EVIDENCE THAT LOCUSTATACHYKININ-I IS INVOLVED IN RELEASE OF ADIPOKINETIC HORMONE FROM LOCUST CORPORA-CARDIACA

The glandular cells of the corpus cardiacum of the locust Locusta migr atoria, known to synthesize and release adipokinetic hormones (AKH), a re contacted by axons immunoreactive to an antiserum raised against th e locust neuropeptide locustatachykinin I (LomTK I). Electron-microsco pical immunocytochemistry reveals LomTK immunoreactive axon terminals, containing granular vesicles, in close contact with the glandular cel ls cells. Release of AKH I from isolated corpora cardiaca of the locus t has been monitored in an in vitro system where the amount of AKH I r eleased into the incubation saline is determined by reversed phase hig h performance liquid chromatography with fluorometric detection. We co uld show that LomTK I induces release of AKH from corpora cardiaca in a dose-dependent manner when tested in a range of 10-200 mu M. This is thus the first clear demonstration of a substance inducing release of AKH, correlated with the presence of the substance in fibers innervat ing the AKH-synthesizing glandular cells, in the insect corpora cardia ca.