Effects of isolation and transplantation of the corpus cardiacum on hormone release from its glandular cells after flight in Locusta migratoria. A quantitative electron microscopical study.

The glandular lobe of the corpus cardiacum (CC) of Locusta migratoria contains secretory cells and axon terminals. It is generally accepted that the glandular cells produce an adipokinetic hormone which stimulates the release of diglycerides from the fat body. The axon terminals are supposed to be involved in the regulation of the secretory activity of these cells. CC were transplanted into locust hosts. The secretory activity of the glandular cells and axons was studied in the transplants as well as the intact host CC. Quantitative electron microscopical examination of the glandular cells of the CC in animals both at rest and after flight shows that only in the host CC the secretory activity of the glandular cells is stimulated by flight, as indicated by an increase in the activity of the Golgi zones and in the number of exocytotic pits. In the axon terminals release of secretory products, indicated by synaptic vesicles and membrane indentations, is reduced as a result of the transplantation. It is concluded that the glandular cells need excitatory input from outside the CC for stimulation of their secretory activity. Furthermore, it is proposed that the transplanted glandular cells decrease the level of activity of the intact host cells by way of a negative feedback mechanism.