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T Roenneberg

Publications and source records attributed to T Roenneberg.

9 recordsLinked to original sources
PubMed1991

Gonyauline: a novel endogenous substance shortening the period of the circadian clock of a unicellular alga.

The circadian clock in the unicellular alga Gonyaulax polyedra is accelerated by a substance in extracts from the cells themselves. The extracts have been fractionated using the circadian rhythm of bioluminescence as bioassay. The active substance, termed gonyauline, has been isolated and characterized as a novel low molecular weight cyclopropanecarboxylic acid (S-methyl-cis-2-(methylthio) cyclopropanecarboxylic acid). Synthetic gonyauline has a similar shortening effect on the period of the circadian clock.

Animals↗
PubMed1991

Are the effects of light on phase and period of the Gonyaulax clock mediated by different pathways?

The effects of different wavelengths of light on period, phase shifting, entrainment and after-effects of the circadian clock of the motile marine dinoflagellate Gonyaulax polyedra are described. Phase shifting and entrainment by light can be explained by the action of a single blue sensitive light input pathway. However, tonic effects of light on the period under free-running conditions, and also after-effects on period resulting from single 4 h light exposures, appear to involve two input pathways with different absorption and temperature characteristics. These results suggest different mechanisms for the control of phase and period of the circadian clock.

Animals↗
PubMed1990

Annual rhythm of human reproduction: I. Biology, sociology, or both?

The annual rhythm of human reproduction was analyzed on the basis of more than 3000 years of monthly birth rates covering 166 regions of the globe. The following variables were used to characterize the annual rhythm of human conception (birth minus 9 months): amplitude, phase of maximum and minimum, phase and length of the time span when rates are above the annual mean (alpha), and the steepest upward slope (delta max) of the curve fitted to the rates. The waveform of the annual rhythm is characteristic for geographical regions (e.g., unimodal or bimodal) and persists as such for many years. In most countries, the onset of alpha coincides with delta max and lies close to the spring equinox. This phase of the rhythm is the most stable over time. In many populations, the rhythm has changed in recent years, specifically in amplitude and phase. The phase of the rhythm depends on latitude, with a 6-month difference between the Northern and Southern Hemispheres. The latitudinal distribution of amplitudes is less systematic. In spite of the many social influences on timing of conceptions, we conclude that the seasonal component in human reproduction is based on biological factors.

Birth Rate↗
PubMed1990

Annual rhythm of human reproduction: II. Environmental correlations.

Annual rhythms of human conception rates (based on a worldwide selection of statistics) were correlated with photoperiod, monthly averages of daily hours of sunshine, minimum and maximum temperature, and humidity. Our results show for the first time on a global scale that photoperiod, as shown for many animals, may also influence the physiology of human reproduction. At higher latitudes, where changes in daylength are pronounced, a steep increase in human conceptions coincides with the vernal equinox. Temperature also appears to be a major influencing factor. Conception rates are above the annual mean at temperatures between 5 degrees and 20 degrees C, and temperature extremes decrease the probability of conceptions. In regions with cold winters and moderate summers, the number of conceptions correlates positively with temperature; close to the equator, where winters are more moderate than the hot summers, this correlation is negative. Regions with both hot summers and cold winters tend to have a bimodal conception rhythm. The influence of photoperiod is dominant before 1930, whereas the impact of temperature dominates in later years. With industrialization, people are increasingly shielded from both photoperiod (by indoor work) and temperature (by heating and air conditioning), which may explain the deseasonalization of the human conception rhythm. Photoperiod and temperature and the specific changes in their impact can account for several features of the annual human conception rhythm: latitude dependence, waveform, phase and amplitude, and their specific changes over time.

Climate↗
PubMed1989

A circadian rhythm of population behavior in Gonyaulax polyedra.

Like other flagellates, Gonyaulax polyedra exhibits diurnal vertical migration and pattern formation. Shape and size of the aggregations depend on container type, light intensity, and cell density. In Petri dishes, cells form oval "swarms"; within these, cells move downward in the highly dense center and rise up at the periphery. We have investigated the daily rhythm of this swarming activity in Petri dishes illuminated from the side, using time-lapse video recordings. At night, a "lawn" of cells forms at the bottom of the dish toward the light source (independent of light intensity). Before dawn, cells rise toward the surface and aggregate in swarms. The daily vertical migration occurs independent of light direction and intensity. The diurnal swarms, however, form every day at the same location within the dish, at a distance from the light that depends on light intensity, indicating a self-selection of light intensity. In constant light and temperature and with negligible vertical nutrient differences, all aspects of the rhythm continue to oscillate for up to 3 weeks, when the rhythm of the population becomes desynchronized. Under cycles of bright white-dim red light (WR), cell entrain to WR 10:10 but free run in WR 8:8 and shorter cycles, showing relative coordination (von Holst, 1939) to the driving light cycle. They also entrain to the 24-hr multiple of WR 6:6. Under nonentrained conditions, swarming activity is still influenced by light changes, and in spite of the apparent free run, the phasing of the averaged activity varies systematically with different T-cycle frequencies.

Animals↗
PubMed1988

Creatine accelerates the circadian clock in a unicellular alga.

The circadian clock is considered to be a universal feature of eucaryotic organisms, controlling the occurrence and rates of many different aspects of life, ranging from single enzymatic reactions and metabolism to complex behaviours such as activity and rest. Although the nature of the underlying cellular/biochemical oscillator is still unknown, many substances are known to influence either phase or period of circadian rhythms in different organisms. These include D2O, electrolytes and ion channel inhibitors, small organic molecules such as alcohols and aldehydes, inhibitors of protein synthesis and amino-acid analogues. Certain transmitter and neurochemical drugs also influence the circadian clock in higher animals. We report here that the period of free-running circadian rhythms in the unicellular marine alga Gonyaulax polyedra is shortened by extracts from mammalian cells. The effect is dose-dependent, accelerating the circadian clock by as much as 4 hours per day. The substance responsible for this effect has been isolated from bovine muscle and identified as creatine. Authentic creatine has identical biological effects at micromolar concentrations and is known in animal systems for its involvement in cellular energy metabolism. A period shortening substance with similar chemical properties is also present in extracts of Gonyaulax itself.

Animals↗
PubMed1985

Topographical distribution of the summation property of Y-ganglion cells in the cat retina.

The stimulus response characteristics (SRCs) of 33 phasic retinal ganglion cells were established on the basis of extracellular recordings in the optic tract of anaesthetized and paralyzed cats. All SRCs were best described with two straight lines in double logarithmic coordinates. The near threshold light intensity summation was found to be linear, on the average up to 4.8 times threshold. The cells' threshold, defined as smallest response outside the 95%-confidence interval of the spontaneous activity (SpA) distribution, is dependent on the slope of the gain near threshold (linear gain) and the standard deviation of the spontaneous activity (SpA-scatter) prior to stimulation. The slope of the double logarithmic relationship at higher intensities (non-linear gain) - corresponding to the exponent of the power function - increases with threshold intensity. The linear, near threshold gain was used to describe the retinotopic distribution of the cells' threshold- and suprathreshold sensitivity. This sensitivity is high in the center of the retina decreasing steadily towards the periphery. Threshold, as well as linear and non-linear gain are interdependent parts of the SRC, specific for each ganglion cell and, furthermore, the geometrical mean between threshold activity and the response activity at the intersection point of the two regression lines is constant around 30 imp/s, irrespective of the cell's range of operation. The entire course of the SRC can therefore be predicted on the basis of the SpA-scatter and threshold intensity. The homogeneous population of investigated Y-ganglion cells proved to be a set of cells with summation characteristics, changing systematically with threshold and the distance of the receptive field from area centralis.

Animals↗