A possible role of Schisto FLRFamide in inhibition of adipokinetic hormonerelease from locust corpora cardiaca

The distribution and actions of FMRFamide-related peptides (FaRPs) in the c orpora cardiaca of the locust Locusta migratoria were studied. Antisera to FMRFamide and SchistoFLRFamide (PDVDHVFLRFamide) label neuronal processes t hat impinge on glandular cells in the glandular lobe of the corpora cardiac a known to produce adipokinetic hormones. Electron microscopic immunocytoch emistry revealed that these FaRP-containing processes form synaptoid contac ts with the glandular cells. Approximately 12% of the axon profiles present in the glandular part of the corpus cardiacum contained SchistoFLRFamide-i mmunoreactive material. Retrograde tracing of the axons in the nervus corpo ris cardiaci II with Lucifer yellow revealed 25-30 labelled neuronal cell b odies in each lateral part of the protocerebrum. About five of these in eac h hemisphere reacted with the SchistoFLRFamide-antiserum. Double-labelling immunocytochemistry showed that the FaRP-containing processes in the glandu lar lobe of the corpora cardiaca are distinct from neuronal processes, reac ting with an antiserum to the neuropeptide locustatachykinin. The effect of the decapeptide SchistoFLRFamide and the tetrapeptide FMRFamide on the rel ease of adipokinetic hormone I (AKH I) from the cells in the glandular part of the corpus cardiacum was studied in vitro. Neither the deca- nor the te trapeptide had any effect on the spontaneous release of AKH I. Release of A KH I induced by the phosphodiesterase inhibitor IBMX, however, was reduced significantly by both peptides. These results point to an involvement of Fa RPs as inhibitory modulators in the regulation of the release of adipokinet ic hormone from the glandular cells.