Light and High Potassium Cause Similar Phase Shifts of the Aplysia Eye Circadian Rhythm

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Abstract
The eye of Aplysia, with its circadian rhythm of spontaneous optic nerve impulses (Jacklet, 1969a), is a model system for studying the cellular mechanisms of circadian rhythms generated by nervous tissue (Jacklet, 1981). An approach to determine the mechanisms of rhythms is to apply pulses of experimental agents and then observe the shifts in phase of subsequent cycles of the rhythm. If the size and direction of the phaseshifts are dependent upon the phase of the cycle when the pulse was given (phasedependent phase shifts), it is evidence that the rhythm timing mechanism has been perturbed. The specific cellular process acted on is then believed to be important in the cellular clock mechanism. Some agents cause phase-dependent phase shifts and the shifts are plotted in phase response curves (PRCs). It is useful to compare the PRCs produced by different agents in order to identify similar or dissimilar actions on the cellular clock (Jacklet, 1978).