Circadian rhythm in the neurally isolated lamina-medulla-complex of the cricket, Gryllus bimaculatus

Efferent neuronal activities of the neurally isolated lamina-medulla-complex of the cricket (Gryllus bimaculatus) optic lobe were recorded extracellularly from the optic stalk using a suction electrode. The multiple unit activities of the lamina-medulla-compound eye-system exhibited clear circadian rhythms under constant conditions. In constant light, all specimens exhibited a peak discharge frequency in the subjective night, free-running with a period longer than 24 h. On the other hand, either diurnal or nocturnal increase occurred in specimens kept under constant darkness or in insects with optic nerve severed. Removal of the cerebral lobe and/or suboesophageal ganglion did not affect these rhythms. These results may be regarded as almost conclusive evidence that the lamina-medulla-complex involves a neural mechanism, i.e. a circadian oscillator, which can generate periodic activity without any neural input from the other central nervous system structures.