exercise. The last group of experiments tested the hypothesis that there would be an interaction between mealtime and exercise time (i.e. time of day) versus order (i.e. which comes first) effects. We compared groups that exercised for 4?h at noon and were fed either in the morning or evening and groups that were fed for 4?h at noon and either exercised in the morning or evening. We found that the groups that were fed before exercise gained less body and fat weight and more skeletal muscle weight compared to the groups that exercised before eating. Corresponding to the body and fat weight changes, the respiratory exchange ratio (RER) was lower and energy expenditure was higher in the groups fed before exercise than in the groups fed after exercise, and these effects on energy metabolism were also observed in the early stage of HFD feeding before obesity. When obese mice fed a HFD for 12 weeks were exposed to a combination of feeding and exercise timing in an effort to reduce body weight, eating followed by exercise resulted in greater weight loss, similar to the experiments conducted to prevent weight gain. These results demonstrate that a combination of daily timing of eating and exercise may influence weight gain and that eating followed by exercise may be effective for minimizing increases in body and fat weight as well as maximizing increases in skeletal muscle weight.     

Time-related eating patterns and chronotype are associated with diet quality in pregnant women

Animal studies strongly suggest that timed feeding can have beneficial physiological effects, including protection against the obesogenic and metabolic consequences of a high-fat diet. However, the relationship between variables related to the timing of eating and diet quality in pregnancy women, which is considered as a period of nutritional vulnerability, is still poorly described in the literature. Therefore, the aim of the present study was to investigate the associations between time-related eating patterns and chronotype with diet quality of pregnant women. This cross-sectional study was conducted with 100 pregnant women in the first gestational trimester (≤12 weeks of gestation). The information regarding food intake was obtained by three 24-Hour Dietary Recall (24HR). Time-related eating patterns, i.e., the interval between the first and the last meal (eating duration), nightly fasting, time of the first and last meals, and number of meals eating on a day were determined. Chronotype was derived using the mid-sleep time on free days on weekends, with a further correction for calculated sleep debt. Diet quality was evaluated using the Brazilian Healthy Eating Index-Revised (BHEI-R), validated for the Brazilian population. Linear regression modeling analyses adjusted for confounders were used to investigate the association between time-related eating patterns and chronotype with diet quality. The BHEI-R total score was negatively associated with time of the first meal (β = ?0.355; p = 0.002; r² adjusted = 0.141), and positively associated with eating duration (β = 0.262; p = 0.024; r² adjusted = 0.086) and number of meals (β = 0.273; p = 0.019; r² adjusted = 0.091). In addition, the score of total fruit component was negatively associated with chronotype (β = ?0.236; p = 0.033; r² adjusted = 0.078), time of the first meal (β = ?0.393; p = 0.001; r² adjusted = 0.171), and positively associated with eating duration (β = 0.259; p = 0.022; r² adjusted = 0.087) and number of meals (β = 0.376; p = 0.001; r² adjusted = 0.159). The score for whole fruit component was negatively associated with time of the first meal (β = ?0.388; p = 0.001; r² adjusted = 0.152), and positively associated with number of meals (β = 0.403; p = 0.001; r² adjusted = 0.164). A longer eating duration, earlier time of the first meal, higher number of meals and morningness tendency are associated with a better diet quality in the first gestational trimester – higher scores of the total BHEI-R and/or fruit components. We suggest that nutritional guidelines should consider time-related eating patterns and chronotype to ensure good diet quality of pregnant women since the beginning of gestation, contributing on prevention of metabolic-nutritional complications.     

Circadian rhythms in human erythrocytes in vitro not confirmed

Abstract

Human erythrocytes, white and resealed erythrocyte ghosts, and hemolysates were analysed for the occurrence of circadian and ultradian rhythms in vitro. Although the experimental conditions were extensively varied, we did not find any indication for the existence of rhythmicity. These results are at variance with the reports by others.     

Biological rhythms in birds — development, insights and perspectives

The aim of this review is to show that probably the internal clock of precocial birds is imprinted in the prenatal period by exogenous factors (zeitgeber). The activity of organ functions occurs early during embryonic development, before this function is ultimately necessary to ensure the survival of the embryo. Prenatal activation of some functional systems may have a training effect on the postnatal efficiency.The development of physiological control systems is influenced by endogenous and exogenous factors during the late prenatal and early postnatal period: epigenetic adaptation processes play an important role in the development of animals; they have acquired characteristics which are innated but not genetically fixed. As a rule, the actual value during the determination period has a very strong influence on the set-point of the system. This will be explained using the example of thermoregulation.It is shown in detail that it seems to be possible to imprint the prenatal development of circadian rhythms by periodic changes of the light-dark cycle but not by rhythmic influence of acoustic signals.Altogether, there are more questions open than solved concerning the perinatal genesis of circadian rhythms in birds. Topics are given for the future research.     

Time of day difference in postprandial glucose and insulin responses: Systematic review and meta-analysis of acute postprandial studies

ABSTRACT

Current dietary trends show that humans consume up to 40% of their energy intake during the night. Those who habitually eat during the night are observed to have an increased risk of metabolic conditions such as type-2 diabetes and cardiovascular disease. Increasing evidence suggest that a biological consequence of eating during the night is a larger postprandial glucose response, compared to meals eaten earlier in the day. However, findings from individual acute postprandial studies have been inconsistent, due to variations in protocols. Therefore, this review aimed to systematically summarize findings from acute postprandial studies and investigate whether postprandial glucose and insulin response at night differs to during the day in healthy adults. This would indicate a possible physiological mechanism linking habitual nighttime eating and increased risk of metabolic conditions. Seven electronic databases were searched in February 2018. Included studies met the following criteria: had a day-time test between 0700 – 1600h, a nighttime test between 2000 and 0400h, the test meals were identical and consumed by the same participant at both day and night time points, preceded by a 3-h fast (minimum). Primary outcome measures were postprandial glucose and insulin incremental area under the curve (iAUC) or area under the curve (AUC). Studies that reported numerical data were included in the meta-analyses, conducted using Stata statistical software (version 13.0, StataCorp, College Station, TX, USA). For eligible studies that did not report numerical data, their authors’ conclusions on the effect of time of day on the primary outcome measures were summarized qualitatively. Full text of 172 articles were assessed for eligibility. Fifteen studies met the eligibility criteria, ten of which were included in the meta-analyses. Meta-analysis for glucose showed a lower postprandial glucose response in the day compared to during the night, after an identical meal (SMD = ?1.66; 95% CI, ?1.97 to ?1.36; p < .001). This was supported by the findings from included studies ineligible for meta-analysis. Meta-analysis also showed a lower postprandial insulin response in the day compared to during the night (SMD = ?0.35; 95% CI, ?0.63 to ?0.06; p = .016). However, findings from included studies ineligible for meta-analysis were inconsistent. Our results suggest poor glucose tolerance at night compared to the day. This may be a contributing factor to the increased risk of metabolic diseases observed in those who habitually eat during the night, such as shift workers.     

Rhythmic cortisol secretion in the equine: Analysis and physiological mechanisms

Abstract

Four Thoroughbred mares (no. 1–4) were maintained under constant temperature (24°C) and controlled light (L/D:12/12 with lights on at 06.00 hr) conditions. They were fed and watered ad libitum with fresh feed and water given at 09.00 hr. After a 45‐day pre‐conditioning period, blood samples were obtained by veinipuncture at 4‐hr intervals for 14 days to determine circadian and day‐to‐day variation. The horses exhibited a circadian rhythm with maximum values attained at about 12.00 hr, however, there are periods of days in which no rhythm is distinguishable. Ultradian rhythms with mean periods of 105 to 128 and 24 to 31 min are superimposed upon the circadian rhythm. The individual rhythms are quite variable from horse to horse and within the same horse. During periods of decline in plasma cortisol with metabolic half‐lives of approximately 70 min, secretion of cortisol was very low or had ceased. During periods of increasing plasma concentration, secretion was occurring at a faster rate than degradation. Rapid decreases in plasma concentration (metabolic half‐life of approximately 30 min) was accompanied by a rise in specific activity indicating cortisol with a high specific activity was entering the plasma pool from other storage pools.     

Effect of constant and fluctuating temperature on the circadian foraging rhythm of the red imported fire ant,Solenopsis invicta Buren (Hymenoptera: Formicidae)

Understanding circadian foraging rhythms activity of the red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae) foragers at different temperatures is an important step towards developing control measures in Integrated Pest Management (IPM) programs. In this study, the circadian foraging rhythm activities of S. invicta foragersat different temperature were investigated under laboratory and field conditions. Results indicated that the foraging activity increased after sunrise, and maximum foraging occurred at 14:00 (foraging rate was 69.22 ± 0.57 and 72.58 ± 1.15 foragers/min in the first and second year, respectively) in the tea fields of Guangzhou during autumn. Furthermore, foragers demonstrated circadian rhythms and exhibited a unimodal after 24 h. A significant correlation was found between foraging activity and temperature. S. invicta colonies were active at moderate soil temperatures (approximately 26.65 °C to 29.24 °C). The preferred temperature of the colonies was 26 °C, followed by 22 °C and 18 °C in the laboratory. The individual S. invicta activity was maximum at 17:00 (18.67 ± 1.66 times /10 min) and minimum at 5:00 (8.33 ± 2.51 times/10 min) at 26 °C. The fluctuating temperature had a significant impact on individual locomotor activity (r = 0.8979, P < 0.01) but did not alter the rhythm activity. Our results demonstrated that temperature might play an important role in circadian foraging rhythms activity of S. invicta. These results may have implications for the development of more effective fire ant management strategies.     

Chronotype and energy intake timing in relation to changes in anthropometrics: a 7-year follow-up study in adults

Individuals with a later preference for the daily activities (evening types) tend to have unhealthier behaviors, which could increase their risk for obesity when compared those with an earlier preference (morning types). Furthermore, later food intake timing, another behavior more characteristic of evening types, has been associated with obesity. However, chronotype differences in the long-term weight change and the role of chronotype in the association between energy intake timing and obesity risk are not clear. To study this we first examined the independent associations of chronotype and energy intake timing with anthropometric changes and then whether chronotype modified the association between energy intake timing and obesity risk. Our data included 1097 Finns from DILGOM (DIetary Lifestyle and Genetic Determinants of Obesity and Metabolic syndrome) 2007 (baseline) and 2014 (follow-up) and from Findiet 2007. Chronotype was assessed with a shortened version of Horne and Östberg’s morningness–eveningness questionnaire. Energy intake timing (as percentages of the total energy intake in the morning/evening) was assessed with 48-h dietary recalls. Weight, body mass index (BMI), and waist circumference were based on measured and self-reported values. Analysis of co-variance and multivariable logistic regression models were used for statistical analyses. Evening typed women had greater weight gain (+ 2.3 kg vs. + 0.3 kg, P = 0.016) and increase in BMI (0.7 kg/m² vs. ?0.1 kg/m², P = 0.024) than morning typed women. After excluding participants with depression, these associations attenuated to non-significant. Compared to participants whose energy intake was proportionally lowest during evening, those with proportionally highest energy intake during evening were more likely with obesity (BMI≥ 30 kg/m²) after follow-up (OR 1.97, 95% CI 1.21–3.21, Ptrend = 0.042). Participants’ chronotype did not modify this association (Pinteract = 0.95). In conclusion, our findings indicated that evening energy intake may play a role in obesity regardless of the chronotype. Furthermore, evening typed women were more prone to increases in their anthropometrics, which seem to be at least partly explained by depression. Further studies of this topic are warranted.     

TIME-OF-DAY EFFECTS ON THE INTERNAL SIMULATION OF MOTOR ACTIONS: PSYCHOPHYSICAL EVIDENCE FROM POINTING MOVEMENTS WITH THE DOMINANT AND NON-DOMINANT ARM

It is well known that circadian rhythms modulate human physiology and behavior at various levels. However, chronobiological data concerning mental and sensorimotor states of motor actions are still lacking in the literature. In the present study, we examined the effects of time-of-day on two important aspects of the human motor behavior: prediction and laterality. Motor prediction was experimentally investigated by means of imagined movements and laterality by comparing the difference in temporal performance between right and left arm movements. Ten healthy participants had to actually perform or to imagine performing arm-pointing movements between two targets at different hours of the day (i.e., 08:00, 11:00, 14:00, 17:00, 20:00, and 23:00?h). Executed and imagined movements were accomplished with both the right and left arm. We found that both imagined and executed arm pointing movements significantly fluctuated through the day. Furthermore, the accuracy of motor prediction, investigated by the temporal discrepancy between executed and imagined movements, was significantly better in the afternoon (i.e., 14:00, 17:00, and 20:00?h) than morning (08:00 and 11:00?h) and evening (23:00?h). Our results also revealed that laterality was not stable throughout the day. Indeed, the smallest temporal differences between the two arms appeared at 08:00 and 23:00?h, whereas the largest ones occurred at the end of the morning (11:00?h). The daily variation of motor imagery may suggest that internal predictive models are flexible entities that are continuously updated throughout the day. Likewise, the variations in temporal performance between the right and the left arm during the day may indicate a relative independence of the two body sides in terms of circadian rhythms. In general, our findings suggest that cognitive (i.e., mental imagery) and motor (i.e., laterality) states of human behavior are modulated by circadian rhythms. (Author correspondence: charalambos.papaxanthis@u-bourgogne.fr)     

Effects of suprachiasmatic nuclei lesions on circadian and ultradian rhythms in body temperature in ocular enucleated rats

Abstract

To test the hypothesis that an oscillator located outside the suprachiasmatic nuclei (SCN) controls the circadian rhythm of body temperature, we conducted a study with 14 blinded rats, 10 of which receiving a SCN lesion. Body temperature was automatically and continuously recorded for about one month by intraperitoneal radio transmitters. Food intake, drinking and locomotor activity were also recorded. Periodograms revealed that 3 rats with histologically verified total bilateral SCN lesions did not exhibit any circadian rhythmicity. The 7 other rats appeared to have partial lesions. They showed shortening of period and severe amplitude reduction in all functions. Thus, no support was found for the hypothesis of a separate circadian ‘temperature oscillator’ located outside the SCN. Nevertheless, after large partial lesions body temperature showed more persistency than some of the other behavioral rhythms.

Ultradian rhythms in temperature persisted after partial and total lesions. Other functions showed parallel ultradian rhythms. In intact rats the ultradian peaks were restricted predominantly to the subjective night. After total lesions these peaks became more or less homogeneously distributed in time but more heterogeneously after partial lesions. So the SCN plays a role in the temporal structure of ultradian rhythms but does not generate them. Non‐24‐hour actograms showed instabilities of period and phase of ultradian rhythms. Intact and lesioned rats were similar with respect to the mean (about 3.5 hrs) and standard deviation (about 1.5 hrs) of ultradian periods in temperature. These features indicate that a mechanism outside the SCN is underlying ultradian rhythmicity, capable of generating short‐term oscillations. Two approaches, homeostatic sleep‐wake relaxation oscillations and multiple circadian oscillators, are discussed.     

侧脑室注射orexin-A对大鼠昼夜摄食的影响

目的:探讨侧脑室注射orexin-A对大鼠昼夜摄食的影响。方法:将Wistar大鼠随机分组,采用单剂量侧脑室注射和连续侧脑室注射以及外周注射法,分别于日间和夜间给药,测量大鼠24小时内各阶段的摄食量以及相应生化指标。结果:在光照期间,侧脑室微量注射orexin-A,大鼠4小时内摄食量显著增加(P0.05),且呈剂量依赖关系(P0.05)。在夜间初期(18:00)侧脑室注射orexin-A,大鼠食物摄入量无显著差异(P0.05)。但在中午12:00给予侧脑室注射orexin-A,注射后4小时内大鼠摄食量显著高于NS对照组(P0.05)。连续8日给予orexin-A侧脑室注射,可使注射后日间摄食量显著增加(P0.05),而夜间摄食量显著减少(P0.05),但24小时内总的摄食量不变(P0.05)。orexin-A并未改变棕色脂肪组织温度、末梢血糖、血浆瘦素等指标的水平。结论:orexin-A对大鼠摄食的调节具有昼夜节律性。     

Calcium and Photoentrainment in Chick Pineal Cells Revisited: Effects of Caffeine, Thapsigargin, EGTA, and Light on the Melatonin Rhythm

Abstract: Chick pineal cells in dispersed cell culture display a persistent, photosensitive, circadian rhythm of melatonin production and release. Light pulses have at least two distinguishable effects on these cells, i.e., acute suppression of melatonin output and phase shifts (entrainment) of the underlying circadian pacemaker. Previous results linked calcium influx through voltage-sensitive calcium channels in the plasma membrane to acute regulation of melatonin synthesis but denied a role for such influx in entrainment. Those experiments did not, however, address the role of intracellular calcium metabolism. Here we describe the effects of pulses of caffeine, thapsigargin, and EGTA on the melatonin rhythm, and their interactions with the effects of light pulses. Caffeine had two distinguishable effects on these cells, acute enhancement of melatonin output (attributable to phosphodiesterase inhibition) and phase shifts of the circadian pacemaker with a light-like pattern (attributable to effects on intracellular calcium). Phase shifts induced by light and caffeine were not additive. Thapsigargin (which specifically blocks the pump that replenishes intracellular calcium stores, thereby increasing cytoplasmic calcium and depleting intracellular stores) had no phase-shifting effects by itself but reduced the size of the phase advances induced by caffeine or light. Low calcium solution acutely suppressed melatonin output without inducing phase shifts or affecting those induced by caffeine or light. However, addition of EGTA (which specifically chelates calcium, thereby lowering cytoplasmic calcium and depleting intracellular stores) did reduce the size of phase advances induced by caffeine or light, in normal medium or in low calcium solution, without inducing a phase shift by itself at that phase. Taken together, these results point toward a role for intracellular calcium fluxes in entrainment of the circadian pacemaker.     

Effects of physiological cycles of infused melatonin on circadian rhythmicity in pigeons

Summary The role of the hormone melatonin in the circadian system of pigeons (Columba livia) was investigated. Using an automatic infusion system, melatoni at physiological levels was delivered for 10 h each day to cannulated, pinealectomized (P-X) pigeons in constant darkness. These cyclic infusions of melatonin entrained feeding rhythms in P-X pigeons while vehicle infusions were ineffective entraining agents. When the retinae of P-X pigeons were removed (E-X), feeding rhythms were abolished in constant darkness. When cyclic melatonin infusions were delivered to these birds (E-X and P-X), feeding rhythmicity was restored whereas vehicle infusions alone did not restore rhythmicity. When melatonin infusions were terminated in E-X/P-X pigeons, feeding rhythms persisted for several days but eventually decayed. Blood melatonin levels were measured in both P-X and E-X/P-X birds infused cyclically with exogenous melatonin and were found to be within the physiological range both in level and pattern. These results strongly suggest that endogenous melatonin, released by the pineal gland and the retinae, regulates the timing of feeding rhythms by entraining other oscillators in the circadian system of the pigeon.Abbreviations P-X pinealectomized - E-X bilaterally enucleated - T period of infusion cycle - LD light: dark cycle - DD constant darkness