Ultrastructure of two opposite types of abdominal perisympathetic organs in the heteropteran, Roscius elongatus Stål (Pyrrhocoridae). Abundant release of neurosecretory product by intraganglionic organs.

The ultrastructural study of perisympathetic organs (POs) in Roscius elongatus revealed the existence of two opposite neurohemal structures. Distal POs formed a network at the end of each of the first pro-, meso-, metathoracic, and abdominal nerves. They display a thin branched structure favoring contact between axon endings and hemolymph. The distal metathoracic POs contained two types of neurosecretory ending, and the distal abdominal POs three types. On the contrary, "subjacent" POs, strangely located laterally in the abdominal area of the ganglionic nerve mass, display a dense compact structure, containing only one type of neurosecretory ending. These characters demonstrate that the "subjacent" POs, earlier classified as transverse POs because they are symmetrically located, are in fact median POs. In transverse POs, signs of extrusion by exocytosis were observed only in one type of neurosecretory ending. In "subjacent" POs unusual pictures were found indicating abundant release by single or compound exocytosis. Such pictures prove that "subjacent" POs have a neurohemal function despite their dense structure and internal localization. Physiological implications of these opposite structures are discussed.