PARTIAL IDENTIFICATION, SYNTHESIS AND IMMUNOLOCALIZATION OF LOCUSTAMYOINHIBIN, THE 3RD MYOINHIBITING NEUROPEPTIDE ISOLATED FROM LOCUSTA-MIGRATORIA

A blocked neuropeptide that suppresses the motility of the cockroach h indgut has been isolated from an extract of 9000 brain-corpora cardiac a-corpora allata-suboesophageal ganglion complexes of Locusta migrator ia. Biological activity was monitored during HPLC purification by obse rving the myoinhibiting activity of column fractions on the isolated h indgut of Leucophaea maderae. Due to the low amount of material left a fter deblocking, this myoinhibiting peptide - designated as locustamyo inhibin or Lom-MIH - could only be partially sequenced: -X-Tyr-X'-Lys- Gln-Ser-Ala-Phe-Asn-Ala-Val-Ser-NH2. Nevertheless, the carboxy-termina l nonamer sequence (Lom-MIH(5-13)) was synthesized and also displayed myoinhibiting activity, indicating that the biologically active core l ies in the carboxy-terminal sequence. Lom-MIH shows no sequence simila rities with other peptides from vertebrate or invertebrate sources and is the third myoinhibiting peptide identified in Locusta migratoria. A polyclonal antiserum was raised against Lom-MIH(5-13) and used to in vestigate the distribution of immunoreactive peptide in the central ne rvous system and its associated neurohaemal structures. Two groups of neurons with somata in the optic lobes show locustamyoinhibin (Lom-MIH )-like immunoreactivity. These groups have somata at the dorsal and ve ntral edge of the lamina ganglionaris. The neurons have dense ramifica tions in the lamina, with processes extending into the first optic chi asma and into the accessory medulla. Four cell bodies were detected in the protocerebrum, and two cells were found at the externo-lateral ed ge of the tritocerebrum. No immunoreactive perikarya could be observed in the suboesophageal ganglion nor in the ganglia of the ventral nerv e cord. Neither the corpora cardiaca nor the neurohaemal organs of the ventral nerve cord showed immunolabelling. Therefore, our findings pr ovide anatomical evidence for a central neurotransmitter role of Lom-M IH.