Several isoforms of locustatachykinins may be involved in cyclic AMP-mediated release of adipokinetic hormones from the locust Corpora cardiaca

Four locustatachykinins (LomTK I-IV) were identified in about equal amounts in extracts of corpora cardiaca of locusts, using reverse-phase high-perfo rmance liquid chromatography and radioimmunoassay with synthetic LomTK I-IV as standards. Brain extracts also contained the four isoforms in roughly e quimolar concentrations. Retrograde tracing of the nervi corporis cardiaci II (NCC II) in vitro with Lucifer yellow in combination with LomTK immunocy tochemistry revealed that about half of the secretomotor neurons in the lat eral part of the protocerebrum projecting into the glandular lobe of the co rpora cardiaca (CCG) contain LomTK-immunoreactive material. Since the four LomTKs are present in the CCG, these four or five neurons in each hemispher e are likely to contain colocalized LomTK I-IV. The role of two of the LomT Ks in the regulation of the release of adipokinetic hormones (AKHs) from th e adipokinetic cells in the CCG in the locust was investigated. Experiments performed in vitro showed that LomTK I and II induced release of AKH in a dose-dependent manner. These peptides also rapidly and transiently elevated the cyclic AMP-content of the CCG. The peak level of cyclic AMP occurred a bout 45 seconds after stimulation with LomTK. These results support the pro posal that LomTKs are involved in controlling the release of the adipokinet ic hormones and suggest that all LomTK isoforms may participate in this cyc lic AMP-mediated event. (C) 1999 Academic Press.