Photoperiodic entrainment of locomotor activity in crickets (Gryllus bimaculatus) lacking the optic lobe pacemaker

The locomotor activity of 40 crickets receiving bilateral optic lamina-medulla removal as 7th-instar nymph was recorded under a light cycle and then constant darkness, and the records were analyzed statistically by an autocorrelogram and maximal entropy spectrum method. The activity of the nymphal stage was severely reduced and no rhythmicity was detected for the first few weeks following the operation. After the imaginal moult, activity gradually increased up to 20 times the nymphal activity. About 50% of the adult crickets restored a rhythmicity with peaks in the light phase, unlike the nocturnal rhythm of intact crickets. The synchronization of the activity was probably due to the newly established neural connection between the retina and the cut end of the optic stalk. The onset of the rhythmic activity preceded lights-on, suggesting the involvement of an endogenous mechanism. In constant darkness, a half of the rhythmic cricket lost the rhythmicity. However, 21% of the crickets retained the rhythmicity and the remaining 26% exhibited an ultradian rhythmicity. On the basis of these results, the involvement of moltiple oscillators, outside the optic lobe, in the regulation of the circadian locomotor rhythm is discussed.