Octopamine immunoreactive cell populations in the locust thoracic‐abdominal nervous system

Abstract

We describe octopamine‐immunoreactive somata and their projections in the pro‐ meso‐, meta‐ and pregenital abdominal‐ganglia of locusts. Immunoreactive midline somata were identified as dorsal‐ and ventral‐ unpaired median (DUM‐ and VUM‐, respectively) neurones due to their: characteristic large size and positions of somata, primary neurites in DUM‐tracts giving rise to T‐junctions, and bilaterally projecting axons. In the prothoracic ganglion there are most likely 8 such cells; in the meso‐ and metathoracic, some 20 each; and in each individual pregenital abdominal ganglion, typically 3. All appear to project to peripheral nerves and their numbers correspond to the number of peripherally projecting DUM‐cells identified to date in each ganglion. We suggest that probably all peripherally projecting DUM‐cells are octopaminergic in the examined ganglia. Presumptive DUM‐interneurones are not octopamine‐immunoreactive, but, confirming other studies, are shown to label with an antiserum to γ‐amino butyric acid (GABA). Other octopamine‐immunoreactive neurones include a pair of midline, prothoracic, anterior medial cells, not necessarily DUM‐cells, and a pair of ventral lateral somata in each thoracic‐ and the first abdominal ganglion. The latter project intersegmentally in ventral tracts. Intersegmentally projecting octopamine‐immunoreactive fibers in dorsal tracts probably arise from a prothoracic DUM‐cell, which leaves through suboesophageal nerves, or descending suboesophageal DUM‐cells. Thus, the octopamine‐immunoreactive system of thoracic and pregenital abdominal ganglia in locust comprises all peripherally projecting DUM‐cells and a plurisegmental network.