The synthesis of neurosecretory protein during the fifth instar of Locusta migratoria migratorioides

Abstract

The synthesis of a neurosecretory protein during the fifth instar of female locusts has been estimated by incorporation of [ 3H]cystine and rocket immunoelectrophoresis. Highest specific activity of neurosecretory protein was found both in the brain and corpora cardiaca on Day 6 of the instar. Eightfold as much radiolabelled cystine is incorporated in neurosecretory protein (of the brain) than into other proteins of the brain on this day. An earlier, though less pronounced, peak of synthetic activity by the median neurosecretory cells during the fifth instar closely parallels changes in previously established ecdysone titres. The two ecdysone peaks which occur in fifth-instar Locusta (data of A. Bouthier, J.-L. Pennetier, B. Mauchamp, and R. Lafont, 1975, C. R. Acad. Sci. Paris 280, 1837–1840) follow the peaks of neurosecretory synthesis within 24 hr. Such parallels between neurosecretory synthesis and ecdysone titres again raise the possibility of a prothoracotropin being synthesised by the median neurosecretory cells of Locusta.