LOCALIZATION OF OCTOPAMINERGIC NEURONS IN INSECTS

This paper reviews data on the localization of octopaminergic neurones revealed by immunocytochemistry in insects, primarily the locusts Sch istocerca gregaria and Locusta migratoria, cricket Gryllus bimaculatus , and cockroach Periplaneta americana. Supporting evidence for their o ctopaminergic nature is mentioned where available. In orthopteran vent ral ganglia, the major classes of octopamine-like immunoreactive (-LI) neurones include: (1) efferent dorsal and ventral unpaired median (DU M, VUM) neurones; (2) several intersegmentally projecting DUM interneu rones in the suboesophageal ganglion; other DUM interneurones are prob ably GABAergic; (3) a pair of anterior median cells in the prothoracic ganglion; (4) a single pair of ventral cells in most thoracic and som e other ganglia; these appear to be plurisegmentally projecting intern eurones. Eight categories of octopamine-LI neurones occur in the ortho pteran brain. The basic projections of three types are described here: one class project to the optic lobes to form wide field projections. Another type descends to cross into the tritocerebral commissure and m ay invade the contralateral brain hemisphere. A further class is the m edian neurosecretory cells with axons in the nervi corpori cardiaci I. Available data for the honey bee Apis mellifera and moth Manduca sext a indicate that the octopamine-LI cell types found in orthopterans als o occur in holometabolous insects. Immunocytochemical evidence suggest s that some octopaminergic DUM cells contain an FMRFamide-related pept ide and the amino acid taurine as putative cotransmitters.