Sulphide Silver Staining for Endogenous Heavy Metals Reveals Subsets of Dorsal Unpaired Median (Dum) Neurones In Insects

Abstract

ABSTRACT The central nervous systems of many insects contain segmentally arranged groups of unpaired midline neurones. These have been called DUM (dorsal unpaired median) neurones because of the position of their cell bodies. The larger DUM neurones, with bilaterally symmetrical peripheral axons, have been most extensively studied in grasshoppers and locusts. DUM cells in the metathoracic ganglion modulate tension of skeletal muscle, potentiate synaptic transmission at neuromuscular junctions and slow a myogenic rhythm (Evans and O’Shea, 1977, 1978; Whim and Evans, 1989), whereas those in the abdominal ganglia alter tension in visceral muscle (Lange and Orchard, 1984). In fireflies, DUM neurones of the terminal abdominal ganglia control flashing by activating the photocytes of the lantern (Christensen and Carlson, 1981). The effects are mediated by the biogenic amine octopamine (Carlson and Jalenak, 1986; Evans and O’Shea, 1977, 1978; Morton and Evans, 1984; Orchard and Lange, 1985), which is also implicated in other modulatory actions (see Ramirez and Orchard, 1990, for references). In grasshoppers, in addition to the octopamine-containing efferent DUM neurones, there are a substantial number of local and intersegmental DUM interneurones with small cell bodies (Thompson and Siegler, 1989, 1991).