ANATOMY AND TARGETS OF DORSAL UNPAIRED MEDIAN NEURONS IN THE TERMINALABDOMINAL-GANGLION OF THE MALE COCKROACH PERIPLANETA-AMERICANA L

The morphology of the Dorsal Unpaired Median (DUM) neurones in the Ter minal Abdominal Ganglion (TAG) of the adult male cockroach Periplaneta americana were described based on wholemount preparations and paraffi n sections and by using anterograde and retrograde cobalt mapping, oct opamine-like immunohistochemistry, and double immunofluorescence techn ique with both conjugated gamma-aminobutyric acid (GABA) and odopamine antisera. Among 60 +/- 6 neurones with large somata (diameter 40 to 6 0 mu m) on the dorsal midline surface of the TAG that were stained wit h toluidine blue, about 36 efferent DUM neurones exhibited octopamine- like immunoreactivity. The DUM neurones were arranged in three cluster s (anterior, median and posterior) corresponding to the 7th-11th abdom inal ganglia of the fused TAG. Anterior efferent DUM neurones with one , two, and four pairs of lateral neurites entered segmental nerves VII B; VIIB and phallic nerves; IXB and phallic nerves; VIIIA, IXA, X, and IX, respectively. Three octopamine-like immunoreactive DUM neurones i nnervating heart chambers via segmental nerves (VIIA, VIIIA, and IXA) in the last abdominal segments occurred within abdominal ganglia 7, 8, and 9. Together with octopamine-like immunoreactive efferent DUM neur ones, GABA-like immunoreactive dorsal midline neurones with small soma ta (10 to 20 mu m) also occurred within the median group. The spatial distribution of DUM neurones in the TAG suggested that they had their origins in the median neuroblast, as for DUM neurones in the grasshopp er. (C) 1996 Wiley-Liss, Inc.