PERTURBATION OF A CIRCADIAN-RHYTHM BY SINGLE AND PERIODIC SIGNALS AND ITS MATHEMATICAL SIMULATION

Adaptive characteristics of circadian rhythm are based on their capacity to be synchronized by external signals, particularly light signals. The effect of both single and periodic light signals on the electroretinogram (ERG) circadian rhythm in crayfish is studied. In a previous work (Lara-Aparicio er al., Bull. math. Biol. 55, 97-110, 1993) we developed a mathematical model simulating the emergence of the ERG circadian rhythm during the ontogeny of the crayfish. In the present work we have tested the familiar wave-shift behaviour of an oscillator with a single limit cycle. Two new facts, not present in a simpler model, now appear, which simulate adequately the experimental results, i.e. the presence of a transient stage and the shape of the perturbed wave which changes according to the characteristics of the external light signals

synchronization by light of the erg circadian-rhythm during ontogeny in the crayfish

The present paper was aimed at establishing the time course for development of the light entrainment mechanism of the ERG. Chronic ERG recordings were obtained from juvenile crayfish during different stages of their ontogenetic development, by measuring (as a phase-response curve, PRC), the effect produced by single 15-min. light pulses on the period and phase of the ERG amplitude rhythm. It was found that the circadian rhythm of the ERG appears at relatively early stages of development (4th week after hatching) and that the entrainment mechanism developes after the crayfish has reached 2-5 months of age. The role played by the visual photoreceptors in the expression of the ERG rhythm as well as in its entrainment is discussed

effect of monochromatic light upon the erg circadian-rhythm during ontogeny in crayfish (procambarus-clarkii)

1. The aim of this work was to investigate if the asymmetric development of the two sets of visual photoreceptors responsible for short wave and long wave sensitivity during crayfish ontogeny influences the characteristics of the electroretinogram (ERG) amplitude rhythm. 2. The parameters of the ERG rhythm of juvenile (2-12 weeks) and adult stages were studied in free-running conditions under blue, red or white light flash test. 3. It was found that monochromatic light produces significant changes in the ERG circadian rhythm parameters in juvenile stages and has a synchronizing effect on the ultradian rhythm prior to the ERG circadian rhythm. 4. Based on these results we propose the existence of two sets of circadian photoreceptors related to two independent systems involved in the synchronization of the ERG circadian rhythm (a short wave and a long wave detection system)