Does Gonyaulax polyedra measure a week?

Cell communication was investigated in Gonyaulax polyedra by mixing two cultures grown on opposite lighting regimens, as reported in a companion paper. Herein, using the same data, 7-d (circaseptan) rhythms are also shown to characterize the luminescence of this cellular organism. A fraction of a culture of G. polyedra, grown in 12 h of light (L), alternating with 12 h of darkness (D), was exposed for 3 d to an LD-shift by 11 h. The circadian glow rhythm was compared under free-running conditions (LL) for cultures previously kept on the two differing LD regimens and for mixed cultures. A circaseptan modulation of the circadian amplitude is detected in cultures that had not undergone an LD shift and in some of the mixed cultures, but not in the shifted cultures. A statistically significantly lower circaseptan amplitude (less than 50%) and acrophase advance of over 120 degrees or 56 h (p less than 0.001) characterizes the mixed cultures, as compared to the original unshifted cultures, a finding that could mean that G. polyedra communicates along a circaseptan frequency. Whether a prior phase-shift known to affect circaseptan behavior in another unicell, Acetabularia mediterranea, led to an alteration of the time structure of G. polyedra remains an interesting subject for further study in this model, a model attractive to students of unicellular rhythms and underlying mechanisms that henceforth should be studied at multiple circadian and circaseptan frequencies. Circadian and circaseptan interrelations can both serve as markers for mechanisms of intercellular communication.     

Rhythmic Patterns in Incidence of Peptic Ulcer Perforation Over 5.5 Decades in Norway

The incidence of ulcer perforation in 1480 patients treated in the Bergen area of Norway between 1935 and 1990 was analyzed for daily (circa-dian), weekly (circaseptan), and yearly (circannual) time effects. A circadian rhythm was found overall that was reproducible and fairly stable across seasons, decades, and days of the week. After subgrouping, a circadian rhythm was found in younger patients, males, and duodenal perforations, while a 12h (circasemidian) rhythm characterized ulcer perforation for women and for gastric ulcers. Duodenal perforations showed highest incidence in the afternoon, while gastric perforations showed a major peak around noon and a secondary peak near midnight. For duodenal ulcer perforation, the circannual pattern was characterized by a 6-month rhythm, with significantly higher incidence in May-June-July and in November-December in most subgroups. A circaseptan rhythm was not found, but there was a significantly higher incidence on Thursday-Friday as compared to Sunday-Monday. The pathophysiological mechanisms underlying the perforation of an ulcer thus seemed to show pronounced circadian and 6-month rhythmic variations, much less so circaseptan or circannual rhythms. While it is likely that exogenous environmental and/or societal factors play a significant role, variations in ulcer perforation may be related to endogenous biological rhythms in pathophysiological factors since the circadian pattern of duodenal perforations follows that for gastric acidity. Knowledge of the temporal patterns in peptic ulcer perforation and associated pathophysiologic factors should prove useful in optimizing the chronotherapeutic management of ulcer disease.     

Correlation of circadian changes in tyrosine aminotransferase and tryptophan-2-3-dioxygenase in rat liver to irradiation at different times of the day

Male SPF Wistar rats adapted to a 12:12 h light: dark regimen were irradiated at 3-hour intervals in the course of 24 h with a dose of 14.35 Gy X-rays; 24 h after irradiation or sham irradiation and starvation for the same length of time, and also in fed intact rats, tyrosine aminotransferase and tryptophan-2-3-dioxygenase activity in the liver and the serum corticosterone level were determined. Although lethal irradiation modified the given enzyme activities, it did not abolish their circadian rhythm, evidently in association with the low sensitivity in association with the low sensitivity of the liver to ionizing radiation. In irradiated animals (compared with sham-irradiated animals), the serum corticosterone concentration fell during the light part of the day and at the beginning of the dark part.     

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

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

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

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

Effect of chronic intracerebroventricular infusion of corticotropin-releasing factor on circadian corticosterone rhythm in the rat

The effects of chronic (14 day) intracerebroventricular infusion of various amounts of ovine corticotropin-releasing factor (oCRF) on the circadian blood corticosterone rhythm in male rats were examined. Control (saline-infused) rats showed distinct blood corticosterone rhythms over 48 h with nadirs at 0900 h and peaks at 2100 h on days 6-7 and 13-14. oCRF at 3 pmol/h did not affect the circadian corticosterone rhythm on these days. When oCRF was infused at a rate of 12 pmol/h, blood corticosterone was increased throughout the 48 h periods. A significant circadian rhythm remained at days 6-7, but continuous infusion for an additional 7 days disrupted the rhythm. Higher doses of oCRF (48 and 240 pmol/h) obliterated the rhythm during both periods; the disruption was characterized by an increase in corticosterone during the lights-on period without a substantial change in the evening maximum. Thus, the blood corticosterone concentration was eventually confined within a narrow range, not exceeding the normal circadian peak, over a wide dose range of centrally administered CRF. Significant effects of oCRF on body and adrenal weight were observed only at the two highest doses used. These findings may provide some insight into the state of the hypothalamic-pituitary-adrenal axis in animals exposed to chronic stress and in patients with depression.     

DoesGonyaulax polyedra measure a week?

Cell communication was investigated inGonyaulax polyedra by mixing two cultures grown on opposite lighting regimens, as reported in a companion paper (1). Herein, using the same data, 7-d (circaseptan) rhythms are also shown to characterize the luminescence of this cellular organism. A fraction of a culture ofG. polyedra, grown in 12 h of light (L), alternating with 12 h of darkness (D), was exposed for 3 d to an LD-shift by 11 h. The circadian glow rhythm was compared under free-running conditions (LL) for cultures previously kept on the two differing LD regimens and for mixed cultures. A circaseptan modulation of the circadian amplitude is detected in cultures that had not undergone an LD shift and in some of the mixed cultures, but not in the shifted cultures. A statistically significantly lower circaseptan amplitude (<50%) and acrophase advance of over 120° or 56 h (p<0.001) characterizes the mixed cultures, as compared to the original unshifted cultures, a finding that could mean thatG. polyedra communicates along a circaseptan frequency. Whether a prior phase-shift known to affect circaseptan behavior in another unicell,Acetabularia mediterranea, led to an alteration of the time structure ofG. polyedra remains an interesting subject for further study in this model, a model attractive to students of unicellular rhythms and underlying mechanisms that henceforth should be studied at multiple circadian and circaseptan frequencies. Circadian and circaseptan interrelations can both serve as markers for mechanisms of intercellular communication.     

Diurnal Variation of Plasmatic Melatonin,Corticosterone and Variation of General Activity in Pigeons under Light-Dark Cycle and Constant Light

This work analyzed the diurnal variation of general activity and plasmatic levels of melatonin and corticosterone in pigeons submitted to a 12:00:12:00 h light-dark cycle (lights on at 6:00 a.m.) or to constant light. In both conditions pigeons were observed in 5-min sessions at times 03:00, 06:00, 09:00, 12:00, 15:00, 18:00, 21:00 and 24:00 h during two successive days. Behavior was video taped in the home cages for posterior categorization and quantification. Radioimmunoassays were used to evaluate plasmatic levels of melatonin and corticosterone. Blood samples were obtained at the times of behavioral observation. In the light-dark condition the results showed day-night variation of general activity (p &lt; 0.001) and a robust diurnal rhythm of plasmatic melatonin (p &lt; 0.001). Both of these variations as well as the oscillatory secretion of corticosterone disappeared under constant light condition. The parallel changes in general activity and blunting of melatonin rhythm secretion in constant light condition agree with previous evidences that melatonin may regulate behavioral oscillations in the pigeon. The present data are related to the proposition that the timing system in pigeons may involve neuroendocrine relations characterized by interactions between blood born signalization by melatonin and corticosterone.     

High-performance liquid chromatographic separation of corticosteroids in plasma of rats. Its application to the determination of the circadian rhythm of 18-hydroxycorticosterone related to aldosterone and corticosterone

An efficient separation of corticosteroids in plasma of rats was obtained by reversed-phase high-performance liquid chromatography (HPLC). Plasma corticosteroid assays with HPLC separation were used to determine the circadian rhythm of 18-hydroxycorticosterone (18-OHB) and its possible relationship to aldosterone or corticosterone in conscious rats under standard conditions (regular diet; 12-hour light and 12-hour dark cycle). Significant circadian rhythms of plasma corticosterone, 18-OHB and aldosterone were observed with peak values at 20.00 h and nadir values at 08.00 h. The mean ratio of plasma 18-OHB to aldosterone during 24 h was 2.4. The circadian rhythm of 18-OHB was also correlated with that of plasma aldosterone or corticosterone.     

The chronopathology of breast pre-cancer

Breast temperatures have been measured by the automated instrumentation called the 'Chronobra' for 16 progesterone cycles in women at normal risk for breast cancer and for 15 cycles in women at high risk for breast cancer. Circatrigintan and circaseptan rhythm parameters have been examined by the single and population mean cosinor technique. In the first analysis there was strong evidence for a loss of the 28-day rhythm and its replacement by a 7-day rhythm (? frequency multiplication). In the more rigorous population mean cosinor method the presence of a phase and frequency synchronized rhythm with a period at or close to 28 days was sustained in the normal-risk subjects and it was confirmed that this rhythm is absent in the high-risk subjects. At tau = 7 days there was no rhythm detected in the normal-risk subjects and only a weak effect (p = 0.07) in the high-risk subjects. In other words, the circaseptan expression was detected in the high-risk breasts but then not in every case. The MESOR of the high-risk cases was highly significantly warmer than in the controls.     

Circadian variation of DSIP-like material in rat plasma

Levels of delta-sleep-inducing peptide-like immunoreactivity (DSIP-LI) in rat plasma were measured by radioimmunoassay and found to exhibit a circadian rhythm that parallelled the normal rhythm for corticosterone. The maximal plasma levels of both substances were observed to occur at about 1700h. The lowest concentrations of DSIP-LI and corticosterone were detected at 2400h and 1000h, respectively. Exposure to constant levels of illumination abolished the rhythm of DSIP-LI. It is possible that the temporal parallelism between the levels of DSIP-LI and corticosterone may represent a functional relationship between both compounds.     

Development of Adrenocortical Cyclic Nucleotide (Cyclic AMP and Cyclic GMP) and Corticosterone Orcadian Rhythms in Male and Female Rats

The daily rhythm of the adrenocortical cyclic nucleotides (cyclic AMP and cyclic GIMP) was studied in infant male and female Wistar rats before and after the establishment of an adult-like daily rhythm of plasma corticosterone. As in this strain the rhythm of corticosterone is known to be present on postnatal day 18, pups of 2 and 3 weeks of age were studied. The dams and the pups as well as the young adult animals were kept on a controlled 12L-12D photoperiod. Groups of 8-10 pups were killed at 4-hr intervals throughout the day. Plasma corticosterone levels and adrenal cyclic AMP and cyclic GMP concentrations were simultaneously measured and the daily patterns established. Pups of 2 weeks of age showed neither plasma corticosterone nor adrenal cyclic AMP rhythms whereas pups of 3 weeks of age exhibited a typical adult-like circadian rhythm for both variables. The patterns for adrenal cyclic GMP differed according to sex: In female pups no cyclic GMP circadian rhythm could be detected at either 2 or 3 wk. In male pups of 3 wk a typical mature rhythm for adrenal cyclic GMP was evident whereas in younger male pups (2 wk) a circadian rhythm was detected. This circadian rhythm, however, differed from mature circadian rhythm in that its peak was located at 1300 hr instead of 0700 hr. These results demonstrate that, unlike that of cyclic AMP the adrenal cyclic GMP circadian rhythm does not appear at the same time as the plasma corticosterone circadian rhythm. Moreover, a circadian rhythmicity for adrenal cyclic GMP can be found in the absence of any corticosterone circadian rhythm. These facts argue against the view of cyclic GMP being a mediator of ACTH-stimulated steroidogenesis.     

Development of Adrenocortical Cyclic Nucleotide (Cyclic AMP and Cyclic GMP) and Corticosterone Orcadian Rhythms in Male and Female Rats

The daily rhythm of the adrenocortical cyclic nucleotides (cyclic AMP and cyclic GIMP) was studied in infant male and female Wistar rats before and after the establishment of an adult-like daily rhythm of plasma corticosterone. As in this strain the rhythm of corticosterone is known to be present on postnatal day 18, pups of 2 and 3 weeks of age were studied. The dams and the pups as well as the young adult animals were kept on a controlled 12L-12D photoperiod. Groups of 8–10 pups were killed at 4-hr intervals throughout the day. Plasma corticosterone levels and adrenal cyclic AMP and cyclic GMP concentrations were simultaneously measured and the daily patterns established. Pups of 2 weeks of age showed neither plasma corticosterone nor adrenal cyclic AMP rhythms whereas pups of 3 weeks of age exhibited a typical adult-like circadian rhythm for both variables. The patterns for adrenal cyclic GMP differed according to sex: In female pups no cyclic GMP circadian rhythm could be detected at either 2 or 3 wk. In male pups of 3 wk a typical mature rhythm for adrenal cyclic GMP was evident whereas in younger male pups (2 wk) a circadian rhythm was detected. This circadian rhythm, however, differed from mature circadian rhythm in that its peak was located at 1300 hr instead of 0700 hr. These results demonstrate that, unlike that of cyclic AMP the adrenal cyclic GMP circadian rhythm does not appear at the same time as the plasma corticosterone circadian rhythm. Moreover, a circadian rhythmicity for adrenal cyclic GMP can be found in the absence of any corticosterone circadian rhythm. These facts argue against the view of cyclic GMP being a mediator of ACTH-stimulated steroidogenesis.     

Repeated stress at the same time of day does not mimic timed feeding in its effects on the plasma corticosterone rhythm in rats

The present study examined whether mild restraint stress occurring at the same time each day would entrain an anticipatory peak in the circadian plasma corticosterone rhythm associated with the time of stress. Rats were stressed by tube restraint for 2 h in the morning on 23 consecutive days, and plasma corticosterone concentrations were measured at 4h intervals over the next 2 days. Plasma corticosterone patterns were similar in control and restrained rats, and no anticipatory corticosterone peak occurred in stressed rats before the time when stress would have occurred. However, periodic regression analysis of the data indicated that timed stress did advance the acrophase of the circadian corticosterone rhythm by 1.7 h. This effect was minimal and could not explain the anticipatory rise in corticosterone concentrations seen in restricted feeding paradigms. Thus, it is unlikely that any stress associated with restricted feeding entrains corticosterone rhythms to anticipate the time of feeding, and some aspect of feeding per se is likely involved in producing the corticosterone peak that anticipates the time of restricted feeding.     

Different light-dark cycles affect growth rate and food intake of mice

The adaptation of the endogenous rhythm of an organism to external cycles may influence the development of physiological processes in animals. Light not only synchronizes the circadian system, but also exerts profound direct effects: the immediate reduction of melatonin release at night-time and the inhibition of locomotor activity in nocturnal rodents after a light pulse are well-known examples, yet little is known about effects of different light/dark (LD) cycles on the level of corticosterone, growth hormone and growth rate. Mice were raised under different period length of LD cycle including LD5:5 (light: 5 h; dark: 5 h), LD12:12 (light: 12 h; dark: 12 h) and LD16:16 (light: 16 h; dark: 16 h) for four weeks. Mice in LD5:5 and LD16:16 groups manifested higher locomotor activity, plasma corticosterone and growth hormone concentrations and growth rate than the LD12:12 group. The results suggest that different LD cycles may affect many physiological processes including growth rate, food intake and hormones, and the change of growth rate in different LD cycles may be related to the level of corticosterone and growth hormone concentrations. The results also suggest that both the long-period LD cycle and short-period LD cycles can improve the growth of mice, but they disturbed the biorhythm stabilization and affected hormone secretion; in general, these conditions would not promote the animals' survival.     

Circadian rhythm of circulating corticosterone and urinary excretion of catecholamines, serotonin and their catabolites in rats treated with imipramine

The circadian rhythm of serum corticosterone was assessed in rats entrained to a 12:12 LD cycle and treated with tricyclic imipramine (25 mg/kg/day) via osmotic pumps for a period of 14 days; urinary excretion of catecholamines, serotonin and their catabolites was also assessed. We observed that imipramine did not modify the phase position of the corticosterone rhythm but rather lowered the animal's responsiveness as shown by the lower peak of corticosterone at 2000 and by the smaller amplitude of its circadian rhythm; moreover imipramine had no effect on urinary excretion of catecholamines, serotonin and their catabolites during LD cycle.     

Gradual adjustment of circaseptan-circadian blood pressure and heart rate rhythms after a trans-9-meridian flight.

Circadian and circaseptan adjustment of blood pressure and heart rate after a transmeridian flight by a family of four was relatively fast, but it was not abrupt; it was not completed during the first week in the new setting. Gradual changes continued for the ensuing three weeks. The circadian and circaseptan rhythm characteristics and their adjustment in particular differed among variables in the husband: the circadian component of heart rate adjusted more rapidly than that of blood pressure. The adjustment also differed among two members of the family. A new phenomenon, namely a difference in circadian rhythm adjustment between husband and wife, is also described herein: the wife's circadian rhythm in blood pressure advanced by 9 hours within the 4-week span of recording following a 9-hour advance in living routine (after a 9-zone transmeridian flight); since both schedule and rhythm moved in the same direction (albeit not at the same rate), the behavior may be dubbed concursive. By contrast, the husband delayed to achieve the same adjustment: his behavior was anticursive. The phenomenon of a difference in direction of adjustment for different variables in the same subject has been described earlier as polarity, now qualified as intra-individual polarity, to separate it from the precedent of an intrafamilial or more broadly inter-individual polarity or partitioning, reported apparently for the first time and dubbed 'cursion'.     

根田鼠粪便皮质酮的检测效能

为验证根田鼠粪便皮质酮的可检测效能,本研究检测根田鼠粪便皮质酮含量的昼夜变化,并检测急性应激后和慢性应激期间根田鼠粪便皮质酮含量变化,及其慢性应激个体的HPA 轴负反馈功能。结果表明,根田鼠粪便皮质酮水平具有明显的似昼夜节律,粪便中皮质酮含量的最高点出现在08:00 和24:00,最低点在12:00 和16:00;在终止急性应激12 h 后,根田鼠粪便皮质酮含量显著增加,且有性别间差异;慢性应激根田鼠粪便皮质酮含量始终保持在高水平;再次急性应激,慢性应激根田鼠个体的粪便皮质酮含量较对照个体升高的时间延后。上述结果说明,根田鼠的粪便皮质酮含量能够反映机体所处的生理状态及应激水平,因此,该方法可用于野外根田鼠种群的相关研究并具有可靠性。     

Influence of the corticosterone rhythm on photic entrainment of locomotor activity in rats

The question of involvement of glucocorticoid hormones as temporal signals for the synchronization of the timekeeping system was addressed in rats with different corticosterone status. The authors showed that adrenalectomy had no effects on the synchronization of wheel-running activity rhythms to a steady-state LD 12:12 cycle, regardless of whether it was compensated for by a corticosterone replacement therapy that either reinstated constant plasma concentrations of the hormone or mimicked its natural rhythm. However, after a 12-h phase shift (daylight reversal), the lack of circulating corticosterone induced a significant shortening of the resynchronization rate (less than 3 days vs. 7 days). Normalization required restoration of a rhythmic corticosterone secretion that was synchronized to the new photoperiod. Under constant darkness, the corticosterone rhythm did not show any synchronizing effect, providing evidence that it participates in entrainment of the locomotor activity rhythm through modulation of light effects. It is proposed that, under stable lighting conditions, circulating glucocorticoids contribute to stabilizing activity rhythms by reinforcing resistance of the circadian timing system to variations of the photoperiod. Experimental evidence that serotonergic neurons are involved in relaying their modulatory effects to the clock is also presented.     

Circadian rhythm of circulating corticosterone and prolactin levels in spontaneously hypertensive rats

Circulating levels of corticosterone and prolactin were measured by radioimmunoassay at hourly intervals during a 24 h period to establish the diurnal rhythm of these hormones in spontaneously hypertensive rats (SHR). Corticosterone levels exhibited a distinct circadian variation with concentrations reaching a zenith at 2000 h and a nadir at 1200 h in male and female SHR. Corticosterone levels in females were consistently greater than males. Circulating prolactin levels were greater during the light h than dark in the female; the opposite occurred in males. Measurement of pituitary prolactin content tended to be low when serum prolactin levels were high and vice versa. The circadian rhythm of circulating corticosterone and prolactin in the hypertensive SHR was found to be similar to the day-night patterns established for normotensive rats. However, these measurements were made under quiescent conditions. It is suggested that because SHR are hyper-responsive to stress and because corticosterone and prolactin have synchronous effects on stress-induced adrenal steroidogenesis, further investigation of prolactin and corticosterone may reveal a participatory role of these hormones in the pathogenesis of the genetically-programmed hypertension of SHR.