Cellular mechanisms of entrainment.

This review summarizes our current understanding of the signal transduction cascade by which light causes phase shifts of the circadian oscillators found in the eye of Bulla and Aplysia. The isolated retina of these marine mollusks contains a circadian oscillator, a photoreceptor, and a light transduction pathway sufficient for entrainment. This preparation offers unique advantages for the cellular analysis of entrainment and the generation of circadian oscillations. There is evidence that similar cellular mechanisms may underlie mammalian and molluscan circadian oscillations. Thus, the models developed to explain entrainment in the molluscan retina are likely to have utility in exploring the mammalian suprachiasmatic nucleus.