Cytological evidence for serotonin-containing fibers in an abdominal neurohemal organ in a hemipteran.

The abdominal neurohemal organs of the hemipteran Rhodnius prolixus contain an extensive serotonin containing arborization. Endogenous serotonin within fibers and terminals in the neurohemal area were detected with histochemical and immunocytological techniques. The abdominal nerves which contain the neurohemal organs selectively sequester exogenous serotonin. Serotonin and its metabolites are biochemically detected within the mesothoracic ganglion, which is a known source of projections into the neurohemal organ. However, the source of the cell bodies which might send serotonergic fibers to the neurohemal organ remains undetermined because no correspondence was found between immunocytological maps of serotonin-containing cells in the ganglion, and projection maps into neurohemal organ (determined by cobalt back-filling).