Caudal photoreceptors synchronize the circadian rhythms in crayfish—I. Synchronization of ERG and locomotor circadian rhythms

Abstract

1. 1. Electroretinogram (ERG) and motor activity circadian rhythms in crayfish under constant environmental conditions were recorded. 2. 2. Changes on the circadian parameters induced by application of a single light stimulus of 2000 Ix and 10 min duration on either the eyestalk or the 6th abdominal ganglion were analyzed. 3. 3. The synchronization ability exerted by the caudal photoreceptors on the ERG and on motor circadian rhythms is discussed. 4. 4. In gangliectomized crayfish, there is a phase inversion in ERG circadian rhythm and an increment of the total amount of activity in motor circadian rhythm, but there is no evidence of synchronization when a single stimulus is applied on the place occupied by the removed 6th abdominal ganglion. 5. 5. It is proposed that extraocular photoreceptors can participate in the entrainment by light of the circadian rhythms of crayfish.