The distribution of a CRF-like diuretic peptide in the blood-feeding bug Rhodnius prolixus

The blood-feeding bug Rhodnius prolixus ingests a large blood meal, and thi s is followed by a rapid diuresis to eliminate excess water and salt. Previ ous studies have demonstrated that serotonin and an unidentified peptide ac t as diuretic factors. In other insects, members of the corticotropin-relea sing factor (CRF)-related peptide family have been shown to play a role in post-feeding diuresis. Using fluorescence immunohistochemistry and immunogo ld labelling with antibodies to the Locusta CRF-like diuretic hormone (Locu sta-DH) and serotonin, we have mapped the distribution of neurones displayi ng these phenotypes in R. prolixus. Strong Locusta-DH-like immunoreactivity was found in numerous neurones of the central nervous system (CNS) and, in particular, in medial neurosecretory cells of the brain and in posterior l ateral neurosecretory cells of the mesothoracic ganglionic mass (MTGM). Pos itively stained neurohaemal areas were found associated with the corpus car diacum (CC) and on abdominal nerves 1 and 2, In addition, Locusta-DH-like i mmunoreactive nerve processes were found over the posterior midgut and hind gut, Double-labelling studies for Locusta-DH-like and serotonin-like immuno reactivity demonstrated some co-localisation in the CNS; however, no co-loc alisation was found in the medial neurosecretory cells of the brain, the po sterior lateral neurosecretory cells of the MTGM or neurohaemal areas. To c onfirm the presence of a diuretic factor in the CC and abdominal nerves, ex tracts were tested in Malpighian tubule secretion assays and cyclic AMP ass ays. Extracts of the CC and abdominal nerves caused an increase in the rate of secretion and an increase in the level of cyclic AMP in the Malpighian tubules of fifth-instar R, prolixus. The presence of the peptide in neuroha emal terminals of the CC and abdominal nerves that are distinct from seroto nin-containing terminals indicates that the peptide is capable of being rel eased into the haemolymph and that this release can be independent of the r elease of serotonin.