Fate of abdominal ventral unpaired median cells during metamorphosis of the hawkmoth, Manduca sexta.

Each of the unfused abdominal ganglia in the larval, pupal, and adult stages of the hawkmoth, Manduca sexta, has two large ventral median neurons with axons that bifurcate to innervate targets on both sides of the abdomen. Although the dendritic structures of the two neurons are similar, their axons branch to innervate distinct sets of target muscles. During metamorphosis both neurons undergo dendritic regression, followed by growth of new arborizations during adult development. The neurons must innervate different targets in the larva and adult, since many larval muscles degenerate and are replaced during metamorphosis. Both neurons were reactive with an antibody to the neuromodulatory compound, octopamine, in the larval and adult stages. Pairwise intracellular recordings in isolated nerve cords revealed spontaneous excitatory synaptic potentials that occurred in the ventral median neurons of each ganglion in an anterior-to-posterior sequence. The synaptic potentials were eliminated when the interganglionic connective was interrupted posterior to the subesophageal ganglion. The ventral median neurons were also excited by tactile stimulation of the body surface in larvae, pupae and adults.