Interactions between bilaterally paired components of the cockroach circadian system

Summary

The hypothesis that bilaterally redundant, and mutually coupled circadian pacemakers are located near the lobula of the optic lobes of the cockroach,Leucophaea maderae, was investigated in a series of lesion experiments.

• 1. Following removal of one optic lobe electrolytic lesions near the lobula in the dorsal 1/3 of the remaining lobe had no effect on the activity rhythm or its entrainment to a light cycle. Lesions in the ventral 2/3 of the lobula region either had no effect or resulted in aperiodic activity (Figs. 3, 4).

• 2. In animals in which one optic lobe was neurally isolated from its (ipsilateral) compound eye by section of the optic nerve, lesions near the lobula in the dorsal 1/3 of the contralateral lobe had no effect on entrainment of the rhythm. In contrast, lesions in the ventral 2/3's of the lobe, frequently, resulted in loss of entrainment (Figs. 5, 6, 7). Following loss of entrainment, the average freerunning period ($\bar \tau = 24.03 \pm 0.26 h$) was longer than that of intact animals ($\bar \tau = 23.73 \pm 0.2 h$).

• 3. In animals with one cut optic nerve, electrolytic or surgical lesions in the ipsilateral optic lobe, intended to destroy the known monosynaptic connections between the two lobes, had no effect on entrainment or on freerunning period (Figs. 9, 10, 11).

These data collectively support the hypothesis that (a) bilaterally paired pacemakers in the optic lobes are coupled and mutually accelerate each other via a polysynaptic pathway; and (b) that entrainment of each pacemaker by its contralateral eye is mediated by this pathway.