Dorsal unpaired median insect neurons make neurosecretory endings on skeletal muscle

This report presents results of a study in Schistocerca gregaria of large dorsal unpaired median neurons found previously in ganglia of several insects (Crossman et al., 171a; Hoyle, unpublished). Most of these neurons give off a single median neurite that makes a T-branch, providing symmetrical left and right efferent axons. These axons emerge in ganglion nerve trunks and terminate in each of two nerves. They then travel to major skeletal leg muscles. One of the neurons supplies only the extensor tibiae (jumping muscle). The final branches of this neuron parallel the fast axon and supply muscle units that receive the fast axon only. All the muscle fibers in a unit are innervated (multiterminally) by the fast axon, but only a few receive terminals of the dorsal neuron in addition. The endings are of neurosecretory type, containing large numbers of dense core vesicles. Their function is unknown.