Effect of light-dark cycles with different LD time-ratios and different LD intensity-ratios on the activity rhythm of chaffinches

Summary Chaffinches (Fringilla coelebs L.) were kept at light-dark (LD) cycles with two different light intensity ratios (ca. 500.1 and ca. 101 lux) both with 1.83 hours of twilight at the onset and end of light time. The light time/dark time ratio (LD time-ratio) was varied in the range from 420 to 222 hours.Birds at the high LD intensity-ratio (500.1 lux) increased activity time () with increasing light time from LD 420 to 222. Time of activity onset, middle, and end of activity corresponded to onset, middle, and end of light time from LD 420 to 168, but the phase angles of middle and end of activity (related to midpoint of light time and midpoint of artificial dusk respectively) became more positive (advanced) at LD 204 and 222.Birds at the lower LD intensity-ratio (101 lux) increased activity time with increasing light time from LD 816 to 204 but activity time at LD 420 was equivalent to that at LD 816. The phase angles of activity onset and middle (related to midpoint of artificial dawn and midpoint of light time, respectively) became more positive at both long (LD 204) and short (LD 420) light times.By use of different twilight regimes (linear and logarithmic changes in intensity), it was shown that end of activity was more closely related with the rate of change and/or absolute level of light intensity than was onset of activity.During January and February, the birds responded to increased LD time-ratios by an increase of activity time and by strong positive phase angle shifts which correspond to observations of activity patterns of chaffinches exposed to outdoor conditions during the spring breeding season.The free-running circadian periods () of 6 birds measured at 15 lux at the end of the experiments following LD 204 averaged 22.17 hours.From the data on precision, i. e. the period-to-period variation in the phase angles of single birds averaged over all birds of one group and condition, as well as from the number of birds not synchronized with the LD cycles, it is concluded that extreme long and short light times per 24 h represent weaker zeitgebers compared to LD cycles with medium lengths of light time. Likewise, LD cycles with low LD intensity-ratios are weaker zeitgebers than LD cycles with high LD intensity-ratios.This study was carried out while the senior author was on sabbatical leave from the University of Alaska and held a fellowship from the Alexander von Humboldt Stiftung.     

Role of the community effect of cardiomyocyte in the entrainment and reestablishment of stable beating rhythms

To investigate the roles that the community effect and entrainment function of cultured cardiomyocyte play in decreasing beating fluctuation and reestablishing synchronized beating, we developed a single-cell-based two-dimensional network culture assay to measure and compare the dynamics of beating rhythm synchronization of individual cells before and after they form networks. Studying the formation of two-cell networks, we found that their synchronized beating tended to be determined by the cardiomyocyte whose beat rate fluctuated less than that of the other cardiomyocyte. We further found that the strength of this tendency increased with the number of cells in the network. These results indicate that (1) beating fluctuation is one of the important factors influencing the reestablishment of a stable synchronous beating rhythm, (2) the larger networks reduce fluctuation, and (3) the formation of a spatial network can itself stabilize cardiomyocyte beat rates.     

The circadian eclosion rhythm in Sarcophaga argyrostoma: delineation of the responsive period for entrainment

ABSTRACT. The circadian rhythm of pupal eclosion in Sarcophaga argyrostoma shows a declining responsiveness to the phase-shifting effects of single light pulses as development proceeds, the intrapuparial stages becoming largely 'insensitive'. Maximum responses occur in the intra-uterine embryos and first-instar larvae. Pharate adults, however, are responsive to single high temperature pulses. Pupae, pharate adults, and females carrying ovarian eggs, also respond to single stepwise transfers from light to dark, or vice versa, but the peaks of eclosion show a phase angle to the light which differs from that produced by transfers of embryos or larvae. The results are consistent with the view that separate 'larval' and 'adult' clocks occur at different stages of development.     

A circadian rhythm of thermal preference in the ant Camponotus mus: masking and entrainment by temperature cycles

Abstract. Along a stable temperature gradient and under a LD 12:12 h cycle, nurse workers of the ant Camponotus mus Roger 1863 (Hymenoptera: Formicidae) select for the brood two different temperatures daily: 30.8°C at the middle of the light period (circadian phase = 90°), and 27.5°C 8 h later, during the dark period (circadian phase = 210°), this rhythm being of endogenous nature.When a 24 h temperature cycle was superimposed along the thermal gradient, so that the immobile brood experienced a temperature transition as they receive when translocated by nurses (8 h at 30.8°C and 16 h at 27.5°C), no brood translocations occurred.The thermal cycle masked the rhythm of brood translocation when temperature fitted the daily pattern expected by nurses.When the same temperature cycle was presented with a phase-advance, nurses did not tolerate the early thermal increase and removed the brood as temperature rose.However, when workers experienced this new phase relationship between light and temperature cycles for more than 10 days, brood translocations were suppressed.Records under constant conditions of light and temperature indicated that the overt rhythm was locked-on to the expected early increase in temperature, so that the temperature cycle dominated over the LD cycle in resetting brood-carrying activity.     

半导体激光对紫球藻生物学效应的影响

采用波长650nm,功率40mW,功率密度13W／cm^2的半导体激光,对紫球藻（Porphyridium cruentum)进行诱变,辐照时间分别为5min、10min、20min。通过对紫球藻每天细胞数、叶绿素a、第7d细胞干重和胞外多糖产量的测定可知：与对照组比较,3个处理对紫球藻生长及胞外多糖产生影响,5min、10min均有不同程度的促进作用,其中5min作用最明显,而20min则有抑制作用。     

Protein aggregation. The effect of deuterium oxide on large protein aggregates of C-phycocyanin

The amount of 11s aggregate in phycocyanin, normally stimulated by hydrophobic forces, is dramatically increased by the presence of deuterium oxide. Proteins in which hydrophobic forces are not proposed as a mechanism for aggregation are unaffected by deuterium oxide. These observations are consistent with the lower critical micelle concentration reported for ionic detergents in deuterium oxide. Phycocyanin samples containing a majority of material sedimenting faster than 11s were also investigated in the presence of deuterium oxide with the following findings: the most rapidly sedimenting species in water buffer is 24s; in deuterium oxide more than 10% of the protein sediments at 67s and substantial amounts of other species with sedimentation coefficients larger than 24s are present. These large quantities of species sedimenting faster than 24s are found in deuterium oxide buffers from pD5.5 to 7.0. Sucrose-density-gradient studies in deuterium oxide at pD6.0 confirm the presence of large amounts of more rapidly sedimenting species. Spectrophotometric studies on fractions from the sucrose-density-gradient experiments indicate with the presence of higher aggregates a red shift of the visible-absorption maximum and an enhancement of the E(620)/E(280) ratio. Fluorescence-emission studies show a greater relative fluorescence efficiency for these higher aggregates and are consistent with the suggested enhancement of higher aggregates in deuterium oxide. The existence of phycocyanin aggregates of such a large size is suggested to be of importance in vivo, with phycocyanin playing a role as a structural protein.     

The effect of deuterium oxide on light-sensitive Paulownia tomentosa seed germination

The effect of deuterium oxide on the germination of light-sensitive Empress tree (Paulownia tomentosa) seeds was studied. Kinetics of germination in both light- and gibberellic acid (GA₃)-induced seeds was decelerated by increasing concentrations of deuterium oxide (D₂O) in the medium. Deuterium oxide in increasing concentrations also changed the duration of the light necessary for germination, from 5 min in H₂O to more than 3 days in 60% D₂O. A far-red (FR) pulse reversed the effect of inductive, prolonged red (R) irradiation; maximum germination could subsequently be restored by only 5 min of red light. The escape from FR reversibility was delayed from 1 day in water to 2 or 3.5 days in D₂O. The light reactions of D₂O-treated seeds resemble those of skotodormant seeds of the same species.     

The effect of deuterium oxide on protein turnover in Lemna minor

Lemna minor fronds transferred to a sterile culture medium containing 50% (v/v) deuterium oxide (²H₂O) rapidly undergo a loss of soluble protein with a corresponding increase in free amino acids. The loss of protein is due to two factors: (i) the inhibition of protein synthesis for 4 h followed by a slower rate of synthesis than normal, (ii) a rapid 9–10 fold increase in protein degradation. In plants grown for longer periods (3–6 days) in 50% ²H₂O medium, protein synthesis is inhibited by 20% and the rate constant of degradation is 2–3 times that measured in fronds growing in normal (H₂O containing) complete medium. The initial loss of protein is not due to the breakdown of any specific protein fraction. Investigation of several enzymes indicates that all proteins are catabolised in response to ²H₂O treatment. The implications of these results with regard to the interpretation of density-labelling experiments are discussed.     

The effect of pinealectomy on entrainment of the locomotor activity rhythm in sparrows maintained on various short days

Summary Pinealectomy of house sparrows on 3L:21D (3 h light per 24 h) resulted in a significant increase in the time between the onset of perch-hopping activity and lights on (on) as well as the time between the offset of activity and lights of (off). The daily variance in on and off was also increased following the removal of the pineal gland. On longer light cycles (i.e., 5L:19D; 7L:17D), neither on or off, nor the variance of on or off was different between sham-pinealectomized and pinealectomized sparrows. Upon returning the birds to an ultrashort light cycle, 1L:23D, off, as well as the variance in on and off were again found to be significantly larger in the pinealectomized birds when compared to sham-operated controls. These results indicate that the effects of pinealectomy on the entrained rhythm of locomotor activity are most pronounced when birds are exposed to a weak entraining agent, such as an ultrashort light: dark cycle. In view of the observation that pinealectomy can alter the phase relationship between activity onset and offset, it is suggested that the pineal gland may be involved in the coupling of the oscillators that regulate activity onset and offset.     

The effect of growth in 99.8 deuterium oxide on the ultrastructure of winter rye

A preliminary report dealing with the ultrastructural effects of culture in a 99.8% D₂O (deuterium oxide) environment on winter rye (Secale cereale L. cv. Winter) is presented. In general, the cells of D₂O-cultured seedlings appeared similar to the cells of H₂O-cultured seedlings. However, differences were found in chloroplast and dictyosome morphology, and ribosome number.     

The effect of external gamma-irradiation on the distribution of deuterium oxide in the rat body

External gamma-irradiation (7.74 and 15.48 x 10(-2) C/kg) does not influence the distribution of deuterium oxide within a rat body: it is distributed uniformly among the organs and tissues as it is observed in nonirradiated animals. The effect of external irradiation favors the retention of deuterium oxide within the organs and tissues. The delayed excretion of deuterium oxide from the body can enhance the biological effect. This should be taken into account in standardizing the combined radiation effects.     

LD ratios and the entrainment of circadian activity in a nocturnal and a diurnal rodent

Summary The activity rhythms of 5 flying squirrels,Glaucomys volans, and 7 chipmunks,Tamias striatus, were examined under controlled conditions in the laboratory. Free-running, circadian rhythms were demonstrated using a total of 25 LL or DD experiments. With 46 LD schedules the limits of entrainment in a 24-hour day were determined, and the phase angle difference for each schedule measured.Glaucomys was able to synchronize to schedules ranging from 1 second of light per 24-hour day to at least 18 hours light per day with little or no change in the phase angle.Tamias showed an oscillatory type of entrainment when the photoperiod was less than 3 hours per 24-hour day or greater than 23 hours, but in the intervening region was capable of stable entrainment. A tendency was evident for the phase angle difference to become less positive as the LD ratio increased. InGlaucomys single, isolated light pulses of either one second or 24 hours duration were able to bring about relatively large shifts in the phase of the activity rhythm.Dedicated to Professor Jürgen Aschoff on the occasion of his 60th birthday.I wish to acknowledge the hospitality and assistance of the Zoology Department, University of Wisconsin, Madison, the Max-Planck Institute, Erling-Andechs, Germany, and the Belle W. Baruch Coastal Research Institute, University of South Carolina, Columbia. Special thanks are due Dr. John Emlen and Dr. William Reeder of Madison, Prof. J. Aschoff of Erling-Andechs, Dr. John Vernberg and Dr. Winona Vernberg of Columbia, and my husband, Dr. George DeCoursey, for their untiring encouragement and help with these experiments.     

The pattern of entrainment of the human sleep-wake rhythm by the natural photoperiod in the north

Recently, it was shown that the sleep-wake rhythm of the inhabitants of the temperate zone is entrained to sun time. In the North, significant seasonal changes in the photoperiod may interfere with entrainment of the circadian system to sunlight. This investigation assessed the influence of photoperiod characteristics on the sleep length and sleep-wake rhythm of residents of high latitude. The study was conducted in four towns and six villages located between 59.5?N and 67.6?N latitude between the months of October and May from 2009 through 2011 and included 2822 subjects aged 10 to 97 yrs, 1621 of whom were females and 1201 males. The chronotype and sleep length of the subjects were assessed using the Munich Chronotype Questionnaire. The instructions for the questionnaire stressed the need to specify the sleep-wake schedule during the week preceding the date of completing the questionnaire. The study found that the length of sleep and the chronotype of the inhabitants surveyed in Northern European Russia depend on age, sex, type of settlement, and place of residence. The time of sunrise was a stronger predictor of sleep length and chronotype than the time of sunset and day length. A later chronotype and shorter sleep length were found for the subjects during the equinox (sunrise at 06:00 h) than under long-photoperiod conditions (sunrise at 04:00-05:00 h). During short-photoperiod conditions (sunrise at 07:00-10:00 h), no significant changes in the self-reported sleep-wake rhythm were found. The time of sunrise had the strongest impact on the sleep-wake rhythm of 30- to 97-yr-old persons. Sunrise had a stronger influence on chronotype and sleep length in January to May, when the days become longer, than in October to December, when the days become shorter. Age- and season-associated changes were found in the entrainment of the sleep-wake rhythm by photoperiod in the North.     

The state of water in biological systems as studied by proton and deuterium relaxation.

Careful experiments on the measurement of the intensity of the deuterium NMR signal for 2-H2 O in muscle and in its distillate were performed, and they showed that all 2-H2 O muscle is "NMR visible". The spin-lattice relaxation time (T1) of the water protons in the muscle and liver of mice and in egg white has been studied at six frequencies ranging from 4.5 to 6.0 MHz over the temperature range of +37 to --70 degrees C. T1 values of deuterons in 2H2 O of gastrocnemius muscle and liver of mice have been measured at three frequencies (4.5, 9.21 and 15.35 MHz) over the temperature range of +37 to --20 degrees C. Calculations on T1 for both proton and deuteron have been made and compared with the experimental data. It is suggested that the reduction of the T1 values compared to pure water and the frequency dependence of T1 are due to water molecules in the hydration layer of the macromolecules, and that the bulk of water molecules in the biological tissues and egg white undergoes relaxation like ordinary liquid water.     

The discontinuous nature of motor execution II. Merging discrete and rhythmic movements in a single-joint system -- the phase entrainment effect

 Initiation of rapid discrete flexion movements is significantly altered when a secondary rhythmic movement is performed simultaneously with the same limb; the onset of a stimulus-evoked discrete movement tends to occur time-locked to the oscillation: i.e., the rhythmic movement entrains the discrete response. This nonlinear interaction may reflect a specific principle of coordination of motor tasks which are simultaneously executed with the same effector. This part II of a tripartite research report on such single-muscle multiple-task coordination investigates the contribution of the dynamic properties of the muscle and its reflex circuitry to phase entrainment. Assuming a simple threshold-linear relationship between the control signals generated by the central nervous system and the observable kinematic and electromyographic signals, a secondary rhythmic movement will cause an additional phase-dependent delay between the central “go” command and the first observable change in actual kinematics of the compound movement. Several indicators for such threshold-linear interaction are derived and tested on real data obtained in psychophysical experiments. Four healthy subjects performed rapid lateral abductions of the index finger in response to a visual “go” signal. During a portion of the experiments, subjects produced additional low-amplitude oscillatory movements before stimulus presentation with either the same finger (one-handed task), or with the index finger of the other hand (two-handed task). Results showed phase entrainment and modulation of reaction times when the cyclic and the discrete movements were simultaneously executed by the same finger. But there was no entrainment in the bimanual execution of the tasks. The model was capable of reproducing the observed effects. It is concluded that coordination of voluntary movements which are concurrently performed by the same effector involves specific discontinuous operations, which represents an essential part of the mechanism of motor coordination. Phase entrainment reflects this characteristic discontinuous behavior of the lower stages of motor execution and does not necessarily require nonlinear interaction of motor commands at higher levels of motor processing. Received: 5 September 2001 / Accepted in revised form: 19 December 2001