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 this is followed by a rapid diuresis to eliminate excess water and salt. Previous studies have demonstrated that serotonin and an unidentified peptide act as diuretic factors. In other insects, members of the corticotropin-releasing factor (CRF)-related peptide family have been shown to play a role in post-feeding diuresis. Using fluorescence immunohistochemistry and immunogold labelling with antibodies to the Locusta CRF-like diuretic hormone (Locusta-DH) and serotonin, we have mapped the distribution of neurones displaying 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 lateral neurosecretory cells of the mesothoracic ganglionic mass (MTGM). Positively stained neurohaemal areas were found associated with the corpus cardiacum (CC) and on abdominal nerves 1 and 2. In addition, Locusta-DH-like immunoreactive nerve processes were found over the posterior midgut and hindgut. Double-labelling studies for Locusta-DH-like and serotonin-like immunoreactivity demonstrated some co-localisation in the CNS; however, no co-localisation was found in the medial neurosecretory cells of the brain, the posterior lateral neurosecretory cells of the MTGM or neurohaemal areas. To confirm the presence of a diuretic factor in the CC and abdominal nerves, extracts were tested in Malpighian tubule secretion assays and cyclic AMP assays. 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 neurohaemal terminals of the CC and abdominal nerves that are distinct from serotonin-containing terminals indicates that the peptide is capable of being released into the haemolymph and that this release can be independent of the release of serotonin.

A LOCUST OCTOPAMINE-IMMUNOREACTIVE DORSAL UNPAIRED MEDIAN NEURONE FORMING TERMINAL NETWORKS ON SYMPATHETIC NERVES

In insects, octopamine is present in neurohaemal regions of the thoracic sympathetic nervous system, but its cellular source is unknown. We describe a dorsal unpaired median neurone (DUM1b) in the locust metathoracic ganglion that forms a meshwork of varicose, presumably neurohaemal, endings on the surfaces of sympathetic nerves. Other targets include several ventral longitudinal muscles, the spiracle closer muscle, tissue remnants of degenerated nymphal muscles and the salivary glands. Using an established antiserum, DUM1b is shown to be octopamine-immunoreactive, and its target muscles to be covered with octopamine-immunoreactive varicosities. Octopamine influences one of these muscles in essentially the same way that another well-described octopaminergic neurone, DUMEti, modulates the extensor tibiae muscle of the hind leg. We propose that DUM1b is an octopaminergic modulator of muscle contractions and may also influence numerous other body functions by releasing octopamine as a hormone from sympathetic neurohaemal areas.

Fine structure of the abdominal neurosecretory organs of Rhodnius prolixus Stål.

Abdominal segments II–V of female Rhodnius prolixus adults each contain a pair of abdominal neurosecretory organs (ANO). They are attached to the anterolateral borders of their respective tergites and sternites. The ANO consist of neurosecretory neurons containing granules approximately 120 nm in diameter, together with glial and connective tissue elements. Apparent neurohaemal areas are located dorsally.

Potassium-Induced Release of the Diuretic Hormones of Rhodnius Prolixus and Glossina Austeni: Ca Dependence, Time Course and Localization of Neurohaemal Areas

1. Exposure of neurohaemal areas to solutions of elevated K concentration (above 40 mM) causes a maximal release of diuretic hormone in Rhodnius prolixus and Glossina austeni. 2. An involvement of Ca in hormone release is indicated by the reduction caused by low concentrations of this cation (below 2 mM) or by the presence of Mn. 3. During prolonged treatment with K-rich solutions the rate of hormone release is initially high, but then declines. This response parallels that for Ca entry into squid giant axons during maintained potassium depolarization and suggests that the rate of Ca entry controls the rate of hormone release. 4. Tetrodotoxin did not reduce the potassium-induced release of the hormone, suggesting that K acts directly on the neurosecretory axon endings in the neurohaemal areas.