Dinitrogen-fixing endogenous rhythm in Synechococcus RF-1

Abstract Using the Southern hybridization technique, 22 strains of archaebacteria were tested for the presence of DNA sequences homologous to the Anabaena nifH gene, which codes for the Fe protein component of nitrogenase. Total DNA from all the 14 methanogenic strains tested was shown to carry homology to nifH . With total DNA from 3 Halobacterium strains, hybridization was also detected, though unspecific binding cannot completely be excluded. No hybridization was detected with DNA from Thermoplasma acidophilum , nor with the DNA from 4 strains belonging to the sulfur-dependent branch of the archaebacteria. Results strongly support the hypothesis of an ancient origin of nif genes.     

Circadian Rhythm of the Prokaryote Synechococcus sp. RF-1

The prokaryotic Synechococcus sp. RF-1 exhibited a nitrogen fixation circadian rhythm with characteristics remarkably similar to the circadian rhythm of eukaryotes. The rhythm had a free-running period of about 24 hours when the length of the preen-trained cycle did not differ too much from 24 hours, and it was insensitive to changes in temperature from 22°C to 33°C. Because the endogenous rhythm of nitrogen fixation was not affected by a phase-shift of its previous cycles, the circadian rhythm in Synechococcus sp. RF-1 was not considered to be controlled simply by a feedback mechanism.     

Circadian Rhythm in Amino Acid Uptake by Synechococcus RF-1

In the prokaryote Synechococcus RF-1, circadian changes in the uptake of l-leucine and 2-amino isobutyric acid were observed. Uptake rates in the light period were higher than in the dark period for cultures entrained by 12/12 hour light/dark cycles. The periodic changes in l-leucine uptake persisted for at least 72 hours into continuous light (L/L). The rhythm had a free-running period of about 24 hours in L/L at 29°C. A single dark treatment of 12 hours could initiate rhythmic leucine uptake in an L/L culture. The phase of rhythm could be shifted by a pulse of low temperature (0°C). The free-running periodicity was “temperature-compensated” from 21 to 37°C. A 24 hour depletion of extracellular Ca²⁺ before the free-running L/L condition reduced the variation in uptake rate but had little effect on the periodicity of the rhythm. The periodicity was also not affected by the introduction of 25 mm NaNO₃. The uptake rates for 20 natural amino acids were studied at 12 hour intervals in cultures exposed to 12/12 hour light/dark cycles. For eight of these amino acids (l-Val, l-Leu, l-Ile, l-Pro, l-Phe, l-Trp, l-Met, and l-Tyr), the light/dark uptake rate ratios had values greater than 3 and the rhythm persisted in L/L.     

Circadian rhythm of thymosin-alpha 1 in normal and thymectomized mice

Studies by many investigators have demonstrated that the immune system is subject to regular circadian fluctuation. Some rhythms that have been reported include circadian changes in components of the immune system, e.g., lymphocytes, and circadian variation in primary and secondary immune responsiveness. The observation that many of these rhythms are inversely correlated to the glucocorticoid rhythm has led to the suggestion that fluctuations in the immune system may be a result of the glucocorticoid circadian rhythm. This study was designed to see if thymosin-alpha 1 (Tsn-alpha 1), a 28-amino acid polypeptide isolated from bovine thymus that has been reported to influence thymocyte differentiation, might follow a circadian rhythm, and thus play a role in the periodicity of the immune system. In these experiments, groups of 10 C57BL/6 or Swiss Webster mice were sacrificed at 4- or 6-hr intervals over a 24-hr period. Serum Tsn-alpha 1 and corticosterone levels were determined by radioimmunoassay. Results from the first experiment showed that Tsn-alpha 1 undergoes a circadian rhythm (p less than 0.001) with an acrophase (time of peak levels) 1.5 hr after the onset of light, and an amplitude (amount of maximum variation from the 24-hr mean) of 0.493 ng/ml Tsn-alpha 1-like immunoreactivity. These results were confirmed in an experiment in which the animals were placed on a reversed light cycle. In a separate experiment, the Tsn-alpha 1 circadian rhythm persisted in mice thymectomized 6 mo. earlier. In this latter experiment, a significant increase in the amplitude of the corticosterone rhythm in the thymectomized relative to sham-operated controls was also observed. Although these experiments do not imply casuality, it is interesting that the time of peak Tsn-alpha 1 levels can be correlated with the time of optimal immune function.     

昼夜节律系统与成人昼夜节律睡眠觉醒障碍

昼夜节律是存在于所有生命体中、接近24小时的内源性生物节律。昼夜节律与社会或环境节律的长期不同步,会引起睡眠、情绪等一系列变化。本文阐述了昼夜节律系统与睡眠之间的联系,重点介绍成人昼夜节律睡眠觉醒障碍疾病的临床研究成果,以期加强临床医生对该病的认识和诊治。     

Circadian rhythm of the locomotor activity in Drosophila melanogaster and its mutants 'sine oculis' and 'small optic lobes'

ABSTRACT. The locomotor activity patterns of wildtype Drosophila melanogaster and the mutants so (sine oculis) and sol (small optic lobes) were investigated. In all strains the proportions showing circadian rhythmicity, arrhythmicity and more complex patterns which could not be thus classified were similar. The occurrence of abnormal activity patterns is thus not a property of the mutation as previously claimed (Mack & Engelmann, 1981). In flies with a distinct circadian rhythmicity, the period lengths (τ) varied between strains, τ for wildtype Italy and the mutant so was longer than for wildtype Berlin and the mutant sol. As different τ's have been reported by others, τ does not seem to be closely determined for Drosophila melanogaster. Many flies exhibited two rhythms simultaneously, one with τ shorter and one with τ longer than 24 h, apparently implying two-oscillator control of the locomotor activity. The eyeless so mutants were entrained by LD cycles, so the compound eyes are not necessary, and so must possess the relevant photoreceptor(s) elsewhere. This may therefore also be true for the wildtype. Histology of the so adults revealed no correlation between the degree of reduction in the medulla and the occurrence of abnormal activity patterns. Since the only structures common to the medulla of so and sol are known to be large tangential cells, it is concluded that either they are of importance for the rhythmic system, or the oscillator(s) controlling locomotor activity is (are) not located in the medulla.     

Circadian rhythm in adenosine A1 receptor of mouse cerebral cortex

In order to investigate diurnal variation in adenosine A1 receptors binding parameters, Bmax and Kd values of specifically bound N6 - cyclohexyl-[3H]adenosine were determined in the cerebral cortex of mice that had been housed under controlled light-dark cycles for 4 weeks (light on from 7.00 to 19.00 h). Significant differences were found for Bmax values measured at 3-hr intervals across a 24-h period, with low Bmax values during the light period and high Bmax values during the dark period. The amplitude between 03.00 and 18.00 hr was 33%. No substantial rhythm was found in the Kd values. It is suggested that the changes in the density of A1 receptors could reflect a physiologically-relevant mechanism by which adenosine exerts its modulatory role in the central nervous system.     

Circadian temperature rhythm of laboratory swine

The circadian temperature rhythm (CTR) profile holds promise for monitoring the domestic pig's responses to stress and illness. In the present study we quantified the CTR profile of nine growing-finishing swine using a time-series, small-group design. Temperature was monitored using a probe implanted in the ear for 5 1/2 to 9 1/2 consecutive days while the unrestrained pigs were housed singly in pens. The dominant period of the temperature data was estimated with the autocorrelation function and then used in standard cosinor analysis to compute the amplitude (half of the distance between the highest and lowest value within the period), mesor (rhythm-adjusted mean), and acrophase (timing of the cosine maximum). To examine the effect of procedural stress on CTR, we compared data from the first 3 days with those from subsequent days. Eight of the nine (89%) pigs had CTR with a mean (+/- standard error) period of 23.6 (0.5) h, amplitude of 0.18 (0.02) degrees C, mesor of 38.7 (0.24) degrees C, and acrophase at 19:44 h. Mean mesor and acrophase were not different, but amplitude was lower (P = 0.03) during the first 3 days after instrumentation than during subsequent days. We conclude that: 1) laboratory-housed, unrestrained, growing-finishing swine have CTR; 2) our ear-based instrumentation protocol imposes acute stress as reflected in attenuated CTR amplitude during the first 3 days after instrumentation; and 3) CTR adaptation to stress appears to occur over time.     

Circadian rhythm of histamine in the pineal gland

The stimulating effects of 2-guanidinbenzimidazole and phentolamine on sodium transport through the isolated skin of the frog $\text{Rana esculenta}$ are described. These substances only act when added to the epithelial side, suggesting that they affect the permeability of the external barrier of sodium compartment. The role of the imidazole group in the activation of sodium transport is discussed.     

Circadian rhythm in murine reticuloendothelial function

Six separate groups, each composed of 15 comparable inbred female CBA mice, standardized in light daily from 0700 to 1900, alternating with darkness, maintained with food and water available ad libitum, were tested at 4-h intervals for a 24-h span for the phagocytic index, determined 3, 6, 9 and 12 min after the injection of a carbon suspension. By an analysis of variance and the single cosinor method applied to these data a circadian rhythm was demonstrated, with a double amplitude of 20% and an acrophase during the second half of the daily light span. These results extend the scope of immunologic circadian rhythms to the reticuloendothelial system as a feature of a bioperiodic defense mechanism, most active during the habitual rest light span of nocturnally active mice.     

Circadian rhythm disruption: health consequences

Circadian rhythms control many facets of biology and their disruption can be associated with severe pathological conditions. In healthy individuals, disturbances to the sleep-wake cycle can be the root cause of many problems. In the present review, we explore the major factors contributing to circadian rhythm disruption, including sleep disorders, jet lag, and shift work. The consequences of these disruptions on central and peripheral clocks and the important areas of the body controlled by them involve immune function and metabolism, as well as alterations in cognitive abilities, thereby impairing social and occupational behavior. Further work exploring clock genes, light exposure, and cellular changes will be critical for identifying how these factors interact to affect health and behavior.     

Circadian rhythm of corticosterone in diabetic rats

We proposed that the circadian rhythm of corticosterone in diabetic rats would have a different pattern than that in non-diabetic control rats. To test this hypothesis, 20 male Sprague-Dawley rats were given ad libitum access to a stock diet and housed individually in a light and temperature controlled room. Ten rats were made diabetic by two subcutaneous injections of streptozotocin. Ten rats which were not injected served as controls. Thirteen days after induction of the diabetes, tail blood samples were taken every 4 h for 24 h. Plasma corticosterone levels were significantly higher in diabetic rats than in control rats at 3 time points during the light cycle; however, concentrations were similar during the dark cycle. We speculate that diabetes may cause alterations in the steroid feedback mechanism to the hypothalamus and/or pituitary, resulting in an abnormal circadian rhythm of plasma corticosterone.     

Circadian rhythm of irinotecan tolerability in mice

The toxicity of irinotecan (CPT-11), a topoisomerase-I inhibitor largely used in cancer patients, was investigated as a function of the circadian time of its administration in mice, with mortality, body weight loss, leukopenia, neutropenia, intestinal lesions, and bone marrow cell cycle phase distribution as end points. Four experiments were performed on a total of 773 male mice standardized with 12h light/12h darkness. Irinotecan was administered daily for 4 or 10 consecutive days (D1-4 and D1-10, respectively, in different experiments) at one of six circadian stages expressed in hours after light onset (HALO). The survival curves differed significantly as a function of the dosage and circadian time of drug administration by the D1-10 schedule, with 70% survival at 7 or 11 HALO and 51% at 19 or 23 HALO (p=0.039 from log rank test). CPT-11 administration at 19 or 23 HALO resulted in (1) greatest mean body weight loss at nadir; (2) most severe colic and bone marrow lesions and/or slowest recovery; and (3) deepest neutropenia nadir and/or slowest hematologic recovery. These circadian treatment time-related differences were statistically validated. The bone marrow cell cycle data revealed a four to eight-fold larger G2-M phase arrest following irinotecan administration at 19 or 23 HALO in comparison to the other times of drug administration, apparently representative of the repair of more extensive DNA damage (p < 0.001 from ANOVA) when the medication was given at these circadian times. Overall, CPT-11 was better tolerated by mice treated during the light (animals' rest) span. The results support the administration of CPT-11 to cancer patients in the second half of the night, during sleep, in order to improve drug tolerability.