From circadians of the fifties to chronomes in vitro as in vivo.

In a recent review of cellular mechanisms of entrainment, an ocular circadian rhythm of Bulla was reported (1). The isolated retina of this marine mollusk is described to contain a circadian oscillator. A glance at the spontaneous impulse frequency from eyes recorded in darkness at 15 degrees C suggests lower-frequency modulations of the about 24-h rhythm and prompts the quantitative assessment of the broader time structure, the chronome, in this extensively used model of a budding neurochronophysiology. The cultured retina of mollusks is interpreted by the original authors as descriptive of similar cellular mechanisms that may underlie mammalian as well as molluscan physiology. We report here the rhythmometric analysis of the original data by Block et al. (2), taken from Figure 2 of the article by Colwell et al. (1), resolved by computer just as the microscope resolves cellular structure. The results are further compared with those obtained on data kindly provided by Stephan Michel on another retina of Bulla. The findings of multiple chronome components (beyond the circadian system) are placed into the broader context of cell biophysics and its implications for biomedicine within the scope of an international chronome endeavor.