The role of the optic lobe in circadian locomotor rhythm generation in the cricket, Gryllus bimaculatus, with special reference to PDH-immunoreactive neurons

The role of optic lobes in rhythm generation was examined by a combination of surgical operation and immunohistochemistry using anti-β-pigment-dispersing hormone (PDH) antibody. In adult male crickets, Gryllus bimaculatus, one optic lobe was removed and the contralateral optic lobe was surgically lesioned to varying extent. Locomotor rhythms persisted in most crickets with the optic nerve severed or with the lamina region removed, while they were lost when the lamina medulla complex was removed. The rhythm was also lost in all animals with the distal part of the medulla removed. In all cases, fragments of the PDH-immunoreactive neurons (PDH-IRNs) remained undegenerated in the brain, and in the animals with the medulla area partially removed, the shape of the PDH-IRNs showed a rough similarity to that in intact animals, but the number of fibers projecting toward the cerebral lobe was increased. These results confirm our previous conclusion that the optic lobe is indispensable for the generation of locomotor rhythm. They also strongly suggest that the pacemaker resides in the medulla area or between the lamina and the medulla area, and that the PDH-IRNs in the medulla are not the pacemaker neurons.