Insect Circadian Rhythms transmitted by Parabiosis-a Re-examination

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Cymborowski B.
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Fifteen years of research on the hormonal control of insect circadian rhythms has been founded on the original report that rhythms could be transmitted in the blood between parabiosed cockroaches. The interpretation of this experiment has been questioned, however, for the following reasons. (a) No control parabioses were performed using animals with unconnected haemocoels2 (b) The lower (recipient) animal was supposedly made arrhythmic by keeping it in constant light (LL), whereas it is now known that· cockroaches can remain rhythmic for weeks in LL 3 , and that such rhythms may not necessarily be apparent in the loco motor activity4. (c) No cognizance was taken of the phase of the recipient animal, which may therefore have been close to that of the donors. (d) The recipient animal was intact and therefore in possession of a complete neuro-endocrine system whose clock may simply have been re-started by the shock of the operation6
Nature, 236 (68), p. 221-222