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H Broda

Publications and source records attributed to H Broda.

10 recordsLinked to original sources
PubMed1989

Temperature dependence of phase response curves for drug-induced phase shifts.

The effectiveness of drugs active in phase-shifting the circadian rhythm of bioluminescent glow in the unicellular dinoflagellate Gonyaulax polyedra differs, depending upon the time of drug exposure (as pulses). For two drugs tested--cycloheximide and anisomycin, both inhibitors of cytosolic protein synthesis--this function, referred to as the drug phase response curve (dPRC), differs, depending upon the ambient temperature. Since dPRCs may differ at different drug concentrations, the effects observed may be attributable to differences in the effectiveness of or recovery from the drugs at different temperatures.

Animals↗
PubMed1986

Circadian communication between unicells? Effects on period by cell-conditioning of medium.

Populations of Gonyaulax polyedra, in two different phases, about 11 h apart, were mixed, and the intensity of their spontaneous bioluminescence glow recorded for about 2 wk under conditions of constant dim (35 +/- 3 microE/m2/s) white light and constant temperature (19.0 +/- 0.3 degrees C). The phases and amplitudes of glow signals recorded from mixed cultures were compared with those obtained from the arithmetic sum of the intensity data from two control vials. Peaks in control cultures generally remained separate, but there was a spontaneous increase in the period beginning 6-11 d after the onset of constant conditions. This did not occur in cultures in which the medium was exchanged with fresh medium every 2 d. In the actual mixes of two cultures there was a merging of the two subpeaks in the signal, which did not occur when the medium was exchanged. The results indicate that conditioning of the medium by cells may affect the period of the circadian rhythm and that this might result in a type of communication.

Animals↗
PubMed1986

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.

Animals↗
PubMed1986

Acquisition of circadian bioluminescence data in Gonyaulax and an effect of the measurement procedure on the period of the rhythm.

During measurements of the circadian (approximately 24-hr) rhythms of spontaneous bioluminescence in the marine dinoflagellate Gonyaulax polyedra, the individual cultures in vials were shielded from otherwise constant dim light for 1-3 min every 20-60 min by a photomultiplier housing that was moved from vial to vial. The high-frequency dark pulses caused a small but consistent shortening of the free-running circadian period, but there was no indication that the dark pulses caused entrainment. Hardware and software components of the microcomputer-controlled data collection system are described. A microcomputer controlled the movement of the photomultiplier and acquired the data via an analog-to-digital converter. The algorithms distinguished and separately recorded background glow, intermittent flashes, and total light from populations ranging in number from 10(3) to 10(5) cells in volumes from 1 to 10 ml. Fast video display techniques allowed continuous on-line viewing of incoming data, together with a display of the data recorded over the preceding day or two. Detection of mechanical and software errors coupled with recovery systems maintained high reliability of data collection.

Animals↗
PubMed1983

On-line data acquisition and evaluation of long-term measurements of circadian rhythms in individual cells of Acetabularia.

A multitasking time-sharing computer system was implemented for studies of different circadian rhythms in individual cells of the unicellular green alga, Acetabularia. This fully automatized system allows simultaneous data acquisition and analysis. Graphical presentation of untreated and mathematically treated data is permanently available on three graphic displays and on a digital plotter. The sampling rate for the data acquisition in each of the 60 channels connected to the system is 720/24 h. Provisions have been made to guarantee uninterrupted data uptake for these long-term measurements by including an auto-restart module and by providing extremely reliable software for the experimenter using menu techniques.

Acetabularia↗
PubMed1981

Long-term measurement of endogenous diurnal oscillations of the electrical potential in an individual Acetabularia cell.

In Acetabularia mediterranea the transcellular electrical potential along the cell is subjected to diurnal oscillations which persist under constant conditions. The frequency may significantly differ between individual cells even in simultaneous measurements. The free running period of a distinct cell may be subjected to slow changes during long-term measurements. Such measurements have been performed over about 100 days.

Acetabularia↗