Storage site of glycogen phosphorylase activating hormone in larvae of Manduca sexta

Abstract

Corpora cardiaca of Manduca sexta were examined by light and by electron microscopy. In the posterior part of the corpora cardiaca there are 6 or 7 large intrinsic neurosecretory cells whose contents stain strongly with paraldehydfuchsin. These cells are full of neurosecretory granules, with a diameter of about 200 nm (range 80–400 nm), and appear to represent the intrinsic glandular part of the corpora cardiaca of M. sexta. The remainder of the corpora cardiaca consists mainly of axons containing secretory granules of about 100 nm, but larger granules were seen also. Larval corpora cardiaca are the only source of glycogen phosphorylase activating hormone and at least 90% of the total activity was associated with the posterior region of the corpora cardiaca containing the intrinsic neurosecretory cells. The Golgi bodies in these cells appeared to be active. The data suggest that the glycogen phosphorylase activating hormone may be synthesized, stored and released from the intrinsic neurosecretory cells. In corpora cardiaca of larvae starved for 1 h some ultrastructural changes are seen, which might be indications of secretion of the glycogen phosphorylase activating hormone.