Evidence for octopaminergic nature of peripherally projecting DUM-cells, but not DUM-interneurons in locusts

In locusts, a median neuroblast in each segmental ganglion gives rise to numerous unpaired progeny--the well known peripherally projecting dorsal-, occasionally ventral-, unpaired median (DUM-, resp. VUM-) neurones together with the lesser known DUM-interneurones 12. We examine the reputed octopaminergic nature of this nerve cell lineage using an anti-octopamine serum recently developed by M. Eckert and J. Rapus 7. This antiserum labels in each segmental ganglion numerous midline neurones, identifiable as DUM- and VUM-cells by their some sizes and positions, projections in DUM-tracts and characteristic T-junctions with bilaterally projecting axons. All octopamine immunoreactive DUM-, and VUM-neurones appear to project to peripheral nerves; their numbers correspond to the number of peripherally projecting DUM- and VUM-neurones identified so far in the examined ganglia. Presumptive DUM-interneurones, i.e. smaller somata interspersed between the peripherally projecting DUM-cells are not octopamine immunoreactive, but, confirming other studies 25, display GABA-like immunoreactivity. We thus suggest, that of the whole DUM-cell population in the examined ganglia, all and only peripherally projecting DUM-neurons are octopaminergic.