The Compound Eye Regulates Free-Running Period and Stability of the Circadian Locomotor Rhythm in the Cricket .

The circadian system of many multicellular organisms consists of a hierarchical structure of multiple clocks, including central and peripheral clocks. The temporal structure has been analyzed in terms of central-to-peripheral regulation but rarely from the opposite perspective. In this study, the potential control of the central clock in the optic lobe by the peripheral clock in the compound eye was investigated in the cricket . The locomotor activity rhythm of crickets in which one of the two bilateral optic lobe clocks was surgically removed was tested in constant darkness at three environmental temperatures (20°C, 25°C, and 30°C) and compared with that of crickets in which the optic nerve connecting between the compound eye and optic lobe of the intact side was also severed. When the optic nerve was severed at 30°C, the free-running period and its stability were significantly increased and decreased, respectively, compared to those of intact and sham-operated crickets, whereas at 20°C, only the free-running period was significantly lengthened, and at 25°C, no significant changes were observed in these parameters. At 30°C, the changes in these two parameters were reproduced when the anterior half of the compound eye was removed, while the removal of the posterior half induced period lengthening only. Together with previous data, these results suggest that the free-running period and stability of the locomotor rhythm are regulated through reciprocal coupling between the clocks in the compound eye and the optic lobe.