Control of the circadian rhythm of activity in the cockroach. I. The role of the corpora cardiaca, brain and stress.

In a series of papers from 1954 to i960 Harker published the results of her work on the neuro-endocrine control of the circadian rhythm of locomotor activity in the cockroach, Periplaneta americana (see Harker, 1964). The most important conclusions of these papers are: that the rhythm is controlled by a neurosecretory cycle occurring in the sub-oesophageal ganglion and endogenously timed therein; that the continued running of this 'clock' is maintained by a supply of neurosecretion from the corpora cardiaca; and that it has a complex, restricted ability to phase-shift related to its control by a second clock which responds directly to light signals received by the ocelli. Recently three papers have been published by Roberts (1965 a, b, 1966) which cast doubt on several of these conclusions. Failing to repeat some of Harker's work Roberts finds: that it is impossible to transfer rhythms by implanting sub-oesophageal ganglia, that the rhythm continues unchanged when the corpora cardiaca are removed, and that it is not the ocelli which are the relevant photo-receptors. The work reported here was undertaken in an attempt to reconcile some of the conflicting results of these two workers, but it must be emphasized that only a partial reconciliation was effected. The present paper concerns work on the brain, the corpora cardiaca and the possible effects of stress on the expression of the rhythm. In a second paper (Brady, 1967) investigations into the part played by the sub-oesophageal ganglion and ventral nerve cord will be reported.