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Journal of Experimental Biology 58,177-187 (1973)
Published by Company of Biologists 1973

Humoral Regulation of the Cerebral Neurosecretory System of Rhodnius Prolixus (Stal.) During Growth and Moulting

C. G. H. STEEL ¹

¹ Department of Biology, Queen's University, Kingston, Ontario and Imperial College of Science and Technology Field Station, Silwood Park, Ascot, Berks

1. In normal fifth instar Rhodnius the cytological changes occurring in the medial neurosecretory cells (MNC) of the brain are very different before and after the ‘critical period’ for decapitation.

2. When a decapitated insect which has reached the ‘critical period’ (8 days after feeding) is joined in parabiosis to an insect with an intact cerebral endocrine system and which has not yet reached the ‘critical period’ (1 day after feeding) the MNC of the younger insect are induced to switch over from their normal sequence of cytological changes to those characteristic of the older insect. The induced changes do not occur in normal insects of the same age or in insects joined in parabiosis to others of the same age.

3. The nature of the changes indicates that release of stainable neurosecretory material is inhibited and its synthesis stimulated by the older insect. It is inferred that the haemolymph of insects which have reached the ‘critical period’ contains a factor which induces in the MNC an inhibition of release and a stimulation of synthesis. These are the events which occur in the MNC of normal insects at the critical period.

4. Considerable circumstantial evidence suggests that the factor is ecdysone. It may act either directly on the brain or on the corpus allatum. Its contribution to a feedback regulation of the endocrine system controlling growth and moulting is discussed.