Bilaterally projecting neurones in pregenital abdominal ganglia of the locust: anatomy and peripheral targets.

The anatomy and physiology of neurones with axons in left and right homologous nerves was studied in abdominal ganglia of the migratory locust, Locusta migratoria, by using a differential cobalt/nickel staining method. These neurones reside within two clusters at the anterior and posterior ends of all unfused abdominal ganglia. Each cluster contains at least seven neurones with bilaterally projecting axons. All neurones of the anterior cluster possess bilaterally projecting axons which leave the ganglion through nerve 2 (= sternal nerve) or nerve 1 (= tergal nerve). Additional axon collaterals, which are present in some of these neurones leave through either nerve 1 or nerve 2 of the right or left side of the ganglion. With few exceptions, the neurones show further asymmetries in their dendritic arborizations. Neurones of the posterior group also have bilaterally projecting axons that leave the ganglion through nerve 1 or nerve 2. Among these neurones are the two large posterior dorsal unpaired median (DUM) neurones with bilaterally symmetrical axons that were described earlier as DUM1 and DUM2. They innervate the skeletal muscles of an abdominal segment. Two other cells of this cluster have anatomical properties similar to the DUM1 neurone and were termed DUMheart1A and DUMheart1B. The rest resemble the bilaterally projecting neurones of the anterior group. With the exception of the two classic DUM neurones (DUM1 and DUM2), all neurones of the anterior and posterior cluster innervate the heart or a neurohaemal area.