PIGMENT-DISPERSING HORMONE-LIKE PEPTIDE IN THE NERVOUS-SYSTEM OF THE FLIES PHORMIA AND DROSOPHILA - IMMUNOCYTOCHEMISTRY AND PARTIAL CHARACTERIZATION

Beta-pigment-dispersing hormone (beta-PDH) isolated from the fiddler c rab (Rao et al., '85) is a member of an octadecapeptide family of neur opeptides common to arthropods. Whereas earlier studies of these pepti des in insects were limited to orthopterans, this investigation focuse s on dipteran flies. Extracts of heads from the blowfly Phormia terrae novae were assessed in a fiddler crab bioassay for PDH activity. Immun ocytochemistry, dose-response curves, gel filtration chromatography an d reversed-phase HPLC, combined with bioassay and enzyme-linked immuno sorbent assay (ELISA), indicate the presence of PDH-like peptide in th e blowfly. Immunocytochemical mapping of PDH-like immunoreactive (PDHL I) neurons was performed for the entire nervous systems of Phormia and the fruitfly Drosophila with a beta-PDH antiserum. In the cephalic ga nglion (brain, optic lobe and subesophageal ganglion) PDHLI cell bodie s could be detected (34 in Phormia and 16 in Drosophila). In both spec ies, each hemisphere contains 8 PDHLI cell bodies in the optic lobes. These innervate the optic lobe neuropils bilaterally. In Phormia, anot her set of 8 cell bodies are located in each of the lateral neurosecre tory cell groups in the superior protocerebrum. These neurons send axo ns to the corpora cardiaca-hypocerebral ganglion complex and to portio ns of the foregut. In contrast, only the optic lobe neurons display im munoreactivity in Drosophila. Except for the optic lobes, PDHLI proces ses are distributed only in nonglomerular neuropils of the brain of bo th species. In the fused thoracico-abdominal ganglia of Phormia, 28 PD HLI cell bodies were found (only six were found in Drosophila). In bot h species, six abdominal PDHLI neurons are efferents with axons innerv ating the hindgut. We also found that some of the PDHLI neurons in the Phormia brain and abdominal ganglion contain colocalized FMRFamide-li ke immunoreactivity. Since the flies studied here do not display hormo nally controlled, fast pigment migrations, the PDH-like peptide may ha ve a role as neurotransmitter or neuromodulator in the central nervous system, especially in the visual system, and a regulatory role in the stomatogastric system and the hindgut.