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

Decreasing period-length of the endogenous circadian rhythm of oxygen evolution in Acetabularia and its possible relation to aging

Endogenous circadian rhythms observed under constant conditions normally show period length variations. However, a general trend is difficult to identify when cells or organisms are entrained with the usual 24-h-period light/dark cycles. Therefore, these variations in time have been considered as fluctuations. In order to gain more insight into this phenomenon, individual Acetabularia cells were exposed to light/dark cycles of 16 h (LD 8:8) and 33.6 h (LD 16.8:16.8), respectively, i.e., periods which lie distinctly outside the range of the normal circadian entrainment. Employing a high-resolution procedure for data analysis, decreasing period lengths could consistently be detected when cells were kept under constant conditions for several weeks. Possible causes of this decrease are discussed.

High-resolution measurement of circadian periodicities in Acetabularia

Well-expressed endogenous circadian rhythms in Acetabularia acetabulum were spectrally analyzed and recorded in time-period distributions. The stability of the circadian periods under constant conditions and their changes could be monitored continually in step sizes close to the circadian period length. The resolution of period estimates of the circadian component was increased by a factor of approximately 4-10 by adapting analyzed interval lengths to full period sizes of the corresponding main component. Methodological aspects of the applied algorithms are discussed by means of examples that measure the temperature dependency of the circadian period.

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.

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.

Microcomputerized measurement of the circadian locomotor rhythm in microorganisms

A computerized close-up video/photoamplifier system was implemented for the study of circadian locomotor rhythm in a population of a ciliate protozoan, Paramecium. This fully microcomputerized system facilitated automatic long-term measurement of three parameters in parallel: (1) numbers of specimens per 10 min traversing beneath a fixed point in an experimental vessel, (2) times taken by specimens to traverse the point, and (3) interval times between subsequent specimens traversing the point. Stochastic analyses using these parameters can derive the circadian fluctuation of physiological variables, such as swimming speed and the frequency of avoiding reaction (abrupt change in swimming direction). The computerized system simultaneously accomplished the acquisition of these three sets of data, their transient storage, and their graphic display according to given format. The system software was constituted so that an experimenter with little computer knowledge, could easily operate the system by answering questions displayed on the computer monitor.