Conditionality of phase resetting by inhibitors of 80 S translation inGonyaulax polyedra

Summary Gonyaulax polyedra was subjected to a cold treatment of 18 h at 10 °C leading to arrhythmicity. Subsequently, the circadian rhythm of bioluminescence was investigated at the permissive temperature of 20 °C. 1-h pulses of 10 M cycloheximide or 2 M anisomycin, when given after the temperature step-up, resulted only in a very weak resetting of the circadian oscillator, in marked contrast to the behaviour of cells kept continuously in oscillatory conditions at 20 °C. The extremely reduced sensitivity to 80 S inhibition was characteristic for the first cycle after the temperature step-up, whereas cells treated with cycloheximide in the second cycle after re-initiation of rhythmicity showed a gradual recovery of resettability, though the phase response curve was still atypical; treatment in the 3rd cycle after step-up led to a relatively normal phase response curve. The observed insensitivity in the 1st cycle was neither a consequence of insufficient drug action, nor of a transient non-oscillatory behaviour after temperature step-up. Already in the first hours after transfer to 20 °C, 80 S translation was strongly suppressed by cycloheximide, and the cells were also efficiently reset by changes of the light-dark zeitgeber. Resettability of the circadian oscillator by 80 S inhibitors is, therefore, conditional.Abbreviations Ani anisomycin - Chx cycloheximide - CT circadian time - LD light-dark cycle - LL constant light - TCA trichloroacetic acidThis work was supported by the Deutsche Forschungsgemeinschaft