The distribution of proctolin in the central nervous system of the hemipteran bug, Triatoma infestans, was studied by immunohistochemistry using the sensitive avidin-biotin technique combined with nickel salt intensification of the reaction product. Proctolin was present in cells and fibers of the brain and ganglia. In the brain, protocerebral proctolinimmunoreactive cell bodies were found in the pars intercerebralis, the optic lobes, and the lateral soma rind. The deutocerebrum showed positive somata in relation to the antennal motor center and the tritocerebrum had intense immunoreactive fibers but few positive cells.
Proctolin-immunoreactive cell bodies of different sizes were observed in the subesophageal ganglion. Large cell bodies were found mainly rostrally and beaded positive processes were present around the ventral border of the esophageal foramen and in the rostrolateral neuropil of this ganglion.
Small-to medium-sized positive somata were found in the posterior part of the prothoracic ganglion; some of these cells were sending immunoreactive processes to the central neuropil. The meso-metathoracic-abdominal ganglionic mass showed positive cells in all the neuromeres, where some of them were large and had thick immunoreactive granules.
The results show that the labeling pattern of proctolin-like immunoreactivity in Triatoma i. appears to be widespread and unique for its central nervous system. It is suggested that proctolin may serve neuroendocrine, integrative, and motor functions in the brain of T. infestans.