Circadian Rhythm of Optic Nerve Impulses Recorded in Darkness from Isolated Eye of Aplysia

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Science  02 May 1969:
Vol. 164, Issue 3879, pp. 562-563
DOI: 10.1126/science.164.3879.562


The isolated eye of the sea hare Aplysia califomica shows a circadian rhythm of optic nerve impulses when kept in total darkness. Peak activity on the first day of isolation occurs during the projected " dawn" of the light-dark cycle to which the whole animal had previously been entrained. Eyes from animals previously exposed to constant light show a free-running rhythm. This simple photoreceptor provides a quantized output with an ideal control (the other eye) for studies on rhythms.

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