CENTRAL NERVOUS SYSTEM CONTROL OF CIRCADIAN RHYTHMICITY IN THE COCKROACH. I. ROLE OF THE PARS INTERCEREBRALIS

¹ Department of Biology, Princeton University, Princeton, N. J. 08540

1. Ablation of the region of the pars intercerebralis of the cockroach brain induced arrhythmicity of locomotory activity in the animal. Evidence is presented which demonstrates a relationship between the neurosecretory cells of the pars intercerebralis and the circadian rhythm.

a. Surgical removal of the pars intercerebralis, including the lateral and medial neurosecretory cells, results in arrhythmicity and an increased level of activity.

b. In a large number of cases where normal activity and rhythms regenerated post-operatively, neurosecretory cells could be demonstrated histologically to be present and presumably functioning.

2. The suggestion is made that the pars intercerebralis acts as a rhythmic suppressor of general locomotory activity resulting in rhythmic locomotory behavior.

3. In animals where rhythms "regenerate" several weeks post-operatively, the speculation was made that biological regenerative processes, such as regeneration of several nerve tracts of a few remaining neurosecretory cells, in addition to the general recovery from and adjustment to the brain surgery, are the time-consuming processes which must occur before rhythms manifest themselves.

4. Insertion of a gel containing actinomycin D into the pars intercerebralis induced arrhythmicity in the animal. However, when actinomycin D gel was implanted into the fifth abdominal ganglion normal activity and rhythm continued unchanged; when gel containing eosin instead of actinomycin D was inserted into the pars intercerebralis, rhythm regenerated post-operatively.

5. It is still unclear if the corpora pedunculata play some role in activity rhythms, and if secondary effects following ablation of the neurosecretory cells are responsible for inducing arrhythmicity in the animal.

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