Circadian rhythm of responsiveness in crayfish visual units

Abstract

Abstract Metal microelectrodes were implanted in the optic nerve of the crayfish, Procambarus clarki , and the activity of the sustaining fibers (units which react tonically to changes in illumination) was continuously recorded over periods up to 8 weeks. In animals kept in darkness, the response to periodic test light pulses was found to vary in a circadian manner. The duration of the cycles varied between 22 24 hr, with a phase of high responsiveness during the subjective night, which abruptly changed to one of low responsiveness at subjective dawn. The phase, amplitude, and shape of the cycles were modifiable by light pulses. The spontaneous activity of these units in darkness showed a similar fluctuation, and so did the electroretinogram amplitude, the spontaneous motor activity of the animal, as indicated by records from mechanoreceptive and activity fibers (units which are activated, directly or indirectly by body movements), and the motor responsiveness to light. The time course of these cycles suggests that they are driven by a common “clock,” through humoral mechanisms.