Effects of Nymphal Stage Optic Nerve Severance or Optic Lobe Removal on the Circadian Locomotor Rhythm of the Cricket, Gryllus bimaculatus(Physiology)

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Bilateral optic nerve severance and optic lobe removal were performed on the 8thinstar nymphs of the cricket Gryllus bimaculatus DeGeer. Effects of the operations on circadian activity under LD12 : 12 were investigated. Six optic nerve-severed animals revealed free-running rhythms in both the nymphal (diurnal) and adult (nocturnal) stages, indicating that the compound eye is the photoreceptor necessary for entrainment. In the majority, the adult rhythm was ultimately roughly synchronized to light-off, probably due to partial regeneration of the optic nerves. Activity in nine of 16 optic-lobeless nymphs was too low to evaluate the effect of the operation, but in the remaining seven, no significant rhythm could be detected. Four to five days after the imaginal moult, these animals showed the normal sexual-maturation-related increase of activity, but this was still arrhythmic. This arrhythmicity of lobeless nymphs and adults indicates that the optic lobe is indispensable to both nymphal and adult rhythmicity. Some lobeless animals as adults exhibited an atypical rhythm peaking in the light phase; this may be attributable to nerve regeneration between the retina and the cut end of optic tract.
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