Postembryonic changes in circadian photo-responsiveness rhythms of optic lobe interneurons in the cricket Gryllus bimaculatus

The photo-responsiveness of 2 groups of interneurons responding to light in the protocerebrum was investigated at 2 developmental stages, the last instar nymphs and adults, in the cricket Gryllus bimaculatus. The cricket is diurnally active during the nymphal stage but becomes nocturnal as an adult. In both adults and nymphs, light-induced responses of optic lobe light-responding interneurons that conduct light information from the optic medulla to the lobula and the cerebral lobe showed a circadian rhythm peaking during the subjective night. Amplitudes of the rhythms were not significantly different between adults and nymphs, but adults showed more stable day and night states than did nymphs. The medulla bilateral neurons that interconnect the bilateral medulla areas of the optic lobe also showed circadian rhythms in their light-induced responses in both adults and nymphs. The rhythm had a clear peak and a trough in adults, and its amplitude was significantly greater than that of nymphs. These results suggest that the 2 classes of interneurons are differentially controlled by the circadian clock. The difference might be related to their functional roles in the animal's circadian behavioral organization.