Circadian changes in RNA synthesis in the neurosecretory cells of the brain and suboesophageal ganglion of the house cricket

By the use of autoradiography an investigation was made in vitro of the daily cycle of intensity of RNA synthesis in the neurosecretory cells of the pars intercerebralis and the ventral cells of the suboesophageal ganglion in Acheta domesticus cultured under LD 12 : 12 conditions (rhythmic) and LL conditions (non-rhythmic). It was found that RNA synthesis in these centres of the nervous system of rhythmic insects takes place in a cyclic manner. The maximum RNA synthesis in the neurosecretory cells of the pars intercerebralis was observed immediately after the light period began. In the cells of the suboesophageal ganglion, however, we found two periods of intensive RNA synthesis, the first of which was shifted by about 6 hr in relation to the phase of intensive RNA synthesis in the pars intercerebralis. At the same time it was shown that a change takes place in the cross-section area of the nuclei of the neurosecretory cells of the pars intercerebralis and suboesophageal ganglion of crickets cultured under conditions of alternating light and darkness. In insects cultured under constant light conditions, RNA synthesis in the neurosecretory cells of the pars intercerebralis and the suboesophageal ganglion was not found to be cyclic. It is suggested that rhythmic lighting changes play a rôle in the process of forming the cyclic character of RNA synthesis in the centres of the central nervous system examined. The changes observed in the function of the neurosecretory cells of the pars intercerebralis and the suboesophageal ganglion were connected with the locomotor activity of the crickets.