Quantitative Determination of Myotropic Neuropeptide in the Nervous System of the Cockroach <i>Leucophaea Maderae</i>: Distribution and Release of Leucokinins

Abstract

ABSTRACT Being interested in the distribution and function of insect myotropic peptides, we developed a sensitive radioimmunoassay (RIA) using an antiserum directed against the cockroach neuropeptide leucokinin I. The levels of leucokinin immunoreactivity were measured in extracts of different portions of the nervous system, in the retrocerebral complex and in the hemolymph of the cockroach Leucophaea maderae. The brain contains about 1.9pmol of immunoreactive material while the ganglia of the ventral nerve cord each contain less than 10% of this amount. Large amounts of leucokinin immunoreactivity (6.6pmol per tissue) were found in the corpora cardiaca–corpora allata (CC–CA) complex and in the hemolymph the titer was in the nanomolar range. When levels of leucokinins were compared in male and female cockroaches, no differences could be detected in any of the sample tissues. A calcium-dependent release of leucokinin-immunoreactive material could be induced from isolated CC–CA complexes by high-potassium depolarization. The amount of released immunoreactivity, as measured in the bathing saline by RIA, was about 2% of the extractable leucokinin immunoreactivity in the CC–CA complex. In Leucophaea maderae, the leucokinins apparently act both as neuroactive substances in the central nervous system and as neurohormones released into the circulation.